Thesis presented Decembre 04, 2008

Abstract:
This work deals with the implementation and development of Lorentz Microscopy (LTEM) for perpendicular magnetic anisotropy thin foils (FePd) and magnetic flux closure nanostructures (self-assembled Fe and Co dots). An exhaustive overview of magnetic imaging in a Transmission Electron Microscope (TEM) among its different modes is given with a comparison to other magnetic imaging techniques. A method for implementation of LTEM in a conventionnal TEM is also described as all the modes of magnetic imaging in a TEM are compared one to another by mean of simulated images. LTEM enables a locale (nanometer scale) and quantitative observation of magnetic induction in and out of the samples. At the same times it is possible to perform in situ experiment as applying magnetic field to observe micromagnetic configuration evolution. FePd alloys are thus fully characterized with respect to different geometry of the samples with use of Differential Phase Contrast, Transport of Intensity Equation solving and Electron Holography. In situ studies give quantitative information on the films behaviour under applied field by means of Vertical Bloch Lines motion. Study of Fe and Co nanostructures show how it is possible to control different magnetic degrees of freedom in such magnetic flux-closure configurations. A major point is the control of transition between different micromagnetic objects (vortices, symetric and asymetric domain walls) performed with the use of an external magnetic field.

Keywords:
Lorentz Microscopy, Electron Holography, Magnetic Imaging, Perpendicular Anisotropy, Micromagnetism, Bloch Lines, Magnetic degrees of freedom, Flux-closing nanostructures

On-line thesis.