Magnetic ordering effects in the phonon spectra of orthorhombicRMnO3 compounds

Abstract

The phonon properties of orthorhombic manganitesRMnO3 are studied using a Green’s function technique taking into account anharmonicspin–phonon and phonon–phonon interaction terms. The strong spin–phonon interactionleads to anomalies in the phonon energy and the damping around the magnetic phasetransition. The phonon spectrum is discussed for different exchange interactionJ1 and spin–phononinteraction Rsp constants. Independence on the sign of Rsp we obtain softening or hardening of the phonon modes withdecreasing temperature below the phase transition temperatureTN. This is associated with phonon modulation of the exchange interaction. It is shown thatthe phonon energy and the phonon damping depend on the radius of the rare earth ionrR and on the ion doping. The influence of the external magnetic field is discussed,too.