Micromagnetic Studies On Magnetic Thin Films For Ultrahigh-density Magnetic Recording Media

With the rapid increase in magnetic recording density, the area of a single recorded bit becomes smaller and smaller. In this case, two problems should be considered: the first is so called "superparamagnetic limit";the other one is how to realize the read/write of information on the recorded bit of smaller area. Micromagnetic Simulation is believed to be most suitable for understanding the magnetization process on a nano magnetic level, because they start with basic principles(exchange, manetization, anisotropy and morphology) and yield hysteresis loops and magnetization patterns.In this article, we have focused on two kinds of potential candidates for application in magnetic recording media. The FePt alloy with L10 structure has very strong magnetocrystalline anisotropy, this excellence make this kind of material suitable for ultra-high density magnetic recording media. The other kind is NeFeB thin film . Due to its high uniaxial magnetocrystalline anisotropy (10⁷erg/cm³), NdFeB grains could be fined to nanometer-sized while remaining enough thermal stability. Therefore, lager areal density could be realized on these tiny grains.A three-dimensional micromagnetic model with non-uniform grain size distribution has been built up to study the problem. The high magneto-crystalline anisotropy K_u results in a short exchange length l_ex in nanograins, therefore a magnetic grain is divided into smaller grids on the order of l_ex The magnetization reversal mechanism in FePt thin films is diffirent from NdFeB thin film. We have measure the M-H loops, the images of magnetization reversal vectors, the initial magnetization curves, the variety of the coercivity along with the angle 6 (the angle of the external field and the c-axis). And we get the conclusion that the magnetization reversal mechanism in FePt thin film is the domain wall displacement. In NdFeB thin film, the magnetization reversal mechanism is the rotation of the magnetic vectors. And we also have compared the result with the experiment, and it is consistent with the experiment.