Current-Driven Skyrmion Motion Beyond Linear Regime: Interplay between Skyrmion Transport and Deformation

Combining micromagnetic simulation and analytical modeling, we perform an in-depth study on the correlation between current-driven transport characteristics of individual skyrmions and deformation under the influences of Dzyaloshinskii-Moriya interaction, perpendicular magnetic anisotropy, temperature, magnetic fields, and electrical currents. How the system parameters affect the configuration of skyrmions and further influence their transport characteristics (e.g., speed, Hall angle, and mobility) is revealed and dynamic ``phase diagrams'' of skyrmions are presented. Generally, the mobility of a skyrmion increases as its size increases, and the shapes and cores of skyrmions play important roles in their transport behavior. Beyond the small-driving-current regime, a remarkable deformation of skyrmions with expanding size and noncircular shape occur during transport. This leads to an increase of the driving forces and skyrmion mobility, manifesting a nonlinear feature of the skyrmion speed-current curve. Conversely, an increase of the driving forces causes a larger deformation of skyrmions and forms a positive feedback mechanism. Once the current exceeds a critical value, the driving forces are so large that skyrmions cannot maintain their topology and break down. Our work establishes the correlation between transport characteristics and deformation of skyrmions and predicts possible nonlinear and breakdown effects caused by dynamic deformation.