Positive magnetic susceptibility in graphene

Magnetic force microscopy imaging of exfoliated graphene on oxidized silicon substrates was performed. In the magnetic force domain, an attractive force was observed whenever the magnetized tip was over a graphene sample on the substrate. Were the graphene showing diamagnetism as seen in HOPG, the observed force would have been repulsive. No attractive potential was observed on the graphene-free regions. The same regions were also scanned with a non-magnetic probe to check for possible electrostatic forces. None were found. Following up on these measurements, a flake of graphene was placed on the end of a tipless AFM cantilever. Using the AFM to measure any deflections in the cantilever, a magnetic field was applied with measureable deflections observed. ICP-MS analysis of the source graphite revealed magnetic impurities on the level of 8ppm. These results will be discussed in relation to defects within the graphene.