  We consider a hybrid structure formed by graphene and an insulating
antiferromagnet, separated by a dielectric of thickness up to $d\simeq 500
\,nm$. When uncoupled, both graphene and the antiferromagnetic surface host
their own polariton modes coupling the electromagnetic field with plasmons in
the case of graphene, and with magnons in the case of the antiferromagnet. We
show that the hybrid structure can host two new types of hybrid polariton
modes. First, a surface magnon-plasmon polariton whose dispersion is radically
changed by the carrier density of the graphene layer, including a change of
sign in the group velocity. Second, a surface plasmon-magnon polariton formed
as a linear superposition of graphene surface plasmon and the antiferromagnetic
bare magnon. This polariton has a dispersion with two branches, formed by the
anticrossing between the dispersive surface plasmon and the magnon. We discuss
the potential these new modes have for combining photons, magnons, and plasmons
to reach new functionalities.
