Phase behaviour, magnetic and electronic properties in the series Co(1 - x)Ni(x)Cr₂S₄ (0 ≤ x < 1)

Non-stoichiometric phases in the series Co(1 - x)Ni(x)Cr₂S₄ (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.