Ordered Moment of NiS2

The transition metal dichalcogenides exhibit a wide variety of both electrical and magnetic properties, from insulators to superconductors and from ferromagnetism through antiferromagnetism to diamagnetism. NiS2is a semiconductor with an anomalous paramagnetic behavior which leaves in doubt the existence of a local moment. Previous neutron diffraction data have failed to show any ordering down to 4.2°K. Our neutron powder diffraction data on stoichiometric NiS2show a transition at 40°K to a structure which can be described as ordering of the first kind. This is followed by an abrupt transition at 30°K in which additional diffraction peaks appear and these are consistent with ordering of the second kind. Despite the fact that the powder data cannot indicate an unambiguous magnetic structure, the magnitude of the ordered moment can be fixed. The rms moments associated with ordering of the first and second kinds are 1.0 and 0.60 µBper nickel atom, respectively, and the total moment is 1.17 µBper nickel atom.