Simulating rare switching events of magnetic nanostructures with forward flux sampling

摘要

Predicting the thermal stability of magnetic storage devices is an important and challenging task. Here, we demonstrate how the forward flux sampling method (FFS) can be used to determine the thermal stability of magnets with general microstructures for time scales ranging from picoseconds to years. To apply FFS to magnetic systems, we first use the nudged elastic band (NEB) method to determine a minimum energy path connecting the initial with the final state of the magnetic transition. Interfaces defined based on this minimum energy path then provide the basis for the FFS procedure in which dynamical trajectories are generated by integrating a stochastic version of the fundamental equation of motion of the magnetization (Landau-Lifshitz-Gilbert equation) at finite temperature. This approach allows to determine average lifetimes for incoherent reversal processes and it can be applied for any value of the damping constant. We validate the method for a single-grain particle by comparison with the results of direct Langevin simulations carried out and demonstrate its capabilities and efficiency by computing the lifetime of a graded media grain, a magnetic structure with a tailored magnetocrystalline spatial anisotropy profile.