Double exchange magnetic interaction and giant negative magnetoresistivity in the spin glass state of the new compound CuCr 1.6Sb 0.4S 4

Abstract

CuCr 1.6Sb 0.4S 4 crystallizes in the spinel structure with the lattice parameter a=9.9680(1) Å and the anion parameter u=0.3820(1). The very hard magnetization of the sample, the shape of the magnetization isotherms as well as the lack of magnetic saturation even in a field of B=14 T indicate that the antiferromagnetic superexchange interaction dominates the long-range magnetic interactions between the magnetic moments localized on the chromium ions. A high positive value of the paramagnetic Curie–Weiss temperature Θ C–W (equal to 318 K) testifies that the short-range interaction is ferromagnetic and strong which means that in the corresponding microregions the double exchange interaction is present and predominates. A suggestion is made that these microregions behave like superparamagnetic clusters. As the result of the competition of the interactions mentioned above the sample under study reveals a spin glass state at low temperatures, which is confirmed by the temperature dependence of the magnetic susceptibility curves. The spin-freezing temperature is lower than 50 K. CuCr 1.6Sb 0.4S 4 is a semiconductor with a giant negative magnetoresistivity equal to 74% at 38 T and 3 K. The driving force of this effect is the double exchange magnetic interaction. Three values for the activation energy were observed: E 1=0.118 eV, E 2=0.004 eV and E 3=0.033 eV. These are most probably connected with the energy levels generated by the crystal field.