Double exchange magnetic interaction and giant negative magnetoresistivityin the spin glass state of the new compound CuCr1.6Sb0.4S4

CuCr1.6Sb0.4S4 crystallizes in the spinel structure with the lattice parame ter a=9.9680(1) Angstrom and the anion parameter u = 0.3820(1). The very ha rd 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 indica te that the antiferromagnetic superexchange interaction dominates the long- range magnetic interactions between the magnetic moments localized on the c hromium ions. A high positive value of the paramagnetic Curie-Weiss tempera ture Theta (C-W) (equal to 318 K) testifies that the short-range interactio n is ferromagnetic and strong which means that in the corresponding microre gions the double exchange interaction is present and predominates. A sugges tion 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 cur ves. The spin-freezing temperature is lower than 50 K. CuCr1.6Sb0.4S4 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 connecte d with the energy levels generated by the crystal field. (C) 2001 Elsevier Science BN. All rights reserved.