Structural, magnetic, and electronic characterization of double perovskites BixLa2−xMnMO6 (M = Ni, Co; x = 0.25, 0.50)

A newly substituted series of perovskites, Bi_xLa_2−xMnMO₆ with M = Ni, Co and x = 0.25, 0.50, were synthesized using a citrate sol-gel technique. The crystal structure, established from neutron diffraction, is a distorted double perovskite with partial transition metal B-site ordering. These perovskites crystallize in the centrosymmetric space group, P2₁/n, with structures that are similar to the x = 0 end members. All samples are prone to non-stoichiometry involving substitution of Mn onto the Ni/Co sites, in addition to varying degrees of antisite disorder. The neutron powder diffraction and magnetization measurements reveal ferromagnetism in all samples with ordering temperatures between 220 K and 280 K. The M = Co samples have lower Curie temperatures, but higher coercivities. There is a clear link between the degree of transition metal site disorder and the saturation magnetization values. Electrical measurements demonstrate the presence of mixed ionic and electronic conductivity.