Measuring the magnon-photon coupling in shaped ferromagnets: tuning of the resonance frequency

TL;DR

This paper demonstrates how the geometry of ferromagnets influences magnon-photon coupling, enabling operation frequencies above 10 GHz and providing a theoretical framework for designing hybrid quantum systems with tailored magnetic resonances.

Contribution

It shows that ferromagnet shape significantly affects resonance frequency and coupling strength, introducing a method to tune these parameters for hybrid quantum applications.

Findings

Achieved operation frequencies above 10 GHz in shaped Permalloy samples

Validated estimation of magnon-photon coupling using both transmission lines and cavities

Developed a theoretical model matching experimental results

Abstract

Cavity photons and ferromagnetic spins excitations can exchange information coherently in hybrid architectures, at speeds set by their mutual coupling strength. Speed enhancement is usually achieved by optimizing the geometry of the electromagnetic cavity. Here we show that the geometry of the ferromagnet plays also an important role, by setting the fundamental frequency of the magnonic resonator. Using focused ion beam patterning, we vary the aspect ratio of different Permalloy samples reaching operation frequencies above 10 GHz while working at low external magnetic fields. Additionally, we perform broad band ferromagnetic resonance measurements and cavity experiments that demonstrate that the magnon-photon coupling strength can be estimated using either open transmission lines or resonant cavities, yielding very good agreement. Finally, we describe a simple theoretical framework based on electromagnetic and micromagnetic simulations that successfully accounts for the experimental results. This approach can be used to design hybrid quantum systems exploiting whatsoever magnetostatic mode excited in ferromagnets of arbitrary size and shape and to tune their operation conditions.