論文 - 辺土　正人

Electrical Resistivity of (TMTTF)₂PF₆under High Pressure

Araki Chieko, Itoi Miho, Hedo Masato, Uwatoko Yoshiya, Mori Hatsumi

Journal of the Physical Society of Japan ( The Physical Society of Japan )  76   2007年 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Electrical conducting bis(oxalato)platinate complex with direct connection of Cu<SUP>II</SUP> ions

Yamamoto, C; Nishikawa, H; Nihei, M; Shiga, T; Hedo, M; Uwatoko, Y; Sawa, H; Kitagawa, H; Taguchi, Y; Iwasa, Y; Oshio, H

INORGANIC CHEMISTRY ( AMER CHEMICAL SOC )  45 ( 25 ) 10270 - 10276   2006年12月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

　概要を見る

Reactions of K-1.62[Pt(ox)(2)]center dot 2H(2)O and [Cu(bpy)(H2O)(3)](NO3)(2) yielded partially oxidized one-dimensional (1D) bis(oxalato)platinates of [Cu(bpy)(H2O)(n)](6)[Pt(ox)(2)](7)center dot 7H(2)O (n = 2, 3, or 4) (1) and [Cu(bpy)(H2O)(n)](8)[Pt(ox)(2)](10)center dot 8H(2)O (n = 3 or 4) (2). The average oxidation numbers of the platinum ions in 1 and 2 are +2.29 and +2.40, respectively. Complexes 1 and 2 crystallize in the triclinic P (1) over bar and monoclinic C2/c space groups, respectively, and the [Pt(ox)(2)](n-) anions are stacked along the crystallographic b axis with 7-fold periodicity for 1 and 10-fold periodicity for 2. In 1, an oxalato ligand in the platinum chain directly coordinates to a paramagnetic [Cu(bpy)(H2O)(3)](2+) ion, whereas no such direct coordination was observed for 2. The electrical conductivity of 2 at room temperature along the platinum chain is approximately 3 orders of magnitude smaller (sigma(II) = 1.3 x 10(-3) S cm(-1)) than that of 1(sigma(II) = 0.9-0.5 S cm(-1)), and the activation energies of 1 and 2 are 29 and 67 meV, respectively. The longest inter-platinum distances in 1 and 2 are 2.762 and 3.0082 angstrom, respectively, and this is responsible for the lower electrical conductivity of 2. An X-ray oscillation photograph taken along the b axis of 1 reveals the 7-fold periodicity in the 1D chain, consistent with the period of the Peierls distortion estimated from the degree of partial oxidation. The semiconducting state of 1 can therefore be regarded as a commensurate Peierls state. The magnetoresistance of 1 at ambient pressure indicates no interaction between conduction electrons in the platinum chain and local spins of the paramagnetic Cu-II ions. Application of hydrostatic pressures of up to 3 GPa enhances electrical conduction, as is often seen as the usual pressure effect on the electrical conductivity, which is due to enhanced orbital (Pt-5d(z)(2)) overlap by pressure application.

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Effect of pressure on the electronic state in antiferromagnets UPt2Si2 and UIr2Si2

Ikeda Shugo, Nakashima Miho, Matsuda Tatsuma D., Tateiwa Naoyuki, Yamamoto Etsuji, Nakamura Akio, Haga Yoshinori, Hedo Masato, Uwatoko Yoshiya, Onuki Yoshichika

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   75 ( 12 )   2006年12月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Pressure effect on electrical resistivity of Y_1-<i>x</i>Gd<i>_x</i>Co₂

Nakama, T; Takaesua, Y; Yagasaki, K; Sakai, E; Kurita, N; Hedo, M; Uwatoko, Y; Burkov, AT

PHYSICA B-CONDENSED MATTER ( Physica B: Condensed Matter )  378-80 ( SPEC. ISS. ) 169 - 170   2006年05月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

　概要を見る

Electrical resistivity of Y1-xGdxCo2 alloy system has been measured at temperatures from 2 to 300 K in magnetic field up to 15T and under pressure up to 10 GPa. The compounds with the composition near to phase boundary between paramagnetic and ferromagnetic ground state (x(c) approximate to 0.12) show strong enhancement of electrical resistivity at low temperatures. Large positive magnetoresistance was observed in ferromagnetic alloys in composition range 0.15 &lt; x &lt; 0.3. The anomalous magneto resistance as well as the composition dependence of the low-temperature resistivity were explained by an interplay of metamagnetic instability of Co 3d itinerant electrons and structural disorder within rare-earth sublattice. The pressure effect on electrical resistivity for Y1-xGdxCo2 at low temperatures is in agreement with the variation of magnetoresistance with the composition. (c) 2006 Elsevier B.V. All rights reserved.

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Heat capacity measurement of CePd₂Si₂ under high pressure

Hashimoto, M; Tomioka, F; Umehara, I; Fujiwara, T; Hedo, M; Uwatoko, Y

PHYSICA B-CONDENSED MATTER ( ELSEVIER SCIENCE BV )  378-80 ( SPEC. ISS. ) 815 - 816   2006年05月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

　概要を見る

We have performed AC calorimetric measurement under high pressure tip to 1.56GPa using a Cu-Be and Ni-Cr-Al hybrid piston cylinder cell in the temperature range from 2 to 12K in CePd2Si2. It is clearly seen magnetic ordering temperature T-N, and magnetic contribution are suppressed under high pressures. (c) 2006 Elsevier B.V. All rights reserved.

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Anomalous metallic state in (TTM-TTP)I-3 with a highly one-dimensional half-filled band under pressure beyond 7 GPa

Yasuzuka S., Murata Keizo, Fujimoto T., Shimotori M., Kawamoto T., Mori T., Hedo M., Uwatoko Y.

JOURNAL OF LOW TEMPERATURE PHYSICS   142 ( 3-4 ) 197 - 200   2006年02月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Evolution of Hall coefficient in two-dimensional heavy fermion CeCoIn₅

Nakajima, Y; Izawa, K; Matsuda, Y; Behnia, K; Kontani, H; Hedo, M; Uwatoko, Y; Matsumoto, T; Shishido, H; Settai, R; Onuki, Y

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN ( PHYSICAL SOC JAPAN )  75 ( 2 )   2006年02月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

　概要を見る

We report on the pressure dependence of the Hall coefficient RH in quasi-2D heavy fermion CeCoIn5. At ambient pressure, below a temperature associated with the emergence of non-Fermi liquid properties, RH is anomalously enhanced. We found that the restoration of the Fermi liquid state with applied pressure leads to a gradual suppression of this dramatic enhancement. Moreover, the enhancement in RH was found to be confined to an intermediate temperature window, where inelastic electron-electron scattering is dominant. Our results strongly support the presence of cold and hot spots on the Fermi surface probably due to anisotropic scattering by antiferromagnetic fluctuations, which may also prove relevant for the debate on the anomalous normal-state properties of high-T-c cuprates.

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Electrical properties of the dialkyldimethylammomium-Au(dmit)(2) LB films

Masaaki Kitao, Hawki Matsui, Shin-ichi Morita, Yasuhiro F. Miura, Michio Sugi, Masato Hedo, Yoshiya Uwatoko

Transactions of the Materials Research Society of Japan, Vol 31, No 3 ( ELSEVIER SCIENCE BV )  31 ( 3 ) 621 - 624   2006年 [ 査読有り ]

掲載種別: 研究論文（国際会議プロシーディングス）

　概要を見る

The resistance of the Langmuir-Blodgett films based on ditetradecyldimethylammonium-Au(dmit)2 (2C(14)-Au(dmit)(2)) salt was measured along the film plane using electrode gaps of 0.5 turn and 5 mu m in a wide temperature range of 27-290 K. In case the electrode gap is 0.5 mm, the LB film shows a weak metallic behavior from room temperature down to around 200-250 K with a positive temperature derivative of the resistance, but it shows a negative temperature derivative of the resistance below the temperature. However, in case the electrode gap is 5 mu m, the metallic temperature dependence of the resistance extends down to the lower temperature range of 58-106 K. The atomic force microscopy (AFM) has revealed that the LB film consists of crystallites, which are 1-5 mu m in lateral sizes and 4-20 nm in thickness. We hypothesize that the broad minimum of the resistance vs. temperature plot emerges in a crossover region, where metallic nature inside the crystallites are competing with the random potentials set up by grain boundaries and/or defects, and then, the metallic temperature dependence extends down to the lower temperature by narrowing the electrode gap.

Charge density wave and pressure-induced reentrant superconductivity in ZrTe3

Yamaya K, Yomo R, Inagaki K, Tanda S, Abliz M, Hedo M, Uwatoko Y

JOURNAL DE PHYSIQUE IV   131   343 - 345   2005年12月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Effect of pressure on electronic states in canted ferromagnet CePtAl

Ueda T, Nakashima M, Hedo M, Uwatoko Y, Nakashima H, Thamizhavel A, Matsuda TD, Haga Y, Settai R, Onuki Y

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   74 ( 12 ) 3393 - 3394   2005年12月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Electrical resistivity of the perovskite Ba_1-<i>x</i>K<i>_x</i>BiO₃ (x ≤ 0.15) under high pressure

Imai, Y; Kato, M; Noji, T; Koike, Y; Hedo, M; Uwatoko, Y; Mori, N

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS   426 ( I ) 497 - 499   2005年10月 [ 査読有り ]

掲載種別: 研究論文（国際会議プロシーディングス）

　概要を見る

Electrical resistivity measurements of the insulating Ba 1-xKxBiO3 (x = 0, 0.15) under high pressure up to 8 GPa have been performed in order to search for the pressure-induced superconductivity, using a cubic-anvil pressure system. A polycrystal of BaBiO3 has been prepared by the solid-state reaction method. A single crystal of Ba0.85K0.15BiO3 has been synthesized by the electrochemical method from molten salts. The electrical resistivity of both compounds slightly decreases with increasing pressure. However, the temperature dependence still remains semiconductive and no superconductivity is observed. © 2005 Elsevier B.V. All rights reserved.

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Effect of hydrostatic pressure on molecular conductors, Pd(dmit)(2) salts

Ishii Y, Tamura M, Kato R, Hedo M, Uwatoko Y, Mori N

SYNTHETIC METALS   152 ( 1-3 ) 389 - 392   2005年09月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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A change of electronic state tuned by pressure: pressure-induced superconductivity of the antiferromagnet Ce2Ni3Ge5

Nakashima M, Kohara H, Thamizhavel A, Matsuda TD, Haga Y, Hedo M, Uwatoko Y, Settai R, Onuki Y

JOURNAL OF PHYSICS-CONDENSED MATTER   17 ( 28 ) 4539 - 4546   2005年07月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Electrical and magnetic properties of a single crystal UCu₂Si₂

Matsuda, TD; Haga, Y; Ikeda, S; Galatanu, A; Yamamoto, E; Shishido, H; Yamada, M; Yamaura, J; Hedo, M; Uwatoko, Y; Matsumoto, T; Tada, T; Noguchi, S; Sugimoto, T; Kuwahara, K; Iwasa, K; Kohgi, M; Settai, R; Onuki, Y

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN   74 ( 5 ) 1552 - 1556   2005年05月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

　概要を見る

We have succeeded in growing a high-quality single crystal of UCu 2Si2 with the tetragonal structure by the Sn-flux method and measured the electrical resistivity, magnetic susceptibility, magnetization and specific heat. UCu2Si2 is found to order antiferromagnetically below TN = 106 K, and follows a successive ferromagnetic ordering at TC = 100 K. The magnetic properties are highly anisotropic, reflecting the crystal structure. An easy-axis of magnetization is found to be the [001] direction (c-axis) both in the antiferromagnetic and ferromagnetic phases, while the [100] direction (a-axis) corresponds to the hard-axis in magnetization. The magnetization curve in the antiferromagnetic phase indicates a clear metamagnetic transition at a low field of about 1 kOe and changes into a ferromagnetic magnetization curve below TC = 100 K. The saturation moment is determined as 1.75 μB/U at 2 K. The electronic specific heat coefficient is also determined as 20 mJ/(K2·mol). ©2005 The Physical Society of Japan.

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Electrical resistivity and tunneling anomalies in CeCuAs₂

Sampathkumaran, EV; Ekino, T; Ribeiro, RA; Sengupta, K; Nakano, T; Hedo, M; Fujiwara, N; Abliz, M; Uwatoko, Y; Rayaprol, S; Doert, T; Jernetio, JPF

PHYSICA B-CONDENSED MATTER ( ELSEVIER SCIENCE BV )  359   108 - 110   2005年04月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

　概要を見る

The compound CeCuAs2 is found to exhibit negative temperature (T) coefficient of electrical resistivity (rho) under ambient pressure conditions in the entire T-range of investigation (45 mK-300 K), even in the presence of high magnetic fields. Preliminary tunneling spectroscopic measurements indicate the existence of a psuedo-gap at least at low temperatures, thereby implying that this compound could be classified as a Kondo semi-conductor, though rho(T) interestingly is not found to be of an activated type. (c) 2005 Elsevier B.V. All rights reserved.

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Electrical resistivity, specific heat and magnetic susceptibility of tetragonal CeGe_1.66

Nakano, T; Hedo, M; Uwatoko, Y

PHYSICA B-CONDENSED MATTER ( ELSEVIER SCIENCE BV )  359   284 - 286   2005年04月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

　概要を見る

Magnetic susceptibility, specific heat and electrical resistivity measurements have been carried out on polycrystalline specimens of CeGe1.66, forming in a tetragonal structure, which is derived from CeGe2 by creation of vacancies at the Ge site. A shoulder in susceptibility, a jump in specific heat and an inflection in resisitivity attributable to magnetic ordering are observed at 6.7 K. Furthermore, a rapid increase in susceptibility, another jump in specific heat and a rapid decrease in the resistivity due to the ferromagnetic ordering are observed below (T-C =) 5.3 K. The electronic specific heat coefficient gamma is estimated to be about mJ/molK(2) (c) 2005 Elsevier B.V. All rights reserved.

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Pressure dependence of the first-order superconducting phase transition in CeCoIn₅

Tayama, T; Namai, Y; Sakakibara, T; Hedo, M; Uwatoko, Y; Shishido, H; Settai, R; Onuki, Y

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN ( PHYSICAL SOC JAPAN )  74 ( 4 ) 1115 - 1118   2005年04月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

　概要を見る

The pressure dependence of the first-order phase transition (FOPT) at the upper critical field H-c2 in CeCoIn5 has been Studied by magnetization measurements. The FOPT is found to persist at pressures at least up to 1.5 GPa in the c axis and up to 1.38 GPa in the a axis. With increasing pressure, the anisotropy of H-c2 becomes stronger, and the condensation energy decreases significantly. We also observed a notable peak effect near H-c2 under pressure. Our results suggest that the FOPT cannot be accounted for by Pauli limiting alone.

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Pressure effect on competition between charge density wave and superconductivity in ZrTe₃:: Appearance of pressure-induced reentrant superconductivity -: art. no. 132508

Yomo, R; Yamaya, K; Abliz, M; Hedo, M; Uwatoko, Y

PHYSICAL REVIEW B   71 ( 13 )   2005年04月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

　概要を見る

We report on an intricate competition between charge density wave (CDW) formation and superconductivity under pressure up to 11 GPa in the low-dimensional conductor ZrTe3. As pressure increases, the CDW transition temperature TCDW initially increases, then begins to decrease at 2 GPa and abruptly disappears near 5 GPa. On the other hand, while the superconducting transition temperature TC falls to below 1.2 K at ∼0.5 GPa and is not observed at up to 5 GPa above 2.5 K, a superconducting transition emerges beginning at ∼5 GPa and TC increases steeply up to 11 GPa. This is an observation of pressure-induced reentrant superconductivity. The results are discussed in terms of the change in the reduced area of the Fermi surface due to CDW formation. © 2005 The American Physical Society.

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The development of a high pressure micro-cell for magnetization and specific heat measurements: the effect of pressure on the magnetism in CeAg

Uwatoko Y, Fujiwara T, Hedo M, Tomioka F, Umehara I

JOURNAL OF PHYSICS-CONDENSED MATTER   17 ( 11 ) S1011 - S1016   2005年03月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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Altered Ru, Sr atomic environments in strontium ruthenates: XAFS evidence for valence and magnetism

Yoshimura M., Yoshida Y., Ikeda S. I., Shirakawa N., Nagai I., Hara S., Koyama K., Hedo M., Uwatoko Y.

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS   272   E257 - E258   2004年05月 [ 査読有り ]

掲載種別: 研究論文（学術雑誌）

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