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.
The Fe-projected vibrational density of states g͑E͒ in nanoscale 57 Fe / M multilayers, where M = Cr, Co, Cu, Pd, or Ag was measured by nuclear resonant inelastic x-ray scattering. With decreasing Fe thickness, the high-energy phonon peak of Fe near 36 meV is suppressed for the "soft" metals Ag, Pd, and Cu, but much less so for the "hard" metals Co and Cr. This effect is attributed to Fe phonon confinement and interface localization due to an energy mismatch between g͑E͒ of M and of Fe.
The composition dependence of the magnetic as well as structural properties of epitaxial 4 -40 nm Fe 3 Si thin films on MgO͑001͒ have been investigated using ferromagnetic resonance, superconducting quantum interference device magnetometry, and magneto-optical Kerr effect. Magnetic anisotropy energy, g factor, and magnetization were determined for different samples with Si concentrations of 20%, 25%, or 30% at room temperature. Additionally, different annealing procedures were applied. The magnetization was determined to be on the order of 0 M Ϸ 1 T. It was found that the films have a dominating cubic anisotropy K 4 Ϸ 3 ϫ 10 3 J / m 3 which depends on the thermal treatment of the film and is about 1 order of magnitude smaller than the one of bulk Fe. A small uniaxial in-plane anisotropy of interfacial nature was detected. The perpendicular uniaxial anisotropy term, which is dominated by an interface contribution, favors a perpendicular easy axis. From frequency-dependent ferromagnetic resonance measurements an isotropic g factor was extracted g = 2.075͑5͒ for 8 and 40 nm samples and g = 2.080͑5͒ for the 4 nm one. Different thermal treatments of the sample showed no influence on the g factor. The magnetic anisotropy fields and g factor decrease linearly as the Si concentration increases within the D0 3 regime.
The fits of the two-magnon contribution ⌬B 2mag to the overall ferromagnetic resonance linewidth of Fe 100−x Si x ͑x = 20 and 25͒ thin films with thicknesses of 8 nm and 40 nm presented in our paper are incorrect due to an erroneous conversion of M ef f that enters the quantity 0 ͓see Eq. ͑1͔͒ from cgs to SI units and the omission of a prefactor 2 / ͱ 3 within Eq. ͑9͒. The missing prefactor converts the full width at half maximum linewidth used in theory into the peak-to-peak linewidth used in analyzing our experiments. The corrected Eq. ͑9͒ reads:Si 25 sample the in-plane angular dependence at 24 GHz was measured ͓see new Fig. 1͑c͔͒, while for the 40-nm-thick Fe 75 Si 25 sample measurements at a frequency of 9 GHz were repeated and those at 49 GHz additionally performed ͓see the new Fig. 2͑a͔͒. For the latter sample the use of the correct value of 0 results in a slight deviation of the fit of the frequency dependence at small frequencies, which consequently is accompanied by a deviation of the fit of the in-plane angular dependence at 9 GHz. As this deviation is obviously largest at 9 GHz we thus used-in addition to the fit of the frequency dependence-the in-plane angular dependent data measured at 24 GHz to extract the fitting parameters.One may see that the correct fitting parameters yield systematically larger values for the two-magnon scattering rate given by ␥⌫. The constant ⌫ is related to the exact geometry of defects within the sample, which, however, in our case is unknown.The conclusion that two-magnon scattering is more effective along the ͓100͔-as compared to the ͓110͔-direction remains valid after the correction. Besides the magnitude of ⌫, the correct fitting yields a Gilbert parameter for the 40-nm-thick Fe 75 Si 25 sample which is about 20% reduced compared to the thinner 8 nm one. As the sample with higher Fe content ͑Fe 80 Si 20 ͒ exhibits a larger Gilbert-parameter than even the 8-nm-thick Fe 75 Si 25 sample, this indicates that bulk Fe 75 Si 25 is a material with rather small intrinsic magnetic damping.We would like to point out that the work on the present system ͑Fe-rich Fe x Si 1−x films͒ demonstrates and supports earlier experiments by us, 1-3 that have revealed that the two dynamic mechanisms ͑Gilbert damping and magnon-magnon scattering within the magnetic subsystem͒ can be separated by means of frequency-dependent FMR. This offers a more specific and detailed analysis of spin dynamics in magnetic nanostructures.
By magnetic coupling of Fe and Gd via Cr interlayers, the large local moment of Gd can be combined with the high Curie temperature of Fe. The epitaxial growth of a Gd film is studied here by preparing trilayer systems of Fe/Cr/Gd on MgO(100) substrates by molecular-beam epitaxy (MBE). The thickness of the Cr interlayer was varied between 3-5 monolayers. The structural quality of the samples was confirmed by in-situ RHEED and ex-situ XRD measurements. Epitaxial Cr(001)/Fe(001) growth was observed, as expected. By use of 57 Fe-CEMS (Conversion Electron Mössbauer Spectroscopy) in combination with the 57 Fe tracer layer method the Fe/Cr interface could be examined on an atomic scale and well separated Fe/Gd layers for all Cr thicknesses were confirmed. The unusual Gd/Cr crystallographic relationship of Gd(0001) Cr(001), with domains of the hexagonal Gd basal planes randomly oriented in the sample plane and not in registry with the underlying Cr(001) lattice, was found from combined RHEED and X-ray measurements. Annealing of the samples resulted in a remarkable improvement of the crystalline structure of the Gd layers. On the other hand, the appearance of a single line in the CEM spectrum leads to the conclusion that during annealing a small amount of Fe diffuses into the Cr layer. The electronic structure and magnetism of this system is investigated by first principles theory.
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