B-site ordering and magnetic behaviours in Ni-doped double perovskite Sr2FeMoO6

The crystal structure and magnetic properties of polycrystalline Sr-2(Fe1-xNix)MoO6 (0.0 <= x <= 0.2) synthesized via a mechanical activation route have been investigated. Rietveld refinement of the x-ray diffraction data indicates that the long-range order parameter (S) among octahedral B sites in Sr-2(Fe1-xNix)MoO6 is significantly enhanced by an increasing level of Ni doping. The B-site ordering results in a decrease in the lattice dimensions and an increase in lattice tetragonal distortion. Consequently, magnetization of the Ni-doped Sr2FeMoO6 is progressively improved by an increasing level of Ni doping. The Curie temperature (Tc) in Sr-2(Fe1-xNix)MoO6 is also raised systematically by Ni doping, from T-c = 411 K for x = 0 to T-c = 432 K for x = 0.20. Magnetization and Curie temperature in Sr-2(Fe1-xNix)MoO6 depend almost linearly on both the level of Ni doping and B-site long-range order parameter S.