Spontaneous Exact Spin-Wave Fractals in Magnonic Crystals

TL;DR

This paper reports the first observation of spontaneous exact spin-wave fractals in magnonic crystals, demonstrating how increasing microwave power induces a hierarchy of frequency combs through modulational instability.

Contribution

It introduces the experimental discovery of magnetic media spontaneously forming fractal spin-wave patterns via nonlinear dynamics and modulational instability.

Findings

Observation of frequency combs forming hierarchically with increased microwave power

Demonstration of fractal structures in the frequency domain and time domain

First experimental evidence of spin-wave fractals in magnonic crystals

Abstract

Exact fractals of nonlinear waves that rely on strong dispersion and nonlinearity and arise spontaneously out of magnetic media were observed for the first time. The experiments make use of a microwave to excite a spin wave in a quasi-one-dimensional magnonic crystal. When the power of the input microwave (Pin) is low, the output signal has a power-frequency spectrum that consists of a single peak. When Pin is increased to a certain level, the new side modes are generated through modulational instability (MI), resulting in a comb-like frequency spectrum. With a further increase in Pin, each peak in the frequency comb can evolve into its own, finer comb through the MI. As Pin is increased further, one can observe yet another set of finer frequency combs. Such a frequency-domain fractal manifests itself as multiple layers of amplitude modulation in the time-domain signal.