Spin-polarized Transport Of Graphene Nanoribbons Adsorbed With Zero-Dimension Graphene Nanoflakes

As an excellent base material of spin-device, graphene nanoribbons (GNRs) haveextensive applications in spintronics. In this paper, we study the spin-dependenttransport properties of GNRs adsorbed with zero-dimensional graphene nanoflakes(GFs), using Atomistix Toolkit software which is based on the first principle densityfunctional and non-equilibrium Green’s function method.(1) We study the spin-dependent transport properties of two typical edged graphenenanoribbons adsorbed with a zigzag-edged triangle graphene nanoflke (ZTGF),focusing on the effect of size and adsorbing sites. We find that the ZTGF is equivalentto an artificial magnetic molecule, causing the system to produce spin polarization.For armchair-edged graphene nanoribbons (AGNRs), adsorption causes almost100%spin polarization at a single energy level. For zigzag-edged graphene nanoribbons(ZGNRs), a ZTGF adsorbed at the center position not only results in the spinpolarization at the energy level that similar to the AGNRs’ system, but also near theenergy level of edge-states that originate from the symmetry breaking of theedge-states. When the ZTGF is adsorbed on the edge position, the effect of adsorptionis even stronger, which destroys the edge-states more severely.(2) We also study the spin-dependent transport properties of the ZGNRs with twoZTGFs adsorbed anti-symmetrically and symmetrically. Results indicate that there isno spin polarization because the effects from the two anti-symmetrical ZTGFs arecounteracted each other. For symmetrical adsorption system, there is a wide fullyspin-polarized energy range (about0.2eV). This is more important than thepolarization at a single energy level with a single ZTGF adsorption.Our results show that the adsorption of the zero-dimensional graphene nanoflakesis an effective method to control spin polarization of the system. We hope that theresults can provide a physical model and theoretical basis for the design andimplementation of high performance all-carbon-based spin devices.