Magneto-optic imaging of domain walls in ferrimagnetic garnet films

Magneto-optic (MO) imaging is based on Faraday rotation of a linearly polarized incident light beam illuminating a sensitive MO layer (MOL) placed in close contact to the sample. For in-plane magnetized layers of Lu3−xBixFe5−yGayO12 ferrimagnetic garnet films, zig-zag domain formation occurs whenever the sample stray parallel field component, H∥, changes sign. Considering the anisotropy, exchange and magnetostatic energies in the Néel tails, and the contribution of an applied magnetic field, it is possible to describe the zig-zag walls that separate domains with opposite in-plane magnetization. The size of the walls decreases with the spatial derivative of H∥. We studied the evolution of these domains as we steadily forced the change in sign of H∥ to shorter length scales, from hundreds to a few microns. We describe the samples used to control the change in sign of H∥ at the MOL plane, and we analyze the images that evolve from zig-zag walls to much more complex closed domain structures.