Influence of adjacent layers on the damping of magnetization precession in CoxFe100-x films

Abstract

We have measured magnetic damping in polycrystalline Co25Fe75 films adjacent to various nonmagnetic materials (Ti, Cu, Au, NiO) serving as buffer and/or cover layers. It was shown that it is crucial to use a proper buffer layer to achieve low damping in the Co25Fe75 layer. We found that even an ultrathin Cu buffer layer is sufficient to reduce the total damping when inserted between the substrate and the Co25Fe75 layer. The damping measured in the in-plane configuration reduces almost threefold (to αtot< 0.003). Moreover, the Co25Fe75 films with a Cu buffer layer possess low inhomogeneous linewidth broadening, in contrast to those with Au or Ti buffer layers. Using spin pumping into a dielectric antiferromagnetic capping layer (NiO), we determined that the effective spin mixing conductance is 4.8 × 1019 m−2. This value is large compared to those of Pt, Pd, and Au.