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Finding the hyperthermia sweet spot in magnetic nanoflowers: Large-scale micromagnetic simulations reveal the underlying reason for superior heating performance

  • 14 minutes ago
  • 3 min read

By: Elizabeth M. Jefremovas, Lisa Calus, Jonathan Leliaert


Magnetic hyperthermia is an adjuvant cancer therapy which exploits the heat released by magnetic nanoparticles to cause damage to tumoral cells. To release the heat, an alternating magnetic field, applied externally, is employed. Experimental measurements point to iron-oxide nanoparticles with a flower-like morphology (see Fig. 1) as one of the most promising nanoheaters for such a kind of therapy. However, a full understanding of the origin of the nanoflower’s superior performance was lacking up to today.


In this work, a unique large-scale micromagnetic simulation study was carried-out to map how particle size and internal disorder affect the magnetic response and heating performance of nanoflowers. The study was carried out in close collaboration between Dr. Elizabeth Jefremovas, from the University of Luxembourg, and Lisa Calus and Prof. Jonathan Leliaert, from Ghent University, combining complementary expertise in magnetic hyperthermia and micromagnetic modeling.


Figure 1: We asked an artificial intelligence (ChatGPT) to make an impression of the magnetic nanoflowers. The result is quite accurate. The different colors represent different crystallites which together make up the nanoflower. Furthermore, they are in different colors because their anisotropy direction (the preferred direction of the magnetization) is different. This is a key ingredient tuning their superior performance.
Figure 1: We asked an artificial intelligence (ChatGPT) to make an impression of the magnetic nanoflowers. The result is quite accurate. The different colors represent different crystallites which together make up the nanoflower. Furthermore, they are in different colors because their anisotropy direction (the preferred direction of the magnetization) is different. This is a key ingredient tuning their superior performance.

The simulations explicitly resolve the realistic multicore structure of magnetic nanoflowers within a full micromagnetic framework using Mumax3, a GPU-accelerated simulation code developed at the DyNaMat group at Ghent University. Micromagnetism describes magnetization dynamics at the nanoscale, but it is computationally demanding: it requires a nanometer-sized spatial discretization, picosecond-large time steps, and the evaluation of long-range dipolar interactions. Capturing the dynamics of complex three-dimensional nanoflowers therefore becomes especially challenging, even more so when many particle sizes and many independent realizations of internal disorder must be simulated. This groundbreakingly large-scale study was only made possible thanks to a joint effort between Tier 1 GPU clusters of the VSC (Gent) and MeluXina (Luxembourg).


Jefremovas, Calus and Leliaert were able to unravel the magnetization reversal above 70 nm, where it no longer reverses uniformly but instead folds into a vortex state. Suprisingly, within this vortex regime a clear secondary maximum of the coercivity emerges around 100–150 nm, which explains the superior hyperthermia performance of magnetic nanoflowers in this size range. This effect is driven by spin disorder inside the particle which pins the vortex core and hinder its reversal. Two distinct switching modes appear: a core-dominated reversal for smaller vortices and a flux-closure-dominated rotational reversal for larger ones. The peak arises precisely at the transition between these two mechanisms, defining a well-defined hyperthermia “sweet spot.”

Figure 2: Coercivity (a measure for the heat release) vs. size of iron-oxide nanoflowers: Beyond the single-domain regime, a secondary maximum of the coercivity is achieved which explains the superior hyperthermia performance of magnetic nanoflowers.
Figure 2: Coercivity (a measure for the heat release) vs. size of iron-oxide nanoflowers: Beyond the single-domain regime, a secondary maximum of the coercivity is achieved which explains the superior hyperthermia performance of magnetic nanoflowers.

More broadly, the work shows that micromagnetic simulations can directly connect nanoscale magnetization dynamics to macroscopic application performance. Supported by VSC computing resources, these simulations go beyond explaining experimental observations and instead enable predictive design, translating fundamental magnetic behavior at the nanoscale into concrete improvements for biomedical applications.


Read the full scientific publication, selected as editor’s choice, in Small Science here


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