Abstract
The influence of A-site Bi substitution on B-site cation ordering, crystal structure, and magnetic properties of La_(2-x)Bi_xNiMnO_6 double perovskites has been studied. Compounds with and without Bi substitution adopt monoclinic crystal structure with the P2_1/n space group as determined from the Rietveld refinement of x-ray diffraction data. X-ray photoelectron spectroscopy indicated an increase in Mn~(4+)/Mn~(3+) and Ni~(2+)/Ni~(3+) ratios in Bi substituted sample, and hence emphasized improved Ni and Mn ordering. This has been well supported by bond length analysis which suggested a compression in < Mn-O > and elongation in < Ni-O > bond lengths. The Bi substituted compound showed a relatively larger moment as compared to the parent sample, which was attributed to the suppression of antisite disorder i.e., enhanced Ni-Mn cation ordering due to Bi substitution. The temperature-dependent dc magnetization studies reveal a ferromagnetic to paramagnetic phase transition, and the Curie temperature has been observed to increases with Bi substitution. The critical exponent analysis around phase transition also confirmed the increase in the critical temperature for the Bi substituted compound. A detailed analysis of the critical behavior has been performed using different models, which suggested a long-range ferromagnetic ordering for both pure and Bi substituted samples.
NSTL
Elsevier