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

第一部分：非技术总结下一代存储芯片要求超低能耗，目前大部分能耗都浪费在将信息“写入”这些芯片上。 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“写入”方法。众所周知，当电流通过磁性薄膜时，在磁性薄膜的横向于电流的两侧产生电压。 这种所谓的反常霍尔效应广泛用于磁场传感器。 通过询问在磁膜的顶表面和底表面发生了什么的问题，发现磁膜的磁化方向，如从制冷机磁体的南极到北极的方向，在两个表面处都倾斜出膜平面。 这种效应背后的原理将被研究，这种效应将用于开发下一代存储芯片的更有效和更少能耗的“写”过程。 以研究为基础的教育和推广也是该项目的一个组成部分。 利用特拉华州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。 该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影响，以保持美国在全球经济中的技术优势。 自旋-轨道耦合（SOC）可以将充电电流转换成自旋电流，从而实现磁化的电控制。 铁磁导体（FM）中SOC诱导传输的典型示例是异常霍尔效应（AHE），其中垂直于磁化的电流在表面上产生横向自旋电流和电荷累积。将类似的考虑应用于平行于磁化的电流的配置，SOC也应该产生具有与磁化和自旋电流两者正交的自旋的横向自旋电流。 横向自旋围绕磁化方向快速进动，并且在它们退相时对磁化施加扭矩，类似于自旋转移扭矩。 这种横向自旋霍尔效应（TSHE），命名为区别于SHE在重金属中，实验证实，它导致异常自旋轨道扭矩（ASOT）的顶部和底部表面的FM。 该项目旨在了解（1）ASOT的机制，（2）TSHE诱导的自旋轨道扭矩（SOT）行为的亚铁磁体（FiM）与垂直各向异性（PMA），特别是在角动量补偿温度下，在该温度下，自旋动力学由反铁磁耦合控制，以及（3）在单个FM中ASOT和PMA FiM中SOT诱导的自旋动力学。 该提案是建立在最近的实验突破，揭示ASOT行为在一个单一的FM以及MOKE为基础的SOT表征技术，升级与时间分辨和温度的能力。该奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

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.