New Spin-Wave Propagation Length Scales in Low Damping Metallic Ferromagnets

We report ultra-low intrinsic magnetic damping in Co$_{\text{25}}$Fe$_{\text{75}}$ heterostructures, reaching the low $10^{-4}$ regime at room temperature. By using a broadband ferromagnetic resonance technique, we extracted the dynamic magnetic properties of several Co$_{\text{25}}$Fe$_{\text{75}}$-based heterostructures with varying ferromagnetic layer thickness. By estimating the eddy current contribution to damping, measuring radiative damping and spin pumping effects, we extrapolated an intrinsic damping of $\alpha_{\mathrm{0}} \leq 3.05\times10^{-4}$. Furthermore, using Brillouin light scattering microscopy we measured spin-wave propagation lengths of up to $(21\pm1)\,\mathrm{\mu m}$ in a 26 nm thick Co$_{\text{25}}$Fe$_{\text{75}}$ heterostructure at room temperature, which is in excellent agreement with the measured damping.