Ferromagnetic Relaxation by Magnon-Electron Interaction

In the present work, we show that expansion of the fields in the small parameter 4piomegasigma/c²k² allows one to tackle the magnon-electron interaction in the system. In particular, it can be applied to the problem of magnons generated by four-magnon scattering after a large angle rotation such is common in modern switching experiments and technological applications such as magnetic recording.