Magnetic superexchange and covalency parameters of ZnxCd1-xCr2Se4

The cationic substitutions effects at different concentrations, within the ZnxCd1-xCr2 Se-4 lattice (0.35 less than or equal to x less than or equal t o 0.58), on the electronic transfer in chromium's ion are investigated. For this purpose, after taking into account the exchange integrals, we use the Anderson-Kanamori theory of superexchange to determine the transfer integr als b(sigma sigma) and b(pi sigma). Using the conventional molecular orbita l model, the covalency-mixing parameters lambda (sigma) and lambda (x), the electron spin transfer coefficients f(i)(i = sigma, pi, s) and the total c harge C are evaluated. The b(sigma sigma) and b(sigma pi) variation with x, agrees with the passage of the system from ferromagnetic to antiferromagne tic order. For the compound presenting re-entrant behaviour (0.45 less than or equal to x less than or equal to 0.58), f(s) exhibits anomalies. The C increasing with x is consistent with the expected decrease in covalency of the non-magnetic cation in a tetrahedral site. (C) 2000 Elsevier Science B. V. All rights reserved.