Electron magnetic circular dichroism (EMCD) (also known as electron energy-loss magnetic chiral dichroism) is the

EELS Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 19 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...

equivalent of XMCD. The effect was first proposed in 2003 and experimentally confirmed in 2006 by the group of Prof.

Peter Schattschneider Peter Schattschneider (born 1950 in Vienna) is an Austrian physicist and science-fiction writer, a retired professor at the Institute of Solid State Physics and a staff member of the USTEM special unit of the Vienna University of Technology. His ...

at the

Vienna University of Technology TU Wien (TUW; german: Technische Universität Wien; still known in English as the Vienna University of Technology from 1975–2014) is one of the major universities in Vienna, Austria. The university finds high international and domestic recogn ...

. Similarly to XMCD, EMCD is a difference

spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...

of two

spectra taken in a magnetic field with opposite helicities. Under appropriate scattering conditions virtual photons with specific circular polarizations can be absorbed, giving rise to spectral differences. The largest difference is expected between the case where one virtual photon with left

circular polarization In electrodynamics, circular polarization of an electromagnetic wave is a polarization state in which, at each point, the electromagnetic field of the wave has a constant magnitude and is rotating at a constant rate in a plane perpendicular to t ...

and one with right circular polarization are absorbed. By closely analyzing the difference in the EMCD spectrum, information can be obtained on the magnetic properties of the atom, such as its

spin Spin or spinning most often refers to: * Spinning (textiles), the creation of yarn or thread by twisting fibers together, traditionally by hand spinning * Spin, the rotation of an object around a central axis * Spin (propaganda), an intentionally b ...

and orbital

magnetic moment In electromagnetism, the magnetic moment is the magnetic strength and orientation of a magnet or other object that produces a magnetic field. Examples of objects that have magnetic moments include loops of electric current (such as electromagnets ...

. In the case of

transition metal In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that can ...

s such as

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...

cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, pr ...

, and

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to ...

, the absorption spectra for EMCD are usually measured at the L-edge. This corresponds to the excitation of a 2p electron to a 3d state by the absorption of a virtual photon providing the ionisation energy. The absorption is visible as a spectral feature in the electron energy loss spectrum (EELS). Because the 3d electron states are the origin of the magnetic properties of the elements, the spectra contain information on the magnetic properties. Moreover, since the energy of each transition depends on the

atomic number The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...

, the information obtained is element specific, that is, it is possible to distinguish the magnetic properties of a given element by examining the EMCD spectrum at its characteristic energy (708 eV for iron). Since in both EMCD and XMCD the same electronic transitions are probed, the information obtained is the same. However EMCD has a higher spatial resolution and depth sensitivity than its X-ray counterpart. Moreover, EMCD can be measured on any

TEM Tem or TEM may refer to: Acronyms * Threat and error management, an aviation safety management model. * Telecom Expense Management * Telecom Equipment Manufacturer * TEM (currency), local to Volos, Greece * TEM (nuclear propulsion), a Russian ...

equipped with an EELS detector, whereas XMCD is normally measured only on dedicated synchrotron

beamline In accelerator physics, a beamline refers to the trajectory of the beam of particles, including the overall construction of the path segment (guide tubes, diagnostic devices) along a specific path of an accelerator facility. This part is either ...

s. A disadvantage of EMCD in its original incarnation is its requirement of crystalline materials with a thickness and orientation that just precisely gives the correct 90 degree phase shift needed for EMCD. However, a new method has recently demonstrated that electron vortex beams can also be used to measure EMCD without the geometrical constraints of the original procedure.

References

Spectroscopy {{spectroscopy-stub

See also

References