High Spin-Wave Propagation Length Consistent with Low Damping in a Metallic Ferromagnet

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 found the intrinsic damping of a 26,nm thick sample to be $$\alpha_{$0$} \lesssim 3.18\times10^{-4}$. Furthermore, using Brillouin light scattering microscopy we measured spin-wave propagation lengths of up to $(21\pm 1)\mu \mathrm{m}$ in a 26 nm thick Co${}_{\text{25}}$Fe${}_{\text{75}}$ heterostructure at room temperature, which is in excellent agreement with the measured damping.