Density-functional study on the structural and magnetic properties of N-doped graphene oxide

We have systematically investigated the structural and magnetic properties of N-doped graphene oxide by density-functional theory. Our results reveal that both the magnetic properties and the defect stability can be significantly affected by the bonding environment. Graphitic N defect has higher formation energy than both pyridinic and pyrrolic N defects. The pyrrolic N becomes more stable when its adjacent undercoordinated C atoms are bonded to functional groups. Weak spin-polarized or nonmagnetic state emerges when N defect couples to its nearest C atoms via the hybridization of π orbital. In contrast, strong spin-polarized state arises when the defect couples to its adjacent C atoms via the hybridization of σ orbital. Generally, ferromagnetic coupling occurs to those nearest coupled C atoms with dangling bonds. N defects do not incline to aggregate around the vacancies. Moderate N defects can prevent the undercoordinated C atoms from reconstruction. Nevertheless, excessive N defects bring about the undesired electron-doping, and consequently damage the ferromagnetism.