High frequency permeability of nanocrystalline Fe–Cu–Nb–Si–B single and multilayer films

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Abstract
Structure and magnetic properties of Fe–Cu–Nb–Si–B alloy single and multilayer films produced by rf sputtering have been investigated. The 1‐μm‐thick single films are of an amorphous phase in the as‐sputter‐deposited state and are crystallized into a mainly bcc phase with fine grains of nanometer size, as are melt‐quenched ribbons with the same composition. The crystallization behavior and the Curie temperature of these single films are also similar to those of the ribbons. The crystallization‐induced bcc phase possesses a high saturation magnetization of 1.3 T and good soft magnetic properties. For improving permeability at high frequency, an attempt has been made to multilayer the Fe–Cu–Nb–Si–B alloy with nonmagnetic materials such as SiO2. It has been found that Fe75.6Cu0.8Nb1.9Si13.2B8.5(500 nm)/SiO2(5 nm) multilayer films annealed at 500 °C for 1 h also consist of bcc fine crystallites and exhibit permeability as high as 7000 at 1 MHz and low coercivity of about 0.08 Oe.