Unzipping and Making Graphitic Ferromagnets: Ab Initio Study

We study the origins of high-temperature ferromagnetic behavior in graphite by means of unbiased ab-initio calculations and compare them with our data. The experimental results show that oxygen/sulfur-induced edges of graphitic fragments (via unzipping effect) play an essential role in this phenomenon, and that the finite magnetic moment appears if edges in a graphitic ribbon are occupied asymmetrically by either oxygen or sulphur. In particular, our ab-initio calculations performed within the local spin density approximation showed that in the case of pure graphene ribbon, its zig-zag edge carbon atoms carry large magnetic moment (~0.7 $\mu_{B}$/C). In an oxidized graphene, however, the magnetic moment at the edge with absorbed oxygen atoms gets considerably reduced, leading to effective ferromagnetic (more precisely, ferri-magnetic) behavior of the sample. The estimates show that the Curie temperature may be very high owing to peculiar band structure of the edge states. The results suggest ways of controlling magnetic behavior of graphitic systems at room temperature.