Abstract
Neutron diffraction measurements have been made on two single crystals of NiS2 at low temperatures. Two types of antiferromagnetic reflections, i.e. M1 and M2, were observed. M1 corresponds to the first kind of antiferromagnetic ordering in fcc lattice and M2 to the second kind. The Néel temperature for M2 reflections, TN2, was 30±1 K, the same for two crystals, and that for M1, TN1, were 37 K and 51 K, different for two crystals. A distinct anomaly in the intensity of (002) M1 reflection, was observed at TN2. This suggests a strong correlation between M1 and M2 reflections. A spin structure is proposed, which permits the coexistence of both M1 and M2 reflections. This structure explains the observed intensities. The magnetic moment of Ni2+ obtained is considerably smaller than 2μB. Discussions are given on the proposed spin structure, and also on the mechanism for two Néel temperatures and weak ferromagnetism.
