  Igniting interface magnetic ordering of magnetic topological insulators by
building a van der Waals heterostructure can help to reveal novel quantum
states and design functional devices. Here, we observe an interesting exchange
bias effect, indicating successful interfacial magnetic coupling, in
CrI3/MnBi2Te4 ferromagnetic insulator/antiferromagnetic topological insulator
(FMI/AFM-TI) heterostructure devices. The devices originally exhibit a negative
exchange bias field, which decays with increasing temperature and is unaffected
by the back-gate voltage. When we change the device configuration to be
half-covered by CrI3, the exchange bias becomes positive with a very large
exchange bias field exceeding 300 mT. Such sensitive manipulation is explained
by the competition between the FM and AFM coupling at the interface of CrI3 and
MnBi2Te4, pointing to coverage-dependent interfacial magnetic interactions. Our
work will facilitate the development of topological and antiferromagnetic
devices.
