Topological Phases of MnA₂X₄ (A=Bi, Sb; X = Se, Te) under Magnetic Field

The electronic topology and the associated topological protected states of MnBi₂Te₄ (MBT) and related materials bring excellent opportunities for developing next-generation devices. In this work, using density functional theory (DFT), we have studied the electronic properties and topological phases of the MBT family of intrinsic magnetic topological insulators in the presence of an external magnetic field. Our calculations reveal that the topological phase of bulk MnB₂X₄ (B = Sb, Bi; X=Se, Te) depends on the direction of the magnetic spins and the chemistry. Notably, the antiferromagnetic ground state of MnSb₂Se₄ is a trivial insulator, but in the presence of a strong external field, it becomes a nodal point or nodal line Weyl semimetal. Surprisingly, the antiferromagnetic ground state of MnSb₂Te₄ (MST) is a non-trivial insulator. MST is type-II Weyl semimetal when the applied magnetic field is in the z-direction, but becomes insulating with an inverted band gap when the external magnetic field is in-plane. Additionally, we have investigated the evolution of the topological phases of MBT as a fraction of Bi atoms are substituted with Sb. This work indicated how to manipulate the topological phase and electronics phase of the MBT family. All these stoichiometric magnetic materials are excellent candidates for spintronics devices.