Deficiency Effect on Magnetic and Magnetocaloric Properties of La_0.65−x □ _x Ca_0.35MnO₃ Manganites Synthesized Using Sol–Gel Technique

Abstract

Magnetic and magnetocaloric properties of La_0.65−x □ _x Ca_0.35MnO₃ (≤ x ≤ 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 |ΔS _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 $\vert {\Delta } S_{M}^{\text {Max}}\vert$ 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.