Graphene-adsorbed Fe, Co, and Ni trimers and tetramers: Structure, stability, and magnetic moment

Abstract

Recent work has shown that the most stable graphene-adsorbed dimers of Fe, Co, and Ni have top-atom magnetic moments larger than those of the free dimers. Here we investigate the dependence of the binding energy and the top-atom magnetic moment upon composition, cluster size, and cluster dimensionality by considering the trimer and the tetramer, that is, the smallest two-dimensional and three-dimensional clusters, respectively. We find that for trimers the highest binding energy occurs for configurations that are perpendicularly bound and have the largest charge transfer to graphene. For tetramers, the binding energy is highest for the compact configurations with the largest charge transfer to graphene. Binding is generally strongest at the hole site of the graphene lattice. The charge transfer to graphene is mainly from the base atoms, while the s-d orbital configuration of the top atom is close to that in the free cluster, indicating electronic shielding of the top atom from the graphene substrate. Thus, the binding energy of mixed trimers and tetramers to graphene is determined largely by the elemental identity of the base atoms, while the magnetic moment of the top atom depends on the elemental identity of the top atom. We show that graphene-adsorbed mixed clusters FeCo2 and FeCo3 with top Fe atom are strongly bound and have large top-atom magnetic moments, indicating the potential for magnetic storage applications. © 2011 American Physical Society.