Specific Heat Study of Metal-Insulator Transition in Antiferromagnetic Phase of NiS_1.48Se_0.52

Abstract

We prepared a highly homogeneous polycrystal sample of NiS_1.48Se_0.52 in a sense that it undergoes, with increasing temperature, a sharp transition from metal to insulator (M–I) at 38.2 K in the antiferromagnetic phase (T_N∼65 K). The specific heat was measured on a sintered sample from 4.2 to 70 K. The obtained coefficient of the linear electronic specific heat, γ, is as large as 33 mJ/K² mole, and the Debye temperature determined below 20 K is 375 K. Such a large value of γ suggests a strong enhancement due to electron correlations. A clear latent heat of 38 J/mole was observed at the M–I transition. The corresponding entropy change is 1 J/K mole, probably mainly electronic. The magnetic specific heat was also observed and the magnetic entropy was estimated at 1.7 J/K mole. The present results support that the M–I transition in NiS_1.48Se_0.52 is the Mott transition.