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MnBi₆Te₁₀ belongs to the antiferromagnetic topological insulator (TI) family MnBi₂Te₄(Bi₂Te₃)_n with n = 2. It can be constructed by intercalating two consecutive Bi₂Te₃ quintuple layers (QL) between adjacent septuple layers (SL) of MnBi₂Te₄. In previous studies, Bi₂Te₃ was considered as a nonmagnetic spacer, which reduces the antiferromagnetic exchange coupling between SLs [1,2]. Previous work demonstrated that the ground states of MnBi₂Te₄(Bi₂Te₃)_n become ferromagnetic for n > 2, while it remain as an A-type antiferromagnet with T_N ~ 12K in MnBi₆Te₁₀ (n=2) [1, 3-6]. There exists an extra step feature near zero field in the magnetic hysteresis loop of single crystal MnBi₆Te₁₀ below 6K, which cannot be explained by the conventional bulk spin flip transition [3]. In this talk, we will show evidence of an additional ferromagnetic order in MnBi₆Te₁₀ below 6K. Domains of this ferromagnetic order were visualized using our homemade cryogenic magnetic force microscope. Our results indicate that this “hidden” ferromagnetic order originates from the Bi₂Te₃ QLs, presumably due to the presence of Mn_Bi antisite defects.

1.Hu et al., Sci. Adv. 2020; 6 : eaba4275

2.Adv. Sci.2023,10, 2203239

3.PHYSICAL REVIEW MATERIALS4, 054202 (2020)

4.npj Quantum Mater. 5, 54 (2020).

5.PHYSICAL REVIEW B 100, 155144 (2019)

6.PHYSICAL REVIEW B 102, 035144 (2020)