Unexpected Spin-Glass Behavior of the Mixed Sulfide-Selenide Chalcogenides TlCr_5S_(8-y)Se_y (y = 1-7) Mediated by the Nonmagnetic Sublattice

摘要

Spin0glass behavior in the series TlCr_5S_(8-y)Se_y is mediated by the nonmagnetic anionic sublattice. The magnetic susceptibilities of compounds with 1 <- y <- 8 follow a Curie-Weiss law in the high temperature region above 300 K. As the Se content increases, the magnitude of the Weiss constant #theta# drastically decreases from about - 499(3) K for TlCr_5S_7Se to - 180(3) K for TlCr_5Se_8. Substitution of S by Se leads to structural alterations and stronger ferromagnetic exchange interactions according to the well-established Goodenough-Kanamori rules. In the low-temperature region, zero field cooled and field cooled susceptibility curves split below a characteristic freezing temperature T_f, which increases with rising Se content from 23 to 46 K for TlCr_5SeS_7 to TlCr_5Se_7S, respectively. Using an Ising spin model, the magnetic frustration and the observed spin-glass behavior can be explained by considering different ferromagnetic and antiferromagnetic exchange paths. Neutron diffraction patterns at 5 K show no long-range magnetic order. Analyses of broad humps of magnetic scattering in the diffraction patterns in terms of real space distribution functions show that the antiferromagnetic exchange becomes weaker at the expense of increasing ferromagnetic correlations between 120 and 5 K. Nonlinear changes of #theta#, T_f, and the effective magnetic moment per Cr(III) across the TlCr_5S_(8-y)Se_y series, but linear dependencies of T_f and #theta# on composition within the two regions 1 <- y <- 4 and 4 <- y <- 7 in the low and high temperature regimes, respectively, indicate that a critical Cr-Cr interatomic distance is reached at y #approx =#4.