Large Spin-Orbit Torque in a-Plane α-Fe_{2}O_{3}/Pt Bilayers.

Realization of efficient spin-orbit torque switching of the Néel vector in insulating antiferromagnets is a challenge, often complicated by spurious effects. Quantifying the spin-orbit torques in antiferromagnet or heavy metal heterostructures is an important first step toward this goal. Here, we employ magneto-optic techniques to study dampinglike spin-orbit torque (DL-SOT) in a-plane α-Fe_{2}O_{3} (hematite) with a Pt spin-orbit overlayer. We find that the DL-SOT efficiency is 2 orders of magnitude larger than reported in c- and r-plane hematite/Pt using harmonic Hall techniques. The large magnitude of DL-SOT is supported by direct imaging of current-induced motion of antiferromagnetic domains that happens at moderate current densities. Our study introduces a new method for quantifying spin-orbit torque in antiferromagnets with a small canted moment and identifies a-plane α-Fe_{2}O_{3} as a promising candidate to realize efficient SOT switching.