Magnetic vortex oscillator driven by dc spin-polarized current

TL;DR

This paper demonstrates that a magnetic vortex within a nanoscale spin valve can be driven into persistent microwave-frequency oscillations by a dc spin-polarized current, enabling potential applications in microwave devices and studies of vortex dynamics.

Contribution

It shows for the first time that a nonuniform magnetic vortex can be excited into sustained oscillations by dc current, expanding the scope of spin-torque nano-oscillator research.

Findings

Vortex oscillations can be induced by dc current in zero magnetic field.

Oscillations have linewidths narrower than 300 kHz.

Micromagnetic simulations confirm vortex core precession as the oscillation mechanism.

Abstract

Transfer of angular momentum from a spin-polarized current to a ferromagnet provides an efficient means to control the dynamics of nanomagnets. A peculiar consequence of this spin-torque, the ability to induce persistent oscillations of a nanomagnet by applying a dc current, has previously been reported only for spatially uniform nanomagnets. Here we demonstrate that a quintessentially nonuniform magnetic structure, a magnetic vortex, isolated within a nanoscale spin valve structure, can be excited into persistent microwave-frequency oscillations by a spin-polarized dc current. Comparison to micromagnetic simulations leads to identification of the oscillations with a precession of the vortex core. The oscillations, which can be obtained in essentially zero magnetic field, exhibit linewidths that can be narrower than 300 kHz, making these highly compact spin-torque vortex oscillator devices potential candidates for microwave signal-processing applications, and a powerful new tool for fundamental studies of vortex dynamics in magnetic nanostructures.