Thermal Expansion of NiS₂, Ni_0.9Co_0.1S₂, Ni_0.9Cu_0.1S₂ and Ni_0.95Cu_0.05S₂

Abstract

The thermal expansion of NiS₂, Ni_0.9Co_0.1S₂, Ni_0.9Cu_0.1S₂ and Ni_0.95Cu_0.05S₂ has been measured from 4.2 K to room temperature. The anomalies, which correspond to antiferromagnetic ordering and to appearance of weak ferromagnetism, have been observed in all specimens. The lattice, electronic and magnetic Grüneisen constans are determined. The magnetic Grüneisen constant changes its sign from negative to positive corresponding to the metal-semiconductor transition which occurs between Ni_0.9Co_0.1S₂ and Ni_0.93Co_0.07S₂.