Nanostructured systems composed of two or more technologically important materials are useful for device applications and intriguing for the new fundamental physics they may display. Magnetism at the nanoscale is dominated by size and surface effects which combined with other media lead to new spin dynamics and interfacial coupling phenomena. These new properties may prove to be useful for optimizing sensors and devices, increasing storage density for magnetic media, as well as for biomedical applications such as drug delivery, MRI contrast enhancement, and hyperthermia treatment for cancer. In this project we have examined the surface and interface magnetism of composite nanoparticles and multilayer thin films by using conventional DC magnetization and AC susceptibility as well as transverse susceptibility, a method for directly probing the magnetic anisotropy of materials. Au and Fe3O4 synthesized together into three different nanoparticle configurations and ranging in size for 60 nm down to 9nm are used to study how the size, shape, and interfaces affect the most fundamental properties of magnetism in the Au-Fe3O4 system. The findings have revealed ways in which the magnetic properties can be enhanced by tuning these parameters. We have shown that by changing the configurations of the Au and Fe3O4 particles, exotic behavior can be observed such as a large increase in anisotropy field (H[subscript]K ranging from 435 Oe to 1650 Oe) and the presence of exchange bias. Multilayer thin films have been studied as well which combine the important classes of ferromagnetic and ferroelectric materials. In one case, barium hexaferrite/barium strontium titanate thin films, the anisotropic behavior of the ferromagnet is shown to change due to the introduction of the secondary material. In the other example, CrO2/Cr2O3 bilayers, exchange coupling is observed as Cr2O3 is an antiferromagnet as well as a ferroelectric. This coupling is manifest as a uniaxial anisotropy rather than the unidirectional anisotropy associated with exchange biased bilayers. Not only will such multifunctional structures will be useful for technological applications, but the materials properties and configurations can be chosen and tuned to further enhance the desired functional properties.

Ce travail de thèse porte sur le contrôle des propriétés de trois systèmes magnéto-plasmoniques grâce à différents types de nanostructuration. Ces structures sont basées respectivement sur la Propagation de Plasmons de Surface (SPP), les Plasmons de Surface Localisés (LSP) et la spectroscopie d’interférences en réflexion (RIfS). La manipulation des propriétés magnéto-optiques (MO) pour une utilisation dans les biocapteurs est discutée. Le premier système est une structure SPP en couche mince de couches de métaux nobles et d’un matériau magnétique de type multicouche présentant une anisotropie uni-axiale contrôlée. L’anisotropie de la couche magnétique se reflète sur les propriétés plasmoniques. Une amélioration de l’activité magnéto-optique peut être mise à profit pour améliorer la sensibilité de capteurs basés sur cette structure. Le second dispositif est une structure LSP avec nanoparticules d’or et d’une couche magnétique continue. Il est démontré qu’une couche diélectrique entre la couche magnétique et les nanoparticules d’or est indispensable pour préserver la résonance plasmonique. L’épaisseur de la couche magnétique a un effet sur cette dernière qui peut en principe être mise à profit pour influer sur l’activité magnéto-optique. La troisième approche est une structure RIfS composée d’un système multicouche magnéto-plasmonique Ag/ITO/CoFeB/ITO/Ag déposé sur un substrat nanoporeux d’oxyde d’aluminium anodique (AAO). Le signal RIfS dépend de la taille et de la longueur des nanopores. Le diamètre des nanopores affecte également la réponse magnéto-optique en réflexion en générant une inversion du signe des cycles d’aimantation mesurés par effet Kerr. / This PhD dissertation deals with the tuning of the magneto-optical (MO) response of three different magnetoplasmonic systems by using different nanostructuration schemes. They are structures based on SPPs, LSPs and RIfS, respectively. The manipulation of MO activity to be used in biosensors and to improve the sensitivity is also discussed. The first system is thin-film SPP structure consisting of magnetic and plasmonic layers, where the magnetic part is nanostructured multilayers with controlled uni-axial anisotropy. The uni-axial anisotropic properties of the multilayered magnetic materials were clearly reflected on the plasmonic properties of the system. An enhancement in the MO activity can be used to improve the sensitivity of the sensors based on this structure. The second system is a LSP-based magnetoplasmonic structure consisting of Au nanoparticle arrays and continuous magnetic layers. It is demonstrated that a dielectric layer in between Au nanoparticles and ferromagnetic layers is indispensable in order to preserve the plasmonic resonance. The thickness of magnetic layers has an effect on the plasmonic property, which can be further used to tune the MO activity. The third system is a hybrid RIfS structure with a magnetoplasmonic multilayer Ag/ITO/CoFeB/ITO/Ag deposited on a nanoporous AAO substrate. The RIfS signal depends on both the size and the length of the nanopores. The diameter of the nanopores also affects the MO response by generating a reversal in the sign of the Kerr loops. This can be viewed as the tuning factor of MO activity of the structure.