Interface Electronic Complexes and Landau Damping of Magnons in Ultrathin Magnets

The damping of magnons in ultrathin metallic magnets is studied from first-principles. We contrast $\mathrm{Fe}/\mathrm{Cu}(100)$ and $\mathrm{Fe}/\mathrm{W}(110)$ systems for which the influence of the substrate on the magnon life time differs strongly. We introduce the concept of Landau map in momentum space to assess the role of different electronic states in the attenuation. The formation of electronic complexes localized at the film-substrate interface leads to hot spots in the Landau maps and enhances the damping. This finding allows tuning the attenuation of high-frequency magnetization dynamics in nanostructures.

Figure 1

Magnon spectra in iron films. Thick lines denote the dispersion relation, ${\omega }_0(\mathbf{q})$, and the width of the shaded area corresponds to the full width at half maximum on the energy axis. The Stoner spectrum contributing to the damping of marked magnons (●) is analyzed in Fig. 2.

Figure 2

Intensity of Stoner transitions with momentum ${\mathbf{q}}_0$ and energy ${\omega }_0$ in Fe layer resolved for different final $\mathbf{k}$ vectors in the first Brillouin zone. The Stoner states cause the damping of magnons indicated in Fig. 1.

Figure 3

Spectral density of initial (left column) and final (right column) electron states involved in the formation of Stoner pairs contributing to the damping of magnon with momentum ${\mathbf{q}}_0$. Final states with momentum $\mathbf{k}$ along $\overline{\Gamma }\overline{N}$ are shown. ${\mathbf{q}}_0=(0,0.375)(2\pi /a_{\mathrm{W}})$ is marked in Figs. 1a, 1b. Rows from the top: freestanding Fe(110) layer, Fe overlayer of $\mathrm{Fe}/\mathrm{W}(110)$, and topmost layer of clean W(110) surface.