Atomic resolution determination of spin configuration at interfaces in functional materials in the transmission electron microscope
Final Report Abstract
New energy-efficient information and communications technologies place ever-increasing demands on the performance of magnetic materials. The development of materials to meet these challenges requires an atomic-level knowledge of their local spin configurations, in order to predict and control their physical properties. This Joint Sino-German Research Project aimed to develop atomic-scale magnetic imaging and spectroscopy techniques that can be used to provide experimental measurements of spin configurations in functional materials, in order to obtain a fundamental understanding about the physical origins of novel magnetic coupling phenomena. The approach involved the use of a combination of off-axis electron holography and electron magnetic circular dichroism to provide quantitative close-to-atomic-scale and threedimensional information about local magnetization distributions in materials. This information can be correlated with local structural and compositional information to provide a detailed fundamental understanding of the physical origins of the properties of magnetic materials and can be used to provide guidelines for the design of magnetic materials for future applications with improved device functionality. Although this project was affected by unexpected downtime of one of the key transmission electron microscopes that was planned to be used for atomic-scale off-axis electron holography and EMCD experiments, the project goals could be re-adjusted to make maximum progress on the three-dimensional nm-scale (rather than atomic-scale) characterization of magnetization distributions in materials, on theoretical predictions and experimental measurements of new three-dimensional magnetic textures and on correlative quantitative measurements of magnetic properties using electrons and complementary techniques. The project succeeded in generating a wealth of new and unexpected results, while maintaining the original goal of developing new quantitative approaches based on off-axis electron holography and EMCD for the three-dimensional and correlative magnetic characterization of nanoscale and nanostructured materials at the highest spatial resolution. Four key categories of results were obtained during the project: First, the EMCD technique was developed to obtain close-to-atomic-scale magnetic information about materials of current technological interest. This work built on the first demonstration of the measurement of local magnetic information with atomic-scale spatial resolution using electron energy-loss magnetic chiral dichroism, in combination with the use of chromatic-aberration-corrected transmission electron microscopy to reduce the focal spread of inelastically scattered electrons by orders of magnitude when compared with the use of spherical aberration correction alone. Although this microscope was unavailable for the rest of the project, the work was continued by applying the EMCD technique with slightly poorer spatial resolution to study superexchange-based magnetic coupling of cations in a rock-salt-ordered double perovskite oxide, metastable α''-Fe16N2 thin films that display giant saturation magnetization but are mixed on the nanoscale and the magnetic properties of individual antiphase boundaries in spinel ferrite films. Second, a theoretical study was performed to develop EMCD for the study of the magnetic properties of two-dimensional layered van der Waals magnets. It was shown that EMCD is able to quantitatively measure magnetic parameters in such samples in three orthogonal directions on atomic scale. Third, three-dimensional magnetic characterization was performed using both EMCD and off-axis electron holography for materials that included artificial spin ice lattices and magnetic skyrmions studied using electron holographic vector-field electron tomography at liquid nitrogen temperature. Fourth, off-axis electron holography was used to examine a wide range of novel three-dimensional magnetic textures that had been predicted theoretically in chiral magnets but never previously observed, including chiral bobbers, magnetic surface and edge states, magnetic soliton crystals with layered structures that host periodic chiral helimagnetic ordering, twisted magnetic skyrmion braids and highly complex magnetic states in phase separated magnetic high entropy alloys. https://www.fz-juelich.de/SharedDocs/Pressemitteilungen/UK/EN/2021/notifications/2021-10-04-skyrmionen-nanowirbel-en.html
Publications
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Atomic scale imaging of magnetic circular dichroism by achromatic electron microscopy. Nature Materials 17 (2018), 221-225
Z C Wang, A H Tavabi, L Jin, J Rusz, H B Jiang, Y Moritomo, J Mayer, R E Dunin-Borkowski, J Zhu and X Y Zhong
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Effect of cation ratio and order on magnetic circular dichroism in the double perovskite Sr2Fe1+xRe1-xO6. Ultramicroscopy 193 (2018), 137-142
P-L Ho, C-P Yu, Q Zhang, K Song, J P Buban, S-Y Choi, R E Dunin-Borkowski, J Mayer, N-H Tai, J Zhu, L Jin and X Y Zhong
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Experimental observation of chiral magnetic bobbers in B20-type FeGe. Nature Nanotechnology 13 (2018), 451-455
F Zheng, F N Rybakov, A B Borisov, D Song, S Wang, Z-A Li, H Du, N S Kiselev, J Caron, A Kovács, M Tian, Y Zhang, S Blügel and R E Dunin-Borkowski
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Quantification of magnetic surface and edge states in an FeGe nanostripe by off-axis electron holography. Phys. Rev. Lett. 120 (2018) 167204
D Song, Z-A Li, J Caron, A Kovács, H Tian, C Jin, H Du, M Tian, J Li, J Zhu and R E Dunin-Borkowski
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Nanoscale measurement of giant saturation magnetization in α''-Fe16N2 by electron energy-loss magnetic chiral dichroism. Ultramicroscopy 203 (2019), 37-43
X Chen, S Higashikozono, K Ito, L Jin, P-L Ho, C-P Yu, N-H Tai, J Mayer, R E Dunin-Borkowski, T Suemasu and X Y Zhong
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Robust nature of the chiral spin helix in CrNb3S6 nanostructures studied by off-axis electron holography. Phys. Rev. B 102 (2020), 064432
D Song, L Wang, W Wang, F Zheng, J Tang, S Wang, C Zhu, J Caron, A Kovács, Z Liu, D Mandrus, M Tian, H Du and R E Dunin-Borkowski
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Atomic structure and electron magnetic circular dichroism of rock salt structure antiphase boundaries in spinel ferrites. Adv. Funct. Mater. 31 (2021), 2008306
Z Li, J Lu, L Jin, J Rusz, V Kocevski, H Yanagihara, E Kita, J Mayer, R E Dunin-Borkowski, H Xiang and X Y Zhong
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Magnetic skyrmion braids. Nature Communications 12 (2021), 5316
F Zheng, F N Rybakov, N S Kiselev, D Song, A Kovács, H Du, S Blügel and R E Dunin-Borkowski
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Three-dimensional measurement of magnetic moment vectors using electron magnetic chiral dichroism at atomic scale. Phys. Rev. Lett. 127 (2021), 087202
D Song and R E Dunin-Borkowski
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Prospect for measuring two-dimensional van der Waals magnets by electron magnetic chiral dichroism. Ultramicroscopy 234 (2022), 113476
D Song, F Zheng and R E Dunin-Borkowski
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Quantitative imaging of the magnetic field distribution in an artificial spin ice studied by off-axis electron holography. J. Magn. Magn. Mat. 543 (2022), 168535
T Weßels, A Kovács, S Gliga, S Finizio, J Caron and R E Dunin-Borkowski
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Unveiling the three-dimensional spin texture of skyrmion tubes. Nature Nanotechnology
D Wolf, S Schneider, U K Rößler, A Kovács, M Schmidt, R E Dunin-Borkowski, B Büchner, B Rellinghaus and A Lubk
