Theory of Raman scattering and infrared absorption by interacting phonon-magnon states in FeF2

Abstract

It is shown theoretically that, in the presence of a strong magnetic field, effects due to the interaction betweenB 1g ,E g,TA ⊥ phonons and magnons should be important in the Raman and infrared absorption spectrum of FeF2. As a result the two magnon line should split. A microscopic Hamiltonian for the interactions has been derived. The calculated values of theE g phonon-one magnon interaction, 9.9 cm−1, and of theB 1g phonon-two magnon coupling, 6.3 cm−1, are comparable to those in FeCl2⋅2H2O metamagnet, in which C phonon-magnon hybrydization has been observed [1]. It is shown that hybridization between two magnon andB 1g orTA ⊥ phonon can occur in FeF2 if the magnon energy approaches the phonon energy due to increasing magnetic field or increasing temperature.