Coarse-graining in micromagnetic simulations of dynamic hysteresis loops

TL;DR

This paper develops a coarse-graining method for micromagnetic simulations of dynamic hysteresis loops in magnetic hyperthermia, enabling efficient modeling of large systems at slow sweep rates with preserved accuracy.

Contribution

It modifies and applies a renormalization group approach to micromagnetic simulations, allowing accurate and faster computation of hysteresis loops for large nanoparticles.

Findings

The scaling algorithm produces nearly identical loops across different grain sizes.

Sweep-rate scaling with damping parameter enables significant speed-up.

Method applicable to modeling magnetic hyperthermia nanoparticles.

Abstract

Micromagnetic simulations based on the stochastic Landau-Lifshitz-Gilbert equation are used to calculate dynamic magnetic hysteresis loops relevant to magnetic hyperthermia. With the goal to effectively simulate room-temperature loops for large iron-oxide-based systems at relatively slow sweep rates on the order of 1 Oe/ns or less, a previously derived renormalization group approach for coarse-graining (Grinstein and Koch, Phys. Rev. Lett. 20, 207201, 2003) is modified and applied to calculating loops for a magnetite nanorod. The nanorod modelled is the building block for larger nanoparticles that were employed in preclinical studies (Dennis et al., Nanotechnology 20, 395103, 2009). The scaling algorithm is shown to produce nearly identical loops over several decades in the model grain size. Sweep-rate scaling involving the Gilbert damping parameter is also demonstrated to allow orders of magnitude speed-up of the loop calculations.