Modification of the secondary-electron spin polarization in Co/Cu(110) films via gaseous adsorbates

The effect of O and N adsorbates on the magnetic properties of ultrathin Co/Cu(110) films was investigated in situ by measuring the spin polarization of secondary electrons emitted from the surface using Mott polarimetry. The data have been fitted to a function to take into account the exponential attenuation of the signal through the layers above, yielding a room temperature paramagnetic-ferromagnetic transition thickness of d(c) = 3.5 +/- 1.0 monolayers (ML). This evolution was compared to the equivalent evolution for cobalt films grown on O- and N-saturated surfaces. In the case of nitrogen, the onset of ferromagnetism occurs at a thickness of 4.9 +/- 0.5 ML and the saturation polarization is reduced to 65% of the value for the bare cobalt film, implying a dramatic quenching of the magnetic moment in the uppermost layer of the films. For films grown on the oxygen surface, a change in growth mode from three-dimensional to layer-by-layer growth dominates the behavior and this leads to a decrease in d(c) to 2.3 +/- 0.3 ML and a 38% increase in the saturation polarization value.