Enhanced magnetization in highly crystalline and atomically mixed bcc Fe-Co nanoalloys prepared by hydrogen reduction of oxide composites

Fe_xCo_100-x nanoalloys (NAs) with 20 ≤ x ≤ 80 were prepared by hydrogen reduction of Fe-Co oxide nano-composites, which were composed of mixed phases (or domains) of Fe₂O₃ and CoO. In situ X-ray diffraction (XRD) measurements using synchrotron radiation clearly showed development of a solid-solution Fe-Co phase by hydrogen reduction from the oxide composites. High-resolution transmission electron microscopy (TEM), high-angle annular dark-field scanning TEM and powder XRD revealed that Fe-Co NAs form a single crystal structure and the two elements are mixed homogeneously. The saturation magnetization depends on the size and metal composition and shows the highest value (250 emu g^-1) for the Fe ₇₀Co₃₀ NA in the size range of 30-55 nm, which is comparable to that of the Fe₇₀Co₃₀ bulk alloy (245 emu g^-1). This high magnetization is attributable to high crystallinity and homogeneous mixing of constituent atoms, which are attained by thermal treatment of oxide phases under a hydrogen atmosphere.