ERI: Compositionally modulated ferrimagnets for spin-orbitronic devices

该奖项的全部或部分资金来自《2021年美国救援计划法案》(公共法律117-2)。铁磁薄膜具有独特的特性，可能会创造出新的低功耗、高速和高密度的磁性设备。然而，无序可以通过改变薄膜的性质来显著影响器件的运行。该项目的目标是提供对一种广泛的亚铁磁性材料常见的特定类型的无序-成分不均匀-在确定使其成为下一代磁性设备的理想特性方面所起的作用的了解。这项研究将为通过受控生长过程优化这些对未来技术的影响提供框架，进而简化设备架构并提高性能。这项研究还将产生广泛的教育影响，包括支持工程和物理专业代表不足的群体中的一名毕业生，以及让本科生和当地高中生接触到磁性材料的高级研究。参与这项研究的学生将有机会与布鲁克海文国家实验室的科学家合作，获得成像经验以及纳米制造方面的经验。目前基于铁磁材料的自旋电子学技术，包括存储器和逻辑器件，经常受到与能耗、设备可扩展性和稳定性以及速度相关的限制。克服这些限制的一个有希望的方法是亚铁磁性自旋电子学的发展，它保证了反铁磁材料所共有的高速和低功率操作的优点，同时保持了普通过渡金属基铁磁体的直接生长方法和器件读出。这项研究将进一步了解成分调制对过渡金属-稀土铁磁体中Dzyaloshinskii-Moriya相互作用(DMI)的自旋-轨道现象和自旋-轨道扭矩的作用，这是开发高速、低功耗器件的关键。这项研究将通过以下方式解决这一问题：(1)通过受控溅射沉积以及DMI和自旋轨道有效场的系统测量，提高我们对成分调制如何在亚铁磁性单层中产生大的自旋轨道效应的理解；(2)定量地将磁性随薄膜厚度的变化与钴基铁磁体中大的DMI联系起来；(3)提供一个框架，以开发基于上述成分调制的单层、高效的自旋轨道扭矩器件，从而简化其制造要求并提高性能。为了实现这些目标，将通过对静态和动态磁畴构型的克尔显微镜测量以及对磁场和电流驱动的不对称磁畴壁运动的测量来检验不同成分的亚铁磁性薄膜中的DMI和自旋轨道扭矩的强度。电子显微镜、体磁测量和X射线技术将被用来将这些性质直接与组成不均匀联系起来。对标准霍尔交叉和纳米线几何形状的开关过程进行的电测量和直接成像将允许成分调制与器件性能直接联系在一起，包括开关效率和有效磁场的强度，并为更快、更高效的磁存储器、逻辑和信号处理器件铺平道路。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Ferrimagnetic thin films display unique properties which may enable the creation of new low power, high speed, and high-density magnetic devices. However, disorder can significantly influence device operation by modifying thin film properties. The goal of this project is to provide an understanding of the role that a specific type of disorder common to a wide range of ferrimagnetic materials - compositional nonuniformity - plays in determining the properties that make them ideal for next-generation magnetic devices. This research will provide the framework for the optimization of these effects for future technologies through controlled growth processes, and in turn, simplifying device architectures and improving performance. The research will also have a wide educational impact, including supporting one graduate from an underrepresented group in Engineering and Physics as well as exposing undergraduate and local high school students to advanced research in magnetic materials. The students participating in this research will have the opportunity to collaborate with scientists at Brookhaven National Laboratory and gain hands on imaging experience as well as experience in nanofabrication. The educational impact is amplified by the PI’s ongoing participation in outreach programs at the University of Memphis.TechnicalCurrent spintronic technologies based on ferromagnetic materials, including memory and logic devices, often incur limitations related to energy consumption, device scalability and stability, as well as speed. One promising approach to overcoming these limits is the development of ferrimagnetic spintronics, which promises the advantages of high speed and low power operation common to antiferromagnetic materials while maintaining the straightforward growth methods and device readout of common transition metal based ferromagnets. This research will further the understanding of the role of compositional modulation on the spin-orbit phenomena of the Dzyaloshinskii-Moriya Interaction (DMI) and spin-orbit torques in transition metal-rare earth ferrimagnets, key to developing high speed, low power devices. The research will address this by (1) improving our understanding of how compositional modulation allows for the generation of large spin-orbit effects in ferrimagnetic single layers through controlled sputter deposition and systematic measurements of DMI and spin-orbit effective fields, (2) quantitatively linking the variation in magnetic properties through the film thickness to the large DMI in Co-based ferrimagnets, and (3) providing a framework to develop single layer, efficient spin-orbit torque devices based on the aforementioned compositional modulation, thereby simplifying their fabrication requirements and improving performance. To achieve these goals, the strength of DMI and spin-orbit torques in compositionally varied ferrimagnetic films will be examined by Kerr microscopy measurements of static and dynamic domain configurations and measurements of asymmetric domain wall motion driven by magnetic fields and electrical currents. Electron microscopy, bulk magnetometry, and X-ray techniques will be used link these properties directly to composition non-uniformities. Electrical measurements and direct imaging of switching processes taken for standard hall cross and nanowire geometries will allow the compositional modulation to be directly linked to device performance, including switching efficiencies and the strength of effective magnetic fields, and pave the way for faster, more efficient magnetic memory, logic, and signal processing devices.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.