The growing interest in the miniaturization of magnetic storage media and the quest for novel spintronics applications rely on the element-specific detection of spin and orbital magnetic moments in a solid. The most sophisticated technique to reach this aim has been X-ray magnetic circular dichroism (XMCD), largely used in synchrotron beam lines. The spatial resolution limit of this technique is of the order of 20–50 nm. This presents a sensible limit for the study of nanostructured devices.
This book describes energy loss magnetic chiral dichroism (EMCD), a phenomenon in energy loss spectroscopy discovered in 2006. EMCD is the equivalent of XMCD but is based on fast probe electrons in the electron microscope. A spatial resolution of 2 nm has been demonstrated, and the lattice-resolved mapping of atomic spins appears feasible. EMCD is, thus, a promising technique for magnetic studies on the nanometer and sub-nanometer scale, providing the technical and logistic advantages of electron microscopy, such as in situ chemical and structural information, easy access, and low cost.
The first part of the book sets the stage by regarding EMCD in the broader context of anisotropy in electron energy loss spectroscopy (EELS), by introducing the XMCD technique and by a description of the physics of broken rotational symmetry in EELS. The role of the crystal as an electron interferometer for the setup of chiral electronic transitions is also discussed. In addition to the appearance of retardation effects in EELS, theoretical approaches to X-ray absorption spectroscopy are covered. In the theory section, various methods of the calculation of XMCD and EMCD spectra from first principles are covered, namely the multiplet, density functional (reciprocal space), and multiple scattering (cluster) methods.
The experimental part covers a number of EMCD techniques with their particularities, as well as data treatment that is nontrivial in view of low-scattering cross sections. Sum rules for spin and orbital moments, already touched in several chapters, are treated in a separate contribution. The last part of the book focuses on innovative methods in both XMCD and EMCD. X-ray holography will benefit from the high-brightness X-ray sources now under construction. Scanning EMCD promises spin mapping on the atomic level with the generation of electron microscopes now under development.
The color version of the figures in the book can be accessed here.
1. Basic Concepts
• Momentum Resolved ELNES (C. Hébert , J.-C. LeBossé)
• Relativistic Effects and the Magic Angle (J.-C. LeBossé, C. Hébert)
• An Introduction to XMCD (G.Schütz)
• Chirality in EELS and the Role of the Angular Momentum (P. Schattschneider)
2. Calculation Methods
• Multiplet Methods (L. Calmels, J. Rusz)
• DFT Methods (C. Ambrosch, L. Pardini, F. Manghi)
• Multiple-Scattering Theory of Circular Dichroism (J. Rehr , H. Wende)
3. Experimental Chiral/Circular Dichroism
• EMCD Techniques and Geometries (S. Rubino et al.)
• Data Treatment, Artefacts, Noise (K. Leifer, C. Gatel, B. Warot-Fonrose et al.)
• The Role of the Crystal (J. Verbeeck, J. Rusz, S. Rubino)
• Sum Rules in EMCD and XMCD (J. Rusz, J. Rehr, L. Calmels)
4. Related Techniques and Perspectives
• Magnetic Dichroism in X-Ray Holography (S. Eisebitt)
• Prospects for Spin Mapping with Atomic Resolution (M. Stöger-Pollach , J. Verbeeck, P. Schattschneider)
Peter Schattchneider has made many fundamental contributions to the theory of electron-beam imaging and spectroscopic techniques. In this book he reviews the promising new method of dichroism induced, not by light, but by the electron beam of a modern transmission electron microscope, and detected using the energy-loss spectrum. The result is a spin-sensitive imaging method with far higher spatial resolution than similar synchrotron-based methods.
~Prof. John Spence, Arizona State University, USA
This state-of-the-art textbook describes how magnetic properties of solids can be investigated by using x-ray absorption and electron energy-loss spectroscopy. The main emphasis is on the underlying theory but experimental techniques, data analysis and recent results are also well covered. Chiral effects in anisotropic materials, multiplet and density-functional theory, magic-angle and relativistic effects, x-ray holography and the possibility of atomic-scale spin mapping are all described in detail by experts in these various fields.
~Prof. Ray Egerton, University of Alberta, Canada
This nice book provides a very useful approach of a recently developed technique, electron energy loss magnetic chiral dichroism (EMCD), available in transmission electron microscopy to detect if your sample presents anisotropic or magnetic effects (linear dichroism and chirality). The comparison with a previous X-Ray technique known as XMCD (X-ray magnetic circular dichroism), and this EMCD is clearly and usefully exposed. Advantages and disadvantages of both methods are discussed, spatial resolution also. With EMCD, atomic resolution can be hoped with new aberration corrected microscopes. Experimental situations in both cases are very understandably described and also the theory (necessity of the density matrix formulation, mixed dynamical form factor-MDFF) which is taken from the beginning. The figures are also very explicative. A very interesting book for students and searchers.
~Prof. Bernard Jouffrey, École Centrale Paris, France
This book covers the exciting new area of characterization of materials on the nanoscale by studying the chirality of electrons in transmission electron microscopy (TEM). Schattschneider, his team in Vienna and his colleagues all around the world, edited an extremely well written book which will have its impact for the important area of advanced characterisation techniques of materials with high spatial resolution- nearly on the atomic scale. The different techniques can be used by experienced microscopists who are able to understand the physics of the different inelastic scattering processes occurring in a specimen in TEM.
~Prof. Manfred Rühle, MPI for Intelligent Systems, Germany