It has been found that the oxidation process in heat treatment of Fe-Co double-layer films is different depending upon whether the film is Fe/Co or Co/Fe type. The relations between the magnetic properties and microscopic structures of the oxides of the films have been studied by X-ray diffraction, AES and VSM.
Both types of films had perpendicular magnetic anisotropy. When the Fe/Co film was heat treated the upper Fe layer was oxidized, and the oxide grains grown perpendicularly to the substrate are considered to cause the anisotropy. In the case of the Co/Fe film, the Fe layer which had a greater affinity for oxygen than Co, diffused to the surface and was preferentially oxidized. The anisotropy can be attributed to weakening of magnetic interaction between grains by the oxides formed at the Co grain boundaries.