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研究者情報

マスター

アカウント（マスター）

  • 氏名

    植村　哲也(ウエムラ　テツヤ), ウエムラ　テツヤ

所属（マスター）

  • 情報科学研究院　情報エレクトロニクス部門　先端エレクトロニクス分野

所属（マスター）

  • 情報科学研究院　情報エレクトロニクス部門　先端エレクトロニクス分野

独自項目

syllabus

  • 2021, 電子デバイス学特論, Physics of Semiconductor Nano Devices, 修士課程, 情報科学研究科, MOSFET，シリコン集積回路，スケーリング則，ナノ構造，ナノ加工技術，量子効果，先端CMOS技術，磁性体，スピン，バンド構造，スピントロニクスデバイス
  • 2021, 電子デバイス学特論, Physics of Electron Device, 修士課程, 情報科学院, MOSFET，シリコン集積回路，スケーリング則，ナノ構造，ナノ加工技術，量子効果，先端CMOS技術，磁性体，スピン，バンド構造，スピントロニクスデバイス
  • 2021, 電子デバイス学特論, Physics of Semiconductor Nano Devices, 博士後期課程, 情報科学研究科, MOSFET，シリコン集積回路，スケーリング則，ナノ構造，ナノ加工技術，量子効果，先端CMOS技術，磁性体，スピン，バンド構造，スピントロニクスデバイス
  • 2021, 電子デバイス学特論, Physics of Electron Device, 博士後期課程, 情報科学院, MOSFET，シリコン集積回路，スケーリング則，ナノ構造，ナノ加工技術，量子効果，先端CMOS技術，磁性体，スピン，バンド構造，スピントロニクスデバイス
  • 2021, ディジタル回路, Digital Circuit Design, 学士課程, 工学部, 組み合わせ回路、順序回路、CMOS論理ゲート、論理演算回路、算術演算回路、状態遷移機械（ステートマシン, FSM）、メモリ、プログラマブルロジック、FPGA
  • 2021, 応用数学演習Ⅱ, Exercise in Applied Mathematics II, 学士課程, 工学部, 常微分方程式、偏微分方程式、ラプラス変換、フーリエ級数
  • 2021, 電気電子工学演習Ⅲ, Exercise in Electrical and Electronic Engineering III, 学士課程, 工学部, pn接合、トランジスタ、増幅回路、演算増幅器、ブール代数、論理回路

researchmap

プロフィール情報

学位

  • 博士（工学）（京都大学）

プロフィール情報

  • 姓

    植村, ウエムラ

  • 名

    哲也, テツヤ

  • ID各種

    200901018152363278

通称等の別名

    植村 哲也

対象リソース

業績リスト

研究キーワード

  • スピントランジスタ   スピントロニクス   トンネル磁気抵抗   強磁性トンネル接合   スピン注入   磁気ランダムアクセスメモリ   半導体   スピンLED   トンネル異方性磁気抵抗効果   共鳴トンネルダイオード   Co系ホイスラー合金   スピン依存トンネリング   スピン輸送特性   ハーフメタル強磁性体   先端デバイス開発   

研究分野

  • ものづくり技術（機械・電気電子・化学工学） / 電子デバイス、電子機器
  • ものづくり技術（機械・電気電子・化学工学） / 電気電子材料工学

経歴

  • 2016年04月 - 現在 北海道大学 大学院情報科学研究科 教授
  • 2007年04月 - 2016年03月 北海道大学 大学院情報科学研究科 准教授
  • 2004年04月 - 2007年03月 北海道大学 大学院情報科学研究科 助教授
  • 2002年01月 - 2004年03月 北海道大学 大学院工学研究科 助教授
  • 1990年04月 - 2001年12月 日本電気（株） 基礎研究所

学歴

  • 1988年04月 - 1990年03月   京都大学   大学院工学研究科   電気工学専攻修士過程
  • 1984年04月 - 1988年03月   京都大学   工学部   電気工学科

論文

  • Makoto Kohda, Takeshi Seki, Yasushi Yuminaka, Tetsuya Uemura, Keito Kikuchi, Gian Salis
    Appl. Phys. Lett. 123 190502  2023年11月 [査読有り][招待有り]
  • Current-induced domain wall motion in Pd/Co2MnGa with perpendicular magnetic anisotropy
    Takaya Koyama, Yuki Nishioka, Tetsuya Uemura, Michihiko Yamanouchi
    68th Annual Conference on Magnetism and Magnetic Materials, Abstracts, VP1-01  2023年10月 [査読有り][通常論文]
  • Mineto Ogawa, Takuya Hara, Shun Hasebe, Michihiko Yamanouchi, Tetsuya Uemura
    Applied Physics Express 16 6 063002 - 063002 2023年06月01日 [査読有り][通常論文]
     
    Abstract We investigated the effect of an ultrathin Fe interlayer on the growth of MnGa and spin–orbit torque (SOT) induced magnetization switching. MnGa was epitaxially grown on Fe at room temperature without thermal annealing. The MnGa/Fe bilayer was perpendicularly magnetized, and clear magnetization switching of the MnGa/Fe bilayer using the spin current, mainly from the adjacent Ta, was observed. The insertion of the Fe layer reduced the switching current density and increased a SOT-originated effective magnetic field. These results indicate that the MnGa/Fe bilayer is a promising spin source, capable of both perpendicular spin injection into GaAs and electrical manipulation of its spin direction.
  • Microfabrication and Characterization of Ferromagnetic Metal/Nonmagnetic Semiconductor Junctions for Spin Pumping-Induced Highly Efficient Spin Injection
    T.S. Balland, T. Seki, T. Yamazaki, R.Y. Umetsu, M. Ogawa, T. Uemura, K. Takanashi
    IEEE International Magnetics Conference 2023 (INTERMAG 2023), Digest Book DPB-08  2023年05月 [査読有り][通常論文]
  • Spin-orbit torque induced magnetization switching in perpendicularly magnetized MnGa/Fe bilayer grown on GaAs
    Mineto Ogawa, Takuya Hara, Shun Hasebe, Michihiko Yamanouchi, Tetsuya Uemura
    IEEE International Magnetics Conference 2023 (INTERMAG 2023), Digest Book APC-08  2023年05月 [査読有り][通常論文]
  • Daimu Morita, Takuya Hara, Michihiko Yamanouchi, Tetsuya Uemura
    AIP Advances 13 1 2023年01月01日 [査読有り][通常論文]
     
    Spin–orbit torques (SOTs) induced magnetization switching in a perpendicularly magnetized CoFeB film deposited on a Ti/in-plane magnetized Co2MnAl stack was investigated. Deterministic switching of the CoFeB magnetization was demonstrated by applying a current pulse to the stack in a direction parallel or antiparallel to the Co2MnAl magnetization. We found that the hysteresis loops of the anomalous Hall resistance for CoFeB under the constant current is shifted in the out-of-plane magnetic field axis direction depending on the directions of both the applied current and the magnetization of Co2MnAl. The shift amount exhibits an almost linear increase as the current magnitude increases. These results are consistent with the effects caused by SOTs originating from spin currents having an in-plane polarization orthogonal to the Co2MnAl magnetization.
  • Field-free switching of perpendicular magnetization by spin-orbit torques originating from an in-plane magnetized Co2MnAl spin source
    Daimu Morita, Takuya Hara, Michihiko Yamanouchi, Tetsuya Uemura
    67th Annual Conference on Magnetism and Magnetic Materials, Abstracts, EOE-14  2022年10月 [査読有り][通常論文]
  • Yuki Chikaso, Masaki Inoue, Tessei Tanimoto, Keita Kikuchi, Michihiko Yamanouchi, Tetsuya Uemura, Kazuumi Inubushi, Katsuyuki Nakada, Hikari Shinya, Masafumi Shirai
    Journal of Physics D: Applied Physics 55 34 345003 (9pp)  2022年08月25日 [査読有り]
     
    Abstract We investigated the Ge-composition (γ) dependence of the saturation magnetization of Co2Fe(Ga, Ge) (CFGG) thin films and the magnetoresistance (MR) ratio of CFGG-based current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices together with first-principles calculations of the electronic states of CFGG. Theoretical calculations showed that spin polarization is highest at the stoichiometric composition γ = 0.56 in Co2Fe1.03Ga0.41Geγ and that it decreases in off-stoichiometric CFGG, mainly due to the formation of CoFe antisites for Ge-deficient compositions and FeCo antisites for Ge-rich compositions, where CoFe (FeCo) indicates that Co (Fe) atoms replace the Fe (Co) sites. The saturation magnetic moment (μs) per formula unit decreased monotonically as γ increased from 0.24 to 1.54 in Co2Fe1.03Ga0.41Geγ. The μs was closest to the Slater–Pauling value predicted for half-metallic CFGG at the stoichiometric composition γ = 0.56, indicating that stoichiometric CFGG has a half-metallic nature. This is consistent with the result for the theoretical spin polarization. In contrast, the MR ratio of CFGG-based CPP-GMR devices increased monotonically as γ increased from 0.24 to 1.10 and reached an MR ratio of 87.9% at the Ge-rich composition γ = 1.10. Then, the MR ratio decreased rapidly as γ increased from 1.10 to 1.48. Possible origins for the slight difference between the Ge composition at which the highest MR ratio was obtained (γ = 1.10) and that at which the highest spin polarization was obtained (γ = 0.56) are improved atomic arrangements in a Ge-rich CFGG film and the reduction of effective Ge composition due to Ge diffusion in the GMR stacks.
  • Theory and observation of topological Hall torque emerging from band topology
    Y. Araki, M. Yamanouchi, T. Sakai, T. Uemura, J. Ieda
    29th International Conference on LOW TEMPERATURE PHYSICS (LT29) 2022年08月 [査読有り]
  • Takuya Hara, Kohey Jono, Michihiko Yamanouchi, Tetsuya Uemura
    IEEE Transactions on Magnetics 58 8 1400104 (4pp) - 4 2022年08月 [査読有り]
  • Michihiko Yamanouchi, Yasufumi Araki, Takaki Sakai, Tetsuya Uemura, Hiromichi Ohta, Jun’ichi Ieda
    Science Advances 8 15 eabl6192(6pp)  2022年04月15日 [査読有り]
     
    In a ferromagnetic Weyl metal SrRuO 3 , a large effective magnetic field Heff exerted on a magnetic domain wall (DW) by current has been reported. We show that the ratio of Heff to current density exhibits nonmonotonic temperature dependence and surpasses those of conventional spin-transfer torques and spin-orbit torques. This enhancement is described well by topological Hall torque (THT), which is exerted on a DW by Weyl electrons emerging around Weyl points when an electric field is applied across the DW. The ratio of the Heff arising from the THT to current density is over one order of magnitude higher than that originating from spin-transfer torques and spin-orbit torques reported in metallic systems, showing that the THT may provide a better way for energy-efficient manipulation of magnetization in spintronics devices.
  • Spin-orbit torque in structures with magnetization-compensated MnGa/Co2MnSi bilayer
    T. Hara, K. Jono, M. Yamanouchi, T. Uemura
    15th Joint MMM-Intermag Conference 360  2022年01月 [査読有り]
  • Nonmonotonic temperature dependence of current induced effective magnetic field exerted on domain wall in SrRuO3
    M. Yamanouchi, Y. Araki, T. Sakai, T. Uemura, H. Ohta, J. Ieda
    15th Joint MMM-Intermag Conference 386  2022年01月 [査読有り]
  • Kohey Jono, Fumiaki Shimohashi, Michihiko Yamanouchi, Tetsuya Uemura
    AIP Advances 11 2 025205(5pp)  2021年02月01日 [査読有り][通常論文]
  • MnGa/Co2MnSi Bilayer for Spin-Orbit Torque Magnetization Switching
    M. Yamanouchi, K. Jono, F. Shimohashi, T. Uemura
    65th Annual Conference on Magnetism and Magnetic Materials, Abstracts, R2-07  2020年11月 [査読有り][通常論文]
  • Enhancement of magnetoresistance characteristics of Ge-rich Co2Fe(Ga,Ge)-based current-perpendicular-to-plane giant magnetoresistance devices
    K. Nakada, Y. Chikaso, T. Tanimoto, M. Inoue, K. Inubushi, T. Uemura
    65th Annual Conference on Magnetism and Magnetic Materials, Abstracts, R3-12  2020年11月 [査読有り][通常論文]
  • Spin-orbit-torque induced magnetization switching for an ultra-thin MnGa/Co2MnSi bilayer
    K. Jono, F. Shimohashi, M. Yamanouchi, T. Uemura
    2020 International Conference on Solid State Devices and Materials (SSDM2020), Extended Abstracts 599 - 600 2020年09月 [査読有り][通常論文]
  • Ting Li, Wei Yan, Xinhui Zhang, Bing Hu, Kidist Moges, Tetsuya Uemura, Masafumi Yamamoto, Masahito Tsujikawa, Masafumi Shirai, Yoshio Miura
    Physical Review B 101 17 174410(12pp)  2020年05月06日 [査読有り][通常論文]
  • Michihiko Yamanouchi, Nguyen Viet Bao, Fumiaki Shimohashi, Kohey Jono, Masaki Inoue, Tetsuya Uemura
    AIP ADVANCES 9 12 125245-1 - 125245-4 2019年12月 [査読有り][通常論文]
     
    We investigate the magnetic properties and spin-orbit-torque-induced (SOT-induced) magnetization switching in Ta/MnGa/Cr and Ta/MnGa/NiAl structures. Out-of-plane hysteresis loops for the Ta/MnGa/Cr (NiAl) structures are skewed (square). In-plane currents I are applied to Hall devices made of structures exposed to in-plane magnetic fields H-in along the channel direction. Clear asymmetric magnetization switching with respect to the polarity of I and H-in is detected for the Ta/MnGa/NiAl device. Similar asymmetric magnetization switching is observed for the Ta/MnGa/Cr device, although the magnetization is partially switched regardless of the polarity of I and Hin. These results suggest that an in-plane magnetization component opposite to Hin is present in the Cr-buffer structure and that the formation of such a component is suppressed in the NiAl-buffer structure. (C) 2019 Author(s).
  • Effects of spin–orbit torque on domain wall motion in a Ta/MnGa/NiAl structure
    M. Yamanouchi, N.V. Bao, M. Inoue, T. Uemura
    64th Annual Conference on Magnetism and Magnetic Materials, Abstracts, p.773  2019年11月 [査読有り][通常論文]
  • Shimohashi Fumiaki, Nguyen Bao, Yamanouchi Michihiko, Uemura Tetsuya
    JSAP Annual Meetings Extended Abstracts 2019.2 2176 - 2176 2019年09月04日
  • M. Yamanouchi, N. V. Bao, M. Inoue, T. Uemura
    Jpn. J. Appl. Phys. vol.58 10 100903-1 - 100903-4 2019年09月 [査読有り][通常論文]
     
    We investigate the interaction between spin-orbit torque (SOT) and domain walls (DWs) created during magnetization reversal in perpendicularly magnetized ultrathin MnGa sandwiched between Ta and NiAl. We examine the out-of-plane hysteresis loops under various in-plane magnetic fields H(x)s along the current I direction by using magnetotransport measurements. The applied I acts as an effective perpendicular magnetic field H-eff on magnetization under H-x. The slope of H-eff versus I varies proportionally to H-x and becomes saturated above similar to 0.15 T, which is consistent with a model based on magnetization reversal through SOT-assisted chiral DW motion under H-x. (C) 2019 The Japan Society of Applied Physics
  • M. Inoue, K. Inubushi, D. Mouri, T. Tanimoto, K. Nakada, K. Kondo, M. Yamamoto, T. Uemura
    Appl. Phys. Lett. vol.114 062401(5pp)  2019年02月 [査読有り][通常論文]
  • Electrical spin injection into an AlGaAs/GaAs-based 2DEG system with a Co2MnSi spin source up to room temperature
    Z. Lin, D. Pan, M. Rasly, T. Uemura
    14th Joint MMM-Intermag Conference, Abstracts 86  2019年01月 [査読有り][通常論文]
  • Z. Lin, D. Pan, M. Rasly, T. Uemura
    Appl. Phys. Lett. vol.114 1 012405(5pp)  AIP Publishing 2019年01月 [査読有り][通常論文]
  • Origin of bi-quadratic interlayer exchange coupling in Co2MnSi-based pseudo spin valves
    D. Mouri, M. Inoue, K. Inubushi, T. Tanimoto, K. Nakada, M. Yamamoto, T. Uemura
    2018 International Conference on Solid State Devices and Materials (SSDM2018), Extended Abstracts PS-9-08  2018年09月 [査読有り][通常論文]
  • Mn-composition dependence of strength of bi-quadratic interlayer exchange coupling in Co2MnSi-based pseudo spin-valves
    M. Inoue, D. Mouri, K. Inubushi, K. Nakada, M. Yamamoto, T. Uemura
    IEEE International Magnetics Conference 2018 (INTERMAG 2018), Digest Book 855  2018年04月 [査読有り][通常論文]
  • Electrical spin injection into an AlGaAs/GaAs-based high-mobility two-dimensional electron system
    Z. Lin, D. Pan, M. Rasly, T. Uemura
    IEEE International Magnetics Conference 2018 (INTERMAG 2018), Digest Book p.1616  2018年04月 [査読有り][通常論文]
  • Coherent manipulation of nuclear spins in GaAs using electrical spin injection
    T. Uemura
    International Workshop on NanoScience and NanoOptics 2017 2017年11月 [査読無し][招待有り]
  • Mohmoud Rasly, Zhichao Lin, Tetsuya Uemura
    PHYSICAL REVIEW B 96 18 184415(8pp)  2017年11月 [査読有り][通常論文]
     
    We electrically probed the transient response of nuclear spins in an n-GaAs channel by performing Hanle signal and spin-valve signal measurements on an all-electrical spin-injection device having a half-metallic spin source of Co2MnSi. Furthermore, we simulated the Hanle and spin-valve signals by using the time evolution of nuclear-spin polarization under the presence of polarized electron spins by taking both T-1e and T-1 into consideration, where T-1e(-1) is the polarization rate of nuclear spins through the transfer of angular momentum from polarized electron spins and T-1(-1) is the depolarization rate of nuclear spins through the interaction with the lattice. The simulation results reproduced our experimental results on all the nuclear-spin-related phenomena appearing in the Hanle and spin-valve signals at different measurement conditions, providing quantitative explanation for the transient response of nuclear spins in GaAs to a change in magnetic fields and an estimate of the time scales of T-1e and T-1. These experimental and simulated results will deepen the understanding of nuclear-spin dynamics in semiconductors.
  • Influence of Mn composition in Co2MnSi films on magnetoresistance characteristics of Co2MnSi-based current-perpendicular-to-plane spin valves
    M. Inoue, B. Hu, K. Moges, K. Inubushi, K. Nakada, M. Yamamoto, T. Uemura
    2017 International Conference on Solid State Devices and Materials (SSDM2017), Extended Abstracts 989 - 990 2017年09月 [査読有り][通常論文]
  • Masaki Inoue, Bing Hu, Kidist Moges, Kazuumi Inubushi, Katsuyuki Nakada, Masafumi Yamamoto, Tetsuya Uemura
    APPLIED PHYSICS LETTERS 111 8 082403(5pp)  2017年08月 [査読有り][通常論文]
     
    The influence of off-stoichiometry of Co2MnSi (CMS) spin sources on giant magnetoresistance characteristics was investigated for CMS/Ag-based current-perpendicular-to-plane spin valves prepared with various Mn compositions a in Co2Mn alpha Si0.82 electrodes. The magnetoresistance ratio of the prepared CMS/Co50Fe50 (CoFe) (1.1 nm)/Ag/CoFe (1.1)/CMS spin valves systematically increased with a from 11.4% for Mn-deficient alpha = 0.62 to 20.7% for Mn-rich alpha = 1.45 at 290 K. This result suggests that increasing a from a Mn-deficient to Mn-rich value increases the spin polarization by suppressing Co-Mn antisites harmful to the half-metallicity. Thus, our results demonstrate that appropriately controlling the film composition toward a Mn-rich one is highly effective for enhancing the half-metallicity of CMS in CMS-based spin valves, as it is in CMS-based magnetic tunnel junctions. Published by AIP Publishing.
  • Influence of Mn composition in Co2MnSi films on magnetoresistance characteristics of Co2MnSi-based giant magneto-resistance devices
    M. Inoue, B. Hu, K. Moges, K. Inubushi, K. Nakada, M. Yamamoto, T. Uemura
    9th International School and Conference on Spintronics and Quantum Information Technology, Abstract Book 85  2017年06月 [査読有り][通常論文]
  • Zhichao Lin, Mahmoud Rasly, Tetsuya Uemura
    APPLIED PHYSICS LETTERS 110 23 232404 (4pp)  2017年06月 [査読有り][通常論文]
     
    We demonstrated spin echoes of nuclear spins in a spin injection device with a highly polarized spin source by nuclear magnetic resonance (NMR). Efficient spin injection into GaAs from a half-metallic spin source of Co2MnSi enabled efficient dynamic nuclear polarization (DNP) and sensitive detection of NMR signals even at a low magnetic field of similar to 0.1 T and a relatively high temperature of 4.2K. The intrinsic coherence time T-2 of Ga-69 nuclear spins was evaluated from the spin-echo signals. The relation between T-2 and the decay time of the Rabi oscillation suggests that the inhomogeneous effects in our system are not obvious. This study provides an all-electrical NMR system for nuclear-spin-based qubits. Published by AIP Publishing.
  • Electrical control of nuclear spin polarization: Experimental and quantitative modeling
    M. Rasly, Z. Lin, M. Yamamoto, T. Uemura
    IEEE Int’l Magnetics Conf. 2017 (INTERMAG 2017), Digests (USB Memory) GO-12  2017年04月 [査読有り][通常論文]
  • Fabrication of a Spin Injection Device Having a Top-gate Structure
    W. Nomura, T. Miyakawa, M. Yamamoto, T. Uemura
    2016 International Conference on Solid State Devices and Materials (SSDM2016), Extended Abstracts 921 - 922 2016年09月 [査読有り][通常論文]
  • Bing Hu, Kidist Moges, Yusuke Honda, Hong-xi Liu, Tetsuya Uemura, Masafumi Yamamoto, Jun-ichiro Inoue, Masafumi Shirai
    PHYSICAL REVIEW B 94 9 094428(15pp)  2016年09月 [査読有り][通常論文]
     
    In order to elucidate the origin of the temperature (T) dependence of spin-dependent tunneling conductance (G) of magnetic tunnel junctions (MTJs), we experimentally investigated the T dependence of G for the parallel and antiparallel magnetization alignments, G(P) and G(AP), of high-quality Co2MnSi (CMS)/MgO/CMS MTJs having systematically varied spin polarizations (P) at 4.2 K by varying the Mn composition alpha in Co2Mn alpha Si electrodes that exhibited giant tunneling magnetoresistance ratios. Results showed that G(P) normalized by its value at 4.2 K exhibited a notable, nonmonotonic T dependence although its variation with T was significantly smaller than that of G(AP) normalized by its value at 4.2 K, indicating that an analysis of the experimental G(P)(T) is critical to revealing the origin of the T dependence of G. By analyzing the experimental G(P)(T), we clarified that both spin-flip inelastic tunneling via a thermally excited magnon and spin-conserving elastic tunneling in which P decays with increasing T play key roles. The experimental G(AP)(T), including its stronger T dependence for higher P at 4.2 K, was also consistently explained with this model. Our findings provide a unified picture for understanding the origin of the T dependence of G of MTJs with a wide range of P, including MTJs with high P close to a half-metallic value.
  • Highly efficient spin injection from a half-metallic spin source of Co2MnSi and sensitive detection of nuclear spin states
    T. Uemura
    The 18th International Conference on Crystal Growth and Epitaxy (ICCGE18), Technical Digest 243  2016年08月 [査読無し][招待有り]
  • Lijun Li, Inyeal Lee, Dongsuk Lim, Servin Rathi, Moonshik Kang, Tetsuya Uemura, Gil-Ho Kim
    NANOTECHNOLOGY 27 33 335201(6pp)  2016年08月 [査読有り][通常論文]
     
    We fabricated a non-local spin valve with a thin layer of graphite with Co transparent electrodes. The spin-valve effect and spin precession were observed at room temperature. The magnitude of the mangetoresistance increases when temperature decreases. The spin-relaxation time, tau(s), obtained from the fitting of the Hanle curves increases with decreasing temperature with a weak dependence similar to T-0.065 while the spin-diffusion constant D decreases. At room temperature, tau(s) exceeds 100 ps and the spin-diffusion length, lambda(s), is similar to 2 mu m. The temperature dependence of lambda(s) is not monotonic, and it has the largest value at room temperature. Our results show that multilayer graphene is a suitable material for spintronic devices.
  • Roman Fetzer, Hong-xi Liu, Benjamin Stadtmueller, Tetsuya Uemura, Masafumi Yamamoto, Martin Aeschlimann, Mirko Cinchetti
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 49 19 195002(5pp)  2016年05月 [査読有り][通常論文]
     
    The latest improvement of MgO-based magnetic tunnel junctions has been achieved by the combination of CoFe buffer layers and potentially half-metallic ultrathin Co2MnSi electrodes. By this, tunnel magnetoresistance ratios of almost 2000% could be obtained. However, a complete understanding of the underlying processes leading to this enhancement is not yet given. We present a comprehensive study regarding the structural and electronic spin properties of the CoFe(30 nm)-buffered Co2MnSi(3 nm)/MgO(2 nm) buried interface identical to the one formed in actual devices. Low energy electron diffraction experiments show that the ultrathin Co2MnSi layer adopts the lattice constant of the underlying CoFe buffer layer, leading to improved structural conditions at the interface to MgO. In contrast, the Co2MnSi/MgO interface spin polarization at the Fermi level is not affected by the magnetic CoFe buffer layer, as found by interface-sensitive spin-resolved extremely low energy photoemission spectroscopy.
  • Mahmoud Rasly, Zhichao Lin, Masafumi Yamamoto, Tetsuya Uemura
    AIP ADVANCES 6 5 056305(8pp)  2016年05月 [査読有り][通常論文]
     
    As an alternative to studying the steady-state responses of nuclear spins in solid state systems, working within a transient-state framework can reveal interesting phenomena. The response of nuclear spins in GaAs to a changing magnetic field was analyzed based on the time evolution of nuclear spin temperature. Simulation results well reproduced our experimental results for the transient oblique Hanle signals observed in an all-electrical spin injection device. The analysis showed that the so called dynamic nuclear polarization can be treated as a cooling tool for the nuclear spins: It works as a provider to exchange spin angular momentum between polarized electron spins and nuclear spins through the hyperfine interaction, leading to an increase in the nuclear polarization. In addition, a time-delay of the nuclear spin temperature with a fast sweep of the external magnetic field produces a possible transient state for the nuclear spin polarization. On the other hand, the nuclear magnetic resonance acts as a heating tool for a nuclear spin system. This causes the nuclear spin temperature to jump to infinity: i.e., the average nuclear spins along with the nuclear field vanish at resonant fields of As-75, Ga-69 and Ga-71, showing an interesting step-dip structure in the oblique Hanle signals. These analyses provide a quantitative understanding of nuclear spin dynamics in semiconductors for application in future computation processing. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
  • Kidist Moges, Yusuke Honda, Hong-xi Liu, Tetsuya Uemura, Masafumi Yamamoto, Yoshio Miura, Masafumi Shirai
    PHYSICAL REVIEW B 93 13 134403(15pp)  2016年04月 [査読有り][通常論文]
     
    We investigated the factors that critically affect the half-metallicity of the quaternary Heusler alloy Co2(Mn, Fe)Si (CMFS) by examining the film composition dependence of the saturation magnetization per formula unit, mu(s), of CMFS thin films and the tunneling magnetoresistance (TMR) ratio of CMFS/MgO/CMFS magnetic tunnel junctions (MTJs). We also investigated the origin of the giant TMR ratio of up to 2610% at 4.2 K (429% at 290 K) obtained for CMFS MTJs with Mn-rich, lightly Fe-doped CMFS electrodes. Co antisites at the nominal Mn/Fe sites (Co-Mn/Fe antisites) can consistently explain the mu(s) for (Mn + Fe)-deficient CMFS thin films being lower than the half-metallic Z(t) - 24 value and the TMR ratio for MTJs with (Mn + Fe)-deficient CMFS electrodes being lower than that for MTJs with (Mn+ Fe)-rich CMFS electrodes. It was revealed that the Co-Mn/Fe antisite is detrimental to the half-metallicity of the CMFS quaternary alloy, as it is in the Co2MnSi (CMS) ternary alloy. It was also shown that (Mn + Fe)-rich compositions are critical to suppressing these harmful antisites and to retaining the half-metallic electronic state. In addition, a relatively small Fe ratio, rather than a large one, in the total (Mn + Fe) composition led to a more complete half-metallic electronic state. Half-metallicity was more strongly enhanced by increasing the Mn composition in Mn-rich, lightly Fe-doped CMFS than in Mn-rich CMS. This phenomenon is the cause of the giant TMR ratio recently reported for CMFS MTJs. Our findings indicate that the approach to controlling off-stoichiometry and film composition is promising for fully utilizing the half-metallicity of quaternary CMFS thin films as spin source materials.
  • Zhichao Lin, Kenji Kondo, Masafumi Yamamoto, Tetsuya Uemura
    JAPANESE JOURNAL OF APPLIED PHYSICS 55 4 04EN03 (5pp)  2016年04月 [査読有り][通常論文]
     
    A transient response of nuclear spins in GaAs to a change in a magnetic field was analyzed based on the time evolution of nuclear spin temperature. Simulation results well reproduced our experimental results on transient oblique Hanle signals observed in an all-electrical spin injection device, enabling a quantitative understanding of nuclear spin dynamics in the presence of a hyperfine interaction between nuclei and polarized electrons. Analysis regarding the time evolution of nuclear spin temperature revealed that the hysteretic nature of a nuclear field with respect to the sweep direction of an external field was caused by the delay of time response of nuclear spin temperature to a change in the magnetic field. This analysis provides a deep understanding of nuclear spin dynamics in semiconductors. (C) 2016 The Japan Society of Applied Physics
  • Takumi Miyakawa, Takafumi Akiho, Yuya Ebina, Masafumi Yamamoto, Tetsuya Uemura
    APPLIED PHYSICS EXPRESS 9 2 023103(4pp)  2016年02月 [査読有り][通常論文]
     
    Efficient gate control of spin-valve signals and Hanle signals was achieved in a GaAs channel with a p-i-n back-gate structure. Experiments showed that the amplitude of the spin-valve signal (Delta V-NL) under constant-injection-current conditions increased for a cross nonlocal geometry when the channel was depleted by the gate voltage (V-G). In contrast, the V-G dependence of Delta V-NL for a nonlocal geometry was complicated. The gate modulation efficiency of spin signals was approximately 50 times that with a graphene or Si channel. (C) 2016 The Japan Society of Applied Physics
  • Masafumi Yamamoto, Tetsuya Uemura
    Springer Series in Materials Science 222 413 - 444 2016年01月01日 [査読有り][通常論文]
     
    To take full advantage of the half-metallic character of Co-based Heusler alloys, the effect of defects associated with nonstoichiometry has to be understood. In this chapter, recent progress in understanding the effect of nonstoichiometry on the half-metallicy of Heusler alloys, in particular of Co2MnSi (CMS), and its application to highly efficient spin sources for magnetic tunnel junctions (MTJs) and for spin injection into semiconductors is described. The effect of nonstoichiometry on the half-metallic character is experimentally investigated through the saturation magnetization per formula unit (μs) of Co2MnαSiβ thin films and the tunnelingmagnetoresistance (TMR) ratio of fully epitaxial CMS/MgO/CMS MTJs (CMS MTJs) having Co2MnαSiβ electrodes with various values of α. It was found that the μs value was in good agreement with the half-metallic Slater-Pauling value when α was increased to a Mn-rich composition. It was also shown that the TMR ratios at 4.2 and 290K systematically increased with increasing α for the range from a Mn-deficient composition to a certain Mn-rich composition. A site-specific formula unit (SSFU) composition model, which assumes the formation of antisite defects, not vacancies, to accommodate nonstoichiometry, is described. The experimental α dependencies of μs and the TMR ratio have been consistently explained by firstprinciples calculations based on the SSFU composition model. These findings show that harmful defects in Co2MnSi can be suppressed by appropriately controlling the film composition i.e., CoMn antisites detrimental to the half-metallicity can be suppressed with a Mn-rich composition. By applying Mn-rich CMS electrodes for fully epitaxial MgO-based MTJs, giant TMR ratios of up to 1995% at 4.2 K and up to 354% at 290K were demonstrated for CMS MTJs. Furthermore, an efficient spin injection into GaAs was demonstrated for lateral spin-transport devices by applying a half-metallic Mn-rich CMS electrode as a highly effective spin source. In addition, a nuclear field acting on the electron spins being produced by the dynamic nuclear polarization was electrically detected through the observation of transient oblique Hanle signals. Samples with a CMS spin source exhibited higher spin injection efficiency and a larger nuclear field compared to samples with a Co50Fe50 (CoFe) spin source, suggesting that the spin polarization of CMS is higher. These findings demonstrate that controlling defects through the film composition is critical to retain the half-metallicity of CMS. It is also clear that the half-metallic Co2MnSi electrodes are promising as a highly efficient spin source for future spintronic devices.
  • Tetsuya Uemura, Takafumi Akiho, Yuya Ebina, Masafumi Yamamoto
    SPINTRONICS IX 9931 55  2016年 [査読無し][招待有り]
     
    We have developed a novel nuclear magnetic resonance (NMR) system that uses spin injection from a highly polarized spin source. Efficient spin injection into GaAs from a half-metallic spin source of Mn-rich Co2MnSi enabled an efficient dynamic nuclear polarization of Ga and As nuclei in GaAs and a sensitive detection of NMR signals. Moreover, coherent control of nuclear spins, or the Rabi oscillation between two quantum levels formed at Ga nuclei, induced by a pulsed NMR has been demonstrated at a relatively low magnetic field of similar to 0.1 T. This provides a novel all-electrical solid-state NMR system with the high spatial resolution and high sensitivity needed to implement scalable nuclear-spin based qubits.
  • Tetsuya Uemura, Takafumi Akiho, Yuya Ebina, Masafumi Yamamoto
    SPINTRONICS IX 9931 99311L-1 - 99311L-7 2016年 [査読無し][招待有り]
     
    We have developed a novel nuclear magnetic resonance (NMR) system that uses spin injection from a highly polarized spin source. Efficient spin injection into GaAs from a half-metallic spin source of Mn-rich Co2MnSi enabled an efficient dynamic nuclear polarization of Ga and As nuclei in GaAs and a sensitive detection of NMR signals. Moreover, coherent control of nuclear spins, or the Rabi oscillation between two quantum levels formed at Ga nuclei, induced by a pulsed NMR has been demonstrated at a relatively low magnetic field of similar to 0.1 T. This provides a novel all-electrical solid-state NMR system with the high spatial resolution and high sensitivity needed to implement scalable nuclear-spin based qubits.
  • Analysis of transient response of nuclear spins in GaAs with/without nuclear magnetic resonance
    M. Rasly, Z. Lin, M. Yamamoto, T. Uemura
    13th Joint MMM-Intermag Conference, Abstracts 278 - 279 2016年01月 [査読有り][通常論文]
  • Tetsuya Uemura, Takafumi Akiho, Yuya Ebina, Masafumi Yamamoto
    SPINTRONICS IX 9931 140410(R)(5pp) - 99311L-7 2016年 [査読有り][招待有り]
     
    We have developed a novel nuclear magnetic resonance (NMR) system that uses spin injection from a highly polarized spin source. Efficient spin injection into GaAs from a half-metallic spin source of Mn-rich Co2MnSi enabled an efficient dynamic nuclear polarization of Ga and As nuclei in GaAs and a sensitive detection of NMR signals. Moreover, coherent control of nuclear spins, or the Rabi oscillation between two quantum levels formed at Ga nuclei, induced by a pulsed NMR has been demonstrated at a relatively low magnetic field of similar to 0.1 T. This provides a novel all-electrical solid-state NMR system with the high spatial resolution and high sensitivity needed to implement scalable nuclear-spin based qubits.
  • Bias Voltage Dependence of the Spin-dependent Tunneling Conductance of Co2(Mn,Fe)Si-Based Magnetic Tunnel Junctions Exhibiting Giant Tunneling Magnetoresistances
    Kidist Moges, B. Hu, H.x. Liu, T. Uemura, M. Yamamoto
    2015 Intrnational Conference on Solid State Devices and Materials (SSDM2015), Extended Abstracts (DVD, USB memory) 408 - 409 2015年09月 [査読有り][通常論文]
  • Temperature Dependence of Spin-Dependent Tunneling Conductance of Magnetic Tunnel Junctions with Highly Spin-Polarized Electrodes
    B. Hu, Kidist. Moges, H.x. Liu, Y. Honda, T. Uemura, M. Yamamoto
    2015 Intrnational Conference on Solid State Devices and Materials (SSDM2015), Extended Abstracts (DVD, USB memory) 410 - 411 2015年09月 [査読有り][通常論文]
  • Transient Analysis of Oblique Hanle Signals Observed in GaAs
    Z.c. Lin, M. Yamamoto, T. Uemura
    2015 Intrnational Conference on Solid State Devices and Materials (SSDM2015), Extended Abstracts (DVD, USB memory) 432 - 433 2015年09月 [査読有り][通常論文]
  • Takafumi Akiho, Masafumi Yamamoto, Tetsuya Uemura
    APPLIED PHYSICS EXPRESS 8 9 093001(4pp)  2015年09月 [査読有り][通常論文]
     
    We investigated the spin-dependent transport properties of strained InxGa1-xAs (x = 0.04, 0.07, and 0.16) channels grown on GaAs substrates by observing the spin-valve and Hanle signals in a lateral spin-transport device with an Fe spin source. The spin lifetime in the strained InxGa1-xAs channels estimated according to Hanle signals was one order of magnitude smaller than that in GaAs channels, and the spin lifetime depended on the degree of strain induced in the InxGa1-xAs layer. These results are explained by the strain-induced spin-orbit interaction. (C) 2015 The Japan Society of Applied Physics
  • Coherent control of nuclear spins using spin injection from half-metallic Co2MnSi
    T. Akiho, Y. Ebina, M. Yamamoto, T. Uemura
    21st International Conference on Electronic Properties of Two-Dimensional Systems, Abstracts vol.91 186  2015年07月 [査読有り][通常論文]
  • Gate control of spin-valve signal and Hanle signal in GaAs observed by a four-terminal nonlocal geometry
    T. Miyakawa, T. Akiho, Y. Ebina, M. Yamamoto, T. Uemura
    17th International Conference on Modulated Semiconductor Structures, Abstracts 158  2015年07月 [査読有り][通常論文]
  • Tetsuya Uemura, Takafumi Akiho, Yuya Ebina, Masafumi Yamamoto
    PHYSICAL REVIEW B 91 14 2015年04月 [査読有り][通常論文]
     
    We have developed a nuclear magnetic resonance (NMR) system that uses spin injection from a highly polarized spin source. Efficient spin injection into GaAs from a half-metallic spin source of Mn-rich Co2MnSi enabled an efficient dynamic nuclear polarization of Ga and As nuclei in GaAs and a sensitive detection of NMR signals. Moreover, coherent control of nuclear spins, or the Rabi oscillation between two quantum levels formed at Ga nuclei, induced by a pulsed NMR has been demonstrated at a relatively low magnetic field of similar to 0.1 T. This provides a novel all-electrical solid-state NMR system with the high spatial resolution and high sensitivity needed to implement scalable nuclear-spin-based qubits.
  • Roman Fetzer, Siham Ouardi, Yusuke Honda, Hong-xi Liu, Stanislav Chadov, Benjamin Balke, Shigenori Ueda, Motohiro Suzuki, Tetsuya Uemura, Masafumi Yamamoto, Martin Aeschlimann, Mirko Cinchetti, Gerhard H. Fecher, Claudia Felser
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 48 16 164002(12pp)  2015年04月 [査読有り][通常論文]
     
    Half-metallic Co2MnSi-based Heusler compounds have attracted attention because they yield very high tunnelling magnetoresistance (TMR) ratios. Record TMR ratios of 1995% (at 4.2 K) are obtained from off-stoichiometric Co2MnSi-based magnetic tunnel junctions. This work reports on a combination of band structure calculations and spin-resolved and photon-polarisation-dependent photoelectron spectroscopy for off-stoichiometric Heusler thin films with the composition Co2Mn1.30Si0.84. Co and Mn are probed by magnetic dichroism in angle-resolved photoelectron spectroscopy at the 2p core level. In contrast to the delocalised Co 3d states, a pronounced localisation of the Mn 3d states is deduced from the corresponding 2p core level spectra. The valence states are investigated by linear dichroism using both hard x-ray and very-low-photon-energy excitation. When a very low photon energy is used for excitation, the valence bands exhibit a spin polarisation of about 30% at the Fermi energy. First principles calculations reveal that the low spin polarisation might be caused by a spin-flip process in the photoelectron final states.
  • Hong-xi Liu, Takeshi Kawami, Kidist Moges, Tetsuya Uemura, Masafumi Yamamoto, Fengyuan Shi, Paul M. Voyles
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 48 16 164001(9pp)  2015年04月 [査読有り][通常論文]
     
    The influence of off-stoichiometry on the half-metallic character of quaternary Heusler alloy thin films of Co-2(Mn,Fe)Si (CMFS) was investigated by studying the composition dependence of the tunnelling magnetoresistance (TMR) ratio of fully epitaxial CMFS/MgO/CMFS magnetic tunnel junctions (CMFS MTJs) having Co-2(Mn alpha'Fe beta')Si-0.84 electrodes with various Mn and Fe compositions. It was found that MJTs with (Mn + Fe)-rich electrodes had higher TMR ratios than ones with (Mn + Fe)-deficient electrodes at 4.2 and 290 K. These results indicate that the suppression of Co antisites at nominal Mn/Fe sites is critical to obtaining half-metallic quaternary Co-2(Mn,Fe)Si in a similar way as in ternary alloy Co2MnSi. CMFS MTJs with Mn-rich and lightly Fe-doped CMFS electrodes showed giant TMR ratios of 2610% at 4.2 K and 429% at 290 K. These results suggest that Co-based Heusler alloy thin films would be highly applicable to spintronic devices because of their half-metallicity and material diversity arising from not only ternary alloy but also quaternary alloy systems.
  • Roman Fetzer, Benjamin Stadtmueller, Yusuke Ohdaira, Hiroshi Naganuma, Mikihiko Oogane, Yasuo Ando, Tomoyuki Taira, Tetsuya Uemura, Masafumi Yamamoto, Martin Aeschlimann, Mirko Cinchetti
    SCIENTIFIC REPORTS 5 8537(6pp)  2015年02月 [査読有り][通常論文]
     
    Ultraviolet photoemission spectroscopy (UPS) is a powerful tool to study the electronic spin and symmetry features at both surfaces and interfaces to ultrathin top layers. However, the very low mean free path of the photoelectrons usually prevents a direct access to the properties of buried interfaces. The latter are of particular interest since they crucially influence the performance of spintronic devices like magnetic tunnel junctions (MTJs). Here, we introduce spin-resolved extremely low energy photoemission spectroscopy (ELEPS) to provide a powerful way for overcoming this limitation. We apply ELEPS to the interface formed between the half-metallic Heusler compound Co2MnSi and the insulator MgO, prepared as in state-of-the-art Co2MnSi/MgO-based MTJs. The high accordance between the spintronic fingerprint of the free Co2MnSi surface and the Co2MnSi/MgO interface buried below up to 4 nm MgO provides clear evidence for the high interface sensitivity of ELEPS to buried interfaces. Although the absolute values of the interface spin polarization are well below 100%, the now accessible spin-and symmetry-resolved wave functions are in line with the predicted existence of non-collinear spin moments at the Co2MnSi/MgO interface, one of the mechanisms evoked to explain the controversially discussed performance loss of Heusler-based MTJs at room temperature.
  • T. Uemura, M. Yamamoto
    2015 IEEE MAGNETICS CONFERENCE (INTERMAG) CC-01  2015年 [査読無し][招待有り]
  • K. Moges, H. Liu, T. Kawami, T. Uemura, M. Yamamoto
    2015 IEEE MAGNETICS CONFERENCE (INTERMAG) GB-06  2015年 [査読有り][通常論文]
  • B. Hu, H. Liu, T. Kawami, K. Moges, Y. Honda, T. Uemura, M. Yamamoto
    2015 IEEE MAGNETICS CONFERENCE (INTERMAG) GB-11  2015年 [査読有り][通常論文]
  • Akiyori Yamamoto, Yuichiro Ando, Teruya Shinjo, Tetsuya Uemura, Masashi Shiraishi
    PHYSICAL REVIEW B 91 2 024417(6pp)  2015年01月 [査読有り][通常論文]
     
    A quantitative investigation of spin-pumping-induced spin transport in n-GaAs was conducted at room temperature (RT). GaAs has a non-negligible spin-orbit interaction, so that electromotive force due to the inverse spin Hall effect (ISHE) of GaAs contributed to the electromotive force detected with a platinum (Pt) spin detector. The electromotive force detected by the Pt spin detector had opposite polarity to that measured with a Ni80Fe20/GaAs bilayer due to the opposite direction of spin current flow, which demonstrates successful spin transport in the n-GaAs channel. A two-dimensional spin-diffusion model that considers the ISHE in the n-GaAs channel reveals an accurate spin diffusion length of lambda(s) = 1.09 mu m in n-GaAs (N-Si = 4 x 10(16) cm(-3)) at RT, which is approximately half that estimated by the conventional model.
  • Effect of nonstoichiometry on the half-metallicity of Co2(Mn,Fe)Si thin films investigated through saturation magnetization
    Kidist Moges, Y. Honda, T. Uemura, M.Yamamoto, Y. Miura, M. Shirai
    59th Annual Conference on Magnetism and Magnetic Materials, Abstracts 48 - 49 2014年11月 [査読有り][通常論文]
  • Electrical detection of nuclear magnetic resonance in GaAs using transient oblique Hanle effect measurements
    T. Uemura, T. Akiho, Y. Ebina, M. Yamamoto
    59th Annual Conference on Magnetism and Magnetic Materials, Abstracts, 671 - 672 2014年11月 [査読有り][通常論文]
  • Efficient nuclear spin polarization and electrical detection of nuclear magnetic resonance in GaAs using half-metallic spin source
    T. Uemura, M. Yamamoto
    The 3rd Internaional Conference of Asian Union of Magnetics Societies, Abstracts p.263  2014年10月 [査読無し][招待有り]
  • Efficient Dynamic Nuclear Polarization Using Electrical Spin Injection from a Half-Metallic Spin Source
    T. Akiho, Y. Ebina, H.-x. Liu, M. Yamamoto, T. Uemura
    32nd International Conference on the Physics of Semiconductors (ICPS2014), Abstracts, Spintronics & Spin phenomena II 2 - 3 2014年08月 [査読有り][通常論文]
  • Highly efficient spin injection and dynamic nuclear polarization using a half-metallic spin source
    植村 哲也
    The 6th IEEE International Nanoelectronics Conference 2014 (IEEE INEC 2014), Abstracts 2014年07月 [査読無し][招待有り]
  • Tomotsugu Ishikura, Lenanrt-Knud Liefeith, Zhixin Cui, Keita Konishi, Kanji Yoh, Tetsuya Uemura
    APPLIED PHYSICS EXPRESS 7 7 073001(4pp)  2014年07月 [査読有り][通常論文]
     
    The electrical spin injection from Ni81Fe19 (NiFe) into an InAs quantum well through a MgO tunneling barrier has been investigated for potential application to an InAs-based spin field-effect transistor. The insertion of a 2-nm-thick MgO tunnel barrier between NiFe and InAs increased the junction resistance by two orders of magnitude compared with that without a MgO barrier. The sample with a MgO barrier showed a clear nonlocal spin-valve signal at 1.4 K, possibly due to the alleviation of the impedance mismatching problem. The estimated spin polarization was 8.1%, which is higher than any reported in the literature for a NiFe/InGaAs Schottky junction. (C) 2014 The Japan Society of Applied Physics
  • Dependence of degree of temperature dependence of TMR ratio of Co2MnSi/MgO/Co2MnSi MTJs on Mn composition in Co2MnSi electrodes
    Y. Honda, H.-x. Liu, T. Uemura, M. Yamamoto
    IEEE Int’l Magnetics Conf. 2014 (INTERMAG 2014), Digests (USB Memory) 2407 - 2408 2014年05月 [査読有り][通常論文]
  • Yuya Ebina, Takafumi Akiho, Hong-xi Liu, Masafumi Yamamoto, Tetsuya Uemura
    APPLIED PHYSICS LETTERS 104 17 172405(4pp)  2014年04月 [査読有り][通常論文]
     
    The CoFe thickness (t(CoFe)) dependence of spin injection efficiency was investigated for Co2MnSi/CoFe/n-GaAs junctions. The Delta V-NL/I value, which is a measure of spin injection efficiency, strongly depended on t(CoFe), where Delta V-NL is the amplitude of a nonlocal spin-valve signal, and I is an injection current. Importantly, the maximum value of Delta V-NL/I for a Co2MnSi/CoFe/n-GaAs junction was one order of magnitude higher than that for a CoFe/n-GaAs junction, indicating that a Co2MnSi electrode works as a highly polarized spin source. No clear spin signal, on the other hand, was observed for a Co2MnSi/n-GaAs junction due to diffusion of Mn atoms into the GaAs channel. Secondary ion mass spectrometry analysis indicated that the CoFe insertion effectively suppressed the diffusion of Mn into GaAs, resulting in improved spin injection properties compared with those for a Co2MnSi/n-GaAs junction. (C) 2014 AIP Publishing LLC.
  • Xeniya Kozina, Julie Karel, Siham Ouardi, Stanislav Chadov, Gerhard H. Fecher, Claudia Felser, Gregory Stryganyuk, Benjamin Balke, Takayuki Ishikawa, Tetsuya Uemura, Masafumi Yamamoto, Eiji Ikenaga, Shigenori Ueda, Keisuke Kobayashi
    Physical Review B - Condensed Matter and Materials Physics 89 12 2014年03月17日 [査読有り][通常論文]
     
    The tunnel magnetoresistance ratio (TMR) of fully epitaxial magnetic tunnel junctions with an off-stoichiometric Co2MnSi Heusler alloy has been shown to exhibit a systematic dependence on Mn content, reaching 1135% at 4.2 K for Co2Mn1.29Si. In this paper, we explain the behavior of the observed TMR ratio using ab initio calculations and hard x-ray photoelectron spectroscopy (HAXPES). For the Mn-deficient samples, we show that the the drop of the TMR is caused by Co antisite atoms, which impose extra states into the minority-spin band gap. On the other hand, Mn-excess composition shows nearly half-metallic behavior. This result can be intuitively understood since both Co2MnSi and Mn2CoSi are theoretically predicted to be half-metallic ferromagnets. © 2014 American Physical Society.
  • Xeniya Kozina, Julie Karel, Siham Ouardi, Stanislav Chadov, Gerhard H. Fecher, Claudia Felser, Gregory Stryganyuk, Benjamin Balke, Takayuki Ishikawa, Tetsuya Uemura, Masafumi Yamamoto, Eiji Ikenaga, Shigenori Ueda, Keisuke Kobayashi
    PHYSICAL REVIEW B 89 12 125116(10pp)  2014年03月 [査読有り][通常論文]
     
    The tunnel magnetoresistance ratio (TMR) of fully epitaxial magnetic tunnel junctions with an off-stoichiometric Co2MnSi Heusler alloy has been shown to exhibit a systematic dependence on Mn content, reaching 1135% at 4.2 K for Co2Mn1.29Si. In this paper, we explain the behavior of the observed TMR ratio using ab initio calculations and hard x-ray photoelectron spectroscopy (HAXPES). For the Mn-deficient samples, we show that the the drop of the TMR is caused by Co antisite atoms, which impose extra states into the minority-spin band gap. On the other hand, Mn-excess composition shows nearly half-metallic behavior. This result can be intuitively understood since both Co2MnSi and Mn2CoSi are theoretically predicted to be half-metallic ferromagnets.
  • Gui-Fang Li, Yusuke Honda, Hong-Xi Liu, Ken-Ichi Matsuda, Masashi Arita, Tetsuya Uemura, Masafumi Yamamoto, Yoshio Miura, Masafumi Shirai, Toshiaki Saito, Fengyuan Shi, Paul M. Voyles
    Physical Review B - Condensed Matter and Materials Physics 89 1 2014年01月30日 [査読有り][通常論文]
     
    We investigated the effect of nonstoichiometry on the half-metallic character of the Heusler alloy Co2MnSi (CMS) through the Mn composition (α) dependence of the saturation magnetization per formula unit (μs) of Co2MnαSiβ thin films and the tunneling magnetoresistance (TMR) ratio of CMS/MgO/CMS magnetic tunnel junctions (CMS MTJs) having Co2MnαSiβ electrodes. As a basis for understanding the effect of nonstoichiometry in CMS, we developed a generalized form of the site-specific formula unit (SSFU) composition model, which assumes the formation of only antisite defects, not vacancies, to accommodate nonstoichiometry. The α dependence of μs was well explained by density functional calculations with the coherent potential approximation based on the SSFU composition model for α up to a certain critical value (αc)> 1.0. The μs data for Mn-deficient films deviated from the Slater-Pauling predicted data for half-metals due to Co atoms at the nominal Mn sites (CoMn). The theoretical spin polarizations, obtained from only the s- and p-orbital components, Pth(sp), were found to qualitatively explain the α dependence of the TMR ratio except for α > αc. This is in contrast to the theoretical spin polarizations obtained from the s-, p-, and d-orbital components, Pth(spd). A decrease in the TMR ratio observed for CMS MTJs having Mn-deficient electrodes was ascribed to small s- and p-orbital components of the local density of minority-spin in-gap states at the Fermi level that appeared for both antisite CoMn atoms and Co atoms at the regular sites. © 2014 American Physical Society.
  • Gui-fang Li, Yusuke Honda, Hong-xi Liu, Ken-ichi Matsuda, Masashi Arita, Tetsuya Uemura, Masafumi Yamamoto, Yoshio Miura, Masafumi Shirai, Toshiaki Saito, Fengyuan Shi, Paul M. Voyles
    PHYSICAL REVIEW B 89 1 014428(14pp)  2014年01月 [査読有り][通常論文]
     
    We investigated the effect of nonstoichiometry on the half-metallic character of the Heusler alloy Co2MnSi (CMS) through the Mn composition (alpha) dependence of the saturation magnetization per formula unit (mu(s)) of Co2Mn alpha Si beta thin films and the tunneling magnetoresistance (TMR) ratio of CMS/MgO/CMS magnetic tunnel junctions (CMS MTJs) having Co2Mn alpha Si beta electrodes. As a basis for understanding the effect of nonstoichiometry in CMS, we developed a generalized form of the site-specific formula unit (SSFU) composition model, which assumes the formation of only antisite defects, not vacancies, to accommodate nonstoichiometry. The alpha dependence of mu(s) was well explained by density functional calculations with the coherent potential approximation based on the SSFU composition model for alpha up to a certain critical value (alpha(c)) > 1.0. The mu(s) data for Mn-deficient films deviated from the Slater-Pauling predicted data for half-metals due to Co atoms at the nominal Mn sites (Co-Mn). The theoretical spin polarizations, obtained from only the s- and p-orbital components, Pth(sp), were found to qualitatively explain the alpha dependence of the TMR ratio except for alpha > alpha(c). This is in contrast to the theoretical spin polarizations obtained from the s-, p-, and d-orbital components, Pth(spd). A decrease in the TMR ratio observed for CMSMTJs having Mn-deficient electrodes was ascribed to small s- and p-orbital components of the local density of minority-spin in-gap states at the Fermi level that appeared for both antisite Co-Mn atoms and Co atoms at the regular sites.
  • Effect of CoFe insertion on spin injection properties of Co2MnSi/CoFe/n-GaAs junctions
    Y. Ebina, T. Akiho, H. Liu, M. Yamamoto, T. Uemura
    58th Annual Conference on Magnetism and Magnetic Materials, Abstracts vol.58 p.108, AX-01  2013年11月 [査読有り][通常論文]
  • Giant tunnel magnetoresistance in fully epitaxial Co2(Mn,Fe)Si/MgO/Co2(Mn,Fe)Si magnetic tunnel junctions
    T. Kawami, H. Liu, Y. Honda, K. M. Ayele, T. Uemura, F. Shi, P. M. Voyles, M. Yamamoto
    58th Annual Conference on Magnetism and Magnetic Materials, Abstracts vol.58 p.614, FX-03  2013年11月 [査読有り][通常論文]
  • Spin and symmetry properties of the buried Co2MnSi/MgO interface.
    R. Fetzer, Y. Ohdaira, H. Naganuma, M. Oogane, Y. Ando, T. Taira, T. Uemura, M. Yamamoto, M. Aeschlimann, M. Cinchetti
    58th Annual Conference on Magnetism and Magnetic Materials, Abstracts vol.58 p.626, GB-14  2013年11月 [査読有り][通常論文]
  • Spin-dependent transport properties of strained InGaAs channel investigated through all electrical spin injection and detection
    T. Akiho, M. Yamamoto, T. Uemura
    58th Annual Conference on Magnetism and Magnetic Materials, Abstracts vol.58 p.716, HB-10  2013年11月 [査読有り][通常論文]
  • Takafumi Akiho, Jinhai Shan, Hong-Xi Liu, Ken-Ichi Matsuda, Masafumi Yamamoto, Tetsuya Uemura
    Physical Review B - Condensed Matter and Materials Physics 87 23 2013年06月17日 [査読有り][通常論文]
     
    We demonstrated electrical spin injection from a half-metallic Heusler alloy Co2MnSi electrode into a GaAs channel through observation of a spin-valve signal and a Hanle signal in the four-terminal nonlocal geometry. Furthermore, we electrically detected a nuclear field acting on electron spins, which was produced by the dynamic nuclear polarization, through observation of transient oblique Hanle signals. Samples with a Co2MnSi spin source exhibited higher spin-injection efficiency and a larger nuclear field compared to samples with a Co50Fe50 spin source, suggesting that the spin polarization of Co2MnSi is higher. This higher polarization is promising for realizing future spintronic devices and for understanding spin interactions as well as spin-dependent transport properties in a semiconductor channel. © 2013 American Physical Society.
  • Takafumi Akiho, Jinhai Shan, Hong-xi Liu, Ken-ichi Matsuda, Masafumi Yamamoto, Tetsuya Uemura
    PHYSICAL REVIEW B 87 23 235205 (7pp)  2013年06月 [査読有り][通常論文]
     
    We demonstrated electrical spin injection from a half-metallic Heusler alloy Co2MnSi electrode into a GaAs channel through observation of a spin-valve signal and a Hanle signal in the four-terminal nonlocal geometry. Furthermore, we electrically detected a nuclear field acting on electron spins, which was produced by the dynamic nuclear polarization, through observation of transient oblique Hanle signals. Samples with a Co2MnSi spin source exhibited higher spin-injection efficiency and a larger nuclear field compared to samples with a Co50Fe50 spin source, suggesting that the spin polarization of Co2MnSi is higher. This higher polarization is promising for realizing future spintronic devices and for understanding spin interactions as well as spin-dependent transport properties in a semiconductor channel.
  • Roman Fetzer, Jan-Peter Wüstenberg, Tomoyuki Taira, Tetsuya Uemura, Masafumi Yamamoto, Martin Aeschlimann, Mirko Cinchetti
    Physical Review B - Condensed Matter and Materials Physics 87 18 2013年05月17日 [査読有り][通常論文]
     
    The performance of advanced magnetic tunnel junctions built of ferromagnetic (FM) electrodes and MgO as an insulating barrier depends decisively on the properties of the FM/insulator interface. Here we investigate interface formation between the Co-based Heusler compound Co2MnSi (CMS) and MgO by means of Auger electron spectroscopy, low-energy electron diffraction, and low-energy photoemission. The studies are performed for different annealing temperatures (TA) and MgO layer coverages (4, 6, 10, 20, and 50 ML). Thin MgO top layers (tMgO≤10 ML) show distinct surface crystalline distortions, which can only be partly healed out by annealing and, furthermore, lead to distinct adsorption of carbon species after the MgO surface is exposed to air. For tMgO> 10 ML, the MgO layer surface exhibits clearly improved crystalline structure and hence only marginal amounts of adsorbates. We attribute these findings to MgO misfit dislocations occurring at the interface, inducing further defects throughout the MgO layer for up to at least 10 ML. Furthermore, spin-polarized photoemission spectra of the CMS/MgO interface are obtained for MgO coverages up to 20 ML, showing a clear positive spin polarization near the Fermi energy (EF) in all cases. © 2013 American Physical Society.
  • Roman Fetzer, Jan-Peter Wuestenberg, Tomoyuki Taira, Tetsuya Uemura, Masafumi Yamamoto, Martin Aeschlimann, Mirko Cinchetti
    PHYSICAL REVIEW B 87 18 184418 (7pp)  2013年05月 [査読有り][通常論文]
     
    The performance of advanced magnetic tunnel junctions built of ferromagnetic (FM) electrodes and MgO as an insulating barrier depends decisively on the properties of the FM/insulator interface. Here we investigate interface formation between the Co-based Heusler compound Co2MnSi (CMS) and MgO by means of Auger electron spectroscopy, low-energy electron diffraction, and low-energy photoemission. The studies are performed for different annealing temperatures (T-A) and MgO layer coverages (4, 6, 10, 20, and 50 ML). Thin MgO top layers (t(MgO) <= 10 ML) show distinct surface crystalline distortions, which can only be partly healed out by annealing and, furthermore, lead to distinct adsorption of carbon species after the MgO surface is exposed to air. For t(MgO) > 10 ML, the MgO layer surface exhibits clearly improved crystalline structure and hence only marginal amounts of adsorbates. We attribute these findings to MgO misfit dislocations occurring at the interface, inducing further defects throughout the MgO layer for up to at least 10 ML. Furthermore, spin-polarized photoemission spectra of the CMS/MgO interface are obtained for MgO coverages up to 20 ML, showing a clear positive spin polarization near the Fermi energy (E-F) in all cases.
  • Influence of interfacial structural properties on tunnel magnetoresistance in epitaxial magnetic tunnel junctions with Co2MnSi electrode and MgO barrier
    H.-x. Liu, Y. Honda, K.-i. Matsuda, M. Arita, T. Uemura, M. Yamamoto
    12th Joint MMM/Intermag Conf., Abstracts (USB memory) vol.12 p.507, EI-09  2013年01月 [査読有り][通常論文]
  • Transient effects on oblique Hanle signals observed in ferromagnet/semiconductor heterojunctions with non-local four-terminal configuration
    T. Akiho, J.-h. Shan, K.-i. Matsuda, M. Yamamoto, T. Uemura
    12th Joint MMM/Intermag Conf., Abstracts (USB memory) vol.12 p.871, HR-04  2013年01月 [査読有り][通常論文]
  • Enhanced coherent tunneling contribution in epitaxial magnetic tunnel junctions with a Co2MnSi electrode and a MgO barrier due to improved interfacial structural properties
    H.-x. Liu, Y. Honda, K.-i. Matsuda, T. Uemura, M. Yamamoto
    The 2nd Int’l Conf. of Asia Union of Magnetics Societies (ICAUMS 2012), The 36th Annual Conf. on Magnetics in Japan, Abstracts vol2 p.28, 2pD-4  2012年10月 [査読有り][通常論文]
  • Tunnel barrier thickness dependence of Hanle-type signals in CoFe/MgO/n-Ge tunnel junctions investigated through three-terminal configuration
    G.-f. Li, M. Miki, K.-i. Matsuda, T. Uemura, M. Yamamoto
    The 17th Int’l Conf. on Molecular Beam Epitaxy (MBE 2012), Abstracts vol17 p.5, MoA-1-2  2012年09月 [査読有り][通常論文]
  • Tunnel barrier thickness dependence of Hanle-type signals in CoFe/MgO/n-Si and CoFe/MgO/n-Ge junctions investigated through three-terminal configuration
    T. Uemura, G.-f. Li, J. Fujisawa, K. Kondo, K.-i. Matsuda, M. Yamamoto
    2012 Int’l Conf. on Solid State Devices and Materials (SSDM 2012), Extended Abstracts (USB Memory) pp.1223-1224, K-9-4  2012年09月 [査読有り][通常論文]
  • Transient oblique Hanle signals observed in Co2MnSi/CoFe/n-GaAs with non-local four-terminal configuration
    J.-h. Shan, T. Akiho, K.-i. Matsuda, M. Yamamoto, T. Uemura
    2012 Int’l Conf. on Solid State Devices and Materials (SSDM 2012), Extended Abstracts (USB Memory) pp.1219-1220, K-9-2  2012年09月 [査読有り][通常論文]
  • Temperature dependence of spin-dependent tunneling resistances of MgO-buffered Co2MnSi/MgO/Co2MnSi magnetic tunnel junctions
    Y. Honda, H.-x. Liu, K.-i. Matsuda, T. Uemura, M. Yamamoto
    2012 Int’l Conf. on Solid State Devices and Materials (SSDM 2012), Extended Abstracts (USB Memory) pp.1197-1198, K-6-4  2012年09月 [査読有り][通常論文]
  • Gui-fang Li, Tomoyuki Taira, Hong-xi Liu, Ken-ichi Matsuda, Tetsuya Uemura, Masafumi Yamamoto
    JAPANESE JOURNAL OF APPLIED PHYSICS 51 9 093003 (5pp)  2012年09月 [査読有り][通常論文]
     
    Fully epitaxial magnetic tunnel junctions (MTJs) with Co50Fe50 (CoFe) electrodes and a MgO barrier were fabricated on Ge(001) single-crystal substrates via a MgO interlayer. Microfabricated CoFe/MgO/CoFe MTJs with a 10-nm-thick MgO interlayer showed a high tunnel magnetoresistance (TMR) ratio of 218% at 293 K, which is encouraging for monolithic integration of MTJs and Ge field-effect transistors for constructing future-generation nonvolatile logic circuits featuring ultralow-power consumption. Furthermore, MTJs with even a decreased MgO interlayer thickness of 1.0nm showed a relatively high TMR ratio of 110% at 293 K, suggesting the promise of heterostructures consisting of MTJ/MgO interlayer/Ge(001) as a key device structure for spin injection into a Ge channel from an MTJ. (C) 2012 The Japan Society of Applied Physics
  • Hong-xi Liu, Yusuke Honda, Ken-ichi Matsuda, Masashi Arita, Tetsuya Uemura, Masafumi Yamamoto
    JAPANESE JOURNAL OF APPLIED PHYSICS 51 9 093004 (9pp)  2012年09月 [査読有り][通常論文]
     
    Fully epitaxial magnetic tunnel junctions (MTJs) with a Heusler alloy Co2MnSi electrode and a MgO barrier were prepared on MgO-buffered MgO(001) substrates with various layer structures to elucidate the contribution of coherent tunneling to the spin-dependent tunneling characteristics of these MTJs, which potentially feature both the half-metallicity of Co2MnSi and coherent tunneling. MTJs consisting of (from the lower side) Co50Fe50 (CoFe)/MgO/Co2MnSi or CoFe-buffered Co2MnSi/MgO/CoFe showed almost identical, high tunnel magnetoresistance (TMR) ratios of 335% at 290 K (1049% at 4.2 K) and 340% at 290K (879% at 4.2 K), respectively. In contrast, MTJs consisting of MgO-buffered Co2MnSi/MgO/CoFe showed a lower TMR ratio of 173% at 290 K (448% at 4.2 K). The higher TMR ratios obtained for CoFe/MgO/Co2MnSi MTJs and CoFe-buffered Co2MnSi/MgO/CoFe MTJs can be ascribed to the enhanced contribution of coherent tunneling that originated from decreased misfit dislocation densities at the lower and upper interfaces with a MgO barrier. (C) 2012 The Japan Society of Applied Physics
  • Tetsuya Uemura, Kenji Kondo, Jun Fujisawa, Ken-ichi Matsuda, Masafumi Yamamoto
    APPLIED PHYSICS LETTERS 101 13 132411 (4pp)  2012年09月 [査読有り][通常論文]
     
    The MgO thickness dependence of Hanle signals in Co50Fe50/MgO/n-Si tunnel junctions was investigated using a three-terminal geometry. The observed Hanle signal is several orders of magnitude stronger than the predicted value by conventional theory as reported in many literatures. Furthermore, the magnitude of the spin signal depends on the junction resistance rather than the channel resistance, implying that the largest part of the observed Hanle signal is not caused by spin accumulation in the semiconductor region. A possible origin of the observed strong Hanle signal is due to a modulation of the tunneling resistance by a magnetic field, which is induced by the spin precession in localized states formed in the vicinity of the Co50Fe50/MgO interface. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4754545]
  • Hong-xi Liu, Yusuke Honda, Tomoyuki Taira, Ken-ichi Matsuda, Masashi Arita, Tetsuya Uemura, Masafumi Yamamoto
    APPLIED PHYSICS LETTERS 101 13 132418 (5pp)  2012年09月 [査読有り][通常論文]
     
    Giant tunnel magnetoresistance (TMR) ratios of up to 1995% at 4.2K and up to 354% at 290K were obtained for epitaxial Co2MnSi/MgO/Co2MnSi magnetic tunnel junctions (MTJs) featuring a reduced lattice mismatch in the MTJ trilayer by introducing a thin Co2MnSi lower electrode deposited on a Co50Fe50 buffer layer. The obtained giant TMR ratios can be explained by the enhanced contribution of coherent tunneling originating from the increased misfit dislocation spacing at the lower and upper interfaces with a MgO barrier along with the half-metallicity of Co2MnSi electrodes. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4755773]
  • Spin-polarization measurements for Co?2MnSi using Co2MnSi/MgO/NbN epitaxial tunnel junctions
    Ken-ichi Matsuda, Takaho Shinoki, Tomoyuki Taira, Tetsuya Uemura, Masafumi Yamamoto
    The 19th Int’l Conf. on Magnetism (ICM2012), Abstracts of ICM2012 vol.19 p.351, SK06  2012年07月 [査読有り][通常論文]
  • MgO thickness dependence of spin accumulation signal in Co50Fe50/MgO/Si
    T. Uemura, J. Fujisawa, K.-i. Matsuda, M. Yamamoto
    Int’l Magnetics Conf. 2012 (INTERMAG 2012), Digest (USB Memory) AD-06  2012年05月 [査読有り][通常論文]
  • Electrical spin injection from Co2MnSi Heusler alloy into GaAs and electrical detection of dynamic nuclear polarization
    T. Akiho, T. Uemura, K.-i. Matsuda, M. Yamamoto
    Int’l Magnetics Conf. 2012 (INTERMAG 2012), Digest (USB Memory) AD-03  2012年05月 [査読有り][通常論文]
  • Temperature dependence of spin-dependent tunneling conductances of fully epitaxial Co2MnSi-based magnetic tunnel junctions
    H.-x. Liu, Y. Honda, K.-i. Matsuda, T. Uemura, M. Yamamoto
    Int’l Magnetics Conf. 2012 (INTERMAG 2012), Digest (USB Memory) EB-10  2012年05月 [査読有り][通常論文]
  • Possibility of Superconducting Proximity Effect of Equal-spin Triplet Components in NbN/Co2Cr0.6Fe0.4Al/NbN Junctions
    Ken-ichi Matsuda, Tetsuya Uemura, Masafumi Yamamoto
    Int’l Conf. on Topological Quantum Phenomena (TQP2012), Abstracts of TQP2012 vol.1 p.149, PB23  2012年05月 [査読有り][通常論文]
  • Jan-Peter Wüstenberg, Roman Fetzer, Martin Aeschlimann, Mirko Cinchetti, Jan Minár, Jürgen Braun, Hubert Ebert, Takayuki Ishikawa, Tetsuya Uemura, Masafumi Yamamoto
    Physical Review B - Condensed Matter and Materials Physics 85 6 2012年02月15日 [査読有り][通常論文]
     
    Using a combined approach of spin-resolved photoemission spectroscopy, band structure and photoemission calculations we investigate the influence of bulk defects and surface states on the spin polarization of nonstoichiometric Co 2Mn αSi thin films (with α=0.69 and α=1.19) with bulk L2 1 order. We find that for Mn-poor alloys the spin polarization at the Fermi energy (E F) is negative due to the presence of Co Mn antisite and minority surface state contributions. In Mn-rich alloys, the suppression of Co Mn antisites leads to a positive spin polarization at E F, and the influence of minority surface states on the photoelectron spin polarization is reduced. © 2012 American Physical Society.
  • Jan-Peter Wuestenberg, Roman Fetzer, Martin Aeschlimann, Mirko Cinchetti, Jan Minar, Juergen Braun, Hubert Ebert, Takayuki Ishikawa, Tetsuya Uemura, Masafumi Yamamoto
    PHYSICAL REVIEW B 85 6 064407 (10pp)  2012年02月 [査読有り][通常論文]
     
    Using a combined approach of spin-resolved photoemission spectroscopy, band structure and photoemission calculations we investigate the influence of bulk defects and surface states on the spin polarization of nonstoichiometric Co2Mn alpha Si thin films (with alpha = 0.69 and alpha = 1.19) with bulk L2(1) order. We find that for Mn-poor alloys the spin polarization at the Fermi energy (E-F) is negative due to the presence of Co-Mn antisite and minority surface state contributions. In Mn-rich alloys, the suppression of Co-Mn antisites leads to a positive spin polarization at E-F, and the influence of minority surface states on the photoelectron spin polarization is reduced.
  • Takafumi Akiho, Tetsuya Uemura, Masanobu Harada, Ken-ichi Matsuda, Masafumi Yamamoto
    JAPANESE JOURNAL OF APPLIED PHYSICS 51 2 02BM01 (5pp)  2012年02月 [査読有り][通常論文]
     
    The effect of MgO barrier insertion on a spin-valve signal in a four-terminal non-local geometry and on tunneling anisotropic magnetoresistance (TAMR) characteristics in a three-terminal geometry was investigated in Co50Fe50/n-GaAs heterojunctions. Inserting a MgO barrier significantly enhanced the spin-valve signal amplitude by a factor of 38, and the sign of spin polarization was opposite that of a sample without a MgO barrier. The TAMR effect was suppressed in the case of a Co50Fe50/MgO/n-GaAs junction. This suppression of the TAMR effect can be explained by the suppression of Fermi-level pinning and the lowering of Schottky barrier height. (C) 2012 The Japan Society of Applied Physics
  • Non-local electrical detection of Hanle signals in Co2MnSi/Co50Fe50/n-GaAs Schottky tunnel junctions
    T. Akiho, T. Uemura, H. Harada, K.-i., Matsuda, M. Yamamoto
    56th Annual Conf. on Magnetism & Magnetic Materials, Abstracts (USB Memory) vol.56 p.471, GB-12  2011年11月 [査読有り][通常論文]
  • Almost identical oscillations in tunneling resistances as a function of barrier thickness for parallel and antiparallel configurations for fully epitaxial magnetic tunnel junctions with a MgO barrier
    Y. Honda, S. Hirata, H.-x. Liu, K.-i. Matsuda, T. Uemura, M. Yamamoto
    56th Annual Conf. on Magnetism & Magnetic Materials, Abstracts (USB Memory) vol.56 p.426, FP-01  2011年11月 [査読有り][通常論文]
  • Fabrication of epitaxial magnetic tunnel junctions with a Co2MnSi thin film and a MgO barrier on Ge(001) substrates via a MgO interlayer
    G.-f. Li, T.Taira, H.-x. Liu, K. -i. Matsuda, T. Uemura, M. Yamamoto
    56th Annual Conf. on Magnetism & Magnetic Materials, Abstracts (USB Memory) vol.56 p.251, DE-04  2011年11月 [査読有り][通常論文]
  • Spin-dependent transport properties of fully epitaxial magnetic tunnel junctions of CoFe/MgO/CoFe ultrathin layer/Co2MnSi
    H.-x. Liu, T. Taira, Y. Honda, K. -i. Matsuda, T. Uemura, M. Yamamoto, Y. Miura, M. Shirai
    56th Annual Conf. on Magnetism & Magnetic Materials, Abstracts (USB Memory) vol.56 p.260, DE-01  2011年11月 [査読有り][通常論文]
  • Effect of MgO Barrier Insertion on Spin-dependent Transport Properties of CoFe/n-GaAs
    T. Akiho, M. Harada, T. Uemura, K.-i. Matsuda, M. Yamamoto
    2011 Int’l Conf. on Solid State Devices and Materials, Extended Abstracts (USB memory) pp.1460-1461,  2011年09月 [査読有り][通常論文]
  • Fabrication of fully epitaxial magnetic tunnel junctions with CoFe electrodes and a MgO barrier on Ge(001) substrates via a MgO interlayer
    G.-f. Li, T. Taira, H.-x. Liu, K.-i. Matsuda, T. Uemura, M. Yamamoto
    2011 Int’l Conf. on Solid State Devices and Materials, Extended Abstracts (USB memory) pp.1448-1449,  2011年09月 [査読有り][通常論文]
  • Effect of GaAs Surface Structure on Tunneling Anisotropic Magnetoresistance in Epitaxial Co50Fe50/n-GaAs Junctions
    T. Uemura, T. Akiho, M. Harada, K.-i. Matsuda, M. Yamamoto
    2011 Int’l Conf. on Solid State Devices and Materials, Extended Abstracts (USB memory) pp.448-449, P-12-9  2011年09月 [査読有り][通常論文]
  • Xeniya Kozina, Gerhard H. Fecher, Gregory Stryganyuk, Siham Ouardi, Benjamin Balke, Claudia Felser, Gerd Schoenhense, Eiji Ikenaga, Takeharu Sugiyama, Naomi Kawamura, Motohiro Suzuki, Tomoyuki Taira, Tetsuya Uemura, Masafumi Yamamoto, Hiroaki Sukegawa, Wenhong Wang, Koichiro Inomata, Keisuke Kobayashi
    PHYSICAL REVIEW B 84 5 054449 (8pp)  2011年08月 [査読有り][通常論文]
     
    This work reports the measurement of magnetic dichroism in angular-resolved photoemission from in-plane magnetized buried thin films. The high bulk sensitivity of hard x-ray photoelectron spectroscopy (HAXPES) in combination with circularly polarized radiation enables the investigation of the magnetic properties of buried layers. HAXPES experiments with an excitation energy of 8 keV were performed on exchange-biased magnetic layers covered by thin oxide films. Two types of structures were investigated with the IrMn exchange-biasing layer either above or below the ferromagnetic layer: one with a CoFe layer on top and another with a Co(2)FeAl layer buried beneath the IrMn layer. A pronounced magnetic dichroism is found in the Co and Fe 2p states of both materials. The localization of the magnetic moments at the Fe site conditioning the peculiar characteristics of the Co(2)FeAl Heusler compound, predicted to be a half-metallic ferromagnet, is revealed from the magnetic dichroism detected in the Fe 2p states.
  • Tetsuya Uemura, Takafumi Akiho, Masanobu Harada, Ken-ichi Matsuda, Masafumi Yamamoto
    APPLIED PHYSICS LETTERS 99 8 082108 (3pp)  2011年08月 [査読有り][通常論文]
     
    A clear spin-valve signal and a Hanle signal were observed in a Co50Fe50/n-GaAs Schottky tunnel junction through a four-terminal non-local geometry. The sign and magnitude of the spin-valve signal were strongly dependent on the bias current, suggesting that the spin polarization at the Co50Fe50/n-GaAs interface had strong energy dependence. A clear spin-valve signal was observed at temperatures up to 290 K. The magnitude of the spin-valve signal monotonically decreased by a factor of 7.9 as the temperature increased from 10 K to 290 K; this factor was significantly smaller than the factors reported for Fe/n-GaAs junctions which range from 35 to 80. (C) 2011 American Institute of Physics. [doi:10.1063/1.3630032]
  • Electrical detection of spin injection from Co50Fe50 into GaAs at room temperature
    T. Uemura, M. Harada, T. Akiho, K.-i. Matsuda, M. Yamamoto
    15th Int’l Conf. on Modulated Semiconductor Structures (MSS 15), Abstracts vol.15 Tu-P-87  2011年07月 [査読有り][通常論文]
  • Oscillations in spin-dependent tunneling resistances as a function of MgO barrier thickness in epitaxial magnetic tunnel junctions with Heusler alloy Co2MnSi electrodes
    Y. Honda, S. Hirata, H.-x. Liu, K.-i. Matsuda, T. Uemura, M. Yamamoto
    5th Int’l Workshop on Spin Currents, Abstracts vol.5 p.136, P2-36  2011年07月 [査読有り][通常論文]
  • Spin injection from Co50Fe50 into GaAs at room temperature
    T. Akiho, M. Harada, T. Uemura, K.-i. Matsuda, M. Yamamoto
    5th Int’l Workshop on Spin Currents, Abstracts vol.5 p.122, P2-22  2011年07月 [査読有り][通常論文]
  • Spin-dependent tunneling characteristics of Heusler alloy/MgO heterostructures
    M. Yamamoto, T. Uemura, K.-i. Matsuda
    5th Int’l Workshop on Spin Currents, Abstracts vol.5 p.41, CA-1  2011年07月 [査読有り][招待有り]
  • Takafumi Akiho, Tetsuya Uemura, Masanobu Harada, Ken-ichi Matsuda, Masafumi Yamamoto
    APPLIED PHYSICS LETTERS 98 23 232109 (3pp)  2011年06月 [査読有り][通常論文]
     
    The effects of MgO tunnel barriers on both junction resistance and tunneling anisotropic magnetoresistance (TAMR) characteristics of Co2MnSi(CMS)/MgO/n-GaAs junctions and Co50Fe50(CoFe)/MgO/n-GaAs junctions were investigated. The resistance-area (RA) product of the CMS/MgO/n-GaAs junctions showed an exponential dependence on MgO thickness (t(MgO)), indicating that the MgO layer acts as a tunneling barrier. The RA product of CMS/MgO/n-GaAs with t(MgO)< 1 nm was smaller than that of the sample without MgO. The observed spin-valvelike magnetoresistance of CMS/n-GaAs and CoFe/n-GaAs Schottky tunnel junctions attributed to the TAMR effect did not appear in the cases of CMS/MgO/n-GaAs and CoFe/MgO/n-GaAs tunnel junctions. The lowering of the RA product and the suppression of the TAMR effect caused by inserting a thin MgO layer between CMS and n-GaAs were both possibly due to suppression of the Fermi-level pinning of GaAs and lowering of the Schottky barrier height. (c) 2011 American Institute of Physics. [doi:10.1063/1.3595311]
  • Gui-fang Li, Tomoyuki Taira, Ken-ichi Matsuda, Masashi Arita, Tetsuya Uemura, Masafumi Yamamoto
    APPLIED PHYSICS LETTERS 98 26 262505 (3pp)  2011年06月 [査読有り][通常論文]
     
    We prepared Heusler alloy Co2MnSi/MgO heterostructures on single-crystal Ge(001) substrates through magnetron sputtering for Co2MnSi and electron beam evaporation for MgO as a promising candidate for future generation spin-based functional devices. Structural investigations showed that the Co2MnSi/MgO heterostructure was grown epitaxially on a Ge(001) substrate with extremely smooth and abrupt interfaces and showed the L2(1) structure for the Co2MnSi film. Furthermore, a sufficiently high saturation magnetization (mu(s)) value of 5.1 mu(B)/f.u. at 10 K, which is close to the theoretically predicted mu(s) of 5.0 mu(B)/f.u. for half-metallic Co2MnSi, was obtained for prepared Co2MnSi films. (C) 2011 American Institute of Physics. [doi:10.1063/1.3605675]
  • Epitaxial growth of Heusler alloy Co2MnSi/MgO heterostructure on Ge(001) substrate
    G.-f. Li, T. Taira, K.-i. Matsuda, T. Uemura, M. Yamamoto
    Int’l Magnetics Conf. 2011 (INTERMAG 2011), Digest(USB Memory) HC-06  2011年04月 [査読有り][通常論文]
  • Electrical injection and detection of spin-polarized electrons in an epitaxial Co50Fe50/n-GaAs junction
    T. Uemura, M. Harada, T. Akiho, K.-i. Matsuda, M. Yamamoto
    Int’l Magnetics Conf. 2011(INTERMAG 2011), Digests (USB Memory) BP-08  2011年04月 [査読有り][通常論文]
  • Spin-dependent transport properties of Co2MnSi/MgO/n-GaAs tunnel junctions
    T. Akiho, M. Harada, T. Uemura, K.-i. Matsuda, M. Yamamoto
    Int’l Magnetics Conf. 2011 (INTERMAG 2011), Digest(USB Memory) BP-03  2011年04月 [査読有り][通常論文]
  • Tetsuya Uemura, Masanobu Harada, Takafumi Akiho, Ken-ichi Matsuda, Masafumi Yamamoto
    APPLIED PHYSICS LETTERS 98 10 102503 (3pp)  2011年03月 [査読有り][通常論文]
     
    An epitaxial Co50Fe50 layer was grown on As-terminated or Ga-terminated GaAs, and the influence of the termination species on both uniaxial-type tunneling anisotropic magnetoresistance (TAMR) characteristics and magnetocrystalline anisotropy was investigated. The magnetocrystalline anisotropy induced in the Co50Fe50 thin film was strongly dependent on the termination species of the GaAs surface, while the TAMR characteristics were almost unchanged. These experimental findings suggest that the TAMR effect is due to the anisotropy of electronic structure rather than the structural anisotropy. (C) 2011 American Institute of Physics. [doi:10.1063/1.3561759]
  • 植村哲也, 山本眞史
    まてりあ vol.49 12 pp. 566-569 - 569 The Japan Institute of Metals and Materials 2010年12月 [査読有り][招待有り]
  • Satoshi Imai, Ken-ichi Matsuda, Takayuki Ishikawa, Tetsuya Uemura, Masafumi Yamamoto
    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470 S851 - S853 2010年12月 [査読有り][通常論文]
     
    Transport properties of junctions consisting of NbN superconducting electrodes coupled with Co2Co0.6Fe0.4Al (CCFA), a material known for high spin polarization, were investigated. CCFA/NbN bilayers were epitaxially grown on MgO substrate, and then fabricated into NbN/CCFA/NbN lateral junctions by electron-beam lithography. In contrast to the NbTiN/CrO2/NbTiN lateral junction [R.S. Keizer et al., Nature 439 (2006) 825], no Josephson supercurrent through the CCFA channel was observed in our junctions, whose CCFA channel length was 80 nm. A possible explanation for this result is that conversion from spin-singlet Cooper pairs to spin-triplets was strongly suppressed at the NbN/CCFA interface due to the formation of high quality NbN/CCFA interfaces. (C) 2009 Elsevier B.V. All rights reserved.
  • Highly spin-polarized tunneling characteristics at room temperature in magnetic tunnel junctions with a half-metallic Heusler-alloy spin source and a MgO barrier
    H.-x. Liu, T. Taira, Y. Honda, K.-i. Matsuda, T. Uemura, M. Yamamoto
    55th Annual Conf. on Magnetism & Magnetic Materials, Abstracts (CD-ROM) vol.55 pp.370-371, ET-11  2010年11月 [査読有り][通常論文]
  • Giant oscillations of spin-dependent tunneling resistances as a function of MgO barrier thickness in fully epitaxial magnetic tunnel junctions of Co2Cr0.6Fe0.4Al/MgO/Co2Cr0.6Fe0.4Al
    M. Yamamoto, T. Marukame, T. Ishikawa, T. Taira, K.-i. Matsuda, T. Uemura
    55th Annual Conf. on Magnetism & Magnetic Materials, Abstracts (CD-ROM) vol.55 p.165, CB-01  2010年11月 [査読有り][通常論文]
  • Giant tunnel magnetoresistance in half-metallic Co2MnSi-based fully epitaxial magnetic tunnel junctions
    T. Taira, H.-x. Liu, S. Hirata, K.-i. Matsuda, T. Uemura, M. Yamamoto
    55th Annual Conf. on Magnetism & Magnetic Materials, Abstracts (CD-ROM) vol.55 pp.118-119, BH-10  2010年11月 [査読有り][通常論文]
  • Superconducting proximity effect of spin-triplet pairs in NbN/Co2Cr0.6Fe0.4Al/NbN junctions
    K.-i. Matsuda, T. Uemura, M. Yamamoto
    55th Annual Conf. on Magnetism & Magnetic Materials, Abstracts (CD-ROM) vol.55 p.28, AE-10  2010年11月 [査読有り][通常論文]
  • Highly spin-polarized tunneling in Heusler-alloy-based magnetic tunnel junctions with a Co2MnSi upper electrode and a MgO barrier
    H.-x. Liu, T. Taira, Y. Honda, K.-i. Matsuda, T. Uemura, M. Yamamoto
    2010 Int’l Conf. on Solid State Devices and Materials, Extended Abstract (USB-MEMORY) pp.1122-1123, F-6-4  2010年09月 [査読有り][通常論文]
  • Electrical detection of a non-local signal in Co2MnSi/MgO/n-GaAs tunnel junctions
    M. Harada, T. Uemura, T. Akiho, K.-i. Matsuda, M. Yamamoto
    6th Int’l Conf. on the Physics and Application of Spin Related Phenomena in Semiconductors (PASPS-VI),Abstracts vol.6 pp.259-260, P2-46  2010年08月 [査読有り][通常論文]
  • Tetsuya Uemura, Masanobu Harada, Ken-ichi Matsuda, Masafumi Yamamoto
    APPLIED PHYSICS LETTERS 96 25 252106 (3pp)  2010年06月 [査読有り][通常論文]
     
    A strong voltage-dependent tunneling anisotropic magnetoresistance (TAMR) effect was observed in a fully epitaxial Co(2)MnSi/n-GaAs junction and a Co(50)Fe(50)/n-GaAs junction. Angular dependence of the tunnel resistance showed uniaxial-type anisotropic tunnel resistance between the [110] and [1 (1) over bar0] directions in the (001) plane. The voltage at which the TAMR effect was suppressed was close to that at which the differential conductance reached a minimum in both samples, suggesting that the strength and/or the sign of the internal electric field at the Co(2)MnSi/n-GaAs and Co(50)Fe(50)/n-GaAs junctions could be related to the voltage-dependent TAMR effect through spin-orbit interaction. (C) 2010 American Institute of Physics. [doi:10.1063/1.3456558]
  • Masafumi Yamamoto, Takayuki Ishikawa, Tomoyuki Taira, Gui-fang Li, Ken-ichi Matsuda, Tetsuya Uemura
    JOURNAL OF PHYSICS-CONDENSED MATTER 22 16 164212 (9pp)  2010年04月 [査読有り][通常論文]
     
    Fully epitaxial magnetic tunnel junctions (MTJs) with Co-based Heusler alloy Co2MnSi electrodes and a MgO tunnel barrier were fabricated with various values of Mn composition a for Co2Mn alpha Si in Co2Mn alpha Si/MgO/Co2Mn alpha Si MTJs. The tunnel magnetoresistance (TMR) ratios at both 4.2 K and room temperature (RT) increased systematically with increasing a in Co2Mn alpha Si electrodes from Mn-deficient compositions (alpha < 1) up to a certain Mn-rich composition (alpha > 1), demonstrating high TMR ratios of 1135% at 4.2 K and 236% at RT for MTJs with Mn-rich Co2Mn alpha Si electrodes with alpha = 1.29. Identically fabricated Co2Mn beta Ge delta/MgO/Co2Mn beta Ge delta (delta = 0.38) MTJs showed similar dependence of the TMR ratio on Mn composition beta, demonstrating relatively high TMR ratios of 650% at 4.2 K and 220% at RT for beta = 1.40. The Mn composition dependence of the TMR ratio at both 4.2 K and RT observed commonly for both Co2MnSi/MgO/Co2MnSi and Co2MnGe/MgO/Co2MnGe MTJs can be attributed to suppressed minority-spin in-gap states around the Fermi level for Mn-rich Co2MnSi and Co2MnGe electrodes.
  • Takao Marukame, Takayuki Ishikawa, Tomoyuki Taira, Ken-ichi Matsuda, Tetsuya Uemura, Masafumi Yamamoto
    PHYSICAL REVIEW B 81 13 134432 (5pp)  2010年04月 [査読有り][通常論文]
     
    Giant oscillations in spin-dependent tunneling resistances as a function of MgO barrier thickness (t(MgO)) were observed for fully epitaxial magnetic tunnel junctions with Heusler alloy Co2Cr0.6Fe0.4Al electrodes and a MgO barrier. The oscillations in tunneling resistances were well approximated by a superposition of an exponential function of exp(at(MgO)+b) and a periodic function of 1 + C cos[(2 pi/T)t(MgO)+phi] with significantly large amplitudes C similar to 0.16 +/- 0.01 even at 293 K for both parallel and antiparallel magnetization orientations. The period was found to be almost independent of temperature and bias voltage (V). The amplitudes C showed only weak dependence on V at least up to 0.2 V. These features should be a key to understand the origin of the pronounced oscillations.
  • Effect of the Mn composition in Co2MnSi electrodes on tunnel magnetoresistance characteristics of Co2MnSi/MgO/Co2MnSi magnetic tunnel junctions
    T. Ishikawa, H.-x. Liu, T. Taira, K.-i. Matsuda, T. Uemura, M. Yamamoto
    11th Joint MMM/Intermag Conf., Digest (CD-ROM) vol.11 p.1888, HH-04  2010年01月 [査読有り][通常論文]
  • Strong bias-voltage dependence of tunneling anisotropic magneto-resistance in epitaxial ferromagnet/n-GaAs junctions
    T. Uemura, M. Harada, K.-i. Matsuda, M. Yamamoto
    11th Joint MMM/Intermag Conf., Digests (CD-ROM) vol.11 p.1225, EU-17  2010年01月 [査読有り][通常論文]
  • Masafumi Yamamoto, Takayuki Ishikawa, Tomoyuki Taira, Gui-Fang Li, Ken-Ichi Matsuda, Tetsuya Uemura
    Journal of Physics Condensed Matter 22 16 p.1192, ET-03  2010年 [査読有り][通常論文]
     
    Fully epitaxial magnetic tunnel junctions (MTJs) with Co-based Heusler alloy Co2MnSi electrodes and a MgO tunnel barrier were fabricated with various values of Mn composition α for Co2Mn αSi in Co2MnαSi/MgO/Co 2MnαSi MTJs. The tunnel magnetoresistance (TMR) ratios at both 4.2K and room temperature (RT) increased systematically with increasing α in Co2MnαSi electrodes from Mn-deficient compositions (α < 1) up to a certain Mn-rich composition (α > 1), demonstrating high TMR ratios of 1135% at 4.2K and 236% at RT for MTJs with Mn-rich Co2MnαSi electrodes with α = 1.29. Identically fabricated Co2MnβGe δ/MgO/Co2MnβGeδ (δ = 0.38) MTJs showed similar dependence of the TMR ratio on Mn composition β, demonstrating relatively high TMR ratios of 650% at 4.2K and 220% at RT for β = 1.40. The Mn composition dependence of the TMR ratio at both 4.2K and RT observed commonly for both Co2MnSi/MgO/Co 2MnSi and Co2MnGe/MgO/Co2MnGe MTJs can be attributed to suppressed minority-spin in-gap states around the Fermi level for Mn-rich Co2MnSi and Co2MnGe electrodes. © 2010 IOP Publishing Ltd.
  • Takayuki Ishikawa, Hong-xi Liu, Tomoyuki Taira, Ken-ichi Matsuda, Tetsuya Uemura, Masafumi Yamamoto
    APPLIED PHYSICS LETTERS 95 23 232512 (3pp)  2009年12月 [査読有り][通常論文]
     
    Fully epitaxial Co2MnSi (CMS)/MgO/CMS magnetic tunnel junctions (MTJs) with various values of Mn composition alpha in Co2Mn alpha Si electrodes were fabricated and the influence of alpha on the tunnel magnetoresistance (TMR) characteristics of these MTJs was investigated. MTJs with Mn-rich CMS electrodes showed TMR ratios, up to 1135% at 4.2 K and 236% at room temperature for alpha = 1.29, exceeding those of MTJs with CMS electrodes having an almost stoichiometric composition. A possible origin of the higher TMR ratios for alpha beyond 1.0 is a decreased density of gap states existing around the Fermi level in the half-metal gap caused by the suppression of Co-Mn antisites, where a Mn site is replaced by a Co atom, for Mn-rich CMS electrodes. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3272926]
  • Keisuke Sawada, Tetsuya Uemura, Masahiro Masuda, Ken-ichi Matsuda, Masafumi Yamamoto
    IEEE TRANSACTIONS ON MAGNETICS 45 10 3780 - 3783 2009年10月 [査読有り][通常論文]
     
    Devices consisting of single or double magnetic tunnel junctions (MTJs) with cross-magnetization configurations were proposed to enable simultaneous electrical detection of both the structure and motion of a domain wall (DW), and the operation of these devices was confirmed through micromagnetic simulation. Through the tunnel magnetoresistance (TMR) effect of the MTJs, two types of domain-wall structure formed in a ferromagnetic wire were clearly identified: a transverse wall (TW) in which the magnetization at the center of the wall is directed transverse to the wire axis, and a vortex wall (VW) in which the magnetization circulates in the plane about a small perpendicular vortex core. In addition to the structural difference between TW and VW, the velocity of the DW motion was detected through the time response of the TMR.
  • Fabrication and Transport Properties of NbN/Co2Cr0.6Fe0.4Al/NbN Lateral Junctions
    S. Imai, K.-i. Matsuda, T. Ishikawa, T. Uemura, M. Yamamoto
    9th Int’l Conf. on Materials and Mechanisms of Superconductivity (M2S-IX) (USB Memory) vol.9 PS-G-589  2009年09月 [査読有り][通常論文]
  • Tunneling anisotropic magneto-resistance in an epitaxial Co2MnSi/n-GaAs junction
    M. Harada, T. Uemura, Y. Imai, K.-i. Matsuda, M. Yamamoto
    The 14th Int’l Conf. on Modulated Semiconductor Structures (MSS-14), Abstract vol.14 p.195, M5e  2009年07月 [査読有り][通常論文]
  • Spin-dependent tunneling characteristics of fully epitaxial Co2MnGe/MgO/Co2MnGe magnetic tunnel junctions
    T. Taira, S. Hirata, T. Ishikawa, K.-i. Matsuda, T. Uemura, M. Yamamoto
    20th Int’l Colloquium on Magnetic Films and Surfaces (ICMFS2009), Abstracts p.381, P-We30  2009年07月 [査読有り][通常論文]
  • Tunneling spectroscopy of magnetic tunnel junctions with Heusler alloy Co2MnGe electrodes and a MgO barrier
    S. Hirata, T. Taira, T. Ishikawa, K.-i. Matsuda, T. Uemura, M. Yamamoto
    Int’l Conf. on Magnetism (ICM2009), Abstracts p.54, Mo-A-5.4-07  2009年07月 [査読有り][通常論文]
  • Spin-dependent electronic structure of Heusler alloy Co2MnSi upper electrodes in magnetic tunnel junctions
    T. Ishikawa, N. Itabashi, T. Taira, K.-i. Matsuda, T. Uemura, M. Yamamoto
    Int’l Conf. on Magnetism (ICM2009), Abstracts p.54, Mo-A-5.4-05  2009年07月 [査読有り][通常論文]
  • Transport properties of a junction consisting of two NbN electrodes coupled by a Co-based Heusler alloy Co2Cr0.6Fe0.4Al channel
    K.-i. Matsuda, S. Imai, T. Ishikawa, T. Uemura, M. Yamamoto
    Int’l Conf. on Magnetism (ICM2009), Abstracts p.55, Mo-A-5.4-13  2009年07月 [査読有り][通常論文]
  • Spin-dependent tunneling in half-metallic Heusler alloy-based magnetic tunnel junctions with a MgO barrier
    M. Yamamoto, T. Ishikawa, T. Taira, T. Marukame, K.-i. Matsuda, T. Uemura
    Int’l Conf. on Magnetism (ICM2009), Abstracts p.155, Tu-JPH6-01  2009年07月 [査読有り][通常論文]
  • Tetsuya Uemura, Keisuke Sawada, Ken-ichi Matsuda, Masafumi Yamamoto
    APPLIED PHYSICS LETTERS 95 1 012502 (3pp)  2009年07月 [査読有り][通常論文]
     
    A device consisting of double magnetic tunnel junctions with cross-magnetization configurations is proposed to enable simultaneous electrical detection of both the structure and motion of a domain-wall (DW). Operation of this device has been confirmed through micromagnetic simulation. Owing to the cross-magnetization configurations, two types of DW structure formed in a ferromagnetic wire were clearly identified: a transverse wall (TW) in which the magnetization at the center of the wall is directed transversely to the wire axis and a vortex wall (VW) in which the magnetization circulates in the plane around a small perpendicular vortex core. In addition to the structural difference between TW and VW, the velocity of the DW motion was detected through the time response of the tunneling magnetoresistance. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3168514]
  • Simulation of tunneling magnetoresistance used to detect domain-wall structure and motion in a ferromagnetic wire
    K. Sawada, T. Uemura, M. Masuda, K.-i. Matsuda, M. Yamamoto
    IEEE Int’l Magnetics Conf. 2009, Digests (CD-ROM) BD-07  2009年05月 [査読有り][通常論文]
  • Tetsuya Uemura, Yosuke Imai, Masanobu Harada, Ken-ichi Matsuda, Masafumi Yamamoto
    APPLIED PHYSICS LETTERS 94 18 BQ-13  2009年05月 [査読有り][通常論文]
     
    Magnetic and transport properties of a fully epitaxial CoFe/n-GaAs junction were investigated. The CoFe film grown on the GaAs showed strong magnetic anisotropy in which uniaxial anisotropy with an easy axis of [110] dominated with a slight cubic anisotropy having easy axes of [110] and [1100] superimposed. Tunneling anisotropic magnetoresistance (TAMR) was observed at 4.2 K in the CoFe/n-GaAs junction. Angular dependence of the tunnel resistance showed uniaxial-type anisotropic tunnel resistance between the [110] and [110] directions in the (001) plane that varied strongly with a bias voltage. The observed TAMR effect can be explained by the anisotropic electronic structure due to Rashba and Dresselhaus spin-orbit interactions.
  • Tetsuya Uemura, Yosuke Imai, Masanobu Harada, Ken-ichi Matsuda, Masafumi Yamamoto
    APPLIED PHYSICS LETTERS 94 18 182502 (3pp)  2009年05月 [査読有り][通常論文]
     
    Magnetic and transport properties of a fully epitaxial CoFe/n-GaAs junction were investigated. The CoFe film grown on the GaAs showed strong magnetic anisotropy in which uniaxial anisotropy with an easy axis of [110] dominated with a slight cubic anisotropy having easy axes of [110] and [1100] superimposed. Tunneling anisotropic magnetoresistance (TAMR) was observed at 4.2 K in the CoFe/n-GaAs junction. Angular dependence of the tunnel resistance showed uniaxial-type anisotropic tunnel resistance between the [110] and [110] directions in the (001) plane that varied strongly with a bias voltage. The observed TAMR effect can be explained by the anisotropic electronic structure due to Rashba and Dresselhaus spin-orbit interactions.
  • Takayuki Ishikawa, Naoki Itabashi, Tomoyuki Taira, Ken-ichi Matsuda, Tetsuya Uemura, Masafumi Yamamoto
    JOURNAL OF APPLIED PHYSICS 105 7 07B110 (6pp)  2009年04月 [査読有り][通常論文]
     
    We used tunneling spectroscopy to examine the spin-dependent electronic structure of Co2MnSi (CMS) electrodes facing a MgO barrier and the key tunneling mechanism in fully epitaxial CMS/MgO/CMS magnetic tunnel junctions (MTJs) that showed high tunnel magnetoresistance ratios up to 182% at room temperature and 705% at 4.2 K. Consequently, we developed a model of the spin-dependent electronic structure for CMS electrodes and a tunneling model that can consistently explain the observed tunneling spectra. Here, we show that lower (upper) CMS electrodes possess a half-metal gap of 0.40 eV (0.32 eV) with the Fermi level (E-F) near the middle of the half-metal gap for both lower and upper CMS electrodes. Furthermore, we found strong evidence for the existence of interface states in the interfacial region of CMS electrodes facing a MgO barrier, as well as evidence of residual states in the bulk region of upper CMS electrodes, in both cases for minority spins around E-F, and we show that interface states play a critical role for spin-dependent tunneling in these half-metallic CMS-based MTJs. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3089732]
  • Siham Ouardi, Benjamin Balke, Andrei Gloskovskii, Gerhard H. Fecher, Claudia Felser, Gerd Schoenhense, Takayuki Ishikawa, Tetsuya Uemura, Masafumi Yamamoto, Hiroaki Sukegawa, Wenhong Wang, Koichiro Inomata, Yoshiyuki Yamashita, Hideki Yoshikawa, Shigenori Ueda, Keisuke Kobayashi
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 42 8 084010 (7 pp)  2009年04月 [査読有り][通常論文]
     
    This work reports on high energy photoelectron spectroscopy from the valence band of buried Heusler thin films (Co2MnSi and Co2FeAl0.5Si0.5) excited by photons of about 6 keV energy. The measurements were performed on thin films covered by MgO and SiOx with different thicknesses from 1 to 20 nm of the insulating layer and additional AlOx or Ru protective layers. It is shown that the insulating layer does not affect the high energy spectra of the Heusler compound close to the Fermi energy. The high resolution measurements of the valence band close to the Fermi energy indicate a very large electron mean free path of the electrons through the insulating layer. The spectra of the buried thin films agree well with previous measurements from bulk samples. The valence band spectra of the two different Heusler compounds exhibit clear differences in the low lying s bands as well as close to the Fermi energy.
  • Tomoyuki Taira, Takayuki Ishikawa, Naoki Itabashi, Ken-ichi Matsuda, Tetsuya Uemura, Masafumi Yamamoto
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 42 8 084015 (9 pp)  2009年04月 [査読有り][通常論文]
     
    We investigated the spin-dependent tunnelling characteristics of fully epitaxial magnetic tunnel junctions (MTJs) consisting of a Heusler alloy Co2MnGe (CMG) lower electrode, a MgO barrier and a Co50Fe50 upper electrode, which were fabricated as a function of T-a, where T-a is the temperature at which the MTJ trilayer was in situ annealed right after deposition of the upper electrode. We found that the tunnel magnetoresistance (TMR) ratio increased discontinuously and significantly from 92% at room temperature (RT) (244% at 4.2 K) to 160% at RT (376% at 4.2 K) when T-a was increased from 475 to 500 degrees C. We also found that the dI/dV versus V characteristics of fabricated MTJs for the parallel (P) and antiparallel (AP) magnetization configurations changed discontinuously and markedly with increasing T-a from 475 degrees C or less to 500 degrees C or higher; i.e. the dI/dV versus V characteristics of the MTJs with T-a of 475 degrees C or less exhibited distinct peak structures at V similar to 0.22V for P and at V similar to -0.38 and 0.27V for AP, where the bias voltage (V) was defined with respect to the CMG lower electrode. On the other hand, these structures were not observed in the dI/dV versus V characteristics of the MTJs when T-a was 500 degrees C or higher. We ascribe the peak structures in the dI/dV versus V characteristics to the existence of peak structures in the interfacial density of states at the CMG electrode-MgO barrier interface arising from possible thermodynamically unstable interface bonding in CMG/MgO/Co50Fe50 MTJs with T-a of 475 degrees C or less. We attribute the discontinuous and complete disappearance of these peaks in the dI/dV versus V characteristics to the change in the interface bonding from thermodynamically unstable bonding for T-a of 475 degrees C or less to stable bonding for T-a of 500 degrees C or higher. The significant increase in the TMR ratio with increasing T-a from 475 to 500 degrees C is attributed to the increase in the interfacial spin polarization at the Fermi level associated with the change in the spin-dependent interfacial density of states.
  • Takayuki Ishikawa, Naoki Itabashi, Tomoyuki Taira, Ken-ichi Matsuda, Tetsuya Uemura, Masafumi Yamamoto
    APPLIED PHYSICS LETTERS 94 9 092503 (3pp)  2009年03月 [査読有り][通常論文]
     
    We investigated at 4.2 K the differential conductance (dI/dV) versus V characteristics of fully epitaxial Co2MnSi/MgO/Co2MnSi magnetic tunnel junctions (MTJs) featuring high tunnel magnetoresistance ratios of about 700% at 4.2 K (about 180% at room temperature). We developed a tunneling model to explain the observed tunneling spectra and showed the critical role played by interface states for minority spins existing around the Fermi level of Co2MnSi electrodes facing a MgO tunnel barrier in the spin-dependent tunneling characteristics of these MTJs with half-metallic electrodes.
  • Tomoyuki Taira, Takayuki Ishikawa, Naoki Itabashi, Ken-ichi Matsuda, Tetsuya Uemura, Masafumi Yamamoto
    APPLIED PHYSICS LETTERS 94 7 072510 (3pp)  2009年02月 [査読有り][通常論文]
     
    We found that the tunnel magnetoresistance ratio of fully epitaxial Co2MnGe/MgO/Co50Fe50 magnetic tunnel junctions (MTJs) increased discontinuously and significantly from 92% at room temperature (RT) (244% at 4.2 K) for T-a of 475 degrees C to 160% at RT (376% at 4.2 K) for T-a of 500 degrees C, where T-a is the temperature at which the MTJ trilayer was in situ annealed right after deposition of the upper electrode. We also found that the dI/dV versus V characteristics for the parallel and antiparallel magnetization configurations changed discontinuously and markedly with increasing T-a from 475 degrees C or less to 500 degrees C or higher. These significant changes are discussed in terms of a possible change in the spin-dependent interfacial density of states.
  • K. -i. Matsuda, Y. Akimoto, T. Uemura, M. Yamamoto
    25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 5 150 p.25, PB-Th118  2009年 [査読有り][通常論文]
     
    The superconducting proximity effect was examined in both Nb/PdNi (SF) bilayer films and Nb/PdNi/Nb (SFS) Josephson junctions. In Nb/PdNi bilayer films, nonmonotonic behavior of T(c) was observed as a function of PdNi thickness d(F). The effective exchange energy E(ex) extracted from the data was about 13 meV. In Nb/PdNi/Nb (SFS) Josephson junctions, the existence of a crossover between the 0 state and the pi state was confirmed in the PdNi thickness dependence of I(c). For the junction with d(F) = 9 nm, such a crossover was observed in the temperature dependence of I(c). E(ex) estimated from the junctions characteristics was about 19 meV. These behaviors can be interpreted from the view point of a damped oscillatory superconducting order parameter induced at the SF interface.
  • K. -i. Matsuda, Y. Akimoto, T. Uemura, M. Yamamoto
    25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 5 150 052155 (4pp)  2009年 [査読有り][通常論文]
     
    The superconducting proximity effect was examined in both Nb/PdNi (SF) bilayer films and Nb/PdNi/Nb (SFS) Josephson junctions. In Nb/PdNi bilayer films, nonmonotonic behavior of T(c) was observed as a function of PdNi thickness d(F). The effective exchange energy E(ex) extracted from the data was about 13 meV. In Nb/PdNi/Nb (SFS) Josephson junctions, the existence of a crossover between the 0 state and the pi state was confirmed in the PdNi thickness dependence of I(c). For the junction with d(F) = 9 nm, such a crossover was observed in the temperature dependence of I(c). E(ex) estimated from the junctions characteristics was about 19 meV. These behaviors can be interpreted from the view point of a damped oscillatory superconducting order parameter induced at the SF interface.
  • Tunnel magnetoresistance characteristics of post-deposition-annealed Co2MnGe/MgO/CoFe tunnel junctions
    T. Taira, T. Ishikawa, K.-i. Matsuda, T. Uemura, M. Yamamoto
    2008 Material Research Society (MRS) Fall Meeting, Abstracts(CD-ROM) L2.1  2008年12月 [査読有り][通常論文]
  • Tunneling conductance characteristics for Co2Cr0.6Fe0.4Al/MgO/Co2Cr0.6Fe0.4Al magnetic tunnel junctions
    N. Itabashi, T. Ishikawa, K. Yonemura, K.-i. Matsuda, T. Uemura, M. Yamamoto
    2008 Material Research Society (MRS) Fall Meeting, Abstracts (CD-ROM) L2.10  2008年12月 [査読有り][通常論文]
  • Tunneling spectroscopy of fully epitaxial Co2MnSi/MgO/Co2MnSi magnetic tunnel junctions
    T. Ishikawa, N. Itabashi, T. Taira, K.-i. Matsuda, T. Uemura, M. Yamamoto
    2008 Material Research Society (MRS) Fall Meeting, Abstracts (CD-ROM) L5.1  2008年12月 [査読有り][通常論文]
  • Tetsuya Uemura, Masafumi Yamamoto
    JOURNAL OF APPLIED PHYSICS 104 12 123911 (5pp)  2008年12月 [査読有り][通常論文]
     
    Three-valued epitaxial Co50Fe50/MgO/Co50Fe50 magnetic tunnel junctions (MTJs) were developed for nonvolatile ternary content addressable memory (TCAM) application. Four remanent magnetization states in the single-crystalline Co50Fe50 electrode, due to cubic anisotropy with easy axes of the < 110 > directions, result in four possible angular-dependent tunnel magnetoresistance ratios. Three states selected from among the four states were separated by more than 56% at room temperature. Analysis of the asteroid curve for Co50Fe50 indicated that a magnetic field along 22.5 degrees from the < 110 > directions made it possible to change the magnetization direction of the selected cell without disturbing those of the half-selected cells in the MTJ arrays. A nonvolatile TCAM cell using the three-valued MTJ for three-level data storage was proposed, and its operation was verified by circuit simulation. The TCAM cell reduces the device count to 5, a value 1/3 that of conventional complementary metal-oxide semiconductor-based TCAMs.
  • Half-metallic electronic structure of Co2MnSi electrodes proved by tunneling spectroscopy
    T. Ishikawa, N. Itabashi, T. Taira, K.-i. Matsuda, T. Uemura, M. Yamamoto
    53rd Magnetism and Magnetic Materials Conf., Abstracts(CD-ROM) vol.53 p.232, DD-07  2008年11月 [査読有り][通常論文]
  • Spin-dependent tunneling characteristics of Co2MnGe/MgO/CoFe tunnel junctions
    T. Taira, T. Ishikawa, K.-i. Matsuda, T. Uemura, M. Yamamoto
    53rd Magnetism and Magnetic Materials Conf., Abstracts (CD-ROM) vol.53 p.230, DD-02  2008年11月 [査読有り][通常論文]
  • Tunneling spectroscopy of Co2Cr0.6Fe0.4Al/MgO/CoFe magnetic tunnel junctions
    K. Yonemura, T. Ishikawa, N. Itabashi, K.-i. Matsuda, T. Uemura, M. Yamamoto
    53rd Magnetism and Magnetic Materials Conf., Abstracts (CD-ROM) vol.53 p.301, ED-07  2008年11月 [査読有り][通常論文]
  • Spin-dependent electronic structures of Co2Cr0.6Fe0.4Al electrodes investigated through tunneling spectroscopy
    N. Itabashi, T. Ishikawa, K. Yonemura, K.-i. Matsuda, T. Uemura, M. Yamamoto
    53rd Magnetism and Magnetic Materials Conf., Abstracts (CD-ROM) vol.53 pp. 480-481, GT-03  2008年11月 [査読有り][通常論文]
  • Masahiro Masuda, Tetsuya Uemura, Ken-ichi Matsuda, Masafumi Yamamoto
    IEEE TRANSACTIONS ON MAGNETICS 44 11 3996 - 3998 2008年11月 [査読有り][通常論文]
     
    Fully epitaxial magnetic tunnel junctions (MTJs) consisting of a Co2MnSi (CMS) upper free layer, a MgO tunnel barrier, and a Co50Fe50 lower pinned layer were fabricated for sensor application. The fabricated MTJs exhibited clear exchange-biased tunnel magnetoresistance (TMR) characteristics with a relatively high TMR ratios of 94% at room temperature (209% at 4.2 K) with V-half of approximately -0.52 and +0.54 V. Almost hysteresis-free TMR characteristics with sensitivity of approximately 0.4%/Oe were obtained with a cross magnetization configuration, in which the magnetization of the CMS free layer was oriented perpendicularly to that of the pinned layer.
  • Spin-dependent tunneling spectroscopy of fully epitaxial magnetic tunnel junctions with Heusler alloy Co2Cr0:6Fe0:4Al electrodes and a MgO barrier
    N. Itabashi, T. Ishikawa, K.-i. Matsuda, T. Uemura, M. Yamamoto
    25th Int’l Conf. on Low Temp. Physics, Official Conf. Book vol.25 p.258, PD-Mo244  2008年08月 [査読有り][通常論文]
  • Fabrication and characterization of magnetic tunnel junction field sensors with a Co2MnSi thin film
    M. Masuda, T. Uemura, K.-i. Matsuda, M. Yamamoto
    IEEE Int'l Magnetics Conf. Europe 2008,Technical Digests (CD-ROM) p.269, BD-04  2008年05月 [査読有り][通常論文]
  • Spin-dependent tunneling conductance in fully epitaxial Co2MnSi/MgO/Co2MnsI tunnel junctions
    T. Ishikawa, N. Itabashi, K. Matsuda, T. Uemura, M. Yamamoto
    IEEE Int'l Magnetics Conf. Europe 2008,Technical Digests (CD-ROM) p.33, AC-07  2008年05月 [査読有り][通常論文]
  • S. Kawagishi, T. Uemura, Y. Imai, K. -I. Matsuda, M. Yamamoto
    JOURNAL OF APPLIED PHYSICS 103 7 07A703 (3pp)  2008年04月 [査読有り][通常論文]
     
    The structural, magnetic, and electrical properties of Co2MnSi (CMS)/MgO (0-3.0 nm)/n-GaAs tunnel junctions were investigated. CMS films with L2(1)-ordered structures were grown epitaxially on GaAs. The crystallographic relations were CMS(001)[100]parallel to GaAs(001)[110] when a thin MgO interlayer was inserted between the CMS and the GaAs, and CMS(001)[110]parallel to GaAs(001)[110] when the CMS film was directly grown on GaAs without a MgO interlayer. The CMS film without a MgO interlayer showed strong magnetic anisotropy consisting of uniaxial anisotropy with an easy axis of CMS[1-10] (GaAs[1-10]) direction and cubic anisotropy with easy axes of CMS < 110 > directions. The uniaxial anisotropy was weakened in the samples with a MgO interlayer. The magnetization value of the CMS film with a 3.0-nm-thick MgO layer was approximately 820 emu/cm(3) (3.9 mu(B)/f.u.) at room temperature (RT), a value slightly higher (similar to 7%) than that of the sample without MgO. The resistance value of the CMS/MgO (3.0 nm)/n-GaAs junction was approximately two to three orders of magnitude higher than that of the CMS/n-GaAs junction at RT. The potential height and width of the tunnel barrier in the CMS/MgO/n-GaAs junction were estimated to be 0.6 eV and 3.3 nm, respectively. (c) 2008 American Institute of Physics.
  • Ken-ichi Matsuda, Yosuke Akimoto, Tetsuya Uemura, Masafumi Yamamoto
    JOURNAL OF APPLIED PHYSICS 103 7 07C711 (3pp)  2008年04月 [査読有り][通常論文]
     
    We investigated magnetic and transport properties of variable-thickness bridges (VTBs) having a Nb/Pd(0.85)Ni(0.15) bilayer microbridges. It was found that the superconducting critical current I(c) of the VTBs monotonically decreased with increasing PdNi thickness d(F), while nonmonotonic behavior of the superconducting transition temperature T(c) was observed as a function of d(F) in large Nb/PdNi bilayer films. (C) 2008 American Institute of Physics.
  • Toshiaki Saito, Toshikazu Katayama, Ai Emura, Noa Sumida, Nanae Matsuoka, Takayuki Ishikawa, Tetsuya Uemura, Masafumi Yamamoto, Daisuke Asakura, Tsuneharu Koide
    JOURNAL OF APPLIED PHYSICS 103 7 07D712 (3pp)  2008年04月 [査読有り][通常論文]
     
    The electronic and magnetic states of an epitaxially grown full-Heusler alloy Co2MnSi (CMS) 1.1 nm (4 ML) thick ultrathin film and a CMS 50-nm-thick film both facing an epitaxial MgO(001) tunnel barrier were element-specifically studied by means of x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). The observed XAS and XMCD spectra revealed that both the CMS films were not oxidized. The Co and Mn spin magnetic moments for the 4 ML thick CMS film obtained by applying the sum rules were close to those for the 50-nm-thick one and the theoretical values for bulk CMS with the L2(1) structure. These results indicate that 4 ML thick CMS ultrathin films facing a MgO barrier still retain the electronic and magnetic states for the L2(1) structure. (C) 2008 American Institute of Physics.
  • Takayuki Ishikawa, Shinya Hakamata, Ken-ichi Matsuda, Tetsuya Uemura, Masafumi Yamamoto
    JOURNAL OF APPLIED PHYSICS 103 7 07A919 (3pp)  2008年04月 [査読有り][通常論文]
     
    Fully epitaxial magnetic tunnel junctions (MTJs) were fabricated with full-Heusler alloy Co2MnSi thin films as both lower and upper electrodes and with a MgO tunnel barrier. The fabricated MTJs showed clear exchange-biased tunnel magnetoresistance (TMR) characteristics with high TMR ratios of 179% at room temperature (RT) and 683% at 4.2 K. In addition, the TMR ratio exhibited oscillations as a function of the MgO tunnel barrier thickness (t(MgO)) at RT, having a period of 0.28 nm, for t(MgO) ranging from 1.8 to 3.0 nm.
  • Tetsuya Uemura, Yosuke Imai, Saori Kawagishi, Ken-ichi Matsuda, Masafumi Yamamoto
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 40 6 2025 - 2027 2008年04月 [査読有り][通常論文]
     
    The structural and magnetic properties of Co-2 MnSi (CMS) thin films epitaxially grown on GaAs substrates by sputtering were investigated. The CMS film directly grown on GaAs showed a cube-on-cube crystallographic relation, while it was rotated by 45 degrees in the (001) plane when a thin MgO layer was inserted between the CMS and GaAs. The CMS film directly grown on GaAs showed strong magnetic anisotropy consisting of a uniaxial anisotropy with an easy axis of CMS[1 (1) over bar0] (GaAs[1 (1) over bar0] direction and a cubic anisotropy with easy axes of CMS < 110 > directions. The uniaxial anisotropy was weakened in the samples with a MgO interlayer. The magnetization value of the CMS film with a 3.0-nm-thick MgO was approximately 820 emu/cm(3) (3.9 mu B/f.u.) at room temperature, a value slightly higher (similar to 7%) than that of the sample without MgO. (c) 2007 Elsevier B.V. All rights reserved.
  • Heusler alloy-based fully epitaxial magnetic tunnel junctions with a MgO barrier
    M. Yamamoto, T. Uemura, K.-i. Matsuda
    2008 RCIQE Int’l Seminar on “Advanced Semiconductor Materials and Devices”, Collected Abstracts pp.29-37  2008年03月 [査読無し][招待有り]
  • Ken-Ichi Matsuda, Yosuke Akimoto, Tetsuya Uemura, Masafumi Yamamoto
    Journal of Applied Physics 103 7 p.489, HQ-10  2008年 [査読有り][通常論文]
     
    We investigated magnetic and transport properties of variable-thickness bridges (VTBs) having a Nb Pd0.85 Ni0.15 bilayer microbridges. It was found that the superconducting critical current Ic of the VTBs monotonically decreased with increasing PdNi thickness dF, while nonmonotonic behavior of the superconducting transition temperature Tc was observed as a function of dF in large NbPdNi bilayer films. © 2008 American Institute of Physics.
  • Toshiaki Saito, Toshikazu Katayama, Ai Emura, Noa Sumida, Nanae Matsuoka, Takayuki Ishikawa, Tetsuya Uemura, Masafumi Yamamoto, Daisuke Asakura, Tsuneharu Koide
    Journal of Applied Physics 103 7 p.116, BQ-06  2008年 [査読有り][通常論文]
     
    The electronic and magnetic states of an epitaxially grown full-Heusler alloy Co2 MnSi (CMS) 1.1 nm (4 ML) thick ultrathin film and a CMS 50-nm -thick film both facing an epitaxial MgO(001) tunnel barrier were element-specifically studied by means of x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). The observed XAS and XMCD spectra revealed that both the CMS films were not oxidized. The Co and Mn spin magnetic moments for the 4 ML thick CMS film obtained by applying the sum rules were close to those for the 50-nm -thick one and the theoretical values for bulk CMS with the L 21 structure. These results indicate that 4 ML thick CMS ultrathin films facing a MgO barrier still retain the electronic and magnetic states for the L 21 structure. © 2008 American Institute of Physics.
  • Masafumi Yamamoto, Taluto Marukame, Takayuki Ishikawa, Ken-ichi Matsuda, Tetsuya Uemura
    ADVANCES IN SOLID STATE PHYSICS 47 105 - 116 2008年 [査読有り][通常論文]
     
    Co-based full-Heusler alloy (C02YZ) thin films are highly preferable ferromagnetic materials in spintronic devices because of the half-metallic ferromagnetic nature at room temperature (RF) theoretically predicted for some of these alloys. We developed fully epitaxial magnetic tunnel junctions (MTJs) that have a C02YZ thin film Of C02C1'0.6Fe0.4A1 (CCFA), C02MnSi (CMS), or C02MnGe (CMG) as a lower electrode, and a MgO tunnel barrier, and have demonstrated a relatively high tunnel magnetoresistance (TMR) ratio of 109% at Rr (317% at 4.2 K) for CCFA/M90/C050 Fe50 MTJs and a TMR ratio of 90% at Xr (192% at 4.2K) for CMS/MgO/CO5oFe5o MTJs. A high tunneling spin polarization of 0.88 at 4.2 K was estimated for epitaxial CCFA films with the B2 structure. The demonstrated higli TMR ratios confirmed that fully epitaxial MTJs with a MgO tunnel barrier are promising as a key device structure for fully utilizing the high spin polarization of Co-based full-Heusler alloy thin films.
  • Masafumi Yamamoto, Taluto Marukame, Takayuki Ishikawa, Ken-ichi Matsuda, Tetsuya Uemura
    ADVANCES IN SOLID STATE PHYSICS 47 105 - 116 2008年 [査読有り][通常論文]
     
    Co-based full-Heusler alloy (C02YZ) thin films are highly preferable ferromagnetic materials in spintronic devices because of the half-metallic ferromagnetic nature at room temperature (RF) theoretically predicted for some of these alloys. We developed fully epitaxial magnetic tunnel junctions (MTJs) that have a C02YZ thin film Of C02C1'0.6Fe0.4A1 (CCFA), C02MnSi (CMS), or C02MnGe (CMG) as a lower electrode, and a MgO tunnel barrier, and have demonstrated a relatively high tunnel magnetoresistance (TMR) ratio of 109% at Rr (317% at 4.2 K) for CCFA/M90/C050 Fe50 MTJs and a TMR ratio of 90% at Xr (192% at 4.2K) for CMS/MgO/CO5oFe5o MTJs. A high tunneling spin polarization of 0.88 at 4.2 K was estimated for epitaxial CCFA films with the B2 structure. The demonstrated higli TMR ratios confirmed that fully epitaxial MTJs with a MgO tunnel barrier are promising as a key device structure for fully utilizing the high spin polarization of Co-based full-Heusler alloy thin films.
  • Ananda Putra, Akira Kakugo, Hidentitsu Furukawa, Jian P. Gong, Yoshihito Osada, Tetsuya Uemura, Masafumi Yamamoto
    POLYMER JOURNAL 40 2 137 - 142 2008年 [査読有り][通常論文]
     
    Acetobacterxylinum, which is an aerobic bacterium, synthesizes bacterial cellulose (BC) with unoriented microfibril network in form of gel at the air and liquid interface (BC-air). In this work, we discovered that BC gel produced on an oxygen permeable substrate of polydimethylsiloxane (PDMS) shows strong birefringence with colorful images, indicating a liquid crystal-like structure. Furthermore, we found that uni-axially oriented BC gels can be obtained by culturing the BC on the PDMS with ridged morphology. The degree of orientation of BC gels, as revealed by the birefringence, increases with the decrease in the ridge size of the PDMS substrate. An optimum ridge size of 4.5 mu m was observed where the BC gels show the highest birefringence (Delta n), the highest fracture stress (sigma), highest swelling degree (q), the lowest elastic modulus (E), and the thickest BC fibril. The optimum ridge size is related to the contour length of the bacteria cells. When the ridge size was smaller than 4.5 mu m, the Delta n steeply decreased to a value comparable to that on smooth flat PDMS mold surface. The fracture stress, sigma of the uni-axially oriented BC gel under elongation was 4.6 MPa, which was 2.3 times higher than that of BC-air (sigma = 2 MPa).
  • Electrical characterization of epitaxial Co2MnSi/MgO/n-GaAs tunnel junctions
    S. Kawagishi, T. Uemura, Y. Imai, K.-i. Matsuda, M. Yamamoto
    52nd Magnetism and Magnetic Materials Conf., Abstracts vol.52 p.38, AG-09  2007年11月 [査読有り][通常論文]
  • Spin-dependent tunneling in fully epitaxial Co2MnSi/MgO/Co2MnSi magnetic tunnel junctions
    T. Ishikawa, S. Hakamata, K.-i. Matsuda, T. Uemura, M. Yamamoto
    52nd Magnetism and Magnetic Materials Conf., Abstracts vol.52 p.13, AB-07  2007年11月 [査読有り][通常論文]
  • Oscillations in tunneling resistance as a function of MgO barrier thickness in fully epitaxial magnetic tunnel junctions of Co2Cr0.6Fe0.4Al/MgO/Co50Fe50
    M. Yamamoto, T. Marukame, T. Ishikawa, K. Matsuda, T. Uemura
    52nd Magnetism and Magnetic Materials Conf., Abstracts vol.52 p.14, AB-11  2007年11月 [査読有り][通常論文]
  • Highly spin-polarized tunneling in Heusler alloy-based fully epitaxial magnetic tunnel junctions with a MgO tunnel barrier
    M. Yamamoto, T. Marukame, T. Ishikawa, K. Matsuda, T. Uemura
    52nd Magnetism and Magnetic Materials Conf., Abstracts vol.52 p.204, DB-01  2007年11月 [査読有り][通常論文]
  • Epitaxial growth and characterization of Co2MnSi thin films on GaAs with MgO interlayer
    T. Uemura, T. Yano, Y. Imai, K. Matsuda, M. Yamamoto
    The 13th Int’l Conf. on Modulated Semiconductor Structures (MSS13), Abstracts vol.13 pp.172-173  2007年07月 [査読有り][通常論文]
  • T. Marukame, T. Ishikawa, S. Hakamata, K.-i. Matsuda, T. Uemura, M. Yamamoto
    J. Magn. Soc. Jpn. vol.31 no. 4 pp. 344-350 - 350 The Magnetics Society of Japan 2007年07月 [査読有り][通常論文]
     
    Fully epitaxial magnetic tunnel junctions (MTJs) were fabricated with a full-Heusler alloy Co2Cr0.6Fe0.4Al (CCFA) thin film and a MgO tunnel barrier. Cross-sectional high-resolution transmission electron microscope observations clearly showed that all layers of CCFA/MgO/Co50Fe50 MTJ layer structures were grown epitaxially and were single-crystalline. The fully epitaxial CCFA/MgO/Co50Fe50 MTJs, where we used the difference in the coercive forces to form the antiparallel magnetization configurations between the lower and upper electrodes, demonstrated high tunnel magnetoresistance (TMR) ratios of 90% at room temperature (RT) and 240% at 4.2 K. This result suggested that a CCFA film composition close to the stoichiometric one is essential for obtaining high spin polarizations in CCFA thin films. The fully epitaxial CCFA/MgO/Co50Fe50 MTJs with exchange-biasing, where a Co50Fe50 upper electrode was used in a synthetic ferrimagnetic Co50Fe50/Ru/Co90Fe10 trilayer exchange-biased with an IrMn layer through the Co90Fe10/IrMn interface, exhibited high TMR ratios of 109% at RT and 317% at 4.2 K. From the obtained TMR ratio of 317% at 4.2 K, a high tunneling spin polarization of 0.88 at 4.2 K was estimated for epitaxial CCFA films with the B2 structure. These results confirm the promise of an epitaxial MTJ using a Co-based full-Heusler alloy as a key device structure for utilizing the potentially high spin polarization of this material system.
  • T. Uemura, T. Yano, K.-I. Matsuda
    THIN SOLID FILMS 515 20-21 8013 - 8016 2007年07月 [査読有り][通常論文]
     
    The structural and magnetic properties of Co2Cr0.6Fe0.4Al (CCFA) thin films epitaxially grown on GaAs substrates by sputtering were investigated. The CCFA film directly grown on GaAs showed a cube-on-cube crystallographic relation, while it was rotated by 45 degrees in the (001) plane when a thin MgO layer was inserted between the CCFA and GaAs. Both samples showed strong magnetic anisotropy, in which a uniaxial anisotropy with an easy axis of [110](GaAs) or [1-10](GaAs) dominated with a slight cubic anisotropy having easy axes of < 110 >(CCFA) superimposed. The uniaxial anisotropy constants were approximately 1.6 times as large as the cubic anisotropy constants for both samples. (C) 2007 Elsevier B.V. All rights reserved.
  • Ken-ichi Matsuda, Hirotaka Niwa, Yosuke Akimoto, Tetsuya Uemura, Masafumi Yamamoto
    IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY 17 2 3529 - 3532 2007年06月 [査読有り][通常論文]
     
    We investigated the superconducting proximity effect in both Nb(35 nm)/PdNi superconductor (S)-ferromagnet (F) bilayer and Nb-Nb(10 nm)/PdNi-Nb (S-SF-S) variable-thickness bridges (VTBs). In Nb(35 nm)/PdNi(dF nm) SF bilayer, non-monotonic behavior of the superconducting transition temperature T. was observed as a function of PdNi thickness, d(F) This non-monotonic behavior of T, can be interpreted from the view point of damped oscillatory superconducting order parameter induced in F-layer, and the effective exchange energy E,, extracted from the data was approximately 150 K. On the other hand, in VTBs, it was found that the superconducting critical current I. was monotonically decreased with increasing d(F).
  • T. Marukame, T. Ishikawa, S. Hakamata, K-I Matsuda, T. Uemura, M. Yamamoto
    IEEE TRANSACTIONS ON MAGNETICS 43 6 2782 - 2784 2007年06月 [査読有り][通常論文]
     
    Fully epitaxial magnetic tunnel junctions (MTJs) of Co2Cr0.6Fe0.4Al (CCFA)/MgO/CCFA with exchange biasing were fabricated. The fabricated MTJs showed clear exchange-biased tunnel magnetoresistance (TMR) characteristics due to the CCFA/Ru/Co90Fe10/IrMn exchange-biased synthetic ferrimagnetic layer. The TMR characteristics were investigated as a function of in situ annealing temperature (T-a) for the upper CCFA layer. We obtained TMR ratios of 60% at room temperature (RT) and 238% at 4.2 K for MTJs with T-a of 400 degrees C, while those for MTJs with T-a of RT (i.e., having an as-deposited upper CCFA layer) were 17% at RT and 80% at 4.2 K. These results clearly suggest that the spin polarization of the as-deposited upper CCFA layer was significantly increased by in situ annealing.
  • Tetsuya Uemura, Takao Marukame, Ken-ichi Matsuda, Masafumi Yamamoto
    IEEE TRANSACTIONS ON MAGNETICS 43 6 2791 - 2793 2007年06月 [査読有り][通常論文]
     
    A four-state magnetic random access memory (MRAM) was developed using an epitaxial Co50Fe50-MgO-Co50Fe50 magnetic tunnel junction (MTJ) with a tunnel magnetoresistance (TMR) ratio of 145% at room temperature (RT). Four remanent magnetization states in the single-crystalline Co50Fe50 electrode, due to the cubic anisotropy with easy axes of the < 110 > directions, result in four possible angular-dependent TMRs, each separated by more than 20% at RT. Analysis of the asteroid curve for Co50Fe50 indicated that the magnetic field along 22.5 degrees from the < 110 > directions made it possible to change the magnetization direction of the selected cell without disturbing those of the half-selected cells.
  • T. Uemura, T. Marukame, K.-i. Matsuda, M. Yamamoto
    37th Int’l Symposium on Multiple-Valued Logic, CD-ROM vol.37 pp.49-1 - 49-6  2007年05月 [査読有り][通常論文]
  • Shinya Hakamata, Takayuki Ishikawa, Takao Marukame, Ken-ichi Matsuda, Tetsuya Uemura, Masashi Arita, Masafumi Yamamoto
    JOURNAL OF APPLIED PHYSICS 101 9 09J513 (3pp)  2007年05月 [査読有り][通常論文]
     
    We fabricated magnetic tunnel junctions (MTJs) with a Co-based full-Heusler alloy thin film of Co2MnGe (CMG) and a MgO tunnel barrier. The microfabricated MTJs with a Co-rich CMG film showed relatively high tunnel magnetoresistance ratios of 83% at room temperature and 185% at 4.2 K. These values are much higher than those previously obtained for CMG/MgO MTJs with a Co-deficient CMG film. (c) 2007 American Institute of Physics.
  • Highly spin-polarized tunneling in fully epitaxial magnetic tunnel junctions with a Co-based full-Heusler alloy thin film and a MgO barrier
    M. Yamamoto, T. Marukame, T. Ishikawa, K. Matsuda, T. Uemura
    71stAnnual Meeting 2007 of the German Physical Society and DPG-Spring Meeting of the Division Condensed Matter, Verhandlungen vol.71 p.487, MA22.2  2007年03月 [査読有り][通常論文]
  • T. Yano, T. Uemura, K. -i. Matsuda, M. Yamamoto
    JOURNAL OF APPLIED PHYSICS 101 6 063904 (4pp)  2007年03月 [査読有り][通常論文]
     
    The effect of a MgO interlayer on the structural and magnetic properties of Co2Cr0.6Fe0.4Al (CCFA) thin films epitaxially grown on GaAs substrates by sputtering was investigated. When the MgO interlayer thickness was 1.0 nm or less, the CCFA films were grown with a cube-on-cube relation to GaAs and no significant decrease in either the x-ray diffraction intensity or saturation magnetization was observed. In contrast, when the MgO thickness was 1.5 nm or more, the CCFA film was rotated by 45 degrees in the (001) plane with respect to GaAs, and both the x-ray diffraction intensity and saturation magnetization decreased. All samples showed strong magnetic anisotropy, in which a uniaxial anisotropy with an easy axis of [110](GaAs) or [1-10](GaAs) dominated with a slight cubic anisotropy having an easy axis of < 110 >(CCFA) superimposed. (c) 2007 American Institute of Physics.
  • Tetsuya Uemura, Toshifumi Yano, Ken-ichi Matsuda, Masafumi Yamamoto
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 2 E696 - E698 2007年03月 [査読有り][通常論文]
     
    The structural and magnetic properties of Co2Cr0.6Fe0.4Al (CCFA) thin. lms epitaxially grown on GaAs substrates by sputtering were investigated. The CCFA film directly grown on GaAs showed a cube-on-cube crystallographic relation, while it was rotated by 45 degrees in the (001) plane when a thin MgO layer was inserted between the CCFA and GaAs. Both samples showed strong magnetic anisotropy, in which a uniaxial anisotropy with an easy axis of [110](GaAs) or [1-10](GaAs) dominated with a slight cubic anisotropy having easy axes of < 110 >(CCFA) superimposed. The uniaxial anisotropy constants were approximately 1.6 times as large as the cubic anisotropy constants for both samples. (C) 2006 Elsevier B.V. All rights reserved.
  • H. Kijima, T. Ishikawa, T. Marukame, K.-I. Matsuda, T. Uemura, M. Yamamoto
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 2 2006 - 2008 2007年03月 [査読有り][通常論文]
     
    Fully epitaxial magnetic tunnel junctions (MTJs) were fabricated with a Co-based full-Heusler alloy Co2MnSi (CMS) thin film having the ordered L2(1) structure as a lower electrode, a MgO tunnel barrier, and a Co50Fe50 upper electrode. Reflection high-energy electron diffraction patterns observed in situ for each layer in the MTJ layer structure during fabrication clearly indicated that all layers of the CMS lower electrode, MgO tunnel barrier, and Co50Fe50 upper electrode grew epitaxially. The microfabricated fully epitaxial CMS/MgO/Co50Fe50 MTJs demonstrated relatively high tunnel magnetoresistance ratios of 90% at room temperature and 192% at 4.2 K. (c) 2006 Elsevier B.V. All rights reserved.
  • T. Marukame, H. Kijima, T. Ishikawa, K.-i. Matsuda, T. Uemura, M. Yamamoto
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 2 1946 - 1948 2007年03月 [査読有り][通常論文]
     
    Spin- dependent transport properties were investigated for fully epitaxial magnetic tunnel junctions ( MTJs) having a cobalt- based full-Heusler alloy Co2MnSi ( CMS) thin film as a lower electrode, an MgO tunnel barrier, and a Co50Fe50 upper electrode. In the bias voltage dependence of the differential conductance ( G dI/ dV) for the antiparallel and parallel magnetisation confgurations ( G(AP) and G(P), respectively), a clear crossover between GP and GAP occurred with increasing negative bias voltage at both room temperature and 4.2K ( the bias voltage was defined with respect to the lower CMS electrode). This results in GAP becoming larger than GP in a bias voltage region beyond the characteristic voltage of about - 0.4V at which the crossover occurs. A possible transport mechanism leading to the observed crossover between GP and GAP for the CMS/ MgO/ Co50Fe50 MTJs is direct tunneling that reflects the electronic density of states in the minority- spin band of the CMS electrode. (c) 2006 Elsevier B. V. All rights reserved.
  • T. Ishikawa, T. Marukame, S. Hakamata, K.-i. Matsuda, T. Uemura, M. Yamamoto
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 2 1897 - 1899 2007年03月 [査読有り][通常論文]
     
    Exchange- biased epitaxial magnetic tunnel junctions ( MTJs) with a Heusler alloy Co2Cr0.6Fe0.4Al ( CCFA) lower electrode, a MgO tunnel barrier, and a Co50Fe50 upper electrode were fabricated. Reflection high- energy electron diffraction observations indicated that all layers of the CCFA/ MgO/ Co50Fe50 MTJ layer structure were grown epitaxially. The fabricated epitaxial MTJs exhibited clear exchange-biased tunnel magnetoresistance ( TMR) characteristics with high TMR ratios of 102% at room temperature and 291% at 4.2 K. From the TMR ratios, a high effective spin polarization of 0.86 at 4.2K was obtained for the epitaxial CCFA films with the B2 structure. (c) 2006 Elsevier B. V. All rights reserved.
  • Spin-dependent tunneling in fully epitaxial magnetic tunnel junctions with a Heusler alloy thin film and a MgO barrier
    M. Yamamoto, T. Uemura, K.-i. Matsuda
    The 2nd RIEC Int’l Workshop on Spintronics?MgO-based Magnetic Tunnel Junctions?, Abstracts vol.2 2007年02月 [査読無し][招待有り]
  • Dependence of magnetoresistance characteristics of magnetic tunnel junctions with a Heusler alloy thin film of either Co2MnGe or Co2MnSi on film composition
    S. Hakamata, T. Ishikawa, T. Marukame, K. Matsuda, T. Uemura, M. Arita, M. Yamamoto
    10th Joint MMM/Intermag Conf., Abstracts vol.10 p.443, GD-10  2007年01月 [査読有り][通常論文]
  • Fabrication of fully epitaxial Co2Cr0.6Fe0.4Al/MgO/Co2Cr0.6Fe0.4Al
    T. Marukame, T. Ishikawa, S. Hakamata, K. Matsuda, T. Uemura, M. Yamamoto
    10th Joint MMM/Intermag Conf., Abstracts vol.10 p.209, DD-07  2007年01月 [査読有り][通常論文]
  • Four-state magnetoresistance in epitaxial CoFe-based magnetic tunnel junction
    T. Uemura, T. Marukame, K. Matsuda, M. Yamamoto
    10th Joint MMM/Intermag Conf., Abstracts vol.10 p.47, AP-08  2007年01月 [査読有り][通常論文]
  • Takao Marukame, Takayuki Ishikawa, Shinya Hakamata, Ken-ichi Matsuda, Tetsuya Uemura, Masafumi Yamamoto
    APPLIED PHYSICS LETTERS 90 1 012508 (3pp)  2007年01月 [査読有り][通常論文]
     
    Fully epitaxial magnetic tunnel junctions (MTJs) with exchange biasing were fabricated with a full-Heusler alloy Co2Cr0.6Fe0.4Al (CCFA) thin film and a MgO tunnel barrier, where a Co50Fe50 upper electrode was used in a synthetic ferrimagnetic Co50Fe50/Ru/Co90Fe10 trilayer exchange-biased with an IrMn layer through the Co90Fe10/IrMn interface. The fabricated MTJs exhibited clear exchange-biased tunnel magnetoresistance (TMR) characteristics with high TMR ratios of 109% at room temperature and 317% at 4.2 K. A high tunneling spin polarization of 0.88 at 4.2 K was estimated for epitaxial CCFA films with the B2 structure. (c) 2007 American Institute of Physics.
  • T. Ishikawa, T. Marukame, H. Kijima, K. -I. Matsuda, T. Uemura, M. Arita, M. Yamamoto
    APPLIED PHYSICS LETTERS 89 19 192505 (3pp)  2006年11月 [査読有り][通常論文]
     
    Fully epitaxial, exchange-biased magnetic tunnel junctions (MTJs) were fabricated with a Co-based full-Heusler alloy Co2MnSi (CMS) thin film as a lower electrode, a MgO tunnel barrier, and a Co50Fe50 upper electrode. The microfabricated CMS/MgO/Co50Fe50 MTJs exhibited relatively high tunnel magnetoresistance ratios of 90% at room temperature and 192% at 4.2 K. The bias voltage dependence of differential conductance (dI/dV) for the parallel and antiparallel magnetization configurations suggested the existence of a basic energy gap structure for the minority-spin band of the CMS electrode with an energy difference of about 0.4 eV between the bottom of the vacant minority-spin conduction band and the Fermi level.
  • T. Ishikawa, T. Marukame, K. -i Matsuda, T. Uemura, M. Yamamoto
    IEEE TRANSACTIONS ON MAGNETICS 42 10 3002 - 3004 2006年10月 [査読有り][通常論文]
     
    We fabricated trilayer structures consisting of a Co-based full-Heusler alloy Co2Cr0.6Fe0.4Al (CCFA) layer, a Ru ultrathin film, and a Co90Fe10 layer, and demonstrated well-established antiferromagnetic coupling in the fabricated structures. Furthermore, we observed a clear exchange bias effect in a CCFA/Ru/Co90Fe10/IrMn layer structure with a typical exchange bias field of about 430 Oe at room temperature. These results indicate that the use of a CCFA thin film in antiferromagnetically coupled trilayers is advantageous for obtaining a strong exchange bias field.
  • H. Kijima, T. Ishikawa, T. Marukame, H. Koyama, K. Matsuda, T. Uemura, M. Yamamoto
    IEEE TRANSACTIONS ON MAGNETICS 42 10 2688 - 2690 2006年10月 [査読有り][通常論文]
     
    Full-Heusler alloy Co2MnSi (CMS) thin films were epitaxially grown on MgO-buffered MgO substrates through magnetron sputtering. The films were deposited at room temperature and subsequently annealed in situ at 600 degrees C. X-ray pole figure measurements of the annealed films showed 111 peaks with fourfold symmetry, providing direct evidence that these films were epitaxial and crystallized in the L2(1) structure. The annealed films had sufficiently flat surface morphologies with root-mean-square roughness of about 0.22 nm at a film thickness of 50 nm. The saturation magnetization of the annealed films was 4.5 mu(B)/f.u. at 10 K, corresponding to about 90 % of the Slater-Pauling value for CMS.
  • T. Marukame, T. Ishikawa, W. Sekine, K. Matsuda, T. Uemura, M. Yamamoto
    IEEE TRANSACTIONS ON MAGNETICS 42 10 2652 - 2654 2006年10月 [査読有り][通常論文]
     
    Highly spin-polarized tunneling with tunnel magnetoresistance (TMR) ratios of 90% at room temperature and 240% at 4.2 K was demonstrated for fully epitaxial magnetic tunnel junctions fabricated using a cobalt-based full-Heusler alloy Co2Cr0.6Fe0.4Al (CCFA) thin film having a composition close to the stoichiometric one and a MgO tunnel barrier. A high tunneling spin polarization of 0.79 at 4.2 K was obtained for the epitaxial CCFA films from the TMR ratios. This adds to the promise of the fully epitaxial MTJ as a key device structure for utilizing the intrinsically high spin polarizations of Co-based full-Heusler alloy thin films.
  • Magnetic and Transport Properties of Nb/PdNi Bilayers
    K.-i. Matsuda, H. Niwa, Y. Akimoto, T. Uemura, M. Yamamoto
    IEEE Int’l Conf. on Appl. Supercond., CD-ROM 2MM04  2006年08月 [査読有り][通常論文]
  • Fabrication of exchange-biased epitaxial magnetic tunnel junctions with a Co-based full-Heusler alloy thin film
    T. Ishikawa, S. Hakamata, T. Marukame, K.-i. Matsuda, T. Uemura, M. Yamamoto
    Int’l Conf. on Magnetism (ICM2006), Abstracts p.582  2006年08月 [査読有り][通常論文]
  • Analysis of magnetic anisotropy for Co2Cr0.6Fe0.4Al thin films epitaxially grown on GaAs
    T. Uemura, T. Yano, K.-i. Matsuda, M. Yamamoto
    Int’l Conf. on Magnetism (ICM2006), Abstracts p.313, DD-07  2006年08月 [査読有り][通常論文]
  • Spin-dependent transport properties of fully epitaxial Co2MnSi/MgO/CoFe tunnel junctions
    T. Marukame, H. Kijima, T. Ishikawa, K.-i. Matsuda, T. Uemura, M. Yamamoto
    Int’l Conf. on Magnetism (ICM2006), Abstracts p.198  2006年08月 [査読有り][通常論文]
  • Fabrication of fully epitaxial magnetic tunnel junctions using Co2MnSi thin film and MgO tunnel barrier
    H. Kijima, T. Ishikawa, T. Marukame, K. -i. Matsuda, T. Uemura, M. Yamamoto
    Int’l Conf. on Magnetism (ICM2006), Abstracts p.30  2006年08月 [査読有り][通常論文]
  • MgO barrier thickness dependence of tunnel magnetoresistance in fully epitaxial magnetic tunnel junctions with Co2Cr0.6Fe0.4Al thin film
    T. Marukame, T. Ishikawa, H. Kijima, K.?i. Matsuda, T. Uemura, M. Yamamoto
    19th Int’l Colloquium on Magnetic Films and Surfaces (ICMFS 2006), Colloquium Digest vol.19 pp.448-449, P-12-9  2006年08月 [査読有り][通常論文]
  • Spin-dependent conductance versus voltage characteristics of fully epitaxial magnetic tunnel junctions with a Co-based full-Heusler alloy thin film and a MgO barrier
    M. Yamamoto, T. Marukame, K.?i. Matsuda, T. Uemura
    19th Int’l Colloquium on Magnetic Films and Surfaces (ICMFS 2006), Colloquium Digest vol.19 pp.440-441  2006年08月 [査読有り][通常論文]
  • Structural and magnetic properties of Co2Cr0.6Fe0.4Al thin films epitaxially grown on GaAs with and without MgO interlayer
    T. Uemura, T. Yano, K.?i. Matsuda, M. Yamamoto
    19th Int’l Colloquium on Magnetic Films and Surfaces (ICMFS 2006), Colloquium Digest vol.19 pp.20-21, DD-07  2006年08月 [査読有り][通常論文]
  • Takao Marukame, Takayuki Ishikawa, Ken-Ichi Matsuda, Tetsuya Uemura, Masafumi Yamamoto
    APPLIED PHYSICS LETTERS 88 26 262503 (3pp)  2006年06月 [査読有り][通常論文]
     
    Fully epitaxial magnetic tunnel junctions (MTJs) were fabricated with a Co-based full-Heusler alloy Co2Cr0.6Fe0.4Al (CCFA) thin film, whose composition was close to the stoichiometric one, and a MgO tunnel barrier. Cross-sectional high-resolution transmission electron microscope observations indicated that all layers of the CCFA/MgO/Co50Fe50 MTJ layer structure were grown epitaxially and were single crystalline. The microfabricated CCFA/MgO/Co50Fe50 MTJs exhibited high tunnel magnetoresistance (TMR) ratios of 90% at room temperature and 240% at 4.2 K. A high tunneling spin polarization of 0.79 at 4.2 K was obtained for the epitaxial CCFA films from the TMR ratios.
  • T Uemura, R Miura, T Yamazuki, T Sone, KI Matsuda, M Yamamoto
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 32 1-2 383 - 386 2006年05月 [査読有り][通常論文]
     
    Anisotropic tunnel magneto-resistance (TMR) of (Ga,Mn)As/AlAs/(Ga,Mn)As magnetic tunnel junctions (MTJs) was investigated by both experimentation and simulation. The TMR ratios measured at 8 K for the fabricated MTJs with magnetic fields applied in the (0 0 1) plane along the [100], [1 (1) over bar0], and [110] directions were 39%, 19%, and 10%. These asymmetrical TMR ratios can be explained by the magnetic anisotropy of (Ga,Mn)As, in which the cubic magnetic anisotropy dominated the magnetization switching with its easy axis along the (10 0) directions, whereas the uniaxial anisotropy contributed slightly with its easy axis along the [110] direction. Two models of magnetization reversal were considered: (1) the coherent rotation model and (2) the domain-wall displacement model, for the analysis. As a result, the domain-wall displacement model accurately explained both the TMR ratio and switching field of the fabricated MTJ with 8 x 8 mu m(2) junction size. (c) 2006 Elsevier B.V. All rights reserved.
  • T Marukame, T Ishikawa, K Matsuda, T Uemura, M Yamamoto
    JOURNAL OF APPLIED PHYSICS 99 8 08A904 (3pp)  2006年04月 [査読有り][通常論文]
     
    We fabricated fully epitaxial magnetic tunnel junctions (MTJs) using a Co-based full-Heusler alloy Co2MnGe (CMG) thin film as a lower electrode, an MgO tunnel barrier, and a Co50Fe50 upper electrode and investigated their tunnel magnetoresistance (TMR) characteristics. The microfabricated MTJs showed strongly temperature-dependent TMR characteristics with typical TMR ratios of 70% at 7 K and 14% at room temperature (RT). Furthermore, the TMR characteristics exhibited the following notable features in the bias voltage (V) dependence: (1) a cusplike V dependence within a range of similar to +/- 200 mV around V=0 at 7 K, which was smeared out at RT, and (2) a V dependence with pronounced asymmetry regarding the polarity, showing negative TMR ratios in a certain negative bias voltage range around -400 mV at both 7 K and RT (V was defined with respect to the lower CMG electrode). A possible transport mechanism leading to the notably asymmetric V dependence along with the negative TMR for a certain bias voltage region is direct tunneling that reflects the spin-dependent density of states of the CMG electrode. (C) 2006 American Institute of Physics.
  • T Ishikawa, T Marukame, K Matsuda, T Uemura, M Arita, M Yamamoto
    JOURNAL OF APPLIED PHYSICS 99 8 08J110 (3pp)  2006年04月 [査読有り][通常論文]
     
    Full-Heusler alloy Co2MnGe thin films were epitaxially grown on MgO (001) substrates using magnetron sputtering. The films were deposited at room temperature and subsequently annealed in situ at temperatures ranging from 400 to 600 degrees C. X-ray pole figure measurements for the annealed films showed (111) peaks with fourfold symmetry, which gives direct evidence that these films are epitaxial and crystallized in the L2(1) structure. Furthermore, cross-sectional transmission electron microscope images of a fabricated film indicated that it is single crystalline. The annealed films had sufficiently flat surface morphologies with roughnesses of about 0.26 nm rms at film thicknesses of 45 nm. The saturation magnetization of the annealed films was 4.49 mu(B)/f.u. at 10 K, corresponding to about 90% of the Slater-Pauling value for Co2MnGe. (C) 2006 American Institute of Physics.
  • M Yamamoto, T Marukame, T Ishikawa, K Matsuda, T Uemura, M Arita
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 39 5 824 - 833 2006年03月 [査読有り][通常論文]
     
    Cobalt-based full-Heusler alloy thin films have recently attracted much interest as highly desirable ferromagnetic electrodes for spintronic devices because of the half-metallic ferromagnetic nature theoretically predicted for some of these alloys and because of their high Curie temperatures, which are well above room temperature (RT). In this study, Co-based full-Heusler alloy thin films of Co2Cr0.6Fe0.4Al (CCFA) and Co2MnGe (CMG) were epitaxially grown on MgO-buffered MgO (001) substrates using magnetron sputtering. The films were deposited at RT and subsequently annealed in situ at temperatures ranging from 400 to 600 degrees C. X-ray pole figure measurements of the CCFA films indicated that these films were epitaxial and crystallized in the B2 structure. X-ray pole figure measurements of the annealed CMG films showed (111) peaks with four-fold symmetry, which provides direct evidence that these films were epitaxial and crystallized in the L2(1) structure. Furthermore, cross-sectional transmission electron microscope images of a fabricated CMG film indicated that it was single-crystalline. The annealed films of CCFA and CMG had sufficiently flat surface morphologies with roughness of about 0.23 nm rms for 100 nm thick CCFA films and 0.26 nm rms for 45 nm thick CMG films. Using these epitaxially grown thin films, we fabricated fully epitaxial magnetic tunnel junctions (MTJs) consisting of a Co-based or full-Heusler thin film of either CCFA or CMG as a lower electrode, a MgO tunnel barrier and a Co50Fe50 (CoFe) upper electrode. All layers were successively deposited in an ultrahigh vacuum chamber through the combined use of magnetron sputtering and electron beam evaporation. Reflection high-energy electron diffraction patterns observed in situ for each layer during preparation clearly indicated that all layers grew epitaxially in both the CCFA/MgO/CoFe and CMG/MgO/CoFe MTJ layer structures. The microfabricated epitaxial CCFA/MgO/CoFe MTJs demonstrated relatively high tunnel magnetoresistance (TMR) ratios, for MTJs using a full-Heusler alloy, of 42% at RT and 74% at 55 K. On the other hand, the microfabricated epitaxial CMG/MgO/CoFe MTJs showed strongly temperature-dependent TMR characteristics with typical TMR ratios of 14% at RT and 70% at 7 K. These results confirm the promise of epitaxial MTJs as a key device structure for clarifying and utilizing the potentially high spin-polarization of Co-based full-Heusler alloy thin films.
  • Epitaxially grown full-Heusler alloy thin films and application to magnetic tunnel junctions
    M. Yamamoto, T. Uemura, K.-i. Matsuda
    The 3rd Int’l Symp. on Ubiquitous Knowledge Network Environment, Collected Papers vol.3 pp.79-92  2006年02月 [査読無し][招待有り]
  • H. Kijima, T. Ishikawa, T. Marukame, H. Koyama, K. Matsuda, T. Uemura, M. Yamamoto
    INTERMAG 2006 - IEEE International Magnetics Conference vol.19 377  2006年 [査読有り][通常論文]
  • T. Marukame, T. Ishikawa, H. Kijima, W. Sekine, K. Matsuda, T. Uemura, M. Yamamoto
    INTERMAG 2006 - IEEE International Magnetics Conference 723  2006年 [査読有り][通常論文]
  • T. Ishikawa, T. Marukame, H. Niwa, K. Matsuda, T. Uemura, M. Yamamoto
    INTERMAG 2006 - IEEE International Magnetics Conference 577  2006年 [査読有り][通常論文]
  • H. Kijima, T. Ishikawa, T. Marukame, H. Koyama, K. Matsuda, T. Uemura, M. Yamamoto
    INTERMAG 2006 - IEEE International Magnetics Conference 377  2006年 [査読有り][通常論文]
  • K Matsuda, T Kasahara, T Marukame, T Uemura, M Yamamoto
    JOURNAL OF CRYSTAL GROWTH 286 2 389 - 393 2006年01月 [査読有り][通常論文]
     
    We demonstrate that single-crystalline epitaxial films of the Hensler alloy Co2Cr0.6Fe0.4Al (CCFA) featuring excellent surface flatness can be grown on MgO (0 0 1) substrates by magnetron sputtering deposition at room temperature and subsequent annealing at high temperatures. X-ray pole figure measurements reveal that the films exhibit the B2-type structure and the [1 0 0] direction of the films is rotated by 45 degrees from the [100] direction of the MgO substrate. Moreover, their Curie temperatures and saturation magnetizations are also improved by annealing. The surface roughness is about 0.2 nm rms according to atomic force microscopy. (c) 2005 Elsevier B.V. All rights reserved.
  • Structural and magnetic properties of epitaxially grown full-Heusler alloy Co2MnGe thin films deposited using magnetron sputtering
    T. Ishikawa, T. Marukame, K. ?i. Matsuda, T. Uemura, M. Yamamoto
    50th Annual Conf. on Magnetism & Magnetic Materials, Abstract vol.50 p.370, GD-04  2005年10月 [査読有り][通常論文]
  • Tunnel magnetoresistance in epitaxial magnetic tunnel junctions using full-Heusler alloy Co2MnGe thin film and MgO tunnel barrier
    T. Marukame, T. Ishikawa, K. ?i. Matsuda, T. Uemura, M. Yamamoto
    50th Annual Conf. on Magnetism & Magnetic Materials, Abstract vol.50 p.18, AC-09  2005年10月 [査読有り][通常論文]
  • T Marukame, T Kasahara, KI Matsuda, T Uemura, A Yamamoto
    IEEE TRANSACTIONS ON MAGNETICS 41 10 2603 - 2605 2005年10月 [査読有り][通常論文]
     
    We have fabricated fully epitaxial magnetic tunnel junctions (MTJs) using a Co-based full-Heusler alloy Co-2 Cr-0.6, Fe-0.4 Al (CCFA) thin film and an MgO tunnel barrier. The CCFA thin film for the lower ferromagnetic electrode was deposited by magnetron sputtering on an MgO-buffered MgO single-crystal substrate, and the MgO tunnel barrier was formed by electron beam evaporation. The microfabricated epitaxial CCFA/MgO/CoFe MTJs showed high tunnel magnetoresistance ratios of 42% at room temperature and 74% at 55 K.
  • T. Kasahara, K.-i. Matsuda, T. Marukame, T. Uemura, M. Yamamoto
    J. The Magnetics Society of Japan vol.29 no. 9 pp. 895-899 - 899 The Magnetics Society of Japan 2005年09月 [査読有り][通常論文]
     
    Epitaxial Co2Cr0.6Fe0.4Al full-Heusler alloy thin films, featuring excellent surface flatness of less than 0.2 nm rms in roughness, were grown on MgO(001) substrates by magnetron sputtering deposition at room temperature and subsequent annealing at temperatures ranging from 500 to 600 °C . The ferromagnetic properties of the films in terms of Curie temperature and saturation magnetization were also improved by annealing process.
  • T Marukame, K Matsuda, T Uemura, M Yamamoto
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 44 8 6012 - 6015 2005年08月 [査読有り][通常論文]
     
    We report on the preparation and structural proper-ties of MgO/Fe bilayers (a MgO thin film on an Fe thin film), Fe/MgO bilayers (an Fe thin film on a MgO thin film), and Fe/MgO/Fe trilayers, all grown by magnetron sputtering on SrTiO3(001) substrates. We investigated the structural properties of these heterostructures with X-ray diffraction (XRD) (theta-2 theta scan, rocking curve and pole figure measurements), atomic force microscopy (AFM), and high-resolution transmission electron microscopy (HRTEM). Single-crystalline epitaxial growth was confirmed by the X-ray pole figure measurements for both the MgO/Fe and Fe/MgO bilayers, which were the basic layer components for the Fe/MgO/Fe trilayer. The cross-sectional HRTEM clearly indicated epitaxial growth of the Fe/MgO/Fe trilayer structures on the SrTiO3(001) substrates with excellent flat interfaces having roughness of less than a few angstroms.
  • Analysis of anisotropic tunnel magneto-resistance of GaMnAs/AlAs/GaMnAs magnetic tunnel junction
    T. Uemura, R. Miura, T. Sone, K. Matsuda, M. Yamamoto
    12th Int’l Conf. on Modulated Semiconductors (MSS 12), Abstract vol12 THU-PC1  2005年07月 [査読有り][通常論文]
  • High Tunnel Magnetoresistance in Epitaxial Co2Cr0.6Fe0.4Al/MgO/CoFe Tunnel Junctions
    T. Marukame, T. Kasahara, K. Matsuda, T. Uemura, M. Yamamoto
    IEEE Int’l Magnetics Conf., Digests p.235, DD-07  2005年04月 [査読有り][通常論文]
  • T Uemura, K Sekine, K Matsuda, M Yamamoto
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 44 4B 2604 - 2607 2005年04月 [査読有り][通常論文]
     
    LaSrMnO(3) ((LSMO) thin films were grown on SrTiO)((STO)-buffered Si(001) substrates by RF magnetron sputtering, and their magnetic and electrical properties as well as their crystalline structures were characterized. The LSMO film exhibited a polycrystalline nature with a strong preferred orientation to the c-axis. Compared with single-crystalline' samples, the electrical and magnetic properties of the LSMO films on STO-buffered Si substrates obtained in this study were different in the following points. (1) A lower metal-insulator transition temperature than the Curie temperature, T)(, determined from magnetization measurements. (2) A large negative in magnetoresistance with a clear hysteresis below T)(3)(C)(C). (3) An increased coercivity in the low temperature region below 170K. These features can be explained by the existence of localized ferromagnetic regions and spin-polarized tunneling between them.
  • Epitaxial growth and characterization of full-Huesler alloy Co2Cr0.6Fe0.4Al thin films for magnetic tunnel junctions
    T. Marukame, T. kasahara, K. Matsuda, T. Uemura, M. Yamamoto
    2nd Int. Workshop on Ubiquitous Knowledge Network Environment, Proceedings vol.2 pp.383-389, DD-07  2005年03月 [査読無し][通常論文]
  • Fully epitaxial magnetic tunnel junctions using full-Heusler alloy thin film
    M. Yamamoto, T. Uemura, K. Matsuda
    2nd Int. Workshop on Ubiquitous Knowledge Network Environment, Proceedings vol.2 pp.289-299  2005年03月 [査読無し][招待有り]
  • T Marukame, T Kasahara, K Matsuda, T Uemura, M Yamamoto
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 44 16-19 L521 - L524 2005年 [査読有り][通常論文]
     
    Fully epitaxial magnetic tunnel junctions (MTJs) were fabricated using a Co-based full-Heusler alloy CO2Cr0.6Fe0.4Al (CCFA) thin film and a MgO tunnel barrier. The fabricated MTJs had the following layer structure: MgO buffer layer/CCFA lower electrode/MgO tunnel barrier/CoFe upper electrode, grown on a MgO single-crystal substrate. All layers were successively deposited in an ultrahigh vacuum chamber through the combined use of magnetron sputtering and electron beam evaporation. RHEED patterns observed in situ for each layer during preparation clearly indicated that all layers grew epitaxially with the (001) basal plane. The microfabricated epitaxial CCFA/MgO/CoFe MTJs demonstrated relatively high tunnel rnagneto-resistance ratios, for MTJs using a full-Heuster alloy, of 42% at room temperature and 74% at 55 K. These results confirm the promise of an epitaxial MTJ using a Co-based full-Heusler alloy as a key device structure utilizing the potentially high spin polarization of this material system.
  • T Uemura, M Yamamoto
    JOURNAL OF MULTIPLE-VALUED LOGIC AND SOFT COMPUTING 11 5-6 467 - 479 2005年 [査読有り][通常論文]
     
    We proposed a novel four-valued magnetic random access memory (MRAM), that uses a double barrier magneto tunnel junction (MTJ) and a resonant tunneling diode (RTD) connected in series. The double barrier MTJ in the form FM1/I/FM2/I/FM1, where FM1 and FM2 represent ferromagnetic materials with different coercive forces and I represents an insulator, respectively, can take four distinct resistance values, depending on the direction of magnetization of each ferromagnetic layer. The RTD can increase the magneto-resistance (MR) ratio of the MTJ without area penalty due to the NDR characteristics and compactness. The circuit simulation showed that the GaAs/A1As-based triple barrier RTD with its peak-to-valley current ratio of 20 increased the effective MR ratio from 15% to more than 1700%. The cell area per bit is 2F(2)/bit, which is suitable for a ultra-high density memory.
  • T Uemura, T Sone, K Matsuda, M Yamamoto
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 44 42-45 L1352 - L1354 2005年 [査読有り][通常論文]
     
    Magnetic anisotropy of GaMnAs/AlAs/GaMnAs magnetic tunnel junctions (MTJs) was investigated through tunnel magnetoresistance (TMR). The TMR ratio measured at 8 K for the fabricated MTJs took its maximum value of approximately 39% along the < 100 > direction, and decreased to about 19 and 10% in the [110] and [1 (1) over bar0] directions, respectively. This anisotropic TMR ratio suggests that the cubic magnetic anisotropy with its easy axis along the < 100 > directions is dominant, whereas the uniaxial anisotropy with its easy axis along the [110] direction slightly exists. The domain-wall displacement model, rather than the coherent rotation model, accurately explained the angular dependences of both the switching field and the TMR ratios. Temperature dependences of anisotropic TMR ratios revealed that lower than 25 K the maximum TMR ratio was obtained along the < 100 > directions, whereas higher than 25 K the maximum was obtained along the [110] direction, indicating crossover of the easy axis directions.
  • T. Uemura, K. Sekine, K. Matsuda and M. Yamamoto
    T. Uemura, K. Sekine, K. Matsuda, M. Yamamoto
    49th Annual Conf. on Magnetism and Magnetic Materials, Abstracts vol49 p.54  2004年11月 [査読有り][通常論文]
  • Epitaxial growth of Fe/MgO/Fe heterostructures on SrTiO3 substrates by magnetron sputtering
    T. Marukame, K.-i. Matsuda, T. Uemura, M. Yamamoto
    49th Annual Conf. on Magnetism and Magnetic Materials, Abstracts vol49 p.329  2004年11月 [査読有り][通常論文]
  • Magnetic and Electrical Properties of (La, Sr)MnO3 Sputtered on SrTiO3-buffered Si Substrate
    T. Uemura, Y. Takagi, K. Sekine, K. Matsuda, M. Yamamoto
    2004 Int’l Conf. on Solid State Devices and Materials, Extended Abstracts pp.600-601  2004年09月 [査読有り][通常論文]
  • T Uemura, S Honma, T Marukame, M Yamamoto
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 43 4B 2114 - 2117 2004年04月 [査読有り][通常論文]
     
    A novel magnetic random access memory (MRAM) cell consisting of a magnetic tunnel junction (MTJ) and negative differential resistance (NDR) device connected in parallel is described. The NDR characteristics are used to increase the effective magnetoresistance (MR) ratio of the MTJ. Circuit simulations were performed for the memory cell with a triple-barrier resonant-tunneling diode (RTD) to confirm the efficacy of the basic operation. Furthermore, a hybrid circuit built from the CoFe-based MTJ and GaAs-based interband tunnel diode was fabricated. The circuit showed that the effective MR ratio was enhanced almost tenfold from its original value of 11% to 103%.
  • K Uesugi, M Kurimoto, Suemune, I, M Yamamoto, T Uemura, H Machida, N Shimoyama
    PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES 21 2-4 727 - 731 2004年03月 [査読有り][通常論文]
     
    Diodes with GaAsNSb/GaAs multiple quantum wells (MQWs) were gown on p-GaAs(001) substrates by metalorganic molecular-beam epitaxy. Negative differential resistance (NDR) characteristics were clearly observed at room temperature. The peak-to-valley current ratio was as high as 6 and the peak current density was similar to1.7 A/cm(2). The NDR characteristics were also observed for a GaAsNSe/GaAs MQW diode and a GaAsNSe-based tunnel junction diode. The mechanism of the observed NDR is discussed considering the band offsets in the nitrogen-related GaAsNSb/GaAs and GaAsNSe/GaAs MQWs. (C) 2003 Elsevier B.V. All rights reserved.
  • T Uemura, S Honma, T Marukame, M Yamamoto
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS 43 1A-B L44 - L46 2004年01月 [査読有り][通常論文]
     
    A novel magnetic random access memory (MRAM) cell consisting of a magnetic tunnel junction (MTJ) and a tunnel diode connected in series is described. The negative differential resistance (NDR) characteristics of the tunnel diode were used to increase the tunneling magnetoresistance (TMR) ratio of the MTJ. The basic operation was successfully confirmed by both simulation and experiment. The fabricated circuit showed that the effective MR ratio was enhanced from its original value of 15 to 890%. In the simulation, a sufficient operating margin of the bias voltage was obtained by using the MTJ with its TMR ratio of 30%.
  • Proposal and Experimental Demonstration of Novel MRAM Cell Using Magnetic Tunnel Junction in Combination with Negative Differential Resistance Device
    M. Yamamoto, T. Uemura
    1st Int. Workshop on Ubiquitous Knowledge Network Environment, Proceedings vol.1 pp.469-480  2003年11月 [査読無し][招待有り]
  • T Uemura, S Honma, T Marukame, M Yamamoto
    ELECTRONICS LETTERS 39 21 1549 - 1551 2003年10月 [査読有り][通常論文]
     
    A novel magnetic random access memory cell consisting of a magneto-tunnel junction (MTJ) and tunnel diode connected in parallel is described. The negative differential resistance characteristics of the tunnel diode were used to increase the tunnelling magneto-resistance (TMR) ratio of the MTJ. The fabricated circuit showed that the TMR ratio was enhanced from its original value of 11 to 103%.
  • Demonstration of Enhanced Tunneling Magneto Resistance Ratio for a Magnetic Tunnel Junction Connected in Parallel with a Tunnel Diode
    T. Uemura, S. Honma, T. Marukame, M. Yamamoto
    2003 Int’l Conf. on Solid State Devices and Materials, Extended Abstracts pp.618-619  2003年09月 [査読有り][通常論文]
  • T Uemura, T Marukame, M Yamamoto
    IEEE TRANSACTIONS ON MAGNETICS 39 5 2809 - 2811 2003年09月 [査読有り][通常論文]
     
    A novel spin filter consisting of a triple-barrier resonant tunneling system in the form F/I/N/I/F/I/F is proposed, where F, I, and N represent a ferromagnetic material, an insulator, and a nonmagnetic material, respectively. The spin-dependent tunneling current in the triple-barrier resonant tunneling system is calculated theoretically on the basis of a Tsu-Esaki formula to investigate the output tunnel current polarization. Detailed calculations using the GaMnAs/AlAs/GaAs material system show that the two clear split peaks originating from up- and down-spin holes appear in the current-voltage (I-V) curve due to spin splitting of the energy levels formed in the ferromagnetic quantum well. The polarization can reach more than 98 % at the peak positions in the I-V curve.
  • Observation of Large Room-temperature Negative Differential Resistance in GaAsNSe/GaAs and GaAsNSb/GaAs Superlattices Grown on (001) GaAs
    K. Uesugi, M. Kurimoto, I. Suemune, M. Yamamoto, T. Uemura, H. Machida, N. Shimoyama
    The 11th Int’l. Conf. on Modulated Semiconductor Structures (MSS11), Workbook vol.11 pp.266-267  2003年07月 [査読有り][通常論文]
  • T. Uemura, T. Marukame, M. Yamamoto
    Intermag 2003 - Program of the 2003 IEEE International Magnetics Conference GD-03  2003年 [査読有り][通常論文]
     
    In this paper, a new type of spin filter that uses a triple-barrier structure was proposed. The proposed device consists of a non-magnetic and a ferromagnet QW. The inherent peaked I-V characteristics in the triple barrier resonant structure result in a distinct peak separation of the up-spin and the down-spin components regarding the bias voltage, which leads to an exceedingly high spin polarization. The spin dependent tunneling current and the tunnel-barrier-width dependence of both the spin polarization and the current density were theoretically calculated.
  • T Uemura, M Yamamoto
    33RD INTERNATIONAL SYMPOSIUM ON MULTIPLE-VALUED LOGIC, PROCEEDINGS vol.33 273 - 278 2003年 [査読有り][通常論文]
     
    We proposed a novel four-valued magnetic random access memory (MRAM), that uses a double barrier magneto tunnel junction (MTJ) and a resonant tunneling diode (RTD) connected in series. The double barrier MTJ in the form FM1/I/FM2/I/FM1, where FM1 and FM2 represent ferromagnetic materials with different coercive forces and I represents an insulator, respectively, can take four distinct resistance values, depending on the direction of magnetization of each ferromagnetic layer The RTD can increase the tunneling magneto-resistance (TMR) ratio of the MTJ without area penalty due to the nonlinear nature of the NDR characteristics and compactness. The SPICE simulation showed that the RTD with its peak-to-valley current ratio of 12 could increase the effective TMR ratio from 15 % to more than 100 %. The cell area per bit is 2F(2)/bit, which is suitable for an ultra-high density memory.
  • Chun Yong Jin, Uemura Tetsuya, Baba Toshio
    Japanese Journal of Applied Physics 39 12 L1273 - L1276 公益社団法人 応用物理学会 2000年 
    A novel method using electron-beam (EB) lithography and regrowth for fabricating self-aligned InGaAs-based surface tunnel transistors (STTs) with sub-micron gate lengths has been developed. The shape of regrowth layer on the gate region is significantly affected not only by the gate lengths but also by the thickness of the regrowth layer. During regrowth, (111) facets are formed at the edges of the gate region while the (100) surface is maintained at the center. The shape changes to triangular consisting of (111) facets as gate length decreases below 150 nm due to the slow growth rate of the (111) facets compared to the (100) surface. The 80-nm STTs were fabricated by controlling the shape of the regrowth layer, and no deposition of the regrowth layer on the sidewall, which causes leakage current, occurred. The successful operation of InGaAs-based 80-nm STTs with clear negative differential resistance (NDR) characteristics and a gate-controlled peak current was obtained at room temperature.
  • Chun Yong Jin, Uemura Tetsuya, Baba Toshio
    Japanese Journal of Applied Physics 38 10 L1163 - L1165 公益社団法人 応用物理学会 1999年 
    A self-aligned process for fabricating surface tunnel transistors (STTs) has been developed in an attempt to improve both miniaturization and integration of STTs. In this process, the keys to obtaining a flat regrown layer and fine tunnel junctions are to keep from contaminating the surface during the lithography process before regrowth and to control the side-wall profile of the gate region in which tunnel junctions are formed. The carbon contamination can be reduced significantly by using a double hard mask consisting of Si3N4 and SiO2, and oxygen contamination can be removed by atomic hydrogen irradiation. The side-wall profile, that is etched surface morphology and side-wall angle, can be optimized by adjusting the composition of the H3PO4:H2O2:H2O etching solution. During regrowth, a flat surface morphology and fine tunnel junctions were obtained at the low temperature of 400°C. Self-aligned InGaAs-based STTs with gate-controlled negative differential resistance (NDR) characteristics showing a peak-to-valley (P/V) ratio of 2.5 were obtained.
  • Uemura Tetsuya, Baba Toshio
    Japanese Journal of Applied Physics 35 3 1668 - 1675 公益社団法人 応用物理学会 1996年 
    We demonstrated a novel three-terminal tunnel device, the Surface Tunnel Transistor (STT), in which lateral interband tunneling current between source and drain is controlled by a gate voltage. The STT consists of a highly degenerate drain whose polarity is opposite that of the source, a channel with an insulated gate, and a source connected to the channel. The basic characteristics of the STTs were investigated by fabricating three types of STTs with mesa structures using a GaAs/AlGaAs system, as well as by a two-dimensional device simulation. An enhancement-type STT (E-STT) in which no electrons are accumulated on the channel surface at thermal equilibrium exhibited unsaturated transistor characteristics due to interband tunneling under source-drain reverse bias conditions. To increase the current density, a modulation doped STT (MD-STT) in which the channel was formed by modulation doping was also fabricated, and a tunneling current about 104 times larger than that of the E-STT was obtained. Moreover, the MD-STT showed negative differential resistance (NDR) characteristics under source-drain forward bias conditions. A channel doped STT (CD-STT) in which the channel region was directly doped with donors showed improved NDR characteristics with a peak current density of 3.7 µ A/µ m and a peak-to-valley current ratio (PVR) of 1.5 at room temperature. These values are larger than those of the MD-STT by a factor of 103 and 1.5, respectively. Furthermore, a PVR as high as 4.8 was obtained for the CD-STT by inserting a blocking layer between the drain and the overlapped channel layer to reduce the valley current.
  • Uemura Tetsuya, Baba Toshio
    Japanese Journal of Applied Physics 33 10 L1363 - L1366 社団法人応用物理学会 1994年10月01日 
    We propose and demonstrate a new type of Surface Tunnel Transistor (STT) which displays improved negative differential resistance (NDR) characteristics. In this device, called channel-doped STT (CD-STT), the channel region is direclly doped with donors in order to increase the channel carrier density. A peak current is obtained that is 103 times larger than that of a conventional STT. To reduce the valley current further, a blocking layer consisting of an i-GaAs is inserted at the gate/drain overlap region. The resulting device, called blocking layer inserted STT (BLI-STT), exhibits excellent NDR characteristics with a peak-to-valley ratio (PVR) of 4.8 at room temperature, a value which is more than 4 times larger than that of a conventional STT.
  • Uemura Tetsuya, Baba Toshio
    Jpn J Appl Phys 33 2 L207 - L210 社団法人応用物理学会 1994年02月15日 
    Negative differential resistance (NDR) due to an interband tunneling has been observed at room temperature for the first time in a Surface Tunnel Transistor (STT) under forward-bias conditions. To produce clear NDR characteristics, the electron density in the channel was designed to be high enough to induce band overlap at the channel/drain junction. In order to increase the tunneling current further, a channel doped structure, in which a thin n+-GaAs layer was inserted between a p+-GaAs layer (drain) and an i-GaAs layer, was proposed. This channel doped STT exhibited a peak current density of 8 µ A/µ m, which is 280 times larger than that of the conventional STT.
  • Uemura Tetsuya, Baba Toshio
    Jpn J Appl Phys 31 12 L1727 - L1729 社団法人応用物理学会 1992年12月20日 
    A depletion-type Surface Tunnel Transistor (D-STT) is proposed to increase the tunneling current compared to that of the enhancement-type STT (E-STT) previously reported. The most important feature of the D-STT is the use of a modulation doped structure in order to accumulate a high concentration of electrons under the gate. GaAs/AlGaAs D-STTs, which are fabricated by using an MBE regrowth technique, exhibit depletion-mode transistor action with a larger operation current than that displayed by the E-STT. This increase in current is due to a higher two-dimensional electron gas concentration at the i-GaAs surface. Moreover, the high gate leakage current which limits GaAs E-STT operation is reduced in the case of the D-STT by a factor of $10^{6}$.

MISC

  • 酒井貴樹, 野土翔登, 長浜太郎, 植村哲也, 山ノ内路彦 応用物理学会北海道支部/日本光学会北海道支部合同学術講演会講演予稿集 56th-17th (CD-ROM) 2021年
  • 植村 哲也 応用物理 83 (3) 194 -199 2014年03月
  • Co2MnSi/MgO/Co2MnSi強磁性体トンネル接合におけるスピン依存トンネル抵抗の温度依存性
    本田佑輔, 劉宏喜, 植村哲也, 山本眞史 第49回応用物理学会北海道支部学術講演会講演予稿集 vol.49 p.5, A-5 2013年12月 [査読無し][通常論文]
  • Co2MnSi/CoFe/n-GaAs接合における高いスピン注入効率の実証
    蝦名優也, 秋保貴史, 劉宏喜, 山本眞史, 植村哲也 第49回応用物理学会北海道支部学術講演会講演予稿集 vol.49 p.4, A-4, 2013年12月 [査読無し][通常論文]
  • Spin lifetime in strained InGaAs channels investigated through all electrical spin injection and detection
    T. Akiho, M. Yamamoto, T. Uemura 第18回半導体スピン工学の基礎と応用(PASPS18)，Program and Abstracts vol.18 p.13, A5 2013年12月 [査読無し][通常論文]
  • Co2MnSi/CoFe/n-GaAs 接合における動的核スピン偏極
    秋保貴史, 劉宏喜, 山本眞史, 植村哲也 第37回日本磁気学会学術講演概要集 2013 vol.37 p.366, 6aC-8 2013年09月 [査読無し][通常論文]
  • Co2MnSi/CoFe/n-GaAs 接合におけるスピン注入特性に及ぼす CoFe 挿入層の効果
    蝦名優也, 秋保貴史, 劉宏喜, 山本眞史, 植村哲也 第37回日本磁気学会学術講演概要集 2013 vol.37 p.365, 6aC-7 2013年09月 [査読無し][通常論文]
  • Co2(Mn, Fe)Si/MgO/ Co2(Mn, Fe)Si エピタキシャル MTJ の巨大トンネル磁気抵抗
    川見豪, 劉宏喜, 本田佑輔, 植村哲也, F.-y. Shi, P. M. Voyles, 山本眞史 第37回日本磁気学会学術講演概要集 2013, p. 53, 3pC- vol.37 p.53, 3pC-8 2013年09月 [査読無し][通常論文]
  • Co2MnSi 薄膜の飽和磁化およびトンネルスピン偏極率に対する非化学量論的組成の影響
    本田佑輔, 李桂芳, 劉宏喜, 有田正志, 松田健一, 植村哲也, 山本眞史, 齊藤敏明, 三浦良雄, 白井正文 第37回日本磁気学会学術講演概要集 2013 vol.37 p.52, 3pC-7 2013年09月 [査読無し][通常論文]
  • Highly-efficient dynamic nuclear polarization in GaAs using a Heusler-alloy spin source
    T. Akiho, H.-x. Liu, K.-i. Matsuda, M. Yamamoto, T. Uemura 2013年（平成25年）第74回応用物理学会秋季学術講演会，講演予稿集(DVD-ROM) vol.74 10-041,20a-C15-3 2013年09月 [査読無し][通常論文]
  • Giant tunneling magnetoresistance in fully epitaxial Co2(Mn, Fe)Si/MgO/ Co2(Mn, Fe)Si magnetic tunnel junctions
    T. Kawami, H.-x. Liu, Y. Honda, T. Uemura, F.-y. Shi, P. M. Voyles, M. Yamamoto 2013年（平成25年）第74回応用物理学会秋季学術講演会，講演予稿集(DVD-ROM) vol.74 10-018,18a-C15-4 2013年09月 [査読無し][通常論文]
  • スピントロニクス材料としてのハーフメタルホイスラー合金
    山本眞史, 植村哲也 2013年（平成25年）第74回応用物理学会秋季学術講演会，講演予稿集(DVD-ROM) vol.74 077,18p-C15-2 2013年09月 [査読無し][招待有り]
  • Annealing temperature dependence of spin signals observed inCo2MnSi/CoFe/n-GaAs through four-terminal non-local geometry
    T. Akiho, J. Shan, K.-i. Matsuda, M. Yamamoto, T. Uemura 第60回応用物理学会春季学術講演会，講演予稿集 (DVD-ROM) vol.60 10-049, 28a-A7-5, 2013年03月 [査読無し][通常論文]
  • Influence of interfacetermination layeron temperature dependenceof tunneling magnetoresistance of Co2MnSi/MgO-based magnetic tunnel junctions
    H.-x. Liu, Y. Honda, K.-i. Matsuda, T. Uemura, M. Yamamoto, F.-y. Shi, P. Voyles 第60回応用物理学会春季学術講演会，講演予稿集 (DVD-ROM) vol.60 10-038, 30p-A7-7 2013年03月 [査読無し][通常論文]
  • 藤澤潤, 松田健一, 山本眞史, 植村哲也 第48回応用物理学会北海道支部学術講演会講演予稿集 59 2013年01月11日 [査読無し][通常論文]
  • Co2MnSi/CoFe/MgO/SiにおけるHanle信号のMgO膜厚依存性
    藤澤潤, 松田健一, 山本眞史, 植村哲也 2013年 (平成25年) 第48回応用物理学会北海道支部学術講演会講演予稿集 vol.48 p.59, B-27 2013年01月 [査読無し][通常論文]
  • Nb/ Cu50Ni50二層薄膜の電気伝導特性と超電導近接効果
    蝦名優也, 松田健一, 植村哲也, 山本眞史 2013年 (平成25年) 第48回応用物理学会北海道支部学術講演会講演予稿集 vol.48 p.58, B-26 2013年01月 [査読無し][通常論文]
  • GaAsショットキートンネル障壁を介した強磁性体からInGaAsチャネルへのスピン注入
    鳥野剛史, 松田健一, 山本眞史, 植村哲也 2013年 (平成25年) 第48回応用物理学会北海道支部学術講演会講演予稿集 vol.48 p.17, A-17 2013年01月 [査読無し][通常論文]
  • CoFe/MgO/SC(SC = Si or Ge)におけるHanle信号の半導体種依存性
    植村哲也, 李桂芳, 藤澤潤, 松田健一, 山本眞史 第17回半導体スピン工学の基礎と応用(PASPS17)，Program and Abstracts vol.17 p.25,P5 2012年12月 [査読無し][通常論文]
  • 高スピン偏極材料を用いたGaAsへのスピン注入
    植村哲也, 秋保貴史, 松田健一, 山本眞史 第17回半導体スピン工学の基礎と応用(PASPS17)，Program and Abstracts vol.17 p.19, B5 2012年12月 [査読無し][招待有り]
  • Co50Fe50電極からGaAs へのスピン注入の電気的検出
    植村哲也, 秋保貴史, 原田雅亘, 松田健一, 山本眞史 第35回日本磁気学会学術講演概要集 vol.35 p.338, 30aB-3 2012年09月 [査読無し][通常論文]
  • 非局所四端子配置を用いたCo2MnSi/CoFe/n-GaAs ショットキートンネル接合におけるoblique Hanle 信号の過渡特性
    単津海, 秋保貴史, 松田健一, 山本眞史, 植村哲也 2012年 (平成24年) 秋季第73回応用物理学会学術講演会, 講演予稿集 (DVD-ROM) vol.73 10-100, 14a-H6-10 2012年09月 [査読無し][通常論文]
  • MgO tunnel barrier thickness dependence of three-terminal Hanle-type signals in CoFe/MgO/n-Ge tunnel junctions
    G.-f. Li, M. Miki, K.-i. Matsuda, T. Uemura, M. Yamamoto 2012年 (平成24年) 秋季第73回応用物理学会学術講演会, 講演予稿集 (DVD-ROM) vol.73 10-052, 13p-H6-6 2012年09月 [査読無し][通常論文]
  • Co2MnSi/MgO/NbN接合を用いたホイスラー合金Co2MnSiのスピン偏極率評価
    松田健一, 篠木崇帆, 植村哲也, 山本眞史 2012年 (平成24年) 秋季第73回応用物理学会学術講演会, 講演予稿集 (DVD-ROM) vol.73 10-020, 12a-H6-2 2012年09月 [査読無し][通常論文]
  • Temperature dependence of spin-dependent tunneling resistances of fully epitaxial Co2MnSi-based magnetic tunnel junctions
    H.-x. Liu, Y. Honda, K.-i. Matsuda, T. Uemura, M. Yamamoto 2012年 (平成24年) 秋季第73回応用物理学会学術講演会, 講演予稿集 (DVD-ROM) vol.73 10-009, 11p-H6-9 2012年09月 [査読無し][通常論文]
  • CoFe/MgO/Siにおけるスピン蓄積信号のMgO膜厚依存性
    植村哲也, 藤澤 潤, 松田健一, 山本眞史 2012年 (平成24年) 春季第59回応用物理学関係連合講演会講演予稿集 (DVD-ROM) vol.59 10-056, 17a-B4-9 2012年03月 [査読無し][通常論文]
  • Co2MnSiホイスラー合金を用いたGaAsへの電気的スピン注入および動的核スピン偏極の電気的検出
    秋保貴史, 植村哲也, 松田健一, 山本眞史 2012年 (平成24年) 春季第59回応用物理学関係連合講演会講演予稿集 (DVD-ROM) vol.59 10-059, 17a-B4-12 2012年03月 [査読無し][通常論文]
  • Fabrication of fully epitaxial magnetic tunnel junctions with a Heusler alloy Co2MnSi thin film and a MgO barrier on Ge(001) substrates
    G.-f. Li, T. Taira, H.-x. Liu, K.-i. Matsuda, T. Uemura, M. Yamamoto 2012年 (平成24年) 春季第59回応用物理学関係連合講演会講演予稿集 (DVD-ROM) vol.59 10-005, 16a-B4-5 2012年03月 [査読無し][通常論文]
  • Spin-dependent transport characteristics of epitaxial magnetic tunnel junctions of CoFe/MgO/CoFe ultrathin layer/Co2MnSi
    H.-x. Liu, Y. Honda, T. Taira, K.-i. Matsuda, T. Uemura, Y. Miura, M. Shirai, M. Yamamoto 2012年 (平成24年) 春季第59回応用物理学関係連合講演会講演予稿集 (DVD-ROM) vol.59 10-006, 16a-B4-6 2012年03月 [査読無し][通常論文]
  • Co2MnSi/CoFe/n-GaAsにおけるスピン輸送と核磁場の検出
    秋保貴史, 原田雅亘, 植村哲也, 松田健一, 山本眞史 2012年 (平成24年) 第47回応用物理学会北海道支部学術講演会講演予稿集 vol.47 p.78, C-9 2012年01月 [査読無し][通常論文]
  • Tunnel magnetoresistance in fully epitaxial CoFe/MgO/CoFe magnetic tunnel junctions on Ge(001) substrates via a MgO interlayer
    G.-f. Li, T. Taira, H.-x. Liu, K.-i. Matsuda, T. Uemura, M. Yamamoto 2012年 (平成24年) 第47回応用物理学会北海道支部学術講演会講演予稿集 vol.47 p.77, C-8 2012年01月 [査読無し][通常論文]
  • Co2MnSi/MgO/NbNヘテロ構造を用いたホイスラー合金Co2MnSiのスピン偏極率評価
    篠木崇帆, 松田健一, 平智幸, 植村哲也, 山本眞史 2012年 (平成24年) 第47回応用物理学会北海道支部学術講演会講演予稿集 vol.47 p.73, C-4 2012年01月 [査読無し][通常論文]
  • Spin-polarized transport in fully epitaxial CoFe/MgO/CoFe ultrathin layer/Co2MnSi magnetic tunnel junction
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    山本眞史, 丸亀孝生, 石川貴之, 平智幸, 松田健一, 植村哲也 2010年 (平成22年) 秋季第71回応用物理学会学術講演会講演予稿集 (DVD-ROM) vol.71 10-064, 14p-J-4 2010年09月 [査読無し][通常論文]
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    原田雅亘, 秋保貴史, 植村哲也, 松田健一, 山本眞史 2010年 (平成22年) 秋季第71回応用物理学会学術講演会講演予稿集 (DVD-ROM) vol.71 10-056, 17p-A-1 2010年09月 [査読無し][通常論文]
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    H.-x. Liu, T. Taira, Y. Honda, K.-i. Matsuda, T. Uemura, M. Yamamoto 2010年 (平成22年) 秋季第71回応用物理学会学術講演会講演予稿集 (DVD-ROM) vol.71 10-002, 14a-F-2 2010年09月 [査読無し][通常論文]
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  • 石川貴之, 板橋直樹, 平智幸, 松田健一, 植村哲也, 山本眞史 第32回日本磁気学会学術講演会講演概要集 170 2008年09月12日 [査読無し][通常論文]
  • 平智幸, 石川貴之, 松田健一, 植村哲也, 山本眞史 第32回日本磁気学会学術講演会講演概要集 172 2008年09月12日 [査読無し][通常論文]
  • 板橋直樹, 石川貴之, 松田健一, 植村哲也, 山本眞史 第32回日本磁気学会学術講演会講演概要集 285 2008年09月12日 [査読無し][通常論文]
  • 平智幸, 石川貴之, 松田健一, 植村哲也, 山本眞史 2008年秋季第69回応用物理学会学術講演会講演予稿集 (2) 666 2008年09月02日 [査読無し][通常論文]
  • 松田健一, 秋元陽介, 植村哲也, 山本眞史 2008年秋季第69回応用物理学会学術講演会講演予稿集 (1) 258 2008年09月02日 [査読無し][通常論文]
  • 石川貴之, 板橋直樹, 平智幸, 松田健一, 植村哲也, 山本眞史 2008年秋季第69回応用物理学会学術講演会講演予稿集 (2) 655 2008年09月02日 [査読無し][通常論文]
  • 米村和希, 石川貴之, 松田健一, 植村哲也, 山本眞史 2008年秋季第69回応用物理学会学術講演会講演予稿集 (2) 654 2008年09月02日 [査読無し][通常論文]
  • 板橋直樹, 石川貴之, 松田健一, 植村哲也, 山本眞史 2008年春季第55回応用物理学関係連合講演会講演予稿集 (2) 786 2008年03月27日 [査読無し][通常論文]
  • 石川貴之, 板橋直樹, 松田健一, 植村哲也, 山本眞史 2008年春季第55回応用物理学関係連合講演会講演予稿集 (2) 786 2008年03月27日 [査読無し][通常論文]
  • PUTRA Ananda, KAKUGO Akira, FURUKAWA Hidemitsu, GONG Jian Ping, OSADA Yoshihito, UEMURA Tetsuya, YAMAMOTO Masafumi 第42回高分子学会北海道支部研究発表会講演要旨集 51 2008年01月29日 [査読無し][通常論文]
  • 板橋直樹, 石川貴之, 松田健一, 植村哲也, 山本眞史 第43回応用物理学会北海道支部学術講演会講演予稿集 51 2008年01月10日 [査読無し][通常論文]
  • 袴田真矢, 石川貴之, 松田健一, 植村哲也, 山本眞史 第43回応用物理学会北海道支部学術講演会講演予稿集 49 2008年01月10日 [査読無し][通常論文]
  • 秋元陽介, 松田健一, 植村哲也, 山本眞史 第43回応用物理学会北海道支部学術講演会講演予稿集 4 2008年01月10日 [査読無し][通常論文]
  • 平智幸, 石川貴之, 袴田真矢, 松田健一, 植村哲也, 山本眞史 第43回応用物理学会北海道支部学術講演会講演予稿集 50 2008年01月10日 [査読無し][通常論文]
  • 今井洋介, 河岸沙織, 植村哲也, 松田健一, 山本眞史 第43回応用物理学会北海道支部学術講演会講演予稿集 54 2008年01月10日 [査読無し][通常論文]
  • 米村和希, 石川貴之, 松田健一, 植村哲也, 山本眞史 第43回応用物理学会北海道支部学術講演会講演予稿集 52 2008年01月10日 [査読無し][通常論文]
  • 増田昌洋, 植村哲也, 松田健一, 山本眞史 第43回応用物理学会北海道支部学術講演会講演予稿集 53 2008年01月10日 [査読無し][通常論文]
  • 河岸沙織, 今井洋介, 植村哲也, 松田健一, 山本眞史 第43回応用物理学会北海道支部学術講演会講演予稿集 47 2008年01月10日 [査読無し][通常論文]
  • 石川貴之, 袴田真矢, 松田健一, 植村哲也, 山本眞史 第43回応用物理学会北海道支部学術講演会講演予稿集 48 2008年01月10日 [査読無し][通常論文]
  • A. Putra, A. Kakugo, H. Furukawa, J. P. Gong, Y. Osada, T. Uemura, M. Yamamoto Polymer 49 (7) 1885 -1891 2008年01月 [査読無し][通常論文]
  • 袴田真矢, 石川貴之, 松田健一, 植村哲也, 山本眞史 第31回日本応用磁気学会学術講演会講演概要集 36 2007年09月11日 [査読無し][通常論文]
  • 丸亀孝生, 石川貴之, 米村和希, 松田健一, 植村哲也, 山本眞史 第31回日本応用磁気学会学術講演会講演概要集 39 2007年09月11日 [査読無し][通常論文]
  • 齊藤敏明, 片山利一, 石川貴之, 山本眞史, 植村哲也, 浅野裕司, 江村藍, 角田乃亜, 松岡七絵, 朝倉大輔, 小出常晴 第31回日本応用磁気学会学術講演会講演概要集 42 2007年09月11日 [査読無し][通常論文]
  • 植村哲也, 増田昌洋, 松田健一, 山本眞史 第31回日本応用磁気学会学術講演会講演概要集 38 2007年09月11日 [査読無し][通常論文]
  • 石川貴之, 袴田真矢, 平智幸, 松田健一, 植村哲也, 山本眞史 第31回日本応用磁気学会学術講演会講演概要集 37 2007年09月11日 [査読無し][通常論文]
  • 平智幸, 石川貴之, 袴田真矢, 松田健一, 植村哲也, 山本眞史 2007年秋季第68回応用物理学会学術講演会講演予稿集 (1) 491 2007年09月04日 [査読無し][通常論文]
  • 今井洋介, 河岸沙織, 松田健一, 植村哲也, 山本眞史 2007年秋季第68回応用物理学会学術講演会講演予稿集 (1) 475 2007年09月04日 [査読無し][通常論文]
  • 増田昌洋, 植村哲也, 松田健一, 山本眞史 2007年秋季第68回応用物理学会学術講演会講演予稿集 (1) 475 2007年09月04日 [査読無し][通常論文]
  • 石川貴之, 丸亀孝生, 袴田真矢, 松田健一, 植村哲也, 山本眞史 2007年春季第54回応用物理学関係連合講演会講演予稿集 (1) 512 2007年03月27日 [査読無し][通常論文]
  • 袴田真矢, 石川貴之, 丸亀孝生, 松田健一, 植村哲也, 山本眞史 2007年春季第54回応用物理学関係連合講演会講演予稿集 (1) 513 2007年03月27日 [査読無し][通常論文]
  • 植村哲也, 丸亀孝生, 松田健一, 山本眞史 2007年春季第54回応用物理学関係連合講演会講演予稿集 (1) 530 2007年03月27日 [査読無し][通常論文]
  • 丸亀孝生, 石川貴之, 袴田真矢, 松田健一, 植村哲也, 山本眞史 2007年春季第54回応用物理学関係連合講演会講演予稿集 (1) 514 2007年03月27日 [査読無し][通常論文]
  • Magnetic and transport properties of Nb/Pd0.85Ni0.15 bilayer structures
    H. Niwa, K. Matsuda, Y. Akimoto, T. Uemura, M. Yamamoto The 4th Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop, Collected Papers vol.4 p.50, AP-08 2007年03月 [査読無し][通常論文]
  • Epitaxial growth and characterization of Co2Cr0.6Fe0.4Al thin films on GaAs with MgO interlayer
    T. Yano, T. Uemura, K. Matsuda, M. Yamamoto The 4th Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop, Sapporo, Collected Papers vol.4 p.49, DD-07 2007年03月 [査読無し][通常論文]
  • Fabrication of magnetic tunnel junction field sensors using a Co2MnSi thin film
    S. Yasuda, M, Masuda, T. Uemura, M. Yamamoto The 4th Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop, Collected Papers vol.4 p.48 2007年03月 [査読無し][通常論文]
  • Spin-dependent tunneling in fully epitaxial Co2MnSi/MgO/Co50Fe50 magnetic tunnel junctions
    T. Ishikawa, T. Marukame, K.-i. Matsuda, T. Uemura, M. Yamamoto The 4th Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop, Collected Papers vol.4 p.46 2007年03月 [査読無し][通常論文]
  • Spin-polarized tunneling in fully epitaxial magnetic tunnel junctions with a full-Heusler alloy thin film
    M. Yamamoto, T. Uemura, K.-i. Matsuda The 4th Int’l Symposium on Ubiquitous Knowledge Network Environment, Collected Papers vol.4 pp.131-145 2007年03月 [査読無し][招待有り]
  • 松田 健一, 丹羽 浩貴, 秋元 陽介, 植村 哲也, 山本 眞史 日本物理学会講演概要集 62 (1) 773 -773 2007年02月28日
  • 丸亀 孝生, 石川 貴之, 松田 健一, 植村 哲也, 山本 眞史 電子情報通信学会技術研究報告. ED, 電子デバイス 106 (520) 51 -56 2007年01月25日 
    Co系フルホイスラー合金Co_2Cr_<0.6>Fe_<0.4>Al(CCFA)とMgOトンネルバリアを用いたエピタキシャル強磁性トンネル接合(MTJ)を製作した.保磁力差型MTJにおいて,CCFA薄膜の組成を化学量論的な値に近づけることにより,室温で90%(4.2Kで240%)に達するTMR比が得られた.さらに交換バイアス型MTJにおいて室温で109%,4.2Kで317%の高いTMR比が得られた.得られたTMR比よりB2構造を有するエピタキシャルCCFA薄膜の実効的なスピン偏極率を見積もったところ,4.2Kで0.88(室温で0.57)の高い値が得られた.これらの結果より,Co系ホイスラー合金薄膜の本質的に高いスピン偏極率を活用する上で,すべての層が単結晶エピタキシャル成長の強磁性トンネル接合の構造が有用であることが示された.
  • 植村哲也, 丸亀孝生, 松田健一, 山本眞史 電子情報通信学会技術研究報告 106 (521(SDM2006 228-244)) 57 -62 2007年01月25日 [査読無し][通常論文]
     
    Co_<50>Fe_<50>/MgO/Co_<50>Fe_<50>構造を有するエピタキシャル強磁性トンネル接合(MTJ)を作製し、室温で約145%の比較的高いトンネル磁気抵抗(TMR)比を得た。本素子において、単結晶Co_<50>Fe_<50>層の立方磁気異方性による4方向の自発磁化に対応した4値のTMR特性を実証した。4値状態に対し、隣接する抵抗値のTMR比は最小でも約20%であった。また、アステロイド曲線の解析から、Co_<50>Fe_<50>の<110>方向から22.5°の方向に磁場を印加することで、選択書き込みが可能であることを示した。さらに、この多値MTJ素子を用いた不揮発性3値連想メモリ(TCAM)を提案し、その基本動作を回路シミュレーションにより確認した。提案した回路は不揮発性を有する上に従来の回路に比べ素子数が約1/3に低減でき、低消費電力化、高集積化に有利である。
  • PUTRA Ananda, KAKUGO Akira, FURUKAWA Hidemitsu, GONG Jian Ping, OSADA Yoshihito, UEMURA Tetsuya, YAMAMOTO Masafumi 第18回高分子ゲル研究討論会講演要旨集 5 -6 2007年01月19日 [査読無し][通常論文]
  • 松田健一, 丹羽浩貴, 秋元陽介, 植村哲也, 山本眞史 第42回応用物理学会北海道支部学術講演会講演予稿集 44 2007年01月11日 [査読無し][通常論文]
  • 石川貴之, 丸亀孝生, 袴田真也, 松田健一, 植村哲也, 山本眞史 第42回応用物理学会北海道支部学術講演会講演予稿集 47 2007年01月11日 [査読無し][通常論文]
  • 矢野敏史, 植村哲也, 松田健一, 山本眞史 第42回応用物理学会北海道支部学術講演会講演予稿集 41 2007年01月11日 [査読無し][通常論文]
  • Shinya Hakamata, Takayuki Ishikawa, Takao Marukame, Ken-Ichi Matsuda, Tetsuya Uemura, Masashi Arita, Masafumi Yamamoto Journal of Applied Physics 101 (9) p.47 2007年 [査読無し][通常論文]
     
    We fabricated magnetic tunnel junctions (MTJs) with a Co-based full-Heusler alloy thin film of Co2 MnGe (CMG) and a MgO tunnel barrier. The microfabricated MTJs with a Co-rich CMG film showed relatively high tunnel magnetoresistance ratios of 83% at room temperature and 185% at 4.2 K. These values are much higher than those previously obtained for CMG/MgO MTJs with a Co-deficient CMG film. © 2007 American Institute of Physics.
  • Takao Marukame, Takayuki Ishikawa, Shinya Hakamata, Ken-Ichi Matsuda, Tetsuya Uemura, Masafumi Yamamoto Applied Physics Letters 90 (1) p.45, DD-07 2007年 [査読無し][通常論文]
     
    Fully epitaxial magnetic tunnel junctions (MTJs) with exchange biasing were fabricated with a full-Heusler alloy Co2 Cr0.6 Fe0.4 Al (CCFA) thin film and a MgO tunnel barrier, where a Co50 Fe50 upper electrode was used in a synthetic ferrimagnetic Co50 Fe50 Ru Co90 Fe10 trilayer exchange-biased with an IrMn layer through the Co90 Fe10 IrMn interface. The fabricated MTJs exhibited clear exchange-biased tunnel magnetoresistance (TMR) characteristics with high TMR ratios of 109% at room temperature and 317% at 4.2 K. A high tunneling spin polarization of 0.88 at 4.2 K was estimated for epitaxial CCFA films with the B2 structure. © 2007 American Institute of Physics.
  • 山本眞史, 丸亀孝生, 石川貴之, 松田健一, 植村哲也 第114回表面技術協会講演大会講演要旨集 332 -335 2006年09月25日 [査読無し][通常論文]
  • 丹羽浩貴, 松田健一, 秋元陽介, 植村哲也, 山本眞史 2006年秋季第67回応用物理学会学術講演会講演予稿集 (1) 245 2006年08月29日 [査読無し][通常論文]
  • 丸亀孝生, 石川貴之, 木嶋飛元, 松田健一, 植村哲也, 山本眞史 2006年秋季第67回応用物理学会学術講演会講演予稿集 (1) 430 2006年08月29日 [査読無し][通常論文]
  • 石川貴之, 丸亀孝生, 袴田真矢, 松田健一, 植村哲也, 山本眞史 2006年秋季第67回応用物理学会学術講演会講演予稿集 (1) 430 2006年08月29日 [査読無し][通常論文]
  • Design and analysis of magnetic random access memory consisting of magnetic tunnel junction and tunnel diode
    T. Uemura, M. Yamamoto 15th Int’l Workshop on Post-Binary ULSI Systems, Proceedings vol.15 pp.55-60 2006年05月 [査読無し][通常論文]
  • Fabrication of microfluidic channel integrated with MOSFET
    S. Yasuda, T. Uemura, K. -i. Matsuda, M. Yamamoto The 3rd Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop, Collected Papers vol.3 p.69 2006年02月 [査読無し][通常論文]
  • Magnetic and Structural Properties of Pd1-xNix Thin Films for Superconductor / Ferromagnet / Superconductor p-Josephson junction devices
    H. Niwa, K.-i. Matsuda, Y. Akimoto, T. Uemura, M. Yamamoto The 3rd Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop, Collected Papers vol.3 p.68 2006年02月 [査読無し][通常論文]
  • Anisotropic tunnel magneto-resistance in (Ga,Mn)As/AlAs/(Ga,Mn)As magnetic tunnel junctions
    T. Sone, T. Uemura, K. ?i. Matsuda, M. Yamamoto The 3rd Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop, Collected Papers vol.3 p.67 2006年02月 [査読無し][通常論文]
  • Epitaxial growth of Co2Cr0.6Fe0.4Al thin films on GaAs substrate by magnetron sputtering
    T. Yano, T. Uemura, K. ?i. Matsuda, M. Yamamoto The 3rd Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop, Collected Papers vol.3 p.66, DD-07 2006年02月 [査読無し][通常論文]
  • Dependence of tunnel magnetoresistance on MgO tunnel barrier thickness in epitaxial magnetic tunnel junctions using Heusler alloy thin film
    W. Sekine, T. Marukame, K. ?i. Matsuda, T. Uemura, M. Yamamoto The 3rd Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop, Collected Papers vol.3 p.55 2006年02月 [査読無し][通常論文]
  • Fabrication of fully epitaxial magnetic tunnel junctions using full-Heusler alloy Co2MnSi thin film
    H. Koyama, H. Kijima, K. ?i. Matsuda, T. Uemura, M. Yamamoto The 3rd Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop, Collected Papers vol.3 p.54 2006年02月 [査読無し][通常論文]
  • Epitaxial growth and characterization of full-Heusler alloy Co2MnGe thin films
    T. Ishikawa, T. Marukame, K. ?i. Matsuda, T. Uemura, M. Yamamoto The 3rd Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop, Collected Papers vol.3 p.52 2006年02月 [査読無し][通常論文]
  • Tunnel magnetoresistance characteristics of fully epitaxial magnetic tunnel junctions using Co2MnGe thin film
    T. Marukame, T. Ishikawa, K.-i. Matsuda, T. Uemura, M. Yamamoto The 3rd Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop, Collected Papers vol.3 p.51 2006年02月 [査読無し][通常論文]
  • Effect of ferromagnetic-layer thickness on the critical current in Nb/Pd1-xNix/Nb Josehpson p-junctions
    K. -i. Matsuda, H. Niwa, Y. Akimoto, T. Uemura, M. Yamamoto 2006 RCIQE Int. Seminar for 21st Century COE Program: “Quantum Nanoelectronics for Meme-Media-Based Information Technologies (IV)”, Collected Abstracts p.95 2006年02月 [査読無し][通常論文]
  • Characterization of anisotropic tunnel magneto-resistance in (Ga,Mn)As/AlAs/(Ga,Mn)As magnetic tunnel junctions
    T. Uemura, T. Sone, K, ?i. Matsuda, M. Yamamoto 2006 RCIQE Int. Seminar for 21st Century COE Program: “Quantum Nanoelectronics for Meme-Media-Based Information Technologies (IV)”, Collected Abstracts p.89 2006年02月 [査読無し][通常論文]
  • Epitaxially grown Co2MnGe thin films and application to fully epitaxial magnetic tunnel junctions
    T. Marukame, T. Ishikawa, K. -i. Matsuda, T. Uemura, M. Yamamoto 2006 RCIQE Int. Seminar for 21st Century COE Program: “Quantum Nanoelectronics for Meme-Media-Based Information Technologies (IV)”, Collected Abstracts p.83 2006年02月 [査読無し][通常論文]
  • H. Kijima, T. Ishikawa, T. Marukame, H. Koyama, K. Matsuda, T. Uemura, M. Yamamoto INTERMAG 2006 - IEEE International Magnetics Conference vol.3 377 2006年 [査読無し][通常論文]
  • T Marukame, T Kasahara, K Matsuda, T Uemura, M Yamamoto JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS 44 (16-19) L521 -L524 2005年 [査読無し][通常論文]
     
    Fully epitaxial magnetic tunnel junctions (MTJs) were fabricated using a Co-based full-Heusler alloy CO2Cr0.6Fe0.4Al (CCFA) thin film and a MgO tunnel barrier. The fabricated MTJs had the following layer structure: MgO buffer layer/CCFA lower electrode/MgO tunnel barrier/CoFe upper electrode, grown on a MgO single-crystal substrate. All layers were successively deposited in an ultrahigh vacuum chamber through the combined use of magnetron sputtering and electron beam evaporation. RHEED patterns observed in situ for each layer during preparation clearly indicated that all layers grew epitaxially with the (001) basal plane. The microfabricated epitaxial CCFA/MgO/CoFe MTJs demonstrated relatively high tunnel rnagneto-resistance ratios, for MTJs using a full-Heuster alloy, of 42% at room temperature and 74% at 55 K. These results confirm the promise of an epitaxial MTJ using a Co-based full-Heusler alloy as a key device structure utilizing the potentially high spin polarization of this material system.
  • Multilevel Magnetic Random Access Memory Consisting of Magnetic Tunnel Junction and Resonant Tunnel Diode
    T. Uemura, M. Yamamoto “Satellite Session on Quantum Nano Electronics for Meme-Media-Based Information Technologies”, 7th Hokkaido University-Seoul National University Joint Symposium, Collected Abstracts vol.7 pp.77-78 2004年07月 [査読無し][通常論文]
  • Epitaxial growth of Fe/MgO/Fe heterostructures by magnetron sputtering
    T. Marukame, M. Yamamoto, T. Uemura, K. Matsuda “Satellite Session on Quantum Nano Electronics for Meme-Media-Based Information Technologies”, 7th Hokkaido University-Seoul National University Joint Symposium, Collected Abstracts vol.7 pp.71-72 2004年07月 [査読無し][通常論文]
  • Epitaxial growth of Co2Cr0.6Fe0.4Al Heusler alloy films on MgO (001) substrate
    K. Matsuda, T. Kasahara, T. Marukame, T. Uemura, M. Yamamoto “Satellite Session on Quantum Nano Electronics for Meme-Media-Based Information Technologies”, 7th Hokkaido University-Seoul National University Joint Symposium, Collected Abstracts vol.7 pp.69-70 2004年07月 [査読無し][通常論文]
  • 植村 哲也, 本間 怜, 丸亀 孝生, 山本 眞史 電子情報通信学会総合大会講演論文集 2004 (2) "S -55"-"S-56" 2004年03月08日
  • Characterization of (La, Sr)MnO3-d Films Deposited by Magnetron Sputtering on Si Substrate
    T. Uemura, K. Sekine, K. Matsuda, M. Yamamoto 2004 RCIQE Int. Seminar for 21st Century COE Program: “Quantum Nanoelectronics for Meme-Media-Based Information Technologies (II)”, Collected Abstracts p.151 2004年02月 [査読無し][通常論文]
  • Demonstration of Functional Magnetic Tunnel Junction with Negative Differential Resistance
    T. Uemura, S. Honma, T. Marukame, M. Yamamoto 2004 RCIQE Int. Seminar for 21st Century COE Program: “Quantum Nanoelectronics for Meme-Media-Based Information Technologies (II)”, Collected Abstracts p.150 2004年02月 [査読無し][通常論文]
  • Preparation and characterization of Co2Cr0.6Fe0.4Al Heusler alloy thin films grown on MgO substrate by magnetron sputtering
    T. Kasahara, K. Matsuda, T. Marukame, T. Uemura, M. Yamamoto 2004 RCIQE Int. Seminar for 21st Century COE Program: “Quantum Nanoelectronics for Meme-Media-Based Information Technologies (II)”, Collected Abstracts p.144 2004年02月 [査読無し][通常論文]
  • 植村 哲也, 本間 怜, 丸亀 孝生, 山本 眞史 電子情報通信学会技術研究報告. SDM, シリコン材料・デバイス 103 (631) 41 -46 2004年01月23日 
    強磁性トンネル接合(MTJ)と負性抵抗(NDR)素子を並列および直列に接続した二種類の新規MRAMセルを提案し,その基本動作をシミュレーションならびに実験により実証した.NDR素子により,MTJ素子の平行時と反平行時の磁気抵抗(MR)比を増大させることができる.MTJ素子としてCoFe/AlOxからなる二重トンネル接合素子を,NDR素子としてGaAsバンド間トンネルダイオードを用いた上記提案のMRAMセルを試作し,そのMR比を評価した.その結果/実効的なMR比がMTJ素子単独の場合の15%から最大890%にまで飛躍的に増大できることを確認した.さらに,単体としてのTMR比が30%以上のMTJを用いることにより十分な動作マージンが確保できることを示した.
  • Analysis of a Triple Barrier Structure Consisting of Ferromagnetic and Non-magnetic Quantum Wells
    T. Marukame, T. Uemura, M. Yamamoto 2003 RCIQE Int. Seminar on “Quantum Nanoelectronics for Meme-Media-Based Information Technologies”, Collected Abstracts p.128 2003年02月 [査読無し][通常論文]
  • UEMURA Tetsuya, BABA Toshio IEICE transactions on electronics 85 (7) 1486 -1490 2002年07月01日 
    A novel multiple-valued transfer gate (T-gate) consisting of multiple-junction surface tunnel transistors (MJSTTs) and hetero-junction FETs (HJFETs) was developed and its operation was confirmed by both simulation and experiment. The number of the devices required to form the T-gate can be drastically reduced because of the high functionality of the MJSTT; namely only three MJSTTs and three HJFETs are required to fabricate the three-valued T-gate. This number of transistors is less than half that of a conventional circuit. The fabricated circuit exhibited abasic T-gate operation with various logic functions. Furthermore, only one T-gate is needed to form a multiple-valued D-flip-flop (D-FF) circuit.
  • 植村 哲也, 馬場 寿夫 電子情報通信学会総合大会講演論文集 2001 (2) 82 -82 2001年03月07日
  • 全 容震, 植村 哲也, 馬場 寿夫 電子情報通信学会技術研究報告. ED, 電子デバイス 100 (642) 21 -26 2001年02月22日 
    表面トンネルトランジスタ(STT)の高速動作を目指して、電子ビーム露光と再成長を用いてセルフアライン構造を有する微細STT素子の作製を行なった。ゲート領域での再成長層の形状は、ゲート長と再成長層の膜厚により大きく変化することが分かった。再成長中、ゲート領域のエッジでは(111)ファセットが、中央部では(100)面がそれぞれ形成されるが、ゲート長が150nm以下になると成長速度の遅い(111)ファセットだけが残り最終的な再成長層の形状は三角形になる。再成長層形状制御により良好なトンネル接合を有するゲート長80nmのSTTが実現でき、またその特性評価からゲート変調された明瞭な負性抵抗特性を観測し、正常なトランジスタ動作していることを確認したので報告する。
  • 植村 哲也, 馬場 寿夫 電子情報通信学会ソサイエティ大会講演論文集 2000 (2) 167 -168 2000年09月07日
  • 植村 哲也, 馬場 寿夫 電子情報通信学会技術研究報告. ED, 電子デバイス 100 (147) 67 -72 2000年06月21日 
    多値論理回路において最も基本的かつ重要なロジックユニットの一つである多値Tゲート回路を多重接合型表面トンネルトランジスタ(MJSTT)とFETで構成する新たな回路を提案するとともに、その基本動作を確認した。MJSTTの機能性により、3値Tゲートおよび3値エッジトリガー型Dフリップフロップ回路が従来のFETのみの回路に比べ、半数以下の素子数(6個)で形成でき、本方式は素子数・配線数の低減に有効であることを示した。
  • 植村 哲也, 馬場 寿夫 電子情報通信学会総合大会講演論文集 2000 (2) 59 -59 2000年03月07日
  • 馬場 寿夫, 植村 哲也 電子情報通信学会ソサイエティ大会講演論文集 1997 (2) 175 -176 1997年08月13日 
    我々は、微細化に適する新しい量子効果素子として半導体中のバンド間トンネル電流を直接ゲート電極により制御する表面トンネル卜ランジスタ(STT, Surface Tunnel Transistor)を提案している。これまでにGaAs系素子試作によりその動作を確認しているが、実用的な観点から高速動作や機能性の向上が求められている。本報告では最近の成果であるInGaAs系材料による動作電流密度の向上、多重接合STTの提案とその動作実証、および多値メモリー動作の確認を中心に、研究の現状と展望について述べる。
  • BABA Toshio, UEMURA Tetsuya IEICE transactions on electronics 80 (7) 875 -880 1997年07月25日 
    New functional surface tunnel transistors (STTs) with multiple interband-tunnel-junctions in a symmetric source-to-drain structure are proposed to reduce the number of fabrication steps and to increase functionality. These devices have p^+/n^+ interband tunnel junctions in series between a p^+ source and a p^+ drain through n^+ channels. We successfully fabricated GaAs-based multiple-junction STTs (MJ-STTs) using molecular-beam epitaxy regrowth. This fabrication method eliminates the need for two of the photo-masks in the conventional process for asymmetric planar STTs. In the preliminary experiments using multiple-junction p^+/n^+ diodes, we found that the peak-voltage increment in negative-differential-resistance (NDR) characteristics due to the reverse-biased tunnel junction is negligible, while the first-peak voltage is roughly proportional to the number of forward-biased tunnel junctions. Moreover, the number of NDR characteristics are completely determined by the number of tunnel junctions. The fabricated STTs with multiple junctions, up to eight junctions, exhibited clear transistor operation with multiple NDR characteristics, which were symmetric with the drain bias. These results indicate that any number of gate-controlled NDR characteristics can be realized in MJ-STTs by using an appropriate number of tunnel junctions in series. In addition, as an example of a functional circuit using MJ-STTs, we implemented a tri-stable circuit with a four-junction STT and a load resistor connected in series. The tri-stable operation was confirmed by applying a combination of a reset pulse and a set pulse for each stable point.
  • 植村 哲也, 馬場 寿夫 電子情報通信学会技術研究報告. ED, 電子デバイス 94 (22) 47 -53 1994年04月22日 
    表面トンネルトランジスタ(STT)の高性能化を目的に、チャネルに直接ドーピングを行い、チャネルの縮退度を高めた構造を作製した。その結果、従来構造に比べ、3桁以上の動作電流密度の増加とバンド間のトンネリングに基づく明瞭な負性抵抗(NDR)特性を室温において得た。さらに、STTの機能デバイスとしての応用を示すために、一つのSTT素子と一つの負荷抵抗からなる双安定回路を構築し、その動作を確認した。また、NDR特性を劣化させるバレイ電流の原因を明かにするため、STTと同様の再成長界面を有するp^+-n^+トンネルダイオード構造を作製し、NDR特性の温度依存性とpn再成長界面の不純物濃度を評価した。その結果、バレイ電流は主にpn再成長界面における残留酸素により形成されるトラップ準位を介したトンネル電流であることが示唆された。

書籍等出版物

  • Heusler Alloys
    M. Yamamoto, T. Uemura (担当:共著範囲:第１８章)
    Springer International Publishing Switzerland 2016年01月 486 413-444

講演・口頭発表等

  • Coherent manipulation of nuclear spins in GaAs using electrical spin injection  [招待講演]
    T. Uemura
    International Workshop on NanoScience and NanoOptics 2017 2017年11月 口頭発表（招待・特別）
  • Coherent Control of Nuclear Spins in Semiconductor using Electrical Spin Injection  [招待講演]
    植村 哲也
    2016 RCIQE International Seminar 2016年03月 口頭発表（招待・特別）
  • Half-metallic Heusler alloys for the spin sources of spintronic devices  [招待講演]
    Masafumi Yamamoto, Tetsuya Uemura
    13th RIEC International Workshop on Spintronics 2015年11月 口頭発表（招待・特別）
  • Manupulation of nuclear spins in GaAs using a half-metallic spin source of Co2MnSi  [招待講演]
    T. Uemura, M. Yamamoto
    IEEE Int’l Magnetics Conf. 2015 2015年05月 口頭発表（招待・特別）
  • Co2MnSi/MgO/Co2MnSi強磁性体トンネル接合におけるスピン依存トンネル抵抗の温度依存性  [通常講演]
    本田佑輔, 劉宏喜, 植村哲也, 山本眞史
    第49回応用物理学会北海道支部学術講演会 2013年12月 口頭発表（一般） 北海道大学, 札幌市
  • Co2MnSi/CoFe/n-GaAs接合における高いスピン注入効率の実証  [通常講演]
    蝦名優也, 秋保貴史, 劉宏喜, 山本眞史, 植村哲也
    第49回応用物理学会北海道支部学術講演会 2013年12月 口頭発表（一般） 北海道大学, 札幌市
  • Spin lifetime in strained InGaAs channels investigated through all electrical spin injection and detection  [通常講演]
    T. Akiho, M. Yamamoto, T. Uemura
    第18回半導体スピン工学の基礎と応用(PASPS18) 2013年12月 口頭発表（一般） 大阪大学，豊中市
  • Effect of CoFe insertion on spin injection properties of Co2MnSi/CoFe/n-GaAs junctions  [通常講演]
    Y. Ebina, T. Akiho, H. Liu, M. Yamamoto, T. Uemura
    58th Annual Conference on Magnetism and Magnetic Materials 2013年11月 Denver, Colorado, USA
  • Giant tunnel magnetoresistance in fully epitaxial Co2(Mn,Fe)Si/MgO/Co2(Mn,Fe)Si magnetic tunnel junctions  [通常講演]
    T. Kawami, H. Liu, Y. Honda, K. M. Ayele, T. Uemura, F. Shi, P. M. Voyles, M. Yamamoto
    58th Annual Conference on Magnetism and Magnetic Materials 2013年11月 Denver, Colorado, USA
  • Spin and symmetry properties of the buried Co2MnSi/MgO interface.  [通常講演]
    R. Fetzer, Y. Ohdaira, H. Naganuma, M. Oogane, Y. Ando, T. Taira, T. Uemura, M. Yamamoto, M. Aeschlimann, M. Cinchetti
    58th Annual Conference on Magnetism and Magnetic Materials 2013年11月 Denver, Colorado, USA
  • Spin-dependent transport properties of strained InGaAs channel investigated through all electrical spin injection and detection  [通常講演]
    T. Akiho, M. Yamamoto, T. Uemura
    58th Annual Conference on Magnetism and Magnetic Materials 2013年11月 Denver, Colorado, USA
  • Co2MnSi/CoFe/n-GaAs 接合における動的核スピン偏極  [通常講演]
    秋保貴史, 劉宏喜, 山本眞史, 植村哲也
    第37回日本磁気学会学術講演会 2013年09月 口頭発表（一般） 北海道大学, 札幌市
  • Co2MnSi/CoFe/n-GaAs 接合におけるスピン注入特性に及ぼす CoFe 挿入層の効果  [通常講演]
    蝦名優也, 秋保貴史, 劉宏喜, 山本眞史, 植村哲也
    第37回日本磁気学会学術講演会 2013年09月 口頭発表（一般） 北海道大学, 札幌市
  • Co2(Mn, Fe)Si/MgO/ Co2(Mn, Fe)Si エピタキシャル MTJ の巨大トンネル磁気抵抗  [通常講演]
    川見豪, 劉宏喜, 本田佑輔, 植村哲也, F.-y. Shi, P. M. Voyles, 山本眞史
    第37回日本磁気学会学術講演会 2013年09月 口頭発表（一般） 北海道大学, 札幌市
  • Co2MnSi 薄膜の飽和磁化およびトンネルスピン偏極率に対する非化学量論的組成の影響  [通常講演]
    本田佑輔, 李桂芳, 劉宏喜, 有田正志, 松田健一, 植村哲也, 山本眞史, 齊藤敏明, 三浦良雄, 白井正文
    第37回日本磁気学会学術講演会 2013年09月 口頭発表（一般） 北海道大学, 札幌市
  • Highly-efficient dynamic nuclear polarization in GaAs using a Heusler-alloy spin source  [通常講演]
    T. Akiho, H.-x. Liu, K.-i. Matsuda, M. Yamamoto, T. Uemura
    2013年（平成25年）第74回応用物理学会秋季学術講演会 2013年09月 口頭発表（一般） 同志社大学，京田辺市
  • Giant tunneling magnetoresistance in fully epitaxial Co2(Mn, Fe)Si/MgO/ Co2(Mn, Fe)Si magnetic tunnel junctions  [通常講演]
    T. Kawami, H.-x. Liu, Y. Honda, T. Uemura, F.-y. Shi, P. M. Voyles, M. Yamamoto
    2013年（平成25年）第74回応用物理学会秋季学術講演会 2013年09月 口頭発表（一般） 同志社大学，京田辺市
  • スピントロニクス材料としてのハーフメタルホイスラー合金  [招待講演]
    山本眞史, 植村哲也
    2013年（平成25年）第74回応用物理学会秋季学術講演会 2013年09月 口頭発表（基調） 同志社大学，京田辺市
  • Annealing temperature dependence of spin signals observed inCo2MnSi/CoFe/n-GaAs through four-terminal non-local geometry  [通常講演]
    T. Akiho, J. Shan, K.-i. Matsuda, M. Yamamoto, T. Uemura
    第60回応用物理学会春季学術講演会 2013年03月 口頭発表（一般） 神奈川工科大学，厚木市
  • Influence of interfacetermination layeron temperature dependenceof tunneling magnetoresistance of Co2MnSi/MgO-based magnetic tunnel junctions  [通常講演]
    H.-x. Liu, Y. Honda, K.-i. Matsuda, T. Uemura, M. Yamamoto, F.-y. Shi, P. Voyles
    第60回応用物理学会春季学術講演会 2013年03月 口頭発表（一般） 神奈川工科大学，厚木市
  • Co2MnSi/CoFe/MgO/SiにおけるHanle信号のMgO膜厚依存性  [通常講演]
    藤澤潤, 松田健一, 山本眞史, 植村哲也
    2013年 (平成25年) 第48回応用物理学会北海道支部学術講演会 2013年01月 口頭発表（一般） 釧路市生涯学習センター「まなぼっと幣舞」，釧路市
  • Nb/ Cu50Ni50二層薄膜の電気伝導特性と超電導近接効果  [通常講演]
    蝦名優也, 松田健一, 植村哲也, 山本眞史
    2013年 (平成25年) 第48回応用物理学会北海道支部学術講演会 2013年01月 口頭発表（一般） 釧路市生涯学習センター「まなぼっと幣舞」，釧路市
  • GaAsショットキートンネル障壁を介した強磁性体からInGaAsチャネルへのスピン注入  [通常講演]
    鳥野剛史, 松田健一, 山本眞史, 植村哲也
    2013年 (平成25年) 第48回応用物理学会北海道支部学術講演会 2013年01月 口頭発表（一般） 釧路市生涯学習センター「まなぼっと幣舞」，釧路市
  • Influence of interfacial structural properties on tunnel magnetoresistance in epitaxial magnetic tunnel junctions with Co2MnSi electrode and MgO barrier  [通常講演]
    H.-x. Liu, Y. Honda, K.-i. Matsuda, M. Arita, T. Uemura, M. Yamamoto
    12th Joint MMM/Intermag Conf. 2013年01月 Chicago, Illinois, USA
  • Transient effects on oblique Hanle signals observed in ferromagnet/semiconductor heterojunctions with non-local four-terminal configuration  [通常講演]
    T. Akiho, J.-h. Shan, K.-i. Matsuda, M. Yamamoto, T. Uemura
    12th Joint MMM/Intermag Conf. 2013年01月 Chicago, Illinois, USA
  • CoFe/MgO/SC(SC = Si or Ge)におけるHanle信号の半導体種依存性  [通常講演]
    植村哲也, 李桂芳, 藤澤潤, 松田健一, 山本眞史
    第17回半導体スピン工学の基礎と応用(PASPS17) 2012年12月 口頭発表（一般） 九州大学伊都キャンパス，稲森フロンティア研究センター，福岡市
  • 高スピン偏極材料を用いたGaAsへのスピン注入  [招待講演]
    植村哲也, 秋保貴史, 松田健一, 山本眞史
    第17回半導体スピン工学の基礎と応用(PASPS17) 2012年12月 口頭発表（招待・特別） 九州大学伊都キャンパス，稲森フロンティア研究センター，福岡市
  • Electrical spin injection and electrical detection of dynamic nuclear polarization in ferromagnet/semiconductor heterojunctions  [招待講演]
    T. Akiho, J.-h. Shan, K.-i. Matsuda, M. Yamamoto, T. Uemura
    International Workshop on Spintronic Nano Materials 2012 2012年11月 口頭発表（招待・特別） Hokkaido Univ., Sapporo, Japan
  • Enhanced coherent tunneling contribution in epitaxial magnetic tunnel junctions with a Co2MnSi electrode and a MgO barrier due to improved interfacial structural properties  [通常講演]
    H.-x. Liu, Y. Honda, K.-i. Matsuda, T. Uemura, M. Yamamoto
    The 2nd Int’l Conf. of Asia Union of Magnetics Societies (ICAUMS 2012), The 36th Annual Conf. on Magnetics in Japan 2012年10月 Nara Prefectural New Public Hall, Nara, Japan
  • Co50Fe50電極からGaAs へのスピン注入の電気的検出  [通常講演]
    植村哲也, 秋保貴史, 原田雅亘, 松田健一, 山本眞史
    第35回日本磁気学会学術講演会 2012年09月 口頭発表（一般） 朱鷺メッセ国際会議場，新潟市
  • 非局所四端子配置を用いたCo2MnSi/CoFe/n-GaAs ショットキートンネル接合におけるoblique Hanle 信号の過渡特性  [通常講演]
    単津海, 秋保貴史, 松田健一, 山本眞史, 植村哲也
    2012年 (平成24年) 秋季第73回応用物理学会学術講演会 2012年09月 口頭発表（一般） 愛媛大学＆松山大学，松山市
  • MgO tunnel barrier thickness dependence of three-terminal Hanle-type signals in CoFe/MgO/n-Ge tunnel junctions  [通常講演]
    G.-f. Li, M. Miki, K.-i. Matsuda, T. Uemura, M. Yamamoto
    2012年 (平成24年) 秋季第73回応用物理学会学術講演会 2012年09月 口頭発表（一般） 愛媛大学＆松山大学，松山市
  • Co2MnSi/MgO/NbN接合を用いたホイスラー合金Co2MnSiのスピン偏極率評価  [通常講演]
    松田健一, 篠木崇帆, 植村哲也, 山本眞史
    2012年 (平成24年) 秋季第73回応用物理学会学術講演会 2012年09月 口頭発表（一般） 愛媛大学＆松山大学，松山市
  • Temperature dependence of spin-dependent tunneling resistances of fully epitaxial Co2MnSi-based magnetic tunnel junctions  [通常講演]
    H.-x. Liu, Y. Honda, K.-i. Matsuda, T. Uemura, M. Yamamoto
    2012年 (平成24年) 秋季第73回応用物理学会学術講演会 2012年09月 口頭発表（一般） 愛媛大学＆松山大学，松山市
  • Tunnel barrier thickness dependence of Hanle-type signals in CoFe/MgO/n-Ge tunnel junctions investigated through three-terminal configuration  [通常講演]
    G.-f. Li, M. Miki, K.-i. Matsuda, T. Uemura, M. Yamamoto
    The 17th Int’l Conf. on Molecular Beam Epitaxy (MBE 2012) 2012年09月 Nara Prefectural New Public Hall, Nara, Japan
  • Tunnel barrier thickness dependence of Hanle-type signals in CoFe/MgO/n-Si and CoFe/MgO/n-Ge junctions investigated through three-terminal configuration  [通常講演]
    T. Uemura, G.-f. Li, J. Fujisawa, K. Kondo, K.-i. Matsuda, M. Yamamoto
    2012 Int’l Conf. on Solid State Devices and Materials (SSDM 2012) 2012年09月 Kyoto International Conference Center, Kyoto, Japan
  • Transient oblique Hanle signals observed in Co2MnSi/CoFe/n-GaAs with non-local four-terminal configuration  [通常講演]
    J.-h. Shan, T. Akiho, K.-i. Matsuda, M. Yamamoto, T. Uemura
    2012 Int’l Conf. on Solid State Devices and Materials (SSDM 2012) 2012年09月 Kyoto International Conference Center, Kyoto, Japan
  • Temperature dependence of spin-dependent tunneling resistances of MgO-buffered Co2MnSi/MgO/Co2MnSi magnetic tunnel junctions  [通常講演]
    Y. Honda, H.-x. Liu, K.-i. Matsuda, T. Uemura, M. Yamamoto
    2012 Int’l Conf. on Solid State Devices and Materials (SSDM 2012) 2012年09月 Kyoto International Conference Center, Kyoto, Japan
  • Spin-polarization measurements for Co?2MnSi using Co2MnSi/MgO/NbN epitaxial tunnel junctions  [通常講演]
    Ken-ichi Matsuda, Takaho Shinoki, Tomoyuki Taira, Tetsuya Uemura, Masafumi Yamamoto
    The 19th Int’l Conf. on Magnetism (ICM2012) 2012年07月 BEXCO, Busan, Korea
  • MgO thickness dependence of spin accumulation signal in Co50Fe50/MgO/Si  [通常講演]
    T. Uemura, J. Fujisawa, K.-i. Matsuda, M. Yamamoto
    Int’l Magnetics Conf. 2012 (INTERMAG 2012) 2012年05月 Vancouver Convention Center, Vancouver, Canada
  • Electrical spin injection from Co2MnSi Heusler alloy into GaAs and electrical detection of dynamic nuclear polarization  [通常講演]
    T. Akiho, T. Uemura, K.-i. Matsuda, M. Yamamoto
    Int’l Magnetics Conf. 2012 (INTERMAG 2012) 2012年05月 Vancouver Convention Center, Vancouver, Canada
  • Temperature dependence of spin-dependent tunneling conductances of fully epitaxial Co2MnSi-based magnetic tunnel junctions  [通常講演]
    H.-x. Liu, Y. Honda, K.-i. Matsuda, T. Uemura, M. Yamamoto
    Int’l Magnetics Conf. 2012 (INTERMAG 2012) 2012年05月 Vancouver Convention Center, Vancouver, Canada
  • Possibility of Superconducting Proximity Effect of Equal-spin Triplet Components in NbN/Co2Cr0.6Fe0.4Al/NbN Junctions  [通常講演]
    Ken-ichi Matsuda, Tetsuya Uemura, Masafumi Yamamoto
    Int’l Conf. on Topological Quantum Phenomena (TQP2012) 2012年05月 Nagoya University, Nagoya, Japan
  • CoFe/MgO/Siにおけるスピン蓄積信号のMgO膜厚依存性  [通常講演]
    植村哲也, 藤澤 潤, 松田健一, 山本眞史
    2012年 (平成24年) 春季第59回応用物理学関係連合講演会 2012年03月 口頭発表（一般） 早稲田大学，東京都新宿区
  • Co2MnSiホイスラー合金を用いたGaAsへの電気的スピン注入および動的核スピン偏極の電気的検出  [通常講演]
    秋保貴史, 植村哲也, 松田健一, 山本眞史
    2012年 (平成24年) 春季第59回応用物理学関係連合講演会 2012年03月 口頭発表（一般） 早稲田大学，東京都新宿区
  • Fabrication of fully epitaxial magnetic tunnel junctions with a Heusler alloy Co2MnSi thin film and a MgO barrier on Ge(001) substrates  [通常講演]
    G.-f. Li, T. Taira, H.-x. Liu, K.-i. Matsuda, T. Uemura, M. Yamamoto
    2012年 (平成24年) 春季第59回応用物理学関係連合講演会 2012年03月 口頭発表（一般） 早稲田大学，東京都新宿区
  • Spin-dependent transport characteristics of epitaxial magnetic tunnel junctions of CoFe/MgO/CoFe ultrathin layer/Co2MnSi  [通常講演]
    H.-x. Liu, Y. Honda, T. Taira, K.-i. Matsuda, T. Uemura, Y. Miura, M. Shirai, M. Yamamoto
    2012年 (平成24年) 春季第59回応用物理学関係連合講演会 2012年03月 口頭発表（一般） 早稲田大学，東京都新宿区
  • Co2MnSi/CoFe/n-GaAsにおけるスピン輸送と核磁場の検出  [通常講演]
    秋保貴史, 原田雅亘, 植村哲也, 松田健一, 山本眞史
    2012年 (平成24年) 第47回応用物理学会北海道支部学術講演会 2012年01月 口頭発表（一般） 北海道大学，札幌市
  • Tunnel magnetoresistance in fully epitaxial CoFe/MgO/CoFe magnetic tunnel junctions on Ge(001) substrates via a MgO interlayer  [通常講演]
    G.-f. Li, T. Taira, H.-x. Liu, K.-i. Matsuda, T. Uemura, M. Yamamoto
    2012年 (平成24年) 第47回応用物理学会北海道支部学術講演会 2012年01月 口頭発表（一般） 北海道大学，札幌市
  • Co2MnSi/MgO/NbNヘテロ構造を用いたホイスラー合金Co2MnSiのスピン偏極率評価  [通常講演]
    篠木崇帆, 松田健一, 平智幸, 植村哲也, 山本眞史
    2012年 (平成24年) 第47回応用物理学会北海道支部学術講演会 2012年01月 口頭発表（一般） 北海道大学，札幌市
  • Spin-polarized transport in fully epitaxial CoFe/MgO/CoFe ultrathin layer/Co2MnSi magnetic tunnel junction  [通常講演]
    H.-x. Liu, Y. Honda, T. Taira, K.-i. Matsuda, T. Uemura, Y. Miura, M. Shirai, M.Yamamoto
    2012年 (平成24年) 第47回応用物理学会北海道支部学術講演会 2012年01月 口頭発表（一般） 北海道大学，札幌市
  • Spin transport properties of fully epitaxial magnetic tunnel junctions of CoFe/MgO/CoFe ultrathin layer/Co2MnSi  [通常講演]
    H.-x. Liu, T. Taira, Y. Honda, K. -i. Matsuda, T. Uemura, M. Yamamoto, Y. Miura, M. Shirai
    5th Int’l Symposium on Global COE Program of Center for Next-Generation Information Technology Based on Knowledge Discovery and Knowledge Federation 2012年01月 Hokkaido University, Sapporo, Japan
  • Tunnel magnetoresistance in fully epitaxial CoFe/MgO/CoFe magnetic tunnel junctions on Ge(001) substrates via a MgO interlayer  [通常講演]
    G.-f. Li, T. Taira, H.-x. Liu, K. ?i. Matsuda, T. Uemura, M. Yamamoto
    5th Int’l Symposium on Global COE Program of Center for Next-Generation Information Technology Based on Knowledge Discovery and Knowledge Federation 2012年01月 Hokkaido University, Sapporo, Japan
  • Co2MnSiを用いたGaAsへのスピン注入および動的核スピンの検出  [通常講演]
    秋保貴史, 原田雅亘, 植村哲也, 松田健一, 山本眞史
    第16回半導体スピン工学の基礎と応用(PASPS16) 2011年11月 口頭発表（一般） 東京工業大学，東京都目黒区
  • Non-local electrical detection of Hanle signals in Co2MnSi/Co50Fe50/n-GaAs Schottky tunnel junctions  [通常講演]
    T. Akiho, T. Uemura, H. Harada, K.-i., Matsuda, M. Yamamoto
    56th Annual Conf. on Magnetism & Magnetic Materials 2011年11月 Scottsdale, Arizona, USA
  • Almost identical oscillations in tunneling resistances as a function of barrier thickness for parallel and antiparallel configurations for fully epitaxial magnetic tunnel junctions with a MgO barrier  [通常講演]
    Y. Honda, S. Hirata, H.-x. Liu, K.-i. Matsuda, T. Uemura, M. Yamamoto
    56th Annual Conf. on Magnetism & Magnetic Materials 2011年11月 Scottsdale, Arizona, USA
  • Fabrication of epitaxial magnetic tunnel junctions with a Co2MnSi thin film and a MgO barrier on Ge(001) substrates via a MgO interlayer  [通常講演]
    G.-f. Li, T.Taira, H.-x. Liu, K. -i. Matsuda, T. Uemura, M. Yamamoto
    56th Annual Conf. on Magnetism & Magnetic Materials 2011年11月 Scottsdale, Arizona, USA
  • Spin-dependent transport properties of fully epitaxial magnetic tunnel junctions of CoFe/MgO/CoFe ultrathin layer/Co2MnSi  [通常講演]
    H.-x. Liu, T. Taira, Y. Honda, K. -i. Matsuda, T. Uemura, M. Yamamoto, Y. Miura, M. Shirai
    56th Annual Conf. on Magnetism & Magnetic Materials 2011年11月 Scottsdale, Arizona, USA
  • Epitaxial growth of Heusler alloy Co2MnSi thin films on Ge(001) substrates via a MgO interlayer  [通常講演]
    G.-f. Li, T. Taira, K.-i. Matsuda, M. Arita, T. Uemura, M. Yamamoto
    第35回日本磁気学会学術講演会 2011年09月 口頭発表（一般） 朱鷺メッセ国際会議場，新潟市
  • Effect of MgO Barrier Insertion on Spin-dependent Transport Properties of CoFe/n-GaAs  [通常講演]
    T. Akiho, M. Harada, T. Uemura, K.-i. Matsuda, M. Yamamoto
    2011 Int’l Conf. on Solid State Devices and Materials 2011年09月 Nagoya, Japan
  • Fabrication of fully epitaxial magnetic tunnel junctions with CoFe electrodes and a MgO barrier on Ge(001) substrates via a MgO interlayer  [通常講演]
    G.-f. Li, T. Taira, H.-x. Liu, K.-i. Matsuda, T. Uemura, M. Yamamoto
    2011 Int’l Conf. on Solid State Devices and Materials 2011年09月 Nagoya, Japan
  • Effect of GaAs Surface Structure on Tunneling Anisotropic Magnetoresistance in Epitaxial Co50Fe50/n-GaAs Junctions  [通常講演]
    T. Uemura, T. Akiho, M. Harada, K.-i. Matsuda, M. Yamamoto
    2011 Int’l Conf. on Solid State Devices and Materials 2011年09月 Nagoya, Japan
  • Co2MnSi/MgO/Co2MnSi エピタキシャルMTJ におけるトンネル抵抗のバリア膜厚に対する磁化平行と反平行に共通する振動  [通常講演]
    本田佑輔, 平田進之佑, 劉宏喜, 松田健一, 植村哲也, 山本眞史
    2011年秋季第72回応用物理学会学術講演会 2011年08月 口頭発表（一般） 山形大学，山形市
  • Co50Fe50を用いたGaAs への室温におけるスピン注入  [通常講演]
    植村哲也, 秋保貴史, 原田雅亘, 松田健一, 山本眞史
    2011年秋季第72回応用物理学会学術講演会 2011年08月 口頭発表（一般） 山形大学，山形市
  • CoFe/n-GaAsヘテロ接合におけるスピン依存伝導特性のMgO層挿入効果  [通常講演]
    秋保貴史, 植村哲也, 原田雅亘, 松田健一, 山本眞史
    2011年秋季第72回応用物理学会学術講演会 2011年08月 口頭発表（一般） 山形大学，山形市
  • Structural and magnetic properties of epitaxially grown Heusler alloyCo2MnSi/MgO heterostructures on Ge(001) substrates  [通常講演]
    G.-f. Li, T. Taira, K.-i. Matsuda, M. Arita, T. Uemura, M. Yamamoto
    2011年秋季第72回応用物理学会学術講演会 2011年08月 口頭発表（一般） 山形大学，山形市
  • Electrical detection of spin injection from Co50Fe50 into GaAs at room temperature  [通常講演]
    T. Uemura, M. Harada, T. Akiho, K.-i. Matsuda, M. Yamamoto
    15th Int’l Conf. on Modulated Semiconductor Structures (MSS 15) 2011年07月 Tallahassee, FL, USA
  • Oscillations in spin-dependent tunneling resistances as a function of MgO barrier thickness in epitaxial magnetic tunnel junctions with Heusler alloy Co2MnSi electrodes  [通常講演]
    Y. Honda, S. Hirata, H.-x. Liu, K.-i. Matsuda, T. Uemura, M. Yamamoto
    5th Int’l Workshop on Spin Currents 2011年07月 Sendai, Japan
  • Spin injection from Co50Fe50 into GaAs at room temperature  [通常講演]
    T. Akiho, M. Harada, T. Uemura, K.-i. Matsuda, M. Yamamoto
    5th Int’l Workshop on Spin Currents 2011年07月 Sendai, Japan
  • Spin-dependent tunneling characteristics of Heusler alloy/MgO heterostructures  [招待講演]
    M. Yamamoto, T. Uemura, K.-i. Matsuda
    5th Int’l Workshop on Spin Currents 2011年07月 口頭発表（招待・特別） Sendai, Japan
  • Epitaxial growth of Heusler alloy Co2MnSi/MgO heterostructure on Ge(001) substrate  [通常講演]
    G.-f. Li, T. Taira, K.-i. Matsuda, T. Uemura, M. Yamamoto
    Int’l Magnetics Conf. 2011 (INTERMAG 2011) 2011年04月 Taipei, Taiwan
  • Electrical injection and detection of spin-polarized electrons in an epitaxial Co50Fe50/n-GaAs junction  [通常講演]
    T. Uemura, M. Harada, T. Akiho, K.-i. Matsuda, M. Yamamoto
    Int’l Magnetics Conf. 2011(INTERMAG 2011) 2011年04月 Taipei, Taiwan
  • Spin-dependent transport properties of Co2MnSi/MgO/n-GaAs tunnel junctions  [通常講演]
    T. Akiho, M. Harada, T. Uemura, K.-i. Matsuda, M. Yamamoto
    Int’l Magnetics Conf. 2011 (INTERMAG 2011) 2011年04月 Taipei, Taiwan
  • Co2MnSi電極とMgOバリアを用いたエピタキシャルMTJにおけるスピン依存トンネル抵抗のMgOバリア膜厚に対する顕著な振動  [通常講演]
    本田佑輔, 平田進之佑, 李桂芳, 劉宏喜, 松田健一, 植村哲也, 山本眞史
    2011年 (平成23年) 春季第58回応用物理学関係連合講演会 2011年03月 口頭発表（一般） 神奈川工科大学，厚木市
  • Epitaxial growth of Co2MnSi/MgO heterostructures on Ge(001) substrates  [通常講演]
    G.-f. Li, T. Taira, K.-i. Matsuda, T. Uemura, M. Yamamoto
    2011年 (平成23年) 春季第58回応用物理学関係連合講演会 2011年03月 口頭発表（一般） 神奈川工科大学，厚木市
  • Co50Fe50/n-GaAsにおけるスピン注入の電気的検出  [通常講演]
    植村 哲也, 原田 雅亘, 秋保 貴史, 松田 健一, 山本 眞史
    2011年 (平成23年) 春季第58回応用物理学関係連合講演会 2011年03月 口頭発表（一般） 神奈川工科大学，厚木市
  • 強磁性体/n-GaAsヘテロ接合におけるトンネル特性のMgO層挿入効果  [通常講演]
    原田雅亘, 秋保貴史, 植村哲也, 松田健一, 山本眞史
    2011年 (平成23年) 第46回応用物理学会北海道支部学術講演会 2011年01月 口頭発表（一般） 室蘭工業大学，室蘭市
  • Co2MnSi薄膜を用いた強磁性トンネル接合におけるスピン依存トンネル抵抗のMgOバリア膜厚依存性  [通常講演]
    平田進之佑, 李桂芳, 本田佑輔, 松田健一, 植村哲也, 山本眞史
    2011年 (平成23年) 第46回応用物理学会北海道支部学術講演会 2011年01月 口頭発表（一般） 室蘭工業大学，室蘭市
  • Epitaxial growth of Heusler alloy Co2MnSi thin films on MgO-buffered Ge substrate  [通常講演]
    G. -f. Li, T. Taira, K.-i. Matsuda, T. Uemura, M. Yamamoto
    4th Int’l Symposium on Global COE Program of Center for Next-Generation Information Technology Based on Knowledge Discovery and Knowledge Federation 2011年01月 Hokkaido University, Sapporo, Japan
  • High tunnel magnetoresistance in fully epitaxial CoFe-buffered Co2MnSi/MgO/Co2MnSi magnetic tunnel junctions  [通常講演]
    H.-x. Liu, T. Taira, K. -i. Matsuda, T. Uemura, M. Yamamoto
    4th Int’l Symposium on Global COE Program of Center for Next-Generation Information Technology Based on Knowledge Discovery and Knowledge Federation 2011年01月 Hokkaido University, Sapporo, Japan
  • Co2MnSi/n-GaAs接合におけるトンネル異方性磁気抵抗効果のMgO層挿入効果  [通常講演]
    秋保貴史, 原田雅亘, 植村哲也, 松田健一, 山本眞史
    第15回半導体スピン工学の基礎と応用(PASPS15) 2010年12月 口頭発表（一般） 筑波大学，つくば市
  • Highly spin-polarized tunneling characteristics at room temperature in magnetic tunnel junctions with a half-metallic Heusler-alloy spin source and a MgO barrier  [通常講演]
    H.-x. Liu, T. Taira, Y. Honda, K.-i. Matsuda, T. Uemura, M. Yamamoto
    55th Annual Conf. on Magnetism & Magnetic Materials 2010年11月 Atlanta, Georgia, USA
  • Giant oscillations of spin-dependent tunneling resistances as a function of MgO barrier thickness in fully epitaxial magnetic tunnel junctions of Co2Cr0.6Fe0.4Al/MgO/Co2Cr0.6Fe0.4Al  [通常講演]
    M. Yamamoto, T. Marukame, T. Ishikawa, T. Taira, K.-i. Matsuda, T. Uemura
    55th Annual Conf. on Magnetism & Magnetic Materials 2010年11月 Atlanta, Georgia, USA,
  • Giant tunnel magnetoresistance in half-metallic Co2MnSi-based fully epitaxial magnetic tunnel junctions  [通常講演]
    T. Taira, H.-x. Liu, S. Hirata, K.-i. Matsuda, T. Uemura, M. Yamamoto
    55th Annual Conf. on Magnetism & Magnetic Materials 2010年11月 Atlanta, Georgia, USA
  • Superconducting proximity effect of spin-triplet pairs in NbN/Co2Cr0.6Fe0.4Al/NbN junctions  [通常講演]
    K.-i. Matsuda, T. Uemura, M. Yamamoto
    55th Annual Conf. on Magnetism & Magnetic Materials 2010年11月 Atlanta, Georgia, USA
  • Co2MnSi/MgO/n-GaAs接合におけるスピン依存伝導特性  [通常講演]
    植村哲也, 原田雅亘, 秋保貴史, 松田健一, 山本眞史
    第34回日本磁気学会学術講演会 2010年09月 口頭発表（一般） つくば国際会議場，つくば市
  • High tunnel magnetoresistance in fully epitaxial Co50Fe50-buffered Co2MnSi/MgO/Co2MnSi magnetic tunnel junctions  [通常講演]
    H.?x. Liu, T. Taira, Y. Honda, K. -i. Matsuda, T. Uemura, M. Yamamoto
    第34回日本磁気学会学術講演会 2010年09月 口頭発表（一般） つくば国際会議場，つくば市
  • NbN/Co2Cr0.6Fe0.4AL/NbN接合の微分伝導度特性とその温度依存性  [通常講演]
    松田健一, 植村哲也, 山本眞史
    2010年 (平成22年) 秋季第71回応用物理学会学術講演会 2010年09月 口頭発表（一般） 長崎大学，長崎市
  • Giant oscillations in spin-dependent tunneling resistances as a function of barrier thickness in fully epitaxial magnetic tunnel junctions with a MgO barrier  [通常講演]
    山本眞史, 丸亀孝生, 石川貴之, 平智幸, 松田健一, 植村哲也
    2010年 (平成22年) 秋季第71回応用物理学会学術講演会 2010年09月 口頭発表（一般） 長崎大学，長崎市
  • Co2MnSi/MgO/n-GaAsトンネル接合におけるスピン依存伝導特性  [通常講演]
    原田雅亘, 秋保貴史, 植村哲也, 松田健一, 山本眞史
    2010年 (平成22年) 秋季第71回応用物理学会学術講演会 2010年09月 口頭発表（一般） 長崎大学，長崎市
  • High tunnel magnetoresistance of up to 450% at room temperature in epitaxial magnetic tunnel junctions with a Heusler-alloy spin source and a MgO barrier  [通常講演]
    H.-x. Liu, T. Taira, Y. Honda, K.-i. Matsuda, T. Uemura, M. Yamamoto
    2010年 (平成22年) 秋季第71回応用物理学会学術講演会 2010年09月 口頭発表（一般） 長崎大学，長崎市
  • Tunnel magnetoresistance characteristics of fully epitaxial Co2MnAl/MgO/CoFe MTJs with various Mn compositions in Co2MnAl electrodes  [通常講演]
    李桂芳, 平智幸, 平田進之佑, 松田健一, 植村哲也, 山本眞史
    日本金属学会2010年秋期(第147回)大会 2010年09月 口頭発表（一般） 北海道大学，札幌市
  • Highly spin-polarized tunneling in Heusler-alloy-based magnetic tunnel junctions with a Co2MnSi upper electrode and a MgO barrier  [通常講演]
    H.-x. Liu, T. Taira, Y. Honda, K.-i. Matsuda, T. Uemura, M. Yamamoto
    2010 Int’l Conf. on Solid State Devices and Materials 2010年09月 Tokyo, Japan
  • Electrical detection of a non-local signal in Co2MnSi/MgO/n-GaAs tunnel junctions  [通常講演]
    M. Harada, T. Uemura, T. Akiho, K.-i. Matsuda, M. Yamamoto
    6th Int’l Conf. on the Physics and Application of Spin Related Phenomena in Semiconductors (PASPS-VI) 2010年08月 Tokyo, Japan
  • Co2MnGe/MgO/Co2MnGe 強磁性トンネル接合のスピン依存コンダクタンス特性  [通常講演]
    平田進之佑, 平智幸, 石川貴之, 松田健一, 植村哲也, 山本眞史
    2010年 (平成22年) 春季第57回応用物理学関係連合講演会 2010年03月 口頭発表（一般） 東海大学，平塚市
  • Defects induced in nonstoichiometric Co2MnGe thin films investigated through saturation magnetization  [通常講演]
    G.-f. Li, T. Taira, S. Hirata, Y. Honda, K. ?i. Matsuda, T. Uemura, M. Yamamoto
    2010年 (平成22年) 春季第57回応用物理学関係連合講演会 2010年03月 口頭発表（一般） 東海大学，平塚市
  • Co2MnSi/n-GaAs接合におけるトンネル異方性磁気抵抗効果と結晶磁気異方性に対する接合界面構造依存性  [通常講演]
    原田雅亘, 秋保貴史, 植村哲也, 松田健一, 山本眞史
    2010年 (平成22年) 春季第57回応用物理学関係連合講演会 2010年03月 口頭発表（一般） 東海大学，平塚市
  • Fabrication of Heusler-alloy-based magnetic tunnel junctions having an upper Co2MnSi electrode with various Mn compositions and having a Co50Fe50 lower electrode  [通常講演]
    H.-x. Liu, T. Ishikawa, K.-i. Matsuda, T. Uemura, M. Yamamoto
    2010年 (平成22年) 春季第57回応用物理学関係連合講演会 2010年03月 口頭発表（一般） 東海大学，平塚市
  • Influence of film composition on the saturation magnetization of Co2MnGe thin films  [通常講演]
    G.-f. Li, T. Taira, S. Hirata, Y. Honda, K.?i. Matsuda, T. Uemura, M. Yamamoto
    2010年 (平成22年) 春期第146回日本金属学会講演会 2010年03月 口頭発表（一般） 筑波大学，つくば市
  • ホイスラー合金Co2MnGeを用いた強磁性トンネル接合におけるコンダクタンス特性の薄膜組成依存性  [通常講演]
    平田進之佑, 平智幸, 松田健一, 植村哲也, 山本眞史
    2010年 (平成22年) 春期第146回日本金属学会講演会 2010年03月 口頭発表（一般） 筑波大学，つくば市
  • ホイスラー合金によるスピン流の創出と制御  [招待講演]
    植村哲也, 石川貴之, 原田雅亘, 平智幸, 松田健一, 山本眞史
    2010年 (平成22年) 春期第146回日本金属学会講演会 2010年03月 口頭発表（基調） 筑波大学，つくば市
  • Effect of nonstoichiometry on saturation magnetization of Heusler alloy Co2MnGe thin films  [通常講演]
    G.-f. Li, T. Taira, S. Hirata, Y. Honda, K. ?i. Matsuda, T. Uemura, M. Yamamoto
    2010年 (平成22年) 第45回応用物理学会北海道支部学術講演会 2010年01月 口頭発表（一般） 北海道大学，札幌市
  • NbN/Co2Cr0.6Fe0.4Al/NbN 接合の作製とその電気伝導特性  [通常講演]
    今井悟嗣, 石川貴之, 松田健一, 植村哲也, 山本眞史
    2010年 (平成22年) 第45回応用物理学会北海道支部学術講演会 2010年01月 口頭発表（一般） 北海道大学，札幌市
  • Co2MnSi/n-GaAs ショットキー接合におけるトンネル異方性磁気抵抗効果  [通常講演]
    原田雅亘, 秋保貴史, 植村哲也, 松田健一, 山本眞史
    2010年 (平成22年) 第45回応用物理学会北海道支部学術講演会 2010年01月 口頭発表（一般） 北海道大学，札幌市
  • Co2MnGe/MgO/Co2MnGe 強磁性トンネル接合におけるスピン依存コンダクタンス特性の薄膜組成依存性  [通常講演]
    平田進之佑, 平智幸, 石川貴之, 松田健一, 植村哲也, 山本眞史
    2010年 (平成22年) 第45回応用物理学会北海道支部学術講演会 2010年01月 口頭発表（一般） 北海道大学，札幌市
  • NbN/MgO/Co 系ホイスラー合金エピタキシャル三層構造の作製とトンネル特性  [通常講演]
    板橋直樹, 平智幸, 松田健一, 植村哲也, 山本眞史
    2010年 (平成22年) 第45回応用物理学会北海道支部学術講演会 2010年01月 口頭発表（一般） 北海道大学，札幌市
  • Tunnel magnetoresistance characteristics of Heusler-alloy-based magnetic tunnel junctions having an upper Co2MnSi electrode with various Mn compositions and having a Co50Fe50 lower electrode  [通常講演]
    H.-x. Liu, T. Ishikawa, K. -i. Matsuda, T. Uemura, M. Yamamoto
    The 3rdInt’l Symposium on Global COE Program of Center for Next-Generation Information Technology Based on Knowledge Discovery and Knowledge Federation 2010年01月 Hokkaido University, Sapporo, Japan
  • Effect of nonstoichiometry on saturation magnetization of Heusler alloy Co2MnGe thin film  [通常講演]
    G.-f. Li, T. Taira, S. Hirata, Y. Honda, K. ?i. Matsuda, T. Uemura, M. Yamamoto
    The 3rdInt’l Symposium on Global COE Program of Center for Next-Generation Information Technology Based on Knowledge Discovery and Knowledge Federation 2010年01月 Hokkaido University, Sapporo, Japan
  • Tunneling spectroscopy of Co2MnGe/MgO/Co2MnGe magnetic tunnel junctions  [通常講演]
    T. Taira, S. Hirata, G.-f. Li, K.-i. Matsuda, T. Uemura, M. Yamamoto
    The 3rdInt’l Symposium on Global COE Program of Center for Next-Generation Information Technology Based on Knowledge Discovery and Knowledge Federation 2010年01月 Hokkaido University, Sapporo, Japan
  • Effect of the Mn composition in Co2MnSi electrodes on tunnel magnetoresistance characteristics of Co2MnSi/MgO/Co2MnSi magnetic tunnel junctions  [通常講演]
    T. Ishikawa, H.-x. Liu, T. Taira, K.-i. Matsuda, T. Uemura, M. Yamamoto
    11th Joint MMM/Intermag Conf. 2010年01月 Washington DC, USA
  • Strong bias-voltage dependence of tunneling anisotropic magneto-resistance in epitaxial ferromagnet/n-GaAs junctions  [通常講演]
    T. Uemura, M. Harada, K.-i. Matsuda, M. Yamamoto
    11th Joint MMM/Intermag Conf. 2010年01月 Washington DC, USA
  • Spin-dependent tunneling characteristics of Co2MnGe/MgO/Co2MnGe magnetic tunnel junctions  [通常講演]
    T. Taira, S. Hirata, T. Ishikawa, K.-i. Matsuda, T. Uemura, M. Yamamoto
    11th Joint MMM/Intermag Conf. 2010年01月 Washington DC, USA
  • Fabrication and Transport Properties of NbN/Co2Cr0.6Fe0.4Al/NbN Lateral Junctions  [通常講演]
    S. Imai, K.-i. Matsuda, T. Ishikawa, T. Uemura, M. Yamamoto
    9th Int’l Conf. on Materials and Mechanisms of Superconductivity (M2S-IX) 2009年09月 Shinjuku, Tokyo, Japan
  • Tunneling anisotropic magneto-resistance in an epitaxial Co2MnSi/n-GaAs junction  [通常講演]
    M. Harada, T. Uemura, Y. Imai, K.-i. Matsuda, M. Yamamoto
    The 14th Int’l Conf. on Modulated Semiconductor Structures (MSS-14) 2009年07月 Kobe, Japan
  • Spin-dependent tunneling characteristics of fully epitaxial Co2MnGe/MgO/Co2MnGe magnetic tunnel junctions  [通常講演]
    T. Taira, S. Hirata, T. Ishikawa, K.-i. Matsuda, T. Uemura, M. Yamamoto
    20th Int’l Colloquium on Magnetic Films and Surfaces (ICMFS2009) 2009年07月 Berlin, Germany
  • Tunneling spectroscopy of magnetic tunnel junctions with Heusler alloy Co2MnGe electrodes and a MgO barrier  [通常講演]
    S. Hirata, T. Taira, T. Ishikawa, K.-i. Matsuda, T. Uemura, M. Yamamoto
    Int’l Conf. on Magnetism (ICM2009) 2009年07月 Karlsruhe, Germany
  • Spin-dependent electronic structure of Heusler alloy Co2MnSi upper electrodes in magnetic tunnel junctions  [通常講演]
    T. Ishikawa, N. Itabashi, T. Taira, K.-i. Matsuda, T. Uemura, M. Yamamoto
    Int’l Conf. on Magnetism (ICM2009) 2009年07月 Karlsruhe, Germany
  • Transport properties of a junction consisting of two NbN electrodes coupled by a Co-based Heusler alloy Co2Cr0.6Fe0.4Al channel  [通常講演]
    K.-i. Matsuda, S. Imai, T. Ishikawa, T. Uemura, M. Yamamoto
    Int’l Conf. on Magnetism (ICM2009) 2009年07月 Karlsruhe, Germany
  • Spin-dependent tunneling in half-metallic Heusler alloy-based magnetic tunnel junctions with a MgO barrier  [通常講演]
    M. Yamamoto, T. Ishikawa, T. Taira, T. Marukame, K.-i. Matsuda, T. Uemura
    Int’l Conf. on Magnetism (ICM2009) 2009年07月 Karlsruhe, Germany
  • Simulation of tunneling magnetoresistance used to detect domain-wall structure and motion in a ferromagnetic wire  [通常講演]
    K. Sawada, T. Uemura, M. Masuda, K.-i. Matsuda, M. Yamamoto
    IEEE Int’l Magnetics Conf. 2009 2009年05月 Sacramento, CA, USA
  • Tunneling Anisotropic Magneto-resistance in an Epitaxial CoFe/n-GaAs Junction  [通常講演]
    T. Uemura, Y. Imai, M. Harada, K.-i. Matsuda, M. Yamamoto
    IEEE Int’l Magnetics Conf. 2009 2009年05月 Sacramento, CA, USA
  • Tunnel magnetoresistance characteristics of post-deposition-annealed Co2MnGe/MgO/CoFe tunnel junctions  [通常講演]
    T. Taira, T. Ishikawa, K.-i. Matsuda, T. Uemura, M. Yamamoto
    2008 Material Research Society (MRS) Fall Meeting 2008年12月 Boston, MA, USA
  • Spin-polarized tunneling in fully epitaxial magnetic tunnel junctions with Heusler alloy thin films and a MgO barrier  [通常講演]
    M. Yamamoto, T. Ishikawa, K.-i. Matsuda, T. Uemura
    2008 Material Research Society (MRS) Fall Meeting 2008年12月 Boston, MA, USA
  • Tunneling conductance characteristics for Co2Cr0.6Fe0.4Al/MgO/Co2Cr0.6Fe0.4Al magnetic tunnel junctions  [通常講演]
    N. Itabashi, T. Ishikawa, K. Yonemura, K.-i. Matsuda, T. Uemura, M. Yamamoto
    2008 Material Research Society (MRS) Fall Meeting 2008年12月 Boston, MA, USA
  • Tunneling spectroscopy of fully epitaxial Co2MnSi/MgO/Co2MnSi magnetic tunnel junctions  [通常講演]
    T. Ishikawa, N. Itabashi, T. Taira, K.-i. Matsuda, T. Uemura, M. Yamamoto
    2008 Material Research Society (MRS) Fall Meeting 2008年12月 Boston, MA, USA
  • Half-metallic electronic structure of Co2MnSi electrodes proved by tunneling spectroscopy  [通常講演]
    T. Ishikawa, N. Itabashi, T. Taira, K.-i. Matsuda, T. Uemura, M. Yamamoto
    53rd Magnetism and Magnetic Materials Conf. 2008年11月 Austin, TX, USA
  • Spin-dependent tunneling characteristics of Co2MnGe/MgO/CoFe tunnel junctions  [通常講演]
    T. Taira, T. Ishikawa, K.-i. Matsuda, T. Uemura, M. Yamamoto
    53rd Magnetism and Magnetic Materials Conf. 2008年11月 Austin, TX, USA
  • Tunneling spectroscopy of Co2Cr0.6Fe0.4Al/MgO/CoFe magnetic tunnel junctions  [通常講演]
    K. Yonemura, T. Ishikawa, N. Itabashi, K.-i. Matsuda, T. Uemura, M. Yamamoto
    53rd Magnetism and Magnetic Materials Conf. 2008年11月 Austin, TX, USA
  • Spin-dependent electronic structures of Co2Cr0.6Fe0.4Al electrodes investigated through tunneling spectroscopy  [通常講演]
    N. Itabashi, T. Ishikawa, K. Yonemura, K.-i. Matsuda, T. Uemura, M. Yamamoto
    53rd Magnetism and Magnetic Materials Conf. 2008年11月 Austin, TX, USA
  • Transport Properties of Nb/PdNi bilayers and Nb/PdNi/Nb Josephson junctions  [通常講演]
    K.-i. Matsuda, Y. Akimoto, T. Uemura, M. Yamamoto
    25th Int’l Conf. on Low Temp. Physics 2008年08月 Amsterdam, The Netherlands
  • Spin-dependent tunneling spectroscopy of fully epitaxial magnetic tunnel junctions with Heusler alloy Co2Cr0:6Fe0:4Al electrodes and a MgO barrier  [通常講演]
    N. Itabashi, T. Ishikawa, K.-i. Matsuda, T. Uemura, M. Yamamoto
    25th Int’l Conf. on Low Temp. Physics 2008年08月 Amsterdam, The Netherlands
  • Fabrication and characterization of magnetic tunnel junction field sensors with a Co2MnSi thin film  [通常講演]
    M. Masuda, T. Uemura, K.-i. Matsuda, M. Yamamoto
    IEEE Int'l Magnetics Conf. Europe 2008 2008年05月 Madrid, Spain
  • Spin-dependent tunneling conductance in fully epitaxial Co2MnSi/MgO/Co2MnsI tunnel junctions  [通常講演]
    T. Ishikawa, N. Itabashi, K. Matsuda, T. Uemura, M. Yamamoto
    IEEE Int'l Magnetics Conf. Europe 2008 2008年05月 Madrid, Spain
  • Heusler alloy-based fully epitaxial magnetic tunnel junctions with a MgO barrier  [招待講演]
    M. Yamamoto, T. Uemura, K.-i. Matsuda
    2008 RCIQE Int’l Seminar on “Advanced Semiconductor Materials and Devices” 2008年03月 口頭発表（基調） Sapporo, Japan
  • Magnetic and transport properties of superconductor/ferromagnet bilayer microbridges  [通常講演]
    K.-i. Matsuda, Y. Akimoto, T. Uemura, M. Yamamoto
    52nd Magnetism and Magnetic Materials Conf. 2007年11月 Tampa, Florida, USA
  • Electrical characterization of epitaxial Co2MnSi/MgO/n-GaAs tunnel junctions  [通常講演]
    S. Kawagishi, T. Uemura, Y. Imai, K.-i. Matsuda, M. Yamamoto
    52nd Magnetism and Magnetic Materials Conf. 2007年11月 Tampa, Florida, USA
  • Electronic and magnetic properties of Heusler alloy Co2MnSi epitaxial ultrathin films facing a MgO barrier investigated by X-ray magnetic circular dichroism  [通常講演]
    T. Saito, T. Katayama, A. Emura, N. Sumida, N. Matsuoka, T. Ishikawa, T. Uemura, M. Yamamoto, D. Asakura, T. Koide
    52nd Magnetism and Magnetic Materials Conf. 2007年11月 Tampa, Florida, USA
  • Spin-dependent tunneling in fully epitaxial Co2MnSi/MgO/Co2MnSi magnetic tunnel junctions  [通常講演]
    T. Ishikawa, S. Hakamata, K.-i. Matsuda, T. Uemura, M. Yamamoto
    52nd Magnetism and Magnetic Materials Conf. 2007年11月 Tampa, Florida, USA
  • Oscillations in tunneling resistance as a function of MgO barrier thickness in fully epitaxial magnetic tunnel junctions of Co2Cr0.6Fe0.4Al/MgO/Co50Fe50  [通常講演]
    M. Yamamoto, T. Marukame, T. Ishikawa, K. Matsuda, T. Uemura
    52nd Magnetism and Magnetic Materials Conf. 2007年11月 Tampa, Florida, USA
  • Highly spin-polarized tunneling in Heusler alloy-based fully epitaxial magnetic tunnel junctions with a MgO tunnel barrier  [通常講演]
    M. Yamamoto, T. Marukame, T. Ishikawa, K. Matsuda, T. Uemura
    52nd Magnetism and Magnetic Materials Conf. 2007年11月 Tampa, Florida, USA
  • Epitaxial growth and characterization of Co2MnSi thin films on GaAs with MgO interlayer  [通常講演]
    T. Uemura, T. Yano, Y. Imai, K. Matsuda, M. Yamamoto
    The 13th Int’l Conf. on Modulated Semiconductor Structures (MSS13) 2007年07月 Genova, Italy
  • Four-state Magnetic Random Access Memory and Ternary Content Addressable Memory using CoFe-based Magnetic Tunnel Junctions  [通常講演]
    T. Uemura, T. Marukame, K.-i. Matsuda, M. Yamamoto
    37th Int’l Symposium on Multiple-Valued Logic 2007年05月 Oslo, Norway
  • Magnetic and transport properties of Nb/Pd0.85Ni0.15 bilayer structures  [通常講演]
    H. Niwa, K. Matsuda, Y. Akimoto, T. Uemura, M. Yamamoto
    The 4th Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop 2007年03月 Sapporo, Japan
  • Epitaxial growth and characterization of Co2Cr0.6Fe0.4Al thin films on GaAs with MgO interlayer  [通常講演]
    T. Yano, T. Uemura, K. Matsuda, M. Yamamoto
    The 4th Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop 2007年03月 Japan
  • Fabrication of magnetic tunnel junction field sensors using a Co2MnSi thin film  [通常講演]
    S. Yasuda, M, Masuda, T. Uemura, M. Yamamoto
    The 4th Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop 2007年03月 Sapporo, Japan
  • Improved tunnel magnetoresistance characteristics of magnetic tunnel junctions with a Heusler alloy Co2MnGe thin film  [通常講演]
    S. Hakamata, T. Ishikawa, T. Marukame, K.-i. Matsuda, T. Uemura, M. Yamamoto
    The 4th Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop 2007年03月 Sapporo, Japan
  • Spin-dependent tunneling in fully epitaxial Co2MnSi/MgO/Co50Fe50 magnetic tunnel junctions  [通常講演]
    T. Ishikawa, T. Marukame, K.-i. Matsuda, T. Uemura, M. Yamamoto
    The 4th Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop 2007年03月 Sapporo, Japan
  • High tunnel magnetoresistance in fully epitaxial Co2Cr0.6Fe0.4Al/MgO/Co50Fe50 magnetic tunnel junctions with exchange biasing  [通常講演]
    T. Marukame, T. Ishikawa, S. Hakamata, K.-i. Matsuda, T. Uemura, M. Yamamoto
    The 4th Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop 2007年03月 Sapporo, Japan
  • Spin-polarized tunneling in fully epitaxial magnetic tunnel junctions with a full-Heusler alloy thin film  [招待講演]
    M. Yamamoto, T. Uemura, K.-i. Matsuda
    The 4th Int’l Symposium on Ubiquitous Knowledge Network Environment 2007年03月 口頭発表（基調） Sapporo, Japan
  • Spin-dependent tunneling in fully epitaxial magnetic tunnel junctions with a Heusler alloy thin film and a MgO barrier  [招待講演]
    M. Yamamoto, T. Uemura, K.-i. Matsuda
    The 2nd RIEC Int’l Workshop on Spintronics?MgO-based Magnetic Tunnel Junctions? 2007年02月 口頭発表（基調） Sendai, Japan
  • Dependence of magnetoresistance characteristics of magnetic tunnel junctions with a Heusler alloy thin film of either Co2MnGe or Co2MnSi on film composition  [通常講演]
    S. Hakamata, T. Ishikawa, T. Marukame, K. Matsuda, T. Uemura, M. Arita, M. Yamamoto
    10th Joint MMM/Intermag Conf. 2007年01月 Baltimore, USA
  • Fabrication of fully epitaxial Co2Cr0.6Fe0.4Al/MgO/Co2Cr0.6Fe0.4Al  [通常講演]
    T. Marukame, T. Ishikawa, S. Hakamata, K. Matsuda, T. Uemura, M. Yamamoto
    10th Joint MMM/Intermag Conf. 2007年01月 Baltimore, USA
  • Four-state magnetoresistance in epitaxial CoFe-based magnetic tunnel junction  [通常講演]
    T. Uemura, T. Marukame, K. Matsuda, M. Yamamoto
    10th Joint MMM/Intermag Conf. 2007年01月 Baltimore, USA
  • Magnetic and Transport Properties of Nb/PdNi Bilayers  [通常講演]
    K.-i. Matsuda, H. Niwa, Y. Akimoto, T. Uemura, M. Yamamoto
    IEEE Int’l Conf. on Appl. Supercond. 2006年08月 Seatle, USA
  • Fabrication of exchange-biased epitaxial magnetic tunnel junctions with a Co-based full-Heusler alloy thin film  [通常講演]
    T. Ishikawa, S. Hakamata, T. Marukame, K.-i. Matsuda, T. Uemura, M. Yamamoto
    Int’l Conf. on Magnetism (ICM2006) 2006年08月 Kyoto, Japan
  • Analysis of magnetic anisotropy for Co2Cr0.6Fe0.4Al thin films epitaxially grown on GaAs  [通常講演]
    T. Uemura, T. Yano, K.-i. Matsuda, M. Yamamoto
    Int’l Conf. on Magnetism (ICM2006) 2006年08月 Kyoto, Japan
  • Spin-dependent transport properties of fully epitaxial Co2MnSi/MgO/CoFe tunnel junctions  [通常講演]
    T. Marukame, H. Kijima, T. Ishikawa, K.-i. Matsuda, T. Uemura, M. Yamamoto
    Int’l Conf. on Magnetism (ICM2006) 2006年08月 Kyoto, Japan
  • Fabrication of fully epitaxial magnetic tunnel junctions using Co2MnSi thin film and MgO tunnel barrier  [通常講演]
    H. Kijima, T. Ishikawa, T. Marukame, K. -i. Matsuda, T. Uemura, M. Yamamoto
    Int’l Conf. on Magnetism (ICM2006) 2006年08月 Kyoto, Japan
  • Epitaxial growth of Co-based full-Heusler alloy thin films of Co2Cr0.6Fe0.4Al, Co2MnGe and Co2MnSi on MgO-buffered MgO substrate  [通常講演]
    T. Ishikawa, T. Marukame, H. Kijima, K.-i. Matsuda, T. Uemura, M. Yamamoto
    19th Int’l Colloquium on Magnetic Films and Surfaces (ICMFS 2006) 2006年08月 Sendai, Japan
  • MgO barrier thickness dependence of tunnel magnetoresistance in fully epitaxial magnetic tunnel junctions with Co2Cr0.6Fe0.4Al thin film  [通常講演]
    T. Marukame, T. Ishikawa, H. Kijima, K.?i. Matsuda, T. Uemura, M. Yamamoto
    19th Int’l Colloquium on Magnetic Films and Surfaces (ICMFS 2006) 2006年08月 Sendai, Japan
  • Spin-dependent conductance versus voltage characteristics of fully epitaxial magnetic tunnel junctions with a Co-based full-Heusler alloy thin film and a MgO barrier  [通常講演]
    M. Yamamoto, T. Marukame, K.?i. Matsuda, T. Uemura
    19th Int’l Colloquium on Magnetic Films and Surfaces (ICMFS 2006) 2006年08月 Sendai, Japan
  • Tunnel magnetoresistance in fully epitaxial Co2MnSi/MgO/Co50Fe50 magnetic tunnel junctions  [通常講演]
    H. Kijima, T. Ishikawa, T. Marukame, K.?i. Matsuda, T. Uemura, M. Yamamoto
    19th Int’l Colloquium on Magnetic Films and Surfaces (ICMFS 2006) 2006年08月 Sendai, Japan
  • Structural and magnetic properties of Co2Cr0.6Fe0.4Al thin films epitaxially grown on GaAs with and without MgO interlayer  [通常講演]
    T. Uemura, T. Yano, K.?i. Matsuda, M. Yamamoto
    19th Int’l Colloquium on Magnetic Films and Surfaces (ICMFS 2006) 2006年08月 Sendai, Japan
  • Design and analysis of magnetic random access memory consisting of magnetic tunnel junction and tunnel diode  [通常講演]
    T. Uemura, M. Yamamoto
    15th Int’l Workshop on Post-Binary ULSI Systems 2006年05月 Singapore
  • Highly spin-polarized tunneling in fully epitaxial magnetic tunnel junctions using full-Heusler alloy Co2Cr0.6Fe0.4Al thin film and MgO tunnel barrier  [通常講演]
    T. Marukame, T. Ishikawa, H. Kijima, W. Sekine, K.?i. Matsuda, T. Uemura, M. Yamamoto
    IEEE Int'l Magnetics Conf. 2006 2006年05月 San Diego, CA, USA
  • Exchange bias effect on full-Heusler alloy Co2Cr0.6Fe0.4Al epitaxial thin films  [通常講演]
    T. Ishikawa, T. Marukame, H. Niwa, K.?i. Matsuda, T. Uemura, M. Yamamoto
    IEEE Int'l Magnetics Conf. 2006 2006年05月 San Diego, CA, USA
  • Epitaxial growth of full-Heusler alloy Co2MnSi thin films on MgO-buffered MgO substrates  [通常講演]
    H. Kijima, T. Ishikawa, T. Marukame, H. Koyama, K, ?i. Matsuda, T. Uemura, M. Yamamoto
    IEEE Int'l Magnetics Conf. 2006 2006年05月 San Diego, CA, USA
  • Fabrication of microfluidic channel integrated with MOSFET  [通常講演]
    S. Yasuda, T. Uemura, K. -i. Matsuda, M. Yamamoto
    The 3rd Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop 2006年02月 Sapporo, Japan
  • Magnetic and Structural Properties of Pd1-xNix Thin Films for Superconductor / Ferromagnet / Superconductor p-Josephson junction devices  [通常講演]
    H. Niwa, K.-i. Matsuda, Y. Akimoto, T. Uemura, M. Yamamoto
    The 3rd Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop 2006年02月 Sapporo, Japan
  • Anisotropic tunnel magneto-resistance in (Ga,Mn)As/AlAs/(Ga,Mn)As magnetic tunnel junctions  [通常講演]
    T. Sone, T. Uemura, K. ?i. Matsuda, M. Yamamoto
    The 3rd Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop 2006年02月 Sapporo, Japan
  • Epitaxial growth of Co2Cr0.6Fe0.4Al thin films on GaAs substrate by magnetron sputtering  [通常講演]
    T. Yano, T. Uemura, K. ?i. Matsuda, M. Yamamoto
    The 3rd Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop 2006年02月 Sapporo, Japan
  • Dependence of tunnel magnetoresistance on MgO tunnel barrier thickness in epitaxial magnetic tunnel junctions using Heusler alloy thin film  [通常講演]
    W. Sekine, T. Marukame, K. ?i. Matsuda, T. Uemura, M. Yamamoto
    The 3rd Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop 2006年02月 Sapporo, Japan
  • Fabrication of fully epitaxial magnetic tunnel junctions using full-Heusler alloy Co2MnSi thin film  [通常講演]
    H. Koyama, H. Kijima, K. ?i. Matsuda, T. Uemura, M. Yamamoto
    The 3rd Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop 2006年02月 Sapporo, Japan
  • Epitaxial growth of full-Heusler alloy Co2MnSi thin films on MgO substrates by magnetron sputtering  [通常講演]
    H. Kijima, H. Koyama, K. ?i. Matsuda, T. Uemura, M. Yamamoto
    The 3rd Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop 2006年02月 Sapporo, Japan
  • Epitaxial growth and characterization of full-Heusler alloy Co2MnGe thin films  [通常講演]
    T. Ishikawa, T. Marukame, K. ?i. Matsuda, T. Uemura, M. Yamamoto
    The 3rd Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop 2006年02月 Sapporo, Japan
  • Tunnel magnetoresistance characteristics of fully epitaxial magnetic tunnel junctions using Co2MnGe thin film  [通常講演]
    T. Marukame, T. Ishikawa, K.-i. Matsuda, T. Uemura, M. Yamamoto
    The 3rd Int’l Symp. on Ubiquitous Knowledge Network Environment, Quantum Nanoelectronics Workshop 2006年02月 Sapporo, Japan
  • Epitaxially grown full-Heusler alloy thin films and application to magnetic tunnel junctions  [招待講演]
    M. Yamamoto, T. Uemura, K.-i. Matsuda
    The 3rd Int’l Symp. on Ubiquitous Knowledge Network Environment 2006年02月 口頭発表（基調） Sapporo, Japan
  • Effect of ferromagnetic-layer thickness on the critical current in Nb/Pd1-xNix/Nb Josehpson p-junctions  [通常講演]
    K. -i. Matsuda, H. Niwa, Y. Akimoto, T. Uemura, M. Yamamoto
    2006 RCIQE Int. Seminar for 21st Century COE Program: “Quantum Nanoelectronics for Meme-Media-Based Information Technologies (IV)” 2006年02月 Sapporo, Japan
  • Characterization of anisotropic tunnel magneto-resistance in (Ga,Mn)As/AlAs/(Ga,Mn)As magnetic tunnel junctions  [通常講演]
    T. Uemura, T. Sone, K, ?i. Matsuda, M. Yamamoto
    2006 RCIQE Int. Seminar for 21st Century COE Program: “Quantum Nanoelectronics for Meme-Media-Based Information Technologies (IV)” 2006年02月 Sapporo, Japan
  • Epitaxially grown Co2MnGe thin films and application to fully epitaxial magnetic tunnel junctions  [通常講演]
    T. Marukame, T. Ishikawa, K. -i. Matsuda, T. Uemura, M. Yamamoto
    2006 RCIQE Int. Seminar for 21st Century COE Program: “Quantum Nanoelectronics for Meme-Media-Based Information Technologies (IV)” 2006年02月 Sapporo, Japan
  • Structural and magnetic properties of epitaxially grown full-Heusler alloy Co2MnGe thin films deposited using magnetron sputtering  [通常講演]
    T. Ishikawa, T. Marukame, K. ?i. Matsuda, T. Uemura, M. Yamamoto
    50th Annual Conf. on Magnetism & Magnetic Materials 2005年10月 San Jose, CA, USA
  • Tunnel magnetoresistance in epitaxial magnetic tunnel junctions using full-Heusler alloy Co2MnGe thin film and MgO tunnel barrier  [通常講演]
    T. Marukame, T. Ishikawa, K. ?i. Matsuda, T. Uemura, M. Yamamoto
    50th Annual Conf. on Magnetism & Magnetic Materials 2005年10月 San Jose, CA, USA
  • Analysis of anisotropic tunnel magneto-resistance of GaMnAs/AlAs/GaMnAs magnetic tunnel junction  [通常講演]
    T. Uemura, R. Miura, T. Sone, K. Matsuda, M. Yamamoto
    12th Int’l Conf. on Modulated Semiconductors (MSS 12) 2005年07月 Alburquerque, New Mexico, USA
  • High Tunnel Magnetoresistance in Epitaxial Co2Cr0.6Fe0.4Al/MgO/CoFe Tunnel Junctions  [通常講演]
    T. Marukame, T. Kasahara, K. Matsuda, T. Uemura, M. Yamamoto
    IEEE Int’l Magnetics Conf. 2005年04月 Nagoya, Japan
  • Epitaxial growth and characterization of full-Huesler alloy Co2Cr0.6Fe0.4Al thin films for magnetic tunnel junctions  [通常講演]
    T. Marukame, T. kasahara, K. Matsuda, T. Uemura, M. Yamamoto
    2nd Int. Workshop on Ubiquitous Knowledge Network Environment 2005年03月 Sapporo, Japan
  • Fully epitaxial magnetic tunnel junctions using full-Heusler alloy thin film  [招待講演]
    M. Yamamoto, T. Uemura, K. Matsuda
    2nd Int. Workshop on Ubiquitous Knowledge Network Environment 2005年03月 口頭発表（基調） Sapporo, Japan
  • Fabrication of fully epitaxial magnetic tunnel junctions using full-Heusler alloy Co2Cr0.6Fe0.4Al  [通常講演]
    T. Marukame, T. Kasahara, K. Matsuda, T. Uemura, M. Yamamoto
    2005 RCIQE Int. Seminar for 21st Century COE Program: “Quantum Nanoelectronics for Meme-Media-Based Information Technologies (III)” 2005年02月 Sapporo, Japan
  • T. Uemura, K. Sekine, K. Matsuda and M. Yamamoto  [通常講演]
    T. Uemura, K. Sekine, K. Matsuda, M. Yamamoto
    49th Annual Conf. on Magnetism and Magnetic Materials 2004年11月 Jacksonville, Florida, USA
  • Epitaxial growth of Fe/MgO/Fe heterostructures on SrTiO3 substrates by magnetron sputtering  [通常講演]
    T. Marukame, K.-i. Matsuda, T. Uemura, M. Yamamoto
    49th Annual Conf. on Magnetism and Magnetic Materials 2004年11月 Jacksonville, Florida, USA
  • Magnetic and Electrical Properties of (La, Sr)MnO3 Sputtered on SrTiO3-buffered Si Substrate  [通常講演]
    T. Uemura, Y. Takagi, K. Sekine, K. Matsuda, M. Yamamoto
    2004 Int’l Conf. on Solid State Devices and Materials 2004年09月 Tokyo, Japan
  • Multilevel Magnetic Random Access Memory Consisting of Magnetic Tunnel Junction and Resonant Tunnel Diode  [通常講演]
    T. Uemura, M. Yamamoto
    “Satellite Session on Quantum Nano Electronics for Meme-Media-Based Information Technologies”, 7th Hokkaido University-Seoul National University Joint Symposium 2004年07月 Sapporo, Japan
  • Epitaxial growth of Fe/MgO/Fe heterostructures by magnetron sputtering  [通常講演]
    T. Marukame, M. Yamamoto, T. Uemura, K. Matsuda
    “Satellite Session on Quantum Nano Electronics for Meme-Media-Based Information Technologies”, 7th Hokkaido University-Seoul National University Joint Symposium 2004年07月 Sapporo, Japan
  • Epitaxial growth of Co2Cr0.6Fe0.4Al Heusler alloy films on MgO (001) substrate  [通常講演]
    K. Matsuda, T. Kasahara, T. Marukame, T. Uemura, M. Yamamoto
    “Satellite Session on Quantum Nano Electronics for Meme-Media-Based Information Technologies”, 7th Hokkaido University-Seoul National University Joint Symposium 2004年07月 Sapporo, Japan
  • Characterization of (La, Sr)MnO3-d Films Deposited by Magnetron Sputtering on Si Substrate  [通常講演]
    T. Uemura, K. Sekine, K. Matsuda, M. Yamamoto
    2004 RCIQE Int. Seminar for 21st Century COE Program: “Quantum Nanoelectronics for Meme-Media-Based Information Technologies (II)” 2004年02月 Sapporo, Japan
  • Demonstration of Functional Magnetic Tunnel Junction with Negative Differential Resistance  [通常講演]
    T. Uemura, S. Honma, T. Marukame, M. Yamamoto
    2004 RCIQE Int. Seminar for 21st Century COE Program: “Quantum Nanoelectronics for Meme-Media-Based Information Technologies (II)” 2004年02月 Sapporo, Japan
  • Preparation and characterization of Co2Cr0.6Fe0.4Al Heusler alloy thin films grown on MgO substrate by magnetron sputtering  [通常講演]
    T. Kasahara, K. Matsuda, T. Marukame, T. Uemura, M. Yamamoto
    2004 RCIQE Int. Seminar for 21st Century COE Program: “Quantum Nanoelectronics for Meme-Media-Based Information Technologies (II)” 2004年02月 Sapporo, Japan
  • Proposal and Experimental Demonstration of Novel MRAM Cell Using Magnetic Tunnel Junction in Combination with Negative Differential Resistance Device  [招待講演]
    M. Yamamoto, T. Uemura
    1st Int. Workshop on Ubiquitous Knowledge Network Environment 2003年11月 口頭発表（基調） Sapporo, Japan
  • Demonstration of Enhanced Tunneling Magneto Resistance Ratio for a Magnetic Tunnel Junction Connected in Parallel with a Tunnel Diode  [通常講演]
    T. Uemura, S. Honma, T. Marukame, M. Yamamoto
    2003 Int’l Conf. on Solid State Devices and Materials 2003年09月 Tokyo, Japan
  • Observation of Large Room-temperature Negative Differential Resistance in GaAsNSe/GaAs and GaAsNSb/GaAs Superlattices Grown on (001) GaAs  [通常講演]
    K. Uesugi, M. Kurimoto, I. Suemune, M. Yamamoto, T. Uemura, H. Machida, N. Shimoyama
    The 11th Int’l. Conf. on Modulated Semiconductor Structures (MSS11) 2003年07月 Nara, Japan
  • Proposal of Four-Valued MRAM based on MTJ/RTD Structure  [通常講演]
    T. Uemura, M. Yamamoto
    33rd Int’l Symp. on Multiple-Valued Logic 2003年05月 Tokyo, Japan
  • Proposal and Analysis of a Ferromagnetic Triple-Barrier Resonant-Tunneling Spin Filter  [通常講演]
    T. Uemura, T. Marukame, M. Yamamoto
    Int’l Magnetics Conf. (INTERMAG2003) 2003年04月 Boston, Massachusetts, U.S.A.
  • Analysis of a Triple Barrier Structure Consisting of Ferromagnetic and Non-magnetic Quantum Wells  [通常講演]
    T. Marukame, T. Uemura, M. Yamamoto
    2003 RCIQE Int. Seminar on “Quantum Nanoelectronics for Meme-Media-Based Information Technologies” 2003年02月 Sapporo, Japan

所属学協会

  • IEEE   日本磁気学会   応用物理学会   

共同研究・競争的資金等の研究課題

  • 日本学術振興会：科学研究費助成事業 挑戦的研究(萌芽)
    研究期間 : 2022年06月 -2025年03月 
    代表者 : 山ノ内 路彦, 植村 哲也
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2020年04月 -2023年03月 
    代表者 : 植村 哲也, 近藤 憲治
     
    本研究の目的は，磁性ワイル半金属材料において発現する強いスピン軌道相互作用を利用した強磁性体磁化制御の学理を確立し，高速性・低消費電力性に優れたスピントロニクスデバイスを実現することである．そのため，ワイル半金属であることが理論的に指摘されているホイスラー合金（以下，ワイル型ホイスラー合金とよぶ）をスピン源としたスピン軌道トルク(SOT)の特性を理論および実験により明らかにするとともに，これを利用した強磁性体磁化制御を確立する． 2020年度は主に，ワイル型ホイスラー合金の探索とその異常ホール効果を活用した強磁性体の磁化制御に取り組んだ．具体的には，フェルミ準位近傍にワイル点があることが理論的に示され，また実験的にも大きな異常ホール効果が観測されているCo2MnAlやCo2MnGaのホイスラー合金薄膜に着目し，それらの結晶構造解析，及び異常ホール効果や縦磁気抵抗効果などの磁気輸送特性評価を通じて，薄膜の成膜条件を最適化した．さらにこれらをスピン源として，MnGa/Co2MnSi強磁性体二層膜のSOT磁化反転を実証した． また，磁性ワイル半金属の磁気伝導率を理論的に検討した．有効モデルとして，Type-IとType-IIの両方のタイプを表現できる有効ハミルトニアンを使用し，このモデルの磁気伝導率をBerry曲率が考慮された古典ボルツマン方程式によって計算したところ，Type-Iのワイル半金属では従来から知られた，カイラルアノマリによる負の磁気抵抗効果が得られたが，Type-IIのワイル半金属では，カイラルアノマリによる負の磁気抵抗効果のみならず，正の磁気抵抗効果がカイラルアノマリによっておこることが分かった．これは，Type-IIでは磁場印可によって形成されるランダウ準位の曲率が変わらず，Type-Iではランダウ準位の曲率が反転することが原因であることを見出した．
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2017年04月 -2020年03月 
    代表者 : 植村 哲也, 近藤 憲治
     
    本研究の目的は，スピン軌道相互作用の大きい非磁性層と，スピン偏極率が本質的に100%となるハーフメタル強磁性体からなる積層構造において生じるスピン軌道トルクの学理を解明し，高速性・低消費電力性に優れた新規スピントロニクスデバイス実現のための基盤技術を創出することである．そのため，優れたハーフメタル性が実証されているCo基ホイスラー合金を電極とした強磁性トンネル接合と強いスピン軌道相互作用を有する非磁性材料を組み合わせた，新規磁気抵抗素子ならびに高周波自励発振デバイスを開拓し，Co基ホイスラー合金に対する明瞭なSOT磁化反転を実証した．
  • 日本学術振興会：科学研究費助成事業 基盤研究(C)
    研究期間 : 2016年10月 -2019年03月 
    代表者 : 近藤 憲治, 植村 哲也
     
    多くの研究者が、グラフェンのようなハニカム構造の量子スピンホール効果を研究してきた。しかしながら、その多くは開放端条件において、エッジをzigzag型であると仮定して電子構造を計算していた。その理由はarmchairのエッジ形状だと、バルクが量子スピンホール相であっても電子構造をよく見るとフェルミ・レベルにおいてギャップが存在するからである。一般的にバルク・エッジ対応によって、バルクで計算した量子スピンホール相の成立条件とリボンで計算した量子スピンホール相の成立条件は一致することになっている。しかしながら、ナノリボンにおいては、成立していないことを具体的な計算で確かめた。
  • 日本学術振興会：科学研究費助成事業 挑戦的萌芽研究
    研究期間 : 2015年04月 -2017年03月 
    代表者 : 植村 哲也, 近藤 憲治
     
    半導体中の核スピンは量子力学的な重ね合わせ状態を長く維持することができ，量子計算機の量子ビットとして有望である．本研究では，強磁性電極から半導体への電気的スピン注入と核電気共鳴(NER)効果を併用し、電気的制御のみで核スピンをナノメートルスケールの空間分解能で選択的に制御できる素子を開発した．具体的には，高いスピン偏極率を有するCo2MnSi電極からGaAsへの高効率スピン注入と，スピン注入信号のゲート電圧による高効率制御を実証した．さらに，注入した電子スピンを用いて，GaおよびAs原子の核スピンを高効率に偏極し，ゲート電極に印加した高周波電場により核スピンに対するNER操作を実証した．
  • 文部科学省：科学研究費補助金(基盤研究(B))
    研究期間 : 2013年 -2015年 
    代表者 : 植村 哲也
     
    半導体中の核スピンは量子力学的な重ね合わせ状態を比較的長く維持することができ，量子計算機の量子ビットとして有望である．本研究では，強磁性体から半導体へのスピン注入を用いた新たな核磁気共鳴(NMR)デバイスを開発した．高いスピン偏極率を有するハーフメタル強磁性体Co2MnSiからGaAsへの高効率スピン注入を実証し，さらに注入した電子スピンを用いて，GaおよびAs原子の核スピンを高効率に偏極できること，および，核スピンに対するNMR操作を電気的に高感度に検出できることを示した．さらに，Ga原子の核スピン準位間のラビ振動を実証し，核スピンのコヒーレント制御にスピン注入素子で初めて成功した．
  • 日本学術振興会：科学研究費助成事業 基盤研究(A)
    研究期間 : 2011年05月 -2014年03月 
    代表者 : 山本 眞史, 植村 哲也, 松田 健一
     
    本研究の目的は本質的に大きなスピン偏極率を有するハーフメタル材料のCo基ホイスラー合金と，高移動度半導体チャネル(Ge等)を融合する高品質エピタキシャルヘテロ構造の実現を通して，次世代半導体スピントロニクスの基盤を構築することである．平成24年度は，強磁性CoFe電極からMgOバリアを通したn-Geチャネルへのスピン注入の特性を実験的に詳細に検討し，以下の知見を明らかにした． CoFe/MgO/n-Ge接合に対して，2.25 nmから2.75 nm の範囲のMgOバリア厚み(t_MgO)に対して，室温で，3端子配置により明瞭なHanle信号(磁化は面内，磁場を面に垂直に印加)および逆Hanle信号(磁場を面内に印加)を観測した(スピン注入の方向: 強磁性体から半導体チャネルへのスピン注入)．また，スピン信号ΔVの大きさ(Hanle信号と逆Hanle信号の和)から見積もったspin-RA積(ΔRsA=(ΔV/I_bias)A)は，例えばt_MgO=2.4 nmの接合に対して，半導体へのスピン注入の標準理論(Fert and Jaffres, 2001)の値の4桁大きな値であった．さらに，spin-RA積はt_MgOに対して指数関数的な依存性を示すことを見出した．一方，標準理論では，spin-RA積はt_MgOに対して依存性を示さない．このように，これらの実験結果は，観測されたHanle信号が半導体Geチャネルでのスピン蓄積によるというモデルでは説明できない．この結果を説明するため，トンネル接合界面に存在する局在状態での，磁場によるスピンの歳差運動によりスピン偏極率が低下し，このためフェルミレベルでのアップスピンとダウンスピンの波数が変化し，結果として，トンネル確率が磁場によって変調されるというモデルを提案した．
  • 日本学術振興会：科学研究費助成事業 基盤研究(C)
    研究期間 : 2010年 -2012年 
    代表者 : 松田 健一, 山本 眞史, 植村 哲也
     
    本研究では、Co 基ホイスラー合金ハーフメタル強磁性体と超伝導体からなるエピタキシャルへテロ構造の作製に成功した。また、このヘテロ構造についてその電気伝導特性測定から、スピン偏極超伝導成分の存在を示唆する結果を得た。
  • 文部科学省：科学研究費補助金(基盤研究(B))
    研究期間 : 2009年 -2011年 
    代表者 : 植村 哲也, 山本 眞史, 松田 健一
     
    半導体中の伝導電子のスピンを操作し、これまでにない新しい機能を有する電子/光デバイスを創出するための基盤技術を確立することを目的に、スピン偏極率の高いハーフメタル材料として知られているCo系ホイスラー合金をスピン注入源とし、GaAsやSiなど種々の半導体への高効率スピン注入を実証した。さらに、注入した電子の半導体中におけるスピン緩和時間の見積もりや核スピンとの相互作用を解明し、スピン依存伝導特性を明らかにした。
  • 日本学術振興会：科学研究費助成事業 基盤研究(A)
    研究期間 : 2008年 -2010年 
    代表者 : 山本 眞史, 植村 哲也, 松田 健一
     
    ハーフメタル特性に由来する潜在的に高いスピン偏極率を有するホイスラー合金薄膜は,スピントロニクスデバイスの強磁性電極材料として有望である.本研究では,ホイスラー合金薄膜のハーフメタル特性を十分に活用するための高品質ヘテロ構造を開発すると共に,優れたデバイス特性を実証した.さらに,ホイスラー合金薄膜を上部・下部両電極に用い,MgOバリアを用いるエピタキシャル強磁性トンネル接合デバイスのスピン依存トンネル抵抗が室温においてMgOバリア厚に対し顕著な振動的依存性を示すことを見出した.
  • 日本学術振興会：科学研究費助成事業 特定領域研究
    研究期間 : 2007年 -2010年 
    代表者 : 山本 眞史, 植村 哲也, 松田 健一
     
    電子の電荷に加えて,電子のスピンを併せて活用するスピントロニクスにおいてスピン源が必須である.本研究では,ホイスラー合金が潜在的に有する,スピン源として理想的なハーフメタル特性を,デバイス構造の中で実現するための重要な知見を明らかにした.具体的には,ホイスラー合金薄膜組成の適切な制御により,ハーフメタル特性に対して特に有害となる欠陥の抑制が可能となり,ハーフメタル特性が顕著に増大することを明らかにした.さらに,これに合わせてホイスラー合金とMgOバリアからなるエピタキシャルヘテロ界面構造の向上により,優れたデバイス特性が得られることを明らかにした.
  • 文部科学省：科学研究費補助金(基盤研究(C))
    研究期間 : 2007年 -2008年 
    代表者 : 植村 哲也
     
    半導体中の伝導電子のスピンを操作し、これまでにない新しい機能を有する電子/光デバイスの研究が盛んに行われている。その実現の第一歩は、スピン偏極した電子を半導体内に発生させることであり、強磁性電極から半導体にスピン偏極した電子を電気的に注入する方法(スピン注入)が有効である。本研究では、高効率スピン注入の実現に向け、スピン偏極率の高いハーフメタル材料であるCo系ホイスラー合金薄膜を半導体GaAs上に高品質に形成するとともに、ホイスラー合金/GaAsヘテロ接合構造におけるスピン依存伝導特性を明らかにした。このことにより、将来の新しいスピン機能デバイスの創出にむけた基盤技術を確立した。
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2006年 -2007年 
    代表者 : 山本 眞史, 植村 哲也, 松田 健一, 齊藤 敏明
     
    本研究では、Co系ホイスラー合金(Co_2YZ)のハーフメタル特性を活用する室温動作のスピントロニクスデバイス基盤技術を構築することを目的とした。急峻で、かつ、原子レベルで平坦なCo_2YZ薄膜とMgOトンネルバリアの界面を実現するとともに、 Co_2YZ/MgOを用いたエピタキシャル強磁性トンネル接合(MTJ)デバイス技術を開発した。さらに、試作したMTJに対して室温において良好なトンネル磁気抵抗(TMR)特性を実証した。 1)本技術の特徴は以下の通りである:a)MTJ3層構造のすべての層の単結晶エピタキシャル成長,b)急峻で、かつ、原子レベルで平坦なCo_2YZ/MgOバリア界面,c)MgOバリアとの界面領域において、酸化のない、優れた電子的・磁気的状態を有するCo_2YZ薄膜。 2)Co_2Cr_0.6Fe_0.4Al/MgO/CoFe MTJについて、室温において109%(4.2Kにおいて317%)の比較的高いTMR比を実証した。 3)Co_2MnSi(CMS)薄膜を下部・上部両電極に用いた全層エピタキシャル構造の交換バイアス型CMS/MgO/CMS MTJ製作技術を開発した。上部CMS電極堆積後のin situアニールにおけるアニール温度(T_a)を高くするとともに、TMR比が高くなることを明らかにした。また、典型的なTMR 比として、T_a=600℃に対して、室温で179%(4.2Kで683%)の高い値を実証した。 以上、Co系ホイスラー合金とMgOバリアからなる単結晶エピタキシャルヘテロ構造が、ハーフメタル特性を活用する室温動作のスピントロニクスデバイスの基本構造として高い可能性を有していることを示した。
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2004年 -2005年 
    代表者 : 山本 眞史, 植村 哲也, 松田 健一
     
    本研究では、強磁性エピタキシャル多重障壁構造の製作技術を確立すると共に、スピン共鳴トンネルデバイスの基盤技術を構築することを目的とした。本研究では,強磁性電極材料として,ハーフメタル強磁性特性に由来する高いスピン偏極率が理論的に指摘され、かつ、キュリー温度が室温よりも十分に高いCo系フルホイスラー合金を検討対象とした。さらに,Co系ホイスラー合金とMgOとの間の格子ミスマッチが数%と比較的小さいことに着目し、MgO基板上へのCo系ホイスラー合金薄膜のエピタキシャル成長を実現した。具体的には、Co_2(Cr_<0.6>Fe_<0.4>)Al(CCFA)とCo_2MnGe(CMG)のエピタキシャル薄膜を製作し、優れた表面平坦性(表面粗さのrms値が、約0.25nm程度)を実現した。さらに、このホイスラー合金エピタキシャル薄膜の上への2nm程度のMgOバリア、さらに、その上への強磁性Co_<50>Fe_<50>薄膜のエピタキシャル成長を実現した。すなわち、Co系ホイスラー合金薄膜と、MgOバリアを用いた全層エピタキシャルの強磁性トンネル接合(MTJ)を実現した。これらのエピタキシャル構造を用いてMTJを試作評価し、室温において、良好なトンネル磁気抵抗(TMR)特性が得られることを示した(CCFA-MTJに対して、室温で42%のTMR比)。さらに、エピタキシャル構造の2重障壁構造を製作し、単一障壁構造と同程度のTMR比(室温で42%程度)を有すること、TMR比が1/2となるバイアス電圧の値が単一障壁構造の約2倍程度と、良好な特性を有することを示した。以上、ハーフメタル強磁性体としてスピン偏極率が大きいと予想されるCo系ホイスラー合金薄膜を用いた強磁性エピタキシャル多重障壁構造の製作技術、および、スピン共鳴トンネルデバイスの基盤技術を構築した。
  • 文部科学省：科学研究費補助金(基盤研究(C))
    研究期間 : 2004年 -2005年 
    代表者 : 植村 哲也
     
    本研究の目的は、高い読み出し信号比を有するMRAMの創出に向け、共鳴トンネルダイオード(RTD)やバンド間トンネルダイオード(ITD)をはじめとする負性抵抗(NDR)素子と、強磁性トンネル接合(MTJ)を組み合わせた融合回路を開発することである。具体的には、MTJとNDR素子の直列または並列接続集積構造を有するMRAMセルを構成し、そのピーク電圧もしくはピーク電流がMTJの磁化状態により明確に変化することを利用する。まず、NDR素子としてGaAsバンド間トンネルダイオード、MTJとしてCoFe/AlOx系MTJを用い、その磁気抵抗(MR)比が最大890%と飛躍的に増大できることを実証し、本研究の基本原理を確認した。次に、MTJ素子ならびにNDR素子の構造最適化を図り、MTJ素子では、Co系ホイスラー合金やペロブスカイト型Mn酸化物、さらには、強磁性半導体を用いたMTJを試作し、室温で、最大90%におよぶ大きなMR比を得た。これにより、実用的なバイアス電源の設定マージンを確保できる見通しが得られた。また、NDR素子としてRTDを検討し、ピーク・バレイ電流比の大きい2重量子井戸型RTDを分子線エピタキシャル成長法により作製し、その構造と電気的特性の関係を実験的に明らかにした。メモリセルの構成として、RTDとMTJを直列接続した場合と並列接続した場合、また、セル選択用トランジスタを用いる場合と用いない場合のそれぞれについて、回路性能と作製プロセスの両面から各方式の特徴を明らかにした。また、実験的に得られたMTJおよびRTDの素子特性を組み入れたSPICEモデルを構築し、試作したプロトタイプセルの評価結果をベースに、セル占有面積、アクセス速度、消費電力、動作マージン、などのメモリ性能が集積度向上につれてどのように推移するかを回路シミュレーションにより解析した。これにより、高速・大容量のMRAM実現の観点から、本研究のRTD/MTJ融合システムのポテンシャリティの高さを示した。
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2001年 -2002年 
    代表者 : 山本 眞史, 植村 哲也, 雨宮 好仁
     
    不揮発で高速・高密度のランダムアクセスメモリは次世代のユビキタス情報ネットワークに必須のデバイスである。強磁性トンネル接合デバイスを用いるMRAMは有力な候補の一つである。従来の研究では、MRAM応用を目指したトンネル磁気抵抗デバイスとして、強磁性単一障壁構造を用いている。本研究では、MRAMの高性能化のための重要な課題であるトンネル磁気抵抗比の増大に対して、強磁性多重障壁構造におけるスピン共鳴トンネル現象の活用の可能性を追求した。具体的に、強磁性3重障壁構造におけるスピン共鳴トンネル現象に着目し、電流-電圧(I-V)特性を理論的に解析した。この結果、I-V特性は、スピンの磁化方向に依存するそれぞれピーク型のI-V特性となること、すなわち、スピンの共鳴トンネル現象に由来する非常に強い非線形性を示すことを明らかにした。メモリとしては、エミッタ/コレクタ電極および第一の強磁性量子井戸の磁化方向を固定し、第2の強磁性量子井戸の磁化方向を第一の強磁性量子井戸磁化方向に対して、平行(メモリ"1")あるいは反平行("0")に制御することにより、非揮発性メモリを構成できる。交換分裂エネルギー(2h_0)および保持力の大きさの観点から、材料系について検討し、室温で強磁性を示す遷移金属強磁性体の中では、Ni系材料が適することを明らかにした。本デバイスの有する強い非線形I-V特性により、"1"と"0"の読み出し電流比が従来に比較して飛躍的に大きくなり、MRAMの高集積化、高集積化に有望である。具体的に、本デバイスとMOSトランジスタを組み合わせた回路シミュレーションにより、読み出し電流比が、10^4%程度の非常に大きな値になることを示した。以上、強磁性多重障壁構造におけるスピンに依存する共鳴トンネル現象が、MRAMの高性能化に新しい可能性を与えることを示した。

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