Critical behaviour and magnetic interactions in the diluted systems ZnxHg1−xCr2Se4 (0⩽x⩽1)

We study the magnetic properties and the critical behaviour of the B-spinel Zn x Hg 1− x Cr 2 Se 4 in the concentration range 0⩽ x ⩽1. Using the mean field theory and the probability distribution of the interactions, the exchange integrals were calculated up to second nearest neighbours. The critical region is studied by the high-temperature series expansion extrapolated with the Pade approximants method. The critical temperatures the critical exponents associated with the magnetic susceptibility ( γ ) and the correlation length ( ν ) are obtained. The values of T c and T N obtained by this method are in accordance with those predicted by magnetic measurements. The values of γ and ν are sensitive to the dilution ratio x . For the compounds situated in the long-range order (LRO) region (0⩽ x ⩽0.4 and 0.6⩽ x ⩽1), they are close to those of 3D Heisenberg model. For a concentration situated in the perturbed phase ( x =0.5), γ and ν deviate rapidly from the values predicted by this model and approach the values found in re-entrant systems.