Volume 39A, number 2 PHYSICS LETTERS 24 April 1972 TWO MAGNON LIGHT AND NEUTRON SCATTERING IN CoF 2 C.R. NATOLI F.N.A. Laboratory, CNEN Casaccia, Roma, Italy and J. RANNINGER Institut Laue-Langevin, Cedex 156, 3 8 - Grenoble-Gare, France Received 26 February 1972 Using a pseudo spin 1/2 Hamiltonian including an effective anisotropy field we explain the experimental findings of light and neutron scattering in CoF~. Using a spin Hamiltonian Elliot and Thorpe [ 1 ] were able to reproduce the light spectra for RbMnF 3 [1], MnF 2 [2] and NiF 2 [3] by taking into account the spin wave interaction. The effect of this interac- tion leads to a shift of the peak position to lower fre- quencies and to a broadening of the peak compared to the non interacting case. This effect is the more pronounced the stronger the interaction is. For CoF 2 the agreement with experiment has how- ever been rather unsatisfactory. Using a pseudo-spin 1/2 Hamiltonian due to Lines [4] H=~ z z +i - - + I SmSm+ 6 ~J(~mSm+6 + SmSm+8) m8 + L A ~ (s z - s~+~) m8 - , ..'.-" ,, ..y _ i \ / ' X \ \ / / ,/ '... \,\ /" / "'.. "\ • ° ~ o / o °,,°°o • • • ~ 105 110 115 120 125 130 .~ cttl Fig. 1. Raman P~ scattering cross-section; dotted curve - no anisotropy field a = 0, T = 0, I" = 0; dot-dashed curve ~ = 0.63, T = 0, P' = 0; full curve a = 0.63, T = IT N, F' = 5 × 10-2; dashed curve-experiment [6]. 105