Chemically selective gas-induced spin polarization changes in ultrathin fcc Co films

The influence of submonolayer quantities of O and N adsorbed on ultrathin Co/Cu(001) films as a function of Co thickness has been studied using spin polarized secondary electron spectroscopy. The gaseous adsorbate was prepared by depositing Co on (root 2x2 root 2)R45 degrees-O and c(2x2)-N reconstructed Cu(001) utilizing surfactant effects to reproducibly control quantity. Adsorbed quantities were monitored by Auger electron spectroscopy and surface reconstructions by low energy electron diffraction. The secondary electron spin polarization increases with the Co film thickness, following an exponential law, and the chemical interaction between the adsorbate and the Co reduces polarization to (98 +/- 2)% in the case of O and (84 +/- 3)% in the case of N compared to the uncovered substrate. For both, the onset of ferromagnetism is suppressed by approximately 1 ML. The effects on polarization and the onset of ferromagnetism are attributed to the partial cancellation of the magnetic moment in the Co layer adjacent to the adsorbate. The estimated reduction in moment is comparable to the results of theoretical predictions. (C) 2008 American Institute of Physics.