FMR line width and field dependent domain wall mobility in garnets films

The domain wall mobility derived from the generalized Landau-Lifshitz equation taking into account nonconservation of magnetization modulus yields two distinctly different damping constants. The first one is related to ferromagnetic resonance line width which is independent of in-plane field. The second is due to the presence of the domain wall and is transverse field dependent. The relative importance of the two constants depends very much on the presence or absence of the in-plane field. The formulation also allows us to make a reasonable estimate of the longitudinal susceptibility of the sample.