Study of the effect of dipole interactions on hyperthermia heating the cluster composed of superparamagnetic nanoparticles

Abstract

In the present work, we investigate the effect of dipole interactions on hyperthermia heating the cluster composed of multi superparamagnetic nanoparticles via time-quantified Monte Carlo simulation. The dynamic hysteresis loop area of non-interacting particles calculated by a modified Rosensweig's model is shown to be proportional to the field frequency. The inverse of the total number of Monte Carlo steps per field cycle is considered as a computational frequency in our modelling. By comparing the two proportionality constants gained from the simulation and from the Rosensweig's model, respectively, the time scale of one Monte Carlo step is estimated. The shape of the cluster is characterised by treating it as an equivalent ellipsoid. When the morphology of cluster is highly anisotropic such in a chain and cylinder, dipole interactions align the moments of the particles to the morphology anisotropy axis of the cluster. The strength of such alignment depends on the magnitude of morphology anisotropy of the cluster. The alignment helps improve heating capability of the chain and cylinder clusters at the most angles between the field direction and morphology anisotropy axis. However, when the field direction is away from the axis too much, the high energy barrier will hamper the cluster to maintain the magnetization, leading to a reduced heating efficiency. Once the cluster loses its morphology anisotropy (i.e. cube), the influence of dipole interactions on hysteresis losses is reduced to the minimum; the probability to obtain an improved heating becomes very low no matter with the type of particle arrangement.