Optimal Size of Nanoparticles for Magnetic Hyperthermia: A Combined Theoretical and Experimental Study
Résumé
Progresses in the prediction and optimization of the heating of magnetic nanoparticles in an alternative magnetic field are highly desirable for their application in magnetic hyperthermia. Here a model system consisting of metallic iron nanoparticles with a size ranging from 5.5 to 28 nm is extensively studied. Different regimes as a function of the nanoparticles size are evidenced: single-domain superparamagnetic, single-domain ferromagnetic and multi-domain. Ferromagnetic single-domain nanoparticles are the best candidates and display the highest specific losses reported in the literature so far (11.2±1 mJ g-1). Measurements are analysed using state-of-the-art analytical formula and numerical simulations of hysteresis loops. Several features expected theoretically are observed for the first time experimentally: i) the correlation between the nanoparticle diameter and their coercive field ii) the correlation between the amplitude of the coercive field and the losses iii) the variation of the optimal size with the amplitude the magnetic field. None of these features are predicted by the linear response theory-generally used to interpret hyperthermia experiments-but are a natural Submitted to 2 2 consequence of theories deriving from the Stoner-Wohlfarth model; they also appear clearly in numerical simulations. These results open the path to a more accurate description, prediction and analysis of magnetic hyperthermia.
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