One-step room temperature synthesis of very small γ-Fe2O3 nanoparticles

O. MOSCOSO LONDOÑO; M. CARRIÃO; C. COSIO-CASTAÑEDA; V. BILOVOL; L. M. SOCOLOVSKY; R. MARTÍNEZ SÁNCHEZ; E. J. LEDE; R MARTINEZ GARCIA

MATERIALS RESEARCH BULLETIN

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2013

0025-5408

Very small maghemite nanoparticles (~3 nm) are obtained through a one-step synthesis at room temperature. The fast neutralization reaction (co-precipitation) of a ferric solution (FeCl3 aqueous) in a basic medium (NH4OH concentrated) produces an intermediate phase, presumably two-line ferrihydrite, that in oxidizing conditions is transformed to maghemite nanoparticles. The synthesis of maghemite, as final product of the reaction, was characterized by High-Resolution Transmission Electron Microscopy (HR-TEM), X-ray Absorption Fine Structure (XAFS), Mössbauer spectroscopy, and magnetometry. The XAFS technique allowed the analysis of the crystallographic variations into maghemite nanoparticles as a result of modification in its surface/volume ratio. Mössbauer spectroscopy at low temperature (4.2 K) confirms the presence of Fe(III) in tetrahedral and octahedral interstices, in the stoichiometry corresponding to maghemite. The specific magnetization, M vs H (3K and 300 K, up to 7T) and temperature dependence of the magnetization (50 Oe by ZFC mode, 2 K ≤ T ≤ 300 K) indicate that maghemite nanoparticles of 3 nm are in superparamagnetic state with a blocking temperature close to 36 K.