Engineering ferromagnetic lines in graphene by local oxidation and hydrogenation using nanoscale lithography

Graphene-based spintronics has attracted much attention owing to the weak spin-orbit interaction and long spin relaxation length in graphene. For implementation of practical and high-density graphene-based spintronic devices, we need to define nanoscale areas with room-temperature ferromagnetism on graphene. Here we report the room-temperature ferromagnetism observed in nanoscale functionalized (oxidized and hydrogenated) graphene using atomic force microscope lithography without involving potential surface contamination and chemical agents. By performing magnetic force microscope (MFM) measurements, we can clearly distinguish the local ferromagnetic signal of selectively functionalized graphene from that of surrounding non-magnetic pristine graphene. The nanoscale functionalized graphene shows experimental evidence of room-temperature ferromagnetism: (1) larger MFM signal than that of graphene; (2) repulsive and attractive interaction with an MFM tip the magnetization of which points into and out of the graphene, respectively; and (3) MFM signal reversal after applying a high magnetic field at an elevated temperature of 400 K. Our first-principles calculations reveal that unpaired spins are present at non-passivated dangling bonds of vacancies on functionalized graphene and the stable ferromagnetic exchange interactions between them are favored. Therefore, nanoscale functionalized graphene is a good candidate for use as the spin injector or detector of high-density graphene-based spintronic devices.