RAMAN SCATTERING BY FOUR MAGNONS IN NiO AND KNiF3

Γ3+ excitations have been observed by Raman scattering in KNiF3 at 1270 cm−1(17.9J), and in NiO at 2800 cm−1 (18.9J). These excitations are identified as 4 magnon (4M) excitations by agreement of the peak frequencies with calculated values, and in the case of NiO by the temperature shift. Scattering by 4M is the highest order non‐resonant Raman scattering yet observed. The excitation of 4M in Ni0 is interpreted in terms of excited state propagation effects, since it is possible to show both experimentally and theoretically that the 4M spectral density is negligible which arises from kinematic corrections to the harmonic spin deviation operators in the bilinear exchange process creating 2M.