Raman spectrum of NiCl2

The Raman spectrum of NiCl2 has been measured at various temperatures above and below the antiferromagnetic ordering temperature TN=52.3K. Two prominent bands at 175.2 and 270.9 cm-1 (6K) were observed at all temperatures and are assigned to the Eg and A1gk=0 optic phonons, respectively. A careful search was made for Raman peaks due to one- and two-magnon scattering at temperatures below TN but none were found. It is concluded that their intensity must be less than 1/30th the intensity of the A1g phonon. These results, coupled with earlier measurements of Raman scattering by magnons in FeCl2, CoCl2 and CoBr2, indicate a need for theoretical investigations of the magnon-photon coupling mechanism for these highly anisotropic layered compounds.