Anomalous magnetic transport in ferromagnetic graphene junctions

We investigate magnetotransport in a ferromagnetic-normal-ferromagnetic graphene junction where a gate electrode is attached to the normal segment. It is shown that the charge conductance can be maximal at an antiparallel configuration of the magnetizations. Moreover, we demonstrate that both the magnitude and the sign of the spin-transfer torque can be controlled by means of the gate voltage in the normal segment. In this way, the present system constitutes a spin-transfer torque transistor. These anomalous phenomena are attributed to the combined effect of the exchange field and the Dirac dispersion of graphene. Our prediction opens up the possibility of moving domain walls parallel or antiparallel to the current in a controllable fashion by means of a local gate voltage.

Figure 1

Schematic of the model: A graphene sheet where ferromagnetism is induced by a proximate host material. The left layer is assumed to have a soft magnetization, thus tunable in direction, whereas the magnetization of the right layer is fixed.

Figure 2

Normalized charge conductance $G_c$ as a function of $\phi$ and $V$ for $h/E_F=0.5$, 2, and 5, from left to right.

Figure 3

Normalized spin-transfer torque ${\tau }_s^y$ as a function of $\phi$ and $V$ for $h/E_F=0.5$, 2, and 5, from left to right.

Figure 4

Normalized spin-transfer torque ${\tau }_s^z$ as a function of $\phi$ and $V$ for $h/E_F=0.5$, 2, and 5, from left to right.