New ferrimagnetic spinel compositions in the system MCr2S4?xSex where M=Fe,Co, Mn

Phase relationship between ferrimagnetic semiconducting spinels of the type MCr₂S₄ and defect NiAs compositions of the type MCr₂Se₄ (where M=Mn, Fe, Co) are established. It was found that the amount of Se which can be substituted, with retention of the spinel structure, decreases from MnCr₂S_4?xSe_x (x=0 to x=2) to FeCr₂S_4?xSe_x (x=0 to x=1·25) to CoCr₂S_4?xSe_x (x=0 to x=1). This phenomena is accounted for on the basis of sulfide spinel stability and unit cell size. The Curie temperatures of the spinel compositions decrease slowly with increasing Se content. This is presumably caused by weakening of the spinel A-B superexchange interaction.