Magneto-optic waveguide hysteresis loops of ‘‘planar’’ magnetic garnet films

Abstract

Epitaxial films of modified yttrium iron garnet which are used as optical waveguides for magneto-optic devices have nominally planar anisotropy so that their magnetization can be aligned by small in-plane fields. Films grown on (111) substrates usually have some residual cubic anisotropy that is difficult to measure in the active layer of the double- or triple-layer films used in single-mode waveguides. A new method to determine the magnetic properties of the optically active layer itself has been developed. It is based on magneto-optical hysteresis loops in which the Faraday rotation of the waveguided light is plotted against one component of a rotating in-plane magnetic field. Steps in these hysteresis loops are directly related to the sixfold symmetry of the magnetocrystalline anisotropy of these films. The influence of linear birefringence on the measured Faraday rotation, the magnetostrictive effects associated with the pressure of the prism used for optical coupling into the waveguide, and the advantages of end-fire coupling are discussed. These hysteresis loops are being used in the design of materials for magneto-optic isolators and other waveguide devices.