  The quantum Hall and longitudinal resistances in multi-terminal ferromagnetic
graphene p-n junctions under a perpendicular magnetic field are investigated.
In the Hall measurements, the transverse contacts are assumed to be located at
p-n interface to avoid the mixing of edge states at the interface and the
resulting quantized resistances are then topologically protected. According to
the charge carrier type, the resistances in four-terminal p-n junction can be
naturally divided into nine different regimes. The symmetric Hall and
longitudinal resistances are observed, with lots of new robust quantum plateaus
revealed due to the competition between spin splitting and local potentials.
