Magneto-optical properties of metallic bilayer thin films

Metallic bilayer thin films are discussed as a novel and encouraging approach to substantially increasing the figure of merit R^1/2-θ_K in magnetooptical data storage media with a potential gain of more than a factor of two. It is demonstrated by Kerr-rotation and reflectivity measurements in a wide photon energy range that for the metallic bilayer model system Fe₅₀ Co₅₀ on top of Au, the figure of merit R^1/2-θ_K is enhanced by up to 65% at a high level of reflectivity, which allows further enhancement by conventional dielectric layers. It is shown that Fresnel´s formulas allow a quantitative description of the observed optical and magnetooptical response over the whole energy range. These model calculations allow general conclusions regarding optimum metal combinations with respect to the maximum figure of merit. With a proper choice of the reflector metal the magnetooptical medium can be adapted to any wavelength determined by a particular application