Ferromagnetic spin-valves and tunneling junctions are among the most fundamental and important spintronics devices. Their functionality is based on two effects: the giant or tunneling magnetoresistance for electrical readout and the spin-transfer torque allowing for electrical switching. It has been predicted that the same functionality could be achieved with antiferromagnetic junctions, which would provide various advantages over ferromagnets, such as a much faster switching speed. However, these devices are very sensitive to disorder and have never been experimentally demonstrated [1].

 

Here we show that the key to obtaining robust spin-transfer torque and magnetoresistance in antiferromagnets is utilizing lower symmetry antiferromagnets, in which electrical current is spin-polarized [2]. We consider junctions composed of non-collinear antiferromagnets and find a spin-transfer torque and magnetoresistance with a magnitude and robustness against disorder comparable to ferromagnetic junctions [3]. Furthermore, our calculations reveal novel aspects of the torque in non-collinear junctions. In particular, we find that apart from the conventional spin-transfer torque, a novel self-generated torque appears. This torque is similar to a spin-orbit torque but has a non-relativistic origin. We also find that a torque appears for any configuration of the junction, in contrast to ferromagnetic junctions where the torque vanishes in the parallel or antiparallel configurations.

 

[1] J. Železný et al., Nature Physics 14, 220–228 (2018)

[2] J. Železný et al., Phys. Rev. Lett. 119, 187204 (2017)

[3] S. Ghosh et al., arXiv:2109.01399 (2021)