Exchange-coupled Fe/Fe3O4 magnetic nanocomposite powder prepared by eutectoid decomposition of FeO

This report presents a new route to fabricating a ferrite-based magnetic nanocomposite consisting of a ferromagnetic metal (α-Fe) and a ferrimagnetic spinel ferrite (Fe3O4). The process is based on the eutectoid decomposition of FeO, leading to the formation of a lamellar nanostructure of α-Fe and Fe3O4. A sandwiched nanostructure of this type is preferable for exchange coupling between adjacent lamellae, because each lamella is subjected to exchange coupling via either side of the interface. It was found that decomposition of FeO takes place preferentially in the temperature range of 723–773 K, in which the decomposition is almost fully completed within 10 h. The room-temperature magnetization measurements gave rise to a high saturation magnetization above 100 emu/g, which is larger than that of single-phase Fe3O4. Since a smooth magnetization curve with single-phase-like behavior was observed despite the coexistence of two magnetic phases, the two phases could be magnetically exchange-coupled. Due to the ease of tuning the magnetic properties of the spinel ferrites with the substitution of constituent metal ions, the fabrication process described here could represent a potential route to making a variety of iron-based metal/ferrite magnetic nanocomposites.