Direct probe of magnetic field effects on phonons by ultrasound propagation in a quasi-two-dimensional honeycomb magnet Na$_2$Co$_2$TeO$_6$

TL;DR

This study uses ultrasound measurements to investigate how magnetic fields influence phonons in Na$_2$Co$_2$TeO$_6$, revealing strong spin-lattice coupling and magnetic order details in this honeycomb magnet.

Contribution

It provides the first detailed ultrasound-based analysis of magnetic field effects on phonons in Na$_2$Co$_2$TeO$_6$, highlighting spin-lattice interactions and magnetic ground state characteristics.

Findings

Ultrasound detects significant spin-lattice coupling.

Identifies ferrimagnetic order below 27 K.

Supports a triple-Q magnetic ground state.

Abstract

We study the phonon behavior of a Co-based honeycomb frustrated magnet Na$_2$Co$_2$TeO$_6$ under magnetic field applied perpendicular to the honeycomb plane. The temperature and field dependence of the sound velocity and sound attenuation unveil prominent spin-lattice coupling in this material, promoting ultrasound as a sensitive probe for magnetic properties. An out-of-plane ferrimagnetic order is determined below the N\'eel temperature $T_N=27$~K. A comprehensive analysis of our data further supports a triple-Q ground state of Na$_2$Co$_2$TeO$_6$. Furthermore, the ultrasound data were systematically compared to the thermal transport results from literature, to unveil the importance of phononic contribution to the observed transport behaviors.