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_{mathrm{0}} lesssim 3.18times10^{-4}$. Furthermore, using Brillouin light scattering microscopy we measured spin-wave propagation lengths of up to $(21pm1),mathrm{mu m}$ in a 26 nm thick Co$_{text{25}}$Fe$_{text{75}}$ heterostructure at room temperature, which is in excellent agreement with the measured damping.
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