This thesis focuses on magnetic features in single and hybrid nanostructures. Magnetic material based on a spinel iron oxide structure (MeFe2O4; Me: Fe2+; Co2+,) and coated by a mesoporous structure as well as by peculiar molecules (e.g. DNA) and by several types of polymers, have been investigated. The objective of the study is the design of single/hybrid nanoarchitectures with the aim of controlling the magnetic properties as well as their magnetic structure, which may serve as a basis for delivering and harvesting molecules in nanotechnological applications. The magnetic properties of nanoparticles are particularly sensitive to the particle size, being determined by finite size effects on the core properties, related to the reduced number of spins cooperatively linked within the particle, and by surface effects, becoming more important as the particle size decreases physical properties differ greatly from their parent massive materials. Accordingly, the first part of the thesis is dedicated to the study of the different fundamental concepts of magnetism at the nanoscale. We present morpho-structural and magnetic investigation of Fe3O4 and CoFe2O4 nanoparticles. In case of Fe3O4 synthetized with co-precipitation method we have investigated: (i) the temperature effect, (ii) the reaction atmosphere effect and (iii) Cobalt doping effect in tuning specially the magnetic properties. The results reveal a significant change in the magnetic properties (i.e., saturation magnetization and coercive field) due to the Co-doping effect. While in the other cases magnetic properties were independent on the change in the experimental parameters within the experimental error. The effect of surface modification for Fe3O4 nanoparticles with mesoporous silica, DNA molecules and polyacrylic acid, gallic acid, oleic acid and polyethylene glycol was deeply investigated specially from magnetic point of view. The analysis of different cases shows the important role of the functionalization in tuning the properties of the magnetic core. We found that the surface coating has a large influence on changing the saturation magnetization, easy axis orientation in case of oleic acid and mesoporous silica respectively, as compared to the other cases where a change in the interparticle distance by 5% was the main observed change.vi In case of CoFe2O4 prepared with polyol method and coated with mesoporous silica structure also a small but evident decrease in the interparticle interactions is observed. on the other hand, we also introduce a hybrid nanoarchitecture combining crystalline cobalt ferrite and the amorphous parent material, that behaves as an artificial single-phase material with enhanced magnetic anisotropy, well above the values achievable by the individual components. Apart from the experimental investigation micromagnetic modeling is presented as a tool to interpret the magnetic state of the nanocomposite. We compare the simulated result with the experimental one proving the observed large magnetic anisotropy and elucidating the active role of each phase. Finally, we have introduced a theoretical investigation of permanent magnets with cubic geometry disposed in different configurations. Furthermore, experiments have been carried out using a home-made circuit, along with the development of a simple method for data treatment that enable to understand the behavior of the nanoparticles in an applied magnetic field.

Design magnetic hybrid nanomaterials for molecules harvesting/ delivery

SLIMANI, SAWSSEN
2022

Abstract

This thesis focuses on magnetic features in single and hybrid nanostructures. Magnetic material based on a spinel iron oxide structure (MeFe2O4; Me: Fe2+; Co2+,) and coated by a mesoporous structure as well as by peculiar molecules (e.g. DNA) and by several types of polymers, have been investigated. The objective of the study is the design of single/hybrid nanoarchitectures with the aim of controlling the magnetic properties as well as their magnetic structure, which may serve as a basis for delivering and harvesting molecules in nanotechnological applications. The magnetic properties of nanoparticles are particularly sensitive to the particle size, being determined by finite size effects on the core properties, related to the reduced number of spins cooperatively linked within the particle, and by surface effects, becoming more important as the particle size decreases physical properties differ greatly from their parent massive materials. Accordingly, the first part of the thesis is dedicated to the study of the different fundamental concepts of magnetism at the nanoscale. We present morpho-structural and magnetic investigation of Fe3O4 and CoFe2O4 nanoparticles. In case of Fe3O4 synthetized with co-precipitation method we have investigated: (i) the temperature effect, (ii) the reaction atmosphere effect and (iii) Cobalt doping effect in tuning specially the magnetic properties. The results reveal a significant change in the magnetic properties (i.e., saturation magnetization and coercive field) due to the Co-doping effect. While in the other cases magnetic properties were independent on the change in the experimental parameters within the experimental error. The effect of surface modification for Fe3O4 nanoparticles with mesoporous silica, DNA molecules and polyacrylic acid, gallic acid, oleic acid and polyethylene glycol was deeply investigated specially from magnetic point of view. The analysis of different cases shows the important role of the functionalization in tuning the properties of the magnetic core. We found that the surface coating has a large influence on changing the saturation magnetization, easy axis orientation in case of oleic acid and mesoporous silica respectively, as compared to the other cases where a change in the interparticle distance by 5% was the main observed change.vi In case of CoFe2O4 prepared with polyol method and coated with mesoporous silica structure also a small but evident decrease in the interparticle interactions is observed. on the other hand, we also introduce a hybrid nanoarchitecture combining crystalline cobalt ferrite and the amorphous parent material, that behaves as an artificial single-phase material with enhanced magnetic anisotropy, well above the values achievable by the individual components. Apart from the experimental investigation micromagnetic modeling is presented as a tool to interpret the magnetic state of the nanocomposite. We compare the simulated result with the experimental one proving the observed large magnetic anisotropy and elucidating the active role of each phase. Finally, we have introduced a theoretical investigation of permanent magnets with cubic geometry disposed in different configurations. Furthermore, experiments have been carried out using a home-made circuit, along with the development of a simple method for data treatment that enable to understand the behavior of the nanoparticles in an applied magnetic field.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11567/1089350
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