EPR study of nano-structured graphite

We report on a systematic temperature dependent X-band electron paramagnetic resonance (EPR) study of nano-sized graphite particles prepared by ball-milling. In as-prepared samples a very intense and sharp EPR resonance at $g=2.0035$ has been measured. The EPR linewidth shows a Korringa-like linear temperature dependence arising due to the coexistence and strong exchange coupling of itinerant and localized edge states. With a prolonged aging in inert atmosphere changes in the EPR signal suggest gradual structural reconstruction where the localized edge-states dominate the EPR signal. In this case the EPR spin susceptibility shows a maximum at $\approx 23\, {\rm K}$ indicating the development of antiferromagnetic correlations as expected for the graphene lattice with a bipartite symmetry.