Bi-doped suppression of antisite disordering and associated magnetic properties of La2?xBixMnNiO6 (x??=??0 and 1)

Here we report synthesis, structure, microstructure and magnetic properties of La2?xBixMnNiO6 (x??=??0 and 1) double perovskites. Ricciardo et al (2009 Mater. Res. Bull. 44 239) have attempted to synthesize LaBiMnNiO6 (x??=??1), but no further characterization was done due to large impurity content in the sample. We have been able to synthesize LaBiMnNiO6 phase at ambient pressure with traces of impurity at 750 C using sol-gel method. This achievement leads us to compare the structural and magnetic properties of LaBiMnNiO6 with parent phase La2MnNiO6 to highlight the effect of Bi-doping in double perovskite. In contrast to the biphasic rhombohedral (R-3c) and monoclinic (P2(1)/n) crystal structures of La2MnNiO6, LaBiMnNiO6 crystallized in single monoclinic (P2(1)/n) phase. The EDX mapping confirmed the chemical homogeneity of the samples. The electron diffraction confirms the ordered structure of the sample. The microstructure analysis from HAADF-STEM revealed random distribution of misfit dislocations in the structure. Such defects are created to relax the strain due to unusual replacement of Mn/Ni atoms by La/Bi. We observed a decrease in T-C with a large increase in magnetic moment of LaBiMnNiO6 compare to La2MnNiO6. There is also large suppression of low-temperature magnetic anomaly in Bi-substituted sample. The lowering of T-C can be rationalized to the local structural distortion associated with the stereoactive 6s(2)-lone pair electron of Bi3+. On the other hand, the increase in magnetic moment and suppression of low-temperature magnetic anomaly for LaBiMnNiO6 can be ascribed to the suppression of antisite disorder in Bi-substituted sample.