Stripline ͑SL͒, vector network analyzer ͑VNA͒, and pulsed inductive microwave magnetometer ͑PIMM͒ techniques were used to measure the ferromagnetic resonance ͑FMR͒ linewidth for a series of Permalloy films with thicknesses of 50 and 100 nm. The SL-FMR measurements were made for fixed frequencies from 1.5 to 5.5 GHz. The VNA-FMR and PIMM measurements were made for fixed in-plane fields from 1.6 to 8 kA/ m ͑20-100 Oe͒. The results provide a confirmation, lacking until now, that the linewidths measured by these three methods are consistent and compatible. In the field format, the linewidths are a linear function of frequency, with a slope that corresponds to a nominal Landau-Lifshitz phenomenological damping parameter ␣ value of 0.007 and zero frequency intercepts in the 160-320 A / m ͑2-4 Oe͒ range. In the frequency format, the corresponding linewidth versus frequency response shows a weak upward curvature at the lowest measurement frequencies and a leveling off at high frequencies.

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.

Ferromagnetic resonance ͑FMR͒ derivative linewidths were measured from 3 to 12 GHz on 50 nm thick sputtered polycrystalline Fe-Ti-N films with 3 at. % titanium and a nitrogen content ͑x N ͒ from 1.9 to 12.7 at. %. The measurements were made with both stripline and waveguide FMR spectrometers. Linewidths were generally lowest at x N = 7 at. %, with derivative linewidth ͑⌬H͒ values in the 15-25 Oe range and a nominally linear increase with frequency ͑f͒. This minimum linewidth composition is connected with the bcc to bct structural transition in the Fe-Ti-N system. Linewidths increased at both larger and smaller x N values and were accompanied by the development of a more rounded frequency profile that is indicative of two-magnon scattering. All of the ⌬H vs f data could be fitted successfully with a constant inhomogeneity broadening linewidth of 8 -11 Oe, a two-magnon scattering ͑TMS͒ linewidth from the random grain-to-grain fluctuations in the effective anisotropy field directions for the polycrystal, and a magnon-electron ͑m-e͒ intrinsic relaxation term modeled through Gilbert damping with a single ␣ value of 0.003. The actual fits were done through the convolution of a Gaussian linewidth for the inhomogeneity term and a Lorentzian linewidth for the TMS and m-e terms. The fitted anisotropy field parameters from the TMS analysis ranged between 398 and 883 Oe, with the minimum also at the bcc to bct structural transition at x N = 7 at. %.

Hexagonal M-type barium ferrite (BaM) films have been prepared by pulsed laser deposition. Optimal preparation conditions gave pure single phase films with the narrowest possible ferromagnetic resonance (FMR) linewidths. The films were deposited on c-plane sapphire substrates with a KrF excimer laser at wavelength of 248 nm and fluence of 1.7 J/cm2. The minimum linewidth films were obtained for an oxygen partial pressure of 300 mTorr and a substrate temperature of 910 °C, and were 0.85 μm thick. X-ray diffraction indicated pure single crystal BaM phase with local c-axis deviations less than 0.15°. Vibrating sample magnetometry data gave hysteresis loops with minimal hysteresis and small coercive force, saturation induction 4πMs of 4.2 kG and uniaxial anisotropy field HA of 16.4 kOe. The HA matches the anisotropy for bulk and the 4πMs is about 10% below literature values for the bulk. The FMR spectra were measured from 50 to 75 GHz by shorted wave guide techniques with the static field perpendicular to the film. The optimized film uniform mode half power FMR linewidth at 60.3 GHz was 27 Oe. This linewidth was a linear function of the frequency with a response coefficient of 0.5 Oe/GHz and nearly zero frequency intercept. Within experimental error, this linewidth response is the same as for bulk crystals. The FMR spectra show additional standing spin wave (SSW) resonances which could be indexed to give field positions that scale with the square of index n except for low order modes. The scaling gave a standard exchange energy parameter, Aex, of 6.4×10−7 erg/cm. The SSW linewidths scaled with n2. Application of the Kittel thickness variation model to the SSW linewidth data gave an estimated thickness variation of the film of about 7%.

A two magnon scattering theory for microwave relaxation in magnetic systems is formulated in the framework of the Hamiltonian formalism. The paper provides general expressions for inhomogeneity coupling coefficients in the case of localized inhomogeneities. An approximate solution for the relaxation rate of the ferromagnetic resonance uniform mode relaxation rate is presented. Two examples of the application of the theory are presented, one for bulk polycrystalline ferrites and one for polycrystalline metallic thin films.