EMCD with an electron vortex filter: Limitations and possibilities

Abstract

We discuss the feasibility of detecting spin polarized electronic transitions with a vortex filter. This approach does not rely on the principal condition of the standard energy loss magnetic chiral dichroism (EMCD) technique, the precise alignment of the crystal, and thus paves the way for the application of EMCD to new classes of materials and problems. The dichroic signal strength in the L 2,3 -edge of ferromagnetic cobalt is estimated on theoretical grounds. It is shown that magnetic dichroism can, in principle, be detected. However, as an experimental test shows, count rates are currently too low under standard conditions.

Electron vortices: Beams with orbital angular momentum

“…On the other hand, since the transmitted intensities in these cases are expected to be small, the experimental conditions must be optimised so that long collection times may be utilised. Experimental feasibility study is encouraging (Schachinger et al, 2017), especially for amorphous magnetic materials.…”

Ultrafast electron microscopy for probing magnetic dynamics

“…74 EMCD offers atomic-resolution magnetic contrast, [75][76][77] but the high dose necessary for a good signal-to-noise ratio may restrict the usability of this technique for short electron pulses. Magnetic dichroism with electron orbital angular momentum post-selection [78][79][80][81][82] relies on similar mechanisms but has the potential for an adequate signal-to-noise ratio even with femtosecond pulses and kHz repetition rates. Spin-polarized transmission electron microscopy 83,84 may prove capable of both inelastic and elastic magnetic imaging.…”

Elastic propagation of fast electron vortices through amorphous materials

“…The fact that these EVBs carry OAM has led to the proposition and demonstration of many applications ranging from the measurement of magnetic properties with atomic resolution (Verbeeck et al, 2010;Rusz et al, 2014;Idrobo et al, 2016;Schachinger et al, 2017), the study of the dynamics of Landau states (Schattschneider, Schchinger et al, 2014;Schachinger et al, 2015), sample chirality (Juchtmans et al, 2015) and symmetry properties of plasmon resonances (Guzzinati et al, 2017), to the manipulation of nanoparticles . Despite the huge potential of EVBs and the fact that their creation and propagation through vacuum are well understood (Schattschneider & Verbeeck, 2011;Schattschneider et al, 2012;Schachinger et al, 2015), knowledge of their propagation through matter is still somewhat lacking.…”

“…for nanoparticles. Thirdly, EVBs would allow techniques such as energy-loss magnetic chiral dichroism (EMCD) for measuring magnetic properties down to the nanoscale in crystalline samples to be applied also to amorphous materials (Schachinger et al, 2017). However, it is usually assumed that an as-produced, ideal vortex beam stays that way and propagates practically unperturbed through the sample.…”