Metamagnetic Behavior in Heavy-Fermion Compound YbIr2Zn20

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.