Role of defect electronic states in the ferromagnetism in graphite

The mechanism of ferromagnetism in carbon-based materials, which contain only s and p electrons in contrast to traditional ferromagnets based on 3d or 4f electrons, is important but unclear. Here, by means of near-edge x-ray-absorption fine-structure (NEXAFS) and bulk magnetization measurements, we demonstrate that the origin of ferromagnetism in C-12(+) ion implanted highly oriented pyrolytic graphite (HOPG) is closely correlated with the defect electronic states near the Fermi level. The angle-dependent NEXAFS spectra imply that these defect-induced electronic states are extended on the graphite basal plane. We attribute the origin of electronic states to the vacancy defects created under C-12(+) ion implantation. The intensity of the observed ferromagnetism in HOPG is sensitive to the defect density, and the narrow implantation dosage window that produces ferromagnetism is optimized.