Dependence of Angular Dispersion on Grain Size in Evaporated Permalloy Films

Abstract

Permalloy films of nearly zero magnetostriction composition were evaporated in groups corresponding to two different thickness ranges. The mean grain size D was made to vary from 150 to 550 Å corresponding to different substrate temperatures. Angular dispersion α₅₀ was found to increase with increasing grain size; but the product of dispersion and anisotropy field, α₅₀ H_k, was found to be nearly independent of grain size from about 200 to 550 Å. No dependence on film thickness t was observed. From ripple theory Hoffmann has predicted that α₅₀ should be proportional to σ²D³/tH_k, where σ is an average of the randomly varying torque resulting from the anisotropy energy in each grain. While the experimental results agree with the predicted dependence on H_k, the lack of dependence of α₅₀ H_k on D and t requires modifications to the ripple theory. Possible modifications are discussed.