The magnetic relaxation processes following the dynamical excitation of the spin system of ferromagnets are investigated by ferromagnetic resonance ͑FMR͒ between 1 and 70 GHz using epitaxial Fe 3 Si films as a prototype system. Two relaxation channels, i.e., dissipative, isotropic Gilbert damping G as well as anisotropic two-magnon scattering ⌫, are simultaneously identified by frequency and angle dependent FMR and quantitatively analyzed. The scattering rates due to two-magnon scattering at crystallographic defects for spin waves propagating in ͗100͘ and ͗110͘ directions, ␥⌫ ͗100͘ = 0.25͑2͒ GHz and ␥⌫ ͗110͘ = 0.04͑2͒ GHz, and the Gilbert damping term G = 0.051͑1͒ GHz are determined. We show that changing the film thickness from 8 to 40 nm and slightly modifying the Fe concentration influence the relaxation channels. Our results, which reveal the contributions of longitudinal and transverse relaxation processes may be of general importance for the understanding of spin-wave dynamics in magnetic structures.

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The longest relaxation time and sharpest frequency content in ferromagnetic precession is determined by the intrinsic (Gilbert) relaxation rate G. For many years, pure iron (Fe) has had the lowest known value of G = 57 MHz for all pure ferromagnetic metals or binary alloys. We show that an epitaxial iron alloy with vanadium (V) possesses values of G which are significantly reduced to 35 +/- 5 MHz at 27% V. The result can be understood as the role of spin-orbit coupling in generating relaxation, reduced through the atomic number Z.