Even-Odd Layer-Dependent Exchange Bias Effect in MnBi₂Te₄ Chern Insulator Devices

Magnetic topological materials with coexisting magnetism and nontrivial band structures exhibit many novel quantum phenomena, including the quantum anomalous Hall effect, the axion insulator state, and the Weyl semimetal phase. As a stoichiometric layered antiferromagnetic topological insulator, thin films of MnBi₂Te₄ show fascinating even-odd layer-dependent physics. In this work, we fabricate a series of thin-flake MnBi₂Te₄ devices using stencil masks and observe the Chern insulator state at high magnetic fields. Upon magnetic field training, a large exchange bias effect is observed in odd but not in even septuple layer (SL) devices. Through theoretical calculations, we attribute the even-odd layer-dependent exchange bias effect to the contrasting surface and bulk magnetic properties of MnBi₂Te₄ devices. Our findings reveal the microscopic magnetic configuration of MnBi₂Te₄ thin flakes and highlight the challenges in replicating the zero magnetic field quantum anomalous Hall effect in odd SL MnBi₂Te₄ devices.