ATOMISTIC MODELLING OF MAGNETISATION REVERSAL PROCESSES IN RECORDING MEDIA

Magnetic materials used in the magnetic recording industry have been developed for several decades. However, since the areal recording desity is increased to around 1 Tbit/in2,some new physical challenges have become clear: particularly the need of using high magnetic anisotropy materials to overcome the super- paramagnetic effect. The requirement of acceptable signal to noise ratio leads to a reduction in grain size. In order to maintain thermal stability it is necessary to increase the magnetic anisotropy K. This leads to unrealistically high write fields. The main challenge is to reduce the write field, which is being met by advanced design and the potential use of Heat Assisted Magnetic Recording. In the meantime, the research on the reversal processes has also attracted much attention because of the use of ultra-fast technology and also the high speed of writing and reading processes in recording media. From the theoretical point of view, an atomistic model can obtain detailed information which is difficult to obtain from experiments. Also it can break through the limitation of micromagnetic calculations in ultra-fast processes and thermal effects because of using a Heisenberg direct exchange model and at the atomic level, especially studying the interface between two coupled materials. In this thesis, an atomistic model is used to simulate the properties of magnetic recording media studying the reversal processes, as well as the exchange coupling, anisotropy and thermal effects of small magnetic particles. Firstofall,theinter-granular exchange coupling is calculated by doping magnetic atoms into the spacing between magnetic recording grains, and indirectly by adding a capping layer onto the granular recording layer,to control the exchange coupling and further the switching field of the magnetic media. This result shows that an optimised interface exchange parameter is important to reduce the coercivity. Secondly, the reversal processes of many independent single domain particles is studied, determining several important parameters such as field, temperature and time scale,to better understand some critical physical problems in the heat assisted magnetic recording process. Furthermore, a larger scale atomistic model is used to simulate the whole heat assisted magnetic recording process in a granular recording media with grain size distribution, demonstrating the full atomistic model is capable to simulate a realistic system. Finally, an exchange coupled composite media is simulated to develop the potential application of this material in recording media.