Faculty Profiles - NAKANO Tomohito

Papers - NAKANO Tomohito

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Coexistence of distinct Ce 4f-electron states at inequivalent crystallographic sites: CePtGe2 case

Hayato Muto, Tomohito Nakano, Tatsuya Watanabe, Ryota Takahashi, Naoya Takeda, Jun Gouchi, Yoshiya Uwatoko, Michal Dušek, Jan Prokleška, Jiří Pospíšil, Vladimír Sechovský

Journal of Magnetism and Magnetic Materials 613 172670 - 172670 2025.2

First-order transition under a magnetic ordered state in SmPtSi<sub>2</sub> Reviewed

Tomohito Nakano, Eisuke Takahashi, Shuto Yamaguchi, Naoya Takeda, Klára Uhlířová, Jan Prokleška, Jiří Pospíšil, Vladimír Sechovský, Kazuyuki Matusbayashi, Hanming Ma, Yoshiya Uwatoko

Physica Scripta 99 ( 8 ) 085923 - 085923 2024.7

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：IOP Publishing

Abstract

We have synthesized polycrystalline and single-crystalline samples of SmPtSi<sub>2</sub>, and measured their resistivity, specific heat, magnetization, and Seebeck coefficient. The existence of two magnetic phase transitions has been confirmed, one at T <sub>H</sub> = 8.6 K and the other T <sub>L</sub> = 5.6 K. A hump-type anomaly in resistivity, a lambda-type anomaly in specific heat, a downward bend in magnetization, and a semiconductor-like increase in the Seebeck coefficient were observed at T <sub>H</sub>, indicating an antiferromagnetic transition accompanied by a gap opening on the Fermi surface. In contrast, a sharp drop in resistivity, a sharp spike in specific heat, and a drop in magnetization were observed at T <sub>L</sub>. The Seebeck coefficient showed metallic temperature dependence below T <sub>L</sub>. With increasing pressure, T <sub>H</sub> and T <sub>L</sub> shifted to higher temperatures. The transition at T <sub>L</sub> was no longer observed at pressures above 1.5 GPa. These findings suggest that the transition at T <sub>L</sub> is a transition from an antiferromagnetic ordered state with the gap on the Fermi surface to a different antiferromagnetic state.

DOI： 10.1088/1402-4896/ad59e0

Other Link： https://iopscience.iop.org/article/10.1088/1402-4896/ad59e0/pdf

Y-Substitution Effects on Electrical Resistivity of (Ce<sub>1−</sub><i><sub>y</sub></i>Y<i><sub>y</sub></i>)PtGe<sub>2</sub> Reviewed

Hayato Muto, Shoma Onuma, Tatsuya Watanabe, Ryota Takahashi, Tomohito Nakano, Naoya Takeda, Jun Gouchi, Yoshiya Uwatoko, Klára Uhlířová, Jan Prokleška, Vladimír Sechovský

Proceedings of the 29th International Conference on Low Temperature Physics (LT29) 38 011078-1 - 011078-5 2023.5

Transport and Thermal Properties of α-Mn under Pressure Reviewed

Tomohito Nakano, Kei Fukuhra, Arisa Tomaru, Hayato Muto, Naoya Takeda, Yusuke Amakai, Shigeyuki Murayama

Proceedings of the 29th International Conference on Low Temperature Physics (LT29) 38 011072-1 - 011072-6 2023.5

Magnetic separation of nickel-plating waste liquid using a high temperature superconducting bulk magnet

T Oka, K Sudo, J L Dadiel, N Sakai, H Seki, M Miryala, M Murakami, T Nakano, M Ooizumi, K Yokoyama, M Tsujimura

Superconductor Science and Technology 35 ( 9 ) 094006 - 094006 2022.9

Publishing type：Research paper (scientific journal) Publisher：IOP Publishing

Abstract

Ni is one of the important metal resources. Because Ni-containing waste liquid is drained after several plating turns in the factories, an effective recycling technique should be developed. A unique magnetic separation technique using high temperature superconducting bulk magnet has succeeded in collecting Ni-sulfate crystals, which were fabricated from the Ni-plating waste liquid. Pulsed-field magnetizing method was employed to activate the bulk magnet up to 2.80 T, which produced a field space of 1.40 T on the surface of the waste channel. Green coarse crystals were attracted from the flowing stream of Ni-saturated liquid containing weakly-magnetic particles of Ni-compounds. The magnetically-collected particles were identified as paramagnetic NiSO<sub>4</sub>/6H<sub>2</sub>O crystals, and slight differences in Ni concentration and grain size were observed between the particles attracted and not-attracted to the 1.8 T magnetic pole. In both cases, the large grains were found to consist of a single phase. The compound can be used as a raw material in the Ni-recycle process. This preferential extraction suggests a novel recycling method of Ni resource.

DOI： 10.1088/1361-6668/ac7f61

Other Link： https://iopscience.iop.org/article/10.1088/1361-6668/ac7f61/pdf

La-Substitution Effects on Multisite Ce Compound CePtGe<inf>2</inf>

Hayato Muto, Shoma Onuma, Tomohito Nakano, Naoya Takeda, Jun Gouchi, Yoshiya Uwatoko, Klára Uhlířová, Jan Prokleška, Vladimír Sechovský

Journal of the Physical Society of Japan 91 ( 7 ) 2022.7

Publishing type：Research paper (scientific journal)

The CePtGe2 compound, which shows antiferromagnetic transition at Néel temperature TN = 3.8 K, has two crystallographically inequivalent Ce sites. Recently, the coexistence of a localized f-electron state at one of two Ce sites and an itinerant heavy f-electron state at the other Ce site has been suggested. In this study, we have prepared polycrystalline samples of (Ce1-xLax)PtGe2 (x = 0 ∼ 0.2) and have measured their electrical resistivity and magnetization. The specific heat for x = 0.2 has been measured also. With increasing x, the downward bending of the temperature dependence of the resistivity and the cusp-type anomaly in the susceptibility associated with TN shift to lower temperatures with a linear extrapolation of TN directing to 0 K at x ∼ 0.5. Also, the saturation magnetization decreases linearly with increasing x, pointing to the disappearance of magnetic moments at the same La concentration. These results indicate that only the Ce ions with the localized f-electron are substituted by La ions. On the other hand, the transition from the antiferromagnetic state to the ferromagnetic-like polarized magnetic state at a very weak magnetic field, which is comparable to that of conventional Ferrite magnets, was realized via the La-substitution.

DOI： 10.7566/JPSJ.91.074712

Pressure dependence of the magnetic ground state in CePtSi2

S. E. Dissanayake, F. Ye, W. Tian, M. Matsuda, H. Muto, S. Suzuki, T. Nakano, S. Watanabe, J. Gouchi, Y. Uwatoko

Physical Review B 105 ( 24 ) 2022.6

Publishing type：Research paper (scientific journal)

CePtSi2 was reported to exhibit an antiferromagnetic order below T∗=1.8 K at ambient pressure, a valence state change at ∼1.2 GPa, and superconductivity in the range between 1.4 and 2.1 GPa with a maximum transition temperature of 0.14 K [T. Nakano, Phys. Rev. B 79, 172507 (2009)1098-012110.1103/PhysRevB.79.172507]. We have performed polycrystalline and single-crystal neutron diffraction experiments to determine the magnetic structure under ambient and high pressures. We found incommensurate magnetic peaks with a magnetic propagation vector of (0.32,0,0.11) at ambient pressure below TSDW∼1.25 K. Those magnetic peaks originate from a spin-density-wave order with the easy axis along the c axis and an averaged ordered moment of 0.45(5)μB, suggesting that there may be an intermediate phase between T∗ and TSDW. Applying pressures, the magnetic propagation vector shows no change and the magnetic order disappears around 1.0 GPa, which is much lower than the critical pressure for the superconducting phase. The results suggest that other than magnetic fluctuations may play a primary role in the superconducting pairing mechanism.

DOI： 10.1103/PhysRevB.105.245111

High-Pressure Thermopower of the Mott Insulator Ca<inf>2</inf>RuO<inf>4</inf>

Isuzu Sano, Tomohito Nakano, Akitoshi Nakano, Hiroki Taniguchi, Fumihiko Nakamura, Ichiro Terasaki

Journal of the Physical Society of Japan 91 ( 3 ) 2022.3

Publishing type：Research paper (scientific journal)

We have measured and analyzed the thermopower of single-crystal samples of the Mott insulator Ca2RuO4 in high pressure up to 0.9 GPa. We find that the thermopower rapidly changes at a metal-insulator transition temperature, which is explained in terms of a percolation theory. In contrast, the thermopower in the insulator phase slightly decreases with increasing pressure well below the transition temperature, and is associated with thermodynamic quantities through the Kelvin formula. The pressure dependence is compared with the current-density dependence, and a possible origin for the current-enhanced thermopower is proposed.

DOI： 10.7566/JPSJ.91.033703

Feasible waste liquid treatment from electroless nickel-plating by intense magnetic field of HTS bulk magnets

T. Oka, M. Furusawa, K. Sudo, L. Dadiel, N. Sakai, H. Seki, M. Miryala, M. Murakami, T. Nakano, M. Ooizumi, K. Yokoyama, M. Tsujimura

Progress in Superconductivity and Cryogenics (PSAC) 23 ( 3 ) 37 - 40 2021

Publishing type：Research paper (scientific journal)

Nickel (Ni) is a kind of the rare earth resources. Since Ni-containing waste is drained after several plating operations in the factories, the effective recycling technique has been expected to be introduced. An actual magnetic separation technique using HTS bulk magnet generating the strong magnetic field has succeeded in collecting the paramagnetic slurry containing Ni-sulphate coarse crystals which were fabricated from the Ni-plating waste. The Ni compound in the collected slurry was identified as NiSO4/6H2O, showing slight differences in the particle size and magnetic susceptibility between the samples attracted and not-attract to the magnetic pole. This preferential extraction suggests us a novel recycling method of Ni resource because the compound is capable of recycling back to the plating processes as a raw material.

DOI： 10.9714/psac.2021.23.3.037

Novel magnetizing technique using high temperature superconducting bulk magnets for permanent magnets in interior permanent magnet rotors

T. Oka, S. Hasebe, J. Ogawa, S. Fukui, T. Nakano, N. Sakai, M. Miryala, M. Murakami, K. Yokoyama

Superconductor Science and Technology 33 ( 8 ) 2020.8

Publishing type：Research paper (scientific journal)

A novel magnetizing technique for permanent magnets (PMs) embedded in interior permanent magnet (IPM) motors has been proposed as a safer and more effective process than the conventional processes using copper pulse-coils. In the new process, the high temperature superconducting (HTS) bulk magnet, emitting an intense magnetic field of over 3 T, was employed to activate the rotor and PMs inside. A magnetic pole containing the HTS bulk magnet was scanned on the surface of the IPM rotor, resisting against the extremely strong attractive force between the magnet and rotor. Following experiments in the past, numerical simulation studies have been conducted to evaluate the magnetic field-trapping performances of the PMs. In this study, the numerical analysis of the magnetization behaviours was conducted for the PMs embedded in the rotor of the commercial air-conditioner motor in a hybrid car. The simulation results showed us that the demagnetized Nd-Fe-B plates in the rotor were fully magnetized in the intense static magnetic fields on the magnetic pole containing the HTS bulk magnet. The magnetizing behaviour in this peculiar magnetizing operation was made understandable by estimating the anisotropic easy-direction of the PM plates embedded in the rotor. The novel activation method for PM is characterized as a no-shock and no-heating method, which would promote the degree of freedom in the IPM motor design.

DOI： 10.1088/1361-6668/ab9543

Superconductivity of the ternary stannide Y<inf>5</inf>Co<inf>6</inf>Sn<inf>18</inf>

Naoki Kase, Taishi Anada, Yusuke Terui, Tomohito Nakano, Naoya Takeda

Physica B: Condensed Matter 587 2020.6

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

Superconductivity is newly discovered in a single crystal of Y5Co6Sn18 at superconducting transition temperature T-c = 0.7 K. The single crystals are grown by a Sn flux method. Superconducting and normal properties of Y5Co6Sn18 are investigated by means of electrical resistivity rho(T) and specific heat C(T) measurements. Superconductivity is of bulk nature because of the jump at T-c from specific heat measurements. The Sommerfeld constant gamma and Debye temperature Theta(D) are estimated to be 9.6 mJ/(mol .K-2) and 450 K. The upper critical filed mu H-0(c2)(0) is estimated to be 0.825 T obtained from rho(T) in several magnetic fields.

DOI： 10.1016/j.physb.2020.412149

Magnetizing Technique for Permanent Magnets in IPM Motor Rotors Using HTS Bulk Magnet

T. Oka, S. Hasebe, J. Ogawa, S. Fukui, T. Nakano, K. Yokoyama, M. Miryala, N. Sakai, M. Murakami

IEEE Transactions on Applied Superconductivity 30 ( 4 ) 2020.6

Publishing type：Research paper (scientific journal)

A unique activation technique for permanent Nd-Fe-B magnets which were embedded in the rotors of interior permanent magnet (IPM) motors has been developed as a magnetizing tool with use of high temperature superconducting (HTS) bulk magnet. The experimental and numerical simulation studies were conducted to evaluate the magnetic field-trapping performances of the rotor of air-conditioner compressor in the hybrid-type automobiles. The sample rotor containing six demagnetized permanent magnet plates were exposed in the intense static magnetic fields above the magnetic pole which contained the bulk magnet generating over 4 T. As a result, the sample magnets were perfectly magnetized in the static magnetic field. The precise simulation on the flux distribution in the rotor clarified that it is important to make the flux direction in the rotor core and the easy magnetization axis of PM identical. We convinced this activation technique should enable us to promote the degrees of freedom of motor designing and its processing.

DOI： 10.1109/TASC.2020.2989181

Coexistence of localized and heavy itinerant states in antiferromagnetic CePtG e2 Reviewed

Tomohito Nakano, Shoma Onuma, Naoya Takeda, Klára Uhlířová, Jan Prokleška, Vladimír Sechovský, Jun Gouchi, Yoshiya Uwatoko

Physical Review B 100 ( 3 ) 2019.7

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

Two conflicting ground states, i.e., an antiferromagnetic ground state at 3.8K and aferromagnetic ground state at 5.1 K, have been reported for CePtGe2, which has two nonequivalent crystallographic Ce sites. In this study, we have prepared polycrystalline and single-crystalline CePtGe2 samples and measured their magnetization, specific heat, resistivity, and Seebeck coefficient. The observed bend in resistivity, peak in magnetic susceptibility, and lambda-type anomaly in specific heat at T-N = 3.8K and the metamagnetic transition in this CePtGe2 suggest antiferromagnetism at low temperatures. No evidence of ferromagnetic order was found in the studied temperature range, indicating possible crystal polymorphism with ferromagnetic character. The large susceptibility around TN and the Schottky-type specific heat indicate a well-localized f -electron state. However, the large residual gamma and X(0) indicate an itinerant heavy f -electron state. These findings suggest the coexistence of localized and heavy itinerant states corresponding to f electrons at the two Ce sites in this antiferromagnetic CePtGe2. The field dependence of magnetization indicates a sudden increase in magnetization at weak magnetic fields (similar to 0.2T), followed by a plateau at fields above 0.2 T, resulting in a possible different polarized metamagnetic state via interaction between localized and itinerant f electrons.

DOI： 10.1103/PhysRevB.100.035107

Pressure-Induced Superconductivity in CePtSi<sub>2</sub> Invited Reviewed International coauthorship

中野智仁

高圧力の科学と技術 29 ( 4 ) 283 - 289 2019

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of High Pressure Science and Technology

<p>In this article, I introduce the pressure-induced superconductivity in CePtSi<sub>2</sub> with its discovering process. At ambient pressure, the orthorhombic CePtSi<sub>2</sub> shows an antiferromagnetic order below <i>T</i><sub>N</sub>=1.8 K. <i>T</i><sub>N</sub> disappears above 1.2 GPa, and a superconducting phase appears with <i>T</i><sub>c</sub>～0.1 K. Significant decrease of the <i>A</i> coefficient in resistivity and discrepancy between quantum critical point (QCP) and the center of the superconducting phase suggest the valence mediated superconductivity as that observed in CeCu<sub>2</sub> (Si,Ge)<sub>2</sub>.</p>

DOI： 10.4131/jshpreview.29.283

Collecting Ni-Sulfate Compound from Electroless Plating Waste by Magnetic Separation Technique with Use of HTS Bulk Magnets

T. Oka, S. Sasaki, H. Sasaki, S. Fukui, J. Ogawa, T. Sato, T. Nakano, M. Ooizumi, M. Tsujimura, K. Yokoyama

Journal of Physics: Conference Series 1054 ( 1 ) 2018.7

Publishing type：Research paper (international conference proceedings)

© Published under licence by IOP Publishing Ltd. The authors have developed a useful technique for extracting the Ni-sulfate compound from the "processed waste/fluid" of the electroless Ni-plating processes. After forming the fine NiHPO3 precipitate from the waste, the coarse NiSO4 crystals were synthesized through the reaction with the concentrated sulfuric acid. In the experiment, the open-gradient magnetic separation was employed to collect the NiSO4 crystals from the muddy mixture composed of these compounds. The experiments were practically conducted with use of the Gd123-based HTS bulk magnets generating up to 3.99 T, which were activated by the field cooling magnetizing method operated at 35 K. Intense magnetic field emitted from the bulk magnet attracted the paramagnetic fluid and coarse NiSO4 crystals on the bottom of the water channel, forming a giant drop of NiSO4-saturated clear fluid and the slurry of nickel sulfate hexahydrate. This preferential collection suggests a feasible recycling process of Ni resource as a raw material in the plating processes.

DOI： 10.1088/1742-6596/1054/1/012047

Fundamental properties of a new samarium compound SmPtSi<inf>2</inf> Reviewed

Shuto Yamaguchi, Eisuke Takahashi, Naoki Kase, Tomohito Nakano, Naoya Takeda, Kazuyuki Matsubayashi, Yoshiya Uwatoko

Physica B: Condensed Matter 536 297 - 299 2018.5

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

We have discovered a new orthorhombic ternary compound SmPtSi2. We succeeded in growing a single crystal of SmPtSi2; prepared a polycrystalline sample of this compound, and measured their susceptibility, specific heat, and resistivity. The temperature dependence of susceptibility of the polycrystalline sample is close to that of Sm3+ at high temperatures, and its specific heat shows anomalies at T-H = 8.6 K and T-L = 5.6 K. The resistivity of a single crystal of SmPtSi2 shows a hump-type anomaly just below T-H and a sudden decrease at T-L, indicating that these anomalies are intrinsic and that SmPtSi2 exhibits a two-step transition.

DOI： 10.1016/j.physb.2017.10.028

A review article: Compact magnetic field generators containing HTS bulk magnets cooled by refrigerators and their feasible applications

Tetsuo Oka, Jun Ogawa, Satoshi Fukui, Takao Sato, Tomohito Nakano, Kazuya Yokoyama, Takashi Nakamura, Hiroyuki Fujishiro, Koshichi Noto

High-Temperature Superconductors: Occurrence, Synthesis and Applications 291 - 306 2018.1

Publishing type：Part of collection (book)

Various types of strong magnetic field generators with use of HTS bulk magnets and the small-scale refrigerators have been actually proposed and experimentally estimated for the feasible applications. The most characteristic feature of bulk magnets is regarded as compact and strong field generators with respect to their magnetic field spaces or their machine structures of themselves. Among them, the magnetic flux density of the face-toface magnetic poles reached 3.2 T and 4.4 T when they were activated by the pulsed field magnetization and the field cooling method, respectively. Furthermore, a very small bulk magnet generating 2.8 T and the system featured by the wide magnetic poles containing seven magnets have been constructed with use of ST pulse tube coolers in order to expand the feasible application areas. On the other hand, although the bulk magnets are characterized by their steep field distributions, we attempted to gain the uniform magnetic field space, and successfully achieved the uniformity of 385 ppm in 4 mm range by combining the deformed magnetic field profiles which generated between the face-to-face magnetic poles. The performances of these unique systems have exceeded those of the conventional electromagnet or any permanent magnets by far, demonstrating the superiority to other strong magnetic field generators.

Superconducting gap symmetry of the BiS2-based superconductor LaO0.5F0.5BiSSe elucidated through specific heat measurements Reviewed

Naoki Kase, Yusuke Terui, Tomohito Nakano, Naoya Takeda

PHYSICAL REVIEW B 96 ( 21 ) 2017.12

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

In this study, the superconducting gap symmetry of LaO0.5F0.5BiSSe is elucidated through specific heat measurements with one single crystal of LaO0.5F0.5BiSSe. A clear jump is observed at 3.95 K in LaO0.5F0.5BiSSe, suggesting bulk superconductivity. From specific heat measurements, Delta C-e/gamma T-c and 2 Delta(0)/k(B)T(c) are obtained as 2.31 and 4.5. These values indicate strong electron-phonon coupling superconductivity. The temperature (T) and magnetic-field (H) dependence of the electronic specific heat C-e(T, H) suggests that superconductivity is fully gapped. Our handmade system successfully elucidates superconducting gap symmetry of the BiS2-based compound with a small single crystal.

DOI： 10.1103/PhysRevB.96.214506

Upper critical field of the single crystal La(O,F)BiSe2 Reviewed

Y. Terui, N. Kase, T. Nakano, N. Takeda

Journal of Physics: Conference Series 871 ( 1 ) 5 pages - 12005 2017.7

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Institute of Physics Publishing

Single crystal growth and superconducting properties of LaO0.5F0.5BiSe2 are studied. Single crystals of LaO0.5F0.5BiSe2 were grown by a CsCl-flux method. Electrical resistivity ρ(T) measurements were performed to elucidate its superconducting properties. The ρ(T) shows metallic behavior and superconducting transition at 4.0 K. From ρ(T) measurements in several magnetic fields, upper critical fields Hc2∥ab(0) and Hc2∥c (0) are estimated to be 7.05 T and 0.52 T, respectively. The superconducting anisotropic parameter Γ is determined to be 13.6.

DOI： 10.1088/1742-6596/871/1/012005

Superconducting gap of the single crystal β-PdBi2 Reviewed

H. Matsuzaki, K. Nagai, N. Kase, T. Nakano, N. Takeda

Journal of Physics: Conference Series 871 ( 1 ) - 12004 2017.7

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Institute of Physics Publishing

We investigate superconducting and normal properties of the single crystal of β-PdBi2. The electrical resistivity ρ(T) shows superconductivity at Tc = 5.0 K. Residual resistivity ratio (RRR) is estimated to be 2.9 obtained from ρ(300 K)/ρ(5.0 K). The Hc2 curve obtained from ρ(T) in magnetic fields shows cleat enhancement from the Wertharmer-Helfand-Hohenberg theory in dirty limit. Specific heat C(T) measurement shows that clear jump is observed at Tc = 4.8 K. T-dependence of the electronic specific heat Ce(T) suggests full-gap symmetry with a single gap and strong coupling with ΔCe/γTc = 1.8.

DOI： 10.1088/1742-6596/871/1/012004

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