Rhombohedral-to-cubic structural phase transition in (LaBi)0.7Ba0.3MnO3 manganites: an investigation on the “Cause and Effect” and magneto caloric response

Abstract

The major objective of this study was to revisit the first reported lanthanum-based colossal magneto resistive manganite (LaBa)MnO₃ and substitute lanthanum with bismuth to steadily tune its magnetic transition temperature to different temperature regimes. The substitution was expected to result in structural, morphological and magnetic modifications owing to the Lewis acidic nature of the Bi³⁺ ion and the large diffusivity of Bi₂O₃ at high processing temperatures. Unexpectedly, a whole new spectrum of physical properties was observed after Bi³⁺ substitution in La_0.7Ba_0.3MnO₃. A substitution-induced structural transition from Rc to Pmm was manifested at around 20% of Bi substitution. Reversal to a highly symmetrical structure upon Bi substitution in La-based manganites is rare, so the reason for concentration-dependent phase change was investigated meticulously using X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. A-site cationic vacancies generated owing to Bi segregation from the lattice were found responsible for these structural transitions. The temperature-dependent magnetization study revealed Bi³⁺-assisted steady tuning of the Curie temperature from 333 K to room temperature (293 K) upon 0% to 10% substitution. The exceptional occurrence of transition temperature at 315 K, significant magnetic entropy change of 2.5 J kg⁻¹ K⁻¹ and adiabatic temperature change of ≈1.5 K at a magnetizing intensity of just 2 T in 5% Bi-substituted sample indicate its potential in magnetic refrigeration and medical applications, such as magnetic hyperthermia-based cancer therapy. This work presents a qualitative and preliminary investigation of a magnetic specimen for magnetic hyperthermia using a magnetic isotherm.