Magneto-optical anisotropy study of ${\mathrm{Fe}}_n/{\mathrm{Au}}_n$ superlattices

Extended experimental and theoretical study of the observed large magneto-optical anisotropy (MOA) is presented for a series of ${\mathrm{Fe}}_n/{\mathrm{Au}}_n$ superlattices prepared by molecular beam epitaxy with $n=1,2,3\mathrm{}$ of Fe and Au atomic planes of (001) orientation. The anisotropy of the off-diagonal component of the optical conductivity tensor with respect to the change of the magnetization direction is determined in the photon energy range 0.8–5.8 eV from the measurements of the magneto-optical polar and longitudinal saturated complex Kerr angles and the optical data measured by the spectroscopic ellipsometry. The magnitude of the observed anisotropy, decreasing with the increase of n, and its energy dependence are well reproduced by the band structure calculations performed within the local spin-density approximation to the density functional theory. The results of the calculations show that the microscopic origin of the large MOA is the interplay of the strong spin-orbit coupling on Au sites and the large exchange splitting on Fe sites via Au d-Fe d hybridization of the electronic states at the interfaces. The high sensitivity of the MOA to the interface structure is studied by ab initio modeling of the effects of substitutional disorder and the roughness at the interfaces. It is shown that a good agreement with the experiment is obtained when the interface roughness effect is taken into account. The orientation anisotropy of the d orbital moment is calculated from the first principles and analyzed on the basis of d orbital symmetry consideration. The relationship between the orbital moment anisotropy and the MOA is discussed.