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研究者情報

マスター

アカウント（マスター）

  • 氏名

    柳澤　達也(ヤナギサワ　タツヤ), ヤナギサワ　タツヤ

所属（マスター）

  • 理学研究院　物理学部門　凝縮系物理学分野

所属（マスター）

  • 理学研究院　物理学部門　凝縮系物理学分野

独自項目

syllabus

  • 2021, 磁性物理学, Magnetism, 修士課程, 理学院, 電子相関、近藤効果、多極子、中性子散乱、磁気フラストレーション、熱電物性
  • 2021, 量子光物性, Quantum Optical Physics, 修士課程, 理学院, 表面界面物性、薄膜、ナノ材料、ナノ電磁場制御、光エネルギー変換
  • 2021, 物理学特別講義, Special Lectures for Modern Physics, 学士課程, 理学部, 電子相関、近藤効果、多極子、中性子散乱、磁気フラストレーション、熱電物性
  • 2021, 電磁気学Ⅰ, Electromagnetism I, 学士課程, 理学部, マクスウェル方程式, ガウスの法則、静電場、静電ポテンシャル、境界値問題、ポアソン方程式、導体、誘電体、アンペールの法則、ベクトルポテンシャル、ビオ・サヴァールの法則、ローレンツ力
  • 2021, 電磁気学演習Ⅰ, Seminar in Electromagnetism I, 学士課程, 理学部, マクスウェル方程式、ガウスの法則、静電場、静電ポテンシャル、境界値問題、ポアソン方程式、導体、誘電体、アンペールの法則、ベクトルポテンシャル、ビオ・サヴァールの法則、ローレンツ力
  • 2021, 物理学特別講義Ａ, Special Lectures for Modern Physics A, 学士課程, 理学部, 電子相関、近藤効果、多極子、中性子散乱、磁気フラストレーション、熱電物性
  • 2021, 物理学特別講義Ａ, Special Lectures for Modern Physics A, 学士課程, 理学部, 表面界面物性、薄膜、ナノ材料、ナノ電磁場制御、光エネルギー変換

researchmap

プロフィール情報

学位

  • 博士（理学）（新潟大学）

プロフィール情報

  • プロフィール

    超音波を用いて、強相関電子系の多極子自由度の研究をしています。

  • 姓

    柳澤, ヤナギサワ

  • 名

    達也, タツヤ

  • ID各種

    D-8278-2019, 200901066748675336

対象リソース

業績リスト

研究キーワード

  • 拡張多極子   四極子近藤効果   URu2Si2   アメリカ:ドイツ:チェコ   充填スクッテルダイト   電子-格子相互作用   カゴ状化合物   ラットリング   国際情報交換   局所電荷ゆらぎ   強相関系   ウラン化合物   高次多極子   反強磁性   異方的超伝導   5f電子系   重い電子系   隠れた秩序   アクチナイド   超伝導   極低温   超音波   強相関電子物性   Superconductibity   Very Low Temperature   Ultrasound   Physics of Correlated Electrons   

研究分野

  • 自然科学一般 / 磁性、超伝導、強相関系

経歴

  • 2022年07月 - 現在 北海道大学 大学院理学研究院 教授
  • 2012年01月 - 2022年06月 北海道大学 大学院理学研究院 准教授
  • 2008年02月 - 2011年12月 北海道大学 創成研究機構 特任助教（テニュアトラック）
  • 2007年04月 - 2008年01月 新潟大学 大学院自然科学研究科 科研費研究員
  • 2005年 - 2007年 カリフォルニア大学サンディエゴ校 日本学術振興会海外特別研究員
  • 2004年 - 2005年 カリフォルニア大学サンディエゴ校 日本学術振興会特別研究員
  • 2003年 - 2004年 新潟大学大学院自然科学研究科 日本学術振興会特別研究員

学歴

  •         - 2003年   新潟大学   大学院自然科学研究科   エネルギー基礎科学（博士後期課程）修了
  •         - 2001年   新潟大学   大学院自然科学研究科   物質制御科学専攻（博士前期課程）修了
  •         - 1999年   新潟大学   理学部   物理学科

委員歴

  • 2013年09月 - 現在   日本物理学会北海道支部   支部幹事
  • 2018年10月 - 2021年09月   物性委員会   事務局員   http://bussei-group.org/office/
  • 2012年10月 - 2013年09月   日本物理学会   領域８運営委員
  • 2010年05月 - 2011年04月   日本物理学会 領域10(フォノン分科)   運営委員

受賞

  • 2021年04月 公益財団法人 豊田理化学研究所 豊田理研スカラー 研究助成金
     精密超音波測定法による多チャンネル近藤効果の実証 
    受賞者: 柳澤達也
  • 2009年09月 北海道科学技術総合振興センター ノーステック財団 研究開発助成事業 若手研究者理事長賞
     1万気圧超の静水圧力下における高精度超音波測定技術の開発 
    受賞者: 柳澤 達也https://www.noastec.jp/kinouindex/data2010/contents/04.html

論文

  • Tatsuya Yanagisawa
    JPSJ News and Comments 21 2024年11月14日 [査読無し][通常論文]
  • Michal Vališka, Tetiana Haidamak, Andrej Cabala, Jiří Pospíšil, Gaël Bastien, Vladimír Sechovský, Jan Prokleška, Tatsuya Yanagisawa, Petr Opletal, Hironori Sakai, Yoshinori Haga, Atsuhiko Miyata, Denis Gorbunov, Sergei Zherlitsyn
    Physical Review Materials 8 9 2024年09月 [査読有り]
     
    The first-order transition line in the H-T phase diagram of itinerant electron metamagnets terminates at the critical end point - analogous to the critical point on the gas-liquid condensation line in the p-T phase diagram. To unravel the impact of critical magnetic fluctuations on the crystal lattice of a metamagnet at the critical end point, we performed an ultrasonic study of the itinerant electron metamagnet UTe2 across varying temperatures and magnetic fields. At temperatures exceeding 9 K, a distinct V-shaped anomaly emerges, precisely centered at the critical field of the metamagnetic transition in the isothermal field dependence of elastic constants. This anomaly arises from lattice instability, triggered by critical magnetic fluctuations via strong magnetoelastic interactions. Remarkably, this effect is maximized precisely at the critical-end-point temperature. Comparative measurements of another itinerant metamagnet, UCoAl, reveal intriguing commonalities. Despite significant differences in the paramagnetic ground state, lattice symmetry, and the expected metamagnetic transition process between UTe2 and UCoAl, both exhibit similar anomalies in elastic properties near the critical end point.
  • Fusako Kon, Chihiro Tabata, Hiraku Saito, Taro Nakajima, Hiroyuki Hidaka, Tatsuya Yanagisawa, Hiroshi Amitsuka
    Journal of the Physical Society of Japan 93 4 2024年04月15日 [査読有り]
  • Ruo Hibino, Tatsuya Yanagisawa, Yoshito Mikami, Hiroyuki Hidaka, Hiroshi Amitsuka, Sergei Zherlitsyn, Joachim Wosnitza, Yu Yamane, Takahiro Onimaru
    Journal of the Physical Society of Japan 92 7 2023年07月15日 
    We measured the elastic constants (C11 − C12)=2 and C44 of the non-Kramers system Y0.63Pr0.37Ir2Zn20 (Pr-37% system) by means of ultrasound to check how the single-site quadrupolar Kondo effect is modified by increasing the Pr concentration. The Curie-like softening of (C11 − C12)=2 of the present Pr-37% system on cooling from 5 to 1 K can be reproduced by a multipolar susceptibility calculation based on the non-Kramers Γ3 doublet crystalline-electric-field ground state. Further, on cooling below 0.15 K, a temperature dependence proportional to pffiffiffi T was observed in (C11 − C12)=2. This behavior rather corresponds to the theoretical prediction of the quadrupolar Kondo “lattice” model, unlike that of the Pr-3.4% system, which shows a logarithmic temperature dependence based on the “single-site” quadrupolar Kondo theory. In addition, we discuss the possibility to form a vibronic state by the coupling between the low-energy phonons and the electric quadrupoles of the non-Kramers doublet in the Pr-37% system, since we found a low-energy ultrasonic dispersion in the temperature range between 0.15 and 1 K.
  • Ruo Hibino, Tatsuya Yanagisawa, Yoshito Mikami, Hiroyuki Hidaka, Hiroshi Amitsuka, Sergei Zherlitsyn, Joachim Wosnitza, Yu Yamane, Takahiro Onimaru
    JPS Conf. Proc. 38 011089  2023年05月22日 [査読有り]
  • D. I. Gorbunov, R. Hibino, Y. Skourski, T. Yanagisawa, A. V. Andreev, S. Zherlitsyn, J. Wosnitza
    Physical Review B 106 14 2022年10月01日 [査読有り]
     
    U3Cu4Ge4 is a uniaxial ferromagnet that displays a first-order magnetization process (FOMP) at 25 T for field applied along the hard b axis. Here, we report on ultrasound and magnetostriction measurements of U3Cu4Ge4 in static and pulsed magnetic fields up to 40 T. The FOMP causes stepwise anomalies in the magnetoelastic properties. U3Cu4Ge4 elongates along the a and c axes and shrinks along the b axis, leading to an almost zero volume effect. The sound velocities of the longitudinal and transverse acoustic waves decrease sharply at the FOMP, whereas the sound attenuation shows pronounced peaks. An analysis of the ultrasound data using a mean-field theory suggests the existence of quadrupolar interactions and crystal-electric-field effects. The 5f electronic states are between itinerant and localized, typical of uranium-based intermetallic compounds.
  • P. C. Ho, D. E. Maclaughlin, M. B. Maple, Lei Shu, A. D. Hillier, O. O. Bernal, T. Yanagisawa, P. K. Biswas, Jian Zhang, Cheng Tan, S. D. Hishida, T. McCullough-Hunter
    Physical Review B 106 14 2022年10月01日 [査読有り]
     
    The Pr-rich end 0≤x≤0.25 of the alloy series Pr1-xNdxOs4Sb12 has been studied using muon spin rotation and relaxation. The end compound PrOs4Sb12 is an unconventional heavy-fermion superconductor, which exhibits a spontaneous magnetic field associated with broken time-reversal symmetry (TRS) in the superconducting phase. No such field is observed in the Nd-doped alloys for x≥0.05, indicating that TRS has been restored. The superfluid density from the vortex-lattice field distribution is insensitive to Nd concentration for x 0.2, indicating that TRS restoration does not have a strong effect on the superconducting state. No Nd3+ static magnetism, ordered or disordered, is found down to the lowest temperatures of measurement.
  • Hiroyuki Hidaka, Shun Yanagiya, Eikai Hayasaka, Yuma Kaneko, Tatsuya Yanagisawa, Hiroshi Tanida, Hiroshi Amitsuka
    Journal of the Physical Society of Japan 91 9 2022年09月15日 [査読有り]
     
    The Ce-based metallic compound CeCoSi with a tetragonal structure exhibits successive phase transitions: a hidden ordering, whose order parameter is unidentified, at T0 ∼ 12 K and an antiferromagnetic ordering at TN = 9.4 K. [Tanida et al., J. Phys. Soc. Jpn. 88, 054716 (2019).] We performed specific heat, magnetoresistivity (MR), and magnetization (M) measurements for single crystals of CeCoSi at low temperatures in magnetic fields B of up to 14 T and constructed detailed magnetic field–temperature phase diagrams for both B k ½100] and [001]. In the longitudinal MR measurements for B k ½100], the sign of MR changes from negative in a paramagnetic state to positive in the hidden ordered state, which suggests a change in electronic state across T0. In addition, the longitudinal MR and magnetization processes for B k ½100] show anomalies upon the application of B in both ordered states, suggesting the presence of B-induced regions. Similar B-induced regions may exist in the magnetic phase diagram for B k ½001]. The emergence of B-induced regions may be attributed to a change in the symmetry of the order parameter or domain alignment on applying B.
  • Hiroyuki Hidaka, Yoshihiko Ihara, Tatsuya Yanagisawa, Hiroshi Amitsuka
    Journal of the Physical Society of Japan 90 9 093701 - 093701 2021年09月15日 [査読有り]
     
    9Be-NMR measurements were performed using single crystalline SmBe13 in order to investigate a magnetic structure of a low-temperature ordering state microscopically. We observed a spectral broadening in the ordered state, and the broadened spectral shape depends on the magnetic field directions. By comparing the experimentally obtained and simulated NMR spectra for magnetic fields along the cubic [001] and [011] directions, we argue a helical structure with a basal plane tilted from the (001) plane in low-field ordering region under the assumption of a helical with a propagation vector of (0, 0, 1/3) found in other RBe13 compounds (R = rare earths). Such a tilted helical structure is explained by a combination of an ellipse helical in the (001) plane and a longitudinal magnetic density wave along the [001] direction. Considering a magnetic easy axis parallel to [001] revealed by the magnetization measurements, the peculiar helical structure in SmBe13 may be built on delicate balance among exchange interactions, dipole-dipole interaction, and singleion magnetic anisotropy due to the crystalline electric field.
  • T. Yanagisawa, H. Matsumori, H. Saito, H. Hidaka, H. Amitsuka, S. Nakamura, S. Awaji, D. I. Gorbunov, S. Zherlitsyn, J. Wosnitza, K. Uhlířová, M. Vališka, V. Sechovský
    Physical Review Letters 126 15 2021年04月12日 [査読有り][通常論文]
     
    We present acoustic signatures of the electric quadrupolar degrees of freedom in the honeycomb-layer compound UNi4B. The transverse ultrasonic mode C66 shows softening below 30 K both in the paramagnetic phase and antiferromagnetic phases down to ∼0.33 K. Furthermore, we traced magnetic field-temperature phase diagrams up to 30 T and observed a highly anisotropic elastic response within the honeycomb layer. These observations strongly suggest that Γ6(E2g) electric quadrupolar degrees of freedom in localized 5f2 (J=4) states are playing an important role in the magnetic toroidal dipole order and magnetic-field-induced phases of UNi4B, and evidence some of the U ions remain in the paramagnetic state even if the system undergoes magnetic toroidal ordering.
  • Hiroyuki Hidaka, Kota Mizuuchi, Eikai Hayasaka, Tatsuya Yanagisawa, Jun Ohara, Hiroshi Amitsuka
    Physical Review B 102 17 2020年11月06日 [査読有り]
     
    The beryllide GdBe13 with the NaZn13-type face-centered-cubic structure has been known to undergo a proper helical-magnet ordering from experimental studies using polycrystalline samples. In the present study, we carried out electrical resistivity, specific heat, and magnetization measurements of single-crystalline GdBe13 in order to investigate a mechanism of its helical ordering. These measurements reveal that the present compound is a metallic system exhibiting the magnetic ordering of local Gd3+ moments at TN = 24.8 K accompanied with strong magnetic fluctuations extending to temperatures well above TN. Furthermore, we constructed a magnetic field-temperature (B-T) phase diagram for B [001]. It consists of a multidomain state, which is composed of magnetic structures with B applied parallel and perpendicular to the helical plane, in the lower-magnetic-field region below ∼0.45T and a possible single-domain conical one in the higher-field region in the ordering state. The helical structure of GdBe13 characterized by an incommensurate ordering vector q0 of (0, 0, 0.285) is discussed on the basis of a competition of Heisenberg exchange interactions between the Gd3+ moments assuming an one-dimensional layer crystal. The sequential change in the exchange interactions determined by a mean-field (MF) calculation can be essentially understood by the Ruderman-Kittel-Kasuya-Yosida interaction via anisotropic Fermi surfaces, whereas the orientation of the magnetic moments will be determined by the dipole-dipole interaction. On the other hand, the MF theory predicts a much smaller critical field Bc than the experimentally obtained one. To discuss the deviation of Bc from the MF calculation, we show a possibility of a fluctuation-induced first-order transition.
  • Hiroyuki Hidaka, Kota Mizuuchi, Tatsuya Yanagisawa, Hiroshi Amitsuka
    Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2019) 2020年03月19日 [査読有り]
  • Shintaro Nakamura, Satoshi Awaji, Tatsuya Yanagisawa, Takeaki Saito, Takeshi Matsumura, Akira Ochiai
    Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2019) 2020年03月19日 [査読有り]
  • Rare-Earth Atomic Motion in RBe13 (R: La, Pr, Sm)
    Satoshi Tsutsui, Yusei Shimizu, Hiroyuki Hidaka, Akinari Kohriki, Ryoya Murata, Yoshitaka Yoda, Tatsuya Yanagisawa, Hiroshi Amitsuka
    JPS Conf. Proc 30 011115-1 - 011115-6 2020年03月19日 [査読有り][通常論文]
  • Satoru Hamamoto and Yuina Kanai-Nakata and Hidenori Fujiwara and Kentaro Kuga and Takayuki Kiss and Atsushi Higashiya and Atsushi Yamasaki and Shin Imada and Arata Tanaka and Kenji Tamasaku and Makina Yabashi and Tetsuya Ishikawa and Hiroyuki Hidaka and Tatsuya Yanagisawa and Hiroshi Amitsuka and Akira Sekiyama
    JPS Conf. Proc. 29 012010  2020年02月 [査読有り][通常論文]
  • Tatsuya Yanagisawa and Hiroyuki Hidaka and Hiroshi Amitsuka and Sergei Zherlitsyn and Joachim Wosnitza and Yu Yamane and Takahiro Onimaru
    JPS Conf. Proc. 29 015002  2020年02月 [査読有り][通常論文]
  • Yanagisawa, T., Hidaka, H., Amitsuka, H., Nakamura, S., Awaji, S., Green, E.L., Zherlitsyn, S., Wosnitza, J., Yazici, D., White, B.D., Maple, M.B.
    Philosophical Magazine 100 10 1 - 14 2020年 [査読有り][通常論文]
     
    In this study, ultrasonic measurements were performed on a single crystal of cubic PrNi$_2$Cd$_{20}$, down to a temperature of 0.02 K, to investigate the crystalline electric field ground state and search for possible phase transitions at low temperatures. The elastic constant $(C_{11}-C_{12})/2$, which is related to the $\Gamma_3$-symmetry quadrupolar response, exhibits the Curie-type softening at temperatures below $\sim$30 K, which indicates that the present system has a $\Gamma_3$ non-Kramers doublet ground state. A leveling-off of the elastic response appears below $\sim$0.1 K toward the lowest temperatures, which implies the presence of level splitting owing to a long-range order in a finite-volume fraction associated with $\Gamma_3$-symmetry multipoles. A magnetic field-temperature phase diagram of the present compound is constructed up to 28 T for $H \parallel$ [110]. A clear acoustic de Haas-van Alphen signal and a possible magnetic-field-induced phase transition at $H \sim$26 T are also detected by high-magnetic-field measurements.
  • Hamamoto, S., Kanai, Y., Fujioka, S., Nakatani, Y., Fujiwara, H., Kuga, K., Kiss, T., Higashiya, A., Yamasaki, A., Imada, S., Tanaka, A., Tamasaku, K., Yabashi, M., Ishikawa, T., Hidaka, H., Yanagisawa, T., Amitsuka, H., Matsumoto, K.T., Onimaru, T., Takabatake, T., Sekiyama, A.
    Journal of Electron Spectroscopy and Related Phenomena 238 2020年 [査読有り][通常論文]
     
    © 2019 Elsevier B.V. We report the core-level photoemission study of cubic PrBe13, PrIr2Zn20 and PrB6 using linearly polarized hard X-ray. We have successfully observed linear dichroism (LD) in Pr3+ 3d core-level photoemission spectra reflecting the 4f ground-state symmetry for all the compounds. The observed LDs and polarization-dependent spectra are reproduced by ionic-model calculations including the full multiplet theory and the local crystalline electric field (CEF) splitting. We have confirmed that LDs in Pr3+ 3d core-level photoemission spectra are able to determine unambiguously the Pr3+ 4f ground-state symmetry.
  • Hidaka, H., Mizuuchi, K., Yanagisawa, T., Amitsuka, H.
    Journal of the Physical Society of Japan 88 3 2019年 [査読有り][通常論文]
     
    Magnetic susceptibility, specific heat, and electrical resistivity measurements have been performed on single-crystal EuBe13 in the temperature range between 2 and 300 K to investigate its phonon property and the valence state of the Eu ion. The obtained temperature dependence of the magnetic susceptibility curves obey a typical Van Vleck susceptibility for Eu3+ with a nonmagnetic ground state in the entire measured temperature range. In the case of the specific heat, we observed the coexistence of Debye and Einstein phonon modes with characteristic Debye and Einstein temperatures of ~ 835 K and ~167 K, respectively, which are in good agreement with those previously reported for other isostructural MBe13 compounds (M = rare earths and actinides). The temperature dependence of the resistivity for EuBe13 shows an unusual T-cubed like dependence at low temperatures, as also observed for the nonmagnetic isostructural compound LaBe13, which can be reproduced well by calculations based on electron--phonon scattering using the estimated Debye temperature and Einstein temperature. We also summarized the relationship between the Eu-valence state and the free distance between the Eu ion and the first-nearest-neighbor atoms in several Eu-based cubic compounds, and argued that EuBe13 takes the Eu3+ state despite its larger free distance than other Eu3+ compounds.
  • Yanagisawa, T., Hidaka, H., Amitsuka, H., Zherlitsyn, S., Wosnitza, J., Yamane, Y., Onimaru, T.
    Physical Review Letters 123 6 2019年 [査読有り][通常論文]
     
    Ultrasonic investigations of the single-site quadrupolar Kondo effect in diluted Pr system Y$_{0.966}$Pr$_{0.034}$Ir$_2$Zn$_{20}$ are reported. The elastic constant $(C_{11}-C_{12})/2$ is measured down to ~40 mK using ultrasound for the dilute system Y$_{0.966}$Pr$_{0.034}$Ir$_2$Zn$_{20}$ and the pure compound YIr$_2$Zn$_{20}$. We found that the elastic constant $(C_{11}-C_{12})/2$ of the Pr-dilute system exhibits a logarithmic temperature dependence below $T_0$ ~0.3 K, where non-Fermi-liquid (NFL) behavior in the specific heat and electrical resistivity is observed. This logarithmic temperature variation manifested in the $\Gamma_3$-symmetry quadrupolar susceptibility is consistent with the theoretical prediction of the quadrupolar Kondo effect by D. L. Cox. On the other hand, the pure compound YIr$_2$Zn$_{20}$ without $4f$-electron contributions shows nearly no change in its elastic constants evidencing negligible phonon contributions. In addition, clear acoustic de Haas-van Alphen (dHvA) oscillations in the elastic constant were detected for both compounds on applying magnetic field. This is mainly interpreted as contribution from the Fermi surface of YIr$_2$Zn$_{20}$.
  • Tabata Chihiro, Ihara Yoshihiko, Shimmura Shogo, Miura Naoyuki, Hidaka Hiroyuki, Yanagisawa Tatsuya, Amitsuka Hiroshi
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 87 11 2018年11月 [査読有り][通常論文]
     
    The magnetically ordered phase of body-centered-tetragonal UAu2Si2 was explored through Si-29-NMR experiments on a magnetically oriented powder sample. The field-swept NMR spectra show asymmetric peak splitting in a magnetic field applied along the tetragonal [001] axis below the magnetic phase transition temperature, T-N = 20K. This splitting is well explained by the occurrence of a magnetic order with a propagation vector of k = (2/3, 0, 0) and magnetic moments pointing parallel to the [001] axis, providing collateral evidence for uncompensated (++-)-type antiferro-magnetic ordering with a spontaneous [001] magnetization component.
  • Klára Uhlířová, Naoyuki Miura, Vladimír Tkáč, Jan Prokleška, Maciej Chrobak, Zbigniew Tarnawski, Hiroyki Hidaka, Tatsuya Yanagisawa, Vladimír Sechovský, Hiroshi Amitsuka
    Physica B: Condensed Matter 536 516 - 518 2018年05月01日 [査読有り][通常論文]
     
    Single crystals of ThBe13 and LuBe13 have been prepared using aluminum flux method. The crystals structure of both compounds was confirmed to be cubic of the NaZn13-type with the lattice parameters a = 10.183(6) Å and a = 10.395(3) Å for LuBe13 and ThBe13, respectively. The low temperature measurements of electrical resistance and ac susceptibility have revealed a BCS-type of superconductivity in ThBe13 below Tc = 125 mK. LuBe13 has been found to be superconducting below Tc = 630 mK.
  • Hidaka, H., Nagata, R., Tabata, C., Shimizu, Y., Miura, N., Yanagisawa, T., Amitsuka, H.
    Physical Review Materials 2 5 2018年 [査読有り][通常論文]
     
    The beryllides MBe13 (M = rare earths and actinides) crystallize in a NaZn13-type cubic structure, which can be categorized as a cage-structured compound. In this study, powder X-ray diffraction measurements have been performed on LaBe13, SmBe13, and UBe13 in the temperature range between 7 and 300 K in order to investigate their crystallographic characteristics systematically. They keep the NaZn13-type cubic structure down to the lowest temperature. We estimated their Debye temperature to be 600 - 750 K from analyses of the temperature dependence of a lattice parameter, being in good agreement with the values reported previously. Rietveld refinements on the obtained powder patterns revealed that the M atom in the 8a site is located in an almost ideal snub cube formed by 24 Be atoms in the 96i site, whose caged structure is unchanged even at the low temperatures. In addition, it is argued from the temperature variation of an isotropic mean-square displacement parameter that the MBe13 compounds commonly have a low-energy phonon mode, which can be described by a model assuming an Einstein oscillation of the M atom with a characteristic temperature of ~ 160 K.
  • Saito, H., Uenishi, K., Miura, N., Tabata, C., Hidaka, H., Yanagisawa, T., Amitsuka, H.
    Journal of the Physical Society of Japan 87 3 33702  2018年 [査読有り][通常論文]
     
    Magnetization measurements under direct electric currents were performed for toroidal magnetic ordered state of UNi$_4$B to test a recent theoretical prediction of current-induced magnetization in a metallic system lacking local inversion symmetry.We found that each of the electric currents parallel to [$2\bar{1}\bar{1}0$] and [$0001$] in the hexagonal 4-index notation induces uniform magnetization in the direction of [$01\bar{1}0$].The observed behavior of the induced magnetization is essentially consistent with the theoretical prediction; however it also shows an inconsistency suggesting that the antiferromagnetic state of UNi$_4$B could not simply be regarded as a uniform toroidal order in the ideal honeycomb layered structure.
  • Yanagisawa, T., Mombetsu, S., Hidaka, H., Amitsuka, H., Cong, P.T., Yasin, S., Zherlitsyn, S., Wosnitza, J., Huang, K., Kanchanavatee, N., Janoschek, M., Maple, M.B., Aoki, D.
    Physical Review B 97 15 2018年 [査読有り][通常論文]
     
    The elastic properties of URu2Si2 in the high magnetic field region above 40 T, over a wide temperature range from 1.5 to 120 K, were systematically investigated by means of high-frequency ultrasonic measurements. The investigation was performed at high magnetic fields to better investigate the innate bare 5f-electron properties, since the unidentified electronic thermodynamic phase of unknown origin, the so-called "hidden order" (HO), and associated hybridization of conduction and f electrons (c-f hybridization) are suppressed at high magnetic fields. From the three different transverse modes we find contrasting results both the Γ4(B2g) and Γ5(Eg) symmetry modes C66 and C44 show elastic softening that is enhanced above 30 T, while the characteristic softening of the Γ3(B1g) symmetry mode (C11-C12)/2 is suppressed in high magnetic fields. These results underscore the presence of a hybridization-driven Γ3(B1g) lattice instability in URu2Si2. However, the results from this work cannot be explained by using existing crystalline electric field schemes applied to the quadrupolar susceptibility in a local 5f2 configuration. Instead, we present an analysis based on a band Jahn-Teller effect.
  • Vališka, M., Saito, H., Yanagisawa, T., Tabata, C., Amitsuka, H., Uhlířová, K., Prokleška, J., Proschek, P., Valenta, J., Míšek, M., Gorbunov, D.I., Wosnitza, J., Sechovský, V.
    Physical Review B 98 17 2018年 [査読有り][通常論文]
     
    © 2018 American Physical Society. Thermal expansion, magnetostriction, and magnetization measurements under magnetic field and hydrostatic pressure were performed on a UAu2Si2 single crystal. They revealed a large anisotropy of magnetoelastic properties manifested by prominent length changes, leading to a collapse of the unit-cell volume accompanied by breaking the fourfold symmetry (similar to that in URu2Si2 in the hidden-order state) in the antiferromagnetic state as consequences of strong magnetoelastic coupling. The magnetostriction curves measured at higher temperatures confirm a bulk character of the 50K weak ferromagnetic phase. The large positive pressure change of the ordering temperature predicted from Ehrenfest relation contradicts the more than an order of magnitude smaller pressure dependence observed by the magnetization and specific heat measured under hydrostatic pressure. A comprehensive magnetic phase diagram of UAu2Si2 in magnetic field applied along the c axis is presented. The ground-state antiferromagnetic phase is suppressed by a field-induced metamagnetic transition that changes its character from second to first order at the tricritical point.
  • Satoshi Tsutsui, Yoshio Kobayashi, Jin Nakamura, Michael K. Kubo, Shota Amagasa, Yasuhiro Yamada, Yoshitaka Yoda, Yusei Shimizu, Yusei Shimizu, Hiroyuki Hidaka, Tatsuya Yanagisawa, Hiroshi Amitsuka, Akira Yamada, Ryuji Higashinaka, Tatsuma D. Matsuda, Yuji Aoki
    Hyperfine Interactions 238 2017年11月 [査読有り][通常論文]
     
    © 2017, Springer International Publishing AG, part of Springer Nature. Synchrotron-Radiation-based 149 Sm Mössbauer spectroscopy was applied to Sm intermetallics, SmBe 13 and SmTi 2 Al 20 . Temperature dependence of the Mössbauer parameters in SmBe 13 indicate the Sm valence state is purely trivalent. SmBe 13 also showed second-order Doppler shift in synchrotron-radiation-based 149 Sm Mössbauer spectroscopy. The Mössbauer parameters obtained in SmTi 2 Al 20 suggest that the Sm valence is fluctuating and the magnitude of the magnetic moment is reduced by hybridization between 4f and conduction electrons and/or effect of crystal electric field.
  • Hidaka Hiroyuki, Yamazaki Seigo, Shimizu Yusei, Miura Naoyuki, Tabata Chihiro, Yanagisawa Tatsuya, Amitsuka Hiroshi
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 86 7 2017年06月13日 [査読有り][通常論文]
     
    The physical properties of single-crystalline SmBe$_{13}$ with a NaZn$_{13}$-type cubic structure have been studied by electrical resistivity ($\rho$), specific heat ($C$), and magnetization ($M$) measurements in magnetic fields of up to 9 T. The temperature ($T$) dependence of $\rho$ shows normal metallic behavior without showing the Kondo -ln$T$ behavior, suggesting the weak hybridization effect in this system. Analyses of the temperature dependence of $C$ suggest that the Sm ions of this compound are trivalent and that the crystalline-electric-field (CEF) ground state is a $\Gamma_8$ quartet with a first-excited state of a $\Gamma_7$ doublet located at the energy scale of $\sim$ 90 K. Mean-field calculations based on the suggested CEF level scheme can reasonably well reproduce the $T$ dependence of magnetic susceptibility ($\chi$) below $\sim$ 70 K. These results in the paramagnetic state strongly indicate that the 4$f$ electrons are well localized with the Sm$^{3+}$ configuration. At low temperatures, the 4$f$ electrons undergo a magnetic order at $T_{\rm M}$ $\sim$ 8.3 K, where $\chi$($T$) shows an antiferromagnetic-like cusp anomaly. From the positive Curie--Weiss temperature obtained from the mean-field calculations and from a constructed magnetic phase diagram with multiple regions, we discussed the magnetic structure of SmBe$_{13}$ below $T_{\rm M}$, by comparing with other isostructural MBe$_{13}$ compounds showing helical-magnetic ordering.
  • Hiroyuki Hidaka, Yusei Shimizu, Yusei Shimizu, Seigo Yamazaki, Naoyuki Miura, Ryoma Nagata, Chihiro Tabata, Chihiro Tabata, Shota Mombetsu, Tatsuya Yanagisawa, Hiroshi Amitsuka
    Journal of the Physical Society of Japan 86 2 2017年01月17日 [査読有り][通常論文]
     
    ©2017 The Physical Society of Japan. The thermal and electrical transport properties of single-crystalline LaBe 13 have been investigated by specific-heat (C) and electrical-resistivity (ρ) measurements. The specific-heat measurements in a wide temperature range revealed the presence of a hump anomaly near 40 K in the C(T)/T curve, indicating that LaBe 13 has a low-energy Einstein-like-phonon mode with a characteristic temperature of ∼177 K. In addition, a superconducting transition was observed in the ρ measurements at the transition temperature of 0.53 K, which is higher than the value of 0.27 K reported previously by Bonville et al. Furthermore, an unusual T 3 dependence was found in ρ(T) below ∼50 K, in contrast to the behavior expected from the electron-electron scattering or the electron-Debye phonon scattering.
  • Pei Chun Ho, John Singleton, John Singleton, Paul A. Goddard, Fedor F. Balakirev, Shalinee Chikara, Tatsuya Yanagisawa, M. Brian Maple, M. Brian Maple, David B. Shrekenhamer, David B. Shrekenhamer, Xia Lee, Avraham T. Thomas, Avraham T. Thomas
    Physical Review B 94 20 2016年11月01日 [査読有り][通常論文]
     
    © 2016 American Physical Society. MHz conductivity, torque magnetometer, and magnetization measurements are reported on single crystals of CeOs4Sb12 and NdOs4Sb12 using temperatures down to 0.5 K and magnetic fields of up to 60 tesla. The field-orientation dependence of the de Haas-van Alphen and Shubnikov-de Haas oscillations is deduced by rotating the samples about the [010] and [01-1] directions. The results indicate that NdOs4Sb12 has a similar Fermi surface topology to that of the unusual superconductor PrOs4Sb12, but with significantly smaller effective masses, supporting the importance of local phonon modes in contributing to the low-temperature heat capacity of NdOs4Sb12. By contrast, CeOs4Sb12 undergoes a field-induced transition from an unusual semimetal into a high-field, high-temperature state characterized by a single, almost spherical Fermi-surface section. The behavior of the phase boundary and comparisons with models of the band structure lead us to propose that the field-induced phase transition in CeOs4Sb12 is similar in origin to the well-known α-γ transition in Ce and its alloys.
  • Chihiro Tabata, Chihiro Tabata, Naoyuki Miura, Klára Uhlířová, Michal Vališka, Hiraku Saito, Hiroyuki Hidaka, Tatsuya Yanagisawa, Vladimír Sechovský, Hiroshi Amitsuka
    Physical Review B 94 21 2016年08月22日 [査読有り][通常論文]
     
    © 2016 American Physical Society. Single-crystalline UAu2Si2 has been grown by a floating-zone melting method, and its magnetic, thermal, and transport properties have been investigated through measurements of magnetization, specific heat, and electrical resistivity to reveal its peculiar magnetism. It is shown that UAu2Si2 undergoes a second-order phase transition at Tm = 19 K, which had been believed to be ferromagnetic ordering in the literature, from a paramagnetic phase to an uncompensated antiferromagnetic phase with spontaneous magnetization along the tetragonal c axis (the easy magnetization direction). The magnetic entropy analysis points to the itinerant character of 5f electrons in the magnetic ordered state of UAu2Si2 with large enhancement of the electronic specific heat coefficient of γ∼150 mJ/K2mol at 2 K. It also reveals the relatively isotropic crystalline electric field effect of this compound, with contrast to the other relative isostructural compounds. The observed magnetization curves strongly suggest that there is a parasitic ferromagnetic component developing below ∼50 K in high coercivity with the easy axis along the tetragonal c axis. The results are discussed in the context of evolution of magnetism within the entire family of isostr uctural UT2Si2 compounds.
  • Satoshi Tsutsui, Ryo Masuda, Yasuhiro Kobayashi, Yoshitaka Yoda, Kota Mizuuchi, Yusei Shimizu, Hiroyuki Hidaka, Tatsuya Yanagisawa, Hiroshi Amitsuka, Fumitoshi Iga, Makoto Seto
    Journal of the Physical Society of Japan 85 8 2016年08月 [査読有り][通常論文]
     
    ©2016 The Physical Society of Japan. Synchrotron radiation 149 Sm Mössbauer spectroscopy in the energy domain has successfully been carried out on Sm 2 O 3 , SmBe 13 , and SmB 6 . The isomer shift values were determined in these compounds to discuss their Sm valence state. We also investigated the time window effect on spectra, which is useful for measuring spectra with "high-energyresolution". This effect makes it possible to discuss the frequency of valence fluctuation in Sm compounds as well as determine Sm valence state precisely using the 149 Sm Mössbauer effect. We discussed the fluctuation of the Sm valence in SmB 6 .
  • S. Mombetsu, T. Murazumi, H. Hidaka, T. Yanagisawa, H. Amitsuka, P. -C. Ho, M. B. Maple
    PHYSICAL REVIEW B 94 8 2016年08月 [査読有り][通常論文]
     
    We present high-frequency ultrasonic measurements on the filled skutterudite SmOs4Sb12 under hydrostatic pressure. The results clarify that the 4f electrons in this compound transform from delocalized at ambient pressure to localized at high pressures with a crossover pressure of approximately 0.7 GPa. This drastic change in the 4f electrons under pressure is apparently related to the non-Fermi-liquid state, which appears in an intermediate-pressure range of 0.5-1.5 GPa. The results of our analysis strongly suggest that the ferro-octupolar interaction becomes dominant at high pressure. Moreover, we report the pressure dependence of the ultrasonic dispersion, which is due to rattling, over a wide range of ultrasonic frequencies up to 323 MHz. The drastic change in the ultrasonic dispersions and the frequency-dependent elastic anomaly in the C-11 mode at lower temperatures imply a possible coupling between rattling phonons and 4f electrons.
  • Shota Mombetsu, Tatsuya Yanagisawa, Hiroyuki Hidaka, Hiroshi Amitsuka, Shadi Yasin, Sergei Zherlitsyn, Jochen Wosnitza, Pei Chun Ho, M. Brian Maple
    Journal of the Physical Society of Japan 85 4 2016年03月30日 [査読有り][通常論文]
     
    © 2016 The Physical Society of Japan. Our ultrasound results obtained in pulsed magnetic fields show that the filled-skutterudite compound SmOs 4 Sb 12 has the Γ 67 quartet crystalline-electric-field ground state. This fact suggests that the multipolar degrees of freedom of the Γ 67 quartet play an important role in the unusual physical properties of this material. On the other hand, the elastic response below ≈20 T cannot be explained using the localized 4 f-electron model, which does not take into account the Kondo effect or ferromagnetic ordering. The analysis result suggests the presence of a Kondo-like screened state at low magnetic fields and its suppression at high magnetic fields above 20 T even at low temperatures.
  • Yusei Shimizu, Yoshinori Haga, Tatsuya Yanagisawa, Hiroshi Amitsuka
    Physical Review B 93 2 2016年01月06日 [査読有り][通常論文]
     
    Static dc magnetization M(H) measurements were performed for a single crystal of UBe13 down to 0.1 K in magnetic fields up to 80 kOe for H(100) and H(110). For both field directions, an unusual magnetic anomaly was observed at HMag∗∼20-30 kOe in the superconducting mixed state. This anomaly was seen in the thermal-equilibrium-magnetization curves as well as the increasing- and decreasing-field processes of the raw magnetization curves, implying a change of the thermodynamic property at HMag∗. Furthermore, the magnetic anisotropy of the superconducting diamagnetic response is found to be significant above HMag∗, possibly associated with the anisotropy of the upper critical field Hc2. Considering the suppression of reduced upper critical field h∗ and the dramatic decrease of Maki parameter κ2 around 0.9Tc, the paramagnetic effect is present in UBe13. The paramagnetic effect in UBe13 could become anisotropic at low temperature below ∼Tc/2. An alternative explanation of the magnetic anisotropy is however that the anisotropy of the nonlinear susceptibility for the heavy electrons in the vortex cores becomes significant below ∼Tc/2.
  • Yusei Shimizu, Yoshinori Haga, Tatsuya Yanagisawa, Hiroshi Amitsuka
    PHYSICAL REVIEW B 93 2 2016年01月 [査読有り][通常論文]
     
    Static dc magnetization M(H) measurements were performed for a single crystal of UBe13 down to 0.1 K in magnetic fields up to 80 kOe for H parallel to < 100 > and H parallel to < 100 >. For both field directions, an unusual magnetic anomaly was observed at H-Mag* similar to 20-30 kOe in the superconducting mixed state. This anomaly was seen in the thermal-equilibrium-magnetization curves as well as the increasing-and decreasing-field processes of the raw magnetization curves, implying a change of the thermodynamic property at H-Mag*. Furthermore, the magnetic anisotropy of the superconducting diamagnetic response is found to be significant above H-Mag*, possibly associated with the anisotropy of the upper critical field H-c2. Considering the suppression of reduced upper critical field h* and the dramatic decrease of Maki parameter kappa(2) around 0.9T(c), the paramagnetic effect is present in UBe13. The paramagnetic effect in UBe13 could become anisotropic at low temperature below similar to T-c/2. An alternative explanation of the magnetic anisotropy is however that the anisotropy of the nonlinear susceptibility for the heavy electrons in the vortex cores becomes significant below similar to T-c/2.
  • S. Mombetsu, T. Murazumi, K. Hiura, S. Yamazaki, Y. Shimizu, H. Hidaka, T. Yanagisawa, H. Amitsuka, S. Yasin, S. Zherlitsyn, J. Wosnitza
    TMU INTERNATIONAL SYMPOSIUM ON NEW QUANTUM PHASES EMERGING FROM NOVEL CRYSTAL STRUCTURE 683 2016年 [査読有り][通常論文]
     
    Ultrasonic measurements were performed on the cage-structure compound SmBe13. We have investigated the magnetic field temperature phase diagram of this material by using pulsed magnetic fields. We found that the low-temperature magnetic order is suppressed by a magnetic field of 43 T for H parallel to [001], which is smaller than the estimated value from mean-field approximation assuming the Gamma(8) quartet crystal-electric-field ground state and simple antiferromagnetic order. We found that the elastic constant C-44 shows softening below the ordering temperature and has a local minimum below 7 T. These facts suggest that the low temperature state is not a simple antiferromagnetically ordered state. In addition, no elastic anomaly due to rattling modes was found in the present measurements.
  • Hiroyuki Hidaka, Shinya Otani, Hiraku Saito, Kaori Tatsumi, Tatsuya Yanagisawa, Hiroshi Amitsuka
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 385 428 - 432 2015年07月 [査読有り][通常論文]
     
    We have performed electrical-resistivity measurements under hydrostatic pressures ranging up to 4.47 GPa on the cubic compound CeAg. A pressure-temperature phase diagram has been revised in a high-pressure range above similar to 2.1 GPa, where the system is known to enter into an unidentified phase through a first-order phase transition. We have found that the electrical resistivity shows a clear kink anomaly below similar to 4 K in this unknown phase. The anomaly shifts to lower temperature with increasing pressure, and shows a tendency to reach absolute zero at similar to 6 GPa, suggesting the presence of a pressure induced quantum critical point around this pressure. We have also observed that a first order phase boundary line, which separates the phase diagram into two regions of a tetragonal phase and the unidentified phase, seems to terminate in a critical end point located at (P-CEP, T-CEP) similar to(3.2 GPa, 200 K). This suggests that the crystal symmetry of the unidentified phase above similar to 2.1 GPa is also tetragonal. (C) 2015 Elsevier B.V. All rights reserved
  • D. Yazici, T. Yanagisawa, B. D. White, M. B. Maple
    PHYSICAL REVIEW B 91 11 115136.1-115136.7  2015年03月 [査読有り][通常論文]
     
    Temperature-dependent magnetization, specific-heat, and electrical-resistivity measurements were performed on single crystals of PrNi2Cd20 and PrPd2Cd20. Neither compound shows any evidence for magnetic order above 2 K. Magnetization measurements suggest that Pr ions assume a nonmagnetic Gamma(1) singlet or non-Kramers Gamma(3) doublet ground state. A broad peak, which is identified as a Schottky anomaly, is observed in the specific heat at low temperature. Low-lying excitations involving the 4f electrons persist down to 2 K for both PrNi2Cd20 and PrPd2Cd20 and related features are also observed in the magnetization and electrical resistivity.
  • Tatsuya Yanagisawa, Kenta Hiura, Shota Mombetsu, Taro Murazumi, Hiroyuki Hidaka, Hiroshi Amitsuka, Naoyuki Tateiwa, Yoshinori Haga
    INTERNATIONAL CONFERENCE ON STRONGLY CORRELATED ELECTRON SYSTEMS 2014 (SCES2014) 592 2015年 [査読有り][通常論文]
     
    The elastic properties of localized 5f-electron system U3Pd20Si6 were studied by means of ultrasonic measurements under magnetic fields. We have measured elastic constants C-11, (C-11-C-12)/2, C-44 and C-L110 = C-B + (C-11-C-12)/6 + C-44 in order to check a possible contribution of electric quadrupoles on the magnetically ordered phases of this compound for Gamma(1) Gamma(3), Gamma(5) and Fi e F3 e F5 symmetries elastic response, respectively. We discovered that an elastic anomaly, which is accompanied by ultrasonic attenuation maximum of F5symmetry mode, at around T* similar to 16 K in zero magnetic field and shifts to lower temperatures with increasing magnetic fields. Since the T* seems to be continuously connected to the lower boundary of a 'spin-flop' region in the magnetic field-temperature phase diagram of U3Pd20Si6, we conclude that a fluctuation of the spin-system of the 8c-site ion exists even just below TN and couples to elastic wave via magneto-elastic coupling with F5-symmetry quadrupoles of U's 5f electron or local charge distributions of the guest U ion.
  • C. Tabata, T. Inami, S. Michimura, M. Yokoyama, H. Hidaka, T. Yanagisawa, H. Amitsuka
    PHILOSOPHICAL MAGAZINE 94 32-33 3691 - 3701 2014年11月 [査読有り][通常論文]
     
    We performed synchrotron X-ray diffraction measurements on a small single crystal of [GRAPHICS] with approximate dimensions of [GRAPHICS] . A backscattering diffraction set-up (2 [GRAPHICS] ) in combination with a Si(660) monochromator ensures a high instrumental resolution of [GRAPHICS] , where [GRAPHICS] denotes a lattice-plane spacing and [GRAPHICS] is its spread expressed as the full width at half maximum (FWHM). We carefully measured the (550) Bragg peak in the temperature range between 5 and 25K, and found it to show no signature of broadening and splitting when "Hidden Order (HO)" sets in below 17.5K. Temperature variation of the peak position closely follows the behaviour of the known linear thermal expansion coefficient. Detailed analysis of the peak width reveals that the tetragonal fourfold rotational symmetry of [GRAPHICS] is conserved in HO within the experimental accuracy of the orthorhombicity of [GRAPHICS] . We also found that the (550) peak profile exhibits a temperature-independent fine structure, which indicates that the tetragonal [GRAPHICS] -axis lattice parameter of the used crystal is distributed with a FWHM of [GRAPHICS] .
  • Tatsuya Yanagisawa
    Philosophical Magazine 94 32-33 3775 - 3788 2014年11月 [査読有り][通常論文]
     
    This paper reports recent progress of ultrasonic measurements on URu$_2$Si$_2$, including ultrasonic measurements under hydrostatic pressure, in pulsed-magnetic fields, and the effect of Rh-substitution. The observed changes of the elastic responses shed light on the orthorhombic-lattice instability with $\Gamma_3$-symmetry existing within the hidden order and the hybridized 5$f$-electron states of URu$_2$Si$_2$.
  • P. -C. Ho, D. E. MacLaughlin, Lei Shu, O. O. Bernal, Songrui Zhao, A. A. Dooraghi, T. Yanagisawa, M. B. Maple, R. H. Fukuda
    PHYSICAL REVIEW B 89 23 235111.1-235111.7  2014年06月 [査読有り][通常論文]
     
    Positive-muon (mu(+)) Knight shifts have been measured in the paramagnetic states of Pr1-xNdxOs4Sb12 alloys, where x = 0, 0.25, 0.45, 0.50, 0.55, 0.75, and 1.00. In Pr-substituted NdOs4Sb12 (x 0.75), but not in NdOs4Sb12, Clogston-Jaccarino plots of mu(+) Knight shift K versus magnetic susceptibility. exhibit an anomalous saturation of K(chi) at similar to 0.5% for large susceptibilities (low temperatures), indicating a reduction of the coupling strength between mu(+) spins and 4f paramagnetism for temperatures less than or similar to 15 K. We speculate that itinerant Pr3+ quadrupolar excitations, invoked to mediate the superconducting Cooper-pair interaction, might modify the mu(+) -4f ion indirect spin-spin interaction.
  • D. E. MacLaughlin, P. -C. Ho, Lei Shu, O. O. Bernal, Songrui Zhao, A. A. Dooraghi, T. Yanagisawa, M. B. Maple, R. H. Fukuda
    PHYSICAL REVIEW B 89 14 2014年04月 [査読有り][通常論文]
     
    Muon spin rotation and relaxation (mu SR) experiments have been carried out to characterize magnetic and superconducting ground states in the Pr1-xNdxOs4Sb12 alloy series. In the ferromagnetic end compound NdOs4Sb12 the spontaneous local field at positive-muon (mu(+)) sites below the ordering temperature T-C is greater than expected from dipolar coupling to ferromagnetically aligned Nd3+ moments, indicating an additional indirect RKKY-like transferred hyperfine mechanism. For 0.45 <= x <= 0.75, mu(+) spin relaxation rates in zero and weak longitudinal applied fields indicate that static fields at mu(+) sites below T-C are reduced and strongly disordered. We argue this is unlikely to be due to reduction of Nd3+ moments, and speculate that the Nd3+-mu(+) interaction is suppressed and disordered by Pr doping. In an x = 0.25 sample, which is superconducting below T-C = 1.3 K, there is no sign of "spin freezing" ( static Nd3+ magnetism), ordered or disordered, down to 25 mK. Dynamic mu(+) spin relaxation is strong, indicating significant Nd- moment fluctuations. The mu(+) diamagnetic frequency shift and spin relaxation in the superconducting vortex-lattice phase decrease slowly below T-C, suggesting pair breaking and/or possible modification of Fermi-liquid renormalization by Nd spin fluctuations. For 0.25 <= x <= 0.75, the mu SR data provide evidence against phase separation; superconductivity and Nd3+ magnetism coexist on the atomic scale.
  • Maclaughlin, D.E., Ho, P.-C., Shu, L., Bernal, O.O., Zhao, S., Dooraghi, A.A., Yanagisawa, T., Maple, M.B., Fukuda, R.H.
    Physical Review B - Condensed Matter and Materials Physics 89 14 144419.1-144419.12  2014年04月 [査読有り][通常論文]
  • Polarized Light Microscopic Study of the Hidden Order Phase in URu2Si2
    Chihiro Tabata, Masashi Tokunaga, Makoto Yokoyama, Hiroyuki Hidaka, Tatsuya Yanagisawa, Hiroshi Amitsuka
    JPS Conf. Proc. 3 011062  2014年 [査読有り][通常論文]
  • Simultaneous Measurements of Elastic Constant and Resistivity near the Tc of Non-BCS-Type Superconductor PrOs4Sb1
    Shota Mombetsu, Taro Murazumi, Kenta Hiura, Hiroyuki Hidaka, Tatsuya Yanagisawa, Hiroshi Amitsuka, M. Brian Maple
    JPS Conf. Proc. 3 015021  2014年 [査読有り][通常論文]
  • Yusei SHIMIZU, Yoshinori HAGA, Tatsuya YANAGISAWA, Hiroshi AMITSUKA, Dai AOKI, Jean-Pascal BRISON, Daniel BRAITHWAITE
    JPS Conf. Proc. 3 015009-1 - 015009-6 2014年 [査読有り][通常論文]
  • T. Yanagisawa, S. Mombetsu, H. Hidaka, H. Amitsuka, M. Akatsu, S. Yasin, S. Zherlitsyn, J. Wosnitza, K. Huang, M. Janoschek, M. B. Maple
    Physical Review B - Condensed Matter and Materials Physics 88 19 195150-1 - 195150-5 2013年11月26日 [査読有り][通常論文]
     
    We have measured the elastic constant (C11-C12)/2 in URu2Si2 by means of high-frequency ultrasonic measurements in pulsed magnetic fields H [001] up to 61.8 T in a wide temperature range from 1.5 to 116 K. We found a reduction of (C11-C12)/2 that appears only in the temperature and magnetic field region in which URu 2Si2 exhibits a heavy-electron state and hidden order. This change in (C11-C12)/2 appears to be a response of the 5f electrons to an orthorhombic and volume conservative strain field εxx-εyy with Γ3 symmetry. This lattice instability is likely related to a symmetry-breaking band instability that arises due to the hybridization of the localized f electrons with the conduction electrons and is probably linked to the hidden-order parameter of this compound. © 2013 American Physical Society.
  • Tatsuya Yanagisawa, Shota Mombetsu, Hiroyuki Hidaka, Hiroshi Amitsuka, Mitsuhiro Akatsu, Shadi Yasin, Sergei Zherlitsyn, Jochen Wosnitza, Kevin Huang, M. Brian Maple
    J. Phys. Soc. Jpn. 82 (2012) 013601 82 1 2013年01月 [査読有り][通常論文]
     
    We have performed ultrasonic measurements on single-crystalline URu2Si2 with
    pulsed magnetic fields, in order to check for possible lattice instabilities
    due to the hybridized state and the hidden-order state of this compound. The
    elastic constant (C11-C12)/2, which is associated with a response to the
    {\Gamma}3-type symmetry-breaking (orthorhombic) strain field, shows a
    three-step increase at H > 35 T for H || c at low temperatures, where
    successive meta-magnetic transitions are observed in the magnetization. We
    discovered a new fact that the absolute change of the softening of (C11-C12)/2...
  • Yusei Shimizu, Yoshinori Haga, Yoichi Ikeda, Tatsuya Yanagisawa, Hiroshi Amitsuka
    PHYSICAL REVIEW LETTERS 109 21 217001.1-217001.5  2012年11月 [査読有り][通常論文]
     
    We have performed precise dc magnetization measurements for a single crystal of UBe13 down to 0.14 K, up to 80 kOe. We observed a magnetic anomaly in the superconducting (SC) mixed state at a field, named H-Mag* (similar to 26 kOe, at 0.14 K), implying that UBe13 has a magnetically unusual SC state. We studied the magnetization curves of UBe13, assuming that the H-Mag* anomaly originates from (1) and unusual SC diamagnetic response, or (2) a peculiarity of the normal-state magnetization due to vortices in the SC mixed state. The origin of the H-Mag* anomaly is discussed.
  • IKEDA Yoichi, ARAKI Shingo, KOBAYASHI Tatsuo C, Shimizu Yusei, Yanagisawa Tatsuya, Amitsuka Hiroshi
    J Phys Soc Jpn 81 8 83701 - 083701-4 Physical Society of Japan 2012年06月25日 [査読有り][通常論文]
     
    The effects of Ni substitution on Ce(Cu1-xNix)2Si2 have been studied by specific heat and electrical resistivity measurements. The specific heat measurement has revealed that the enhanced quantum fluctuations around an antiferromagnetic quantum critical point are markedly suppressed by Ni substitution, and that the Fermi liquid state recovers in the Ni-rich region (x \gtrsim 0.12). The characteristic T-linear dependence of the resistivity has been observed at approximately x \sim 0.10 together with a sign of superconductivity. The variation of n in the form of \rho - \rho_{0} = aT^{n} again...
  • 網塚浩, 田端千紘, 日高宏之, 柳澤達也, 横山淳, LUMSDEN M. D, KANCHANAVATEE N, BUTCH N. P, MAPLE M. B
    NSL News Lett 12-Jan 13,51-54  2012年 [査読無し][通常論文]
  • 柳澤達也
    物性研究 97 4 791 - 823 物性研究刊行会 2012年01月 [査読有り][通常論文]
  • H. Hidaka, S. M. Ramos, E. N. Hering, M. B. Fontes, E. B. Saitovitch, S. Otani, T. Wakabayashi, Y. Shimizu, T. Yanagisawa, H. Amitsuka
    INTERNATIONAL CONFERENCE ON STRONGLY CORRELATED ELECTRON SYSTEMS (SCES 2011) 391 2012年 [査読有り][通常論文]
     
    We have measured the electrical resistivity of clathrate Ce3Pd20Ge6 under high pressure up to 3.86 GPa in order to investigate pressure effects on two successive phase transitions: O-2(0)-type ferroquadrupole order on Ce-8c site at T-Q = 1.2 K and antiferromagnetic order on Ce-4a site at T-N = 0.75 K. With applying pressure, T-Q stays nearly constant at low pressures and gradually decreases above 2 GPa, while T-N first increases and then decreases above 2.5 GPa. From these results, critical pressures, where T-N T-Q become 0, are roughly estimated to be around 5 - 6 GPa. In addition, we found that the magnetic resistivity, which is obtained by subtracting the resistivity of La3Pd20Ge6 from that Ce3Pd20Ge6, exhibits -lnT dependence in two different temperature ranges, suggesting presence of two different Kondo temperatures originated in the two crystallographic Ce-sites.
  • Yusei Shimizu, Yoshinori Haga, Kenichi Tenya, Tatsuya Yanagisawa, Hiroyuki Hidaka, Hiroshi Amitsuka
    INTERNATIONAL CONFERENCE ON STRONGLY CORRELATED ELECTRON SYSTEMS (SCES 2011) 391 2012年 [査読有り][通常論文]
     
    We have studied anomalous upper critical field B-c2(T) of a single crystal of UBe13 by DC magnetization measurements down to 0.14 K and up to 8 T. We have observed a broad anomaly and a peak effect below B-c2 in magnetization curves. Although a possibility of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state has been proposed as an origin of the unusual upper critical field by previous works, our results have shown that thermal equilibrium magnetization curves reveal no step-like behavior, which could be observed at 1st-order phase transition from a superconducting mixed state to the FFLO state. We have also investigated anisotropy of B-c2 for B parallel to < 001 > and B parallel to < 110 >, and found that B-c2 for B parallel to < 001 > is larger than B-c2 for B parallel to < 110 > below similar to 0.5 K. These results might indicate that the anomalous upward curvature of B-c2 in UBe13 is related to anisotropy of B-c2 rather than the FFLO state.
  • T. Yanagisawa, H. Saito, Y. Watanabe, Y. Shimizu, H. Hidaka, H. Amitsuka
    INTERNATIONAL CONFERENCE ON STRONGLY CORRELATED ELECTRON SYSTEMS (SCES 2011) 391 2012年 [査読有り][通常論文]
     
    Ultrasonic investigations of the elastic constants of non-5f compound ThRu2Si2 were performed in order to highlight possible quadrupolar response in the elastic constants of heavy fermion compound URu2Si2, by using the ThRu2Si2 for backgrounds to subtract the phonon contributions in the elastic constants of URu2Si2. We confirmed that the all-elastic constants of ThRu2Si2 show no elastic anomaly, i.e., increasing monotonically and saturating toward low temperatures, which can be understood regular phonon contributions for the solid states. The background-subtracted (C-11-C-12)2 of URu2Si2 keeps decreasing with decreasing temperatures from 300 K, while other share modes C-44 and C-66 show little change. These contrasts suggest that the Gamma(3)-type quadrupole moment O-2(2) will be still dominant and active in URu2Si2 at low temperatures.
  • Hiroyuki Hidaka, Sosuke Takahashi, Yusei Shimizu, Tatsuya Yanagisawa, Hiroshi Amitsuka
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 Supplement A SA102.1-SA102.3  2011年07月 [査読有り][通常論文]
     
    The electrical resistivity rho of the ferromagnet U4Ru7Ge6 has been studied under high pressure up to similar to 4.5 GPa by using an indenter-type high-pressure cell. The Curie temperature T-C = 11.2 K at ambient pressure decreases monotonously with increasing pressure, and seems to disappear at similar to 2.6 GPa, where an enhancement of the coefficient A assuming Fermi liquid regime is observed. This result indicates a presence of a quantum critical point (QCP) of U4Ru7Ge6 at around 2.6 GPa. In addition, non-Fermi liquid behavior (rho similar to T-5/3) predicted by the SCR theory of three dimensional ferromagnet is also observed near the QCP.
  • YANAGISAWA Tatsuya, TATEIWA Naoyuki, MAYAMA Taichi, SAITO Hitoshi, HIDAKA Hiroyuki, AMITSUKA Hiroshi, HAGA Yoshinori, NEMOTO Yuichi, GOTO Terutaka
    J Phys Soc Jpn 80 Supplement A SA105.1-SA105.3  2011年07月 [査読有り][通常論文]
     
    Ultrasonic measurements of U3Pd20Si6 were performed in order to investigate elastic properties of the cage-structured compound U3Pd20Si6 and also examine a presence of ultrasonic dispersion (UD) due to off-center rattling, which has been observed in the elastic constant C-44 of similar systems R3Pd20Ge6 (R = La - Nd). At temperatures over antiferromagnetic ordering at T-N = 19 K, neither an up-turn anomaly nor frequency dependence of the elastic constants, regarding the UD, was found. On the other hand, the elastic constant C-44 shows pronounced softening due to crystalline electric field effect of U4+ ion's Gamma(5) triplet ground state for both 4a and 8c sites. Below T-N, precipitous elastic softening accompanied by a sudden depression of ultrasonic echo was observed in each ultrasonic mode. A drastic change of Delta C-44/C-44 similar to 30% at T-N, in particular, implies a strong magneto-elastic coupling of 5f-electrons or a possible contribution of a ferroquadrupole interaction to the antiferromagnetism in U3Pd20Si6.
  • Yusei Shimizu, Yoichi Ikeda, Takumi Wakabayashi, Kenichi Tenya, Yoshinori Haga, Hiroyuki Hidaka, Tatsuya Yanagisawa, Hiroshi Amitsuka
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 Supplement A SA100.1-SA100.3  2011年07月 [査読有り][通常論文]
     
    Low-temperature specific heat and static dc magnetizetion measurements have been performed for the superconducting state of the heavy-fermion compound UBe13. The superconducting phase diagram B-c2-T (B parallel to [110]) has been obtained by our specific heat and magnetization measurements. From the slope of the upper critical field and specific heat jumps at superconducting transition temperatures in magnetic fields, we have also obtained a temperature dependence of Ginzburg-Landau parameter kappa(2) along [110]. It has been revealed that kappa(2) decreases with decreasing temperature down to 0.5 K, which indicates that a paramagnetic effect may be present at least down to 0.5 K for [110].
  • Shimizu Yusei, Ikeda Yoichi, Wakabayashi Takumi, Haga Yoshinori, Tenya Kenichi, Hidaka Hiroyuki, Yanagisawa Tatsuya, Amitsuka Hiroshi
    J Phys Soc Jpn 80 9 93701 - 093701-4 Physical Society of Japan 2011年06月13日 [査読有り][通常論文]
     
    We have performed low-temperature specific-heat measurements in magnetic fields for a single crystal UBe13. It has been observed that our sample exhibits a superconducting transition at an intermediate temperature (T_{\text{c } } \sim 0.81 K) between previously reported values for two variant samples called H type and L type. The specific heat C(T) of our sample shows a T^{3} behavior below {\sim}0.7 T_{\text{c } }, which is similar to the behavior of the H-type sample, suggesting the existence of point nodes in the superconducting gap function. We have obtained the upper-critical-field curves ...
  • Yanagisawa Tatsuya, Ikeda Yoichi, Saito Hitoshi, Hidaka Hiroyuki, Amitsuka Hiroshi, Araki Koji, Akatsu Mitsuhiro, Nemoto Yuichi, Goto Terutaka, Ho Pei-Chun, Baumbach Ryan E, Maple M. Brian
    Journal of the Physical Society of Japan 80 4 43601 - 043601-4 Physical Society of Japan 2011年04月 [査読有り][通常論文]
     
    Elastic properties of the filled skutterudite compound SmOs4Sb12 have been investigated by ultrasonic measurements. The elastic constant C11(ω) shows two ultrasonic dispersions at ∼15 and ∼53 K for frequencies ω between 33 and 316 MHz, which follow a Debye-type formula with Arrhenius-type temperaturedependent relaxation times and remain unchanged even with applied magnetic fields up to 10 T. The corresponding activation energies were estimated to be E2 = 105 K and E1 = 409 K, respectively. The latter, E1, is the highest value reported thus far in the Sb-based filled skutterudites. The prese...
  • P. C. Ho, T. Yanagisawa, W. M. Yuhasz, A. A. Dooraghi, C. C. Robinson, N. P. Butch, R. E. Baumbach, M. B. Maple
    Physical Review B - Condensed Matter and Materials Physics 83 2 024511.1-024511.6  2011年01月31日 [査読有り][通常論文]
     
    Superconductivity, magnetic order, and the high field ordered phase have been investigated in the filled skutterudite system Pr1-xNd xOs4Sb12 as a function of composition x in magnetic fields up to 9 T and at temperatures between 50 mK and 10 K. Electrical resistivity measurements indicate that the high field ordered phase, which has been identified with antiferroquadruoplar order, persists to x ∼ 0.5. The superconducting critical temperature Tc of PrOs4Sb 12 is depressed linearly with Nd concentration to x ∼ 0.55, whereas the Curie temperature TFM of NdOs4Sb12 is depressed linearly with Pr composition to (1-x) ∼ 0.45. In the superconducting region, the upper critical field Hc2(x,0) is depressed quadratically with x in the range 0 < x 0.3, exhibits a kink at x ≈ 0.3, and then decreases linearly with x in the range 0.3 ≲ x ≲ 0.6. The behavior of Hc2(x,0) appears to be a result of pair breaking caused by the applied magnetic field and the exchange field associated with the polarization of the Nd magnetic moments in the superconducting state. From magnetic susceptibility measurements, the correlations between the Nd moments in the superconducting state appear to change from ferromagnetic in the range 0.3 ≲ x ≲ 0.6 to antiferromagnetic in the range 0 < x ≲ 0.3. Specific-heat measurements on a sample with x = 0.45 indicate that magnetic order may occur in the superconducting state, as is also inferred from the depression of Hc2(x,0) with x. © 2011 American Physical Society.
  • P. -C. Ho, T. Yanagisawa, W. M. Yuhasz, A. A. Dooraghi, C. C. Robinson, N. P. Butch, R. E. Baumbach, M. B. Maple
    PHYSICAL REVIEW B 83 2 2011年01月 [査読有り][通常論文]
     
    Superconductivity, magnetic order, and the high field ordered phase have been investigated in the filled skutterudite system Pr1-xNdxOs4Sb12 as a function of composition x in magnetic fields up to 9 T and at temperatures between 50 mK and 10 K. Electrical resistivity measurements indicate that the high field ordered phase, which has been identified with antiferroquadruoplar order, persists to x similar to 0.5. The superconducting critical temperature T-c of PrOs4Sb12 is depressed linearly with Nd concentration to x similar to 0.55, whereas the Curie temperature T-FM of NdOs4Sb12 is depressed linearly with Pr composition to (1 - x) similar to 0.45. In the superconducting region, the upper critical field H-c2(x, 0) is depressed quadratically with x in the range 0 < x less than or similar to 0.3, exhibits a kink at x approximate to 0.3, and then decreases linearly with x in the range 0.3 less than or similar to x less than or similar to 0.6. The behavior of H-c2(x, 0) appears to be a result of pair breaking caused by the applied magnetic field and the exchange field associated with the polarization of the Nd magnetic moments in the superconducting state. From magnetic susceptibility measurements, the correlations between the Nd moments in the superconducting state appear to change from ferromagnetic in the range 0.3 less than or similar to x less than or similar to 0.6 to antiferromagnetic in the range 0 < x less than or similar to 0.3. Specific-heat measurements on a sample with x = 0.45 indicate that magnetic order may occur in the superconducting state, as is also inferred from the depression of H-c2(x, 0) with x.
  • Yusei Shimizu, Yoichi Ikeda, Takumi Wakabayashi, Kenichi Tenya, Yoshinori Haga, Hiroyuki Hidaka, Tatsuya Yanagisawa, Hiroshi Amitsuka
    INTERNATIONAL CONFERENCE ON STRONGLY CORRELATED ELECTRON SYSTEMS (SCES 2010) 273 2011年 [査読有り][通常論文]
     
    Static dc magnetization measurements in the superconducting mixed state of a single crystal UBe13 along the [110] axis were performed by means of a capacitance Faraday-force method down to 0.24 K. Below the upper critical field B-c2, not only a peak effect but also an additional broad anomaly have been observed in magnetization curves. We report superconducting phase diagram of UBe13 obtained by our magnetization measurements, including these anomalies.
  • H. Hidaka, A. Tanaka, S. Takahashi, T. Yanagisawa, H. Amitsuka
    INTERNATIONAL CONFERENCE ON STRONGLY CORRELATED ELECTRON SYSTEMS (SCES 2010) 273 2011年 [査読有り][通常論文]
     
    We have studied the effects of pressure on the incommensurate (IC)-commensurate (C) antiferromagnetic (AFM) phase transition of UPd2Si2 by measuring the electrical resistivity up to 4.21 GPa. We observed that the low-temperature C-AFM (type-I) phase expands and prevails over the IC-AFM phase as pressure is increased. The obtained pressure-temperature phase diagram strongly suggests the existence of a novel bicritical point, more specifically, the so-called Lifshitz point at P-c similar to 3.4 GPa, where magnetic modulation continuously changes from IC to C.
  • T. Yanagisawa, H. Saitoh, H. Hidaka, H. Amitsuka, T. Cichorek, Z. Henkie, M. B. Maple
    INTERNATIONAL CONFERENCE ON STRONGLY CORRELATED ELECTRON SYSTEMS (SCES 2010) 273 2011年 [査読有り][通常論文]
     
    Ultrasonic measurements with frequencies varying between 73 and 160 MHz were performed for the LaRu4As12 single crystal. This As-based filled skutterudite compound is a BCS-type superconductor with T-SC as high as 10.3 K. In order to examine a presence of off-center rattling motion in LaRu4As12, we measured elastic constants C-L111 = (C-11 2C(12) 4C(44))/3 and C-T111 = (C-11- C-12 +4C(44))/3, which are related to longitudinal and transverse sound waves propagating along the [111] direction, respectively. No ultrasonic dispersion was found in the whole temperature range from 1.4 to 300 K.
  • T Yanagisawa, H Saito, T Mayama, Y Ikeda, H Hidaka, M Yokoyama, H Amitsuka
    Journal of Physics: Conference Series 200 1 012236 - 012236 2010年02月 [査読有り]
  • H. Amitsuka, T. Inami, M. Yokoyama, S. Takayama, Y. Ikeda, I. Kawasaki, Y. Homma, H. Hidaka, T. Yanagisawa
    INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009) 200 2010年 [査読有り][通常論文]
     
    We have studied a puzzling phase below 17.5 K of URu2Si2 by means of resonant Xray scattering (RXS) near the U M-IV absorption edge (E similar to 3.73 keV), using a high-quality single-crystalline sample with low residual stress. We reconfirm that a commensurate (003) superlattice reflection comes purely from antiferromegnetic dipolar order with ordering wave vector Q(AF) = (1, 0, 0). No other traces of significant RXS have been detected in a major region of (h0l) plane, indicating absence of quadrupolar order within a searched Q range including a conceivable nesting vector Q* = (1.4, 0, 0).
  • T. Yanagisawa, H. Saito, T. Mayama, Y. Ikeda, H. Hidaka, M. Yokoyama, H. Amitsuka
    INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009) 200 2010年 [査読有り][通常論文]
     
    Ultrasonic measurements on Rh-substitution system U(Ru1-xRhx)(2)Si-2 (x = 0,0.02 and 0.07) were performed in order to investigate lattice properties for low temperature phase transitions of 'hidden order'(HO) phase and antiferromagnetc (AFM) phase. Elastic constant C-11 vs. T of the x = 0.02 and 0.07 samples exhibit a depression below 80 K, which is similar to a softening in the non-doped sample which had already been reported. The C-11 of x = 0.02 exhibits a step-like anomaly at 14.0 K and an additional softening of 3.2% with minimum at 6.7 K, which correspond to HO and AFM transitions, respectively. The C-11 in x = 0.07 sample only exhibits a shoulder-like anomaly at around 17 K and continue to depress down to 4.2 K.
  • Yoichi Ikeda, Makoto Yokoyama, Daichi Nishikawa, Hiroyuki Hidaka, Tatsuya Yanagisawa, Kenichi Tenya, Shuzo Kawarazaki, Taku J. Sato, Hideki Yoshizawa, Hiroshi Amitsuka
    Journal of Physics: Conference Series 200 SECTION 1 2010年 [査読有り][通常論文]
     
    Elastic neutron-scattering experiment was performed on the heavy-fermion superconductor URu2Si2 under uniaxial stress in order to search a sign of a hidden order parameter. Contour maps of neutron-scattering at 1.5 K were achieved by mesh scanning. No additional magnetic signal exists in (h0l) and (hhl) planes except for a well-known weak antiferromagnetic signal with magnetic-propagation vector of Q = (100) within the present experimental accuracy and scanned area. © 2010 IOP Publishing Ltd.
  • Hiroyuki Hidaka, Yoichi Ikeda, Ikuto Kawasaki, Tatsuya Yanagisawa, Hiroshi Amitsuka
    PHYSICA B-CONDENSED MATTER 404 19 3005 - 3007 2009年10月 [査読有り][通常論文]
     
    We have carried out specific heat measurements on EuIn2P2 at high magnetic fields perpendicular to the c-axis in the hexagonal crystal structure in order to understand its thermal properties. The temperature dependence of the specific heat exhibits a clear lambda-type anomaly due to a magnetic transition at T-C = 24 K, indicating that the magnetic transition is of second-order. The lambda-type anomaly becomes markedly broader with increasing the magnetic field. This remarkable field-dependence is consistent with the results of previous magnetization measurements which suggest that Eu2+ magnetic moments align ferromagnetically perpendicular to the c-axis below T-C. In addition, a hump in the specific heat is observed around 7 K, which can be ascribed to the Zeeman splitting of the Eu2+ multiplet by internal magnetic fields. (C) 2009 Elsevier B.V. All rights reserved.
  • Ikuto Kawasaki, Daichi Nishikawa, Hiroyuki Hidaka, Tatsuya Yanagisawa, Kenichi Tenya, Makoto Yokoyama, Hiroshi Amitsuka
    PHYSICA B-CONDENSED MATTER 404 19 2908 - 2911 2009年10月 [査読有り][通常論文]
     
    In order to investigate magnetic properties around a quantum critical point of CePt1-xRhx alloys, we have performed the ac-susceptibility (chi(ac)) measurements with field frequency ranging from omega/2 pi = 0 (dc magnetization) to 1113 Hz for temperature down to 100mK on polycrystalline CePt1-xRhx (x = 0.5, 0.6). The in-phase component of chi(ac) exhibits a pronounced peak at T-f. The peak magnitude and T-f show significant field-frequency dependence. In addition, a staircaselike hysteresis loop of magnetization was observed below 200mK. From the dynamical analyses of chi(ac) we suggest that CePt0.5Rh0.5 and CePt0.4Rh0.6 can be described as cluster-glass systems. (C) 2009 Published by Elsevier B.V.
  • Tatsuya Yanagisawa, Taichi Mayama, Hiroyuki Hidaka, Hiroshi Amitsuka, Akio Yamaguchi, Koji Araki, Yuichi Nemoto, Terutaka Goto, Naoya Takeda, Pei-Chun Ho, M. Brian Maple
    PHYSICA B-CONDENSED MATTER 404 19 3235 - 3237 2009年10月 [査読有り][通常論文]
     
    Ultrasonic measurements on a Pr0.55Nd0.45Os4Sb12 single crystal for temperature down to 20mK and frequencies up to 245 MHz were performed in order to investigate off-center rattling motion of rare-earth ions. The elastic constant C-11 exhibits double ultrasonic dispersions at similar to 15 and similar to 40 K, which are similar to the features found in NdOs4Sb12. The estimated activation energy E-1 = 240 K corresponding to the 40 K-dispersion, possesses an intermediate value between PrOs4Sb12 (E-1 = 115 K) and NdOs4Sb12 (E-1 = 337 K). (C) 2009 Elsevier B.V. All rights reserved.
  • Terutaka Goto, Tomyuki Watanabe, Seiji Tsuduku, Haruki Kobayashi, Yuichi Nemoto, Tatsuya Yanagisawa, Mitsuhiro Akatsu, Genki Ano, Osamu Suzuki, Naoya Takeda, Andreas Donni, Hideaki Kitazawa
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 78 2 2009年02月 [査読有り][通常論文]
     
    Low-temperature elastic properties of the clathrate compound Ce3Pd20Si6 were investigated using ultrasonic measurements. Pronounced softening of elastic constants (C-11 - C-12)/2 and C-44 with decreasing temperature indicates a precursor of electric quadrupole ordering due to it Gamma(8) quartet ground sate with an orbital degeneracy for 8c site of it Ce ion. A minimum of (C-11 - C-12)/2 at T-C = 170 mK indicates a transition from paramagnetic phase I to an ordered phase III. Applied magnetic fields induce an antiferro-quadrupole (AFQ) ordered phase II with highly anisotropic character depending on the field direction, which resembles the AFQ phase with O-xy-type order parameter in CeB6 with the Gamma(8) ground sate. The order parameter of the phase III may be characterized by either magnetic dipole or magnetic octupole. The Gamma(7) ground state at 4a site may fall into it singlet screened by conduction electrons at low temperatures Without long-range magnetic ordering.
  • Goto Terutaka, Watanabe Tomoyuki, Tsuduku Seiji, KOBAYASHI Haruki, NEMOTO Yuichi, YANAGISAWA Tatsuya, AKATSU Mitsuhiro, ANO Genki, SUZUKI Osamu, TAKEDA Naoya, DONNI Andreas, KITAZAWA Hideaki
    Journal of the Physical Society of Japan 78 2 "024716 - 1"-"024716-9" 社団法人日本物理学会 2009年02月 [査読有り][通常論文]
     
    Low-temperature elastic properties of the clathrate compound Ce_3Pd_<20>Si_6 were investigated using ultrasonic measurements. Pronounced softening of elastic constants (C_<11>-C_<12>)/2 and C_<44> with decreasing temperature indicates a precursor of electric quadrupole ordering due to a Γ_8 quartet ground sate with an orbital degeneracy for 8c site of a Ce ion. A minimum of (C_<11>-C_<12>)/2 at T_C=170mK indicates a transition from paramagnetic phase I to an ordered phase III. Applied magnetic fields induce an antiferro-quadrupole (AFQ) ordered phase II with highly anisotropic character dep...
  • Tatsuya Yanagisawa, Pei-Chun Ho, William M. Yuhasz, M. Brian Maple, Yuri Yasumoto, Hiromu Watanabe, Yuichi Nemoto, Terutaka Goto
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 7 074607.1-074607.5 - 1"-"074607-5" 2008年07月 [査読有り][通常論文]
     
    The off-center rattling of Nd rare-earth ions in the filled skutterudite compound NdOs4Sb12 has been investigated by ultrasonic measurement. The longitudinal C-11 mode for frequencies between 34 and 253MHz shows a marked frequency dependence in elastic constant and ultrasonic attenuations at two different temperatures centered at around 45 and 15K. The relaxational frequency dependence of ultrasonic dispersion reveals a thermally activated Gamma(23)-type off-center motion of Nd-ions, involving local charge fluctuations with Gamma(23) symmetry in the (OsSb3)(4) cage. An attempt time tau(0,(1)) = 7.5 x 10(-12) s and an activation energy E-1 = 337 K were obtained from fits to the dispersion at around 45 K. The presence of another dispersion at lower temperatures of around 15 K implies that the rattling in NdOs4Sb12 has an additional low-energy excitation characterized by a lower activation energy E-2 similar to 67 K with an attempt time tau(0,(2)) = 5.1 x 10(-11) s.
  • M. B. Maple, Z. Henkie, R. E. Baumbach, T. A. Sayles, N. P. Butch, P. C. Ho, T. Yanagisawa, W. M. Yuhasz, R. Wawryk, T. Cichorek, A. Pietraszko
    Journal of the Physical Society of Japan 77 7 - 13 The Physical Society of Japan 2008年07月 [査読有り][通常論文]
     
    In order to elucidate the variety of correlated electron phenomena found in filled skutterudite compounds, experiments were performed on single crystals of ternary Ce- and Pr-based filled skutterudite arsenides LnT 4 As 12 (Ln = Ce, Pr; T = Fe, Ru, Os) and pseudoternary Pr-based skutterudite antimonides Pr(Os 1-x Ru x ) 4 Sb 12 and Pr 1-x Nd x Os 4 Sb 12 . For example, the intermediate valence compound CeRu 4 As 12 exhibits non-Fermi liquid characteristics, while the compounds PrT 4 As 12 display ferromagnetic order (18 K) for T = Fe, BCS superconductivity (2.4 K) for T = Ru, unknown order (2.3 K) and antiferromagnetic order (2.2 K) for T = Os. PrOs 4 As 12 appears to be a Kondo lattice system with a small Kondo temperature (∼ 1 K) and an electronic specific heat coefficient γ ∼ 1 J/mol K 2 . The T-x phase diagrams of Pr(Os 1-x Ru x ) 4 Sb 12 and Pr 1-x Nd x Os 4 Sb 12 reveal regions of superconductivity with different order parameter symmetry and magnetic order. ©2008 The Physical Society of Japan.
  • P-C Ho, N. P. Butch, V. S. Zapf, T. Yanagisawa, N. A. Frederick, S. K. Kim, W. M. Yuhasz, M. B. Maple, J. B. Betts, A. H. Lacerda
    JOURNAL OF PHYSICS-CONDENSED MATTER 20 21 2008年05月 [査読有り][通常論文]
     
    To study the possible competition between unconventional and Bardeen-Cooper-Schrieffer superconductivity in the filled skutterudites Pr(Os(1-x)Ru(x))(4)Sb(12), the evolution of superconductivity and the high field ordered phase in single-crystal specimens has been investigated by means of electrical resistivity measurements in magnetic fields up to 18 T. Whereas the upper critical field H(c2)(T) curves have conventional shapes for x < 0.4, the H(c2)(T) curves are nearly linear for x greater than or similar to 0.4. For all x, H(c2)(0) matches the calculated value of the orbital critical field. Features in the electrical resistivity associated with the high field ordered phase, observed clearly for PrOs(4)Sb(12), weaken with increasing x and vanish for x greater than or similar to 0.1.
  • T. A. Sayles, W. M. Yuhasz, J. Paglione, T. Yanagisawa, J. R. Jeffries, M. B. Maple, Z. Henkie, A. Pietraszko, T. Cichorek, R. Wawryk, Y. Nemoto, T. Goto
    Physical Review B - Condensed Matter and Materials Physics 77 14 2008年04月29日 [査読有り][通常論文]
     
    A variety of thermodynamic and transport measurements were made on high-quality single crystals of the Pr-based filled skutterudite compound PrFe4 As12. Abrupt features in magnetization, ac susceptibility, specific heat, resistivity, thermoelectric power, and ultrasonic velocity reveal the onset of long range ferromagnetic order below ΘC =18K. The low-temperature magnetic susceptibility is characterized by a Curie-Weiss law with an effective moment of 3.52 μB /f.u. and a saturation magnetization of 2.3 μB /f.u., which is consistent with a magnetic Γ5 triplet ground state. A gaplike reduction of the large electronic specific heat coefficient of 340mJ/mol K2 and several other features point to a strongly correlated electron behavior that is likely coupled to a change in magnetic and/or structural order near T12K. Furthermore, this complex magnetic state is found to be strongly field dependent, as evidenced by a change in the easy axis at low fields and an additional contribution to thermal conductivity appearing only at high fields. © 2008 The American Physical Society.
  • T. A. Sayles, W. M. Yuhasz, J. Paglione, T. Yanagisawa, J. R. Jeffries, M. B. Maple, Z. Henkie, A. Pietraszko, T. Cichorek, R. Wawryk, Y. Nemoto, T. Goto
    PHYSICAL REVIEW B 77 14 2008年04月 [査読有り][通常論文]
     
    A variety of thermodynamic and transport measurements were made on high-quality single crystals of the Pr-based filled skutterudite compound PrFe4As12. Abrupt features in magnetization, ac susceptibility, specific heat, resistivity, thermoelectric power, and ultrasonic velocity reveal the onset of long range ferromagnetic order below Theta(C)=18 K. The low-temperature magnetic susceptibility is characterized by a Curie-Weiss law with an effective moment of 3.52 mu(B)/f.u. and a saturation magnetization of 2.3 mu(B)/f.u., which is consistent with a magnetic Gamma(5) triplet ground state. A gaplike reduction of the large electronic specific heat coefficient of 340 mJ/mol K-2 and several other features point to a strongly correlated electron behavior that is likely coupled to a change in magnetic and/or structural order near T-*similar or equal to 12 K. Furthermore, this complex magnetic state is found to be strongly field dependent, as evidenced by a change in the easy axis at low fields and an additional contribution to thermal conductivity appearing only at high fields.
  • T. Yanagisawa, W. M. Yuhasz, P-C. Ho, M. B. Maple, H. Watanabe, Y. Yasumoto, Y. Nemoto, T. Goto
    PHYSICA B-CONDENSED MATTER 403 5-9 735 - 738 2008年04月 [査読有り][通常論文]
     
    Ultrasonic investigation for the single crystals of ferromagnetic filled skutterudite compound NdOs4Sb12 was performed. A marked frequency dependence of the ultrasonic dispersion has been observed in a longitudinal elastic constant C-11 at temperature centered around 45 K; however, no dispersion was measured in the transverse elastic constant C-44. Such a clear mode difference in the ultrasonic dispersion, which has been found in PrOs4Sb12, strongly suggests that Nd ion in NdOs4Sb12 bears thermally activated off-center rattling effect. (C) 2007 Elsevier B.V. All rights reserved.
  • P. -C. Ho, T. Yanagisawa, N. P. Butch, W. M. Yuhasz, C. C. Robinson, A. A. Dooraghi, M. B. Maple
    PHYSICA B-CONDENSED MATTER 403 5-9 1038 - 1040 2008年04月 [査読有り][通常論文]
     
    We report the results of recent electrical resistivity measurements on the two pseudoternary systems Pr(Os1-xRux)(4)Sb-12 and Pr1-xNdxOs4Sb12, which show the evolution of superconductivity (SC) and the high field ordered phase (HFOP) with respect to the substituent concentration. In Pr(Os1-xRux)(4)Sb-12, there appears to be competition between unconventional and conventional SC, whereas in Pr1-xNdxOs4Sb12, there is competition between SC and ferromagnetism (FM). Features in the electrical resistivity related to the HFOP disappear for x >= 0.1 in Pr(Os1-xRux)(4)Sb-12, and persist up to at least x similar to 0.5 in Pr1-xNdxOs4Sb12. (c) 2007 Elsevier B.V. All rights reserved.
  • T. A. Sayles, W. M. Yuhasz, J. Paglione, T. Yanagisawa, J. R. Jeffries, M. B. Maple, Z. Henkie, A. Pietraszko, T. Cichorek, R. Wawryk, Y. Nemoto, T. Goto
    PHYSICA B-CONDENSED MATTER 403 5-9 869 - 870 2008年04月 [査読有り][通常論文]
     
    Magnetization M(H,T), specific heat C(T), and electrical resistivity p(T), measurements were performed on single crystals of the Pr-based filled skutterudite compound PrFe4As12. M(H) isotherms indicate a saturation magnetization of 2.3 mu(B)/f.u., and Arrott analysis reveals a Curie temperature T-C = 18.2 K and saturated moment Mat = 2.0 mu(B)/f.u. Curie-Weiss analysis of magnetic susceptibility, chi, reveals two distinct regions: for T > 100 K, the effective moment mu(eff) = 3.98 mu(B) and the Curie-Weiss temperature theta(CW) = 4.1 K, while for 19.5 < T< 75 K, mu(eff) = 3.52 mu(B) and theta(CW) = 17.7 K. C(T) and rho(7) show distinct features at T-C, while the ac susceptibility exhibits lower temperature features, possibly associated with changes in magnetic structure. (c) 2007 Elsevier B.V. All rights reserved.
  • T. Yanagisawa, W. M. Yuhasz, T. A. Sayles, P. -C. Ho, M. B. Maple, H. Watanabe, Y. Yasumoto, Y. Nemoto, T. Goto
    PHYSICAL REVIEW B 77 9 2008年03月 [査読有り][通常論文]
     
    Elastic constant measurements down to 0.48 K and in magnetic fields up to 11 T were performed on a single crystal of the filled skutterudite compound PrOs(4)As(12). The longitudinal C(L111)= C(B)+ 4C(44)/3 mode shows Curie-type softening below similar to 25 K, which is explained in terms of the quadrupole susceptibility modified by a crystalline electric field with a Gamma((2))(4) ground state. A detailed H-T phase diagram for H parallel to[111] is compiled with the elastic anomalies, which appear on the boundaries of two ordered phases at temperatures below 2.3 K and in fields below 3 T. The intermediate phase between 2 and 2.5 T assumes the aspect of antiferroquadrupolar ordering.
  • K. Araki, T. Goto, Y. Nemoto, T. Yanagisawa, B. Luethi
    EUROPEAN PHYSICAL JOURNAL B 61 3 257 - 259 2008年02月 [査読有り][通常論文]
     
    The temperature dependence of the elastic constants in Tb3Ga5O12 was measured and analysed with a simple crystal field model. The magneto-elastic coupling constants have been deduced from this experiment. The coupling constant g(Gamma 5), related to the c(44) mode, is anomalously large. These coupling constants are important for the interpretation of the phonon Hall effect.
  • R. Wawryk, O. Zogal, A. Pietraszko, S. Paluch, T. Cichorek, W. M. Yuhasz, T. A. Sayles, P. -C. Ho, T. Yanagisawa, N. P. Butch, M. B. Maple, Z. Henkie
    JOURNAL OF ALLOYS AND COMPOUNDS 451 1-2 454 - 456 2008年02月 [査読有り][通常論文]
     
    We have grown single crystals of LaOs4As12 and PrOs4As12, which crystallize in the LaFe4P12-type structure (Im (3) over bar space group) with the lattice parameters of 8.542(1)angstrom and 8.520(1)angstrom, respectively. From a narrow La-139 NMR line, we estimated an appreciable Knight shift (K-139) and a relatively long spin-lattice-relaxation time in the non-4f electron system LaOs4As12. Surprisingly, while K-139 vary non-monotonically with temperature, the magnetic susceptibility increases upon cooling over the whole temperature range. Interestingly, the high-temperature dependence of the thermoelectric power of LaOs4As12 is remarkably similar to that one of PrOs(4)AS(12). (C) 2007 Elsevier B.V. All rights reserved.
  • Yuri Yasumoto, Akio Yamaguchi, Tatsuya Yanagisawa, Yuichi Nemoto, Terutaka Goto, Akira Ochiai
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 242 - 244 2008年01月 [査読有り][通常論文]
     
    Off-center rattling of La-ion in the filled skutterudite compound LaOs4Sb12 has been investigated by means of ultrasonic measurements. An elastic constant C-11 shows a remarkable frequency dependence in elastic constant and ultrasonic attenuation at around 25 K. This frequency dependent ultrasonic dispersion reveals thermally activated Gamma(23)-type off-center rattling of La-ion. An attempt time tau(0) = 5.0x10(-11) sec and an activation energy E = 127 K were obtained from the analysis.
  • Yuichi Nemoto, Tatsuya Yanagisawa, Yuri Yasumoto, Haruki Kobayashi, Akio Yamaguchi, Seiji Tsuduku, Terutaka Goto, Naoya Takeda, Akira Ochiai, Hitoshi Sugawara, Hideyuki Sato, Hideaki Kitazawa
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 153 - 158 2008年01月 [査読有り][通常論文]
     
    We have performed ultrasonic experiments on clathrate compounds ROs4Sb12 and R3Pd20Ge6 to explore rattling and tunneling of a guest rattler's motion. We have found frequency dependence of the elastic constants and ultrasonic attenuations, which is called as ultrasonic dispersion, due to thermally activated rattling. At low temperatures, Curie-type elastic softening obeying 1/T with antiferro-type intersite interaction, which corresponds to quantum tunneling, appears and continues even to the lowest 20 mK in LaOs4Sb12 and La3Pd20Ge6. The understanding of the local charge fluctuation, rattling and tunneling, being coupled to conduction electrons in metals is a basic issue in the aspect of electron-phonon interaction in strongly correlated phenomena such as heavy fermion state, superconductivity and multi-channel Kondo screening effect.
  • Haruki Kobayashi, Seiji Tsuduku, Osamu Suzuki, Tatsuya Yanagisawa, Yuichi Nemoto, Terutaka Goto, Andreas Doenni, Hideaki Kitazawa, Naoya Takeda
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 263 - 265 2008年01月 [査読有り][通常論文]
     
    Electric quadrupole effects in a Pr-based clathrate compound Pr3Pd20Si6 have been investigated by ultrasonic measurements. Elastic constants of (C-11 - C-12)/2 and C-44 in Pr3Pd20Si6 show curie-type softenings with decreasing temperature below 20 K, which are described in terms of quadrupole effects of 4f-electron for the ground state either Gamma(3) doublet or Gamma(5) triplet. H-T phase diagram of Pr3Pd20Si6 under the magnetic fields along [110] is obtained from elastic anomalies in (C-11 - C-12)/2 mode.
  • Kouji Araki, Terutaka Goto, Yuichi Nemoto, Tatsuya Yanagisawa, Bruno Luethi
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 269 - 271 2008年01月 [査読有り][通常論文]
     
    We have investigated elastic properties of a garnet-type single crystal Tb3Ga5O12 by ultrasonic measurements. Temperature dependence of the transverse elastic constants (C-11 - C-12)/2 and C-44 shows strong Curie-type softening below 150 K with minima around 30 - 50 K and also below 5 K. These effects are due to quadrupole susceptibilities for the crystalline electric field system with a pseudo-doublet Gamma(3) ground state and an excited triplet Gamma(5) at 57.3 K. Magnetic field dependence of the (C-11 - C-12)/2 mode in H parallel to [110] shows step-like anomaly due to a level crossing at around 9.5 T.
  • Kouji Araki, Terutaka Goto, Yuichi Nemoto, Tatsuya Yanagisawa, Bruno Lüthi
    Journal of the Physical Society of Japan 77 269 - 271 2008年 [査読有り][通常論文]
     
    We have investigated elastic properties of a garnet-type single crystal Tb 3 Ga 5 O 12 by ultrasonic measurements. Temperature dependence of the transverse elastic constants (C 11 C 12 )/2 and C 44 shows strong Curie-type softening below 150 K with minima around 30 - 50 K and also below 5 K. These effects are due to quadrupole susceptibilities for the crystalline electric field system with a pseudo-doublet Γ 3 ground state and an excited triplet Γ 5 at 57.3 K. Magnetic field dependence of the (C 11 C 12 )/2 mode in H ∥ [110] shows step-like anomaly due to a level crossing at around 9.5 T. ©2008 The Physical Society of Japan.
  • Haruki Kobayashi, Seiji Tsuduku, Osamu Suzuki, Tatsuya Yanagisawa, Yuichi Nemoto, Terutaka Goto, Andreas Dönni, Hideaki Kitazawa, Naoya Takeda
    Journal of the Physical Society of Japan 77 263 - 265 2008年 [査読有り][通常論文]
     
    Electric quadrupole effects in a Pr-based clathrate compound Pr 3Pd20Si6 have been investigated by ultrasonic measurements. Elastic constants of (C11 - C12)/2 and C44 in Pr3Pd20Si6 show curie-type softenings with decreasing temperature below 20 K, which are described in terms of quadrupole effects of 4f-electron for the ground state either Γ3 doublet or Γ5 triplet. H-T phase diagram of Pr3Pd20Si6 under the magnetic fields along [110] is obtained from elastic anomalies in (C11 - C12)/2 mode. ©2008 The Physical Society of Japan.
  • T. Yanagisawa, Y. Yasumoto, Y. Nemoto, T. Goto, W. M. Yuhasz, P. C. Ho, M. B. Maple, Z. Henkie, A. Pietraszko
    Journal of the Physical Society of Japan 77 225 - 228 2008年 [査読有り][通常論文]
     
    Ultrasonic investigation of a single crystal of the filled skutterudite antiferromagnetic compound PrOs4As12 was performed. Curie-type softening appeared in CL111 = CB + 4/3C 44 and CT111 = 2/3 (C11-C12)/2 + 4/3C44, is explained in terms of the quadrupole susceptibility modified by a crystalline electric field with a Γ4 (2)-triplet ground state and a Γ1-singlet first excited state. The quadrupole susceptibility analysis finds that the intersite quadrupole interactions in this compound are negative, indicating an antiferro-quadrupolar type interaction. Additional ultrasonic features, appeared in an ordered phase under magnetic fields between 2 T and 3 T for H∥ [111] and H∥ [110], suggest the existence of another intermediate phase boundary. Magnetic field-temperature (H-T) phase diagrams for H∥ [111] and H∥ [110], which exhibits strong magnetic anisotropy, were obtained. ©2008 The Physical Society of Japan.
  • Yuri Yasumoto, Akio Yamaguchi, Tatsuya Yanagisawa, Yuichi Nemoto, Terutaka Goto, Akira Ochiai
    Journal of the Physical Society of Japan 77 242 - 244 2008年 [査読有り][通常論文]
     
    Off-center rattling of La-ion in the filled skutterudite compound LaOs 4Sb12 has been investigated by means of ultrasonic measurements. An elastic constant C11 shows a remarkable frequency dependence in elastic constant and ultrasonic attenuation at around 25 K. This frequency dependent ultrasonic dispersion reveals thermally activated Γ23-type off-center rattling of La-ion. An attempt time τ0 = 5.0×10-11 sec and an activation energy E = 127 K were obtained from the analysis. ©2008 The Physical Society of Japan.
  • Yuichi Nemoto, Tatsuya Yanagisawa, Yuri Yasumoto, Haruki Kobayashi, Akio Yamaguchi, Seiji Tsuduku, Terutaka Goto, Naoya Takeda, Akira Ochiai, Hitoshi Sugawara, Hideyuki Sato, Hideaki Kitazawa
    Journal of the Physical Society of Japan 77 153 - 158 2008年 [査読有り][通常論文]
     
    We have performed ultrasonic experiments on clathrate compounds ROs 4Sb12 and R3Pd20Ge6 to explore rattling and tunneling of a guest rattler's motion. We have found frequency dependence of the elastic constants and ultrasonic attenuations, which is called as ultrasonic dispersion, due to thermally activated rattling. At low temperatures, Curie-type elastic softening obeying 1/T with antiferro-type intersite interaction, which corresponds to quantum tunneling, appears and continues even to the lowest 20 mK in LaOs4Sb12 and La3Pd20Ge6. The understanding of the local charge fluctuation, rattling and tunneling, being coupled to conduction electrons in metals is a basic issue in the aspect of electron-phonon interaction in strongly correlated phenomena such as heavy fermion state, superconductivity and multi-channel Kondo screening effect. ©2008 The Physical Society of Japan.
  • Observation of vacancy in silicon using low-temperature ultrasonic measurements
    T. Goto, H. yamada-Kaneta, M. Hikin, H. Watanabe, K. Sato, Y. Nemoto, T. Yanagisawa, S. Nakamura
    Proceeding of the science and technology of silicon materials 2007 69 - 74 2007年11月 [査読無し][通常論文]
  • Piezoelectric ZnO sputtering on crystalline silicon for low-temperature ultrasonic measurements
    H. Watanabe, T. Goto, H. Yamada-Kaneta, Y. Nemoto, M. Hikin, T. Yanagisawa, S. Nakamura
    Proceeding of the forum on the science and technology of silicon materials 2007 141 - 142 2007年11月 [査読無し][通常論文]
  • Lei Shu, D. E. MacLaughlin, Y. Aoki, Y. Tunashima, Y. Yonezawa, S. Sanada, D. Kikuchi, H. Sato, R. H. Heffner, W. Higemoto, K. Ohishi, T. U. Ito, O. O. Bernal, A. D. Hillier, R. Kadono, A. Koda, K. Ishida, H. Sugawara, N. A. Frederick, W. M. Yuhasz, T. A. Sayles, T. Yanagisawa, M. B. Maple
    PHYSICAL REVIEW B 76 1 2007年07月 [査読有り][通常論文]
     
    Zero- and longitudinal-field muon spin relaxation experiments have been carried out in the alloy series Pr(Os1-xRux)(4)Sb-12 and Pr1-yLayOs4Sb12 to elucidate the anomalous dynamic muon spin relaxation observed in these materials. The damping rate Lambda associated with this relaxation varies with temperature, applied magnetic field, and dopant concentrations x and y in a manner consistent with the "hyperfine enhancement" of Pr-141 nuclear spins first discussed by Bleaney [Physica (Utrecht) 69, 317 (1973)]. This mechanism arises from Van Vleck-like admixture of magnetic Pr3+ crystalline-electric-field-split excited states into the nonmagnetic singlet ground state by the nuclear hyperfine coupling, thereby increasing the strengths of spin-spin interactions between Pr-141 and muon spins and within the Pr-141 spin system. We find qualitative agreement with this scenario and conclude that electronic spin fluctuations are not directly involved in the dynamic muon spin relaxation.
  • Tatsuya Yanagisawa, William M. Yuhasz, Pei-Chun Ho, M. Brian Maple, Hiromu Watanabe, Takafumi Ueno, Yuichi Nemoto, Terutaka Goto
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 2 223 - 225 2007年03月 [査読有り][通常論文]
     
    Elastic constants of filled-skutterudite NdOs4Sb12 single crystals have been investigated by means of ultrasonic measurements. Transverse C-44 and longitudinal C-11 modes show Curie-type softening, which is proportional to the reciprocal temperature from 10K down to 0.9K. This softening can be explained in terms of the quadrupolar susceptibility modified by crystalline electric field with a Gamma(8) quartet ground state in O-h symmetry. The C-11 mode also shows a broad shoulder and a small dip around 45 and 13 K, respectively. A Debye-type frequency dependence of the anomalies in the longitudinal C-11 mode resembles an ultrasonic dispersion in PrOs4Sb12, which is expected to be due to the "rattling'' effect, a thermally activated off-center motion of the rare-earth atom in the Sb-cage. (c) 2006 Elsevier B.V. All rights reserved.
  • M. B. Maple, Z. Henkie, W. M. Yuhasz, P.-C. Ho, T. Yanagisawa, T. A. Sayles, N. P. Butch, J. R. Jeffries, A. Pietraszko
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 2 182 - 187 2007年03月 [査読有り][通常論文]
     
    Recent experiments on the Pr-based filled skutterudite arsenides and antimonides PrOs4Sb12, PrdOs(1-x)Ru(x))(4)Sb-12, Pr1-xNdxOs4Sb12, PrFe4As12, PrRu4As12, and PrOs4As12 are reviewed. The heavy fermion compound PrOs4Sb12 exhibits unconventional strong-coupling superconductivity below T-c = 1.85K that breaks time reversal symmetry, apparently consists of several distinct superconducting phases, and may involve triplet spin pairing of electrons. Studies of the alloy systems PrdOs(1-x)Ru(x))(4)Sb-12 and Pr1-xNdxOs4Sb12 revealed rich T-x phase diagrams and a strong suppression of the high field ordered phase and the unconventional superconductivity of PrOs4Sb12 with Ru substitution. Among the three Pr-based filled skutterudite arsenides, PrFe4As12 has a ferromagnetic ground state, PrRu4As12 exhibits conventional BCS superconductivity, and PrOs4As12 is an antiferromagnet. (c) 2006 Elsevier B.V. All rights reserved.
  • W. M. Yuhasz, P- C. Ho, T. A. Sayles, T. Yanagisawa, N. A. Frederick, M. B. Maple, P. Rogl, G. Giester
    JOURNAL OF PHYSICS-CONDENSED MATTER 19 7 2007年02月 [査読有り][通常論文]
     
    The filled skutterudite compound PrOs4P12 was synthesized in single-crystal form using a molten metal flux growth technique. Low-temperature magnetization, specific heat, and electrical resistivity measurements showed no indication of a phase transition down to 0.1 K but had features indicative of crystalline electric field (CEF) effects. Analyses of these features in terms of a cubic CEF suggest a Gamma(1) singlet or a Gamma(3) doublet ground state separated by 30-50 K from a Gamma(5) triplet first excited state.
  • Terutaka Goto, Yuichi Nemoto, Takashi Yamaguchi, Tatsuya Yanagisawa, Takafumi Ueno, Tomoyuki Watanabe, Naoya Takeda, Osamu Suzuki, Hideaki Kitazawa, Hitoshi Sugawara, Hideyuki Sato
    PHYSICA B-CONDENSED MATTER 383 1 115 - 119 2006年08月 [査読有り][通常論文]
     
    We have investigated an off-center local oscillator of a guest atom in cage of clathrate compounds R3Pd20Ge6 (R = La, Ce, Pr, Nd) and a filled skutterudite PrOs4Sb12 using ultrasonic measurements. The observation of ultrasonic dispersions in transverse C-44 mode of R3Pd20Ge6 and in transverse (C-11 - C-12)/2 mode of PrOs4Sb12 revealed the rattling of the off-center oscillator characterized by a relaxation time with Arrhenius-type temperature dependence. A low-temperature softening of C-44 in La3Pd20Ge6 below 3 K down to 20 mK and a softening of (C-11 - C-12)/2 in PrOs4Sb12 above the heavy Fermion superconducting transition indicate the charge fluctuation due to the degenerate off-center oscillators. (c) 2006 Elsevier B.V. All rights reserved.
  • M. B. Maple, N. A. Frederick, P. -C. Ho, W. M. Yuhasz, T. Yanagisawa
    JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM 19 3-5 299 - 315 2006年07月 [査読有り][通常論文]
     
    Research carried out during the last several years on the heavy fermion superconductor PrOs4Sb12 is reviewed. The compound PrOs4Sb12 exhibits unconventional strong coupling superconductivity below a superconducting critical temperature T-c = 1.85 K. The superconducting state breaks time reversal symmetry, apparently consists of several distinct superconducting phases, some of which may have point nodes in the energy gap, and may involve triplet spin pairing of electrons. The determination of the Pr3+ energy level scheme in the crystalline electric field, as well as the discovery and characterization of the high field-ordered phase (HFOP), which has been identified with antiferroquadrupolar order, are described. Studies of the substitutional systems Pr(Os1-xRux)(4)Sb-12, Pr1-xLaxOs4Sb12, and Pr1-xNdxOs4Sb12 are summarized and compared.
  • MB Maple, NP Butch, NA Frederick, PC Ho, Jeffries, JR, TA Sayles, T Yanagisawa, WM Yuhasz, SX Chi, HJ Kang, JW Lynn, PC Dai, SK McCall, MW McElfresh, MJ Fluss, Z Henkie, A Pietraszko
    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 103 18 6783 - 6789 2006年05月 [査読有り][通常論文]
     
    Electrical resistivity, specific heat, and magnetization measurements to temperatures as low as 80 mK and magnetic fields up to 16 T were made on the filled skutterudite compound PrOs4As12. The measurements reveal the presence of two ordered phases at temperatures below approximately 2.3 K and in fields below approximately 3 T. Neutron-scattering experiments in zero field establish an antiferromagnetic ground state < 2.28 K. In the antiferromagnetically ordered state, the electronic-specific heat coefficient y approximate to 1 J/mol-K-2 below 1.6 K and 0 <= H <= 1.25 T. The temperature and magnetic-field dependence of the electrical resistivity and specific heat in the paramagnetic state are consistent with single-ion Kondo behavior with a low Kondo temperature on the order of 1 K. The electronic-specific heat in the paramagnetic state can be described by the resonance-level model with a large zero-temperature electronic-specific heat coefficient that decreases with increasing magnetic field from approximately 1 J/mol(.)K(2) at 3 T to approximately 0.2 J/mol(.)K(2) at 16 T.
  • Yuichi Nemoto, Takafumi Ueno, Naoya Takeda, Takashi Yamaguchi, Tatsuya Yanagisawa, Terutaka Goto, Hitoshi Sugawara, Hideyuki Sato
    PHYSICA B-CONDENSED MATTER 378-80 184 - 186 2006年05月 [査読有り][通常論文]
     
    Ultrasonic attenuation measurements have been firstly performed for a large single crystal of PrOs4Sb12 with the dimensions of 5.97 x 0.6 x 0.6 mm(3). Remarkable frequency dependence around 20-40K has been observed in the elastic constant and attenuation coefficient of the longitudinal C-11 mode associated with E-g symmetry strain in part, which results from a thermally activated off-center rattling with E-g symmetry of a Pr ion inside a Sb icosahedron cage. Parameters of a characteristic time tau(0) = 3.1 x 10(-11) s and an activation energy E = 225 K were obtained. This E-g rattling involving a local charge fluctuation inside a Sb cage periodically arranged may couple to the conduction electrons. As a result, the electron-phonon coupling would lead to heavy fermion and its superconductivity in PrOs4Sb12. (c) 2006 Elsevier B.V. All rights reserved.
  • WM Yuhasz, NP Butch, TA Sayles, PC Ho, Jeffries, JR, T Yanagisawa, NA Frederick, MB Maple, Z Henkie, A Pietraszko, SK McCall, MW McElfresh, MJ Fluss
    PHYSICAL REVIEW B 73 14 2006年04月 [査読有り][通常論文]
     
    Magnetization, specific heat, and electrical resistivity measurements were made on single crystals of the filled skutterudite compound PrOs4As12. Specific heat measurements indicate an electronic specific heat coefficient gamma similar to 50-200 mJ/mol K-2 at temperatures 10 K <= T <= 18 K, and similar to 1 J/mol K-2 for T <= 1.6 K. The combined measurements reveal the presence of two, or possibly three, ordered phases at temperatures below similar to 2.3 K and in fields below similar to 3 T. The low temperature phase displays antiferromagnetic characteristics, while the nature of the ordering in the other phase(s) has yet to be determined.
  • Yuhasz, W.M., Butch, N.P., Sayles, T.A., Ho, P.-C., Jeffries, J.R., Yanagisawa, T., Frederick, N.A., Maple, M.B., Henkie, Z., Pietraszko, A., McCall, S.K., McElfresh, M.W., Fluss, M.J.
    Physical Review B - Condensed Matter and Materials Physics 73 14 2006年04月 [査読有り][通常論文]
     
    Magnetization, specific heat, and electrical resistivity measurements were made on single crystals of the filled skutterudite compound Pr Os4 As12. Specific heat measurements indicate an electronic specific heat coefficient γ∼50-200 mJ mol K2 at temperatures 10 K≤T≤18 K, and ∼1 J mol K2 for T≤1.6 K. The combined measurements reveal the presence of two, or possibly three, ordered phases at temperatures below ∼2.3 K and in fields below ∼3 T. The low temperature phase displays antiferromagnetic characteristics, while the nature of the ordering in the other phase(s) has yet to be determined. © 2006 The American Physical Society.
  • R Watanuki, G Sato, K Suzuki, M Ishihara, T Yanagisawa, Y Nemoto, T Goto
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 74 8 2169 - 2172 2005年08月 [査読有り][通常論文]
     
    Physical properties of DyB4 have been studied by magnetization, specific heat, and ultrasonic measurements. The magnetic entropy change and ultrasonic properties in intermediate phase 11 indicate that the degeneracy of internal degrees of freedom is not fully lifted in spite of the formation of magnetic order. The ultrasonic attenuation and huge softening Of C-44 in phase 11 suggest the existence of electric-quadrupolar (orbital) fluctuations of 4f-electrons. These unusual properties originate from a geometrical quadrupolar frustration.
  • T Yanagisawa, T Moriwaki, Y Nemoto, T Goto, R Watanuki, K Suzuki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 74 6 1666 - 1669 2005年06月 [査読有り][通常論文]
     
    We have performed dilatometric measurements by the capacitance method on tetragonal rare earth compounds DyB2C2 and HoB2C2 that show anti ferro-quadrupole (AFQ) ordering. The tetragonal structure is invariant across the paramagnetic phase to the AFQ phase at T-Q = 24.7 K in DyB2C2. In the case of intermediate phase IV of HoB2C2, between T-C1, = 5.9 K and T-C2 = 5.0 K, the lattice length along the [101] direction reveals an abrupt increase, while the lengths along the [100] and [110] directions shrink slightly. This lattice distortion is described in terms of triclinic strain epsilon(yz) = epsilon(zx) not equal 0 indicating the spontaneous ferro-quadrupole moment < O-yz > = < O-zx > not equal 0. A plausible model, based on an octupole ordering < T-x > = < T-y > = < T-z > not equal 0, in phase IV of HoB2C2, is argued.
  • T Yanagisawa, T Goto, Y Nemoto, R Watanuki, K Suzuki, O Suzuki, G Kido
    PHYSICA B-CONDENSED MATTER 359 959 - 961 2005年04月 [査読有り][通常論文]
     
    Elastic properties of tetragonal HoB2C2 showing anti ferro-quadrupole (AFQ) ordering have been investigated by means of ultrasonic measurements. An anisotropic RKKY interaction would be responsible for the AFQ phase II of HoB2C2, which has an anisotropic field-temperature (H-T) phase diagram. We succeeded in obtaining the H T phase diagram for H parallel to [001] by using a hybrid magnet up to 30 T in NIMS, and found the presence of AFQ phase II over 4 T for H parallel to [001] in HoB2C2. The critical magnetic field H-C[001] = 26.3 T suggests a distinct stability of AFQ phase II in fields along the principal axis by contrast with relatively unstable behavior under fields H-C[110] = 3.9 T and H-C[100] = 2.0 T in basal plane. (c) 2005 Elsevier B.V. All rights reserved.
  • T Goto, Y Nemoto, K Sakai, K Onuki, T Yamaguchi, M Akatsu, T Yanagisawa, H Sugawara, H Sato
    PHYSICA B-CONDENSED MATTER 359 822 - 826 2005年04月 [査読有り][通常論文]
     
    We have made ultrasonic measurements on a filled skutterudite PrOs4Sb12 showing a heavy Fermion superconductivity at T-C = 1.85 K. The elastic constants (C-11 - C-12)/2 and C-44 of PrOs4Sb12 exhibit low-temperature softenings below 20 K down to T-C, indicating a quadrupole fluctuation of Pr3+ ion. A minimum of (C-11 - C-12)/2 in magnetic fields along the [1 1 0] direction around 8 T shows a level crossing of one of a excited Gamma(4)((2)) triplet to a ground state Gamma(1) singlet. An ultrasonic dispersion in (C-11 - C-12)/2 around 30 K suggests a thermally activated off-center rattling of Pr ion in a cage of Sb-icosahedron. The observed relaxation time shows the Arrhenius-type temperature dependence tau = tau(0) exp(E/k(B)T) with an attempt time tau(0) = 8.8 x 10(-11) s and an activation energy E = 168 K. The charge fluctuation of the off-center motion and the quadrupole fluctuation of the 4f electron may participate in the formation of the heavy fermion and the superconductivity in PrOs4Sb12. (c) 2005 Elsevier B.V. All rights reserved.
  • T Yamaguchi, Y Nemotoa, T Goto, M Akatsu, T Yanagisawa, O Suzuki, H Kitazawa, T Komatsubara
    PHYSICA B-CONDENSED MATTER 359 296 - 298 2005年04月 [査読有り][通常論文]
     
    We have made ultrasonic measurements on clathrate crystals Ce3Pd20Ge6 and La3Pd20Ge6 with a cage filled by a rare-earth atom. The elastic constants C-44 of both compounds show a marked dependence in ultrasonic frequencies of 10-300 MHz around 10-30 K, which are caused by a thermally activated rattling of the off-center rare-earth ion in the cage over the potential hill. At low temperatures below 3 K down to 20 mK, C-44 of La3Pd20Ge6 without 4f-electron exhibits a softening proportional to 1/T, which indicates a tunneling of the off-center rare-earth ion in the cage through the potential hill. (c) 2005 Elsevier B.V. All rights reserved.
  • T Yanagisawa, T Goto, Y Nemoto, R Watanuki, K Suzuki, O Suzuki, G Kido
    PHYSICAL REVIEW B 71 10 2005年03月 [査読有り][通常論文]
     
    The magnetic phase diagram for antiferroquadrupole (AFQ) ordering in tetragonal HoB2C2 has been investigated by measurements of elastic constants C-11, C-44, and C-66 in fields along the basal x-y plane as well as the principal [001]-axis. The hybrid magnet (GAMA) in Tsukuba Magnetic Laboratory was employed for high field measurements up to 30 T. The AFQ phase is no longer observed above 26.3 T along the principal [001]-axis in contrast to the relatively small critical field of 3.9 T in fields applied along the basal [110]-axis. The quadrupolar intersite interaction of O-xy and/or O-2(2) is consistent with the anisotropy in the magnetic phase diagram of the AFQ phase in HoB2C2.
  • Tatsuya Yanagisawa, Terutaka Goto, Yuichi Nemoto, Ryuta Watanuki, Kazuya Suzuki, Osamu Suzuki, Giyuu Kido
    Physical Review B - Condensed Matter and Materials Physics 71 2005年01月20日 [査読有り][通常論文]
     
    The magnetic phase diagram for antiferro-quadrupole (AFQ) ordering in
    tetragonal HoB$_2$C$_2$ has been investigated by measurements of elastic
    constants $C_{11}$, $C_{44}$ and $C_{66}$ in fields along the basal $x$-$y$
    plane as well as the principal [001]-axis. The hybrid magnet (GAMA) in Tsukuba
    Magnetic Laboratory was employed for high field measurements up to 30 T. The
    AFQ phase is no longer observed above 26.3 T along the principal [001] axis in
    contrast to the relatively small critical field of 3.9 T in fields applied
    along the basal [110] axis. The quadrupolar intersite interaction of...
  • T Goto, Y Nemoto, K Onuki, K Sakai, T Yamaguchi, M Akatsu, T Yanagisawa, H Sugawara, H Sato
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 74 1 263 - 266 2005年01月 [査読有り][通常論文]
     
    We have made ultrasonic measurements on a filled skutterudite PrOs4Sb12 showing a heavy fermion superconductivity at T-C = 1.85 K. The softening of the elastic constant with decreasing temperature has been found above T-C. The (C-11 - C-12)/2 in applying magnetic fields along the [110] axis at 1.0 K exhibits a minimum around 8 T, which is well accounted for by the one-ion quadrupolar susceptibility reflecting the level crossing of one of an excited Gamma(4)((2)) triplet to a ground state Gamma(1) singlet. The softening of (C-11 - C-12)/2 proportional to reciprocal temperature just above T-C may be dominated by the tunneling of an off-center Pr-ion in an Sb-icosahedron cage.
  • Goto T, Nemoto Y, Yamaguchi T, Akatsu M, Yanagisawa T, Suzuki O, Kitazawa H
    PHYSICAL REVIEW B - Condensed Matter and Materials Physics 70 184126  2004年09月17日 [査読有り][通常論文]
     
    We present tunneling and rattling motions of an off-center guest atom in cage referring to a clathrate crystal La_3Pd_{20}Ge_6. The elastic constant C_{44} of La_3Pd_{20}Ge_6 shows a Debye-type dispersion around 20 K obeying a relaxation time tau = tau_0exp(E/k_{B}T) with an attempt time tau_0 = 2.0*10^{-12} sec and an activation energy E = 197 K. At low temperatures below 3 K down to 20 mK, the C_{44} shows a softening of C_{44} = C_{44}^0(T-T_C^0)/(T-Theta) with T_C^0 = -337.970 mK and Theta = -338.044 mK. These facts are attributed to two different types of the off-center motions with Gamma_5 symmetry in 4a-site cage of La_3Pd_{20}Ge_6, a thermally activated rattling motion over the potential hill and a tunneling motion through the potential hill at low temperatures.
  • T Goto, Y Nemoto, K Sakai, T Yamaguchi, M Akatsu, T Yanagisawa, H Hazama, K Onuki, H Sugawara, H Sato
    PHYSICAL REVIEW B 69 18 2004年05月 [査読有り][通常論文]
     
    The elastic properties of a filled skutterudite PrOs4Sb12 with a heavy fermion superconductivity at T-C=1.85 K have been investigated. The elastic softening of (C-11-C-12)/2 and C-44 with lowering temperature down to T-C indicates that the quadrupolar fluctuation due to the CEF state plays a role for the Cooper paring in superconducting phase of PrOs4Sb12. A Debye-type dispersion in the elastic constants around 30 K revealed a thermally activated Gamma(23) rattling due to the off-center Pr-atom motion obeying tau=tau(0) exp(E/k(B)T) with an attempt time tau(0)=8.8x10(-11) s and an activation energy E=168 K. It is remarkable that the charge fluctuation of the off-center motion with Gamma(23) symmetry may mix with the quadrupolar fluctuation and enhance the elastic softening of (C-11-C-12)/2 just above T-C.
  • Terutaka Goto, Yuichi Nemoto, Kazuhiro Sakai, Takashi Yamaguchi, Mitsuhiro Akatsu, Tatsuya Yanagisawa, Hirofumi Hazama, Kei Onuki, Hitoshi Sugawara, Hideyuki Sato
    Physical Review B - Condensed Matter and Materials Physics 69 2004年04月08日 [査読有り][通常論文]
     
    The elastic properties of a filled skutterudite PrOs_4Sb_{12} with a heavy
    Fermion superconductivity at T_C=1.85 K have been investigated. The elastic
    softening of (C_{11}-C_{12})/2 and C_{44} with lowering temperature down to T_C
    indicates that the quadrupolar fluctuation due to the CEF state plays a role
    for the Cooper paring in superconducting phase of PrOs_4Sb_{12}. A Debye-type
    dispersion in the elastic constants around 30 K revealed a thermally activated
    Gamma_{23} rattling due to the off-center Pr-atom motion obeying
    tau=tau_{0}exp(E/k_{B}T) with an attempt time tau_0=8.8*10^{-11} se...
  • 山口 隆, 根本 祐一, 赤津 光洋, 柳澤 達也, 後藤 輝孝, 鈴木 修, 北澤 英明, 木戸 義勇
    日本物理学会講演概要集 59 1 1 - 5 社団法人日本物理学会 2004年03月03日 [査読無し][通常論文]
     
    We present tunneling and rattling motions of an off-center guest atom in cage
    referring to a clathrate crystal La_3Pd_{20}Ge_6. The elastic constant C_{44}
    of La_3Pd_{20}Ge_6 shows a Debye-type dispersion around 20 K obeying a
    relaxation time tau = tau_0exp(E/k_{B}T) with an attempt time tau_0 =
    2.0*10^{-12} sec and an activation energy E = 197 K. At low temperatures below
    3 K down to 20 mK, the C_{44} shows a softening of C_{44} =
    C_{44}^0(T-T_C^0)/(T-Theta) with T_C^0 = -337.970 mK and Theta = -338.044 mK.
    These facts are attributed to two different types of the off-center motions
    with Ga...
  • Y Nemoto, T Yamaguchi, T Horino, M Akatsu, T Yanagisawa, T Goto, O Suzuki, A Donni, T Komatsubara
    PHYSICAL REVIEW B 68 18 2003年11月 [査読有り][通常論文]
     
    Lattice effects in a cerium based clathrate compound Ce3Pd20Ge6 with a cubic Cr23C6-type structure have been investigated by ultrasonic and thermal expansion measurements. Elastic softenings of (C-11-C-12)/2 and C-44 proportional to the reciprocal temperature 1/T above T-Q1=1.25 K are well described in terms of the quadrupole susceptibility for the ground state Gamma(8) quartet. A huge softening of 50% in (C-11-C-12)/2 and a spontaneous expansion DeltaL/L=1.9x10(-4) along the [001] direction in particular indicate the ferroquadrupole ordering of O-2(0) below T-Q1. The elastic anomalies associated with the antiferromagnetic ordering at T-N2=0.75 K and the incommensurate antiferromagnetic ordering are also found. Notable frequency dependence of C-44 around 10 K is accounted for by the Debye-type dispersion indicating a Gamma(5) rattling motion of an off-center Ce ion along the [111] direction with eight fractionally occupied positions around the 4a site in a cage. The thermally activated Gamma(5) rattling motion obeying a relaxation time tau=tau(0) exp (E/k(B)T) with an attempt time tau(0)=3.1x10(-11) sec and an activation energy E=70 K dies out with decreasing temperature, and then the off-center tunneling state of Ce ion in the 4a-site cage will appear at low temperatures.
  • Yuichi Nemoto, Takashi Yamaguchi, Takenobu Horino, Mitsuhiro Akatsu, Tatsuya Yanagisawa, Terutaka Goto, Osamu Suzuki, Andreas Donni, Takemi Komatsubara
    Physical Review B - Condensed Matter and Materials Physics 68 2003年10月23日 [査読有り][通常論文]
     
    Lattice effects in a cerium based clathrate compound Ce_3Pd_20Ge_6 with a
    cubic Cr_23C_6-type structure have been investigated by ultrasonic and thermal
    expansion measurements. Elastic softenings of (C_11-C_12)/2 and C_44
    proportional to the reciprocal temperature 1/T above T_Q1 = 1.25 K are well
    described in terms of the quadrupole susceptibility for the ground state
    Gamma_8 quartet. A huge softening of 50 % in (C_11-C_12)/2 and a spontaneous
    expansion DL/L = 1.9x10^-4 along the [001] direction in particular indicate the
    ferroquadrupole ordering of O_2^0 below T_Q1. The elastic anomalies a...
  • T Goto, M Akatsu, T Yanagisawa, T Yamaguchi, Y Nemoto, O Suzuki, S Nakamura, S Kunii, R Watanuki, K Suzuki
    JOURNAL OF PHYSICS-CONDENSED MATTER 15 28 S2101 - S2107 2003年07月 [査読有り][通常論文]
     
    The quadrupole orderings and lattice effects in 4f-electron systems with orbital degeneracy in rare earth compounds have been investigated by ultrasonic and thermal expansion measurements. A ferroquadrupole (FQ) O-xy-type ordering associated with a trigonal distortion in HoB6 with a Gamma(5) ground state is presented. The trigonal distortion in ordered phase IV CexLa1-xB6 (x = 0.75 and 0.70) with a Gamma(8) ground state indicates O-xy-type FQ ordering in phase IV. In both systems, HoB6 and CexLa1-xB6, C-44 anomalies are observed. In tetragonal HoB2C2, an ordered phase IV appears near a tetra-critical point, where the antiferroquadrupole phase II and antiferromagnetic phase III compete with each other. Noticeable ultrasonic attenuation and softening of elastic constants in phase IV of HoB2C2 due to quadrupole fluctuation with a slow relaxation time tau similar to 7 x 10(-9) s are found.
  • Y Nemoto, T Yanagisawa, K Hyodo, T Goto, S Miyata, R Watanuki, K Suzuki
    PHYSICA B-CONDENSED MATTER 329 641 - 642 2003年05月 [査読有り][通常論文]
     
    Elastic constants of tetragonal system DyB2C2 with antiferro-quadrupole (AFQ) ordering have been measured by using ultrasonic method. Remarkable elastic softenings of the C-44 and (C-11 - C-12)/2 have been observed towards the AFQ transition at T-Q = 25 K. The present results show that a CEF ground state is a pseudo-quartet consisting of two Kramers doublets of E-1/2 and E-3/2 in C-4h site symmetry of Dy3+ ion. The dominant softening Of C-44 probably leads to the order parameter of O-yz and O-zx in AFQ phase. Magnetic phase diagram applied fields along the [100] direction determined by field dependence of the C-44 is presented. (C) 2003 Elsevier Science B.V. All rights reserved.
  • T Yanagisawa, Y Nemoto, T Goto, S Miyata, R Watanuki, K Suzuki
    PHYSICA B-CONDENSED MATTER 329 624 - 625 2003年05月 [査読有り][通常論文]
     
    Elastic properties of the ternary rare earth compound HoB2C2 with a tetragonal symmetry have been investigated by means of ultrasonic measurements. The elastic constants Of C-44, C-66 and (C-11 - C-12)/2 exhibit the characteristic softening below about 40 K. In order to analyze quadrupole susceptibility, we assume a pseudo-degeneracy model consisting of a ground state E-doublet and an excited state A- or B-singlet at energy Deltasimilar to5.0 K. The considerable softening of the elastic constant and ultrasonic attenuation in phase IV between T-C1 = 5.9 K and T-C2 = 5.0 K have been found. The slow relaxation rate of 7 x 10(-9) s suggests that the fluctuation of quadrupole moments is enhanced in phase IV. We also show a H-T phase diagram of HoB2C2 under magnetic fields along [100]. (C) 2003 Elsevier Science B.V. All rights reserved.
  • T Yanagisawa, T Goto, Y Nemoto, S Miyata, R Watanuki, K Suzuki
    PHYSICAL REVIEW B 67 11 2003年03月 [査読有り][通常論文]
     
    The elastic properties of HoB2C2 undergoing an antiferroquadrupole ordering with a tetragonal structure have been investigated by means of ultrasonic measurements. The transverse (C-11-C-12)/2, C-44, and C-66 modes exhibit characteristic softenings with decreasing temperature in a paramagnetic phase I down to an ordered phase IV at T-C1=5.9 K. The softening of (C-11-C-12)/2, C-44 and C-66 is described by a formula C-Gamma=C-Gamma(0)(T-T-C(0))/(T-Theta) due to the quadrupole-strain interaction for the 4f state of HoB2C2 consisting of a ground E doublet with orbital degeneracy and an excited singlet with a small-energy splitting Delta. The significant softening of the elastic constant and the ultrasonic attenuation in phase IV between T-C1=5.9 K and T-C2=5.0 K have been found. The ultrasonic dispersion in phase IV indicates the slowing down of the quadrupole fluctuation time, tau=7x10(-9) sec.
  • Yanagisawa, T., Goto, T., Nemoto, Y., Miyata, S., Watanuki, R., Suzuki, K.
    Physical Review B - Condensed Matter and Materials Physics 67 11 1151291 - 1151298 2003年03月 [査読有り][通常論文]
     
    The elastic properties of HoB2C2 undergoing an antiferroquadrupole ordering with a tetragonal structure have been investigated by means of ultrasonic measurements. The transverse (C 11 -C 12 )/2, C 44 , and C 66 modes exhibit characteristic softenings with decreasing temperature in a paramagnetic phase I down to an ordered phase IV at T C? = 5.9 K. The softening of of (C 11 -C 12 )/2, C 44 and C 66 is described by a formula CΓ = C Γ 0 (T-T C 0 )(T-Θ) due to the quadrupole-strain interaction for the 4f state of HoB 2 C 2 consisting of a ground E doublet with orbital degeneracy and an excited singlet with a small-energy splitting Δ. The significant softening of the elastic constant and the ultrasonic attenuation in phase IV between T C1 = 5.9 K and T C2 = 5.0 K have been found. The ultrasonic dispersion in phase IV indicates the slowing down of the quadrupole fluctuation time, τ = 7 × 10 -9 sec.
  • T Goto, T Yanagisawa, K Hyodo, Y Nemoto, S Miyata, R Watanuki, K Suzuki
    ACTA PHYSICA POLONICA B 34 2 1173 - 1176 2003年02月 [査読有り][通常論文]
     
    The antiferroquadrupole orderings of the ternary rare earth compounds HoB2C2 and DyB2C2 have been investigated by means of ultrasonic measurements. The transverse (C-11-C-12)/2, C-44, C-66 modes in HoB2C2 exhibit characteristic softening above T-c2 = 5.0 K, which consist with an E-doublet and a singlet for the ground state. Considerable elastic softening and ultrasonic attenuation in phase IV below T-c1 = 5.9 K of HoB2C2 indicates an enhancement of the quadrupole fluctuation with a relaxation rate tau = 7 x 10(-9) sec. A softening of the transverse elastic constant C-44 in DyB2C2 above T-Q = 24.7 K indicates accidentally degenerated Kramers doublets of E-1/2 and E-3/2 for the ground state.
  • Tatsuya Yanagisawa, Terutaka Goto, Yuichi Nemoto, Shingo Miyata, Ryuta Watanuki, Kazuya Suzuki
    Physical Review B - Condensed Matter and Materials Physics 67 11 8  2003年 [査読有り][通常論文]
     
    The elastic properties of (formula presented) undergoing an antiferroquadrupole ordering with a tetragonal structure have been investigated by means of ultrasonic measurements. The transverse (formula presented) (formula presented) and (formula presented) modes exhibit characteristic softenings with decreasing temperature in a paramagnetic phase I down to an ordered phase IV at (formula presented) The softening of (formula presented) (formula presented) and (formula presented) is described by a formula (formula presented) due to the quadrupole-strain interaction for the (formula presented) state of (formula presented) consisting of a ground E doublet with orbital degeneracy and an excited singlet with a small-energy splitting (formula presented) The significant softening of the elastic constant and the ultrasonic attenuation in phase IV between (formula presented) and (formula presented) have been found. The ultrasonic dispersion in phase IV indicates the slowing down of the quadrupole fluctuation time, (formula presented). © 2003 The American Physical Society.
  • Goto, T., Yanagisawa, T., Nemoto, Y., Miyata, S., Watanuki, R., Suzuki, K.
    Journal of the Physical Society of Japan 71 SUPPL. 88 - 90 2002年12月 [査読有り][通常論文]
     
    We have investigated the elastic constants of the ternary rare earth compound H0B 2 C 2 with a tetragonal structure by means of the ultrasonic method. The elastic constants of (C 11-C 12 )/2, C 44 and C 66 , corresponding to the transverse ultrasonic modes exhibit the softening proportional to reciprocal temperature below about 40 K. This softening is commonly enhanced in the ordered phase IV below T c1 =5.9 k. An abrupt increase of elastic constants is found in the ordered phase III below T c2 =5.0 k characterized by the simultaneous antiferro-type ordering of electric quadrupole and magnetic dipole moments. The quadrupole susceptibility based on a model consisting of a ground state E-doublet and an excited singlet with a low energy in H0B 2 C 2 is employed for the analysis of the softening above T c1 =5.9 K. The enhancement of the elastic softening in the phase IV of H0B 2 C 2 resembles to the soft C 44 mode in the phase IV in Ce o.75 La o.25 B 6 . © 2002 The Physical Society of Japan.
  • Yanagisawa, T., Nemoto, Y., Goto, T., Onuki, Y.
    Journal of the Physical Society of Japan 71 SUPPL. 267 - 269 2002年12月 [査読有り][通常論文]
     
    We have performed low-temperature ultrasonic measurements on CeRu 2 Si 2 by using a dilution refrigerator down to 20 mK with a superconducting magnet up to 16 T. The longitudinal modes exhibit huge softening of 20% around a metamagnetic transition point Hc∼7.7 T, while the transverse modes show softening of about 1%. This result suggests that the coupling of the volume strain b to the order parameter with total symmetry plays a crucial role for the metamagnetic transition in CeRu 2 Si 2 . In the vicinity of H c , the enormous ultrasonic attenuation has been observed in the longitudinal ultrasonic modes. The relaxation time r increases considerably near the metamagnetic transition due to a critical slowing-down. We also show the detailed magnetic phase diagram of CeRu 2 Si 2 down to 20 mK around H c © 2002 The Physical Society of Japan.
  • T Yanagisawa, Y Nemoto, T Goto, Y Onuki
    PHYSICA B-CONDENSED MATTER 312 271 - 273 2002年03月 [査読有り][通常論文]
     
    We have performed ultrasonic measurements on CeRu2Si2 down to 20 mK in magnetic fields up to 16 T. The longitudinal C-11 and C-33 exhibit considerable softening of 20% which coincide with ultrasonic absorption around the metamagnetic point H-C = 7.7 T. The transverse C-44 and C-66 show only a small softening of approximate to 0.8 % around H-C. The softening in the longitudinal C-11 and C-33 comprising a volume strain suggests that the coupling of the order parameter with total symmetry to the volume strain plays a crucial role for the metamagnetic transition in CeRu2Si2. (C) 2002 Elsevier Science B.V. All rights reserved.
  • Goto Terutaka, Yanagisawa Tatsuya, Nemoto Yuichi
    Journal of the Physical Society of Japan 71 0 88 - 90 Physical Society of Japan 2002年 [査読有り][通常論文]
  • Yanagisawa Tatsuya, Nemoto Yuichi, Goto Terutaka
    Journal of the Physical Society of Japan 71 0 267 - 269 Physical Society of Japan 2002年 [査読有り][通常論文]
  • Terutaka Goto, Tatsuya Yanagisawa, Yuichi Nemoto, Shingo Miyata, Ryuta Watanuki, Kazuya Suzuki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 71 88 - 90 2002年01月 [査読有り][通常論文]
     
    We have investigated the elastic constants of the ternary rare earth compound HoB2C2 with a tetragonal structure, by means of the ultrasonic method. The elastic constants of (C-11- C-12)/2, C-44 and C-66,, corresponding to the transverse ultrasonic modes exhibit the softening proportional to reciprocal temperature below about 40 K. This softening is commonly enhanced in the ordered phase IV below T-C1 = 5.9 K. An abrupt increase of elastic constants is found in the ordered phase UI below T-C2 = 5,0 K characterized by the simultaneous antiferro-type ordering of electric quadrupole and magnetic dipole moments. The quadrupole susceptibility based on a model consisting of a ground state E-doublet and an excited singlet with a low energy in HoB2C2 is employed for the analysis of the softening above T-C1 = 5.9 K. The enhancement of the elastic softening in the phase IV of HoB2C2 resembles to the soft C44 mode in the phase IV in Ce0,751La0.25B6.
  • Yanagisawa Tatsuya, Nemoto Yuichi, Goto Terutaka, Onuki Yoshichika
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 71 267 - 269 2002年01月 [査読有り][通常論文]
     
    We have performed low-temperature ultrasonic measurements on CeRu2Si2 by using a dilution refrigerator down to 20 niK with a superconducting magnet up to 16 T. The longitudinal modes exhibit huge softening of 20% around a metamagnetic transition point H-C similar to 7.7 T, while the transverse modes show softening of about 1%. This result suggests that the coupling of the volume strain epsilon(B) to the order parameter with total symmetry plays a crucial role for the metamagnetic.transition in CeRu2Si2. In the vicinity of H-C, the enormous ultrasonic attenuation has been observed in the longitudinal ultrasonic modes. The relaxation time tau increases considerably near the metamagnetic transition due to a critical stowing-down. We also show the detailed magnetic phase diagram of CeRu2Si2 down to 20 mK around H-C.

MISC

講演・口頭発表等

担当経験のある科目（授業）

  • 電磁気学演習I北海道大学理学部物理学科
  • 電磁気学I北海道大学理学部物理学科
  • 現代物理学概論北海道大学
  • 物理学 2北海道大学
  • 外国語文献購読 2北海道大学
  • 自然科学実験北海道大学
  • 物理学 1北海道大学
  • 教育法（理科 2）北海道大学
  • 物理学 2北海道大学
  • 外国語文献購読 3北海道大学
  • 物理学実験III・IV北海道大学

所属学協会

  • 日本物理学会   Physical Society of Japan   

共同研究・競争的資金等の研究課題

  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2023年04月 -2028年03月 
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  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2023年04月 -2028年03月 
    代表者 : 鬼丸 孝博, 大槻 純也, 田端 千紘, 柳澤 達也, 大原 繁男, 吉田 紘行, 網塚 浩, 井澤 公一, 小林 達生, 小林 夏野, 木俣 基
  • 日本学術振興会：科学研究費助成事業 基盤研究(C)
    研究期間 : 2022年04月 -2025年03月 
    代表者 : 柳澤 達也
  • 日本学術振興会：科学研究費助成事業 国際共同研究加速基金(国際共同研究強化(B))
    研究期間 : 2021年10月 -2025年03月 
    代表者 : 柳澤 達也
  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2019年04月 -2023年03月 
    代表者 : 井原 慶彦, 柳澤 達也, 松井 一樹, 吉田 紘行, 福岡 脩平, 小濱 芳允
     
    研究初年度となる2019年度は、本研究計画の主要装置となる小型パルス磁場発生装置の電源のエネルギーをを既存の10kJから30kJへと拡充し、更新した電源を用いてこれまでのところ20テスラ超までの磁場発生に成功した。これは、小規模の研究室における発生磁場としては最強レベルであり、ここまでの強磁場をコンパクトな磁場発生装置で勘弁に発生できることを実証できたことはすでに非常に意義がある。また、マグネットの強度を改善することで予定していた30テスラを超える磁場発生が可能であることが分かった。実際のマグネット改造は2年度への課題とした。 測定系では、まず超音波測定装置を立ち上げ、重い電子系物質において2 K以下までの超音波測定を可能にした。今回立ち上げた装置を用いて、量子振動の観測に成功し、実際の物性研究を行うに十分な測定精度を持つことが確認できた。特に、今回は高速オシロスコープを取り入れたデジタル分光方式を採用し、新しい測定原理に基づく超音波測定を実施できるようになったことは意義が深い。この方式は、パルス磁場中測定だけでなく、定常磁場中にも応用でき、測定難易度を下げることが期待される。 次に、核磁気共鳴分光装置に関しては、周波数の高速変調技術を確立し、5ミリ秒という短いパルス磁場発生時間中に非常に広帯域の周波数スペクトルの観測に成功した。この技術を用いて、20テスラまでのスペクトル測定はもとより、東京大学物性研究所における共同利用実験では53テスラまでのNMRスペクトル測定に成功し、その実用性が実証済みである。 最後に、3つ目のプローブとなる熱測定は、東京大学物性研究所においてすでに稼働しているパルス磁場中熱測定システムを用いた実験を行い、測定技術の移植を行っている。2019年度は測定に必要な装置群およびプローブの準備を行い、2020年度の立ち上げに備えた。
  • 文部科学省：基盤研究(B)
    研究期間 : 2019年04月 -2023年03月 
    代表者 : 井原 慶彦
     
    19H01832 本研究計画では、非常に高い磁場領域で実現する新奇物性を先端的な精密測定を用いて観測し、その起源を解明していく。一般的な超伝導磁石を用いた強磁場発生法では、15テスラ程度の磁場が限界であるが、瞬間的に強磁場を発生させるパルス磁場技術ではこれをはるかに超える30テスラ超級の磁場を発生させることができる。しかし、数十ミリ秒のあいだに数十テスラの磁場変動が起こるため、パルス磁場下での精密測定は困難であった。そこで、最新の磁場制御技術により数ミリ秒の間磁場の時間変動が全く無くなる準定常磁場を利用することで、複数の精密測定を実現し、これらを多角的に用いた研究により強磁場物性を開拓する。
  • 日本学術振興会：科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2018年04月 -2020年03月 
    代表者 : 柳澤 達也
     
    公募研究D01班の鬼丸らとの共同研究としてPrを非磁性のYによって希釈したY1-xPrxIr2Zn2単結晶試料（x = 0.0, 0.034, 0.37）の系統的な超音波実験を行った。その結果、x=0.034の希釈極限試料では四極子近藤効果を実証する上での決め手となる弾性定数(C11-C12)/2の対数的温度変化の観測に成功した。一方、x = 0.37の中間濃度試料の極低温領域では対数的よりはむしろT^(1/2)に比例する温度依存性を示すことがわかった。また新たに超音波分散を発見した。 公募研究B01班の平井らとの共同研究として、パイロクロア酸化物Cd2Re2O7の逐次構造相転移にたいして予言されている電気トロイダル四極子秩序の実験的証拠を得るために、横波弾性 定数(C11-C12)/2とC44を横波超音波で測定し、秩序変数の対称性の検証を試みた。その結果、中間相において、巨大な周波数変化を伴う超音波吸収の増大と弾性定数のソフト化を観測した。 上記の成果は強相関電子系の多極子自由度を観測する本研究の目的と合致し、本新学術領域内での新たな共同研究が芽生えたことで、超音波測定技術を活かした今後のさらなる研究発展が期待できる。よって、当初の計画以上に進展したと言える。東北大金属材料研究所の25T-SCMに同軸管内蔵の２軸ゴニオメータを組み合わせ、URu2Si2のc面内磁気異方性を弾性定数で検証する実験の準備を終えた。しかし、本年度マグネットの不具合が発生し共同利用実験は延期となった。 研究当初から開発を続けている高温測定装置は耐熱同軸管の高温領域でのテストが完了し、冷却水系の安全スイッチ、防爆用のキャビネットなどを新たに設置し単結晶Siを用いた予備測定に漕ぎ着けた。しかし研究期間内にBaMn2As2の高温領域における弾性応答の測定は達成できなかったため、今後も研究を継続する予定。
  • 日本学術振興会：科学研究費助成事業 基盤研究(C)
    研究期間 : 2017年04月 -2020年03月 
    代表者 : 柳澤 達也
     
    ドレスデン強磁場研究所において、UNi4Bの極低温・強磁場における弾性定数C66の測定を継続して行った。昨年度まではH || [01-10]方向のみであった磁場-温度相図を、c面内で90度回転させたH || [2-1-10]方向についても完成させた。その結果、c面内磁場方向によって弾性応答が全く異なることを発見した。当初六方晶を仮定していた結晶場モデルを精密化し、零磁場でT*~330 mK付近においてソフト化が抑制される振る舞いが、試料内の微小な直方晶歪みの存在を仮定することで説明がつくことが判った。この結果は最近行われた放射光実験、中性子回折実験から報告されている、本系の結晶構造が直方晶Cmcmもしくはそれよりも低対称であるという事実とも矛盾しない。カンタムデザイン社PPMSと超音波装置を組み合わせ、磁場中においても電流下超音波測定を行ったが、有意な電流による弾性応答の変化は観られなかった。 非従来型超伝導を示す籠状化合物UBe13の弾性定数C11の測定をT ≧ 20 mK、H ≦ 16 Tの磁場・温度領域で行い、極低温に磁場に鈍感なソフト化が存在し、そのソフト化が対数的温度変化を示すことが解った。この結果は、本物質が示す非フェルミ液体的振る舞いが弾性定数にも顔を出しており、その起源として磁場に鈍感な四極子近藤効果が考えられる。また、本系のUサイトは反転対称性を持たないため、奇パリティ多極子の関与も示唆する。 一方、本研究と並行して遂行していた「国際共同研究加速基金」による研究で海外研究施設に滞在中に、籠状化合物合成の過程でU-Pd-Biから成る未知の三元系立方晶化合物が偶然得られた。本年度はその磁化・電気抵抗測定をカリフォルニア大で行ったところ、150 K付近で反強磁性的転移を示すことが解り、新たな研究シーズとして期待できる。
  • 文部科学省：新学術領域研究(研究領域提案型)
    研究期間 : 2018年04月 -2020年03月 
    代表者 : 柳澤 達也
     
    18H04297
  • 文部科学省：基盤研究(C)
    研究期間 : 2017年04月 -2020年03月 
    代表者 : 柳澤 達也
     
    17K05525
  • 文部科学省：国際共同研究加速基金(国際共同研究強化)
    研究期間 : 2016年03月 -2019年03月 
    代表者 : 柳澤 達也
     
    15KK0146
  • 日本学術振興会：科学研究費助成事業 挑戦的萌芽研究
    研究期間 : 2015年04月 -2018年03月 
    代表者 : 網塚 浩, 柳澤 達也, 日髙 宏之, 齋藤 開, 鹿内 奈南, 山本 将隆, 中尾 裕則, 田端 千紘, 谷田 博司, 世良 正文, 松村 武, Sechovský Vladimir, Uhlířová Klára, Vališka Michal, Zherlitsyn Sergei, Wosnitza Jochen, Süllow Stefan
     
    本研究の目的は、電子スピンの渦状配置に対応する「トロイダルモーメント」が秩序した金属磁性体に関して予言された新奇な電気磁気効果を実験で検証することにある。現実の強的トロイダル秩序系の候補である層状ウラン化合物UNi4Bの単結晶について電流下での精密磁化測定を行った結果、電流強度に比例して一様磁化が生じることを観測し、理論予想が本質的に正しいことを証明した。一方で電流方向に対する磁化の応答方向が理論予想と単純には合致しない結果も得られ、本系の結晶および磁気構造を精密に再検討する必要があるという新たな課題も提起した。また、同様の電流誘起磁化現象を示す二つの反強磁性体を新たに見出した。
  • 文部科学省：挑戦的萌芽研究
    研究期間 : 2015年04月 -2018年03月 
    代表者 : 網塚 浩
     
    15K13509 本研究の目的は、電子スピンの渦状配置に対応する「トロイダルモーメント」が秩序した金属磁性体に関して予言された新奇な電気磁気効果を実験で検証することにある。現実の強的トロイダル秩序系の候補である層状ウラン化合物UNi4Bの単結晶について電流下での精密磁化測定を行った結果、電流強度に比例して一様磁化が生じることを観測し、理論予想が本質的に正しいことを証明した。一方で電流方向に対する磁化の応答方向が理論予想と単純には合致しない結果も得られ、本系の結晶および磁気構造を精密に再検討する必要があるという新たな課題も提起した。また、同様の電流誘起磁化現象を示す二つの反強磁性体を新たに見出した。
  • 日本学術振興会：科学研究費助成事業 国際共同研究加速基金(国際共同研究強化)
    研究期間 : 2016年 -2018年 
    代表者 : 柳澤 達也, メイプル ブライアン, ツェリツィン セルゲイ, セコフスキー ウラジミール, 網塚 浩, グリーン エリザベス, 中村 慎太郎, 淡路 智
     
    Γ3非クラマース2重項基底状態を持つ立方晶系化合物において，非磁性の基底状態が有する電気四極子自由度に起因した風変わりな物性が理論提案され，その検証が進められている. 本研究ではその候補物質であるカゴ状化合物PrNi2Cd20や，その類似物質群の諸物性について，カリフォルニア大学，ドレスデン強磁場研究所，カレル大学，東北大学金属材料研究所，北海道大学の国際共同研究によって研究を推進し，極低温・強磁場における超音波測定の手法を駆使することで，四極子秩序や四極子近藤効果などの新規物性に関する実験的傍証を得ることに成功した.
  • 日本学術振興会：科学研究費助成事業 基盤研究(C)
    研究期間 : 2014年04月 -2017年03月 
    代表者 : 柳澤 達也, 網塚 浩, 日髙 宏之
     
    高い対称性を持つ籠状結晶構造に宿る、局所電荷揺らぎや多極子自由度などの複数の量子自由度の結合・拮抗に由来すると考えられる、風変わりな物性に着目し、超音波測定の手法を用いて弾性応答の観点から、カゴ状化合物の量子基底状態を調べた。特に磁場に鈍感な重い電子状態を示すSmOs4Sb12については、パルス磁場を用いた弾性応答により結晶場基底状態を判別し、静水圧力下実験から低温秩序相にΓ67基底状態が有する磁気八極子の相関が強く影響していることを明らかにした。また、カリフォルニア大学との共同研究により作成した新規籠状物質PrNi2Cd20はΓ3非クラマース二重項基底状態を持つことを明らかにした。
  • 文部科学省：科学研究費補助金(基盤研究(C))
    研究期間 : 2014年04月 -2017年03月 
    代表者 : 柳澤 達也
     
    26400342
  • 日本学術振興会：科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2011年04月 -2013年03月 
    代表者 : 柳澤 達也
     
    1. 重い電子超伝導物質PrOs_4Sb_12の電気抵抗と弾性定数の同時測定を磁場中で行い，弾性応答の観点から超伝導相図の再構築を試みた．その結果，本系の非BCS超伝導は測定感度内で弾性定数C_11(= C_B+4/3*(C_11-C_12)/2)に変化をもたらさないことがわかった．一方，過去の報告（~17 MHz)では結晶場以外の寄与による弾性定数(C_11-C_12)/2のソフト化がT_c近傍まで続き，T_c以下でソフト化が停止するとされており，本研究結果と大きく矛盾する．ここで，本研究では320 MHzまでの高周波測定を行い，複数の周波数帯において再現性を確認していることを鑑みると，過去の測定では，超音波の低い指向性によって異なる超音波モードの混在が起こっている可能性が高いという結論に至った． 2. Uを内包するカゴ状結晶構造を持つクラスレート化合物U_3Pd_20Si_6の磁場中超音波測定を行った。試料表面を研磨し，測定精度のさらなる向上を試みた結果，T_N直下において超音波の吸収・散乱が生じ測定が困難になる領域が磁場の印可に伴い拡大することを発見した．その領域は過去の報告にある低温・高磁場領域のスピンフロップ相に繋がることが予想され，大きな弾性異常とスピンフロップ状態の複雑な磁気構造からは高次多極子の寄与が示唆される．尚, 本系8cサイトのUのサイトシンメトリーはTdでありパリティ混成に起因する奇パリティの電気・磁気多極子が関与している可能性も考えられる． 3. ラットリングを示すカゴ状化合物探索の一環として，神戸大菅原氏から提供されたEuOs4Sb12の超音波測定を行なった．本系は零磁場で9 K付近に強磁性転移を示すが，磁場中での弾性定数測定の結果，8 T, 10 K近傍でキュリー点が消失した後に，超音波分散らしき周波数依存性を伴う弾性異常を発見した．
  • 日本学術振興会：科学研究費助成事業 若手研究(B)
    研究期間 : 2011年 -2012年 
    代表者 : 柳澤 達也
     
    URu2Si2の未解明の秩序相「隠れた秩序」の候補として近年提案されている多極子秩序模型を検証する為にドレスデン強磁場センターに於いて最大磁場68.7Tのロングパルス磁場を用いたURu2Si2の弾性定数(C11-C12)/2モードの超音波測定を行った.その結果,URu2Si2の弱磁場・低温領域ではΓ3対称性の格子不安定性を伴ったc-f混成による重い電子状態が形成されており,高磁場領域ではその混成が切れ,同時に格子不安定性も消失していることがわかった.
  • 文部科学省：科学研究費補助金(新学術領域研究(研究領域提案型), 新学術領域研究(研究領域提案型))
    研究期間 : 2011年 -2012年 
    代表者 : 柳澤 達也
     
    23102701 (1)、磁場に鈍感な重い電子状態を示し,同時に磁場に依存しない局所フォノン自由度を持つ充填スクッテルダイト化合物SmOs4Sb12の強磁場下における超音波測定を行うことで,結晶場基底状態を明らかにすることを目的とし,平成23年11月にドイツ,ドレスデン強磁場研究所で62Tパルス磁場下超音波実験を行った.その結果,4.2Kに於ける弾性定数C11の磁場依存性は10T付近で極小をとり,高磁場領域ではdHvA振動を繰り返しながら励磁と共にゆるやかに上昇する傾向を示した.立方晶系においてC11はΓ1対称性のOBとΓ3対称性の四極子感受率の和として記述されるため,高磁場領域でOBの影響が小さいと仮定した場合,本実験結果はΓ8四重項基底状態を示唆する結果である. (2)、ラットリングを示すカゴ状化合物探索の一環として,EuOs4Sb12の単結晶試料育成を試行したものの,超音波実験に使用できる1立方ミリメートル程度の単結晶サイズを得る事ができず,現在も試行を繰り返している.一方,カゴ状結晶構造を持つ重い電子超伝導体として古くから知られるUBe13とその類似物質群RBe13(R=ランタノイド)の単結晶育成に成功し,1立方ミリメートル程度の単結晶を得た.試料評価と研磨を行い,超音波実験の準備をほぼ完了した. (3)、キャパシタンス法による熱膨張セルをCADで設計し,民間の金属加工業者(0.1mピッチネジ部品)と...
  • 文部科学省：科学研究費補助金(若手研究(B))
    研究期間 : 2011年 -2012年 
    代表者 : 柳澤 達也
     
    23740250 １、重い電子系URu2Si2の隠れた秩序相の問題に対し，Rh希釈系のU(Ru1-xRhx)2Si2 (x = 0，0.02，0.07)単結晶試料を用いて高分解能超音波測定 (測定周波数f ≦ 175MHz)を行い，弾性応答の観点から反強四極子秩序の検証を行なった．Rhドープによって誘起される反強磁性秩序相での弾性応答を初めて観測した．反強磁性相での横波弾性定数C44，C66，(C11-C12)/2の変化量が，縦波弾性定数C11に比べてそれぞれ１/60, 1/500, 1/20程度であることから，これらのモードに対応する歪みは生じておらず，10E-5の精度内でRhドープ系における反強磁性転移前後で格子の対称性が保たれていることを確認した．一方，母物質に現れる弾性定数(C11-C12)/2のソフト化が隠れた秩序が消失するx = 0.07においても現れ、極低温で一定値に収束する振る舞いを得た．２、参照物質ThRu2Si2の弾性定数を測定し、それをURu2Si2の弾性定数と比較し，擬似的に格子・フォノンの寄与を差し引く事により、5f電子の弾性定数への寄与を浮き彫りにした．その結果、URu2Si2ではΓ3対称性の歪み場に対応する弾性定数(C11-C12)/2だけに5f電子の寄与に依るソフト化が生じていることが解った。３、平成23年楠瀬らによって提案された、隠れた秩序変数の有力な候補であ...
  • 日本学術振興会：科学研究費助成事業 新学術領域研究(研究領域提案型)
    研究期間 : 2009年 -2010年 
    代表者 : 柳澤 達也
     
    充填スクッテルダイト化合物SmOs_4Sb_<12>はその電子比熱係数(γ=820mJ mol^<-1>K^<-2>)が30Tの高磁場下比熱測定に於いても磁場に依存せず増強されたままであることから,「磁場に鈍感な重い電子系」として注目されている.この電子比熱係数の磁場に対する堅牢性は従来型のスピン自由度に由来する磁気近藤効果の理論では説明できないため,4f電子の持つ電気多極子自由度に由来する多チャンネル近藤効果や,ゲストイオンの局所振動(局所電荷分布の自由度)と電子系の結合による新規多体効果などの新たな理論提案が活発に為されている. 本研究ではそのようなエキゾチックな多体効果の由来となる局所電荷自由度を実験的に観測できる超音波をプローブとして用い,新たにフラックス法で育成したSmOs_4Sb_<12>の単結晶に対して超音波精密測定を行った.その結果,横波弾性定数C_<44>は結晶場効果によるソフト化を示し,多体効果により低温で収束する振る舞いを示した.一方、縦波弾性定数C_<11>においてはエネルギーと時間スケールの異なる2つの超音波分散の観測に成功した.また新潟大学後藤研究室との共同研究でヘリウム3冷凍機を用いた磁場中極低温実験を行い,10Tの磁場下においてもその超音波分散が全く磁場の影響を受けないことを明らかにし,磁場に鈍感な重い電子系であるSmOs_4Sb_<12>のゲストSmイオンが,磁場依存しない局所非調和振動の自由度を有することを実験的に初めて証明した.超音波分散の現象論的解析からラットリングの活性エネルギーと特性時間を見積もり,それらとアインシュタイン温度,電子比熱係数γ等の系統変化に相関があることを指摘した.
  • 文部科学省：科学研究費補助金(新学術領域研究(研究領域提案型))
    研究期間 : 2009年 -2010年 
    代表者 : 柳澤 達也
     
    21102501 充填スクッテルダイト化合物SmOs_4Sb_<12>はその電子比熱係数(γ=820mJ mol^<-1>K^<-2>)が30Tの高磁場下比熱測定に於いても磁場に依存せず増強されたままであることから,「磁場に鈍感な重い電子系」として注目されている.この電子比熱係数の磁場に対する堅牢性は従来型のスピン自由度に由来する磁気近藤効果の理論では説明できないため,4f電子の持つ電気多極子自由度に由来する多チャンネル近藤効果や,ゲストイオンの局所振動(局所電荷分布の自由度)と電子系の結合による新規多体効果などの新たな理論提案が活発に為されている.本研究ではそのようなエキゾチックな多体効果の由来となる局所電荷自由度を実験的に観測できる超音波をプローブとして用い,新たにフラックス法で育成したSmOs_4Sb_<12>の単結晶に対して超音波精密測定を行った.その結果,横波弾性定数C_<44>は結晶場効果によるソフト化を示し,多体効果により低温で収束する振る舞いを示した.一方、縦波弾性定数C_<11>においてはエネルギーと時間スケールの異なる2つの超音波分散の観測に成功した.また新潟大学後藤研究室との共同研究でヘリウム3冷凍機を用いた磁場中極低温実験を行い,10Tの磁場下においてもその超音波分散が全く磁場の影響を受けないことを明らかにし,磁場に鈍感な重い電子系であるSmOs_4Sb_<12>のゲス...
  • 日本学術振興会：科学研究費助成事業 特別推進研究
    研究期間 : 2006年 -2010年 
    代表者 : 後藤 輝孝, 根本 祐一, 北澤 英明, 鈴木 博之, 金田 寛, 柳澤 達也, 家富 洋, 大野 義章, 武田 直也, 鶴田 健二, 酒井 治, 赤津 光洋, 石井 勲, 三本 啓輔
     
    超音波歪みは明確な対称性を備え、電子やイオンの量子系が持つ電気四極子と結合するので、超音波計測による弾性定数や吸収係数の測定により、四極子感受率を観測できる。本研究では、低温での高分解超音波位相差計測を駆使し、希土類化合物の局在4ｆ電子の非クラマース2重項,カゴ状化合物の局所振動のラットリング,ボロン添加シリコン結晶中の原子空孔軌道などに現れる「電荷揺らぎに由来する強相関量子相」を研究した。
  • 文部科学省：科学研究費補助金(若手研究(B))
    研究期間 : 2008年 -2009年 
    代表者 : 柳澤 達也, 後藤 輝孝, 武田 直也, 根本 祐一
     
    20740192 充填スクッテルダイト化合物Pr_<1-x>Nd_xOs_4Sb_<12> (x=0.45, 0.25, 1.0)の純良単結晶を育し,弾性定数C11の周波数依存性(34MHz~245MHz)の精密測定を行った.PrOs_4Sb_<12>(x =0)で観測される単一の超音波分散は希釈系に於いても観測され,Nd濃度xの増加に伴い徐々に高温側にシフトする結果が得られた.一方で,x=0.45の試料では極低温T=0.25Kにおいて弾性定数C11が極小をとる,これはPrイオンが超伝導に寄与しているにも関わらずNdイオンの結晶場基底状態の縮退が解けていること示す結果である.さらに,終端物質x=1.0のNdOs_4Sb_<12> について,強磁相内(2T≤H≤10T, T≤1K)の領域に於いて磁場に鈍感な弾性定数のソフト化が存在することを初めて明らかにした.これらの結果はLaOs_4Sb_<12>, PrOs_4Sb_<12>と同様に,NdOs_4Sb_<12> に於いてもオフセンタートンネリングが極低温で存在することを示しており,本系の重い電子状態の発現機構に縮退したオフセンター自由度が関与していることを強く示唆する.
  • 文部科学省：科学研究費補助金(基盤研究(B))
    研究期間 : 2007年 -2009年 
    代表者 : 網塚 浩, 天谷 健一, 横山 淳, 日高 宏之, 柳澤 達也
     
    5f電子系超伝導体URu_2Si_2で長年の謎となっていた弱い反強磁性が結晶中の残留応力により不均一に誘起された磁気秩序相に起因することを微視的に初めて明らかにした。更にこの系の超伝導が隠れた秩序と呼ばれる未知秩序領域内だけで生じ、反強磁性とは共存しないことを示すと共に、隠れた秩序として可能な機構の限定を行った。また関連系の研究から量子相転移点近傍の電子物性及び5f電子の磁性について幾つかの新知見を得た。
  • 多極子自由度・オフセンタ自由度を有する希土類化合物の磁性と超伝導の研究
    科学技術振興調整費による総合研究
    研究期間 : 2007年
  • Novel magnetism and superconductivity on rare-earth compounds which possess multipolar and/or off-center degrees of freedom
    SCF Comprehensive Joint Research (General Research)
    研究期間 : 2007年
  • 日本学術振興会：科学研究費助成事業 特別研究員奨励費
    研究期間 : 2003年 -2004年 
    代表者 : 柳澤 達也
     
    1 HoB_2C_2のIV相に関して行った熱膨張実験と、物質・材料研究機構のハイブリッドマグネットを用いて行った超音波実験によって得られた弾性定数・H-T相図を考察した結果、以下の結論が得られた。 (1)対称性の低下により、立方晶においてΓ_4対称性とΓ_5対称性に区分されていた八極子が、正方晶系においては混合して現れる。IV相の秩序変数は・==≠0と結論した。 (2)H-T相図の強い磁気異方性より、HoB_2C_2の八極子相互作用にも異方性があることがわかった。その結果、八極子秩序==≠0によって誘起される強四極子モーメントにも異方性が現れる。これは熱膨張測定によって得られた結果ε_<ε_=ε_=1.2×10^<-4>とも一致する。 2 充填スクッテルダイトPrOs_4Sb_<12>の超音波実験に共同研究として参加した。PrOs_4Sb_<12>のでは、カゴ状化合物La_3Pd_<20>Ge_6とCe_3Pd_<20>Ge_6で発見された希土類イオンのラットリング振動に類似した弾性定数の分散を観測した。また、磁場中でのPrOs_4Sb_<12>の弾性定数を四極子感受率によって解析し、結晶場基底状態をΓ_1対称性と結論づけた。 3 申請者は平成16年4月から渡米し、カリフォルニア大サンディエゴ校のMaple研究室で充填スクッテルダイトの研究を行った。超音波実験を行うために、LaOs_4Sb_<12>,LaRu_4Sb_<12>,La(Os_<0.5>Ru_<0.5>)_4Sb_<12>の単結晶作成を試み、La(Os_<0.5>Ru_<0.5>)_4Sb_<12>の単結晶を得ることに成功した。日本に試料を持ち帰り、新潟大学後藤研究室で^3He冷凍機を用いた超音波測定を行い、PrOs_4Sb_<12>で観測されたラットリングに起因する超音波分散と同様の弾性異常を観測した。

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