High Permeability in Broadband of Co-sputtered [Fe-Fe₂₀Ni₈₀/Cr]_n Multilayer Films

To achieve high microwave permeability in wide-band for the micron-thick magnetic films, [Fe-Fe₂₀Ni₈₀/Cr]_n multilayer structure was proposed by co-sputtering Fe and FeNi to form the magnetic layers and Cr to form the interlayers. The multilayer structure contributes to the high permeability by reducing the coercivity and diminishing out-of-plane magnetization. The maximum imaginary permeability of [Fe-Fe₂₀Ni₈₀/Cr]_n multilayer film reaches a large value of 800 at 0.52 GHz even though its overall thickness exceeds 1 µm. Besides, the magnetic resonance frequency of the multilayer film can be modulated from 0.52 to 1.35 GHz by adjusting the sputtering power of Fe from 0 to 86 W, and its bandwidth for μ″ > 200 (Δf) is as large as 2.0 GHz. The desirable broad Δf of magnetic permeability, which can be well fitted by the Landau-Lifshitz-Gilbert equations, is due to dual magnetic resonances originated from double magnetic phases of Fe and FeNi that are of different saturation magnetization. The micron-thick multilayer films with high permeability in extended waveband are promising candidate for electromagnetic noise suppression application.