Magnetoelastic signatures of the conical state and charge density waves in antiferromagnetic FeGe

TL;DR

This study reveals two distinct energy scales in FeGe, a kagome antiferromagnet, associated with magnetic and charge-density-wave fluctuations, using ultrasound and neutron diffraction measurements.

Contribution

It identifies magnetic stiffness as a key parameter controlling spin-lattice dynamics and demonstrates ultrasound as an effective probe of coupled collective modes.

Findings

Field-tunable magnetic fluctuation channel at ~35 K linked to the conical state.

Field-independent charge-density-wave fluctuation channel at ~100 K.

Ultrasound measurements reveal exchange-renormalized magnetic stiffness softening.

Abstract

Kagome systems host intertwined spin, charge, and lattice degrees of freedom that drive emergent collective states. Here, we identify two distinct energy scales in the noncollinear kagome magnet FeGe: a field-tunable magnetic fluctuation channel at $\sim 35$~K associated with the conical state, and a field-independent channel at $\sim 100$~K linked to charge-density-wave fluctuations. Ultrasound measurements provide direct access to the exchange-renormalized magnetic stiffness, whose softening governs the acoustic anomaly and follows a symmetry-constrained quadratic field dependence. We further predict a linear temperature dependence of neutron diffraction intensities at fixed field and a quadratic field suppression at fixed temperature. These results identify magnetic stiffness as a key control parameter of spin-lattice dynamics and establish ultrasound as a sensitive probe of coupled collective modes.