Magnon Polarons induced by a magnetic field gradient

TL;DR

This paper proposes a theoretical method to generate and control magnon polarons using magnetic field gradients, enabling new manipulation techniques in magnonic and spintronic devices.

Contribution

It introduces a novel approach to induce magnon-phonon coupling via magnetic field gradients and develops a general theoretical framework for arbitrary magnetic materials.

Findings

Magnetic field gradients can induce magnon-phonon coupling.

The coupling strength depends on the gradient magnitude.

Predicted magnon polaron bandgap similar to YIG with feasible gradients.

Abstract

In this work, we report the theoretical possibility of generating magnon polaron excitations through a space-varying magnetic field. The spatial dependence of the magnetic field in the Zeeman interaction gives rise to a magnon-phonon coupling when a magnetic field gradient is applied, and such a coupling depends directly on the strength of the gradient. It is also predicted that the direction of the magnetic field gradient allows control over which phonon polarization couples to the magnons in the material. Here we develop the calculations of the magnon-phonon coupling for an arbitrary (anti)ferromagnet, which are later used to numerically study its consequences. These results are compared to the ones obtained with the phenomenological magnetoelastic coupling in YIG, where we show that the magnon polaron bandgap seen in YIG can be also obtained with a magnetic field gradient of $\sim 0.1$T/m which can be achieved with the current experimental techniques. Our results propose a new way of controlling the magnetoelastic coupling in an arbitrary material and open a new route to exploit the magnon-phonon interaction in magnonic and spintronic devices.