Micromagnetic Simulation Of High Frequency Saturation Mechanism For Nanocrystalline Alloy In Mesoscopic Scale

With the development of the ferromagnetic technology and the miniaturization of the modern electron equipment,soft magnetic cores of the nanocrystalline(NC)alloys have been intensively studied for their excellent soft magnetic properties.This kind of novel magnetic material is expected to be widely applied in many fields including the energy,communication,electrical and automotive industries.In practical applications,NC alloys will confront with a variety of complex operation conditions and may work under special circumstance such as magnetic saturation and do biasing.However,at present the mathematical modeling problems for the NC alloys under high-frequency saturation conditions is becoming more and more serious due to lacks of fundamental research.To advance the engineering application of the nano-new materials,the NC alloys with the typical composition of Fe73.5Cu1Nb3Si13.5B9 was taken as the research object,the high-frequency saturation characteristics of the material was taken as the research goal and the micro-magnetic simulation was taken as the research method,the effects of different factors on the high-frequency saturation magnetization process for the NC alloys was studied quantitatively from the mesoscopic as well as macroscopic scales.Specific work contents are as follows:(1)The energy equations and magnetization precession equation of the magnetic system were established after deeply studying the theory of micro-magnetism.Based on the random anisotropy model,a three-dimension spherical model for the NC alloys was built.Then the static magnetic properties of this model were tested and compared with the experimental data.The results suggest that the change trend of the coercivity with the particle size of the model is consistent with the theory proposed by G.Herzer.The magnetic parameters calculated are close to the experimental data of NC powder alloys,which verifies the correctness of the 3D model.(2)The NC alloys may face saturation problems with different high-frequency operation circumstances,which were summarized as two typical situations.One case is 'dynamic saturation(DS)' where the alternating field contains weak dc biasing field.Another situation is 'static saturation(SS)' where the hybrid field comprises of not only alternating field but also strong dc biasing field.The definitions of two saturation cases including DS and SS were determined quantitatively by observing the change trajectory of the macro-working points for the NC alloys.The results suggest that the ratio of the applied dc biasing to the amplitude of alternating field equal to 90%is the cut-off point between DS and SS.(3)At the mesoscopic level,the external and internal factors that affect saturation magnetization process for the NC alloys were analyzed respectively under two types of saturation fields.Two parameters including saturation time and rotational velocity of the magnetic moment were employed.The external factors,which determine the working condition of the NC alloys,are the dc biasing field and the frequency of the alternating field.The influences of the above two factors are related to the type of saturated field.The internal factor,which is the grain size of NC alloys,is essential to the soft magnetic properties of the alloys.The effects of this factor are independent of the type of saturation field.(4)On the macro level,two physical parameters including complex permeability and magnetization rate were employed for research.The effects of the frequency and dc biasing field on high-frequency saturation properties for NC alloys were researched respectively.The results show that the change tendency of complex permeability with the frequency and dc biasing field is basically accordance with the theoretical analysis.Magnetization rate,which rises with the frequency,increases first and then decreases with increasing dc biasing.(5)Under the same magnetic field conditions,the effects of variable frequency and variable biasing field on magnetization rate(macro-parameter)as well as moment rotation velocity(mesoscopic parameter)for NC alloys were compared quantitatively.The results suggest that the change rates of the research parameters on two different levels are close to each other,that is,the meso-level and macro-level calculations are consistent and the two-scale mutual verification is realized.The simulation will enrich the theoretical basis and the analytical method for the equivalent modeling of the NC alloys under high-frequency saturation circumstances,and provide technical support for the preparation of the NC alloys.