Coupling of topology and magnetic ordering in Axion Insulator and Weyl semimetal phases of MnB₂X₄ (A = Sb, Bi; X = Se, Te)

Axion insulators have been the subject of enormous interest because these materials can carry spin-polarized edge states even in the absence of an external magnetic field. Our calculations reveal that the ferromagnetic phase of bulk MnB₂X₄ (B = Sb, Bi; X=Se, Te) is either a nodal line or Weyl semimetal, depending on the direction of the spins. In the ground state antiferromagnetic phase, they instead become antiferromagnetic topological insulators, a type of Axion insulator. The intrinsic time reversal symmetry breaking at the surface of MnB₂X₄ removes the Dirac cone feature seen in typical topological insulators, allowing the observation of the half-integer quantum anomalous Hall effect (QAHE). We find that the direction of magnetic moment and the magnetic properties depend on the choice of chalcogenide, while the choice of B atom modifies the amount of band inversion. These stoichiometric magnetic materials are excellent candidates for spintronic devices. We also, investigated vibrational properties of all these materials to understand the how chemical substitutions effect the optical properties of the materials.