Structural and magnetic properties of single-crystalline spinel systems ZnCr2−xAlxSe4 (x = 0.15 and 0.23)

Single crystals of the spinel solid solutions ZnCr2−xAlxSe4 with x = 0.15 and 0.23 were grown and studied by X-ray diffraction and macroscopic magnetic measurements. The solubility of Al3+ ions in the parent compound ZnCr2Se4 is very limited and only weakly substituted single crystals can be obtained. The spinel structure is hardly modified by this admixture and regular cation distribution is preserved. Alike ZnCr2Se4, the two compounds investigated order antiferromagnetically at low temperatures. Both the Néel temperatures and the paramagnetic Curie temperatures are similar to that reported for the parent selenide. Also the effective magnetic moments are close to that of ZnCr2Se4 and compatible with trivalent Cr ions. In contrast, the saturation magnetic moments measured above the metamagnetic phase transitions in strong magnetic fields and calculated per one Cr atom, appear to be strongly affected by the Al-substitution, being rapidly suppressed with rising Al-content.