Ultrahigh frequency properties of amorphous Co-Fe-Zr-B thin films

We have investigated ultrahigh frequency magnetic properties of amorphous Co-Fe-Zr-B alloy films deposited on glass substrates by dc magnetron sputtering. Microstructural characterization carried out on these films shows the amorphous nature of the films. The Co-Fe-Zr-B film with a thickness of similar to 2300 A exhibits excellent soft magnetic properties in the as-deposited condition, e.g., easy axis coercivity (H-c) of similar to1.5 Oe and 4 pi Ms of similar to8.4 kG. The in-plane uniaxial anisotropy field (H-k) is as high as similar to 28 Oe. This large anisotropy field significantly enhances the ferromagnetic resonance frequency (f(res)) to similar to1.86 GHz. The relative permeability mu ' of this film is shown to be similar to 200 and to stay nearly constant in the frequency range of 0.1 GHz-0.75 GHz. The full width at half maximum (Deltaf) for the peak in the imaginary part of the permeability at resonance is similar to0.35 GHz. It is also found that the soft magnetic properties as well as the ultrahigh frequency properties of amorphous films have a strong dependence on film thickness. This is attributed to the change in the microstructure of films, which is closely related to the film growth conditions.