Crystallographic and magnetic studies of cation-deficient spinels [formula omitted

Abstract

Crystallographic studies are carried out on the cation-deficient spinel compounds Ga 2 3 Cr 2S 4 and Al 2 3 +x Cr 2−x S 4 ( 1 3 ≤ x ≤ 5 3 ) . X-Ray analysis of both compounds indicates that there exist 1 3 vacancy per formula unit in 8 a positions and all chromium atoms in 16 d positions, with the rest of the metal positions occupied by gallium or aluminum atoms. Aluminum atoms give a wide range of substitution for chromium atoms, but gallium atoms do not. It is found by electron diffraction that vacancy ordering occurs in Ga 2 3 Cr 2S 4 below about 1100°C, as well as in InCr 5 3 S 4 . The magnetic properties of these compounds are investigated. Both InCr 5 3 S 4 and the disordered form of Ga 2 3 Cr 2S 4 exhibit weak ferromagnetism at low temperatures. The facts are explained in terms of the vacancy distribution in the 8 a positions.