Controllable Domain Wall Memories with Magnetic Topological Insulator

TL;DR

This work tackles the fixed, lithography-dependent pinning of domain walls in racetrack memories by introducing MTI-based pinning sites whose strength is electrically tunable via interfacial exchange torques. By leveraging the strong spin-momentum locking at MTI surfaces, the authors model and demonstrate current-controlled pinning and depinning through Slonczewski-like torques at FM–MTI interfaces, validated with micromagnetic simulations. The proposed FM–MTI domain-wall memory offers reconfigurable pinning, higher speed, and lower shift currents than conventional in-plane memories, with potential for compact, low-power neuromorphic and non-Boolean computing using activation-function-like behavior. Overall, the approach provides a scalable path toward programmable domain-wall control and functional, sigmoid-like hardware neurons driven by spin-orbit torques at MTI interfaces.

Abstract

Domain wall memories have undergone several changes over the years for faster shift, read, and write operations; however, fundamental issues persist due to creating pinning sites topographically along the nanowire. The deformity in notches creates non-uniform pinning strength, leading to multiple faults during shift operation. This study proposes a novel approach to address these challenges and gain greater control over domain manipulation for advanced applications in Boolean and non-Boolean paradigms. Utilizing the magnetic topological insulator (MTI) can create pinning sites without potentially faulty topographical notches made through complex lithography. Moreover, applying an external current enables precise control over the pinning potentials at these sites. Micromagnetic simulations validate the effectiveness of MTI-based pinning sites, showcasing their potential for future applications. Our approach introduces an alternative method for creating pinning sites by cross-architecture of ferromagnetic nanowires and MTI nanobars, inducing exchange interaction at their intersection points. This method offers simplicity of fabrication and enables control over the pinning strength by external current.

Figures (10)

• Figure 1: Structure of the proposed device (not drawn to scale). MTI nanobars lie orthogonal on top of the nanowire to create pinning sites at the cross-section. The dashed box area represents the read/write port of the nanowire.
• Figure 2: Control signals for read, write, and shift operations.
• Figure 3: Experimental setup for pinning and depinning domain walls. All time stamp is in nanoseconds(ns). All distances are in nanometers(nm). Pictures not drawin to scales.
• Figure 4: Domain walls pinned at PMA FM-MTI crosspoints. (Left) Initial Magnetization; (Right) Final Magnetization.
• Figure 5: Domain wall pinning at the MTI-FM interface. All values are in nm. The gray area of the TI represents a vacuum.