Reciprocal and real space maps for EMCD experiments

Abstract

Electron magnetic chiral dichroism (EMCD) is an emerging tool for quantitative measurements of magnetic properties using the transmission electron microscope (TEM), with the possibility of nanometer resolution. The geometrical conditions, data treatment and electron gun settings are found to influence the EMCD signal. In this article, particular care is taken to obtain a reliable quantitative measurement of the ratio of orbital to spin magnetic moment using energy filtered diffraction patterns. For this purpose, we describe a method for data treatment, normalization and selection of mirror axis. The experimental results are supported by theoretical simulations based on dynamical diffraction and density functional theory. Special settings of the electron gun, so called telefocus mode, enable a higher intensity of the electron beam, as well as a reduction of the influence from artifacts on the signal. Using these settings, we demonstrate the principle of acquiring real space maps of the EMCD signal. This enables advanced characterization of magnetic materials with superior spatial resolution.

Applications of STEM-EELS to complex oxides

“…Hence, we carried out a real-space characterization at the sub-nanometer scale of magnetic and electronic properties, via aberration corrected STEM and EELS, which was used to probe the local magnetization of a single nanoparticle at room temperature [67]. Just like macroscopically averaged x-ray magnetic circular dichroism (XMCD), electron magnetic circular dichroism (EMCD) can be measured in transition metal oxides by studying the L 2,3 edges of transition metals while illuminating nanometer-sized specimen areas [72][73][74][75].…”

Electron magnetic chiral dichroism in CrO2 thin films using monochromatic probe illumination in a transmission electron microscope

“…STEM probe ( $1.7 nm) has been used to demonstrate $2 nm spatial resolutions in EMCD experiment [6,7]. This approach requires acquisition of spectra in spectroscopy mode (in the first case) of EELS by physically placing objective aperture at the diffraction plane at two different positions.…”

“…EMCD is the electron counterpart of the well known x-ray magnetic circular dichroism (XMCD) technique which has been extensively used for studying the element specific orbital and spin magnetic moments of various materials [2][3][4][5]. EMCD has the advantage of superior spatial resolution ( $ 2 nm has already been demonstrated) [6,7] and provides bulk information as compared to XMCD which is mostly surface sensitive and difficult to routinely achieve spatial resolution below 100 nm [8]. Recent progress in x-ray optics and soft x-ray magnetic microscopy could improve the lateral resolution to about 15 nm [9].…”

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

“…Since its inception [2], it went through a rapid development with significant improvements in spatial resolution and signal to noise ratio [3][4][5][6][7]. Theoretical studies provided understanding of the interplay of dynamical diffraction effects and inelastic excitations that give rise to EMCD signal [8,9] and its relation to the ground-state expectation values [10] such as spin and orbital magnetic moments via sum rules [11,12].…”