Effects of Zn Substitution in the Magnetic and Morphological Properties of Fe-Oxide-Based Core–Shell Nanoparticles Produced in a Single Chemical Synthesis

Magnetic, compositional, and morphological properties of Zn–Fe-oxide core–shell bimagnetic nanoparticles were studied for three samples with 0.00, 0.06, and 0.10 Zn/Fe ratios, as obtained from particle-induced X-ray emission analysis. The bimagnetic nanoparticles were produced in a one-step synthesis by the thermal decomposition of the respective acetylacetonates. The nanoparticles present an average particle size between 25 and 30 nm as inferred from transmission electron microscopy (TEM). High-resolution TEM images clearly show core–shell morphology for the particles in all samples. The core is composed by an antiferromagnetic (AFM) phase with a Wustite (Fe1–yO) structure, whereas the shell is composed by a ZnxFe3–xO4 ferrimagnetic (FiM) spinel phase. Despite the low solubility of Zn in the Wustite, electron energy-loss spectroscopy analysis indicates that Zn is distributed almost homogeneously in the whole nanoparticle. This result gives information on the formation mechanisms of the particle, indicati...