Chaos in nanomagnet via feedback current

TL;DR

This paper investigates chaotic behavior in nanomagnet dynamics driven by feedback current, combining numerical simulations and analytical theory to reveal multiple attractors and transitions caused by feedback effects.

Contribution

It provides the first combined numerical and analytical study of chaos in nanomagnet dynamics with feedback current, highlighting multiple attractors and transition mechanisms.

Findings

Positive Lyapunov exponent indicates chaos for certain feedback rates.

Transient chaos transitions to steady oscillations depending on feedback parameters.

Multiple attractors exist due to feedback, causing complex magnetization dynamics.

Abstract

Nonlinear magnetization dynamics excited by spin-transfer effect with feedback current is studied both numerically and analytically. The numerical simulation of the Landau-Lifshitz-Gilbert equation indicates the positive Lyapunov exponent for a certain range of the feedback rate, which identifies the existence of chaos in a nanostructured ferromagnet. Transient behavior from chaotic to steady oscillation is also observed in another range of the feedback parameter. An analytical theory is also developed, which indicates the appearance of multiple attractors in a phase space due to the feedback current. An instantaneous imbalance between the spin-transfer torque and damping torque causes a transition between the attractors, and results in the complex dynamics.