We report on the preparation and optical properties of single-crystal films of Cd${\mathrm{Cr}}_2$${\mathrm{S}}_4$. The present data show no large blue shift associated with magnetic ordering near the Curie temperature contrary to that previously observed in bulk Cd${\mathrm{Cr}}_2$${\mathrm{S}}_4$ data. A large red shift correlated to the magnetic ordering is observed for a peak in the highly absorbing region. The weakness and narrowness of this absorption is inconsistent with that expected for band-to-band transitions resulting in unbound electrons and holes. We suggest an exciton model to explain this absorption.

• Received 10 November 1969

DOI:https://doi.org/10.1103/PhysRevLett.23.1499