Unveiling a Bulk Antiferromagnetic Order via the Polarity of Spin-Orbit Torque Ratchet at Ferromagnet/Antiferromagnet Interface

Resolving the bulk order in an antiferromagnet (AFM) is technically difficult because of the absence of net magnetization in nature. Exchange-coupling, an AFM with a ferromagnet (FM) serves as an alternative approach to study the order of AFM via the exchange bias effect, however, it has been considered only revealing the order at the FM/AFM interface. This study reports an approach to unveil the bulk order of an AFM via the ratchet effect in an FM (Co)/AFM (IrMn)-based SOT device, which is associated with a hidden effect behind the exchange bias. It has been shown the ratchet polarity could be determined only when the exchange bias was completely facilitated, in which an analog (digital) switching was observed while the SOT switching was driven to be against (following) the direction of exchange bias. Although the exchange bias can be reversibly switched accompanying with SOT, but the built-in asymmetry via the ratchet polarity may reveal the hidden bulk order of IrMn. Finally, the plasticity on the SOT switching was observed with a tailorable threshold and the remarkable sensitivity in response to the various pulse-current modules. It suggests the Co/IrMn-based SOT device may be an ideal hardware system to be applied to the artificial neuron network for the advanced memory applications.