Magnonic band structure in CoFeB/Ta/NiFe meander-shaped magnetic bilayers

TL;DR

This study explores the magnonic band structure in nanoscale CoFeB/Ta/NiFe meander-shaped magnetic bilayers, revealing how dipolar coupling influences spin-wave modes through experimental and simulation methods.

Contribution

It provides the first detailed experimental and simulation analysis of magnonic band structures in three-dimensional bilayer meander structures with complex mode distributions.

Findings

Dispersive modes oscillate periodically over Brillouin zones.

Modes extend over entire sample, localized in specific layers.

Dipolar coupling affects the magnonic band structure.

Abstract

In this work, we investigate the spin-wave propagation in three-dimensional nanoscale CoFeB/Ta/NiFe meander structures fabricated on a structured SiO2/Si substrate. The magnonic band structure has been experimentally determined by wavevector-resolved Brillouin light scattering (BLS) spectroscopy and a set of stationary modes interposed by two dispersive modes of Bloch type have been identified. The results could be understood by micromagnetic and finite element simulations of the mode distributions in both real space and the frequency domain. The dispersive modes periodically oscillate in frequency over the Brillouin zones and correspond to modes, whose spatial distributions extend over the entire sample and are either localized exclusively in the CoFeB layer or the entire CoFeB/Ta/NiFe magnetic bilayer. Stationary modes are mainly concentrated in the vertical segments of the CoFeB and NiFe layers and show negligible amplitudes in the horizon-tal segments. The findings are compared with those of single-layer CoFeB meander structures with the same geometry parameters, which reveals the influence of the dipolar coupling between the two ferromagnetic layers on the magnonic band structure.