Nonstoichiometry, point defects, and magnetoresistance of Sr2FeMoO6−δ

Abstract

The phase stability, nonstoichiometry, point defects, and magnetoresistance (MR) of polycrystalline Sr2FeMoO6−δ (SFMO) were studied. Thermogravimety at 1200 °C in combination with x-ray diffraction shows that single-phase SFMO exists between −10.2≤log pO2≤−13.7 at 1200 °C. At lower oxygen partial pressure mass loss signals reductive decomposition; at higher pO2 a mass gain indicates oxidative decomposition into SrMoO4 and SrFeO3−x. The nonstoichiometry δ at 1200 °C was measured as function of pO2 and oxygen vacancies were found to represent majority defects. The vacancy concentration increases with decreasing pO2; a maximum nonstoichiometry of δ=0.086 is observed close to the lower phase boundary. Samples with different δ were prepared at 1200 °C and various pO2. The variation of structural parameters, magnetization, and MR is discussed in relation to oxygen nonstoichiometry δ. Maximum MR=6.5% at 298 K and 1 T is observed for samples with large δ.