  We calculate the dispersion equations for magnetoplasmons in a single layer,
a pair of parallel layers, a graphite bilayer and a superlattice of graphene
layers in a perpendicular magnetic field. We demonstrate the feasibility of a
drift-induced instability of magnetoplasmons. The magnetoplasmon instability in
a superlattice is enhanced compared to a single graphene layer. The energies of
the unstable magnetoplasmons could be in the terahertz (THz) part of the
electromagnetic spectrum. The enhanced instability makes superlattice graphene
a potential source of THz radiation.
