Using Dipolar Interactions to Improve Magnetic-Hyperthermia Performance of Low-anisotropy Nanoparticles: Theoretical Study of Chain-Like Structures

DANIELA PAOLA VALDÉS; E. LIMA JR.; R. D. ZYSLER; DE BIASI, EMILIO

Conferencia; 2020 Annual Conference on Magnetism and Magnetic Materials; 2020

Improvement of the Specific Power Absorption (SPA) is a key factor for future use of magneticnanoparticles (NPs) in magnetic fluid hyperthermia (MFH) clinical protocols, since it allowsworking with low concentration of NPs, avoiding toxic effects and simplifying the hard taskof localizing a great amount of NPs in a target tumour. In addition, in vitro and in vivoexperiments generally lead to interacting NP systems due to agglomeration in the cellularenvironment. In the particular case of linear aggregates, the impact of dipolar interactions onthe SPA of the system is still an open discussion: there are reports of both beneficial anddetrimental effects on the SPA.In this work, the effect of interparticle dipolar interaction is analysed in one-dimensional idealchains of NPs with low uniaxial anisotropy along the chain. Starting from a previously reportednon-linear probabilistic model, interactions were taken into account by incorporating adipolar contribution in the local field felt by each NP.The main focus was done in the repercussion of interactions on the enclosed area of thehysteresis loops, that can be translated into the SPA in a MFH experiment. For that reason,chains with different orientation 𝜙! (regarding the external field 𝐻) were simulated. Weconfirmed that interactions in these kind of low anisotropy systems help to increase de area ofthe loops, both for individual orientations and randomly-oriented chains (see Figure). Weinterpreted this increment as a consequence of an effective delay between the local field felt bya NP and the external field. We decomposed the dipolar field in the parallel (𝐻"#$ ∥ ) andperpendicular components and obtained that both of them exhibithysteresis when plotted as a function of the external field, as does the magnetization.Nevertheless, these loops present some morphological changes when compared with themagnetization hysteresis loops, changes that were correlated with the relative increment of thearea as a function of 𝜙!. The relative area contribution was evaluated and it was seen that forthe parallel (perpendicular) spatial configuration, is the most relevant component.This means that, if we plan to simulate a chain with 𝜙! close to 𝜋⁄2, the dipolar field cannotbe modelled as a component parallel to the external field, as usually done.In conclusion, low anisotropy linear arrangements help to significantly enhance MFH in NPsystems, obtaining a better heating performance, with the parallel configuration being the mostfavoured one.