Edge State Induced Spintronic Properties of Graphene Nanoribbons: A Theoretical Perspective

Abstract

Low-dimensional carbon-based nanomaterials have generated enormous interest in the scientific community due to their quantum confinement induced novel electronic, magnetic, optical, thermal, mechanical, and chemical properties. The synthesis of two-dimensional graphene has provided a fertile experimental platform for studying these exotic properties and harnessing them for promising carbon-based nanoelectronic devices. This chapter reviews the edge-induced spintronic properties of nanographene ribbons (GNR) from a theoretical perspective and discusses their possible applications in nanoscale devices. The presence of edges bears a crucial impact on the low-energy spectrum of the itinerant Dirac electrons in graphene. Nanoribbons with zigzag edges (ZGNR) possess robust localized edge states near the Fermi energy that induces ferrimagnetic spin polarization along the zigzag edge. In contrast, such localized edge states are absent in nanoribbons with armchair edges (AGNR). We discuss how applying a transverse electric field to ZGNRs, or chemical modification of its edges, can break the spin degeneracy and lead to a half-metallic state which shows spin polarization of the current or the spin-filtering behavior that is very crucial for spintronic device applications. The presence of edges also endows GNRs with peculiar transport properties characterized by the absence of Anderson localization, making them ideal for ultra-low power electronics. Our review highlights the edge states’ role as the origin of GNR’s diverse physical and chemical properties. It hence has a significant bearing on the future realization of carbon nanomaterial electronics.