Anisotropy in Nickel-Iron Films: The Pair-Strain Model

Abstract

A systematic investigation has been made of magnetically induced uniaxial planar anisotropy in a series of 27 Ni–Fe normal incidence, vapor‐deposited films spanning the composition range 65% Ni to 100% Ni. The small experimental data scatter permits an unambiguous presentation of the compositional dependence. A series of magnetic annealing treatments was applied under various temperature and field conditions; each produced changes in the compositional dependence of anisotropy. The data can be closely fitted to a theoretical model (for the compositional dependence) based on mechanisms of magnetostrictively induced anisotropic strain and short‐range iron‐pair order. The component of anisotropy associated with strain is in good agreement with theoretical predictions for its magnitude, and is found to be characterized by the deposition substrate temperature, or (after long anneal) the anneal temperature. An activation energy of around 0.9 eV (for the films in this study) fits the annealing behavior of the strain component. The remaining anisotropy, although well represented in its compositional form by the c²(1−c)² form expected for pair order, does not respond to annealing treatment with a discrete relaxation time. Two possible explanations are considered.