Optimizing high-frequency properties of stripe domain ferrite doped CoFe thin films by means of a Ta buffer layer

The permeability mu and resonant frequency f(r) of stripe domain ferrite doped CoFe thin films are enhanced from 14 to 22 and 6.0 GHz to 6.4 GHz, respectively, by using Ta buffer layer. The observed enhancement of both permeability and resonant frequency seems to deviate from Snoek's law which expects the value of mu decrease as the f(r) increases. Compared to the case of using Permalloy (Ni80Fe20) buffer layer where mu is enhanced to 25 and f(r) is reduced to 4.1 GHz, the present result suggests that the employment of Ta buffer layer may be useful in the quest for high permeability magnetic thin films at GHz frequency range.