Uncovering the Missing Physics in the Metrology of Spin-Orbit Torques

磁性设备为计算机存储器提供了其他技术无法比拟的优点——它们可以在不施加电源的情况下保留信息，它们可以承受无限次数的写入和读取操作而不会磨损，它们可以快速和高密度地制造。然而，在电子领域的广泛应用将需要找到一种以更低功耗将信息写入磁存储器的方法。最近，人们发现了一种很有前途的新机制，可以非常有效地控制磁记忆，称为“自旋轨道扭矩”，但存在一个问题，即用于测量这种机制强度的不同实验方法往往给出不一致的值。这个项目正在调查哪些缺失的科学没有得到适当的考虑，从而导致了这些相互矛盾的结果。该研究的实际目的是实现可靠的自旋轨道扭矩测量。这将为优化下一代磁存储技术提供科学基础，其目标是为从机器学习到低功耗物联网网络的应用提供更高的性能和更低的能耗。该项目培养研究生和本科生先进的器件制造、测量技术、计算机建模以及科学传播和其他专业技能。毕业生通常会在电子硬件公司的研究实验室找到工作。该项目的参与者也积极参与公共推广项目，特别是康奈尔纳米制造设施和4-H俱乐部之间的合作伙伴关系。技术摘要近年来对电荷电流、自旋电流和磁体之间相互作用的理解取得了进展，导致了磁记忆技术的发展，其中磁体的方向是由自旋电流施加的扭矩有效地控制的。然而，这个领域面临着一个基本的科学难题，因为不同的实验技术用于测量自旋轨道扭矩（电流驱动磁操纵的已知最有效的机制）经常给出相互矛盾的结果。这表明用于分析这些测量的智力框架缺少基本的物理学。该项目正在进行实验，以测试短波长磁振子的激发、加热、非线性输运效应、铁磁体发出的自旋电流或其他尚未被认识到的效应是否可以解释这种缺失的物理现象。该项目的最终目标是建立可信赖的测量技术，用于开发具有更高性能和更低能耗的新一代磁存储设备，用于从机器学习到低功耗物联网网络的应用。该项目培养研究生和本科生先进的器件制造、测量技术、计算机建模以及科学传播和其他专业技能。该项目的参与者也积极参与公共推广项目，特别是康奈尔纳米制造设施和4-H俱乐部之间的合作伙伴关系。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。

Non-Technical AbstractMagnetic devices offer a combination of virtues for computer memory that no other technology can match – they can retain information with no applied power, they can withstand an unlimited number of writing and reading operations without wearing out, and they can be made fast and high-density. However, widespread applications in electronics will require finding a way to write information to magnetic memories with lower power. Recently, a promising new mechanism has been discovered for controlling magnetic memories very efficiently, known as “spin-orbit torque,” but there is a problem that different experimental methods used to measure the strength of this mechanism often give inconsistent values. This project is investigating what is the missing science that has not been properly taken into account, causing these conflicting results. The practical aim of the research is to enable trustworthy measurements of spin-orbit torques. This will provide the scientific foundation to optimize the next generation of magnetic memory technologies, with the goal that they will enable improved performance and lower energy consumption for applications ranging from machine learning to low-power internet-of-things networks. This project trains graduate and undergraduate students in advanced device fabrication, measurement techniques, and computer modeling along with science communication and other professional skills. Graduates typically find employment in research laboratories of electronics hardware companies. Participants in the project are also active in public outreach programs, in particular a partnership between the Cornell Nanofabrication Facility and 4-H clubs.Technical AbstractRecent advances in understanding the interactions between charge currents, spin currents, and magnets have led to the development of magnetic-memory technologies in which the orientation of magnets is efficiently controlled by torques exerted from spin currents. However, this field faces a fundamental-science puzzle because different experimental techniques used to measure spin-orbit torques (the most-efficient known mechanism for current-driven magnetic manipulation) often give contradictory results. This indicates that the intellectual framework used to analyze these measurements is missing essential physics. This project is performing experiments to test whether the excitation of short-wavelength magnons, heating, nonlinear transport effects, spin currents emitted by ferromagnets, or other yet-to-be recognized effects might explain this missing physics. The ultimate project goal is to establish trustworthy measurement techniques for use in the development of a new generation of magnetic memory devices with improved performance and lower energy consumption, for applications ranging from machine learning to low-power internet-of-things networks. This project trains graduate and undergraduate students in advanced device fabrication, measurement techniques, and computer modeling along with science communication and other professional skills. Participants in the project are also active in public outreach programs, in particular a partnership between the Cornell Nanofabrication Facility and 4-H clubs.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.