Light Scattering Investigations of Magnetic Anisotropies in Ultrathin Epitaxial Co Films

Using Brillouin light scattering, the properties of magnetic anisotropies in ultrathin epitaxial Co films grown on single-crystal Cu substrates are investigated. All relevant magnetic anisotropy contributions are determined, in situ in an ultrahigh vacuum system for the (001)-oriented films, as well as ex situ for other film orientations, which are covered with a Cu cap layer. For (001)-oriented films we find a large in-plane anisotropy contribution of fourfold symmetry. For this contribution the volume and the surface part cancel to zero at the same thickness as found for the onset of ferromagnetic order. This finding is indicative for a stabilization of ferromagnetic order in Co/Cu(001) by in-plane anisotropy contributions. In (1 1 13)-oriented films, which are composed of (001)-terraces aligned along the [11̅0]-direction and spaced by 6.5 atomic distances, an additional uniaxial in-plane anisotropy contribution is found which is identified as being of magneto-elastic origin. For (110)-oriented films three ranges of thickness dependence of the in-plane and out-of-plane anisotropy contributions are found which correlate in the thin-film regime with the growth properties. (111)-oriented films show a linear dependence of the perpendicular anisotropy on the reciprocal film thickness over the full investigated thickness range of 2 to 20 Å.