Abstract
Transmittance spectra of single crystals have been studied in the far-infrared spectral range in the external magnetic fields up to 9 T and at low temperatures down to 1.5 K. The temperature and magnetic-field dependencies of the antiferromagnetic resonance (AFMR) modes have been measured below and above the magnetic ordering temperature of Tb moments . Both the quasiferromagnetic and quasiantiferromagnetic modes of AFMR demonstrate hardening at . The quasiantiferromagnetic mode gains electric-dipole activity along the axis below and thus behaves as a hybrid, i.e., both electric- and magnetic-dipole active, mode. In addition to AFMR modes, below we observed the appearance of electromagnon excitation at about , which is electric-dipole active along the axis. The electromagnon is optically active only in a narrow temperature range, at , and in a narrow range of magnetic fields 2.4–2.7 T applied along the axis at . We argue that this electromagnon appears in magnetic phases, which are compatible with a spontaneous electric polarization along the axis.
1 More- Received 15 November 2016
DOI:https://doi.org/10.1103/PhysRevB.95.054427
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