Infrared reflectivity of the phonon spectra in multiferroic TbMnO3

TL;DR

This study investigates how phase transitions in multiferroic TbMnO3 influence its infrared phonon spectra, revealing magnetic and ferroelectric effects on phonon behavior and dielectric properties.

Contribution

It provides detailed analysis of phonon spectra changes across phase transitions in TbMnO3, highlighting the role of electromagnons and Mn displacements in ferroelectricity.

Findings

Antiferromagnetic transition affects phonon parameters along all axes.

Electromagnon along the a-axis significantly contributes to dielectric constant.

A specific phonon along the c-axis shows anomalies at the ferroelectric transition, linked to Mn vibrations.

Abstract

We measured the temperature dependent infrared reflectivity spectra of TbMnO3 with the electric field of light polarized along each of the three crystallographic axes. We analyzed the effect, on the phonon spectra, of the different phase transitions occurring in this material. We show that the antiferromagnetic transition at TN renormalizes the phonon parameters along the three directions. Our data indicate that the electromagnon, observed along the a direction, has an important contribution to the building of the dielectric constant. Only one phonon, observed along the c-axis, has anomalies at the ferroelectric transition. This phonon is built mostly from Mn vibrations, suggesting that Mn displacements are closely related to the formation of the ferroelectric order.