Orientation dependence of the polar Kerr effect in fcc and hcp Co

Anisotropy of the energy dependent polar magneto-optical Kerr effect as a function of the angle between the magnetization and crystallographic axes is reported. The results are obtained on epitaxially oriented opaque films of hcp Co grown in two different crystallographic orientations by molecular beam epitaxy. Respective Kerr spectra of fcc Co films are found to be insensitive to the magnetization direction. This Kerr anisotropy is correlated with the presence of strong magnetocrystalline anisotropy in the hcp phase of Co. A perturbation theory treatment of the spin orbit coupline correctly predicts the order of magnitude of this new effect.