Electron Microscopy Investigation of Magnetization Process in Thin Foils and Nanostructures
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1026-C22-04
Electron Microscopy Investigation of Magnetization Process in Thin Foils and Nanostructures Aurelien Masseboeuf1, Fabien Cheynis2, Jean-Christophe Toussaint2, Olivier Fruchart2, Christophe Gatel1,3, Alain Marty1, and Pascale Bayle-Guillemaud1 1 INAC/SP2M, CEA Grenoble, 17 rue des martyrs, Grenoble Cedex 9, 38054, France 2 Institut Neel/MNM, CNRS, Building D, BP166, F-38042 Grenoble Cedex 9, Grenoble, France 3 CEMES-UPR 8011, CNRS, BP 94347 - 29, rue Jeanne Marvig, Toulouse Cedex, 31055, France ABSTRACT This paper presents an investigation of magnetization configuration evolution during insitu magnetic processes, in materials exhibiting planar and perpendicular magnetic anisotropy. Transmission electron microscopy (TEM) has been used to perform magnetic imaging. Fresnel contrast in Lorentz Transmission Electron Microscopy (LTEM), phase retrieval methods such as Transport of Intensity Equation (TIE) solving and electron holography have all been implemented. These techniques are sensitive to magnetic induction perpendicular to the electron beam, allowing the mapping of magnetic induction distribution with a spatial resolution better than 10nm and can be extended to allow dynamical studies during in-situ observation. Thin foils of FePd alloys with a strong perpendicular magnetic anisotropy (PMA) and self-assembled Fe dots have been examined. Both are studied during magnetization processes, exhibiting the capacities of in-situ magnetic imaging in a TEM. INTRODUCTION Magnetic imaging in the TEM [1] has been improved during the last decade with the development of new induction mapping techniques such as Transport of Intensity Equation (TIE) solving [2] from Fresnel images. Also, improvements in electron holography [3] have allowed the technique to become a common way to observe magnetic induction distributions at a very fine scale. Nevertheless, to achieve quantitative phase reconstruction, this technique requires specialist equipment, such as a biprism and a field emission gun (FEG) source to be used in conjunction with special sample preparation geometries (known thickness and a hole for reference beam). Other mapping techniques obtained from Lorentz TEM (LTEM) by TIE solving or Differential Phase Contrast [4], can use conventional samples for the analysis but have to overcome several artifacts to become truly quantitative. For all these techniques, the interest is to be able to perform in-situ magnetization processes using the objective lens to apply an axial field. In this paper, we describe in-situ magnetization studies of two kinds of material with different sample geometries. The first section deals with the investigation by electron holography and LTEM of a continuous magnetic layer observed in plan view and cross-sectional orientation. This thin foil is a bi-layer of bi-metallic FePd alloys : a chemically-disordered soft underlayer with vanishing anisotropy and a chemically-ordered L10 FePd exhibiting a strong perpendicular magnetic anisotropy (PMA) grown on top. This system is potentially a good cand
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