Here we present a detailed study of the THz and FIR response of the mixed perovskite manganite system Eu1−xHoxMnO3 for holmium concentrations x = 0.1 and 0.3. We compare the magnetic excitations of the four different magnetically ordered phases (A-type antiferromagnetic, sinusoidally modulated collinear, helical phases with spin planes perpendicular to the crystallographic a and c axes). The transition between the two latter phases goes hand in hand with a switching of the ferroelectric polarization from P||a to P||c. Special emphasis is paid to the temperature dependence of the excitations at this transition. We find a significant change of intensity indicating that the exchange striction mechanism cannot be the only mechanism to induce dipolar weight to spin-wave excitations. We also focus on excitations within the incommensurate collinear antiferromagnetic phase and find a so far unobserved excitation close to 40 cm−1. A detailed analysis of optical weight gives a further unexpected result: In the multiferroic phase with P||c all the spectral weight of the electromagnons comes from the lowest phonon mode. However, for the phase with the polarization P||a additional spectral weight must be transferred from higher frequencies.
@article{arxiv.1601.04486,
title = {Electromagnons, magnons, and phonons in Eu$_{1-x}$Ho$_x$MnO$_3$},
author = {Zhenyu Chen and M. Schmidt and Zhe Wang and F. Mayr and J. Deisenhofer and A. A. Mukhin and A. M. Balbashov and A. Loidl},
journal= {arXiv preprint arXiv:1601.04486},
year = {2016}
}