Parallel pumping of magnetic vortex gyrations in spin-torque nano-oscillators

TL;DR

This paper demonstrates the parametric excitation of magnetic vortex oscillations in spin-torque nano-oscillators using parallel pumping with rf currents, revealing mechanisms of amplification and instability.

Contribution

It provides the first experimental demonstration and theoretical analysis of parallel pumping of vortex gyrations in magnetic tunnel junctions.

Findings

Large vortex oscillations can be parametrically excited by rf currents.

Experimental results align with theories of parametric amplification and instability.

Amplitude saturation and coexistence of stable regimes are explained by energy nonlinearities.

Abstract

We experimentally demonstrate that large magnetic vortex oscillations can be parametrically excited in a magnetic tunnel junction by the injection of radio-frequency (rf) currents at twice the natural frequency of the gyrotropic vortex core motion. The mechanism of excitation is based on the parallel pumping of vortex motion by the rf orthoradial field generated by the injected current. Theoretical analysis shows that experimental results can be interpreted as the manifestation of parametric amplification when rf current is small, and of parametric instability when rf current is above a certain threshold. By taking into account the energy nonlinearities, we succeed to describe the amplitude saturation of vortex oscillations as well as the coexistence of stable regimes.