High-Frequency Properties and Thickness-Dependent Damping Factor of ${\rm FeCo}{\hbox {\textendash }}{\rm SiO}_{2}$ Thin Films

Soft magnetic nanogranular Fe₇₀Co₃₀-SiO₂ thin films were fabricated on Si substrates using radio frequency (rf) magnetron sputtering in an argon ambient. The electrical, magnetic and high-frequency properties of these thin films were studied in details. SiO₂ chips were placed in the erosion race-track of the alloy Fe₇₀Co₃₀ (at.%) target and change the number of chips result in the different film composition. The optimal films with desired properties of low coercivity, Hc ~ 2.5 Oe, high saturation magnetization, 4π Ms ~ 11.6 kGs and high electrical resistivity ρ ~ 1600 μΩcm were obtained. Permeability spectra measured shows that its natural ferromagnetic resonant (FMR) frequency (f_r) and initial permeability were about 4.05 GHz and 120, respectively. The tested results shown that the film thickness had an important effect on films properties, it can convenient adjust the f_r and damping factor of films. With the increase of film thickness from 50 nm to 1200 nm, the f_r of films ranged from 2.86 GHz to 4.05 GHz. The excellent soft magnetic properties were ascribed to exchange coupling among magnetic particles.