LLB MACRO-SPIN MODELLING OF NANOGRANULAR L1o FePt HIGH ANISOTROPY THIN FILMS

New recording media and recording methods are required if magnetic data storage is to continue the historic growth seen in the areal density, beyond the level currently imposed by the superparamagnetic limit. High anisotropy nano-granular L1o FePt thin films are currently being studied as a proposed material capable of continuing the exponential growth in areal density. FePt is so successful at maintaining a permanent magnetisation, that no applicable
magnetic field is capable of reversing the magnetisation, as in the recording process. Heat assisted magnetic recording is a proposed method of lowering the anisotropy, of the high anisotropy recording media, to a level that can be recorded in. In this thesis a nano-granular high anisotropy FePt thin film is modelled using the newly developed Landau-Lifshit-Bloch equation (to model the dynamic motion if the magnetisation) combined with a voronoi construction. The HAMR process is described over a range of maximum temperatures and modelled thin films of increasing anisotropy. It is shown that a 12000Oe applied field and a maximum temperature of Tc are required to reverse the magnetisation to the desired level. The model is used to demonstrate the lowering of the anisotropy field at elevated temperatures, allowing relatively low applied fields to set the magnetisation. The LLB equation also recovers the newly discovered fast acting linear reversal mode, at temperatures close to the Curie point.