Light scattering by magnons in CoO, MnO, andα−MnS

Light scattering in antiferromagnetic crystals CoO, MnO, and $\alpha -\mathrm{MnS}$ has been studied experimentally in the temperature range from 6 to 300 K. The spectra showed peaks associated with one-magnon and two-magnon excitations. These structures diminished with increasing temperature, becoming unobservable above the Néel temperature. Polarization of the scattered light, which is important for the identification of the structures, was investigated for CoO. Raman scattering due to phonons was observed for MnO. The measured spectra for MnO and $\alpha -\mathrm{MnS}$ also showed photoluminescence, the spectral position of which was found to be independent of the frequency of incident radiation. A theoretical treatment of magnon excitations was worked out which takes into account the existence of many single-ion states. The existing information on magnons in these crystals can be satisfactorily interpreted.