Abstract

Non-stoichiometric phases in the series Co_1 − xNi_xCr₂S₄ (0 ≤ x < 1) were prepared at high temperatures. In the composition range 0 ≤ x ≤ 0.35 single-phase materials, isostructural with the end-member spinel CoCr₂S₄ are observed, whereas materials in the composition range 0.85 ≤ x < 1 adopt the Cr₃S₄ structure of the end-member NiCr₂S₄. Rietveld refinements using powder neutron diffraction data demonstrate that in the spinel structure nickel cations are accommodated exclusively at tetrahedral sites and in the Cr₃S₄ phases at octahedral sites in an ordered defect layer. All single-phase materials are semiconductors. Spinel-type phases appear to be ferrimagnetic with saturation moments in the range 2.4–2.6 μ_B, and Curie temperatures which increase with increasing nickel content. The Cr₃S₄-type materials exhibit a magnetic behaviour similar to NiCr₂S₄ and Cr₃S₄, which are complex antiferromagnets.