CU-2((1-Z))MNZGA2SE4 ALLOYS - PHASE-DIAGRAM AND EFFECTS OF MN ORDERING ON MAGNETIC-BEHAVIOR

X-ray powder diffraction, differential thermal analysis, and magnetic susceptibility measurements on polycrystalline samples are used to det ermine the details of the T(z) phase diagram of the alloy system Cu-2( 1-z)MnzGa2Se4. At high temperatures, there is a single phase solid sol ution across the complete diagram in a disordered zincblende phase. Ho wever, at lower temperatures, the single-phase range is limited to rel atively wide terminal fields, which are ordered structures based on a zincblende subcell. Several different ordered phases are found to occu r and the values of the Curie-Weiss constant a are used to investigate the changes in ordering with composition. It is shown that these orde ring changes cause discontinuous changes in the slope of the graphs ag ainst composition of the lattice parameters, optical energy gap, and N eel temperature values.