Abstract
The effect of CO adsorption on the magnetic easy axis of Co/Pd(111) magnetic thin films has been studied by C 1s x-ray photoelectron spectroscopy (XPS) and Co L-edge x-ray magnetic circular dichroism (XMCD) in absorption spectroscopy. We found by the XMCD measurements that the CO adsorption at 200 K induces the spin reorientation transition of a 4–6 monolayer (ML) Co thin film, but it does not cause spin reorientation at 300 K. Simultaneous XPS measurement showed that the C 1s spectrum has a single peak at 285.8 eV at 300 K, while it has an additional shoulder at 285.3 eV at 200K. The main peak is associated with the CO atop adsorption, and the shoulder might be ascribed either to bridge or hollow site adsorption. Temperature and CO coverage dependences of XMCD and C 1s XPS spectra reveal that the bridge or hollow site CO adsorption is responsible for the spin reorientation of the Co thin film. This is the first direct observation to correlate the magnetic anisotropy of a magnetic thin film with the molecular adsorption site.
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