Structural and magnetic study of zinc-doped magnetite nanoparticles and ferrofluids for hyperthermia applications

P MENDOZA ZELIS, G A PASQUEVICH, S J STEWART, M B FERNANDEZ VAN RAAP, J APHESTEGUY, I J BRUVERA, C LABORDE, B PIANCIOLA, S JACOBO AND F H SANCHEZ

JOURNAL OF PHYSICS - D (APPLIED PHYSICS)

IOP PUBLISHING LTD

Lugar: Londres; Año: 2013 vol. 46

0022-3727

Artículo incluído en los highlights 2013 de JPD-AP por los editores Cubic-like shaped ZnxFe3−xO4 particles with crystallite mean sizes D between 15 and 117 nmwere obtained by co-precipitation. Particle size effects and preferential occupation of spineltetrahedral site by Zn2+ ions led to noticeable changes of physical properties. D 30 nmparticles displayed nearly bulk properties, which were dominated by Zn concentration. ForD 30 nm, dominant magnetic relaxation effects were observed by M¨ossbauer spectroscopy,being the mean blocking size DB ∼ 13 to 15 nm. Saturation magnetization increased with xup to x ∼ 0.1?0.3 and decreased for larger x. Power absorbed by water and Chitosan-basedferrofluids from a 260 kHz radiofrequency field was measured as a function of x, fieldamplitude H0 and ferrofluid concentration. For H0 = 41 kAm−1 the maximum specificabsorption rate was 367Wg−1 for D = 16 nm and x = 0.1. Absorption results are interpretedwithin the framework of the linear response theory for H0 41 kAm−1. A departure towards asaturation regime was observed for higher fields. Simulations based on a two-level descriptionof nanoparticle magnetic moment relaxation qualitatively agree with these observations. Thefrequency factor of the susceptibility dissipative component, derived from experimentalresults, showed a sharp maximum at D ∼ 16 nm. This behaviour was satisfactorily describedby simulations based on moment relaxation processes, which furthermore indicated acrossover from N´eel to Brown mechanisms at D ∼ 18 nm. Hints for further improvement ofmagnetite particles as nanocalefactors for magnetic hyperthermia are discussed.