Field-Free Switching of a Spin-Orbit-Torque Device Through Interlayer-Coupling-Induced Domain Walls

Abstract

The spin-orbit-torque (SOT) device is a promising candidate for the next-generation magnetic random-access memory; however, the static in-plane field needed to induce deterministic switching is a main obstacle for its application in circuits. In this work, we employ the exchange coupling between the $\mathrm{Co}$/$\mathrm{Ni}$/$\mathrm{Co}$ trilayer and $\mathrm{Tb}$/$\mathrm{Co}$ multilayers in a device to form the domain wall (DW), by whose current-driven propagation the field-free magnetization switching is achieved. The SOT efficiency of the device is highly dependent on the chirality of the N\'eel-type DW. Meanwhile, the coexistence of two switching modes results in an asymmetric switching phase diagram. We find the competition between the uniform external field and the Dzyaloshinskii--Moriya interaction induces negative feedback to the pinning effect, resulting in a sharp switching process and straight DW profile. Finally, a synthetic antiferromagnetic device is investigated by experiment and micromagnetic simulation to verify the feasibility of using this proposal as the free layer of a magnetic tunneling junction.