Multiplet features and magnetic properties of Fe on Cu(111): From single atoms to small clusters

Fe atoms adsorbed on Cu(111) have been used as an atomic-scale model system for performing spin-based logic operations and to build the smallest stable magnet. In pursuit of understanding the strength of the adatom/substrate hybridization in this system, small Fe clusters down to single atoms adsorbed on a Cu(111) surface were studied using X-ray Absorption Spectroscopy and X-ray Magnetic Circular Dichroism experiments. The spin and orbital moments as well as the magnetic anisotropy energies were extracted experimentally and compared with density functional theory and multiplet calculations. The results show an unexpectedly sharp atomic-like multiplet feature for single Fe atoms which disappears with increasing coverage and cluster size. This indicates a surprisingly weak hybridization of the Fe 3d states to the electronic states of the Cu(111) substrate.