EXCHANGE INTEGRALS AND MAGNETIC-PROPERTIES OF MIXED CHROMIUM SPINEL SYSTEMS - ZN(1-X)A(X)CR(2)X(4) (A=CD,HG AND X=S,SE)

A lot of magnetic measurements are accomplished in order to improve the phase diagrams of the systems Zn1-xCdxCr2S4 and Zn1-xCdxCr2Se4 particularly in the region of intermediate concentrations with mixed structure. The exchange integrals for the first and second coordination spheres (J and K) are calculated in terms of dilution for the three systems Zn1-xCdxCr2Se4, Zn1-xCdxCr2S4, and Zn1-xHgxCr2Se4. The evolution of the structure and the magnetic properties with the substitution of diamagnetic ions at tetrahedral sites is the result of the competition between the ferromagnetic and antiferromagnetic interactions. Besides, the magnetic properties are compared with the phase diagrams (T, x) of these systems. Because of its complicated antiferromagnetic structure, the sulfur compound seems to have particular characteristics among the mixed spinel systems.