Room temperature low magnetic damping in polycristalline Co_2-xMn_1+xGe

We studied the static and dynamic magnetic properties of polycristalline Co_2-xMn_1+xGe Heusler thin films by SQUID magnetometry and ferromagnetic resonance. We found that when varying the stoichiometry, the effective magnetic damping can vary up to two orders of magnitude. We relate the variation in magnetic relaxation to the extrinsic mechanisms of damping that depend on the microstructure of the films. Transmission electron microscopy reveals that our samples display periodic planar Mn-O clusters due to deposition method, with the samples richer in Mn having larger grains that pass through the Mn-O planes. We observe an increased non-linear frequency dependence of the FMR linewidth in these samples, which we attribute to the grain to grain two-magnon scattering processes. With decreasing Mn content, the contribution of the two-magnon scattering processes diminishes that we connect with the grain shape and size. Our results suggest a strong connection between the microstructure and extrinsic magnetic damping contributing to the understanding of magnetic relaxation in polycristalline films.