Giant Coulomb blockade magnetoresistance in magnetic tunnel junctions with a granular layer

Abstract

We investigate spin-dependent electron transport through a zigzag graphene nanoribbon sample with two ferromagnetic strips deposit on two sides of the graphene ribbon. Our results show that, for the antiparallel configurations of ferromagnetic strips, the conductance exhibits zero conductance plateau when the Fermi energy locates around the Dirac point and the sample shows the properties of a semiconductor. But for the parallel configurations, the energy band spectrum is metallic and the conductance is always equal to or larger than e(2)/h. Thus the huge giant magnetoresistance effect can be achieved by altering the configurations of the ferromagnetic strips. Moreover, we study the spin-dependent conductance for the parallel configuration. It is found that the device shows half-metal behavior, in which it acts as a conductor to carriers of one spin orientation but as an insulator to those of the opposite spin orientation. So the present device can be applied as a spin filter. In addition, we study the consequence of the short-range Anderson disorder and find that the spin filtering effect and magnetoresistance effect still remain even in the strong disorder limit.