Structure and magnetism in deficient La0.7−x□xSr0.3CoO3 (0 ≤ x ≤ 0.2) perovskite cobaltites

The lanthanum-deficient mixed valence cobaltites La0.7−x□xSr0.3CoO3 (0 ≤ x ≤ 0.2) have been elaborated and investigated by X-ray diffraction (XRD) and magnetic characterizations. All our samples have been synthesized by the solid state reaction method at high temperature. Redox titrations showed that all our samples are oxygen sub-stoichiometric. The oxygen sub-stoichiometry content increases with increasing lanthanum-deficient content. The charge compensation mechanism due to the lanthanum deficiency induces oxygen vacancy rather than Co3+ to Co4+ conversion. X-ray diffraction analysis using Rietveld refinement show that all our samples are single phase and crystallize in the rhombohedral structure with R3¯c space group. Lanthanum vacancy leads to a gradual decrease of the unit cell volume. Magnetic measurements show that all our deficient samples exhibit a paramagnetic to ferromagnetic transition with decreasing temperature. With increasing La-deficient amount, the Curie temperature TC increases. A discrepancy between M(T) curves performed in field-cooled (FC) and zero-field-cooled (ZFC) modes has been observed at low temperature. Our results indicate that the higher the La-deficient amount the weaker the separation and the higher the magnetization.