Electric-dipole active two-magnon excitation in {\textit{ab}} spiral spin phase of a ferroelectric magnet Gd$_{\textbf{0.7}}$Tb$_{\textbf{0.3}}$MnO$_{\textbf 3}$

N. Kida; Y. Yamasaki; R. Shimano; T. Arima; Y. Tokura

doi:10.1143/JPSJ.77.123704

paper

Electric-dipole active two-magnon excitation in {\textit{ab}} spiral spin phase of a ferroelectric magnet Gd $_{0.7}$ Tb $_{0.3}$ MnO $_{3}$

arXiv:0811.4098 · doi:10.1143/JPSJ.77.123704

Abstract

A broad continuum-like spin excitation (1--10 meV) with a peak structure around 2.4 meV has been observed in the ferroelectric $ab$ spiral spin phase of Gd $_{0.7}$ Tb $_{0.3}$ MnO $_{3}$ by using terahertz (THz) time-domain spectroscopy. Based on a complete set of light-polarization measurements, we identify the spin excitation active for the light $E$ vector only along the a-axis, which grows in intensity with lowering temperature even from above the magnetic ordering temperature but disappears upon the transition to the $A$ -type antiferromagnetic phase. Such an electric-dipole active spin excitation as observed at THz frequencies can be ascribed to the two-magnon excitation in terms of the unique polarization selection rule in a variety of the magnetically ordered phases.

11 pages including 3 figures

Electric-dipole active two-magnon excitation in {\textit{ab}} spiral spin phase of a ferroelectric magnet Gd0.7​Tb0.3​MnO3​

Abstract

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Electric-dipole active two-magnon excitation in {\textit{ab}} spiral spin phase of a ferroelectric magnet Gd $_{0.7}$ Tb $_{0.3}$ MnO $_{3}$