Physical Mechanisms and Limits of Skyrmions for Information Processing and Storage

磁skyrion是一种受拓扑保护的圆形自旋结构，其外围的自旋垂直极化，中心的自旋向相反方向极化，而在两者之间，自旋在两个相反的极化之间平稳过渡。Skyrmions存在于某些磁材料中，如B20磁体，其中逆对称的破坏引起了Dzyaloshinskii-Moriya相互作用。根据Dzyaloshinskii-Moriya相互作用和对称海森堡相互作用的比值，粒子半径在3nm到100nm之间。人们已经在大块和薄膜中观察到Skyrmion晶格和孤立的Skyrmion，移动Skyrmion所需的电流比移动更传统的磁畴壁所需的电流小4到5个数量级。由于其体积小、稳定性好、个体产生和湮灭的可演示性以及在低电流下的易移动性，skyrmions正被研究用于磁信息存储。对于这样的应用，需要理解天空粒子的产生、湮灭、衰变和读出的过程。该项目将研究这些过程，并将优化一种利用纳秒电流脉冲产生和湮灭低能skyrion的新方法。使用拓扑霍尔效应的读出将被分析。我们将研究利用skyrmion作为状态变量的四种不同架构。一个成功的项目可能会导致自旋和基于拓扑的计算的新方法。利用低能量、稳定、高温、拓扑保护的状态可以在存储和计算技术中获得高回报。开发的软件将向公众开放。磁Skyrmions是一种受拓扑保护的粒子状自旋结构，目前正在研究用于磁信息存储的应用。提出了利用skyrmion状态变量进行信息处理的四种不同架构，并确定了有关skyrmion系统的潜在物理机制和基本限制的开放问题。这些问题将使用理论和计算方法来回答，包括Landau-Lifshitz-Gilbert方程、从头算密度泛函理论和非平衡格林函数形式主义。对于自旋系统的Landau-Lifshitz-Gilbert动力学模拟，将应用一个随机场来包括有限温度下热波动的影响。本文将优化一种利用纳秒电流脉冲产生和湮灭skyrmions的低能新方法。晶格版本的拓扑电荷将用于分析微观动力学过程。它提供了局部触发拓扑跃迁的自旋轨迹和方向的清晰图像，它揭示了skyrmion的拓扑起源。S在有限温度下的稳定性，它标志着天空粒子产生或毁灭的确切时刻。耦合的Landau-Lifshitz-Gilbert /非平衡格林函数方法将用于研究拓扑霍尔电压对skyrmions读出的使用以及自旋波与skyrmions的相互作用对非布尔全息信息处理的影响。

A magnetic skyrmion is a topologically protected, circular, swirling spin texture in which the spins on the periphery are polarized vertically, the central spin is polarized in the opposite direction, and, in between, the spins smoothly transition between the two opposite polarizations. Skyrmions exist in certain helimagnetic materials such as the B20 magnets in which broken inversion symmetry gives rise to the Dzyaloshinskii-Moriya interaction. The radius of a skyrmion ranges from 3 nm to 100 nm depending on the ratio of the Dzyaloshinskii-Moriya interaction and the symmetric Heisenberg interaction. Skyrmion lattices and isolated skyrmions have been observed in bulk and in thin films, and the electrical current required to move a skyrmion is 4 to 5 orders of magnitude less than that required to move a more conventional magnetic domain wall. Because of the their small size, their stability, the demonstration of their individual creation and annihilation, and their facile movement with low current, skyrmions are being investigated for magnetic information storage applications. For such applications, an understanding of the process of skyrmion creation, annihilation, decay, and readout is required. This project will investigate these processes, and it will optimize a new method for low-energy skyrmion creation and annihilation using nanosecond current pulses. Read-out using the topological Hall effect will be analyzed. Four different architectures exploiting the skyrmion as the state variable will be investigated. A successful project could lead to new approaches to spin and topological based computing. The exploitation of low-energy, stable, high-temperature, topologically protected states can result in high-payoff in the technologies of memory and computation. The developed software will be made available to the public.Magnetic Skyrmions are topologically protected, particle-like spin textures that are being investigated for magnetic information storage applications. Four different architectures that exploit a skyrmion state variable for information processing are proposed, and open questions concerning the underlying physical mechanisms and fundamental limits of the Skyrmion systems are identified. These questions will be answered using theoretical and computational methods including the Landau-Lifshitz-Gilbert equation, ab initio density functional theory, and the non-equilibrium Green function formalism. For the Landau-Lifshitz-Gilbert dynamical simulations of the spin system, a stochastic field will be applied to include the effect of thermal fluctuations at finite temperature. A new method for low-energy creation and annihilation of skyrmions using a nanosecond current pulse will be optimized. The lattice version of the topological charge will be used to analyze the microscopic dynamical processes. It provides a clear picture of the spin trajectories and orientations that locally trigger a topological transition, it reveals the topological origin of a skyrmion?s stability at finite temperatures, and it signals the exact moment at which a skyrmion is created or destroyed. A coupled Landau-Lifshitz-Gilbert / non-equilibrium Green function approach will be used to investigate the use of the topological Hall voltage for skyrmion readout and the interaction of spin waves with skyrmions for non-boolean, holographic information processing.