Exchange integrals and magnetic properties of mixed chromium spinel systems: Zn1-xAxCr2X4(A = Cd, Hg and X = S, Se)

Many magnetic measurements have been accomplished in order to improve the phase diagrams of the systems Zn1-x Cd Cr2 S4 and Zn1-xCdxCr2Se4 particularly in the region of the intermediate concentration with mixed structure. We have computed, in this paper, the exchange integrals for the first and second coordination sphere (J and K) versus to dilution for the three systems: Zn1-x Cd Cr2 S4, Zn1-xCdxCr2Se4 and Zn 1-xHgxCr2Se4. The evolution of the structure and the magnetic properties with the dilution of diamagnetic ions in tetraedric site is the results of the competition between the ferromagnetic and antiferromagnetic interactions. Besides we have presented a compared magnetic properties with the phase diagrams (T,X) of these systems. Because of its complicated antiferromagnetic structure, the sulphur compound seems to have particular characteristics among the mixed spinel systems. (author). 12 refs, 7 figs, 1 tab