Anisotropy of 'Planar' Magnetic Garnet Films by Magneto-Optic Waveguide Hysteresis Loops

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 vertical axis is given by the Faraday rotation of the waveguided light, and a rotating in- plane field is used. The influence of linear birefringence on the measured Faraday rotation and magnetostrictive effects associated with the pressure of the prism used for optical coupling into the waveguide are discussed. Properties of Bi-substituted YIG films with a range of saturation magnetizations, and their effects on magneto-optic isolators and other waveguide devices are presented.