Positional Stability of Skyrmions in a Racetrack Memory with Notched Geometry

Magnetic skyrmions are chiral spin textures with attractive features, such as ultrasmall 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 in 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, we compute the energy barriers associated with stabilizing notches along a racetrack. We vary the material parameters, specifically, the strength of the chiral Dzyaloshinskii-Moriya interactions, the notch geometry, and the thickness of the racetrack, to obtain 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 approximately 45 kBT for a racetrack of 5-nm thickness that can provide a positional lifetime of years for skyrmions for long-term memory applications, while requiring a moderate amount of current (approximately 1010 A/m2) to move the skyrmions. Furthermore, we derive quasianalytical equations to estimate the energy barrier. We also explore other pinning mechanisms, such as local variation of the 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.