Structural and Magnetocaloric Properties of Classical Rare-Earth Manganite Ceramics

Abstract

Structure, microstructure, chemical and phase composition, as well as magnetic state and magnetocaloric effect of the $\text{La}_{0.9}\text{Mn}_{1.1}\mathrm{O}_{3}$ manganite have been investigated by X-ray diffraction, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and magnetic methods. The $\text{La}_{0.9}\text{Mn}_{1.1}\mathrm{O}_{3}$ ceramics have been synthesized using a two-step solid-state reaction method at an annealing temperature of $1150^{\circ}\mathrm{C}$ (22 h). Based on the X-ray diffraction results, a crystal structure of the $\text{La}_{0.9}\text{Mn}_{1.1}\mathrm{O}_{3}$ ceramic has a rhombohedral $R-3c$ (No. 167) type of symmetry. Chemical and phase composition of the $\text{La}_{0.9}\text{Mn}_{1.1}\mathrm{O}_{3}$ sample has been confirmed by energy-dispersive X-ray spectroscopy. The average grain size has been determined by means of Nano Measure 1.2.5 software and is 1.6 $\mu \mathrm{m}$. Based on the magnetic data, $\text{La}_{0.9}\text{Mn}_{1.1}\mathrm{O}_{3}$ ceramic displays a ferromagnetic to paramagnetic phase transition at the Curie temperature $T_{\mathrm{C}}=227\mathrm{K}$ with a high magnetic entropy change $\Delta S_{\mathrm{M}}{}^{\max}=-3.50\mathrm{J}/(\text{kg}\cdot \mathrm{K})$ at the field of 2 T. Moreover, the magnetic parameters in the paramagnetic state have been defined using the Curie- Weiss law.