Introducing ferromagnetism and anisotropic magnetoresistance in monolayer CVD graphene by nitrogen doping

We demonstrate a method to dope monolayer chemical vapor deposited (CVD) graphene with nitrogen and make it ferromagnetic. CVD graphene was first functionalized with hydroxyl groups by treating with H₂O₂ in the presence of UV light and then annealed in ammonia gas to dope it with nitrogen. Magnetization measurements showed a ferromagnetic hysteresis loop at low temperatures with a coercivity of 222 Oe at 2 K. We also investigated the effect of a change in the angle of the applied magnetic field on the anisotropic magnetoresistance effect (AMR) in the doped CVD graphene devices. Graphene shows positive AMR for temperatures from 2 K to 50 K, negative AMR at 100 K and 150 K, and no AMR for temperatures higher than 150 K. A maximum AMR of 0.92% was observed at 2 K for an in-plane magnetic field of 30 kOe. Magnetic force microscopy also confirms the introduction of magnetism in CVD graphene after doping, and electron spin resonance spectroscopy shows resonance when scanned in a magnetic field, which confirms the presence of unpaired electrons in doped graphene. The process introduced in this paper for nitrogen doping of graphene with attendant magnetism could pave the way for the applications of graphene in spintronics and other devices.