Full-wave Band Magnetic Film/Powder Ferromagnetic Resonance Line Width Testing System

Ferromagnetic resonance linewidth measurement is an important tool to measure the magnetization dynamics of magnetic materials.It plays a vital role in studying the internal physical mechanism of magnetic materials and improving the performance of magnetic devices.With the development of electronic devices towards multi-function,high frequency and integration,the ferromagnetic resonance testing system as a measuring tool is also facing new challenges.Not only the magnetic films need to be controllable and measurable in the RF,microwave and millimeter wave bands,but also the magnetic powders and magnetic particles need to be controllable and measurable in the full wave band.Therefore,the direction of developing ferromagnetic resonance linewidth measurement is wide-band and high-precision,and the vector network analyzer with this characteristic is just in line with the test needs.Based on the vector network analyzer,a ferromagnetic resonance linewidth measurement system for magnetic thin films/powders is developed.The main work of this thesis is as follows:1.Using vector network analyzer as microwave signal source,a ferromagnetic resonance linewidth measurement system for magnetic thin films/powders was built and tested.The system features wide frequency band,automatic measurement,and can test magnetic films and magnetic powders by changing fixtures.In order to realize the system,the grounded coplanar waveguide and rectangular cavity waveguide are designed,simulated and machined,the test fixture is modeled and fabricated,and the sliding platform is designed and machined.After all of these procedures,Lab VIEW controlling system is programmed.The computer controls the Gauss meter,vector network analyzer and program-controlled power supply through USB cable and RS232 cable.The frequency range of the machined waveguide resonators is 2.6～3.95GHz,9.84～15GHz,26.3～40GHz and 49.8～75.8GHz respectively;the operating frequency of grounded coplanar waveguide is in the range of 1～50GHz.2.Improving the accuracy of the resonant linewidth is explored from three aspects:（1）a four parameter method is established to fit the resonant linewidth and resonant frequency.By introducing reflection coefficient,the analytical model of resonant frequency and linewidth of thin film samples is improved.By comparing with S₂₁estimation model and|S₂₁|estimation model,it is found that the three fitting methods have no significant difference in fitting the resonance field.But the four parameter method shows obvious advantages on fitting the resonance linewidth,and the advantage enlarged in lower frequency.（2）By adding non-magnetic borosilicate glass between the magnetic film sample and the coplanar waveguide to adjust the spacing,the experimental results show that the resonant linewidth can be reduced by adjusting the spacing between the sample and the signal line in a certain range.To ensure the microwave signal absorption of the sample,the spacer get the best value near 100μm.（3）The decoupling model of the resonator is established,and the influence of reducing the coupling coefficient between the resonator and the sample on the test is analyzed.The experiment verifies that the decoupling has the effect of removing double peaks and reducing linewidth for some samples with narrow line width and relatively large size.In this thesis,a testing system integrating the testing of magnetic thin films and magnetic powders is built,and the automatic testing is realized.In addition,a useful exploration is made on how to further remove the measurement error and reduce the measured linewidth,which provides ideas for improving the testing accuracy.