Effect of dipolar interactions on cavity magnon-polaritons

TL;DR

This paper investigates how dipolar interactions between YIG spheres affect the strong coupling with a cavity, revealing reduced coupling strength and increased losses as the spheres are brought closer, with implications for dense magnetic systems.

Contribution

It provides a model explaining the impact of dipolar interactions on photon-magnon coupling strength and magnetic losses in strongly coupled systems.

Findings

Coupling strength decreases with closer sphere proximity.

Magnetic losses increase as spheres are brought nearer.

A model of inhomogeneous broadening explains experimental observations.

Abstract

The strong photon-magnon coupling between an electromagnetic cavity and two yttrium iron garnet (YIG) spheres has been investigated in the context of a strong mutual dipolar interaction between the spheres. A decrease in the coupling strength between the YIG spheres and the electromagnetic cavity is observed, along with an increase of the total magnetic losses, as the distance between the spheres is decreased. A model of inhomogeneous broadening of the ferromagnetic resonance linewidth, partly mitigated by the dipolar narrowing effect, reproduces the reduction in the coupling strength observed experimentally. These findings have important implications for the understanding of strongly coupled photon-magnon system involving densely packed magnetic objects, such as ferromagnetic nanowires arrays, in which the total coupling strength with an electromagnetic cavity might become limited due to mutual dipolar interactions.