Cationic ordering in Sr 2FeMoO 6 prepared by a new chemical route

Abstract

We report a novel technique to produce ultra-fine crystallites (<50 nm) of Sr 2FeMoO 6 at relatively low temperatures. Powders that were fired at 850 °C for 2 h have almost a single-phase structure. Longer annealing times improve cationic ordering and increase the saturation magnetization. Several thermal conditions were tried to get samples with different amounts of disorder. Mössbauer spectra at room temperature show broad and complex absorption lines for all samples, reflecting the effect of multiple metal neighbor environments on the magnetic field of iron ions and the different relaxation regimes caused by the chemical disorder. Spectra taken at low temperatures allowed resolving the spectra into three magnetic sextets that were assigned to Fe atoms with well-ordered first neighbors Mo environments, disordered Mo environments, and Fe ions in B′ crystallographic sites with six Fe first neighbors. The magnetization data at room temperature yielded by a SQUID magnetometer show a significant reduction of the saturation magnetic moment with decreasing annealing temperature. These results indicate that there is a correlation between the defect concentration and the magnetic properties.