Controllable spin transport in ferromagnetic graphene junctions

We study spin transport in normal/ferromagnetic/normal graphene junctions where a gate electrode is attached to the ferromagnetic graphene. We find that, due to the exchange field of the ferromagnetic graphene, spin current through the junctions has an oscillatory behavior with respect to the chemical potential in the ferromagnetic graphene, which can be tuned by the gate voltage. In particular, we obtain a spin current reversal controllable by the gate voltage. Our prediction of high controllability of spin transport in ferromagnetic graphene junctions may contribute to the development of spintronics.

Figure 1

(Color online) Schematic of the model of a normal/ferromagnetic/normal graphene junction with corresponding Dirac cones. In the ferromagnetic graphene, different Dirac cones correspond to the different chemical potentials of majority and minority spins.

Figure 2

(Color online) Conductance as a function of $\chi$ tunable by the gate voltage, in the limit of $U\to \infty$. (a) Spin-resolved conductances where the phases of $G_{\uparrow }$ (solid line) and $G_{\downarrow }$ (dotted line) are shifted by a half period, ${\chi }_{\uparrow }-{\chi }_{\downarrow }=\pi ∕2$. (b) Spin conductance $G_s$, which oscillates with the period $\pi$ with respect to $\chi$ but is never damped.

Figure 3

(Color online) Spin conductance $G_s$ as a function of $\chi$ for several values of $k_{F}L$ with ${\chi }_{+}-{\chi }_{-}=\pi ∕2$.

Figure 4

(Color online) $G_s$ as a function of ${\chi }_H$, which is proportional to the exchange field, for several values of $k_{F}L$. Here, we choose $\chi =\pi ∕4$.