Effects of Nanostructure and Dipolar Interactions on Magnetohyperthermia in Iron Oxide Nanoparticles

Abstract

Magnetohyperthermia properties of magnetic nanoparticle colloids are strongly affected by their intrinsic magnetic properties and dipolar interactions among themselves. The intrinsic magnetic properties are related to the nanoparticle (NP) size, geometry, phase composition, magnetic anisotropy, and saturation magnetization. The dipole-dipole interactions are determined by colloid nanoparticle concentrations and the possible existence of clustering on the colloidal suspension. Here we have observed that oxygen atmosphere and pressure changes during the final stage of thermal decomposition are critical to modify the size of the iron oxide NPs from 8 to near 20 nm, and consequently their overall magnetic properties. Size-dependent magnetic parameters such as anisotropy, magnetic moment per particle, blocking temperature, and dipolar interaction energy were inferred using different phenomenological approaches. A detailed magnetohyperthermia analysis was performed by applying the linear response theory. A good correlation between experimental and theoretical specific absorption rate values was obtained for a frequency of 260 kHz and applied field of 52 kA/m. These results were observed for the different sizes of nanoparticles, and disagreement between the experimental results and the model increases at lower frequencies.