Tuning the Spin-Orbit Torque Efficiency via Exchange Bias Direction Modification in Pt/IrMn/Py Trilayers

Spin transport, as the core of spintronics, provides an alternative to electron charge transport used in conventional electronics. Recent studies have demonstrated that spin transport through antiferromagnetic (AFM) insulators would be affected by the relative orientation of the spin polarization (s) and the Néel vector (n). However, there has been limited research on this transport regime in metallic AFMs. Here, we experimentally investigated the relative direction between s and n in relation to spin transport in the Pt/IrMn/Py trilayer. Due to the exchange bias coupling at the AFM/ferromagnetic interface, n can be aligned along the direction of the annealing (or cooling) field. Spin-torque ferromagnetic resonance (ST-FMR) and magnetization switching measurements were performed at different directions of the cooling field. The results show that the value of spin-orbit torque (SOT) efficiency and critical switching current density depends on the relative orientation between s and n. Our results indicate that controlling n of the metallic AFM can be an effective method for modulating SOT efficiency in AFM-based spintronic devices.