Tailored magnetic transitions and magnetocaloric properties towards room temperature in La0.67-xBixSr0.33MnO3 (x=0.05-0.25) manganites

Abstract

A series of Bi-doped manganites, i.e, La0.67-xBixSr0.33MnO3 (x = 0.05, 0.1, 0.15, 0.2, 0.25), were synthesized using the conventional solid-state method. X-ray diffraction analysis confirmed a mixed-phase structure, with La0.67-xBixSr0.33MnO3 in rhombohedral (R-3c) and Mn3O4 in tetragonal (I41/amd) phases coexisting and the fraction of the tetragonal phase is increasing with increase in the Bi content. Scanning Electron Microscopy revealed surface homogeneity with polygonal morphology. X-ray Photoelectron Spectroscopy confirmed the mixed oxidation states of Mn, showing a systematic decrease in the Mn3+/Mn4+ ratio with increase in Bi content. Magnetic measurements using a Vibrating Sample Magnetometer demonstrated a decline in the Curie temperature with increase in Bi substitution, linked to lattice distortions and weakening of Mn3+-O-Mn4+ ferromagnetic interactions. The magnetocaloric properties were determined from both isothermal magnetization studies and direct measurement of adiabatic change studies. The study provides insights into the effect of Bi in La0.67Sr0.33MnO3 on transition temperatures and magnetocaloric properties, highlighting its potential impacts on magnetic refrigeration applications towards room temperatures.