Critical slowing down near the multiferroic phase transition in MnWO$_4$

TL;DR

This study uses broadband dielectric spectroscopy to observe critical slowing down of electromagnons near the multiferroic phase transition in MnWO4, revealing soft-mode behavior and unique scaling properties.

Contribution

It reports the first observation of electromagnon softening and critical dynamics near the multiferroic transition in MnWO4 using radiofrequency and microwave spectroscopy.

Findings

Critical slowing down of electromagnons near T_N2

Electromagnons exhibit soft-mode behavior similar to ferroelectrics

Scaling exponent of slowing down exceeds one, indicating unconventional critical dynamics

Abstract

By using broadband dielectric spectroscopy in the radiofrequency and microwave range we studied the magnetoelectric dynamics in the multiferroic chiral antiferromagnet MnWO$_4$. Above the multiferroic phase transition at $T_{N2} \approx 12.6$ K we observe a critical slowing down of the corresponding magnetoelectric fluctuations resembling the soft-mode behavior in canonical ferroelectrics. This electric field driven excitation carries much less spectral weight than ordinary phonon modes. Also the critical slowing down of this mode scales with an exponent larger than one which is expected for magnetic second order phase transition scenarios. Therefore the investigated dynamics have to be interpreted as the softening of an electrically active magnetic excitation, an electromagnon.