We report a systematic study on charge transport properties of thermally reduced graphene
oxide (rGO) layers, from room temperature to 2 K and in presence of magnetic fields up to
7 T. The most conductive rGO sheets follow different transport regimes: at room temperature
they show an Arrhenius-like behavior. At lower temperature they exhibits a thermally
activated behavior with resistance R following a R = R0exp(T0/T)p law with p = 1/3, consistently
with 2D Mott Variable Range Hopping (VRH) transport mechanism. Below a given
temperature Tc, we observe a crossover from VHR to another regime, probably due to a
shortening of the characteristic lengths of the disordered 2D system. The temperature Tc
depends on the reduction grade of the rGO. Magnetoresistance DR/R of our rGO films shows
as well a crossover between positive and negative and below liquid He temperature DR/R
reaches values larger than 60%, surprisingly high for a \u2013 nominally \u2013 non magnetic
material
