Magnetic couplings and superparamagnetic properties of spinel ferrite nanoparticles

The relationship between macroscopic magnetic properties and magnetic couplings is investigated using various spinel ferrite nanoparticles. The synthesis of CoCrxFe2-xO4 nanoparticles with variable size and composition is described and the magnetic characterization performed as a function of size and composition. The effects of surface ligand modification upon the magnetic properties of MnFe2O4, CoFe2O4 and Fe3O4 nanoparticles are reported. These studies are the first experiments that systematically vary the surface chemistry in order to deduce a correlation between surface ligands and magnetic properties. The influence of interparticle interactions upon magnetic properties is investigated for CoFe2O4 and MnFe2O4 nanoparticles diluted in eicosane. Interparticle interaction effects are further studied using MnFe2O4/polystyrene core/shell nanoparticles. The synthesis and magnetic characterization of MnFe 2O4/polystyrene core/shell nanoparticles as well as silica coated CoFe2O4 and MnFe2O4 nanoparticles are also addressed. The results of this thesis contribute to the knowledge of nanomagnetism in spinel ferrites by systematically investigating the effects of magnetocrystalline anisotropy, exchange coupling interactions, surface chemistry and anisotropy, and interparticle interactions upon the magnetic properties of spinel ferrite nanoparticles.