Structure and magnetic properties of amorphous and polycrystalline Fe3O4 thin films

Half-metallic Fe3O4 films prepared by DC magnetron reactive sputtering with a tantalum(Ta) buffer layer was investigated. Primary emphasis is placed on the structural impact on its magnetic properties. The experimental results show that the amorphous Fe3O4 films exhibit a superparamagnetic response at a large-scale from 20 nm to 150 nm, and the magnetoresistance (MR) isn't detected. By contrast, the polycrystalline Fe3O4 films possess large saturation magnetization Ms of 420 A/(kg·cm) and a clear magnetoresistance with a field of 40 kA/m. The unusual properties for the amorphous Fe3O4 film are attributed to the existing large density of the similar structure as anti-phase boundaries in the film.