Ab-initio calculation of C and CO adsorption on the Co (110) surface

Abstract

The adsorption energies, structural, electrical and magnetic properties of adsorption of C and CO on the fcc Co (110) surface have been investigated using density functional theory. The preferential adsorption site for the fcc Co (110) has been calculated. For the case of C adsorption, the preferential adsorption site is the long-bridge for both the 0.5 and 1.0 monolayers (ML) coverages. Whilst for the CO case, the preferential adsorption sites are at the atop and short-bridge site for 0.5 and 1.0 ML coverages respectively. Structurally, the first two layers of the bare Co (110) surface expand whereas the second and third layers contract. Upon adsorption of either C or CO, however, the degree of expansion and compression reduces. Magnetically, the adsorbates were found to couple ferrimagnetically to the surface and suppress the magnetic moment of the Co layers beneath them. The C adsorbate has a much stronger suppression effect as compared to the CO adsorbate. At 0.5 ML coverage, the C adatom suppresses up to 47% of the magnetic moment in the surface layer compared to a clean Co (110), whereas the CO adsorbate only suppresses up to 16%. For the 1.0 ML coverage case, both the C and CO adsorbates suppress almost equivalently well at 68% and 63% respectively. We also report on a correlation between the amount of charge transfer and the degree of suppression of the surface magnetic moment. Finally, we observe that the electronic charge is shared in the [001] direction for the C adsorbate and in the [11¯0] direction for the CO adsorbate. This anisotropy of surface bonding, in conjunction with the ligand field theory, explains the mechanism behind the spin reorientation transition that occurs uniquely on the CO/Co(110) system.