Dynamics of Elliptical Magnetic Skyrmion in Defective Racetrack

Recently, it has been reported that the skyrmion Hall effect can be suppressed in an elliptical skyrmion-based device. Given that defects are unavoidable in materials, it is necessary and important to investigate the dynamics of an elliptical skyrmion in a defective racetrack device. In this work, the current-driven dynamics of an elliptical skyrmion in a defective racetrack device are systematically studied using micromagnetic simulations. The system energy analysis reveals that the magnetic parameters of the circular defect play critical roles in determining the type (repulsive or attractive) and the magnitude of the force on the elliptical skyrmion. The simulated trajectories show that the primary motion modes of the elliptical skyrmion in the defective racetrack can be divided into four types, which are dependent on the values of the Dzyaloshinskii-Moriya interaction (DMI) constant D, the perpendicular magnetic anisotropy constant K, the magnitude of the driving current density J, and the size d of the defect. Further investigation of the motion-mode phases of the skyrmion reveals the synthetic effects of D, K, J, and d. Finally, the minimum depinning current density J, which linearly depends on the parameters of D and K, is obtained for a skyrmion completely pinned in the defect. Our findings give insights into the dynamics of an elliptical skyrmion in the presence of a defect with different magnetic parameters in a racetrack device and may be useful for performance enhancement of skyrmion-based racetrack memory devices.