Current-Induced Dynamics of Multiple Skyrmions with Domain-Wall Pair and Skyrmion-Based Majority Gate Design

As an intriguing, ultrasmall, particle-like magnetic texture, skyrmions have attracted a lot of research interest for next-generation, ultradense, low-power magnetic memory/logic designs. Previous studies have demonstrated a single skyrmion domain-wall pair collision in a specially designed magnetic racetrack junction. We investigate the dynamics of multiple skyrmions with a domain-wall pair in a magnetic racetrack. The numerical micromagnetic simulation results indicate that the domain-wall pair could be pinned or depinned by a rectangular notch pinning site depending on both the number of skyrmions in the racetrack and the magnitude of driving current density. Such an emergent dynamical property could be used to implement a threshold-tunable step function in which the inputs are skyrmions and the threshold may be tuned by the driving current density. Threshold-tunable step functions are widely used in logic and neural network applications. We also present a three-input skyrmion-based majority logic gate design to demonstrate the potential application of such dynamic interactions of multiple skyrmions and domain-wall pairs.