Effect of sodium substitution on the structural, magnetic and magnetocaloric properties of La0.5Ca0.5MnO3 perovskite manganites

The perovskite-type La0.5Ca0.5−xNaxMnO3 (0.05≤x≤0.2) ceramic samples were prepared using the solid-state reaction at high temperature. The X-ray powder diffraction refinement by means of the Rietveld technique reveals that all our samples are single phase and crystallize in the orthorhombic structure with Pbnm space group. Lattice parameters and unit cell volume are found to increase with increasing the average A-site ionic radius 〈rA〉. The substitution of calcium by monovalent element (Na) in La0.5Ca0.5MnO3 drives the system from a charge ordering state to a ferromagnetic behaviors observed near room temperature for all our substituted compounds with a Curie temperature TC slightly decreasing from 297 K for x=0.05 to 278 K for x=0.2. Magnetic entropy change |ΔSM|, deduced from magnetization measurements versus magnetic applied field at several temperatures, shifts to higher values with increasing Na content and reaches 1.14 J/kg K and 3.1 J/kg K for La0.5Ca0.3Na0.2MnO3 under magnetic applied field of 2 T and 7 T respectively.