Infrared study of the charge-ordered multiferroic LuFe(2)O(4)

TL;DR

This study investigates the temperature-dependent infrared reflectivity of LuFe(2)O(4), revealing significant phonon spectrum changes across its charge-order transition and providing insights into its multiferroic properties.

Contribution

It provides detailed infrared spectral analysis of LuFe(2)O(4) across the charge-order transition, linking phonon mode changes to structural symmetry alterations.

Findings

Phonon spectrum changes dramatically at T_CO=320K

Transition from rhombohedral to monoclinic symmetry confirmed

Low-temperature peak in sub-THz region discussed

Abstract

The reflectivity of a large LuFe(2)O(4) single crystal has been measured with the radiation field either perpendicular or parallel to the c axis of its rhombohedral structure, from 10 to 500K, and from 7 to 16000 cm-1. The transition between the two-dimensional and the three-dimensional charge order at T_(CO) = 320 K is found to change dramatically the phonon spectrum in both polarizations. The number of the observed modes above and below T_(CO), according to a factor-group analysis, is in good agreement with a transition from the rhombohedral space group R{bar 3}m to the monoclinic C2/m. In the sub-THz region a peak becomes evident at low temperature, whose origin is discussed in relation with previous experiments.