# Detecting Light Dark Matter with Magnons

## TL;DR

This paper proposes using magnon excitations in magnetic materials as a novel method to detect light dark matter with spin-dependent interactions, complementing existing phonon-based detection techniques.

## Contribution

It introduces a new detection approach utilizing magnon excitations for spin-dependent dark matter interactions and provides formulas for excitation rates with a proof-of-concept analysis.

## Key findings

- Magnons can be excited by dark matter with spin-dependent couplings.
- Projected sensitivity of yttrium iron garnet to certain dark matter models.
- Magnon detection complements phonon-based methods for dark matter searches.

## Abstract

Scattering of light dark matter with sub-eV energy deposition can be detected with collective excitations in condensed matter systems. When dark matter has spin-independent couplings to atoms or ions, it has been shown to efficiently excite phonons. Here we show that, if dark matter couples to the electron spin, magnon excitations in materials with magnetic dipole order offer a promising detection path. We derive general formulae for single magnon excitation rates from dark matter scattering, and demonstrate as a proof of principle the projected reach of a yttrium iron garnet target for several dark matter models with spin-dependent interactions. This highlights the complementarity of various collective excitations in probing different dark matter interactions.