Infrared Absorption and Raman Scattering by Two-Magnon Processes in NiO

Strong two-magnon ($2M$) Raman scattering has been observed from NiO along with first- and second-order phonon scattering. The shape of the $2M$ scattering peak is well described by a simple-cubic Green's function for interacting spin waves with an intersublattice exchange J₂ = 148 cm^-1. The temperature shift of the scattering peak is identical to that of the 2000-cm^-1 ir absorption peak described by Newman and Chrenko, but energy considerations require the absorption peak to be a phonon sideband of the $2M$ scattering peak, which is not seen in absorption.