Spin waves in the easy-plane ferromagnets

The modified version of the spin operator diagram technique is presented with regard to the dynamical properties of the easy-plane ferromagnets. The non-interacting spin wave (SW) spectrum and scattering amplitudes are obtained with the help of the spin Hamiltonian diagonalization procedure⁸). The SW relaxation frequencies due to the processes of the SW scattering on each other and on the longitudinal spin components thermal fluctuations are calculated.