Linear and Chiral Dichroism in the Electron Microscope

Linear and Chiral Dichroism in the Electron Microscope

by Peter Schattschneider

278 pages, 153.00 x 229.00 mm, 126 B/W

  • Hardcover
  • ISBN: 9789814267489
  • Published: March 2012

  • eBook - PDF
  • ISBN: 9789814303170
  • Published: February 2012

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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.