研究者詳細 - 小山　佳一

論文 - 小山　佳一

分割表示 496 件中 201 - 220 件目／全件表示 >>

K. Koyama, R. Sakakura and K. Watanabe . Development of an extraction type magnetometer under low temperature and high magnetic fields over 20 T by the hybrid magnet . J. Phys.: Conf. Ser.156 12019 2009年査読

Y. Mitsui, K. Koyama and K. Watanabe . X-ray diffraction measurements in high magnetic field and at high temperatures . Sci. Technol. Adv. Mater.10 14612 2009年査読

T. Akiya, H. Kato, M. Sagawa and K. Koyama . Enhancement of coercivity in Al and Cu added Nd-Fe-B sintered magnets by high field annealing . IOP Conf. Ser.: Mat. Sci. Eng.1 12034 2009年査読

Y. Yamato, M. Matsukawa, Y. Murano, R. Suryanarayanan, S. Nimori, M. Apostu, A. Revcolevschi, K. Koyama, N. Kobayashi . Colossal electroresistance and colossal magnetoresistive step in paramagnetic insulating phase of single crystalline bilayered manganite (La0.4Pr0.6)1.2Sr1.8Mn2O7 . Appl. Phys. Lett.94 92507 2009年査読

Y. Yamato, M. Matsukawa, S. Nimori, R. Suryanarayanan, Y. Murano, Y. Nakanishi, M. Apostu, A. Revcolevschi, K. Koyama, and N. Kobayashi . Effect of pressure on Lattice distortion, transport and magnetic properties of Pr-substituted La1.2Sr1.8Mn2O7 bilayered manganite . J. Phys.: Condens Matter21 486001 2009年査読

H.C. Hsu, F.C. Chou, K. Koyama, K. Watanabe and H.L. Liu . Spin-phonon coupling in antiferromagnetic Bi2Sr2CoO6+δ: An intrared reflectance study . Phys. Rev. B79 155109 2009年査読

M. Hiroi M, T. Rokkaku, K. Matsuda, T. Hisamatsu, I. Shigeta, M. Ito, T. Sakon, K. Koyama, K. Watanabe, S. Nakamura, T. Nojima, T. Nakano, L. Chen, T. Fujiwara, Y. Uwatoko, H. Manaka, and N. Terada . Ferromagnetism and spin-glass transitions in the Heusler compounds Ru2-xFexCrS . Phys. Rev. B79 224423 2009年査読

A.V. Andreev, K. Koyama, E.A. Tereshina, J. Prokleska, and K. Watanabe . Magnetoelasticity of (Lu0.8Ce0.2)2Fe17 intermetallic compound . J. Alloys and Compounds477 62 - 67 2009年査読

T Kawamata, N Sugawara, M Uesaka, N Kaneko, T Kajiwara, H Yamane, K Koyama, K Kudo, N Kobayashi, Y Koike . Single-Crystal Growth of Pb2V3O9 and the Bose-Einstein Condensed State of Triplons Studied by Thermal Conductivity, Specific Heat and Magnetization Measurements . J. Phys.: Conf. Ser.150 42087 2009年査読

Y. Yamato, Y. Nakanishi, M. Matsukawa, R. Suryanarayanan, S. Nimori, M. Apostu, A. Revcolevschi, K. Koyama, N. Kobayashi . Anomalous pressure effect on steplike magnetostriction of (La0.4Pr0.6)(1.2) Sr1.8Mn2O7 bilayered manganese oxide . 25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 4150 2009年

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 report the pressure effect on a steplike magnetostriction of single crystalline (La0.4Pr0.6)(1.2)Sr(1.8)Mb(2)O(7) bilayered manganite, for our understandings of the ultrasharp nature of the field-induced first-order transition from a paramagnetic insulator and to a ferromagnetic metal phase. Application of pressure suppresses a steplike transformation and causes a broad change in the magnetostriction. A delocalization of carriers is promoted with the applied pressure, resulting in the suppressed steplike behaviour. The steplike behaviour observed is closely related to the existence of localized carriers.

DOI： 10.1088/1742-6596/150/4/042121

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S. Ebisu, K. Koyama, H. Omote, S. Nagata . High field magnetization processes in single crystals of α-Tb <inf>2</inf>S<inf>3</inf> and α-Dy<inf>2</inf>S<inf>3</inf> . Journal of Physics: Conference Series150 2009年査読

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）

Rare earth sesquisulfides α-Tb2S3 and α-Dy2S3 possess orthorhombic crystal structure having two independent rare earth sites. High field magnetization processes for single crystals of these compounds have been investigated up to μoH 18 T. Some step-like transitions have been observed in both compounds. The magnetization of α-Tb2S3 single crystal under the field along the 6-axis at T 1.4 K shows a steep increase of about 4.5 μB, which corresponds to a half of full saturation moment of free Tb3+, at μoH 2.2 T. It is considered that the reorientation of Tb3+ moments on only one Tb site into a ferromagnetic arrangement occurs. When the magnetic field is perpendicular to the b-axis, one-step transition at μoH 0.7 T for Hc and two-step transitions at 0.7 and 1.2 T for Ha are observed. As for α-Dy 2S3, the magnetization curve at T 1.5 K shows two-step transitions at 1.3 and 1.6 T (Hb), three or four dull steps (Ha or c). The total height of two steps in the M-H curve for Hb corresponds to a half of full Dy3+ moment. © 2009 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/150/4/042027

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Y. Furutani, H. Nishihara, T. Kanomata, K. Kobayashi, R. Kainuma, K. Ishida, K. Koyama, K. Watanabe, T. Goto . Field-induced-moment nuclear Coupling for Co-59 in a Heusler alloy Co2TiGa . 25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 4150 2009年

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 positive hyperfine field at Co nucleus in a Heusler alloy Co2TiGa is discussed to be not dominated by the orbital hyperfine field from a quite different point of view from former studies. Field-induced-moment nuclear coupling for Co-59 via spin-orbit interaction on Co atom in Co2TiGa is discussed to be small from the observed high-field shift of the NMR of Co-59 in the ferromagnetic state of only +0.83 % in contrast to the case of CoCl2 center dot 2H(2)O with +29%.

DOI： 10.1088/1742-6596/150/4/042037

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H. Okada, Y. Kusakari, E. Matsuoka, H. Onodera, K. Koyama, K. Watanabe, T. Kanomata . Transport properties of Heusler compounds Ru2CrGe and Ru2CrSn under high magnetic fields . 25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 4150 2009年

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 have performed the specific heat and the electrical resistivity measurements under high magnetic fields for Heusler compounds Ru2CrGe and Ru2CrSn. We found that the electrical resistivity for Ru2CrGe shows an upturn in the vicinity of 130 K and changes a metallic to a semiconducting-like behavior with decreasing temperature. By applying magnetic field, a negative magnetoresistance was observed below 200 K. On the other hand, the electrical resistivity for Ru2CrSn shows a semimetallic-like behavior. The results of the electrical resistivity in Ru2CrGe suggest that the compound has a gap-like structure in the electronic structure at the Fermi level. Moreover, it was found that another phase transition occurs in Ru2CrGe and Ru2CrSn, in addition to the magnetic transition.

DOI： 10.1088/1742-6596/150/4/042153

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E. G. Gerasimov, N. V. Mushnikov, K. Koyama, T. Kanomata, K. Watanabe . Positive magnetoresistance and large magnetostriction at first-order antiferro-ferromagnetic phase transitions in RMn(2)Si(2) compounds . JOURNAL OF PHYSICS-CONDENSED MATTER20 ( 44 ) 2008年11月査読

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

The magnetostriction and magnetoresistance associated with the field-induced and spontaneous first-order antiferro-ferromagnetic (AF-F) phase transitions have been studied for quasi-single-crystalline samples of La(0.25)Sm(0.75)Mn(2)Si(2), La(0.25)Y(0.75)Mn(2)Si(2) and La(0.27)Y(0.73)Mn(2)Si(2) compounds with natural layered ThCr(2)Si(2)-type structure. It was found that both the spontaneous and field-induced AF-F transitions are accompanied by a large volume magnetostriction Delta V/V approximate to 2 x 10(-3) and anisotropic linear changes of the lattice parameters Delta a/a approximate to 1.6 x 10(-3), Delta c/c approximate to -0.75 x 10(-3). The field-induced AF-F magnetic phase transition has been observed in magnetic fields applied both along the c-axis and in the basal plane, and the magnetostriction value is virtually independent of the direction of applied field. It has been found also that the magnetoresistance is positive in these compounds (the value of the electrical resistance in the ferromagnetic state is higher than that in the antiferromagnetic state) for the fields applied both along the c-axis and in the basal plane. The value of the magnetoresistance observed along the c-axis is 30 times as high as that in the basal plane. The obtained results indicate that the electronic band structure changes are likely responsible for the AF-F magnetic phase transitions observed in the RMn(2)X(2) compounds.

DOI： 10.1088/0953-8984/20/44/445219

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Y. Yamato, M. Matsukawa, T. Kumagai, R. Suryanarayanan, S. Nimori, M. Apostu, A. Revcolevschi, K. Koyama, N. Kobayashi . Effect of pressure on the steplike magnetostriction of single crystalline bilayered manganite (La(0.4)Pr(0.6))(1.2)Sr(1.8)Mn(2)O(7) . PHYSICAL REVIEW B78 ( 13 ) 2008年10月査読

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 report the effect of pressure on the steplike magnetostriction of single crystalline bilayered manganite (La(0.4)Pr(0.6))(1.2)Sr(1.8)Mn(2)O(7), for our understanding of the ultrasharp nature of the field-induced first-order transition from a paramagnetic insulator to a ferromagnetic metal phase. The application of pressure suppresses a steplike transformation and causes a broad change in the magnetostriction. The injection of an electric current to the crystal also weakens the steplike variation in both the magnetostriction and magnetoresistance. The stabilization of ferromagnetic interaction or the delocalization of charge carriers is promoted with the applied pressure or applied current, resulting in the suppressed steplike behavior. Our findings suggest that the step phenomenon is closely related to the existence of localized carriers such as the short-range charge-orbital-ordered clusters.

DOI： 10.1103/PhysRevB.78.132411

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T. Fujita, H. Okada, K. Koyama, K. Watanabe, S. Maekawa, M. W. Chen . Unusually Small Electrical Resistance of Three-Dimensional Nanoporous Gold in External Magnetic Fields . PHYSICAL REVIEW LETTERS101 ( 16 ) 2008年10月査読

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 report the electric conductivity of three-dimensional (3D) nanoporous gold at low temperatures and in strong magnetic fields. It was found that topologically disordered 3D nanoporosity leads to extremely low magnetoresistance and anomalous temperature dependence as the characteristic length of nanoporous gold is tuned to be similar to 14 nm. This study underscores the importance of 3D topology of a nanostructure on electronic transport properties and has implications in manipulating electron transport by tailoring 3D nanostructures.

DOI： 10.1103/PhysRevLett.101.166601

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Hiroaki Kato, Takahiro Akiya, Kunihiro Koike, Keiichi Koyama, Masato Sagawa . Coercivity enhancement induced by high-magnetic-field annealing in sintered Nd-Fe-B magnets . Proceedings of The 20th Workshop on Rare Earth Permanent Magnets and Applications 2008年9月招待

A. V. Andreev, E. A. Tereshina, E. Santava, I. Satoh, T. Yamamura, Y. Shiokawa, K. Koyama, K. Watanabe . Magnetic properties of U-2(Fe1-xNix)(13.6)Si-3.4 single crystals . JOURNAL OF ALLOYS AND COMPOUNDS461 ( 1-2 ) 6 - 8 2008年8月

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 concentration evolution of crystal structure, magnetic moment and anisotropy constants in U-2(Fe1-xNix)(13.6)Si-3.4 investigated on single crystals grown by the Czochralski method is found to be similar to that in the previously studied U-2(Fe1-xNix)(13.6)Si-3.4 system, only the Ni solubility is limited by x = 0.3 in difference with unlimited Co solubility. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2007.06.086

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M. Ohtsuka, J. Sekino, K. Koyama, T. Takagi, K. Itagaki . Magnetostructural phase transformation and shape memory effect of Fe-added Ni(2)MnGa films . EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS158 173 - 178 2008年5月査読

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

The magnetostructural phase transformation and shape memory effect (SME) of Fe-added Ni(2)MnGa films were investigated. The free-standing films were heat-treated at 1073 K for 3.6 ks and constraint-aged (CA) at various conditions (473 similar to 723 K, 0 similar to 14.4 ks) to make the two-way SME. The reversible two-way SME by the temperature change was confirmed through the martensitic transformation (MT) and its reversion. The gradient of strain-temperature curve, the effective recovery strain and the width of thermal hysteresis were dependent on the CA conditions. The magnetic field (MF) induced structural phase transformation was evaluated by an XRD apparatus in high MF up to 5 T. It was confirmed that the martensitic phase was stabilized by the MF. Furthermore, the SME by the MF was observed around MT temperature on cooling process for the CA film. It was concluded that the MF induced SME appeared by the induction of the MT with MF.

DOI： 10.1140/epjst/e2008-00672-4

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K. Koyama, H. Onodera, and K. Watanabe . Magnetization measurements of DyB2C2 under high pressure and high magnetic fields . Physica B403 1607 - 1608 2008年査読

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論文 - 小山　佳一