  Charge transfer plays a key role at the interfaces of heterostructures, which
can affect electronic structures and ultimately the physical properties of the
materials. However, charge transfer is difficult to manipulate externally once
the interface formed. Here, we report electrically tunable charge transfer in
Fe3GeTe2/Cr2Ge2Te6/Fe3GeTe2 all-magnetic van der Waals heterostructures, which
can be exploited to selectively modify the magnetic properties of the top or
bottom Fe3GeTe2 electrodes. The directional charge transfer from metallic
Fe3GeTe2 to semiconducting Cr2Ge2Te6 remarkably modifies magnetic anisotropy
energy of Fe3GeTe2, leading to the dramatically suppressed coercivity. The
electrically selective control of ferromagnets demonstrated in this study could
stimulate the development of spintronic devices based on van der Waals magnets.
