On the Conditions of the Magneto-Optical Kerr Effect Enhancement in Metallic Bilayers

The magneto-optical Kerr rotation spectra of Fe/Ag, Fe/Au, and Ni/Cu bilayers are measured and calculated based on Fresnel's equations. The theoretical spectra agree with the measured ones. A magneto-optical Kerr effect enhancement peak is observed near 600 and 500 nm for the bilayers Fe/Ag and Fe/Au, respectively, with the Fe layer thickness less than the light penetration depth. No Kerr effect enhancement occurs for Ni/Cu bilayers for any thickness of the Ni layer. It is concluded that the plasma or the absorption edge of the reflector in bilayers is neither a necessary nor a satisfactory condition but provides an important opportunity for the enhancement. Whether the enhancement occurs depends not only on the optical constants of the reflector but also on the optical and magneto-optical parameters of the top ferromagnetic layer.