  We study the collective charge excitations (plasmons) in spin polarized
graphene, and derive explicit expressions for their dispersion in the undamped
regime. From this, we are able to calculate the critical wave vector beyond
which the plasmon enters the electron-hole continuum, its quality factor
decreasing sharply. We find that the value of the critical wave vector is
strongly spin polarization-dependent, in a way that has no analog in ordinary
two-dimensional electron gases. The origin of this effect is in the coupling
between the plasmon and the inter-band electron-hole pairs of the minority spin
carriers. We show that the effect is robust with respect to the inclusion of
disorder and we suggest that it can be exploited to experimentally determine
the spin polarization of graphene.
