Robust spin transfer torque in antiferromagnetic tunnel junctions

Abstract

We theoretically study the current-induced spin torque in antiferromagnetic tunnel junctions, composed of two semi-infinite antiferromagnetic layers separated by a tunnel barrier, in both clean and disordered regimes. We find that the torque enabling electrical manipulation of the N\'eel antiferromagnetic order parameter is out of plane, $\ensuremath{\sim}\mathbf{n}\ifmmode\times\else\texttimes\fi{}\mathbf{p}$, while the torque competing with the antiferromagnetic exchange is in plane, $\ensuremath{\sim}\mathbf{n}\ifmmode\times\else\texttimes\fi{}(\mathbf{p}\ifmmode\times\else\texttimes\fi{}\mathbf{n})$. Here, $\mathbf{p}$ and $\mathbf{n}$ are the N\'eel order parameter direction of the reference and free layers, respectively. Their bias dependence shows behavior similar to that in ferromagnetic tunnel junctions, the in-plane torque being mostly linear in bias, while the out-of-plane torque is quadratic. Most importantly, we find that the spin transfer torque in antiferromagnetic tunnel junctions is much more robust against disorder than that in antiferromagnetic metallic spin valves due to the tunneling nature of spin transport.