Yusuke Hirose

Heavy Fermion State in YbIr2Zn20

We measured the high-field magnetization and de Haas–van Alphen (dHvA) oscillations for YbIr 2 Zn 20 with a cubic crystal structure, together with the electrical resistivity and magnetic susceptibility. The magnetic susceptibility χ with an effective magnetic moment of Yb 3+ becomes temperature-independent at low temperatures, with a broad peak at T χmax =7.4 K for H ∥ . The corresponding magnetization indicates a metamagnetic transition at H m =120 kOe, consistent with a T χmax 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 ρ=ρ 0 + A T 2 under magnetic field, and the \(\sqrt{A}\) 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 4 f -itinerant energy band calculations, the 4 f electrons are fou...

Metamagnetic Behavior in Heavy-Fermion Compound YbIr2Zn20

The metamagnetic behavior in the heavy-fermion compound YbIr 2 Zn 20 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 ≃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 ρ=ρ 0 + A T 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 4 f -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.

Heavy Fermion State Based on the Kondo Effect in EuNi2P2

EuNi2P2 is known as a heavy fermion compound with an electronic specific heat coefficient γ=100 mJ/(K2 \(\cdot\)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 100 K in the temperature dependence of thermal expansion. The temperature dependences of the \(4f\)-electron contribution to the volume thermal expansion Δ V/V)4f and the average Eu valence are found to show good scaling in EuNi2P2.

Fermi Surface and Superconducting Properties of Non-centrosymmetric LaNiC2

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...

Fermi Surface and Magnetic Properties of Antiferromagnet EuBi3

EuBi3 with the AuCu3-type cubic structure is known to be a Eu-divalent antiferromagnet with the Neel temperature \(T_{\text{N}}\simeq 7.5\) K. We succeeded in growing a high-quality single crystal by the Bi self-flux method. The magnetization at 1.3 K for the magnetic field along the \(\langle 100\rangle\) direction increases linearly as a function of magnetic field, and saturates at a critical field \(H_{\text{c}}=225\) kOe, reaching a saturated magnetic moment of 7 µB/Eu. \(H_{\text{c}}\) 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 anti ferromagnetic state is found to be stable under pressures up to 8 GPa, where the Neel temperature increases with increasing pressure, being \(T_{\text{N}}=16.5\) K at 8 GPa. From the results of de Haas–van Alphen experiments on EuBi3 and energy band calculations for the non-\(4f\...

Electrical and Magnetic Properties of Quasicrystal Approximants RCd6 (R: Rare Earth)

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 160 K 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-4 f reference compounds YCd 6 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 Neel 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 Neel temperature of GdCd 6 , while the the Neel temperature of RCd 6...

Fermi Surface Property and Characteristic Crystalline Electric Field Effect in PrIr2Zn20

We measured the de Haas–van Alphen (dHvA) oscillations, electrical resistivity, magnetic susceptibility, magnetization, and specific heat of PrIr 2 Zn 20 , which has recently been suggested as a he...

First-Order Antiferromagnetic Transition and Fermi Surfaces in Semimetal EuSn3

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 Neel 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...

Magnetic and Superconducting Properties of CeRhGe2 and CePtSi2

We synthesized a new compound of CeRhGe 2 with the orthorhombic CeNiSi 2 -type structure. By measuring the electrical resistivity, magnetic susceptibility, magnetization, specific heat, and neutron scattering for single crystals, CeRhGe 2 was found to order antiferromagnetically below T N = 7.6 K with an ordered moment of 1.3 µ B /Ce oriented along the magnetic easy-axis of the c -axis. Similar measurements were also carried out for CePtSi 2 single crystals. From the experimental results of anisotropic magnetic susceptibility and magnetization, the crystalline electric field (CEF) scheme was obtained for CeRhGe 2 and CePtSi 2 , together with the similar compound CeNiGe 2 . Furthermore, we carried out pressure experiments by measuring the electrical resistivity of CePtSi 2 and CeRhGe 2 . In the quantum critical region where the Neel temperature becomes zero, we observed superconductivity in CePtSi 2 and most likely CeRhGe 2 , at 1.5 and 7.1 GPa, respectively. The upper critical field of CePtSi 2 was found ...

Metamagnetic Transition in Heavy Fermion Compounds YbT2Zn20 (T : Co, Rh, Ir)

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).