sp-Electron magnetic clusters with a large spin in graphene.

Motivated by recent experimental data (Sepioni, M.; et al. Phys. Rev. Lett. 2010, 105, 207-205), we have studied the possibility of forming magnetic clusters with spin S > (1)/(2) on graphene by adsorption of hydrogen atoms or hydroxyl groups. Migration of hydrogen atoms and hydroxyl groups on the surface of graphene during the delamination of HOPG led to the formation of seven atom or seven OH-group clusters with S = (5)/(2) that were of a special interest. The coincidence of symmetry of the clusters with the graphene lattice strengthens the stability of the cluster. For (OH)(7) clusters that were situated greater than 3 nm from one another, the reconstruction barrier to a nonmagnetic configuration was approximately 0.4 eV, whereas for H(7) clusters, there was no barrier and the high-spin state was unstable. Stability of the high-spin clusters increased if they were formed on top of ripples. Exchange interactions between the clusters were studied and we have shown that the ferromagnetic state is improbable. The role of the chemical composition of the solvent used for the delamination of graphite is discussed.