CU2(1-Z)MNZIN2SE4 ALLOYS - PHASE-DIAGRAM AND EFFECTS OF MN ORDERING ON MAGNETIC-BEHAVIOR

X-ray powder diffraction, differential thermal analysis and magnetic s usceptibility measurements on polycrystalline samples were used to det ermine the details of the T(z) phase diagram of the alloy system Cu-2( 1-z)Mn(z)ln(2)Se(4). At room temperature, the terminal solid solutions extend over the ranges 0 < z < 0.30 and 0.90 < 1.0. Values of Curie-W eiss theta from magnetic susceptibility data were determined for singl e phase samples in each range andused to determine the ordering of the Mn in each case. The magnetic data indicate that for 0 < z < 0.30 and T > 200 degrees C, the Mn is randomly distributed over the cation sub lattice, the phase having space group 1 (4) over bar 2d. However, at l ower temperatures, for 0.05 < z < 0.30, the Mn atoms order to occupy o nly the 4a sites resulting in probable antiferromagnetic behaviour. Th e high z alloys all show a random distribution of Mn on the cation sti es, and the compound Mnln(2)Se(4) (z = 1.0) was found to be spin-glass , with T-g = 2.7 K and theta = -94 K. (C) 1997 Elsevier Science Ltd.