EFFECT OF THE HOLLOW TOPOLOGY ON THE SPIN DYNAMICS IN IRON OXIDE MAGNETIC NANOPARTICLES

This thesis has been developed within the framework of a general research concerning novel systems based on magnetic nanoparticles with different spin topologies that present, consequently, different static and dynamic magnetic properties. In particular the experimental investigation and data analysis were focused on the effect of the hollow core spins topology on the static and dynamic properties. Nanoparticles with a hollow magnetic core (HNP) of variable dimensions constituted of maghemite (-Fe2O3) and/or magnetite (Fe3O4) have been studied, while nanoparticles having a full core (FNP) and the same magnetic phase, were used as reference systems with superparamagnetic monodomain conventional behaviour. All the data and the interpretations presented here are new. In particular, the evidence of a second spin population in the HNPs, ascribed to the presence of a thick, disordered surface spin layers not present in the FNPs, is experimentally highlighted by means of magnetization and NMR relaxometric data. It is worth noticing that iron oxides with different spin topology could have an important role in biomedicine other than recording and spintronics applications. This thesis, finding a phenomenological relationship among experimental data concerning the basic magnetic properties and the dynamic paratemers that reflect the efficiency of the investigated samples in specific applications (e.g. the nuclear relaxivity in MRI), could give a strong contribution to the future development of the nanotechnology based on magnetic hollow nanoparticles.