  The magnetic proximity effect can induce a spin dependent exchange shift in
the band structure of graphene. This produces a magnetization and a spin
polarization of the electron/hole carriers in this material, paving the way for
its use as an active component in spintronics devices. The electrostatic
control of this spin polarization in graphene has however never been
demonstrated so far. We show that interfacing graphene with the van der Waals
antiferromagnet CrSBr results in an unconventional manifestation of the quantum
Hall effect, which can be attributed to the presence of counterflowing
spin-polarized edge channels originating from the spin-dependent exchange shift
in graphene. We extract an exchange shift ranging from 27 to 32 meV, and show
that it also produces an electrostatically tunable spin polarization of the
electron/hole carriers in graphene ranging from -50 % to +69 % in the absence
of a magnetic field. This proof of principle provides a starting point for the
use of graphene as an electrostatically tunable source of spin current and
could allow this system to generate a large magnetoresistance in gate tunable
spin valve devices.
