High-frequency permeability spectra of FeCoSiN/Al₂O₃ laminated films: Tuning of damping by magnetic couplings dependent on the thickness of each ferromagnetic layer

In this work, we investigate the high-frequency permeability spectra of as-sputtered FeCoSiN/Al₂O₃ laminated films, and discuss their dependence on the thickness of each FeCoSiN layer, based on the phenomenological Landau–Lifshitz–Gilbert equation. The damping factor and coercivity show their minima with lamination, deviating from the expectation based on the grain size confinement effect. Such dependences on the layer thickness indicate the influence of magnetic coupling. The decreases in the damping factor and the coercivities with lamination can be partially attributed to the decrease in the magnetostatic coupling induced by ripple structures. The enhanced damping and enlarged coercivity values obtained with further lamination are ascribed to the enhanced Néel couplings. The dependences show that the lamination can be effective in tuning the magnetization dynamics by changing the magnetic couplings.