Positional stability of skyrmions in a racetrack memory with notched geometry

TL;DR

This study uses micromagnetic simulations to analyze the stability of skyrmions in racetrack memory with notched geometries, identifying optimal conditions for long-term stability and efficient movement.

Contribution

It introduces a detailed analysis of energy barriers for skyrmion stability in notched racetrack geometries, providing design guidelines for reliable skyrmion-based memory.

Findings

Energy barriers up to ~45 kBT for 5 nm thick racetracks.

Notched geometry offers the highest energy barrier among tested pinning mechanisms.

Skyrmions can be reliably stored and moved with moderate current densities.

Abstract

Magnetic skyrmions are chiral spin textures with attractive features, such as ultra-small size, solitonic nature, and easy mobility with small electrical currents that make them promising as information-carrying bits in low-power high-density memory, and logic applications. However, it is essential to guarantee the positional stability of skyrmions for reliable information extraction. Using micromagnetic simulations for the minimum energy path (MEP), we compute the energy barriers associated with stabilizing notches along a racetrack. We vary material parameters, specifically, the strength of the chiral Dzyaloshinskii-Moriya interactions (DMI), the notch geometry, and the thickness of the racetrack to get the optimal barrier height. We find that the reduction of skyrmion size as it squeezes past the notch gives rise to the energy barrier. We find a range of energy barriers up to ~ 45 kBT for a racetrack of 5 nm thickness that can provide years long positional lifetime of skyrmions for long-term memory applications while requiring a moderate amount of current (~ 10^10 A/m2) to move the skyrmions. Furthermore, we derive quasi-analytical equations to estimate the energy barrier. We also explore other pinning mechanisms, such as a local variation of material parameters in a region, and find that notched geometry provides the highest energy barrier. Our results open up possibilities to design practical skyrmion-based racetrack geometries for spintronics applications.