Abstract
Strontium ferromolybdate (Sr2FeMoO6–δ , SFMO) is a material exhibiting promising magnetoresistive properties. We have synthesized SFMO samples out of simple oxides (SrCO3, Fe2O3, and MoO3 or partially reduced SrFeO3–x (SFO) and SrMoO4–y (SMO) precursors. The samples have been experimentally investigated using X-ray diffraction, temperature-dependent magnetization, Mössbauer effect and ferromagnetic resonance measurements. Samples of the first type contain a high density of defects, especially [FeMo], [MoFe] antisites, and do not exhibit any superstructural ordering of the iron and molybdenum ions (P = 0%). These samples comprise iron cations in a mixed valence state, Fe2+ / 3+, and are characterized by a higher magnetic inhomogeneity than those synthesized out of precursors. The use of the latter increases the sample density and brings about a growth acceleration, synthesis temperature reduction, as well as the appearance of a superstructural ordering of the Fe3+ and Mo5+ cations with P = 64%. The samples exhibit magnetic anisotropy and consist of nanosize grains. Zero-field-cooling measurements of the temperature dependences of the magnetization reveal a sudden leap of the magnetization at low temperatures (below 23 K) that witnesses the existence of magnetic regions with a low coercivity, in which a superparamagnetic state exists. The obtained results are important for the optimization of the synthesis technology of SFMO for device applications.
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