The electrical transport properties of graphene doped with gadolinium (Gd) adatoms have been measured. The gate voltage dependence of the conductivity shows that Gd produces n doping of graphene. The charged Gd ions act as scattering centers, lowering the sample mobility for both electrons and holes. The doping efficiency of Gd at 77 K reproduces theoretical predictions (0.7 electron per Gd adatom). On raising the sample temperature to even 150 K, clustering effects are observed and substantially modify the transport
