Terahertz spectroscopy in the pseudo-Kagome system Cu3Bi(SeO3)2O2Br

Terahertz (THz) transmission spectra have been measured as a function of temperature and magnetic field on single crystals of Cu3Bi(SeO3)(2)O2Br. In time-domain THz spectra without magnetic field, two resonance absorptions are observed below the magnetic ordering temperature T-N similar to 27.4 K. The corresponding resonance frequencies increase with decreasing temperature and reach energies of 1.28 and 1.23 meV at 3.5 K. Multifrequency electron spin resonance transmission spectra as a function of the applied magnetic field show the field dependence of four magnetic resonance modes, which can be modeled as a ferromagnetic resonance including demagnetization and anisotropy effects.