The permalloy problem and anisotropy in nickeliron magnetic films

Flux-field methods have been developed for the separate measurement of the uniaxial anisotropy field H U and the mean domain anisotropy field H A of magnetic films. H U = H A represents the ideal uniaxial case but many films have H A > H U . If H U is experimentally reduced to zero the residual domain anisotropy is randomly oriented; its most probable origin is crystal anisotropy. The occurrence of good uniaxial properties with a low value of H U , as found near 83% nickel-iron, is a consequence of a minimum value of H A at that composition. The composition dependence of H A and the low value of H A at 83% nickel represent a new aspect of the permalloy problem. It is proposed that the magnetocrystalline anisotropy is reduced by crystal oriented magnetoelastic energy arising from isotropic stress and anisotropic magnetostriction. Near 83% nickel these two anisotropy terms are mutually opposed and give minimum net anisotropy at a composition which depends on the stress. The lower the crystal energy the more perfect is the alignment of magnetization caused by magnetic interactions. This alignment further reduces the effective local anisotropy until in the limiting case of perfect alignment H A = H U .