![]() Crystals with different symmetries require electron probes with different phase distributions. EMCD arising from magnetic moments aligned along the electron beam direction, in a crystal with in-plane fourfold symmetry, can be detected using an aberrated electron probe containing fourfold astigmatism (known as C 34 in Krivanek’s notation, or A 3 in Haider’s notation ). calculations, the key to reveal EMCD signals emerging from different magnetic orderings is to set a phase distribution of an atomic size electron probe that maximizes the symmetric component of EMCD at the spectrometer plane. We use an aberrated electron probe, which still maintains an atomic size, and detect the antiferromagnetic ordering of Mn moments in LaMnAsO by observing a dichroic signal in the Mn L-edge.ĮMCD in STEM has been identified previously only in ferromagnets, because the size of the electron probes has been larger than the period over which the magnetic moment directions vary in antiferromagnets or ferrimagnets. In this study, we experimentally verify the theoretical prediction of Rusz et al. Furthermore, the aberrated probes allow the collection of EEL spectra using the transmitted beam, which results in EMCD with intrinsically larger signal-to-noise ratios than those obtained via nanodiffraction techniques, where most of the transmitted electrons are discarded. These novel aberrated probes then can be utilized to obtain chiral dichroic signals in materials via electron energy-loss spectroscopy (EELS) with high spatial resolution. According to inelastic electron diffraction calculations, aberrated probes can have tails with a phase distribution that plays an analogous role to polarization of X-rays when interacting with a material. However, it has been recently argued on theoretical grounds that in some cases, it is desirable to have an atomic size electron probe with customized aberrations. The reasoning is that smaller probes result in images and spectra with better spatial resolutions. ![]() Until now, the goal of aberration correction in STEM has been to produce electron probes with sizes as small as possible. Utilizing crystal as the beam splitter, it was possible to achieve spatial resolutions of about 1–2 nm. More recently, it was recognized that in transmission electron microscopy (TEM), under particular scattering conditions, magnetic dichroism could also be probed via energy-loss magnetic circular dichroism (EMCD) spectroscopy. This effect, known as dichroism, has allowed polarized X-ray spectroscopy techniques, i.e., X-ray magnetic linear and circular dichroism (XMLD and XMCD), to probe the magnetic properties of materials since the mid-1980s. In the presence of a magnetic field, ferromagnets, paramagnets, antiferromagnets, and ferrimagnets exhibit different photon absorption cross sections that depend on the polarization of the incident photons. ![]()
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