Distribution of metal ions and magnetic properties in spinel system Zn(1-x)Ga2x/3Cr2Se4

A system of zinc-chromium selenides with Ga3+ substitution have been prepared by the chemical transport method. The X-ray structure of the single crystals and their magnetic properties have been studied to determine the cation distribution in the fee cubic spinel. The magnetic properties of the system appeared to be strongly dependent on a location of the Ga admixture on the tetrahedral or the octahedral positions of the spinel sublattice. Three crystals with different stoichiometry revealed distinct values of the saturation magnetic moment, mu(sat), i.e., 5.2, 3.8, and < 0.1 mu(B). The Zn2+ ion deficiency forced Ga3+ to occupy the tetrahedral sites and left all the Cr3+ ions on the octahedral sites in (Zn0.63Ga0.37)[Cr-2]Se-4, for which a slightly lowered value of magnetic moments have been observed. In (Zn(0.95)square(0.05)) [Ga(0.03)Cr(1.93)square(0.04)]Se-4, a lack of stoichiometry caused the Ga ions to locate on the octahedral sites. The small number of Ga3+ at these sites was able to considerably affect the magnetic exchange interactions. At high Ga3+ concentration in (Zn)[Ga0.4Cr1.6]Se-4, it turned out that the saturation magnetic moment's value was below the limit of observations, (C) 1999 Academic Press.