Antiferromagnetic Switching in Mn$_2$Au Using a Novel Laser Induced Optical Torque on Ultrafast Timescales

Abstract: Efficient manipulation of the N\'eel vector in antiferromagnets can be induced by generation of spin orbit (SOT) or spin-transfer (STT) torques. Here we predict another possibility for antiferromagnetic domain switching by using a non-zero staggered field induced from optical laser excitation. We present results on the atomistic scale dynamic simulations from the application of a novel laser induced torque using optical frequencies for all-optical switching (AOS) of the N\'eel vector in the antiferromagnet Mn$_2$Au. The driving mechanism takes advantage of the sizeable 'exchange enhancement' characteristic of antiferromagnets, allowing for small picosecond 90 and 180 degree precessional switching with laser fluences on the order of mJ/cm$^2$. The symmetry of these novel torques are highly dependent on the time-varying magnetisation direction, creating a sign change in the torque which greatly minimises the "over-shooting problem" common to SOT and STT. Lastly, we demonstrate the opportunity for this laser optical torque to deterministically switch single magnetic domains.