TEM-based study of oxidation of FeCo high moment alloy at elevated temperatures

FeCo (60%-70% Fe, 30%-40% Co at.%) alloys have been used as write transducer materials due to their large saturation magnetization at room temperature (μ0M = 2.45 T). In this research, we investigate the influence of oxidation on the magnetic moment of a Fe70Co30 material at elevated temperatures in the application of heat assisted magnetic recording. We find that the moment of Fe70Co30 decreases after oxidation for all temperatures explored and that Co does not take part in the oxidation process. The moment loss is mainly due to the formation of ferrimagnetic Fe3O4 or γ-Fe2O3 as well as the change of the Fe/Co ratio in the FeCo alloy. A 2 nm Cr underlayer has been employed to change the FeCo texture from (1 1 0) to (0 0 2). This also increases the grain size of the FeCo thin film. In the case of the (0 0 2) textured sample, voids form between the FeCo film and the oxide layer, which could be the direct result of Fe cations diffusion.