Abstract
The effects of monovalent doping in the A-site on the structural, magnetic and magnetocaloric properties in La0.65M0.3M′0.05MnO3 (M=Ba, Ca and M′=Na, Ag, K) powder perovskite manganites have been investigated. Our samples have been synthesized by the conventional solid state reaction at high temperature. X-ray diffraction analysis using the Rietveld refinement show that all our shynthetized samples are single phase and crystallize in the orthorhombic structure with Pbnm space group for the samples where the A-site is occupied by Ca and monovalent element and in the rhombohedral system with R3̄c space group for the samples where the A-site is occupied by Ba and monovalent element. Magnetization measurements versus temperature in a magnetic applied field of 50 mT indicate that all our investigated samples display a paramagnetic-ferromagnetic transition with decreasing temperature. A positive slope in the isotherm plots of M2 versus H/M is a clear indication of a second order phase transition from ferromagnetic to paramagnetic phase. From the measured magnetization data of La0.65M0.3M′0.05MnO3 (M=Ca, Ba and M′=Na, Ag, K) samples as a function of magnetic applied field, the associated magnetic entropy change, |ΔSM|, close to their respective Curie temperature and the relative cooling power RCP have been determined. The La0.65Ca0.3Ag0.05MnO3 compound has the highest |ΔSM| value of 5.16 J/Kg K at 245 K upon a magnetic field change of 5 T. The RCP values are comparable and almost the same for both series (about 70% of that of pure Gd), indicating that our compounds are suitable candidates to be used in magnetic refrigeration.
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