Tailoring Heat Dissipation in Ordered Arrays of Dipolar Coupled Magnetic Nanoparticles

TL;DR

This study uses simulations to analyze how dipolar interactions, particle size, and temperature influence hysteresis and heat dissipation in ordered magnetic nanoparticle arrays, revealing conditions that enhance magnetic heating efficiency.

Contribution

It provides new insights into the effects of dipolar interactions and particle size on hysteresis behavior and heat dissipation in magnetic nanoparticle arrays, relevant for hyperthermia applications.

Findings

Dipolar interactions can induce ferromagnetic behavior at room temperature.

Hysteresis loop area is maximized for certain particle sizes and interaction strengths.

Heat dissipation decreases rapidly with temperature for smaller particles and weaker interactions.

Abstract

The main aim of the present work is to analyse the effect of dipolar interaction strength $\lambda$, particle size $D$ and temperature $T$ on the hysteresis mechanism in ordered arrays of magnetic nanoparticles (MNPs) using computer simulations. The anisotropy axes of the MNPs are assumed to have random orientation to mimic the real system. In the absence of thermal fluctuations and dipolar interaction, the hysteresis follows the Stoner and Wohlfarth model irrespective of $D$, as expected. The hysteresis loop area is minimal for particle sizes $D \approx8-16$ nm at $T=300$ K and $\lambda=0.0$, indicating the dominance of superparamagnetic character. Switching magnetic interaction on is able to move the MNPs from superparamagnetic to a ferromagnetic state even at room temperature; therefore, magnetic interaction of enough strength enhances the hysteresis loop area. Interestingly, the hysteresis loop area is significant and is the same as that of Stoner and Wohlfarth particle even $T=300$ K and negligible dipolar interaction for ferromagnetic MNPs ($D>16$ nm). The coercive field $\mu^{}_oH^{}_c$ and blocking temperature $T^{}_B$ also get enhanced with an increase in $\lambda$ and $D$. The rigorous analysis of the coercive field $\mu^{}_oH^{}_c$ vs temperature data also reveals significant deviation from $T^{3/4}$ dependence of $\mu^{}_oH^{}_c$ because of dipolar interaction. The amount of heat dissipated $E^{}_H$ and $\mu_oH^{}_c$ decrease rapidly with $T$ for $D\approx 8-16$ nm and $\lambda\leq0.6$. On the other hand, $E^{}_H$ and $\mu^{}_oH^{}_c$ depend weakly on $T$ with $D>16$ nm, even in the weak dipolar limit. The present work should provide a better understanding of magnetic hyperthermia to researchers working on this subject. For physicists, it would be interesting to test experimentally the results described in this article.