XY theoritical phase diagrams of the thiospinels AB2xB′2−2xS4

Abstract Randomly diluted frustrated helimagnetic and ferromagnetic systems with spinel structure, ZnCr2xAl2−2xS4 and CdCr2xln2−2xS4, respectively, were studied in the framework of the XY model. Using the replica method, the variational principle and taking into account exchange integrals up to the fourth nearest neighbour (nn), J4 in the case of HM and up to the second (nn) J2 in the case of FM, the T vs. x magnetic phase diagrams were established. The dramatic effect of frustration is evidenced, which leads to the disappearance of long-range order and the appearance of spin-glass state for great dilution. The obtained results are in agreement with those obtained by magnetic measurements.