Spin-Orbit-Torque Oscillators Driven by Out-of-Plane Spin Currents

Spin torque oscillators are important candidates for many spintronic applications, ranging from neuromorphic computing to magnetic recording. Many conventional spin-torque oscillators suffer from small cone angle precession, susceptibility to thermal fluctuations, and expensive manufacturing, all of which make conventional spin-torque oscillators difficult for commercial uses. We explore the use of a new class of spin-torque oscillators that operate by running a current in-plane and utilizing spin-orbit effects to drive oscillations. The in-plane current through a ferromagnetic layer generates a spin-current where both the flow and spin direction are out-of-plane. The out-of-plane spin current tilts the magnetic moment of a ferromagnet out of plane, enabling sustained oscillations around the demagnetization field. In-plane spin currents are also generated in this process, via the spin Hall effect, which may reduce the performance of the oscillations resulting from the out-of-plane spin currents. To understand the conditions necessary to drive self-sustained oscillations, we vary the spin direction of the out-of-plane flowing spin current from 0° (out-of-plane) to 90° (in-plane) across a variety of spin current densities. Particular attention is being placed on small out of plane torques, resulting from low angled spin polarization, and their ability to enable self-sustained oscillations. Finally, we determine the temperature dependence of the amplitude and frequency of self-sustained oscillations in this novel spin-orbit torque oscillator. Our micromagnetic simulations of this easy plane, spin-orbit torque oscillator will help researchers determine how to employ unconventional spin currents in novel spintronic devices.