Eur. Phys. J. B 71, 411-418 (2009)
https://doi.org/10.1140/epjb/e2009-00215-3

Far-infrared optical excitations in multiferroic TbMnO₃

¹ Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, 86135 Augsburg, Germany
² General Physics Institute of the Russian Academy of Sciences, 119991 Moscow, Russia
³ Moscow Power Engineering Institute, 105835 Moscow, Russia

Corresponding author: ^a michael.schmidt@physik.uni-augsburg.de

Received: 1 April 2009
Published online: 23 June 2009

Abstract

We provide a detailed study of the reflectivity of multiferroic TbMnO₃ for wave numbers from 40 cm^-1 to 1000 cm^-1 and temperatures 5 K < T < 300 K. Excitations are studied for polarization directions E || a, the polarization where electromagnons are observed, and for E || c, the direction of the spontaneous polarization in this material. The temperature dependencies of eigenfrequencies, damping constants and polar strengths of all modes are studied and analyzed. For E || a and below the spiral ordering temperature of about 27 K we observe a transfer of optical weight from phonon excitations to electromagnons, which mainly involves low-frequency phonons. For E || c an unusual increase of the total polar strength and hence of the dielectric constant is observed indicating significant transfer of dynamic charge probably within manganese-oxygen bonds on decreasing temperatures.