Low spin-wave damping in amorphous Co₄₀Fe₄₀B₂₀ thin films

A characterization of the magnetic properties of amorphous Co₄₀Fe₄₀B₂₀ thin films, developed for low damping applications in magnon spintronics, using vector network analyzer ferromagnetic resonance (VNA-FMR) and the magneto-optical Kerr effect is presented. Our films show a very weak uniaxial anisotropy and a low Gilbert damping parameter (⁠$α=0.0042$⁠). The saturation magnetization $MS$ extracted from the FMR measurements is 1250 kA/m. The frequency dependence of the first perpendicular standing spin waves mode on the applied magnetic field is used to determine the exchange constant A for this alloy resulting in a value of $1.5×10−11 J/m$⁠. These values are discussed in comparison to literature values for different CoFeB compositions and other related alloys.