研究者情報

マスター

アカウント（マスター）

• 氏名

  山ノ内　路彦(ヤマノウチ　ミチヒコ), ヤマノウチ　ミチヒコ

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, 電気電子工学実験Ⅰ, Electrical and Electronic Engineering Laboratories I, 学士課程, 工学部, バイポーラトランジスタ，増幅回路，MOSFET，CMOS，演算増幅器，論理回路，順序回路，ディジタル回路
• 2021, 電気電子工学実験Ⅱ, Electrical and Electronic Engineering Laboratories II, 学士課程, 工学部, 偏光，旋光，回折，屈折，結晶構造，X線回折，半導体物性，ホール効果，電気磁気エネルギー，電力
• 2021, 電気電子工学実験Ⅲ, Electrical and Electronic Engineering Laboratories III, 学士課程, 工学部, 半導体プロセス，MOSFET，集積回路特性評価，SPICE，回路シミュレーション，アセンブリ言語
• 2021, 応用数学Ⅱ, 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

researchmap

プロフィール情報

学位

• 博士(工学)（東北大学）

プロフィール情報

• 姓

  山ノ内, ヤマノウチ

• 名

  路彦, ミチヒコ

• ID各種

  201301017344298492

対象リソース

https://www.ist.hokudai.ac.jp/labo/nanodev/
https://www.ist.hokudai.ac.jp/labo/nanodev/index_english.html

業績リスト

研究キーワード

• スピントロニクス   spintronics   

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

経歴

• 2020年09月 - 現在 北海道大学 大学院情報科学研究院
• 2014年05月 - 2020年08月 北海道大学 電子科学研究所 准教授
• 2012年04月 - 2014年04月 東北大学 電気通信研究所 助教
• 2010年04月 - 2012年03月 東北大学 省エネルギー・スピントロニクス集積化システムセンター 助教
• 2007年04月 - 2010年03月 日立製作所(株) 基礎研究所 研究員
• 2006年10月 - 2007年03月 国立研究開発法人科学技術振興機構
• 2006年10月 - 2007年03月 独立行政法人科学技術振興機構 ERATO大野半導体スピントロニクスプロジェクト 研究員

学歴

• 2003年10月 - 2006年09月   東北大学
• 2003年10月 - 2006年09月   東北大学   大学院   工学研究科 電子工学専攻 博士課程
• 2002年04月 - 2003年09月   東北大学
• 2002年04月 - 2003年09月   東北大学   大学院   工学研究科 電子工学専攻 修士課程
• 1998年04月 - 2002年03月   東北大学
• 1998年04月 - 2002年03月   東北大学   工学部   電気・電子・情報・応物系

委員歴

• 2016年04月 - 2018年03月   応用物学会北海道支部   庶務幹事

受賞

• 2007年03月 東北大学大学院工学研究科 「電気・情報優秀賞」(博士)
   

  受賞者: 山ノ内 路彦
• 2006年09月 応用物理学会 第20回応用物理学会 講演奨励賞
   

  受賞者: 山ノ内 路彦
• 2005年12月 財団法人青葉工学振興会 第11回研究奨励賞
   

  受賞者: 山ノ内 路彦

論文

• Effect of an ultrathin Fe interlayer on the growth of MnGa and spin-orbit-torque induced magnetization switching

  Mineto Ogawa, Takuya Hara, Shun Hasebe, Michihiko Yamanouchi, Tetsuya Uemura

  Applied Physics Express 16 6 063002 - 063002 2023年06月14日 [査読有り]
   

  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.
• Deterministic field-free switching of perpendicular magnetization by spin–orbit torques originating from in-plane magnetized Co2MnAl

  Daimu Morita, Takuya Hara, Michihiko Yamanouchi, Tetsuya Uemura

  AIP Advances 13 1 2023年01月30日 [査読有り]
   

  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.
• Effect of off-stoichiometric composition on half-metallic character of Co₂Fe(Ga,Ge) investigated using saturation magnetization and giant magnetoresistance effect

  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 - 345003 2022年08月25日 

  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 Co₂Fe_1.03Ga_0.41Ge_γ and that it decreases in off-stoichiometric CFGG, mainly due to the formation of Co_Fe antisites for Ge-deficient compositions and Fe_Co antisites for Ge-rich compositions, where Co_Fe (Fe_Co) indicates that Co (Fe) atoms replace the Fe (Co) sites. The saturation magnetic moment (μ_s) per formula unit decreased monotonically as γ increased from 0.24 to 1.54 in Co₂Fe_1.03Ga_0.41Ge_γ. The μ_s 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.
• Spin-Orbit Torque in Structures With Magnetization-Compensated MnGa/Co2MnSi Bilayer

  Takuya Hara, Kohey Jono, Michihiko Yamanouchi, Tetsuya Uemura

  IEEE Transactions on Magnetics 58 8 2022年08月01日 

  We have systematically investigated the spin-orbit torque (SOT)-induced effective magnetic field in a structure consisting of a Ta heavy metal layer and an antiferromagnetically coupled Mn1.8Ga1/Co2MnSi (CMS) bilayer around the magnetization compensation point by varying CMS film thickness. The efficiency of SOT generation takes the maximum around the compensation point, and it is approximately six times as large compared with that in the devices with a MnGa single structure. The enhancement of SOT efficiency can be explained mainly by the reduction in saturation magnetic moment around the compensation point. Moreover, a significant enhancement of the effective spin Hall angle was observed around the compensation point because of the inversion of the magnetization configuration before and after the compensation point.
• Observation of topological Hall torque exerted on a domain wall in the ferromagnetic oxide SrRuO ₃

  Michihiko Yamanouchi, Yasufumi Araki, Takaki Sakai, Tetsuya Uemura, Hiromichi Ohta, Jun’ichi Ieda

  Science Advances 8 15 2022年04月15日 

  In a ferromagnetic Weyl metal SrRuO ₃ , a large effective magnetic field H_eff exerted on a magnetic domain wall (DW) by current has been reported. We show that the ratio of H_eff 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 H_eff 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 induced magnetization switching for an ultrathin MnGa/Co2MnSi bilayer

  Kohey Jono, Fumiaki Shimohashi, Michihiko Yamanouchi, Tetsuya Uemura

  AIP Advances 11 2 025205 - 025205 2021年02月01日 [査読有り]
  
• Current-induced effective magnetic field in La0.67Sr0.33MnO3/LaAlO3/SrTiO3 structures

  Michihiko Yamanouchi, Tatsuro Oyamada, Hiromichi Ohta

  AIP Advances 10 015129  2020年01月14日 [査読有り][通常論文]
  
• Magnetic properties and spin-orbit-torque-induced magnetization switching in Ta/MnGa grown on Cr and NiAl buffer layers

  Michihiko Yamanouchi, Nguyen Viet Bao, Fumiaki Shimohashi, Kohey Jono, Masaki Inoue, Tetsuya Uemura

  AIP ADVANCES 9 12 2019年12月 [査読有り]
   

  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).
• Interaction between spin-orbit torque and domain walls in a Ta/MnGa/NiAl structure

  Michihiko Yamanouchi, Nguyen Viet Bao, Masaki Inoue, Tetsuya Uemura

  JAPANESE JOURNAL OF APPLIED PHYSICS 58 10 2019年10月 [査読有り]
   

  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
• Peculiar magnetotransport properties in La0.67Sr0.33MnO3/LaAlO3/SrTiO3

  Michihiko Yamanouchi, Tatsuro Oyamada, Hiromichi Ohta

  AIP Advances 9 035129  2019年03月 [査読有り][通常論文]
  
• Current-induced modulation of coercive field in the ferromagnetic oxide SrRuO3

  Michihiko Yamanouchi, Tatsuro Oyamada, Koichi Sato, Hiromichi Ohta, Jun’ichi Ieda

  IEEE Transactions on Magnetics 1400604  2019年02月 [査読有り][通常論文]
  
• Gate tunable spin-orbit coupling and weak antilocalization effect in an epitaxial La2/3Sr1/3MnO3 thin film

  Shao-Pin Chiu, Michihiko Yamanouchi, Tatsuro Oyamada, Hiromichi Ohta, Juhn-Jong Lin

  PHYSICAL REVIEW B 96 8 085143-1 - 085143-7 2017年08月 [査読有り][通常論文]
   

  Epitaxial La2/3Sr1/3MnO3 (LSMO) films have been grown on SrTiO3 (001) substrates via pulsed laser deposition. In a 22-nm-thick LSMO film with a low residual resistivity of rho(0) approximate to 59 mu Omega cm, we found a zero-field dip in the magnetoresistance (MR) below 10 K, manifesting the weak antilocalization (WAL) effect due to strong spin-orbit coupling (SOC). We have analyzed the MR data by including the D'yakonov-Perel' spin-relaxation mechanism in the WAL theory. We explain that the delocalized spin-down electron sub-band states play a crucial role for facilitating marked SOC in clean LSMO. Moreover, we find that the SOC strength and gate voltage tunability are similar to those in a two-dimensional electron gas at the LaAlO3/SrTiO3 interface, indicating the presence of an internal electric field near the LSMO/SrTiO3 interface. In a control measurement on a 5-nm-thick high resistivity (rho(0) approximate to 280 mu Omega cm) LSMO film, we observe only a small zero-field peak in MR from weak localization effect, indicating negligible SOC.
• Adiabatic spin-transfer-torque-induced domain wall creep in a magnetic metal

  S. DuttaGupta, S. Fukami, C. Zhang, H. Sato, M. Yamanouchi, F. Matsukura, H. Ohno

  NATURE PHYSICS 12 4 333 - U167 2016年04月 [査読有り][通常論文]
   

  The dynamics of elastic interfaces is ageneral field of interest in statistical physics, where magnetic domain wall has served as a prototypical example. Domainwall 'creep' under the action of sub-threshold driving forces with thermal activation is known to be described by a scaling law with a certain universality class(1-10), which represents the mechanism of the interaction of domain walls with the applied forces over the disorder of the system. Here we show different universality classes depending on the driving forces, magnetic field or spin-polarized current, in a metallic system, which have hitherto been seen only in a magnetic semiconductor(3,6). We reveal that an adiabatic spin-transfer torque plays a major role in determining the universality class of current-induced creep, which does not depend on the intricacies of material disorder. Our results shed light on the physics of the creep motion of domain walls and other elastic systems.
• Solid-Phase Epitaxial Growth of A-Site-Ordered Perovskite Sr4-xErxCo4O12-delta: A Room Temperature Ferrimagnetic p-Type Semiconductor

  Takayoshi Katase, Hidefumi Takahashi, Tetsuya Tohei, Yuki Suzuki, Michihiko Yamanouchi, Yuichi Ikuhara, Ichiro Terasaki, Hiromichi Ohta

  ADVANCED ELECTRONIC MATERIALS 1 12 1500199  2015年12月 [査読有り][通常論文]
   

  The oxygen-deficient Sr4-xErxCo4O12-delta (SECO), one of the ordered perovskite oxides, is a room-temperature (RT) ferrimagnetic semiconductor that arises from the A-site-ordered structure. Development of such a material can lead to the realization of spintronic heterojunction devices; however, to this point there have been difficulties in achieving the A-site-ordered structure in SECO thin films. Here, single-crystalline film growth of SECO with perfectly aligned A-site-ordered structure on (LaAlO3)(0.3)(Sr2TaAlO6)(0.7) substrates by solid-phase epitaxy (SPE) method is demonstrated. The brownmillerite-type, A-site-disordered structure of the as-grown epitaxial film clearly changes into well-aligned A-site-ordered structure after heat treatment at 1050 degrees C in air; the aligned ordered structure in the film is clearly visualized at atomic level. This ordering induces ferrimagnetism with Curie temperature (T-c) approximate to 310 K and it is found that the SECO film with p-type semiconductivity exhibits anomalous Hall effect at the temperature up to 300 K, which is suitable for the test bench to demonstrate advanced spintronic heterojunction devices, operating at RT. The present SPE method is expected to serve as a powerful technique for the fabrication of thin films and exploration of potential characteristics of A-site-ordered perovskite oxides.
• Dependence of magnetic properties of MgO/CoFeB/Ta stacks on CoFeB and Ta thicknesses

  Kyota Watanabe, Shinya Ishikawa, Hideo Sato, Shoji Ikeda, Michihiko Yamanouchi, Shunsuke Fukami, Fumihiro Matsukura, Hideo Ohno

  JAPANESE JOURNAL OF APPLIED PHYSICS 54 4 04EM04  2015年04月 [査読有り][通常論文]
   

  We investigate the dependence of magnetic properties of MgO/CoFeB/Ta stacks on thicknesses of CoFeB ranging from 2 to 30 nm and Ta from 1 to 10nm before and after annealing at 300-400 degrees C for 1-3 h. The annealing increases the saturation magnetic moment per unit area and reduces the magnitude of the damping constant in CoFeB. The annealing effect becomes smaller with increasing CoFeB thickness and with decreasing Ta thickness, indicating that the effect is related to B diffusion from CoFeB to Ta. We show that the amount of diffused B can be controlled by Ta layer thickness and annealing duration. (C) 2015 The Japan Society of Applied Physics
• In-plane anisotropy of a nano-scaled magnetic tunnel junction with perpendicular magnetic easy axis

  Eriko Hirayama, Shun Kanai, Koji Sato, Michihiko Yamanouchi, Hideo Sato, Shoji Ikeda, Fumihiro Matsukura, Hideo Ohno

  JAPANESE JOURNAL OF APPLIED PHYSICS 54 4 04EM03  2015年04月 [査読有り][通常論文]
   

  We investigate magnetic properties of a 100-nm-diameter CoFeB/MgO magnetic tunnel junction (MTJ) with perpendicular magnetic easy axis by homodyne-detected ferromagnetic resonance (FMR) and junction resistance measurements. The resonant frequency depends clearly on the direction of the in-plane magnetic field, which is also the case for the angle dependence of the junction resistance. A good correspondence between the two independent measurements indicates the presence of unintentionally introduced in-plane magnetic anisotropy in the present MTJ. (C) 2015 The Japan Society of Applied Physics
• Perpendicular-anisotropy CoFeB-MgO based magnetic tunnel junctions scaling down to 1X nm

  S. Ikeda, H. Sato, H. Honjo, E. C.I. Enobio, S. Ishikawa, M. Yamanouchi, S. Fukami, S. Kanai, F. Matsukura, T. Endoh, H. Ohno

  Technical Digest - International Electron Devices Meeting, IEDM 2015- February 33.2.1 - 33.2.4 2015年02月20日 [査読有り][通常論文]
   

  CoFeB-MgO based magnetic tunnel junction with perpendicular easy axis (p-MTJ) shows a high potential to be used in spintronics based very large scale integrated circuits and spin-transfer-torque magnetorestive random access memories. In this paper, we review development of p-MTJ using single CoFeB-MgO and double CoFeB-MgO interface structures. The TMR ratio shows 164% after annealing at 400 °C, indicating the CoFeB-MgO p-MTJs have capability for back-end-of-line. Scaling properties of p-MTJs using double CoFeB-MgO interface structure are also reviewed.
• Localized precessional mode of domain wall controlled by magnetic field and dc current

  Ryo Hiramatsu, Kab-Jin Kim, Takuya Taniguchi, Takayuki Tono, Takahiro Moriyama, Shunsuke Fukami, Michihiko Yamanouchi, Hideo Ohno, Yoshinobu Nakatani, Teruo Ono

  APPLIED PHYSICS EXPRESS 8 2 023003  2015年02月 [査読有り][通常論文]
   

  We present evidence of a localized magnetic domain-wall (DW) oscillator in Co/Ni nanowires. It is found that a DW is localized by the simultaneous application of a high magnetic field larger than the depinning field and a dc current smaller than the threshold current. A one-dimensional model and micromagnetic simulation reveal that the localized DW is in a precessional mode. Our results suggest that a localized magnetic DW oscillator can be realized by appropriately adjusting the magnetic field and dc current. (C) 2015 The Japan Society of Applied Physics
• 23pAD-1 磁場および電流によって制御された磁壁発振器

  平松 亮, Kim Kab-Jin, 谷口 卓也, 東野 隆之, 森山 貴広, 深見 俊輔, 山ノ内 路彦, 大野 英男, 仲谷 栄伸, 小野 輝男

  日本物理学会講演概要集 70 1196 - 1196 一般社団法人日本物理学会 2015年
• Domain Wall Motion Device for Nonvolatile Memory and Logic - Size Dependence of Device Properties

  Shunsuke Fukami, Michihiko Yamanouchi, Shoji Ikeda, Hideo Ohno

  IEEE TRANSACTIONS ON MAGNETICS 50 11 6971556  2014年11月 [査読有り][通常論文]
   

  Current-induced magnetic domain wall (DW)-motion device with a three-or four-terminal structure has considerable potential to trigger a profound transformation in memory and logic technologies. In this paper, we give an overview of DW-motion devices and describe their structure, operation method, and characteristics. Previous studies on the DW motion in nanowires with a Co/Ni multilayer are also reviewed. We also report on the experimental results regarding device properties, such as critical current, the time and energy required to displace the DW in the device, and retention properties with various device sizes down to 20 nm. The results reveal that writing properties are enhanced while sufficient retention properties are maintained as the device size is reduced, indicating that the DW-motion device has high scalability and compatibility with conventional semiconductor-based cells as well as ultralow power capability.
• Properties of magnetic tunnel junctions with a MgO/CoFeB/Ta/CoFeB/MgO recording structure down to junction diameter of 11nm

  H. Sato, E. C.I. Enobio, M. Yamanouchi, S. Ikeda, S. Fukami, S. Kanai, F. Matsukura, H. Ohno

  Applied Physics Letters 105 6 2014年08月11日 [査読無し][通常論文]
   

  We investigate properties of perpendicular anisotropy magnetic tunnel junctions (MTJs) with a recording structure of MgO/CoFeB/Ta/CoFeB/MgO down to junction diameter (D) of 11nm from 56nm. Thermal stability factor (Δ) of MTJ with the structure starts to decrease at D=30nm. D dependence of Δ agrees well with that expected from magnetic properties of blanket film taking into account the change in demagnetizing factors of MTJs. Intrinsic critical current (I< inf> C0< /inf> ) reduces with decrease of D in the entire investigated D range. A ratio of Δ to I< inf> C0< /inf> shows continuous increase with decrease of D down to 11nm. © 2014 AIP Publishing LLC.
• Interface control of the magnetic chirality in CoFeB/MgO heterostructures with heavy-metal underlayers

  Jacob Torrejon, Junyeon Kim, Jaivardhan Sinha, Seiji Mitani, Masamitsu Hayashi, Michihiko Yamanouchi, Hideo Ohno

  NATURE COMMUNICATIONS 5 2014年08月 [査読有り][通常論文]
   

  Recent advances in the understanding of spin orbital effects in ultrathin magnetic hetero-structures have opened new paradigms to control magnetic moments electrically. The Dzyaloshinskii-Moriya interaction (DMI) is said to play a key role in forming a Neel-type domain wall that can be driven by the spin Hall torque. Here we show that the strength and sign of the DMI can be changed by modifying the adjacent heavy-metal underlayer (X) in perpendicularly magnetized X/CoFeB/MgO heterostructures. The sense of rotation of a domain wall spiral is reversed when the underlayer is changed from Hf, Ta to W and the strength of DMI varies as the filling of 5d orbitals, or the electronegativity, of the heavy-metal layer changes. The DMI can even be tuned by adding nitrogen to the underlayer, thus allowing interface engineering of the magnetic texture in ultrathin magnetic heterostructures.
• Electric-field effects on magnetic anisotropy and damping constant in Ta/CoFeB/MgO investigated by ferromagnetic resonance

  A. Okada, S. Kanai, M. Yamanouchi, S. Ikeda, F. Matsukura, H. Ohno

  APPLIED PHYSICS LETTERS 105 5 2014年08月 [査読有り][通常論文]
   

  We investigate electric-field effects on the effective magnetic anisotropy energy density K-eff and the Gilbert damping constant alpha in Ta/CoFeB/MgO structures with CoFeB thickness t ranging from 1.4 to 1.8 nm by ferromagnetic resonance. The electric field-induced modulation ratio of the areal energy density K(eff)t does not depend on the CoFeB thickness, indicating that the electric-field effect on the magnetic anisotropy originates from the modulation of CoFeB/MgO-interfacial magnetic anisotropy. A clear electric-field modulation of alpha is observed for the structure with t = 1.4 nm, and almost no modulation for the structures with t >= 1.5 nm. (C) 2014 AIP Publishing LLC.
• Influence of Heavy Ion Irradiation on Perpendicular-Anisotropy CoFeB-MgO Magnetic Tunnel Junctions

  Daisuke Kobayashi, Yuya Kakehashi, Kazuyuki Hirose, Shinobu Onoda, Takahiro Makino, Takeshi Ohshima, Shoji Ikeda, Michihiko Yamanouchi, Hideo Sato, Eli Christopher Enobio, Tetsuo Endoh, Hideo Ohno

  IEEE TRANSACTIONS ON NUCLEAR SCIENCE 61 4 1710 - 1716 2014年08月 [査読有り][通常論文]
   

  A non-volatile memory element called a perpendicular-anisotropy magnetic tunnel junction was fabricated using CoFeB/MgO/CoFeB film stack technology. It exhibits two stable resistance values, high or low, depending on the relative directions of the magnetizations of the two ferromagnetic CoFeB layers. After being programmed into the high resistance state with a current injection scheme based on the spin transfer torque theory, the tunnel junction was exposed to 15-MeV Si ions under different voltage stress conditions. The tested structure remained in the programmed high resistance state after being bombarded with 10-100 Si ions, even under the stressed situations. A time-domain analysis proved that this result is due to the perfect immunity of the tested magnetic tunnel junction to single event upsets. Some degradation in resistance due to the heavy-ion irradiation was detected through a precise parameter analysis based on a tunneling theory but it was negligibly small (1%). There were no statistically significant changes in the thermal stability factor before and after irradiation, and this means the long-term retention properties remained unchanged.
• Magnetization reversal induced by in-plane current in Ta/CoFeB/MgO structures with perpendicular magnetic easy axis

  C. Zhang, M. Yamanouchi, H. Sato, S. Fukami, S. Ikeda, F. Matsukura, H. Ohno

  Journal of Applied Physics 115 17 2014年05月07日 [査読無し][通常論文]
   

  © 2014 AIP Publishing LLC. We investigate in-plane current-induced magnetization reversal under an in-plane magnetic field in Hall bar shaped devices composed of Ta/CoFeB/MgO structures with perpendicular magnetic easy axis. The observed relationship between the directions of current and magnetization switching and Ta thickness dependence of magnetization switching current are accordance with those for magnetization reversal by spin transfer torque originated from the spin Hall effect in the Ta layer.
• Anomalous temperature dependence of current-induced torques in CoFeB/MgO heterostructures with Ta-based underlayers

  Junyeon Kim, Jaivardhan Sinha, Seiji Mitani, Masamitsu Hayashi, Saburo Takahashi, Sadamichi Maekawa, Michihiko Yamanouchi, Hideo Ohno

  PHYSICAL REVIEW B 89 17 174424  2014年05月 [査読有り][通常論文]
   

  We have studied the underlayer thickness and temperature dependencies of the current-induced effective field in CoFeB/MgO heterostructures with Ta-based underlayers. The underlayer thickness at which the effective field saturates is found to be different between the two orthogonal components of the effective field; i.e., the dampinglike term tends to saturate at a smaller underlayer thickness than the fieldlike term. For large underlayer thickness films in which the effective field saturates, we find that the measurement temperature significantly influences the size of the effective field. A striking difference is found in the temperature dependence of the two components: the dampinglike term decreases whereas the fieldlike term increases with increasing temperature. Using a simple spin diffusion-spin transfer model, we find that all of these results can be accounted for provided the real and imaginary parts of an effective spin mixing conductance are negative. These results imply that either spin transport in this system is different from conventional metallic interfaces or effects other than spin diffusion into the magnetic layer need to be taken into account in order to model the system accurately.
• Magnetization switching in a CoFeB/MgO magnetic tunnel junction by combining spin-transfer torque and electric field-effect

  S. Kanai, Y. Nakatani, M. Yamanouchi, S. Ikeda, H. Sato, F. Matsukura, H. Ohno

  APPLIED PHYSICS LETTERS 104 21 212406  2014年05月 [査読有り][通常論文]
   

  We propose and demonstrate a scheme for magnetization switching in magnetic tunnel junctions, in which two successive voltage pulses are applied to utilize both spin-transfer torque and electric field effect. Under this switching scheme, a CoFeB/MgO magnetic tunnel junction with perpendicular magnetic easy axis is shown to switch faster than by spin-transfer torque alone and more reliably than that by electric fields alone. (C) 2014 AIP Publishing LLC.
• Co/Pt multilayer-based magnetic tunnel junctions with a CoFeB/Ta insertion layer

  S. Ishikawa, H. Sato, M. Yamanouchi, S. Ikeda, S. Fukami, F. Matsukura, H. Ohno

  JOURNAL OF APPLIED PHYSICS 115 17 17C719  2014年05月 [査読有り][通常論文]
   

  We investigate properties of magnetic tunnel junctions (MTJs) having a Co/Pt multilayer as a recording layer. A CoFeB layer is inserted between MgO barrier and the recording layer in order to enhance the tunnel magnetoresistance ratio. We show that an additional layer of Ta inserted between CoFeB and Co/Pt multilayer is effective in improving the MTJ properties after annealing. A high effective magnetic anisotropy energy per unit area over 1.2mJ/m(2) is obtained after annealing at 300 degrees C. Using a 1.6 nm-thick CoFeB insertion layer, both high thermal stability factor of 92 and high tunnel magnetoresistance ratio of 91% are achieved in a MTJ with 17 nm in diameter. (C) 2014 AIP Publishing LLC.
• Distribution of critical current density for magnetic domain wall motion

  S. Fukami, M. Yamanouchi, Y. Nakatani, K. -J. Kim, T. Koyama, D. Chiba, S. Ikeda, N. Kasai, T. Ono, H. Ohno

  JOURNAL OF APPLIED PHYSICS 115 17 17D508  2014年05月 [査読有り][通常論文]
   

  The bit-to-bit distribution of a critical current density for magnetic domain wall (DW) motion is studied using Co/Ni wires with various wire widths (ws). The distribution inherently decreases with the w, and the ratio of standard deviation to average is 9.8% for wires with w = 40 nm. It is found that a self-distribution within one device, which is evaluated through repeated measurement, is a dominant factor in the bit-to-bit distribution. Micromagnetic simulation reveals that the distribution originates from DW configuration, which varies with device size. (C) 2014 AIP Publishing LLC.
• Co/Pt multilayer based reference layers in magnetic tunnel junctions for nonvolatile spintronics VLSIs

  Hideo Sato, Shoji Ikeda, Shunsuke Fukami, Hiroaki Honjo, Shinya Ishikawa, Michihiko Yamanouchi, Kotaro Mizunuma, Fumihiro Matsukura, Hideo Ohno

  JAPANESE JOURNAL OF APPLIED PHYSICS 53 4 04EM02  2014年04月 [査読有り][通常論文]
   

  We investigated properties of Co/Pt multilayer for reference layer in CoFeB-MgO magnetic tunnel junctions with perpendicular easy axis. The sufficient thermal stability factor of 284 was obtained under zero applied field in 40-nm-diameter Co/Pt multilayer based reference layer annealed at 350 degrees C. By applying a synthetic ferrimagnetic (SyF) structure to the Co/Pt multilayer based reference layer, the shift of the center of minor resistance-magnetic field curves was suppressed, leading to higher thermal stability of antiparallel magnetization configuration than that without a SyF structure. (C) 2014 The Japan Society of Applied Physics
• Quantitative characterization of the spin-orbit torque using harmonic Hall voltage measurements

  Masamitsu Hayashi, Junyeon Kim, Michihiko Yamanouchi, Hideo Ohno

  PHYSICAL REVIEW B 89 14 144425  2014年04月 [査読有り][通常論文]
   

  Solid understanding of current induced torques is a key to the development of current and voltage controlled magnetization dynamics in ultrathin magnetic heterostructures. To evaluate the size and direction of such torques, or effective fields, a number of methods have been employed. Here, we examine the adiabatic (low-frequency) harmonic Hall voltage measurement that has been used to study the effective field. We derive an analytical formula for the harmonic Hall voltages to evaluate the effective field for both out of plane and in-plane magnetized systems. The formula agrees with numerical calculations based on a macrospin model. Two different in-plane magnetized films, Pt|CoFeB|MgO and CuIr|CoFeB|MgO are studied using the formula developed. The effective field obtained for the latter system shows relatively good agreement with that estimated using spin torque switching phase diagram measurements reported previously. Our results illustrate the versatile applicability of harmonic Hall voltage measurement for studying current induced torques in magnetic heterostructures.
• MgO/CoFeB/Ta/CoFeB/MgO recording structure with low intrinsic critical current and high thermal stability

  H. Sato, M. Yamanouchi, S. Ikeda, S. Fukami, F. Matsukura, H. Ohno

  Journal of the Magnetics Society of Japan 38 No. 2-2 56 - 60 2014年03月20日 [査読有り][通常論文]
  
• Effect of spin Hall torque on current-induced precessional domain wall motion

  Yoko Yoshimura, Tomohiro Koyama, Daichi Chiba, Yoshinobu Nakatani, Shunsuke Fukami, Michihiko Yamanouchi, Hideo Ohno, Kab-Jin Kim, Takahiro Moriyama, Teruo Ono

  APPLIED PHYSICS EXPRESS 7 3 033005  2014年03月 [査読有り][通常論文]
   

  Two important mechanisms for current-induced domain wall (DW) dynamics, namely, precessional DW motion driven by the adiabatic spin transfer torque and steady DW motion induced by the spin Hall torque, have been proposed and experimentally confirmed. However, the effect of the spin Hall torque on precessional DW motion has not been reported yet. Here, we show that the spin Hall torque affects the precessional DW motion when the in-plane field is applied. It is found that the in-plane field induces a half rotation time difference during DW precession, which gives rise to the nonvanishing spin Hall torque on the precessional DW motion. (C) 2014 The Japan Society of Applied Physics
• Advances in Spintronics Devices for Microelectronics - From Spin-transfer Torque to Spin- orbit Torque

  S. Fukami, H. Sato, M. Yamanouchi, S. Ikeda, F. Matsukura, H. Ohno

  2014 19TH ASIA AND SOUTH PACIFIC DESIGN AUTOMATION CONFERENCE (ASP-DAC) 684 - 691 2014年 [査読有り][通常論文]
   

  Recent advances in spintronics devices make it possible to open a new era of microelectronics. In this paper, we review the spintronics devices utilizing spin-transfer torques (STTs) and spin-orbit torques (SOTs) developed in recent years. The progresses of two-terminal STT device with CoFeB-MgO based magnetic tunnel junction (MTJ), three-terminal magnetic domain wall (DW) motion device with Co/Ni multilayer, and three-terminal SOT device with Cu-based channel are described. Integrated circuits with the developed spintronics devices are also reviewed.
• Electric Field-Induced Magnetization Switching in CoFeB-MgO-Static Magnetic Field Angle Dependence

  Shun Kanai, Michihiko Yamanouchi, Shoji Ikeda, Yoshinobu Nakatani, Fumihiro Matsukura, Hideo Ohno

  IEEE TRANSACTIONS ON MAGNETICS 50 1 article number 4200103  2014年01月 [査読有り][通常論文]
   

  We investigate switching probabilities of electric field-induced magnetization switching in CoFeB/MgO based magnetic tunnel junction with perpendicular magnetic easy axis under static magnetic field with various directions. The switching takes place through magnetization precession with the period determined by the magnitude of the in-plane component of magnetic field. The experimental results are well reproduced by macro-spin simulation. The simulation reveals that decoherence induced by thermal fluctuations and/or other effects limit the switching probabilities in the present system.
• Magnetotransport measurements of current induced effective fields in Ta/CoFeB/MgO

  Chaoliang Zhang, Michihiko Yamanouchi, Hideo Sato, Shunsuke Fukami, Shoji Ikeda, Fumihiro Matsukura, Hideo Ohno

  APPLIED PHYSICS LETTERS 103 26 262407  2013年12月 [査読有り][通常論文]
   

  We evaluate current-induced effective magnetic fields in perpendicularly magnetized Ta/CoFeB/MgO structures from the external magnetic field angle dependence of the Hall resistance. We confirm the presence of two components of effective fields. The dependence of their magnitudes on Ta thickness implies that both components are related to the spin current in Ta layer generated by the spin Hall effect. (C) 2013 AIP Publishing LLC.
• Influence of heavy ion irradiation on perpendicular-anisotropy CoFeB-MgO magnetic tunnel junctions

  Daisuke Kobayashi, Yuya Kakehashi, Kazuyuki Hirose, Shinobu Onoda, Takahiro Makino, Takeshi Ohshima, Shoji Ikeda, Michihiko Yamanouchi, Hideo Sato, Eli Christopher Enobio, Tetsuo Endoh, Hideo Ohno

  Proceedings of the European Conference on Radiation and its Effects on Components and Systems, RADECS 2013年10月28日 [査読有り][通常論文]
   

  A non-volatile memory element that is called a perpendicular-anisotropy magnetic tunnel junction has been fabricated in a CoFeB/MgO/CoFeB film stack technology. It exhibits two stable resistance values, high or low, depending on the relative direction of magnetization of the two ferromagnetic CoFeB layers. After programmed into the high resistance state with a current injection scheme based on the spin transfer torque theory, the tunnel junction has been exposed to 15-MeV Si ions in different voltage stress conditions. It has been observed that the tested structure remains in the programmed high resistance state after received the bombardments of several tens of Si ions and more, even under the stressed situations. A time-domain analysis has proven that this result is due to the perfect immunity of the tested magnetic tunnel junction to single event upsets. A resistance degradation due to the heavy-ion irradiation has been detected through a precise parameter analysis based on a tunneling theory but negligibly small, 1%.
• Demonstration of a Nonvolatile Processor Core Chip with Software-Controlled Three-Terminal MRAM Cells for Standby-Power Critical Applications

  R. Nebashi, Y. Tsuji, H. Honjo, N. Sakimura, A. Morioka, K. Tokutome, S. Miura, S. Fukami, M. Yamanouchi, K. Kinoshita, T. Hanyu, T. Endoh, N. Kasai, H. Ohno, T. Sugibayashi

  2013 International Conference on Solid State Devices and Materials (SSDM) M-8-3 1102 - 1103 2013年09月24日 [査読有り][通常論文]
  
• In-plane magnetic field dependence of electric field-induced magnetization switching

  S. Kanai, Y. Nakatani, M. Yamanouchi, S. Ikeda, F. Matsukura, H. Ohno

  APPLIED PHYSICS LETTERS 103 7 072408  2013年08月 [査読有り][通常論文]
   

  Electric field-induced magnetization switching through magnetization precession is investigated as a function of in-plane component of external magnetic field for a CoFeB/MgO-based magnetic tunnel junction with perpendicular easy axis. The switching probability is an oscillatory function of the duration of voltage pulses and its magnitude and period depend on the magnitude of in-plane magnetic field. Experimental results are compared with simulated ones by using Landau-Lifshitz-Gilbert-Langevin equation, and possible factors determining the probability are discussed. (C) 2013 AIP Publishing LLC.
• Depinning probability of a magnetic domain wall in nanowires by spin-polarized currents

  S. Fukami, M. Yamanouchi, S. Ikeda, H. Ohno

  NATURE COMMUNICATIONS 4 2293  2013年08月 [査読有り][通常論文]
   

  Current-induced magnetic domain wall motion is attractive for manipulating magnetization direction in spintronics devices, which open a new era of electronics. Up to now, in spite of a crucial significance to applications, investigation on a current-induced domain wall depinning probability, especially in sub-nano to a-few-nanosecond range has been lacking. Here we report on the probability of the depinning in perpendicularly magnetized Co/Ni nanowires in this timescale. A high depinning probability was obtained even for 2-ns pulses with a current density of less than 10(12)Am(-2). A one-dimensional Landau-Lifshitz-Gilbert calculation taking into account thermal fluctuations reproduces well the experimental results. We also calculate the depinning probability as functions of various parameters and found that parameters other than the coercive field do not affect the transition width of the probability. These findings will allow one to design high-speed and reliable magnetic devices based on the domain wall motion.
• CoNi Films with Perpendicular Magnetic Anisotropy Prepared by Alternate Monoatomic Layer Deposition

  Shunsuke Fukami, Hideo Sato, Michihiko Yamanouchi, Shoji Ikeda, Hideo Ohno

  APPLIED PHYSICS EXPRESS 6 7 073010  2013年07月 [査読有り][通常論文]
   

  We investigate the magnetic properties of CoNi and CoPt films prepared by an alternate monoatomic layer deposition and discuss the possible existence of a metastable superlattice structure. We find that, as has been reported for the CoPt and CoPd films, the CoNi film also exhibits a perpendicular magnetic anisotropy when the monoatomic Co and Ni layers are stacked alternately, suggesting the possible formation of superlattice structure. Since the CoNi film contains neither noble nor rare-earth metals, it should be an attractive material system for applications. (C) 2013 The Japan Society of Applied Physics
• MgO/CoFeB/Ta/CoFeB/MgO Recording Structure in Magnetic Tunnel Junctions With Perpendicular Easy Axis

  Hideo Sato, Michihiko Yamanouchi, Shoji Ikeda, Shunsuke Fukami, Fumihiro Matsukura, Hideo Ohno

  IEEE TRANSACTIONS ON MAGNETICS 49 7 4437 - 4440 2013年07月 [査読有り][通常論文]
   

  Junction size (D) dependence of thermal stability factor (Delta) and intrinsic critical current (I-Co) were investigated for MgO/CoFeB/Ta/CoFeB/MgO recording structure in magnetic tunnel junctions (MTJs) having a CoFeB reference layer and a synthetic ferrimagnetic (SyF) reference layer. Delta of the recording structure shows almost constant value down to 40 nm, whereas I-Co shows a linear dependence on the recording layer area, as similarly observed in recording structure with single-interface. Average absolute intrinsic critical current density is 3.5 MA/cm(2), which is comparable to previously reported value for recording structure with single-interface. A MgO/CoFeB(1.4)/Ta(0.4)/CoFeB(1.0)/MgO double-interface recording structure in MTJ with SyF reference layer shows Delta of 59 at D = 29 nm.
• Electrical endurance of Co/Ni wire for magnetic domain wall motion device

  S. Fukami, M. Yamanouchi, H. Honjo, K. Kinoshita, K. Tokutome, S. Miura, S. Ikeda, N. Kasai, H. Ohno

  Applied Physics Letters 102 22 222410  2013年06月03日 [査読有り][通常論文]
   

  We investigated electrical endurance of perpendicularly magnetized Co/Ni wires, which are a promising candidate material system for current-induced domain wall motion device. Monitoring the wire resistance while applying dc stress is shown to be a promising way to evaluate the electrical breakdown. An electromigration model describes well the observed time-to-failure as a function of temperature and current density. The dc stress current density which leads to 10-yr lifetime with 50% failure at 150 °C was twice as large as the threshold current density for domain wall motion, suggesting that the device with Co/Ni wire is highly durable against electrical stresses. © 2013 AIP Publishing LLC.
• Size dependence of magnetic properties of nanoscale CoFeB-MgO magnetic tunnel junctions with perpendicular magnetic easy axis observed by ferromagnetic resonance

  Kotaro Mizunuma, Michihiko Yamanouchi, Hideo Sato, Shoji Ikeda, Shun Kanai, Fumihiro Matsukura, Hideo Ohno

  Applied Physics Express 6 6 063002  2013年06月 [査読有り][通常論文]
   

  The junction diameter D dependence of effective magnetic fields in a recording layer of CoFeB-MgO magnetic tunnel junctions with perpendicular magnetic easy axis is evaluated by ferromagnetic resonance measurements using the homodyne detection technique. The effective perpendicular magnetic field increases with decreasing D, which reflects mainly the reduction of the demagnetizing factor normal to the film plane. The stray field from a reference layer also increases with reducing D, which is in agreement with the D dependence of the shift field of the center of minor resistance versus perpendicular magnetic field curves with respect to zero magnetic field. © 2013 The Japan Society of Applied Physics.
• Enhanced interface perpendicular magnetic anisotropy in Ta vertical bar CoFeB vertical bar MgO using nitrogen doped Ta underlayers

  Jaivardhan Sinha, Masamitsu Hayashi, Andrew J. Kellock, Shunsuke Fukami, Michihiko Yamanouchi, Hideo Sato, Shoji Ikeda, Seiji Mitani, See-hun Yang, Stuart S. P. Parkin, Hideo Ohno

  APPLIED PHYSICS LETTERS 102 24 242405  2013年06月 [査読有り][通常論文]
   

  We show that the magnetic characteristics of Ta vertical bar CoFeB vertical bar MgO magnetic heterostructures are strongly influenced by doping the Ta underlayer with nitrogen. In particular, the saturation magnetization drops upon doping the Ta underlayer, suggesting that the doped underlayer acts as a boron diffusion barrier. In addition, the thickness of the magnetic dead layer decreases with increasing nitrogen doping. Surprisingly, the interface magnetic anisotropy increases to similar to 1.8 erg/cm(2) when an optimum amount of nitrogen is introduced into the Ta underlayer. These results show that nitrogen doped Ta serves as a good underlayer for spintronic applications including magnetic tunnel junctions and domain wall devices. (C) 2013 AIP Publishing LLC.
• Two-barrier stability that allows low-power operation in current-induced domain-wall motion

  Kab-Jin Kim, Ryo Hiramatsu, Tomohiro Koyama, Kohei Ueda, Yoko Yoshimura, Daichi Chiba, Kensuke Kobayashi, Yoshinobu Nakatani, Shunsuke Fukami, Michihiko Yamanouchi, Hideo Ohno, Hiroshi Kohno, Gen Tatara, Teruo Ono

  NATURE COMMUNICATIONS 4 2011  2013年06月 [査読有り][通常論文]
   

  Energy barriers in magnetization reversal dynamics have long been of interest because the barrier height determines the thermal stability of devices as well as the threshold force triggering their dynamics. Especially in memory and logic applications, there is a dilemma between the thermal stability of bit data and the operation power of devices, because larger energy barriers for higher thermal stability inevitably lead to larger magnetic fields (or currents) for operation. Here we show that this is not the case for current-induced magnetic domain-wall motion induced by adiabatic spin-transfer torque. By quantifying domain-wall depinning energy barriers by magnetic field and current, we find that there exist two different pinning barriers, extrinsic and intrinsic energy barriers, which govern the thermal stability and threshold current, respectively. This unique two-barrier system allows low-power operation with high thermal stability, which is impossible in conventional single-barrier systems.
• Three terminal magnetic tunnel junction utilizing the spin Hall effect of iridium-doped copper

  Michihiko Yamanouchi, Lin Chen, Junyeon Kim, Masamitsu Hayashi, Hideo Sato, Shunsuke Fukami, Shoji Ikeda, Fumihiro Matsukura, Hideo Ohno

  APPLIED PHYSICS LETTERS 102 21 212408  2013年05月 [査読有り][通常論文]
   

  We show a three terminal magnetic tunnel junction (MTJ) with a 10-nm thick channel based on an interconnection material Cu with 10% Ir doping. By applying a current density of less than 10(12) A m(-2) to the channel, depending on the current direction, switching of a MTJ defined on the channel takes place. We show that spin transfer torque (STT) plays a critical role in determining the threshold current. By assuming the spin Hall effect in the channel being the source of the STT, the lower bound of magnitude of the spin Hall angle is evaluated to be 0.03. (C) 2013 AIP Publishing LLC.
• Magnetic properties of MgO-[Co/Pt] multilayers with a CoFeB insertion layer

  S. Ishikawa, H. Sato, M. Yamanouchi, S. Ikeda, S. Fukami, F. Matsukura, H. Ohno

  JOURNAL OF APPLIED PHYSICS 113 17 17C721  2013年05月 [査読有り][通常論文]
   

  Magnetic properties of MgO-[Co/Pt] multilayers with a CoFeB insertion layer were investigated and the structure was adopted as a recording layer in magnetic tunnel junctions (MTJs) with perpendicular magnetic easy-axis to attain a high thermal stability. Perpendicular easy-axis was obtained with the Pt thickness range of 0.6-1.2 nm and the CoFeB thickness range of 0.6-1.5 nm. As-made MTJs employing the CoFeB-[Co/Pt] multilayer structure as a recording layer showed tunnel magnetoresistance of 40% on average. A high thermal stability factor over 200 was obtained in the MTJs with the size of 25 nm in diameter. (C) 2013 American Institute of Physics.
• Layer thickness dependence of the current-induced effective field vector in Ta vertical bar CoFeB vertical bar MgO

  Junyeon Kim, Jaivardhan Sinha, Masamitsu Hayashi, Michihiko Yamanouchi, Shunsuke Fukami, Tetsuhiro Suzuki, Seiji Mitani, Hideo Ohno

  NATURE MATERIALS 12 3 240 - 245 2013年03月 [査読有り][通常論文]
   

  Current-induced effective magnetic fields can provide efficient ways of electrically manipulating the magnetization of ultrathin magnetic heterostructures. Two effects, known as the Rashba spin orbit field and the spin Hall spin torque, have been reported to be responsible for the generation of the effective field. However, a quantitative understanding of the effective field, including its direction with respect to the current flow, is lacking. Here we describe vector measurements of the current-induced effective field in Ta vertical bar CoFeB vertical bar MgO heterostructrures. The effective field exhibits a significant dependence on the Ta and CoFeB layer thicknesses. In particular, a 1 nm thickness variation of the Ta layer can change the magnitude of the effective field by nearly two orders of magnitude. Moreover, its sign changes when the Ta layer thickness is reduced, indicating that there are two competing effects contributing to it. Our results illustrate that the presence of atomically thin metals can profoundly change the landscape for controlling magnetic moments in magnetic heterostructures electrically.
• Low-current domain wall motion MRAM with perpendicularly magnetized CoFeB/MgO magnetic tunnel junction and underlying hard magnets

  T. Suzuki, H. Tanigawa, Y. Kobayashi, K. Mori, Y. Ito, Y. Ozaki, K. Suemitsu, T. Kitamura, K. Nagahara, E. Kariyada, N. Ohshima, S. Fukami, M. Yamanouchi, S. Ikeda, M. Hayashi, M. Sakao, H. Ohno

  Digest of Technical Papers - Symposium on VLSI Technology 2013年 

  We have developed magnetic domain wall (DW) motion cells with a perpendicularly magnetized CoFeB free layer and underlying hard magnets. Low current writing operation of 0.16 mA and a high MR ratio of 80% were attained for the 130-nm-wide free layer. Write/read operation for a 16kb array and high endurance features were also confirmed. © 2013 JSAP.
• Comprehensive study of CoFeB-MgO magnetic tunnel junction characteristics with single- and double-interface scaling down to 1X nm

  H. Sato, T. Yamamoto, M. Yamanouchi, S. Ikeda, S. Fukami, K. Kinoshita, F. Matsukura, N. Kasai, H. Ohno

  2013 IEEE INTERNATIONAL ELECTRON DEVICES MEETING (IEDM) 6724550  2013年 [査読有り][通常論文]
   

  We study characteristics of CoFeB-MgO magnetic tunnel junction with perpendicular easy-axis (p-MTJ) at a reduced dimension down to 1X nm fabricated by hard-mask process. CoFeB-MgO p-MTJ with double-interface shows higher thermal stability down to 1X nm than that with single-interface. Thermal stability factor of 58 and intrinsic critical current of 24 mu A are obtained in the CoFeB-MgO magnetic tunnel junction with perpendicular easy-axis using double-interface structure at a diameter of 20 nm phi.
• Spin

  S. Ikeda, H. Sato, M. Yamanouchi, H. Gan, K. Miura, K. Mizunuma, S. Kanai, S. Fukami, F. Matsukura, N. Kasai, H. Ohno

  Recent progress of perpendicular anisotropy magnetic tunnel junctions for nonvolatile VLSI 2 3 1240003(1) - 1240003(12) 2012年12月04日 [査読有り][通常論文]
  
• Recent progress of perpendicular anisotropy magnetic tunnel junctions for nonvolatile VLSI

  S. Ikeda, H. Sato, M. Yamanouchi, H. Gan, K. Miura, K. Mizunuma, S. Kanai, S. Fukami, F. Matsukura, N. Kasai, H. Ohno

  SPIN 2 1240003  2012年12月 [査読有り][通常論文]
  
• Boron Composition Dependence of Magnetic Anisotropy and Tunnel Magnetoresistance in MgO/CoFe(B) Based Stack Structures

  Shoji Ikeda, Ryohei Koizumi, Hideo Sato, Michihiko Yamanouchi, Katsuya Miura, Kotaro Mizunuma, Huadong Gan, Fumihiro Matsukura, Hideo Ohno

  IEEE TRANSACTIONS ON MAGNETICS 48 11 3829 - 3832 2012年11月 [査読有り][通常論文]
   

  We investigated magnetic anisotropy and tunnelmagnetoresistance (TMR) properties in MgO/(Co0.25Fe0.75)(100-x)B-x stack structures with, x = 0, 15, 20, and 25 (in at.%). After annealing at 350 degrees C, the easy axis of magnetization switches from in-plane to perpendicular direction in 1.5-nm-thick CoFeB with the B composition near x = 15. The effective magnetic anisotropy energy density (K-eff) shows a maximum of 1.9 x 10(5) J/m(2) in the 1.5 nm-thick CoFeB film with x = 20 annealed at 350 degrees C. K-eff is determined by the competition between contributions of interface anisotropy energy per effective CoFeB thickness (K-i/t*, where t* is the effective CoFeB layer thickness) and demagnetization energy (-M-s(2)/2 mu(0)). Bulk magnetic anisotropy energy (K-b) is negligibly small with comparison to those two terms. To obtain MgO/ferromagnetic stack structure with a high K-eff, materials and structures that reduce demagnetization energy while maintaining a high K-i and a thin t* have to be explored. In MTJs with the higher B compositions, high TMR ratio is obtained at higher annealing temperature. High TMR ratio of 136% is observed in a MTJ with x = 25 annealed at 350 degrees C.
• Electric field-induced magnetization reversal in a perpendicular-anisotropy CoFeB-MgO magnetic tunnel junction

  S. Kanai, M. Yamanouchi, S. Ikeda, Y. Nakatani, F. Matsukura, H. Ohno

  APPLIED PHYSICS LETTERS 101 12 022414  2012年09月 [査読有り][通常論文]
   

  The electric field-induced similar to 180 degrees magnetization reversal is realized for a sputtered CoFeB/MgO-based magnetic tunnel junction with perpendicular magnetic easy axis in a static external magnetic field. Application of bias voltage with nanoseconds duration results in a temporal change of magnetic easy axis in the free layer CoFeB to in-plane, which induces precessional motion of magnetization in the free layer. The magnetization reversal takes place when the bias voltage pulse duration is adjusted to a half period of the precession. We show that the back and forth magnetization reversal can be observed by using successive application of half-period voltage pulses. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4753816]
• Scalability Prospect of Three-Terminal Magnetic Domain-Wall Motion Device

  Shunsuke Fukami, Nobuyuki Ishiwata, Naoki Kasai, Michihiko Yamanouchi, Hideo Sato, Shoji Ikeda, Hideo Ohno

  IEEE TRANSACTIONS ON MAGNETICS 48 7 2152 - 2157 2012年07月 [査読有り][通常論文]
   

  We studied a scaling property of a three-terminal domain wall (DW)-motion device, which is one of the promising candidates for future low-power nonvolatile memory and logic-in-memory architecture. Using several assumptions, we derived the scaling factor of the switching current, switching time, resistance of the write-current path, and data storage stability. We also quantitatively evaluated the variation of these parameters with the device size. It was found that the switching current and time decrease almost linearly with the device size, while the variation of the resistance of the write-current path is negligible. The switching current and time for 32-nm-wide device are less than 100 mu A and 2 ns, respectively. A required critical field which assures a sufficient thermal stability of stored data was calculated for each generation. Furthermore, future issues and intrinsic limiter for the size reduction were discussed.
• Observation of magnetic domain-wall dynamics transition in Co/Ni multilayered nanowires

  Kab-Jin Kim, D. Chiba, K. Kobayashi, S. Fukami, M. Yamanouchi, H. Ohno, Soong-Geun Je, Sug-Bong Choe, T. Ono

  APPLIED PHYSICS LETTERS 101 2 022407  2012年07月 [査読有り][通常論文]
   

  We observe a transition of domain-wall (DW) dynamics in ferromagnetic wires made of Co/Ni multilayers by use of transport measurement. As the wire width reduces, DW dynamics exhibits a transition from dendrite growth to pure DW motion. The threshold width is found to be about 300 nm and strongly depends on the relative dragging direction of the magnetic field and the current on DW: parallel (antiparallel) direction results in much smaller (larger) threshold width. It should be considered as a building block for DW-motion-based device applications. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4733667]
• Current-Induced Domain Wall Motion in Perpendicularly Magnetized Co/Ni Nanowire under In-Plane Magnetic Fields

  Yoko Yoshimura, Tomohiro Koyama, Daichi Chiba, Yoshinobu Nakatani, Shunsuke Fukami, Michihiko Yamanouchi, Hideo Ohno, Teruo Ono

  APPLIED PHYSICS EXPRESS 5 6 063001  2012年06月 [査読有り][通常論文]
   

  We have investigated current-induced domain wall (DW) motion in a perpendicularly magnetized Co/Ni nanowire under in-plane (hard-axis) and perpendicular (easy-axis) external magnetic fields. The DW velocity was found to be almost independent of them in the range of +/- 50 Oe. The result shows that reliable device operation against an external magnetic field disturbance can be achieved using the present system. (C) 2012 The Japan Society of Applied Physics
• Spatial control of magnetic anisotropy for current induced domain wall injection in perpendicularly magnetized CoFeB vertical bar MgO nanostructures

  Masamitsu Hayashi, Michihiko Yamanouchi, Shunsuke Fukami, Jaivardhan Sinha, Seiji Mitani, Hideo Ohno

  APPLIED PHYSICS LETTERS 100 19 192411  2012年05月 [査読有り][通常論文]
   

  Magnetic anisotropy of perpendicularly magnetized CoFeB vertical bar MgO films is spatially tailored using depth controlled Ar ion etching with patterned etching masks. Nanowires with patterned etching have significantly reduced coercivity compared to those without the etching. We show that the sign of the anisotropy can be locally changed by partially etching the MgO layer, and as a consequence, 90 degrees domain walls can be created at the boundary of etched/non-etched region. Direct current application to the nanowire can result in moving such 90 degrees domain walls, which can prove as an efficient mean to inject domain walls into perpendicularly magnetized nanowires. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4711016]
• Domain wall dynamics driven by spin transfer torque and the spin–orbit field

  M. Hayashi, Y. Nakatani, S. Fukami, M. Yamanouchi, S. Mitani, H. Ohno

  Journal of Physics Condensed Material 24 2 024221  2012年01月 [査読有り][通常論文]
   

  We have studied current-driven dynamics of domain walls when an in-plane magnetic field is present in perpendicularly magnetized nanowires using an analytical model and micromagnetic simulations. We model an experimentally studied system, ultrathin magnetic nanowires with perpendicular anisotropy, where an effective in-plane magnetic field is developed when current is passed along the nanowire due to the Rashba-like spin-orbit coupling. Using a one-dimensional model of a domain wall together with micromagnetic simulations, we show that the existence of such in-plane magnetic fields can either lower or raise the threshold current needed to cause domain wall motion. In the presence of the in-plane field, the threshold current differs for positive and negative currents for a given wall chirality, and the wall motion becomes sensitive to out-of-plane magnetic fields. We show that large non-adiabatic spin torque can counteract the effect of the in-plane field.
• CoFeB Thickness Dependence of Thermal Stability Factor in CoFeB/MgO Perpendicular Magnetic Tunnel Junctions

  H. Sato, M. Yamanouchi, K. Miura, S. Ikeda, R. Koizumi, F. Matsukura, H. Ohno

  IEEE MAGNETICS LETTERS 3 3000204  2012年 [査読有り][通常論文]
   

  Thermal stability factor Delta of the recording layer was studied in perpendicular anisotropy CoFeB/MgO magnetic tunnel junctions (p-MTJs) with various CoFeB recording layer thicknesses and junction sizes. In all series of p-MTJs with different thicknesses, Delta is virtually independent of the junction sizes of 48-81 nm in diameter. The values of Delta increase linearly as the recording layer thickness increases. The slope of the linear fit is explained well by a model based on nucleation-type magnetization reversal.
• Origin of the collapse of tunnel magnetoresistance at high annealing temperature in CoFeB/MgO perpendicular magnetic tunnel junctions

  H. D. Gan, H. Sato, M. Yamanouchi, S. Ikeda, K. Miura, R. Koizumi, F. Matsukura, H. Ohno

  APPLIED PHYSICS LETTERS 99 25 252507  2011年12月 [査読有り][通常論文]
   

  We have investigated a tunnel magnetoresistance (TMR) ratio of CoFeB/MgO perpendicular magnetic tunnel junctions (p-MTJs) with a 40 nm diameter as a function of an annealing temperature T(a). The TMR ratio at room temperature (RT) increases with increasing T(a) and reaches 149% at T(a) = 350 degrees C, and further increase of T(a) results in a strong reduction of the TMR ratio, i.e., 2% at T(a) = 400 degrees C. The temperature dependence of the junction resistance versus magnetic field loops reveals that the reduced TMR ratio at RT is due to the disappearance of a stable antiparallel magnetization configuration. We find that reduction of dipole coupling restores the TMR ratio. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3671669]
• Junction size effect on switching current and thermal stability in CoFeB/MgO perpendicular magnetic tunnel junctions

  H. Sato, M. Yamanouchi, K. Miura, S. Ikeda, H. D. Gan, K. Mizunuma, R. Koizumi, F. Matsukura, H. Ohno

  APPLIED PHYSICS LETTERS 99 4 042501  2011年07月 [査読有り][通常論文]
   

  Junction size dependence of critical current (I(C0)) for spin transfer torque switching and thermal stability factor (E/k(B)T) was examined in CoFeB/MgO perpendicular magnetic tunnel junctions (p-MTJs). The I(C0) increased with increasing recording layer area (S(rec)). On the other hand, the E/k(B)T showed almost constant values even though the S(rec) was increased from similar to 1500 nm(2) (44 nm phi) to similar to 5000 nm(2) (76 nm phi). Both I(C0) and E/k(B)T behavior can be explained with assuming that the nucleation type magnetization reversal takes place in CoFeB/MgO p-MTJs. (C) 2011 American Institute of Physics. [doi:10.1063/1.3617429]
• Tunnel Magnetoresistance Properties of Double MgO-Barrier Magnetic Tunnel Junctions With Different Free-Layer Alloy Compositions and Structures

  Huadong Gan, Shoji Ikeda, Michihiko Yamanouchi, Katsuya Miura, Kotaro Mizunuma, Jun Hayakawa, Fumihiro Matsukura, Hideo Ohno

  IEEE TRANSACTIONS ON MAGNETICS 47 6 1567 - 1570 2011年06月 [査読有り][通常論文]
   

  We investigated tunnel magnetoresistance (TMR) properties in double MgO-barrier magnetic tunnel junctions (DMTJs) with (Co25Fe75)(100-x)B-x free-layers with x = 15, 20, and 25 (in at.%) sputtered at different power. The TMR ratio of DMTJs increased with sputtering power, which is ascribed to the B composition reduction in the CoFeB free-layer with increasing sputtering power. The x-ray diffraction measurement showed that crystallization into (001)-oriented texture of CoFeB film sandwiched between the two MgO-layers as well as an improvement of (001) orientation of top MgO-barrier are realized. The TMR ratio over 200% was obtained in DMTJs with a (Co25Fe75)(85)B-15 free-layer sputtered at 0.88 and 1.77 W/cm(2)
• Tunnel magnetoresistance properties and annealing stability in perpendicular anisotropy MgO-based magnetic tunnel junctions with different stack structures

  K. Mizunuma, S. Ikeda, H. Sato, M. Yamanouchi, H. D. Gan, K. Miura, H. Yamamoto, J. Hayakawa, F. Matsukura, H. Ohno

  JOURNAL OF APPLIED PHYSICS 109 7 07C711  2011年04月 [査読有り][通常論文]
   

  We have investigated the effect of stack structures on tunnel magnetoresistance (TMR) properties in perpendicular anisotropy MgO-based magnetic tunnel junctions (p-MTJs) with CoFe/Pd multilayer and CoFeB insertion. By adopting Ta and Ru cap-layers, the TMR ratios of 113 and 106% are obtained at annealing temperature (T-a) of 325 degrees C, respectively. Particularly, the Ru cap-layer is effective in realizing a TMR ratio of 100% at T-a = 350 degrees C. By replacing (Co25Fe75)(80)B-20 with (Co25Fe75)(85)B-15, the TMR ratio increased quickly at low Ta, reaching a maximum of 120% at T-a = 300 degrees C. (C) 2011 American Institute of Physics. [doi:10.1063/1.3554092]
• Current-induced effective field in perpendicularly magnetized Ta/CoFeB/MgO wire

  T. Suzuki, S. Fukami, N. Ishiwata, M. Yamanouchi, S. Ikeda, N. Kasai, H. Ohno

  APPLIED PHYSICS LETTERS 98 14 142502  2011年04月 [査読有り][通常論文]
   

  The current-induced effective field in perpendicularly magnetized Ta/CoFeB/MgO wire was investigated. A threshold field decrease of 6.4 kOe/mA was observed by measuring the threshold field of Hall resistance versus the magnetic field curve with various bias currents. The decrease was probably caused by the in-plane effective field, mainly due to the Rashba effect. The effective field of the Ta/CoFeB/MgO wire was smaller and opposite in direction compared to that of Pt/Co/AlO(x) previously reported. (C) 2011 American Institute of Physics. [doi:10.1063/1.3579155]
• Dependence of magnetic anisotropy on MgO thickness and buffer layer in Co20Fe60B20-MgO structure

  M. Yamanouchi, R. Koizumi, S. Ikeda, H. Sato, K. Mizunuma, K. Miura, H. D. Gan, F. Matsukura, H. Ohno

  Journal of Applied Physics 109 7 07C712-(1) - 07C712-(3) 2011年04月01日 [査読有り][通常論文]
   

  We investigated the dependence of perpendicular magnetic anisotropy in CoFeB-MgO on the MgO layer thickness. Magnetization curves show that a clear perpendicular magnetic easy axis is obtainable in a 1.5-nm thick CoFeB layer by depositing MgO of more than three monolayers. We investigated anisotropy in CoFeB-MgO deposited on four different buffer layers. Results show that a counter interface of CoFeB-nonmagnetic metal affects the perpendicular anisotropy of CoFeB/MgO. © 2011 American Institute of Physics.
• Pd Layer Thickness Dependence of Tunnel Magnetoresistance Properties in CoFeB/MgO-Based Magnetic Tunnel Junctions with Perpendicular Anisotropy CoFe/Pd Multilayers

  Kotaro Mizunuma, Michihiko Yamanouchi, Shoji Ikeda, Hideo Sato, Hiroyuki Yamamoto, Hua-Dong Gan, Katsuya Miura, Jun Hayakawa, Fumihiro Matsukura, Hideo Ohno

  APPLIED PHYSICS EXPRESS 4 2 023002  2011年02月 [査読有り][通常論文]
   

  The authors investigated tunnel magnetoresistance (TMR) properties in [CoFe/Pd]-multilayer/CoFeB/MgO/CoFeB/[Pd/CoFe]-multilayer magnetic tunnel junctions (MTJs) having two different Pd layer thicknesses. By reducing the Pd layer thickness from 1.2 to 0.2 nm, the TMR ratio was enhanced from 7 to 101% at the annealing temperature (T(a)) of 300 degrees C. The thin Pd layers resulted in high residual B concentration in the CoFeB layer after high-T(a) annealing and in the suppression of crystallization of the CoFeB layer from the fcc(111)-Pd layer side. (C) 2011 The Japan Society of Applied Physics
• Current-induced domain wall motion in perpendicularly magnetized CoFeB nanowire

  S. Fukami, T. Suzuki, Y. Nakatani, N. Ishiwata, M. Yamanouchi, S. Ikeda, N. Kasai, H. Ohno

  APPLIED PHYSICS LETTERS 98 8 082504  2011年02月 [査読有り][通常論文]
   

  Current-induced domain wall motion in perpendicularly magnetized CoFeB nanowires with a stack structure of Ta(1.0 nm)/CoFeB(1.2 nm)/MgO(2.0 nm)/Ta(1.0 nm) was investigated. Domain wall motion driven by adiabatic spin-transfer torque was observed at a current of about 74 mu A, corresponding to a current density of 6.2 x 10(7) A/cm(2). The obtained results were compared with those of a micromagnetic simulation and the spin polarization of the CoFeB was estimated to be 0.72. (C) 2011 American Institute of Physics. [doi:10.1063/1.3558917]
• Domain Structure in CoFeB Thin Films With Perpendicular Magnetic Anisotropy

  Michihiko Yamanouchi, Albrecht Jander, Pallavi Dhagat, Shoji Ikeda, Fumihiro Matsukura, Hideo Ohno

  IEEE MAGNETICS LETTERS 2 3000304  2011年 [査読有り][通常論文]
   

  Domain structures in CoFeB-MgO thin films with a perpendicular easy magnetization axis were observed by magneto-optic Kerr-effect microscopy at various temperatures. The domain-wall surface energy was obtained by analyzing the spatial period of the stripe domains and fitting established domain models to the period. In combination with superconducting quantum interference device measurements of magnetization and anisotropy energy, this leads to an estimate of the exchange stiffness and domain-wall width in these films. These parameters are essential for determining whether domain walls will form in patterned structures and devices made of such materials.
• A 32-Mb SPRAM With 2T1R Memory Cell, Localized Bi-Directional Write Driver and '1'/'0' Dual-Array Equalized Reference Scheme

  Riichiro Takemura, Takayuki Kawahara, Katsuya Miura, Hiroyuki Yamamoto, Jun Hayakawa, Nozomu Matsuzaki, Kazuo Ono, Michihiko Yamanouchi, Kenchi Ito, Hiromasa Takahashi, Shoji Ikeda, Haruhiro Hasegawa, Hideyuki Matsuoka, Hideo Ohno

  IEEE JOURNAL OF SOLID-STATE CIRCUITS 45 4 869 - 879 2010年04月 [査読有り][通常論文]
   

  A 32-Mb SPin-transfer torque RAM (SPRAM) chip was demonstrated with an access time of 32 ns and a cell write-time of 40 ns at a supply voltage of 1.8 V. The chip was fabricated with 150-nm CMOS and a 100 x 200-nm tunnel magneto-resistive (TMR) device element. A required thermal stability of 67 of the TMR device was estimated by taking into account the disturbances during read operations and data retention periods of 10 years for nonvolatile operation. The 32-Mb SPRAM chip features three circuit technologies suitable for a large-scale array: 1) a two-transistor, one-resistor (2T1R) type memory cell for achieving a sufficiently large write current despite the small cell size, 2) a compact read/write separated hierarchy bit/source-line structure with a localized bi-directional write driver for efficiently distributing write current, and 3) a '1'/'0' dual-array equalized reference scheme for stable read operation.
• SPRAM with large thermal stability for high immunity to read disturbance and long retention for high-temperature operation

  K. Ono, T. Kawahara, R. Takemura, K. Miura, M. Yamanouchi, J. Hayakawa, K. Ito, H. Takahashi, H. Matsuoka, S. Ikeda, H. Ohno

  2009 Symposium on VLSI Technology 228 - 229 2009年06月 [査読有り][通常論文]
  
• 32-Mb 2T1R SPRAM with localized bi-directional write driver and ‘1’/‘0’ dual-array equalized reference cell

  R. Takemura, T. Kawahara, K. Miura, H. Yamamoto, J. Hayakawa, N. Matsuzaki, K. Ono, M. Yamanouchi, K. Ito, H. Takahashi, S. Ikeda, H. Hasegawa, H. Matsuoka, H. Ohno

  2009 Symposium on VLSI Circuits 84 - 85 2009年06月 [査読有り][通常論文]
  
• A disturbance-free read scheme and a compact stochastic-spin-dynamics-based MTJ circuit model for Gb-scale SPRAM

  K. Ono, T. Kawahara, R. Takemura, K. Miura, H. Yamamoto, M. Yamanouchi, J. Hayakawa, K. Ito, H. Takahashi, S. Ikeda, H. Hasegawa, H. Matsuoka, H. Ohno

  Technical Digest - International Electron Devices Meeting, IEDM 9.3.4 - 9.3.4 2009年 [査読有り][通常論文]
   

  A magnetic-tunnel-junction (MTJ) circuit model, which considers spin dynamics under finite temperature, electrical bias, a stochastic process, and spin-transfer torque, was developed. Switching behaviors simulated by this model were verified by experimental measurements. Moreover, a disturbance-free read scheme for Gbit-scale spin-transfer torque RAM (SPRAM) was also developed. The feasibility of this scheme was confirmed by circuit simulation using the model and on-chip measurement of switching probability. © 2009 IEEE.
• Current-induced magnetization switching in MgO barrier magnetic tunnel junctions with CoFeB-based synthetic ferrimagnetic free layers

  Jun Hayakawa, Shoji Ikeda, Katsuya Miura, Michihiko Yarnanouchi, Young Min Lee, Ryutaro Sasaki, Masahiko Ichimura, Kenchi Ito, Takayuki Kawahara, Riichiro Takemura, Toshiyasu Meguro, Fumihiro Matsukura, Hiromasa Takahashi, Hideyuki Matsuoka, Hideo Ohno

  IEEE TRANSACTIONS ON MAGNETICS 44 7 1962 - 1967 2008年07月 [査読有り][通常論文]
   

  We investigated the effect of using a synthetic ferrimagnetic (SyF) free layer in MgO-based magnetic tunnel junctions (MTJs) on current-induced magnetization switching (CIMS), particularly for application to spin-transfer torque random access memory (SPRAM). The employed SyF free layer had a Co40Fe40B20/Ru/Co40Fe40B20 and Co20Fe60B20/Ru/Co20Fe60B20 structures, and the MTJs (100 x (150-300) nm(2)) were annealed at 300 degrees C. The use of SyF free layer resulted in low intrinsic critical current density (J(c0)) without degrading the thermal-stability factor (E/k(B)T, where E, k(B), and Tare the energy potential, the Boltzmann constant, and temperature, respectively). When the two CoFeB layers of a strongly antiferromagnetically coupled SyF free layer had the same thickness, J(c0) was reduced to 2-4 X 10(6) A/cm(2). This low J(c0) may be due to the decreased effective volume under the large spin accumulation at the CoFeB/Ru. The E/k(B)T was over 60, resulting in a retention time of over ten years and suppression of the write current dispersion for SPRAM. The use of the SyF free layer also resulted in a bistable (parallel/antiparallel) magnetization configuration at zero field, enabling the realization of CIMS without the need to apply external fields to compensate for the offset field.
• TMR Design Methodology for SPin-Transfer Torque RAM (SPRAM) with Nonvolatile and SRAM Compatible Operations

  R. Takemura, T. Kawahara, J. Hayakawa, K. Miura, K. Ito, M. Yamanouchi, S. Ikeda, H. Takahashi, H. Matsuoka, H. Ohno

  Joint Non-Volatile Semiconductor Memory Workshop 2008, and 2008 International Conference on Memory Technology and Design (NVSMW/ICMTD) 54 54 - 56 2008年05月 [査読有り][通常論文]
  
• Universality classes for domain wall motion in the ferromagnetic semiconductor (Ga, Mn)As

  M. Yamanouchi, J. Ieda, F. Matsukura, S. E. Barnes, S. Maekawa, H. Ohno

  SCIENCE 317 5845 1726 - 1729 2007年09月 [査読有り][通常論文]
   

  Magnetic domain wall motion induced by magnetic fields and spin-polarized electrical currents is experimentally well established. A full understanding of the underlying mechanisms, however, remains elusive. For the ferromagnetic semiconductor (Ga, Mn)As, we have measured and compared such motions in the thermally activated subthreshold, or "creep," regime, where the velocity obeys an Arrhenius scaling law. Within this law, the clearly different exponents of the current and field reflect different universality classes, showing that the drive mechanisms are fundamentally different.
• Switching of tunnel magnetoresistance by domain wall motion in (Ga,Mn)As-based magnetic tunnel junctions

  M. Fukuda, M. Yamanouchi, F. Matsukura, H. Ohno

  APPLIED PHYSICS LETTERS 91 5 052503  2007年07月 [査読有り][通常論文]
   

  Switching of tunnel magnetoresistance in magnetic tunnel junctions (MTJs) has been achieved by magnetic domain wall motion in one of the electrodes. The fabricated devices have two (Ga,Mn)As-based MTJs with a common bottom (Ga,Mn)As electrode, in which the domain wall motion takes place both by magnetic field and by current. This configuration allows not only the observation of switching but also time-resolved detection of the position of the domain wall by the tunnel magnetoresistance. (c) 2007 American Institute of Physics.
• Domain wall resistance in perpendicularly magnetized (Ga,Mn) As

  D. Chiba, M. Yamanouchi, F. Matsukura, T. Dietl, H. Ohno

  JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 2 2078 - 2083 2007年03月 [査読有り][通常論文]
   

  Domain wall (DW) resistance in perpendicularly magnetized (Ga, Mn) As has been investigated. The observed DW resistance is decomposed into extrinsic and intrinsic contributions. The former is explained quantitatively by the zig-zaging current due to an abrupt polarity change of the Hall electric field at DW. The latter is consistent with the disorder-induced mixing of spin channels due to small non-adiabacity of carrier spins subject to spatially varying local magnetic moment and is shown to be an order of magnitude greater than a contribution from anisotropic magnetoresistance. (c) 2006 Elsevier B.V. All rights reserved.
• Current-assisted domain wall motion in ferromagnetic semiconductors

  Michihiko Yamanouchi, Daichi Chiba, Fumihiro Matsukura, Hideo Ohno

  JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 45 5A 3854 - 3859 2006年05月 [査読有り][通常論文]
   

  We investigated the effect of electrical currents on magnetization reversal in ferromagnetic semiconductors. We fabricated a Hall bar-shaped device with a stepped channel from (Ga,Mn)As and that with a partially gated channel from (In,Mn)As. These structures realize in-plane patterning of coercivity H-C and allow us to study the dynamics of domain walls under application of currents by monitoring the Hall resistance. In both devices, we show that there exists a region, where its H-C is strongly influenced by the direction of the applied current. In addition, we demonstrate the current induced domain wall movement under a fixed magnetic field. These phenomena can be observed at current density of 10(4) A/cm(2) lower. Possible mechanisms are discussed.
• Velocity of domain-wall motion induced by electrical current in the ferromagnetic semiconductor (Ga,Mn)As

  M Yamanouchi, D Chiba, F Matsukura, T Dietl, H Ohno

  PHYSICAL REVIEW LETTERS 96 9 096601  2006年03月 [査読有り][通常論文]
   

  Current-induced domain-wall motion with velocity spanning over 5 orders of magnitude up to 22 m/s has been observed by the magneto-optical Kerr effect in (Ga,Mn)As with perpendicular magnetic anisotropy. The data are employed to verify theories of spin transfer by the Slonczewski-like mechanism as well as by the torque resulting from spin-flip transitions in the domain-wall region. Evidence for domain-wall creep at low currents is found.
• Domain-wall resistance in ferromagnetic (Ga,Mn)As

  D Chiba, M Yamanouchi, F Matsukura, T Dietl, H Ohno

  PHYSICAL REVIEW LETTERS 96 9 096602  2006年03月 [査読有り][通常論文]
   

  A series of microstructures designed to pin domain walls (DWs) in (Ga,Mn)As with perpendicular magnetic anisotropy has been employed to determine extrinsic and intrinsic contributions to DW resistance. The former is explained quantitatively as resulting from a polarity change in the Hall electric field at DW. The latter is 1 order of magnitude greater than a term brought about by anisotropic magnetoresistance and is shown to be consistent with disorder-induced mistracking of the carrier spins subject to spatially varying magnetization.
• Control of magnetization reversal in ferromagnetic semiconductors by electrical means

  M. Yamanouchi, D. Chiba, F. Matsukura, H. Ohno

  Nature 428 539  2004年04月 [査読有り][通常論文]
  
• Current-induced domain-wall switching in a ferromagnetic semiconductor structure

  M. Yamanouchi, D. Chiba, F. Matsukura, H. Ohno

  Nature 428 6982 539 - 541 2004年04月01日 [査読有り][通常論文]
   

  Magnetic information storage relies on external magnetic fields to encode logical bits through magnetization reversal. But because the magnetic fields needed to operate ultradense storage devices are too high to generate, magnetization reversal by electrical currents is attracting much interest as a promising alternative encoding method. Indeed, spin-polarized currents can reverse the magnetization direction of nanometre-sized metallic structures through torque however, the high current densities of 107-10 8 A cm-2 that are at present required exceed the threshold values tolerated by the metal interconnects of integrated circuits. Encoding magnetic information in metallic systems has also been achieved by manipulating the domain walls at the boundary between regions with different magnetization directions, but the approach again requires high current densities of about 107 A cm-2. Here we demonstrate that, in a ferromagnetic semiconductor structure, magnetization reversal through domain-wall switching can be induced in the absence of a magnetic field using current pulses with densities below 105 A cm-2. The slow switching speed and low ferromagnetic transition temperature of our current system are impractical. But provided these problems can be addressed, magnetic reversal through electric pulses with reduced current densities could provide a route to magnetic information storage applications.
• Electrical magnetization reversal in ferromagnetic semiconductors

  Matsukura, F, Chiba, D, Yamanouchi, M, Ohno, H, Badawy, W, Moussa, W

  2004 International Conference on Mems, Nano and Smart Systems, Proceedings 128 - 128 2004年 [査読有り][通常論文]
  
• Electrical manipulation of magnetization reversal in a ferromagnetic semiconductor

  D. Chiba, H. Yamanouchi, F. Hatsukura, H. Ohno

  Science 301 5635 943 - 945 2003年08月15日 [査読有り][通常論文]
   

  We report electrical manipulation of magnetization processes in a ferromagnetic semiconductor, in which low-density carriers are responsible for the ferromagnetic interaction. The coercive force HC at which magnetization reversal occurs can be manipulated by modifying the carrier density through application of electric fields in a gated structure. Electrically assisted magnetization reversal, as well as electrical demagnetization, has been demonstrated through the effect. This electrical manipulation offers a functionality not previously accessible in magnetic materials and may become useful for reversing magnetization of nanoscale bits for ultrahigh-density information storage.
• Electric field effect on the magnetic properties of III-V ferromagnetic semiconductor (In, Mn)As and ((Al),Ga,Mn)As

  D Chiba, M Yamanouchi, F Matsukura, E Abe, Y Ohno, K Ohtani, H Ohno

  JOURNAL OF SUPERCONDUCTIVITY 16 1 179 - 182 2003年02月 [査読有り][通常論文]
   

  We have investigated the magnetotransport properties of field-effect transistors (FET) having a III-V ferromagnetic semiconductor channel layer. One can control not only the ferromagnetic transition temperature T-C but also the magnetization and the coercive force of (In,Mn) As channel layers isothermally and reversibly by gate electric fields. A small change of the magnetization upon application of gate electric fields is also observed in FETs with a (Ga,Mn) As channel. Results on a (Al,Ga,Mn) As channel FET are also presented.
• Electric Field Control of Ferromagnetism in III-V Ferromagnetic Semiconductor

  D. Chiba, M. Yamanouchi, F. Matsukura, Y. Ohno, K. Ohtani, H. Ohno

  Proceedings of the 26th International Conference on the Physics of Semiconductor F2.2  2002年07月 [査読有り][通常論文]
   

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MISC

• 強磁性酸化物SrRuO₃におけるワイル電子に起因したスピントルク

  山ノ内路彦 日本物理学会講演概要集(CD-ROM) 78 (2) 2023年
• Pt/SrRuO₃積層構造におけるスピン軌道トルクと磁壁の相互作用

  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
• Spin-orbit-torque induced magnetization switching for an ultra-thin MnGa grown on NiAl buffer layer

  Shimohashi Fumiaki, Nguyen Bao, Yamanouchi Michihiko, Uemura Tetsuya JSAP Annual Meetings Extended Abstracts 2019.2 2176 -2176 2019年09月04日
• Sign reversal of current-induced effective magnetic field in La_0.67Sr_0.33MnO₃ heterostructures

  Yamanouchi Michihiko, Oyamada Tatsuro, Ohta Hiromichi JSAP Annual Meetings Extended Abstracts 2019.1 1900 -1900 2019年02月25日
• La_0.67Sr_0.33MnO₃/2DES-LaAlO₃/SrTiO₃における特異な磁気輸送特性

  小山田 達郎, 太田 裕道, 山ノ内 路彦 応用物理学会学術講演会講演予稿集 2018.2 2021 -2021 2018年09月05日
• La_0.67Sr_0.33MnO₃/SrTiO₃ヘテロ構造における電流誘起有効磁場の膜厚依存性

  小山田 達郎, 片瀬 貴義, 太田 裕道, 山ノ内 路彦 応用物理学会学術講演会講演予稿集 2017.1 2047 -2047 2017年03月01日
• La_0.67Sr_0.33MnO₃/SrTiO₃におけるスイッチング磁界への電流誘起効果

  山ノ内 路彦, 小山田 達郎, 片瀬 貴義, 太田 裕道 応用物理学会学術講演会講演予稿集 2016.2 1933 -1933 2016年09月01日
• 27aKF-1 垂直磁化Co/Ni細線中の磁壁電流駆動におけるスピンホール効果の影響(スピントロニクス(磁化ダイナミクス),領域3(磁性,磁気共鳴))

  吉村 瑶子, 小山 知弘, 森山 貴広, Kim Kab-Jin, 千葉 大地, 仲谷 栄伸, 深見 俊輔, 山ノ内 路彦, 大野 英男, 小野 輝男 日本物理学会講演概要集 68 (2) 415 -415 2013年08月26日
• 27pXA-6 Current pulse width dependence of magnetic domain wall motion in the presence of bias magnetic field

  Kim Kab-Jin, Chiba D., Nakatani Y., Fukami S., Yamanouchi M., Ohno H., Ono T. 日本物理学会講演概要集 68 (1) 540 -540 2013年03月26日
• 20aCC-10 垂直磁化Co/Ni細線における面内磁場下の磁壁電流駆動(II)(20aCC スピントロニクス(磁化ダイナミクス),領域3(磁性,磁気共鳴))

  吉村 瑤子, 小山 知弘, 千葉 大地, 深見 俊輔, 山ノ内 路彦, 大野 英男, 仲谷 栄伸, 小野 輝男 日本物理学会講演概要集 67 (2) 427 -427 2012年08月24日
• 27aAA-9 垂直磁化Co/Ni細線における面内磁場下の磁壁電流駆動(27aAA スピントロニクス(磁気渦・磁壁・磁気抵抗・スピントルク),領域3(磁性,磁気共鳴))

  吉村 瑤子, 小山 知弘, 千葉 大地, 深見 俊輔, 山ノ内 路彦, 大野 英男, 仲谷 栄伸, 小野 輝男 日本物理学会講演概要集 67 (0) 533 -533 2012年 [査読無し][通常論文]
  
• High-speed and reliable domain wall motion device: Material design for embedded memory and logic application

  S. Fukami, M. Yamanouchi, T. Koyama, K. Ueda, Y. Yoshimura, K. J. Kim, D. Chiba, H. Honjo, N. Sakimura, R. Nebashi, Y. Kato, Y. Tsuji, A. Morioka, K. Kinoshita, S. Miura, T. Suzuki, H. Tanigawa, S. Ikeda, T. Sugibayashi, N. Kasai, T. Ono, H. Ohno Digest of Technical Papers - Symposium on VLSI Technology 61 -62 2012年 [査読無し][通常論文]
   

  High-speed capability and excellent reliability of a magnetic domain wall (DW) motion device required for embedded memory and logic-in-memory applications were achieved by optimizing the film stack structure of Co/Ni wire. Low-current with high-speed writing, high heat resistance, low error rate, wide operation range for temperature and magnetic field, high retention, and high endurance features were confirmed. © 2012 IEEE.
• 強磁性半導体における磁壁の電流駆動

  千葉 大地, 山ノ内 路彦, 松倉 文[ヒロ], 大野 英男 まぐね = Magnetics Japan 4 (8) 390 -395 2009年08月01日
• 22aWB-7 強磁性半導体(Ga,Mn)Asにおける磁壁のクリープ運動(実験)(微小領域磁性,領域3,磁性,磁気共鳴)

  松倉 文礼, 山ノ内 路彦, 大野 英男 日本物理学会講演概要集 62 (2) 452 -452 2007年08月21日
• 積層フェリ自由層トンネル磁気抵抗効果素子を備えたSPRAMのリードディスターブ耐性と書き込み電流のばらつきの低減

  三浦 勝哉, 河原 尊之, 竹村 理一郎, 早川 純, 山ノ内 路彦, 池田 正二, 佐々木 龍太郎, 伊藤 顕知, 高橋 宏昌, 松岡 秀行, 大野 英男 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 107 (194) 135 -138 2007年08月16日 

  磁性体メモリの一つであるSPin-transf torque RAM(SPRAM)は,高速動作,低電力化が可能な不揮発メモリとして期待されている.SPRAMはメモリセルとして,MgO障壁層を備えたトンネル磁気抵抗(TMR)素子を用いる.このTMR素子は,自由層に用いる磁性体の熱安定性を大きくすることによって,読み出しの際の誤書き込み(ディスターブ)および書き込み電流のばらつきを低減することができる.熱安定性の大きいと期待される積層フェリ(SyF)自由層を用いた場合,他の構造と比べて読み出しディスターブと書き込み電流のばらつきがともに抑制されており,読み出しと書き込み動作が安定化することが明らかとなった.さらに,syF自由層の記録保持時間,読み出し電流,読み出し時間の関係を調査した結果,1.5ns以下の高速な読み出しが可能であることがわかった.
• 強磁性半導体における磁壁と伝導

  千葉 大地, 山ノ内 路彦, 松倉 文礼 固体物理 42 (2) 99 -106 2007年02月
• (Ga, Mn)As MTJにおけるスピン注入磁化反転

  千葉 大地, 北 智洋, 山ノ内 路彦, 松倉 文〓, 大野 英男 日本応用磁気学会研究会資料 145 7 -12 2006年01月30日
• 27aYP-5 強磁性半導体保磁力パターニング構造における電流誘起磁壁移動(主題:磁性ナノ構造における電流誘起磁壁移動,領域3シンポジウム,領域3(磁性,磁気共鳴))

  山ノ内 路彦, 千葉 大地, 松倉 文礼, 大野 裕三, 大野 英男 日本物理学会講演概要集 60 (1) 481 -481 2005年03月04日
• 強磁性の電界制御

  千葉 大地, 山ノ内 路彦, 松倉 文礼 固体物理 38 (9) 612 -618 2003年09月

講演・口頭発表等

• 強磁性酸化物SrRuO3におけるワイル電子に起因したスピントルク  [招待講演]

  山ノ内路彦

  日本物理学会第78回年次大会 2023年09月 シンポジウム・ワークショップパネル（指名）
• Effects of spin-orbit torque on domain wall motion in Ta/MnGa/NiAl structure

  M. Yamanouchi, N. V. Bao, M. Inoue, T. Uemura

  64th Annual Conference on Magnetism and Magnetic Materials (2019 MMM Conference) 2019年11月 口頭発表（一般）
• Current-induced effective magnetic field in La0.67Sr0.33MnO3/LaAlO3/SrTiO3

  M. Yamanouchi, T. Oyamada, H. Ohta

  64th Annual Conference on Magnetism and Magnetic Materials (2019 MMM Conference) 2019年11月 口頭発表（一般）
• 強磁性酸化物における電流誘起有効磁場  [通常講演]

  山ノ内路彦

  強的秩序とその操作に関わる第9回研究会－若手夏の学校－ 2019年09月 口頭発表（招待・特別）
• Effects of current on domain wall motion in SrRuO3

  M. Yamanouchi, T. Oyamada, K. Sato, H. Ohta, J. Ieda

  2019 Joint MMM-Intermag Conference 2019年01月 ポスター発表
• Anomalous magnetotransport properties of La0.67Sr0.33MnO3/LaAlO3/SrTiO3

  M. Yamanouchi, T. Oyamada, H. Ohta

  2019 Joint MMM-Intermag Conference ポスター発表
• Current-induced modulation of switching magnetic field in La0.67Sr0.33MnO3/SrTiO3 structures

  M. Yamanouchi, T. Oyamada, T. Katase, H. Ohta

  61st Annual Conference on Magnetism and Magnetic Materials (2016 MMM Conference) 2016年 口頭発表（一般）
• Quantitative determination of intrinsic energy barrier for current induced domain wall motion  [通常講演]

  8th International Symposium on Metallic Multilayers (MML2013) 2013年 ポスター発表
• Influence of in-plane magnetic fields on current-induced domain wall motion in a perpendicularly magnetized Co/Ni nanowire  [通常講演]

  8th International Symposium on Metallic Multilayers (MML2013) 2013年 ポスター発表
• Current-induced effective field vector in Ta│CoFeB│MgO with various layer thicknesses  [通常講演]

  8th International Symposium on Metallic Multilayers (MML2013) 2013年 ポスター発表
• Temperature dependence of spin polarization in Co/Ni nanowires with different Co and Ni thicknesses determined from magnetic domain wall dynamics  [通常講演]

  8th International Symposium on Metallic Multilayers (MML2013) 2013年
• Monoatomically-layered CoNi film with perpendicular magnetic anisotropy  [通常講演]

  8th International Symposium on Metallic Multilayers (MML2013) 2013年 ポスター発表
• (Co100-xFex)80B20 composition dependence of interface anisotropy in MgO/CoFeB/Ta stack structure  [通常講演]

  8th International Symposium on Metallic Multilayers (MML2013) 2013年 ポスター発表
• MgO/CoFeB/Ta/CoFeB/MgO recording structure with low critical current and high thermal stability  [通常講演]

  JSPS York-Tohoku Symposium on Magnetic Materials and Spintronic Devices 2013年
• Low-Current Domain Wall Motion MRAM with Perpendicularly Magnetized CoFeB/MgO Magnetic Tunnel Junction and Underlying Hard Magnets  [通常講演]

  2013 Symposia on VLSI Circuits 2013年
• 垂直磁気異方性CoFeB-MgO磁気トンネル接合のトンネル磁気抵抗特性の温度依存性  [通常講演]

  第32回電子材料シンポジウム(EMS32) 2013年 ポスター発表
• Electric-field induced magnetization switching in CoFeB-MgO with different magnetic field angles  [通常講演]

  International Symposium on Advanced Magnetic Materials and Applications (ISAMMA) 2013年
• Electrical reliability of Co/Ni wire for domain wall motion devices  [通常講演]

  International Symposium on Advanced Magnetic Materials and Applications (ISAMMA) 2013年
• CuIrチャネルを用いた3端子磁気トンネル接合  [通常講演]

  東北大学電気通信研究所ナノ・スピン実験施設研究発表会 2013年
• Spin hall effect in switching of three terminal magnetic tunnel junction with culr channel  [通常講演]

  Joint European Magnetic Symposia (JEMS) 2013年
• 垂直磁気異方性CoNi超格子膜の作製と磁気特性の評価  [通常講演]

  第37回日本磁気学会学術講演会 2013年
• Co/Ni細線における磁壁デピニング確率の測定と計算  [通常講演]

  第37回日本磁気学会学術講演会 2013年
• Tuneable chiral domain wall motion by intertwined spin Hall effect and spin transfer torque in ultrathin TaN/CoFeB/MgO  [通常講演]

  Donostia International Conference on Nanoscaled Magnetism and Applications (ICNMA) 2013年
• Co/Pt multilayer based reference layers in magnetic tunnel junction for novolatile spintronics VLSIs  [通常講演]

  International Conference on Solid State Devices and Materials (SSDM) 2013年
• Demonstration of a nonvolatile processor core chip with software-controlled trhee-terminal MRAM cells for standby-power critical applications  [通常講演]

  International Conference on Solid State Devices and Materials (SSDM) 2013年
• 垂直磁化Co/Ni細線中の磁壁電流駆動におけるスピンホール効果の影響  [通常講演]

  日本物理学会秋季大会 2013年
• Distribution of critical current density for magnetic domain wall motion  [通常講演]

  58th Magnetism and Magnetic Materials (MMM) 2013年
• Magnetization reversal induced by in-plane current in Ta/CoFeB/MgO structures with perpendicular magnetic easy axis  [通常講演]

  58th Magnetism and Magnetic Materials (MMM) 2013年
• Co/Pt multilayer-based magnetic tunnel junctions with thin Ta spacer layer  [通常講演]

  58th Magnetism and Magnetic Materials (MMM) 2013年
• Temperature dependence of thermal stability factor of CoFeB-MgO magnetic tunnel junctions with perpendicular easy-axis  [通常講演]

  58th Magnetism and Magnetic Materials (MMM) 2013年
• Two-barrier stability in current-induced domain-wall motion device  [通常講演]

  58th Magnetism and Magnetic Materials (MMM) 2013年 ポスター発表
• Cuベースチャネル3端子磁気トンネル接合  [通常講演]

  応用物理学会スピントロニクス研究会・日本磁気学会スピンエレクトロニクス専門研究会共同主催研究会「元素戦略、環境調和を視野に入れたスピントロニクスの新展開」 2013年
• 垂直磁化容易CoFeB-MgO磁気トンネル接合における電流誘起磁化反転の面内磁場依存性  [通常講演]

  応用物理学会東北支部講演会 2013年
• MgO/Fe(B)/MgO積層膜の磁気特性  [通常講演]

  応用物理学会東北支部講演会 2013年
• Temperature dependence of electric-field effects on magnetic anisotropies in Ta-CoFeB-MgO  [通常講演]

  Physics and Applications of Spin-related Phenomena in Semiconductors (PASPS-18) 2013年 ポスター発表
• 20-nm magnetic domain wall motion memory with ultralow-power operation  [通常講演]

  2013 IEEE International Electron Devices Meeting (IEDM) 2013年
• Comprehensive study of CoFeB-MgO magnetic tunnel junction characteristics with single- and double-interface scaling down to 1X nm  [通常講演]

  2013 IEEE International Electron Devices Meeting (IEDM) 2013年
• Quantitative determination of intrinsic energy barrier for current induced domain wall motion  [通常講演]

  8th International Symposium on Metallic Multilayers (MML2013) 2013年 ポスター発表
• Influence of in-plane magnetic fields on current-induced domain wall motion in a perpendicularly magnetized Co/Ni nanowire  [通常講演]

  8th International Symposium on Metallic Multilayers (MML2013) 2013年 ポスター発表
• Current-induced effective field vector in Ta│CoFeB│MgO with various layer thicknesses  [通常講演]

  8th International Symposium on Metallic Multilayers (MML2013) 2013年 ポスター発表
• Temperature dependence of spin polarization in Co/Ni nanowires with different Co and Ni thicknesses determined from magnetic domain wall dynamics  [通常講演]

  8th International Symposium on Metallic Multilayers (MML2013) 2013年
• Monoatomically-layered CoNi film with perpendicular magnetic anisotropy  [通常講演]

  8th International Symposium on Metallic Multilayers (MML2013) 2013年 ポスター発表
• (Co100-xFex)80B20 composition dependence of interface anisotropy in MgO/CoFeB/Ta stack structure  [通常講演]

  8th International Symposium on Metallic Multilayers (MML2013) 2013年 ポスター発表
• MgO/CoFeB/Ta/CoFeB/MgO recording structure with low critical current and high thermal stability  [通常講演]

  JSPS York-Tohoku Symposium on Magnetic Materials and Spintronic Devices 2013年
• Low-Current Domain Wall Motion MRAM with Perpendicularly Magnetized CoFeB/MgO Magnetic Tunnel Junction and Underlying Hard Magnets  [通常講演]

  2013 Symposia on VLSI Circuits 2013年
• 垂直磁気異方性CoFeB-MgO磁気トンネル接合のトンネル磁気抵抗特性の温度依存性  [通常講演]

  第32回電子材料シンポジウム(EMS32) 2013年 ポスター発表
• Electric-field induced magnetization switching in CoFeB-MgO with different magnetic field angles  [通常講演]

  International Symposium on Advanced Magnetic Materials and Applications (ISAMMA) 2013年
• Electrical reliability of Co/Ni wire for domain wall motion devices  [通常講演]

  International Symposium on Advanced Magnetic Materials and Applications (ISAMMA) 2013年
• CuIrチャネルを用いた3端子磁気トンネル接合  [通常講演]

  東北大学電気通信研究所ナノ・スピン実験施設研究発表会 2013年
• Spin hall effect in switching of three terminal magnetic tunnel junction with culr channel  [通常講演]

  Joint European Magnetic Symposia (JEMS) 2013年
• 垂直磁気異方性CoNi超格子膜の作製と磁気特性の評価  [通常講演]

  第37回日本磁気学会学術講演会 2013年
• Co/Ni細線における磁壁デピニング確率の測定と計算  [通常講演]

  第37回日本磁気学会学術講演会 2013年
• Tuneable chiral domain wall motion by intertwined spin Hall effect and spin transfer torque in ultrathin TaN/CoFeB/MgO  [通常講演]

  Donostia International Conference on Nanoscaled Magnetism and Applications (ICNMA) 2013年
• Co/Pt multilayer based reference layers in magnetic tunnel junction for novolatile spintronics VLSIs  [通常講演]

  International Conference on Solid State Devices and Materials (SSDM) 2013年
• Demonstration of a nonvolatile processor core chip with software-controlled trhee-terminal MRAM cells for standby-power critical applications  [通常講演]

  International Conference on Solid State Devices and Materials (SSDM) 2013年
• 垂直磁化Co/Ni細線中の磁壁電流駆動におけるスピンホール効果の影響  [通常講演]

  日本物理学会秋季大会 2013年
• Distribution of critical current density for magnetic domain wall motion  [通常講演]

  58th Magnetism and Magnetic Materials (MMM) 2013年
• Magnetization reversal induced by in-plane current in Ta/CoFeB/MgO structures with perpendicular magnetic easy axis  [通常講演]

  58th Magnetism and Magnetic Materials (MMM) 2013年
• Co/Pt multilayer-based magnetic tunnel junctions with thin Ta spacer layer  [通常講演]

  58th Magnetism and Magnetic Materials (MMM) 2013年
• Temperature dependence of thermal stability factor of CoFeB-MgO magnetic tunnel junctions with perpendicular easy-axis  [通常講演]

  58th Magnetism and Magnetic Materials (MMM) 2013年
• Two-barrier stability in current-induced domain-wall motion device  [通常講演]

  58th Magnetism and Magnetic Materials (MMM) 2013年 ポスター発表
• Cuベースチャネル3端子磁気トンネル接合  [通常講演]

  応用物理学会スピントロニクス研究会・日本磁気学会スピンエレクトロニクス専門研究会共同主催研究会「元素戦略、環境調和を視野に入れたスピントロニクスの新展開」 2013年
• 垂直磁化容易CoFeB-MgO磁気トンネル接合における電流誘起磁化反転の面内磁場依存性  [通常講演]

  応用物理学会東北支部講演会 2013年
• MgO/Fe(B)/MgO積層膜の磁気特性  [通常講演]

  応用物理学会東北支部講演会 2013年
• Temperature dependence of electric-field effects on magnetic anisotropies in Ta-CoFeB-MgO  [通常講演]

  Physics and Applications of Spin-related Phenomena in Semiconductors (PASPS-18) 2013年 ポスター発表
• 20-nm magnetic domain wall motion memory with ultralow-power operation  [通常講演]

  2013 IEEE International Electron Devices Meeting (IEDM) 2013年
• Comprehensive study of CoFeB-MgO magnetic tunnel junction characteristics with single- and double-interface scaling down to 1X nm  [通常講演]

  2013 IEEE International Electron Devices Meeting (IEDM) 2013年
• Thickness dependence of thermal stability factor in CoFeB/MgO perpendicular magnetic tunnel junctions  [通常講演]

  International Magnetics Conference (INTERMAG) 2012年
• CoFeB composition dependence of magnetic anisotropy and tunnel magnetoresistance in CoFeB/MgO stack structures  [通常講演]

  International Magnetics Conference (INTERMAG) 2012年
• Factors Determining Thermal Stability in CoFeB-MgO Perpendicular Junctions  [通常講演]

  9th RIEC International Workshop on Spintronics 2012年
• Electromotive Forces in (Ga, Mn)As-based Structures  [通常講演]

  9th RIEC International Workshop on Spintronics 2012年
• Magnetic Anisotropy of Co/Pt based Electrodes for Magnetic Tunnel Junctions with perpendicular Magnetic Easy Axis  [通常講演]

  9th RIEC International Workshop on Spintronics 2012年 ポスター発表
• High-Speed and Reliable Domain Wall Motion Device: Material Design for Embedded Memory and Logic Application  [通常講演]

  2012 Symposium on VLSI Technology 2012年
• Retention time under currents and magnetic fields in a CoFeB/MgO perpendicular magnetic tunnel junction  [通常講演]

  19th International Conference on Magnetism (ICM2012) 2012年 ポスター発表
• 垂直磁気トンネル接合におけるCo/Pt電極の磁気異方性のPt膜厚および熱処理温度依存性  [通常講演]

  第31回電子材料シンポジウム 2012年
• Perpendicular CoFeB-MgO magnetic tunnel junction  [通常講演]

  SPIE Nanoscience+Engineering 2012 2012年
• CoFeB-MgO垂直磁化容易磁気トンネル接合における強磁性共鳴のホモダイン検出  [通常講演]

  第73回応用物理学会学術講演会 2012年
• MgO/CoFeB/Ta/CoFeB/MgO構造を用いた垂直磁気容易磁気トンネル接合  [通常講演]

  第73回応用物理学会学術講演会 2012年 ポスター発表
• 垂直磁気異方性CoFeB-MgO接合における電界誘起磁化反転  [通常講演]

  第73回応用物理学会学術講演会 2012年
• Domain wall depinning probability - Experiment and Theory  [通常講演]

  21th International Colloquium on Magnetic Films and Surfaces (ICMFS) 2012年 ポスター発表
• Ferromagnetic resonance by means of homodyne detection technique in CoFeB/MgO magnetic tunnel junctions with perpendicular easy axis  [通常講演]

  21th International Colloquium on Magnetic Films and Surfaces (ICMFS) 2012年 ポスター発表
• Magnetic Anisotropy in CoFe(B)/MgO Stack Structures  [通常講演]

  International Conference of the Asian Union of Magnetics Societies (ICAUMS) 2012年 ポスター発表
• Spintronics devices for nonvolatile memory and logic  [通常講演]

  12th Non-Volatile Memory Technology Symposium (NVMTS) 2012年
• Thickness dependence of thermal stability factor in CoFeB/MgO perpendicular magnetic tunnel junctions  [通常講演]

  International Magnetics Conference (INTERMAG) 2012年
• CoFeB composition dependence of magnetic anisotropy and tunnel magnetoresistance in CoFeB/MgO stack structures  [通常講演]

  International Magnetics Conference (INTERMAG) 2012年
• Factors Determining Thermal Stability in CoFeB-MgO Perpendicular Junctions  [通常講演]

  9th RIEC International Workshop on Spintronics 2012年
• Electromotive Forces in (Ga, Mn)As-based Structures  [通常講演]

  9th RIEC International Workshop on Spintronics 2012年
• Magnetic Anisotropy of Co/Pt based Electrodes for Magnetic Tunnel Junctions with perpendicular Magnetic Easy Axis  [通常講演]

  9th RIEC International Workshop on Spintronics 2012年 ポスター発表
• High-Speed and Reliable Domain Wall Motion Device: Material Design for Embedded Memory and Logic Application  [通常講演]

  2012 Symposium on VLSI Technology 2012年
• Retention time under currents and magnetic fields in a CoFeB/MgO perpendicular magnetic tunnel junction  [通常講演]

  19th International Conference on Magnetism (ICM2012) 2012年 ポスター発表
• 垂直磁気トンネル接合におけるCo/Pt電極の磁気異方性のPt膜厚および熱処理温度依存性  [通常講演]

  第31回電子材料シンポジウム 2012年
• Perpendicular CoFeB-MgO magnetic tunnel junction  [通常講演]

  SPIE Nanoscience+Engineering 2012 2012年
• CoFeB-MgO垂直磁化容易磁気トンネル接合における強磁性共鳴のホモダイン検出  [通常講演]

  第73回応用物理学会学術講演会 2012年
• MgO/CoFeB/Ta/CoFeB/MgO構造を用いた垂直磁気容易磁気トンネル接合  [通常講演]

  第73回応用物理学会学術講演会 2012年 ポスター発表
• 垂直磁気異方性CoFeB-MgO接合における電界誘起磁化反転  [通常講演]

  第73回応用物理学会学術講演会 2012年
• Domain wall depinning probability - Experiment and Theory  [通常講演]

  21th International Colloquium on Magnetic Films and Surfaces (ICMFS) 2012年 ポスター発表
• Ferromagnetic resonance by means of homodyne detection technique in CoFeB/MgO magnetic tunnel junctions with perpendicular easy axis  [通常講演]

  21th International Colloquium on Magnetic Films and Surfaces (ICMFS) 2012年 ポスター発表
• Magnetic Anisotropy in CoFe(B)/MgO Stack Structures  [通常講演]

  International Conference of the Asian Union of Magnetics Societies (ICAUMS) 2012年 ポスター発表
• Spintronics devices for nonvolatile memory and logic  [通常講演]

  12th Non-Volatile Memory Technology Symposium (NVMTS) 2012年

共同研究・競争的資金等の研究課題

• 磁性ワイル半金属磁気トンネル接合

  日本学術振興会：科学研究費助成事業

  研究期間 : 2022年06月 -2025年03月 

  代表者 : 山ノ内 路彦, 植村 哲也
• ワイル点を有する強磁性体における電流誘起磁壁移動

  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 : 山ノ内 路彦

   

  本研究では、ワイル点を有する強磁性体においてワイル点が電流誘起磁壁移動に与える効果を明らかにすることを主目的としている。本年度は、フェルミ準位近傍にワイル点を有する強磁性体SrRuO3において、前年度より広い範囲で温度を変え、ワイル点とフェルミ準位の相対的位置を系統的に変化させた時に電流が磁壁に及ぼす有効磁場がどのように変化するかを詳細に調べることにより、本研究の目的の達成をめざした。その結果、単位電流当たりに誘起される有効磁場は温度に対して2つのピークをもつ特異な温度依存性を示し、かつその大きさは強磁性金属で報告されている値よりも2桁程度大きいことがわかった。これらの結果は従来機構では説明できないため、SrRuO3における電流誘起磁壁移動はこれまでに観測されていない新たな機構に関係していると推察された。そのような中で、最近になって、フェルミ準位近傍にワイル点を有する強磁性体においては、磁壁を横切るように電界を印加すると、ワイル点近傍のワイルフェルミオンによってトポロジカルホールトルクと呼ばれる新規のトルクが磁壁に作用することが理論的に示され、本研究で観測された有効磁場との関連が期待された。実験結果とトポロジカルホールトルクによる有効磁場の理論計算を比較したところ、この有効磁場の特異な温度依存性、及び大きさは、ともにトポロジカルホールトルクで説明できることがわかった。これらの結果から、ワイル点を有する強磁性体においては、ワイルフェルミオンに起因したトポロジカルホールトルクによって、高効率な電流誘起磁壁移動や特異な温度依存性を示す電流誘起磁壁移動が発現すると考えられる。
• 原子層制御による新しい材料機能探索

  日本学術振興会：科学研究費助成事業

  研究期間 : 2013年06月 -2018年03月 

  代表者 : 太田 裕道, 平松 秀典, 片瀬 貴義, 山ノ内 路彦

   

  原子レベルで厚さ制御された薄膜「ナノ層」を作製し、新しい材料機能の探索を行うとともに、作製した試料を他班に提供することでナノ構造情報の開拓に取り組んだ。主な結果を列挙する。1. 酸化物人工超格子で熱を電気に変換する性能をバルク比2倍の増強に成功した、2. 透明酸化物半導体薄膜の電子移動度抑制の起源を解明し、高電子移動度を実現した、3. 半導体二次元電子ガスが高い熱電変換出力因子を示すことを見出した、4. 光透過率・電気抵抗率・磁気的性質を同時に変えられる薄膜デバイスを実現した、5. 金属テープ基板上で、実用レベルに匹敵する臨界電流密度を示す鉄系超伝導薄膜を実現した。
• 酸化物ヘテロ構造におけるスピン軌道トルク

  文部科学省：科学研究費補助金(若手研究(A) )

  研究期間 : 2015年04月 -2017年03月 

  代表者 : 山ノ内路彦
• ＧａＡｓ／ＡｌＧａＡｓ量子細線構造におけるスピン永久旋回状態の形成とスピン輸送

  日本学術振興会：科学研究費助成事業

  研究期間 : 2012年04月 -2014年03月 

  代表者 : 大野 裕三, 山ノ内 路彦

   

  スピン軌道相互作用（SOI)はスピントロニクスにおいて非常に重要な働きをする。なぜなら，SOIによる有効磁界によってスピンを操作したり，またスピン緩和の原因となるからである。本研究では、時間分解カー回転測定法を用いて，Rashba SOIとDresselhaus SOIがきわめて近い変調ドープGaAs/AlGaAs量子井戸を用い，幅1～10ミクロン幅に加工した細線構造におけるスピンアンサンブルのダイナミクスを調べた．また，時空間分解カー回転顕微鏡を構築し，ゲート付きGaAs/AlGaAs量子井戸において永久スピン旋回状態を実証した.
• 半導体・磁性体ハイブリッド構造におけるスピン制御とスピンダイナミクスの光検出

  日本学術振興会：科学研究費助成事業

  研究期間 : 2011年11月 -2014年03月 

  代表者 : 大野 裕三, 山ノ内 路彦

   

  本研究では，垂直磁化を有するCoFeBを強磁性層とするCoFeB/MgO/GaAs磁気トンネル接合を有する３端子阻止を作製し，磁気輸送特性測定，および顕微カー回転測定を行い，半導体GaAsにおけるスピン蓄積とスピン検出を実施した．磁気輸送測定では，スピン注入・蓄積を示唆するHanle効果を確認した．一方で，顕微カー回転測定においては±2Tの強い面内磁界を印加してもカー回転信号が残った．以上の結果から，明瞭なスピン注入・蓄積の光検出はできなかった．本研究を通じて，MgOとGaAs界面が面直スピン注入において重要であることがわかった．
• 面内磁化膜における内因性ピニング

  文部科学省：科学研究費補助金(若手研究(B))

  研究期間 : 2012年 -2013年 

  代表者 : 山ノ内 路彦

   

  面内磁化膜において電流誘起磁壁移動の閾値電流の内因性ピニング、及び外因性ピニング依存性を調べるため、必要な積層膜の作製方法と素子構造を検討した。そして外因性ピニングが内因性ピニングより小さい面内磁化膜細線の作製方法、及び面内磁化膜細線において電流磁場を利用して細線内に磁壁を初期配置する構造を提案した。また、それらの知見をもとに面内磁化膜において電流誘起磁壁移動を調べるための素子を試作した。
• スピン注入磁壁移動の機構と応用に関する研究

  日本学術振興会：科学研究費助成事業

  研究期間 : 2003年 -2005年 

  代表者 : 山ノ内 路彦

   

  今年度は、強磁性半導体ガリウムマンガン砒素における電流誘起磁壁移動の機構を調べるために、面直方向に磁化容易軸をもつガリウムマンガン砒素において、電流誘起磁壁移動速度の電流密度依存性および温度依存性を測定し、現在提案されている理論との比較を行った。まず、磁壁移動速度を評価するための素子作成を行った。バッファ層として、徐々にインジウム組成を変えたインジウムアルミニウム砒素を用いることにより、転位に起因した表面の凹凸を低減した。幅5μmのチャネルを形成した後、チャネル表面を部分的にエッチングすることにより、面内に保磁力の異なる2つの領域を作製した。磁壁移動速度の評価は以下のように行った。保磁力差を利用して外部磁場により、領域境界に磁壁を配置した後、電流パルスを印加して磁壁を移動させた。磁壁の位置はカー効果偏光顕微鏡を用いて観察した。磁壁が掃引した面積をチャネル幅で割ったものを実効磁壁移動距離d_と定義し、d_のパルス幅w_p依存性を測定した。d_はw_pに対してほぼ線形に変化することが分かった。そこで、その傾きを実効磁壁移動速度v_と定義し、v_の電流密度jおよび温度T_a依存性を測定した。v_はjとT_aの関数で10^<-4>〜10^1m/sオーダにわたって制御可能であり、そのj依存性には少なくとも2つの領域があることが分かった。高電流密度領域(>3x10^5 A/cm^2)においては、v_はjにほぼ線形に変化し、最高で22m/sの磁壁移動速度が得られた。理論との比較から、この領域の電流誘起磁壁移動機構はキャリアスピンから局在磁気スピンへのスピンのトランスファによって説明できることが分かった。低電流密度領域においては、v_のj依存性は現象論的なスケーリング則に従い、電流により磁壁のクリープが誘起されていると考えられる

産業財産権

• 特許第5492144号:垂直磁化磁気抵抗効果素子及び磁気メモリ  2014年03月07日

  大野 英男, 池田 正二, 山ノ内 路彦, 佐藤 英夫, 三浦 勝哉  株式会社日立製作所, 国立大学法人東北大学  201203057215523953
• 特許第5456035号:トンネル磁気抵抗効果素子及びそれを用いたランダムアクセスメモリ  2014年01月17日

  山本 浩之, 高橋 宏昌, 伊藤 顕知, 早川 純, 山ノ内 路彦  株式会社日立製作所  201403091863078203
• 特許第5386637号:トンネル磁気抵抗効果素子及びそれを用いた磁気メモリセル並びに磁気ランダムアクセスメモリ  2013年10月11日

  山ノ内 路彦, 黒崎 洋輔, 早川 純, 高橋 宏昌  株式会社日立製作所  201403076782251700
• 特許第5166600号:トンネル磁気記録素子、磁気メモリセル及び磁気ランダムアクセスメモリ  2012年12月28日

  早川 純, 山ノ内 路彦  株式会社日立製作所  201303076003569319
• 特許第5075802号:磁気メモリセル及び磁気ランダムアクセスメモリ  2012年08月31日

  山ノ内 路彦, 高橋 宏昌, 早川 純  株式会社日立製作所  201003056449612975
• WO2011-145146:トンネル磁気抵抗効果素子及びそれを用いた磁気メモリセル並びに磁気ランダムアクセスメモリ  2011年11月24日

  山ノ内 路彦, 黒崎 洋輔, 早川 純, 高橋 宏昌  株式会社日立製作所  201303061404591190
• WO2010-143248:トンネル磁気抵抗効果素子及びそれを用いたランダムアクセスメモリ  2010年12月16日

  山本 浩之, 高橋 宏昌, 伊藤 顕知, 早川 純, 山ノ内 路彦  株式会社日立製作所  201203033722320430
• WO2010-100678:トンネル磁気記録素子、磁気メモリセル及び磁気ランダムアクセスメモリ  2010年09月10日

  早川 純, 山ノ内 路彦  株式会社日立製作所  201203095912507450