Terahertz spectroscopy of multiferroic EuFe3(BO3)4

The terahertz spectra of a rare-earth iron borate with the huntite structure are obtained for the first time. We study the low-temperature (4.0–90 K) α-polarized transmittance spectra of the EuFe₃(BO₃)₄ single crystal in the region 0.9–6.0 THz. Pronounced shifts of phonon frequencies and appearance of new phonon modes at the temperature _TS=58 K$T_S=58\text{K}$ of the R32→P₃₁21$R32\to P{3}_{1}21$ structural phase transition are observed. Additional shifts of phonon frequencies occur at the temperature _TN=34 K$T_N=34\text{K}$ of the magnetic ordering of the Fe subsystem, thus evidencing the spin–phonon coupling in this multiferroic material.