Chaotic Spin Dynamics of a Long Nanomagnet Driven by a Current

TL;DR

This paper investigates the complex spin dynamics of a long nanomagnet driven by electrical currents, revealing bifurcation behaviors, chaos, and turbulence, supported by Melnikov theory predictions.

Contribution

It introduces a Melnikov integral approach to predict chaos in nanomagnet spin dynamics under DC and AC currents, highlighting new theoretical insights.

Findings

DC current induces complex bifurcation and weak chaos.

AC current leads to limit cycles or turbulence depending on damping.

Melnikov theory predicts chaos and transient chaos accurately.

Abstract

We study the spin dynamics of a long nanomagnet driven by an electrical current. In the case of only DC current, the spin dynamics has a sophisticated bifurcation diagram of attractors. One type of attractors is a weak chaos. On the other hand, in the case of only AC current, the spin dynamics has a rather simple bifurcation diagram of attractors. That is, for small Gilbert damping, when the AC current is below a critical value, the attractor is a limit cycle; above the critical value, the attractor is chaotic (turbulent). For normal Gilbert damping, the attractor is always a limit cycle in the physically interesting range of the AC current. We also developed a Melnikov integral theory for a theoretical prediction on the occurrence of chaos. Our Melnikov prediction seems performing quite well in the DC case. In the AC case, our Melnikov prediction seems predicting transient chaos. The sustained chaotic attractor seems to have extra support from parametric resonance leading to a turbulent state.