Crossover Phase Diagram in Heavy Fermion Compound YbCo2Zn20

Abstract

We studied the electronic state and metamagnetic behavior in the heavy fermion compound YbCo 2 Zn 20 by measuring the specific heat, ac-susceptibility, and electrical resistivity under magnetic fields. The magnetic specific heat in the form of C mag / T increases steeply with decreasing temperature below 10 K and becomes constant with an extremely large value 8 J/(K 2 ·mol) below about 0.2 K, indicating a Fermi-liquid nature in this temperature range. The magnetic entropy increases rapidly below 10 K and reaches R ln 8 around 60 K, suggesting a small crystalline-electric-field (CEF) splitting energy. From the precise electrical resistivity measurements, together with the C ( H )/ T and χ ac ( T ) measurements, it was found that there are two crossover lines at low temperatures in the H – T phase diagram for H ∥<100>. The Fermi-liquid state evolves at lower temperatures than these crossover lines.