Simulations of magnetic nanoparticles with internal magnetization dynamics for magnetic hyperthermia

Abstract

Ferrofluids, suspensions of magnetic nanoparticles, are versatile materials used for magnetic hyperthermia, among other applications. We developed a simulation framework to study the complex behavior of a multiparticle system in a viscous medium and to understand the structure formation and its impact on relaxation processes and heat dissipation. The simulations combine Langevin dynamics and the internal magnetization dynamics by solving the coupled Landau-Lifshitz-Gilbert equation. We simulate a system of multiple single-domain particles with uniaxial anisotropy in an aqueous fluid with thermal fluctuations and dipole-dipole interactions. The simulations reveal the self-aggregated structures of the particles depending on temperature, external field, and material parameters. Self-agglomeration must be avoided to ensure the stability of the ferrofluid. With the right parameters, the particles in our simulations can behave superparamagnetically due to the inclusion of a stochastic term in the effective field. In general it is difficult to find parameters for stable ferrofluids that also have high hysteresis losses, but this simulation framework can facilitate the search for optimal parameters. It can also help to more accurately predict the behavior of ferrofluids in the high-frequency regime, as well as provide deeper insight into the behavior of the individual magnetic nanoparticles.