Abstract text (incl. figure legends and references)

Electron magnetic circular dichroism (EMCD) [1] is an electron energy loss spectroscopy (EELS) based technique in the TEM which can measure element specific magnetic moments of the materials. When used in STEM mode, the spatial resolution of EMCD analysis is defined by the size of the electron probe which in the modern instruments can easily reach atomic resolution. Although atomic resolution EMCD should be feasible, it is quite demanding due to various challenges.

Classical EMCD experiments are performed with the crystal tilted into two (or three) beam condition and acquisition of two (or four) conjugate EELS spectra at specific off-axis angular positions in the reciprocal space. A disadvantage of using such diffraction geometry is that the atomic planes are parallel to the electron probe, losing the atomic column resolution. Atomic-plane resolved EMCD measurements[2] have been demonstrated using such diffraction geometry. To achieve the atomic (column) resolution, the crystal must be tilted to a zone axis. The EMCD experiments in a zone axis are non-trivial due to complex distribution of the magnetic signal and high dynamical diffraction effects.

In this work, we have used different custom-made hardware apertures to address various challenges in the EMCD experiments. We have used double hole and quadruple apertures to simultaneously acquire the multiple EELS spectra required for the EMCD experiment, removing the need of multiple electron beam scans [3], [4]. We have also demonstrated the simultaneous acquisition of the EMCD signals and the crystal orientation which allowed us to study the effects of small crystal mistilts on the EMCD signals. Finally, we have used complex shaped apertures to acquire the EMDC signals in the zone axis geometry. We demonstrated the detection of EMCD signals under atomic resolution conditions using such apertures[5]. We also propose strategies based on the use of virtual apertures to achieve atomic resolution EMCD measurements.

[1] P. Schattschneider et al., "Detection of magnetic circular dichroism using a transmission electron microscope," Nature, vol. 441, no. 7092, pp. 486–488, May 2006, doi: 10.1038/nature04778.

[2] Z. Wang et al., "Atomic scale imaging of magnetic circular dichroism by achromatic electron microscopy," Nature Materials 2018 17:3, vol. 17, no. 3, pp. 221–225, Feb. 2018, doi: 10.1038/S41563-017-0010-4.

[3] H. Ali, T. Warnatz, L. Xie, B. Hjörvarsson, and K. Leifer, "Quantitative EMCD by use of a double aperture for simultaneous acquisition of EELS," Ultramicroscopy, vol. 196, pp. 192–196, Jan. 2019, doi: 10.1016/j.ultramic.2018.10.012.

[4] H. Ali, J. Rusz, T. Warnatz, B. Hjörvarsson, and K. Leifer, "Simultaneous mapping of EMCD signals and crystal orientations in a transmission electron microscope," Scientific Reports, vol. 11, no. 1, p. 2180, Dec. 2021, doi: 10.1038/s41598-021-81071-4.

[5] H. Ali, D. Negi, T. Warnatz, B. Hjörvarsson, J. Rusz, and K. Leifer, "Atomic resolution energy-loss magnetic chiral dichroism measurements enabled by patterned apertures," Physical Review Research, vol. 2, no. 2, p. 023330, Jun. 2020, doi: 10.1103/physrevresearch.2.023330.

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