Self-injection locking of a vortex spin torque oscillator by delayed feedback

TL;DR

This paper experimentally studies how delayed feedback can synchronize and enhance the performance of vortex spin torque oscillators, revealing oscillatory behavior and control mechanisms for their non-autonomous dynamics.

Contribution

It demonstrates the effects of delayed feedback on spin torque oscillators and models their behavior, offering new control strategies for spintronic and neuro-inspired devices.

Findings

Power and linewidth are optimized at specific delay times.

Oscillatory dependence of frequency, power, and linewidth on phase difference.

Model accurately describes the self-injection and synchronization phenomena.

Abstract

The self-synchronization of spin torque oscillators is investigated experimentally by re-injecting its radiofrequency (rf) current after a certain delay time. We demonstrate that the emission power and the spectral linewidth are improved for optimal delay times. Moreover by varying the phase difference between the emitted power and the re-injected one, we find a clear oscillatory dependence with a 2\pi\ periodicity of the frequency of the oscillator as well as its power and linewidth. Such periodical behavior within the self-injection regime is well described by the general model of nonlinear auto-oscillators including not only a delayed rf current but also all spin torque forces responsible for the self-synchronization. Our results reveal new approaches for controlling the non-autonomous dynamics of spin torque oscillators, a key issue for rf spintronics applications as well as for the development of neuro-inspired spin-torque oscillators based devices.