Magnetic Effects in the Paraxial Regime of Elastic Electron Scattering

TL;DR

This study computationally investigates magnetic effects in elastic electron scattering using vortex, spin-polarized, and aberrated electron beams in magnetic solids, revealing conditions for detectable magnetic signals at atomic resolution.

Contribution

It provides a comprehensive analysis of magnetic signals in elastic electron scattering with vortex and other electron beams, demonstrating enhanced signals at atomic resolution compared to prior studies.

Findings

Strongest magnetic signals from vortex beams with high orbital angular momentum.

Low acceleration voltage and small convergence angles improve magnetic signal strength.

Relative magnetic signals of about 10^{-4} are achievable at atomic resolution.

Abstract

Based on a recent claim [Phys. Rev. Lett. 116, 127203 (2016)] that electron vortex can be used to image magnetism at the nanoscale in elastic scattering experiments, using transmission electron microscopy, a comprehensive computational study is performed to study magnetic effects in the paraxial regime of elastic electron scattering in magnetic solids. Magnetic interactions from electron vortex beams, spin polarized electron beams and beams with phase aberrations are considered, as they pass through ferromagnetic FePt or antiferromagnetic LaMnAsO. The magnetic signals are obtained by comparing the intensity over a disk in the diffraction plane for beams with opposite angular momentum or aberrations. The strongest magnetic signals are obtained from vortex beams with large orbital angular momentum, where relative magnetic signals above $10^{-3}$ are indicated for $10\hbar$ orbital angular momentum, meaning that relative signals of one percent could be expected with the even larger orbital angular momenta, which have been produced in experimental setups. All results indicate that beams with low acceleration voltage and small convergence angles yield stronger magnetic signals, which is unfortunately problematic for the possibility of high spatial resolution imaging. Nevertheless, under atomic resolution conditions, relative magnetic signals in the order of $10^{-4}$ are demonstrated, corresponding to an increase with one order of magnitude compared to previous work.