Spin–Orbit Torque Driving Magnetization Switching with a Reduced Current Density in Perpendicular Synthetic Antiferromagnets

Manipulation of magnetization using spin–orbit torque (SOT) holds great promise for the advancement of energy-efficient and high-performance spintronic devices. Here, we report on SOT-induced perpendicular magnetization switching in a synthetic antiferromagnet composed of perpendicular CoPt layers and an in-plane Ni layer stack. In this system, antiferromagnetic interlayer exchange coupling is established between two perpendicular ferromagnetic sublayers, while the inserted Ni layer introduces structural asymmetry, allowing current to drive magnetization switching without the need for an external assistant field. Both experimental and simulated results indicate a substantial reduction in the reversal magnetic field for one of the CoPt sublayers due to competition between the perpendicular anisotropy and interlayer coupling. Consequently, a reduced critical current density of 6.25 × 10¹⁰ A/m² is achieved. Furthermore, the simulated magnetization dynamics confirm that current-induced magnetization switching can be stabilized in two antiparallel magnetization states starting from the saturation state. To facilitate the implementation of multistate output under low driving currents, we propose a feasible device architecture incorporating antiferromagnetic and ferromagnetic multilayers. This work demonstrates that the synthetic antiferromagnet is a promising scheme to minimize driving current, enable field-free magnetization switching, and perform multistate output in SOT-based devices.