Spin magnetism induced by chemical tuning of topology in Graphene*

Introducing vacancies into the graphene lattice causes the asymmetry in sub-lattices, resulting in spin-polarized localized states near the Dirac point. Chemical modification also tunes topology of graphene lattice due to vacancies in pi-electron network of graphene induced by covalent bonding to other elements. In this study, we have tuned the topology of honeycomb lattice by oxidizing graphene in two methods, and examined its structure and magnetism. Graphene oxide was synthesized by Hummers and Brodie methods (HGO and BGO). According to FT-IR, XPS and XRD, -OH and C-O-C groups are more likely to be introduced to HGO and BGO, respectively. HGO shows an order of magnitude larger localized spin density than that of BGO. The difference in functional groups between HGO and BGO explains the larger spin magnetism for HGO. In the case of introduction of C-O-C, oxygen atom bonds to adjacent carbon atoms, remaining symmetry in sub-lattices of graphene. In contrast, attaching -OH group occurs randomly on carbon atoms of graphene and breaks symmetry in two sub-lattices, resulting in the emergence of the localized states and the spin magnetism.