  The need to acquire multiple angle-resolved electron energy loss spectra
(EELS) is one of the several critical challenges associated with electron
magnetic circular dichroism (EMCD) experiments. If the experiments are
performed by scanning a nanometer to atomic-sized electron probe on a specific
region of a sample, the precision of the local magnetic information extracted
from such data highly depends on the accuracy of the spatial registration
between multiple scans. For an EMCD experiment in a 3-beam orientation, this
means that the same specimen area must be scanned four times while keeping all
the experimental conditions same. This is a non-trivial task as there is a high
chance of morphological and chemical modification as well as non-systematic
local orientation variations of the crystal between the different scans due to
beam damage, contamination and spatial drift. In this work, we employ a
custom-made quadruple aperture to acquire the four EELS spectra needed for the
EMCD analysis in a single electron beam scan, thus removing the above-mentioned
complexities. We demonstrate a quantitative EMCD result for a beam convergence
angle corresponding to sub-nm probe size and compare the EMCD results for
different detector geometries.
