Spin dynamics in ferromagnets: Gilbert damping and two-magnon scattering

Abstract

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.

Current-induced spin torque resonance of a magnetic insulator

“…2(a)]. The large effective intrinsic damping α 0 in our samples can be understood in terms of efficient two-magnon scattering induced by roughness in thin ferromagnetic films [33,34], especially when magnetized in the film plane [35].…”

Long-living terahertz magnons in ultrathin metallic ferromagnets

“…There are other sources of damping, for example, phonon and impurity scattering, two-magnon scattering and spin-orbit damping. These damping mechanisms are not as strong as Landau damping and are only important for the limit of lowfrequency (gigahertz) excitations 18 . If there are no low-energy Stoner excitations, with energies in the range of magnons' energy, the Landau damping will be inoperative and magnons shall live for a longer time.…”

Tunable ferromagnetic resonance behavior in Co2FeSi film by post-annealing

“…The FMR linewidth first decreases then increases with increasing the T a and exhibits a minimum at T a = 450 • C. It is well known that the FMR linewidth of thin films has three main contributions: (1) inhomogeneity term (∆H inh ) which is independent of frequency, (2) Gilbert damping term (∆H Gil ) which is intrinsic in nature and dependent on frequency, and (3) two-magnon scattering term (∆H 2mag ) which is extrinsic in nature and frequency dependent. [17][18][19] The overall linewidth can be written as, 20,21 …”

“…In equation (2), we exclude the contribution from two-magnon scattering, since the two-magnon scattering leads to a nonlinear behavior in ∆H, which cannot be observed here. 20 Based on the fitting results, the obtained values of α and ∆H inh are plotted in FIG. 3 (d).…”