Evidence for non-cubic magnetostriction in epitaxial bubble garnets

Abstract

Epitaxial bubble garnet films grown on non-magnetic garnet substrates exhibit a dominant growth or stress induced uniaxial anisotropy, which is responsible for the stripe and bubble domain structures, and the intrinsic cubic magnetocrystalline anisotropy which can affect bubble device performance. The anisotropy constants have been deduced from measurements of stripe domain nucleation in the garnet films. We extend this measurement technique and its interpretation so that it also yields values of the magnetoelastic interactions. The measurement is based on observing the details of the topography of the nucleating domain structure, specifically the orientation of the nucleating stripe domains as a function of the orientation and magnitude of the applied magnetic field. The interpretation is based on a micromagnetic analysis of the conditions for homogeneous second order stripe domain nucleation. The contributions to the phenomena of the cubic anisotropy and of the magnetostriction are included in the analysis as perturbations. The theory produces predictions which are compatible with qualitative earlier experiments reported in the literature. It provides a satisfactory quantitative account of systematic new observations we have made on a GdTmY bubble garnet film with the specific objective of measuring magnetostriction. Analysis of the experimental data yields strong evidence for a non-cubic component of the magnetostriction possibly associated with the same growth-kinetic mechanism that gives rise to the non-cubic anisotropy. The sign and magnitude of the macroscopic non-cubic magnetoelastic constant is estimated from the experimental results.