▎ 摘　　要

Magnetism of graphene can be created by atomic defects, either hydrogen adsorption or single-carbon vacancy formation, owing to the unpaired pi electrons around the defects. Here we explore, based on rigorous first principles calculations, the possibility of voltage manipulation of two such types of pi magnetism in graphene via a scanning tunneling microscope tip. We find a remarkably different behavior. For the hydrogen, the magnetic moment can be switched on and off with voltage-induced doping, whereas, for the carbon vacancy, the spin splitting of the pi bands persists, almost independent of the extent of doping, due to the coupling between the pi and the sigma bonds. Furthermore, the local atomic structures near the vacancy can be reversibly manipulated by a coordination mechanism between an intermediate tip-defect distance and a moderate tip voltage, consequently leading to the reversal of spin polarization of the pi bands. Voltage control of the local magnetic states may open a new avenue for potential applications in spintronics.