Experimental and theoretical study of electron-beam-induced spin-reorientation transition reversal in the CO/Co(1 1 0) system

The spin-reorientation transition (SRT) of Co films on Cu(1 1 0) due to adsorption of CO is investigated using in situ Mott polarimetry to measure the secondary electron spin polarization (SESP). The polarization along the [0 0 1] axis is found to decrease in time as the residual gas adsorbs on the surface, while the polarization along the orthogonal axis increases. By subsequently exposing the films to an electron beam for an extended period, the CO on the surface is perturbed and the process is reversed. The SESP is consequently observed to follow the opposite evolution to that seen during the initial SRT, with the SESP reverting to 83.6 ± 1.1% of its initial value after the complete reversal. Density functional theory calculations suggest that this is due to the electron-beam dissociation of the CO, leaving behind C on the cobalt surface. Furthermore, the calculations show that the C adatom results in a reduction in the SESP signal to 81% of the clean Co(1 1 0) surface, which is in good quantitative agreement with our experimental results. The experimental SESP data are also fitted to an analytical model taking into account the interaction of the electron beam with the surface adsorbate to yield an average electronic cross-section for the process of σ = (5.8 ± 1.1) × 10-18 cm2 and a strikingly small CO coverage responsible for the effect of just 0.065 ± 0.012 ML. A series of in situ magneto-optical Kerr effect measurements were also performed across the sample to show that this reversal effect is localized and confirm the ability to pattern the magnetization by locally modifying the magnetic anisotropy of the system via an electron-beam exposure. (paper)