Co₂₅Fe₇₅ Thin Films with Ultralow Total Damping

We demonstrate ultralow total Gilbert damping of 0.0013 for Co₂₅Fe₇₅ thin films grown on a Si/SiO2 substrate by dc magnetron sputtering. While ultralow intrinsic damping in this material has previously been reported, spin-pumping contributions from the seed and capping layers increased the total damping of the material from the intrinsic value. We show that by engineering the seed and capping layers to minimize the spin-pumping contribution we can significantly reduce the total damping. As an additional figure of merit, the minimum full-width half-maximum resonance linewidth of 1 mT at a resonance frequency of 10 GHz can be achieved in Co₂₅Fe₇₅ films of only 12nm thickness. Ferromagnetic resonance measurements taken in the in-plane geometry exhibit a slightly enhanced total damping parameter of 0.002, which is of great importance for magnonics applications. We further characterize the structural and morphological character of the films grown with many different seed layer stacks to understand the optimum conditions for minimization of both the total magnetic damping as well as the inhomogeneous linewidth broadening. We find great sensitivity of the qualitative behavior of the in-plane resonance linewidth as a function of film structure and morphology.