Faculty Profiles - KOBAYASHI Tatsuo

Papers - KOBAYASHI Tatsuo

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High-quality single-crystal growth and a change of the electronic states under pressure in CeRh2Si2 Reviewed

S. Araki, R. Settai, T. C. Kobayashi, Y. Onuki

Journal of Magnetism and Magnetic Materials 226-230 ( I ) 80 - 82 2001

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier

We succeeded in growing a high-quality single crystal of CeRh2Si2 with a residual resistivity ratio of 110. Under a pressure of 1.1 GPa, superconductivity is found below Tc = 0.38 K, where a Néel temperature of TN = 36K is suppressed down to almost zero. © 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(00)00785-X

Neutron scattering studies in the linear-chain Haldane materials, NDMAZ and NDMAP Reviewed

Y Koike, N Metoki, Y Morii, T Kobayashi, T Ishii, M Yamashita

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 69 ( 12 ) 4034 - 4042 2000.12

Language：English Publishing type：Research paper (scientific journal) Publisher：PHYSICAL SOC JAPAN

Neutron scattering experiments were carried out in order to investigate the field-induced. antiferromagnetic long-range order and spin dynamics for the new Haldane compounds Ni(C5H14N2)(2)N-3 (ClO4) (NDMAZ) and Ni(C5H14N2)(2)N-3 (PF6) (NDMAP). We observed the energy gaps corresponding to the excited triplet, Delta (chi) = 1.61 meV, Delta (gamma) = 1.76 meV, Delta (z) = 3.2 meV for NDMAZ and Delta (chi), = 0.48 meV, Delta (gamma), = 0.64 meV for NDMAP. The dispersion in NDMAZ was well explained by the theoretical curve with the intra-chain interaction J = 50 K. The field dependence of the gap energy below critical field (H-c), was observed for NDMAZ and NDMAP as applying the field perpendicular to the chain direction. The field dependence of the excitation levels in NDMAZ was well explained by the fermionic field-theory treatment of the one-dimensional Heisenberg antiferromagnetic Hamiltonian with these gap energies and g-value, 2.3. In NDMAP, we found that the excitation peaks at Q = (0 0 0.5) became unobservably weak above H-c. This result would indicate a level crossing between the ground and the excited level at H-c and the change of the ground state above H-c. No trace of the magnetic Bragg peak due to the field induced ordering could be observed in the present study with our non-deuterated single crystal sample.

DOI： 10.1143/JPSJ.69.4034

Specific heat and effect of pressure on the electrical resistivity of CePtGa single crystal Reviewed

Y Uwatoko, M Kosaka, M Shirakawa, G Oomi, N Mori, T Kobayashi, H Tatewaki, K Shimizu, K Amaya

PHYSICA B 284 1321 - 1322 2000.7

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Specific heat and effect of pressure on the electrical resistivity of CePtGa single crystal have been measured upto 30 kbar. A sharp peak in the ratio of specific heat to temperature and in electrical resistivity is observed at 33 and 3.5 K, respectively, which is ascribed to an antiferromagnetic transition. The results reveal that T-N decreases linearly with increasing pressure upto 30 kbar. (C) 2000 Elsevier Science B.V. All rights reserved.

Pressure dependence of quadrupole ordering temperature T-Q in CeB6 Reviewed

TC Kobayashi, K Hashimoto, S Eda, K Shimizu, K Amaya, Y Onuki

PHYSICA B 281 553 - 554 2000.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Pressure dependence of electrical resistance in CeB6 is investigated up to 13 GPa. A maximum in temperature dependence of the resistance shifts to higher temperature by the application of pressure. The quadrupole ordering temperature T-Q shows no obvious pressure dependence at zero field, while the field dependence of T-Q is enhanced slightly under high pressure. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(99)00947-3

Metamagnetic transition of CeRh2Si2 under high fields and high pressures at various temperatures Reviewed

T Hamamoto, K Kindo, TC Kobayashi, Y Uwatoko, S Araki, R Settai, Y Onuki

PHYSICA B 281 64 - 65 2000.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

High-field magnetization measurements in a heavy fermion antiferromagnet CeRh2Si2 were performed under high pressures at various temperatures to study the nature of the metamagnetism. Metamagnetic transitions were observed not only in the antiferromagnetic state but also in the paramagnetic stale at various pressures, The metamagnetism in CeRh2Si2 does not originate from the rearrangement of antiferromagnetic moments but from the recovery of the local moment from the Kondo singlet state by applying high magnetic fields. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

Pressure-dependence of superconducting behavior in CeRh2Si2 Reviewed

TC Kobayashi, T Muramatsu, M Takimoto, K Hanazono, K Shimizu, K Amaya, S Araki, R Settai, Y Onuki

PHYSICA B 281 7 - 8 2000.6

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Electrical resistance has been investigated in a high-quality polycrystal of CeRh2Si2 under high pressures of up to 5.4 GPa. We found a resistance drop corresponding to superconductivity in the pressure range from 0.7 to 2.9 GPa. The relative decrease of the resistance shows a maximum in the vicinity of a critical pressure Pc. An onset temperature of superconductivity is about 0.6 K. (C) 2000 Elsevier Science B.V. All rights reserved.

Electrical studies in DAC Reviewed

Report,Research Center for Materials Science at Extreme Conditions,Osaka University ( 5 ) 218 - 222 2000

Electrical resistance measurement in hydrostatic pressure up to lO GPa using a diamond anvil cell Reviewed

Report,Research Center for Materials Science at Extreme Conditions,Osaka University ( 5 ) 223 - 226 2000

Two gaps in (VO)(2)P2O7: Observation using high-field magnetization and NMR Reviewed

T Yamauchi, Y Narumi, J Kikuchi, Y Ueda, K Tatani, TC Kobayashi, K Kindo, K Motoya

PHYSICAL REVIEW LETTERS 83 ( 18 ) 3729 - 3732 1999.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMERICAN PHYSICAL SOC

The alternating one-dimensional Heisenberg S = 1/2 chain compound with spin gap, (VO)(2)P2O7, has been studied by the high-field magnetization and P-31 NMR measurements. Two critical phenomena at 25 +/- 1 and 46 +/- 2 T are observed in the magnetization curve, which are considered to be a crossover between the ground state and the excited state in two kinds of gap systems. P-31 NMR also revealed the coexistence of two magnetic systems with independent spin gaps. Results obtained from the present and previous studies are well explained by the model in which two kinds of magnetic chains along the b axis behave as alternating spin chains with independent gap energies.

DOI： 10.1103/PhysRevLett.83.3729

Field-induced 3D-LRO of Haldane-gap antiferromagnet NDMAZ Reviewed

A Koda, TC Kobayashi, K Amaya, H Yamashita

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 196 443 - 445 1999.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The heat capacity and magnetization measurements of the single crystal of Haldane-gap antiferromagnet NDMAZ were carried out at low temperatures down to 0.1 K and under magnetic fields up to 14 T. We have observed three-dimensional long-range ordering of NDMAZ at around T similar or equal to 0.3 K above H similar or equal to 13 T (H parallel to c), which is ascribed to both the field-induced gap quenching and the existence of finite interchain interaction. Applying the higher external held, the transition temperature reaches up to 0.6 K at H = 14 T, showing a negative curvature with respect to the external field. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(98)00804-X

Magnetic and transport properties of CeRh2Si2 under high pressures Reviewed

T Muramatsu, S Eda, TC Kobayashi, MI Eremets, K Amaya, S Araki, R Settai, Y Onuki

PHYSICA B-CONDENSED MATTER 259-61 61 - 62 1999.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Magnetic and transport properties have been investigated in the single crystal of CeRh2Si2 under high pressures. We found that the magnetic susceptibility under high pressure shows a broad maximum like CeRu2Si2. In the present pressure range up to 13 kbar where the ordered state is suppressed, no obvious evidence of the superconducting transition is observed down to 50 mK. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(98)00909-0

Metallization and superconductivity in CsI at pressures up to 220 GPa Reviewed

M. I. Eremets, K. Shimizu, T. C. Kobayashi, K. Amaya

Journal of Physics Condensed Matter 10 ( 49 ) 11519 - 11523 1998.12

Language：English Publishing type：Research paper (scientific journal)

The pressure range for electrical transport measurements has been dramatically increased up to 220 GPa in the 0.05-300 K temperature region and at magnetic fields of up to 10 T. Metallization of caesium iodide was found at a pressure of 115 GPa. A superconducting transition with T c = 2 K was observed above 180 GPa. T c decreases with increasing pressure. The superconducting transition shifts to lower temperatures and disappears under magnetic field above 0.3 Tesla.

DOI： 10.1088/0953-8984/10/49/037

Observation of pressure-induced superconductivity in the megabar region Reviewed

K. Amaya, K. Shimizu, M. I. Eremets, T. C. Kobayashi, S. Endo

Journal of Physics Condensed Matter 10 ( 49 ) 11179 - 11190 1998.12

Language：English Publishing type：Research paper (scientific journal)

A review of recent developments in high-pressure techniques and their application in the search for superconductivity at low temperature is presented. We have focused the discussion mainly on the experimental results obtained by our group for simple molecular systems.

DOI： 10.1088/0953-8984/10/49/008

Orbital Frustration and Resonating Valence Bond State in the Spin-1/2 Triangular Lattice LiNiO 2 Reviewed

Kitaoka Yoshio, Kobayashi Tatsuo, Kōda Akihiro, Wakabayashi Hayato, Niino Yoshihiro, Yamakage Hirokazu, Taguchi Shinichiro, Amaya Kiichi, Yamaura Kazunari, Takano Mikio, Hirano Atushi, Kanno Ryoji

J Phys Soc Jpn 67 ( 11 ) 3703 - 3706 1998.11

Language：English Publisher：The Physical Society of Japan (JPS)

From the 7Li nuclear magnetic resonance (NMR) and specific heatmeasurements of LiNiO2, consisting of a spin-1/2 triangular lattice, itis demonstrated that the previously suggested spin-glass-like freezingbelow Tsg=8 K, which is caused by defects of Li ions, is not the trueground state, but rather a quantum disordered state is realized without aspin gap. This state is characterized by power-law behavior of thetemperature dependence of the specific heat below 0.5 K. A spin-liquidstate with short-range ferromagnetic correlations is suggested from newinsight into the frustration of orbital ordering for doubly degenerateeg shells in the triangular lattice.

DOI： 10.1143/JPSJ.67.3703

Metallic CsI at Pressure of up to 220 Gigapascals Reviewed

M. I. Eremets, K. Shimizu, T. C. Kobayashi, K. Amaya

Science 1998.4

Enhancement of superconducting transition temperature in CeCu2Ge2 under high pressures Reviewed

T. C. Kobayashi, T. Miyazu, N. Takeshita, K. Shimizu, K. Amaya, Y. Kitaoka, Y. Onuki

J. Phys. Soc. Jpn. 67 ( 3 ) 996 - 999 1998.4

Language：English Publishing type：Research paper (scientific journal) Publisher：The Physical Society of Japan (JPS)

Enhancement of superconducting transition temperature T c is confirmed at around 16 GPa in the pressure-induced superconductor CeCu2Ge2.The superconducting Hc-T c phase diagrams at the low-T c and high-T c pressure regions indicates that the heavy quasi particles form the singlet Cooper pairs.At both low-T c and high-T c pressure regions, Fermi liquid behavior of ρ∼ AT2 is observed only at low temperatures below 1 K in the normal state induced by the external field above Hc2.At 21 GPa where the superconductivity disappears down to 50 mK, the temperature region following ρ∼ AT2 increases drastically up to 40 K and the coefficient A decreases rapidly.These results indicate that the strongly correlated electrons are responsible essentially for the appearance of superconductivity in this system.

DOI： 10.1143/JPSJ.67.996

Magnetic-to-nonmagnetic transition in the ferromagnetic heavy-fermion compound CeRu2Ge2 at high pressures Reviewed

T. C. Kobayashi, T. Miyazu, K. Shimizu, K. Amaya, Y. Kitaoka, Y. Onuki, M. Shirase, T. Takabatake

Phys. Rev. B 57 ( 9 ) 5025 - 5028 1998.4

Phase diagram of a new spin-Peierls compound: p-CyDOV Reviewed

T. Hamamoto, Y. Narumi, K. Kindo, K. Mukai, Y. Shimobe, T. C. Kobayashi, T. Muramatsu, K. Amaya

Physica B 246 36 - 39 1998

Magnetic Properties of Oxygen Physisorbed in Cu-Trans-1,4-Cyclohexanedicarboxylic Acid Reviewed

Wasuke Mori, Tatsuo C. Kobayashi, Junji Kurobe, Kuichi Amaya, Yasuo Narumi, Takayuki Kumada, Koichi Kindo, Hiroko Aruga Katori, Tuneaki Goto, Noboru Miura, Satoshi Takamizawa, Hirokazu Nakayama, Kizashi Yamaguchi

MOLECULAR CRYSTALS AND LIQUID CRYSTALS SCIENCE AND TECHNOLOGY SECTION A-MOLECULAR CRYSTALS AND LIQUID CRYSTALS 306 1 - 7 1997.10

Language：English Publishing type：Research paper (scientific journal) Publisher：GORDON BREACH SCI PUBL LTD

Magnetic properties of oxygen physisorbed in Cu-trans-1,4-cyclohexanedicarboxylic acid having one-dimensional micropores are studied. O-2 is well known as a magnetic molecule with S=1. In the case of the low adsorption, temperature dependence of the susceptibility shows the Schottky-type broad peak and the high-field magnetization process has a step at around 34T with saturation moment of 2 mu(B)/O-2. These results are interpreted by the dimer model of S=1/2 with an antiferromagnetic exchange interaction. Broadening of the step of magnetization with increasing the adsorption may be due to the interdimer interaction or the distribution of the intra-dimer exchange interaction. Linear magnetization process which is characteristic of one-dimensional Heisenberg antiferromagnet has not been observed even in the full pore region.

DOI： 10.1080/10587259708044542

Observation of weak ferromagnetism in organic verdazyl radical crystal, p-CyDpTV Reviewed

Kazuo Mukai, Masaaki Nuwa, Tomonari Morishita, Takaki Muramatsu, Tatsuo C. Kobayashi, Kiichi Amaya

Chemical Physics Letters 272 ( 5-6 ) 501 - 505 1997.7

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier

Magnetic property of 3-(4-cyanophenyl)-1,5-diphenyl-6-thioxoverdazyl (p-CyDpTV) radical crystal has been studied in the temperature range of 0.05-300 K in external magnetic fields 3, 11, 30, and 100 Oe by using SQUID magnetometer. Weak ferromagnetic behavior was observed at TN = 0.41 K. Below TN, the spontaneous magnetization Ms(T) increased rapidly, reaching a maximum of 31.1 emu/mol at 0.05 K. Spin-canting angle was estimated to be 0.32° at 0.05 K. Near TN, Ms(T) α [1-(T/TN)]β with the critical exponent of β = 0.36, in agreement with that expected for an isotropic three-dimensional (3D) Heisenberg spin system. © 1997 Elsevier Science B.V.

DOI： 10.1016/S0009-2614(97)00529-0

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