Controlling Magnets and Electrons Using Spin-Orbit Interactions

非技术摘要：在许多应用中，基于微小磁层的南北磁极的取向来存储信息的磁存储器件是替代硅基随机存取存储器的有吸引力的替代方案。磁性存储器具有优势：它们即使在关闭电源的情况下也能保留信息，而且永远不会磨损。同时，它们可以制造得非常密集、快速和廉价。阻碍磁存储器广泛应用的剩余挑战是减少写入它们的信息所需的电能。这个项目正在调查与解决这一挑战相关的物理问题。该研究小组正专注于一种有希望的新物理效应，当一层薄薄的磁性材料与第二种含有钨或钽等重原子的材料耦合时，它将具有所谓的强自旋轨道相互作用。该团队正在研究材料和设备几何结构，使这些自旋-轨道相互作用能够以创纪录的低应用能量值驱动磁开关。他们还在研究与磁层的相互作用如何影响具有强烈自旋-轨道相互作用的材料的电学性质的相关影响。这个项目有助于开发高性能的磁记忆和逻辑，对参与研究的研究生和本科生进行教育，并参与以与4-H的伙伴关系为重点的外联活动。技术摘要：该项目正在研究薄层磁性材料与具有强烈自旋-轨道相互作用的薄层材料耦合时出现的新物理现象。研究小组正在研究自旋-轨道耦合对磁层的影响，以及磁相互作用对具有强烈自旋-轨道耦合的材料内部电子的影响。该研究部分地建立在主要调查者和合作者关于电流产生的可用于非常有效地操纵磁存储设备的磁化方向的“自旋轨道力矩”的最新发现的基础上，它试图回答这一领域中几个最重要的悬而未决的问题：(1)有没有一种实用的方法来利用破坏的对称性将自旋-轨道扭矩重新定向到最适合应用的方向？(2)从具有强烈自旋-轨道耦合的界面上散射的自旋极化电子能否通过尚不清楚的机制产生自旋-轨道扭矩？(3)一些f电子元素中存在的大自旋和轨道矩能否被用来增强自旋-轨道扭矩？该项目还在探索磁性和自旋轨道材料之间的界面相互作用带来的其他新的科学机会，以更好地控制磁性薄膜的性质(例如，磁阻尼、Dzyaloshinskii-Moriya相互作用、磁各向异性)和自旋-轨道材料内电子的自旋和山谷动力学(例如，光学性质的磁性控制、谷霍尔效应、谷铁磁性和超导)。

Non-technical Abstract:Magnetic memory devices that store information based on the orientation of the north and south magnetic poles of a tiny magnetic layer are an attractive alternative for replacing silicon-based random access memories for many applications. Magnetic memories have the advantages: they retain information even with the electrical power turned off and they never wear out. At the same time they can be made very dense, fast, and inexpensive. The remaining challenge standing in the way of widespread application of magnetic memories is to reduce the electrical energy required to write their information. This project is investigating physics questions related to solving this challenge. The research team is focusing on promising new physical effects that emerge when a thin layer of magnetic material is coupled to a second material containing heavy atoms such as tungsten or tantalum so that it possesses what is known as strong spin-orbit interactions. The team is studying materials and device geometries that enable these spin-orbit interactions to drive magnetic switching with record-low values of applied energy. They are also investigating related effects of how interaction with a magnetic layer can affect the electrical properties of the material with strong spin-orbit interactions. This project contributes to the development of high-performance magnetic memory and logic, the education of graduate students and undergraduates involved in the research, and participation in outreach activities focused on a partnership with 4-H.Technical Abstract:This project is investigating new physics phenomena that emerge when a thin layer of magnetic material is coupled to thin layer of a material with strong spin-orbit interactions. The research team is examining both the effects of the spin-orbit coupling on the magnetic layer, and the effect of magnetic interactions on electrons inside the material with strong spin-orbit coupling. This research builds, in part, on recent discoveries by the principal investigator and collaborators concerning current-generated "spin-orbit torques" that can be used to manipulate very efficiently the magnetization direction of magnetic memory devices, and it seeks to answer several of the most important unresolved questions in this field: (1) Is there a practical way to use broken symmetries to reorient spin-orbit torques into the direction most desired for applications? (2) Can the scattering of spin-polarized electrons from an interface with strong spin-orbit coupling generate spin-orbit torques via mechanisms that are not yet understood? (3) Can the large spin and orbital moments present in some f-electron elements be used to enhance spin-orbit torques? The project is also exploring other new scientific opportunities enabled by interfacial interactions between magnetism with spin-orbit materials, to better control both the properties of the magnetic film (e.g., magnetic damping, Dzyaloshinskii-Moriya interactions, magnetic anisotropy) and the spin and valley dynamics of electrons within the spin-orbit material (e.g., magnetic control of optical properties, valley Hall effect, valley ferromagnetism, and superconductivity).