Cation distribution and magnetic properties of ternary Zn2.33-xCO2Sb0.67O4 spinels

The series of spinels Zn2.33-xCoxSb0.67O4 (0.23 less than or equal to x less than or equal to 2.33) was prepared by ceramic technology. The crystal structures were refined from the x-ray diffraction data using the Rietveld profile method. The high-temperature magnetic susceptibility was measured by the Faraday method in the temperature range 290-600 K and the data were fitted to the Curie-Weiss law. The cation distribution in these diluted magnetics is obtained from x-ray diffraction and high-temperature magnetic susceptibility measurements. It was found that, for x less than or equal to 0.93 Co2+, ions occupy exclusively the octahedral position in the spinel type of structure. In the low-concentration region a strong clustering of magnetic ions is observed. In the range 1.33 less than or equal to x less than or equal to 2.33, Co2+ ions are distributed in both tetrahedral and octahedral cationic sites. The Curie-Weiss paramagnetic temperature Theta is negative in the whole range of concentrations, as the consequence of a predominant antiferromagnetic interaction. The appearance of the Co2+ ions in tetrahedral sites (around x = 1.33) leads to a drop in the absolute Theta-value. The effective magnetic moments of Co2+ ions are about 4.60(mu B) for x less than or equal to 1.33 and depend on the Co2+ concentration for x > 1.33.