Annealing influence on the Gilbert damping parameter and the exchange constant of CoFeB thin films

We present a study of the influence of the annealing temperature Ta on the magnetic properties of Co40Fe40B20 thin films. Using a vector network analyzer ferromagnetic resonance (VNA-FMR) setup and the magneto-optical Kerr effect, the dependence of the Gilbert damping parameter α, the exchange constant A, the saturation magnetization as well as the coercive field and the Kerr signal on Ta is reported. Additionally, the correlation with the crystalline properties of the films studied by X-ray diffractometry is discussed. We found that while the damping parameter α and the coercive field show sharp changes starting at a certain Ta value, the exchange constant A and the Kerr signal show a steady evolution. A differential modification of the film surface compared to the bulk is discussed as a possible reason. In any case, we found that the low damping values are preserved at the first onset of crystallization.