Surface effects and structural dependence of magneto-optical spectra: Ultrathin Co films and CoPt_n alloys and multilayers

First-principles calculations of the optical conductivities and magneto-optical Kerr effects for bulk and thin films of Co and for CoPt_n alloys (n = 1 and 3) and multilayer (n = 3) are carried out using the full potential linearized augmented plane wave method with the local spin density approximation. For fcc bulk Co, we obtain a negligible dependence of the polar Kerr rotation on the direction of magnetization. By contrast, the calculated Kerr spectra of CoPt_n are found to be very sensitive to structural changes. For Co(001) and Co(111) ultrathin films, the surface effects cause a redshift for the high-energy peaks in the magneto-optic Kerr effect (MOKE) spectra, mainly due to band narrowing. Except for the free standing Co(001) monolayer, the profile of their MOKE spectra, however, is very close to that of bulk Co.