Unconventional Spin-Transfer Torque in Noncollinear Antiferromagnetic Junctions

Ferromagnetic spin valves and tunneling junctions are crucial for spintronics applications and are one of the most fundamental spintronics devices. Motivated by the potential unique advantages of antiferromagnets for spintronics, we theoretically study junctions built out of noncollinear antiferromagnets that exhibit a spin-polarized current. We demonstrate a large and robust magnetoresistance and spin-transfer torque. This is in contrast to simple antiferromagnets in which these effects can also exist but are very sensitive to disorder. We show that the spin-transfer torque is capable of ultrafast switching between parallel and antiparallel states of the junction, analogously to the ferromagnetic junctions. However, we also demonstrate a novel behavior stemming from the non-collinear magnetic order. In particular, we find that, unlike in the ferromagnetic junctions, the spin-transfer torque is present even in the parallel or anti-parallel states of the junction and that a new type of self-generated torque appears in the noncollinear junctions. In addition to the junctions, we discuss the self-generated torque in non-collinear bulk systems.