Metamagnetism of few-layer topological antiferromagnets

MnBi$_2$Te$_4$ (MBT) is a promising antiferromagnetic topological insulator whose films provide access to novel and technologically important phases, including quantum anomalous Hall states axion insulators. MBT device behavior expected be sensitive the various collinear non-collinear magnetic phases that are accessible in applied fields. Here, we use classical Monte Carlo simulations electronic structure models calculate ground state phase diagram as well optical properties for few layer with thicknesses up six septuple layers. Using interaction parameters appropriate MBT, find it possible prepare variety of different stacking sequences, some which have sufficient symmetry disallow non-reciprocal response transport coefficients. Other arrangements do yield large Faraday Kerr signals, even when Chern number vanishes.