Causes of the Inhomogeneity in the Magnitude of the Anisotropy Field in Thin Nickel—Iron Films

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Abstract
The inhomogeneity in the magnitude of the anisotropy field of vacuum‐deposited nickel—iron films has been determined, from the data of Oredson and Torok, and from new data presented here, as a function of film composition. From this data, the contributions from the magnetocrystalline anisotropy of the randomly oriented crystallites, and from local uniaxial strains has been determined for various substrate temperatures and sources. For example, for evaporation from a ring source onto a substrate at 300°C, (δHb)2=(2.87×10−10)η2+ (1.25×10−8) K12+0.133. The constant term is attributed to shape anisotropy due to film‐surface roughness and to the edge of the film and to variations in the magnitude of the anisotropy field due to temperature variations across the film during deposition. The contribution due to magnetocrystalline anisotropy and that due to magnetostriction plus local strain are roughly equal. Hoffmann recently proposed a theory which gives the size of a domain, and shows that the effect of the randomly oriented crystallite anisotropies can be characterized by an effective anisotropy constant Keff=N−½K1 where N is the number of crystallites in a domain. Extending this theory, a similar relationship is found for the effective uniaxial strain due to the random strains. From this, a theoretical curve of δHb vs composition is obtained which is a fairly good fit to the data.