(Submitted on 19 Jan 2017)
We present an investigation of the multiferroic lacunar spinel compound GeV4 S8 using time-domain terahertz spectroscopy. We find three absorptions which either appear or shift at the antiferromagnetic transition temperature, TN∼17K , as magnetic moments develop on vanadium tetrahedra. Two of these absorptions are interpreted as phonons coupled to the magnetic state and one is interpreted as a magnon. We also observe isosbestic points in the dielectric constant in both the temperature and frequency domains. Further, we perform analysis on the isosbestic features to reveal an interesting collapse into a single curve of the dielectric constant as a function of both frequency and temperature, behavior which exists throughout the phase transitions. This analysis suggests the importance of spectral changes in the terahertz range which are linear in frequency and temperature
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