Control of exchange bias using spin-orbit torque through an antiferromagnetic insulator*

Enabling electrical control of antiferromagnetic (AFM) properties is one of the key requirements for the development of novel spintronic technologies. We present a device concept in which the spin configuration of an AFM insulator (FeF₂) can be modified taking advantage of the spin-orbit-coupling existing in heavy metals (HM), such as W or Pt. We consider a trilayer, HM|AFM|FM, where the top ferromagnetic (FM) layer is used to monitor the changes in the AFM spin configuration. We performed magneto-optical Kerr effect measurements to probe the FM hysteresis loops as a function of temperature (T) and applied current (I). We found that the exchange bias (EB) and coercivity (H_c) produced at the top AFM|FM interface can be strongly modified by the I passing at bottom HM layer. We attribute this effect to an active spin-orbit torque generated at the HM|AFM interface. that reaches the AFM|FM top interface modifying amplitude and sign of EB. We found a critical current beyond which the effect on the EB and H_c is irreversible. Temperature-dependent control experiments using normal metals (NM) such as Au in NM|AFM|FM and without AFM in HM|FM confirmed that the effect is produced by the SOT induced by the HM and is not caused by thermal heating, Oersted field or other potentially spurious effects.