Characteristic magnetic phase diagram in heavy-fermion compound YbCo ₂Zn₂₀

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.