| 1. |
|
|
| 2. |
|
|
| 3. |
- Pohl, Darius, et al.
(author)
-
Atom size electron vortex beams with selectable orbital angular momentum
- 2017
-
In: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 7
-
Journal article (peer-reviewed)abstract
- The decreasing size of modern functional magnetic materials and devices cause a steadily increasing demand for high resolution quantitative magnetic characterization. Transmission electron microscopy (TEM) based measurements of the electron energy-loss magnetic chiral dichroism (EMCD) may serve as the needed experimental tool. To this end, we present a reliable and robust electron-optical setup that generates and controls user-selectable single state electron vortex beams with defined orbital angular momenta. Our set-up is based on a standard high-resolution scanning TEM with probe aberration corrector, to which we added a vortex generating fork aperture and a miniaturized aperture for vortex selection. We demonstrate that atom size probes can be formed from these electron vortices and that they can be used for atomic resolution structural and spectroscopic imaging - both of which are prerequisites for future atomic EMCD investigations.
|
|
| 4. |
- Pohl, Darius, et al.
(author)
-
Electron vortex beams prepared by a spiral aperture with the goal to measure EMCD on ferromagnetic films via STEM
- 2015
-
In: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 150, s. 16-22
-
Journal article (peer-reviewed)abstract
- X-ray magnetic circular dichroism is a well established method to study element specific magnetic properties of a material, while electron magnetic circular dichroism (EMCD), which is the electron wave analogue to XMCD, is scarcely used today. Recently discovered electron vortex beams, that carry a discrete orbital angular momentum (OAM) L, are also predicted to reveal dichroic signals. Since electron beams can be easily focused down to sub-nanometer diameters, this novel technique promises the possibility to quantitatively determine local magnetic properties with unrivalled lateral resolution. As the spiralling wave front of the electron vortex beam has an azimutally growing phase shift of up to 2 pi and a phase singularity in its axial center, specially designed apertures are needed to generate such non-planar electron waves. We report on the preparation and successful implementation of spiral apertures into the condenser lens system of an aberration-corrected FEL Titan(3) 80-300 transmission electron microscope (TEM). This setup allows to perform scanning TEM (STEM) with vortex beams carrying user-selected OAM. First experiments on the interaction of the vortex beam with a poly-crystalline sample are presented. Within the achieved signal to noise ratio no EMCD signal has been detected. This finding is supported by simulations of inelastic scattering of a beam generated by spiral aperture.
|
|
| 5. |
- Schneider, Sebastian, et al.
(author)
-
Magnetic properties of single nanomagnets : Electron energy-loss magnetic chiral dichroism on FePt nanoparticles
- 2016
-
In: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 171, s. 186-194
-
Journal article (peer-reviewed)abstract
- Electron energy-loss magnetic chiral dichroism (EMCD) allows for the quantification of magnetic properties of materials at the nanometer scale. It is shown that with the support of simulations that help to identify the optimal conditions for a successful experiment and upon implementing measurement routines that effectively reduce the noise floor, EMCD measurements can be pushed towards quantitative magnetic measurements even on individual nanoparticles. With this approach, the ratio of orbital to spin magnetic moments for the Fe atoms in a single Ll(0) ordered FePt nanoparticle is determined to be m(l)/m(s) = 0.08 +/- 0.02. This finding is in good quantitative agreement with the results of XMCD ensemble measurements. (C) 2016 Elsevier B.V. All rights reserved.
|
|
| 6. |
- Schneider, Sebastian, et al.
(author)
-
Simple method for optimization of classical electron magnetic circular dichroism measurements : The role of structure factor and extinction distances
- 2018
-
In: Physical Review Materials. - : AMER PHYSICAL SOC. - 2475-9953. ; 2:11
-
Journal article (peer-reviewed)abstract
- Electron magnetic circular dichroism (EMCD), the electron wave analog of x-ray magnetic circular dichroism (XMCD), allows for the element specific measurement of the spin and orbital magnetic moments with up to nanometer resolution. However, due to dynamical diffraction effects, the signal-to-noise ratios of EMCD spectra are often very low. We describe a simple set of rules, how to set up a geometry for a classical EMCD experiment on an arbitrary crystal structure to get a maximum dichroic signal. The procedure is based on an evaluation of the structure factor and extinction distances. Proof-of-concept simulations and experiments on a FeGe crystal present a successful test of these guidelines.
|
|
| 7. |
|
|
| 8. |
|
|
