Pressure-tuned first-order phase transition and accompanying resistivity anomaly in CeZn_1−δSb₂

The Kondo lattice system CeZn_0.66Sb₂ is studied by electrical resistivity and ac magnetic susceptibility measurements at several pressures. At P=0 kbar, ferromagnetic and antiferromagnetic transitions appear at 3.6 and 0.8 K, respectively. The electrical resistivity at T_N dramatically changes from the Fisher-Langer type (ferromagneticlike) to the Suezaki-Mori (SM) type near 17 kbar, i.e., from a positive divergence to a negative divergence in the temperature derivative of the resistivity. The pressure-induced SM-type anomaly, which shows thermal hysteresis, is easily suppressed by a small magnetic field (1.9 kOe for 19.8 kbar), indicating a weakly first-order nature of the transition. By subtracting a low-pressure data set, we directly compare the resistivity anomaly with the SM theory without any assumption on backgrounds, where the negative divergence in dρ∕dT is ascribed to enhanced critical fluctuations in the presence of superzone gaps.