Effects of thermal treatment on structure and magnetic properties of nonstoichiometric perovskite‐type oxides La_0.67Sr_0.15□_0.18MnO_3‐δ

Abstract The structural and magnetic properties of La_0.67Sr_0.15□_0.18MnO_3‐δ manganites obtained with various thermal treatment conditions have been studied. X‐ray diffraction studies show that all the samples crystallize with the rhombohedral symmetry and the space group is R‐3c. No change in structural symmetry is found for all samples with thermal treatment. However, the bond angles of MnOMn and O1MnO2 deviate from 180 and 90 °, respectively, indicating the presence of Jahn–Teller type distortion in the MnO₆ octahedron. And the oxygen content shows determinant affect on compound magnetic properties. With increasing oxygen content induced by thermal treatments, the Curie temperatures T_C increases systematically from ∼280 to ∼303 K, showing the dependence of sample magnetic properties on sintering processes. A maximum value of |ΔS_M(T, H)| is measured to be more than 5 J/kg · K near the curie temperature, indicating the potential of utilizing the strong magnetocaloric effect of these materials in magnetic refrigeration.