Simulation of Exchange Spring Recording Medias

The aim of this thesis is to investigate and understand the switching behaviour of magnetic grains in high density magnetic recording media, 1Tbit per square inch and above, and by doing so to overcome the discrepancies between simulation and experimental results associated with the quantitative switching field and its applied field angle. This work will bridge the gap between the experiments and simulation results, by considering a realistic micromagnetic model of CoCrPt media thin films to study their magnetization reversal dynamicsat finite temperatures as a function of magnetic structure, interlayer coupling and thermal activation.
The utility of a simplified one-grain model was investigated in describing the switching field of such media at finite temperatures. Together with experiments it is shown that thermal activation modifies the Stoner-Wohlfarth angle dependency of the switching field by reducing the depth of the minimum that occurs at 45 degrees. Whereas inter/intra granular exchange coupling introduces a clear shift in the angle of applied field at which the minimum switching field occurs.
For the first time ever grain interface layers and grain boundaries interactions are explicitly considered in a descriptive micromagnetic model, the overall magnetization switching behaviour of such grains shows a deviation from Stoner-Wohlfarth like behaviour, highlighting their importance on the quantitative and qualitative value of the switching field. The study shows that these layers are essential to understand and predict the magnetization behaviour of such magnetic grains. This work suggests and hypothesis that the presence of such a grain boundary in magnetic grains of recording media might pose a fundamental limit on the diameter that could be achieved in future.