Micromagnetic simulations of clusters of nanoparticles with internal structure: Application to magnetic hyperthermia

TL;DR

This study uses micromagnetic simulations to analyze how internal structures of iron oxide nanoparticles affect magnetic hyperthermia performance, revealing limitations of the macrospin approximation and emphasizing the importance of detailed internal modeling.

Contribution

It introduces a coarse-graining micromagnetic simulation method for complex NPs and compares results with macrospin models, highlighting the significance of internal structure in magnetic hyperthermia.

Findings

Magnetostatic interactions enhance heating in chains and triangles.

Macrospin approximation fails to accurately predict hysteresis loops for complex NPs.

Internal structure significantly influences local and collective magnetic responses.

Abstract

Micromagnetic simulation results on dynamic hysteresis loops of clusters of iron oxide nanoparticles (NPs) with internal structure composed of nanorods are compared with the widely used macrospin approximation. Such calculations allowing for nanorod-composed NPs is facilitated by a previously developed coarse-graining method based on the renormalization group approach. With a focus on applications to magnetic hyperthermia, we show that magnetostatic interactions improve the heating performance of NPs in chains and triangles, and reduce heating performance in fcc arrangements. Hysteresis loops of triangular and fcc systems of complex NPs are not recovered within the macrospin approximation, especially at smaller interparticle distances. For triangular arrangements, the macrospin approximation predicts that magnetostatic interactions reduce loop area, in contrast to the complex NP case. An investigation of the local hysteresis loops of individual NPs and macrospins in clusters reveals the impact of the geometry of their neighbours on individual versus collective magnetic response, inhomogenous heating within clusters, and further differences between simulating NPs with internal structure and the use of the macrospin approximation. Capturing the internal physical and magnetic structure of NPs is thus important for some applications.