Magnetic Imaging of Antiferromagnetic Domain Walls in Magnetic Topological Materials*

The study and control of domains and domain walls (DW) in topological materials is crucial to understanding and utilizing their exotic phenomena, such as axion insulator and quantum anomalous Hall states^1-3. Domains of alternating sign in these materials cancel out these states and thus it is imperative to understand how these antiferromagnetic (AFM) domains form and can be controlled. Despite many efforts, it has been challenging to directly visualize AFM domains or DWs with nanoscale resolution in general, especially in magnetic field. Here, we report the magnetic imaging of domains and DWs in several uniaxial AFMs, the topological insulator MnBi₂Te₄ family⁴ and the topological semimetal EuMnBi₂⁵, using cryogenic magnetic force microscopy (MFM)⁶. Our MFM results reveal higher magnetic susceptibility or net moments inside the DWs than in domains. DWs in these AFMs form randomly with strong thermal and magnetic field dependences.

¹ Otrokov, M. M. et al. PRL. 122, 107202 (2019).
² Deng, Y. et al. arXiv:1904.11468 (2019).
³ Liu, C. et al. arXiv:1905.00715 (2019).
⁴ Yan, J., -Q.. et al. PRB 100, 104409 (2019).
⁵ Masuda, H. et al. Sci. Adv. 2, 1–7 (2016).
⁶ Sass, P. M. et al. arXiv:1910.06488 (2019).