Vibrational Spectra and Elastic, Piezoelectric, and Magnetoelectric Properties of HoFe_3(BO_3)_4 and HoAl_3(BO_3)_4 Crystals

摘要

Raman spectra of light are obtained for HoFe_3(BO_3)_4 and HoAl_3(BO_3)_4 crystals at various temperatures and are used for determining the frequencies of crystal lattice vibrations at the center of the Brillouin zone. It is also found that the HoFe_3(BO_3)_4 crystal exhibits a phase transition at T_c ≈ 366 K. The magnetoelectric effect in the paramagnetic phase of these compounds is studied experimentally. The lattice vibration frequencies, elastic and piezoelectric moduli, Born dynamic charges, and the high-frequency permittivity are calculated using the density functional method. A peculiar behavior of the transverse acoustic vibration branch is observed in the Γ → Z direction of the Brillouin zone of the HoFe_3(BO_3)_4 crystal. The electric polarization induced by an external field is estimated using the calculated values of piezoelectric moduli and experimental values of magnetostriction.