Temperature Dependence of Magnon-Pair Modes in Antiferromagnets and Paramagnets

Abstract

The temperature dependence of magnon‐pair excitations has been obtained in the simple antiferromagnets RbMnF₃ and FeF₂, by the technique of inelastic light scattering. At low temperatures the pair‐mode frequency is nearly twice that of a Brillouin‐zone boundary magnon, decreased slightly by magnon‐magnon interaction effects. As the temperature is increased, the magnon‐pair modes broaden and decrease in frequency. The excitation evolves smoothly as T is raised above T_N into the paramagnetic phase. In both materials, light scattering from the paramagnetic vestiges of the magnon‐pair modes could be observed up to 300°K. Together with earlier results on NiF₂, these data indicate the trends in magnon‐pair temperature behavior for materials with different spins and different magnon‐magnon interaction effects. These trends may be useful in guiding theories for magnon‐pair excitations.