Field-Induced Quadrupolar Ordered Phase for H∥<111> in Heavy-Fermion Compound YbCo₂Zn₂₀

Abstract

Magnetic susceptibility, high-field magnetization up to 500 kOe, and specific heat in a wide temperature range from 0.06 to 300 K were measured for single crystals of the cubic heavy-fermion compound YbCo 2 Zn 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 C mag =T below $1 K is approximately explained by the resonant level model for S ¼ 1=2 with the Kondo temperature T K ¼ 1 K, and an extremely large C mag =T ' 8 J/(K 2 Ámol) below about 0.2 K is explained by considering the magnetic entropy of the doublet ground state in the 4f crystalline electric field (CEF) scheme of an Yb 3þ 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 À 3 -type quadrupole moment O 0 2 .

Quantum Criticality and Heavy Fermion State in YbCo2Zn20under Pressure and Magnetic Field

“…Correspondingly, the metamagnetic behavior, which is typical in heavy fermion compounds, is observed at a low magnetic field H m 6 kOe [2]. Moreover, we observed a field-induced quadrupolar phase for the magnetic field H along the 111 direction in magnetic fields larger than H Q = 60 kOe [3].…”

“…H || <100> We also obtained the pressure vs magnetic field phase diagram for the magnetic field along the H 111 direction, as shown in Fig. 3(a), where the field-induced quadrupolar phase is realized in magnetic fields larger than H Q =60 kOe at 0 GPa [3], and this H Q value decreases as a function of pressure. It is noticed that the H Q value is still observed at 2.7 GPa, which is larger than P c 1.8 GPa.…”

Field-Induced Order in Heavy-Fermion Compound YbCo2Zn20

“…This result evidences that the field-induced phase has different character from the pressure-induced antiferromagnetic one from a microscopic point of view. This is consistent with the behavior in the pressure-magnetic field phase diagram in which pressure-induced ordered phase does not connect to the field-induced one [5,10].…”

“…An application of small fields of about 0.5 T induces metamagnetic transitions [2,5]. With further increasing fields above the metamagnetic transitions, strong reduction of the effective mass m * and correspondingly the A coefficient in the electrical resistivity was observed [2,6,7].…”

“…With further increasing fields above the metamagnetic transitions, strong reduction of the effective mass m * and correspondingly the A coefficient in the electrical resistivity was observed [2,6,7]. Furthermore, when the field is applied close to 111 , novel field-induced ordered state is realized above 6 T [5,8]. In contrast to the pressure-induced magnetic phase, bulk measurements and meanfield analyses suggest the primary order parameter for the field-induced phase as antiferroquadrupole.…”