Research On The Dynamics Of 360° Domain Walls And Multi-domain Walls Driven By Current And Spin Waves

In recent years,the technology of domain wall motion has developed rapidly.The next generation of magnetic memory and logic devices developed on this basis have also attracted widespread attention.How to effectively drive the fast and stable movement of domain wall is the focus of current research.The domain walls can be of transverse wall(TW),vortex wall(VW)and composite 360 wall.In the past decade,the theoretical study of current-driven domain wall motion has been mature.It has been found that current-driven domain wall motion is due to spin Transfer Torque(STT)between carriers and domain walls.The study of current drive single domain wall get a lot of development.But,some problems still plague people and has to surmount,such as Walker breakdown,some domain walls(such as 360 wall)are easily destroyed under the action of current,information distortion in multi-domain wall motion,and Joule heat inevitably in current drive.Spin wave driven domain wall motion can compensate for the shortcomings of energy consumption and Joule heat in current drive.However,the reason of the spin driven domain wall is still controversial.The scattering field of single domain wall(such as transverse wall)is long,which is not conducive to the recording of multi-domain wall information in nano wire "track".A 360 wall composed of two opposite chiral transverse walls can avoid this disadvantage.In this paper,the method of micromagnetic simulation is used to study how to enhance the dependability of domain walls in current and the dynamic behavior and characteristics of 360 domain walls driven by spin wave are calculated by LLG(Landau-Lifshitz-Gilbert)equation.In the chapter 1,we introduce the development of magnetic storage technology and its main applications,the background knowledge of domain wall,and some methods to promote domain wall motion.Finally,we introduce the research progress and development of domain wall motion.In the chapter 2,we introduces the theoretical calculation method of this paper,describes the classical spin dynamics equation Landau-Lifshitz-Gilbert equation,the calculation and simulation steps of effective field,and further introduces the LLG(Landau-Lifshitz-Gilbert)equation including the rotation moment.In the chapter 3,we introduce our study about current-driven 360°domain wall.Previous work has shown that 360°domain wall has higher storage density and smaller scattering field than 180°domain wall,which is more conducive to information storage.But,some disadvantages in the 360°domain wall.When the 360°domain wall is driven by a larger current,it will be annihilated.We call this current the critical current uc.The critical current is far less than 180°domain wall.The current uw of Walker breaker down is driven by current.To solve this problem,we improve the critical current of 360°domain wall by adjusting in-plane anisotropy.The results show that by adjusting in-plane anisotropy,the critical current of 360°domain wall can be increased and kept at a suitable width,which is more conducive to practical application.In the chapter 4,the dynamic behavior of more than 360°domain walls driven by spin waves is studied.The results show that the motion of domain wall driven by current can produce Joule heat,which affects the use of devices.The spin-wave driving domain wall does not need charge transport,so it will not generate Joule heat.At the same time,the 360°domain wall has many advantages over the 180°domain wall.So we want to use the spin-wave driving more 360°domain wall to realize multi-bit data storage.Our study shows that the velocity of the spin-wave-driven domain walls of more than 360° decreases with the increase of the number of domain walls.At the same time,we find that the position of the peak velocity of the spin-wave-driven domain walls of more than 360°remains unchanged.