磁畴壁结构动力学及其应用研究

发布时间：2018-01-01 15:29

本文关键词：磁畴壁结构动力学及其应用研究　出处：《兰州大学》2016年博士论文　论文类型：学位论文

【摘要】：自旋电子学将电子的自旋属性和电荷属性紧密地联系了起来,这两个自由度的结合为开发性能优异的电子器件提供了更广阔的空间。赛道存储器,自旋纳米振荡器,STT-MRAM就是其中三种典型的自旋电子学器件,有着巨大的应用前景,然而在实现应用之前仍有一些问题需要解决。本论文主要通过微磁学模拟和实验的手段,针对赛道存储器和自旋纳米振荡器等自旋电子学器件遇到的一些问题进行研究。(一)赛道存储器问题研究Parkin起初设计的赛道存储器是基于面内磁化纳米带中的180度畴壁。相比之下,基于360度畴壁的赛道存储器具有更高的存储密度和较强的抗磁场干扰能力。在第三章中,我们首先设计了简单的产生360度畴壁的电极结构并通过微磁学模拟发现,要成功产生360度畴壁,电流脉冲的下降过程需要缓慢降低以防止畴壁湮灭。然后利用平行纳米带中360度畴壁和180度畴壁的耦合,或者两个360度畴壁的耦合提高了360度畴壁的稳定性,从而使360度畴壁的极限速度提高了81.1%。第四章中,我们研究了磁振子(自旋波)与360度畴壁的相互作用,自旋波的传播过程没有电荷输运,所以为解决焦耳热的问题提供了一种新的思路。微磁学模拟研究发现,自旋波也可以驱动360度畴壁运动,而且根据材料参数和自旋波频率的不同,畴壁可以沿着自旋波方向或者反方向运动。此外,通过被360度畴壁反射的自旋波研究了自旋波的多普勒效应。通过透射自旋波研究了自旋波的相位移动效应。垂直各向异性材料纳米带中的畴壁宽度非常窄,而且临界电流密度也比面内磁化样品中要低,所以非常有利于提高赛道存储器的存储密度并降低功耗。产生磁畴壁是研究其应用的一个非常关键的步骤,传统上是利用一个与纳米带垂直的直线电极来产生畴壁。第五章中,我们提出了一个非常高效的在垂直各向异性纳米带中注入磁畴的Π型的电极结构。这种方法可以用5.35×1011 A/m2的电流脉冲在15 ns的脉冲时间内在Co/Ni多层膜中成功产生一个磁畴。实验和计算结果都证明这种方法的能耗只有传统方法的30%左右。最后,我们通过反常霍尔效应测量了磁畴壁在十字叉结构处的钉扎和脱钉扎现象,并通过电流对脱钉扎场进行了调控。(二)自旋纳米振荡器问题研究自旋纳米振荡器有很多非常优异的性能,然而其输出功率是一个瓶颈问题,现在有一种非常好的解决思路就是制作振荡器阵列,然后通过多个振荡器信号的叠加来提高输出功率。第六章中,我们研究了点电流驱动隧道结结构中磁Skyrmion的振荡,并依此原理设计了一种新型的基于磁Skyrmion的自旋纳米振荡器。该振荡器可以在一个器件中同时输出多路信号,故而有望提高振荡器的输出功率。信号的线宽可以小于1 MHz。此外,该电极可以在108 A/m2的电流密度下工作且工作频率最小可以接近0 MHz,最大可以到GHz量级。
[Abstract]:Spin electronics closely links the spin and charge properties of electrons. The combination of these two degrees of freedom provides a wider space for the development of excellent electronic devices. Spin nanometer oscillator (STT-MRAM) is one of the three typical spin electronics devices, which has a great application prospect. However, there are still some problems to be solved before the application. Some problems encountered by spin electronics devices such as racetrack memory and spin nanometer oscillator are studied. (1). Research on racetrack memory problem Parkin originally designed the racetrack memory based on the 180-degree domain walls in the in-plane magnetized nanobelts. Track memory based on 360-degree domain walls has higher storage density and stronger resistance to magnetic field interference. In Chapter 3. We first designed a simple electrode structure to generate 360-degree domain walls and found that it was necessary to successfully generate 360-degree domain walls by micromagnetic simulation. In order to prevent domain wall annihilation, the current pulse drop process needs to be slowly reduced, and then the coupling of 360 degree domain wall and 180 degree domain wall in parallel nanoribbons is used. Or the coupling of two 360-degree domain walls improves the stability of the 360-degree domain walls, thus increasing the limit speed of the 360-degree domain walls by 81.1. 4th. We study the interaction between magnetic oscillator (spin wave) and 360-degree domain wall. There is no charge transport in the propagating process of spin wave. It provides a new way to solve the problem of Joule fever. The micromagnetic simulation results show that the spin wave can also drive 360 degree domain wall motion, and according to the material parameters and the frequency of spin wave. The domain walls can move either in the spin direction or in the opposite direction. The Doppler effect of spin wave is studied by the reflection of 360 degree domain wall and the phase shift effect of spin wave is studied by transmission spin wave. The width of domain wall in vertical anisotropic nanobelts is very narrow. And the critical current density is lower than that in the in-plane magnetized sample, so it is very helpful to improve the storage density and reduce the power consumption of the racetrack memory. The generation of magnetic domain wall is a very important step to study its application. Traditionally, a linear electrode perpendicular to the nanobelts is used to generate domain walls. Chapter 5th. In this paper, we propose a highly efficient electrode structure for injecting magnetic domains into vertically anisotropic nanoribbons with a current pulse of 5.35 脳 1011 A / m ~ 2 and a current pulse of 15 脳 10 ~ (11) A / m ~ (2). A magnetic domain was successfully generated in the Co/Ni multilayer in the pulse time of ns. The experimental and computational results show that the energy consumption of this method is only about 30% of that of the traditional method. The phenomenon of pinning and de-pinning of magnetic domain wall at cross cross structure is measured by anomalous Hall effect. The spin nanometer oscillator has a lot of excellent performance, but its output power is a bottleneck problem. Now there is a very good solution to the idea is to make an oscillator array, and then through the superposition of multiple oscillator signals to improve the output power. Chapter 6th. We study the oscillations of magnetic Skyrmion in a point-current-driven tunnel junction. Based on this principle, a novel spin nanoscilloscope oscillator based on magnetic Skyrmion is designed, which can output multiple signals simultaneously in a single device. Therefore, it is expected to increase the output power of the oscillator. The line width of the signal can be less than 1 MHz. The electrode can work at a current density of 108A / m ~ 2 and the minimum operating frequency can be close to 0 MHz, and the maximum working frequency can be up to the order of GHz.
【学位授予单位】：兰州大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O342

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