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 $J_2$ = 148 ${\mathrm{cm}}^{-1\mathrm{}}$. The temperature shift of the scattering peak is identical to that of the 2000-${\mathrm{cm}}^{-1\mathrm{}}$ 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.