Dynamics Of Magnetic Skyrmion In Nanostripe

Magnetic skyrmion is a type of topologically protected spin texture.Due to its special topological structure,it can be stabilized in small size and motivated by an ultra-low current density.Since the magnetic skyrmion found at B20-type Mn Si by S.Mühlbauer et.al.in 2009,this spin structure has appealed extensive and long-lasting attention all over the world.Based on the magnetic skyrmion,researchers designed many new spintronic devices,such as skyrmion racetrack memory,logical devices,artificial neural,spin-transfer nano-oscillators,etc.Among all these devices,the skyrmion racetrack memory is the absolute key research topic as modern society is always in hunger for advanced storage technology.In this thesis,we explored the dynamics of magnetic skyrmion in the nano-stripe by micromagnetic simulations,and then put forward some new thoughts and optimization methods.Presently,there exist two problems in the magnetic racetrack memory —skyrmion Hall effect and the low velocity of skyrmion motion.The skyrmion Hall effect means that the skyrmion will deviate away from the direction of motivating current due to its topological property,which will make the information(coded as skyrmions)missing or dislocated.To avoid that,the common method is to design a narrow drain or fence to restrict the motion of skyrmion,which needs an ultrahigh accuracy of nanotechnology to control the width of the drain.In our work,we proposed a new method that controlling the motion of skyrmion by etching the non-magnetic layer of a three-layer film,whereby the direction of Dzyaloshinskii-Moriya interaction can be modulated.The direction of Dzyaloshinskii-Moriya interaction is different between two sides of the etched edge,and it results in that the original round skyrmion will be contorted into a pretty heart shape.The heart-shaped skyrmion motivated by spin current moves spontaneously along the etched edge,thus we don’t need to consider the scale of nano-manufacture.The transportation velocity of data is mainly determined by the velocity of skyrmion.However,the skyrmion velocity is in the same order of magnetic domain(about 100 m/s)and the Joule-heating is also a big problem when there is a high current density.We deem that the velocity of data transportation can be enhanced by combine spin pumping with skyrmions.In chapter 4,we systematically investigated the spin pumping of skyrmion,then connect the spin pumping voltage signal with the deformation of PZT material.As the deformations should always propagate in the velocity of acoustic wave,the transportation velocity of data would reach a maximum of 3018.8 m/s.In addition to the racetrack memory,the nanostripe with skyrmion can be also utilized to develop spin wave devices.We investigated the propagation of spin wave on the nanostripe with skyrmion chain.In this model,skyrmion cannot only serve as the potential well which will break the dispersion relation curve,but can also be the medium of spin wave.As for the high frequency band,the skyrmion chain contributes to the broken and mismatch of the dispersion relation of the first-order and second-order spin wave,and this mismatch results in the frequency separation phenomenon.As for the low-frequency band,the skyrmion itself is the propagation medium,and its special structure makes the local spin wave propagate in only one direction.