Intrinsic ferromagnetic and antiferromagnetic axion insulators in van der Waals materials MnX2B2T6 family

Abstract

The MnBi2Te4 family has attracted significant attention due to its rich topological states such as the quantum anomalous Hall (QAH) insulator state, the axion insulator state, and the magnetic Weyl semimetal state. Nevertheless, the intrinsic antiferromagnetic (AFM) interlayer coupling in MnBi2Te4 partly hinders the realization of the "higherature"QAH effect. Here, by using first-principles electronic structure calculations, we design a new class of materials MnX2B2T6 (X=Ge, Sn, or Pb; B=Sb or Bi; T=Se or Te) based on the X2B2T5 structures rather than the Bi2Te3 family. We find that each septuple-layer MnB2T4 is sandwiched by two [XT] layers, which may turn the AFM interlayer coupling into a ferromagnetic (FM) coupling. The calculations specifically demonstrate that MnGe2Sb2Te6, MnGe2Bi2Te6, and MnPb2Bi2Te6 are FM axion insulators, while MnGe2Sb2Se6, MnGe2Bi2Se6, MnSn2Sb2Te6, and MnSn2Bi2Te6 are A-type AFM axion insulators. These seven materials all have an out-of-plane easy axis of magnetization. The MnX2B2T6 family thus offers a promising platform beyond the MnBi2Te4 family for the realization of the quantized magnetoelectric effect and "higherature"QAH effect in future experiments.