Induced Magnetic Anisotropy of Evaporated Films Formed in a Magnetic Field

Abstract

The origin of the induced magnetic anisotropy in evaporated films of pure iron and nickel-iron alloys formed at normal incidence in a magnetic field was investigated. The temperature dependence of the anisotropy K _u , its relations to film thickness, substrate temperature, and substrate material, and the relaxation phenomena of the anisotropy during isothermal annealings with and without a magnetic field were systematically studied. The temperature dependence of K _u is neither explained by the crystal anisotropy nor by shape anisotropy. The observed relations between K _u and film thickness etc. suggest that the stress induced in the interior of the film, rather than the stress of limited parts of the film, is responsible for the anisotropy if the anisotropy due to the atomic pair orientation is not considered. The interior stress may be caused by the structure defects formed during evaporation. The relaxation phenomena of K _u in the alternate isothermal heat treatments reveals that the anisotropy has originated partly from a directional alignment of such imperfections as vacancies, dislocations, and impurities. It is also suggested that magnetostriction may play an important role in this directional alignment.