Position Error-Free Control of Magnetic Domain-Wall Devices via Spin-Orbit Torque Modulation

Abstract

Magnetic domain-wall devices such as racetrack memory and domain-wall shift registers facilitate massive data storage as hard disk drives with low power portability as flash memory devices. Here, the key issue to be addressed is how perfectly the domain-wall motion can be controlled without deformation, as it can replace the mechanical motion of hard disk drives. However, such domain-wall motion in real media is subject to the stochasticity of thermal agitation with quenched disorders, resulting in severe deformations with pinning and tilting. Herein, we propose a new concept of domain-wall control with a position error-free scheme. The primary idea involves spatial modulation of the sign of the spin-orbit torque along nanotrack devices. The domain wall is then locked at the modulation boundary by the compression forces from both sides under current injection. Unidirectional unlocking can be achieved based on the broken inversion symmetry of the modulation boundary geometry. The validity of the proposed scheme is confirmed via a micromagnetic simulation and experiments. In the experiments, devices with periodic modulation are observed to demonstrate position error-free operation over the entire observation range for microscale and nanoscale devices. Thus, the present error-free scheme provides the final missing puzzle in magnetic domain-wall device development.