Power Absorption in Fe3O4 Nanoparticles

G F GOYA; ENIO LIMA JR.; A D ARELARO; T TORRES; C MARQUINA; H R RECHENBERG; M RICARDO IBARRA

Dublin, Ireland

Simposio; JEMS 08 – IV Joint European Magnetic Symposia; 2008

The synthesis of novel magnetic materials, mainly magnetic nanoparticles (MNPs) for heating purposes in biomedical applications (i.e., magnetic hyperthermia) has gained interest along the last years. However, power delivery from MNPs is still on the low range (1- 10 W per gram of tissue) as compared to traditional microwave or conduction-based hyperthermia methods, wichh can deliver up to 2-3 KWatts into the target region. Particles largen than 20 nm are difficult to stabilize in water. Therefore, most of the experimental work reported so far has been focused on nanoparticles with single-domain magnetic structure. In order to explore the influence of particle size on the power absorption we have synthesized magnetite-based nanoparticles with average size from 3 nm up to 12 nm, using high temperature decomposition of Fe(acac)3 in the presence of a long chain alcohol. The final size of the nanoparticles was controlled by the molar ration Precursor:surfactante. Large particles (d > 12 nm) were prepared by re-growth method using previously synthesized particles as seeds for the next ones. High resolution TEM (HRTEM) images and X-ray diffraction (XRD) data confirmed that the average particle size increased with increasing molar precursor/surfactant ratio. Magnetization and ac susceptibility measurements showed that the saturation magnetization Ms at room temperature of all samples were lower than the expected 92-98 emu/gof bulk magnetite, but increase as the average size increases. Power absorption experiments conducted in an adiabatic system at f=260 kHz and B0=16 mT revealed a strong increase in the specific power absoprtion (SPA) for particles with d = 25 nm, with SPA value of 130 W/g.