Magnetoelastic Effects in Thin Ferromagnetic Films

Abstract

A method is described for the evaporation of ferromagnetic films onto a very thin water soluble polymer coating on glass substrates and their subsequent removal onto a liquid glycerin film. Determination of the change in magnetic anisotropy on removal provides a measure of the substrate constraint contribution to the anisotropy energy. Data are given for both Ni-Fe and Ni-Co alloys in the entire range 0 to 100% Ni, deposited at 100°C. Significant changes in anisotropy upon removal were observed for almost all Ni-Fe alloys and for Ni-Co alloys in the range 0 to 40% Co. However, essentially a zero percentage change was observed for pure Fe, 83% No-Fe and the entire range 0 to 60% Ni in the Ni-Co alloys. These date are in disagreement with present theories of the constraint energy except for qualitative agreement in very limited composition ranges. It has been suggested that the discrepancy between experimental and theoretical prediction for the anisotropy energy in thin films may result from the use of bulk material magnetoelastic constants which are inappropriate for thin films. However, this study of the magnetic properties of epitaxial films strongly suggests the equivalence of the magnetoelastic parameters in thin films and bulk materials. In this study a technique was developed for the preparation of step-free epitaxial films of Ni-Fe and Ni-Co alloys deposited at 400°C. The strain sensitivity ΔHk/Ɛ has been measured by ferromagnetic resonance along the [100] and [110] directions in the (001) plane for compositions ranging from 44 to 87% Ni in the Ni-Fe alloys and from 70 to 82% Ni in the Ni-Co alloys. The data are in good agreement with the theoretical predictions 3(C11-C12)λ100/M and 6C44λ111/M along the [100] and [110] directions respectively, evaluated using bulk parameters. In addition, the strain sensitivity of polycrystalline films deposited at 100°C and 400°C for Ni-Fe alloys and 400°C for Ni-Co alloys has been measured. Contrary to previous investigations, a systematic temperature dependence is found. Moreover, it is shown that the isotropic material model used previously by others to calculate the strain sensitivity in polycrystalline films is incorrect. However, the apparent proper formulation does not predict experimentally determined result. This discrepancy remains unexplained. New data for the crystalline anisotropy constant K1 in constrained epitaxial films of Ni-Fe and Ni-Co are presented. Significant deviations from values in bulk material are observed. However, these deviations are believed to result from the substrate constraint and not material differences inherent in thin films.