Interface Effects on Magneto-Optic Kerr and Reflectivity Spectra in Ultrathin Fe/Au and Fe/Ag Systems

Abstract

Molecular beam epitaxy grown Au/Fe (t)/Au, Au/Fe/Au (t)/Fe/Au and Ag/Fe (t)/Ag sandwiches on MgO (001) substrates were investigated by means of classical and magneto-optic (MO) Kerr ellipsometry and relative reflectance spectroscopy at photon energies between 1.5 and 6 eV. The layer thickness t varied between 1.0 and 2.5nm for Au spacer and between 0.8 and 1.8nm for Fe. The MO polar and longitudinal Kerr effect spectra in Ag/Fe (t)/Ag can be explained using a single off-diagonal permittivity tensor element. This is not the case in Au/Fe (t)/Au, Au/Fe/Au (t)/Fe/Au. Deviations of the longitudinal spectra from the model indicate the anisotropy in the permittivity tensor and are assigned to an Fe-Au interface layer of reduced symmetry. The interface effect, observed between 3 and 4.2 eV, is best resolved in Au/Fe/Au (t)/Fe/Au, but can also be seen on Au/Fe (t)/Au. The relative reflectance spectra in Au/Fe/Au (t)/Fe/Au with an Au reference reflector show a narrowing of the Au peak centered at the photon energy of 3.5 eV. It is proposed that the narrowing is induced by adjacent Fe layer with in-plane magnetization.