Field-driven Magnetic Domain Wall Dynamics In Magnetic Nanowires And Their Regulation

In recent years,the research and development of magnetic memory devices has attracted people's attention,and the research based on the motion of magnetic domain walls is also a current hot spot.Mechanical hard disks and solid-state hard disks are relatively common information storage methods at present,and the principle of storing information through magnetic domain movement is different from mechanical hard disks and solid-state hard disks.The mechanical hard disk reads and writes information with the magnetic head through the high-speed operation of the magnetic disk,and its read and write speed is slow and limited by the mechanical movement of the magnetic disk.Although solid-state drives have faster read and write speeds,the flash memory particles they use have a limited lifespan,have a limited number of reads and writes,and are relatively expensive.Reading and writing information through the movement of magnetic domains is neither limited by the mechanical movement of the magnetic disk nor limited by the lifespan of the flash memory particles.How to stably and quickly drive the magnetic domain walls to move in magnetic storage materials has become a hot issue to be solved.In the past research,the study of driving magnetic domain motion by electric current and spin wave has been relatively mature,but there are still many shortcomings.For example,there will be Walker breakdown,Joule heating and some domain wall distortions in current driving,and the understanding of the physical mechanism of spin wave driving is still controversial.In order to improve the storage density,the memory is made into a three-dimensional structure.At this time,the movement of domain walls in the three-dimensional structure driven by an external field has not been well understood.In this paper,the micromagnetic simulation method based on the LLG(Landau-Lifshitz-Gilbert)equation is used to study the possible interaction between the spin wave and the domain wall,and to study the motion of the domain wall in the U-shaped nanowire driven by the external field..In the first chapter,we introduce the development process of magnetic storage technology and the current main related applications,the related background knowledge of domain walls,and some methods to promote the movement of domain walls.Finally,we briefly introduce the research progress and development status of domain wall motion.In the first chapter,we introduce the development process of magnetic storage technology and the current main related issues,the related background knowledge of domain walls,and some methods of driving domain walls to move.Finally,we briefly introduce the research progress and existence of field-driven domain wall question.The second chapter introduces the theoretical calculation method of this paper,describes the classical spin dynamics equation(Landau-Lifshitz-Gilbert equation),the calculation and simulation steps of the effective field,and further introduces the extension of the spin transfer torque.LLG equation.The third chapter we study the interaction between spin waves and multi-domain walls and find that TWVW structures can be transformed into TWTW structures(i.e.360° walls)or completely annihilated under the action of spin waves,depending on the frequency of the spin waves and amplitude.In contrast,multiple TWs(STWs)structures show good robustness.That is,similar to a single TW,STWs can be driven in unison by spin waves.On the other hand,its phase shift always increases linearly with the number of TWs,and the resonance can be enhanced at the same frequency as the TW mode.Its induced STW motion and STW-controlled phase shift have potential applications in future information storage and reading.The fourth chapter studies the relationship between the external field-driven magnetic domain wall movement properties and U-shaped bending in U-shaped magnetic nanowires.The results show that the U-shaped bending of the magnetic nanowire hinders the movement of the current-driven magnetic domain wall,and the reduction of the moving speed at the bending point increases with the reduction of its bending radius;on the other hand,the addition of spin waves can The current drives the movement of the magnetic domain walls.Among them,the speed of the magnetic domain wall driven by the spin wave increases linearly with the increase of its amplitude,and with the increase of its frequency,it is a multimodal non-monotonic relationship.Further,adding a suitable spin wave energy at the U-shaped bend of the magnetic nanowire completely eliminates the slow bending of the current-driven magnetic domain wall,so as to ensure the uniform and smooth movement of the current-driven magnetic domain wall in the curved magnetic nanowire,thereby realizing Reliable development of 3D Racetrack Memory technology.