Research On Dynamic Properties Of Skyrmion String Driven By Magnetic Field And Electric Current

Skyrmion is a topological magnetic soliton with quasiparticle properties,which has good stability and novel dynamics,and has promising applications in the fields of high density,low energy consumption,non-volatile information storage and logic operations.In recent years,some more complex three-dimensional topological magnetic structures have also attracted attention,such as skyrmion string and Hopfion.On the one hand,these new topologies exhibit more exotic physical properties;on the other hand,they can be effectively regulated as new information carriers through various means such as magnetic and electric fields.Therefore,this thesis investigates the dynamics of skyrmion strings driven by magnetic fields and currents.The main results obtained are as follows:The breathing resonance mode and the gyrotropic mode of the skyrmion string are investigated under the driving of an alternating magnetic field.The results show that for the skyrmion string driven by a perpendicular alternating magnetic field,the resonance characteristics of these two breathing resonance modes are influenced by the external static magnetic field,the length of the skyrmion string and other parameters.As the length of the skyrmion string increases,it shows multiple gyrotropic modes;the gyrotropic modes of different layers of 2D-skyrmion are mainly related to the driving frequency;at the same time,when the applied driving frequency is the same,the gyrotropic modes of different layers of 2D-skyrmion also vary,especially at the top and bottom surfaces of the skyrmion string.This is mainly due to the different topological distribution of the magnetic moments.The kinetic properties of the skyrmion string were investigated under the influence of spinpolarised currents.The results show that: the speed and trajectory of the skyrmion string can be effectively regulated by the current density and other parameters;when the skyrmion string passes through surface defects,skyrmion bobbers can be generated,and the number and speed of the skyrmion bobbers can be regulated by the driving current density.Based on this,a prototype diode device based on current-driven skyrmion string is proposed,which has the characteristics of forward transport of skyrmion string and skyrmion bobber and reverse cut-off;a logic gate unit based on current-driven skyrmion string is proposed,the function of which can be changed by varying the magnitude of the driving current,thus realising both of AND and OR gate logic functions.The research results of this thesis provide a theoretical basis and new ideas for the further design of microwave devices and logic devices based on skyrmion string.