Coarse-graining in micromagnetic simulations of dynamic hysteresis loops

We use micromagnetic simulations based on the stochastic Landau-Lifshitz-Gilbert equation to calculate dynamic magnetic hysteresis loops at finite temperature that are invariant with simulation cell size. As a test case, we simulate a magnetite nanorod, the building block of magnetic nanoparticles that have been employed in preclinical studies of hyperthermia. With the goal to effectively simulate loops for large iron-oxide-based systems at relatively slow sweep rates on the order of 1 Oe ns^-1or less, we modify and employ a previously derived renormalization group approach for coarse-graining (Grinstein and Koch 2003Phys. Rev. Lett.20207201). The scaling algorithm is shown to produce nearly identical loops over several decades in the model cell volume. We also demonstrate sweep-rate scaling involving the Gilbert damping parameter that allows orders of magnitude speed-up of the loop calculations.