Structure and 100MHz soft magnetic properties in multilayers and granular thin films

Recent developments in high-frequency magnetic thin films are overviewed. The topics discussed are multi-layered nanocrystalline films and two-phase granular alloy films with high electrical resistivity. First, it is shown that Fe/Fe-Hf-C multilayers are promising high-frequency films with saturation magnetization Bs = 20kG and permeability μ′= 6,000 up to 10~20MHz, which are at the highest levels among these types of magnetic thin films. Second, it is shown that (Fe,Co,Ni)-(Si,B,Zr etc.)-(F,O,N) granular alloy films posses uniquely high electrical resistivity ρ as 10³~10 μΩ-cm together with high Bs of about 10kG, and consequently exhibit remarkable frequency dependence of μ′ and loss μ″ up to 500MHz. These new-types of thin films are possible candidate materials for future high-frequency devices such as “magnetic integrated circuits”. The properties are attributed to the two-phase granular structure, consisting of metallic grains and less conductive intergrains.