  The differences between spin relaxation in graphene and in other materials
are discussed. For relaxation by scattering processes, the Elliot-Yafet
mechanism, the relation between the spin and the momentum scattering times
acquires a dependence on the carrier density, which is independent of the
scattering mechanism and the relation between mobility and carrier
concentration. This dependence puts severe restrictions on the origin of the
spin relaxation in graphene. The density dependence of the spin relaxation
allows us to distinguish between ordinary impurities and defects which modify
locally the spin-orbit interaction.
