Micromagnetic Studies Of High Frequency Permeability On Soft Magnetic Thin Films

In this thesis, firstly we track back the development course of magnetic recording and micromagnetics, then present a review of the current state-of-art research and progress pattern in the future of the soft magnetic pole tip in the thin film inductive head. A brief introduction of micromagnetism and its computational realization is shown in Chapter 2. Combining the research activities and results in our lab, we performed a series of micromagnetic simulation of high frequency permeability in FeCo and FeAlN thin film head.High saturation magnetization FeCo and FeAIN thin films attract more and more attention for recording heads and TMR, GMR to achieve high recording density. In order to supply theoretical reference to the design of the magnetic head and the choice of the material performance, we performed a series of micromagnetic simulation of high frequency permeability in different materials and different conditions.Based on careful analysis on the anisotropy field mechanism in soft magnetic thin films, Random Anisotropy Model (RAM) is introduced for us to choose cluster with the size of exchange length as simulation element instead of nanocrystalline grain. In our model, magnetostatic interaction in thin films is carefrully considered.Firstly, the simulation results of the inactive magnetic nature in FeCo and FeAIN thin film are given and compared with the experiment results and agrees well. Then the high frequency permeability on macroscopic view in FeCo and FeAIN thin film is studied, and that cofirms the nature that initial permeability and isotropic field are inverse proportion. In the work of study and analysis the initial permeability, very wide frequency range is chosen.Because the thin film for micromagnetic device (the pole-tip in an inductive thin film head, free layer of MRAM)is very small, the high frequency permeability on mesoscopic view is studied by micromagnetic simulation. The study of micromagnetic simulation indicate as follows:1. The simulation results of macroscopic inactive magnetic nature of that two thin films agree well with experiment results.2. When mesoscopic high frequency permeability is studied , three different unit form are chosen. The aspect ratio are 1,2, and 4, and we find when it is 1, the result is best.3. When mesoscopic high frequency permeability is studied ,"ladder" and "vortex" domain structures are chosen to studied. The initial permeability of "ladder" is higher than that of "vortex" domain structure. And the high frequency curve of "ladder" is more smooth than that of"vortex" domain structure. That implys noise of "ladder"domain structure is lower. We can also see the frequency range of "ladder" domain structure is wilder.4. When mesoscopic high frequency permeability is studied , we give the results of how permeability varies in FeCo and FeAIN thin films with external fields. The high ftequency response is much better in FeCo thin film than that in FeAIN thin film. At last, according to the analyse of equation of magnetic loss, we explain the cause of that the simulation results of FeCo when the applied field is 12Hk is not good.5. When mesoscopic high frequency permeability is studied , Three different bias field are chosen. The results indicate that the bigger the bias field is, the smaller the initial permeability is.