The influence of the Dzyaloshinskii-Moriya interaction on the spin-wave dispersion in an Fe double-layer grown on W(110) is measured for the first time. It is demonstrated that the Dzyaloshinskii-Moriya interaction breaks the degeneracy of spin-waves and leads to an asymmetric spin-wave dispersion relation. An extended Heisenberg spin Hamiltonian is employed to obtain the longitudinal component of the Dzyaloshinskii-Moriya vectors from the experimentally measured energy asymmetry. [5,6] and multiferroics [7,8].In nanomagnetism, where the surface effects are noticeable, the spin-orbit coupling is one of the most important intrinsic magnetic perturbations, which creates novel phenomena. Recently, it has been shown that a strong spin-orbit coupling in the presence of the broken inversion symmetry at the surface leads to the DM interaction, which stabilizes a noncollinear spin structure for a Mn monolayer on W(110) [9] and W(100) [10] surfaces.An ultrathin Fe film grown on W(110) is another system that is believed to show the DM interaction [11][12][13]. Magnetic excitations in this quasi-two-dimensional spin system have been studied theoretically since many years [14][15][16][17][18][19][20][21]. In the description of the collective magnetic excitations, only the symmetric exchange interaction was considered and the DM interaction has been neglected. In such systems, where DM interaction is relatively large, it should, in principle, change the intrinsic properties of the spin-waves (SWs). Only very recently, the influence of the DM interaction on the spin-wave dispersion has been predicted to give rise to an asymmetric spin-wave dispersion in an Fe monolayer on W(110) [22]. However, the effect of the DM interaction on the spin-wave dispersion in low dimensional systems has never been measured experimentally.In this Letter we report the first experimental evidence of the influence of DM interaction on the spin-wave dispersion in a double-layer Fe. We show that in the presence of the DM interaction the spin-wave dispersion is asymmetric. By measuring the highly resolved spin polarized electron energy loss (SPEEL) spectra in both energy loss and gain regimes and by reversing the magnetization of the film, we measure the DM interaction driven asymmetry in the spin-wave dispersion of Fe double-layer grown on W(110). By using an extended Heisenberg spin Hamiltonian, the energy asymmetry is modeled giving rise to a quantitative determination of the longitudinal components of DM vectors.The iron layer was deposited onto a clean W(110) single crystal at room temperature (RT). Special care has been taken concerning the cleaning of the W crystal as described elsewhere [23]. Prior to the SPEELS measurements, the structural, chemical and magnetic properties were checked by means of low energy electron diffraction, Auger electron spectroscopy and magneto optical Kerr effect measurements. The Fe films reveal the expected structural and magnetic properties well-known from literature [24][25][26]. The SPEELS measurements were perf...

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.

We report the first observation of high wave vector magnon excitations in a ferromagnetic monolayer. Using spin-polarized electron energy loss spectroscopy, we observed the magnon dispersion in one atomic layer (ML) of Fe on W(110) at 120 K. The magnon energies are small in comparison to the bulk and surface Fe(110) excitations. We find an exchange parameter and magnetic anisotropy similar to that from static measurements. Our results are in sharp contrast to theoretical calculations, indicating that the present understanding of magnetism of the ML Fe requires considerable revision.

We provide direct experimental evidence which demonstrates that, in the presence of a large spin-orbit coupling, the lifetime, amplitude, group, and phase velocity of the magnons propagating along two opposite (but crystallographically equivalent) directions perpendicular to the magnetization are different. A real time and space representation reveals that magnons with the same energy (eigenfrequency) propagate differently along two opposite directions. Our findings can inspire ideas for designing new spintronic devices.

The main idea behind magnonics is to use the elementary magnetic excitations (magnons) for information transfer and processing. One of the main challenges, hindering the application of ultrafast terahertz magnons in magnonics, has been the short lifetime of these excitations in metallic ferromagnets. Here, we demonstrate that the engineering of the electronic structure of a ferromagnetic metal, by reducing its dimensionality and changing its chemical composition, opens a possibility to strongly suppress the relaxation channels of terahertz magnons and thereby enhance the magnons' lifetime. For the first time, we report on the long-lived terahertz magnons excited in ultrathin metallic alloy films. On the basis of the first-principles calculations, we explain the microscopic nature of the long lifetime being a consequence of the peculiar electronic hybridizations of the species. We further demonstrate a way of tailoring magnon energies (frequencies) by varying the chemical composition of the film.