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1. Epitaxial growth and magnetic properties of kagome metal FeSn/elemental ferromagnet heterostructures

   https://doi.org/10.1063/5.0188457  

   Laxmeesha, Prajwal M.; Tucker, Tessa D.; Rai, Rajeev Kumar; Li, Shuchen; Yoo, Myoung-Woo; Stach, Eric A.; Hoffmann, Axel; May, Steven J. (February 2024, Journal of Applied Physics)

   Binary kagome compounds TmXn (T = Mn, Fe, Co; X = Sn, Ge; m:n = 3:1, 3:2, 1:1) have garnered recent interest owing to the presence of both topological band crossings and flatbands arising from the geometry of the metal-site kagome lattice. To exploit these electronic features for potential applications in spintronics, the growth of high-quality heterostructures is required. Here, we report the synthesis of Fe/FeSn and Co/FeSn bilayers on Al2O3 substrates using molecular beam epitaxy to realize heterointerfaces between elemental ferromagnetic metals and antiferromagnetic kagome metals. Structural characterization using high-resolution x-ray diffraction, reflection high-energy electron diffraction, and electron microscopy reveals that the FeSn films are flat and epitaxial. Rutherford backscattering spectroscopy was used to confirm the stoichiometric window where the FeSn phase is stabilized, while transport and magnetometry measurements were conducted to verify metallicity and magnetic ordering in the films. Exchange bias was observed, confirming the presence of antiferromagnetic order in the FeSn layers, paving the way for future studies of magnetism in kagome heterostructures and potential integration of these materials into devices. 

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2. Atomic layer molecular beam epitaxy of kagome magnet RMn6Sn6 (R = Er, Tb) thin films

   https://doi.org/10.1063/5.0182595  

   Cheng, Shuyu; Liu, Binzhi; Lyalin, Igor; Zhou, Wenyi; Hwang, Jinwoo; Kawakami, Roland K (April 2024, APL Materials)

   Kagome lattices have garnered substantial interest because their band structure consists of topological flat bands and Dirac cones. The RMn6Sn6 (R = rare earth) compounds are particularly interesting because of the existence of the large intrinsic anomalous Hall effect (AHE), which originates from the gapped Dirac cones near the Fermi level. This makes RMn6Sn6 an outstanding candidate for realizing the high-temperature quantum AHE. The growth of RMn6Sn6 thin films is beneficial for both fundamental research and potential applications. However, most of the studies on RMn6Sn6 have focused on bulk crystals, and the synthesis of RMn6Sn6 thin films has not been reported so far. Here, we report the atomic layer molecular beam epitaxy growth, structural and magnetic characterizations, and transport properties of ErMn6Sn6 and TbMn6Sn6 thin films. It is especially noteworthy that TbMn6Sn6 thin films have out-of-plane magnetic anisotropy, which is important for realizing the quantum AHE. Our work paves the avenue toward the control of the AHE using devices patterned from RMn6Sn6 thin films. 

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3. Imaging real-space flat band localization in kagome magnet FeSn

   https://doi.org/10.1038/s43246-022-00328-1  

   Multer, Daniel; Yin, Jia-Xin; Hossain, Md. Shafayat; Yang, Xian; Sales, Brian C.; Miao, Hu; Meier, William R.; Jiang, Yu-Xiao; Xie, Yaofeng; Dai, Pengcheng; et al (December 2023, Communications Materials)

   Abstract Kagome lattices host flat bands due to their frustrated lattice geometry, which leads to destructive quantum interference of electron wave functions. Here, we report imaging of the kagome flat band localization in real-space using scanning tunneling microscopy. We identify both the Fe₃Sn kagome lattice layer and the Sn₂honeycomb layer with atomic resolution in kagome antiferromagnet FeSn. On the Fe₃Sn lattice, at the flat band energy determined by the angle resolved photoemission spectroscopy, tunneling spectroscopy detects an unusual state localized uniquely at the Fe kagome lattice network. We further show that the vectorial in-plane magnetic field manipulates the spatial anisotropy of the localization state within each kagome unit cell. Our results are consistent with the real-space flat band localization in the magnetic kagome lattice. We further discuss the magnetic tuning of flat band localization under the spin–orbit coupled magnetic kagome lattice model. 

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4. An atomically tailored chiral magnet with small skyrmions at room temperature

   https://doi.org/10.1038/s42005-023-01444-1  

   Liu, Tao; Selcu, Camelia M; Wang, Binbin; Bagués, Núria; Wu, Po-Kuan; Hartnett, Timothy Q; Cheng, Shuyu; Pelekhov, Denis; Bennett, Roland A; Corbett, Joseph Perry; et al (December 2023, Communications Physics)

   Abstract Creating materials that do not exist in nature can lead to breakthroughs in science and technology. Magnetic skyrmions are topological excitations that have attracted great attention recently for their potential applications in low power, ultrahigh density memory. A major challenge has been to find materials that meet the dual requirement of small skyrmions stable at room temperature. Here we meet both these goals by developing epitaxial FeGe films with excess Fe using atomic layer molecular beam epitaxy (MBE) far from thermal equilibrium. Our atomic layer design permits the incorporation of 20% excess Fe while maintaining a non-centrosymmetric crystal structure supported by theoretical calculations and necessary for stabilizing skyrmions. We show that the Curie temperature is well above room temperature, and that the skyrmions have sizes down to 15 nm as imaged by Lorentz transmission electron microscopy (LTEM) and magnetic force microscopy (MFM). The presence of skyrmions coincides with a topological Hall effect-like resistivity. These atomically tailored materials hold promise for future ultrahigh density magnetic memory applications. 

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5. Visualizing symmetry-breaking electronic orders in epitaxial Kagome magnet FeSn films

   https://doi.org/10.1038/s41467-023-41831-4  

   Zhang, Huimin; Oli, Basu Dev; Zou, Qiang; Guo, Xu; Wang, Zhengfei; Li, Lian (December 2023, Nature Communications)

   Abstract Kagome lattice hosts a plethora of quantum states arising from the interplay of topology, spin-orbit coupling, and electron correlations. Here, we report symmetry-breaking electronic orders tunable by an applied magnetic field in a model Kagome magnet FeSn consisting of alternating stacks of two-dimensional Fe₃Sn Kagome and Sn₂honeycomb layers. On the Fe₃Sn layer terminated FeSn thin films epitaxially grown on SrTiO₃(111) substrates, we observe trimerization of the Kagome lattice using scanning tunneling microscopy/spectroscopy, breaking its six-fold rotational symmetry while preserving the translational symmetry. Such a trimerized Kagome lattice shows an energy-dependent contrast reversal in dI/dV maps, which is significantly enhanced by bound states induced by Sn vacancy defects. This trimerized Kagome lattice also exhibits stripe modulations that are energy-dependent and tunable by an applied in-plane magnetic field, indicating symmetry-breaking nematicity from the entangled magnetic and charge degrees of freedom in antiferromagnet FeSn. 

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