Effect of Pressure on the Magnetic and Electrical Transition Point of the NiAs-Type NiS

In order to study the nature of the first-order antiferromagnetic transition in NiS the electrical resistivity in the vicinity of the transition point has been investigated at the hydrostatic pressures up to 7 kbar. The transition has characteristics of semiconductive-metallic transformation. The transition point, observed at 230°K at atmospheric pressure, is lowered as the hydrostatic pressure is increased, with the rate ( d T t / d P )=-(6.0±0.3) deg./kbar. The transition can be described in terms of the electronic rearrangement in d -orbitals of nickel atoms between localized-collective electronic states.