Magnons in a Quasicrystal: Propagation, Localization and Extinction of Spin Waves in Fibonacci Structures

TL;DR

This paper demonstrates the direct imaging of spin wave propagation and localization in a one-dimensional magnonic quasicrystal, revealing complex spectra with mini-band gaps influenced by quasiperiodicity, advancing magnonic metamaterials.

Contribution

It provides the first direct x-ray microscopic observation of spin waves in a magnonic quasicrystal and introduces a simple model for magnonic gap estimation.

Findings

Observation of propagating and evanescent spin waves in Fibonacci structures

Identification of mini-band gaps due to quasiperiodicity

Validation of a model for magnonic gap positions

Abstract

Magnonic quasicrystals exceed the possibilities of spin wave (SW) manipulation offered by regular magnonic crystals, because of their more complex SW spectra with fractal characteristics. Here, we report the direct x-ray microscopic observation of propagating SWs in a magnonic quasicrystal, consisting of dipolarly coupled permalloy nanowires arranged in a one-dimensional Fibonacci sequence. SWs from the first and second band as well as evanescent waves from the band gap between them are imaged. Moreover, additional mini-band gaps in the spectrum are demonstrated, directly indicating an influence of the quasiperiodicity of the system. The experimental results are interpreted using numerical calculations and we deduce a simple model to estimate the frequency position of the magnonic gaps in quasiperiodic structures. The demonstrated features of SW spectra in one-dimensional magnonic quasicrystals allows utilizing this class of metamaterials for magnonics and makes them an ideal basis for future applications.