Controlling Magnets and Electrons Using Spin-Orbit Interactions

非技术摘要：基于微小磁性层的北磁极和南磁极的方向存储信息的磁性存储器设备是用于许多应用的替代硅基随机存取存储器的有吸引力的选择。 磁性存储器有优点：即使在电源关闭的情况下，它们也能保留信息，而且永远不会磨损。同时，它们可以被制造得非常致密、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其信息所需的电能。该项目正在研究与解决这一挑战有关的物理问题。 该研究小组专注于有希望的新物理效应，当磁性材料薄层与含有钨或钽等重原子的第二种材料耦合时，这种效应就会出现，从而使其具有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值驱动磁开关。 他们还在研究与磁性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的相关效应。 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，并参与外展活动，重点是与4-H.技术摘要：该项目正在研究新的物理现象时出现的磁性材料的薄层耦合到具有强自旋轨道相互作用的材料的薄层。 研究小组正在研究自旋轨道耦合对磁性层的影响，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主要研究者和合作者最近发现的关于电流产生的“自旋轨道转矩”的基础上，该转矩可用于非常有效地操纵磁存储设备的磁化方向，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，可以利用对称性的破缺，将自旋-轨道力矩重新定向到最适合应用的方向？(2)自旋极化电子从强自旋-轨道耦合界面的散射能否通过尚不清楚的机制产生自旋-轨道力矩？(3)在某些f-电子元素中存在的大的自旋和轨道矩能用来增强自旋-轨道矩吗？ 该项目还在探索其他新的科学机会，这些机会是由磁性与自旋轨道材料之间的界面相互作用实现的，以更好地控制磁性薄膜的性质（例如，磁阻尼、Dzyaloshinskiii-Moriya相互作用、磁各向异性）以及自旋-轨道材料内的电子的自旋和谷动力学（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).