Chaotic Antiferromagnetic Nano-Oscillator driven by Spin-Torque

TL;DR

This paper theoretically investigates a terahertz antiferromagnetic nano-oscillator driven by spin torque, identifying conditions for chaotic behavior and analyzing the transition mechanisms using bifurcation theory.

Contribution

It introduces a detailed theoretical model of a spin-torque driven antiferromagnetic nano-oscillator and characterizes the onset of chaos near the spin-flop transition.

Findings

Chaotic regimes occur at low threshold currents near the spin-flop transition.

Chaos is preceded by quasiperiodic dynamics on a two-frequency torus.

The transition to chaos involves a Neimark-Sacker bifurcation.

Abstract

We theoretically describe the behavior of a terahertz nano-oscillator based on an anisotropic antiferromagnetic dynamical element driven by spin torque. We consider the situation when the polarization of the spin-current is perpendicular to the external magnetic field applied along the anisotropy easy-axis. We determine the domain of the parametric space (field, current) where the oscillator demonstrates chaotic dynamics. Characteristics of the chaotic regimes are analyzed using conventional techniques such as spectra of the Lyapunov exponents. We show that the threshold current of the chaos appearance is particularly low in the vicinity of the spin-flop transition. In this regime, we consider the mechanism of the chaos appearance in detail when the field is fixed and the current density increases. We show that the appearance of chaos is preceded by a regime of quasiperiodic dynamics on the surface of a two-frequency torus arising in phase space as a result of the Neimark-Sacker bifurcation.