Spin Wave Sidebands in MnF₂

Abstract

It is shown that the observed features of the spinwave sideband structures in MnF₂ can be understood by assuming the transition mechanism proposed earlier and led to a successful interpretation of the infrared two magnon absorption.
Selection rules of the magnon induced optical transition are discussed taking explicitly the symmetry of the crystal and orbitals into account. The results predict that the line shapes of the σ and π absorption should be opposite to those of the infrared absorption as is really the case. Calculated line shapes are in qualitative agreement in the case of σ1 (σ-polarized, at 18477.1 cm⁻¹) and π1(π-polarized, at 18460.8 cm⁻¹), but not with σ2 (at 18485.3 cm⁻¹). Sidebands in FeF₂ are also discussed.