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

Abstract

We demonstrate a method to dope monolayer of chemical vapor deposited (CVD) graphene with nitrogen and make it ferromagnetic. CVD graphene was first functionalised with hydroxyl groups by treating with H2O2 in the presence of UV light and then annealed in ammonia gas to dope it with nitrogen. Magnetisation measurements showed ferromagnetic hysteresis loop at low temperatures with a coercivity of 222 Oe at 2 K. We also investigated the effect of change in the angle of applied magnetic eld on 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 in-plane magnetic eld of 30 kOe. Magnetic force microscopy (MFM) also confirms introduction of magnetism in CVD graphene after doping and electron spin resonance (ESR) spectroscopy shows resonance when scanned in magnetic eld, which confirms 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.