Switching of Exchange-Coupled Perpendicularly Magnetized Layers Under Spin-Orbit Torque

We proposed a multilayer structure to reduce the critical spin current density of perpendicularly magnetized layers switched by spin-orbit torque (SOT) from the spin Hall effect. In the structure, we introduced exchange-coupled perpendicularly magnetized layers composed of soft and hard magnetic layers in lieu of a single magnetic layer. The switching loops and dynamic processes under periodic spin currents have been studied by micromagnetic simulation. We have found that the critical spin current density can be substantially reduced when the saturation magnetization of the soft layer is sufficiently low. Moreover, the critical spin current density is quite insensitive to the change of exchange interaction between the two magnetic layers, which enables the multilayer structure to tolerate the variation of material composition or structure imperfections during fabrication. The introduction of exchange-coupled layers provides a way to design and optimize the SOT-driven devices and paves the path for their applications.