Electron paramagnetic resonance study of nanostructured graphite

We report on a systematic temperature-dependent x-band electron paramagnetic resonance (EPR) study of nanosized 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 line width 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 $\ensuremath{\approx}23\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ indicating the development of antiferromagnetic correlations as expected for the graphene lattice with a bipartite symmetry.