Current-driven skyrmion expulsion from magnetic nanostrips

We study the current-driven skyrmion expulsion from magnetic nanostrips using micromagnetic simulations and analytic calculations. We explore the threshold current density for the skyrmion expulsion, and show that this threshold is determined by the critical boundary force as well as the spin-torque parameters. Using a simple model describing the skyrmion and locally-tilted edge magnetization, we reveal the underlying physics of the dependence of the critical boundary force on the magnetic parameters. This work provides a fundamental understanding of the skyrmion expulsion and the interaction between the skymion and boundaries of devices.