各向异性对电流驱动畴壁运动影响的微磁学模拟

发布时间：2018-05-01 04:46

本文选题：自旋动力学方法 + 铁磁纳米条　；参考：《扬州大学》2014年硕士论文

【摘要】：使用极化电流操控磁性材料中的畴壁运动在开发新一代固态数据存储器、逻辑器件和微波器件方面有着很重要的潜在应用。由自由电子引起的自旋转移力矩效应导致的畴壁运动在理论和实验上都获得了充分的研究。目前面临一个主要的问题是对于实际应用驱动畴壁持续运动所需的电流太大。最近,有研究者发现增加磁性系统中的垂直各向异性可以增强横向畴壁的运动。然而相应的物理机制并没有获得清楚的解释。在磁性纳米带系统中,涡旋畴壁是一种基本的畴壁类型。电流驱动涡旋畴壁除了会发生沿纳米带长度方向的运动还伴随着涡旋中心垂直于纳米带方向的运动,因而涡旋畴壁的运动比横向畴壁更加复杂。从理论讲,相比于横向畴壁研究涡旋畴壁的运动可以获得更加丰富的物理机制。此外,在高密度的数据存储器设计中,纳米线与纳米线之间的距离被放得非常近,所以相邻纳米带中的畴壁间的相互作用就变得非常重要。在本文中我们基于微磁模拟的方法首先研究了垂直各向异性对单条纳米带中电流驱动涡旋畴壁运动的影响,然后分析了垂直各向异性对两条纳米带中涡旋畴壁间耦合作用的影响。第一章绪论部分主要介绍了磁性材料在计算机领域中应用的发展,畴壁的相关知识以及畴壁运动方面已有的理论研究结果。第二章介绍了本论文工作所采用的微磁模拟方法——自旋动力学模拟。第三章详细分析了包含自旋转移力矩的显式Landau-Lifshitz-Gilbert方程中每一项对电流驱动涡旋畴壁运动的影响。并对涡旋中心横向运动与涡旋中心和横向壁部分的极化之间的关系进行了分析。在第四章中给出了不同垂直各向异性下电流驱动畴壁运动的情况。研究显示驱动畴壁在水平方向和垂直方向运动的力随着垂直各向异性和电流的增大而增大。然而,随着垂直各向异性的增加,由束缚势能引起的束缚力起初增加而后又减小。所以当电流值较小时,随着垂直各向异性的增加,畴壁的水平速度先是减小而后又增加。而当电流值较大时,畴壁沿水平方向的速度随垂直各向异性的增加单调增加。另一方面,畴壁横向运动的速度随垂直各向异性的增加而单调增加。在本章中还定量给出这些效应背后的物理机制。在最后一章中呈现了两条纳米带中施加相反电流时耦合的两涡旋畴壁间的振荡行为。主要分析垂直各向异性对耦合畴壁间的振荡行为的影响,结果显示垂直各向异性可以改变耦合涡旋畴壁间的静磁相互作用。
[Abstract]:Using polarization current to control domain wall motion in magnetic materials has important potential applications in the development of a new generation of solid-state data memory, logic devices and microwave devices. The domain wall motion caused by the spin transfer moment effect caused by free electrons has been fully studied theoretically and experimentally. At present, a major problem is that the current required to drive the continuous motion of domain walls is too large for practical applications. Recently, researchers have found that increasing vertical anisotropy in magnetic systems can enhance the motion of transverse domain walls. However, the corresponding physical mechanism has not been clearly explained. The vortex domain wall is a basic type of domain wall in the magnetic nanoscale system. The motion of vortex domain wall driven by current is more complicated than that of transverse domain wall because of the movement of vortex domain wall along the length of nanobelts and perpendicular to the direction of nanometer band. Theoretically speaking, the physical mechanism of vortex domain wall motion is more abundant than that of transverse domain wall. In addition, in high-density data memory design, the distance between nanowires and nanowires is very close, so the interaction between domain walls in adjacent nanowires becomes very important. In this paper, based on the method of micromagnetic simulation, we first study the effect of vertical anisotropy on the current driven vortex domain wall motion in a single nanocrystalline strip. Then the effect of vertical anisotropy on the coupling of vortex domain walls in two nanobelts is analyzed. The first chapter introduces the application of magnetic materials in the field of computer, the related knowledge of domain walls and the theoretical results of domain wall motion. In the second chapter, the micromagnetic simulation method, spin dynamics simulation, is introduced. In chapter 3, the effects of each term in the explicit Landau-Lifshitz-Gilbert equation including the spin transfer moment on the motion of the domain wall of the current-driven vortex are analyzed in detail. The relationship between the transverse motion of the vortex center and the polarization of the vortex center and the lateral wall is analyzed. In chapter 4, the motion of domain wall driven by current under different vertical anisotropy is given. It is shown that the force of driving domain wall moving in horizontal direction and vertical direction increases with the increase of vertical anisotropy and current. However, with the increase of vertical anisotropy, the binding force caused by binding potential energy increases at first and then decreases. So when the current value is small, the horizontal velocity of domain wall decreases and then increases with the increase of vertical anisotropy. When the current value is large, the velocity of domain wall along horizontal direction increases monotonously with the increase of vertical anisotropy. On the other hand, the velocity of transverse motion of domain wall increases monotonously with the increase of vertical anisotropy. The physical mechanisms behind these effects are also quantified in this chapter. In the last chapter, the oscillatory behavior between the two vortex walls coupled with the opposite current applied in the two nanoribbons is presented. The effect of vertical anisotropy on oscillatory behavior between coupled domain walls is analyzed. The results show that vertical anisotropy can change the magnetostatic interaction between coupled vortex walls.
【学位授予单位】：扬州大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM271

【共引文献】