Research Of The Skyrmion Dynamics On Magnetic Nanotubes

The magnetic skyrmions,a topologically protected spin texture,have been a prominent topic of condensed matter physics since the first experimental observations.Magnetic skyrmions are believed to be the promising candidate of information carriers in spintronics because of their topologically stability,nanoscale and low driving currents.However,the skyrmion Hall effect due to the nontrivial topology of skyrmions can induce a skyrmion accumulation or even annihilation at the edge of the devices,which hinders the real-world applications.Since the nanotube is edgeless in the tangential direction,the skyrmion cannot vanish at edges even in the presence of the skyrmion Hall effect.This fact motivates us to investigate the skyrmion motion on nanotubes.In this work,we theoretically investigate the current-driven skyrmion motion on magnetic nanotubes by micromagnetic simulations.Firstly,in order to see how a skyrmion can exist on magnetic nanotubes,we numerically calculate the phase diagram by tuning DMI parameters and the thickness of the namotube.When DMI is small,the stable state is a single domain.When DMI is intermediate,the stable state is an isolated skyrmion.From the inner surface to the outer surface,the skyrmion size is getting larger.From the simulations,the isolated skyrmion is tilted to the right.This is because of the extra effective DMI induced by the curvature of the tube.When DMI is larger,the stable state is a stretched skyrmion where the skyrmion is elongated like a spiral reaching the ends of the nanotube.The stretched skyrmion forms a right-handed spiral on the tube when D>0,or a left-handed spiral when D<0.Then we investigate the current-driven skyrmion dynamics in infinite long nanotubes.By perfoming micromagnetic simulations,we find that the skyrmion motion exhibits a helical trajectory on the nanotube,with its axial propagation velocity proportional to the current density,and the stable skyrmion propagation can survive in the presence of a very large current density.As a comparison,on a planar film,the trajectory of skyrmion motion bent away from the direction of the driving current due to the skyrmion Hall effect.Consequently,the skyrmion will annihilate at the edge.Finally,we investigate the thickness-dependence of skyrmion velocity on nanotubes.For different thickness,the skyrmion axial velocity is almost a constant,and shows no apparent difference in comparison with that in planar flims.However,the skyrmion angular velocity increases with the thickness,which is different from that in planar flims,where the skyrmion velocity stays unchanged when thickness increases.