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 ~2300 A exhibits excellent soft magnetic properties in the as-deposited condition, e.g., easy axis coercivity (H_c) of ~1.5 Oe and 4 πMs of ~8.4 kG. The in-plane uniaxial anisotropy field (H_k) is as high as ~28 Oe. This large anisotropy field significantly enhances the ferromagnetic resonance frequency (f_res) to ~1.86 GHz. The relative permeability μ´ of this film is shown to be ~200 and to stay nearly constant in the frequency range of 0.1 GHz-0.75 GHz. The full width at half maximum (Δf) for the peak in the imaginary part of the permeability at resonance is ~0.35 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