Key to the advancement of magnetic materials is the exploitation of emergent magnetic behavior arising from nanoscale confinement. A comprehensive understanding of this behavior requires a technique capable of resolving it and mapping its relationship to parallel nanoscale property domains such as local structural imperfections, chemical environment, and interfacial proximity. The relatively young electron absorption spectroscopy technique known as Electron Magnetic Circular Dichroism (EMCD)  promises to meet these criteria, and it has already demonstrated qualitative  and quantitative [3, 4] results for parallel electron probe illumination on sample regions in the sub 100 nanometer range. While this already represents a spatial resolution superior to what can be achieved with x-rays , the use of parallel electron illumination means that high spatial resolution can only be achieved through the use of energy filtered diffraction patterns [3, 6] or energy filtered TEM imaging techniques .
In this work, we describe our progress in the development of an experimental methodology utilizing convergent electron probes for the purposes of acquiring EMCD datasets. We name this method STEM-EMCD (see figure 1) and argue that it has two significant advantages over parallel beam illumination schemes. First, the use of a convergent probe allows for the acquisition of arbitrarily large datasets, extending the effective acquisition time on a region of interest well beyond what is feasible for a single-shot experiment using parallel illumination. This substantially improves the signal to noise ratio of EMCD spectral pairs, as shown in figure 1, and can be employed in such a way to mitigate significant beam damage. Second, the diameter of the electron probe can be reduced to one nanometer or less. If appropriate multivariate statistical methods are used to exploit spectral redundancy in the datacubes, it becomes possible to accurately approximate the raw data using a significantly reduced parameter space, dramatically suppressing the influence of statistical noise. We demonstrate that this allows for sum rules to be applied on individual spectral pairs, enabling real-space maps of magnetic transitions to be generated with a spatial resolution approaching that of the beam diameter, as shown in figure 2. We conclude with a discussion of some of the challenges still faced by the STEM-EMCD method as well as its prospects for directly addressing some of the most elusive questions in contemporary research in nanomagnetism.
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To cite this abstract:Thomas Thersleff, Shunsuke Muto, Jakob Spiegelberg, Ján Rusz, Klaus Leifer; Nanoscale maps of magnetic behavior using STEM-EMCD. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/nanoscale-maps-of-magnetic-behavior-using-stem-emcd/. Accessed: December 14, 2019
EMC Abstracts - https://emc-proceedings.com/abstract/nanoscale-maps-of-magnetic-behavior-using-stem-emcd/