Comparing Dynamics, Pinning and Ratchet Effects for Skyrmionium, Skyrmions, and Antiskyrmions

We compare the driven dynamics of skyrmions, antiskyrmions, and skyrmionium interacting with random disorder, circular defects, and asymmetric potentials. When interacting with a line defect at a constant drive, skyrmions and antiskyrmions show an acceleration effect for motion along the wall and a drop in velocity when they can cross the barrier. In contrast, skyrmionium travels at a reduced velocity when moving along a wall, and exhibits an increase in velocity once it can cross the barrier. For point defects, skyrmionium can be pinned for a finite fixed period of time, while for skyrmions and antiskyrmions, the Magnus force creates a deflection from the defect and an acceleration effect. For a given drive, skyrmionium moves twice as fast as skyrmions; however, skyrmionium is more susceptible to pinning effects than skyrmions and antiskyrmions. Additionally, there is a critical threshold where the skyrmionium transforms to a skyrmion that is associated with a drop in the velocity of the texture. We show that all three textures exhibit diode and ratchet effects when interacting with an asymmetric substrate, but skyrmions and antiskyrmions show a stronger ratcheting effect than skyrmionium due to the Magnus force.