Abstract
The authors interpret the spin-wave lineshape in the two-dimensional ferromagnet K2CuF4 by a theory developed for small wavelengths, as is relevant for inelastic neutron scattering, applicable for temperatures both above and below the Curie temperature. The agreement between theory and experimental results is rather good. However, at high temperatures, when the spin-wave lineshape is very broad, the present theory, which is available for energies near the spin-wave energy omega q, gives only qualitative results.