  We present a joint experiment-theory study on the role of fluorine adatoms in
spin and momentum scattering of charge carriers in dilute fluorinated graphene
and bilayer graphene. The experimental spin-flip and momentum scattering rates
and their dependence on the density of fluorine and carrier doping are obtained
through weak localization and conductivity measurements, respectively, and
suggest the role of fluorine as resonant magnetic impurities. For the estimated
fluorine concentration of a few 100 ppm, the observed spin lifetimes are in the
range of 1-10\,ps. Theoretically, we established tight-binding electronic
structures of fluorinated graphene and bilayer graphene by fitting to density
functional supercell calculations and performed a comprehensive analysis of the
spin-flip and momentum scattering rates within the same devices, aiming to
develop a consistent description of both scattering channels. We find that
resonant scattering in graphene is very sensitive to the precise position of
the resonance level, as well as to the magnitude of the exchange coupling
between itinerant carriers and localized spins. The experimental data point to
the presence of weak spin-flip scatterers that, at the same time, relax the
electron momentum strongly, nearly preserving the electron-hole symmetry. Such
scatterers would exhibit resonance energies much closer to the neutrality point
than what density functional theory predicts in the dilute limit. The inclusion
of a magnetic moment on fluorine adatoms allowed us to qualitatively capture
the carrier density dependence of the experimental rates but predicts a greater
(weaker) spin (momentum) relaxation rate than the measurements. We discuss
possible scenarios that may be responsible for the discrepancies. Our
systematic study exposes the complexities involved in accurately capturing the
behavior of adatoms on graphene.
