研究者データベース

網塚 浩(アミツカ ヒロシ)
理学研究院 物理学部門 凝縮系物理学分野
教授

基本情報

所属

  • 理学研究院 物理学部門 凝縮系物理学分野

職名

  • 教授

学位

  • 博士(理学)(北海道大学)

連絡先

  • amiamiphys.sci.hokudai.ac.jp

ホームページURL

J-Global ID

研究キーワード

  • 極低温物性実験   

研究分野

  • 自然科学一般 / 磁性、超伝導、強相関系

担当教育組織

職歴

  • 2006年04月 - 現在 北海道大学 大学院理学研究院(改組)物理学部門 教授
  • 2005年04月 - 2006年03月 北海道大学 大学院理学研究科 物理学部門 教授
  • 2000年04月 - 2005年03月 北海道大学 大学院理学研究科 物理学部門 助教授
  • 1995年10月 - 2000年04月 北海道大学 大学院理学研究科 物理学専攻 講師
  • 1995年05月 - 1996年02月 アムステルダム大学(オランダ) Van der Waals –Zeeman 研究所 文部省在外研究員(若手)
  • 1995年04月 - 1995年09月 北海道大学 大学院理学研究科 物理学専攻 助手
  • 1989年07月 - 1995年03月 北海道大学 理学部 物理学科 助手

学歴

  • 1989年04月 - 1989年06月   北海道大学   理学研究科   物理学専攻 博士後期課程
  • 1987年04月 - 1989年03月   北海道大学   理学研究科   物理学専攻 修士課程
  •         - 1987年03月   北海道大学   理学部卒業

所属学協会

  • 日本中性子科学会   国際ミュオン科学会   日本物理学会   

研究活動情報

論文

  • 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 2023年07月15日
  • Keita Ushida, Tatsuya Yanagisawa, Ruo Hibino, Masato Matsuda, Hiroyuki Hidaka, Hiroshi Amitsuka, Georg Knebel, Jacques Flouquet, Dai Aoki
    Proceedings of the 29th International Conference on Low Temperature Physics (LT29) 2023年05月22日
  • Ruo Hibino, Tatsuya Yanagisawa, Yoshito Mikami, Hiroyuki Hidaka, Hiroshi Amitsuka, Sergei Zherlitsyn, Joachim Wosnitza, Yu Yamane, Takahiro Onimaru
    Proceedings of the 29th International Conference on Low Temperature Physics (LT29) 2023年05月22日 [査読有り]
  • 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]
  • Hiroyuki Hidaka, Yoshihiko Ihara, Tatsuya Yanagisawa, Hiroshi Amitsuka
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 90 9 2021年09月 [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.
  • Chihiro Tabata, Hajime Sagayama, Hiraku Saito, Hironori Nakao, Hiroshi Amitsuka
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 90 6 2021年06月 [査読有り]
     
    The crystal structure of the magnetoelectric metal UNi4B was determined from high-resolution synchrotron X-ray diffraction experiments using single-crystalline samples. The direct method and the least-square refinement indicate a structural model with the space group Cmcm (no. 63, D-2h(17)), where U atoms form a pseudo-triangular lattice in the U-Ni-B layers stacking along the a-axis alternately with the Ni layers. The refined values of the structural parameters including anisotropic atomic displacement parameters are provided for all atoms in the unit cell. The obtained structural model is discussed in terms of the magnetoelectric effect reported for this compound.
  • J. Willwater, S. Sullow, M. Reehuis, R. Feyerherm, H. Amitsuka, B. Ouladdiaf, E. Suard, M. Klicpera, M. Valiska, J. Pospisil, Sechovsky, V
    PHYSICAL REVIEW B 103 18 2021年05月 [査読有り]
     
    We present an extensive powder and single-crystal neutron scattering investigation of the crystallographic structure and magnetic order of the frustrated metallic f-electron magnet UNi4B. We carry out a full refinement of the crystallographic structure and conclude that the low-temperature lattice symmetry is orthorhombic [space group Pmm2; cell parameters: a = 6.963(4), b = 14.793(9), c = 17.126(8) angstrom]. We determine the magnetically ordered structure, concluding that below T-N = 19.5 K, the material undergoes a transition into a partially ordered antiferromagnetic state. The magnetic structure is consistent with the existence of toroidal order in this material. We further test the proposal of a second magnetic transition occurring at 330 mK, concluding that the thermodynamic anomalies observed at these temperatures do not reflect modifications of the magnetic structure. Our study provides a consistent picture of the interrelationship of structural and magnetic properties in the frustrated magnet UNi4B previously unresolved.
  • T. Yanagisawa, H. Matsumori, H. Saito, H. Hidaka, H. Amitsuka, S. Nakamura, S. Awaji, D. Gorbunov, S. Zherlitsyn, J. Wosnitza, K. Uhlirova, M. Valiska, Sechovsky, V
    PHYSICAL REVIEW LETTERS 126 15 2021年04月 [査読有り]
     
    We present acoustic signatures of the electric quadrupolar degrees of freedom in the honeycomb-layer compound UNi4B. The transverse ultrasonic mode C-66 shows softening below 30 K both in the paramagnetic phase and antiferromagnetic phases down to similar 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 Gamma(6) (E-2g) electric quadrupolar degrees of freedom in localized 5f(2) (J = 4) states are playing an important role in the magnetic toroidal dipole order and magnetic-field-induced phases of UNi4 B, and evidence some of the U ions remain in the paramagnetic state even if the system undergoes magnetic toroidal ordering.
  • J. Willwater, N. Steinki, D. Menzel, R. Reuter, H. Amitsuka, Sechovsky, V, M. Valiska, M. Jaime, F. Weickert, S. Suellow
    PHYSICAL REVIEW B 103 5 2021年02月 [査読有り]
     
    We present a detailed study of the magnetic and electronic properties of U2Rh3Si5, a material that has been demonstrated to exhibit a first-order antiferromagnetic phase transition. From a high-magnetic-field study, together with extensive experiments in moderate fields, we establish the magnetic phase diagrams for all crystallographic directions. The possibility of an electronic phase in a narrow interval above the Neel temperature as a precursor of a magnetic phase is discussed.
  • Hiroyuki Hidaka, Kota Mizuuchi, Eikai Hayasaka, Tatsuya Yanagisawa, Jun Ohara, Hiroshi Amitsuka
    PHYSICAL REVIEW B 102 17 2020年11月 [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 T-N = 24.8 K accompanied with strong magnetic fluctuations extending to temperatures well above T-N. Furthermore, we constructed a magnetic field-temperature (B-T) phase diagram for B parallel to [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 similar to 0.45 T and a possible single-domain conical one in the higher-field region in the ordering state. The helical structure of GdBe(13 )characterized by an incommensurate ordering vector q(0) 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 B-c than the experimentally obtained one. To discuss the deviation of B-c from the MF calculation, we show a possibility of a fluctuation-induced first-order transition.
  • Tatsuya Yanagisawa, Hiroyuki Hidaka, Hiroshi Amitsuka, Shintaro Nakamura, Satoshi Awaji, Elizabeth L. Green, Sergei Zherlitsyn, Joachim Wosnitza, Duygu Yazici, Benjamin D. White, M. Brian Maple
    PHILOSOPHICAL MAGAZINE 100 10 1268 - 1281 2020年05月 [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.
  • 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]
  • 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, Yuina Kanai-Nakata, Hidenori Fujiwara, Kentaro Kuga, Takayuki Kiss, Atsushi Higashiya, Atsushi Yamasaki, Shin Imada, Arata Tanaka, Kenji Tamasaku, Makina Yabashi, Tetsuya Ishikawa, Hiroyuki Hidaka, Tatsuya Yanagisawa, Hiroshi Amitsuka, Akira Sekiyama
    Proceedings of J-Physics 2019: International Conference on Multipole Physics and Related Phenomena 2020年02月13日 [査読有り]
  • Tatsuya Yanagisawa, Hiroyuki Hidaka, Hiroshi Amitsuka, Sergei Zherlitsyn, Joachim Wosnitza, Yu Yamane, Takahiro Onimaru
    Proceedings of J-Physics 2019: International Conference on Multipole Physics and Related Phenomena 2020年02月13日 [査読有り]
  • S. Hamamoto, Y. Kanai, S. Fujioka, Y. Nakatani, H. Fujiwara, K. Kuga, T. Kiss, A. Higashiya, A. Yamasaki, S. Imada, A. Tanaka, K. Tamasaku, M. Yabashi, T. Ishikawa, H. Hidaka, T. Yanagisawa, H. Amitsuka, K. T. Matsumoto, T. Onimaru, T. Takabatake, A. Sekiyama
    JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA 238 2020年01月 [査読有り][通常論文]
     
    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.
  • T. Yanagisawa, H. Hidaka, H. Amitsuka, S. Zherlitsyn, J. Wosnitza, Y. Yamane, T. Onimaru
    PHYSICAL REVIEW LETTERS 123 6 2019年08月 [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$_{20}$.
  • Hiroyuki Hidaka, Kota Mizuuchi, Tatsuya Yanagisawa, Hiroshi Amitsuka
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 88 3 2019年03月 [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.
  • D. Menzel, D. Schroeter, N. Steinki, S. Suellow, A. Fernandez Scarioni, H. W. Schumacher, H. Okuyama, H. Hidaka, H. Amitsuka
    IEEE TRANSACTIONS ON MAGNETICS 55 2 1500204  2019年02月 [査読有り][通常論文]
     
    Thin film MnSi has been epitaxially grown on Si(111) substrate and investigated in terms of magnetoresistance and Hall measurements under applied hydrostatic pressure up to 2.58 GPa. Although the behavior of the thin films is qualitatively similar to bulk material, at a high pressure above 2 GPa, an additional magnetic ordering occurs, resulting in a reduction of the potential scattering by spin fluctuations. This ordering is stabilized at the applied pressure showing visible effects in the magnetotransport data. Comparing the behavior of thin films with the bulk material under pressure, it seems quite likely that this additional ordering is of skyrmionic nature, which has as yet not been unambiguously evidenced in epitaxial B20 thin films on a substrate under ambient pressure.
  • Chihiro Tabata, Yoshihiko Ihara, Shogo Shimmura, Naoyuki Miura, Hiroyuki Hidaka, Tatsuya Yanagisawa, Hiroshi Amitsuka
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 87 11 2018年11月15日 [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.
  • M. Valiska, H. Saito, T. Yanagisawa, C. Tabata, H. Amitsuka, K. Uhlirova, J. Prokleska, P. Proschek, J. Valenta, M. Misek, D. Gorbunov, J. Wosnitza, Sechovsky, V
    PHYSICAL REVIEW B 98 17 2018年11月 [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.
  • Klara Uhlirova, Naoyuki Miura, Vladimir Tkac, Jan Prokleska, Maciej Chrobak, Zbigniew Tarnawski, Hiroyki Hidaka, Tatsuya Yanagisawa, Vladimir Sechovsky, Hiroshi Amitsuka
    PHYSICA B-CONDENSED MATTER 536 516 - 518 2018年05月 [査読有り][通常論文]
     
    © 2017 Elsevier B.V. Single crystals of ThBe 13 and LuBe 13 have been prepared using aluminum flux method. The crystals structure of both compounds was confirmed to be cubic of the NaZn 13 -type with the lattice parameters a = 10.183(6)Å and a = 10.395(3)Å for LuBe 13 and ThBe 13 , respectively. The low temperature measurements of electrical resistance and ac susceptibility have revealed a BCS-type of superconductivity in ThBe 13 below T c = 125mK. LuBe 13 has been found to be superconducting below T c = 630mK.
  • Hiroyuki Hidaka, Ryoma Nagata, Chihiro Tabata, Yusei Shimizu, Naoyuki Miura, Tatsuya Yanagisawa, Hiroshi Amitsuka
    PHYSICAL REVIEW MATERIALS 2 5 053603-1 - 053603-7 2018年05月 [査読有り][通常論文]
     
    The beryllides MBe13 (M = rare earths and actinides) crystallize in a NaZi(1)-type cubic structure, which can be categorized as a cage-structured compound. In this study, powder x-ray diffraction measurements have been performed on LaBei(1,) SmBei(1,) and UBei(1 )in the temperature range between 7 and 300 K in order to investigate their crystallographic characteristics systematically. They keep the NaZni(1 )-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-II 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 MBei1 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 similar to 60 K.
  • Yasuki Kishimoto, Haruki Matsuno, Hisashi Kotegawa, Hideki Tou, Hiraku Saito, Hiroshi Amitsuka, Yoshiya Homma, Ai Nakamura, Dexin Li, Fuminori Honda, Dai Aoki
    PHYSICA B-CONDENSED MATTER 536 564 - 566 2018年05月 [査読有り][通常論文]
     
    We have performed a susceptibility M/H and B-11 NMR measurements to investigate the static magnetic anisotropy of a single crystal UNi4B. The Knight shift K-11 and the hyperfine coupling constant A(hf) evaluated by K-11-M/H plot show anisotropic behavior between H parallel to[11 (2) over bar0] and H parallel to[0001], reflecting the bulk susceptibility. The evaluated transferred term A(tr) of A(hf) for H parallel to[11 (2) over bar0] is much larger than the one for H parallel to[0001]. The strong hybridization in the [0001]-plane due to a itinerant 5f-electron is strongly associated with the unique magnetic structure in this compound.
  • T. Yanagisawa, S. Mombetsu, H. Hidaka, H. Amitsuka, P. T. Cong, S. Yasin, S. Zherlitsyn, J. Wosnitza, K. Huang, N. Kanchanavatee, M. Janoschek, M. B. Maple, D. Aoki
    PHYSICAL REVIEW B 97 15 155137  2018年04月 [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 Gamma(4)(B-2g) and Gamma(5)(E-g) symmetry modes C-66 and C-44 show elastic softening that is enhanced above 30 T, while the characteristic softening of the Gamma(3)(B-1g) symmetry mode (C-11 - C-12)/2 is suppressed in high magnetic fields. These results underscore the presence of a hybridization-driven Gamma(3)(B-1g) 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 5f(2) configuration. Instead, we present an analysis based on a band Jahn-Teller effect.
  • Hiraku Saito, Kenta Uenishi, Naoyuki Miura, Chihiro Tabata, Hiroyuki Hidaka, Tatsuya Yanagisawa, Hiroshi Amitsuka
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 87 3 33702  2018年03月 [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.
  • Chihiro Tabata, Milan Klicpera, Bachir Ouladdiaf, Hiraku Saito, Michal Valiska, Klara Uhlirova, Naoyuki Miura, Vladimir Sechovsky, Hiroshi Amitsuka
    PHYSICAL REVIEW B 96 21 2017年12月 [査読有り][通常論文]
     
    The magnetic structure of tetragonal UAu2Si2 was investigated by single-crystal neutron-diffraction experiments. Below T-N= 20 K it orders antiferromagnetically with a propagation vector of k = (2/3,0,0) and magnetic moments of uranium ions pointing along the tetragonal c axis. Weak signs of the presence of a ferromagnetic component of magnetic moment were traced out. Taking into account a group theory calculation and experimental results of magnetization and Si-29 nuclear magnetic resonance, the magnetic structure is determined to be a squared-up antiferromagnetic structure, with a stacking sequence (+ + -) of the ferromagnetic ac-plane sheets along the a axis. This result highlights similar magnetic correlations in UAu2Si2 and isostructural URu2Si2.
  • Tsutsui Satoshi, Kobayashi Yoshio, Nakamura Jin, Kubo Michael K, Amagasa Shota, Yamada Yasuhiro, Yoda Yoshitaka, Shimizu Yusei, Hidaka Hiroyuki, Yanagisawa Tatsuya, Amitsuka Hiroshi, Yamada Akira, Higashinaka Ryuji, Matsuda Tatsuma D, Aoki Yuji
    Hyperfine Interactions 238 1 100  Springer International Publishing 2017年11月 [査読有り][通常論文]
     
    Synchrotron-Radiation-based Sm-149 Mossbauer spectroscopy was applied to Sm intermetallics, SmBe13 and SmTi2Al20. Temperature dependence of the Mossbauer parameters in SmBe13 indicate the Sm valence state is purely trivalent. SmBe13 also showed second-order Doppler shift in synchrotron-radiation-based Sm-149 Mossbauer spectroscopy. The Mossbauer parameters obtained in SmTi2Al20 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.
  • Hiroyuki Hidaka, Seigo Yamazaki, Yusei Shimizu, Naoyuki Miura, Chihiro Tabata, Tatsuya Yanagisawa, Hiroshi Amitsuka
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 86 7 074703-1 - 074703-6 2017年07月 [査読有り][通常論文]
     
    The physical properties of single-crystalline SmBe13 with a NaZn13-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 similar to 90 K. Mean-field calculations based on the suggested CEF level scheme can reasonably well reproduce the T dependence of magnetic susceptibility (chi) below similar to 70 K. These results in the paramagnetic state strongly indicate that the 4 f electrons are well localized with the Sm3+ configuration. At low temperatures, the 4 f electrons undergo a magnetic order at T-M similar to 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 SmBe13 below T-M, by comparing with other isostructural MBe13 compounds showing helical-magnetic ordering.
  • Hiroyuki Hidaka, Yusei Shimizu, Seigo Yamazaki, Naoyuki Miura, Ryoma Nagata, Chihiro Tabata, Shota Mombetsu, Tatsuya Yanagisawa, Hiroshi Amitsuka
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 86 2 023704-1 - 023704-4 2017年02月 [査読有り][通常論文]
     
    The thermal and electrical transport properties of single-crystalline LaBe13 have been investigated by specific-heat (C) and electrical-resistivity (rho) measurements. The specific-heat measurements in a wide temperature range revealed the presence of a hump anomaly near 40K in the C(T)= T curve, indicating that LaBe13 has a low-energy Einstein-like-phonon mode with a characteristic temperature of similar to 177 K. In addition, a superconducting transition was observed in the. measurements at the transition temperature of 0.53 K, which is higher than the value of 0.27K reported previously by Bonville et al. Furthermore, an unusual T-3 dependence was found in rho(T) below similar to 50 K, in contrast to the behavior expected from the electron-electron scattering or the electron-Debye phonon scattering.
  • Maiku Abe, Shingo Ebata, Hiroshi Amitsuka, Hiromitsu Uehara, Satomi Tajima, Tomokazu Yoshizawa
    16TH INTERNATIONAL CONFERENCE ON SCIENTOMETRICS & INFORMETRICS (ISSI 2017) 1676 - 1677 2017年 [査読有り]
  • Chihiro Tabata, Naoyuki Miura, Klara Uhlirova, Michal Valiska, Hiraku Saito, Hiroyuki Hidaka, Tatsuya Yanagisawa, Vladimir Sechovsky, Hiroshi Amitsuka
    PHYSICAL REVIEW B 94 21 2016年12月 [査読有り][通常論文]
     
    Single-crystalline UAu$_2$Si$_2$ 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 UAu$_2$Si$_2$ 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 UAu$_2$Si$_2$ with large enhancement of the electronic specific heat coefficient of $\gamma$ $\sim$ 150 mJ/K$^2$mol 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 $\sim$ 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 isostructural U$T_2$Si$_2$ compounds.
  • 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.
  • Tsutsui Satoshi, Masuda Ryo, Kobayashi Yasuhiro, Yoda Yoshitaka, Mizuuchi Kota, Shimizu Yusei, Hidaka Hiroyuki, Yanagisawa Tatsuya, Amitsuka Hiroshi, Iga Fumitoshi, Seto Makoto
    Journal of the Physical Society of Japan 85 8 083704  The Physical Society of Japan 2016年08月 [査読有り][通常論文]
     
    Synchrotron radiation Sm-149 Mossbauer spectroscopy in the energy domain has successfully been carried out on Sm2O3, SmBe13, and SmB6. 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-energy-resolution". 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 Sm-149 Mossbauer effect. We discussed the fluctuation of the Sm valence in SmB6.
  • 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04月 [査読有り][通常論文]
     
    Our ultrasound results obtained in pulsed magnetic fields show that the filled-skutterudite compound SmOs$_4$Sb$_{12}$ has the $\Gamma_{67}$ quartet crystalline-electric-field ground state. This fact suggests that the multipolar degrees of freedom of the $\Gamma_{67}$ quartet play an important role in the unusual physical properties of this material. On the other hand, the elastic response below $\approx$ 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, Shunichiro Kittaka, Toshiro Sakakibara, Yoshinori Haga, Etsuji Yamamoto, Hiroshi Amitsuka, Yasumasa Tsutsumi, Kazushige Machida
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 400 52 - 55 2016年02月15日 [査読有り][通常論文]
     
    In order to gain insight into the superconducting (SC) gap of UBe13, we studied its quasiparticle excitations by means of heat-capacity measurements. Quite unexpectedly, we found the isotropic C(H) alpha H behavior in low fields at low temperatures, implying the absence of nodal quasiparticle excitations. This result indicates that the SC gap in UBe13 is fully open over the Fermi surfaces. Furthermore, we observed a characteristic oscillation of heat capacity both in the SC and non-Fermi-liquid normal states above similar to 2 T, and the angular variation of heat capacity possibly originates from anisotropic magnetic response of the heavy-electron state. Our result regarding the low-energy quasiparticle excitations in the SC and normal states will be a clue to understand the unusual nature of UBe13. (C) 2015 Elsevier BY. All rights reserved.
  • 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 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.
  • 柳澤 達也, Kanchanavatee N., Janoschek M., Maple M. B., 青木 大, 門別 翔太, 日高 宏之, 網塚 浩, Cong P. T., Yashin S., Zherlitsyn S., Wosnitza J., Huang K.
    日本物理学会講演概要集 71 1960 - 1960 一般社団法人 日本物理学会 2016年
  • 田端 千紘, 三浦 植幸, Uhlířová Klára, Vališka Michal, Sechovský Vladimír, 齋藤 開, 日高 宏之, 柳澤 達也, 網塚 浩
    日本物理学会講演概要集 71 1752 - 1752 一般社団法人 日本物理学会 2016年 

    UAu_2_Si_2_は約19Kで強磁性的な秩序を起こすということを除いて、その低温物性は明らかになっていなかった。最近、我々は本物質の単結晶育成に初めて成功し、詳細な基礎物性測定やNMR測定から19Kの秩序が強磁性ではなく、自発磁化を伴うが本質的には反強磁性であることを明らかにしてきた。本講演では磁気抵抗測定の結果を紹介し、輸送現象の側面から本物質の秩序に伴う磁性の変化について議論する。

  • 三浦 植幸, Uhlířová Klára, Prchal Jiří, 田端 千紘, Sechovský Vladimír, 日高 宏之, 柳澤 達也, 網塚 浩
    日本物理学会講演概要集 71 1755 - 1755 一般社団法人 日本物理学会 2016年 

    UBe_13_はエキゾチックな超伝導を示す重い電子系であり、また、転移温度以上では非フェルミ流体異常を示す。磁性希釈極限系Th_1-x_U_x_Be_13_$(x \leq 0.11)$ では通常フェルミ状態が実現することを我々は既に明らかにしているが、$x = 1$における非フェルミ状態へどのように移行するのかは自明ではない。本公演では全U濃度($0 \leq x \leq 1$)における低温物性(磁化率、電気抵抗、比熱)の実験結果を紹介し、UBe_13_における非フェルミ流体異常の起源について議論する。

  • 清水 悠晴, 橘高 俊一郎, 河野 洋平, 榊原 俊郎, 芳賀 芳範, 山本 悦嗣, 網塚 浩, 町田 一成
    日本物理学会講演概要集 71 1963 - 1963 一般社団法人日本物理学会 2016年
  • 藤岡 正弥, 石丸 学, 渋谷 泰蔵, 神原 陽一, 田畑 千紘, 網塚 浩, 田中 将嗣, 高野 義彦, 海住 英生, 西井 準治
    日本物理学会講演概要集 71 1989 - 1989 一般社団法人日本物理学会 2016年
  • 田端 千紘, 井原 慶彦, 新村 省悟, 三浦 植幸, 齋藤 開, 日高 宏之, 柳澤 達也, 網塚 浩
    日本物理学会講演概要集 71 1961 - 1961 一般社団法人 日本物理学会 2016年
  • 清水 悠晴, 河野 洋平, 橘高 俊一郎, 芳賀 芳範, 山本 悦嗣, 網塚 浩, 榊原 俊郎
    日本物理学会講演概要集 71 1754 - 1754 一般社団法人 日本物理学会 2016年 

    UBe13(立方晶NaZn13構造)は低温で非常に大きな電子比熱を持ち、極低温約0.8Kで非従来型超伝導を示す重い電子系超伝導体である。本研究では、UBe13における異常な超伝導・非フェルミ液体常伝導状態の起源の理解を深めるため、極低温精密物性測定を行っている。講演では[111]軸方向に関する極低温磁化測定の結果をこれまでに発表した[100]方向の結果と併せて報告する。

  • 岸本 恭来, 小手川 恒, 藤 秀樹, 齋藤 開, 網塚 浩, 本間 佳哉, 仲村 愛, 李 徳新, 本多 史憲, 青木 大
    日本物理学会講演概要集 71 2163 - 2163 一般社団法人 日本物理学会 2016年 

    UNi4BはT〜20 Kでトロイダル磁気秩序が発現する。この磁気状態で電流を印加することにより磁化を増強など非常に興味深い振る舞いを示すことが理論的に予測されている。今回我々は、電流を印加しながらNMR実験を行うことでUNi4Bの電流磁気効果を検証した。当日はその結果を発表する予定である。

  • 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]
     
    © 2016 American Physical Society. 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.
  • Masaya Fujioka, Manabu Ishimaru, Taizo Shibuya, Yoichi Kamihara, Chihiro Tabata, Hiroshi Amitsuka, Akira Miura, Masashi Tanaka, Yoshihiko Takano, Hideo Kaiju, Junji Nishii
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 138 31 9927 - 9934 2016年 [査読有り][通常論文]
  • 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 012032-1 - 012032-6 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.
  • D. Rauch, P. Horenburg, S. Hartwig, F. J. Litterst, S. Suellow, H. Luetkens, C. Baines, S. Yamazaki, H. Hidaka, H. Amitsuka, E. Bauer
    PHYSICAL REVIEW B 92 11 2015年09月08日 [査読有り][通常論文]
     
    © 2015 American Physical Society. We present a study of the alloying series of the noncentrosymmetric f-electron intermetallic CePt3B1-xSix by means of muon spin rotation and relaxation measurements. In addition, we include a high-pressure magnetization investigation of the stoichiometric parent compound CePt3B. From our data we establish the nature of the magnetic ground state properties of the series, derive the ordered magnetic moment as function of stoichiometry, and gain insight into the evolution of the symmetry of the ordered magnetic state with x. We thus can verify the notion that the behavior of the sample series can essentially be understood within the framework of the Doniach phase diagram. Further, our findings raise the issue of the role the Dzyaloshinskii-Moriya magnetic interaction plays in correlated electron materials and its effect on magnetic fluctuations in such materials.
  • 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]
     
    © 2015 Elsevier B.V. All rights reserved. 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 ∼2.1GPa, 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 ∼ 4 K in this unknown phase. The anomaly shifts to lower temperature with increasing pressure, and shows a tendency to reach absolute zero at ∼6GPa, 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 ( PCEP , TCEP ) ∼(3.2GPa,200K). This suggests that the crystal symmetry of the unidentified phase above ∼2.1GPa is also tetragonal.
  • Yusei Shimizu, Shunichiro Kittaka, Toshiro Sakakibara, Yoshinori Haga, Etsuji Yamamoto, Hiroshi Amitsuka, Yasumasa Tsutsumi, Kazushige Machida
    PHYSICAL REVIEW LETTERS 114 14 147002-1 - 147002-6 2015年04月 [査読有り][通常論文]
     
    Low-energy quasiparticle excitations in the superconducting (SC) state of UBe13 were studied by means of specific-heat (C) measurements in a rotating field. Quite unexpectedly, the magnetic-field dependence of C(H) is linear in H with no angular dependence at low fields in the SC state, implying that the gap is fully open over the Fermi surfaces, in stark contrast to previous expectations. In addition, a characteristic cubic anisotropy of C(H) was observed above 2 T with a maximum (minimum) for H parallel to[001] ([111]) within the (1 (1) over bar0) plane, in the normal as well as in the SC states. This oscillation possibly originates from the anisotropic response of the heavy quasiparticle bands, and might be a key to understand the unusual properties of UBe13
  • 小濱 芳允, 横山 淳, 金道 浩一, 網塚 浩
    日本物理学会講演概要集 70.1 2299  一般社団法人 日本物理学会 2015年
  • 田端 千紘, 井原 慶彦, 網塚 浩, 三浦 植幸, Uhlirova Klara, Valiska Michal, Sechovsky Vladimir, 新村 省悟, 齋藤 開, 日高 宏之, 柳澤 達也
    日本物理学会講演概要集 70 1667 - 1667 一般社団法人 日本物理学会 2015年
  • 稲垣 宏幸, Zherlitsyn S., Wosnitza J., 門別 翔太, 清水 悠晴, 柳澤 達也, 日高 宏之, 網塚 浩, Yazici D., Maple M. B., Cong P. T.
    日本物理学会講演概要集 70 1673 - 1673 一般社団法人 日本物理学会 2015年
  • 柳澤 達也, Wosnitza J., Yazici D., White B. D., Maple M. B., 門別 翔太, 日高 宏之, 網塚 浩, Cong P. T., Zherlitsyn S.
    日本物理学会講演概要集 70 2032 - 2032 一般社団法人 日本物理学会 2015年
  • 田端 千紘, 井原 慶彦, 新村 省悟, 齋藤 開, 三浦 植幸, 日高 宏之, 柳澤 達也, 網塚 浩
    日本物理学会講演概要集 70 2347 - 2347 一般社団法人 日本物理学会 2015年
  • 清水 悠晴, 河野 洋平, 榊原 俊郎, 橘高 俊一郎, 芳賀 芳範, 山本 悦嗣, 網塚 浩
    日本物理学会講演概要集 70 2350 - 2350 一般社団法人日本物理学会 2015年
  • 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 012095-1 - 012095-8 2015年 [査読有り][通常論文]
     
    Conference proceedings, SCES2014
  • 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] .
  • J. Engelke, D. Menzel, H. Hidaka, T. Seguchi, H. Amitsuka
    PHYSICAL REVIEW B 89 14 144413  2014年04月 [査読有り][通常論文]
     
    In MnSi thin films themagnetic properties of the B20 compound are influenced by induced uniaxial anisotropy. In comparison to bulk MnSi the critical magnetic fields are enhanced and the Skyrmion phase is found to be enlarged within the magnetic phase diagram. Furthermore the ordering temperature depends on the film thickness reaching 43 K for films of around 10 nm and is considerably higher than in bulk crystals (T-c,T-bulk = 29 K). In bulk MnSi the ordering temperature can be reduced by pressure, where at 1.46 GPa the magnetic order is completely suppressed and a non-Fermi-liquid behavior characterized by a T-3/2 law of the resistivity is observed. We present resistance measurements on MnSi thin films under applied pressure of up to 3.44 GPa. Qualitatively, the behavior is similar to bulk MnSi. However, the critical pressure is considerably enhanced to 3.1 GPa, which is assumed to be a consequence of strain. At high pressure non-Fermi-liquid behavior evidenced by a T-3/2 behavior of the resistance is observed up to T-lin = 30 K, i. e., in a larger temperature range than for bulk MnSi. Uniaxial anisotropy might play an important role in this breakdown of Fermi-liquid behavior, since it stabilizes nontrivial spin structures.
  • 田端 千紘, 山崎 聖悟, 伊藤 孝, 髭本 亘, 三浦 植幸, 清水 悠晴, 日高 宏之, 柳澤 達也, 網塚 浩
    日本物理学会講演概要集 69 553 - 553 一般社団法人 日本物理学会 2014年
  • 松野 治貴, 網塚 浩, 森田 恭平, 小手川 恒, 藤 秀樹, 芳賀 芳範, 山本 悦嗣, 大貫 惇睦, 清水 悠晴, 柳澤 達也
    日本物理学会講演概要集 69 645 - 645 一般社団法人 日本物理学会 2014年
  • 松野 治貴, 大貫 惇睦, 森田 恭平, 小手川 恒, 藤 秀樹, 清水 悠晴, 柳澤 達也, 網塚 浩, 芳賀 芳範, 山本 悦嗣
    日本物理学会講演概要集 69 363 - 363 一般社団法人 日本物理学会 2014年
  • 日浦 健太, 柳澤 達也, 門別 翔太, 村住 太郎, 稲垣 宏幸, 日高 宏之, 網塚 浩, 立岩 尚之, 芳賀 芳範
    日本物理学会講演概要集 69 460 - 460 一般社団法人 日本物理学会 2014年
  • 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]
  • Takeshi Mito, Midori Hattori, Gaku Motoyama, Yoshio Sakai, Takehide Koyama, Koichi Ueda, Takao Kohara, Makoto Yokoyama, Hiroshi Amitsuka
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 82 12 2013年12月 [査読有り]
     
    The local symmetry at the Ru(4d) and Si(4e) sites in URu2Si2 was investigated above and below the hidden-order temperature T-O = 17.5K by measuring Ru-101-nuclear quadrupole resonance (NQR) and Ru-99-nuclear magnetic resonance (NMR) in single-crystalline samples and Ge-73-NMR in a 10%-Ge-73-substituted polycrystalline sample. For both sites, no evidence of symmetry change below T-O was observed. The asymmetry parameter eta of the electric field gradient, which reflects the local rotation symmetry, was estimated to be zero with accuracies of 0.0010-0.0015 and 0.05 for the 4d and 4e sites, respectively. The results suggest that the symmetry change at T-O is extremely small or intrinsically invisible by the present method.
  • 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 2013年11月26日 
    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.
  • 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 88 19 195150-1 - 195150-5 2013年11月 [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 URu2Si2 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.
  • Ikuto Kawasaki, Isa Watanabe, Hiroshi Amitsuka, Keisuke Kunimori, Hiroshi Tanida, Yoshichika Onuki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 82 8 2013年08月 [査読有り][通常論文]
     
    The superconducting properties of the noncentrosymmetric superconductor LaPt3Si were investigated by mu SR spectroscopy. Within experimental accuracy, spontaneous internal fields were not observed in the superconducting phase by zero-field mu SR experiments. Transverse-field mu SR experiments revealed the coexistence of the intermediate and mixed states in the superconducting phase, which are characteristic features of type-I and type-II superconductors, respectively. We found that the observed anomalous field distribution is consistent with the results of a recent numerical calculation for type-1.5 superconductors.
  • 松野 治貴, 網塚 浩, 森田 恭平, 小手川 恒, 藤 秀樹, 芳賀 芳範, 山本 悦嗣, 大貫 惇睦, 清水 悠晴, 柳澤 達也
    日本物理学会講演概要集 68 554 - 554 一般社団法人 日本物理学会 2013年
  • 三浦 植幸, 清水 悠晴, 山崎 聖悟, 齋藤 開, 田端 千紘, 門別 翔太, 日高 宏之, 柳澤 達也, 網塚 浩
    日本物理学会講演概要集 68 555 - 555 一般社団法人 日本物理学会 2013年
  • 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...
  • Takahiro Nakada, Makoto Yokoyama, Chihiro Tabata, Hideki Igarashi, Hiroyuki Hidaka, Hiroshi Amitsuka, Kenichi Tenya, Taku J. Sato
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 81 SUPPL.B SB020(1) - SB020(4) 2012年12月 [査読有り][通常論文]
     
    The nature of competition between incommensurate (IC) and commensurate (C) antiferromagnetic (AF) orders in UPd2Si2 was investigated by performing elastic neutron scattering experiments under uniaxial stress σ. It is found that applying σ along tetragonal [010] direction reduces the IC-AF order, and then stabilizes the C-AF order. The transition temperature from IC- to C-AF phases TNl is enhanced from 109 K (σ = 0) to 112.5 K at (0.8 GPa), while the onset of IC-AF transition TNh is unchanged from 132 K under σ. In addition, c-axis component qz of the IC-AF modulation at 115 K also increases from 0.736 (σ = 0) to 0.747 (0.8 GPa). The magnitude of C-AF moment at 5 K is estimated to be 2.2 μB/U in the entire σ range presently investigated (σ ≤ 0.8 GPa). These features are similar to those obtained from the investigations using hydrostatic pressure p, indicating that applications of p and σ∥ [010] commonly induce the crystal strains which inherently affect a delicate balance of frustrated magnetic interactions between uranium 5f moments. © 2012 The Physical Society of Japan.
  • Yusei Shimizu, Yoshinori Haga, Yoichi Ikeda, Tatsuya Yanagisawa, Hiroshi Amitsuka
    PHYSICAL REVIEW LETTERS 109 21 2012年11月20日 [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.
  • Shigeru Takagi, Shu Ishihara, Makoto Yokoyama, Hiroshi Amitsuka
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 81 11 2012年11月 [査読有り][通常論文]
     
    The hidden order (HO) in URu2Si2 has been investigated by both Si-29 and Ru-99 NMR on a single crystal. Tiny, but finite additional broadening of the spectrum in the HO phase in both Si-29 and Ru-99 NMR with external magnetic field applied along the crystallographic [100] or [110] direction, and its persistence as H-ext -> 0 in Si-29 NMR clearly indicate the existence of internal hyperfine field, and the breaking of the time-reversal symmetry in the HO phase can therefore be concluded. We discuss which symmetry of the D-4h symmetry group of the URu2Si2 crystal structure is compatible with the observed dependence on the crystal-axis direction of the existence or nonexistence of the internal hyperfine field. Then, by imposing a strong constraint that the wave-vector of the HO is also Q(0) = [0, 0, 1], the wave-vector of the pressure-induced antiferromagnetism, we show that the two-dimensional representation E-remains as the only possible candidate for the HO symmetry. Since dipoles are obviously excluded from the major HO parameter, we conclude the E-multipole (octupole or triakontadipole) to be the HO parameter. We further discuss that the E- multipole, but with no associated dipoles, seems to be a key feature of the HO in URu2Si2.
  • Yoichi IKEDA, Shingo ARAKI, Tatsuo C. KOBAYASHI, Yusei SHIMIZU, Tatsuya YANAGISAWA, Hiroshi AMITSUKA
    Journal of the Physical Society of Japan 81 8 083701-1 - 083701-4 2012年08月 [査読有り][通常論文]
     
    The effects of Ni substitution on Ce(Cu1-xNix)(2)Si-2 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 greater than or similar to 0: 12). The characteristic T-linear dependence of the resistivity has been observed at approximately x similar to 0.10 together with a sign of superconductivity. The variation of n in the form of rho - rho(0) = aT(n) against T-1(max), at which the resistivity peaks, coincides with the case of high-pressure experiments on pure CeCu2Si2. The anomalous T-linear behavior appears to occur in the crossover region from the Kondo regime to the valence fluctuation regime rather than in the conventional antiferromagnetic quantum critical region.
  • T. Mito, M. Hattori, G. Motoyama, Y. Sakai, T. Koyama, K. Ueda, T. Kohara, M. Yokoyama, H. Amitsuka
    INTERNATIONAL CONFERENCE ON STRONGLY CORRELATED ELECTRON SYSTEMS (SCES 2011) 391 2012年 
    In order to study local symmetries at the 4e(Si)- and 4d(Ru)-sites above and below hidden order transition temperature T-O = 17.5 K in URu2Si2, we have investigated the nuclear quadrupole interaction by Ge-73-nuclear magnetic resonance (NMR) measurement on a 10% Ge-73-substituted sample URu2(Si0.9Ge0.1)(2), and by Ru-101-nuclear quadrupole resonance (NQR) measurement on a pure single crystal sample. The present Ge-73-NMR measurements do not give any evidence for change in the local symmetry at 4e-site within experimental accuracy. On the other hand, the precise measurement of Ru-101-NQR frequency has detected an anomaly just below T-O as sensitively as the thermal expansion measurement dose. Its temperature dependence shows a linear relation with that of the in-plane lattice parameter, which may be a clue to clarify a modification in microscopic charge distribution at T-O.
  • 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]
  • 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 012019-1 - 012019-4 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.
  • T. Yanagisawa, H. Saito, Y. Watanabe, Y. Shimizu, H. Hidaka, H. Amitsuka
    INTERNATIONAL CONFERENCE ON STRONGLY CORRELATED ELECTRON SYSTEMS (SCES 2011) 391 012079-1 - 012079-4 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.
  • 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.
  • Yuji Furukawa, Yuzuru Sumida, Ken-ichi Kumagai, Ferdinando Borsa, Hiroyuki Nojiri, Yusei Shimizu, Hiroshi Amitsuka, Ken-ichi Tenya, Paul Koegerler, Leroy Cronin
    INTERNATIONAL CONFERENCE ON FRUSTRATION IN CONDENSED MATTER (ICFCM) 320 012047-1 - 6 2011年09月28日 [査読有り][通常論文]
     
    Static and dynamical properties of Cu2+ (3d(9); S = 1/2) spins in a twisted Heisenberg triangular spin tube, [(CuCl(2)tachH)(3)Cl]Cl-2, have been investigated by nuclear magnetic resonance (NMR) and magnetization measurements in the temperature range T = 0.05-300 K. Magnetization curves below 0.5 K show a clear change in slope around 5 T, attributed to a signature of 1/3 plateau in magnetization. From a systematic measurement of nuclear spin-lattice relaxation rates as a function of temperature and external field, the fluctuation frequency of Cu2+ spins is found to decrease with decreasing temperature, revealing an unusual slow spin dynamics at low temperatures.
  • Takeshi Mito, Midori Hattori, Gaku Motoyama, Hideki Sakai, Takehide Koyama, Koichi Ueda, Takao Kohara, Makoto Yokoyama, Hiroshi Amitsuka
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 2011年07月 [査読有り][通常論文]
     
    In order to investigate the local symmetry at the Si(4e)-site above and below hidden order temperature T-O = 17.5 K in URu2Si2, we have carried out Ge-73-nuclear magnetic resonance (NMR) measurement on 10% Ge-73-substituted sample URu2(Si0.9Ge0.1)(2). The specific heat measurement on the present sample shows a clear second-order transition, indicating that the hidden order is still a bulk property. Besides, equally split Ge-73-NMR lines due to the nuclear quadrupole interaction gives evidence for fairly uniform electric-field gradient at the Ge-substituted sites, Although this is the first attempt to investigate the local symmetry at the 4e-site by proving electric interactions, no evidence for symmetry lowering below T-O has been obtained at present.
  • Hiroyuki Hidaka, Sosuke Takahashi, Yusei Shimizu, Tatsuya Yanagisawa, Hiroshi Amitsuka
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 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.
  • Yusei Shimizu, Yoichi Ikeda, Takumi Wakabayashi, Kenichi Tenya, Yoshinori Haga, Hiroyuki Hidaka, Tatsuya Yanagisawa, Hiroshi Amitsuka
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 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].
  • Tatsuya Yanagisawa, Naoyuki Tateiwa, Taichi Mayama, Hitoshi Saito, Hiroyuki Hidaka, Hiroshi Amitsuka, Yoshinori Haga, Yuichi Nemoto, Terutaka Goto
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 SA105-1 - SA105-3 2011年07月 [査読有り][通常論文]
     
    Conference proceedings, Heavy Electrons 2010 (ICHE2010)
  • Kazuyuki Matsuhira, Chihiro Sekine, Makoto Wakeshima, Yukio Hinatsu, Hiroshi Amitsuka, Hiroyuki Mitamura, Toshiro Sakakibara, Seishi Takagi
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 2011年07月 [査読有り][通常論文]
     
    We report the specific heat and thermoelectric power S (T) of filled skutterudite PrOs4P12, which has a Gamma(1) crystalline electric field ground state. The electronic specific heat coefficient gamma of PrOs4P12 indicates a weak enhanced value (gamma(Pr)/gamma(La) similar to 2.3) in comparison with that of LaOs4P12. The influence in the specific heat by c-f hybridization effect is discussed. S (T) of PrOs4P12 exhibits a small maximum around 10 K although there is no such maximum for LnOs(4)P(12) (Ln = La, Nd, and Gd). Consequently, S/T for Ln = Pr increases below 20 K, which is consistent with the enhanced gamma. We also report the magnetization process to 46 Tin PrOs4P12.
  • 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 ...
  • Tatsuya Yanagisawa, Yoichi Ikeda, Hitoshi Saito, Hiroyuki Hidaka, Hiroshi Amitsuka, Koji Araki, Mitsuhiro Akatsu, Yuichi Nemoto, Terutaka Goto, Pei-Chun Ho, Ryan E. Baumbach, M. Brian Maple
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 4 043601-1-043601-4  2011年04月 [査読無し][通常論文]
     
    Elastic properties of the filled skutterudite compound SmOs4Sb12 have been investigated by ultrasonic measurements. The elastic constant C-11(omega) shows two ultrasonic dispersions at similar to 15 and similar to 53K for frequencies omega between 33 and 316 MHz, which follow a Debye-type formula with Arrhenius-type temperature-dependent relaxation times and remain unchanged even with applied magnetic fields up to 10 T. The corresponding activation energies were estimated to be E-2 = 105K and E-1 = 409 K, respectively. The latter, E-1, is the highest value reported thus far in the Sb-based filled skutterudites. The presence of magnetically robust ultrasonic dispersions in SmOs4Sb12 implies a possibility that an emergence of a magnetically insensitive heavy fermion state in this system is associated with a novel local charge degree of freedom, which causes the ultrasonic dispersion.
  • H. Hidaka, A. Tanaka, S. Takahashi, T. Yanagisawa, H. Amitsuka
    INTERNATIONAL CONFERENCE ON STRONGLY CORRELATED ELECTRON SYSTEMS (SCES 2010) 273 012032-1-012032-4  2011年 [査読無し][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 012065-1-012065-4  2011年 [査読無し][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.
  • 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 012084-1-012084-4  2011年 [査読無し][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.
  • Anna Toth, Premala Chandra, Piers Coleman, Gabriel Kotliar, Hiroshi Amitsuka
    Physical Review B 82 23 235116-1-235116-4  2010年12月 [査読無し][通常論文]
     
    The dilute Kondo compound, Th1-xUxRu2Si2, displays non-Fermi-liquid behavior but no zero-point entropy; it thus appears to elude description by known single-ion models. It may also provide a clue to the underlying local degrees of freedom in its dense counterpart, URu2Si2. Here we use high-resolution magnetization studies to cross-check the thermodynamic consistency of previous experiments. Measurement of the field dependence of the temperature scale, T-F(H), associated with Fermi-liquid behavior probes the nature of the underlying impurity fixed point. We find that T-F(H) grows linearly with applied field, in contrast to the quadratic form expected for the two-channel Kondo model. We use a scaling argument to show that the observed behavior of T-F(H) is consistent with the absence of zero-point entropy, suggesting novel impurity behavior in this material. More generally, we suggest the field magnetization as a probe of single-ion physics and make predictions for its behavior in other actinide compounds.
  • T. Kurosawa, N. Momono, H. Amitsuka, M. Oda, M. Ido
    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 470 S42 - S43 2010年12月 [査読無し][通常論文]
     
    We investigate the residual gamma-value of the specific heat under the magnetic field H for Ni-substituted La2-xSrxCu1-yNiyO4(x = 0.15, y = 0.015; T-c = 26.5K) and La2-xSrxCuO4(x = 0.15; T-c = 37.0 K) crystals. The reduction of the SC gap estimated by applying the Volovik's relation to Delta gamma vs. H curve is too small to explain the suppression of T-c in Ni-substituted samples, where Delta gamma is the change of gamma under H. We point out the possibility that T-c of Ni-substituted sample decreases through the reduction of the area of the coherent nodal d-wave gap in momentum space, which will play an important role in causing the superconductivity. (C) 2009 Elsevier B.V. All rights reserved.
  • M. Bleckmann, A. Otop, S. Suellow, R. Feyerherm, J. Klenke, A. Loose, R. W. A. Hendrikx, J. A. Mydosh, H. Amitsuka
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 322 17 2447 - 2453 2010年09月 [査読無し][通常論文]
     
    We present a detaild comparison of the physical properties of as-cast and annealed single crystalline UPt2Si2. We discuss the implications of such phase transitions occuring at comparatively low temperatures for the ground state properties of heavy fermion systems and related correlated electron materils. (C) 2010 Elsevier B.V. All rights reserved.
  • H. Nobukane, K. Inagaki, K. Ichimura, K. Yamaya, S. Takayanagi, I. Kawasaki, K. Tenya, H. Amitsuka, K. Konno, Y. Asano, S. Tanda
    PHYSICA B-CONDENSED MATTER 405 11 S277 - S278 2010年06月 [査読無し][通常論文]
     
    We have found parity-violating current-voltage (I-V) curves in a single domain of Sr2RuO4 superconductors The Induced voltage V is an even function of bias current I below superconducting transition temperature The anomalous I-V curves show that positive voltage is detected regardless of the current direction The result implies the parity violation of I-V curves (C) 2009 Elsevier B V All rights reserved
  • 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]
  • M Yokoyama, Y Ikeda, I Kawasaki, D Nishikawa, K Tenya, K Kuwahara, H Amitsuka
    Journal of Physics: Conference Series 200 1 012239 - 012239 2010年01月01日 [査読有り]
     
    We investigated effects of magnetic field H on antiferromagnetic (AF) structures in CeRh1-xCoxIn5 by performing the elastic neutron scattering measurements. By applying H along the [1 (1) over bar0] direction, the incommensurate AF state with the propagation vector of q(h1) = (1/2, 1/2, 0.297) observed at H = 0 is replaced by the commensurate AF state with the q(c2) = (1/2, 1/2, 1/4) modulation above 2 T for x = 0.23, while the AF states with the q(c1) = (1/2, 1/2, 1/2) and q(h2) = (1/2, 1/2, 0.42) modulations seen at H = 0 change into a single q(c1)-AF state above similar to 1.6 T for x = 0.7. These results suggest the different types of AF correlation for Co concentrations of 0.23 and 0.7 in an applied magnetic field H.
  • Hiroyoshi Nobukane, Katsuhiko Inagaki, Satoshi Tsuchiya, Yasuhiro Asano, Koichi Ichimura, Kazuhiko Yamaya, Shigeru Takayanagi, Ikuto Kawasaki, Kenichi Tenya, Hiroshi Amitsuka, Satoshi Tanda
    JAPANESE JOURNAL OF APPLIED PHYSICS 49 2 020209-1-020209-3  2010年 [査読無し][通常論文]
     
    We report our approach to measuring the transport properties in a single chiral order parameter domain of microscale Sr2RuO4 single crystals. Sr2RuO4 single crystals were grown by the solid-phase reaction. Microscale single crystals were deposited from a dispersed liquid, and selected from the result of the chemical composition and crystallinity of the dispersed crystals. The selected crystals attached to gold electrodes show superconducting properties. We also found the anomalous current-voltage characteristics that show that induced voltage is an even function of bias current. (C) 2010 The Japan Society of Applied Physics
  • T. Yanagisawa, H. Saito, T. Mayama, Y. Ikeda, H. Hidaka, M. Yokoyama, H. Amitsuka
    INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009) 200 012236-1-012236-5  2010年 [査読無し][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.
  • 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 012007-1-012007-4  2010年 [査読無し][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).
  • Yoichi Ikeda, Makoto Yokoyama, Daichi Nishikawa, Hiroyuki Hidaka, Tatsuya Yanagisawa, Kenichi Tenya, Shuzo Kawarazaki, Taku J. Sato, Hideki Yoshizawa, Hiroshi Amitsuka
    INTERNATIONAL CONFERENCE ON MAGNETISM (ICM 2009) 200 SECTION 1 012065-1-012065-4  2010年 [査読無し][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.
  • 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 [査読無し][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.
  • 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 [査読無し][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.
  • Hiroyuki Hidaka, Yoichi Ikeda, Ikuto Kawasaki, Tatsuya Yanagisawa, Hiroshi Amitsuka
    PHYSICA B-CONDENSED MATTER 404 19 3005 - 3007 2009年10月 [査読無し][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.
  • M. Yokoyama, I. Kawasaki, S. Oinuma, N. Oyama, K. Tenya, H. Amitsuka
    PHYSICA B-CONDENSED MATTER 404 17 2539 - 2542 2009年09月 [査読無し][通常論文]
     
    We performed the elastic neutron scattering experiments on the mixed compounds CeRh1-xCoxIn5, and found that doping Co into CeRhIn5 dramatically changes the antiferromagnetic (AF) structure. The incommensurate AF state with the propagation vector of q(h) = (1/2,1/2,similar to 0.3) observed in pure CeRhIn5 is suppressed with increasing x, and new AF states with an incommensurate q(1) = (1/2,1/2,similar to 0.4) and a commensurate q(c) = (1/2,1/2,1/2) modulations simultaneously develop near the AF quantum critical point: x(c)similar to 0.8. These results suggest that the AF correlations with the q(c) and q(1) modulations enhanced in the intermediate Co concentrations may play a crucial role in the evolution of the superconductivity observed above x similar to 0.4. (C) 2009 Elsevier B.V. All rights reserved.
  • H. Nobukane, K. Inagaki, K. Ichimura, K. Yamaya, S. Takayanagi, I. Kawasaki, K. Tenya, H. Amitsuka, K. Konno, Y. Asano, S. Tanda
    SOLID STATE COMMUNICATIONS 149 29-30 1212 - 1215 2009年08月 [査読無し][通常論文]
     
    We observed an unconventional parity-violating vortex in single domain Sr2RuO4 single crystals using a transport measurement. The current-voltage characteristics of submicron Sr2RuO4 show that the induced voltage has anomalous components which are even functions of the bias current. The results may suggest that the vortex itself has a helical internal structure characterized by a Hopf invariant (a topological invariant). We also discuss that the hydrodynamics of such a helical vortex causes the parity violation to retain the topological invariant. (C) 2009 Elsevier Ltd. All rights reserved.
  • Y. H. Matsuda, J. L. Her, T. Inami, K. Ohwada, Z. W. Ouyang, K. Okada, H. Nojiri, A. Mitsuda, H. Wada, K. Yoshimura, H. Amitsuka, N. Kawamura, M. Suzuki, A. Kotani
    14TH INTERNATIONAL CONFERENCE ON X-RAY ABSORPTION FINE STRUCTURE (XAFS14), PROCEEDINGS 190 012019-1-012019-6  2009年 [査読無し][通常論文]
     
    L-edge X-ray magnetic circular dichroism (XMCD) and X-ray absorption spectra (XAS) in several rare-earth elements have been studied in high magnetic fields up to 40 T using a pulsed magnet. XMCD spectrum of Eu in a typical valence fluctuating compound, EuNi2(Si0.18Ge0.82)(2), shows a characteristic two peak structure, reflecting the valence fluctuation. However, in another valence fluctuating compound, YbInCu4, it is found that the XMCD spectrum of Yb shows only a single peak. In contrast to XMCD, two absorption bands in XAS are observed in both EuNi2(Si0.18Ge0.82)(2) and YbInCu4. The intensity ratio between the two absorption bands changes significantly with increasing magnetic field in these materials, suggesting the field-induced valence change. The high magnetic field XMCD and XAS measurements have also been conducted in an antiferromagnetic heavy fermion compound CeRh2Si2. The Ce valence is found to be nearly trivalent and insensitive to magnetic field. The XMCD at Ce L-2-edge increases rapidly around 26 T corresponding to the metamagnetic transition. The XMCD spectra in CeRh2Si2 at high magnetic fields show only a single peak as was reported in a heavy fermion ferromagnetic compound CeRu2Ge2 [1].
  • H. Nobukane, S. Tsuchiya, K. Konno, K. Inagaki, S. Tanda, I. Kawasaki, H. Amitsuka, K. Tenya, Y. Maeno
    25TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT25), PART 5 150 052187-1-052187-4  2009年 [査読無し][通常論文]
     
    We observed the power law and the critical exponent of quantum phase transitions by measuring a transient response in an Al/AlOx/Al junction of U(1) superconductors and Sr2RuO4 single crystals of SU(2) superconductors, when magnetic field decreased rapidly from more than the critical field to zero magnetic field below T = 0.1 K. In the Al/AlOx/Al junction, the result shows that the domain length xi is a power function of the quench time tau(Q). The critical exponent is 0.30 +/- 0.01. Moreover, in the Sr2RuO4 crystal, the result shows xi is a power function of tau(Q) and the critical exponent is 0.40 +/- 0.01. From the results of U(1) and SU(2) superconductors, we consider the critical exponents observed by the quenching are derived by a mean-field value in charged systems. Using typical U(1) and SU(2) superconductors, we find that the magnetic quench is efficient method to study formation processes of topological defects for a quantum phase transition near T = 0. http://iopscience.iop.org/article/10.1088/1742-6596/150/5/052187/pdf
  • M. Yokoyama, N. Oyama, H. Amitsuka, S. Oinuma, I. Kawasaki, K. Tenya, M. Matsuura, K. Hirota, T. J. Sato
    Physical Review 77 22 224501-1-224501-5  2008年06月03日 [査読無し][通常論文]
     
    The elastic neutron-scattering experiments were carried out on the solid solutions CeRh1-x Cox In5 to clarify the nature of the antiferromagnetic (AF) state in the vicinity of the quantum critical point: xc ∼0.8. The incommensurate AF order with the wave vector of qh = (1/2,1/2,∼0.3) observed in pure CeRhIn5 is weakly suppressed upon doping with Co, and a commensurate qc = (1/2,1/2,1/2) and an incommensurate q1 = (1/2,1/2,∼0.42) AF structures evolve at intermediate Co concentrations. The AF orders with qc and q1 are enhanced at x=0.7, and furthermore, the qh AF order vanishes. These results suggest that the AF correlations with the qc and q1 modulations are significantly enhanced in the intermediate x range, and may be connected with the evolution of the superconductivity observed above x∼0.3. © 2008 The American Physical Society.
  • Kee Hoon Kim, Yoon Seok Oh, P. A. Sharma, N. Harrison, H. Amitsuka, J. A. Mydosh
    PHYSICA B-CONDENSED MATTER 403 5-9 721 - 725 2008年04月 [査読無し][通常論文]
     
    We investigate the Hall coefficient R-H, resistivity, and magnetization of URu2Si2, and U(Ru0.96Rh0.04)(2)Si-2 in the high field regime up to 45 T to trace the electronic structure changes in both high and low temperature regimes. We find that at high temperatures above similar to 7 K, temperature- and field-dependent positions of R-H maxima and magneto resistance maxima coincide with a coherent temperature T-coh at each field. These systematically decrease in temperatures with increasing fields and extrapolate to zero at the field-induced putative quantum critical point (QCP). This observation suggests a collapse of a new energy scale, i.e., a coherent temperature of a heavy quasiparticle band, at the putative field-induced QCP. At lower temperatures, we show there are discontinuous changes of the Hall number n(H) = 1/R(H)e at the phase boundaries. This behavior illustrates that the phase formation is caused by first order reconstructions of the Fermi surface, which we interpret to the polarization of Fermi surface pockets seen in de-Haas van-Alphen (dHvA) measurements. (C) 2007 Elsevier B.V. All rights reserved.
  • M. Yokoyama, N. Oyama, H. Amitsuka, S. Oinuma, I. Kawasaki, K. Tenya, M. Matsuura, K. Hirota
    PHYSICA B-CONDENSED MATTER 403 5-9 812 - 814 2008年04月 [査読無し][通常論文]
     
    Polarized neutron scattering experiments were performed on mixed compound CeRh0.6Co0.4In5 to clarify the nature of the low-temperature ordered states. Three nonequivalent Bragg peaks, characterized by the wave vectors of q(h)similar to(1/2,1/2,0.3), q(1)similar to(1/2,1/2,0.4) and q(c) = (1/2, 1/2, 1/2), were observed at 1.4K. These Bragg peaks are found to occur entirely in spin-flip channel. This indicates that these Bragg peaks originate from the magnetic scattering, i.e., the antiferromagnetic orders with three different modulations appear in this compound. (c) 2007 Elsevier B.V. All rights reserved.
  • H. Amitsuka, K. Matsuda, M. Yokoyama, I. Kawasaki, S. Takayama, Y. Ishihara, K. Tenya, N. Tatelwa, T. C. Kobayashi, H. Yoshizawa
    PHYSICA B-CONDENSED MATTER 403 5-9 925 - 927 2008年04月 [査読無し][通常論文]
     
    Elastic neutron-scattering and ac-susceptibility measurements have been performed on a 20 single crystal of URu2Si2 under hydrostatic pressure up to similar to 1.1 GPa using Fluorinert 70 & 77 and Daphne oil 7373 as pressure-transmitting media. Daphne oil produces better hydrostaticity of the applied pressure than Fluorinert, resulting in a slight shift of the phase boundary between hidden order and antiferromagnetic order to a lower pressure. The superconducting phase is also influenced, but never overlaps with the antiferromagnetic phase. (c) 2007 Elsevier B.V. All rights reserved.
  • T. Sakakibara, J. Custers, K. Yano, A. Yamada, T. Tayama, Y. Aoki, H. Sato, H. Sugawara, H. Amitsuka, M. Yokoyama
    PHYSICA B-CONDENSED MATTER 403 5-9 990 - 993 2008年04月 [査読無し][通常論文]
     
    Measurements of the angle-resolved specific heat C(H, theta) have been performed on PrOs4Sb12 and PrOs4Sb12 in order to examine their superconducting gap structures. In the filled skutterudite PrOs4Sb12, a clear fourfold angular dependence is observed with H rotated in the (10 0) planes, whose field variation suggests gap minima along [10 0] directions. Interestingly, a reversed angular oscillation of C(H, theta) has been observed in the normal state above H-c2 which continues to grow as the high-field antiferroquadrupole phase is approached. In URu2Si2, C(H, theta) with H rotated around the tetragonal c-axis suggests that the nodal structure has rotational symmetry. Comparison between the C(H) data for a- and c-axes indicates the existence of point nodes along the [0 0 1] direction. (c) 2007 Elsevier B.V. All rights reserved.
  • K. Tenya, R. Yamahana, M. Yokoyama, H. Amitsuka, K. Deguchi, Y. Maeno
    PHYSICA B-CONDENSED MATTER 403 5-9 1101 - 1103 2008年04月 [査読無し][通常論文]
     
    In order to investigate the chiral-superconducting characteristics as well as the vortex-pinning properties, detailed magnetization measurements of the single crystal Sr2RuO4 have been performed in the field parallel to the [0 0 1] direction. Anomalous pinning features are found at weak fields in the magnetization curves: Tiny flux-jumps successively appear around zero field at temperatures up to at least 0.2 K. At higher temperatures, a small peak of the hysteretic magnetization is observed below 0.1 kOe, which is so-called second magnetization peak (SNIP). The magnitude of the hysteretic magnetization is strongly dependent on (independent of) the field-gradient in the field region below (above) the field where the SNIP appears. Possible origins are discussed from the viewpoints of the pairing symmetry together with the topological change in the vortex-lattice configuration. (C) 2007 Elsevier B.V. All rights reserved.
  • I. Kawasaki, K. Tenya, M. Yokoyama, H. Amitsuka
    PHYSICA B-CONDENSED MATTER 403 5-9 1284 - 1286 2008年04月 [査読無し][通常論文]
     
    We have performed specific heat C and magnetic susceptibility chi measurements on the pseudo-binary alloys CePt1-xRhx, synthesized by mixing CePt (a ferromagnetic Kondo-lattice system) and CeRh (an intermediate valence system). As Rh is substituted for Pt, CePt1-xRhx shows a continuous change in the ground state from ferromagnetic order (T-C similar to 6K at x = 0) to a nonmagnetic valence-fluctuation state for x > 0.8. We found a non-Fermi-liquid-like behavior which is characterized by the power law T dependence of C(T) and chi(T), for a wide x range above the ferromagnetic quantum critical point (x(c)similar to 0.8). (C) 2007 Elsevier B.V. All rights reserved.
  • Stefan Suellow, Anna Otop, Anja Loose, Jens Klenke, Oleksandr Prokhnenko, Ralf Feyerherm, Ruud W. A. Hendrikx, John A. Mydosh, Hiroshi Amitsuka
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 2 024708-1-024708-5  2008年02月 [査読無し][通常論文]
     
    We present a detailed study of the physical properties of single crystalline UPt2Si2. By neutron diffraction we establish the presence of frozen-in strain disorder on the Pt(2)/Si(2) ligand sites within the tetragonal crystal structure. Further, the system undergoes an antiferromagnetic transition at T-N = 32K. In the range T-N < T < T-irr similar or equal to 36 K we observe a cluster glass like phase as result of the disorder. The highly anomalous behavior of the electronic transport properties-metallic along the tetragonal a and localized along the c axis-is a result of the specific type of disorder. Altogether, UPt2Si2 emerges as a model compound to study disorder effects in f electron intermetallics.
  • K. Yano, T. Sakakibara, T. Tayama, M. Yokoyama, H. Amitsuka, Y. Homma, P. Miranovic, M. Ichioka, Y. Tsutsumi, K. Machida
    PHYSICAL REVIEW LETTERS 100 1 017004-1-017004-4  2008年01月 [査読無し][通常論文]
     
    To identify the superconducting gap structure in URu(2)Si(2), we perform field-angle-dependent specific heat measurements for the two principal orientations in addition to field rotations, and a theoretical analysis based on microscopic calculations. The Sommerfeld coefficient gamma(H)'s in the mixed state exhibit a distinctly different field dependence. This comes from point nodes and the substantial Pauli paramagnetic effect of URu(2)Si(2). These two features combined give rise to a consistent picture of superconducting properties, including a possible first order transition of H(c2) at low temperatures.
  • A. V. Silhanek, M. Jaime, N. Harrison, C. D. Batista, H. Amitsuka, S. Nakatsuji, L. Balicas, K. H. Kim, J. A. Mydosh
    PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 460 682 - 683 2007年09月 [査読無し][通常論文]
     
    U(Ru0.96Rh0.04)(2)Si-2 is an anisotropic itinerant 5f heavy electron system which exhibits a single field induced magnetic phase concealing a quantum critical point. We show that the boundary of this phase corresponds to a first order transition as revealed by (1) a large and symmetric specific heat anomaly, (2) an asymmetric magnetocaloric effect on entering and exiting this phase, and (3) a clear history and time-dependent specific heat. We explore the thermodynamic similarities with the mixed valence compound YbInCu4 and show that the out-of-equilibrium properties are analogous to those depicted by the critical state model for hard superconductors. (C) 2007 Elsevier B.V. All rights reserved.
  • H. Amitsuka, K. Matsuda, I. Kawasaki, K. Tenya, M. Yokoyama, C. Sekine, N. Tateiwa, T. C. Kobayashi, S. Kawarazaki, H. Yoshizawa
    J. Mag. Mag. Mater. 310 2 214 - 220 2007年03月 [査読有り][通常論文]
  • K. Matsuda, M. Yokoyama, K. Tenya, H. Amitsuka, H. Yoshizawa
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 2 337 - 339 2007年03月 [査読無し][通常論文]
     
    We have performed the elastic neutron-scattering and the AC magnetic susceptibility measurements under hydrostatic pressure for URu2Si2 to construct a reliable T-P phase diagram, focusing on the relationship between the hidden order (HO), pressure-induced antiferromagnetism (AF), and non-BCS-type superconductivity (SC). For this purpose, we used the same pressure condition and the same single crystalline sample through all the measurements, because the HO-to-AF phase transition is very sensitive to the experimental conditions such as the quality of sample and applied pressure. The neutron scattering experiment performed under pressures ranging from P = 0.5 to 1.07 GPa showed that the phase transition between HO and AF occurs very sharply at P-M = 0.7GPa for T -> 0. The ordered moment mu(o) of the high-pressure AF phase is estimated to be similar to 0.4 mu(B)/U. (c) 2006 Elsevier B. V. All rights reserved.
  • M. Yokoyama, K. Matsuda, H. Amitsuka, K. Tenya, N. Aso, H. Yoshizawa
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 2 328 - 330 2007年03月 [査読無し][通常論文]
     
    Inelastic neutron scattering experiments were performed on U(Ru1-x xRh(x))(2)Si-2 with x 0 and 0.02 in order to investigate the variations of the antiferromagnetic ( AF). fluctuations with doping Rh. We have found that the energy of the magnetic excitation observed at Q (1, 0, 0) in the hidden order (HO) phase markedly decreases from similar to 2.6meV (x = 0) to similar to 0 (x = 0.02) with increasing x. In addition, the staggered susceptibility chi Q estimated from the inelastic peak develops in the HO phase at x 0.02, while it is suppressed at x = 0. These results indicate that the AF. fluctuation in the HO phase is signifi. cantly enhanced with doping Rh. (c) 2006 Elsevier B.V. All rights reserved.
  • A. Morishita, K. Matsuda, T. Wakabayashi, I. Kawasaki, K. Tenya, H. Amitsuka
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 2 283 - 285 2007年03月 [査読無し][通常論文]
     
    We investigated specific heat and magnetic susceptibility for the dilute systems R1-xPrxRu2Si2 (R = Th and Y; x 0: 05 and 0.1). The 4f electronic specific heat C-4f/T shows a Schottky-peak anomaly at similar to 10 K, and the 4f contribution to the magnetic susceptibility chi(4f) shows a saturation tendency below this temperature. These features are common to the R Th and Y systems and scaled by the doped Pr concentration. The experimental results are fairly well described by the singlet-singlet crystalline-electric-field (CEF) level scheme. The Kondo screening seems not to occur in these dilute magnetic systems. (c) 2006 Elsevier B.V. All rights reserved.
  • H. Amitsuka, K. Matsuda, I. Kawasaki, K. Tenya, M. Yokoyama
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 2 214 - 220 2007年03月 [査読無し][通常論文]
     
    The pressure-temperature phase diagram of the heavy-electron superconductor URu2Si2 has been reinvestigated by AC-susceptibility and elastic neutron-scattering (NS) measurements performed on a small single- crystalline rod (2mm in diameter, 6mm in length) in a Cu-Be clamp-type high- pressure cell (P < 1: 1GPa). At ambient pressure, this sample shows the weakest antiferromagnetic (AF) Bragg reflections reported so far, corresponding to the volume-averaged staggered moment of mu similar to 0.011 mu(B)/U. Under applied pressure, the AF scattering intensity exhibits a sharp increase at P similar to 0.7GPa at low temperatures. The saturation value of the AF scattering intensity above 0.7 GPa corresponds to mu(o) similar to 0.41 mu(B)/U, which is in good agreement with that (similar to 0.39 mu(B)/U) observed above 1.5 GPa in our previous NS measurements. The superconductivity is dramatically suppressed by the evolution of AF phase, indicating that the superconducting state coexists only with the hidden order phase. The presence of parasitic ferro- and/or antiferromagnetic phases with transition temperatures T-1(*) = 120(5), T-2(*) = 36(3) and T-3(*) = 16: 5(5) K and their relationship to the low-T ordered phases are also discussed. (c) 2006 Elsevier B.V. All rights reserved.
  • Yoon Seok Oh, Kee Hoon Kim, N. Harrison, H. Amitsuka, J. A. Mydosh
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 2 855 - 857 2007年03月 [査読無し][通常論文]
     
    Comparative study of U(Ru1-xRhx)(2)Si-2 (x = 0 and 4%) through resistivity, magnetic susceptibility, and Hall coefficient measurements reveals that the coherence temperature, T-coh, of the Rh 4% doped sample clearly decreases by about 10-20% as compared with that of undoped one located around 50 K. Furthermore, T*, a characteristic temperature below which the resistivity shows the T-2 dependence, is also found to decrease by almost the same factor. These findings suggest that the low Rh doping sensitively destroys the itinerant band gap due to the hidden order (HO) through the reduction of the Fermi surface volume in the quasi-particle band. (c) 2006 Elsevier B.V. All rights reserved.
  • Shigeru Takagi, Slut Ishihara, Satoru Saitoh, Hiko-ichiro Sasaki, Hiroshi Tanida, Makoto Yokoyama, Hiroshi Amitsuka
    Journal of the Physical Sciety of Japan 76 3 033708  2007年03月 [査読無し][通常論文]
     
    The still unidentified hidden order (HO) phase below T-0 = 17.5 K in the heavy-electron superconductor URu2Si2 has been investigated by Si-29 NMR on a single crystal under external magnetic field H-ext || c-axis and ambient pressure P. For a previously proposed model of the small-moment antiferromagnetism (SMAF), in which tiny-moment antiferromagnetism (AF) under ambient P is ascribed to spatially homogeneous AF with an ordered moment mu(SMAF) = 0.02-0.04 mu(B), splitting of the line would be expected on the basis of a scaling from the corresponding splitting in the P-induced AF. However, we observed at T = 4.5 K no splitting of the line. This clearly indicates that the SMAF model cannot describe the ambient-P properties. Below To down to similar to 14 K, the 29 Si NMR line shows additional broadening over the paramagnetic width. The additional contribution, however, disappears below similar to 14 K, which indicates that the HO itself produces almost zero internal field at the 29Si site along the c-axis at low temperatures in the HO phase.
  • Single-Site Effects of Pr Ions Doped in ThRu2Si2
    A. Morishita, Y. Saito, K. Matsuda, T. Wakabayashi, I. Kawasaki, K. Tenya, H. Amitsuka
    Topological Aspects of Critical Systems and Networks 184  2007年 [査読有り][通常論文]
  • Magnetizatioin Study of Pairing and Votex States in Sr2RuO4
    K. Tenya, R. Yamahana, A. Ishii, H. Amitsuka, M. Yokoyama, K. Deguchi, Y. Maeno
    Topological Aspects of Critical Systems and Networks 178  2007年 [査読有り][通常論文]
  • Y. S. Oh, Kee Hoon Kim, P. A. Sharma, N. Harrison, H. Amitsuka, J. A. Mydosh
    PHYSICAL REVIEW LETTERS 98 1 016401  2007年01月 [査読無し][通常論文]
     
    Temperature- and field-dependent measurements of the Hall effect of pure and 4% Rh-doped URu2Si2 reveal low density (0.03 hole/U) high mobility carriers to be unique to the "hidden order" phase and consistent with an itinerant density-wave order parameter. The Fermi surface undergoes a series of abrupt changes as the magnetic field is increased. When combined with existing de Haas-van Alphen data, the Hall data expose a strong interplay between the stability of the "hidden order," the degree of polarization of the Fermi liquid, and the Fermi surface topology.
  • Makoto Yokoyama, Hiroshi Amitsuka
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 76 136 - 139 2007年01月 [査読無し][通常論文]
     
    We have investigated the nature of the competition between hidden order and antiferromagnetic (AF) order in URu2Si2 by performing the neutron scattering experiments under hydrostatic-pressure P, uniaxial-stress sigma, and Rh-substitution conditions. Hidden order observed at ambient pressure in pure URu2Si2 is found to be replaced by the AF order by applying P, s along the tetragonal basal plane, and by doping Rh. We discuss these experimental results on the basis of the crystalline strain calculations, and suggest that this phase transition is generated by the 0.1% increase of the tetragonal c/a ratio. We have also found that the magnetic excitation observed in the hidden order phase vanishes in the AF phase. We show that this variation can be qualitatively explained by assuming the hidden order parameter to be quadrupole.
  • Topological Aspects of Critical Systems and Networks
    World Scientific Publishing Co. Pte. Ltd. 2007年 [査読無し][通常論文]
  • Makoto Yokoyama, Hiroshi Amitsuka, Kei Matsuda, Akifumi Gawase, Narumi Oyama, Ikuto Kawasaki, Kenichi Tenya, Hideki Yoshizawa
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 10 023702  2006年10月 [査読無し][通常論文]
     
    We performed elastic neutron scattering experiments on solid solution CeRh1-xCoxIn5 with x = 0.4 to clarify the nature of the antiferromagnetic (AF) phase in the vicinity of the quantum critical point. We observed the incommensurate AF order below T-Nh = 3.5 K. The structure of the incommensurate AF order is basically unchanged from that for pure CeRhIn5. We further found the evolution of a new commensurate AF order with the modulation of q(c) = (1/2, 1/2, 1/2) below T-Nc, = 2.9 K. The volume-averaged moments for the incommensurate and commensurate AF phases are 0.38 mu(B)/Ce and 0.21 mu(B)/Ce, respectively, which are reduced from the incommensurate AF moment (0.75 mu(B)/Ce) for pure CeRhIn5. We suggest from these results that the commensurate magnetic correlation may be tightly coupled with the superconductivity observed below T-c = 1.4 K.
  • P. A. Sharma, N. Harrison, M. Jaime, Y. S. Oh, K. H. Kim, C. D. Batista, H. Amitsuka, J. A. Mydosh
    Physical Review Letters 97 15 156401  2006年10月 [査読無し][通常論文]
     
    A dramatic increase in the total thermal conductivity (kappa) is observed in the hidden order (HO) state of single crystal URu2Si2. Through measurements of the thermal Hall conductivity, we explicitly show that the electronic contribution to kappa is extremely small, so that this large increase in kappa is dominated by phonon conduction. An itinerant BCS or mean-field model describes this behavior well: the increase in kappa is associated with the opening of a large energy gap at the Fermi surface, thereby decreasing electron-phonon scattering. Our analysis implies that the "hidden order" parameter is strongly coupled to the lattice, suggestive of a broken symmetry involving charge degrees of freedom.
  • M. Yokoyama, A. Gawase, H. Amitsuka, K. Tenya, H. Yoshizawa
    PHYSICA B-CONDENSED MATTER 378-80 80 - 81 2006年05月 [査読無し][通常論文]
     
    We have performed the elastic neutron scattering measurements under the uniaxial stress sigma for the antiferromagnetic (AF) state in CePd2Si2, and found an anisotropy in the sigma dependence of the AF state. The magnitude of the staggered moment is reduced with increasing sigma applied along the tetragonal [110] direction, while it shows nearly independent of sigma for sigma parallel to [001]. Similar behavior is also observed in the sigma dependence of the Neel temperature. From these results, we suggest that both the volume compression and the increase of the c/a ratio lead to the suppression of the AF state. (c) 2006 Elsevier B.V. All rights reserved.
  • A. V. Silhanek, N. Harrison, C. D. Batista, M. Jaime, A. Lacerda, H. Amitsuka, J. A. Mydosh
    Physica B: Condensed Matter 378-80 373 - 375 2006年05月 [査読無し][通常論文]
     
    We discuss recent specific heat data in high magnetic fields on URu2Si2 and 4% Rh-doped URu2Si2 as well as previously published de Haas-van Alphen data at lower magnetic fields in pure URu2Si2: both of which are consistent with quasiparticle bands formed from a hybridization between 5f-electron Gamma(5) doublets and regular conduction electrons. The system exhibits itinerant electron metamagnetism that gives rise to a putative quantum critical point at similar to 34-37T (depending on the % of Rh) that is subsequently unstable to field-induced phases. (c) 2006 Elsevier B.V. All rights reserved.
  • Kee Hoon Kim, N. Harrison, H. Amitsuka, M. Jaime, J. A. Mydosh
    PHYSICA B-CONDENSED MATTER 378-80 31 - 35 2006年05月 [査読無し][通常論文]
     
    This paper presents a brief summary of recent electrical transport, magnetization and specific heat measurements on U(Ru1-xRhx)(2)Si-2) (x = 0, 2, 2.5, 3, and 4%) in magnetic fields up to 45 T. The results uncover the formation of multiple phases near their putative metamagnetic quantum critical points at low temperatures. From the established magnetic field versus temperature phase diagram in our series of samples, we find a clear correlation between the field-dependence of the phases and that of the putative quantum critical point. This provides an archetypal example that the field-tuned metamagnetic quantum criticality is intimately related to the formation of thermodynamic phases. (c) 2006 Elsevier B.V. All rights reserved.
  • K Tenya, S Yasuda, M Yokoyama, H Amitsuka, K Deguchi, Y Maeno
    PHYSICA B-CONDENSED MATTER 378-80 495 - 496 2006年05月 [査読無し][通常論文]
     
    Static magnetization measurements of Sr2RuO4 have been performed down to 0.1 K. An anomalous increase of magnetization is observed at H-2 which is located just below H-c2. The onset field H-2 gradually decreases with temperature and seems to merge with H-c2 around I K. Besides the above anomaly, a small kink is found in the magnetization curves at around 9 kOe. These magnetization behaviors are analyzed from the viewpoint of the Ginzburg-Landau theory. (c) 2006 Elsevier B.V. All rights reserved.
  • M. Jaime, A. V. Silhanek, K. H. Kim, N. Harrison, L. Balicas, H. Amitsuka, J. A. Mydosh
    PHYSICA B-CONDENSED MATTER 378-80 82 - 83 2006年05月 [査読無し][通常論文]
     
    Specific heat, magnetocaloric effect and magnetization experiments were performed on the 5f-electron system U(Ru0.96Rh0.04)(2)Si-2. This compound exhibits a non-magnetic ground state with a single magnetic field-induced phase between H = 26 and 38 T. We show that the transition into this phase is first-order as revealed by a large irreversible specific heat anomaly and asymmetric magnetocaloric effect. A comparative analysis with the valence transition compound YbInCu4, where similar irreversibility and asymmetry exists, is presented. (c) 2006 Published by Elsevier B.V.
  • Yoon Seok Oh, Kee Hoon Kim, N. Harrison, P. A. Sharma, H. Amitsuka, J. A. Mydosh
    PHYSICA B-CONDENSED MATTER 378-80 989 - 990 2006年05月 [査読無し][通常論文]
     
    We investigate the evolution of Hall coefficient R-H in U(Ru0.96Rh0.04)(2)Si-2 across a field-induced phase II, formed to avoid a putative quantum critical point, using a mid-pulse magnet up to 45 T. R-H values at low temperatures increased sharply when the system enters phase II from the neighboring fermi-liquid states stabilized outside phase II. This observation is consistent with a large fermi surface reconstruction to open a partial gap inside phase II. (c) 2006 Elsevier B.V. All rights reserved.
  • K. Kuwahara, M. Kohgi, K. Iwasa, M. Nishi, K. Nakajima, M. Yokoyama, H. Amitsuka
    PHYSICA B-CONDENSED MATTER 378-80 581 - 582 2006年05月 [査読無し][通常論文]
     
    We report the field-induced magnetic form factor of the heavy-electron system URu2Si2 obtained by using polarized neutrons. The neutron experiments were performed on the two single crystals at 60 K by applying a magnetic field of 6 T along the tetragonal c-axis. The observed magnetic form factor is close to the theoretical 5f form factor of the free U3+ or U4+ ions calculated by the dipole approximation as other U-based intermetallic superconductors. However, the extrapolated value at sin theta/lambda = 0 (0.07 mu(B)/U) is smaller than the bulk magnetization value (0.10 mu(B)/N). Therefore, this result indicates some contribution other than 5f electrons to the bulk magnetization of URu2Si2. (c) 2006 Elsevier B.V. All rights reserved.
  • AV Silhanek, M Jaime, N Harrison, VR Fanelli, CD Batista, H Amitsuka, S Nakatsuji, L Balicas, KH Kim, Z Fisk, JL Sarrao, L Civale, JA Mydosh
    PHYSICAL REVIEW LETTERS 96 13 026403  2006年04月 [査読無し][通常論文]
     
    We report measurements and analysis of the specific heat and magnetocaloric effect-induced temperature changes at the phase boundary into the single magnetic field-induced phase (phase II) of U(Ru0.96Rh0.04)(2)Si-2, which yield irreversible properties similar to those at the valence transition of Yb1-xYxInCu4. To explain these similarities, we propose a bootstrap mechanism by which lattice parameter changes caused by an electric quadrupolar order parameter within phase II become coupled to the 5f-electron hybridization, giving rise to a valence change at the transition.
  • K Tenya, S Yasuda, M Yokoyama, H Amitsuka, K Deguchi, Y Maeno
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 2 103703  2006年02月 [査読無し][通常論文]
     
    We report on detailed measurements of the magnetization of Sr2RuO4 in the superconducting mixed state, performed on a high-quality single crystal in a magnetic field parallel to the [100] axis. A small but distinct kink structure is found at around 9 kOe in the magnetization curve, indicating the presence of an additional superconducting phase transition that has been theoretically predicted to be evidence of the superconductivity with a two-component order parameter. An anomalous increase of magnetization is also observed just below the upper critical field. These anomalies disappear when the field is tilted from the [100] axis by only 3-5 degrees. Possible origins of such magnetization behavior are discussed from the viewpoint of a spin-triplet pairing scenario with a two-component order parameter.
  • Hiroshi Amitsuka, Makoto Yokoyama, Kei Matsuda, Kenichi Tenya, Hideki Yoshizawa
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 58 - 62 2006年01月 
    A review of recent attempts to understand the pressure-temperature phase diagram of URu2 Si-2 is given. At ambient (and weak) pressures, the low-T properties of this system are dominated by an unidentified ordered state (hidden order: HO) and non-trivial superconductivity, while by applying hydrostatic (or uniaxial or chemical) pressures, a change to a regime dominated by antiferromagnetic order (AF) is observed. In between these two regimes, an unusual heterogeneous metallic state is found. This change in regime is clearly demonstrated by neutron scattering, NMR and mu SR measurements. The experimental results and strain analyses show that the low-T state of this system is extremely sensitive to the shape effects, and a slight increase in the axial strain delta(c/a)/( c/a ) (equivalent to(eta) over cap) can easily change the ground state from HO to AF. The critical value is estimated to be very small ((eta) over capc similar to 10(-3) ), suggesting that a strain distribution in a crystal is responsible for the observed heterogeneity. We will demonstrate this by showing our recent neutron-scattering experimental data using a high-quality single crystal.
  • Antiferromagnetic Defects in Non-Magnetic Hidden Order of the Heavy-Electron System URu2Si2
    H. Amitsuka, K. Tenya, M. Yokoyama
    Topology in Ordered Phases 247  2006年 [査読有り][通常論文]
  • Superconductivity in URu2Si2 Under High Pressure
    K.Tenya, I. Kawasaki, H. Amitsuka, M. Yokoyama, N. Tateiwa, T. C. Kobayashi
    Topology in Ordered Phases 277  2006年 [査読有り][通常論文]
  • M Yokoyama, H Amitsuka, K Tenya, K Watanabe, S Kawarazaki, H Yoshizawa, JA Mydosh
    PHYSICAL REVIEW B 72 21 2005年12月 
    We have performed elastic neutron scattering experiments under uniaxial stress sigma applied along the tetragonal [100], [110], and [001] directions for the heavy-electron compound URu2Si2. We found that antiferromagnetic (AF) order with large moment is developed with sigma along the [100] and [110] directions. If the order is assumed to be homogeneous, the staggered ordered moment mu(o) continuously increases from 0.02 mu(B)/U(sigma=0) to 0.22 mu(B)/U (0.25 GPa). The rate of increase partial derivative mu(o)/partial derivative sigma is similar to 1.0 mu(B)/GPa, which is four times larger than that for the hydrostatic pressure (partial derivative mu(o)/partial derivative P similar to 0.25 mu(B)/GPa). Above 0.25 GPa, mu(o) shows a tendency to saturate, similar to the hydrostatic pressure behavior. For sigma parallel to[001], mu(o) shows only a slight increase to 0.028 mu(B)/U(sigma=0.46 GPa) with a rate of similar to 0.02 mu(B)/GPa, indicating that the development of the AF state highly depends on the direction of sigma. We have also found a clear hysteresis loop in the isothermal mu(o)(sigma) curve obtained for sigma parallel to[110] under the zero-stress-cooled condition at 1.4 K. This strongly suggests that the sigma-induced AF phase is metastable, and separated from the "hidden order" phase by a first-order phase transition. We discuss these experimental results on the basis of crystalline strain effects and elastic energy calculations, and show that the c/a ratio plays a key role in the competition between these two phases.
  • S Saitoh, S Takagi, M Yokoyama, H Amitsuka
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 74 8 2209 - 2213 2005年08月 
    The still unclarified hidden order phase below To = 17.5 K in the heavy-electron system URu2Si2 has been studied by Ru-101 NQR on a single crystal under H-ext = 0 and ambient P. Considering an invariant form of the quadrupole coupling between a Ru-101 nucleus and U 5f electrons, which is compatible with the symmetry of the U-Ru bonds, it is shown that U 5f quadrupoles can be probed by Ru-101 NQR and that the singlet ground-state models for the (5f)(2) configuration of U can naturally explain the observed large T-dependence of the NQR frequency (101)v(2Q)(T) above T-o. (101)v(2Q)(T) shows a slight but significant increase below TQ congruent to 13.5 K. Combining with general considerations on the effects on Ru-101 NQR of a possible symmetry-breaking electric field gradient (EFG) or hyperfine field due to hidden order, we discuss that the increase can be interpreted as arising from symmetry -breaking EFG components of V-yz and/or V-zx, due to quadrupole order. In this interpretation the onset of the quadrupole order is retarded by about 4 K below T-o. which is discussed in connection with related measurements.
  • AV Silhanek, N Harrison, CD Batista, M Jaime, A Lacerda, H Amitsuka, JA Mydosh
    PHYSICAL REVIEW LETTERS 95 2 2005年07月 [査読有り][通常論文]
     
    We present specific heat measurements of 4% Rh-doped URu2Si2 at magnetic fields around the proposed metamagnetic transition field H(m)similar to 34 T, revealing striking similarities to the isotructural Ce analog CeRu2Si2 for H > H-m. This suggests that strongly renormalized hybridized-band models apply equally well to both systems. The vanishing bandwidths as H -> H-m are consistent with a quantum-critical point close to H-m. The existence of a phase transition into an ordered phase in the vicinity of H-m for 4% Rh-doped URu2Si2, but not for CeRu2Si2, is consistent with a stronger superexchange in the case of the U 5f system. Irreversible processes at the transition indicate a strong coupling of the 5f orbitals to the lattice, most suggestive of electric quadrupolar order.
  • KH Kim, N Harrison, H Amitsuka, GA Jorge, M Jaime, JA Mydosh
    PHYSICA B-CONDENSED MATTER 359 32 - 34 2005年04月 [査読有り][通常論文]
     
    The magnetization and resistivity studies in magnetic fields up to 45 T were used to establish magnetic field versus temperature phase diagram and quantum criticality in U(Ru1-xRhx)(2)Si-2. For x = 4%, the hidden order is completely destroyed, stabilizing a single field-induced phase II. A correlation between the field dependence of this phase and that of the quantum critical point, combined with the suppression of the T-2 coefficient of the resistivity within it, shows that the field-tuned quantum criticality is intimately related to the phase formation. (c) 2005 Elsevier B.V. All rights reserved.
  • M Yokoyama, H Amitsuka, S Roh, Kawasaki, I, K Tenya, H Yoshizawa
    PHYSICA B-CONDENSED MATTER 359 1129 - 1131 2005年04月 [査読有り][通常論文]
     
    We have investigated magnetic excitations for a mixed phase of hidden order (HO) and the anti ferromagnetic (AF) order in U(Ru1-xRhx)(2)Si-2 (x <= 0.03) by means of inelastic neutron scattering. The inelastic peaks observed at Q = (1, 0, 0) and (1,0.4,0) in the HO phase for x = 0 and 0.015 at 1.4 K are found to be strongly reduced in the AF dominant compositions of x = 0.02 and 0.03. Similar behavior is observed as the HO is replaced by the AF order upon cooling for x = 0.02. The x-T region in which the strong reduction of inelastic peaks is observed corresponds to the AF-rich region, indicating that the magnetic excitations typical for the HO-phase vanish in the AF phase. (c) 2005 Published by Elsevier B.V.
  • K Tenya, Kawasaki, I, K Tameyasu, S Yasuda, M Yokoyama, H Amitsuka, N Tateiwa, TC Kobayashi
    PHYSICA B-CONDENSED MATTER 359 1135 - 1137 2005年04月 [査読有り][通常論文]
     
    Magnetization measurements of URu2Si2 have been performed under hydrostatic pressures. The superconducting transition temperature decreases linearly with pressure up to 1.1 GPa and disappears above 1.5 GPa. The hysteretic magnetization shows characteristic behaviors at high pressures, suggesting that the pinning properties are changed due to the switch of the normal state to the antiferromagnetic state. (c) 2005 Elsevier B.V. All rights reserved.
  • K Matsuhira, Y Doi, M Wakeshima, Y Hinatsu, H Amitsuka, Y Shimaya, R Giri, C Sekine, Shirotani, I
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 74 3 1030 - 1035 2005年03月 [査読無し][通常論文]
     
    Sm-based filled skutterudite phosphides SmFe4P12, SmRu4P12 and SmOs4P12 synthesized at high temperatures and high pressures have been studied by specific heat measurements in magnetic fields. SmFe4P12 shows an anomaly at 1.6 K attributed to a ferromagnetic transition. SmRu4P12 shows a metal-insulator transition at 16 K. This transition consists of two successive transitions, which suggests orbital and antiferromagnetic orderings. SmOS4P12 shows a sharp anomaly at 4.5 K due to an antiferromagnetic ordering. We discuss the characteristic behavior of those phase transitions and the crystalline electric field state in SmT4P12 (T = Fe, Ru and Os). Interestingly, the magnetic entropy of SmFe4P12 have only 0.16R ln 2 below the ferromagnetic ordering temperature. This suggests a strong spin fluctuation effect. On the other hand, the variation of magnetic entropy in SmRu4P12 and SmOs4P12 reaches to nearly R In 4 below the ordering temperature.
  • 横山 淳, 網塚 浩
    波紋 15 4 236 - 239 The Japanese Society for Neutron Science 2005年 
    We show the results of recent microscopic investigations for hydrostatic-pressure, uniaxial-stress and Rh-substitution effects on the hidden order and antiferromagnetic phases in URu2Si2. On the basis of these results, we discuss the nature of the unusual two-phase competition, and suggest a quadrupolar order as a candidate for the hidden order.
  • Yokoyama, M., Amitsuka, H., Itoh, S., Kawasaki, I., Tenya, K. and Yoshizawa, H.: "Magnetic Excitations in U(Ru1-xRhx)2Si2 (x =< 0.03)", Physica B: Condensed Matter, 359-361: 1129-1131 (2005)*
    2005年 [査読無し][通常論文]
  • Tenya, K., Kawasaki, I., Tameyasu, K., Yasuda, S., Yokoyama, M., Amitsuka, H., Tateiwa, N. and KobayashiT.C.: "Magnetization Study of Heavy Fermion Superconductor URu2Si2 under High Pressures", Physica B: Condensed Matter, 359-361: 1135-1137 (2005)*
    2005年 [査読無し][通常論文]
  • Saitoh, S., Takagi, S., Yokoyama, M. and Amitsuka, H.: "101Ru NQR and Hidden Order in URu2Si2", J. Phys. Soc. Jpn., 74: 2209-2213 (2005)*
    2005年 [査読無し][通常論文]
  • Yokoyama, M., Amitsuka, H., Tenya, K., Watanabe, K., Kawarazaki, S., Yoshizawa, H. and Mydosh, J.A.: "Competition between Hidden Order and Antiferromagnetism in URu2Si2 under Uniaxial Stress Studied by Neutron scattering", Phys. Rev. B, 72: 214419-1-9 ・・・
    2005年 [査読無し][通常論文]
     
    Yokoyama, M., Amitsuka, H., Tenya, K., Watanabe, K., Kawarazaki, S., Yoshizawa, H. and Mydosh, J.A.: "Competition between Hidden Order and Antiferromagnetism in URu2Si2 under Uniaxial Stress Studied by Neutron scattering", Phys. Rev. B, 72: 214419-1-9 (2005)*
  • Kim, K.H., Harrison, N., Amitsuka, H., Jorge, G.A., Jaime, M. and Mydosh J.A.: "Link between Magnetic Field-Induced Quantum Criticality and Phase Formation in U(Ru1-xRhx)2Si2", Physica B: Condensed Matter, 32-34: 359-361 (2005)*
    2005年 [査読無し][通常論文]
  • KH Kim, N Harrison, H Amitsuka, GA Jorge, M Jaime, JA Mydosh
    PHYSICAL REVIEW LETTERS 93 20 2004年11月 [査読有り][通常論文]
     
    Simplification of the magnetic field-versus-temperature phase diagram and quantum criticality in URu2Si2 dilutely doped with Rh are studied by measuring the magnetization and resistivity in magnetic fields of up to 45 T. For x=4%, the hidden order is completely destroyed, leaving a single field-induced phase II. A correlation between the field dependence of this phase and that of the quantum critical point, combined with the suppression of the T-2 coefficient of the resistivity within it, implicates field-tuned quantum criticality as an important factor in phase formation.
  • A Amato, MJ Graf, A de Visser, H Amitsuka, D Andreica, A Schenck
    JOURNAL OF PHYSICS-CONDENSED MATTER 16 40 S4403 - S4420 2004年10月 
    The behaviour of the so-called weak-moment antiferromagnetic states, observed in the heavy-fermion superconductors UPt3 and URu2Si2, is discussed in view of recent muSR results obtained as functions of control parameters such as chemical substitution and external pressure. In UPt3, the Pd substitution for Pt reveals the dynamical character of the weak-moment order. On the other hand, muSR measurements performed on samples in which Th substitutes U suggest that crystallographic disorder on the magnetic sites deeply affects the fluctuation timescale. In URu2Si2, a phase separation between the so-called hidden order state, present at ambient pressure, and an antiferromagnetic state, occurring under pressure, is observed. In view of the pressure-temperature phase diagram obtained by muSR, it is deduced that the respective order parameters have different symmetries.
  • Neutron Scattering Study on Competition between Hidden Order and Antiferromagnetism in U(Ru1-xRhx)2Si2 (x<0.05)
    M. Yokoyama, H. Amitsuka, S.Itoh, I. Kawasaki, K. Tenya, H. Yoshizawa
    J. Phys. Soc. Jpn. 73 545  2004年 [査読有り][通常論文]
  • Amato, A., Graf, M.J., de Visser, A., Amitsuka, H., Andreica, D., and Schenck, A., "Weak-Magnetism Phenomena in Heavy-Fermion Superconductors: Selected MuSR Studies", J. Phys.: Condens. Matter 16: S4403-S4420 (2004).*
    2004年 [査読無し][通常論文]
  • Kim, K.H., Harrison, N., Amitsuka, H., Jorge, G.A., Jaime, M., and Mydosh, J.A., "Nexus between Quantum Criticality and Phase Formation in U(Ru1-xRhx)2Si2", Phys. Rev. Lett. 93: 206402-1-4 (2004).*
    2004年 [査読無し][通常論文]
  • K Kuwahara, H Sagayama, K Iwasa, M Kohgi, S Miyazaki, J Nozaki, J Nogami, M Yokoyama, H Amitsuka, H Nakao, Y Murakami
    ACTA PHYSICA POLONICA B 34 8 4307 - 4310 2003年08月 
    We have performed high pressure X-ray diffraction measurements on a powder sample of the tetragonal heavy-electron compound URu2Si2 at low temperatures and pressure up to 3 GPa, in order to investigate a pressure-induced phase transition at P-c = similar to1.5 GPa, which was indicated in the neutron diffraction experiment under pressure. The pressure variations of the lattice parameters a and c at 15 K decrease monotonously with increasing pressure. No discontinuity of the lattice parameters of URu2Si2 around P-c is observed within experimental error.
  • H Amitsuka, M Yokoyama
    PHYSICA B-CONDENSED MATTER 329 452 - 455 2003年05月 
    Recent high-pressure studies have been particularly effective in revealing unusual properties of inhomogeneous magnetism in the heavy-electron superconductor URu2Si2, In this paper a narrow selection of the important experimental observations elucidating the pressure-induced two-phase competition is reviewed. (C) 2003 Elsevier Science B.V. All rights reserved.
  • GIRI R, SEKINE C, SHIMAYA Y, SHIROTANI I, MATSUHIRA K, DOI Y, HINATSU Y, YOKOYAMA M, AMITSUKA H
    Physica B 329 458 - 459 2003年05月 [査読無し][通常論文]
     
    Filled skutterudites SmFe4P12 and SmOs4P12 have been prepared at high temperature and high pressure. The temperature dependence of electrical resistivity in both compounds shows metallic behavior. The magnetic susceptibility and specific heat measurements indicate that indicate that SmFe4P12 shows a ferromagnetic ordering at 1.5 K, whereas SmOs4P12 is an antiferromagnet with a T-N of 4.6 K. (C) 2003 Elsevier Science B.V. All rights reserved.
  • K Matsuda, Y Kohori, T Kohara, H Amitsuka, K Kuwahara, T Matsumoto
    JOURNAL OF PHYSICS-CONDENSED MATTER 15 14 2363 - 2373 2003年04月 
    We have investigated the low-temperature phase appearing below T-O = 17.5 K in URu2Si2 by means of (29) Si nuclear magnetic resonance (NMR) in a pressure range from 0 to 17.5 kbar across the pressure-induced phase transition at P-c = 15 kbar. At pressures below P-c we have observed the 21 Si NMR lines arising from antiferromagnetic (AF) and paramagnetic (PM) regions in the sample, giving evidence for a phase-separated AF ordering below T-o. The AF region increases in volume fraction with increasing pressure up to P-c. In the PM region, the temperature-dependence of the nuclear spin-lattice relaxation rate at Si sites shows a rapid decrease below T-o, strongly suggesting the occurrence of a phase transition driven by a hidden order parameter. As applied pressure exceeds P-c the AF ordering appears uniformly at T-o throughout the sample. In the pressure range from 0 to 17.5 kbar, the magnitude of the internal field at Si sites in the AF region remains constant (similar to920 Oe), which indicates that the AF ordered moment is unchanged by pressure across P-c.
  • H Amitsuka, K Tenya, M Yokoyama, A Schenck, D Andreica, FN Gygax, A Amato, Y Miyako, YK Huang, JA Mydosh
    PHYSICA B-CONDENSED MATTER 326 1-4 418 - 421 2003年02月 
    We have studied the low-temperature phase below 17.5 K in the heavy-fermion superconductor URu2Si2 using the zero-field muSR technique under hydrostatic pressures P up to 0.85 GPa. The measurements qualitatively confirm the previous results of NMR and neutron scattering that pressure induces unusual evolution of an inhomogeneous antiferromagnetic (AF) phase which spatially competes with some nonmagnetic 'hidden order'. The AF volume fraction, however, develops abruptly at around a pressure of 0.6 GPa, in contrast to the P-linear variations in the NMR results. Moreover, the onset temperature of the AF-volume evolution is clearly lower than 17.5 K, whereas the nominal Neel temperature seems to be about 20 K. These experimental results suggest that the AF phase exists as a metastable state. (C) 2002 Elsevier Science B.V. All rights reserved.
  • M Yokoyama, J Nozaki, H Amitsuka, K Watanabe, S Kawarazaki, H Yoshizawa, JA Mydosh
    ACTA PHYSICA POLONICA B 34 2 1067 - 1070 2003年02月 
    We have investigated the nature of the antiferromagnetic (AF) phase induced by uniaxial stress sigma in URu2Si2, by performing elastic neutron scattering measurements up to 0.4 GPa. We have found that the AF Bragg-peak intensity shows a clear hysteresis loop with sigma under the zero-stress cooling condition. The result strongly suggests that the sigma-induced AF phase is metastable and separated from the coexisting "hidden ordered" phase by a first-order phase transition. We also present the analyses of the crystalline strain effects, and suggest that the c/a ratio plays an important role in the competition between these two phases.
  • Amitsuka, H. and Yokoyama M., "Inhomogeneous Magnetism and Hidden Order in URu2Si2", Physica B, 329-333:452-455(2003)*
    2003年 [査読無し][通常論文]
  • Kuwahara, K., Sagayama, H., Iwasa, K., Kohgi, M., Miyazaki, S., Nozaki, J., Nogami, A., Yokoyama, M., Amitsuka, H., Nakao H. and Murakami Y.:"High Pressure X-Ray Diffraction Study of URu2Si2", Acta Phys. Pol. B, 34:4307-4310(2003)*
    2003年 [査読無し][通常論文]
  • Matsuda, K., Kohori., Y., Kohara, T., Amitsuka, H., Kuwahara, K. and Matsumoto, T., "The Appearance of Homogeneous Antiferromagnetism in URu2Si2 under High Pressure: A 29Si Nuclear Magnetic Resonance Study", J. Phys.: Condens. Matter, 15:2363-2383(2003).*
    2003年 [査読無し][通常論文]
  • Yokoyama, M., Nozaki, J., Amitsuka, H., Watanabe, K., Kawarazaki, S., Yoshizawa H. and Mydosh J.A., "Nonequilibrium Antiferromagnetic State in the Heavy Electron Compound URu2Si2", Acta Phys. Pol. B, 34:1067-1070(2003)*
    2003年 [査読無し][通常論文]
  • Giri, R., Sekine, C., Shimaya, Y., Shirotani, I., Matsuhira, K., Doi, Y., Hinatsu, Y., Yokoyama M. and Amitsuka, H., "Magnetic Properties of Sm-Based Filled Skutterudite Phosphides", Physica B, 329-333:458-459(2003)*
    2003年 [査読無し][通常論文]
  • M Yokoyama, H Amitsuka, K Kuwahara, K Tenya, T Sakakibara
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 71 12 3037 - 3042 2002年12月 [査読無し][通常論文]
     
    Low temperature properties of the dilute uranium alloys La1-xUxRu2Si2 (x less than or equal to 0.07) have been investigated by means of magnetic susceptibility chi, magnetization m, specific heat C-P and electrical resistivity rho measurements to clarify the single-U-site effects of URu2Si2. Local 5f electrons show a strong magnetic anisotropy along the tetragonal c axis, as is observed in other dilute alloys Th1-xUxRu2Si2 and Y1-xUxRu2Si2. As temperature is lowered below similar to60 K, the c-axis susceptibility chi(c) follows a In T function, and rho decreases in proportion to chi(c). The 5f electronic specific heat C-P(5f)/T exhibits a broad peak at similar to10 K. The entropy change associated with this anomaly below 30 K is estimated to be only about 0.3R ln 2. Although the local Fermi liquid behavior is observed in chi, C-P and rho at very low temperatures, the ln T decrease in rho and the small entropy change provide a remarkable contrast with those expected in the usual magnetic dilute alloys.
  • S Kawarazaki, Y Uwatoko, M Yokoyama, Y Okita, Y Tabata, T Taniguchi, H Amitsuka
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS 41 10 6252 - 6255 2002年10月 
    A handy insertable device to manipulate hydrostatic pressure or uniaxial stress on a sample in a cryostat for neutron scattering experiments is described. The pressure that is generated in a miniature hydraulic oil-cylinder on the top of the inserting stick is transmitted to the sample via a long piston-cylinder unit made of a thick stainless-steel tube and a fiber-reinforced plastics (FRP) rod. One can thus in situ tune the pressure or the stress on the sample without handling the pressure-cell at room temperature outside the cryostat. The device is designed to fit into the ILL-type Orange cryostat so that it can he used ill many neutron scattering facilities. A newly designed uniaxial-stress cell and hydrostatic pressure cell to he used with this system are also described. The result of measurement of the hysteresis effect of uniaxial stress oil the antiferromagnetism of URu2Si2 at 1.4 K is presented.
  • T Sakakibara, T Tayama, K Tenya, M Yokoyama, H Amitsuka, D Aoki, Y Onuki, Z Kletowski, S Kunii
    JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 63 6-8 1147 - 1153 2002年06月 [査読有り][通常論文]
     
    0312RevUO
  • MATSUHIRA K, HINATSU Y, TENYA K, AMITSUKA H, SAKAKIBARA T
    J. Phys. Soc. Jpn. 71 6 1576 - 1582 2002年06月 [査読無し][通常論文]
     
    We report the magnetic properties of pyrochlore rare earth oxides R2Sn2O7 (R=Pr, Nd, Gd, Tb, Dy, Ho, Er, Tin and Yb). The magnetic susceptibility has been measured at temperatures down to 0.1 K, Among them, some compounds show the magnetic anomaly below 1 K. Nd2Sn2O7 and Gd2Sn2O7 show an antiferromagnetic ordering at 0.9 K and 1.0 K. respectively. Tb2Sn2O7 shows a ferromagnetic ordering at 0.87 K. Although both Er3+ and Yb3+ are a Kramers ion, no magnetic anomaly is observed at least down to 0.15 K. We found that Dy2Sn2O7 and Ho2Sn2O7 show 'spin ice' behavior. In addition, it is suggested that Pr2Sn2O7 is a new spin ice compound.
  • H Amitsuka, M Yokoyama, S Miyazaki, K Tenya, T Sakakibara, W Higemoto, K Nagamine, K Matsuda, Y Kohori, T Kohara
    PHYSICA B-CONDENSED MATTER 312 390 - 396 2002年03月 
    The origin and nature of the low-temperature please appearing below 17.5 K (equivalent to T-0) in URu2Si2 is still not fully understood. Since the weak antiferromagnetic state (WAF; mu(ord) similar to0.02-0.04 muB) developing below around To is not simply reconciled with a large reduction in the magnetic entropy (similar to0.2R ln 2), the existence of some hidden order parameter has been argued, where WAF is considered to be of a secondary nature. The paper reviews recent development of microscopic characterization of WAF based on neutron scattering and Si-29 NMR under high pressure. It is demonstrated that, at least, for pressures ranging from similar to0.3 to similar to0.83 GPa, there are spatially competing two different ordered states in the crystal: a normal-moment (similar to0.25 mu(B)/U) antiferromagnetic state and some unknown, non-magnetically ordered state. Simple extrapolation to ambient pressure suggests that WAF originates from one percent volume fraction of this antiferromagnetic phase. We also discuss the unusual magnetic properties at ambient pressure, presenting our latest results of zero-field and longitudinal-field muSR experiments. (C) 2002 Elsevier Science B.V. All rights reserved.
  • K Matsuda, Y Kohori, T Kohara, H Amitsuka, T Matsumoto
    PHYSICA B-CONDENSED MATTER 312 504 - 505 2002年03月 
    Si-29 NMR has been performed under pressure to study the antiferromagnetic (AF) ordering with a "tiny staggered moment" below T-o = 17.5 K in URu2Si2. In the pressure range between 3.0 and 8.3 kbar, we have observed the Si-29 NMR lines arising from the AF- and the paramagnetic-regions in the sample. This gives definite evidence for spatially inhomogeneous development of AF ordering below T-o. The AF volume fraction is enhanced by applied pressure, whereas the magnitude of internal field at Si-site in the AF region remains constant (910 Oe) up to 8.3 kbar. In the AF region, the ordered moment is about an order of magnitude larger than 0.031 mu(B)/U. (C) 2002 Elsevier Science B.V. All rights reserved.
  • T Nakano, K Fujita, Y Ohmori, S Murayama, K Hoshi, H Amitsuka, Y Onuki, M Ocio, J Hammann
    PHYSICA B-CONDENSED MATTER 312 440 - 442 2002年03月 
    Specific heat measurements have been performed on single-crystalline Ce(Ru1-xRhx)(2)Si-2 (x = 0.15,0.35) in various magnetic fields parallel to the c-axis. For x = 0.15, the magnetic specific heat C,; shows a jump due to the spin density wave for B 6T. For x = 0.35, C-mag/T shows the NFL behavior for B<6T and the FL behavior for B>6T. (C) 2002 Elsevier Science B.V. All rights reserved.
  • M Yokoyama, K Tenya, H Amitsuka
    PHYSICA B-CONDENSED MATTER 312 498 - 500 2002年03月 
    We have investigated Th dilution effects for URu2Si2 by performing magnetic susceptibility chi and specific heat C measurements in a rich U-concentration range. We have observed that sharp and clear anomalies seen in chi and C of the pure URu2Si2 at T-0 = 17.5 K become weak and unclear by substituting only five percent of U with Th. At the same time, the magnitude of the c-axis susceptibility chi(c) and C/T at low temperature is enhanced, indicating that the gap formation in the density of states for heavy quasi-particles is sensitively suppressed. For 10% of Th substitution, on the other hand, we have found a new kink anomaly to appear in chi(c) at similar to 13.7 K, where C also shows a hump. This suggests the presence of antiferromagnetic instability in URu2Si2. (C) 2002 Elsevier Science B.V. All rights reserved.
  • Makoto Yokoyama, Hiroshi Amitsuka, Kenji Watanabe, Shuzo Kawarazaki, Hideki Yoshizawa, John A. Mydosh
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 71 264 - 266 2002年01月 
    We have performed the elastic neutron scattering experiments under uniaxial stress sigma along the tetragonal [100], [110] and [001] directions for URu2Si2. For sigma parallel to [100] and [110], the antiferromagnetic moment mu(0) is strongly enhanced from 0.02 mu(B)/U (sigma = 0) to 0.22 mu(B)/U (sigma = 0.25 GPa) at 1.5 K. The rate of increase partial derivative mu(0)/partial derivative sigma is roughly estimated to be similar to 1.0 mu(B)/GPa, which is much larger than that for the hydrostatic pressure (similar to 0.25 mu(B)/GPa). Above 0.25 GPa, mu(0) shows a tendency to saturate similar to the behavior in the hydrostatic pressure, For sigma parallel to [001], on the other hand, mu(0) shows only a slight increase to 0.028 mu(B)/U (sigma = 0.46 GPa) with a rate of similar to 0.02 mu(B)/GPa. The observed anisotropy suggests that the competition between the hidden order and the antiferromagnetic state in URu2Si2 is strongly coupled with the tetragonal four-fold symmetry and the c/a ratio, or both.
  • Hiroshi Amitsuka, Atsushi Nogami, Kenichi Tenya, Makoto Yokoyama, Shikou Miyazaki, Toshiro Sakakibara, Masahiko Nakayama, Noriaki Kimura, Haruyoshi Aoki, Takemi Komatsubara
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 71 124 - 126 2002年01月 [査読有り][通常論文]
     
    We report on high-precision magnetization measurements on the non-Kram.ers cubic compound Pr3Pd20Ge6 for temperatures down to similar to 80 mK, in fields applied parallel to the [100] and [110] directions up to 8.5 T. Multistep-like structures of the magnetization curves are fourid below about 1 K for both the field directions. Temperature variations of the magnetic susceptibility show no tendency to saturate down to 80 inK, implying that the crystalline-electric-field (CEF) lowest state of 4f electrons for at least one of the Pr sites is the magnetic triplet Gamma(5). No significant anomaly is observed at 0.26 K, where quadrupole order is suggested front ultrasonic sound velocity measurements. An application of a simple CEF model is discussed.
  • Toshiro Sakakibara, Kenichi Tenya, Makoto Yokoyama, Hiroshi Amitsuka, Satoru Kunii
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 71 48 - 51 2002年01月 [査読有り][通常論文]
     
    We have examined the magnetization M of Ge0.75La0.25B6 under uniaxial pressures applied along the [001] direction, focusing our attention on the mysterious phase IV ordering, Magnetization of phase IV, which is nearly isotropic at an ambient pressure, becomes strongly anisotropic at a relatively weak uniaxial pressure of 60 MPa. On entering phase IV from the paramagnetic phase I, M(T) increases (decreases) for the field direction II parallel to [001] ([110]), suggesting that the order parameter is intrinsically anisotropic. Interestingly, M(T) for H parallel to [001] exhibits an upward-bending at the ordering temperature TI-IV, and TI-IV (H) seems to increase in magnetic field unlike the case of ordinary antiferromagnetic orderings. The results are discussed in view of a spontaneous ordering of an octupole moment in phase IV.
  • Matsuda, K., Kohori, Y., Kohara, T., Amitsuka, H. and Matsumoto, T.:"29^Si NMR Study of URu2Si2 under Pressure", Physica B, 312-313:504-505(2002).*
    2002年 [査読無し][通常論文]
  • Yokoyama, M., Tenya, K. and Amitsuka, H.:"Thorium Dilution Effects of the Heavy Electron Compound URu2Si2", Physica B, 312-313:498-500(2002)*
    2002年 [査読無し][通常論文]
  • Amitsuka, H., Yokoyama, M., Miyazaki, S., Tenya, K., Sakakibara, T., Higemoto, W., Nagamine, K., Matsuda, K., Kohori, Y. and Kohara, T.:"Hidden Order and Weak Antiferromagnetism in URu2Si2", Physica B, 312-313:390-396(2002)*
    2002年 [査読無し][通常論文]
  • Matsuhira, K., Hinatsu, Y., Tenya, K., Amitsuka, H. and Sakakibara T.:"Low-Temperature Magnetic Properties of Pyrochlore Stannates", J. Phys. Soc. Jpn., 71:1576-1582(2002)*
    2002年 [査読無し][通常論文]
  • Sakakibara, T., Tayama, T., Tenya, K., Yokoyama, M., Amitsuka, H., Aoki, D., Onuki, Y., Kletowski, Z. and Kunii, S.:"Multipole ordering in f electron systems", J. Phys. Chem. Solids, 63:1147-1153(2002)*
    2002年 [査読無し][通常論文]
  • Amitsuka, H., Nogami, A., Tenya, K., Yokoyama, M., Miyazaki, S., Sakakibara, T., Nakayama, M., Kimura, N., Aoki, H. and Komatsubara, T.:"Low-Temperature Magnetization Study on the non-Kramers Cubic System Pr3Pd20Ge6", J. Phys. Soc. Jpn., 71 Suppl.:124-・・・
    2002年 [査読無し][通常論文]
     
    Amitsuka, H., Nogami, A., Tenya, K., Yokoyama, M., Miyazaki, S., Sakakibara, T., Nakayama, M., Kimura, N., Aoki, H. and Komatsubara, T.:"Low-Temperature Magnetization Study on the non-Kramers Cubic System Pr3Pd20Ge6", J. Phys. Soc. Jpn., 71 Suppl.:124-126(2002)*
  • Yokoyama, M., Amitsuka, H., Watanabe, K., Kawarazaki, S., Yoshizawa, H. and Mydosh, J.A.:"Effects of Uniaxial Stress on Antiferromagnetic Moment in the Heavy Electron Compound URu2Si2", J. Phys. Soc. Jpn., 71 Suppl.: 264-266(2002)*
    2002年 [査読無し][通常論文]
  • Amitsuka, H., Tenya, K., Yokoyama, M., Schenck, A., Andreica, D., Gygax, F.N., Amato, A., Miyako, Y., Huang Ying Kai and Mydosh, J.A.:"Inhomogeneous Magnetism in URu2Si2 Studied by Muon Spin Relaxation under High Pressure", Physica B, 326:418-421(2002)*
    2002年 [査読無し][通常論文]
  • Sakakibara, T., Tenya, K., Yokoyama, M., Amitsuka, H. and Kunii, S.:"Anomalous Uniaxial Pressure Effect on the Phase IV Ordering in Ce0.75La0.25B6", J. Phys. Soc. Jpn., 71 Suppl.:48-51(2002)*
    2002年 [査読無し][通常論文]
  • K Matsuda, Y Kohori, T Kohara, K Kuwahara, H Amitsuka
    PHYSICAL REVIEW LETTERS 87 8 2001年08月 
    From Si-29 NMR study, we present evidence for spatially inhomogeneous development of antiferromagnetic (AF) ordering below T-o = 17.5 K in URu2Si2. In the pressure range between 3.0 and 8.3 kbar. we have observed the Si-29 NMR lines arising from the AF region as well as the previously observed Si-29 NMR line which correspond to the nonmagnetic region in the sample. The AF volume fraction is enhanced by applied pressure, whereas the magnitude of internal field at the Si site remains constant (910 Oe) up to 8.3 kbar. In the AF region, the ordered moment is about an order of magnitude larger than 0.03 mu (B)/U.
  • T Nagata, H Fujino, K Satoh, N Yamamori, J Akimitsu, S Katano, M Nishi, K Kakurai, M Hiroi, M Sera, N Kobayashi, K Tenya, H Amitsuka, T Takigawa, H Inago, T Sakakibara
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 70 8 2419 - 2424 2001年08月 [査読無し][通常論文]
     
    We report specific heat, magnetic susceptibility and neutron scattering measurements on the single crystals of Sr14-xCaxCu24O41. The specific heat data of Sr2.5Ca11.5Cu24O41 (x = 11.5) showed a sharp phase transition at T-N approximate to 2.3 K, and T-N was decreased with decreasing the Ca content x. Susceptibility measurements for x = 9, 10 and 11.5 revealed that this phase transition is due to antiferromagnetic ordering. In the neutron scattering experiments for x = 10 and 11.5, we observed several Bragg peaks, corresponding to the antiferromagnetic ordering confirmed in the specific heat and susceptibility measurements. A possible magnetic structure on the chain and ladder sites has been proposed. In this system, the singlet state and antiferromagnetic ordering induced by Ca substitution for Sr coexist at ambient pressure and the dissolved hole pairs move under high pressure, leading to the occurrence of superconductivity.
  • T Tayama, T Sakakibara, K Kitami, M Yokoyama, K Tenya, H Amitsuka, D Aoki, Y Onuki, Z Kletowski
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 70 1 248 - 258 2001年01月 [査読有り][通常論文]
     
    Antiferro-quadrupolar (AFQ) ordering in the cubic Gamma (3) ground state system PrPb3 has been studied by means of magnetization and specific heal measurements under magnetic fields Ii. Field variation of the AFQ transition temperature T-Q (0.4K at H 0) has teen determined for the three crystallographic directions (100), (110) and (111). The obtained T-Q(H) is strongly anisotropic, with T-Q((100))(H) the largest (similar to0.7K at 6T). The AFQ phase diagram and the magnetization behavior observed for H \ \ (100) are well explained by a model that incorporates both antiferromagnetic and antiferroquadrupolar interactions. The interactions between field-induced staggered magnetic moments stabilize the AFQ order. This simple model, however, seriously fails to explain the observed anisotropy: T-Q((100))(H) > T-Q((110))(H) > T-Q((111))(H). Reconsidering the field-induced multipole moments in the AFQ phase, we propose that inclusion of a weak ferro-octupolar interaction between rs type octupole moments is important in reproducing the anisotropic phase diagram of PrPb3.
  • 中野 智仁, 大森 善幸, 村山 茂幸, 保志 賢介, 網塚 浩, 大貫 惇睦, Ocio M, Hammann J
    日本物理学会講演概要集 56 0 494 - 494 一般社団法人日本物理学会 2001年 [査読無し][通常論文]
  • Matsuda, K., Kohori, Y., Kohara, T., Kuwahara, K., Amitsuka, H., "Spatially Inhomogeneous Development of Antiferromagnetism in URu_2Si_2: Evidence from ^29Si NMR under Pressure", Phys. Rev. Lett., 87:87203-1-4(2001)*
    2001年 [査読無し][通常論文]
  • Tayama, T., Sakakibara, T., Kitami, K., Yokoyama, M., Tenya, K., Amitsuka, H., Aoki, D., Onuki, Y., Kletowski, Z.:"Antiferro-Quadrupolar Ordering and Multipole Interactions in PrPb_3", J. Phys. Soc. Jpn., 70:248-258(2001)*
    2001年 [査読無し][通常論文]
  • Nagata, T., Fujino, H., Satoh, K., Yamamori, N., Akimitsu, J., Katano, S., Nishi, M., Kakurai, K., Hiroi, M., Sera, M., Kobayashi, N., Tenya, K., Amitsuka, H., Takigawa, T., Inago, H.: "Antiferromagnetic Ordering in the Spin Ladder Compound; Sr_14-xCa_・・・
    2001年 [査読無し][通常論文]
     
    Nagata, T., Fujino, H., Satoh, K., Yamamori, N., Akimitsu, J., Katano, S., Nishi, M., Kakurai, K., Hiroi, M., Sera, M., Kobayashi, N., Tenya, K., Amitsuka, H., Takigawa, T., Inago, H.: "Antiferromagnetic Ordering in the Spin Ladder Compound; Sr_14-xCa_xCu_24O_41", J. Phys. Soc. Jpn., 70: 2419-2424(2001)*
  • T Honma, Y Inada, R Settai, S Araki, Y Tokiwa, T Takeuchi, H Sugawara, H Sato, K Kuwahara, M Yokoyama, H Amitsuka, T Sakakibara, E Yamamoto, Y Haga, A Nakamura, H Harima, H Yamagami, Y Onuki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 69 8 2647 - 2659 2000年08月 [査読無し][通常論文]
     
    In order to investigate the 5f electronic properties in a ferromagnet UGa2 with the hexagonal structure, we have performed the magnetic, elastic, transport and de Haas-van Alphen experiments. From these properties, the crystal distortion is found to occur below 100 K in the basal plane, which is most likely driven by the development of a ferromagnetic moment oriented along the [1 1 (2) over bar 0] direction. (C) 2000 Elsevier Science B.V. All rights reserved.
  • T. Honma, E. Yamamoto, Y. Haga, R. Settai, S. Araki, Y. Inada, T. Takeuchi, K. Kuwahara, H. Amitsuka, T. Sakakibara, H. Sugawara, H. Sato, A. Nakamura, Y. Onuki
    Physica B: Condensed Matter 281-282 195 - 196 2000年06月01日 
    The 5f electronic properties in the ferromagnet UGa2 with the hexagonal structure were investigated. High quality samples were grown and their electrical resistivity, thermal expansion, elastic constant, Hall coefficient and de Haas-van Alphen oscillation were measured. Two characteristic temperatures were found: a Curie temperature at 123 K and another at 100 K below which the crystal is distorted in the basal plane. This distortion is most likely driven by the development of a ferromagnetic moment oriented along the [1 1 2̄ 0] direction.
  • K Kuwahara, A Okumura, M Yokoyama, K Tenya, H Amitsuka, T Sakakibara
    PHYSICA B 281 238 - 239 2000年06月 
    In previous ultrasonic measurements on the tetragonal compound URu2Si2 in zero magnetic field, we found a tendency of the softening below similar to 70 K in the transverse 1/2(c(11) - c(12)) mode. The results strongly suggest the presence of the lattice instability in this system. We here present the experimental results of the temperature dependence of elastic constants, c(11-) 1/2(c(11) - c(12)) and c(66) in magnetic fields along the tetragonal c-axis up to 12 T. The 1/2(c(11) - c(12)) mode increases as the magnetic field is increased, while the c(11) and c(66) modes decrease. The small but distinct held effects imply that the elastic anomaly in the transverse mode is caused by electrons. (C) 2000 Published by Elsevier Science B.V. All rights reserved.
  • K Matsuda, Y Kohori, T Kohara, K Kuwahara, H Amitsuka
    PHYSICA B-CONDENSED MATTER 281 989 - 990 2000年06月 
    We have performed Si-29 NMR and Ru-101 NQR measurements on a single crystalline URu2Si2. From the Si-29 NMR measurements, any appreciable internal field at Si site was not observed in the antiferromagnetic state, indicating that tiny magnetic moments of U are not static but fluctuating faster than the NMR frequency. From the Ru-101 NQR line which is much narrower than that of polycrystalline powder, the electric quadrupole interaction parameter (va) was precisely evaluated to be 5.713 MHz at 4.2 K. (C) 2000 Elsevier Science B.V. All rights reserved.
  • M Yokoyama, H Amitsuka, K Kuwahara, A Okumura, K Tenya, T Sakakibara
    PHYSICA B 281 395 - 396 2000年06月 
    We have investigated single-U-site properties of the dilute U alloys La1-xUxRu2Si2 for x less than or equal to 0.07. Contrary to usual Kondo effect, electrical resistivity due to U ions shows a In T decrease as temperature decreases. The 5f specific heat C-P(5f)/T exhibits a broad peak at similar to 10 K, and entropy change associated with this anomaly below 30 K is estimated to be only about 0.3 R In 2. These properties differ greatly from those seen in the usual dilute magnetic alloys. (C) 2000 Elsevier Science B.V. All rights reserved.
  • C Sekine, T Inaba, Shirotani, I, M Yokoyama, H Amitsuka, T Sakakibara
    PHYSICA B 281 303 - 305 2000年06月 [査読有り][通常論文]
     
    We have investigated the field dependence of the metal-insulator (MI) transition displayed by the filled skutterudite PrRu4P12 by means of specific heat measurements. The MI transition is not caused by a crystallographic transformation with breaking cubic symmetry, a valence transition nor a magnetic phase transition. Although the origin of the MI transition is still unclear, it is possible that an antiferro-quadrupolar ordering or a local-structure change of P atom is related to this transition. A lambda-like second order-type anomaly is observed at T-MI = 62.3 K. No field dependence of the MI transition is detected up to 12 T. A held-induced peak is observed much below T-MI (below 10 K). The magnetic entropy approaches the value similar to R In 2 above 10 K, which suggests that the crystalline-electric-field ground state of PrRu4P12 is the non-Kramer's doublet Gamma(3). (C) 2000 Elsevier Science B.V. All rights reserved.
  • H Amitsuka, K Kuwahara, M Yokoyama, K Tenya, T Sakakibara, M Mihalik, AA Menovsky
    Physica B 281 326 - 331 2000年06月 [査読無し][通常論文]
     
    Single-U-ion properties of heavy-electron compound URu2Si2 have been investigated by a series of diluting experiments on R1-xUxRu2Si2 (R = Th, Y, and La: x less than or equal to 0.07). A strong uniaxial magnetic anisotropy of local 5f moments is commonly observed throughout the dilutions. From a large enhancement of chi and C/T as T-->18, we suggest a non-Kramers, magnetic doublet Gamma(5) (f(2)) to be eminently suitable for the crystal-field lowest level, contrary to general Views of low-lying singlets for the periodic system. We further demonstrate the absence of the conventional Kondo effect in all these dilutions. A strong suppression of 5f moments at low temperatures accompanies a non-trivial In T decrease in rho and a small change in the magnetic entropy. Specific-heat measurements in magnetic fields up to 12 T have revealed no sign of the residual entropy, eliminating the simple application of the two-channel Kondo theory to the present alloys. We also discuss a puzzling phase transition at 17.5 K of URu2Si2 in relation to the single-ion physics, providing our latest results of neutron-scattering experiments under high pressure, (C) 2000 Elsevier Science B.V. All rights reserved.
  • T Sakakibara, S Honma, T Tayama, K Tenya, H Amitsuka, T Matsumura, T Suzuki
    PHYSICA B 281 566 - 568 2000年06月 [査読無し][通常論文]
     
    Magnetization of TmTe has been examined at temperatures down to 50 mK. in order to study the antiferroquadrupolar (AFQ) and antiferromagnetic (AF) ordered states. On cooling, magnetic susceptibility chi(T) increases enormously and appears to diverge in zero field at T-N = 0.22 K, evidencing that a ferromagnetic correlation is induced by the anisotropy due to the underlying AFQ order at T-O approximate to 1.8 K. In the magnetization process in the AFQ phase For field parallel to the [0 0 1] direction. a small metamagnetic jump is observed at similar to 1.9 T which might bt:related to a change in the quadrupolar order parameter, (C) 2000 Elsevier Science B.V. All rights reserved.
  • T Takikawa, T Sakakibara, K Matsuhira, K Tenya, H Amitsuka, S Kunii
    PHYSICA B-CONDENSED MATTER 281 561 - 562 2000年06月 [査読有り][通常論文]
     
    Magnetization of Ce0.75La0.25B6 has been measured under uniaxial pressure P similar or equal to 0.11 GPa applied parallel to the [1 1 0] direction in magnetic fields H up to 5T at temperatures between 0.4 and 3 K, with a special interest in the strain effect on a new exotic ordered state (phase-IV). The magnetic susceptibility chi of phase-IV, which is isotropic at P = 0, becomes remarkably anisotropic under pressure as chi([1 1 0]) > chi([1 1 0]), indicating that the magnetic state of phase-IV is very sensitive to the uniaxial strain. Effect of pressure is also evidenced in the magnetic response in phase-m antiferromagnetic state especially at low-field region. (C) 2000 Elsevier Science B.V. All rights reserved.
  • K Tenya, K Kuwahara, H Amitsuka, T Sakakibara, H Ohkuni, Y Inada, E Yamamoto, Y Haga, Y Onuki
    PHYSICA B-CONDENSED MATTER 281 991 - 992 2000年06月 [査読無し][通常論文]
     
    Magnetization measurements of a heavy fermion compound URu2Si2 have been performed in the superconducting state. Broad peak structure of the irreversible magnetization was observed around 50 kOe for H parallel to n. The Ginzburg-landau parameter obtained from the equilibrium magnetization slightly decreases for H parallel to c with decreasing temperature, suggesting the presence of the paramagnetic suppression of the superconductivity. However, the suppression is not so large as expected from the H-c2(T) curve. Thermodynamic critical field appears to show unusual temperature dependence. (C) 2000 Elsevier Science B.V. All rights reserved.
  • Y Miyako, Y Yamamoto, Y Tabata, K Marumoto, M Sato, T Taniguchi, T Takeuchi, S Kawarazaki, H Amitsuka, M Ocio, P Pari, J Hammann
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 69 77 - 90 2000年05月 
    The low temperature properties of Ce(Ru1-xRhx)(2)Si-2 (0 less than or equal to x less than or equal to 1), U(Ru1-xRhx)(2)Si-2 (0 less than or equal to x less than or equal to 1) and UxLa1-xRu2Si2 (0 less than or equal to x less than or equal to 0.15) are reviewed with emphasis on experiments of susceptibility, non-linear susceptibility, specific heat, resistivity, thermal expansion, neutron scattering and mu SR. New experimental data has led to new insights to the physical understanding of these heavy fermions. In Rh rich side, antiferromagnetic order associated with the localized character of the f-electrons sets in for both Ce(Ru1-xRhx)(2)Si-2 (0 less than or equal to x less than or equal to 1) and U(Ru1-xRhx)(2)Si-2 (0 less than or equal to x less than or equal to 1) compounds. For Ce(Ru1-xRhx)(2)Si-2 compound, x-dependence of the material is investigated in detail. In Ru rich side, the ground state is a Fermi liquid for x < 0.03; an anisotropic spin density wave (SDW) appears for 0.03 < x < 0.4 with a maximum T-N = 5.5 K at x = 0.15. The nature of the anisotropic SDW is characterized by the anisotropic anomaly in the resistivity below T-N The anisotropy of the SDW is discussed from the view point of nesting of the Fermi surfaces of itinerant heavy fermion quasi-particle bands. Another interesting feature is the non-Fermi liquid behavior observed for x = 0.4 and 0.5. Appearance of quantum Griffiths's like phase is indicated for x = 0.5 from the measurements of mu SR, low field ac-susceptibilty and nonlinear susceptibiltiy. The temperature dependence of the susceptibility and the magnetoresistance with 0.1 T de-field are well explained in terms of the mean field theory based on spin fluctuations. The phase transition of URu2Si2 at 17.5 K(= T-o) is considered to be due to quadrupolar ordering from the behaviors of a sharp anomaly in nonlinear susceptibility at T-o and very large consumption of entropy below T-o compared to a small staggered ordered moment, 0.02 mu(B) We recently found that the phase transition is not due to magnetic origin by neutron scattering experiment under pressure. The susceptibility and magnetization in dilute alloys of UxLa1-xRu2Si2 are well explained by assuming a non-Kramers doublet ground state of the J = 4 crystalline field level. From these experiments, the phase transition of URu2Si2 at T-o is understood by the model of quadrupolar ordering of the non-Kramers doublet which coexists with antiferromagntic short range order.
  • T Sakakibara, T Tayama, K Kitami, M Yokoyama, K Tenya, H Amitsuka, D Aoki, Y Onuki, Z Kletowski, T Matsumura, T Suzuki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 69 25 - 32 2000年05月 
    Effect of magnetic field on the antiferro-quadrupolar (AFQ) phase in the cubic compounds PrPb3 and TmTe has been studied by means of magnetization and specific heat measurements. In PrPb3, it is found that the AFQ transition temperature T-Q (=0.4 K at H=0) remarkably increases in magnetic field. This behavior is well explained by antiferromagnetic interactions between the field-induced staggered magnetic moment in the AFQ phase. Analysis of the observed anisotropy T-Q([100])(H) > T-Q([110])(H), however, strongly suggests the presence of a weak ferro-octupolar interaction. In TmTe, magnetic susceptibility chi(T) increases enormously on cooling and appears to diverge upon an antiferromagnetic (AF) transition at T-N=0.22 K. The results imply that a ferromagnetic moment is induced in the AF phase by an alternating anisotropy due to the preexisting AFQ order at T(Q)approximate to 1.8 K. This is possible when both AF and AFQ states are described by the same wave vector, in agreement with recent neutron diffraction studies.
  • H Amitsuka, M Yokoyama, K Tenya, T Sakakibara, K Kuwahara, M Sato, N Metoki, T Honma, Y Onuki, S Kawarazaki, Y Miyako, S Ramakrishnan, JA Mydosh
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 69 5 - 12 2000年05月 [査読有り][通常論文]
     
    A puzzling phase transition at T-o similar to 17.5 K of the heavy-electron 5f system URu2Si2 is characterized by development of an unusually small staggered moment mu(o) concomitant with large bulk anomalies and sharp magnon excitations. Through elastic and inelastic neutron scattering, we have studied the influence of pressure P up to similar to 2.8 GPa on this phase transition. For pressures less than 1.3 GPa, mu(o) at 1.4 K is quasi-linearly enhanced from similar to 0.017(3) mu(B) to similar to 0.25(2) mu(B), while its onset temperature increases only ten present. We have also observed a sharp phase transition at P-c similar to 1.5 GPa, above which a 3D-Ising type of antiferromagnetic phase (mu(o) similar to 0.4 mu(B)) appears. Sharp magnon excitations at Q = (1,0,0) and (1,0.4,0) collapse in this high-P phase. The lattice parameter a decreases discontinuously at P-c even for T > T-o, indicating that pressure induces a significant change in electronic states in a higher characteristic energy scale. We show that the observed magnetic instability could qualitatively well be explained by competition between quadrupolar and dipolar interactions in a non-trivial Gamma(5) doublet.
  • N Metoki, Y Koike, Y Haga, T Honma, M Sato, Y Onuki, N Kimura, K Maesawa, H Amitsuka, M Yokoyama, K Kuwahara, Y Miyako
    PHYSICA B-CONDENSED MATTER 280 1-4 362 - 367 2000年05月 [査読有り][通常論文]
     
    We review recent neutron scattering studies on uranium-based heavy-fermion superconductors. The coupling between magnetic and superconducting order parameters was observed in UPt3, UPd2Al3, URu2Si2, and UhTi(2)Al(3). In UPd2Al3, the superconducting gap appears in the spin excitation spectra. These results are indicative of the strong interplay between magnetism and superconductivity. We also report the unusual behaviors of the weak antiferromagnetic ordering, the long-range magnetic correlation in UPt3 at ultra-low temperatures, and the pressure-induced magnetic transition from the weak (0.02 mu(B)/U) to a high moment state (0.4 mu(B)/U) at 1.5 GPa in URu2Si2. (C) 2000 Elsevier Science B.V. All rights reserved.
  • Kuwahara, K., Okumura, A., Yokoyama, M., Tenya, K., Amitsuka, H. and Sakakibara, T.: ``Elastic Constants of URu_2Si_2 in Magnetic Fields", Physica B, 281&282: 238-239(2000)*
    2000年 [査読無し][通常論文]
  • Honma, T., Inada, Y., Settai, R., Araki, S., Tokiwa, Y., Takeuchi, T., Sugawara, H., Sato, H., Kuwahara, K., Yokoyama, M., Amitsuka, H., Sakakibara, T., Yamamoto, E., Haga, Y., Nakamura, A., Harima, H., Yamagami, H. and Onuki, Y.: ``Magnetic and Fermi ・・・
    2000年 [査読無し][通常論文]
     
    Honma, T., Inada, Y., Settai, R., Araki, S., Tokiwa, Y., Takeuchi, T., Sugawara, H., Sato, H., Kuwahara, K., Yokoyama, M., Amitsuka, H., Sakakibara, T., Yamamoto, E., Haga, Y., Nakamura, A., Harima, H., Yamagami, H. and Onuki, Y.: ``Magnetic and Fermi Surface Properties of the Ferromagnetic Compound UGa_2", J. Phys. Soc. Jpn., 69: 2647-2659(2000)*
  • Miyako, Y., Yamamoto, Y., Tabata, Y., Marumoto, K., Sato, M., Taniguchi, T., Takeuchi, T., Kawarazaki, S., Amitsuka, H., Ocio, M., Pari P. and Hammann J.: ``Spin Fluctuations and Antiferromagnetic Phase Transitions in Heavy Fermions of Kramers (Ce comp・・・
    2000年 [査読無し][通常論文]
     
    Miyako, Y., Yamamoto, Y., Tabata, Y., Marumoto, K., Sato, M., Taniguchi, T., Takeuchi, T., Kawarazaki, S., Amitsuka, H., Ocio, M., Pari P. and Hammann J.: ``Spin Fluctuations and Antiferromagnetic Phase Transitions in Heavy Fermions of Kramers (Ce compound) and Non-Kramers (U compound) Doublets", J. Phys. Soc. Jpn., 69 suppl. A.: 77-90(2000)*
  • Sakakibara, T., Tayama, T., Kitami, K., Yokoyama, M., Tenya, K., Amitsuka, H., Matsumura, T., Aoki, D., Onuki, Y., Kletowski, Z. and Suzuki T.: ``Interplay of Orbital and Magnetic Degrees of Freedom in f-Electron Systems: The case of PrPb_3 and TmTe", ・・・
    2000年 [査読無し][通常論文]
     
    Sakakibara, T., Tayama, T., Kitami, K., Yokoyama, M., Tenya, K., Amitsuka, H., Matsumura, T., Aoki, D., Onuki, Y., Kletowski, Z. and Suzuki T.: ``Interplay of Orbital and Magnetic Degrees of Freedom in f-Electron Systems: The case of PrPb_3 and TmTe", J. Phys. Soc. Jpn., 69 suppl. A.: 25-32(2000)*
  • Amitsuka, H., Yokoyama, M., Tenya, K., Sakakibara, T., Kuwahara, K., Sato, M., Metoki, N., Honma, T., Onuki, Y., Kawarazaki, S., Miyako, Y. and Mydosh, J.A.: ``Pressure-Induced Magnetic Phase Transition of the 5f Electron System URu_2Si_2", J. Phys. So・・・
    2000年 [査読無し][通常論文]
     
    Amitsuka, H., Yokoyama, M., Tenya, K., Sakakibara, T., Kuwahara, K., Sato, M., Metoki, N., Honma, T., Onuki, Y., Kawarazaki, S., Miyako, Y. and Mydosh, J.A.: ``Pressure-Induced Magnetic Phase Transition of the 5f Electron System URu_2Si_2", J. Phys. Soc. Jpn., 69 suppl. A.: 5-12(2000)*
  • Tenya, K., Kuwahara, K., Amitsuka, H., Sakakibara, T., Ohkuni, H., Inada, Y., Yamamoto, E., Haga, Y. and Onuki, Y.: ``Magnetization Study in the Superconducting Mixed State of URu_2Si_2", Physica B, 281&282: 991-992(2000)*
    2000年 [査読無し][通常論文]
  • Matsuda, K., Kohori, Y., Kohara, T., Kuwahara, K. and Amitsuka H.: ``NMR and NQR Studies of URu_2Si_2", Physica B, 281&282: 989-990(2000)*
    2000年 [査読無し][通常論文]
  • Yokoyama, M., Amitsuka, H., Kuwahara, K., Okumura, A., Tenya, K. and Sakakibara T.: ``Unusual Low Temperature Behavior of the Dilute Uranium Alloys La_{1-x}U_{x}Ru_2Si_2, (x =< 0.07)", Physica B, 281&282: 395-396(2000)*
    2000年 [査読無し][通常論文]
  • Takikawa, T., Sakakibara, T., Matsuhira, K., Tenya, K., Amitsuka H. and Kunii S., ``Magnetic Properties of Ce_{0.75}La_{0.25}B_{6} Under Uniaxial Stress", Physica B, 281&282: 561-562(2000)*
    2000年 [査読無し][通常論文]
  • Sakakibara, T., Honma, S., Tayama, T., Tenya, K., Amitsuka, H., Matsumura, T. and Suzuki T.: ``Low Temperature Magnetization of Antiferro-Quadrupolar Ordering System TmTe", Physica B, 281&282: 566-568(2000)*
    2000年 [査読無し][通常論文]
  • Amitsuka, H., Kuwahara, K., Yokoyama, M., Tenya, K., Sakakibara, T., Mihalik, M. and Menovsky, A.A.: ``Non-Fermi-Liquid Behavior in R_{1-x}U_{x}Ru_2Si_2 ( R=Th, Y and La, x =< 0.07)", Physica B, 281&282: 326-331(2000)*
    2000年 [査読無し][通常論文]
  • Sekine, C., Inaba, T., Shirotani, I., Yokoyama, M., Amitsuka, H. and Sakakibara, T.: ``The specific heat of the filled skutterudite PrRu_4P_12 in magnetic fields", Physica B, 281&282: 303-305(2000)*
    2000年 [査読無し][通常論文]
  • Honma, T., Yamamoto, E., Haga, Y., Settai, R., Araki, S., Inada, Y., Takeuchi, T., Kuwahara, K., Amitsuka, H., Sakakibara, T., Sugawara, H., Sato, H., Nakamura, A. and Onuki, Y.: ``Magnetic, Elastic, Transport and Fermi Surface Properties of a Ferromag・・・
    2000年 [査読無し][通常論文]
     
    Honma, T., Yamamoto, E., Haga, Y., Settai, R., Araki, S., Inada, Y., Takeuchi, T., Kuwahara, K., Amitsuka, H., Sakakibara, T., Sugawara, H., Sato, H., Nakamura, A. and Onuki, Y.: ``Magnetic, Elastic, Transport and Fermi Surface Properties of a Ferromagnetic Compound UGa_2", Physica B, 281&282: 195-196(2000)*
  • Metoki, N., Koike, Y., Haga, Y., Honma, T., Sato, M., Onuki, Y., Kimura, N., Maesawa, K., Amitsuka, H., Yokoyama, M., Kuwahara, K. and Miyako, Y.: ``Neutron-Scattering Studies on Heavy-Fermion Superconductors", Physica B, 280: 362-367(2000)*
    2000年 [査読無し][通常論文]
  • H Amitsuka, M Sato, N Metoki, M Yokoyama, K Kuwahara, T Sakakibara, H Morimoto, S Kawarazaki, Y Miyako, JA Mydosh
    PHYSICAL REVIEW LETTERS 83 24 5114 - 5117 1999年12月 [査読有り][通常論文]
     
    We have performed elastic neutron-scattering experiments on the heavy-electron compound URu(2)Si(2) for pressure P up to 2.8 GPa. We have found that the antiferromagnetic (100) Bragg reflection below T(m) similar to 17.5 K is strongly enhanced by applying pressure. For P < 1.1 GPa, the staggered moment mu(0) at 1.4 K increases linearly from similar to 0.017(3)mu(B) to similar to 0.25(2)mu(B), while T(m) increases slightly at a rate similar to 1 K/GPa, roughly following the transition temperature T(0) determined from macroscopic anomalies. We have also observed a sharp phase transition at P(0) similar to 1.5 GPa, above which a 3D-Ising type of antiferromagnetic phase (mu(0) similar to 0.4 mu(B)) appears with a slightly reduced lattice constant.
  • K Matsuhira, T Sakakibara, A Nomachi, T Tayama, K Tenya, H Amitsuka, K Maezawa, Y Onuki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 68 10 3402 - 3406 1999年10月 [査読無し][通常論文]
     
    Matsuhira,K., Sakakibara,T., Nomachi,A., Tayama,T., Tenya,K., Amitsuka,H., Maezawa, K. and Onuki, Y.:"Simultaneous Measurement of Magnetization and Magnetostriction in CeRu_2Si_2 at Very Low Temperatures: A Test of the One-Parameter Scaling Property", J. Phys. Soc. Jpn., 68:3402-3406(1999)
  • M Hedo, Y Kobayashi, Y Inada, E Yamamoto, Y Haga, J Suzuki, N Metoki, Y Onuki, H Sugawara, H Sato, K Tenya, T Tayama, H Amitsuka, T Sakakibara
    PHYSICA B-CONDENSED MATTER 259-61 688 - 689 1999年01月 
    We have carried out the flux dow experiments for two single crystal samples with the residual resistivity ratio RRR = 240 and 12 which differ highly in quality. The peak structure, which is observed in the vicinity of H-c2, is dominant for the RRR = 12 sample, while it is slightly observed for the RRR = 240 sample. The flux flow, however, starts at a low field for the RRR = 12 sample, compared to that for the RRR = 240 sample. It means that a pinning force for the RRR = 12 sample is smaller than that for the RRR = 240 sample. These characteristic features might be closely related to layered defects and Ru-vacancies which exist heavily in the RRR = 12 sample. (C) 1999 Elsevier Science B.V. All rights reserved.
  • K Matsuhira, T Sakakibara, K Tenya, H Amitsuka
    PHYSICA B-CONDENSED MATTER 259-61 73 - 74 1999年01月 
    In order to study the inter-site effects in CeRu2Si2, we have done a series of diluting experiments under constant-volume condition using the pseudo-ternary system Ce1-x(La0.63Y0.37)(x)Ru2Si2. Comparing with impurity Kondo model, we found that there is a non-trivial peak structure in the specific heat of CeRu2Si2 caused by certain inter-site effect. This peak structure becomes weak with increasing x and seems to disappear at x similar to 0.2 where metamagnetism also vanishes. (C) 1999 Elsevier Science B.V. All rights reserved.
  • T Sakakibara, T Tayama, K Tenya, H Amitsuka, D Aoki, Y Onuki, Z Kletowski
    PHYSICA B-CONDENSED MATTER 259-61 340 - 342 1999年01月 
    Quadrupolar ordering in the cubic compound PrPb3 has been studied by DC magnetization measurements at temperatures down to T similar to 50 mK in fields (H parallel to[1 0 0]) up to 8 T. The quadrupolar ordering temperature T-Q(H), below which the magnetic susceptibility is enhanced, is found to increase in H from 0.4 K at H = 0 to 0.6 K at H = 5 T. On cooling below T-Q(H), sharp metamagnetic transitions develop in the magnetization process at around 7 T. The resulting H-T phase diagram can be explained by incorporating magnetic interactions between the field-induced antiferromagnetic moments in the O-2(0) type antiferro-quadrupolar phase. (C) 1999 Elsevier Science B.V. All rights reserved.
  • Magnetization Study of the Phase Diagram of CexLa1-xB6
    T. Sakakibara, T. Tayama, K. Tenya, H. Amitsuka, S. Kunii
    JJAP Series 11 179  1999年 [査読有り][通常論文]
  • H Sato, J Urakawa, Y Aoki, T Namiki, H Sugawara, Y Onuki, H Amitsuka, T Sakakibara
    PHYSICA B-CONDENSED MATTER 259-61 390 - 391 1999年01月 [査読有り][通常論文]
     
    We have investigated the temperature (T) dependence of Hall coefficient (R(H)) and thermoelectric power (TEP) in Y(1 - x)U(x)Pd(3) and Y(1 - x)U(x)RU(2)Si(2). For Y(1 - x)U(x)Pd(3), R(H)(T) roughly follows similar to chi rho expected for the ordinary skew scattering. At high temperatures, R(H) for Y(1 - x)U(x)Ru(2)Si(2) also follows similar to chi rho, however, it sharply decreases below similar to 40 K. TEP also exhibits a clear drop below similar to 40 K followed by a sharp minimum near 8 K. (C) 1999 Elsevier Science B.V. All rights reserved.
  • T Tayama, S Honma, K Tenya, H Amitsuka, T Sakakibara, S Kunii
    PHYSICA B-CONDENSED MATTER 259-61 32 - 33 1999年01月 [査読有り][通常論文]
     
    From DC magnetic susceptibility chi(T) measurement on CexLa1-xB6 (x = 0.75, 0.7, 0.65 and 0.4), Ce concentration dependence of the zero-field ordering temperature is established. The new magnetic state (phase-IV) characterized by an isotropic cusp in chi(T) is clearly seen for x = 0.75, 0.7 and 0.65. Distinct irreversibility in chi(T) observed for x = 0.4 below the cusp temperature indicates that phase-IV changes into a certain glass-like state for x less than or equal to 0.5. (C) 1999 Elsevier Science B.V. All rights reserved.
  • K Tenya, S Yasunami, T Tayama, H Amitsuka, T Sakakibara, M Hedo, Y Inada, Y Haga, E Yamamoto, Y Onuki
    PHYSICA B-CONDENSED MATTER 259-61 692 - 693 1999年01月 [査読無し][通常論文]
     
    Detailed magnetization measurements of CeRu2 single crystals with different purity are performed in order to clarify whether their peak effects are due to the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) transition. The onset field of the peak shifts to lower held side as the sample becomes impure. Regardless of the purity the Ginzburg-Landau parameter kappa(2) continues to increase on cooling from T-c, indicating little paramagnetic suppression of the superconductivity. These results disagree with the scenario of the FFLO transition. (C) 1999 Elsevier Science B.V, All rights reserved.
  • K Tenya, S Yasunami, T Tayama, H Amitsuka, T Sakakibara, M Hedo, Y Inada, E Yamamoto, Y Haga, K Onuki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 68 1 224 - 231 1999年01月 [査読無し][通常論文]
     
    A huge peak of irreversible magnetization in CeRu2 single crystal, together with the equilibrium magnetization. was investigated by means of a static magnetization measurement using a Faraday force magnetometer. The residual resistance ratio of the used crystal exceeds 250, indicating that it is a clean superconductor. Contrary to the previous reports, there is no pinning-free region in the magnetization curves below the upper critical field H-c2. The detailed minor-hysteresis-loop measurement has revealed that the peak structure in the increasing-field magnetization curve around the onset field of the peak strongly depends on previous field-history, resulting in an apparent asymmetry of the peak structure. No trace of paramagnetic suppression of superconductivity in the vortex-penetrated state is observed from the superconducting equilibrium magnetization curves. The peak position, although highly anisotropic, can be interrelated to the peak strength, regardless of the applied field direction. It is likely that the irreversibility peak is due to a synchronization pinning of the defective nux line lattice, rather than due to a first-order transition from the mixed state to the Fulde-Ferrell-Larkin-Ovchinnikov state.
  • Tayama,T., Honma,S., Tenya,K., Amitsuka,H., Sakakibara,T. and Kunii,S.:"Magnetic Phase Diagram of Ce_xLa_1-xB_6 Studied by Magnetization Measurement", Physica, B259-261:32-33(1999)
    1999年 [査読無し][通常論文]
  • Amitsuka,H., Sato,M., Metoki,N., Yokoyama,M., Kuwahara,K., Sakakibara,T., Morimoto,H., Kawarazaki,S., Miyako,Y. and Mydosh, J.A.:"Effect of Pressure on Tiny Antiferromagnetic Moment in the Heavy-Electron Compound URu_2Si_2", Phys. Rev. Lett., 83:5114-・・・
    1999年 [査読無し][通常論文]
     
    Amitsuka,H., Sato,M., Metoki,N., Yokoyama,M., Kuwahara,K., Sakakibara,T., Morimoto,H., Kawarazaki,S., Miyako,Y. and Mydosh, J.A.:"Effect of Pressure on Tiny Antiferromagnetic Moment in the Heavy-Electron Compound URu_2Si_2", Phys. Rev. Lett., 83:5114-5117(1999)
  • Matsuhira,K., Sakakibara,T., Tenya,K. and Amitsuka,H.:"Specific Heat of CeRu_2Si_2 Studied by Constant Volume Dilution", Physica B259-261:73-74(1999)
    1999年 [査読無し][通常論文]
  • Sakakibara,T., Tayama,T., Tenya,K., Amitsuka,H., Aoki,D., Onuki,Y. and Kletowski, Z.:"Magnetization Study of the Antiferro-Quadrupolar Ordering in PrPb_3", Physica B259-261:340-342(1999)
    1999年 [査読無し][通常論文]
  • Amitsuka,H., Kuwahara,K., Okumura,A., Tenya,K., Sakakibara,T., Mihalik,M. and Menovsky, A.A.:"Magnetic Properties of Dilute Uranium Alloys Y_1-xU_xRu_2Si_2(x<0.07)", JJAP Series,11:145-147(1999)
    1999年 [査読無し][通常論文]
  • Sakakibara,T., Tayama,T., Matsuhira,K., Nomachi,A., Honma,S., Tenya,K., Amitsuka,H., Maezawa,K. and Onuki,Y.:"Low Temperature Magnetization and Magnetostriction of CeRu_2Si_2", JJAP Series,11:6-8(1999)*
    1999年 [査読無し][通常論文]
  • Sakakibara,T., Tayama,T., Tenya,K. and Amitsuka,H.:"Magnetization Study of the Phase Diagram of Ce_xLa_1-xB_6",JJAP Series,11:179-181(1999)
    1999年 [査読無し][通常論文]
  • Tenya,K., Yasunami,S., Tayama,T., Amitsuka,H., Sakakibara,T., Hedo,M., Inada,Y., Yamamoto,E., Haga,Y. and Onuki,Y.:"Magnetization Study of the History-Dependent Peak Effect in the Superconducting Mixed State of CeRu_2", J. Phys. Soc. Jpn., 68:224-231(・・・
    1999年 [査読無し][通常論文]
     
    Tenya,K., Yasunami,S., Tayama,T., Amitsuka,H., Sakakibara,T., Hedo,M., Inada,Y., Yamamoto,E., Haga,Y. and Onuki,Y.:"Magnetization Study of the History-Dependent Peak Effect in the Superconducting Mixed State of CeRu_2", J. Phys. Soc. Jpn., 68:224-231(1999)
  • Tenya,K., Yasunami,S., Tayama,T., Amitsuka,H., Sakakibara,T., Hedo,M., Inada,Y., Haga,Y., Yamamoto,E. and Onuki, Y.:"Field-History Dependent Peak Effect in the Superconducting Mixed State of CeRu_2", Physica, B259-261:692-693(1999)
    1999年 [査読無し][通常論文]
  • Hedo,M., Kobayashi,Y., Inada,Y., Yamamoto,E., Haga,Y., Suzuki,J., Metoki,N., Onuki,Y., Sugawara,H., Sato,H., Tenya,K., Tayama,T., Amitsuka,H. and Sakakibara,T.:"Characterization and Flux Flow Experiments in CeRu_2",Physica, B259-261:688-689(1999)
    1999年 [査読無し][通常論文]
  • H Amitsuka, K Kuwahara, T Yoshida, K Tenya, T Sakakibara, M Mihalik, AA Menovsky
    PHYSICA B-CONDENSED MATTER 259-61 412 - 414 1999年01月 [査読無し][通常論文]
     
    We investigate contribution of a single U ion to the electrical resistivity (Ap) in the dilute U alloys R1 - xUxRu2Si2 (R = Th,Y) for x less than or equal to 0.07. Contrary to the conventional Kondo behavior, in both systems hp exhibits an unusual decrease with reducing temperature below a characteristic temperature (T*) of similar to 10 K (R = Th) and 40 K (Y). At higher temperatures, Delta rho is almost independent of T with the amplitude (Delta rho(RT)) of similar to 59 (95) mu Omega cm/U for R = Th (Y). The dependence Delta rho similar to ln T below T* and the relationship Delta rho(T --> 0) similar to 1/2 Delta rho(RT) are found similarly between these two dilutions irrespective of T* and Delta rho(RT), suggesting that these are universal features in the dilute limit of URu2Si2. The ln T decrease in Ap is approximately proportional to the increase in the magnetic susceptibility, which provides a remarkable distinction between the present systems and known reverse-Kondo alloys. (C) 1999 Elsevier Science B.V. All rights reserved.
  • Sato,H., Urakawa,J., Aoki,Y., Namiki,T., Sugawara,H., Onuki,Y., Amitsuka,H. and Sakakibara, T. :"Hall Effect and Thermoelectric Power in the Systems Exhibiting the Non-Fermi Liquid Behaviors", Physica B259-261:390-391(1999)
    1999年 [査読無し][通常論文]
  • Amitsuka,H., Honma,T., Sakakibara,T., Mitamura,H., Goto,T., Abe,H., Suzuki,H., Kitazawa,H., Kido,G., Sugiyama, K., Miyako,Y. and Date, M.:"High Field Study of the 5f states in URu_2Si_2 and the Related Compounds", Proceedings of the 4th International S・・・
    1999年 [査読無し][通常論文]
     
    Amitsuka,H., Honma,T., Sakakibara,T., Mitamura,H., Goto,T., Abe,H., Suzuki,H., Kitazawa,H., Kido,G., Sugiyama, K., Miyako,Y. and Date, M.:"High Field Study of the 5f states in URu_2Si_2 and the Related Compounds", Proceedings of the 4th International Symposium on Advanced Physical Fields, edited by Kido,G.:29-32(1999)
  • Tenya,K., Tayama,T., Amitsuka,H., Sakakibara,T., Kimura,N., Yamamoto,E., Haga,Y., Hedo, M., Maezawa,K., Inada,Y., Settai, R. and Onuki,Y.,:"Magnetization Study of Superconductivity in UPt_3 and CeRu_2", JJAP Series,11:53-55(1999)*
    1999年 [査読無し][通常論文]
  • M Hedo, Y Kobayashi, Y Inada, E Yamamoto, Y Haga, J Suzuki, N Metoki, Y Onuki, H Sugawara, H Sato, K Tenya, T Tayama, H Amitsuka, T Sakakibara
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 67 10 3561 - 3569 1998年10月 
    We measured the electrical resistivity in magnetic fields and the Hall voltage to understand the peak effect in a superconductor with the cubic structure CeRu2. Two samples with residual resistivity ratios of rho(RT)/rho(0) = 240 and 12 were prepared, and the experimental results in the superconducting mixed state were compared between them. The flux flow begins at a high field and the peak effect is observed in a very narrow window in the T vs. H phase diagram near the upper critical field H-c2 for the sample with rho(RT)/rho(0) = 240, while it starts at a lower field and the window where the peak effect is observed becomes wider for the sample with rho(RT)/rho(0) = 12. These characteristic features are mainly related to crystalline defects in the sample.
  • T Honma, H Amitsuka, S Yasunami, K Tenya, T Sakakibara, W Mitamura, T Goto, G Kido, S Kawarazaki, Y Miyako, K Sugiyama, M Date
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 67 3 1017 - 1028 1998年03月 [査読無し][通常論文]
     
    T. Honma, H. Amitsuka, S. Yasunami, K. Tenya, T. Sakakibara, H. Mitamura, T. Goto, G. Kido, S. Kawarazaki, Y. Miyako, K. Sugiyama and M. Date: Incommensurate-Commensurate Magnetic Phase Transitions of the Ising-5f System UPd2Si2: the H-T Phase Diagram and Mean-Field Analysis, (J. Phys. Soc. Jpn. 67, 1017--1028, 1998*)
  • T Matsumura, S Nakamura, T Goto, H Amitsuka, K Matsuhira, T Sakakibara, T Suzuki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 67 2 612 - 621 1998年02月 
    The magnetic susceptibility; elastic constant, specific heat and magnetization of the magnetic semiconductor TmTe have been measured in detail. A phase transition which is likely to be an antiferro quadrupolar ordering was found to occur at 1.8 K. The specific heat measurements under magnetic fields along the three main crystal axes revealed the unusual characters of this phase transition. The (H - T) phase diagram below 5 T is very similar to that of the antiferro quadrupolar ordering in CeB6. Above 5 T, however, the phase line for H parallel to [100] begins to close toward T = 0 K. The physical properties in the paramagnetic region at high temperatures are discussed in the mean field approximation. The theoretical fitting of the elastic softening indicates the antiferro inter-ionic quadrupolar interactions. However, the mean field theory can not explain the specific heat results.
  • JG Park, HC Ri, K Kuwahara, H Amitsuka
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 177 455 - 456 1998年01月 
    We present low field magnetization results of URu2Si2 single crystals, measured after zero-field cooling and field cooling with fields applied along the a- and c-axes. To investigate heat treatment effects on magnetization, we prepared both unannealed and annealed single crystals. In all the samples we studied, we found thermal hysteresis in the low held magnetization, and temperatures where the hysteresis starts differ for the a- and c-axes samples. However it tends to disappear with increasing fields. There are also subtle, but measurable, effects of annealing on the low field magnetization in all the samples. We compare our results with a previous similar study of polycrystalline URu2Si2, and heat treatment effects found in neutron diffraction. (C) 1998 Elsevier Science B.V. All rights reserved.
  • T. Matsumura, S. Nakamura, T. Goto, H. Amitsuka, K. Matsuhira, T. Sakakibara and T. Suzuki: Low Temperature Properties of the Magnetic Semiconductor TmTe, (J. Phys. Soc. Jpn. 67, 612--621, 1998*)
    1998年 [査読無し][通常論文]
  • J.-G. Park, H.-C. Ri, K. Kuwahara and H. Amitsuka: Thermal Hysteresis in Magnetization of Single-Crystal \urs, (J. Magn. \& Magn. Mater. 177-181, 455-456, 1998*)
    1998年 [査読無し][通常論文]
  • M. Hedo, Y. Kobayashi, Y. Inada, E. Yamamoto, Y. Haga, J. Suzuki, N. Metoki, Y. Onuki, H. Sugawara, H. Sato, K. Tenya, T. Tayama, H. Amitsuka and T. Sakakibara: Peak effect in CeRu2: Role of crystalline defects, (J. Phys. Soc. Jpn. 67, 3561-3569, 1998*)
    1998年 [査読無し][通常論文]
  • K Matsuhira, T Sakakibara, H Amitsuka, G Kido
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 66 12 4009 - 4016 1997年12月 [査読無し][通常論文]
     
    The measurement of magnetic susceptibility (X)(T) specific heat C(T), electrical resistivity rho(T) and high field magnetization M(H) have been performed on dilute Ce compounds Ce1-x(La0.63Y0.37)(x)Ru2Si2; in which the lattice parameters are made independent of x to avoid the chemical pressure effect. Non-Fermi-liquid like behavior characterized by nearly logarithmic divergence of (X)(T) down to similar to 200 mK has been observed as x --> 1; which is quite unexpected for the Kondo temperature T-K similar to 24 K of CeRu2Si2. We show that the characteristic behavior of the experimental results is well reproduced by an impurity Kondo model with a wide distribution in T-K ("Kondo disorder"). A simple model for the TK distribution is given. In the present dilute alloys, T-K strongly depends on the local environment of nearest-neighbor distance.
  • K Kuwahara, H Amitsuka, T Sakakibara, O Suzuki, S Nakamura, T Goto, M Mihalik, AA Menovsky, A deVisser, JJM Franse
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 66 10 3251 - 3258 1997年10月 [査読有り][通常論文]
     
    We have performed thermal expansion and elastic constant measurements of the heavy electron system URu2Si2, focusing attention on the Gamma(3)(x(2) - y(2)) and Gamma(4)(xy) symmetry of the tetragonal group D-4h. It is reconfirmed that there is no sizable uniform spontaneous distortion for these two types of symmetry through the puzzling phase transition at T-o = 17.5 K. On the other hand, a weak but significant tendency of softening are found below about 70 K in the transverse (C-11 - C-12)/2 mode. The results strongly suggest the presence of a lattice instability in the Gamma 3 symmetry. From the results, proposed crystalline-electric-field models are also discussed.
  • K Matsuhira, T Sakakibara, H Amitsuka, K Tenya, K Kamishima, T Goto, G Kido
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 66 9 2851 - 2863 1997年09月 [査読有り][通常論文]
     
    In order to study the single-site and inter-site effects in CeRu2Si2, a systematic diluting experiment has been performed with the single crystals of pseudo-ternary alloys Ce1-x(La0.63Y0.37)(x)Ru2Si2 [0 less than or equal to x less than or equal to 1], where the unit cell volume is kept unchanged to avoid the chemical pressure effect. Magnetization process in fields H less than or equal to 200 kOe and at applied pressures P less than or equal to 5 kbar, specific heat C(T), electrical resistivity rho(T) and thermal expansion have been measured at temperatures above 1.5K, with a special attention being paid to the metamagnetic behavior inherent in CeRu2Si2. In a whole Ce concentration range, the system remains in a non-magnetic state. Sharp metamagnetism shows a rapid broadening with x, and disappears at x similar to 0.2 where incoherent Kondo scattering becomes significant in rho(T). By careful analysis of single-site contributions, a peak structure is revealed in C(T) which is not explained by the ''Kondo peak'' alone. The result can be interpreted by a pseudo-gap in the quasi-particle band, which disappears upon dilution. Constant-volume magnetization process M-V(H) is derived from the measured zero-pressure curves, using the scaring hypothesis proved by the high-pressure experiment. Metamagnetism, although becoming much less sharp, still exists in M-V(H), indicating importance of an intrinsic mechanism other than the volume effect.
  • T Tayama, T Sakakibara, K Tenya, H Amitsuka, S Kunii
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 66 8 2268 - 2271 1997年08月 
    DC magnetization of single crystals of CexLa1-xBF6, 0.5 less than or equal to x less than or equal to 1. have been measured at low temperatures (T) down to 40 mK in magnetic field H//[100], and the H - T - x phase diagrams were obtained, At zero field. the antiferro-quadrupolar (AFQ) transition temperature T-Q rapidly decreases with decreasing x and vanishes abruptly between x = 0.75 and 0.7. The Neel temperature T-N, which is lower than T-Q in CeB6, varies more slowly with x and exceeds T-Q for x greater than or similar to 0.8. A clear peak observed in the susceptibility strongly suggests that a new antiferromagnetic (AF) state having no AFQ moment (phase IV) exists for 0.8 greater than or similar to x greater than or similar to 0.5, in addition to the two ordered phases II (AFQ) and III (AF+AFQ). As H increases, a first-order phase IV-III transition is observed with a metamagnetic jump in the magnetization. Successive I (paramagnetic)-IV-III phase transitions are observable in a very narrow-region of the H - T - x space.
  • JG Park, KA McEwen, S deBrion, G Chouteau, H Amitsuka, T Sakakibara
    JOURNAL OF PHYSICS-CONDENSED MATTER 9 14 3065 - 3069 1997年04月 [査読有り][通常論文]
     
    We report measurements of the c-axis magnetization of URu2Si2 Single crystals, both unannealed and annealed, in fields up to 20 T. From our results, we conclude that the kink-type anomaly in the magnetization has a different high-field dependence from the dipole moment as seen in neutron diffraction experiments. Within the experimental error, we are unable to observe the effects of heat treatment on the field dependence. We discuss these new findings together with recent high-field results of resistivity and neutron diffraction experiments.
  • K Kuwahara, H Amitsuka, K Tenya, T Sakakibara, O Suzuki, S Nakamura, T Goto, M Mihalik, AA Menovsky, A deVisser, JJM Franse
    PHYSICA B 230 77 - 79 1997年02月 
    We have performed the thermal expansion alpha(T) and elastic constant c(T) measurements of the heavy electron system URu2Si2, with special attention to the tetragonal symmetry of Gamma(3)(x(2) - y(2)) and Gamma(4) (xy). The experimental results of c(66), 1/2(c(11) - c(12)) and alpha(T) along [+/- 110] do not confirm a sizable uniform distortion for these two types of symmetry through a puzzling phase transition at T-o = 17.5 K. On the other hand, the 1/2(c(11) - c(12)) data, which are missing in the previous detailed study, are found to show a weak but significant tendency of softening below about 70 K, suggesting an elastic response of the quadrupolar moment of J(2/x) - J(2/y).
  • T Sakakibara, T Tayama, H Amitsuka, K Tenya, S Kunii, T Suzuki, A Ochiai
    PHYSICA B 230 307 - 309 1997年02月 
    The ground-state magnetic properties of Ce0.75La0.25B6 and Sm3Te4 have been studied by means of static magnetization measurements at very low temperatures T greater than or equal to 50 mK. In Ce0.75La0.25B6, the H-T phase diagram reveals three different ordered phases: in addition to the two phases (phase II and III) known for CeB6, a new antiferromagnetic state appears before the antiferro-quadrupolar order sets in. In the valence fluctuation compound Sm3Te4, a spin-glass ordering is evidenced at T-g similar to 1.3 K. It is likely that the two valence states (Sm2+, Sm3+) are randomly frozen at low temperature to form effectively a randomly diluted magnet.
  • M Mihalik, FE Kayzel, T Yoshida, K Kuwahara, H Amitsuka, T Sakakibara, AA Menovsky, JA Mydosh, JJM Franse
    PHYSICA B 230 364 - 366 1997年02月 [査読有り][通常論文]
     
    We present heat capacity, AC-susceptibility and DC-susceptibility measurements of UNi2Al3 single crystal. Our results are consistent with the characterisation of UNi2Al3 as heavy-fermion superconductor with superconducting transition at T-c approximate to 1 K, which shows antiferromagnetic ordering below T-N approximate to 5 K.
  • SAM Mentink, H Amitsuka, A deVisser, Z Slanic, DP Belanger, JJ Neumeier, JD Thompson, AA Menovsky, JA Mydosh, TE Mason
    PHYSICA B 230 108 - 110 1997年02月 [査読有り][通常論文]
     
    We investigate the magnetic phase transition in UNi4B by specific heat, c(T), thermal expansion and resistivity under pressure. These experiments reveal that the hexagonal symmetry is not broken at T-N = 20 K, and predicts a hydrostatic pressure dependence of T-N of - 29 mK/kbar, close to the result from resistivity. The anomalous upturn of c/T to 470 mJ/mol K-2 at 0.4 K is reduced to 160 mJ/mol K-2 in 16T parallel to b-axis. The specific heat critical exponent alpha = - 0.15(2) suggests 3D Heisenberg universality in zero field.
  • H Amitsuka, T Sakakibara, A deVisser, FE Kayzel, JJM Franse
    PHYSICA B 230 613 - 615 1997年02月 [査読有り][通常論文]
     
    We have studied non-Fermi liquid properties of the tetragonal diluted uranium alloys Th1-xUxRu2Si2 (x less than or equal to 0.07), by means of thermal expansion measurements in the temperature range 0.5-100 K. As the temperature is lowered below about 10 K, the volume effect alpha(v)(T)/T ( = (alpha(c) + 2 alpha(a))/T) is found to exhibit the tendency to diverge logarithmically, similar to other quantities of the system: C/T similar to - ln T, chi similar to - ln T, rho similar to ln T (or T (1/2)). Interestingly, the sign of the anomaly in a(v)(T) is negative, opposite to the usual Kondo shrink behavior. As a possible interpretation, we discuss the two-channel Kondo model, proposing c-f hybridization effects dominated by the virtual f(2)-f(3) charge fluctuations.
  • K Tenya, M Ikeda, T Tayama, K Kuwahara, H Amitsuka, T Sakakibara, E Yamamoto, K Maezawa, N Kimura, R Settai, Y Onuki
    PHYSICA B 230 345 - 347 1997年02月 [査読有り][通常論文]
     
    The effects of the normal state paramagnetism on the superconductivity of UPt3 and URu2Si2 were investigated by means of static magnetization measurements. While the upper critical field of URu2Si2 seems to be paramagnetically suppressed, no clear spin reduction is observed in the magnetization curves. The paramagnetic polarization in UPt3 for H perpendicular to c (H parallel to c) is as large as (slightly suppressed below) the normal-state value, although the normal state spin susceptibility is considered to be largest for H perpendicular to c. The results of UPt3 point to an odd-parity pairing with a discernible anisotropy in the pair-spin state.
  • Park, J. -G., McEwen, K. A., de Brion, S., Chouteau, G., Amitsuka, H. and Sakakibara, T. : "High-Field Magnetization Study of Single-Crystal URu2Si2", J. Phys. Condens. Matter, 9 : 3065-3069 (1997)*
    1997年 [査読無し][通常論文]
  • Tayama, T., Sakakibara, T., Tenya, K., Amitsuka, H. and Kunii, S. : "Magnetic phase diagram of CexLa1-xB6 studied by static magnetization measurement at very low temperatures", J. Phys. Soc. Jpn., 66 : 2268-2271 (1997)*
    1997年 [査読無し][通常論文]
  • Sakakibara, T., Tayama, T., Amitsuka, H., Tenya, K., Kunii, S., Suzuki, T. and Ochiai, A. : "Low-temperature magnetization study of the heavy-electron systems", Physica, B230-232 : 307-309 (1997)*
    1997年 [査読無し][通常論文]
  • Matsuhira, K., Sakakibara, T., Amitsuka, H., Tenya, K., Kamishima, K., Goto, T. and Kido, G. : "Single-Site and Inter-Site Effects in Heavy Fermion Compound CeRu2Si2 Studied by Constant Volume Dilution", J. Phys. Soc. Jpn., 66 : 2851-2863 (1997)*
    1997年 [査読無し][通常論文]
  • Mentink, S. A. M., Amitsuka, H., de Visser, A., Slanic, Z., Belanger, D. P., Neumeier, J. J., Thompson, J. D., Menovsky, A. A., Mydosh, J. A. and Mason, T. E. : "Thermodynamic Study of the Magnetic Phase Transition in UNi4B", Physica, B230-232 : 108-11・・・
    1997年 [査読無し][通常論文]
     
    Mentink, S. A. M., Amitsuka, H., de Visser, A., Slanic, Z., Belanger, D. P., Neumeier, J. J., Thompson, J. D., Menovsky, A. A., Mydosh, J. A. and Mason, T. E. : "Thermodynamic Study of the Magnetic Phase Transition in UNi4B", Physica, B230-232 : 108-110 (1997)*
  • Mihalik, M., Kayzel, F. E., Yoshida, T., Kuwahara, K., Amitsuka, H., Sakakibara, T., Menovsky, A. A., Mydosh, J. A. and Franse, J. J. M. : "Superconducting and magnetic properties UNi2Al3 single crystal", Physica, B230-232 : 364-366 (1997)*
    1997年 [査読無し][通常論文]
  • Tenya, K., Ikeda, M., Tayama, T., Kuwahara, K., Amitsuka, H., Sakakibara, T., Yamamoto, E., Maezawa, K., Kimura, N., Settai, R. and Onuki, Y. : "Magnetic properties of heavy fermion superconductors UPt3 and URu2Si2", Physica, B230-232 : 345-347 (1997)*
    1997年 [査読無し][通常論文]
  • Kuwahara, K., Amitsuka, H., Sakakibara, T., Suzuki, O., Nakamura, S., Goto, T., Mihalik, M., Menovsky, A. A., de Visser, A. and Franse, J. J. M. : "Lattice Instability and Elastic Response in the Heavy Electron System URu2Si2", J. Phys. Soc. Jpn., 66 :・・・
    1997年 [査読無し][通常論文]
     
    Kuwahara, K., Amitsuka, H., Sakakibara, T., Suzuki, O., Nakamura, S., Goto, T., Mihalik, M., Menovsky, A. A., de Visser, A. and Franse, J. J. M. : "Lattice Instability and Elastic Response in the Heavy Electron System URu2Si2", J. Phys. Soc. Jpn., 66 : 3251-3258 (1997)*
  • Kuwahara, K., Amitsuka, H., Tenya, K., Sakakibara, T., Suzuki, O., Nakamura, S., Goto, T., Mihalik, M., Menovsky, A. A., de Visser, A. and Franse, J. J. M. : "Search for the quadrupolar instability in URu2Si2", Physica, B230-232 : 77-79 (1997)*
    1997年 [査読無し][通常論文]
  • T Tayama, K Tenya, H Amitsuka, T Sakakibara, A Ochiai, T Suzuki
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 65 11 3467 - 3470 1996年11月 [査読無し][通常論文]
     
    The ac susceptibility chi(ac) and the dc magnetization M(H,T) of single crystals of Sm3Te4 have been measured at temperatures as low as 70 mK. A cusp is found in chi(ac) at 1.3 K which is slightly lower than the temperature at which a broad peak of the specific heat was previously observed. Distinct irreversibility is observed in M(H,T) below similar to 1.3 K. The results indicate that the Sm3+ moment undergoes a spin glass transition at T-g similar to 1.3 K. It is likely that the two valence states of Sm2+(J = 0) and Sm3+(J = 5/2) are randomly frozen at low temperatures in the bcc lattice to effectively form a randomly diluted antiferromagnet.
  • Magnetization Study of the Superconducting State of UPt3
    T. Sakakibara, K. Tenya, M. Ikeda, T. Tayama, H. Amitsuka, E. Yamamoto, K. Maezawa, N. Kimura, R. Settai, Y. Onuki
    J. Phys. Soc. Jpn. 65 Suppl. B 202 - 208 1996年10月 [査読有り][通常論文]
  • UPt3における奇パリティ超伝導状態
    藤秀樹, 北岡良雄, 朝山邦輔, 榊原俊郎, 天谷健一, 池田昌隆, 田山孝, 網塚浩, 木村憲彰, 摂待力生, 大貫惇睦, 山本悦嗣, 芳賀芳範, 前沢邦彦, 町田一成
    固体物理 31 763 - 774 1996年09月 [査読有り][通常論文]
  • T. Sakakibara, K. Tenya, M. Ikeda, T. Tayama, H. Amitsuka, E. Yamamoto, K. Maezawa, N. Kimura, R. Settai and Y. Onuki : "Magnetization Study of the Superconducting State of UPt3", J. Phys. Soc. Jpn. Suppl., B65 : 212-218 (1996)*
    1996年 [査読無し][通常論文]
  • T SAKAKIBARA, T TAYAMA, K MATSUHIRA, H MITAMURA, H AMITSUKA, K MAEZAWA, Y ONUKI
    PHYSICAL REVIEW B 51 17 12030 - 12033 1995年05月
  • K TENYA, M IKEDA, T TAYAMA, H MITAMURA, H AMITSUKA, T SAKAKIBARA, K MAEZAWA, N KIMURA, R SETTAI, Y ONUKI
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 64 4 1063 - 1066 1995年04月 [査読有り][通常論文]
     
    Magnetization curves of UPt3 along the c-axis were measured at low temperatures down to 80 mK. Below 350 mK a peak of the irreversible magnetization was found just below the superconducting upper critical field H-c2. However, the peak disappeared above 390 mK, which is much lower than the superconducting critical temperature of 580 mK, suggesting an unconventional mechanism of the flux pinning near H-c2. No distinct anomaly was observed in the magnetization curves at the phase transition between B and C superconducting phases.
  • H AMITSUKA, T HIDANO, T SAKAKIBARA, T SUZUKI, T AKAZAWA, T FUJITA
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 140 1403 - 1404 1995年02月 
    Low-temperature transport, thermal, and magnetic measurements on the dilute uranium alloys U1-xThxPt2Si2 (x less than or equal to 0.07) reveal the non-Fermi liquid behavior suggesting the presence of the unconventional interplay between 5f electrons and conduction electrons. The divergence of the single-site paramagnetic susceptibility as T --> O indicates a magnetically degenerate ground state of the 5f electrons.
  • H. Amitsuka, T. Shimamoto, T. Honma, T. Sakakibara
    PHYSICA B-CONDENSED MATTER 206 461 - 463 1995年02月 
    Magnetic susceptibility X, specific heat C, and electrical resistivity rho have been investigated for dilute uranium alloys UxTh1-xPd2Si2 (x <= 0.07), in the temperature range down to 100 mK. With decreasing x, unusual -In T behavior appears in chi and C/T below about 6 K. A minimum resistance is observed at around 20 K indicating the presence of Kondo scattering, while a non-trivial maximum is also found at around 3.5 K.
  • K. Matsuhira, T. Sakakibara, H. Amitsuka
    PHYSICA B-CONDENSED MATTER 206 326 - 328 1995年02月 
    Magnetic susceptibility chi(T), magnetization M(B) and electrical resistivity rho(T) of the diluted Kondo system Ce1-x(La0.63Y0.37)(x)Ru2Si2, (0 <= x <= 1), have been studied in detail. The disappearance of metamagnetism at x similar to 0.2 coincides with the destruction of coherent scattering in rho(T). In the dilute limit, a continuous increase of chi(T) on cooling down to 2 K is observed. Such a variation can be calculated assuming a distribution of the Kondo temperatures, which could result from local density fluctuations.
  • T. Sakakibara, T. Tayama, H. Mitamura, K. Matsuhira, H. Amitsuka, S. Kunii
    PHYSICA B-CONDENSED MATTER 206 249 - 251 1995年02月 [査読有り][通常論文]
     
    A new Faraday force magnetometer has been developed to perform static magnetization measurements on heavy electron compounds at temperatures down to 100 mK and in fields up to 9 T. The results of the measurements on single crystals of CeB6, CePt2Si2 and CeRu2Si2 reveal new features in the low temperature metamagnetic properties of these compounds.
  • Sakakibara Toshiro, Mitamura Hiroyuki, Tayama Takashi, Amitsuka Hiroshi
    Jpn J Appl Phys 33 9 5067 - 5072 社団法人応用物理学会 1994年09月15日 
    A Faraday force magnetometer has been developed for static magnetization measurements at very low temperatures down to 100 mK and in fields up to 9 T. The magnetic force acting on a specimen located in the adiabatic vacuum chamber of a dilution refrigerator is detected by a newly designed load-sensing variable capacitor. Use of a superconducting magnet with gradient coils enables accurate measurement of magnetic moment with a resolution of better than 1×10-7 A·m2 ( 1×10-4 emu). An application to magnetization measurements on the heavy-electron antiferromagnet CeB6 is presented.
  • Amitsuka Hiroshi, Sakakibara Toshiro
    J Phys Soc Jpn 63 2 736 - 747 一般社団法人日本物理学会 1994年02月15日 
    Specific heat C, electrical resistivity ρ , magnetization M and magnetic susceptibility χ have been measured for the dilute tetragonal heavy-electron compounds UxTh1-xRu2Si2 (x≤0.07), in the temperature range 100 mK≤T≤360 K and in the magnetic fields H up to 55 kOe. Non-Fermi-liquid behavior with unusual lnT dependence of C, ρ and χ has been observed at the low temperatures: as the temperature is lowered below about 10 K, C/T and χ increase logarithmically, and ρ decreases logarithmically. Systematical variations of these quantities with uranium concentration indicate that the observed non-Fermi-liquid behavior is ascribed to the properties of a single U ion embedded in the Th site of the ThRu2Si2 metal. The magnetization curves M vs H/T indicate a strong uniaxial magnetic anisotropy along the tetragonal c-axis as well as a strong reduction of the 5f moment of U ions. A possible interpretation based on the recent developments of the S=1/2 two-channel Kondo model is given.
  • H. Amitsuka, T. Hidano, T. Honma, H. Mitamura, T. Sakakibara
    Physica B: Physics of Condensed Matter 186-188 C 337 - 340 1993年05月02日 
    Single-site properties of 5f-electrons in URu2Si2 have been studied by means of magnetic susceptibility (χ), specific-heat (C) and electrical resistivity (ρ{variant}) measurements on UxTh1-xRu2Si2 single-crystals in the uranium dilute region (x≤0.07). Anomalous In T-dependence has been found in χ, C and ρ{variant} at low temperatures, suggesting an unusual Kondo effect. © 1993.
  • T. Honma, H. Amitsuka, T. Sakakibara, K. Sugiyama, M. Date
    Physica B: Physics of Condensed Matter 186-188 C 684 - 686 1993年05月02日 
    We have performed a set of experiments on magnetic, thermal and transport properties of UPd2Si2 single crystals. Successive phase transitions are observed at T01≅1.33K and T02≅110K. The tetragonal compound is strongly anisotropic and shows a clear metamagnetic transition in the c-axis magnetization below T01. The obtained H-T phase diagram reveals four different phases in the ordered state below T01. © 1993.
  • C SEKINE, T SAKAKIBARA, H AMITSUKA, Y MIYAKO, T GOTO
    JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 61 12 4536 - 4546 1992年12月 [査読有り][通常論文]
     
    Magnetic susceptibility, magnetization and specific heat measurements have been performed on single crystalline Ce(Ru1-xRhx)2Si2 in the Ru rich region(0 less-than-or-equal-to x < 0.5) with a special interest in the small Rh substitution effects on the Kondo temperature T(K), the antiferromagnetic (AF) correlation and the metamagnetic transition in CeRu2Si2. Phase diagrams are obtained in both x-T and H-T planes with fields applied parallel to the tetragonal c-axis. At low Rh concentration, T(K) decreases with x and a weak AF ordering (T(N) less-than-or-equal-to 5.5 K) appears in the region 0.05 <x < 0. 30. The metamagnetic transition field H(M) decreases with x, leveling off and disappearing above x=0.20. This metamagnetic transition clearly exists in the AF ordered samples, where two successive transitions are observed in fields at H(C)(< 4 T) and H(M)(> 5 T). The AF ordering is destroyed above H(C) and the system further undergoes a metamagnetic transition at H(M).
  • T SAKAKIBARA, H AMITSUKA, T GOTO, K SUGIYAMA, Y MIYAKO, M DATE
    PHYSICA B 177 1-4 151 - 154 1992年03月 
    The magnetic phase diagram of single crystals of U(Ru1-xRhx)2Si2 is investigated in fields up to 55 T. Three-step metamagnetic transitions are observed for x < 0.05. Free energy considerations of the transition fields indicate that the partially gapped heavy fermion state with weak antiferromagnetic moment (SDW) in URu2Si2 is destroyed at the first transition field. A possible H-T phase diagram of the gapped state is discussed.
  • Y MIYAKO, T KUWAI, T TANIGUCHI, S KAWARAZAKI, H AMITSUKA, CC PAULSEN, T SAKAKIBARA
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 108 1-3 190 - 192 1992年02月 
    The magnetic phase diagram of U(Ru1-xRhx)2Si2 was obtained from the specific heat, susceptibility and neutron scattering experiments on single and polycrystals. Antiferromagnetic structure changes around x = 0.4 and intersite spin fluctuations which suppress magnetic ordering seem to occur in this composition region x where two different magnetic ordered states are encountered as a function of x. These magnetic properties are quite similar to the case of Ce(Ru1-xRhx)2Si2.
  • T SAKAKIBARA, C SEKINE, H AMITSUKA, Y MIYAKO
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 108 1-3 193 - 195 1992年02月 [査読有り][通常論文]
     
    Magnetic susceptibility, magnetization and specific heat measurements performed on single-crystalline Ce(Ru1-xRhx)2Si2 have revealed a weak antiferromagnetic ordering (T(N) less-than-or-equal-to 5.5 K) in the region 0.05 less-than-or-equal-to x less-than-or-equal-to 0.25. Two transitions observed in the magnetization process for x = 0.1 suggest that a strongly correlated Fermi-liquid state is restored in an applied field, and further undergoes a metamagnetic transition at still higher fields.
  • Y MIYAKO, S KAWARAZAKI, H AMITSUKA, CC PAULSEN, K HASSELBACH
    JOURNAL OF APPLIED PHYSICS 70 10 5791 - 5793 1991年11月 
    The temperature dependence of the nonlinear susceptibility of URu2Si2 has been studied in order to understand the properties of the phase transition at 17.5 K. We have also studied the various magnetic phases of U(Ru1-xRhx2Si2 as a function of x by means of specific heat, susceptibility, and neutron scattering experiments. Special attention has been paid to x = 0.3 where two successive phase transitions occur.
  • H AMITSUKA, T SAKAKIBARA, Y MIYAKO, K SUGIYAMA, A YAMAGISHI, M DATE
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 90-1 47 - 48 1990年12月 
    U(Ru(1-x)Rh(x)2Si2 exhibits metamagnetic(like) transitions in the whole range of x by applying a strong magnetic field. A magnetic phase diagram is obtained as functions of x, transition field H(M) and antiferromagnetic transition temperature T(N).
  • Y KOHORI, M KYOGAKU, T KOHARA, K ASAYAMA, H AMITSUKA, Y MIYAKO
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 90-1 510 - 512 1990年12月 
    Zero field NMR signal of Pt-195 was observed in the antiferromagnetic U(Pt0.95Pd0.05)3. The internal magnetic field is distributed around 22-38 kOe. The transferred hyperfine field from U moments aligned antiferromagnetically does not cancel at the Pt site. On the other hand we could not observe the internal field at Pt site associated with the antiferromagnetic order in UPt3 at 1.4 K within the experimental error of 30 Oe.
  • H AMITSUKA, T SAKAKIBARA, Y MIYAKO
    JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 90-1 517 - 518 1990年12月 [査読有り][通常論文]
     
    We demonstrate here that the peak temperature of the susceptibility is an important parameter to characterize the antiferromagnetic transition temperature and a metamagnetic transition field in coherent Kondo state of mixed compounds U(Ru(1-x)Rh(x))2Si2 for x less-than-or-equal-to 0.06.
  • Yoh Kohori, Masafumi Kyogaku, Takao Kohara, Kunisuke Asayama, Hiroshi Amitsuka, Yoshihito Miyako
    Physica B: Condensed Matter 165-166 381 - 382 1990年08月 [査読有り]

その他活動・業績

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 基盤研究(B)
    研究期間 : 2023年04月 -2026年03月 
    代表者 : 網塚 浩
  • 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 : 2022年04月 -2026年03月 
    代表者 : 松平 和之, 網塚 浩, 筒井 智嗣, 中村 和磨, 長谷川 巧, 山地 洋平, 速水 賢
  • 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, 網塚 浩, 齋藤 開
  • J-Physics:多極子伝導系の物理の研究総括
    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 : 2020年04月 -2021年03月 
    代表者 : 播磨 尚朝, 網塚 浩
  • J-Physics:多極子伝導系の物理の国際展開
    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 : 2015年11月 -2021年03月 
    代表者 : 播磨 尚朝, 網塚 浩, 中辻 知, 青木 大, 野原 実, 石田 憲二
     
    国際ネットワークの形成のために、海外の研究機関に若手研究者の派遣を行った。また、国際的な成果発信も兼ねて領域主催の国際会議を開催した。さらに、東北大金研と協力して国際若手学校を開催した。5月にパリで行われたスピン軌道結合に関する研究会には1名、7月にロシアで開催された国際集会(Dzyaloshinskii-Moriya Interaction and Exotic Spin Structures)に3名の研究者を派遣して、EuPtSiを中心とした研究発信に努めた。 若手研究者の派遣としてはアメリカへ2名(Ames研とNIST)、イギリスへ2名(ISIS)、フランスへ1名(CNRSとCEA-Grenoble)、チェコへ1名(カレル大学)、スイスへ1名(PSI)の派遣を行った。派遣する若手研究者に対しては、申請書を承認したのち出発前に面接を行い、研究テーマや海外での研究活動について助言を行った。9月に開催した国際会議には、海外から著名な研究者16名を招待した。国際若手学校では8件の講義の他に参加者によるショートプレゼンテイションを行って国際交流にも努めた。続けて開催した国際会議では155名の参加を得て、47件の口頭発表を含む139件の研究発表が行われた。さらに、議事録を出版した。若手研究者の発表については、審査ののち5件の優秀ポスター賞を選び表彰した。さらに、9月末に岡山で開催された強相関電子系の国際会議への参加援助を行った。この会議は海外からの300名以上の参加者を含む約850名の参加がある大きな国際会議であり、若手研究者が研究成果を発表して国際的な成果発信と国際交流につとめることができた。
  • 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 : 2015年06月 -2020年03月 
    代表者 : 播磨 尚朝, 網塚 浩, 中辻 知, 青木 大, 野原 実, 藤 秀樹, 石田 憲二
     
    本課題の活動として全体会議やトピカルミーティングを開催した。これにより、新学術領域の個々の研究項目や研究課題の研究協力や研究交流が深まり、より良い研究成果につながった。共用備品を活用することで、幅広い共同研究が可能になった。ものづくり学校により、物質開発の重要性と物質の対称性という新しい観点の重要性を研究者に広く浸透させることが出来た。若手の学校を開催して若手の研究を表彰することで、若手研究者が育った。領域外や国外への研究発信も国際会議や研究論文、ニュースレター、ホームページを通じて行うことが出来た。さらに様々なアウトリーチ活動を通じて研究活動を一般に広く紹介することが出来た。
  • 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 : 2015年06月 -2020年03月 
    代表者 : 網塚 浩, 楠瀬 博明, 藤 秀樹, 高阪 勇輔, 中尾 裕則, 御領 潤
     
    1原子上の電子が持つ電荷・スピン・軌道の結合自由度である電気・磁気多極子、さらにこれらが複数原子上に跨がって形成する電気・磁気クラスターや結合ボンドクラスターを含めた「拡張多極子(Augmented Multipoles)」に基礎を置く固体物性研究を展開し、電荷・スピン・軌道の基本自由度を用いた従来の方法では記述が困難な種々の物性現象の理解を進展させるとともに、新たな機能性の予見も可能となることを理論、実験の両面から明らかにした。
  • 日本学術振興会:科学研究費助成事業 基盤研究(C)
    研究期間 : 2015年04月 -2018年03月 
    代表者 : 小濱 芳允, 黒江 晴彦, 金道 浩一, 網塚 浩
     
    本申請では、パルス強磁場下での熱測定技術を用い、磁場誘起秩序相の研究を行った。 パルス磁場下での熱測定はそもそも難しい技術であり、1. 磁場発生や2. クライオスタットの開発から進めた。1の磁場発生については、60テスラ以上の磁場で超フラットトップ磁場の発生に世界で初めて成功した。2のクライオスタットの開発により、パルス磁場下で3He温度の熱測定が可能になった。このように装置開発にも力点を置きつつ、同時に固体酸素や幾つかの磁性体について磁気熱量効果の研究を完了した。いくつかの重い電子化合物については比熱測定を完了し、論文として発表した。期待通り、多くの研究成果が得られたと考えている。
  • 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。
  • 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(B)
    研究期間 : 2014年04月 -2017年03月 
    代表者 : 浅野 泰寛, 延兼 啓純, 丹田 聡, 網塚 浩
     
    完全反磁性(マイスナー効果)は超伝導体の最も基本的な性質である。ところが超伝導体を小さくすると、常磁性を示す超伝導物質群が存在する。この常磁性マイスナー効果は幾つかの実験があるにもかかわらず、その発現機構は謎のままであった。本研究で我々は、異方的超伝導体(トポロジカル超伝導体)の表面には奇周波数クーパー対と呼ばれる特殊なクーパー対が現れること、また奇周波数クーパー対のために小さな異方的超伝導体は低温において常磁性を示す事を明らかにした。
  • 日本学術振興会:科学研究費助成事業 基盤研究(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。
  • 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 : 2013年04月 -2016年03月 
    代表者 : 秋光 純, 網塚 浩, 高阪 勇輔
     
    URu2Si2単結晶についての後方X線散乱実験を実施した。この結晶に対する(880)ブラッグ回折点の拡がりの温度変化について2次元検出器を用いて注意深く調べた結果、隠れた秩序に伴う正方晶から斜方晶への歪みは、δ(a-b)/(a+b) < 5×10-6の精度で起きていないことを確認した。これは、δ(a-b)/(a+b) ~ 6×10-5の歪みが「存在する」とする過去の報告と矛盾する結果である。
  • 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 : 2011年04月 -2016年03月 
    代表者 : 三宅 康博, Patrick Strasser, 石田 勝彦, 髭本 亘, 牧村 俊助, 松田 恭幸, 久我 隆弘, 藤森 寛, 西山 樟生, 芳賀 芳範, 網塚 浩, 加藤 礼三, 中村 惇平, 二宮 和彦, 伊藤 孝, 小林 庸男, 池戸 豊, 妹尾 仁嗣, 藪内 敦, 山内 一宏, 足立 泰平
     
    本研究班は、超低速ミュオンによる研究を本格的に開始する為、1)熱ミュオニウム発生装置並びに超低速ミュオン顕微鏡光学系を設計・製作し、2)理研班が構築する100μJ/パルス/cm2を超える大強度パルス状ライマンαレーザーシステムと組合わせる。これにより、0.2 eVの超低速ミュオンを従来の10,000倍以上、毎秒10(6)個発生させることを最終目標にしている。現段階では、レーザーシステムの増幅結晶の開発上の課題が残っており、ライマンαレーザー光の強度が1-数 μJ/パルス/cm2にとどまっており、毎秒数百個の収率に留まっている。現在、その条件下で、ナノmμSR法のコミッショニングを進めている。
  • 日本学術振興会:科学研究費助成事業 基盤研究(S)
    研究期間 : 2008年 -2012年 
    代表者 : 佐藤 憲昭, 網塚 浩, 山村 朝雄, 芳賀 芳範, 四竈 樹男, 阿曽 尚文, 神戸 振作, 本間 佳哉, 藤森 伸一, 山上 浩志
     
    本研究課題の最大の目的は、国際規制物資であるウランなどのアクチノイド元素^<*1>を含む化合物の物性研究を行うための拠点を東北大学金属材料研究所アルファ放射体実験室に形成することである。 この目的のために、 単結晶育成^<*2>のためのテトラアーク炉、および育成された試料の基礎物性を評価するための分析装置を金研アルファ放射体実験室に設置・導入した。その結果、 "超伝導を示す磁石"^<*3>における超伝導発現機構の解明に成功を収めた。さらに、アクチノイド元素だけでなく希土類元素^<*4>を含む物質にも研究を展開し、準結晶^<*5>を含む新分野の開拓に貢献した。[*1] ウランなどは国際規制物資として管理され、その取り扱いには厳しい制限が付されている。金研アルファ放射体実験室は、このような国際規制物資を取り扱うことが許可された施設である。 また、 そこには、 アクチノイド元素(周期表で最下段に位置する元素の集合で、トリウム、ウラン、ネプツニウムなどから成る)を安全にハンドルするための多くの装置と経験が蓄積されている。[*2] 目に見える大きさのスケールまで原子が規則正しく配列した結晶を単結晶と呼ぶ。[*3] 従来の物理学では、磁石と超伝導は犬猿の仲であり、磁石は超伝導にはならないと考えられてきた。しかしアクチノイド化合物の中には、磁石でありながら超伝導を示すものがある。磁石が何故超伝導を示すかという問題は、物理学上の重要な課題の 1 つとなっている。[*4] 周期表でアクチノイドの上段に位置する元素の集合で、アクチノイドと類似の性質を示す。[*5] 周期性を持たず、結晶では許されない回転対称性を持つ物質を準結晶と呼ぶ。
  • 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 : 2009年 -2011年 
    代表者 : 天谷 健一, 網塚 浩, 横山 淳
     
    スピン三重項超伝導体Sr_2RuO_4やUPt_3の純良試料に磁場を[ 001]方向に印加し磁化測定を行なうと,極低温下ゼロ磁場近傍においてヒステリシス磁化に微小の「とび」(マイクロフラックスジャンプ)が数多く観測され,スピン一重項超伝導体の純良試料の場合と異なる振る舞いを見せる.本研究では,対称性の異なる超伝導体で発生するフラックスジャンプの類似点・相違点等を詳細に調べ,マイクロフラックスジャンプが,超伝導秩序変数の内部自由度から生じる超伝導ドメイン構造に起因している可能性を指摘した.
  • 日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2007年 -2009年 
    代表者 : 網塚 浩, 天谷 健一, 日高 宏之, 柳澤 達也, 横山 淳
     
    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。
  • 日本学術振興会:科学研究費助成事業 特定領域研究
    研究期間 : 2005年 -2009年 
    代表者 : 金道 浩一, 長田 俊人, 徳永 将史, 大道 英二, 網塚 浩, 海老原 孝雄, 北澤 英明, 杉山 清寛
     
    非破壊100T領域でのスピン科学を展開するために、マグネットの開発を行った。新たなマグネットにより研究が進展したテーマは、「強磁場ESRおよびNMR」、「SPring-8における放射光X線を用いた実験」と「J-PARCにおけるパルス中性子源を用いた実験」である。また、非破壊100T発生および超ロングパルス磁場発生のためのモデルコイルのテスト実験に成功し、実用型のマグネットの製作が始まっている。
  • 絶縁体希釈による充填スクッテルダイト化合物の単サイト電子相関に関する研究
    日本学術振興会:科学研究費助成事業 特定領域研究
    研究期間 : 2006年 -2007年 
    代表者 : 網塚 浩, 天谷 健一
     
    本研究では、高次多極子による量子異常が特に顕著なPrT_4P_<12>及びSmT_4P_<12>(T=Fe, Ru, Os)に注目し、絶縁体CeT_4P_<12>を用いた磁性希釈により、これらの系の基本的単サイト電子相関を解明する。また密接な関連の指摘されるf電子系の研究から、高次多極子に関する物理の進展を図ることを目的とする。本年度の主な成果は以下の通りである。1.昨年に引き続き、単結晶合成法が確立できているCe_<1-x>Pr_xT_4P_<12>(T=Fe, Ru; 0〓x〓0.15)について、組成数を増やし磁化及び磁場中比熱を詳細に測定した。強磁場からの外挿法による解析を精密化し、4f結晶場準位が両系共に1重項-3重項(△〜10K)であることを示した。また理論家との議論により、この結果が周期系に対して提案されているp-f混成を考慮した有効結晶場モデルを支持することがわかった。2.フラックス法によるCe_<1-x>Sm_xT_4P_<12>(T=Fe, Ru)系の作成を試み、ごく最近成功した。約1mm角の結晶が得られ、現在物性測定を進めている。3.類似のかご構造物Pr_3Pd_<20>Ge_6について磁場中中性子弾性散乱実験を行い、磁場誘起相転移に伴う反射ピークの分裂を観測した。4. LaOs_4P_<12>の比熱が絶対零度に向かい増大する振る舞いを観測した。また、250Kの熱サイクルを経ないと再現しない低温異常を新たに見出した。5.希薄磁性化合物La_<1-x>R_xRu_2Si_2(R=Rare-earths)の単結晶を作成し、希土類元素を変化させて磁気異方性、磁化、電子比熱を系統的に調べた。その結果、基底J多重項のみを考慮する従来の結晶場モデルでは磁気異方性を定量的に説明できないことを明らかにした。以上の成果は一部公表し、現在数本の論文にまとめつつある。
  • 強相関5f電子化合物の異常磁性
    日本学術振興会:科学研究費助成事業 基盤研究(B)
    研究期間 : 2001年 -2003年 
    代表者 : 網塚 浩, 天谷 健一
     
    強相関5f電子系の最重要課題であるURu_2Si_2の低温電子状態に焦点を絞り、様々な実験的研究を展開した。この系の低温秩序相の起源、およびそれと密接に関係する超伝導状態、メタ磁性について多くの新たな情報を得、金属中における5f電子物性の理解の進展に貢献した。具体的な成果を以下に列挙する。1.高圧下における中性子散乱およびNMR、μSR実験から、この系の未知秩序状態に静水圧下で反強磁性(AF)秩序が1次転移で誘起され、広い圧力-温度領域で2相分離現象が起こることを見出した。2.一軸応力下中性子散乱実験から、この反強磁性誘起が軸性歪みc/aの僅かな増加に起因することを指摘し、長年の論争であったこの系の微弱磁性の本質が結晶の不完全性によって生じたAF相の「島」であり、系の低温物性は未知の「隠れた秩序(HO)」により支配されていることを示した。3.RuのRh置換(化学圧力効果)によってもHO-AF転移が起こることを確認するとともに、圧力容器無しで相競合を調べられる利点を生かし、相転移に伴う磁化・比熱の振る舞い、磁気励起の消滅過程の詳細を明らかにした。4.メタ磁性のRh濃度依存性を調べ、複数の強磁場相と弱磁場相との関係を明らかにした。5.高圧下極低温精密磁化測定システムを立ちあげ、HO-AF相競合の発達による超伝導特性の変化を調べた結果、磁性相分離の発達は超伝導の凝集エネルギーを減少させるが、超伝導体積率にはほとんど影響を与えないことが分かった。超伝導にのみ寄与するフェルミ面が存在するという5f電子状態の双対性発現の可能性を実験的に示した。本課題およびこれに関連する研究の成果は、学術論文26編として公表するとともに、アメリカ物理学会をはじめとする国際学会等で、9件の招待講演を含む学術講演として公表した。
  • 軌道の秩序と揺らぎによる異常磁性の研究総括
    日本学術振興会:科学研究費助成事業 特定領域研究(B)
    研究期間 : 1999年 -2001年 
    代表者 : 榊原 俊郎, 上田 和夫, 大川 房義, 網塚 浩
     
    本研究課題では、f電子化合物における軌道の自由度に由来する相転移現象や種々の異常な磁気的振舞い、特に反強四重極秩序、隠れた秩序変数、金属絶縁体転移などについての実験的・理論的研究を行った。 f電子系における特徴的な軌道整列現象である反強四重極転移については、典型物質であるPrPb_3について磁気相図を決定し、転移温度が磁場方向に応じて異方的に増大することを見出した。また、この振舞いが反強四重極相において磁場誘起される磁気モーメント間の相互作用で説明出来ることを示した。 秩序変数が未知のCe_xLa_<1-x>B_6のIV相およびURu_2Si_2について詳しく調べた。Ce_xLa_<1-x>B_6では軸性応力下での磁化測定を行い、[100]方向の軸性圧力によってIV相に顕著な磁気異方性が出現することを見出した。これはIV相の秩序変数が本来、異方的な性質を有することを強く示唆し、その可能性としてガンマ5型の八重極秩序が考えられる。弱い反強磁性相と考えられていたURu_2Si_2の秩序状態について圧力下の中性子散乱実験を行った結果、低温圧力下の秩序状態が反強磁性と非磁性2相の非平衡共存状態にあること、反強磁性が圧力によって増強することがわかった。また正方晶主軸を延ばす歪みに対して反強磁性が特に著しく増強される事を明らかにした.URu_2Si_2の非磁性の秩序変数はいまだ未知ではあるが、圧力効果の結果は理論設定に対する条件をかなり狭めることができたと言える。 充填型スクッテルダイトPrRu_4P_<12>で見られる金属絶縁体転移に関して、非クラマース二重項の縮退を結晶変形によってとく理論を構築した。Yb_4As_3で見出された磁場誘起ギャップについては、交替的ジャロシンスキー守谷相互作用によるとする理論を構築した。
  • 5f電子系における局所非フェルミ液体異常とサイト間効果の研究
    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 : 1998年 -1999年 
    代表者 : 網塚 浩, 天谷 健一
     
    重い電子系URu_2Si_2のウランサイトを非磁性イオン、トリウムおよびイットリウム、ランタンで希釈した単結晶について高精度の磁気・熱測定(温度領域0.1K-300K)を行い、局所5f電子状態が以下の共通特性をもつことを明らかにした。(1)正方晶c軸に対する強い1軸磁気異方性、(2)局所反強磁性相関による低温磁化の抑制と比熱の増大、(3)低温エントロピーの小さな変化、(4)降温に伴う電気抵抗の減少。(4)に代表されるように、いずれの希釈系においても従来の近藤効果の兆候が見られないことを明らかにし、2チャンネル近藤理論および非クラマース2重項を結晶場基底状態とするアンダーソン模型から導かれる新しい局所多体電子相関の可能性を議論した。同時に、これらの理論が予想する絶対零度の残留エントロピーが観測されないことを磁場中比熱測定から明らかにし、理論には含まれていない電子-格子相互作用の重要性を指摘した。 周期系URu_2Si_2の微弱反強磁性状態がわずかな加圧によって著しく増強され、さらにある臨界圧で圧力誘起の新しい磁気相転移が起こることを圧力下中性子散乱実験により発見した。加圧に対する物理量の変化をもとに、過去に提案された種々理論の適用性をランダウの現象論を用いて議論し、非時間反転自由度による秩序機構が最も適することを指摘した。さらに上記希釈実験で得た単一ウランサイトの情報と圧力実験の結果に基づき、Uru_2Si_2の異常物性が非クラマースニ重項Γ_5の性質を用いて良く説明できることを指摘した。
  • 低い特性温度を持つ電子系の極低温磁化測定
    日本学術振興会:科学研究費助成事業 基盤研究(A)
    研究期間 : 1997年 -1999年 
    代表者 : 榊原 俊郎, 天谷 健一, 網塚 浩
     
    (1)反強四重極転移系の磁気相図 PrPb_3について反強四重極転移の磁気相図を明らかにした。反強四重極転移温度の上昇は[100]、[110]、[111]の順に抑えられることがわかった。この結果を平均場モデルで解析したところ、反強四重極転移温度の上昇は反強四重極相において磁場誘起される反強磁性モーメント間の磁気相互作用によること、相図の異方性の説明には磁気八重極相互作用が必要であることがわかった。 (Ce,La)B_6系では未知の秩序相であるIV相について、常圧下および一軸応力下の精密な磁化測定を行った。常圧ではIV相に磁気異方性が見られなかった。しかし[110]方向の1軸圧下でIV相に顕著な磁気異方性が現れた。IV相の磁気特性は通常の反強磁性転移では説明できず、1軸応力に極めて敏感な秩序変数であると言える。 TmTeの反強磁性転移(0.2K)に伴い強磁性モーメントが現れることがわかった。これは1.8Kにおける反強四重極秩序の存在、またそれが反強磁性と同じ波数を持つことを意味している。 (2)重い電子系超伝導体の超伝導混合状態における磁化特性 URu2Si2の高純度単結晶試料について超伝導相の磁化測定を行い、常磁性効果を調べた。Tcと直下でG-Lパラメータκ2に顕著な減少が見られ、スピン常磁性による超伝導の抑制効果が存在していると考えられる。この結果はURu2Si2超伝導相の電子対がd波である可能性を強く示唆する。 CeRu_2のピーク効果の原因を調べるために混合状態の磁化過程を詳細に測定した。G-Lパラメータκ2の温度変化からは常磁性効果が存在しないと言え、FFLO相への転移の可能性は少ない。この物質のピーク効果はむしろシンクロナイゼーション効果と呼ばれるピニング力の増大によって説明可能である。
  • 極低温下における重い電子系物質の磁気応答
    日本学術振興会:科学研究費助成事業 重点領域研究
    研究期間 : 1996年 -1996年 
    代表者 : 榊原 俊郎, 天谷 健一, 網塚 浩
     
    本研究では標記研究課題に基づき、(1)重い電子系CeRu_2Si_2のメタ磁性と体積効果、(2)Ce_xLa_<1-x>B_6の磁気相図、(3)重い電子系超伝導体の混合状態における磁気応答について研究を行った。以下に結果を報告する。 (1)重い電子系CeRu_2Si_2のメタ磁性と体積効果 CeRu_2Si_2のメタ磁性磁化と磁歪を極低温下(〜100mK)で同時測定し、熱力学関係式を使って1パラメータースケール則を検証した。その結果、スケール則は低温でも良く成り立っていることがわかった。またスケール則を使って等体積磁化過程を評価したところ、等積過程でもメタ磁性を示すことがわかり、体積効果以外のメタ磁性機構の存在が確認された。 (2)Ce_xLa_<1-x>B_6の磁気相図 La濃度50%〜75%の試料の磁化過程を詳しく調べ、詳細なH・x・T相図を得た。その結果、ゼロ磁場における反強四重極秩序はLa濃度70%付近で突然消失し、替わって反強四重極秩序を伴わない反強磁性相が出現することがわかった。 (3)重い電子系超伝導体の混合状態における磁気応答 CeRu_2の超伝導相におけるピーク効果について、純良単結晶を用いて詳細な磁化測定を行った。その結果、磁化ヒステリシスを平均して得られる熱平衡磁化にはピーク効果近傍で異常がなく、この系のピーク効果が何らかの磁束系の相転移によるものではなく、ピニング機構における何らかの異常によるものであることが判明した。
  • メタ磁性を示す常磁性重い電子系物質の探索と極低温磁化測定
    日本学術振興会:科学研究費助成事業 重点領域研究
    研究期間 : 1994年 -1994年 
    代表者 : 榊原 俊郎, 天谷 健一, 網塚 浩
     
    CeRu_2Si_2、CeCu_6等の非磁性の重い電子化合物がメタ磁性を示すことが知られている。しかしこのメタ磁性がどういう機構で起こるのか、また非磁性の重い電子化合物に普遍の現象かどうか等についてはまだ十分には理解されていない。この点、より多くの新しい実例を見出していくことが必要である。一方典型物質であるCeRu_2Si_2については最近dHvAの実験からメタ磁性転移の前後でフェルミ面極値断面積にかなり顕著な変化が見られ、4f電子の遍歴から局在への転移ではないかと解釈されている。しかし、大きな有効質量を持つ主要なフェルミ面のメタ磁性転移近傍の変化を直接追跡するにはCeRu_2Si_2の転移磁場B_C〜8Tは明かに低すぎる。これにはB_C〜20Tを持つCe系典型物質の探索が必要であろう(5f系ではUPt_3が典型である)。 このような視点から我々はCeRu_2Si_2の周辺物質のCePt_2Si_2を調べた。この物質はCaBe_2Ge_2型構造の非磁性近藤格子(γ〜80mJ/molK^2)と考えられ、CeRu_2Si_2と同様な磁化率の極大を60K付近に持つ。Gignouxらによりこの物質が約3Tでメタ磁性を示すとの報告があり、これを確認するため300mKまでの磁化を詳しく調べたところ、メタ磁性は認められなかった。この物質は不純物(ほとんどfreeなCe^<3+>)が混入しやすく、Gignouxらの結果はこの寄与をBrillouin関数で差し引いて得たものである。我々の測定の結果、この不純物はT_K〜数Kの近藤不純物であり、Gignouxらの解析に問題があることが解った。CaBe_2Ge_2型構造の化合物は一般に低残留抵抗の良質の結晶を得ることが困難であり、今後改善が望まれる。 物質探索と平行して我々は典型物質CeRu_2Si_2のメタ磁性が相転移であるかどうかを調べた。これはdHvA効果とは相補的な情報を与える。高純度試料(残留抵抗比〜400、大貫氏提供)を用いて極低温下(90mK)で磁化測定の結果、磁化に不連続な飛びは無く、B_Cにおける微分磁化率をT=0に外挿しても有限値に留まることがわかった。従ってT=0の極限でも熱力学的な意味での相転移は無いと考えられる。弱磁場領域の4f遍歴状態はB>B_Cの高磁場領域まで連続的につながっていることになる。
  • ウランを含む重い電子系およびその関連物質におけるシングルサイト5f電子状態の研究:トリウムによるウランサイト希釈実験
    日本学術振興会:科学研究費助成事業 奨励研究(A)
    研究期間 : 1993年 -1993年 
    代表者 : 網塚 浩
     
    本研究では、ウランを含む重い電子系とその関連物質に対し、ウランサイトをトリウムで希釈することにより、単一ウランサイトの5f電子状態を実験的に明らかにすることが目的であった。本年度は、3種類の正方晶ウラン化合物UT_2Si_2(T=Ru,Pt,Pd)に焦点をあてた。ウラン濃度1〜7%の希釈系に対する系統的研究から、ウラン濃度に依らない単一ウランサイトの効果を分離することに成功した。本研究の成果は以下の2点に集約される。 1.上記化合物のウラン希薄領域において、下記の単一ウランサイト異常が起こっていることが明らかになった。 (1)約10K以下で降温に伴い、磁化率、比熱が対数発散的に増大する。 (2)Ru,Pt系では、約10K以下で降温に伴い電気抵抗が対数的に減少する。Pd系では対数的に増大した後約1K以下で減少する。 これらの低温異常は、局所強相関電子系として従来より知られている近藤効果が予想する正常フェルミ液体の性質とは明らかに異なるものであり、1個のウランイオンと伝導電子からなる系の基底状態に関して新たな問題を提起する最初の実験事実となった。 2.磁気異方性の観測結果から、上記化合物の結晶場基底状態が、従来予想されていた一重項状態ではなく、二重項状態であることを初めて指摘した。また、これに基づき周期系の物性に対する新しい解釈を提起した。 以上のように、本研究は、上記物質に対する単一ウランサイトの性質を初めて実験的に明らかにすると同時に、ウラン系の物性が従来の近藤格子描像の単純な延長線上では理解しえない可能性を初めて示した点で、十分な成果を収めたと考えられる。
  • 低い特性温度を持つ磁性体の強磁場による研究-三端子容量法を用いた極低温磁化測定
    日本学術振興会:科学研究費助成事業 一般研究(B)
    研究期間 : 1992年 -1993年 
    代表者 : 榊原 俊郎, 綱塚 浩
     
    重い電子系の研究では、その特徴的温度スケールが低いために、その基底状態の挙動を探るためには1K以下の低温が必要になることが多い。しかし磁化に関しては、主として技術的な困難さから、これまで国内ではAC法を除く^3He温度以下での測定はほとんど行なわれていなかった。本研究は最低温度100mKを目標に、磁場9Tまでの新しいファラデー法極低温磁化測定装置を開発し、実用化することが目的である。 ファラデー法磁化測定のポイントは磁場勾配の発生法と力の検出法である。まず、磁場勾配については、均一な中心磁場(最大9T)に任意の大きさの一様な磁場勾配(最大10T/m)を重ね合わせることができる、専用の超伝導マグネットを導入した。またファラデー力の検出には、MITの強磁場施設で微小試料の磁化測定に使われたことのある可動電極キャパシタンス方式を発展させて、小型のキャパシタンス式ロードセル(一種のバネばかりで直径30mm,高さ15mm程度)を独自に製作した。これを高分解能の自動バランスデジタルキャパシタンスブリッジと組み合せることにより、希釈冷凍機の断熱セル中でマイクログラムオーダーの荷重変化が検出可能となった。 種々の試料(CeB_<6'>TmTe等)を用いた極低温磁化測定の結果、新しい知見が数多く得られた。CeB_6は約3.4Kで4重極転移、2.3Kで反強磁性転移を示すことで知られているが、その低温磁気相図はあまりよくわかっていない。(110)方向の磁化測定を行ったところ、約1.5Tの磁場でこれまで知られていなかった非常にシャープな磁化の飛びを0.5K以下で観測した。TmTeは常磁性の重い電子化合物と考えられているが、1K以下の温度でヒステリシスを伴う磁化の異常が見出された。これはΓ_8基底状態が約4Kで軌道整列し、低温ではそのドメインが磁場で配向する効果が見られたものと考えられる。 その他にも、重い電子系Ce化合物、U化合物および3dラーベス相化合物の低温強磁場において、数多くの興味ある結果を得た。
  • 重い電子系における電子相関競合状態の圧力効果:低温高圧下比熱測定
    日本学術振興会:科学研究費助成事業 奨励研究(A)
    研究期間 : 1991年 -1991年 
    代表者 : 網塚 浩
  • 希土類・アクチナイド化合物の磁性と超伝導に関する研究
    日本学術振興会:科学研究費助成事業 国際学術研究
    研究期間 : 1990年 -1991年 
    代表者 : 都 福仁, PATRICK P., OCIO J., THOLENCE J.L, SOULETIE J., FLOUQUET J., 榊原 俊郎, 山岸 昭雄, 朝山 邦輔, 伊達 宗行, HASSELBACH K, OCIO M, TAILLEFER L, DE Visser A, MARCENAT C, REMENYI G, HAEN P, FLOUQUET J, 網塚 浩, 堀 秀信
     
    新しい型の超伝導の可能性が指摘されているUPt_3,URu_2Si_2化合物を中心に研究を行った。UPt_3,URu_2Si_2は高温の局在したウラン金属のf電子がsーf混成により近藤効果を示し50K以下の低温ではフェルミ液体モデルで近似されるコヒ-レント近藤状態になる。この準粒子バンドの一部が17.5Kでギャップを生じ残りのフェルミ面付近の準粒子(重い電子)が約1.4Kで超伝導相転移する。重い電子系でのCooper対の生ずる原因にスピンのゆらぎが関与していることが指摘されて四るが実験的証拠がなく現在最も注目されている問題である。中性子散乱実験、ミュ-中間子の緩和の実験から、UPt_3,URu_2Si_2は各々6K、17.5K以下の温度で磁気的秩序状態が発生することが示唆された。しかしUPt_3,URu_2Si_2共中性子散乱実験は約1/(100)μ_Bの反強磁性をμ SRはスピングラス的秩序状態を示唆し各々の結果は一致していない。またURu_2Si_2では17.5Kで比熱の異常は観測されるが34K付近で磁気秩序状態が生じている。この不一致には試料依存性があるようであるが17.5Kでの比熱の異常は試料によらない。URu_2Si_2,UPt_3の磁気秩序は格子欠陥、不純物等の影響が大きく相転移は明確なものではない。URu_2Si_2の17.5Kでの比熱の異常は磁気相転移ではなくむしろバンド構造の変化による格子歪みの不安定性から生ずるものである。バンド構造の変化は電子多体効果を反映したものと予想され不純物効果が大きいものと思われる。URu_2Si_2では5%〜10%のRhを加えることにより非局在的なフェルミ液体的状態から局在電子による磁気的状態へのクロスオ-バ-が生ずる。局在f電子系のU(Ru_<0.7>Rh_<0.3>)_2Si_2では異方性の大きいイジングスピン系として理解され、3段階の反強磁性相転移が生ずる。Rhが30〜40%付近の結晶では交換相互作用が競合しイジングスピン系の競合系として、いわゆる"悪魔の階段"的な多段階相転移を示す。またリエントラントスピングラス的性質も観測されスピングラス研究の新しい分野として今後も研究を発展させる予定である。
  • 弱い反強磁性を示すウラン系ヘビ-フェルミオンの磁気相図
    日本学術振興会:科学研究費助成事業 重点領域研究
    研究期間 : 1990年 -1990年 
    代表者 : 榊原 俊郎, 網塚 浩
     
    ウラン系ヘビ-フェルミオン化合物はそのほとんどが反強磁性スピン相関を示し、またそれが超伝導転移やメタ磁性転移と関係していると考えられている。従って、磁気相図を詳しく調べること重要な課題である。本研究では典型物質の一つであるURu_2Si_2、および関連物質においてこれまで研究の少ない有限温度・有限磁場の磁気相関を詳しく調べた。以下、概要を述べる。 (1)帯磁率極大とメタ磁性:URu_2Si_2の特微の一つにTmax〜60K付近の帯磁率の大きな山がある。強磁場磁化測定の結果、Tmax以下の温度で磁化過程が非線型性を示し、低温でのメタ磁性へと移行することがわかった。このようなTmaxの原因としては結晶場や反強磁性相関が考えられるが、UをLaやYで薄めていくと消えることから反強磁性相関の可能性が強い。 (2)メタ磁性とSDWエネルギ-:URu_2Si_2の基底状態はT_N=17.5KのSDW状態であると考えられている。一方、低温で見られる鋭いメタ磁性はヘビ-フェルミオン状態からスピン分極した状態への転移と考えられているので、その転移磁場Hc_1にはSDW凝縮エネルギ-が寄与しているはずである。そこで、RuをRhで置換したU(Ru_<1ーX>Rh_X)_2Si_2の相図を詳しく調べた結果、Hc_1はT_Nと相関がありRh置換によりT_Nが低下するにつれてHc_1も下がることが説明された。また、Hc_1の温度変化を詳しく調べたところ、ほぼT^2に比例して低磁場側にシフトしていくことがわかった。これは系の電子比熱がメタ磁性転移とともに増大していることを意味するが、その原因としてSDWギャップが消失したと考えると説明可能である。従って、H【greater than or similar】Hc_1においてもヘビ-フェルミオン状態にある可能性がある。
  • 希土類およびアクチノイドを含む強相関電子系の極低温物性

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