Light scattering by magnetic excitons in (FeMn)F2

The transitions between the low lying crystal field split states A_1g and B_1g of the Fe²⁺ ions in pure FeF₂ and in the mixed antiferromagnet Fe_1-xMn_xF₂ have been investigated with Raman light scattering. From the Raman polarization rules the lines have been identified as arising from the magnetic excitons associated with the transitions. The energy and the line-width of the strongest line are studied as a function of the concentration x. From the energy measurement we estimate that the single ion anisotropy parameter D of the Fe²⁺ ions varies from 6.46 cm^-1 in pure FeF₂ to 8.03 cm^-1 in MnF₂: Fe.