Magnetic Anisotropy And High Frequency Properties Of Granular Magnetic Films

With the integration and miniaturization of electro-magnetic devices,the soft magnetic films with high saturation magnetization Ms,high electrical resistivityρ,low coercive force Hc (therefore,high permeabilityμ),attracted more and more attention.Nanogranular film, composited of magnetic metal and nonmagnetic insulator matrix,is one of the most interesting films because this kind of films takes the advantages of metal(high Ms,T_C,μ)and insulator(p).In this work,a series of soft magnetic nanogranular films(FeCoBNiNb)_x-(SiO₂)_1-x were fabricated by magnetron sputtering.The structures of the samples were characterized by X-ray Diffraction(XRD) and high resolution transmission electron microscope(HRTEM) while the magnetic properties and electrical properties were systematically studied through vibrating sample magnetometer(VSM) and four points method.Meanwhile,the high-frequency characteristics of complex permeability were obtained by using the shorted microstrip transmission-line perturbation method.1.(FeCoBNiNb)_x-(SiO₂)_1-x films were successfully fabricated by magnetron sputtering.The results show the metal particles with size of 2 nm are embedded uniformly in insulating SiO₂ matrix for x=0.88.2.The dependence of anisotropy H_k on incidence angleθwas systematically studied.With decreasingθ,the anisotropy H_k increases.Based on experiments,we thought there are two parts of our anisotropy:(1) the irreversible part and(2) reversible part.3.The dependence of anisotropy H_k on metal volume fraction x was also systematically studied. With decreasing x,the anisotropy H_k increases first,then decreases.When x=0.88,the magnitude of H_k is obviously bigger than that of other samples.4.For the sample of x=0.75,we changed the content of B element,we found that the H_k and M_s decrease monotonously,Hc almost do not change.5.For the sample of x=0.63,the excellent in-plane uniaxial anisotropy 92 Oe as well as very high resistivity of 12.5mΩ·cm were obtained at the same time,which make it quite promising for the application in the high frequency range.6.The permeability spectrumμ=μ'-jμ.shows that the real partμ' is more than 25 below 6 GHz and ferromagnetic resonance frequency reaches 7.8 GHz for the sample x=0.88 withθ=30°,implying that the(FeCoBNiNb)_x-(SiO₂)_1-x granular films could be used in high frequency.