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1. Spin structure and dynamics of the topological semimetal Co3Sn2-xInxS2

   https://doi.org/10.1038/s41535-022-00523-w  

   Neubauer, Kelly J. ; Ye, Feng ; Shi, Yue ; Malinowski, Paul ; Gao, Bin ; Taddei, Keith M. ; Bourges, Philippe ; Ivanov, Alexandre ; Chu, Jiun-Haw ; Dai, Pengcheng ( December 2022 , npj Quantum Materials)

   The anomalous Hall effect (AHE), typically observed in ferromagnetic (FM) metals with broken time-reversal symmetry, depends on electronic and magnetic properties. In Co₃Sn_2-xIn_xS₂, a giant AHE has been attributed to Berry curvature associated with the FM Weyl semimetal phase, yet recent studies report complicated magnetism. We use neutron scattering to determine the spin dynamics and structures as a function ofxand provide a microscopic understanding of the AHE and magnetism interplay. Spin gap and stiffness indicate a contribution from Weyl fermions consistent with the AHE. The magnetic structure evolves fromc-axis ferromagnetism at$$x = 0$$$x=0$to a canted antiferromagnetic (AFM) structure with reducedc-axis moment and in-plane AFM order at$$x = 0.12$$$x=0.12$and further reducedc-axis FM moment at$$x = 0.3$$$x=0.3$. Since noncollinear spins can induce non-zero Berry curvature in real space acting as a fictitious magnetic field, our results revealed another AHE contribution, establishing the impact of magnetism on transport.

    

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2. 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)

   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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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)

   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. Field-free spin-orbit switching of perpendicular magnetization enabled by dislocation-induced in-plane symmetry breaking

   https://doi.org/10.1038/s41467-023-41163-3  

   Liang, Yuhan ; Yi, Di ; Nan, Tianxiang ; Liu, Shengsheng ; Zhao, Le ; Zhang, Yujun ; Chen, Hetian ; Xu, Teng ; Dai, Minyi ; Hu, Jia-Mian ; et al ( December 2023 , Nature Communications)

   Current induced spin-orbit torque (SOT) holds great promise for next generation magnetic-memory technology. Field-free SOT switching of perpendicular magnetization requires the breaking of in-plane symmetry, which can be artificially introduced by external magnetic field, exchange coupling or device asymmetry. Recently it has been shown that the exploitation of inherent crystal symmetry offers a simple and potentially efficient route towards field-free switching. However, applying this approach to the benchmark SOT materials such as ferromagnets and heavy metals is challenging. Here, we present a strategy to break the in-plane symmetry of Pt/Co heterostructures by designing the orientation of Burgers vectors of dislocations. We show that the lattice of Pt/Co is tilted by about 1.2° when the Burgers vector has an out-of-plane component. Consequently, a tilted magnetic easy axis is induced and can be tuned from nearly in-plane to out-of-plane, enabling the field-free SOT switching of perpendicular magnetization components at room temperature with a relatively low current density (~10¹¹A/m²) and excellent stability (> 10⁴cycles). This strategy is expected to be applicable to engineer a wide range of symmetry-related functionalities for future electronic and magnetic devices.

    

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5. Switching the spin cycloid in BiFeO3 with an electric field

   https://doi.org/10.1038/s41467-024-47232-5  

   Meisenheimer, Peter ; Moore, Guy ; Zhou, Shiyu ; Zhang, Hongrui ; Huang, Xiaoxi ; Husain, Sajid ; Chen, Xianzhe ; Martin, Lane W ; Persson, Kristin A ; Griffin, Sinéad ; et al ( December 2024 , Nature Communications)

   Bismuth ferrite (BiFeO₃) is a multiferroic material that exhibits both ferroelectricity and canted antiferromagnetism at room temperature, making it a unique candidate in the development of electric-field controllable magnetic devices. The magnetic moments in BiFeO₃are arranged into a spin cycloid, resulting in unique magnetic properties which are tied to the ferroelectric order. Previous understanding of this coupling has relied on average, mesoscale measurements. Using nitrogen vacancy-based diamond magnetometry, we observe the magnetic spin cycloid structure of BiFeO₃in real space. This structure is magnetoelectrically coupled through symmetry to the ferroelectric polarization and this relationship is maintained through electric field switching. Through a combination of in-plane and out-of-plane electrical switching, coupled with ab initio studies, we have discovered that the epitaxy from the substrate imposes a magnetoelastic anisotropy on the spin cycloid, which establishes preferred cycloid propagation directions. The energy landscape of the cycloid is shaped by both the ferroelectric degree of freedom and strain-induced anisotropy, restricting the spin spiral propagation vector to changes to specific switching events.

    

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