  We present analytical expressions for the current-current correlation
function in graphene for arbitrary frequency, wave vector, doping, and band gap
induced by a mass term. In the static limit we analyze the Landau (orbital) and
Pauli magnetization, as well as the Lindhard correction which describes Friedel
and RKKY oscillations. In the nonrelativistic limit we compare our results with
the situation of the usual two-dimensional electron gas (2DEG). We find that
the orbital magnetic susceptibility (OMS) in gapped graphene is smeared out on
an energy scale given by the inverse mass. The nonrelativistic limit of the
plasmon dispersion and the Lindhard function reproduces the results of the
2DEG. The same conclusion is true for the Pauli part of the susceptibility. The
peculiar band structure of gapped graphene leads to pseudospin paramagnetism
and thus to a special form of the OMS.
