Scattering of electron vortex beams on a magnetic crystal: Towards atomic-resolution magnetic measurements

Use of electron vortex beams (EVB), that is, convergent electron beams carrying an orbital angular momentum (OAM), is a novel development in the field of transmission electron microscopy. They should allow measurement of element-specific magnetic properties of thin crystals using electron magnetic circular dichroism (EMCD)-a phenomenon similar to the x-ray magnetic circular dichroism. Recently, it has been shown computationally that EVBs can detect magnetic signal in a scanning mode only at atomic resolution. In this follow-up work, we explore in detail the elastic and inelastic scattering properties of EVBs on crystals, as a function of beam diameter, initial OAM, acceleration voltage, and beam displacement from an atomic column. We suggest that for a 10-nm layer of bcc iron oriented along (001) zone axis, an optimal configuration for a detection of EMCD is an EVB with OAM of 1 (h) over bar and a full width at half maximum diffraction-limited beam diameter of 1.6 angstrom, acceleration voltage 200 kV, and an annular detector with inner and outer radii of 7 and 44 mrad, respectively.