Theoretical study of the phonon spectra of hexagonal multiferroicsRMnO3

Abstract

The phonon properties of hexagonal multiferroicRMnO3 materials are studied using a Green’s function technique. The calculations are performed onthe basis of the Heisenberg and the transverse Ising model taking into account anharmonicspin–phonon and phonon–phonon interaction terms. The strong spin–phononinteraction leads to an anomaly in the phonon energy and the damping around themagnetic and ferroelectric phase transitions. The phonon spectrum is discussed fordifferent exchange, magnetoelectric and spin–phonon interaction constants. Itis shown that the phonon energy depends on the radius of the rare earth ionrR. The influence of an applied magnetic field on the phonon spectrum is studied, too. Thepredictions are consistent with experimental results.