Novel Transverse Spin Hall Effect Induced Phenomena in Single Ferromagnet and Magnetic Heterostructures

第一部分：非技术概述下一代存储芯片要求超低能耗，目前大部分浪费在“写入”信息到这些芯片中。该项目旨在通过发现磁性材料的新特性来开发一种有效的“书写”方法。众所周知，当电流通过磁性薄膜时，在与电流横向的磁性薄膜两侧会产生电压。这种所谓的反常霍尔效应广泛应用于磁场传感器中。通过询问磁性薄膜的上下表面发生了什么，发现磁性薄膜的磁化方向，就像冰箱磁铁从南极到北极的方向一样，在两个表面都倾斜于薄膜平面之外。我们将研究这种效应背后的原理，并利用这种效应为下一代存储芯片开发更高效、能耗更低的“写”过程。以研究为基础的教育和推广也是这个项目的一个组成部分。利用特拉华大学新建立的最先进的纳米制造设施，将开发几个实验模块，以教授磁性器件制造。这个项目不仅对科学和技术发展感兴趣，而且将对劳动力培训产生长期持久的影响，以保持美国在全球经济中的技术优势。PART 2：技术概述自旋轨道耦合（SOC）可以将电荷电流转换为自旋电流，从而实现磁化的电气控制。在铁磁导体（FM）中，soc诱导输运的一个典型例子是反常霍尔效应（AHE），其中垂直于磁化强度的电流产生横向自旋电流并在表面上积累电荷。将类似的考虑应用于与磁化平行的电流配置，SOC也应该产生与磁化和自旋电流正交的横向自旋电流。横向自旋沿磁化方向快速进动，并在脱相时对磁化强度施加转矩，类似于自旋传递转矩。这种横向自旋霍尔效应（TSHE）是为了区别于重金属中的自旋霍尔效应而命名的，它在实验上得到了证实，并且在调频的上下表面产生了反常的自旋轨道扭矩（ASOT）。本项目旨在了解(1)垂直各向异性（PMA）铁磁体（FiM）上tshe诱导的自旋轨道转矩（SOT）行为，特别是在角矩补偿温度下，自旋动力学受反铁磁耦合控制，以及(3)单个FM中的ASOT和PMA薄膜中的SOT诱导的自旋动力学。该提案是基于最近在单个FM中揭示ASOT行为的实验突破，以及基于moke的SOT表征技术，该技术升级了时间分辨和温度能力。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

PART 1: NON-TECHNICAL SUMMARYNext generation memory chips demand ultralow energy consumption, which is currently mostly wasted in 'writing' information into these chips. This project aims to develop an efficient 'writing' method by discovering novel properties in magnetic materials. It is well-known that when an electrical current passes through a magnetic thin film, a voltage develops at two sides of the magnetic film transverse to the electrical current. This so-called anomalous Hall effect is broadly used in magnetic field sensors. By asking the question of what happens at the top and bottom surfaces of the magnetic films, it was discovered that the magnetization directions, like the direction from south Pole to north pole of a refrigerator magnet, of the magnetic film are tilted out of the film plane at both surfaces. The principle behind this effect will be investigated and the effect will be used to develop a much more efficient and less energy consuming 'write' process for next generation memory chips. Research based education and outreach are also an integral part of this project. Leveraging newly established state-of-the-art Nanofabrication Facility at University of Delaware, several experiment modules will be developed in order to teach about magnetic device fabrication. This project is not only interesting in scientific and technical developments, but also will have long lasting impacts on work force training for maintaining the United States' technological edge in the global economy. PART 2: TECHNICAL SUMMARYSpin-orbit coupling (SOC) can convert a charge current into a spin current, enabling electrical control of magnetization. A quintessential example of SOC-induced transport in a ferromagnetic conductor (FM) is the anomalous Hall effect (AHE), in which an electric current perpendicular to the magnetization generates a transverse spin current and charge accumulations on the surface. Applying similar considerations to the configuration of a current parallel to the magnetization, SOC should also give rise to a transverse spin current with spins orthogonal to both the magnetization and spin current. The transverse spins precess rapidly about the magnetization direction and exert torque on the magnetization as they dephase, in analogy with the spin transfer torque. This transverse spin Hall effect (TSHE), named to distinguish from the SHE in a heavy metal, is experimentally confirmed and it leads to anomalous spin-orbit torque (ASOT) on the top and bottom surfaces of a FM. This project aims to understand (1) the mechanisms for ASOT, (2) the TSHE-induced spin orbit torque (SOT) behavior on a ferrimagnet (FiM) with perpendicular anisotropy (PMA), particularly at the angular moment compensation temperature at which the spin dynamics are governed by the antiferromagnetic coupling, and (3) the spin dynamics induced by ASOT in a single FM and SOT in a PMA FiM. This proposal is built on recent experimental breakthroughs in revealing ASOT behaviors in a single FM as well as a MOKE-based SOT characterization technique that was upgraded with time-resolved and temperature capability.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.