Etude des interactions dipolaires magnetiques dans les reseaux de nanofils ferromagnetiques

Arrays of ferromagnetic nanowires are studied by ferromagnetic resonance (FMR) and by vibrating sample magnetometry (VSM) caracterisation techniques in order to understand the magnetic behaviour of the nanowire network and to determine quantitatively the effect of the dipolar interactions on the magnetic response of the network.; Ni and Co95Fe4B1 alloy nanowires embedded in nanoporous dielectric templates were obtained. Co95Fe4 B1 is a soft and high saturation magnetization alloy specially optimized for high frequency applications. Diblock copolymer membranes and commercial Whatman alumina membranes served as templates for the growth of the nanowires by pulsed current electrodeposition. Since the results for the nanowires embedded in the polymer template are not fully understood, particular attention is devoted to the results obtained from the nanowires grown in alumina templates.; Alternating layers of magnetic and non magnetic metals; called multilayers, were also grown in alumina templates by pulsed voltage electrodeposition. Ni/Cu and CoFeB/Cu multilayered nanowires were grown and were compared to Ni and CoFeB nanowires. The multilayered nanowires were obtained in order to observe the effect of the intra-wire field on the effective field and to exploit the tunability of the magnetic response of the array via the thicknesses of the layers.; The dipolar interaction fields were modeled using an effective demagnetizing field approach. A model was developed in order to take into account the geometry of the membrane (interpore distance and pore diameter) and the structure of the wires (layer thicknesses). The demagnetizing fields, the inter-wire dipolar fields and the intra-wire dipolar fields between magnetic layers of the multilayers were taken into account. Magnetocristalline anisotropy, magnetoelastic anisotropy and exchange interaction between magnetic layers of the multilayer nanowire were neglected in this work.; Ferromagnetic resonance (FMR) and vibrating sample magnetometry (VSM) measurements were performed on the samples in order to extract the effective field acting on the nanowires. The effective field obtained by FMR and VSM were compared, and both were compared with the model. Good agreement was found between the results obtained by FMR, VSM and the model for the monolayer nanowires. The discripancy between FMR and VSM results was highest for very short multilayer nanowires and for multilayers with very thin metallic layers. However, the model does qualitatively predict the effective field behavior of the multilayer nanowires as a function of the magnetic to non magnetic thickness ratio.; In the case of the multilayers, an easy axis along the wires or an easy plane perpendicular to the wires is found, depending upon the magnetic to non-magnetic thickness ratio. This opens new possibilities for the engineering of tunable effective materials for microwave applications.