Selenium doping induced two antiferromagnetic transitions in thiospinel compounds CuCo2S4‐xSex (0 ≤ x ≤ 0.8)

A series of copper thiospinel compounds, CuCo2S4‐xSex (x = 0, 0.2, 0.4, 0.6, 0.8), have been successfully synthesized by solid‐state reaction and their structure and magnetic properties have been studied. The Rietveld refinements of X‐ray diffractions indicate that both the lattice constants and the nearest‐neighbor Cu‐Cu distances increase with increasing selenium doping. A weakly antiferromagnetic transition occurring at about 4 K is observed in CuCo2S4. Two antiferromagnetic transitions at about 3.5 K and 6 K are observed in selenium‐doped samples, which suggest that the exchange couplings associated with Cu‐S(Se)‐Cu and Cu‐Se(S)‐Cu, respectively, are responsible for the two antiferromagnetic transitions. Detailed analysis of the experimental results further indicates that the nearest‐neighbor molecular field coefficient is comparable to the next‐neighbor molecular field coefficient. We propose a reasonable model to explain this phenomenon.