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

信息和通信技术的快速增长继续对全球能源消费产生过大的影响。因此，创造有利于这项技术的新的、节能的电子元件是至关重要的。一种这样的基本设备将恒定电压输入转换为振荡电压输出。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力矩振荡器，与标准的工业制造技术兼容。通过利用新的器件几何结构和最近在铁磁材料中发现的现象，易平面自旋轨道力矩振荡器可以解决困扰传统振荡器的许多问题，如输出信号小、纳米尺度的限制和热不稳定性。这些新型振荡器的应用范围从微波通信到大脑启发的计算。该项目还有一个推广部分，旨在教K-12年级的学生，特别是那些科学服务不足的学校的学生，如何用家庭用品制造简单的磁电机，目的是在早期激发人们对科学的兴趣。这项研究旨在为基于面内电流自旋阀的新型自旋轨道扭矩振荡器提供基础知识，在这种振荡器中，自由层磁化以近90度的大圆锥角进行。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面外自旋电流。这种新的自旋电流可以产生抗阻尼力矩，驱动自旋阀自由层中的大角度进动。这项研究的第一个推力将确定自旋阀中离面自旋电流和由此产生的抗阻尼力矩的机制。为此，将在具有系统变化的组成和结构的自旋阀上进行第一性原理计算和自旋扭矩铁磁共振实验。研究的第二个推力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。成功的结果将使易平面振荡器的信号和稳定性比现有的自旋轨道扭矩振荡器高一个数量级以上，这是因为磁阻摆动更大，对热波动的免疫力更强。此外，这项研究将产生关于非传统自旋电流和自旋力矩的关键基础知识，这些知识可以控制下一代自旋电子器件中的各种磁化动力学(例如，垂直磁开关、超流态交换流)。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。

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.