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

Abstract

We report the first study of electrical resistivity, magnetization, and specific heat on YbCo₂. The measurements on a single-phased sample of YbCo₂ bring no evidence of magnetic ordering down to 0.3 K in a zero magnetic field. The manifestations of low Kondo temperature are observed. The specific heat value divided by temperature, C/T, keeps increasing logarithmically beyond 7 J/mol K² with decreasing temperature down to 0.3 K without no sign of magnetic ordering, suggesting a very large electronic specific heat. Analysis of the magnetic specific heat indicates that the large portion of the low-temperature specific heat is not explained simply by the low Kondo temperature but is due to the strong intersite magnetic correlation in both the 3d and 4f electrons. Temperature-dependent measurements under static magnetic fields up to 7 T are carried out, which show the evolution of field-induced transition above 2 T. The transition temperature increases with increasing field, pointing to a ferromagnetic character. The extrapolation of the transition temperature to zero field suggests that YbCo₂ is in the very proximity of the quantum critical point. These results indicate that in the unique case of YbCo₂, the itinerant electron magnetism of Co 3d-electrons and the Kondo effect within the vicinity of quantum criticality of Yb 4f-local moments can both play a role.

DOI： 10.1088/1361-648x/acca5a

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Other Link： https://iopscience.iop.org/article/10.1088/1361-648X/acca5a/pdf

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier {BV}  

DOI： 10.1016/j.jmmm.2022.169327

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Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

DOI： 10.7566/jpsj.91.074713

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

We performed ultrasonic measurements on (Ta0.952V0.048)(2)NiSe5 to investigate the contribution of acoustic phonons at the zone center to structural and possible excitonic transitions. The transverse elastic constant C-55 with irreducible representation B-2g exhibits softening over 90% above a transition temperature of T-s = 280 K, indicating the soft mode of corresponding TA phonons. Our analysis based on the quadrupole response indicates that the electron-phonon interaction contributes to the excitonic transition in addition to the hybridization between the conduction and valence bands if the excitonic transition is realized.

DOI： 10.7566/JPSJ.91.024601

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Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/PhysRevB.103.014511

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

Temperature dependence of the In-115-NMR spectra of CeRhIn5 is studied with the external magnetic fields 10 degrees off the [100] and [001] axes. Our detailed analyses confirm that the AFM3 phase breaks the four-fold spin symmetry with the commensurate ordering vector of Q = (0. 5, 0.5, 0.25). Based on the observation of anistropic hyperfine fields, we also propose the symmetry lowering of the electronic structure in the AFM3 phase.

DOI： 10.7566/JPSJ.89.094709

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

We performed an ultrasonic measurement for the heavy-fermion compound CeRhIn_5 to investigate the origin of the field-induced anisotropic phase in high magnetic fields. The transverse elastic constant C_T=(C_{11}−C_{12})/2 and the ultrasonic attenuation coefficient αT show clear anomaly at B^★=28.5T, which was discussed as the electronic nematic transition point. In addition, C_T exhibits acoustic de Haas-van Alphen oscillation below 28.5 T. These elastic anomalies around B★ indicate an electric quadrupole ordering of O_{x^2−y^2} accompanied by B_{1g} crystal symmetry breaking and Fermi surface reconstruction due to the quadrupole-strain coupling, which results from itinerant 4f electrons and the p−f hybridized state.

DOI： 10.1103/PhysRevB.101.155125

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

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Journal of the Physical Society of Japan  

DOI： 10.7566/jpscp.30.011122

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DOI： 10.1103/PHYSREVB.101.195146

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©2019 The Physical Society of Japan We studied the pressure effect up to 8 GPa on antiferromagnet CeAl by means of ac specific heat Cac, ac susceptibility χA, and electrical resistivity ρ, and constructed temperature–pressure phase diagram. CeAl undergoes an antiferromagnetic (AFM) ordering at TN1 ∼ 10 K at ambient pressure, which is changed to three successive AFM transition temperatures ðTN2; TN3; TN4Þ above 1.7 GPa. AFM transition temperatures attain a maximum at 6.0 GPa and seem to vanish at P+ = 7.5 GPa. A pressure induced phase, which emerges above 4.5 GPa, is also developed around P+. We analyzed low temperature resistivity in order to study quantum criticality around P+

DOI： 10.7566/JPSJ.88.034707

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© 2018 Author(s). The electronic state of single crystals of CeIr2(Zn1-xCdx)20 and CePt2Cd20 has been studied by measuring the electrical resistivity ρ and specific heat C. We found that by substituting Zn with Cd, the lattice parameter expands, and the electronic specific heat coefficient γ and A coefficient, which is T2-term in ρ, are enhanced. Our experimental results reveal that the electronic state of the intermediate valence compound CeIr2Zn20 changes to a moderately heavy fermion state due to the negative chemical pressure. On the other hand, C and ρ of CePt2Cd20 show a clear jump and an abrupt change of slope below 0.3 K, respectively, due to a magnetic transition. The relation between the hybridization strength and Ce valence state has also been investigated by X-ray absorption experiment.

DOI： 10.1063/1.5043138

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

© 2017 American Physical Society. We report measurements of the de Haas-van Alphen effect in the layered heavy-fermion compound CePt2In7 in high magnetic fields up to 35 T. Above an angle-dependent threshold field, we observed several de Haas-van Alphen frequencies originating from almost ideally two-dimensional Fermi surfaces. The frequencies are similar to those previously observed to develop only above a much higher field of 45 T, where a clear anomaly was detected and proposed to originate from a change in the electronic structure [M. M. Altarawneh et al., Phys. Rev. B 83, 081103 (2011)PRBMDO1098-012110.1103/PhysRevB.83.081103]. Our experimental results are compared with band structure calculations performed for both CePt2In7 and LaPt2In7, and the comparison suggests localized f electrons in CePt2In7. This conclusion is further supported by comparing experimentally observed Fermi surfaces in CePt2In7 and PrPt2In7, which are found to be almost identical. The measured effective masses in CePt2In7 are only moderately enhanced above the bare electron mass m0, from 2m0 to 6m0.

DOI： 10.1103/PhysRevB.96.075138

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

©2017 The Physical Society of Japan. The 4 f crystalline electric field (CEF) of the Pr 3+ ion of PrPt2Cd20 with a cubic crystal structure has been studied by measuring its high-field magnetization up to 45 T, specific heat in a wide temperature range in magnetic fields, and electrical resistivity. Magnetization curves for the magnetic field along the [100] and [110] directions show metamagnetic-like features at approximately 1.5 and 15 T, respectively. The specific heat shows a Schottky peak centered at 2.4 K. These experimental results were explained well by the CEF scheme with the non-Kramers Γ3 doublet ground state with a small overall CEF splitting energy of about 40 K. The specific heat also shows another broad peak below 1 K with an associated entropy release of R ln 2. This peak was interpreted by a split of the Γ3 doublet ground state with an energy of Δ = 0.4 K. These results suggest that the local symmetry of the Pr site is lowered from a cubic one. The possible reasons for this symmetry lowering are discussed.

DOI： 10.7566/JPSJ.86.074711

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

© 2017 American Physical Society. The magnetic structure of the heavy fermion antiferromagnet CePt2In7 is determined using neutron diffraction. We find a magnetic wave vector qM=(1/2,1/2,1/2), which is temperature independent up to TN=5.5 K. A staggered moment of 0.45(1)μB at 2 K resides on the Ce ion. The nearest-neighbor moments in the tetragonal basal plane are aligned antiferromagnetically. The moments rotate by 90 from one CeIn3 plane to another along the c axis. A much weaker satellite peak with an incommensurate magnetic wave vector qM=(1/2,1/2,0.47) seems to develop at low temperature. However, the experimental data available so far are not sufficient to draw a definitive conclusion about the possible coexistence of commensurate and incommensurate magnetic structures in this material.

DOI： 10.1103/PhysRevB.95.161102

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

© 2016 Elsevier B.V. We succeeded in growing five new single crystalline compounds RPt2Cd20(R = La, Ce, Pr, Nd, and Sm) by the Cd self-flux method. These compounds are found to crystallize in the cubic CeCr2Al20-type crystal structure by the X-ray diffraction using single crystals. We measured the electrical resistivity, magnetic properties, and specific heat for all compounds. The resistivity for R = Ce, Nd, and Sm indicates an abrupt decrease, which might correspond to a magnetic transition. It is suggested that the ground state of CePt2Cd20is Γ7doublet from the magnetization measurement. The magnetization of PrPt2Cd20shows a metamagnetic behavior at 1.6 T in the paramagnetic state, which could be due to the crystalline electric field effect with non-Kramers Γ3doublet or Γ1singlet ground state. The contribution of optical phonon modes to the lattice specific heat is discussed in LaPt2Cd20.

DOI： 10.1016/j.jallcom.2016.09.077

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© 2016 IOP Publishing Ltd. We review the nature of strongly correlated electronic states in rare earth and actinide compounds, focusing on localized versus itinerant electronic states in CeRhIn5, quantum critical phenomena in YbIr2Zn20, residual resistivity in CeCu6, metamagnetism in heavy fermion compounds, and unconventional superconductivity in CeIrSi3 without inversion symmetry in the crystal structure, emphasizing that sample quality is essentially important to clarify the characteristic features for the heavy fermion compounds.

DOI： 10.1088/0034-4885/79/11/114501

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© 2016 IOP Publishing Ltd. We succeeded in growing a new high quality single crystal of a ternary uranium compound UPd2Cd20. From the electrical resistivity, magnetization, magnetic susceptibility, and specific heat experiments, UPd2Cd20 is found to be an antiferromagnetic heavy-fermion compound with the Néel temperature = 5 K and exhibits the large electronic specific heat coefficient γ exceeding 500 mJ (K2• mol)-1. This compound is the first one that exhibits the magnetic ordering with the magnetic moments of the U atom in a series of UT2X20 (T: transition metal, X = Al, Zn, Cd). UPd2Cd20 shows typical characteristic features in heavy-fermion systems such as a broad maximum in the magnetic susceptibility at and a large coefficient A of T 2 term in the resistivity.

DOI： 10.1088/0953-8984/28/42/425601

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©2016 The Physical Society of Japan. A diffraction experiment using high-energy X-rays was carried out on YbInCu4. Below the Yb valence transition temperature, the splitting of Bragg peaks was detected in high-order reflections. No superlattice reflections accompanying the valence ordering were found below the transition temperature. These experimental findings indicate that a structural change from a cubic structure to a tetragonal structure without valence ordering occurs at the transition temperature. Such a structural change free from any valence ordering is difficult to understand only in terms of Yb valence degrees of freedom. This means that the structural change may be related to electronic symmetries such as quadrupolar degrees of freedom as well as to the change in Yb valence.

DOI： 10.7566/JPSJ.85.063602

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© 2016 The Physical Society of Japan. The magnetization change ΔM at the superconducting transition of LaIrSi3 has been measured in various magnetic fields H. The observed ΔM in H = 0 is within the range of the Meissner effect induced by the possible residual field, suggesting that the spontaneous magnetization, if it exists, is below the experimental accuracy. This result is in agreement with the results of μSR experiments, in which no spontaneous magnetic field has been observed in the superconducting state.

DOI： 10.7566/JPSJ.85.025002

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© 2016 American Physical Society. We report specific heat measurements on a high-quality single crystal of the heavy-fermion compound CePt2In7 in magnetic fields up to 27 T. The zero-field specific heat data above the Néel temperature, TN, suggest a moderately enhanced value of the electronic specific heat coefficient γ=180mJ/K2mol. For T<TN, the data at zero applied magnetic field are consistent with the existence of an anisotropic spin-density wave opening a gap on almost the entire Fermi surface, suggesting extreme two-dimensional electronic and magnetic structures for CePt2In7. TN is monotonically suppressed by magnetic field applied along the c axis. When a field is applied parallel to the a axis, TN first increases at low field up to about 10 T and then decreases monotonically at a higher field. The magnetic phase diagram based on specific heat measurements suggests that a field-induced quantum critical point is likely to occur slightly below 60 T for both principal orientations of the magnetic field.

DOI： 10.1103/PhysRevB.93.085121

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© Published under licence by IOP Publishing Ltd. We have measured the magnetization of two noncentrosymmetric superconductors: Ir2Ga9 and CePt3Si using a SQUID magnetometer, neither of which has been tested for the time-reversal symmetry in the superconducting state. For Ir2Ga9, the magnetization change ΔM below the superconducting transition temperature Tc ∼ 2.2 K was smaller than 10-5 G in zero magnetic field, suggesting that ΔM originates in the Meissner effect induced by the possible residual field. When CePt3Si was cooled in zero magnetic field, ΔM along the c axis first decreased below Tc+ ∼ 0.75 K (high-Tc phase) and then increased below Tc- ∼ 0.45 K (bulk superconducting phase). Since this behavior cannot be explained by the Meissner effect, it may be a sign of a spontaneous magnetization.

DOI： 10.1088/1742-6596/683/1/012029

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©2015 The Physical Society of Japan. Crossover phase diagrams in the magnetic field versus temperature (H-T) plane of the nonmagnetic heavy-fermion metamagnets UT2Zn20 (T:Ir, Co) are studied by measuring the magnetic and electronic transport properties. The crossover phase diagrams of UIr2Zn20 and UCo2Zn20 are composed of a low-magnetic-field region (LFR) and a high-magnetic-field region (HFR), which are characterized by magnetic properties and the Hall effect, respectively. The LFR is found to form a closed area in the H-T plane, which is a quite different feature from the conventional uranium heavy-fermion compounds and the first observation in uranium compounds. From the drastic anomaly in the Hall effect at a metamagnetic field of UIr2Zn20, it is found that the metamagnetic behavior in UIr2Zn20 corresponds to a crossover from the heavy-fermion state to the field-induced ferromagnetic or polarized paramagnetic state accompanied by the reconstruction or topology change of Fermi surfaces. In UCo2Zn20, on the other hand, no sign of abrupt change in the electronic state at the metamagnetic field is observed. These contrastive crossover phase diagrams and the electronic state changes at the metamagnetic field are due to the different hybridization strengths between the 5 f electrons of U atoms and the d electrons of Ir and Co atoms, leading to the differences in magnetic correlation and crystalline electric field ground state or the degree of itinerancy of 5 f electrons.

DOI： 10.7566/JPSJ.84.074704

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© 2015 The Physical Society of Japan. We have measured the magnetization of single crystals of the non-centrosymmetric superconductor LaNiC2, which is considered to break time-reversal symmetry by μSR measurements. Below the transition temperature Tc ~3K, the emergence of magnetization on the order of 10-5G is observed in zero magnetic field along the c-axis but not along the a-axis. This spontaneous magnetization is larger than the Meissner effect induced by the possible residual field and did not change after applying magnetic fields of up to 15mOe or after warming to room temperature. The results that the direction is related to the lack of inversion symmetry and that the magnitude is sensitive to the crystallinity of the sample suggest some analogy with pyroelectricity.

DOI： 10.7566/JPSJ.84.013702

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

We succeeded in growing single crystals of UPd2Cd20 by the Cd self-flux method. This compound crystallizes in the cubic CeCr2Al20-type structure. From the low-temperature electrical resistivity and Kadowaki-Woods relation, the electronic specific heat coefficient. is estimated to be about 400 mJ/mol . K-2. The magnetic susceptibility of UPd2Cd20 indicates a broad maximum at 6.6 K and a rapid decrease at 5.0 K, which correspond to the formation of the heavy fermion state and the antiferromagnetic transition, respectively. These experimental results strongly suggest that UPd2Cd20 is a new heavy fermion antiferromagnet.

DOI： 10.1016/j.phpro.2015.12.009

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© 2015 The Authors. Published by Elsevier B.V. Precise thermal expansion and magnetostriction measurements were performed on the heavyfermion compound YbAuCu4 in order to examine the crossover valence transition at TV which was proposed by the nuclear magnetic resonance measurements. The temperature dependence of the thermal expansion coefficient α under magnetic fields shows a broad peak, which shifts to higher temperatures with increasing magnetic fields. The corresponding linear thermal expansion Δℓ/ℓ parallel to the magnetic field of 7.0 T shows a marked decrease below about 10 K, indicating a contraction of sample length at low temperatures. These results are discussed in relation to the observed temperature dependence of the nuclear quadrupole frequency νQ under magnetic fields.

DOI： 10.1016/j.phpro.2015.12.057

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© 2015 The Authors. Published by Elsevier B.V. We succeeded in growing single crystals of UPd2Cd20 by the Cd self-flux method. This compound crystallizes in the cubic CeCr2Al20-type structure. From the low-temperature electrical resistivity and Kadowaki-Woods relation, the electronic specific heat coefficient γ is estimated to be about 400mJ/mol ·K2. The magnetic susceptibility of UPd2Cd20 indicates a broad max-imum at 6.6K and a rapid decrease at 5.0K, which correspond to the formation of the heavy fermion state and the antiferromagnetic transition, respectively. These experimental results strongly suggest that UPd2Cd20 is a new heavy fermion antiferromagnet.

DOI： 10.1016/j.phpro.2015.12.009

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

Precise thermal expansion and magnetostriction measurements were performed on the heavy-fermion compound YbAuCu4 in order to examine the crossover valence transition at T-v which was proposed by the nuclear magnetic resonance measurements. The temperature dependence of the thermal expansion coefficient a under magnetic fields shows a broad peak, which shifts to higher temperatures with increasing magnetic fields. The corresponding linear thermal expansion Delta l/l parallel to the magnetic field of 7.0 T shows a marked decrease below about 10 K, indicating a contraction of sample length at low temperatures. These results are discussed in relation to the observed temperature dependence of the nuclear quadrupole frequency nu(Q) under magnetic fields.

DOI： 10.1016/j.phpro.2015.12.057

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DOI： 10.7566/JPSCP.3.011012

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DOI： 10.7566/JPSCP.3.011061

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DOI： 10.7566/JPSCP.3.011082

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DOI： 10.7566/JPSCP.3.011010

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DOI： 10.7566/JPSCP.3.011017

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DOI： 10.7566/JPSCP.3.012026

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

We studied the heavy fermion compound YbCo2Zn20 with an electronic specific heat coefficient γ ≥ 8000 mJ/(K 2·mol) by measuring the de Haas-van Alphen (dHvA) oscillation, Hall effect, magnetic susceptibility, and magnetization at ambient pressure, as well as the electrical resistivity in magnetic fields of up to 320 kOe and at pressures of up to 5 GPa. The detected Fermi surfaces are small in volume, reflecting the small Brillouin zone based on the large cubic lattice constant a = 14.005 A. The cyclotron effective masses, which were determined from the dHvA experiment, are found to be markedly reduced in magnetic fields. In other words, the detected cyclotron masses of 2.2-8.9m0 (m0: the rest mass of an electron) at Hav = 117 kOe are enhanced to 100-500m0 at 0 kOe. By applying pressure, the heavy fermion state disappears at Pc ' 1.8 GPa and orders antiferromagnetically for P > Pc. The field-induced antiferroquadrupolar phase, which is observed only for H k h111i in the magnetic field range from HQ = 60 kOe to H0 Q = 210 kOe, is found to shift to lower magnetic fields and merge with theantiferromagnetic phase at 4.5 GPa. © 2014 The Physical Society of Japan.

DOI： 10.7566/JPSJ.83.044703

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

We grew high-quality single crystals of the antiferromagnet EuSn3 with the AuCu3-type cubic crystal structure by the Sn self-flux method and measured the electrical resistivity, magnetic susceptibility, high-field magnetization, specific heat, thermal expansion, and de Haas-van Alphen (dHvA) effect, in order to study the magnetic and Fermi surface properties. We observed steplike changes in the electrical resistivity and magnetic susceptibility, and a sharp peak of the specific heat and thermal expansion coefficient at a Néel temperature TN = 36.4 K. The first-order nature of the antiferromagnetic transition was ascertained by the observation of thermal hysteresis as well as of latent heat at TN. The present antiferromagnetic transition is found to be not a typical second-order phase transition but a first-order one. From the results of dHvA experiment, we clarified that the Fermi surface is very similar to that of the divalent compound YbSn3, mainly consisting of a nearly spherical hole Fermi surface and eight ellipsoidal electron Fermi surfaces. EuSn3 is possibly a compensated metal, and the occupation of a nearly spherical hole Fermi surface is 3.5% in its Brillouin zone, indicating that EuSn3 is a semimetal. © 2014 The Physical Society of Japan.

DOI： 10.7566/JPSJ.83.024008

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CePt2In7 is an antiferromagnet with TN =5.4K, which shows pressure-induced superconductivity at transition temperature Tc= 2.1 K around a critical pressure Pc =3.2 GPa. We have investigated an anisotropy of the superconducting upper critical field Hc2 in CePt2In7, which posesses two-dimensional tetragonal crystal structure and cylindrical Fermi surfaces elongated along c-axis. At 2.60 GPa, initial slope of Hc2 for H ∥ [001] is smaller than that for H ∥ [100], reflecting the two-dimensional Fermi surface of CePt2In7. However, Pauli paramagnetic suppression is strong for H ∥ [100] compared with that for H ∥ [001] in high magnetic field, and Hc2 (0) for H ∥ [001] seems to be larger than that for H ∥ [100] at 2.60 GPa in CePt2In7.

DOI： 10.1088/1742-6596/592/1/012006

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In order to combine the extreme conditions of high pressure and magnetic field, we have developed a non-metallic diamond anvil cell to avoid Joule-heating in a pulsed-magnetic field. Although the cell is deformed with loading, a maximum pressure of ∼ 8.5 GPa can be applied. Quantum oscillation measurements using tunnel diode oscillator have been performed for heavy fermion antiferromagnet CePt2In7 in a pulsed field and at ambient pressure. The detail of the pressure cell and field-induced Fermi surface changes of CePt2In7 are discussed.

DOI： 10.1088/1742-6596/592/1/012149

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YbT2Zn20 (T: Rh and Ir), which crystallizes in the cubic CeCr2Al20-type structure, is a member of the well-known heavy fermion compounds, indicating a huge electronic specific heat coefficient γ ≃ 500 mJ/(K2·mol). We have measured temperature and magnetic field dependences of Yb valence in YbT2Zn20 (T: Rh and Ir) at ambient pressure by the Lm edge x- ray absorption spectroscopy in order to investigate the valence state of Yb 4f electrons in these compounds. It is revealed that the Yb valence in both compounds significantly decreases with temperature below about 100 K and increases with increasing magnetic field at low temperatures in contrast to the case of YbCo2Zn20.

DOI： 10.1088/1742-6596/592/1/012021

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We succeeded in growing single crystals of tetragonal RCu9Sn4 (R=La, Ce, Pr, and Eu) by the Sn-self-flux method for the first time, and studied the electrical and magnetic properties of these compounds. The magnetism of CeCu9Sn4 and PrCu9Sn4 indicates an Ising anisotropy with the magnetic easy axis parallel to the [001] direction. We revealed that EuCu9Sn4 shows an antiferromagnetic transition with an easy plane type magnetic anisotropy in the present single crystal study.

DOI： 10.1088/1742-6596/592/1/012034

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EuBi3 with the AuCu3-type cubic structure is known to be a Eu-divalent antiferromagnet with the Néel temperature TN ∼ 7:5 K. We succeeded in growing a high-quality single crystal by the Bi self-flux method. The magnetization at 1.3K for the magnetic field along the h100i direction increases linearly as a function of magnetic field, and saturates at a critical field Hc = 225 kOe, reaching a saturated magnetic moment of 7μB/Eu. Hc is well explained by the magnetic exchange interaction based on a two-sublattice model, using the simple relation Hc = (kB/3μB)(TN- θp) namely, Hc [kOe= 4:9 (TN - θp) [K], where θp is the paramagnetic Curie temperature θp = -36 K. The present antiferromagnetic state is found to be stable under pressures up to 8 GPa, where the Néel temperature increases with increasing pressure, being TN = 16:5K at 8 GPa. From the results of de Haas-van Alphen experiments on EuBiT3 and energy band calculations for the non-4f reference compound SrBi3, the Fermi surface is found to consist of three types of nearly spherical Fermi surfaces. © 2013 The Physical Society of Japan.

DOI： 10.7566/JPSJ.82.124708

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We grew a high-quality single crystal EuGa4 with the tetragonal structure by the Ga self-flux method, and measured the electrical resistivity, magnetic susceptibility, high-field magnetization, specific heat, thermoelectric power and de Haas-van Alphen (dHvA) effect, together with the electrical resistivity and thermoelectric power under pressure. EuGa4 is found to be a Eu-divalent compound without anisotropy of the magnetic susceptibility in the paramagnetic state and to reveal the same magnetization curve between H ∥ [100] and [001] in the antiferromagnetic state, where the antiferromagnetic easy-axis is oriented along the [100] direction below a Néel temperature TN = 16:5 K. The magnetization curve is discussed on the basis of a simple two-sublattice model. The Fermi surface in the paramagnetic state was clarified from the results of a dHvA experiment for EuGa4 and an energy band calculation for a non-4f reference compound SrGa4, which consists of a small ellipsoidal hole-Fermi surface and a compensated cube-like electron-Fermi surface with vacant space in center. We observed an anomaly in the temperature dependence of the electrical resistivity and thermoelectric power at TCDW = 150K under 2 GPa. This might correspond to an emergence of the charge density wave (CDW). The similar phenomenon was also observed in EuAl4 at ambient pressure. We discussed the CDW phenomenon on the basis of the present peculiar Fermi surfaces. © 2013 The Physical Society of Japan.

DOI： 10.7566/JPSJ.82.104703

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We report 153Eu and 69;71Ga NMR under a zero magnetic field on the antiferromagnetic state of EuGa4 with TN ≈ 16 K. We have successfully observed a 153Eu zero-field NMR signal with well-resolved nuclear quadrupole splitting in the antiferromagnetic state of EuGa4. 69;71Ga zero-field NMR spectra were also observed below TN. The internal field and nuclear quadrupole frequency are estimated from a simulation of the spectra by the exact diagonalization of the nuclear spin Hamiltonian matrix. The asymmetrically split zero-field NMR spectra were explained by considering a configuration of the magnetic moments of Eu2+ lying in the basal ab-plane. The temperature dependence of the internal field, which is proportional to the sublattice magnetization, can be explained by the Brillouin function with J = S = 7/2. © 2013 The Physical Society of Japan.

DOI： 10.7566/JPSJ.82.103701

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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 CeCr 2Al20-type structure. The metamagnetic behavior was observed at Hm =65 kOe for the magnetic field along the h100i direction below Txmax = 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 ofH >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. © 2013 The Physical Society of Japan.

DOI： 10.7566/JPSJ.82.084705

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We measured the electrical resistivity of CeCu 2 Ge 2 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. © 2013 The Korean Physical Society.

DOI： 10.3938/jkps.63.345

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EuNi2P2 is known as a heavy fermion compound with an electronic specific heat coefficient γ = 100 mJ/(K2·mol) . We grew single crystals and studied their electronic and magnetic properties by measuring the electrical resistivity, magnetic susceptibility, high-field magnetization, specific heat, and thermal expansion. The present heavy fermion state is clarified to be based on the Kondo effect as in CeRu2Si2, revealing an intensive shrinkage of the volume below about 100K in the temperature dependence of thermal expansion. The temperature dependences of the 4f -electron contribution to the volume thermal expansion ΔV/V) 4f and the average Eu valence are found to show good scaling in EuNi2P2. © 2013 The Physical Society of Japan.

DOI： 10.7566/JPSJ.82.083708

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The effect of pressure on the field-induced ordered phase for H {norm of matrix} 〈111〉 in the heavy-fermion compound YbCo 2 Zn 20 , 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 {norm of matrix} 〈111〉 at 0.1 K was constructed in the pressure range up to 4.5 GPa. © 2013 The Korean Physical Society.

DOI： 10.3938/jkps.62.1852

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We succeeded in growing single crystals of YbTIn 5 (T: Co, Rh, Ir), YbGa 4 , YbT 2 Zn 20 (T: Co, Rh, Ir), YbPdGe, Yb 2 Pt 2 Pb, and YbPd 5 Al 2 . The electronic and magnetic properties are clarified by measuring the electrical resistivity, magnetic susceptibility, magnetization, specific heat and de Haas - van Alphen effect. © 2013 The Korean Physical Society.

DOI： 10.3938/jkps.62.1858

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We carried out the de Haas-van Alphen (dHvA) experiment for an antiferromagnet UCd11 and its non-5f reference compound ThCd11 to clarify the Fermi surface properties and the true electronic specific-heat coefficient γ of UCd11. We observed dHvA signals of both compounds and compared the experimental results with the result of theoretical band calculations. The Fermi surfaces of both compounds are found to be small and closed. The cyclotron masses obtained from the dHvA data of UCd11 are compared with those of reference compounds ThCd11, NpCd11, and LaCd11, and the γ value of UCd11 is estimated to be about 100mJK-2mol-1, which is much smaller than the 840mJK-2mol-1 in the previous reports. It is concluded that this large value is mainly not due to heavy quasiparticles but due to the magnetic contribution to the specific heat. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssb.201200765

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We succeeded in growing single crystals of LaNiC 2 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 H c2 in superconductivity are not large for three principal directions. From the low-temperature specific heat measurement, superconductivity in LaNiC 2 is explained by the framework of the BCS-superconductivity, contrary to the above arguments. The upper critical field H c2(0), which was obtained from the specific heat under magnetic fields, is about 2kOe. © 2012 The Physical Society of Japan.

DOI： 10.1143/JPSJ.81.113703

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From the magnetization and magnetoresistance measurements, we constructed the magnetic phase diagram of Yb2Pt2Pb with the Shastry-Sutherland lattice, which consists of characteristic two phases below 1 K with many metamagnetic transitions, revealing magnetic frustrations. © 2012 The Physical Society of Japan.

DOI： 10.1143/JPSJS.81SB.SB058

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The crystal structure of YbPdGe is orthorhombic, with a large lattice constant for the b-axis. Reflecting this crystal structure, the electronic state is well conductive in the a-c plane. Magnetically YbPdGe is a ferromagnet with a Curie temperature TC = 11.4 K, and ferromagnetic moments are most likely oriented along the b-axis. The electronic specific heat coefficient γ = 150 mJ/(K2· mol) and a reduced magnetic entropy at TC suggest that YbPdGe is a heavy fermion ferromagnet. © 2012 The Physical Society of Japan.

DOI： 10.1143/JPSJS.81SB.SB056

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We studied an effect of pressure on the heavy fermion state of YbCo 2Zn20 under magnetic fields. The critical pressure P c, where the electronic state changes from the heavy fermion state to the antiferromagnetic state, is estimated to be Pc≃1.8 GPa. The super-heavy fermion state in the Pc region is found to be strongly destroyed in magnetic fields for H ∥<100>. The field-induced quadrupolar phase, which is most likely realized only for H ∥<100>, is found to be robust even in the antiferromagnetic pressure region. © 2012 The Physical Society of Japan.

DOI： 10.1143/JPSJS.81SB.SB064

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We succeeded in growing a single crystal of YbPd5Al2 with the tetragonal structure. The temperature dependence of electrical resistivity and a small value of the coefficient A in the Fermi liquid relation ρ = ρ0 + AT2 suggest that the 4 f -electrons are well localized. A magnetic ordering was found at To = 0.19 K in the specific heat measurement. On the other hand, the magnetic entropy exhibits only 0.5R ln 2 at To, and the specific heat shows a long tail above To. © 2012 The Physical Society of Japan.

DOI： 10.1143/JPSJS.81SB.SB057

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We measured the de Haas-van Alphen oscillation in divalent compounds YbTIn5 (T : Co, Rh, Ir) and YbCoGa5. The Fermi surfaces, which are characteristic in two kinds of nearly cylindrical Fermi surface, are approximately unchanged in these compounds and are well explained by the results of energy band calculations. The cyclotron mass is found to increase remarkably as the average lattice constant decreases from 5.4 Å in YbIrIn 5 to 5.2 Å in YbCoGa5: m*c = 1.1m0 in YbIrIn5 and 5.1m0 in YbCoGa 5 for dHvA branch β1, revealing a chemical pressure effect. There exists the hybridization between 4 f electrons and conduction electrons in YbCoGa5. © 2012 The Physical Society of Japan.

DOI： 10.1143/JPSJS.81SB.SB059

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We studied an effect of pressure on the electronic state of YbIr 2Zn20under magnetic fields. The heavy fermion state at ambient pressure is found to be changed into an antiferromagnetic state at pressures larger than a critical pressure Pc≃ 5.2 GPa, where the electronic state indicates a superheavy fermion state with an order of the electronic specific specific heat coefficient γ = 20 J/(K 2·mol). The temperature dependence of the electrical resistivity shows a characteristic two-peak structure above 5.0 GPa, implying the combined phenomena between the Kondo effect and the crystalline electric field effect. At 7.6 GPa, the magnetoresistance shows a broad maximum at a critical field Hc, corresponding to a pressure-induced antiferromagnetic phase with the Néel temperature TN = 1.4 K. TN increases with further increasing pressure. © 2012 The Physical Society of Japan.

DOI： 10.1143/JPSJS.81SB.SB063

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We measured the electrical resistivity of a prototype heavy fermion antiferromagnet CeAl3 in the temperature range from 0.1 K to room temperature under various magnetic fields and pressures. The heavy fermion state at ambient pressure is drastically destroyed under a small pressure and magnetic field. © 2012 The Physical Society of Japan.

DOI： 10.1143/JPSJS.81SB.SB053

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Néel temperatures in RIr2Zn20 (R : rare earth) with the cubic caged structure are found to be very low, which are below T N=5.0 K for GdIr2Zn20. This is mainly due to the long R-R distance and R atoms are spherically surrounded by Zn atoms. The corresponding crystalline electric field (CEF) splitting energies are also small, being below 100 K. © 2012 The Physical Society of Japan.

DOI： 10.1143/JPSJS.81SB.SB051

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We measured the electrical resistivity under magnetic field and pressure and de Haas van Alphen (dHvA) oscillations in CeCu6. The A value in the Fermi liquid relation of the electrical resistivity ρ = ρ0 + AT 2 and the cyclotron effective mass are reduced with increasing magnetic fields and pressures. The A value, however, becomes distinct and/or is enhanced at the metamagnetic field, especially, in a characteristic pressure region where the electronic state deviates from the heavy fermion state, for example, at 2.00 GPa. © 2012 The Physical Society of Japan.

DOI： 10.1143/JPSJS.81SB.SB009

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We measured the electrical resistivity, magnetic susceptibility, and specific heat in quasicrystal approximants RCd6. It was confirmed that the structural order-disorder transition of a tetrahedron with 4Cd atoms occurs at about 160 K when the lattice constant a is longer than a = 15.481 Å in YCd6, namely for RCd6 (R: Y, Pr, Nd, Sm, Gd, Tb, Dy and Yb ). The structural transition is found to have a great influence on the low-temperature electrical resistivity. © 2012 The Physical Society of Japan.

DOI： 10.1143/JPSJS.81SB.SB019

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We grew single crystals of an antiferromagnetic heavy-fermion compound UCd11 and a reference compound ThCd11, and carried out the magnetic susceptibility, high-field magnetization, and specific heat measurements in order to get more insight into the heavy fermion state which is realized in the antiferromagnetic state. The specific heat results suggest that the crystalline electric field (CEF) ground state of UCd11 is a doublet and the total splitting energy of the CEF scheme is less than 100 K. The H - T phase diagram for H ∥ <100> is approximately reproduced in the present experiments. © 2012 The Physical Society of Japan.

DOI： 10.1143/JPSJS.81SB.SB023

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We measured the electrical resistivity, magnetic susceptibility, magnetization, and specific heat of the quasicrystal approximants RCd 6 (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 160K when the lattice constant a is larger than 15.481 A in YCd 6, namely, for R = Pr, Nd, Sm, Gd, Tb, Dy, and Yb. At lower temperatures, RCd 6 compounds, except non-4f reference compounds YCd6 and LuCd 6, and a divalent compound YbCd 6, 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 RCd 6 (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 GdCd 6, while the the Néel temperature of RCd 6 (R: Ho, Er, and Tm) without the structural transition approximately follows the de Gennes scaling. Moreover, the electrical resistivity of RCd 6 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 RCd 6 without the structural transition. The contribution of an Einstein oscillator to the phonon specific heat is also discussed in YCd 6 and LuCd 6. © 2012 The Physical Society of Japan.

DOI： 10.1143/JPSJ.81.024720

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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 NpPd5Al 2, 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). © Published under licence by IOP Publishing Ltd.

DOI： 10.1088/1742-6596/400/2/022028

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The metamagnetic behavior, which is typical in heavy fermion compounds, is observed in UCo2Zn20 and UIr2Zn20 at Hm = 80 and 20 kOe, respectively. Reflecting the metamagnetic behavior, the magnetoresistance is suppressed in magnetic fields larger than Hm, and the corresponding A-value of a Fermi liquid relation in the electrical resistivity ρ ρ0+AT2 indicates a peak at around Hm. Pressure suppresses this behavior in UIr2Zn20. © Published under licence by IOP Publishing Ltd.

DOI： 10.1088/1742-6596/391/1/012021

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We studied the magnetic field versus temperature phase diagram of the heavy-fermion compound YbCo2Zn20 with the cubic CeCr2Al20-type structure by measuring the specific heat, ac-susceptibility, and electrical resistivity under magnetic fields. In a low magnetic field region, a metamagnetic behavior was observed at Hm 6 kOe for three principal field directions below Tχmax 0.32 K, at which the temperature dependence of ac-susceptibility shows a local broad maximum. Two crossover lines were found below and above Hm. At high magnetic fields, the heavy-fermion state was rapidly suppressed with increasing magnetic field, and the field-induced ordered phase appeared in a very limited field direction around H || 111 above the transition field HQ= 60 kOe in the temperature range below TQ = 0.6 K. © Published under licence by IOP Publishing Ltd.

DOI： 10.1088/1742-6596/391/1/012072

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Magnetic susceptibility, high-field magnetization up to 500 kOe, and specific heat in a wide temperature range from 0.06 to 300K were measured for single crystals of the cubic heavy-fermion compound YbCo2Zn 20 in order to elucidate the electronic states of the compound at low temperatures. A strong increase in the magnetic specific heat in the form of Cmag=T below ∼1K is approximately explained by the resonant level model for S = 1=2 with the Kondo temperature TK = 1 K, and an extremely large Cmag=T ≃ 8 J/(K2·mol) below about 0.2K is explained by considering the magnetic entropy of the doublet ground state in the 4f crystalline electric field (CEF) scheme of an Yb 3+ ion, which corresponds to an extremely large electronic specific heat coefficient. The field-induced ordered phase for H k h111i, which has recently been found by low-temperature magnetization measurements, was precisely studied by electrical resistivity and specific heat measurements, and was observed in a limited angular range around the h111i direction. On the basis of CEF analyses, the level crossing of the two lowest CEF states is essentially important to understand the field-induced ordered phase, which can be reduced to a field-induced antiferro-quadrupolar ordering based on the Γ3-type quadrupole moment O20 © 2011 The Physical Society of Japan.

DOI： 10.1143/JPSJ.80.114703

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We measured the de Haas-van Alphen (dHvA) oscillations, electrical resistivity, magnetic susceptibility, magnetization, and specific heat of PrIr2Zn20, which has recently been suggested as a heavy-fermion superconductor. Several dHvA branches with small frequencies ranging from 0.33 × 106 to 8.00 × 106 Oe were detected in the dHvA experiment, which were well explained by the results of energy band calculations for LaIr2Zn20 using the lattice parameter of PrIr2Zn20. Moreover, the cyclotron effective mass is small, i.e., less than 1m0 (m0. rest mass of an electron). This means that 4f electrons are fully localized and do not contribute to the Fermi surface. Similar dHvA results were obtained for the reference compound LuIr2Zn20. Thus, superconductivity in PrIr2Zn20, which has been observed very recently below 0.05 K, is not due to heavy quasiparticles. In fact, the present superconductivity disappears at a magnetic field of 20 Oe. From the experimental results of magnetic susceptibility, magnetization, and specific heat, we estimated the 4f crystalline electric field (CEF) scheme of PrIr2Zn20: Γ3 (0 K)-Γ4 (separated from a non-Kramers Γ3 doublet by 36.0 K)-Γ1 (86.4 K)-Γ5 (103 K). On the basis of this CEF scheme, we discuss a broad Schottky peak in the magnetic specific heat at 0.4K and the metamagnetic-like anomaly of magnetization at Hm = 50 kOe for H || h100i. © 2011 The Physical Society of Japan.

DOI： 10.1143/JPSJ.80.074605

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β-US2 with the orthorhombic structure is an interesting compound of which the electrical property is changed from a metallic state to an insulating state at temperatures lower than 80 K. To clarify the present metal-insulator change, we carried out the magnetization and magnetoresistance measurements in magnetic fields up to 50 T. The magentization at 4.2 K saturates above 40 T, reaching 1.75 μB/U at 50 T for the magnetic field along the magentic easy-axis, namely the [001] direction. The corresponding electrical resistivity at 4.2 K is steeply reduced in magnitude from 1 × 103 Ω·cm to 2 × 10-2 Ω·cm at 50 T only when the magnetic field is applied along the [001] direction. The temperature dependence of the electrical resistivity at 50 T indicates a usual metallic behaviour. The conduction electrons are most likely released from the trapped U-sites when the 5f-CEF magnetic moments are fully polarized in high magnetic field of 50 T. The present experimental results are discussed from the viewpoint of the magnetic polaron. © 2011 The Physical Society of Japan.

DOI： 10.1143/JPSJS.80SA.SA104

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The metamagnetic behaviour, which corresponds to one of the characteristic properties in the heavy fermion compounds, was studied by measuring the electrical resistivity under pressure and magnetic field for a typical heavy fermion compound CeCu6 with orthorhombic structure. The transverse magnetoresistance at 100 mK indicated a peak structure at Hm = 20 kOe for the magnetic field H//c-axis under ambient pressure. Hm is found to increase linearly as a function of pressure and indicates Hm = 102 kOe at 1.75 GPa, for example. The quantum critical point is thus likely to exist at a slightly negative pressure value of ∼ 0.21 GPa from extrapolating Hm to zero. The ρ0 and A values in the electrical resistivity ρ = ρ0+AT2 decrease steeply in magnitude with increasing pressure and magnetic field, indicating that the heavy fermion state is destroyed by pressure and magnetic field. © 2011 The Physical Society of Japan.

DOI： 10.1143/JPSJS.80SA.SA065

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We measured electrical resistivity on antiferromagnet Ce2Ir 3Ge5 under high pressure up to 8 GPa. It is shown that the Néel temperature (= 9.5 K) at ambient pressure decreased by increased pressure. The Néel temperature seems to be zero at a critical pressure Pc ≃ 2.0 GPa suddenly. The variation by higher pressure above 2.0 GPa does not seem prominence up to 8 GPa. © 2011 The Physical Society of Japan.

DOI： 10.1143/JPSJS.80SA.SA066

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We studied the Fermi surface properties of YbCu2Si2 and YbCu2Ge2 with the tetragonal structure by measuring the de Haas-van Alphen (dHvA) oscillations, together with the energy band calculations. It was clarified that 4f electrons contribute to the Fermi surface of a valence fluctuating compound YbCu2Si2, but not to that of a divalent compound YbCu2Ge2. Namely, the Fermi surface of YbCu2Si2 contains the 4f-components considerably and the corresponding cyclotron effective mass m *c of the main Fermi surface is large, m *c = 30-40m0 (m0: rest mass of an electron). We also studied the heavy fermion properties of YbT 2Zn20 (T: Co, Rh, Ir) with the cubic caged structure. The metamagnetic behavior or an abrupt nonlinear increase of magnetization was observed at 6 kOe in YbCo2Zn20, 63 kOe in YbRh 2Zn20, and 97 kOe in YbIr2Zn20 for H ∥ «100», which was measured at 60 mK in YbCo2Zn 20 and 1.3 K in YbRh2Zn20 and YbIr 2Zn20. The metamagnetic field is found to be a good parameter to reach the quantum critical point under pressure for YbIr 2Zn20. By measuring the electrical resistivity under pressure and magnetic field, we clarified that the electronic state close to the quantum critical point is realized in YbIr2Zn20 at 5.2 GPa and also YbCo2Zn20 at ambient pressure. The corresponding heavy cyclotron effective mass of 100-500m0 at 0 kOe was estimated from the field dependence of the √A value in the low-temperature electrical resistivity ρ=ρ0 + AT2 under pressure and magnetic field and the cyclotron mass obtained from the dHvA experiment at ambient pressure and high magnetic fields. © 2011 The Physical Society of Japan.

DOI： 10.1143/JPSJS.80SA.SA003

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We studied the Fermi surface properties of YbCu2Si2 and YbCu2Ge2 with the tetragonal structure by measuring the de Haas-van Alphen (dHvA) oscillations, together with the energy band calculations. It was clarified that 4f electrons contribute to the Fermi surface of a valence fluctuating compound YbCu2Si2, but not to that of a divalent compound YbCu2Ge2. Namely, the Fermi surface of YbCu2Si2 contains the 4f-components considerably and the corresponding cyclotron effective mass m(c)* of the main Fermi surface is large, m(c)*=30-40m(0) (m(0) : rest mass of an electron). We also studied the heavy fermion properties of YbT2Zn20 (T : Co, Rh, Ir) with the cubic caged structure. The metamagnetic behavior or an abrupt nonlinear increase of magnetization was observed at 6 kOe in YbCo2Zn20, 63 kOe in YbRh2Zn20, and 97 kOe in YbIr2Zn20 for H parallel to &lt; 100 &gt;, which was measured at 60 mK in YbCo2Zn20 and 1.3 K in YbRh2Zn20 and YbIr2Zn20. The metamagnetic field is found to be a good parameter to reach the quantum critical point under pressure for YbIr2Zn20. By measuring the electrical resistivity under pressure and magnetic field, we clarified that the electronic state close to the quantum critical point is realized in YbIr2Zn20 at 5.2 GPa and also YbCo2Zn20 at ambient pressure. The corresponding heavy cyclotron effective mass of 100-500m(0) at 0 kOe was estimated from the field dependence of the root A value in the low-temperature electrical resistivity rho = rho(0) + AT(2) under pressure and magnetic field and the cyclotron mass obtained from the dHvA experiment at ambient pressure and high magnetic fields.

DOI： 10.1143/JPSJS.80SA.SA003

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We synthesized a new compound of CeRhGe2 with the orthorhombic CeNiSi2-type structure. By measuring the electrical resistivity, magnetic susceptibility, magnetization, specific heat, and neutron scattering for single crystals, CeRhGe2 was found to order antiferromagnetically below TN = 7.6 K with an ordered moment of 1.3 μB/Ce oriented along the magnetic easy-axis of the c-axis. Similar measurements were also carried out for CePtSi2 single crystals. From the experimental results of anisotropic magnetic susceptibility and magnetization, the crystalline electric field (CEF) scheme was obtained for CeRhGe2 and CePtSi2, together with the similar compound CeNiGe2. Furthermore, we carried out pressure experiments by measuring the electrical resistivity of CePtSi2 and CeRhGe2. In the quantum critical region where the Néel temperature becomes zero, we observed superconductivity in CePtSi2 and most likely CeRhGe2, at 1.5 and 7.1 GPa, respectively. The upper critical field of CePtSi2 was found to be highly anisotropic with respect to the three principal field directions. © 2011 The Physical Society of Japan.

DOI： 10.1143/JPSJ.80.024711

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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, T χmax = 5.3K and Hm = 64kOe in YbRh2Zn 20, 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) . © Published under licence by IOP Publishing Ltd.

DOI： 10.1088/1742-6596/273/1/012003

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We measured the electrical resistivity in magnetic field H under pressure P for a heavy fermion compound YbIr2Zn20. The quantum critical point is found to be defined as an electronic state where the metamagnetic transition field Hm becomes zero. This is realized at Pc ≃ 5.2 GPa. The most characteristic feature in the quantum critical pressure region is an anomalously large A value of the electrical resistivity ρ = ρ0 + AT2, reaching A 380μΩcm/K 2 at 5.0 GPa, which is, however, strongly reduced with increasing the magnetic field: A 1.45μΩcm/K2 at 80 kOe. From the result of the de Haas-van Alphen experiment at ambient pressure, the corresponding cyclotron effective mass of conduction electrons at 5.0 GPa is 400 - 500 m 0 (m0: rest mass of an electron). © Published under licence by IOP Publishing Ltd.

DOI： 10.1088/1742-6596/273/1/012013

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We have carried out electrical resistivity experiments on the non-centrosymmetric compound CeIrGe3 under high pressures up to 24 GPa. CeIrGe3 is an antiferromagnet with the Néel temperature TN1=8.5K and a successive magnetic transition at TN2=4.7K at ambient pressure. With increasing pressure, TN1 and TN2 merge around 3 GPa, becomes unchanged up to 10 GPa, and indicates a step-like decrease up to 20 GPa. Further increasing pressure, we have found superconductivity above 20 GPa with a transition temperature of 1.6 K at 24 GPa. The upper critical field for the magnetic field along the tetragonal [0 0 1] direction is expected to be much larger than 15 T. © 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2009.10.126

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The metamagnetic behavior in the heavy-fermion compound YbIr2Zn20 with a cubic structure was studied by magnetization, de Haas-van Alphen (dHvA) oscillation, magnetoresistance, specific heat, thermal expansion, and magnetostriction measurements in single-crystalline samples. A metamagnetic anomaly at H-m similar or equal to 100 kOe was found to exist in all field directions in the cubic crystal structure. The cyclotron effective mass m(c)*, the coefficient A in the Fermi liquid relation of electrical resistivity rho = rho(0) + AT(2), and the electronic specific heat coefficient C/T indicate a peak at the metamagnetic field H-m. The negative thermal expansion and negative volume magnetostriction suggest that the valence of the Yb ion gradually changes from a 4f-itinerant state to a trivalent state with increasing magnetic field, and an almost trivalent state is realized above the metamagnetic field H-m. On the other hand, the topology of the Fermi surface is approximately unchanged below and above H-m in the dHvA experiment.

DOI： 10.1143/JPSJ.79.064609

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We report on the discovery of superconductivity in the noncentrosymmetric antiferromagnet CeIrGe3 below 1.5 K at a pressure of 20 GPa. We performed electrical resistivity measurements in single crystals of CeIrGe 3 in the temperature range 0.04-300 K at pressures up to 24 GPa. From these measurements we deduced the P-T phase diagram. The data imply a crossover from localized to itinerant 4f electrons of the type caused by a Kondo-lattice phenomenon as pressure increases. The antiferromagnetic phase weakens with pressure and eventually vanishes above 22 GPa, indicative of the occurrence of a quantum critical point. Superconductivity appears inside the antiferromagnetic phase near this critical point. After the disappearance of the magnetic ordering a non-Fermi-liquid behavior is observed. Resistivity measurements taken at 24 GPa in magnetic fields up to 8 T strongly suggest that CeIrGe3 has a very large upper critical field for H ∥ [001]. © 2010 The American Physical Society.

DOI： 10.1103/PhysRevB.81.140507

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Antiferromagnets CePd5Al2 and CeRhGe2 with the quasi-two dimensional electronic state have been found to become superconductive by measuring the electrical resistivity under pressure. In these compounds, the Néel temperature decreases at high pressure and becomes approximately zero at critical pressure Pc = 9 GPa in CePd5Al2 and Pc = 7 GPa in CeRhGe2. Superconductivity was observed around Pc. In CePd5Al2, the upper critical field Hc2 is found to be highly anisotropic among H||[001] and [100], reflecting nearly cylindrical Fermi surfaces along the tetragonal [001] direction. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssb.200983055

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

We measured the high-field magnetization and de Haas-van Alphen (dHvA) oscillations for YbIr2Zn20 with a cubic crystal structure, together with the electrical resistivity and magnetic susceptibility. The magnetic Susceptibility chi with an effective magnetic moment of Yb3+ becomes temperature-independent at low temperatures, with a broad peak at T-chi max = 7.4 K for H parallel to &lt; 110 &gt;. The corresponding magnetization indicates a metamagnetic transition at H-m = 120kOe, consistent with a T-chi max vs H-m relation in the Ce- and U-based heavy fermion Compounds. The large cyclotron masses of 4-27 m(0) are detected in the dHvA experiment, and are found to be reduced at magnetic fields higher than H-m = 120 kOe. The resistivity follows the Fermi liquid relation rho = rho(0) +AT(2) under magnetic field, and the root A value is also found to have a maximum at H-m as a function of magnetic field. From the present experimental results, together with the results of 4f-itinerant energy band calculations, the 4f electrons are found to contribute to the heavy fermion state in YbIr2Zn20.

DOI： 10.1143/JPSJ.78.123711

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Language：English   Publishing type：Book review, literature introduction, etc.   Publisher：IOP PUBLISHING LTD  

We review the nature of strongly correlated electronic states in rare earth and actinide compounds, focusing on localized versus itinerant electronic states in CeRhIn5, quantum critical phenomena in YbIr2Zn20, residual resistivity in CeCu6, metamagnetism in heavy fermion compounds, and unconventional superconductivity in CeIrSi3 without inversion symmetry in the crystal structure, emphasizing that sample quality is essentially important to clarify the characteristic features for the heavy fermion compounds.

DOI： 10.1088/0034-4885/79/11/114501

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DOI： 10.11316/jpsgaiyo.71.2.0_2099

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DOI： 10.11316/jpsgaiyo.70.1.0_2010

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