Inelastic electron scattering on magnetic materials – towards atomic resolution measurements of magnetism

Abstract: X-ray magnetic circular dichroism (XMCD) is a well established measurement technique that allows to obtain spin and orbital magnetic moments of elements in a sample. Progress in magnetic nanotechnologies and difficulties to focus photons to areas smaller than 10 nm diameter calls for alternative magnetic characterization techniques that would be quantitative and offer the needed lateral resolution. A transmission electron microscopy analogue of XMCD, the electron magnetic circular dichroism (EMCD) has been observed for the first time a decade ago. Since then the technique was substantially developed and extended beyond the initial experiments. Recent experiments with atomic size probes allow to detect EMCD from lateral areas as small as 0.5 nm². Electrons, being charged particles, interact very strongly with the electrostatic potential in the sample, leading to dynamical diffraction effects. In case of convergent electron probes, the questions of beam coherence and aberrations of electron optics complicate the situation even further. This is exploited in theories, which describe how to shape electron beam phase distribution, in order to maximize its sensitivity to magnetism. We will review the latest state-of-the-art of the technique, with a slight bias towards recent progresses in theoretical understanding of EMCD.