Adsorption and spin-related properties of multi-Co atoms assembled in the half unit cells of Si(111)-(7x7)

Multiple Co atoms were assembled in the half unit cells (HUCs) of a. Si(111)-(7x7) surface via vertical atom manipulation at room temperature. Combining scanning tunneling microscopy and first-principles calculations, we have determined the adsorption sites and spin-related properties of six Co. atoms assembled in both faulted HUCs (FHUCs) and unfaulted HUCs (UHUCs). These multi-Co. atoms do not form metal clusters, which usually have a definite adsorption configuration, because of the strong interaction between Si and Co atoms. Both the adsorption properties and magnetic moments of six. Co. atoms show strong HUC dependence. The six Co atoms in UHUC retain the adsorption sites of isolated single Co atoms, whereas the Co atoms in FHUC indirectly interact with each other via the mediation of Si atoms, leading to a deviation from the adsorption sites of single Co atoms. Around the. suggested U-eff value, the six-Co-atom. configuration in UHUC is calculated to have a large magnetic moment of 11.78 mu B, while the six-Co-atom. configuration in FHUC only has a magnetic moment of 1.02 mu B because of the anti-ferromagnetic-like coupling between the Co spins.