Deficiency Effect on Magnetic and Magnetocaloric Properties of La0.65-x a- x Ca0.35MnO3 Manganites Synthesized Using Sol-Gel Technique

Magnetic and magnetocaloric properties of La0.65-x a- (x) Ca0.35MnO3 (a parts per thousand currency sign x a parts per thousand currency sign 0.15) perovskite manganites were investigated. Our polycrystalline samples were elaborated using sol-gel method. The Rietveld refinement shows that all our samples are single phase and crystallize in the orthorhombic structure with Pbnm space group. Lanthanum deficiency leads to a decrease of the unit cell volume. The surface morphology was carried out using scanning electron microscopy (SEM). Magnetization measurements versus temperature in a magnetic applied field of 50 mT showed that all our deficient samples exhibit a paramagnetic-ferromagnetic transition with decreasing temperature. With increasing lanthanum deficiency, the Curie temperature T (c) decreases from 275 K for x = 0 to 257 K and for x = 0.15. A large magnetic entropy change |Delta S (M) |, deduced from isothermal magnetization curves, has been observed in our samples with a peak centred around their respective transition temperature. The maximum of the magnetic entropy change under a magnetic field change of 5 T is found to decrease from 5.11 J/kg/ K for x = 0 to 3.98 J/kg K and for x = 0.15. The relative cooling power decreases from 237.5J/kg for x = 0 to 217.4 J/kg (-1) and for x = 0.15.