Complex dynamics of nano-oscillators with dual vortex free layers mutually coupled via spin-torques

TL;DR

This paper investigates the complex dynamical behaviors of spin-torque vortex oscillators with two mutually coupled vortex layers, revealing various regimes including chaos, through extensive micromagnetic simulations.

Contribution

It introduces a detailed study of coupled vortex layers in spin-torque oscillators, highlighting new complex dynamical regimes and the effects of layer asymmetry and vortex configurations.

Findings

Identification of self-modulated gyration regimes

Discovery of C-state dynamics in coupled vortex layers

Observation of chaotic transitions between dynamical states

Abstract

Spin-torque vortex oscillators (STVOs) have been shown to exhibit rich and complex dynamical regimes, which are strongly dependent on the polarizer's configuration. Here, we give an overview of the dynamics in an STVO comprising two vortex free layers, where each layer serves as a dynamic polarizer for the other, increasing the number of degrees of freedom and therefore, the complexity of the system. The dynamics are studied through extensive micromagnetic simulations, performed using our own implementation of the coupled equations of motion, implemented in the open-source micromagnetics code Mumax3. We explore the roles of relative vortex configurations and layer asymmetry on the current-driven dynamics, and find several complex regimes, including self-modulated gyration, the emergence of C-state dynamics, as well as chaotic transitions between regular gyration and this C-state.