Controlling Magnets and Electrons Using Spin-Orbit Interactions

摘要：基于微小磁层的南北磁极方向来存储信息的磁存储器件在许多应用中是替代硅基随机存取存储器的一个有吸引力的选择。磁存储器的优点是：即使电源关闭，它们也能保留信息，而且永远不会损耗。同时，它们可以做得非常致密、快速和便宜。阻碍磁存储器广泛应用的另一个挑战是如何减少写入其信息所需的电能。这个项目正在研究与解决这一挑战相关的物理问题。研究小组正专注于研究有希望的新物理效应，当一层薄薄的磁性材料与含有重原子（如钨或钽）的第二层材料耦合时，它就会产生所谓的强自旋轨道相互作用。该团队正在研究材料和器件几何形状，使这些自旋轨道相互作用能够以创纪录的低应用能量驱动磁开关。他们还在研究与磁层的相互作用如何影响具有强自旋轨道相互作用的材料的电学性质。该项目有助于高性能磁存储器和逻辑的发展，参与研究的研究生和本科生的教育，以及参与与4-H合作的外展活动。技术摘要：本项目研究磁性材料薄层与具有强自旋轨道相互作用的材料薄层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自旋轨道耦合的材料内部电子的影响。这项研究部分建立在首席研究员和合作者最近发现的有关电流产生的“自旋轨道扭矩”的基础上，该扭矩可用于非常有效地操纵磁存储器件的磁化方向，并试图回答该领域中几个最重要的未解决问题：(1)是否有一种实用的方法可以使用破碎的对称性将自旋轨道扭矩重新定向到最期望的应用方向？(2)自旋极化电子在强自旋轨道耦合界面上的散射能否通过未知的机制产生自旋轨道力矩？(3)某些f电子元素中存在的大的自旋矩和轨道矩可以用来提高自旋轨道矩吗？该项目还在探索其他新的科学机会，通过磁性与自旋轨道材料之间的界面相互作用，更好地控制磁膜的性质（例如，磁阻尼，Dzyaloshinskii-Moriya相互作用，磁各向异性）和自旋轨道材料中电子的自旋和谷动力学（例如，光学性质的磁控制，谷霍尔效应，谷铁磁性和超导性）。

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).