The influence of hydrodynamic effects on the complex susceptibility response of magnetic fluids undergoing oscillatory fields: New insights for magnetic hyperthermia

Abstract

In this work, we perform Langevin dynamics simulations to examine microstructure-macroscopic related properties of magnetic fluids in an attempt to understand the influence of the long range viscous hydrodynamic and dipolar interparticle interactions on the complex susceptibility response of a magnetic suspension undergoing an oscillatory magnetic field. The simulations use periodic boundary conditions in order to properly compute particle interactions through the Ewald summation technique. The imaginary part of the complex susceptibility predicted by the simulations is presented in terms of the frequency, particle volume fraction, and Péclet number. This property is used to investigate the process of magnetic hyperthermia. A detailed comparison between our simulations and the prediction of an asymptotic theory for a small Péclet number in the absence of hydrodynamic interactions shows an excellent agreement. The influence of the hydrodynamic and dipolar interactions on the average rate of temperature rise is investigated here. The coupling between the particle relaxation time and the forcing frequency of the applied field is also discussed. The simulations exhibit inhomogeneous chainlike structures in the numerical box induced by interparticle dipolar interactions. We find that the presence of these structures enhances magnetic heating production, whereas hydrodynamic interactions weaken this effect. Our results also suggest that the way of combining and controlling physical parameters at moderate frequencies of the applied oscillatory field can improve the heating performance of magnetic hyperthermia.