CoFeB纳米带中自旋波驱动横向畴壁移动动力学研究

【作者】 王旭；

【导师】 姜勇；

【作者基本信息】 天津工业大学 ， 控制科学与工程， 2023， 硕士

【摘要】 人工智能和物联网大数据时代的到来,对信息存储设备的功耗、读写速度和使用寿命提出了更高的要求。以自旋波方式驱动磁性纳米带中畴壁移动的赛道存储器因其低功耗、高存储速度、高密度和寿命长等优点,成为极具应用潜力的新型存储器件。铁磁材料CoFeB具有高饱和磁化强度和低阻尼系数,是制备磁性纳米带的理想材料。由于自旋波的透射和反射机制,畴壁会展现不同的移动特性同时自旋波还会使畴壁产生多频共振,此外畴壁有效场不均匀性的差异也会影响自旋波的透射系数。纳米带中畴壁的移动特性是影响数据存储的关键因素,直接影响存储器的性能。因此,本文采用微磁模拟方法对CoFeB纳米带中自旋波驱动畴壁移动的动力学行为进行研究。本文主要工作如下:(1)介绍了畴壁和自旋波的成因,综述了几种常见驱动畴壁移动的方式并分析对比优缺点,分析了基于自旋波驱动方式的赛道存储器的工作原理和特性,对磁性材料中的静态微磁学方程和动态微磁学方程进行推导并对微磁模拟过程和软件进行简要概述。(2)为了探究CoFeB纳米带中自旋波对畴壁动力学行为的影响,首先计算并绘制了不同自旋波频率下畴壁速度的变化曲线,仿真结果表明CoFeB纳米带中畴壁最大移动速度为384m/s。同时分析对比了当畴壁正向与反向移动时,外加磁场强度和宽度对畴壁动力学行为影响,并通过计算不同条件下自旋波的透射系数分析畴壁速度变化差异出现的原因。验证得出CoFeB纳米带可以满足畴壁高速移动的要求,是制备纳米带的理想材料。(3)为了分析特定自旋波频率下CoFeB纳米带中畴壁出现速度峰值的原因,对比了自旋波输入前后畴壁振动的振幅与频率,同时计算了不同频率下畴壁受迫振动的振幅、速度和反射系数并对它们进行对比分析。模拟结果表明畴壁会在自旋波的诱导下产生受迫振动,并且畴壁受迫振动随自旋波频率的变化与畴壁速度和反射系数的变化曲线有较高的匹配性,证明了畴壁的受迫振动是畴壁速度峰值出现的重要原因。(4)为了探究畴壁有效场对畴壁动力学行为的影响。通过改变纳米带材料的饱和磁化强度和纳米带宽度,从而改变畴壁的有效场,绘制不同条件下畴壁的状态空间图并对其进行数据分析,计算并绘制了不同纳米带宽度和饱和磁化强度下畴壁的速度和透射系数的变化曲线。模拟结果表明自旋波的透射系数随着畴壁有效场不均匀性的提高而减小,造成畴壁速度的改变。因此畴壁的移动特性受到输入磁场和畴壁有效场的影响。更多还原

【Abstract】 The advent of artificial intelligence and Io T big data era has put forward higher requirements on power consumption,read/write speed and service life of information storage devices.Spin-wave driven magnetic nanostrips in the domain wall of the track memory because of its low power consumption,high memory speed,high density and long life,become a new memory device with great potential applications.The ferromagnetic material CoFeB with high saturation magnetization strength and low damping coefficient is an ideal material for the preparation of magnetic nanostrips.Due to the transmission and reflection mechanism of spin waves,the domain walls exhibit different movement characteristics and the spin waves cause multi-frequency resonance of the domain walls.In addition,the differences in the effective field heterogeneity of the domain walls also affect the transmission coefficient of the spin waves.The mobility characteristics of domain walls in nanostrips are the key factors affecting data storage and directly affect the memory performance.Therefore,in this paper,the kinetic behavior of spin wave-driven domain wall movement in CoFeB nanostrips is investigated using a micromagnetic simulation method.The main work of this paper is as follows:(1)The causes of domain walls and spin waves are introduced.Several common modes of domain wall movement are reviewed and their advantages and disadvantages are analyzed.The working principle and characteristics of controllable domain wall mobile devices driven by spin wave are analyzed.The static and dynamic micromagnetic equations in magnetic materials are derived and the simulation process and software of micromagnetic are briefly summarized.(2)In order to investigate the influence of spin waves on the domain wall dynamics in CoFeB nanostrips,we first calculated and plotted the domain wall velocities at different spin wave frequencies,the simulation results show that the maximum velocity of domain wall movement in CoFeB nanorstrips is 384m/s.The effects of the intensity and width of the input magnetic field on the dynamic behavior of the domain walls when the domain walls move forward and backward are analyzed,and the reasons for the variation of the domain walls velocity are analyzed by calculating the transmission coefficients of the spin waves under different conditions.It is verified that CoFeB nanostrips can meet the requirements of high speed movement of domain walls and are ideal materials for the preparation of nanostrips.(3)In order to analyze the causes of velocity peaks at domain walls in CoFeB nanostrips at specific spin wave frequencies,the amplitude and frequency of domain wall vibration before and after spin wave input were compared,and the forced vibration,velocity and reflection coefficients of domain walls at different frequencies were calculated and compared.The simulation results show that the domain wall is induced by the spin wave to generate forced vibration,and the variation of the forced vibration with the spin wave frequency has a high match with the variation curve of the domain wall velocity and reflection coefficient,which proves that the forced vibration of the domain wall is an important reason for the peak of the domain wall velocity.(4)The effect of domain wall effective field on domain wall dynamic behavior was investigated.The effective field of the domain wall is varied by changing the saturation magnetization intensity and the nanostrip width of the nanostrip material.The state space diagrams of the domain walls under different conditions were plotted and analyzed,and the velocity variation curves of the domain walls were calculated and plotted for different nanoband widths and saturation magnetization intensities.The simulation results show that the transmission coefficient of the spin wave decreases with the increase of the effective field inhomogeneity of the domain wall,resulting in the change of the domain wall velocity.Therefore,the moving characteristics of the domain wall are influenced by the input magnetic field and the effective field of the domain wall.更多还原