High Frequency Properties Of Heterostructure Magnetic Materials

In this PhD thesis, we mainly study the topics on increasing the high frequency permeability and the using band by using the heterostructure magnetic materials. We mainly study the effects of grain size distribution on permeability of magnetic materials; study the magnetization reversal process of the magnetization of soft magnetic materials with dynamic method; study the high frequency properties in multilayers; study the high frequency properties in nanoshell and nanotube; study the high frequency properties of FeCo-NiZn ferrite bi-magnetic phase granular thin films.The major finding and innovations are shown as follow:1. Improvement of random anisotropy model. By introducing the distribution, the revised RAM model with grain size distribution can be well fitting with the real magnetic system. It indicate that the grain size distribution play an important role in the study of the magnetic material characteristics of the particle system.2. Development of a method to measure the parameters of magnetic materials with high frequency measurement. When measuring the saturation magnetization of thin film, this method can avoids the error during the film thickness measurement. This method is also useful to study the magnetization reversal process of hard-axis with greater accuracy.3. Adjust the high frequency properties by changing the interlayer interaction in multilayers. We change the interlayer interaction by controlling the thickness of the nonmagnetic interlayer thickness. The high-frequency magnetic permeability (21-894), the resonance frequency (1.4-6.5GHz) and in-plane uniaxial anisotropic field (12-520Oe) can be adjusted in wide range.4. Improve the Snoek's limit in multilayers. With the interface anisotropy changing in multilayers, the energy distribution should be changed in such bi-anisotropic system. Then, the resonance frequency can be increased but do not reduce the permeability.5. Nanotube and nanoshell with high Snoek's limit. With micromagnetic simulation, the Snoek's limit can be enlarged because of the bi-anisotropy. The permeability and resonance frequency can be adjusted by changing the geometrical parameters.6. Obtained such CoFe-NiZn ferrite bi magnetic granular thin films with both high resistivity and excellent high frequency magnetic properties. With NiZn ferrite doping, the resistivity (>1000μΩ cm) can be enlarged, simultaneously, we can also obtain high saturation magnetization (>10kGs), and high resonant frequency (2.88GHz).