High Frequency Soft Magnetic Properties And Intergranular Interaction Of Magnetic Granular Films

With integration and miniaturization of electronic devices,electro-magnetic elements tend to miniaturize and extend to high frequency region.The soft magnetic films with high saturation magnetization 4pMs,high electrical resistivityρ,high permeabilityμ,and low coercive force H_c is one direction for magnetic materials developing.Among them,magnetic granular films,composed of magnetic metal granules and nonmagnetic insulator matrix,attract more and more attention as one of the most promising materials for they take the advantages of high M_s,μ,T_c of magnetic metal and highρof insulator.The exchange coupling between granules is crucial to realize good soft magnetism in granular films.In this thesis,the inter-granular interactions in representative films of (Fe₆₅Co₃₅)_x(SiO₂)_1-xgranular films fabricated by radio frequency magnetron sputtering were investigated via microstructure and ferromagnetic resonance(FMR) study,and the main results are as follow:The film of x=0.42 annealed at 260℃in magnetic field of 1300Oe exhibits good soft magnetic properties with low H_c and good in-plane uniaxial anisotropy, and its resistivity is up to 13.4 mΩcm at the same time.The frequency dependence of complex permeability(μ-f curve)also demonstrates good high frequency properties with FMR frequence as high as 1.8 GHZ,andμ'＞100 when f＜0.7GHz. According to the microstructure measurement,the average particle size and the distance between particles are around 3 nm and 2 nm,respectively,indicating that the exchange coupling condition is satisfied.In the FMR spectra of the sample with static magnetic field H perpendicular to the film plane,several equally spaced spin-wave resonance(SWR)peaks were observed.The calculation based on the Portis' model implies that the spin-wave resonance happens in the film rather than in single granules,which suggests the granules are coupled by exchange coupling,and the whole film behaves as a continuous magnetic film.The soft magnetic properties and high frequency properties of the film of x= 0.34 becomes worse due to the low metal volume fraction.No SWR mode was found in the FMR spectra,implying there is no exchange coupling between the granules.Combine the results of magnetic properties,high frequency properties, microstructure and FMR investigations of the two films,it was confirmed that the exchange coupling between granules played a crucial role in realizing good soft magnetism in magnetic granular films.