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We report for the first time switching and modulation of light in a magneto-optic waveguide that is a single-crystal epitaxially grown iron-garnet film. These experiments involve the Faraday rotation of the magnetic film and the motion of magnetization in the plane of the film. We have modulated light from a 1.152-μm laser up to 80 MHz. We were also able to switch light between two waveguide modes by applying a magnetic field as small as 0.2 Oe.

Diffusion kinetics and mechanisms were studied in the FexO‐MgO (vacuum), NiO‐MgO (vacuum and air), and Fe203‐MgO (air) systems. In the FexO‐MgO system, Fe entered MgO by a redox reaction; the diffusivity and activation energy depended on concentration. In the NiO‐MgO system in air the diffusivity depended on concentration and the activation energy did not; in vacuum both the diffusivity and activation energy were concentration‐independent. In the Fe2O3‐MgO system in the MgO phase the activation energy and diffusivity did not depend on concentration. Because of impurities, the diffusion results were for the extrinsic region. Formation of trivalent ions and consequent chemically created vacancies in the FexO‐MgO and NiO‐MgO (air) systems resulted in the concentration dependence of diffusivity. Concentration dependence of activation energy in the FexO‐MgO system is associated with structural changes due to a change with concentration of the Fe3+ octahedraI/Fe3+ tetrahedral ratio. In the Fe2O3‐MgO system structural changes do not occur during diffusion because this ratio remains constant.