Effect of oxygen content on structural, magnetic and magnetocaloric properties of (La0.7Pr0.3)0.8Sr0.2Mn0.9Co0.1O3 ± δ

The present study reports the effect of oxygen content on the structural, magnetic and magnetocaloric properties in the (La0.7Pr0.3)(0.8)Sr0.2Mn0.9Co0.1O3 +/- delta (delta = +0.02, +0.01, -0.03) in the temperature range of 5-723 K. It has been found that the temperatures of structural phase transitions vary significantly depending on the oxygen index value, delta. In oxygen- deficient samples (delta = -0.03), two structural phase transitions are observed: O' -> O and O -> R (O' - Orbitally ordered orthorhombic phase, O - Orbitally disordered orthorhombic phase, R - Rhombohedral phase). In excess oxygen samples (delta = +0.02, +0.01), the O'-phase is not formed. The O -> R transition temperature increases with decreasing delta from T-O -> R = 353 K (delta = +0.02) to T-O -> R = 623 K (delta = -0.03). Magnetic measurements show that all our compounds exhibit a paramagnetic-ferromagnetic transition at T-C similar to 205 K. The Arrott plots reveal the occurrence of a second order phase transition. It was found that the transition temperature T-C depends on the magnitude of the applied magnetic field, which rarely happens for materials with phase transitions of the second order. It has been shown from evaluation of the Temperature averaged Entropy Change (TEC) that a wide temperature range of MCE does not satisfies the requirements of using the compounds studied as an effective magnetocaloric material for magnetic refrigeration. The substitutions in cation sublattices and oxygen non-stoichiometry have negligible effect on T-C and magnetocaloric effect (MCE). To investigate the magnetic interactions responsible for the magnetic transitions, the analysis was done by using the modified Arrott plot (MAP) method. The obtained values of the critical exponents matched well with those predicted for the isotropic short range 3D-Heisenberg model.