First principles calculation of the phonons modes in the hexagonal $\rm YMnO_3$ ferroelectric and paraelectric phases

TL;DR

This study uses first principles calculations to analyze phonon modes in YMnO_3's ferroelectric and paraelectric phases, confirming phase transition characteristics and proposing a candidate for the electro-magnon mode.

Contribution

It provides detailed phonon mode analysis across phases and supports the ferroelectric to paraelectric transition hypothesis using computational and group theory methods.

Findings

Phonon modes observed at 1200K are consistent with the ferroelectric P6_3cm space group.

The study proposes a candidate for the electro-magnon mode that couples strongly to magnetic interactions.

Good agreement between computational and experimental data in the low-temperature phase.

Abstract

The lattice dynamics of the $\rm YMnO_3$ magneto-electric compound has been investigated using density functional calculations, both in the ferroelectric and the paraelectric phases. The coherence between the computed and experimental data is very good in the low temperature phase. Using group theory, modes continuity and our calculations we were able to show that the phonons modes observed by Raman scattering at 1200K are only compatible with the ferroelectric $P6_{3} cm$ space group, thus supporting the idea of a ferroelectric to paraelectric phase transition at higher temperature. Finally we proposed a candidate for the phonon part of the observed electro-magnon. This mode, inactive both in Raman scattering and in Infra-Red, was shown to strongly couple to the Mn-Mn magnetic interactions.