▎ 摘　　要

The evolution of magnetism for graphene oxide (GO) before and after chemical reduction was investigated by means of static magnetization and electron spin resonance (ESR) spectroscopy. Strong paramagnetism with a saturation magnetization of similar to 1.2 emu/g and weak antiferromagnetic interactions were identified in pristine GO. Apart from spin-half defect centers, ESR spectroscopy indicated the excitation of high spin states, consistently with the high spin (S = 2) magnetic moments derived from the magnetization analysis, corroborating the formation of spatially "isolated" magnetic clusters in GO. A marked reduction of GO's magnetization (similar to 0.17 emu/g) along with an appreciable rise of diamagnetism ( 2.4 x 10(-6) emu/g Oe) was detected after chemical reduction by sodium borohydride, reflecting the drastic removal of paramagnetic defects and the concomitant growth of sp(2) domains in reduced graphene oxide (rGO). ESR revealed a large drop of the spin susceptibility for rGO, which, in addition to the main paramagnetic Curie component, showed an appreciable Pauli contribution. The latter together with the g-factor shift and the broadening of the ESR line indicated the coupling of localized spins with conduction electrons. The rGO ESR signal presented a metallic line shape, which could be analyzed in terms of two separate spectral components, a broad one that may be related to defect states strongly coupled with itinerant spins within the sp(2) clusters and a narrow one due to edge/vacancy defect spins, indicative of rGO's persistent structural inhomogeneity. Published by AIP Publishing.