Ultrathin Co films on flat and vicinal Cu(111) surfaces: per atom determination of orbital and spin moments

We have performed x-ray magnetic circular dichroism, x-ray resonant magnetic scattering and scanning tunnelling microscopy measurements on ultrathin Co films deposited on flat and vicinal Cu(111). The range of film thickness varies between one and 25 monolayers. For the vicinal Cu(111), Co deposition below one monolayer leads to the formation of elongated islands preferentially oriented along the step edges. These islands extend over lateral length scales of up to several thousand ångströms. For the thicker films we still observe that the vicinal surface leads to the occurrence of a preferential uniaxial growth direction. No such preferential growth direction can be identified for the flat surface. In correlation to the Co growth we observe an increase of both the orbital and the spin moment per Co atom on vicinal Cu(111) of about 25% versus what was observed for Co on flat Cu(111). This enhancement is observed in both the x-ray absorption and the reflectivity measurements. Similar to what was earlier reported for Co on Cu(100) we also observe for the case Co on Cu(111) an increase in the ratio m_l /m_s (orbital to spin moments) of 40% for thin Co films. In contrast to what has been reported for Co films on flat and vicinal Cu(100) we do not observe any major variations in the occupancy of the Co 3d states for Co grown on the vicinal Cu(111) surface.