Electron diffraction covering a wide angular range from Bragg diffraction to small-angle diffraction

TL;DR

This paper presents a novel electron diffraction method covering a wide angular range, enabling detailed analysis of magnetic microstructures in various materials with adjustable camera length and magnetic field sensitivity.

Contribution

The authors develop an electron optical system that can switch between Bragg and small-angle diffraction modes, covering an angular range from 10$^{-2}$ to 10$^{-7}$ radians, with adjustable camera length and magnetic field observation capabilities.

Findings

Successfully observed magnetic microstructures in three different materials.

Achieved a wide angular diffraction range from 10$^{-2}$ to 10$^{-7}$ radians.

Demonstrated magnetic field dependence of electron diffraction patterns.

Abstract

We construct an electron optical system to investigate Bragg diffraction (the crystal lattice plane, $10^{-2}$-$10^{-3}$ rad) with the objective lens turned off by adjusting the current in the intermediate lenses. A crossover was located on the selected-area aperture plane. Thus, the dark-field imaging can be performed by using a selected-area aperture to select Bragg diffraction spots. The camera length can be controlled in the range of 0.8 to 4 m without exciting the objective lens. Furthermore, we can observe the magnetic-field dependence of electron diffraction using the objective lens under weak excitation conditions. The diffraction mode for Bragg diffraction can be easily switched to a small-angle electron diffraction mode having a camera length of more than 100 m. We propose this experimental method to acquire electron diffraction patterns that depict an extensive angular range from 10$^{-2}$ to 10$^{-7}$ rad. This method is applied to analyze the magnetic microstructures in three distinct magnetic materials, i.e., a uniaxial magnetic structure of BaFe$_{10.35}$Sc$_{1.6}$Mg$_{0.05}$O$_{19}$, a martensite of a Ni-Mn-Ga alloy, and a helical magnetic structure of Ba$_{0.5}$Sr$_{1.5}$Zn$_{2}$Fe$_{12}$O$_{22}$.