兰州大学机构库 >物理科学与技术学院
径向涡旋和斯格明子动力学的微磁学模拟研究
Alternative TitleMagnetic dynamical study of radial vortex and skyrmion by micromagnetic simulation
马云旭
Subtype博士
Thesis Advisor刘青芳 ; 王建波
2023-05-27
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name理学博士
Degree Discipline物理学
Keyword径向涡旋 Radial vortex 斯格明子 Magnetic skyrmion 微磁学模拟 Micromagnetic simulation 自旋波激发 Spin wave excitation 赛道存储器 Racetrack memory 自旋纳米振荡器 Spin-transfer nano-oscillator
Abstract

磁斯格明子(skyrmion)和径向涡旋(radial vortex)都是具有拓扑保护属性的自旋纳米级磁结构,因其具有潜在的巨大优势而被广泛应用于新一代自旋电子学器件的设计与研发,其中包括信息存储器件和微波发生器件。然而如何抑制甚至克服由于skyrmion霍尔效应导致的信息丢失,以及提高微波发生器的输出信号频率,始终是此类自旋电子学器件走向实际应用的障碍。本论文通过微磁学模拟的方法提出了用以解决上述问题的方案,并研究了在微波磁场及自旋极化电流驱动下径向涡旋翻转的动力学过程,探究了径向涡旋及其衍生结构的自旋波激发模式以及静态垂直磁场对其本征模式的调控。

对于径向涡旋及其衍生结构2π/3π态,发现在微波磁场激励下出现面内逆时针和顺时针的旋转模式以及面外呼吸模式,并且自旋波模式数量也随着结构的复杂化而增多。在施加静态垂直磁场后,改变了各磁结构的内部磁矩分布及各畴壁区域面积,三种磁结构的内外径尺寸发生了规律性的增大或者减小,起到调控自旋波模式本征频率的作用。在利用微波磁场驱动径向涡旋翻转时,可以发现当微波频率接近其本征频率时,各个磁结构对微波产生的响应是最强的,即使是在较低振幅下也能够完成翻转,在不同本征频率的微波磁场下的动态翻转过程分为呼吸模式、自旋波模式以及混合模式。当利用自旋极化电流驱动径向涡旋翻转时,在翻转过程中还出现了进动翻转模式,发现在具有高磁晶各向异性边界的纳米圆盘中,可以阻止径向涡旋核心的翻转从而实现持续进动,以此实现具有较高振荡频率的自旋纳米振荡器。

除上述基于径向涡旋的单频信号发生器外,我们还提出了能够激发多频微波信号的结构。其中垂直磁场辅助下基于人工合成反铁磁skyrmion pair的自旋纳米振荡器,发现当skyrmion pair因外磁场的作用而导致尺寸差异足够大时,较大尺寸的skyrmion产生呼吸行为,从而激发出多频微波信号。除此之外,具有径向不对称性的椭圆skyrmion,其自旋波模式则出现了径向非对称的垂直呼吸模式,并且发现在自旋极化电流作用下的进动过程中同样出现了呼吸行为,此类自旋纳米振荡器实现了单频和多频微波信号的同步输出。

关于赛道存储器的研究,首先提出了基于人工合成反铁磁skyrmion pair的结构,在边界斥力的作用下有效避免了skyrmion霍尔效应,发现电流密度、阻尼系数和层间反铁磁耦合强度都是影响skyrmion速度的重要因素。此外,还提出了同步应用磁skyrmioniun和skyrmion,避免信息编译和环境影响造成的信息丢失和错误,发现二者在人工合成反铁磁结构中具有更快的速度和更高的稳定性。我们的结果对进一步研究具有拓扑磁结构的静态磁特性及其在自旋电子学中应用提供了一定的借鉴意义。

Other Abstract

Magnetic skyrmion and radial vortex both are new nanoscale magnetization with topological protected property. They are widely used in the development of next generation spintronics devices, including racetrack memory and spin transfer nano-oscillators. They have attracted the interest of a growing number of researchers due to the huge advantages, for example small size, easily to integrate, low drive current density, and high stability. However, overcoming the skyrmion Hall effect in the racetrack memory and increasing the oscillation frequency of the spin transfer nano-oscillator have always been the key for practical applications. In this work, we propose some results of solving above problems by means of micromagnetic simulations. We also investigated the switching process of radial vortex driven by microwave magnetic field and spin polarization current, and further explored spin wave modes of kπ radial vortex excited by pulse microwave magnetic field.

For the 2π and 3π radial vortex, the in-plane counterclockwise and clockwise modes and the out-of-plane breathing modes appeared under the excitation of the pulse microwave magnetic field. And the number of spin wave modes increase with increasing the k. In the radial vortex switching process under the effect of microwave magnetic field, it can be found that the response of magnetization to the microwave magnetic field is very strong when the frequency is close to eigenfrequencies. The dynamic switching process under the microwave magnetic field at different eigenfrequencies are divided into breathing mode, spin wave mode and mixed mode. It is also found the precession mode when the spin polarization current is applied to the nanodisk. Then we applied the high magnetocrystalline anisotropy materials to boundary of nanodisk to achieve continuous precession motion by overcoming switching of core. Thus, the spin transfer nano-oscillator with high oscillation frequency is designed.

In addition to the above single frequency signal generator based on radial vortex, we also propose the structures that can excite multi-frequency microwave signals. For the skyrmion pair based oscillator assisted by the vertical magnetic field, it is found that the larger size skyrmion starts breathing when the size difference of the skyrmion pair is big enough. This behavior excites a multi-frequency microwave signal. In addition, spin wave mode of elliptical skyrmion has radial asymmetric breathing mode, so the elliptical skyrmion occurs breathing behavior in the precession process under the effect of spin polarization current. Thus, these two types of oscillator output single-frequency and multi-frequency microwave signals.

 For the study of racetrack memory, we first design the structure based on synthetic antiferromagnetic skyrmion pair, which effectively avoids the skyrmion Hall effect. And it is found that spin polarized current density, damping content and interlayer antiferromagnetic coupling strength are all important factors affecting the speed of skyrmion. In addition, the skyrmioniun and skyrmion are applied synchronously to avoid information loss and errors, which caused by high temperature. And it is found that they have faster speed and higher stability in synthetic antiferromagnetic structures. These results provide reference significance for further research on static characteristics with topological magnetic structures and their application in spintronics.

Subject Area自旋电子学
MOST Discipline Catalogue理学 - 物理学 - 凝聚态物理
URL查看原文
Language中文
Other Code262010_120190906861
Document Type学位论文
Identifierhttps://ir.lzu.edu.cn/handle/262010/539782
Collection物理科学与技术学院
Affiliation
兰州大学物理科学与技术学院
Recommended Citation
GB/T 7714
马云旭. 径向涡旋和斯格明子动力学的微磁学模拟研究[D]. 兰州. 兰州大学,2023.
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