Influence of Cu underlayer on the high-frequency magnetic characteristics of as-sputtered FeCoSiN granular thin films

In this work, we investigate the influence of Cu underlayers on the magnetic properties of as-sputtered FeCoSiN thin films. Different from their traditional improvement in the static magnetic properties of sputtered films, Cu underlayers are found to have a significant influence on the dynamic magnetic properties of as-sputtered FeCoSiN thin film at high frequencies. The permeability spectra and the analyses based on the Landau–Lifshitz–Gilbert equation show that the damping coefficient in the magnetization dynamics significantly increases with the underlayer's thickness, and thus the resonant frequency linewidth increases. The extent of increase shows that using the Cu underlayer is an effective method for tuning the damping in the magnetization dynamics of granular thin films. The increase in the damping coefficient is suggested to be related to the release of the film's stress by the underlayer.