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Topological Kerr effects in two-dimensional magnets with broken inversion symmetry

Nature Physics (2024)Cite this article

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Abstract

The whorls of localized moments in chiral magnetic structures, such as skyrmions, lead to a quantized topological charge, which may make them useful as next-generation information bits. So far, the most reliable way to detect the existence of skyrmions is by using the topological Hall effect, which stems from electron scattering by the emergent magnetic field manifesting the topological charge. Here we employ two-dimensional magnets to establish a magneto-optical hallmark of skyrmions, which we call the topological Kerr effect, using the recently discovered ferromagnet CrVI6 as a material platform. The Kerr angle hysteresis loop of this non-centrosymmetric system exhibits two antisymmetric bumps that are absent in the centrosymmetric CrI3 and VI3. We develop a minimal model to further identify the bumps as direct manifestations of the topological charge, thereby providing a magneto-optical fingerprint of skyrmions with broader applicability.

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Fig. 1: Structure and DM interaction of CrVI6.
Fig. 2: Preparation and characterization of bulk and thin-film samples of CrVI6.
Fig. 3: Magneto-optical Kerr effect measurements and TKE in CrVI6.
Fig. 4: Simulated magneto-optical responses and TKE on a CrVI6 lattice with DMI.

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Data availability

Source data are provided with this paper. All other data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

Code availability

The Spirit code and manual are available at https://spirit-code.github.io/. Codes for reproducing the simulation results are available from the corresponding author upon reasonable request.

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Acknowledgements

We thank C. Gao, M. Tian, H. Du, J. Li, X. Yu, J. Wrachtrup, Q. Sun, Y. Zhang, Y. Wang, X. Wang and many other colleagues from their groups for various suggestions and efforts on potential direct detection of skyrmions in the newly synthesized magnet of CrVI6. This work was supported by the National Natural Science Foundation of China (Grant Nos. 11574316, 11722435, 11804210, 11904350, 11974323, 12374458, U2032218, 12274276, 51627901 and U1932216), the Innovation Programme for Quantum Science and Technology (Grant No. 2021ZD0302800), the Strategic Priority Research Programme of Chinese Academy of Sciences (CAS) (Grant No. XDB0510200), the Anhui Initiative in Quantum Information Technologies (Grant No. AHY170000), the Anhui Provincial Natural Science Foundation (Grant. No. 2008085QA30) and National Synchrotron Radiation Laboratory (KY2060000177). C.L. and Z.S. gratefully acknowledge financial support from the National Key R&D Programme of China (Grant Nos. 2021YFA1600200, 2017YFA0303603 and 2023YFA1607701), the Plan for Major Provincial Science & Technology Project (Grant No. 202003a05020018), the Key Research Programme of Frontier Sciences, CAS (Grant No. QYZDB-SSW-SLH011), and the Users with Excellence Programme of Hefei Science Center, CAS (Grant No. 2021HSC-UE009). A portion of this work was performed on the Steady High Magnetic Field Facilities, High Magnetic Field Laboratory, CAS, and supported by the High Magnetic Field Laboratory of Anhui Province. This research was also partially carried out at the USTC Center for Micro and Nanoscale Research and Fabrication.

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Author notes

  1. These authors contributed equally: Xiaoyin Li, Caixing Liu, Ying Zhang.

Authors and Affiliations

  1. International Center for Quantum Design of Functional Materials (ICQD), and Hefei National Laboratory, University of Science and Technology of China, Hefei, China

    Xiaoyin Li, Shunhong Zhang, Dazhi Hou, Ping Cui & Zhenyu Zhang

  2. High Magnetic Field Laboratory, HFIPS, Chinese Academy of Sciences, Hefei, China

    Caixing Liu, Yuchen Zhang, Wenjie Meng, De Hou, Qingyou Lu & Zhigao Sheng

  3. Department of Materials Science & Engineering, CAS Key Lab of Materials for Energy Conversion, Anhui Laboratory of Advanced Photon Science and Technology, University of Science and Technology of China, Hefei, China

    Ying Zhang, Fanyang Huang, Ruiguo Cao & Bin Xiang

  4. Key Laboratory of Magnetic Molecules and Magnetic Information Materials of the Ministry of Education and Research Institute of Materials Science, Shanxi Normal University, Taiyuan, China

    Huisheng Zhang & Xiaohong Xu

  5. Hefei National Laboratory for Physical Sciences at the Microscale and Anhui Laboratory of Advanced Photon Science and Technology, University of Science and Technology of China, Hefei, China

    Yuchen Zhang & Qingyou Lu

  6. Center for Spintronics and Quantum Systems, State Key Laboratory for Mechanical Behavior of Materials, Department of Materials Science and Engineering, Xi’an Jiaotong University, Xi’an, China

    Tao Li & Tai Min

  7. Key Laboratory for Quantum Matters and Key Laboratory of Photovoltaic Materials, Henan University, Kaifeng, China

    Chaoyang Kang & Weifeng Zhang

  8. Department of Physics, University of Science and Technology of China, Hefei, China

    Dazhi Hou

  9. Institute of Quantum Materials and Physics, Henan Academy of Sciences, Zhengzhou, China

    Weifeng Zhang

Authors
  1. Xiaoyin Li
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Contributions

Z.Z. conceived the central idea and directed the project. H.Z., P.C., X.X. and Z.Z. predicted the CrVI6 monolayer as a new 2D magnet. X.L. and S.Z. performed theoretical modelling and analysis. Ying Zhang synthesized the samples and fabricated the devices for MOKE measurements under supervision of B.X. F.H. and R.C. performed atomic-force-microscopy characterization of the thickness of CrVI6 flakes. C.L. and De Hou performed MOKE measurements under supervision of Z.S. Yuchen Zhang and W.M. performed MFM imaging under supervision of Q.L. T.L., T.M., C.K., W.Z. and X.X. performed various syntheses and characterizations of CrI3 and VI3 crystals, devised methods for protection of the CrVI6 samples at varying Cr/V ratios, and carried out subsequent electrical transport measurements. Dazhi Hou contributed to the conceptual development. All authors contributed to the interpretation of the data. X.L., S.Z. and Z.Z. wrote the paper with input from all the authors.

Corresponding authors

Correspondence to Zhigao Sheng, Bin Xiang or Zhenyu Zhang.

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Supplementary Information

Supplementary Methods, Tables 1–3, Notes 1–3, Figs. 1–13 and Refs. 1–10.

Source data

Source Data Fig. 2

Measured and simulated XRD, magnetization-temperature data and magnetization hysteresis loop of a CrVI6 flake.

Source Data Fig. 3

Kerr rotation angle data of CrIV6 measured at different temperatures.

Source Data Fig. 4

Magnetization hysteresis loop data from LLG simulation; optical Hall conductivity and Kerr rotation angle hysteresis loops from tight-binding calculations; snapshot spin configurations from LLG simulations in Vector Field File Format (.ovf).

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Li, X., Liu, C., Zhang, Y. et al. Topological Kerr effects in two-dimensional magnets with broken inversion symmetry. Nat. Phys. (2024). https://doi.org/10.1038/s41567-024-02465-5

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