Magnonic band structure in vertical meander-shaped CoFeB thin films

TL;DR

This paper investigates the spin wave dispersion in vertical meander-shaped CoFeB thin films, revealing band gaps and mode localization, which could enable advanced three-dimensional magnonic signal processing architectures.

Contribution

It presents the first detailed analysis of spin wave band structure in vertical meander-shaped CoFeB films, combining experimental, simulation, and analytical methods.

Findings

Identification of frequency band gaps at specific wave numbers

Observation of propagating modes in orthogonal segments for certain wavenumbers

Demonstration of three-dimensional wave propagation potential

Abstract

The dispersion of spin waves in vertical meander-shaped CoFeB thin films consisting of segments located at 90{\deg} angles with respect to each other is investigated by Brillouin light scattering spectroscopy. We reveal the periodic character of several dispersive branches as well as alternating frequency ranges where spin waves are allowed or forbidden to propagate. Noteworthy is the presence of the frequency band gaps between each couple of successive modes only for wave numbers k=n$\pi$/a, where n is an even integer number and a is the size of the meander unit cell, whereas the spectra show propagating modes in the orthogonal film segments for the other wavenumbers. The micromagnetic simulations and analytical calculations allow us to understand and explain the results in terms of the mode spatial localization and symmetry. The obtained results demonstrate the wave propagation in three dimensions opening the path for multi-level magnonic architectures for signal processing.