Temperature Dependence of the Width andgFactor of a Purely Electronic Optical Transition in MnF2

We report thermal broadening of the 18418-${\mathrm{cm}}^{-1\mathrm{}}$ purely electronic transition in Mn${\mathrm{F}}_3$ split by an external magnetic field of 25 kOe. A differential broadening of the split line is observed, demonstrating the important role of Raman scattering of magnons as a mechanism for broadening this optical line at low temperatures. A temperature-dependent reduction of the effective $g$ factor is also observed. Calculations based on a simple model give satisfactory agreement with the observations.