Band-gap tuning in magnetic graphene nanoribbons

By using non-collinear density-functional calculations, we clarified the magnetic states of zigzag-edged graphene nanoribbons (ZGNRs). In the novel non-collinear states that were found, the angle 0 between the magnetic moments at the two edges were canted, i.e., 0 < theta < 180 degrees, which was in contrast with the case of antiferromagnetic (AFM; theta = 180 degrees) and ferromagnetic (FM; theta = 0 degrees) states. As theta increased from 0 to 180 degrees, the band gap increased and the total energy decreased. As a result, the AFM state was the ground state and had the maximum band gap, whereas the FM state had the highest energy and no band gap. As a result of the development of nanotechnology, the magnetic fields with canted directions between the two edges can be applied. Therefore, we expect that the spin canting angle theta can be varied by the introduction of magnetic fields, so the band gap of ZGNRs can be controlled. It is thus suggested that ZGNRs are potential candidates for spintronics applications. (C) 2008 The Japan Society of Applied Physics.