Doping Effect on Edge-Terminated Ferromagnetic Graphene Nanoribbons

The doping effect on intramolecular magnetic exchange coupling of an edge-terminated zigzag graphene nanoribbon (ZGNR) with organic radicals was studied with density functional theory calculation. We investigated magnetic behaviors of boron (B)- and nitrogen (N)-doped ZGNRs, terminated with trimethylenemethane (TMM) and 6-oxoverdazyl (OVER) radicals, that is, TMM-ZGNR-TMM, OVER-ZGNR-OVER, and TMM-ZGNR-OVER. A doping with B or N on the spin-coupling pathway of radical-ZGNR-radical changed the spin distribution pattern of each system and hence its magnetic ground configuration, magnetic coupling strength, and magnetic moment. The first doping switched the magnetic ground configuration of a system from antiferromagnetic (AFM) to ferromagnetic (FM) and vice versa. An additional doping switched it back to its original magnetic ground configuration. Moreover, N doping on a radical-terminated edge increased the magnetic coupling strength as compared with the undoped system, while B doping decreased it. Furthermore, B or N doping on a TMM-terminated edge increased the magnetic moment of the system, while the same doping on an OVER-terminated edge decreased it. Our results demonstrate a possibility of reversible spin control of organic magnetic materials from AFM to FM and vice versa by chemical doping and the enhancement of the magnetic coupling strength of edge-terminated ZGNRs.