Localized defects closely related with the magnetism of graphite induced by 12C+ ion implantation

Abstract

The magnetism of highly oriented pyrolytic graphite (HOPG) induced by 70 keV 12C+ ion implantation was investigated by using electron spin resonance (ESR) and theoretical simulations of the electronic structure of defective graphite using spin-polarized density functional theory. The results indicate that defects produced by 12C+ ion implantation can induce magnetic moments which are localized since a L1 line is observed at a fixed resonance field, independent of the angle between the field and the c axis of the HOPG sample. The angle and temperature dependence of the ESR spectra indicates that extrinsic carriers are induced in the implanted layer, and they may have an exchange interaction with local spins to produce a single asymmetric L1 line of the implanted sample. The consistent results given by the ESR spectra and the theoretical simulations of the electronic structure of defective graphite provide a clear explanation for the magnetic order in 12C+ ion-implanted HOPG. The defects produced by the implantation induce local magnetic moments in the sample. Due to the interaction between the local spins and the extrinsic carriers, the local magnetic moments may be coupled through the mediation of itinerant carriers.