Microwave interference from a spin ensemble and its mirror image in waveguide magnonics

TL;DR

This paper studies microwave interference effects in waveguide magnonics caused by a spin ensemble and its mirror image, revealing sinusoidal frequency shifts, oscillatory decay variations, and tunable photon absorption and magnon lifetime enhancements.

Contribution

It demonstrates how the position of a spin ensemble relative to a mirror influences microwave resonance, decay, and photon absorption, providing a method to control magnonic properties.

Findings

Resonance frequency shifts sinusoidally with mirror distance.

Magnon radiative decay oscillates with cosine squared dependence.

Magnon lifetime can be extended over eightfold by positioning near a node.

Abstract

We investigate microwave interference from a spin ensemble and its mirror image in a one-dimensional waveguide. Away from the mirror, the resonance frequencies of the Kittel mode (KM) inside a ferrimagnetic spin ensemble have sinusoidal shifts as the normalized distance between the spin ensemble and the mirror increases compared to the setup without the mirror. These shifts are a consequence of the KM's interaction with its own image. Furthermore, the variation of the magnon radiative decay into the waveguide shows a cosine squared oscillation and is enhanced twofold when the KM sits at the magnetic antinode of the corresponding eigenmode. We can finely tune the KM to achieve the maximum adsorption of the input photons at the critical coupling point. Moreover, by placing the KM in proximity to the node of the resonance field, its lifetime is extended to more than eight times compared to its positioning near the antinode.