The Effect of Strain on the Susceptibility of Polycrystalline Ni–Fe Films

Various ripple effects in uniaxial polycrystalline magnetic films have been related by several authors to an effective single-grain crystalline anisotropy constant K. If either an isotropic planar stress σ or a uniaxial strain ε33 is applied to such a film, the ripple properties are altered. We develop a simple model which includes the effects of such stresses and strains. We thereby evaluate K as an effective crystalline anisotropy given by K=[(K1+Bsε33+¼Bσσ)2+(7/16)(Bσσ)2],1/2where K1 is the fourth order magneto-crystalline anisotropy constant, and B8 and Bσ are appropriate magnetoelastic coupling constants. A convenient ripple parameter is (HP-HK), where HK is the uniaxial anisotropy field of the film and HP is the field in the hard direction at which the in-phase component of the transverse differential susceptibility is a maximum. Measurements of (HP-HK) vs ε33 taken on electroplated cylindrical Ni–Fe films varying in thickness from 3000 Å to a 10,000 Å are presented. While the results are qualitatively in agreement with both Hoffmann's model and Torok's model, there are quantitative discrepancies with both models, particularly Torok's. In as-plated films, (HP-HK) increased more rapidly than expected and was found to be proportional to (ε33)8/3. Several possible mechanisms are proposed to explain this results. It is shown that measurements by several authors on dispersion and susceptibility in as-prepared and annealed films can be explained qualitatively using the proposed formulation for K.