Theory Of Skyrmion Motion Driven By Spin Wave With Orbital Angular Momentum

Wave fields with spiral phase dislocations carrying orbital angular momentum(OAM)have been realized in many branches of physics,such as for photons,sound waves,electron beams,and neutrons.However,the OAM states of magnons(spin waves)-the building block of modern magnetism-and particularly their implications have yet to be addressed.This paper studies the generation and propagation of spin waves with orbital angular momentum in the ferromagnetic nanocylinder from theoretical calculations and numerical simulations,and obtains the eigenmodes of spin waves,revealing the OAM nature of spin waves.Then we build an exchange coupled nanocylinder|nanodisk heterostructure model.Through micromagnetic simulation results,we found that the twisted magnon propagating from the cylinder to the nanodisk can make the Neel-type skyrmion in the disk do a stable circular motion.This result shows the spin wave carrying OAM(twisted magnon)can effectively manipulate topological spin defects and it predict an exotic “magnetic tweezer” effect,which paves the way for the emerging magnetic manipulations by harnessing the OAM degree of freedom of magnons.This paper mainly includes two aspects: one is to study the excitation and propagation of twisted magnons through theoretical calculations and micromagnetic simulations,and the other is to analyze and discuss the dynamics of magnetic skyrmion gyrations under twisted magnons.Then substitute them into the boundary conditions to get the boundary determinant.Through the boundary determinant and the trial frequency,we get the eigenfrequency corresponding to an arbitrary wave vector.Next,we performed simulation through the micromagnetic simulation software Mumax and used Matlab for data processing to obtain the numerically calculated spin wave dispersion relationship curve,and compared with the theoretical calculation results,we found that they were basically consistent.Then we further processed the data to obtain the spatial distribution of the different modes corresponding to the different eigenfrequency of twisted magnons,and finally explored how to excite the spin wave of the specified mode in the cylinder.In the second part of this paper,the dynamics of the magnetic skyrmion driven by the twisted magnon are studied.We first established a model of micromagnetic simulation,determined the values of various magnetic parameters,and analyzed the force of the skyrmion in the nanodisk driven by the twisted magnon through the Thiele equation.Then the software Mumax is used to perform simulation calculations.The results show that the magnetic skyrmion can be driven by the spin wave when l(28)-5 and can make a clockwise circular motion of the stable orbit.Under the spin wave of l(28)(10)5,it can make a counterclockwise circular motion of the stable orbit.Later,we also discussed the effects of the damping value,the Laguerre-Gaussian field strength of the excited vortex spin wave,the orbital angular dynamic quantum number,and the interlayer coupling coefficient on the motion of the skyrmion separately in the paper.These studies further deepen our understanding of the law of skyrmion motion driven by twisted magnons.