Room-temperature intrinsic and extrinsic damping in polycrystalline Fe thin films

We examine room-temperature magnetic relaxation in polycrystalline Fe films. Out-of-plane ferromagnetic resonance measurements reveal Gilbert damping parameters of $\ensuremath{\approx}0.0024$ for films with thicknesses 4--25 nm, regardless their microstructural properties. This observation runs counter to the intuition that various film defects heavily influence damping. The remarkable invariance microstructure suggests intrinsic is mostly fixed by bcc crystal structure within bulk nanoscale grains, limited impact from grain boundaries and roughness. By contrast, in-plane FMR linewidths exhibit distinct nonlinear frequency dependencies, indicating presence strong extrinsic To fit our data, we have used a grain-to-grain two-magnon scattering model two types correlation functions aimed at describing spatial distribution inhomogeneities film. However, neither able reproduce experimental data quantitatively physically reasonable parameters. Our findings advance fundamental understanding structurally disordered films, while demonstrating need deeper examination how disorder governs