Magnetic terahertz resonances above the Néel temperature in the frustrated kagome antiferromagnet averievite

Time-domain magneto-THz spectroscopy is utilized to study the frustrated magnet averievite ${\mathrm{Cu}}_{5\ensuremath{-}x}{\mathrm{Zn}}_x{\mathrm{V}}₂{\mathrm{O}}₁₀$(CsCl). Pronounced THz resonances are observed in unsubstituted samples ($x=0$) when cooling below the onset of short-range magnetic correlations. The influence of external magnetic effects confirms the magnetic origin of these resonances. Increasing Zn substitution suppresses the resonances, as frustration effects dominate, reflecting the nonmagnetic phases for $x>0.25$ compounds. The temperature evolution of the THz spectra is complemented with electron spin resonance spectroscopy. This comparison allows a direct probe of the different contributions from magnetic order, frustration, and structural properties in the phase diagram of averievite. Our results illustrate the effect of magnetic interactions in THz spectra of frustrated magnets.