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 Pr_0.6Sr_0.4MnO₃ 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 Pr_0.6Sr_0.4MnO₃ 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.