▎ 摘　　要

The electronic (quantum) transport in a NG/F-B/FG tunnel junction (where NG, F-B and FG are a normal graphene layer, a ferromagnetic barrier connected to a gate and a ferromagnetic graphene layer, respectively) is investigated. The motions of the electrons in the graphene layers are taken to be governed by the Dirac Equation. Parallel (P) and antiparallel alignment (AP) of the magnetizations in the barrier and in the ferromagnetic graphene are considered. Our work focuses on the oscillation of the electrical), of the spin conductance (G(s)) and of the tunneling magneto resistance (TMR) of this conductance (G(q)) magnetic tunnel junction. We find that, the quantum modulation due to the effect of the exchange field in F-B will be seen in the plots the conductance and of the TMR as functions of the thickness of ferromagnetic barrier (L). The period of two multiplied sinusoidal terms of the modulation are seen to be controlled by varying the gate potential and the exchange field of the F-B layer. The phenomenon, a quantum beating, is built up with two oscillating spin conductance components which have different periods of oscillation related to the splitting of Dirac's energies in the F-B region. The amplitudes of oscillations of G(q), G(s) and TMR are not seen to decrease as the thickness increases. The decaying behaviors seen in the conventional transport through an insulator do not appear. (c) 2008 Elsevier B.V. All rights reserved.