Unusual spin-orbit torque switching in perpendicular synthetic antiferromagnets with strong interlayer exchange coupling.

Synthetic antiferromagnet (SAF) is an outstanding system for controlling magnetic coupling via tuning the layer thickness and material composition. Here, we control the interlayer exchange coupling (IEC) in a perpendicularly magnetized SAF Pt/Co/Ir/CoFeB/MgO multilayer, which is tuned by varying the nonmagnetic layer Ir thickness and the magnetic layer Co thickness. And we study the spin-orbit torque (SOT) driven magnetization switching of the SAF. In the SAF with a weak IEC, the SOT-driven switching behavior is similar to that of a single ferromagnet system, which is dominated by the external magnetic field. In contrast, in the SAF with an ultra-strong IEC, the saturation magnetic field is large than 50 kOe, and the SOT-driven switching behavior is decided by the effective magnetic field. The effective field is correlated to the external magnetic field, the IEC field, magnetic moments of CoFeB and Co, and magnetic anisotropy. These results may advance the understanding of SOT switching of perpendicular SAFs and promote the applications of SAFs with low stray fields and lower power in spintronic devices.