Low-energy μSR and SQUID evidence of magnetism in highly oriented pyrolytic graphite

Low-energy muon spin rotation and SQUID magnetization measurements were performed on proton-irradiated and non-irradiated highly oriented pyrolytic graphite samples. The samples were found to be ferromagnetic above and below room temperature and to include a substantial temperature-dependent surface contribution. Assuming uniformity, the thickness of the magnetic surface layer was estimated to be 13(2) nm. The discovered surface magnetism is intrinsic and not due to irradiation. (C) 2009 Elsevier B.V. All rights reserved.