Theoretical Research On Magnetic Skyrmion Driven By Optical Vortex

Magnetic skyrmions have attracted wide attention due to their topological stability,small size（typically 3-500 nm）,and ultralow threshold force to drive their motion.They show promise for future spintronic applications such as skyrmion racetrack memories and logic devices.On the other hand,the ability of light to carry and deliver orbital angular momentum（OAM）in the form of optical vortices has attracted a lot of interest.In this paper,we studied the dynamic of skyrmions subject to Laguerre-Gaussian optical vortices by micromagnetic simulation,and the OAM transfer effect was analyzed in detail.On this basis,combined with the shortcomings of current-driven magnetic skyrmions and the hindrance of possible defects in the materials,we proposed that the twisted light beam could be used to manipulate the magnetic skyrmions to avoid the influence of the skyrmion hall effect and act as an optical tweezer to enable us displacing skyrmions over large-scale defects in magnetic films to avoid being captured.Firstly,we studied the dynamic process of magnetic skyrmions under the Laguerre-Gaussian optical vortex and found they did periodic circular motion around the optical axis.The velocity of this motion was directly related to the OAM quantum number and the frequency of the vortex light.As for the magnetic system in the text,the speed of magnetic skyrmion could reach51.8 m s^-1 when the OAM quantum number was +5 and the frequency was 1.5 GHz.In addition,the effect of temperature on the structure of the magnetic skyrmions was also simulated.When the temperature is below 200 K,the magnetic skyrmions were intact while they were destroyed beyond this value.In order to verify the applicability of the OAM transfer mechanism,we also explored the process of Bloch skyrmions and the magnetic bubbles under optical vortex.It was found that the former could still make periodic cyclotron motion,while the latter could undergo irreversible deformation of the magnetic structure due to its lack of topological protection.Secondly,this paper also simulated that the skyrmions overflied the large-scale defect driven by optical vortex.The results show that the magnetic skyrmion could overturn the defect without being captured only in a short time 11.5 ns.Then the effect of the point defect on the motion of the magnetic skyrmions were analyzed.It was found that the point defect would not affect the motion of the skyrmons if the optical coefficient was larger than1.2×10^-4 T m^1/2,while it was less than this value,the magnetic skyrmions would annihilate.On the basis of the simulation,we proposed two ways to solve the problem of magnetic deviceization.One was to use the vortex-driven circular track to transport skyrmions.Another was to combine the current and the light field to manipulate skyrmions.Finally,we studied the motion of antiferromagnetic skyrmion driven by Laguerre-Gaussian optical vortex.The results showed that the antiferromagnetic skyrmion could move at the highest speed1400 m s^-1 in a square film with a side length 300 nm.At the same time,if the square film was replaced by a circular film,the speed could be further improved.