Optimization of Multi-Frequency Magnonic Waveguides with Enhanced Group Velocities by Exchange Coupled Ferrimagnet/Ferromagnet Bilayers

TL;DR

This paper demonstrates that exchange-coupled ferrimagnet/ferromagnet bilayers support high-velocity spin wave modes, which can be used to improve multi-frequency spin wave logic devices.

Contribution

It introduces a novel bilayer structure that exhibits enhanced group velocities of spin waves due to exchange coupling, confirmed by broadband spectroscopy and finite element simulations.

Findings

Identification of a high-velocity spin wave mode in the bilayer

Confirmation of mode hybridization via simulations

Potential application in multi-frequency spin wave devices

Abstract

We report broadband spectroscopy and numerical analysis by which we explore propagating spin waves in a magnetic bilayer consisting of a 23 nm thick permalloy film deposited on 130 nm thick $Y_{3}Fe_{5}O_{12}$. In the bilayer, we observe a characteristic mode that exhibits a considerably larger group velocity at small in-plane magnetic field than both the magnetostatic and perpendicular standing spin waves. Using the finite element method, we confirm the observations by simulating the mode profiles and dispersion relations. They illustrate the hybridization of spin wave modes due to exchange coupling at the interface. The high-speed propagating mode found in the bilayer can be utilized to configure multi-frequency spin wave channels enhancing the performance of spin wave based logic devices.