Spin-glass and reentrant spin-glass states in iron sulfospinels having dilute A and B sublattices

The magnetic and electrical properties of new compounds having spinel struc ture Fe1-xCr2(1-x)Sn2xS4 (0.1 less than or equal to x less than or equal to 0.33) (system 1), Fe-0.67 [Fe0.165CrSn0.835]S-4, and Fe-0.67 [Fe0.33Cr0.67 Sn]S-4 has been studied. These compounds are p-type semiconductors with mag netic properties characteristic of the following magnetic-order types: ferr imagnetic (the x=0.1 composition of system 1), spin glass (the x=0.33 compo sition of system 1 and Fe-0.67[Fe0.165CrSn0.835]S-4), and reentrant spin gl ass (the x=0.2 composition of system 1 and Fe-0.67[Fe0.33Cr0.67Sn]S-4). For the spin-glass compositions, the dependence of the freezing temperature T- f, defined as the temperature of the maximum of initial magnetic susceptibi lity, on temperature and magnetic field obeys the Almeida-Thouless relation , and the dependence of T-f on magnetic-field frequency is a power-law func tion. For the spin-glass and reentrant spin-glass compositions, a large pea k in the absolute value of negative isotropic magnetoresistance was found n ear T-f, which becomes as high as 15% in spin glasses and 30% in reentrant spin-glass compositions. In compositions with reentrant behavior, the activ ation energy of conductivity in the region of T-f was found to change by ab out two orders of magnitude. This experimental evidence suggests that the s pin-glass-paramagnet (in spin glasses) and spin-glass-long-range magnetic-o rder transformations are actually phase transitions, and that the spin-glas s region contains ferron-type ferromagnetic clusters. These are the first s pin-glasses among the chalcospinels with magnetically active ions on the te trahedral and octahedral sublattices. (C) 1999 American Institute of Physic s. [S1063-7834(99)01901-2].