Cu2(1-z)MnzIn2Se4 alloys; Phase diagram and effects of Mn ordering on magnetic behaviour

X-ray powder diffraction, differential thermal analysis and magnetic susceptibility measurements on polycrystalline samples were used to determine 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-Weiss theta from magnetic susceptibility data were determined for single 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 sublattice, the phase having space group 1 (4) over bar 2d. However, at lower temperatures, for 0.05 < z < 0.30, the Mn atoms order to occupy only the 4a sites resulting in probable antiferromagnetic behaviour. The high z alloys all show a random distribution of Mn on the cation sties, 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.