Anomalous increasing of the intensity of field dependence optical mode ferromagnetic resonance in the exchange coupled bilayer system

TL;DR

This study investigates the unusual increase in optical ferromagnetic resonance peak intensity in an exchange-coupled FeNi/Co bilayer, combining experimental data and analytical modeling to understand the underlying mechanisms.

Contribution

It provides a combined experimental and theoretical analysis of the increasing optical FMR peak in exchange-coupled bilayers, highlighting the dependence on layer thickness and magnetic field.

Findings

Optical FMR peak intensity increases unexpectedly with magnetic field.

The peak behavior depends on the layer thickness and a critical magnetic field.

The results offer insights into interlayer exchange coupling effects on optical FMR.

Abstract

Acoustic and optical ferromagnetic resonance (FMR) in the interlayer exchange coupled Fe$_{20}$Ni$_{80}$/Co bilayer have been investigated. In the optical mode, unexpected increasing tendencies of peak value at the resonance frequency has been observed under an increasing magnetic field. We presented analytical calculations with which the exchange coupling between Co and Fe$_{20}$Ni$_{80}$ layers, the magnetization and the in-plane uniaxial anisotropy are taken into account, to interpret the increasing of the maximum values of the optical permeability. Both experimental measurements and theoretical calculation show that such tendencies are dependent on the layer thickness t, and that there is a critical field above which the optical peak value begins to decrease. These results might help us to understand the mechanism of interlayer exchange coupling induced optical FMR and might enlighten us to find new possibility of high frequency applications of magnetic materials.