IRON OXIDE NANOPARTICLES AND NANOCOMPOSITES: A DIFFRACTOMETRIC STUDY

Nanosized magnetic structures are currently key materials for advancements in electronics, optoelectronics, magnetic storage, and many bio-inspired applications. What is usually termed ‘‘nanostructured systems’’ comprises those materials whose properties are determined by particles, crystallites, or clusters with characteristic lengths between about 1 and 100 nm. If the grain or domain size becomes comparable or smaller to the characteristic length scale of the interaction processes controlling a particular property, different effects and unusual chemical and physical properties can be expected that are highly attractive in a number of technical applications. In recent times, large advancements have been achieved related to the synthesis and characterization of well-defined, discrete magnetic nanoparticles for both fundamental and technological purposes. However, precise knowledge of the relationships between particle shape and size distribution, surface structure, and the resulting magnetic properties of magnetic nanoparticles is still lacking. In particular, iron oxide nanoparticles have been the subject of many theoretical and experimental studies. The goal of this thesis is to provide a crystallographic structural description of the atomic rearrangements in superparamagnetic maghemite (γ-Fe2O3) nanoparticles and in magneto-plasmonic nano heterostructures formed by metallic gold and magnetite (Fe3O4), looking for a relationship between the structure and the properties. The thesis is organized in 3 chapters. The first chapter is divided in two part: in the first a briefly introduction about nanomaterials is presented, in the second one all the used techniques are described. First the main concepts about powder diffraction are briefly recalled, then the Pair Distribution Function method is introduced, then there is a description of theory about Small angle X-Ray Scattering and finally ESR theory is shortly presented. In the second chapter all the beamlines of the European Synchrotron Radiation Facility, used for the data collection, are described. The heart of the thesis consists in the last chapter where all the data and the results about nanomaterials (γ-Fe2O3) and nanocomposites (Au-Fe3O4) are shown. In this chapter a thorough structural characterization was performed by using X-ray powder diffraction by means of conventional Rietveld analysis, Pair Distribution Function and Small Angle X-ray Scattering; in addition Electron Spin Resonance spectroscopy was performed on the systems to shed light on their magnetic properties.