Electronic transport through a graphene-based ferromagnetic/normal/ferromagnetic junction

Electronic transport in a graphene-based ferromagnetic/normal/ferromagnetic junction is investigated by means of Landauer-B\"{u}ttiker formulism and the nonequilibrium Green's function technique. For the zigzag edge case, the results show that the conductance is always larger than $e^{2}/h$ for the parallel configuration of lead magnetizations, but for the antiparallel configuration the conductance becomes zero because of the band-selective rule. So a magnetoresistance (MR) plateau emerges with the value 100% when the Fermi energy is located around the Dirac point. Besides, choosing narrower graphene ribbons can obtain the wider 100% MR plateaus and the length change of the central graphene region does not affect the 100% MR plateaus. Although the disorder will reduce the MR plateau, the plateau value can be still kept about 50% even in a large disorder strength case. In addition, when the magnetizations of the left and right leads have a relative angle, the conductance changes as a cosine function of the angle. What is more, for the armchair edge case, the MR is usually small. So, it is more favorable to fabricate the graphene-based spin valve device by using the zigzag edge graphene ribbon.