Structural and electromagnetic properties driven by oxygen vacancy in Sr₂FeMoO_6−δ double perovskite

Nonstoichiometric Sr₂FeMoO_6−δ (δ = 0.132 and 0.296) double perovskite compounds have been synthesized by solid-state reaction. Effect of oxygen vacancy on its structural, magnetic and transport properties has been investigated by X-ray diffraction, magnetic and electronic transport measurements. Despite of different oxygen vacancy, both two compounds are of single phase and belong to the same space group, I4/m. Structural refinement shows that oxygen vacancy lowers the degree of ordering on B site and increases the lattice constant. Further structural analysis finds that owing to the oxygen vacancy, Fe atom is compressed, while the Mo atom changes from being compressed to being elongated. As predicted by the theoretical calculation, besides anti-site defects, oxygen vacancy is another important source for the lower Curie temperature of nonstoichiometric Sr₂FeMoO_6−δ. Meanwhile, the hopping integration of electron between Fe–O–Mo–O–Fe is reduced by oxygen vacancy, thus the resistivity and the semiconducting-metallic transition temperature of Sr₂FeMoO_6−δ are enhanced. However, the saturation magnetization (M_S) of Sr₂FeMoO_6−δ at 5 K can be repeated well based on the ferrimagnetization model, suggesting that the anti-site defect is responsible for the reduction of M_S, which is different from the literature results. - Graphical abstract: Magnetization curves of Sr₂FeMoO_6−δ compounds at 5 K. - Highlights: • Structural distortion is introduced to Sr₂FeMoO_6−δ due to the occurrence of Oxygen vacancy. • Magnetic interaction and electron-transfer ability between Fe–O–Mo–O–Fe are reduced by oxygen vacancy. • Anti-site defect contributes to the reduced saturation magnetization of Sr₂FeMoO_6−δ