Damping of CoxFe80−xB20 ultrathin films with perpendicular magnetic anisotropy

We use vector network analyzer ferromagnetic resonance to study the perpendicularly magnetized CoFeB films. We report the dependence of the anisotropy, the g-factor, and the damping upon the Fe-Co compositional ratio in the amorphous and crystalline states. The damping and the anisotropy increase upon crystallization but vary little with composition on the Fe-rich side. At high cobalt content, the anisotropy lowers while the damping and the sample inhomogeneity increase. The compositional dependences seem to extrapolate from the properties of bulk CoFe alloys, with differences that can be understood from the correlated impacts of spin-orbit interaction on anisotropy, g-factor, and damping.