Study of the role of the ligands coordinated at the surface of pure Wuestite nanoparticles prepared following a room temperature organometallic method: Evidence of ferromagnetic - in shell- and antiferromagnetic - in core magnetic behaviors

Highlights: → Pure Wuestite (Fe1-yO) nanoparticles synthesized by organometallic chemistry. → The influence of the surface ligands on the magnetic properties. → Ferromagnetic core-antiferromagnetic shell magnetic nanoparticles. - Abstract: Wuestite particles (Fe1-yO) are synthesized using controlled hydrolysis at room temperature of [Fe(N(SiMe3)2)2] and stabilized by amine ligands. This method leads to 5 nm pure wuestite particles. This phase is clearly identified by transmission electron microscopy and wide angle X-ray scattering. Distortion in the crystallographic structure has been demonstrated. Particular attention is paid on the Fe(III) formation. Moreover, a combination of Moessbauer spectroscopy and SQuID measurements, revealed that the particles are composed of an antiferromagnetic core surrounded by a ferromagnetic shell. According to the Neel theory, the Fe(III) and Fe(II) ions present in the particles are ferromagnetically coupled and the proportion of Fe(III) ions varies from 3.9 to 7.1% as a function of the amine ligand.