Theoretical Study On Influence Of Mesoscopic Structure Of Fe_73.5Cu₁Nb₃Si_13.5B₉ Nanocrystalline Alloy On Its Magnetic Performance

The Fe_73.5Cu₁Nb₃Si_13.5B₉ nanocrystalline alloy shows the excellent soft magnetic properties and the giant magneto-impedance (GMI) effect. In order to explore its excellent soft magnetic properties, large numbers of experimental investigations have been achieved, and numbers of the crystallization mechanisms and the models have been proposed. These models consist mostly of Herzer's effective magnetic anisotropy model and Ji Song et al's two-phase random magnetic anisotropy model. The origin of the excellent soft magnetic properties can be explained by these models, but numbers of experimental results, especially Sawa's doubt and the reason of evident variation of the peak GMI ratio at 500-600℃annealing are not explained in terms of these. In order to research into the above questions, the dissertation consists of several parts as follows.1. Based on the atomic force microscope observation of the there-dimensional mesoscopic structure experimental results of Fe_73.5Cu₁Nb₃Si_13.5B₉ alloy ribbon annealed at different temperatures, on the basis of the experimental results by the X-ray diffraction and the Mossbauer spectroscopy and theoretical study for this alloy ribbon, we have conducted systematic analysis and investigation into the crystalline process of this alloy ribbon annealed at different temperatures, and proposed a number of new concepts of the mesoscopic structure with two-kind Nb-B framework, the agglomeration phase of the nanocrystalline grains, the average numbers of nanocrystalline grains in unit volume. Finally, new hypothesis of the crystallization mechanism and the mesoscopic structure model described for the crystalline process of this alloy were established. This model can be evolved by the two- or three-phase structure model. 2. Based on the experimental results, we propose a model for exploring the influence of the mesoscopic structure on the soft magnetic properties this kind of Fe-based nanocrystalline alloys, and calculate the frequency function-D -function for the soft magnetic properties of Fe_73.5Cu₁Nb₃Si_13.5B₉ nanocrystalline alloy. With this frequency function, we succeed in exploring the influence of the frequency on the soft magnetic properties of Fe_73.5Cu₁Nb₃Si_13.5B₉ nanocrystalline alloy. Analysis shows that the D -function is a complex function, the real part Re( D) shows the inductance and capacitance of nanocrystalline Fe_73.5Cu₁Nb₃Si_13.5B₉, the imaginary part Im(D) shows its resistance. We have built an equivalent parallel RLC model for the mesoscopicstructure of Fe_73.5Cu₁Nb₃Si_13.5B₉ nanocrystalline alloy. Based on the model we have calculated v_extremumGMI=v|_Re(D)=0 ,which is the condition of maximum GMI value forFe_73.5Cu₁Nb₃Si_13.5B₉ nanocrystalline alloy, as well as influence of the factorsμ,σ,ω,R,(?) and micro-magnetic- structure on the maximum GMI value.3. We put forward a physical conception for the mesoscopic impedivity ofFe-based nanocrystalline alloy for the first time, and its formulais obtained by using Maxwell system of equations. The formula shows that the mesoscopic impedivityρof Fe-based nanocrystalline alloy depends on themesoscopic magnetic field intensity (?), mesoscopic magnetic vector potential (?), and mesoscopic permeabilityμ. The mesoscopic magnetic vector potential (?) is causedby the effect of quantum mechanics with the mesoscopic structure in the studied material, and is decided by microcosmic structure of the studied materials. Magneto-resonance frequency shift of nanocrystalline Fe_73.5Cu₁Nb₃Si_13.5B₉ powder for its GMI effect and frequent resonance magnetic field intensity shift of nanocrystalline Fe_73.0Cu_1.0Nb_1.5V_2.0Si_13.5B_9.0 microwire with the multilayer structure for its GMI effect are explained successfully by the formula.4. Based on the producing and the measuring impedance of Fe_73.5Cu₁Nb₃Si_13.5B₉ nanocrystalline powder, pass through abstraction, we propose a model (spherical mesoscopic structure model) exploring for the influence of the mesoscopic structure on the GMI effect this kind of Fe-based nanocrystalline powder. Analysis shows that the GMI effect is closely related to the D- function, which is dependent on the factors, such asμ(the effective magnetic permeability of the nanocrystalline grain),σ(its the electrical conductivity), R (its radius),ω(the driving field frequency), H₀ (the driving field effective magnitude), H_ex (the external DC magnetic field magnitude), and there exist mutual influences amongμ,σ,ω,R. With this model, we can succeed in exploring the influence of H_ex on the resonance frequency, the resonance amplitudevalue, the sensitivity of the impedance curves of Fe_73.5Cu₁Nb₃Si_13.5B₉ nanocrystalline powder. This model provides a way for our researching mechanism of the GMI effect.