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

Indiana University, Bloomington IN

Investigators

Abstract

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.