Efficient and controlled domain wall nucleation for magnetic shift registers

TL;DR

This paper presents a novel method for efficiently nucleating and controlling domain walls in ferromagnetic strips using spin orbit torques and current pulses, enabling practical magnetic shift register devices.

Contribution

The authors introduce a simple, efficient scheme for domain wall nucleation leveraging spin orbit torques and localized fields, advancing magnetic memory device technology.

Findings

Demonstrated controlled domain wall nucleation with current pulses

Achieved high-velocity domain wall manipulation in symmetric multilayers

Enabled binary information writing in shift registers

Abstract

Ultrathin ferromagnetic strips with high perpendicular anisotropy have been proposed for the development of memory devices where the information is coded in tiny domains separated by domain walls. The design of practical devices requires creating, manipulating and detecting domain walls in ferromagnetic strips. Recent observations have shown highly efficient current-driven domain wall dynamics in multilayers lacking structural symmetry, where the walls adopt a chiral structure and can be driven at high velocities. However, putting such a device into practice requires the continuous and synchronous injection of domain walls as the first step. Here, we propose and demonstrate an efficient and simple scheme for nucleating domain walls using the symmetry of the spin orbit torques. Trains of short sub-nanosecond current pulses are injected in a double bit line to generate a localized longitudinal Oersted field in the ferromagnetic strip. Simultaneously, other current pulses are injected through the heavy metal under the ferromagnetic strip. Notably, the Slonczewski-like spin orbit torque assisted by the Oersted field allows the controlled injection of a series of domain walls, giving rise to a controlled manner for writing binary information and, consequently, to the design of a simple and efficient domain wall shift register.