Abstract
We report localization of a magnetic dichroic signal on atomic columns in electron magnetic circular dichroism (EMCD), probed by beam distorted by four-fold astigmatism and electron vortex beam. With astigmatic probe, magnetic signal to noise ratio can be enhanced by blocking the intensity from the central part of probe. However, the simulations show that for atomic resolution magnetic measurements, vortex beam is a more effective probe, with much higher magnetic signal to noise ratio. For all considered beam shapes, the optimal SNR constrains the signal detection at low collection angles of approximately 6–8 mrad. Irrespective of the material thickness, the magnetic signal remains strongly localized within the probed atomic column with vortex beam, whereas for astigmatic probes, the magnetic signal originates mostly from the nearest neighbor atomic columns. Due to excellent signal localization at probing individual atomic columns, vortex beams are predicted to be a strong candidate for studying the crystal site specific magnetic properties, magnetic properties at interfaces, or magnetism arising from individual atomic impurities.
Highlights
Rapid growth in nanotechnology and newly emerging magnetic structures at nano and atomic scale, are simultaneously demanding for tools and techniques, capable of characterizing the electrical and magnetic properties of material at nano and atomic scale[1,2,3,4,5,6,7,8,9,10,11]
We have studied the localization of magnetic dichroic signal on atomic columns in electron magnetic circular dichroism (EMCD), as observed with phase aberrated probes and a vortex beam
Optimization of the signal to noise ratio (SNR) constrains the signal detection within rather small collection angles of ~6–8 mrad
Summary
Rapid growth in nanotechnology and newly emerging magnetic structures at nano and atomic scale, are simultaneously demanding for tools and techniques, capable of characterizing the electrical and magnetic properties of material at nano and atomic scale[1,2,3,4,5,6,7,8,9,10,11]. In this context, with substantial development in instrumental and theoretical front of electron energy-loss spectroscopy (EELS) in (scanning) transmission electron microscopy ((S) TEM); EELS offers such capabilities. The magnetic and nonmagnetic excitations were calculated from the probed and neighboring atomic columns as a function of material thickness to analyze the spatial origins of the EMCD signal
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