Recording media dynamics using a multi-timescale micromagnetic model with atomistic parameterisation

The current state of the art technology for ultra-high density magnetic storage is based on heat assisted magnetic recording (HAMR). As the demand for greater storage density increases the optimisation and improvement of HAMR technologies is crucial. The nature of HAMR requires models capable of correctly describing the magnetisation over temperatures up to and exceeding the material's Curie point. Additionally, the ability to study long term behaviours, such as data storage stability, requires that these models are capable of very large timesteps ranging from seconds to years. An open-source code called MARS incorporating three key solvers has been developed. MARS is capable of modelling systems over all required temperatures via a Landau-Lifshitz-Bloch (LLB) solver as well as over long time periods via a kinetic Monte Carlo (kMC) solver. The source code is available at https://bitbucket.org/EwanRannala/mars .

Using MARS, investigations into numerous key aspects of HAMR systems have been performed: the presence of Curie point distributions, which limit the effectiveness of HAMR performance by inducing variations in the obtained bit positions; the influence of adjacent track erasure and temporal decay on HAMR performance; and the presence of decreasing ferromagnetic resonance (FMR) linewidth at temperatures close to the Curie point which has been attributed to a potential decrease in the system's damping which can influence HAMR performance significantly. The first investigation has resulted in the development of a semi-analytical model capable of extracting the Curie point distribution from experimental thermoremanence measurements. The second has revealed that adjacent track erasure is significant compared to temporal decay for a system with an energy barrier of 80 kBT with no additional signal degradation when adjacent track writes occur after long periods of data storage. The final investigation has shown that the linewidth reduction is due to in-homogeneous line broadening and that the system damping increases as temperatures approach the Curie point.