Spin Transfer Torques Arising from Spin-Orbit Interactions

非技术摘要在过去的两年中，已经发现了一种用于操纵磁性设备（例如磁性随机存取存储器）的新策略，该策略的效率比任何先前已知的技术至少高10倍。 这种方法依赖于利用“自旋轨道耦合”-电子的固有自旋与其在某些材料中的运动方向之间的强烈相互作用。 然而，确切的机制尚未得到解决。 该项目旨在确定这种新效应背后的微观机制，研究如何最好地优化材料和设备以实现应用，并探索通过使用这种新策略来操纵以前未研究过的磁性材料类别可以实现的科学机会。 这项研究直接适用于改进磁存储器和逻辑技术，该项目还将通过为研究生和本科生提供研究教育，帮助他们成为杰出的独立科学家，从而产生额外的广泛影响。技术摘要该项目建立在主要研究者和合作者的演示基础上，即重金属/由于重金属内的自旋霍尔效应，铁磁体双层可以对铁磁体的磁矩提供非常强的转矩。其他研究小组也在类似的样本中提供了与不同的物理机制Rashba效应相关的电流感应扭矩的证据。该项目将寻求回答有关这些重金属/铁磁双层中电流感应扭矩的微观机制，对称性和强度的未解决问题，以及如何最好地优化材料和设备以实现这些扭矩的应用。所采用的方法包括测量纳米制造设备中电流诱导的磁矩重新取向的技术以及相关的自旋泵实验，其中旋进磁铁将自旋电流注入重金属。 该研究涉及调查各种不同的材料和多层几何形状，以及探索新的科学机会，这些机会可以通过使用新的电流感应扭矩来操纵绝缘亚铁磁体和反铁磁体内的自旋，这两类材料中自旋操纵无法使用以前已知的机制有效地实现。 总体项目目标包括对电流和磁体之间相互作用的新的基本理解，以及实际的磁存储器和逻辑器件，这些器件可以使用比以前低得多的功率或更高的频率运行。

Non-technical abstractWithin the past two years, a new strategy has been discovered for manipulating magnetic devices (such as magnetic random access memories) that is at least a factor of 10 more efficient than any previously known technique. This approach relies on taking advantage of "spin-orbit coupling" -- a strong interaction between the intrinsic spin of an electron and its direction of motion in certain materials. However, the exact mechanism has not yet been resolved. This project seeks to determine the microscopic mechanism behind this new effect, to investigate how best to optimize materials and devices to enable applications, and to explore the scientific opportunities that can be enabled by using this new strategy to manipulate classes of magnetic materials that have not been investigated previously. This research is directly applicable to improving technologies for magnetic memory and logic, and the project will also yield additional broad impacts by providing research education to graduate students and undergraduates that helps teach them to be outstanding independent scientists.Technical abstractThis project builds upon demonstrations by the principal investigator and collaborators that an in-plane current in a heavy-metal/ferromagnet bilayer can provide a very strong torque to the magnetic moment of the ferromagnet on account of the spin Hall effect within the heavy metal. Other research groups have also provided evidence of current-induced torques associated with a different physical mechanism, the Rashba effect, in similar samples. The project will seek to answer unresolved questions about the microscopic mechanisms, symmetries, and strengths of current-induced torques in these heavy metal/ferromagnet bilayers, and how best to optimize materials and devices to enable applications of these torques. The methods employed include techniques to measure current-induced reorientations of magnetic moments in nanofabricated devices and related spin-pumping experiments in which a precessing magnet injects a spin current into the heavy metal. The research involves investigating a wide variety of different materials and multilayer geometries, and also the exploration of new scientific opportunities that can be enabled by using the new current-induced torques to manipulate spins within insulating ferrimagnets and antiferromagnets, two classes of materials in which spin manipulation could not be implemented efficiently using previously-known mechanisms. The overall project objectives include both new fundamental understanding about the interactions between electrical currents and magnets and also practical magnetic memory and logic devices that can operate using much lower power or at much higher frequencies than has been possible previously.