Abstract: Permeability characteristics of sputtered soft magnetic Fe40Co40B20 thin films are investigated in the range of 0.5 to 5 GHz by a shortened microstrip transmission line perturbation method. Excellent microwave permeability is achieved at 0.4 Pa argon pressure: f r is 3.32 GHz, the real and imaginary part of permeability at 0.5~GHz are 104 and 61, respectively. In addition, the thickness effect on permeability is also studied. The minimum damping can be achieved at the thinnest film. Different sources contributed to in-plane anisotropy are discussed briefly. The deviation between the peak frequency of the imaginary part and the zero-crossing frequency of the real part of permeability is also presented.

Key words: Fe-Co-B, In-plane anisotropy