Magnetic properties and percolation threshold in diluted B-spinel ZnCr2xAl2-2xS4: a study through high-temperature expansions

By making use of high-temperature series expansions (HTSE) of the correlati on functions, we study the thermal and disorder variation of the short-rang e order (SRO) in the particular B-spinel ZnCr2xAl2-2xS4. We developed the H TSE for the g-dependent static structure factor S(q) to the order 6 in reci procal temperature including both the nearest- and next-nearest-neighbour i nteractions J(1) and J(2), respectively. Respecting the experimental fact t hat the broad diffuse peak of the neutron is situated at the particular wav e vector q(0) = [0 0 0.79] and is insensitive to the temperature for a give n ratio of dilution x, we have estimated the thermal variation of J(1) and J(2) in the case of the pure compound. The bond percolation threshold x(p) of the ZnCr2xAl2-2xS4 is determined by studying the disorder variation of the correlation length xi. The x(p) is c onsidered as the concentration at which xi vanishes. The obtained values ar e x(p) = 0.27 when only J(1) is considered and 0.23 when both J(1) and J(2) are taken into account. (C) 1999 Elsevier Science B.V. All rights reserved .