Magnetic damping in poly-crystalline Co₂₅Fe₇₅: Ferromagnetic resonance vs. spin wave propagation experiments

We report on the investigation of the magnetic damping of a 10 nm thin, poly-crystalline Co₂₅Fe₇₅ film grown by molecular beam epitaxy. Ferromagnetic resonance (FMR) measurements reveal a low intrinsic magnetic damping α_int^FMR=(1.5±0.1)×10-3. In contrast, in patterned micrometer wide stripes, spin wave (SW) propagation experiments performed by time resolved scanning magneto-optical Kerr microscopy yield attenuation lengths on the order of 5-8 μm. From this quantity, we deduce an effective magnetic SW damping α_eff^{SW, exp} =(3.9±0.3)×10^-3. For the system studied, this significant difference between both damping parameters is attributed to the non-negligible extrinsic contributions (local inhomogeneities and two-magnon scattering) to the magnetic losses which manifest themselves as a distinct inhomogeneous FMR linewidth broadening. This explanation is supported by micromagnetic simulations. Our findings prove that poly-crystalline Co₂₅Fe₇₅ represents a promising binary 3d transition metal alloy to be employed in magnonic devices with much longer SW attenuation lengths compared to other metallic systems.