Nanoparticle size threshold for magnetic agglomeration and associated hyperthermia performance

Abstract: The likelihood of magnetic nanoparticles to agglomerate is usually estimated through the ratio between magnetic dipole-dipole and thermal energies, thus neglecting the fact that, depending on the magnitude of the magnetic anisotropy constant ($K$), the particle moment may fluctuate internally and thus undermine the agglomeration process. Based on the comparison between the involved timescales, we study in this work how the threshold size for magnetic agglomeration ($d_{aggl}$) varies depending on the $K$ value. Our results suggest that small variations in $K$ -due to e.g. shape contribution-, might shift $d_{aggl}$ by a few nm. A comparison with the usual \textit{superparamagnetism} estimation is provided, as well as with the energy competition approach. In addition, based on the key role of the anisotropy in the hyperthermia performance, we also analyse the associated heating capability, as non-agglomerated particles would be of high interest for the application.