Investigation of infrared phonon modes in multiferroic single-crystal FeTe$_{2}$O$_{5}$Br

TL;DR

This study comprehensively measures and analyzes the infrared phonon modes in multiferroic FeTe$_{2}$O$_{5}$Br single crystals across a temperature range, revealing all predicted IR-active modes and their lattice dynamics.

Contribution

It provides the first detailed experimental and theoretical characterization of all IR-active phonon modes in FeTe$_{2}$O$_{5}$Br, including mode assignments and displacement patterns.

Findings

All 52 IR-active modes in the ac plane were observed.

43 out of 53 modes along the b axis were detected.

Mode assignments and lattice dynamics were elucidated.

Abstract

Reflection and transmission as a function of temperature (5--300 K) have been measured on single crystals of the multiferroic compound FeTe$_{2}$O$_{5}$Br utilizing light spanning the far infrared to the visible portions of the electromagnetic spectrum. The complex dielectric function and optical properties were obtained via Kramers-Kronig analysis and by fits to a Drude-Lortentz model. Analysis of the anisotropic excitation spectra via Drude-Lorentz fitting and lattice dynamical calculations have lead to the observation of all 52 IR-active modes predicted in the $ac$ plane and 43 or the 53 modes predicted along the b axis of the monoclinic cell. Assignments to groups (clusters) of phonons have been made and trends within them are discussed in light of our calculated displacement patterns.