Structural and magnetic properties in the nonstoichiometric perovskite-type oxides La0.67Sr0.15□0.18MnO3−δ

In this presented work, we report the influence of thermal treatment conditions on the structural and magnetic properties for the A-site deficiency La_0.67Sr_0.15□_0.18MnO_3-δ (nonstoichiometric), which is prepared by the sol-gel method. The purpose of appropriate amount of A-site deficiency is expected to adjust Tc near room temperature. X-ray diffraction studies show that all the samples crystallized in a single phase with the rhombohedral symmetry and the space group is R 3 c. No change in structural symmetry is found for all samples with thermal treatments. That the bond angles of Mn-O-Mn and O1-Mn-O2 deviate from 180° and 90°, respectively, indicates the presence of Jahn-Teller distortion in MnO₆ octahedron. With increasing the oxygen content by thermal treatments, the Curie temperatures Tc increases systematically from -280K to approximately 303K, indicating that the magnetic properties of the samples are closely related with sintering processes. The maximal values of \\ΔS_M(T, H) are measured to be more than 5 J/kg-K near the curie temperature, which indicates that these samples have large enough magnetocaloric effect to be used in magnetic refrigeration.