EMCD: Magnetic Chiral Dichroism in the Electron Microscope
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1026-C13-05
EMCD: Magnetic Chiral Dichroism in the Electron Microscope Stefano Rubino1, Peter Schattschneider1,2, Michael Stöger-Pollach2, Cécile Hébert3, Ján Rusz4,5, Lionel Calmels6, Benedicte Warot-Fonrose6, Florent Houdellier6, Virginie Serin6, and Pavel Novàk5 1 Institute for Solid State Physics, Vienna University of Technology, Wiedner Hauptstrasse 810/138, Vienna, A-1040, Austria 2 Service centre for TEM, Vienna University of Technology, Wiedner Hauptstrasse 8-10/138, Vienna, A-1040, Austria 3 SB-CIME station 12, EPFL, Lausanne, Switzerland 4 Department of Physics, Uppsala University, Box 530, Uppsala, S-751 21, Sweden 5 Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, Prague, CZ18221, Czech Republic 6 Nanomaterieaux group, CEMES-CNRS, Toulouse, France ABSTRACT A new technique called Energy-loss Magnetic Chiral Dichroism (EMCD) has recently been developed [1] to measure Magnetic Circular Dichroism (MCD) in the Transmission Electron Microscope (TEM) with a spatial resolution of 10 nm. This novel technique is the TEM counterpart of X-ray Magnetic Circular Dichroism (XMCD), which is widely used for the characterization of magnetic materials with synchrotron radiation. In this paper we describe several experimental methods which can be used to measure the EMCD signal [1-5] and give a review of the recent improvements of this new investigation tool. The dependence of the EMCD on several experimental conditions (such as thickness, relative orientation of beam and sample, collection and convergence angle) is investigated in the transition metals Iron, Cobalt and Nickel. Different scattering geometries are illustrated; their advantages and disadvantages are detailed, together with current limitations. The next realistic perspectives of this technique will consist in measuring atomic specific magnetic moments, using suitable spin and orbital sum rules [4,6], with a resolution down to 2-3 nm.
INTRODUCTION The TEM is a powerful investigation instrument for material science with a scope comprising tomographic reconstruction of cells, materials characterization, crystal structure and defects, microelectronic devices and spintronics, to name a few. It is one of the most successful applications derived from de Broglie hypothesis on the wave-particle duality of matter i.e. that all particles also have a wave nature. Electrons, with a wavelength much shorter than visible light, have allowed the study of the properties of matter at the nanometer and sub-nanometer scale; it should be mentioned that the synchrotron based X-ray microscopy has also seen a tremendous improvement in spatial resolution, recently reaching the 25 nm limit [7]. In the last decades the TEM capabilities have been augmented by the introduction of Electron Energy Loss Spectrometry (EELS): by measuring the energy lost by the electron beam while passing through a sample it is possible to obtain additional information as atoms are
ionized or plasmons, inter- and intraband transitions are excited (microanalysis). Moreover the
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