High Frequency Properties And Mossbauer Spectra Of Magnetic Materials

In this thesis,the high frequency properties and Mossbauer spectra of magnetic materials were studied.The magnetic materials were NiZn spinel Ferrite,one-dimensional magnetic nanowires and Finemet alloys respectively.With the development of the working frequency of electronic devices to high frequency or very high frequency,it was valuable to study the high frequency performance of magnetic materials.In addition,the properties of the material were caused by the change of microstructure,so in the process of material preparation,it is necessary to understand the microstructure,element composition,crystallization and so on.In this thesis,the Mossbauer spectroscopy method with high energy resolution was introduced,which was helpful to understand the internal structure information of atoms and to further optimize the properties of magnetic materials.The main contents of this paper are as follows:（1）The high frequency properties and microstructure changes of NiZn spinel Ferrite were studied.By studying the Mossbauer spectra of spinel Ferrite,it was found that ion occupation can lead to the change of magnetostatic properties.With the addition of Mn ion,according to the Marshal equation,the net magnetic moment of the molecule decreases and the saturation magnetization of the Ferrite decreases.The hysteretic loop verifies the correctness of this result.With the increase of Mn ion,the real part of permeability and the imaginary part of permeability decrease,and the resonance frequency tends to shift to high frequency.（2）α-Fe magnetic nanowires with a diameter of 90 nm,and 40μm in diameter were prepared by electrochemical deposition with AAO template.The coercive force Hc of the nanowire array was much lower than the theoretical value of 10800 Oe,which was caused by the inconsistent inversion of the magnetic moment of the nanowires,that was the localization nucleation-propagation mechanism.This conclusion was verified by micromagnetic simulation.In order to measure the high frequency electromagnetic parameters of orderedα-Fe annular samples with certain period,regular and ordered by coaxial method,the annular samples were prepared by selective chemical corrosion method.The magnetic properties in the frequency band of 0.5-12 GHz are measured,and it was found that there were multiple resonance absorption peaks,which was caused by the uneven local anisotropy field.The uneven distribution of magnetic moments in nanowires arrays was also verified by Mossbauer spectra of nanowires.（3）Finemet alloy was annealed at 560℃,and the nanostructure of nanocrystal phase and amorphous phase was obtained.The Mossbauer spectra of Finemet alloy were measured.The crystallization degree of the alloy was known from the Mossbauer spectrum fitting results,and the crystal phase ratio was quantitatively analyzed.Four six-line peaks were used to represent four different Fe atomic environments in Fe₃Si,and a wide peak was used to represent amorphous phase.the results show that the nanocrystal phase and amorphous phase of Finemet nanocrystal structure account for57.36%and 42.64%respectively.The crystallization alloy has a wide magnetic loss peak in 0.5-12GHz.When the thickness of absorbing layer was 4mm,the calculated RL at 1.9-3.2 GHz is less than-10 dB,and has better absorption performance.The two-layer absorbing structure of Finemet alloy as absorbent was designed,and the high frequency absorption performance was optimized.Different heat treatment of Finemet alloy,different heat treatment and different thickness of each layer of Finemet alloy,and the combination of layered structure can achieve good electromagnetic wave absorption performance in the range of 1-10 GHz.