Lattice and spin excitations of YFeO3 : A Raman and density functional theory study

Abstract

We report a Raman scattering study of $\mathrm{Y}\mathrm{Fe}{\mathrm{O}}_{3}$ orthoferrite. Polarized Raman measurements in wide temperature range and first-principles calculations provided the assignment of the observed phonon modes to vibrational symmetries and atomic displacements. We did not observe previously reported anomalies in the behavior of phonon frequencies near the temperature of the antiferromagnetic transition. Temperature behavior of frequencies and linewidths of most phonons may be described by known expressions for cubic and quartic anharmonicity, which implies a significant contribution of phonon-phonon interaction. At the same time, several phonons exhibit asymmetric profiles and anomalies in the behavior of their widths, which indicates an interaction with a continuum of some excitations. The most striking evidence of this is the observation of the coupling of the ${B}_{2g}$ phonon at 640 ${\mathrm{cm}}^{\ensuremath{-}1}$ with the two-magnon continuum, expressed in anomalous phonon self-energies in the vicinity of ${T}_{N}$. The appearance of a broad continuum of low-frequency excitations when approaching ${T}_{N}$, which is possibly induced by the damping of spin excitations due to interaction with the lattice, has been revealed. This interaction can lead to additional contributions to the renormalization of phonon self-energies, formally described by formulas for anharmonic effects. Phonon scattering induced by defects has been identified. The temperature behavior of resonant second-order phonon and two-magnon scattering was studied in detail.