Competing magnetic interactions in MnBi₄Te₇

Intrinsic magnetic topological insulators (TIs) MnBi_2nTe_3n+1 provides a promising material platform to realize exotic topological quantum states such as high temperature quantum anomalous Hall insulator and axion insulator. Besides non-trivial band topology, magnetism is another necessary ingredient to realize these quantum states[1-5]. In this talk, we will show a ferromagnetic (FM) phase with T_C~14 K can be realized with a small concentration substitution of Sb for Bi in Mn(Bi,Sb)₄Te₇. We have also observed strong competition between interlayer FM and antiferromagnetic (AFM) coupling. In pristine MnBi₄Te₇, we observed an AFM transition at 13.1 K, followed by a FM transition at 8.9 K, consistent with previous reports[6]. However, in a 60%Sb doped sample, we find a FM phase switches to an AFM phase at ~4.4K. These complex magnetic transitions offer rich opportunities to observe how the topological phases evolve with magnetism. We will also discuss the origin of the AFM and FM competition in this material system.
1.Zhang et al.,PRL,122,206401(2019)
2.Li et al.,Sci. Adv.5,eaaw5685(2019)
3.Otrokov et al.,Nature 576,416(2019)
4.Hu et al.,Nat. Commun.11,97(2020)
5.Yan et al.,PRM 4,054202(2020)
6.Vidal et al.,PRX 9,041065(2019)