  Spin-polarized two-dimensional materials with large and tunable
spin-splitting energy promise the field of 2D spintronics. While graphene has
been a canonical 2D material, its spin properties and tunability are limited.
Here, we demonstrate the emergence of robust spin-polarization in graphene with
large and tunable spin-splitting energy of up to 132 meV at zero applied
magnetic fields. The spin polarization is induced through a magnetic exchange
interaction between graphene and the underlying ferrimagnetic oxide insulating
layer, Tm3Fe5O12, as confirmed by its X-ray magnetic circular dichroism. The
spin-splitting energies are directly measured and visualized by the shift in
their landau fan diagram mapped by analyzing the measured subnikov-de-Haas
oscillations as a function of applied electric fields, showing consistent fit
with our first-principles and machine learning calculations. Further, the
observed spin-splitting energies can be tuned over a broad range between 98 and
166 meV by cooling fields. Our methods and results are applicable to other
two-dimensional (magnetic) materials and heterostructures, and offer great
potential for developing next-generation spin logic and memory devices.
