  The exchange bias (EB) effect is known as a fundamentally and technologically
important magnetic property of a magnetic bilayer film. It is manifested as a
horizontal shift in a magnetic hysteresis loop of a film subject to cooling in
the presence of a magnetic field. The EB effect in van der Waals (vdW)
heterostructures offers a novel approach for tuning the magnetic properties of
the newly discovered single-layer magnets, as well as adds a new impetus to
magnetic vdW heterostructures. Indeed, intriguing EB effects have recently been
reported in a variety of low-dimensional vdW magnetic systems ranging from a
weakly interlayer-coupled vdW magnet (e.g., Fe3GeTe2) to a bilayer composed of
two different magnetic vdW materials (e.g., Fe3GeTe2/CrCl3, Fe3GeTe2/FePS3,
Fe3GeTe2/MnPS3), to bilayers of two different vdW defective magnets (e.g.,
VSe2/MoS2), or to metallic ferromagnet/vdW defective magnet interfaces (e.g.,
Fe/MoS2). Despite their huge potential in spintronic device applications, the
physical origins of the observed EB effects have remained elusive to
researchers. We present here a critical review of the EB effect and associated
phenomena such as magnetic proximity (MP) in various vdW heterostructure
systems and propose approaches to addressing some of the emerging fundamental
questions.
