Magnetic hyperthermia and magnetic dynamic response of aqueous suspension of Fe3O4 nanoparticles coated with oleic acid/chitosane

D. F. CORAL; P. MENDOZA ZÉLIS; V. LASSALLE; P. NICOLÁS; M. L. FERREIRA; M. B. FERNÁNDEZ VAN RAAP

Buenos Aires

Workshop; VII Latin American Workshop on Magnetism, Magnetic Materials and their applications; 2013

The issue on whether dynamic properties of magnetic colloids retrieved from magnetic measurement of low ac-field amplitudes and frequencies can be extrapolated to analyzed Specific Absorption Rate (SAR) data acquired at higher amplitudes and frequencies excitation fields is addressed.  The dynamic response of two colloids of magnetite coated with oleic acid (OA-MAG) and chitosan (CS) in water, displaying high and low heat power release (85 and 5 W/gFe3O4) at a frequency f of 267 kHz and field amplitude of 52 kA/m, were analyzed.  Both colloids are the same in terms of carrier liquid, surfactant and magnetic phase composition. The colloids were prepared by nanoprecipitation under the same experimental condition. The same amount of CS was used to hydrophilize OA-MAG nanoparticles (2/3 of CS/OA-MAG w/w) previously synthesized with different mass ratio of oleic acid to magnetite (1/1 and 4/1), resulting in mean sizes (d) of 10.0±2.9 and 13.4±3.6 nm and hydrodynamic sizes of 168 and 460 nm respectively. From out of phase a.c susceptibility temperature dependence χ"(T), acquired in the frequency range from 5 to 10^4 Hz and field amplitude of 80 A/m, attempt time τ0and energy barrier Ea was obtained and used to analyzed SAR data within linear response theory. Results indicate that the nanoparticles in both colloids relax by Néel mechanism. Simulations of g(d)χ"(τ(d)), using magnetic core size distribution g(d) inferred from VSM, and χ" size dependence introduced by Néel relaxation time and evaluated at a fixed frequency coincident with SAR experiment were calculated. For colloid displaying high heat power release, the maximum of the simulated curve is close to the mean magnetic core size, while for the other colloid is far away. Dipolar magnetic interactions are not negligible in the case of 10 nm nanoparticles, and their influence in the dissipation is also discussed.