# Helimagnon resonances in an intrinsic chiral magnonic crystal

## TL;DR

This study experimentally investigates helimagnon resonances in the chiral magnetic insulator Cu$_2$OSeO$_3$, revealing multiple resonance modes and bandgaps consistent with theoretical bandstructure calculations, advancing understanding of chiral magnonic crystals.

## Contribution

It provides the first experimental identification of multiple helimagnon resonances and bandgaps in an intrinsic chiral magnonic crystal, confirming theoretical predictions.

## Key findings

- Identified three distinct helimagnon resonance sets.
- Resonance frequencies match helimagnon bandstructure calculations.
- Observed magnon band-gaps due to chiral magnetic ordering.

## Abstract

We experimentally study magnetic resonances in the helical and conical magnetic phases of the chiral magnetic insulator Cu$_2$OSeO$_3$ at the temperature $T$=5 K. Using a broadband microwave spectroscopy technique based on vector network analysis, we identify three distinct sets of helimagnon resonances in the frequency range 2 GHz $\leq f \leq$ 20 GHz. The extracted resonance frequencies are in accordance with calculations of the helimagnon bandstructure found in an intrinsic chiral magnonic crystal. The periodic modulation of the equilibrium spin direction that leads to the formation of the magnonic crystal is a direct consequence of the chiral magnetic ordering caused by the Dzyaloshinskii-Moriya interaction. The opening of magnon band-gaps allows for excitation of helimagnons with wave vectors that are multiples of the spiral wave vector.