Fuminori Honda

Tohoku University, Japan

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Publications (65)105.28 Total impact

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    ABSTRACT: Pressure dependence of the Ce valence in CeCu_{2}Ge_{2} has been measured up to 24 GPa at 300 K and to 17 GPa at 18-20 K using x-ray absorption spectroscopy in the partial fluorescence yield. A smooth increase of the Ce valence with pressure is observed across the two superconducting (SC) regions without any noticeable irregularity. The chemical pressure dependence of the Ce valence was also measured in Ce(Cu_{1-x}Ni_{x})_{2}Si_{2} at 20 K. A very weak, monotonic increase of the valence with x was observed, without any significant change in the two SC regions. Within experimental uncertainties, our results show no evidence for the valence transition with an abrupt change in the valence state near the SC II region, challenging the valence-fluctuation mediated superconductivity model in these compounds at high pressure and low temperature.
    Physical Review Letters 08/2014; 113:086403. · 7.73 Impact Factor
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    ABSTRACT: The effect of high pressure exceeding 6 GPa on magnetism and multiferroicity was investigated for the olivine Mn2GeO4 that shows successive magnetic transitions at ambient pressure and a ferroelectric ground state driven by spin-spiral order. We measured heat capacity, dielectric constant, and electric polarization at various pressures using a diamond anvil cell. The pressure evolution of the magnetic structures was also investigated by powder neutron diffraction measurements using a Paris-Edinburgh press. We found that all of the magnetic transition temperatures are enhanced monotonically by applying pressure. Furthermore, the spin-driven ferroelectricity persists up to about 6 GPa but suddenly vanishes by 6.3 GPa. A consistent description of all data is achieved if an incommensurate-commensurate phase transition occurs with pressurization and causes the suppression of ferroelectricity. We discuss the origin of the observed pressure effects on the magnetism and multiferroicity in Mn2GeO4 in terms of a pressure-induced change in the superexchange magnetic interactions.
    02/2014; 89(10).
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    ABSTRACT: L'effet de Haas–van Alphen, une méthode puissante pour explorer les propriétés de la surface de Fermi dans les solides, a été observé dans de nombreux composés du cérium, de l'uranium, du neptunium et du plutonium. Dans cet article, on présente les résultats obtenus pour les supraconducteurs à fermions lourds UPt3 et NpPd5Al2, ainsi que pour le composé UGe2 qui, soumis à une pression externe, devient supraconducteur en présence d'ordre ferromagnétique. On considère aussi certains systèmes analogues caractérisés par des états électroniques remarquables (supraconductivité anisotrope, magnétisme et comportement à fermions lourds).
    Comptes Rendus Physique. 01/2014;
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    ABSTRACT: VSi2 is hexagonal in the crystal structure, and the basal plane stacks along the [0001] direction. Interestingly, each plane is rotated by 60\circ relative to the neighboring one. Therefore, there exist no mirror planes in this chiral structure. We carried out a de Haas--van Alphen (dHvA) experiment and clarified the Fermi surface properties. Each dHvA branch was found to be split into two branches on the basis of the antisymmetric spin--orbit interaction. The magnitude of the antisymmetric spin--orbit interaction in this chiral structure was determined for the first time to be 19 K for dHvA branch α (dHvA frequency F = 7.9 × 107 Oe and cyclotron mass m*c = 1.6 m0), 39 K for branch β (F = 4.1 × 107 Oe and m*c = 3.4 m0), and 110 K for branch γ (F = 1.8 × 107 Oe and m*c = 2.3 m0). These dHvA branches correspond to the main Fermi surfaces, which are well explained by the results of the energy band calculations based on the full potential linear augmented plane wave (FLAPW) method. The present values are mainly due to the V-3d conduction electrons.
    Journal of the Physical Society of Japan 09/2013; 82(9):4604-. · 2.09 Impact Factor
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    ABSTRACT: The f-electron system in rare-earth and actinide compounds exhibit a variety of characteristic properties including heavy fermions and unconventional superconductivity. The Fermi surface properties in rare-earth and actinide compounds are clarified by the de Haas-van Alphen experiments on the basis of the results of energy band calculations. The effect of pressure on the electronic states of CeRhIn5, CeIrSi3, and YbIr2Zn20 is studied in magnetic fields. An electronic instability, including unconventional superconductivity, occurs at 2.4 GPa in CeRhIn5 and 2.6 GPa in CeIrSi3. An abrupt non-linear increase in the magnetization, namely, a metamagnetic behavior, is found in the heavy fermion compounds, including YbT2Zn20 (T: Co, Rh, Ir). A super-heavy fermion state with a specific heat coefficient of 10 J/(K2·mol) is realized in YbIr2Zn20 under pressure.
    Journal- Korean Physical Society 08/2013; 63(3):409-415. · 0.51 Impact Factor
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    ABSTRACT: We measured the electrical resistivity of CeCu2Ge2 under various high pressures and strong magnetic fields. Beyond the previous antiferromagnetic critical pressure P c }~ 8 GPa, the antiferromagnetic phase is found to exist at much higher pressure of 10.9 GPa even in magnetic fields up to 8 T. The pressure vs. temperature phase diagram and the magnetic field vs. temperature phase diagram under high pressure were constructed. The pressure-induced antiferromagnetic phase is still observed and coexists with pressure-induced superconductivity at 10.9 GPa.
    Journal- Korean Physical Society 08/2013; 63(3):345-348. · 0.51 Impact Factor
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    ABSTRACT: We measured the magnetic susceptibility, high-field magnetization, magnetoresistance, specific heat, and Hall coefficient, together with the electrical resistivity under high pressures and magnetic fields, for the heavy-fermion compound YbRh2Zn20 with the cubic CeCr2Al20-type structure. The metamagnetic behavior was observed at Hm = 65 kOe for the magnetic field along the < 100> direction below Tχ_{max} = 5.3 K, at which the temperature of the magnetic susceptibility indicates a broad maximum. The coefficient A of the T2 dependence of electrical resistivity ρ=ρ0 + AT2 and the electronic specific heat coefficient C/T possess a broad maximum at Hm. The metamagnetic field Hm is found to decrease with increasing pressure and to become zero at a critical pressure Pc ≃ 5.2 GPa. Correspondingly, the A value increases drastically in magnitude, and the Fermi liquid relation is no longer satisfied at 5.2 GPa in zero magnetic field, implying a non-Fermi liquid state. On the other hand, at magnetic fields of H > 20 kOe, the low-temperature resistivity exhibits a T2 dependence even at 5.2 GPa. The A coefficient decreases rapidly with increasing magnetic field. These results indicate that an electronic state at 5.2 GPa corresponds to the quantum critical point.
    Journal of the Physical Society of Japan 08/2013; 82(8):4705-. · 2.09 Impact Factor
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    ABSTRACT: The effect of pressure on the field-induced ordered phase for H ‖ 〈111〉 in the heavy-fermion compound YbCo2Zn20, which is presumably a field-induced antiferro-quadrupolar (FI-AFQ) phase, was investigated in the pressure range up to 4.5 GPa and under magnetic fields up to 80 kOe. When pressure is applied, the metamagnetic-like transition at H m =6 kOe shifts to lower fields and disappears around the quantum critical pressure P c ∼1.8 GPa. A pressure-induced antiferromagnetic (PI-AFM) phase appears at pressures above about 2 GPa, and the critical field H c of the PI-AFM phase increases with increasing pressure. On the other hand, the transition field H Q of the FI-AFQ phase decreases gradually without showing any anomalous behavior around P c and becomes obscure around 4 GPa, where H c of the PI-AFM phase and H Q of the FI-AFQ phase become comparable. The magnetic field versus pressure, H-P, phase diagram for H ‖ 〈111〉 at 0.1 K was constructed in the pressure range up to 4.5 GPa.
    Journal- Korean Physical Society 06/2013; 62(12). · 0.51 Impact Factor
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    ABSTRACT: We succeeded in growing single crystals of YbTIn5 (T: Co, Rh, Ir), YbGa4, YbT2Zn20 (T: Co, Rh, Ir), YbPdGe, Yb2Pt2Pb, and YbPd5Al2. The electronic and magnetic properties are clarified by measuring the electrical resistivity, magnetic susceptibility, magnetization, specific heat and de Haas — van Alphen effect.
    Journal- Korean Physical Society 06/2013; 62(12). · 0.51 Impact Factor
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    ABSTRACT: We present the giant and isotropic magnetocaloric effect (MCE) in antiferromagnetic semiconductor EuSe. Near the transition temperature TN = 4.6 K, the maximum value of the magnetic entropy change (−ΔSmmax) and the relative cooling power of EuSe for a field change of 5 T are evaluated to be 37.5 J kg−1 K−1 and 580 J kg−1, respectively, based on the magnetization and specific heat data. The −ΔSmmax value of EuSe obtained in this work is the largest among the low temperature (<20 K) magnetic refrigerant materials reported so far, which is even larger than that of the best known room temperature giant MEC materials.
    Applied Physics Letters 04/2013; 102(15). · 3.79 Impact Factor
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    ABSTRACT: We present an overview of the Fermi-surface properties for antiferromagnets CeRh2Si2, CeIn3, CeRhIn5, and CeIrSi3, which were clarified from the de Haas–van Alphen (dHvA) experiments under strong magnetic fields up to 170 kOe and high pressures up to 3 GPa. A drastic change of the 4f-electronic state from a 4f-localized Fermi surface to a 4f-itinerant Fermi surface occurs in CeRh2Si2, CeIn3, and CeRhIn5 when the pressure P crosses a critical pressure Pc or . Here, the Néel temperature TN disappears and the superconducting state appears at around Pc or . A critical pressure in CeRhIn5 is the pressure when TN is extrapolated to zero in the temperature vs. pressure phase diagram, and/or the antiferromagnetic state disappears completely even in magnetic fields. This is because the antiferromagnetic state is stable against magnetic fields, or in other words, the antiferromagnetic state recovers in magnetic fields. CeIrSi3 without inversion symmetry in the tetragonal structure is also similar to CeRhIn5 in the superconducting and Fermi-surface properties. It is characteristic that a huge upper critical field at zero temperature in superconductivity is realized for in CeIrSi3 with the superconducting transition temperature Tsc = 1.6 K.
    physica status solidi (b) 03/2013; 250(3):583-588. · 1.49 Impact Factor
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    ABSTRACT: We have carried out the electrical resistivity measurements under high pressures up to 24 GPa for CeTX3 (T: Co and Ir, X: Si and Ge), CePd5Al2 and YbIr2Zn20 in order to investigate quantum criticality and superconductivity. Antiferromagnets CeTX3 with the non-centrosymmetric tetragonal structure show superconductivity under high pressures and reveal a huge upper critical field for H‖ [001]. An antiferromagnet CePd5Al2, which is an isostructural family of a heavy fermion superconductor NpPd5Al2, also shows superconductivity under high pressures. In these compounds, superconductivity appears in the vicinity of quantum critical point. On the other hand, YbIr2Zn20 without magnetic ordering approaches to the quantum critical point with increasing pressure and exhibits a super-heavy fermion state exceeding 10 J/(K2· mol).
    Journal of Physics Conference Series 12/2012; 400:022028.
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    ABSTRACT: DC Magnetization of the heavy-fermion compound YbCo2Zn20 was examined at very-low temperatures down to 0.07 K in the field up to 14.5 T. In addition to the nearly-isotropic metamagnetic behavior at 0.6 T, a new metamagnetic behavior is observed in the field variation of magnetization M(H) at 6 T only for H || [111]. For the same field direction, a clear kink appears in the temperature dependence of the magnetization M(T) for fields above 6 T. These results strongly suggest the existence of a new ordered phase induced by magnetic fields. The H - T phase diagram as well as the anisotropy in M(H) above ~ 2 T are best explained by a level crossing of the low-lying crystalline-electric-field states by magnetic fields.
    Journal of Physics Conference Series 12/2012; 391(1):2066-.
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    ABSTRACT: We succeeded in growing single crystals of LaNiC2 with the non-centrosymmetric orthorhombic structure by the Czochralski method, and measured the electrical resistivity, de Haas--van Alphen effect, and specific heat to clarify the Fermi surface and superconducting properties. This compound has been studied from a viewpoint of the triplet superconducting pairing state. In the present experiment, we observed an ellipsoidal Fermi surface and a multiply-connected-pillar Fermi surface, which are split into two Fermi surfaces, reflecting the antisymmetric spin--orbit interaction based on the non-centrosymmetric crystal structure. The two ellipsoidal Fermi surfaces are split by 230 K, for example. The anisotropy of electrical resistivity and upper critical field Hc2 in superconductivity are not large for three principal directions. From the low-temperature specific heat measurement, superconductivity in LaNiC2 is explained by the framework of the BCS-superconductivity, contrary to the above arguments. The upper critical field Hc2(0), which was obtained from the specific heat under magnetic fields, is about 2 kOe.
    Journal of the Physical Society of Japan 11/2012; 81(11):3703-. · 2.09 Impact Factor
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    ABSTRACT: We report on a pressure-induced evolution of exotic superconductivity and spin correlations in CeIr(In$_{1-x}$Cd$_{x}$)$_5$ by means of In-Nuclear-Quadrupole-Resonance (NQR) studies. Measurements of an NQR spectrum and nuclear-spin-lattice-relaxation rate $1/T_1$ have revealed that antiferromagnetism induced by the Cd-doping emerges locally around Cd dopants, but superconductivity is suddenly induced at $T_c$ = 0.7 and 0.9 K at 2.34 and 2.75 GPa, respectively. The unique superconducting characteristics with a large fraction of the residual density of state at the Fermi level that increases with $T_c$ differ from those for anisotropic superconductivity mediated by antiferromagnetic correlations. By incorporating the pressure dependence of the NQR frequency pointing to the valence change of Ce, we suggest that unconventional superconductivity in the CeIr(In$_{1-x}$Cd$_{x}$)$_5$ system may be mediated by valence fluctuations.
    Physical Review Letters 08/2012; 109(11). · 7.73 Impact Factor
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    ABSTRACT: We measured the electrical resistivity, magnetic susceptibility, magnetization, and specific heat of the quasicrystal approximants RCd6 (R: rare earth, Y--Lu) with a body-centered cubic (bcc) crystal structure. Single crystals were grown by the Cd-self flux method and annealing method. We confirmed that the structural order--disorder transition is realized at about 160 K when the lattice constant a is larger than 15.481 Å in YCd6, namely, for R = Pr, Nd, Sm, Gd, Tb, Dy, and Yb. At lower temperatures, RCd6 compounds, except non-4f reference compounds YCd6 and LuCd6, and a divalent compound YbCd6, are found to order antiferromagnetically. We clarified that the structural order--disorder transition has a great influence on the magnetic ordering and transport properties. The Néel temperature of RCd6 (R: Nd, Sm, Tb, and Dy) with the structural order--disorder transition is appreciably higher than the de Gennes scaling normalized by the Néel temperature of GdCd6, while the the Néel temperature of RCd6 (R: Ho, Er, and Tm) without the structural transition approximately follows the de Gennes scaling. Moreover, the electrical resistivity of RCd6 with the structural transition decreases monotonically below the Néel temperature, while it increases below the Néel temperature and a large residual resistivity remains at low temperatures in RCd6 without the structural transition. The contribution of an Einstein oscillator to the phonon specific heat is also discussed in YCd6 and LuCd6.
    Journal of the Physical Society of Japan 02/2012; 81(2):4720-. · 2.09 Impact Factor
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    ABSTRACT: Pressure and temperature dependences of the electronic structure of the heavy-fermion superconductor CeIrSi3 have been investigated using partial fluorescence yield x-ray absorption spectroscopy and resonant x-ray emission spectroscopy at the Ce L3 edge. Ce is in a weakly mixed valence state at ambient pressure, mostly f1 with a small contribution from the f0 component. Pressure-induced increase of the Ce valence becomes apparent above 4 GPa, concomitantly with the disappearance of the superconductivity. No temperature dependence of the Ce valence is observed within the measured temperature range down to 24 K.
    Journal of the Physical Society of Japan 12/2011; 80(12):4701-. · 2.09 Impact Factor
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    ABSTRACT: We studied an electronic state at low temperatures by measuring the specific heat and ac-susceptibility under magnetic fields for a heavy fermion compound YbCo2Zn20. The magnetic specific heat in the form of Cmag/T increases steeply and exhibits an extremely large value 8 J/(K2-mol) below 0.2 K, which corresponds to an electronic specific heat coefficient with a very low Kondo temperature of 0.2-1 K. The magnetic entropy increases rapidly at higher temperatures up to 10 K and reaches Rln8 at 50-60 K, which corresponds to a small crystalline-electric-field (CEF) splitting energy. In addition, we found a metamagnetic anomaly at Hm = 5.7 kOe below the characteristic temperature Tχmax =0.32 K, where the temperature dependence of the ac-susceptibility shows a broad peak. Interestingly, the metamagnetic behavior was observed as the double peak at 4.0 and 7.5 kOe in the magnetic field dependence of the specific heat C/T at 95 mK.
    Journal of Physics Conference Series 02/2011; 273(1):012059.
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    ABSTRACT: We measured the magnetization in high magnetic fields up to 500kOe, together with the magnetic susceptibility, ac-susceptibility and magnetoresistance for heavy fermion compounds YbT2Zn20 (T : Co, Rh, Ir). The metamagnetic behaviour or an abrupt nonlinear increase of magnetization was observed at the magnetic field Hm at temperatures lower than a characteristic temperature Tχmax below which the magnetic susceptibility becomes almost constant : Tχmax = 7.4K and Hm = 97kOe in YbIr2Zn20, Tχmax = 5.3K and Hm = 64kOe in YbRh2Zn20, and Tχmax = 0.32K and Hm = 6kOe in YbCo2Zn20. From the present data and the data in several Ce and U heavy fermion compounds, a simple relation between Tχmax and Hm was obtained : Hm(kOe) = 15Tχmax(K).
    Journal of Physics Conference Series 02/2011; 273(1):012003.
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    ABSTRACT: DC magnetization (M) measurements were done on a single crystal of YbCo2Zn20 at very low temperatures (T) down to 0.07 K in magnetic fields H\parallel[111]. In addition to the metamagnetic behavior at mu0Hm=0.6 T already known, we found a new metamagnetic transition at mu0H'm=6 T whose critical field moves to higher fields with increasing T. Moreover, in fields above 6 T, temperature dependence of the magnetization M(T) shows a kink below 0.6 K. These anomalies indicate the presence of a new field-induced ordered phase. In addition, a broad peak is observed in M(T) in fields above 3 T outside the ordered phase. These results are best explained by a level crossing of the low-lying crystalline-electric-field state with the ground state, possibly assisted by a valence change in magnetic fields.
    Journal of The Physical Society of Japan - J PHYS SOC JPN. 01/2011; 80.

Publication Stats

100 Citations
105.28 Total Impact Points


  • 2013–2014
    • Tohoku University
      • Institute for Materials Research
  • 2010–2014
    • Osaka University
      • • Graduate School of Science
      • • Department of Physics
      • • Low Temperature Center
      Suika, Ōsaka, Japan
  • 2006
    • Japan Atomic Energy Agency
      • Advanced Science Research Center
      Muramatsu, Niigata-ken, Japan
  • 2001–2005
    • Charles University in Prague
      • Faculty of Mathematics and Physics
      Praha, Praha, Czech Republic
  • 2002
    • Kyushu University
      • Department of Physics
      Hukuoka, Fukuoka, Japan
  • 1998–2001
    • Kumamoto University
      • Department of Materials Science and Engineering
      Kumamoto, Kumamoto Prefecture, Japan
  • 1999
    • Gunma University
      • Department of Electronic Engineering
      Maebashi, Gunma Prefecture, Japan