CHARACTERIZATION AND MAGNETIC-PROPERTIES OF R(2-X)CA(X)BANIO(5) OXIDES (R-Y AND SM)

Mixed valence compounds of general formula R(2-x)Ca(x)BaNiO(5) were sy nthesized and X-ray diffraction data revealed that they crystallize wi th orthorhombic symmetry, space group Immm, with the Ca2+ and R(3+) io ns randomly distributed in the 4j crystallographic positions of the la ttice. Systematic variation of the lattice parameters with an increase in x is observed. The magnetic properties of these doped oxides are q uite different from those reported for pure R(2)BaNiO(5) oxides. Dopin g produces a breakdown in the one-dimensional antiferromagnetic correl ations of the nickel sublattice, and the data obtained appear to indic ate the appearance of three-dimensional antiferromagnetic ordering for these doped samples at low temperatures.