Single-step chemical synthesis of ferrite hollow nanospheres

E. LIMA JR.; J. M. VARGAS; R.D. ZYSLER; H.R. RECHENBERG; R. COHEN; J. ARBIOL; G.F. GOYA; A. IBARRA; M.R. IBARRA

Iglesias, Serdegna

Congreso; IX Convegno Nazionale Materiali Nanofasici; 2009

AUSI

We report a single-step chemical synthesis of iron oxide hollow nanospheres of 9.3 nm indiameter. Monodisperse organically passivated (oleic acid) ferrite nanoparticles areprepared by high-temperature organic-phase synthesis. The nanoparticles have a narrowsize distribution with mean diameter of <d> = 9.3 nm. The broadening of the x-ray patternsreflects the existence of crystallite sizes of 2 nm, much lower than the 9.3 nm observedfrom HRTEM. Detailed analysis of magnified HRTEM revealed the polycrystalline nature ofthe nanostructures with the absence of any preferential orientation. High angular annulardark field and STEM analysis reveal that our system is composed by hollow nanoparticles.The large fraction of atoms existing at the inner and outer surfaces gives rise to a highmagnetic disorder with unusual magnetic behavior. An enhancement of the magnetizationat low temperatures, and shift in the field cooling hysteresis loops (exchange bias effect)are observed.M(H,T) and In-field Mossbauer (120 kOe) measurements clearly show that magneticcontribution of the disordered shell plays the fundamental rule in the magnetic properties.The overall magnetic behavior can be explained considering the coexistence of a softsuperparamagnetic phase and a hard phase corresponding to the highly frustrated clusterglasslike phase at the surface regions.