  Magnetic topological materials with coexisting magnetism and non-trivial 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 and a square
hysteresis loop near zero magnetic field in all these devices. Upon magnetic
field training, a large exchange bias effect is observed in odd but not in even
septuple layer (SL) devices. Our theoretical calculations interpret this
even-odd layer-dependent exchange bias effect as a consequence of 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.
