2024/06/18 更新

写真a

イシカワ フミヒロ
石川 文洋
ISHIKAWA Fumihiro
所属
教育研究院 自然科学系 数理物質科学系列 准教授
自然科学研究科 数理物質科学専攻 准教授
理学部 理学科 准教授
職名
准教授
外部リンク

学位

  • 博士(工学) ( 1999年3月   横浜国立大学 )

研究キーワード

  • 強磁場

  • 磁性

  • 高圧

研究分野

  • 自然科学一般 / 磁性、超伝導、強相関系

経歴(researchmap)

  • 東北大学   Institute for Materials Research

    2002年 - 2004年

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  • 東京大学   The Institute for Solid State Physics

    2001年 - 2002年

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  • 横浜国立大学

    1999年 - 2001年

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経歴

  • 新潟大学   理学部 理学科   准教授

    2017年4月 - 現在

  • 新潟大学   自然科学研究科 数理物質科学専攻   准教授

    2012年11月 - 現在

  • 新潟大学   自然科学研究科 数理物質科学専攻   准教授

    2012年11月 - 現在

  • 新潟大学   物性科学   准教授

    2012年11月 - 2017年3月

  • 新潟大学   自然科学研究科 数理物質科学専攻   助教

    2010年4月 - 2012年11月

  • 新潟大学   自然科学研究科 自然構造科学専攻   助教

    2004年4月 - 2010年3月

▶ 全件表示

学歴

  • 横浜国立大学   工学研究科   電子情報工学専攻

    - 1999年

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    国名: 日本国

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  • 横浜国立大学   Graduate School, Division of Engineering

    - 1999年

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  • 横浜国立大学   工学部   電子情報工学科

    - 1994年

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    国名: 日本国

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  • 横浜国立大学   Faculty of Engineering

    - 1994年

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所属学協会

 

論文

  • Phase Transition in Fluid Hydrogen at Room Temperature

    Atsuko Nakayama, Yuya Isurugi, Yuya Serizawa, Satoshi Nakano, Ayako Ohmura, Fumihiro Ishikawa

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   91 ( 9 )   2022年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PHYSICAL SOC JAPAN  

    Rotational and vibration-rotational Raman spectra of fluid hydrogen (H-2) at room temperature were investigated through Raman spectroscopy under pressure. All the rotational and vibration-rotational lines showed rapid pressure changes in Raman shifts at around 0.56 GPa. The peak analyses revealed that the ortho-para conversion of H-2 was generated under pressure beyond 0.56 GPa at room temperature. Supposedly, that the anomalies obtained at 0.56 GPa at room temperature corresponded to a phase transition in fluid phase, inducing a significant change in the ratio of equilibrium composition of ortho- and para-H-2.

    DOI: 10.7566/JPSJ.91.093601

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  • Superconducting and structural properties of the type-I superconductor PdTe2 under high pressure

    Yusaku Furue, Tadachika Fujino, Marc Salis, Huaqian Leng, Fumihiro Ishikawa, Takashi Naka, Satoshi Nakano, Yingkai Huang, Anne de Visser, Ayako Ohmura

    PHYSICAL REVIEW B   104 ( 14 )   2021年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER PHYSICAL SOC  

    The transition metal dichalcogenide PdTe2 has attractive features based on its classification as a type-II Dirac semimetal and the occurrence of type-I superconductivity, providing a platform for discussion of a topological superconductor. Our recent work revealed that type-I superconductivity persists up to pressures of similar to 2.5 GPa and the superconducting transition temperature T-c reaches a maximum at around 1 GPa, which is inconsistent with the theoretical prediction. To understand its nonmonotonic variation and investigate superconductivity at higher pressures, we performed structural analysis by x-ray diffraction at room temperature below 8 GPa and electrical resistivity measurements at low temperatures from 1 to 8 GPa. With regard to the superconductivity beyond 1 GPa, the monotonic decrease in T-c is reproduced without any noticeable anomalies; T-c changes from 1.8 K at 1 GPa to 0.82 K at 5.5 GPa with dT(c)/dP similar to -0.22 K/GPa. The crystal structure with space group P (3) over bar m1 is stable in the pressure range we examined. On the other hand, the normalized pressure-strain analysis (finite strain analysis) indicates that the compressibility changes around 1 GPa, suggesting that a Lifshitz transition occurs. We here discuss the effect of pressure on the superconducting and structural properties based on the comparison of these experimental results.

    DOI: 10.1103/PhysRevB.104.144510

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  • Transport and structural properties of Cu0.25Bi2(TexSe1-x)(3) (x=0.01) under high pressure

    Ayako Ohmura, Masako Matsuzawa, Fumihiro Ishikawa, Yusuke Suzuki, Masashi Komatsu, Shumpei Osuga, Satoshi Nakano, Atsuko Nakayama, Yuh Yamada, Takanari Kashiwagi, Kazuo Kadowaki

    JAPANESE JOURNAL OF APPLIED PHYSICS   56 ( 5 )   2017年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP PUBLISHING LTD  

    Cu0.25Bi2(TexSe1-x)(3) is a material in which tellurium atoms (Te) partially occupy selenium (Se) sites in a crystal structure of the superconductor Cu0.25Bi2Se3. This study focuses on the composition of x = 0.01, Cu0.25Bi2(Te0.01Se0.99)(3), and we performed electrical resistivity measurement and X-ray diffraction under high pressures. Cu0.25Bi2(Te0.01Se0.99)(3) shows slight diamagnetism and a drop in resistivity at ambient pressure; this suggests possible superconductivity at the transition temperature of T-c = 3.2K, which is suppressed at P = 1 GPa. On further compression, a slight drop in resistivity is observed at temperatures of 4.3-5.4K above 10 GPa. This drop is suppressed under magnetic fields, suggesting the occurrence of superconducting transition. The pressure-induced structural phase transition from a trigonal R3m phase to a sevenfold monoclinic C2/m phase occurs at 10.9 GPa. These results suggest that the superconducting transition above 10 GPa occurs in the high-pressure C2/m phase. (c) 2017 The Japan Society of Applied Physics

    DOI: 10.7567/JJAP.56.05FB04

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  • Pressure-induced topological phase transition in the polar semiconductor BiTeBr

    Ayako Ohmura, Yuichiro Higuchi, Takayuki Ochiai, Manabu Kanou, Fumihiro Ishikawa, Satoshi Nakano, Atsuko Nakayama, Yuh Yamada, Takao Sasagawa

    PHYSICAL REVIEW B   95 ( 12 )   2017年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER PHYSICAL SOC  

    We performed x-ray diffraction and electrical resistivity measurement up to pressures of 5 GPa and the first-principles calculations utilizing experimental structural parameters to investigate the pressure-induced topological phase transition in BiTeBr having a noncentrosymmetric layered structure (space group P3m1). The P3m1 structure remains stable up to pressures of 5 GPa; the ratio of lattice constants c/a has a minimum at pressures of 2.5-3 GPa. In the same range, the temperature dependence of resistivity changes frommetallic to semiconducting at 3 GPa and has a plateau region between 50 and 150 K in the semiconducting state. Meanwhile, the pressure variation of band structure shows that the bulk band-gap energy closes at 2.9 GPa and re-opens at higher pressures. Furthermore, according to the Wilson loop analysis, the topological nature of electronic states in noncentrosymmetric BiTeBr at 0 and 5 GPa are explicitly revealed to be trivial and nontrivial, respectively. These results strongly suggest that pressure-induced topological phase transition in BiTeBr occurs at the pressures of 2.9 GPa.

    DOI: 10.1103/PhysRevB.95.125203

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  • Composition induced metal-insulator quantum phase transition in the Heusler type Fe2VAl

    Takashi Naka, Artem M. Nikitin, Yu Pan, Anne de Visser, Takayuki Nakane, Fumihiro Ishikawa, Yuh Yamada, Motoharu Imai, Akiyuki Matsushita

    JOURNAL OF PHYSICS-CONDENSED MATTER   28 ( 28 )   2016年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP PUBLISHING LTD  

    We report the magnetism and transport properties of the Heusler compound Fe2+xV1-xAl at -0.10 <= x <= 0.20 under pressure and a magnetic field. A metal-insulator quantum phase transition occurred at x approximate to -0.05. Application of pressure or a magnetic field facilitated the emergence of finite zero-temperature conductivity sigma(0) around the critical point, which scaled approximately according to the power law (P-P-c)(gamma). At x <= -0.05, a localized paramagnetic spin appeared, whereas above the ferromagnetic quantum critical point at x approximate to 0.05, itinerant ferromagnetism was established. At the quantum critical points at x = -0.05 and 0.05, the resistivity and specific heat exhibited singularities characteristic of a Griffiths phase appearing as an inhomogeneous electronic state.

    DOI: 10.1088/0953-8984/28/28/285601

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  • Angle-Resolved Photoemission Analysis of Electronic Structures for Thermoelectric Properties of Off-Stoichiometric Fe2-xV1+xAl Alloys

    Kazuo Soda, Shota Harada, Toshimitsu Hayashi, Masahiko Kato, Fumihiro Ishikawa, Yuh Yamada, Shin-ichi Fujimori, Yuji Saitoh

    MATERIALS TRANSACTIONS   57 ( 7 )   1040 - 1044   2016年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:JAPAN INST METALS & MATERIALS  

    DOI: 10.2320/matertrans.MF201603

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  • Counting graphene layers based on the light-shielding effect of Raman scattering from a substrate

    Atsuko Nakayama, Suguru Hoshino, Yuh Yamada, Ayako Ohmura, Fumihiro Ishikawa

    APPLIED PHYSICS LETTERS   107 ( 23 )   2015年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER INST PHYSICS  

    We present a method for determining the number of stacked layers in graphene by exploiting its light-shielding effect. If a substrate supporting graphene has Raman-active modes, its Raman bands can be obtained simultaneously with the G and G' bands of graphene. The Raman intensities from the substrate decrease with increasing the number of graphene layers because of the low opacity of graphene for visible light. The relationship between the number of graphene layers n and the relative intensities I-n,I-h/I-0,I-h from the substrate can be represented by I-n,I-h/I-0,I-h = 0.977(2n), on the basis of the optical transmittance of visible light for single-layer graphene. The method is simple, convenient, highly accurate, and can be used to count beyond six layers up to 30 layers. (C) 2015 AIP Publishing LLC.

    DOI: 10.1063/1.4937140

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  • Angle-Resolved Photoemission Analysis on Electronic Structures and Thermoelectric Properties of Off-Stoichiometric Fe2-xV1+xAl

    Kazuo Soda, Shota Harada, Toshimitsu Hayashi, Masahiko Kato, Fumihiro Ishikawa, Yuh Yamada, Shin-ichi Fujimori, Yuhji Saitoh

    JOURNAL OF THE JAPAN INSTITUTE OF METALS AND MATERIALS   79 ( 11 )   607 - 612   2015年

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    記述言語:日本語   掲載種別:研究論文(学術雑誌)   出版者・発行元:JAPAN INST METALS & MATERIALS  

    The electronic states of Heusler(L2(1))-type off. stoichiometric Fe2-xV1+xAl have been investigated by soft X-ray angle-resolved photoelectron spectroscopy (ARPES) in order to clarify the origin of their large thermoelectric powers, which cannot be explained in terms of the rigid band model. In off-normal and normal ARPES, Fe2.05V0.95Al shows a weakly dispersive bulk band around the binding energy of 0.3 eV in the Gamma-X direction and an almost dispersion-less one around 0.3 eV in a gap of dispersive bulk bands in the Gamma-L direction, which is attributed to the anti-site Fe defect. At the Gamma point, the bulk band does not appear to cross the Fermi level E-F, consistent with the rigid band model for the excess Fe content bringing about the increase in the valence electrons, but no band crossing E-F down is found at the X point. The anti-site Fe defect states near E-F might push up the band at the X point and cause the p-type thermoelectric properties, unexpected with the rigid band picture. The change in the electronic structures and thermoelectric properties are discussed on the off-stoichiometry and substitution of the forth element.

    DOI: 10.2320/jinstmet.JA201517

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  • Collapse of CuO Double Chains and Suppression of Superconductivity in High-Pressure Phase of YBa2Cu4O8 査読

    Atsuko Nakayama, Yusuke Onda, Shuhei Yamada, Hiroshi Fujihisa, Masafumi Sakata, Yuki Nakamoto, Katsuya Shimizu, Satoshi Nakano, Ayako Ohmura, Fumihiro Ishikawa, Yuh Yamada

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   83 ( 9 )   2014年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PHYSICAL SOC JAPAN  

    The crystal structure and electrical resistivity of YBa2Cu4O8 (Y124) were studied under high pressure up to 18 GPa using diamond-anvil cells, respectively, in order to clarify its conduction mechanism. Y124 causes the first-order phase-transition into the orthorhombic Immm at pressure around 11 GPa. The high-pressure phase (HPP) also shows the superconductivity, while the manner of temperature dependence of electrical resistance and the pressure dependence of transition temperature, T-c, drastically change above 11 GPa. The CuO2 plane persists in HPP but the CuO double chains collapse with the phase transition and transform into three-dimensional Cu-O network, resulting in the renewal of conduction system.

    DOI: 10.7566/JPSJ.83.093601

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  • Pressure-induced superconductivity in non-stoichiometric bismuth telluride Bi35Te65 査読

    M. Einaga, A. Ohmura, F. Ishikawa, A. Nakayama, Yuh Yamada, S. Nakano, A. Matsushita, K. Shimizu

    18TH APS-SCCM AND 24TH AIRAPT, PTS 1-19   500   192003-1 - 192003-5   2014年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IOP PUBLISHING LTD  

    We performed x-ray diffraction study and electrical resistivity measurement of non-stoichiometric n-type Bi35Te65 under high pressure to investigate pressure-induced superconductivity and structural phase transition. Stoichiometric bismuth telluride (Bi2Te3), which is a p-type semiconductor, has the rhombohedral structure with space group R-3m at ambient condition. Pressure-induced superconductivity of stoichiometric p-type Bi2Te3 occurs in the high-pressure phases which appear above 8 GPa. Bi35Te65 has also the R-3m structure at ambient condition with electron carriers. X-ray diffraction study shows that the R-3m structure remains stable up to 8 GPa at room temperature. The superconducting transition in n-type Bi35Te65 is observed above 6 GPa; the transition temperature is 2.9 K at 6 GPa. The electrical resistivity at room temperature decreases rapidly at pressures from 7 to 8 GPa, indicating the occurrence of structural phase transition. It suggests that the superconducting transition at 6 GPa occurs at the ambient pressure phase with the R-3m structure.

    DOI: 10.1088/1742-6596/500/19/192003

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  • Superconductivity in 122 antimonide SrPt2Sb2

    Motoharu Imai, Satoshi Emura, Mitsuaki Nishio, Yoshitaka Matsushita, Soshi Ibuka, Naoya Eguchi, Fumihiro Ishikawa, Yuh Yamada, Takahiro Muranaka, Jun Akimitsu

    SUPERCONDUCTOR SCIENCE & TECHNOLOGY   26 ( 7 )   2013年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP PUBLISHING LTD  

    Measurements of electrical resistivity rho, magnetization M and specific heat C have revealed that SrPt2Sb2 is a type-II superconducting material with a superconducting critical temperature (T-c) of 2.1 K. The electronic specific heat coefficient gamma and the ratio Delta C(T-c)/gamma(T-c )are 9.2(1) mJ mol(-1) K-2 and 1.29, respectively. The temperature dependence of rho exhibits anomalies around 270 K. Synchrotron x-ray diffraction patterns at 295 and 134 K clearly indicate that SrPt2Sb2 undergoes a structural phase transition in the temperature range from 134 to 295 K, suggesting that the anomalies observed in rho around 270 K are related to a structural phase transition.

    DOI: 10.1088/0953-2048/26/7/075001

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  • Synthesis of New Layered Oxypnictides Sr2CrO2(FeAs)(2)

    Naoya Eguchi, Fumihiro Ishikawa, Michihiro Kodama, Takeshi Wakabayashi, Atsuko Nakayama, Ayako Ohmura, Yuh Yamada

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   82 ( 4 )   2013年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PHYSICAL SOC JAPAN  

    DOI: 10.7566/JPSJ.82.045002

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  • Pressure effect on critical temperature for superconductivity and lattice parameters of AlB<inf>2</inf>-type ternary silicide YbGa<inf>1.1</inf>Si <inf>0.9</inf> 査読

    Ayako Ohmura, Koji Fujimaki, Fumihiro Ishikawa, Yuh Yamada, Naohito Tsujii, Motoharu Imai

    Physical Review B - Condensed Matter and Materials Physics   84 ( 10 )   2011年9月

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    掲載種別:研究論文(学術雑誌)  

    Electrical resistivity and x-ray diffraction measurements have been carried out to investigate the pressure effect on the critical temperature for superconductivity (TC) and lattice parameters of AlB2-type superconducting silicide YbGa1.1Si0.9 (TC = 2.4 K) and its reference material CaGaSi (TC = 4.5 K). The electrical resistivity measurements up to 2.5 GPa reveal that TC decreases with pressure for both silicides and the pressure derivative of TC (dTC/dP) is -0.78 K/GPa and -0.026 K/GPa for YbGa 1.1Si0.9 and CaGaSi, respectively. X-ray diffraction measurements up to 3.5 GPa indicate both silicides do not exhibit structural changes in this pressure range and they have similar values for the bulk moduli: B0=40±2 GPa for YbGa1.1Si0.9 and B 0=42±1 GPa for CaGaSi. The relative pressure derivative of TC (dlnTC/dP) and logarithmic volume derivative of T C (dlnTC/dlnV) are -0.33 GPa-1 and 13 in YbGa1.1Si0.9. These values are about tenfold larger than those for other AlB2-type superconductors. Additionally, the origin of dlnTC/dP and dlnTC/dlnV in YbGa1.1Si 0.9 relative to the pressure effect on the valence of Yb atoms is discussed. © 2011 American Physical Society.

    DOI: 10.1103/PhysRevB.84.104520

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  • Pressure effect on critical temperature for superconductivity and lattice parameters of AlB2-type ternary silicide YbGa1.1Si0.9

    Ayako Ohmura, Koji Fujimaki, Fumihiro Ishikawa, Yuh Yamada, Naohito Tsujii, Motoharu Imai

    PHYSICAL REVIEW B   84 ( 10 )   2011年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER PHYSICAL SOC  

    Electrical resistivity and x-ray diffraction measurements have been carried out to investigate the pressure effect on the critical temperature for superconductivity (T-C) and lattice parameters ofAlB(2)-type superconducting silicide YbGa1.1Si0.9 (T-C = 2.4 K) and its referencematerial CaGaSi (T-C = 4.5 K). The electrical resistivity measurements up to 2.5 GPa reveal that T-C decreases with pressure for both silicides and the pressure derivative of T-C (dT(C)/dP) is -0.78 K/GPa and -0.026 K/GPa for YbGa1.1Si0.9 and CaGaSi, respectively. X-ray diffraction measurements up to 3.5 GPa indicate both silicides do not exhibit structural changes in this pressure range and they have similar values for the bulk moduli: B-0 = 40 +/- 2 GPa for YbGa1.1Si0.9 and B-0 = 42 +/- 1 GPa for CaGaSi. The relative pressure derivative of T-C (dlnT(C)/dP) and logarithmic volume derivative of T-C (dlnT(C)/dlnV) are -0.33 GPa(-1) and 13 in YbGa1.1Si0.9. These values are about tenfold larger than those for other AlB2-type superconductors. Additionally, the origin of dlnT(C)/dP and dlnT(C)/dlnV in YbGa1.1Si0.9 relative to the pressure effect on the valence of Yb atoms is discussed.

    DOI: 10.1103/PhysRevB.84.104520

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  • Effect of substitution of Ca2+ for Eu2+ on pressure-induced superconductivity in EuFe2As2

    Akihiro Mitsuda, Tomohiro Matoba, Satoshi Seike, Fumihiro Ishikawa, Yuh Yamada, Hirofumi Wada

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   80   2011年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PHYSICAL SOC JAPAN  

    To elucidate competition between the Fe-based superconductivity and the antiferromagnetic order of Eu2+, the electrical resistivity of Eu0.85Ca0.15Fe2As2 under high pressure is presented. Under ambient pressure, the Fe-based spin-density-wave (SDW) transition and the antiferromagnetic ordering (AFM) of Eu2+ are observed at T-SDW = 190 K and T-N = 17 K, respectively. With applying pressure, the Fe-based superconductivity with T-c similar to 25 K appears above 1.5 GPa, accompanying collapse of the SDW transition. Compared with EuFe2As2, T-c is close to T-N, which implies strong competition between the superconductivity and the AFM. This competition would lead to non-zero resistivity at lowest temperature.

    DOI: 10.1143/JPSJS.80SA.SA117

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  • Pressure-induced phase transition of Bi2Te3 to a bcc structure

    Mari Einaga, Ayako Ohmura, Atsuko Nakayama, Fumihiro Ishikawa, Yuh Yamada, Satoshi Nakano

    PHYSICAL REVIEW B   83 ( 9 )   2011年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER PHYSICAL SOC  

    The pressure-induced phase transition of bismuth telluride, Bi2Te3, has been studied by synchrotron x-ray diffraction measurements at room temperature using a diamond-anvil cell (DAC) with loading pressures up to 29.8 GPa. We found a high-pressure body-centered cubic (bcc) phase in Bi2Te3 at 25.2 GPa, which is denoted as phase IV, and this phase appears above 14.5 GPa. Upon releasing the pressure from 29.8 GPa, the diffraction pattern changes with pressure hysteresis. The original rhombohedral phase is recovered at 2.43 GPa. The bcc structure can explain the phase IV peaks. We assumed that the structural model of phase IV is analogous to a substitutional binary alloy; the Bi and Te atoms are distributed in the bcc-lattice sites with space group Im (3) over bar m. The results of a Rietveld analysis based on this model agree well with both the experimental data and calculated results. Therefore, the structure of phase IV in Bi2Te3 can be explained by a solid solution with a bcc lattice in the Bi-Te (60 atomic % tellurium) binary system.

    DOI: 10.1103/PhysRevB.83.092102

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  • Pressure-Induced Superconductivity in Eu0.5Ca0.5Fe2As2: Wide Zero-Resistivity Region Due to Suppression of Eu Magnetic Order and Chemical Pressure

    Akihiro Mitsuda, Tomohiro Matoba, Fumihiro Ishikawa, Yuh Yamada, Hirofumi Wada

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   79 ( 7 )   2010年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PHYSICAL SOC JAPAN  

    To clarify competition between FeAs-based superconductivity and antiferromagnetism of Eu2+, and the superconducting properties in EuFe2As2, we investigated a Ca-substituted sample, Eu0.5Ca0.5Fe2As2, under high pressure. Under ambient pressure, the sample exhibits a spin-density-wave (SDW) transition at T-SDW = 191K and antiferromagnetic order at T-N = 4K, but no evidence of superconductivity down to 2K. The Ca-substitution certainly weakens the antiferromagnetism. With increasing pressure, T-SDW shifts to lower temperature and becomes more unclear. Above 1.27 GPa, pressure-induced superconductivity with zero resistivity is observed at around T-c 20K. At 2.14 GPa, T-c reaches a maximum value of 24K and the superconducting transition becomes sharpest. The chemical pressure and the suppression of Eu magnetic order induced by Ca substitution enlarge the zero resistivity region compared to pure EuFe2As2.

    DOI: 10.1143/JPSJ.79.073704

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  • Photocatalytic activities of Ba2RBiO6 (R = La, Ce, Nd, Sm, Eu, Gd, Dy) under visible light irradiation

    Takuya Hatakeyama, Shingo Takeda, Fumihiro Ishikawa, Ayako Ohmura, Atsuko Nakayama, Yuh Yamada, Akiyuki Matsushita, Jinhua Yea

    JOURNAL OF THE CERAMIC SOCIETY OF JAPAN   118 ( 1374 )   91 - 95   2010年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI  

    We succeeded in synthesizing Ba2RBiO6 (R = La, Ce, Nd, Sm, Eu, Gd, and Dy) with a double-perovskite structure. Its photocatalytic activities were then investigated for a degradation of methylene blue (MB) solution and gaseous 2-propanol (IPA). High photocatalytic activities were observed under visible light irradiation and also a rare earth dependence of photocatalytic activities in the IPA degradation. We carried out first-principle calculations of the band structure based on the all-electron Full-potential Linear Augmented Plane-Wave (FLAPW) method and discuss the relationship between the high photocatalytic activities and the band structure in this paper. (C) 2010 The Ceramic Society of Japan. All rights reserved.

    DOI: 10.2109/jcersj2.118.91

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  • Zero-resistance superconducting phase in BaFe2As2 under high pressure

    Fumihiro Ishikawa, Naoya Eguchi, Michihiro Kodama, Koji Fujimaki, Mari Einaga, Ayako Ohmura, Atsuko Nakayama, Akihiro Mitsuda, Yuh Yamada

    PHYSICAL REVIEW B   79 ( 17 )   2009年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER PHYSICAL SOC  

    A single-crystalline sample of BaFe2As2 was prepared by high-pressure synthesis, and temperature dependence of resistivity was measured under high pressures of up to 9.0 GPa. Application of 3.0 GPa pressure suppresses the spin-density wave transition and induces superconductivity with the zero resistance state at a superconducting transition temperature T-c=35 K. T-c decreases monotonically with increasing pressure. The appearance of the superconductivity and the disappearance of the anomaly due to the spin-density wave transition occur simultaneously at a pressure of 3.0 GPa. At 3.0 GPa, a superconducting transition is induced in BaFe2As2; however, the superconductivity is suppressed at higher pressure.

    DOI: 10.1103/PhysRevB.79.172506

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  • Pressure effects on the electrical resistivity of Pr2Ba4Cu7O15-delta oxide superconductor

    Fumihiro Ishikawa, Kazunori Fukuda, Yasunori Hiura, Yusuke Onda, Atsuko Nakayama, Yuh Yamada, Akiyuki Matsushita, Tomoko Kagayama

    25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 5   150   2009年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IOP PUBLISHING LTD  

    The superconductivity of Pr2Ba4Cu7O15-delta (Pr247) is realized at the CuO doublechains. The oxygen deficiency d dependence of the superconducting transition temperature T-c shows the bell-like curve with the maximum of T-c = 20.6 K at delta = 0.64. We investigated the pressure effects on the double-chain superconductivity of Pr247. The resistivity was measured under the pressure of 10 GPa produced by a modified Bridgman anvil type cell. With increasing pressure above 3 GPa, the superconductivity was suppressed and disappeared. The temperature dependence of the resistivity shows a semiconductor like behavior above 5 GPa. The x-ray diffraction using a diamond anvil cell under hydrostatic condition shows that no structural transition occurs below 10 GPa.

    DOI: 10.1088/1742-6596/150/5/052079

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  • Thermoelectric properties of B-doped SrTiO3 singe crystal

    Jun Okamoto, Gen Shimizu, Shugo Kubo, Yasuji Yamada, Hiroyuki Kitagawa, Akiyuki Matsushita, Yuh Yamada, Fumihiro Ishikawa

    16TH INTERNATIONAL SYMPOSIUM ON BORON, BORIDES AND RELATED MATERIALS (ISBB 2008)   176   2009年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:IOP PUBLISHING LTD  

    Effect of boron on the electric and thermoelectric properties of SrTiO3 has been studied. Boron-doped SrTiO3 was prepared by vacuum annealing of SrTiO3 single crystals in presence of boron vapors. The crystals show low resistivity similar to 0.1 Omega.cm and high Seebeck coefficient of several hundreds mu V/K at a room temperature. It was estimated that almost every boron atom incorporated in SrTiO3 crystal provided a charge carrier. Temperature dependence of Seebeck coefficient and figure of merit ZT were measured as a function of carrier concentration.

    DOI: 10.1088/1742-6596/176/1/012042

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  • Physical properties of a new cuprate superconductor Pr2Ba4Cu7O15-delta

    Akiyuki Matsushita, Kazunori Fukuda, Yuh Yamada, Fumihiro Ishikawa, Syun Sekiya, Masato Hedo, Takashi Naka

    SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS   8 ( 6 )   477 - 483   2007年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:NATL INST MATERIALS SCIENCE  

    We present studies of the thermal, magnetic, and electrical transport properties of reduced polycrystalline Pr2Ba4Cu7O15-delta (Pr247) showing a superconducting transition at T-c = 10-16 K, and compare them with those of as-sintered non-superconducting Pr247. The electrical resistivity in the normal state exhibited T-2 dependence up to approximately 150 K. A clear specific heat anomaly was observed at Tc for Pr247 reduced in a vacuum for 24 h, proving the bulk nature of the superconducting state. By the reduction treatment, the magnetic ordering temperature T-N of Pr moments decreased from 16 to 11 K, and the entropy associated with the ordering increased, while the effective paramagnetic moments obtained from the DC magnetic susceptibility varied from 2.72 to 3.13 mu(B). The sign of Hall coefficient changed from positive to negative with decreasing temperature in the normal state of a superconducting Pr247, while that of the as-sintered one was positive down to 5 K. The electrical resistivity under high magnetic fields was found to exhibit T-alpha dependence (alpha = 0.08-0.4) at low temperatures. A possibility of superconductivity in the so-called CuO double chains is discussed. (c) 2007 Published by Elsevier Ltd.

    DOI: 10.1016/j.stam.2007.07.003

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  • Pressure Effects on CuO Double Chain Superconductivity

    Fumihiro Ishikawa, Kazunori Fukuda, Shun Sekiya, Ado Kaeriyama, Yuh Yamada, Akiyuki Matsushita

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   76   92 - 95   2007年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PHYSICAL SOC JAPAN  

    Pressure effects on the Pr2Ba4Cu7O15-delta (Pr247) double chain superconductor was investigated. Its resistivity was measured under a pressure of 8 GPa produced by the modified Bridgman anvil type cell. The magnetic susceptibility measurements up to 1 GPa suggested that the T-c increased and the volume fraction of superconductivity decreased with increasing pressure. In the resistivity measurement, zero resistivityw as not observed above 1 GPa. Moreover, semiconducting behavior was observed at all temperatures at 8 GPa. These results suggest that the superconductivity of Pr247 is suppressed and disappears due to the application of high pressure. The present modified Bridgman anvil type cell is expected to produce a pressure of 10 GPa by the application of a load of 22 tons.

    DOI: 10.1143/JPSJS.76SA.92

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  • Pressure Effects on the Physical and Magnetic Properties of MoSr2YCu2O8-delta Oxide Superconductor

    Ado Kaeriyama, Mitsuru Ueno, Kazunori Fukuda, Kenta Udagawa, Fumihiro Ishikawa, Yuh Yamada, Akiyuki Matsushita

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   76   120 - 121   2007年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PHYSICAL SOC JAPAN  

    We investigated the pressure dependence of the superconducting transition temperature T-c of the MoSr2YCu2O8-delta compound (Mo1212). Superconducting Mo1212 samples were synthesized by a solid-state reaction with multiple annealing processes. T-c-onset of Mo1212 occurred at approximately 40 K at ambient pressure. The pressure dependence of T-c was obtained as 3.3 K/GPa at least up to 8.7 GPa.

    DOI: 10.1143/JPSJS.76SA.120

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  • First-order phase transition at the Curie temperature in MnAs and MnAs0.9Sb0.1

    Fumihiro Ishikawa, Keiichi Koyama, Kazuo Watanabe, Tetsuya Asano, Hirofumi Wada

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   75 ( 8 )   2006年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PHYSICAL SOC JAPAN  

    Structural transformations of MnAs and MnAs0.9Sb0.1 were investigated by X-ray diffraction in high magnetic fields up to 5 T. The temperature dependence of the magnetization was measured in a magnetic field of 0.01 T and the Curie temperature T-C was determined to be 315 K for MnAs and 290 K for MnAs0.9Sb0.1 during heating process. For both compounds, a metarnagnetic transition from a paramagnetic to a ferromagnetic state was observed above T-C. The X-ray diffraction profile at 319 K for MnAs showed a single phase of an orthorhombic MnP-type structure in zero field. An applied magnetic field of 3 T induced the appearance of a hexagonal NiAs-type structure. On further increase of the magnetic field, a single phase with a hexagonal structure was realized above 3.5 T in a forcedferromagnetic state. The X-ray diffraction profile at 295 K for MnAs0.9Sb0.1 showed a hexagonal NiAs-type structure. The coexistence of ferromagnetic and paramagnetic states with different lattice parameters was confirmed in a magnetic field of 2.5 T. The volume expansion induced by a magnetic field was found to be 2.1 % for MnAs and 1.1 % for MnAs0.9Sb0.1.

    DOI: 10.1143/JPSJ.75.084604

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  • High field X-ray diffraction studies on magnetic refrigerants

    Keiichi Koyama, Fumihiro Ishikawa, Kazuo Watanabe

    INTERNATIONAL JOURNAL OF APPLIED ELECTROMAGNETICS AND MECHANICS   23 ( 3-4 )   153 - 163   2006年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOS PRESS  

    In this paper, we review our recent results on magnetic refrigerants MnAs1-xSbx and MnFeAs0.5P0.5 by powder X-ray diffraction measurements in fields up to 5 T and in the temperature range from 8 to 320 K. MnAs shows a first-ordered structural transition with the volume expansion of 2.1% accompanied by a metamagnetic transition, but MnAs0.9Sb0.1 exhibits an isostructural transition with the volume expansion of 1.1%. The cell volume of MnFeAs0.5P0.5 slightly (-0.4%) and continuously decreases with increasing a magnetic field through the metamagnetic transition.

    DOI: 10.3233/JAE-2006-734

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  • Phase Transitions and Disorder Effects in Pure and Doped Frustrated Quantum Antiferromagnet Cs2CuBr4

    Toshio Ono, Hidekazu Tanaka, Takamitsu Nakagomi, Oleksandr Kolomiyets, Hiroyuki Mitamura, Fumihiro Ishikawa, Tsuneaki Goto, Kenji Nakajima, Akira Oosawa, Yoshihiro Koike, Kazuhisa Kakurai, Jens Klenke, Peter Smeibidle, Michael Meissner, Hiroko Aruga Katori

    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   74   135 - 144   2005年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PHYSICAL SOC JAPAN  

    Cs2CuBr4 is an S = 1/2 quasi-two-dimensional frustrated antiferromagnet with a distorted triangular lattice parallel to the bc-plane. Cs2CuBr4 undergoes magnetic ordering at T-N = 1.4 K at zero magnetic field. In the ordered phase below T-N, spins lie in a plane that is almost parallel to the bc-plane and form a helical incommensurate structure with ordering vector q(0) = (0, 0.575, 0). The incommensurate spin structure arises from the spin frustration on the distorted triangular lattice. The magnetization curve has a plateau at approximately one-third of the saturation magnetization for magnetic field H parallel to the b- and c-axes, while no plateau is observed for H parallel to a. The ordering vector q(0) increases with increasing magnetic field parallel to the c-axis, and is locked at q(0) similar or equal to (0, 2/3, 0) in the plateau region, which indicates that the up-up-down spin structure is realized in the plateau state. The magnetization plateau should be attributed to quantum fluctuation. For H parallel to b and H parallel to c, the second anomaly suggestive of tiny plateau is observed at roughly two-third of the saturation magnetization. The magnetic field versus temperature diagram is presented. Small amount of Cl- substitution for Br- produces drastic suppression of T-N. With increasing Cl- concentration x, the magnetic ordering disappears at x similar or equal to 0.17. It is also observed that in Cs2Cu(Br1-xClx)(4) phase transition smears with increasing external field and disappears, irrespective of field direction. This should be attributed to the random field effect.

    DOI: 10.1143/JPSJS.74S.135

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  • X-ray diffraction study of the structural phase transition in MnAs under high magnetic fields 査読

    F Ishikawa, K Koyama, K Watanabe, H Wada

    PHYSICA B-CONDENSED MATTER   346   408 - 412   2004年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    The structural phase transition induced by magnetic fields on MnAs was observed by the X-ray diffraction measurements in high magnetic fields up to 4 T. Magnetization measurements showed that Curie temperature T-C was 315.5 K for increasing temperatures and a metamagnetic transition from the paramagnetic to the ferromagnetic state occurred above T-C. The structural transformation from the hexagonal NiAs-type to the orthorhombic MnP-type structure was confirmed at T-C with increasing temperature from 290 to 319 K via two-phase coexistence region. The X-ray diffraction profiles at 319 K showed the single phase of the MnP-type structure in zero field and applying magnetic field of 3 T caused appearance of the Brag peak of the hexagonal structure. On further increase of magnetic fields, the single phase of the hexagonal structure was observed above 3.5 T in the forced ferromagnetic state. Both the magnetic and structural transitions induced by magnetic fields above T-C were first order with a hysteresis and had a close relationship between each other. (C) 2004 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.physb.2004.01.116

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  • Structural Transformation of MnAs1-xSbx under High Magnetic Fields 査読

    Fumihiro Ishikawa, Keiichi Koyama, Kazuo Watanabe, Tetsuya Asano, Hirofumi Wada

    Materials Transactions   45 ( 2 )   311 - 314   2004年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Japan Institute of Metals (JIM)  

    Structural transformation induced by magnetic fields on MnAs and MnAs 0.9Sb0.1 was investigated by the X-ray diffraction measurements in high magnetic fields up to 5T. The X-ray diffraction profiles at 319 K for MnAs showed a single phase of the orthorhombic MnP-type structure in zero field, and applying a magnetic field of 3 T caused an appearance of the hexagonal NiAs-type structure. On further increase of magnetic fields, the single phase with the hexagonal structure was confirmed above 3.5 T in a forced ferromagnetic state. The X-ray diffraction profiles at 295 K for MnAs 0.9Sb0.1 showed the hexagonal NiAs-type structure. However, the coexistence of two kinds of the NiAs-type structure with different lattice parameters was confirmed in the magnetic field of 2.5 T. The two phase coexistence was also confirmed in the temperature variation measurements in zero magnetic field. The lattice volume of the ferromagnetic phase was 1.1% larger than that of the paramagnetic phase. These results imply that the transition at TC for MnAs0.9Sb0.1 is of the first-order.

    DOI: 10.2320/matertrans.45.311

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  • Magnetic properties of YCo2 hydrides 査読

    K Ishikawa, M Yamaguchi, Yamamoto, I, S Mizusaki, F Ishikawa, T Goto

    JOURNAL OF ALLOYS AND COMPOUNDS   356   227 - 230   2003年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE SA  

    The magnetic and structural influences of hydrogen absorption were studied on the itinerant electron metamagnet YCo2. The system YCo2Hx forms two crystalline hydrides of the alpha phase (0&lt;x&lt;0.3) and the beta phase (1.5&lt;xless than or equal to3.5). The hydride samples also include small amounts of the non-intrinsic ferromagnefic component due to the partial structural disordering upon hydrogen absorption. The high field susceptibility indicated that the alpha phase is an itinerant electron metamagnet in which the critical field is possibly lower than that of YCo2. The beta phase has no metamagnetic transition. The hydrogen-induced changes in the magnetic properties are discussed on the basis of the itinerant electron magnetism. (C) 2003 Elsevier B.V. All rights reserved.

    DOI: 10.1016/S0925-8388(03)00110-5

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  • Magnetic phase diagram of Ce2Fe17 under high pressures in high magnetic fields 査読

    F Ishikawa, T Goto, H Fujii

    PHYSICA B-CONDENSED MATTER   329   657 - 658   2003年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    The magnetization of Ce2Fe17 was precisely measured under high pressures up to 1.2 GPa in magnetic fields up to 18 T. The magnetic phase diagram in the B-T plane is determined at 0, 0.3, 0.4, 0.6, 0.9 and 1.2 GPa. At 0 GPa, five magnetic phases exist and the application of high pressure produces two additional magnetic phases. The shape of the phase diagram changes drastically with increasing pressure. (C) 2003 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0921-4526(02)02511-5

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  • Magneto-thermodynamic effects in chemical reactions

    Yamamoto, I, K Ishikawa, S Mizusaki, Y Shimazu, M Yamaguchi, F Ishikawa, T Goto, T Takamasu

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS   41 ( 1 )   416 - 424   2002年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:INST PURE APPLIED PHYSICS  

    The magnetic field effects on the thermodynamic properties of chemical reactions were systematically studied. In the formulation. the chemical influence of magnetic fields due to magnetostatic energy was represented by the magneto-chemical potential for each component and the magnetic free energy change per unit reaction. Then the general formulae were derived for the magnetic field-induced changes in the equilibrium constant and the Beat, free energy and entropy of reaction. In the calculation, the general formulae were applied to a ferromagnetic metal-hydrogen reaction and the magnetic field effects were numerically evaluated for two reactions in the single system LaCo5-H-2. In the experiment, the magnetic field effects were observed by applying high magnetic fields of 10-30T to the system LaCo5-H-2. The observed results agreed qualitatively and quantitatively with the corresponding calculated ones. This study resolved the issue of the thermodynamic effects of magnetic fields on chemical reactions.

    DOI: 10.1143/JJAP.41.416

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  • Change in the heat of reaction by magnetic fields in LaCo5-H-2 査読

    K Ishikawa, S Mizusaki, Yamamoto, I, F Ishikawa, M Yamaguchi

    JOURNAL OF ALLOYS AND COMPOUNDS   330   52 - 55   2002年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE SA  

    We experimentally investigated the effects of magnetic fields on the heat of reaction by examining the metal-hydrogen system LaCo5-H-2. The heat of reaction was measured in zero field and a magnetic field by the logarithmic pressure vs. inverse temperature method and the calorimetric one. Both the methods gave generally the same results that the magnetic field caused the absolute value of the heat of reaction to increase a little in the alpha + beta region and decrease considerably in the beta + gamma region. These agree well with the calculation based on the general formulation of magneto-thermodynamic effects in chemical reactions. This is the first observation of the magnetic field effect on the heat of reaction. (C) 2002 Elsevier Science B.V. All rights reserved.

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  • Magnetic field effect on the equilibrium hydrogen pressure for the PrCo5-H system 査読

    Yamamoto, I, S Mizusaki, K Ishikawa, F Ishikawa, Y Shimazu, M Yamaguchi

    JOURNAL OF ALLOYS AND COMPOUNDS   330   56 - 58   2002年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE SA  

    The equilibrium hydrogen pressures in the beta(1) + gamma region of the ferromagnetic hydride PrCo5Hlambda have been investigated as a function of the hydrogen composition x under the influence of magnetic fields up to 5 T at 273.2 K. The logarithmic pressure change is increased linearly with increasing magnetic fields and depends on the hydrogen composition. The value DeltaM(s) (die change in saturation magnetization per desorbed molH) is calculated from the relationship between the pressure change and the magnetic field. The results show a peculiar dependence of the DeltaM(s) on the hydrogen composition. The maximum value of DeltaM(s) of 25 J T-1 molH(-1) at x=4.3 is much larger than that observed in other metal-hydrogen systems. (C) 2002 Published by Elsevier Science B.V.

    DOI: 10.1016/S0925-8388(01)01646-2

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  • Magnetic field effect on the heat of reaction in metal-hydrogen systems

    M Yamaguchi, Yamamoto, I, S Mizusaki, K Ishikawa

    JOURNAL OF ALLOYS AND COMPOUNDS   330   48 - 51   2002年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE SA  

    The effects of magnetic fields were generally formulated on the thermodynamic properties of chemical reactions. The magnetic M C field-induced change in the heat of reaction was calculated for the metal-hydrogen system, especially for LaCo5-H-2, on the basis of the general formulation. Independently of this, the heat of reaction under the influence of magnetic fields was estimated from the temperature dependence of the equilibrium hydrogen pressure. The agreement between both the results indicated that magnetic fields influence the heat of reaction in metal-hydrogen systems. (C) 2002 Elsevier Science BY All rights reserved.

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  • Itinerant-electron metamagnetism of Y(Co, Ni)(5) 査読

    H Yamada, K Terao, F Ishikawa, M Yamaguchi, H Mitamura, T Goto

    JOURNAL OF PHYSICS-CONDENSED MATTER   11 ( 2 )   483 - 492   1999年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:IOP PUBLISHING LTD  

    Electronic structures of the pseudo-binary compound Y(Co, Ni)(5) with the CaCu5-type hexagonal structure are calculated in the self-consistent linear muffin-tin orbital method within the atomic sphere approximation, by taking into account the preferential occupation sites for Ni. The calculated bulk moment disappears abruptly near 60% Ni concentration. Above the critical concentration of Ni, a metamagnetic transition from the paramagnetic to the ferromagnetic state is found to occur. These calculated results are consistent with the recently observed ones. It has been shown that the anomalous magnetic behaviours of Y(Co, Ni)(5) can be explained by the detailed shape of the local density-of-states curve of the 3d-transition-metal atoms at the 3g site near the Fermi level.

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  • Effect of superconductivity on magnetoresistance in ferromagnetic tunnel junctions 査読

    Y Shimazu, F Ishikawa, Yamamoto, I, M Yamaguchi

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS SHORT NOTES & REVIEW PAPERS   37 ( 6A )   3299 - 3303   1998年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:JAPAN J APPLIED PHYSICS  

    We studied the magnetoresistance of Ni/Al-Al2O3/Co tunnel junctions at T &gt; 1.4 K. Below the superconducting transition temperature of deposited Al films, a nonmonotonic magnetoresistance was observed. The fractional change in junction resistance was 14% at 1.4 K. The nonmonotonic behavior of the magnetoresistance can be explained in terms of the dependences of the superconducting energy gap and the sheet conductivity of the Al layer on the magnetic field. This explanation was supported by the results of an experiment on an Al-Al2O3/Ni tunnel junction which also showed a large magnetoresistance below T-c due to the superconductivity effect.

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  • Magnetic field-induced effects on the melting temperatures of polymer gels 査読

    Y Matsumoto, Yamamoto, I, M Yamaguchi, Y Shimazu, F Ishikawa

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS   36 ( 10B )   L1397 - L1399   1997年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:JAPAN SOC APPLIED PHYSICS  

    The gel-melting temperature was observed for aqueous agarose and aqueous methyl cellulose gels which were prepared under the influence of magnetic fields up to 5 T. The exposure to magnetic fields during gelation caused the melting temperature to increase in the agarose gels (+1.0K for the 0.2 wt% gel) and to decrease in methyl cellulose gels (-3.5 K for the 0.4 wt% gel). The change in melting temperature was reduced with increasing polymer concentration and was saturated in magnetic fields below 3 T. Stable gel structures were constructed due to the exposure to magnetic fields.

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  • Itinerant electron metamagnetism in Y(Co1-xNix)(3) 査読

    F Ishikawa, Yamamoto, I, M Yamaguchi, MI Bartashevich, K Koui, H Mitamura, T Goto

    PHYSICA B   237   491 - 492   1997年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    Itinerant electron metamagnetism was studied by ultra-high field magnetization for the system Y(CO1-xNix)(3) (x = 0 similar to 0.1). The metamagnetic transition fields were observed to increase with increasing the number of 3d electrons. This is attributed to the decrease in the exchange field acting on the 3d moment.

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  • High field magnetization of metal hydrides under hydrogen pressure 査読

    F Ishikawa, Yamamoto, I, M Yamaguchi, MI Bartashevich, T Goto

    JOURNAL OF ALLOYS AND COMPOUNDS   253   350 - 352   1997年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE SA LAUSANNE  

    The magnetization of the metal hydrides GdFe3Hx (x=0 similar to 3.6) and Dy6Fe23Hx (x=0 similar to 20.3) was measured in magnetic fields up to 29 T at 77 K. For these measurements the hydrides were prepared in situ in a glass holder with gradually varying hydride composition x at room temperature. For each system the magnetization curve varied systematically with hydrogen content. The dependence of magnetization on hydrogen content is discussed.

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  • Thermodynamic theory of magnetic field effects on chemical equilibria and applications to metal-hydrogen systems 査読

    M Yamaguchi, Yamamoto, I, F Ishikawa, T Goto, S Miura

    JOURNAL OF ALLOYS AND COMPOUNDS   253   191 - 194   1997年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE SA LAUSANNE  

    A general thermodynamic theory was constructed on magnetic field effects on chemical equilibria. Introducing the magnetochemical potential or the electromagnetic chemical potential leads to the magnetic field-induced changes in the equilibrium constant in an ideal gas reaction and the electromotive force in an electrochemical system. Applying these general results to metal-hydrogen systems gives the relationships between the equilibrium hydrogen pressure or the equilibrium electrode potential and magnetic fields, which correspond to experimental data.

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  • Magnetic field effects on the chemical equilibrium between metals and hydrogen 査読

    Yamamoto, I, M Yamaguchi, M Fujino, F Ishikawa, T Goto, S Miura

    PHYSICA B   216 ( 3-4 )   399 - 402   1996年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    The magnetic field-induced shift in chemical equilibrium was studied for the ferromagnetic hydride LaCo5Hx-hydrogen system. The hydrogen composition x, which was monitored via the magnetization of the hydride, was observed as a function of magnetic fields up to 14 T under a constant pressure of hydrogen at 313.2 K. The hydrogen composition is gradually changed by 50% from x = 1.88 to x = 0.96 as the applied magnetic field was changed from 2 to 14 T. A thermodynamic theory can explain this effect, taking the change in magnetic free energy into account.

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  • Relationships between the electrical resistivity and the metal hydride phases 査読

    F Ishikawa, H Tega, Yamamoto, I, M Yamaguchi

    JOURNAL OF ALLOYS AND COMPOUNDS   231 ( 1-2 )   182 - 187   1995年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE SA LAUSANNE  

    Electrical resistivity of the unstable metal hydrides LaNi5Hx and LaCo5Hx has been measured in situ by a newly developed method where the samples are under the influence of mechanical stress. An activated sample does not give the bulk resistivity of the hydride, but the resistivity change with hydrogen pressure or temperature is correlated with the transformation of hydride phases. The resistivity of the bulk hydride is tolerably obtained in the first absorption of hydrogen for a virgin sample. The resistivity at 323 K is 1.3, 15.3 and 8.5 mu Omega m for the metal phase (x = 0), the alpha phase (x similar or equal to 0.6) and the beta phase (x = 6.7) of LaNi5Hx, and 1.5, 11.5 and 18.8 mu Omega m for the metal phase (x = 0), the beta phase (x = 3.4) and the gamma phase (x = 4.3) of LaCo5Hx, respectively. These resistivity changes with hydrogen composition are interpreted in relation to disordered-ordered arrangement of hydrogen.

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▶ 全件表示

MISC

  • Investigation of topological phase transition in BiTeBr under high pressure

    A. Ohmura, Y. Higuchi, T. Ochiai, M. Kanou, S. Nakano, F. Ishikawa, A. Nakayama, Yuh Yamada, T. Sasagawa

    JOINT AIRAPT-25TH & EHPRG-53RD INTERNATIONAL CONFERENCE ON HIGH PRESSURE SCIENCE AND TECHNOLOGY, 2015   950   2017年

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    記述言語:英語   出版者・発行元:IOP PUBLISHING LTD  

    The polar semiconductor BiTeBr has the P3m1 symmetry, similar to that of BiTeI, in which a pressure-induced topological phase transition from a trivial semiconductor to a topological insulator has been theoretically predicted. To investigate the topological phase transition in BiTeBr, we performed X-ray diffraction and electrical resistivity measurement under high pressure, and the band calculation using experimental structural parameters. The P3m1 structure is stable up to the pressure of similar to 7 GPa; the ratio of lattice constants (c/a) reaches a minimum at around 3 GPa. Furthermore, the following phenomena are observed at around this pressure; 1) the band-gap energy closes and reopens with pressure, 2) the temperature dependence of resistivity changes from metallic to semiconducting. From theoretical prediction in BiTeI, the topological phase transition is accompanied by the band gap closing/reopening. Therefore, the results obtained in BiTeBr suggest that the topological phase transition occurs at around 3 GPa.

    DOI: 10.1088/1742-6596/950/4/042036

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  • 26pED-12 銅酸化物超伝導体YBa_2Cu_4O_8の圧力誘起相転移 : 高圧相の結晶構造と超伝導(銅酸化物2 領域8(強相関系分野:高温超伝導 強相関f電子系など)) 査読

    中山 敦子, 石川 文洋, 山田 裕, 恩田 裕介, 山田 修平, 藤久 裕司, 坂田 雅文, 中本 有紀, 清水 克哉, 中野 智志, 大村 彩子

    日本物理学会講演概要集   68 ( 0 )   549 - 549   2013年

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    記述言語:日本語  

    DOI: 10.11316/jpsgaiyo.68.2.3.0_549_4

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  • Temperature dependence of Landau coefficients in Lu(Co1-xGax)(2)

    F Ishikawa, T Goto, K Fukamichi, H Yamada

    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   272   505 - 506   2004年5月

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    記述言語:英語   出版者・発行元:ELSEVIER SCIENCE BV  

    High-field magnetization was measured for typical itinerant-electron metamagnets Lu(Co1-xGax)(2) with x = 0.06 and 0.07 at temperatures from 4.2 to 300 K in pulsed magnetic fields up to 45 T. Landau coefficients A(T), B(T) and C(T) were determined by fitting measured M-H curves to the equation, H = A(T)M + B(T)M-3 + C(T)M-5. The temperature dependence of the Landau coefficients was well explained by the theory of the metamagnetic transition considering the magnetovolume effect. (C) 2003 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.jmmm.2003.11.214

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  • Field induced structural transformation in MnAs

    F Ishikawa, K Koyama, K Watanabe, H Wada

    JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS   42 ( 8A )   L918 - L920   2003年8月

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    記述言語:英語   出版者・発行元:INST PURE APPLIED PHYSICS  

    The structural phase transition induced by magnetic fields on the ferromagnetic compound MnAs was observed by the X-ray diffraction measurements in high magnetic fields up to 4 T. Magnetization measurements showed that Curie temperature T-C was 315.5 K for increasing temperatures and a metamagnetic transition from the paramagnetic to the ferromagnetic state occurred above T-C. The structural transformation from the hexagonal NiAs-type to the orthorhombic MnP-type structure was confirmed at T-C with increasing temperature from 290 K. The X-ray profiles at 319 K in the magnetic field showed that the hexagonal structure phase appeared with increasing fields and coexisted with the orthorhombic one. On further increase of magnetic fields, the single phase of the hexagonal structure was observed above 3.5 T in the forced ferromagnetic state. Both the magnetic and structural transitions induced by magnetic fields above T-C were first order with a hysteresis and had a close relationship between each other.

    DOI: 10.1143/JJAP.42.L918

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  • Itinerant-electron metarnagnetism in Y(Co1-xNix)(5)

    F Ishikawa, Yamamoto, I, Umehara, I, M Yamaguchi, MI Bartashevich, H Mitamura, T Goto, H Yamada

    PHYSICA B-CONDENSED MATTER   328 ( 3-4 )   386 - 392   2003年5月

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    記述言語:英語   出版者・発行元:ELSEVIER SCIENCE BV  

    The magnetization processes of the Y(Co1-xNix)(5) system were measured at 4.2 K in pulsed high magnetic fields up to 40 T. The spontaneous magnetization decreases linearly with increasing Ni concentration up to x = 0.4. In the narrow concentration region 0.5less than or equal toxless than or equal to0.6, the magnetization rapidly decreases, but weak ferromagnetism persists up to x = 0.8. On the other hand, the high-field susceptibility exhibits a maximum at x = 0.55. These results show that the magnetic state of Y(Co1-xNix)(5) changes from the high- to the low-moment state at the critical concentration x = 0.55. In the vicinity of this concentration, the magnetization was measured at high pressures up to 1 GPa. The compound Y(CO0.5Ni0.5)(5) shows a very large pressure effect, indicating that it is very close to the critical concentration. (C) 2003 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0921-4526(02)02639-X

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共同研究・競争的資金等の研究

  • ディラック半金属PdTe2における圧力誘起トポロジカル相転移と超伝導特性

    研究課題/領域番号:20H01851

    2020年4月 - 2024年3月

    制度名:科学研究費助成事業

    研究種目:基盤研究(B)

    提供機関:日本学術振興会

    大村 彩子, 名嘉 節, 石川 文洋

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    配分額:17550000円 ( 直接経費:13500000円 、 間接経費:4050000円 )

    本研究の目的は、非自明な表面状態をもつタイプII型ディラック半金属PdTe2において5 GPa付近で理論予測された圧力誘起トポロジカル相転移(リフシッツ転移)と超伝導特性の関係を実験的に解明すること、さらに表面超伝導が磁場下で示す異常な振る舞いの起源を解明してPdTe2のトポロジカル超伝導の可能性を検証することである。初年度に得られた成果は下記の通りである。
    1. 申請時点で超伝導転移温度(Tc)の圧力依存性が5 GPa付近で極大をもつことを見出しており,トポロジカル相転移との関係性が期待された。しかし,その後の二度の再測定ではTc極大の再現性は得られず,いずれも1 GPa以上の圧力域においてTc値は単調に減少した。再現性が得られた結果(1 GPa以上での単調減少)がPdTe2の本質的であると結論付け,少なくとも電気抵抗測定では相転移を示唆する変化は検出されないことがわかった。5 GPa付近の極大については,その発現圧力およびTc値から構成元素であるTeによる圧力誘起超伝導であると推測された。
    2. 初年度は,2種の圧力媒体を用いて10 GPa以下の圧力域で静水圧下X線回折を実施し,低圧域での詳細な圧力変化を観測した。PdTe2の高圧下構造については特に低圧域の情報が不足していたため,本研究で得たデータは物性測定を考察する上で重要な結果となりうる。
    3. 表面超伝導の評価に向けて,表面敏感な測定法と高圧発生技術を組み合わせた新規測定法の確立を目指しており,初年度は第一段階として,1)高圧セルの試料室周辺部の最適化と2)標準的な超伝導試料(常圧試料)を用いた計測系の構築を並行して進めた。その結果,1)では高圧力発生の点での構成部材の最適化はほぼ完了した。しかし,信号検出という点では,1)と2)どちらにおいても改善が必要であることが判明し,次年度以降の課題となった。

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  • Bi系層状ラシュバ物質群における圧力誘起超伝導および構造相転移の研究

    研究課題/領域番号:16K05440

    2016年4月 - 2019年3月

    制度名:科学研究費助成事業

    研究種目:基盤研究(C)

    提供機関:日本学術振興会

    大村 彩子, 山田 裕, 石川 文洋

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    配分額:4810000円 ( 直接経費:3700000円 、 間接経費:1110000円 )

    本研究では、3次元層状ラシュバ物質のBiTeX(X = Cl, Br, I)において圧力で誘起される超伝導転移及び構造相転移の研究を進めた。トポロジカル絶縁体でもあるBiTeClでは、電気抵抗測定とラマン分光測定により、6 GPa以上で発現する圧力誘起超伝導は高圧結晶相に起因することを明らかにした。また、発現圧力や発現時の転移温度は再現するが、抵抗率の温度依存性等については試料に強く依存することがわかった。一方、BiTeBr及びBiTeIでは、放射光X線回折により、30 GPaまでの圧力領域で2つの高圧結晶相が形成され、それぞれ正方晶系及び単斜晶系の構造モデルで説明できることを明らかにした。

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  • 一次元伝導性を持つプラセオ系銅酸化物の単結晶育成と圧力下における異方的伝導性

    研究課題/領域番号:15K05163

    2015年4月 - 2018年3月

    制度名:科学研究費助成事業

    研究種目:基盤研究(C)

    提供機関:日本学術振興会

    石川 文洋, 山田 裕

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    配分額:4680000円 ( 直接経費:3600000円 、 間接経費:1080000円 )

    銅系酸化物Pr2Ba4Cu7O15-δ (Pr247)の単結晶育成を行い,その電気伝導性を測定した。多結晶試料での超伝導の発現の観点から,単結晶による電気伝導性の異方性と一次元伝導に起因した超伝導に着目した。高圧酸素雰囲気下で自己フラックス法での単結晶の育成条件を探査し,急冷過程を含むことで目標物質の育成に成功した。ファンデルポー法による電気抵抗は,その大きさが方位によって1,000倍異なり,低抵抗方向では低温で超伝導の兆候と考えられる抵抗の落ちが観測された。

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  • 鉄オキシニクタイド超伝導体の単結晶育成と高圧下物性の研究

    研究課題/領域番号:23684024

    2011年4月 - 2014年3月

    制度名:科学研究費助成事業

    研究種目:若手研究(A)

    提供機関:日本学術振興会

    石川 文洋

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    配分額:26650000円 ( 直接経費:20500000円 、 間接経費:6150000円 )

    新しい鉄系オキシニクタイドとしてSr2Cr2Fe2As2O2の合成に成功した。鉄ヒ素構造間に多層構造を持つオキシニクタイドは高い超伝導転移温度を示すことが期待されたが、本物質においては置換によるドーピングや13 GPaまでの圧力印加によっても超伝導を誘しなかった。この物質の単結晶育成は、高い融点を克復するためにタングステン金属製のるつぼを用いて行ったが電気炉のアルゴン雰囲気の純度がよくない点と化合物に含まれるヒ素の高い反応性のために成功しなかった。この物質の合成には高圧下合成装置の利用が有望であると考えられる。多重極限化での物性測定を可能としたことで、今後の新しい物質探査に寄与できる。

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  • 圧力を用いた炭素π電子系配列ナノ空間の水素吸蔵についての研究

    研究課題/領域番号:20045003

    2008年 - 2009年

    制度名:科学研究費助成事業

    研究種目:特定領域研究

    提供機関:日本学術振興会

    中山 敦子, 山田 裕, 石川 文洋, 大村 彩子

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    配分額:5000000円 ( 直接経費:5000000円 )

    ナノグラファイト構造をもつ炭素π電子系配列ナノ空間物質は、高圧下で水素(H_2)を吸蔵する。このとき、H_2との間に大きな電気的相互作用が働くことによって、0.7GPa以下では、ハニカム格子を等方的に伸ばすことがこれまでの研究で自明である。この現象を理解し、H_2が炭素π電子系配列ナノ空間の何処にどのような状態で存在するか明らかにするために、メソカーボンマイクロビーズ(MCMB)の高圧H_2およびヘリウム(He)中でのラマンスペクトルを観察した。先に1GPa以下で観察したX線回折の結果を含め、全体を次のように考察した。
    1GPa以下で観察されるMCMBs-H_2とMCMBs-HeのG-bandの圧力変化は、大きく異なる。0.7GPa以下では相反する現象:「ハニカム格子の伸び」と「G-bandのハード化」が同時に起こる。これには、C=C結合の振動を抑制するH_2の配向を考慮する必要がある。ハニカム格子を伸ばすには、Cのπ軌道とHのs軌道の重なりによる電荷移動が必要で、H_2はグラフェンに垂直に配位しなければならない。しかし、層間距離は圧縮されるため、H_2が層間に縦配向することは考えにくい。「グラフェン面へのH_2の串刺し構造」であれば、層間距離が伸びることなくハニカム格子が伸び、しかも、格子振動が固くなる。また、H_2の配向が変化し、ハニカム格子に対して垂直でなくなれば、電気的な相互作用が弱くなり、一時的に格子振動がソフト化しつつ格子が縮むことから、このモデルが妥当であると考える。結論すると、0.7GPa以下では、H_2の層間へのインターカレーションを、また、0.7GPa≦P≦1GPaでは、H_2のハニカム格子に対する配向の変化を示唆する。

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  • フラストレート系CuOジグザグチェーンにおける超伝導の研究

    研究課題/領域番号:20046006

    2008年 - 2009年

    制度名:科学研究費助成事業

    研究種目:特定領域研究

    提供機関:日本学術振興会

    山田 裕, 中山 敦子, 石川 文洋, 大村 彩子

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    配分額:3700000円 ( 直接経費:3700000円 )

    我々は、最近Pr_2Ba_4Cu_7O_<15・δ>(Pr247)酸化物において酸素還元処理を施すことにより超伝導がTc=15K付近で出現することを発見した。これは従来のCuO_2二次元面による超伝導とは異なりCuOジグザグチェーンにおける超伝導であると考えられる。この超伝導の発見は銅系酸化物超伝導体における全く新しい超伝導の出現となるばかりでなく、その結晶構造から、擬一次元伝導機構による初めての超伝導物質であると考えられる。CuOジグザグチェーンは元来フラストレーションスピン系にキャリアーをドープした系である。事実、キャリアー依存性、圧力依存性で様々な量子相が観測されている。そこで我々はこのCuOジグザグチェーンチェーンのキャリア数を制御して、電子輸送特性及び結晶構造解析を調べることによりその物性を解明することを試みた。
    本年度は特に10GPaを超える高圧力下での物性及び結晶構造を明らかにした。その結果、CuOジグザグチェーンを有するY124, Y247, Pr124, Pr247のすべてが10GPa以上で構造相転移を起こすことが確認できた。これはCuOジグザグチェーンを持たないPr123構造では起こらないことからCuOジグザグチェーンが壊れている可能性が高いことが示唆された。さらに電気抵抗の測定により10GPa以上で電気抵抗が急激に減少することから、構造相転移により新しい伝導面が形成された可能性が示唆された。

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  • 10GPa級圧力装置によるプラセオ系銅酸化物超伝導体のホール効果測定

    研究課題/領域番号:20740193

    2008年 - 2009年

    制度名:科学研究費助成事業

    研究種目:若手研究(B)

    提供機関:日本学術振興会

    石川 文洋

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    配分額:4290000円 ( 直接経費:3300000円 、 間接経費:990000円 )

    プラセオ系銅酸化物超伝導体Pr2Ba4Cu7O15-δの圧力下における超伝導特性の変化を解明する目的で、10GPa級の圧力下でのホール効果測定装置の開発を目指した。改良型ブリッジマンアンビル法を用いた圧力発生装置の改良により、10GPaを超える圧力下での電気抵抗測定が可能となった。この測定から約11GPaで電気抵抗に極大値が現れた。この変化は、10GPa近傍で生じる構造相転移によるものと考えられる。

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  • 磁気天秤を用いた5GPa級高圧下精密帯磁率測定装置の開発

    研究課題/領域番号:19654050

    2007年 - 2008年

    制度名:科学研究費助成事業

    研究種目:萌芽研究

    提供機関:日本学術振興会

    山田 裕, 石川 文洋, 大村 彩子, 中西 剛司, 名嘉 節

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    配分額:3300000円 ( 直接経費:3300000円 )

    我々はこれまで超伝導と強磁性が共存するRuSr2GdCu2O8 (Ru1212)酸化物超伝導体あるいは超伝導と反強磁性が共存するMoSr2YCu2O8 (Mo1212)酸化物超伝導体についてその高圧下での物性測定を行ってきた。特にMo1212酸化物超伝導体は、圧力を加えることにより超伝導遷移温度Tcは当初7K/GPaという非常に大きな割合で上昇し、10GPa下でもまだ上昇を続けることが分かった。この機構を明らかにするには共存する磁気秩序(反強磁性)の圧力依存性を高い圧力で精度良く調べることが必要不可欠となった。しかしながらこのような装置は世界中どこにも存在しない。そこで本研究では5GPaを超える高い圧力下において高精度で磁化の温度依存性が測定可能な装置の開発を行うことを目的としている。本年度は硬質プラスチック(PBI)を用いたブリッジマンアンビルセルのクランプ強度試験とジルコニア製のアンビルによる発生圧力試験を行った。設計及び製作を行なった。硬質プラスチック(PBI)の強度計算より算出していたクランプ重量は2トンであったが、実際に荷重をかけたところ2トンクランプすると課題の部分が破壊し、その強度に問題を残す結果となった。一方ジルコニア製のアンビルによる発生加圧試験では、Biの電気抵抗測定により調べたところ、2トンでI-IIの構造相転移に対応する電気抵抗の減少が観測できた。このことから2トンで2GPaを超える圧力が出ていると予想される。以上の結果より高い圧力を発生させるためにはPBIの強度にやや問題があり今後他の硬質プラスチック及びジュラルミン等、非磁性で軽量・強高度の材料を試す必要がある。
    現在既に軽量化した銅ベリルウムセル及びセラミックセルの設計を行っており5GPa級圧力セルの開発は可能であると確信している。

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  • 擬一次元伝導面を有するプラセオ系銅酸化物の新しい超伝導に関する基礎的研究

    研究課題/領域番号:17360310

    2005年 - 2006年

    制度名:科学研究費助成事業

    研究種目:基盤研究(B)

    提供機関:日本学術振興会

    山田 裕, 石川 文洋, 大野 義章, 松下 明行

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    配分額:14600000円 ( 直接経費:14600000円 )

    我々は、Pr2Ba4Cu7015-δ(Pr247)酸化物において酸素還元処理を施すことにより超伝導が出現することを発見した。これは従来のCuO_2二次元面による超伝導とは異なり一次元CuOダブルチェーンによる超伝導であると考えられる。これを解明するためには、良質な試料の合成、特に単結晶の育成、電気抵抗、ホール効果、低温比熱、NQR等の基礎的物性測定、特に超伝導の圧力効果の測定、朝永-Luttinger理論を基礎にしたt-Jモデルを用いた理論的解析が必要となる。本研究では上記の研究を系統的に行うことにより、この超伝導の機構を解明することを目的としている。
    その結果以下のような結果が得られた。
    1.Pr247酸化物の良質試料合成と還元条件の確立を行った。その結果酸素還元量と超伝導遷移温度にベルカーブ的相関があることを明らかにした。またそのときの最高の超伝導遷移温度は24Kであり超伝導の体積分率は70%を超えることが明らかとなった。
    2.Pr247酸化物の超伝導の圧力効果を調べるため改良型ブリッジマンアンビルセルの開発を行い、10GPaまでの高圧力下での物性測定が可能となった。
    3.Pr247酸化物の圧力下での電子輸送特性を測定した。その結果、加圧に伴い超伝導は消失し、その消失する圧力が酸素還元量に依存することを明らかにした。またいずれの試料も8GPa以上では半導体的振る舞いをすることを発見した。
    4.Pr247の結晶構造解析データを基にバンド計算を行い、これによりダブルチェーンにおける朝永-Luttinger理論を基礎にした解析を行った。その結果今回のPr247の超伝導に関する実験結果を良く説明できることを示した。

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  • 遷移金属間化合物の多重極限下における物性

    1999年

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    資金種別:競争的資金

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  • 熱電変換材料の開発

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    資金種別:競争的資金

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