Atomic Scale Imaging of Magnetic Circular Dichroism in Collinear Antiferromagnets

Description

Antiferromagnetic materials have shown broad application prospects in the field of ultrafast ultrahigh density information storage and high-frequency electronic devices due to no stray field, high intrinsic frequency and high resistance to external magnetic field interference, and diverse physical phenomena such as anomalous Hall effect, spin Hall effect, skyrmion, and spin Seebeck effect. The changes in physical property induced by spin direction variations in antiferromagnetic materials is the physical foundation of antiferromagnetic spintronics. However, it is very difficult to directly image spin structure in antiferromagnetic materials due to no net magnetic moment induced by the cancellation between antiparallel magnetic moments. The currently available techniques for measuring antiferromagnetic structure in materials are neutron diffraction and X-ray magnetic linear dichroism, whereas spatial resolution of these two methods is quite limited on the micro-/nano- scale. It has drawn worldwide attention to realize atomic scale magnetic imaging of antiferromagnetic spin structure, yet this great challenge remains. Recently we have developed the method of atomic scale imaging of electron magnetic circular dichroism (EMCD) with atomic plane resolution in a transmission electron microscope (TEM) by combining aberration correction and spatially-resolved EMCD under the parallel beam illumination. According to our previous methodological development, this project aims to access the EMCD spectra of the same magnetic elements located at the neighboring atomic planes with opposite spin directions, atomic plane by atomic plane, in collinear antiferromagnets by further optimizing atomic-plane resolved EMCD method with improved spatial resolution and signal to noise ratio under parallel beam illumination or convergent beam illumination in an aberration-corrected TEM. The spatial resolution of magnetic imaging of antiferromagnetic spin structure inside materials is pushed, for the first time, from micro-/nano- scale to atomic scale. In order to minimize the delocalization effects and improve the signal-to-noise ratios of EMCD spectra, the theoretical simulation of dynamical diffraction and inelastic scattering during the propagation of high-energy electrons inside antiferromagnets is performed to optimize the dynamical diffraction conditions such as crystal structure, diffraction geometry, sample thickness. The quantitative magnetic information, such as orbital and spin magnetic moments, of the antiferromagnetically coupled atoms at the adjacent atomic planes is determined from experimental EMCD spectra atomic plane by atomic plane. This information is essential to obtain a fundamental understanding of the cooperative interplay between spin, charge, lattice and orbital degrees of freedom in antiferromagnets at the atomic level, which is in turn a prerequisite to improve device functionality of antiferromagnetic spintronics.