Separation of the two-magnon scattering contribution to damping for the determination of the spin mixing conductance

We present angle-dependent measurements of the damping properties of epitaxial Fe layers with MgO, Al, and Pt capping layers. Based on the preferential distribution of lattice defects following the crystal symmetry, we make use of a model of the defect density to separate the contribution of two-magnon scattering to the damping from the isotropic contribution originating in the spin pumping effect, viscous Gilbert damping, and the magnetic proximity effect. The separation of the two-magnon contribution, which depends strongly on the defect density, allows for the measurement of a value of the effective spin mixing conductance that is closer to the value exclusively due to spin pumping. The influence of the defect density for bilayer systems due to the different capping layers and to the unavoidable spread in defect density from sample to sample is thus removed. This shows the potential of studying spin pumping phenomena in fully ordered systems in which this separation is possible, contrary to polycrystalline or amorphous metallic thin films.