Influence of Bi³⁺ substitution on the structural and magnetic properties of Pr0.6Sr0.4MnO3 ceramics

We report the structural and magnetic phase transition induced in Pr0.6Sr0.4MnO3 as Pr3+ ions are replaced by Bi3+. Analysis of Rietveld refinement of the X-ray diffraction data reveals a change in crystal symmetry from orthorhombic, space group Pnma for x <= 0.20 to Imma for x > 0.50. Across intermediate Bi3+ substitution (0.25 <= x <= 0.40), a structural phase coexistence of Pnma and Imma symmetry is found. Based on the combined studies of electrical and magnetic properties, a magnetic phase diagram for Bi substituted Pr0.6Sr0.4MnO3 samples is proposed here. The electrical resistivity and magnetization studies for partial Bi3+ substituted samples x <= 0.10 indicate samples to be ferromagnetic metallic with T-C = 310 K and 290 K for x = 0.0 and 0.10 respectively. As Bi3+ concentration increases, T-C decreases, and the system transforms to be antiferromagnetic insulating with T-N = 158 K for x = 0.60 accompanied by a spin glass like state below 10 K. For samples with intermediate Bi3+ concentrations i.e., 0.25 <= x <= 0.40, field induced metamagnetic magnetization loops (M vs. H) imply the competitive coexistence of ferromagnetic and antiferromagnetic interactions in the same matrix. Also, the open loops in field dependent resistance curves (MR vs. H) for 0.20 <= x <= 0.40, specify the field induced transition from insulating to metallic state. The magnetoresistance improves on increasing Bi3+, with MR% reaching a maximum of 100% for 0.20 <= x <= 0.30 samples.