Effect of cubic, tilted uniaxial, and orthorhombic anisotropies on homogeneous nucleation in a garnet bubble film

Abstract

We have studied domain nucleation phenomena in a (111)‐oriented garnet bubble film in the presence of in‐plane fields. From visual observations we have found that as the in‐plane field is lowered from saturation, a homogeneous stripe nucleation occurs at a critical easy axis bias field $H_{\parallel }^n$ , leading to a ``mixed polarity state'' at remanence. For bias fields different from $H_{\parallel }^n$ , inhomogeneous bubble nucleation occurs which is dependent on the defect distribution in the sample and which can give rise to a bubble lattice at remanence. The bias field $H_{\parallel }^n$ depends on the azimuthal angle φ of the in‐plane field in the sample plane; it has threefold (cos3φ) and onefold (cosφ) symmetry components which can be related to cubic and tilted uniaxial anisotropy, respectively. The tilt of the uniaxial anisotropy is found to be along the same direction as, but significantly larger than, the actual tilt of the crystallographic axis, perhaps indicating a large sensitivity of growth anisotropy to misalignment. An orthorhombic anisotropy component is observed in the in‐plane nucleation field. These results are compared to the results of photometric measurements of the type previously proposed by Shumate, Smith, and Hagedorn, and by Krumme, Hansen, and Haberkamp. A phase theory, modified to include finite‐thickness effects phenomenologically, is developed to determine the conditions for second‐order (stripe) nucleation in the presence of cubic, tilted uniaxial, and orthorhombic anisotropy. Analytical expressions are found for $H_{\parallel }^n$ which can be used to evaluate the anisotropies from the data. The results are consistent with independent measurements of these anisotropies on the same specimen.