  Terahertz plasmons and magnetoplasmons propagating along electrically and
chemically doped graphene p-n junctions are investigated. It is shown that such
junctions support non-reciprocal magnetoplasmonic modes which get concentrated
at the middle of the junction in one direction and split away from the middle
of the junction in the other direction under the application of an external
static magnetic field. This phenomenon follows from the combined effects of
circular birefringence and carrier density non-uniformity. It can be exploited
for the realization of plasmonic isolators.
