Anisotropy of Highly Resistive Soft Magnetic Fe-Al-O Granular Films

Investigation of the uniaxial magnetic anisotropy of high-resistivity Fe-Al-O granular films prepared by sputtering showed that application of an external dc field during film deposition and post-annealing treatments had no serious effect on the magnetic anisotropy. In contrast, the incident angle of the sputtered particles to the substrate greatly affected the strength and direction of the anisotropy. These results suggest that the magnetic anisotropy is induced by shape anisotropy. However, the temperature dependence of the anisotropy constant does not obey the usual shape anisotropy relationship Ku (T)∝ Ms2 (T). We propose an anisotopic coupling model in order to explain the uniaxial anisotropy found in these granular films. This model satisfactorily explains the temperature dependence of Ku (T) and Ms (T) for all Fe-Al-O granular films prepared in the present experiment. The agreement between the experiments and the theory implies that the magnetic anisotropy of the granular films is strongly influenced by the magnetism and spatial distribution of the low-Tc intergranular phase.