Collaborative Research: Large-Amplitude, Easy-Plane Spin-Orbit Torque Oscillators

信息和通信技术的快速发展继续对全球能源消费产生巨大影响。因此，创造有利于这项技术的新型节能电子元件是至关重要的。一个这样的基本装置将恒定电压输入转换成振荡电压输出。这项研究的目标是开发一种新的微尺度电子振荡器，称为易平面自旋轨道扭矩振荡器，它与标准的工业制造技术兼容。通过利用新颖的器件几何形状和最近在铁磁材料中发现的现象，易平面自旋轨道转矩振荡器可以解决困扰传统振荡器的许多问题，例如小输出信号，纳米级限制和热不稳定性。这些新型振荡器的应用范围从微波通信到大脑启发计算。这个项目还有一个外联部分，旨在教K-12年级的学生，特别是那些来自科学教育不足的学校的学生，如何用家庭用品制造简单的磁性电机，目的是激发他们从小对科学的兴趣。本研究旨在为基于平面电流自旋阀的新型自旋轨道转矩振荡器提供基础知识，其中自由层磁化以近90度的大锥角进行。这项研究的灵感来自于最近的一项发现，即平面内磁化薄膜中的电流会产生平面外的自旋电流。这种新颖的自旋电流可以产生抗阻尼扭矩，驱动自旋阀自由层的大角度进动。研究的第一个重点是确定自旋阀的面外自旋电流和由此产生的抗阻尼扭矩的机理。为此，将对具有系统变化成分和结构的自旋阀进行第一性原理计算和自旋转矩铁磁共振实验。该研究的第二个重点将通过微磁模拟和电气设备表征来确定自旋阀稳定、大角度进动的关键要求。一个成功的结果将导致易平面振荡器的信号和稳定性比现有的自旋轨道转矩振荡器高一个数量级以上，因为磁电阻的摆动更大，对热波动的免疫能力更强。此外，该研究将产生关于非常规自旋电流和自旋力矩的关键基础知识，这些知识可以在下一代自旋电子器件中控制各种磁化动力学（例如垂直磁开关，类超流体交换流）。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。

The rapid growth of information and communications technology continues to have an outsized impact on global energy consumption. It is therefore crucial to create new, energy-efficient electronic components that benefit this technology. One such essential device converts a constant voltage input into an oscillating voltage output. The goal of this research is to develop a new class of microscale electronic oscillators, called easy-plane spin-orbit torque oscillators, which are compatible with standard industrial fabrication techniques. By exploiting novel device geometries and recently-discovered phenomenon in ferromagnetic materials, easy-plane spin-orbit torque oscillators could address many problems plaguing conventional oscillators, such as small output signal, nanoscale confinement, and thermal instability. Applications for these new oscillators range from microwave communications to brain-inspired computing. This project also has an outreach component designed to teach K-12 students, especially those from schools underserved in science, how to build simple magnetic motors from household items, with the goal of sparking interest in science at an early age.This research aims to produce foundational knowledge for new spin-orbit torque oscillators based on current-in-plane spin valves, in which the free-layer magnetization precesses at a large cone angle of nearly 90 degrees. The research is inspired by a recent discovery that an electric current in an in-plane magnetized film produces an out-of-plane spin current. This novel spin current can then generate an antidamping torque, driving large-angle precession in the free layer of the spin valve. The first thrust of the research will identify the mechanisms of the out-of-plane spin current and the resulting antidamping torque in spin valves. To this end, first-principles calculations and spin-torque ferromagnetic resonance experiments will be performed on spin valves with systematically varied compositions and structures. The second thrust of the research will determine the critical requirements for stable, large-angle precession in spin valves through micromagnetic simulations and electrical device characterization. A successful outcome will lead to easy-plane oscillators with more than an order of magnitude higher signal and stability compared to existing spin-orbit torque oscillators, owing to a larger swing in magnetoresistance and stronger immunity against thermal fluctuations. Furthermore, the research will produce crucial fundamental knowledge on unconventional spin currents and spin torques, which can control a variety of magnetization dynamics (e.g., perpendicular magnetic switching, superfluid-like exchange flow) in next-generation spintronic 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.