Spin-wave analysis in the two-dimensional antiferromagnetK2FeF4. II. Raman scattering

Two-magnon Raman spectra in the two-dimensional basal-plane antiferromagnet ${\mathrm{K}}_2$Fe${\mathrm{F}}_4$ are investigated in the temperature range 2 to 45 K. The spectra are reduced in terms of the spin-wave description developed in the preceding paper. The method used is the equations of motion of Green's functions. The spectrum calculated with first-order decoupling agrees with the one observed at 2 K. In second order, the magnon damping is evaluated rigorously, but within the zone-boundary maximum-dispersion approximation. The damping appears to be strongly dependent on the energy transfer in the scattering process. Calculated second-order spectra account for the line shift in the entire range of temperatures studied.