Faculty Profiles - NAKANO Tomohito

Papers - NAKANO Tomohito

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Magnetic field dependence of resistivity for Ce0.8La0.2(Ru0.85Rh0.15)(2)Si-2 Reviewed

Tomohito Nakano, Satomi Shimada, Shigeyuki Murayama, Masato Hedo, Yoshiya Uwatoko, Ichiro Terasaki

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 310 ( 2 ) 402 - 404 2007.3

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

We measured resistivity of heavy fermion antiferromagnetic Ce0.8La0.2(Ru0.85Rh0.15)(2)Si-2 in magneticfield up to 4T. The resistivity for Ce0.8La0.2(Ru0.85Rh0.15)(2)Si-2 shows a downward bend at T-N, indicating an antiferromagnetic order with a local moment character. For 1T <= B <= 1.75 T, it shows a jump at T-N as in the case of Ce(Ru0.85Rh0.15)(2)Si-2, where the downward bend was no longer observed. This result indicates that instead of the local moment character, a gap is opened on the fermi surface by magnetic field. For B > 1.75 T, the resistivity is proportional to T-2 without any anomalies, suggesting that the developed gap closes again for B > 1.75 T, and the Fermi liquid state is induced by magnetic field. (c) 2006 Published by Elsevier B.V.

DOI： 10.1016/j.jmmm.2006.10.081

Nonlinear thermoelectric properties of layered cobalt oxides Reviewed

Tomohito Nakano, Wataru Kobayashi, Ryoji Funahashi, Kenji Sugiura, Hiromichi Ohta, Kunihito Koumoto, Ichiro Terasaki

International Conference on Thermoelectrics, ICT, Proceedings 26th 121 - 123 2007

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

We synthesized whisker-crystal and thin-film samples of the layered cobalt oxide (Bi2Sr2O4)xCoO2 well known as a candidate of a thermoelectric material, and measured their resistivity, voltage-current characteristics and magnetoresistance with pulsed currents. Resistivity of the whisker sample with a small current density of 2 mA/cm2 increases with decreasing temperature below 100 K, suggesting development of a pseudogap on the density of states. This increase is suppressed by a large current density of 110 A/cm2. The nonlinear voltage-current characteristics are observed both for the whisker and thin-film samples. The negative magnetoresistance of the thin-film sample is suppressed by current density. These suggest that the density of states recovers owing to the suppression of the pseudogap by applying large current density. © 2008 IEEE.

DOI： 10.1109/ICT.2007.4569438

Thermal expansion of CePt3Si under high pressure Reviewed

Masashi Ohashi, Gendo Oomi, Tomohito Nakano, Yoshlya Uwatoko

PHYSICA B-CONDENSED MATTER 378-80 379 - 380 2006.5

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

We have carried out the thermal expansion measurement of CePt3Si under pressure Lip to 3.0 GPa. It is found that a maximum in 1(T) is observed and the temperature showing maximum T increases significantly with increasing pressure having a coefficient partial derivative T-m/partial derivative P = 4 K/GPa. Assuming that T-m corresponds to the Kondo temperature T-K, partial derivative T-K/partial derivative P is smaller than that of typical heavy fermion compounds such as CeCu6. It comes from the fact that two kinds of interactions, the RKKY interaction and the Kondo effect, are competing each other. (c) 2006 Published by Elsevier B.V.

DOI： 10.1016/j.physb.2006.01.134

Giant nonlinear conduction and thyristor-like negative differential resistance in BaIrO3 single crystals Reviewed

Tomohito Nakano, Ichiro Terasaki

PHYSICAL REVIEW B 73 ( 19 ) 2006.5

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

We synthesized single-crystalline samples of monoclinic BaIrO3 using a molten flux method, and measured their magnetization, resistivity, Seebeck coefficient, and nonlinear voltage-current characteristics. The magnetization rapidly increases below the ferromagnetic transition temperature T-C of 180 K, where the resistivity concomitantly shows a hump-type anomaly, followed by a sharp increase below 30 K. The Seebeck coefficient suddenly increases below T-C, and shows linear temperature dependence below 50 K. A most striking feature of this compound is that the anomalously giant nonlinear conduction is observed below 30 K, where a small current density of 20 A/cm(2) dramatically suppresses the sharp increase in resistivity to induce a metallic conduction down to 4 K.

DOI： 10.1103/PhysRevB.73.195106

Thermal expansion and magnetostriction in YbInCu4 under high pressure Reviewed

Y. Saiga, T. Nakano, M. Hedo, Y. Uwatoko, M. Kosaka, N. Mori, T. Goto, K. Yoshimura

LOW TEMPERATURE PHYSICS, PTS A AND B 850 1177 - + 2006

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

YbInCu4 undergoes a first-order isostructural valence transition at T-V = 42K, which is accompanied by a 0.5% volume increase due to cooling. In order to elucidate the valence transition, both the linear thermal expansion and magnetostriction, Delta L/L, of a YbInCu4 single crystal were measured using strain gauges under high pressures of up to 3.0 GPa and a magnetic field of up to 18 T. The abrupt volume change during the valence transition was confirmed to decrease linearly with T-V under a high pressure. It was also observed that T-V was suppressed upon application of a magnetic field. On the basis of the results, we have established a T-P-B phase diagram for the first-order valence transition in YbInCu4.

DOI： 10.1063/1.2355123

Thermoelectronic properties of the strongly-correlated oxide BaIrO3 Reviewed

Tomohito Nakano, Ichiro Terasaki

ICT'06: XXV INTERNATIONAL CONFERENCE ON THERMOELECTRICS, PROCEEDINGS 25th(Pt. 2) 473 - + 2006

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

We synthesized polycrystalline samples of Ba1-xSrxIrO3 (0 <= x <= 0.2) using a solid-state reaction method, and measured their magnetization, resistivity, and thermopower. The thermopower of BaIrO3 slightly increases with decreasing temperature above T-C, and is suddenly enhanced below T-C = 180 K due to the pseudogap in the density of states. At 75 K, it reaches a maximum value of 230 mu V/K. With increasing Sr concentration, the thermopower systematically decreases, accompanied by a slight decrease of T-C. For x = 0.2, the maximum value of the thermopower and T-C are 50 mu V/K and 173 K, respectively. These results indicate that the gap is suppressed by chemical pressure due to the substitution of Sr for Ba.

DOI： 10.1109/ICT.2006.331318

Chemical pressure effect for the SDW phase in heavy fermion Ce(Ru0.85Rh0.15)(2)Si-2 compound Reviewed

T Nakano, H Yamashiro, K Fujita, S Murayama

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 74 ( 5 ) 1602 - 1608 2005.5

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

Susceptibility measurements have been performed on polycrystalline samples Ce1-xRy(Ru0.85Rh0.15)(2)(-) Si-2 (R = Sc, La) in order to clarify the chemical pressure effect for the SDW in the heavy fermion Ce(Ru0.85Rh0.15)(2)Si-2. Lattice parameters a and c both decrease with increasing Sc concentration and increase with increasing La concentration. For Ce1-yScy(Ru0.85Rh0.15)(2)Si-2 system, the Neel temperature T-N decreases with increasing Sc concentration and disappears for y >= 0.2. We observed the Curie-Weiss law in the susceptibility at high temperature and a tendency of the saturation in the low temperature susceptibility. The tendency of the saturation and the Weiss temperature Theta determined from the high temperature susceptibility increase with increasing Sc concentration. These facts can be explained through the increase of the c-f hybridization and itinerancy of the f electron. For Ce1-yLay(Ru-0.85-Rh-0.15)(2)Si-2 system, the T-N slightly decreases with increasing La concentration and the tendency of the saturation becomes weaker with increasing y and is no more observed down to T-N for y > 0. 15. The Theta rapidly decreases with increasing La concentration and becomes almost zero for 37 > 0.15. These facts suggest that the c-f hybridization becomes weak with increasing y and that the itinerant AF phase for y < 0. 15 is replaced by the AF phase with the localized moment for y > 0. 15. The Kondo temperature T-K estimated from Theta is scaled by a single proportional function of the lattice parameter c in both cases for the Sc and La substitution.

DOI： 10.1143/JPSJ.74.1602

Magnetic phase transitions in PrCU2Ge2 Reviewed

T Shigeoka, K Hirata, T Nakano, Y Uwatokob

PHYSICA B-CONDENSED MATTER 359 923 - 925 2005.4

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

Measurements of electrical resistivity and specific heat have been performed on the tetragonal ternary compound PrCu2Ge2. The resistivity shows a inflection and a sharp drop with a hysteresis around 14 and 4K where the specific heat also shows lambda-type anomaly and a jump, respectively, which are associated with magnetic transitions. From the low temperature specific heat, the electronic specific heat coefficient y = 13 mJ/mol K-2 and the hyperfine field H-h = 3000 kOe are estimated. The magnetic entropy indicates the existence of a doublet ground level and a doublet first excited level. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.01.264

Electrical resistivity, specific heat and magnetic susceptibility of tetragonal CeGe1.66 Reviewed

T Nakano, M Hedo, Y Uwatoko

PHYSICA B-CONDENSED MATTER 359 284 - 286 2005.4

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

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.

DOI： 10.1016/j.physb.2005.01.105

Resistivity of antiferromagnetic Ce0.8La0.2(Ru0.85Rh0.15)(2)Si-2 under pressure Reviewed

A Isoda, S Shimada, Y Kanda, S Murayama, H Takano, T Nakano, M Hedo, Y Uwatoko

PHYSICA B-CONDENSED MATTER 359 169 - 171 2005.4

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

We have measured the resistivity of antiferromagnetic Ce0.8La0.2(Ru0.85Rh0.15)(2)Si-2 along the tetragonal c-axis under various hydrostatic pressures. At P = 0 GPa we observe no gap-type jump in the resistivity at T-N as has been observed for Ce(Ru0.85Rh0.15)(2)Si-2 at the spin density-wave (SDW) transition temperature, but rather downward bend with decreasing temperature. At P >= 0.48GPa we observe the gap-type jump just below TN. These facts suggest the recovery of the gap opening due to the Fermi-surface nesting by pressure from a conventional localized antiferromagnetic state. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.01.025

Electrical resistivity and tunneling anomalies in CeCuAs2 Reviewed

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

PHYSICA B-CONDENSED MATTER 359 108 - 110 2005.4

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

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.

DOI： 10.1016/j.physb.2005.01.005

Pressure-induced change in temperature coefficient of electrical resistivity in CeCuAS(2) Reviewed

M Abliz, T Nakano, EV Sampathkumaran, JPF Jemetio, T Doert, M Hedo, Y Uwatoko

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 74 ( 2 ) 508 - 510 2005.2

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

The intermetallic compound, CeCuAs2, crystallizing in a HfCuSi2-type tetragonal structure, has recently been shown to exhibit a negative temperature (T) coefficient of electrical resistivity (p) in the entire T-range of investigation (45 mK to 300 K). Here, we report that an application of external pressure (up to IOGPa) profoundly influences p(T) behavior, reversing the sign of drho/dT at pressures above 8 GPa, presumably arising from increasing 4f hybridization or changes in pseudo-gap. Such a behavior is uncommon among Ce-based intermetallic compounds.

DOI： 10.1143/JPSJ.74.508

High pressure effects on the electrical resist ivity behavior of the Kondo lattice, YbPd2Si2 Reviewed

T Nakano, M Hedo, Y Uwatoko, EV Sampathkumaran

SOLID STATE COMMUNICATIONS 132 ( 5 ) 325 - 328 2004.11

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

We report the influence of external high-pressure (P up to 8 GPa) on the temperature (T) dependence of electrical resistivity (rho) of a Yb-based Kondo lattice, YbPd2Si2, which does not undergo magnetic ordering under ambient pressure condition. There are qualitative changes in the rho(T) behavior due to the application of external pressure. While rho is found to vary quadratically below 15 K (down to 45 mK) characteristic of Fermi-liquids, a drop is observed below 0.5 K for P = 1 GPa, signaling the onset of magnetic ordering of Yb ions with the application of P. The Tat which this fall occurs goes through a peak as a function of P (8 K for P = 2 GPa and about 5 K at high pressures), mimicking Doniach's magnetic phase diagram. We infer that this compound is one of the very few Yb-based stoichiometric materials, in which one can traverse from valence fluctuation to magnetic ordering by the application of external pressure. (C) 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ssc.2004.07.064

Magnetic, electrical resistivity, heat-capacity, and thermopower anomalies in CeCuAs2 Reviewed

K Sengupta, EV Sampathkumaran, T Nakano, M Hedo, M Abliz, N Fujiwara, Y Uwatoko, S Rayaprol, K Shigetoh, T Takabatake, T Doert, JPF Jemetio

PHYSICAL REVIEW B 70 ( 6 ) 2004.8

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

The results of magnetic susceptibility (chi), electrical resistivity (rho), heat-capacity (C), and thermopower (S) measurements on CeCuAs2, forming in the ZrCuSi2-type tetragonal structure, are reported. Our investigations reveal that Ce is trivalent and there is no clear evidence for long range magnetic ordering down to 45 mK. The rho behavior is notable in the sense that (i) the temperature (T)-coefficient of rho is negative in the entire range of measurement (45 mK to 300 K) with large values of rho, while the S behavior is typical of metallic Kondo lattices, and (ii) rho is proportional to T-0.6 at low temperatures, without any influence on the exponent by the application of a magnetic field, which does not seem to classify this compound into hither-to-known non-Fermi liquid (NFL) systems. In contrast to the logarithmic increase known for NFL systems, C/T measured down to 0.5 K exhibits a fall below 2 K. The observed properties of this compound are unusual among Ce systems.

DOI： 10.1103/PhysRevB.70.064406

Crystal structure and structural transition caused by charge-transfer phase transition for iron mixed-valence complex (n-C3H7)(4)N[(FeFeIII)-Fe-II(dto)(3)] (dto = C2O2S2) Reviewed

M Itoi, A Taira, M Enomoto, N Matsushita, N Kojima, Y Kobayashi, K Asai, K Koyama, T Nakano, Y Uwatoko, J Yamaura

SOLID STATE COMMUNICATIONS 130 ( 6 ) 415 - 420 2004.5

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

(n-C3H7)(4)N[(FeFeIII)-Fe-II(dto)(3)] shows a new type of first order phase transition called chare-transfer phase transition around 120 K. where the charge transfer between Fe-II and Fe-III occurs reversibly. Recently, we have succeeded in obtaining single crystals of the title complex and determined the crystal Structure at room temperature. Crystal data: space group P6(3), a = 10.0618(5) Angstrom. c = 16.0424(7) Angstrom. V = 1406.54(12)Angstrom, Z = 2. Moreover. we have investigated the structural transition caused by the charge-transfer phase transition by means of powder X-ray diffraction measurement. When the temperature is decreased. the a-axis. which corresponds to the hexagonal ring size in two-dimensional honeycomb network structure of [Fe-II Fe-III(dto)(3)](infinity). contracts by 0.1 Angstrom at the charge-transfer transition temperature (T-CT) while the c-axis. perpendicular to the honeycomb network layer. elongates by 0.1 Angstrom at T-CT. Consequently, when the temperature is decreased, the unit cell volume decreases without noticeable anomaly around T-CT, which is responsible for the quite sniall vibrational contribution to the entropy change. compared with usual spin crossover transition. Thus, the charge-transfer phase transition around 120 K for (n-C3H7)(4)N[Fe-II Fe-III(dto)(3)] is regarded as spin entropy driven phase transition. (C) 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ssc.2004.02.034

Pressure effect and temperature dependence of lattice constants for Ce(Ru0.85Rh0.15)(2)Si-2 Reviewed

Kazuko Koyama, Tomohito Nakano, Masato Hedo, Yoshiya Uwatoko, Shigeyuki Murayama

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 272 ( 2 ) E109 - E110 2004.5

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

X-ray powder diffraction has been studied on Ce(Ru0.85Rh0.15)(2)Si-2 between 300 and 4 K under pressure up to 32 GPa with a diamond anvil cell, and the lattice constants and the bulk modulus have been obtained. The bulk modulus shows a rapid drop between 100 and 50 K; when the temperature decreases from 300 to 4 K: This tendency is most likely attributed to Kondo effect and/or a sign of a spin density wave. (C) 2003 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.11.217

Resistivity of Ce(Ru1-xRhx)(2)Si-2 under pressure Reviewed

Tomohito Nakano, Ayano Isoda, Masato Hedo, Yoshiya Uwatoko, Shigeyuki Murayama

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 272 E85 - E86 2004.5

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

Resistivity measurement on single-srystalline Ce(Ru0.85Rh0.15)(2)Si-2 sample, which shows a spin-density-wave (SDW) transition at a Neel temperature T-N = 5.5 K; has been performed with excitation current parallel to tetragonal a-axis under hydrostatic pressure. Resistivity shows an inflection around T-N, although a hump-type anomaly is not observed as in the case for the c-axis. This in. ection shifts to lower temperature with increasing pressure. This result indicates that the gap of Fermi surface is open only along the c-axis direction up to P-c. On the other hand, the shoulder corresponding to the Kondo effect exists around T similar to 20 K; and shifts to higher temperature with increasing pressure, indicating an increase of T-K: This is consistent with the result for the c-axis. (C) 2004 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.11.314

Magnetic, electrical resistivity, heat-capacity, and thermopower anomalies in CeCuAs2 Reviewed

K. Sengupta, E. V. Sampathkumaran, T. Nakano, M. Hedo, M. Abliz, N. Fujiwara, Y. Uwatoko, S. Rayaprol, K. Shigetoh, T. Takabatake, T. Doert, J. P. F. Jeme

Physical Review B 70 ( 6 ) 064406-1-5 2004

Resistivity of Ce(Ru0.85Rh0.15)(2)Si-2 under pressure Reviewed

T Nakano, K Fujita, S Murayama, K Hoshi, M Hedo, Y Uwatoko

PHYSICA B-CONDENSED MATTER 329 532 - 534 2003.5

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

Resistivity measurement on single-crystalline Ce(Ru0.85Rh0.15)(2)Si-2 sample which shows a spin-density-wave (SDW) transition at a Neel temperature T-N = 5.5 K has been performed under hydrostatic pressure. A hump-type jump in resistivity due to the SDW transition shifts to lower temperature with increasing pressure, and finally disappears above P = 0.5 GPa. The ratio of gapped part of the Fermi-surface along the c-axis is estimated as similar to0.45 for P = 0 GPa and almost pressure independent. (C) 2003 Published by Elsevier Science B.V.

DOI： 10.1016/S0921-4526(02)02374-8

Specific heat of Ce(Ru1-xRhx)(2)Si-2 at around the SDW phase Reviewed

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 2002.3

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

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<B-c (similar to3.6T). For B-c<B<6T, C-mag/T increases with decreasing temperature with a non-Fermi liquid (NFL) behavior. The paramagnetic Fermi liquid (FL) behavior was observed 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.

DOI： 10.1016/S0921-4526(01)01358-8

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