Chemical synthesis and characterization of magnetite hollow nanospheres

ENIO LIMA JR.; JOSE M. VARGAS; ROBERTO D. ZYSLER; HERCILIO R. RECHENBERG; RENATO COHEN; JORDI ARBIOL; GERARDO F. GOYA; ALFONSO IBARRA; M. RICARDO IBARRA

Rosario

Congreso; 10th Inter-American Congress of Electron Microscopy 2009, CIASEM; 2009

Sociedad Interamericana de Microscopía

We report a single-step chemical synthesis of iron oxide hollow nanospheres of 9.3 nm in diameter. Monodisperse organically passivated (oleic acid) ferrite nanoparticles are prepared by high-temperature organic-phase synthesis. The nanoparticles have a narrow size distribution with mean diameter of <d> = 9.3 nm. The broadening of the x-ray patterns reflects the existence of crystallite sizes of 2 nm, much lower than the 9.3 nm observed from HRTEM. Detailed analysis of magnified HRTEM revealed the polycrystalline nature of the nanostructures with the absence of any preferential orientation. High angular annular dark field and STEM analysis reveal that our system is composed by hollow nanoparticles.Mössbauer data provide further evidence for the formation of iron oxide with high structural disorder, magnetically ordered at 4.2 K and superparamagnetism at room temperature. An unusual magnetic behavior under an applied field is reported, which can be explained by the large fraction of atoms existing at both inner and outer surfaces.