Spin Orbit Torque Switching Mediated by Antiferromagnetic Insulators*

Spin transport and magnetic dynamics in antiferromagnetic (AF) insulators have attracted wide research interests recently. In contrary to the popular belief of AF being an inactive element for spin transport, recent experiments based on spin pumping, nonlocal spin transport and spin Seebeck effect suggest efficient spin current transmission can be realized in various antiferromagnetic systems, via the mediation of antiferromagnetic magnons. In this work, we show initial experimental evidences towards this direction, where by utilizing the current induced spin orbit torque in Pt layer, we achieved magnetic switching in Co_xTb_1-x free layer across a thin AF insulator NiO. In the ultrathin spacer thickness regime (1~2nm), we even observed an enhancement of the spin orbital torque efficiency compared with the Pt/Co_xTb_1-x bilayer film. The realization of magnetic switching in Pt/NiO/Co_xTb_1-x heterostructures provides an existence proof on AF insulator mediated spin orbit torque, enabling promising material platform and device structures for energy favorable spin manipulation.