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

DANIELA P. VALDÉS; ENIO LIMA JR.; ROBERTO D. ZYSLER; EMILIO DE BIASI

Conferencia; 65th Annual Conference on Magnetism and Magnetic Materials; 2020

IEEE Magnetics Society

Improvement of the Specific Power Absorption (SPA) is a key factor for future use of magnetic nanoparticles (NPs) in magnetic fluid hyperthermia (MFH) clinical protocols, since it allows working with low concentration of NPs, avoiding toxic effects and simplifying the hard task of localizing a great amount of NPs in a target tumour. In addition, in vitro and in vivo experiments generally lead to interacting NP systems due to agglomeration in the cellular environment. In the particular case of linear aggregates, the impact of dipolar interactions on the SPA of the system is still an open discussion: there are reports of both beneficial [1] and detrimental [2] effects on the SPA.In this work, the effect of interparticle dipolar interaction is analysed in one-dimensional ideal chains of NPs with low uniaxial anisotropy along the chain. Starting from a previously reported non-linear probabilistic model [3], interactions were taken into account by incorporating a dipolar contribution in the local field felt by each NP.The main focus was done in the repercussion of interactions on the enclosed area of the hysteresis loops, that can be translated into the SPA in a MFH experiment. For that reason, chains with different orientation ϕ_n (regarding the external field H) were simulated. We confirmed that interactions in these kind of low anisotropy systems help to increase de area of the loops, both for individual orientations and randomly-oriented chains (see Figure). We interpreted this increment as a consequence of an effective delay between the local field felt by a NP and the external field. We decomposed the dipolar field in the parallel (H_dip^∥) and perpendicular (H_dip^⊥) components (with respect to H) and obtained that both of them exhibit hysteresis when plotted as a function of the external field, as does the magnetization. Nevertheless, these loops present some morphological changes when compared with the magnetization hysteresis loops, changes that were correlated with the relative increment of the area as a function of ϕ_n. The relative area contribution was evaluated and it was seen that for the parallel (perpendicular) spatial configuration, H_dip^∥ (H_dip^⊥) is the most relevant component. This means that, if we plan to simulate a chain with ϕ_n close to π⁄2, the dipolar field cannot be modelled as a component parallel to the external field, as usually done.In conclusion, low anisotropy linear arrangements help to significantly enhance MFH in NP systems, obtaining a better heating performance, with the parallel configuration being the most favoured one.[1] B. Mehdaoui et al, Phys. Rev. B 87 174419 (2013)[2] L.C. Branquinho et al, Sci. Rep. 3 2887 (2013) [3] E. De Biasi et al, J. Magn. Magn. Mater., 320 312 (2008).