Magnetic and Magnetocaloric Properties of Monovalent Substituted La0.65M0.3M'0.05MnO3 (M=Ba, Ca and M'=Na, Ag, K) Perovskite Manganites

The effects of monovalent doping in the A-site on the structural, magnetic and magnetocaloric properties in La(0.65)M(0.3)M'(0.05)MnO(3) (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 R (3) over barc 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 M(2) versus H/M is a clear indication of a second order phase transition from ferromagnetic to paramagnetic phase. From the measured magnetization data of La(0.65)M(0.3)M'(0.05)MnO(3) (M=Ca, Ba and M'=Na, Ag, K) samples as a function of magnetic applied field, the associated magnetic entropy change, vertical bar Delta S(M)vertical bar close to their respective Curie temperature and the relative cooling power RCP have been determined. The La(0.65)M(0.3)M'(0.05)MnO(3) compound has the highest vertical bar Delta S(M)vertical bar value of 5.16 J/KgK 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 (c) 2009 Elsevier B.V. All rights reserved