Peter Schattschneider & Thomas Schachinger: Vortices and Energy loss magnetic chiral dichroism (EMCD)

Peter Schattschneider and Thomas Schachinger

Institute of Solid State Physics and USTEM, Technische Universität Wien, Austria

Vortices and Energy loss magnetic chiral dichroism (EMCD)

Electron vortices were discovered in 2010 by two independent research groups. They are a solution to the Schrödinger Equation in free space, resembling a spiralling phase surface. They show peculiar properties such as a phase singularity in the center, topological charge, a ring current freely propagating in space, and an inherent quantized angular momentum.

Energy loss magnetic chiral dichroism (EMCD) is an electron-based approach to study element specific magnetic moments with highest spatial resolution. EMCD features an asymmetry in the transition probability to states with positive or negative magnetic quantum numbers (chiral transitions), observed in electron energy loss spectrometry (EELS). The technique is similar to its well established relative on the synchrotron – XMCD – where the asymmetry appears in the fine structure of X-ray ionisation edges of magnetic materials. In combination with the atomic resolution of modern TEMs this opens the road to mapping spins of individual atomic columns.

One of the intriguing consequences of EMCD is that the outgoing probe electrons have topological charge. Such electrons carry quantized orbital angular momentum, similar to vortex electrons. Vice versa, vortex electrons are a promising probe for spin mapping with atomic resolution.

References:
1. P. Schattschneider, St. Rubino, C. Hébert, J. Rusz, J. Kunes, P. Novák, E. Carlino, M. Fabrizioli, G. Panaccione, G. Rossi: Detection of magnetic circular dichroism using a transmission electron microscope; Nature 441, (2006), 486-488.

2. J. Verbeeck, H. Tian, P. Schattschneider: Production and application of electron vortex beams; Nature 467, (2010), 301-304.

Acknowledgement: funding from the Austrian Science Fund, project no. I543-N20.