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

Wüstite 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 wüstite 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 Mössbauer spectroscopy and SQuID measurements, revealed that the particles are composed of an antiferromagnetic core surrounded by a ferromagnetic shell. According to the Néel 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.