Magnetic nanostructures: a promising approac towards RE-free permanent magnets

In this thesis are reported the results of studies conducted at LAboratory for Molecular Magnetism (LA.M.M.) of the University of Firenze concerning the synthesis and characterization of rare-earth free nanostructured materials for permanent magnet applications. In particular, ferrite-based magnetic materials doped with transition metal ions (cobalt, manganese, zinc) are studied with particular attention to the correlation between their magnetic properties and nanostructures. In a first step the magnetic behaviour of single-phase ferrites nanocrystals with enhanced anisotropy was analysed, in order to better understand the correlation between the final properties and particle size, shape, crystallinity, composition, etc. To carry out this task, monodisperse nanocrystals with controlled size, shape and stoichiometry were prepared and the size/shape-dependent evolution of their magnetic properties was studied. In a second step, hybrid bi-magnetic core|shell nanoparticles were prepared focusing on the aftermath and required conditions of exchange-coupling establishment between the two moieties. In particular, crystalline nanocomposites presenting spring-magnet or exchange-bias behaviour were analysed in order to assess the possibility of improving the material performances by control of the interface quality as well as the relative amount or size of the two magnetic phase.