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ELABORATION, ETUDE DES PROPRIETES STRUCTURALES ET MAGNETIQUES DE COUCHES ET RESEAUX DE PLOTS SUBMICRONIQUES A BASE DE COBALT

Abstract : In the first part of this doctoral work, we have studied the correlation between the magnetic domain structure and the macroscopic magnetic properties of epitaxial cobalt thin films with thicknesses varying from 10 to 500 nm. The growth was optimised to get the cobalt film in the hexagonal (0001) cristalline phase. In this cristallographic structure, the magnetocristalline anisotropy is very strong and along the c-axis. This strong perpendicular anisotropy forces the cobalt to split in domains in which the magnetization turns from fully in plane to fully out of plane as the film thickness is increased from 10 to 50 nm. For thicknesses above 50 nm, the domain structure depending on the magnetic history may consists of bubbles, stripes or labyrinthine. The domain topology is independent on the film thickness while the periodicity of the domains varies from 100 to 400 nm and is proportional to the squareroot of the film thickness. We have shown that these well characterized films appear to be model systems for the study of magnetoresistance through magnetic wall as well as observation of domain wall resonance at high frequency. In the second part of this work, the structural and magnetic properties of square dot arrays with dot lateral dimension of 0.5 µm and lattice periodicity of 1 µm have been studied. The arrays 5 by 5 mm² were patterned from the epitaxial cobalt films using X-ray lithography. We have shown that the magnetization reorients from in-plane to perpendicular as a function of dot height. Interestingly, the magnetic domains are shown to be geometrically constrained by the side of the dots. For thick dots, the lateral extension of domains is comparable to the size of the dots leading to the constrain of the perpendicular component of magnetization. For the 25 nm thick dots, the geometrical constrain of the parallel component of magnetization leads to the stabilization of a vortex domain structure with circular rings. Starting from this structure, the magnetization curve displays one pronounced jump of magnetization which implies that the reversal of the magnetization occurs through the collapse of the vortex domain structure. Moreover, magnetic phase transition occurs when the temperature is lowered. The magnetization in each domain switches as a function of temperature from mainly in-plane into a fully perpendicular domain structure.
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Submitted on : Thursday, April 24, 2003 - 9:27:39 AM
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Michel Hehn. ELABORATION, ETUDE DES PROPRIETES STRUCTURALES ET MAGNETIQUES DE COUCHES ET RESEAUX DE PLOTS SUBMICRONIQUES A BASE DE COBALT. Matière Condensée [cond-mat]. Université Louis Pasteur - Strasbourg I, 1997. Français. ⟨tel-00002760⟩

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