Interações magnéticas entre nanopartículas superparamagnéticas e sua influência sobre o fenômeno da hipertermia

Abstract

The effect of heating magnetic nanoparticles from the application of an alternating magnetic field has aroused great interest in the scientific community. In the biomedical field, for example, this effect is used in cancer therapy through magnetic hyperthermia. However, the factors that can influence the heating of these materials are not yet fully understood and have generated several discussions, with discrepancies between the results presented in the literature. Although superparamagnetic systems have been widely explored for applications in magnetic hyperthermia, in most cases the effects of magnetic interactions between nanoparticles on the heating eficiency of these materials are completely neglected. In this work, we aim experimental investigation on the existence of magnetic interactions between superparamagnetic nanoparticles and their influence on magnetic hyperthermia. From the production and structural, morphological, magnetic, and calorimetric characterization of nanoparticles MgFe2O4, γ-Fe2O3, ZnFe2O4, and CuFe2O4 it was made a systematic investigation of the magnetic properties of these samples, which led to the belief that they are associated with the existence of exchange interactions in the system. For this study, it was first confirmed that the samples consist of pure ferrite nanoparticles, without secondary phases and superparamagnetic behavior at room temperature. Nevertheless, it was found that the magnetic response of these samples is not well described by the well-known Langevin function, even taking into account the size distribution of the nanoparticles. To address the reasons for such a deviation of non-interacting behavior of a superparamagnetic system, from equilibrium and dynamic magnetization measurements, it was considered a theoretical approach based on modified Weiss mean field approximation, in which it was used to describe the nature of the interactions present in the samples. From the results, positive values were found for the parameter Θ associated with the mean field and which is directly related to the interactions within the system. This result suggests the existence of magnetizing e ects due to interactions in the system, which, according to the Weiss mean field theory, are fingerprints of the presence of exchange forces between nanoparticles. In addition, it was shown that the equilibrium susceptibility initial and the relaxation time are strongly affected by such interactions, directly influencing the Specific Loss Power (SLP), a key parameter in the context of magnetic hyperthermia.