Thermomagnetic Correlation in La_0.85-xBi_xNa_0.15MnO₃ Soft Ferromagnet due to Nonmagnetic Bi³⁺ Substitution

We report the structural, magnetic, and magnetocaloric properties of Bismuth (Bi)-substituted manganite La_0.85-xBi_xNa_0.15MnO₃ (x=0, 0.1, 0.2, 0.25, and 0.3). X-ray diffraction data implicates the rhombohedral structure with R3 ¯ c space group. Bi₂O₃ has helped in ensuring phase pure, densified compounds even at low sintering temperature and hence avoiding the evaporation of volatile sodium. The increase in grain size and decrease in magnetic transition temperature (T_C) are due to the Bi chemical activity and electronic structure. The samples have shown indirect magnetic transformation from soft ferromagnet to canted ferromagnet/antiferromagnet with Bi. Griffiths phase-like behavior in the inverse magnetic susceptibility was observed for x=0.1; with further increase in Bi, the samples are found to develop the antiferromagnetic competing phase. The phenomenological model was used to model the thermomagnetic behavior of all the samples. The sample with x=0.1 shows an increase in magnetic entropy change upon Bi substitution and the maximum of magnetic entropy change is seen at 275K emphasizing its potential in room temperature magnetic refrigeration.