Spin waves in graphene nanoribbon devices

Abstract

We investigate spin excitations and electronic properties of graphene nanoribbon devices with zigzag edges. The magnetic region of the device is coupled to nonmagnetic metallic leads. The ground state of the magnetic region is described self-consistently within a mean-field scheme. The magnetic moment is site dependent, in contrast with the case of an infinite nanoribbon. Spin excitations are extracted from the transverse dynamic spin susceptibility. Several standing-wave modes can be identified. We study the behavior of these modes as the coupling between the magnetic region and the leads is varied. A central point found is that for a finite zigzag nanoribbon, spin excitations are damped at all finite energies. The signature of antiferromagnetic correlations is still present in the predominantly linear relationship between the standing-mode energy and the mode wave vector. The effect of an external doping is also considered and, as in the infinite case, it is found that ferromagnetic order along the ribbon’s edges becomes unstable at modest doping levels.