Novel Spin Torques in Antiferromagnetic FeRh*

Magnetic order can reduce the symmetry of the underlying crystal lattice, allowing for the generation of spin torques with novel symmetries. By controlling the magnetic ordering of the material, it is therefore possible to control the orientations of the torque and generate torques that are better suited to applications such as switching perpendicularly magnetized nanomagnets and driving dynamics in spin torque oscillators for neurotrophic tasks. Antiferromagnets are better suited to this task than ferromagnets, as they can be prepared into a magnetically ordered state that is robust against external influence. However, spin torques with new symmetries have not yet been observed in collinear antiferromagnetic materials. We report large, highly temperature-dependent unconventional spin torques generated in collinear antiferromagnetic FeRh, and further show the effects of the magnetic ordering direction on spin torque geometries using FeRh. These experimental observations are supported by theoretical calculations of spin torques from FeRh.