Spin-polarized edge and magnetoresistance in graphene flake

We examine spin-polarized edge and magnetoresistance (MR) in Fe/graphene flake (GF)/Fe junctions. For simulating various edge designs, we use the tight-binding approximation, mean-field scheme for the Hubbard model and the Landauer-Buttiker formalism. The Fe electrodes strongly affect electronic states and magnetic properties of the GF and induce magnetism in the edge atoms even in case of armchair interfaces. Also, the edge magnetic moments of the zigzag interface rotate and couple antiferromagnetically with the Fe electrodes. The conductivity of the junctions strongly depend on the relative magnetic orientation of the Fe electrodes, so, the junctions show high MR ratios. Moreover, edge geometry and localized edge state in the GF alter the MR ratios and produce large (small) variation in the MR at low (high) bias voltages. (C) 2011 Elsevier Ltd. All rights reserved.