  Degeneracies in multilayer graphene, including spin, valley, and layer
degrees of freedom, are susceptible to Coulomb interactions and can result into
rich broken-symmetry states. In this work, we report a ferromagnetic state in
charge neutral ABCA-tetralayer graphene driven by proximity-induced spin-orbit
coupling from adjacent WSe2. The ferromagnetic state is further identified as a
Chern insulator with Chern number of 4, and its Hall resistance reaches 78% and
100% quantization of h/4e2 at zero and 0.4 tesla, respectively. Three
broken-symmetry insulating states, layer-antiferromagnet, Chern insulator and
layer-polarized insulator and their transitions can be continuously tuned by
the vertical displacement field. Remarkably, the magnetic order of the Chern
insulator can be switched by three knobs, including magnetic field, electrical
doping, and vertical displacement field.
