Electric carrier concentration in graphite: Dependence of electrical resistivity and magnetoresistance on defect concentration

We investigate the dependence of the electrical resistivity and magnetoresistance of single crystalline micrometer-sized graphite samples of a few tens of nanometers thick on the defect concentration produced by irradiation at low fluences. We show that the carrier density of graphite n is extremely sensitive to the induced defects for concentrations as low as similar to 0.1 ppm and follows n similar to 1/R(V)(2) with R(V) the distance between defects in the graphene plane. These and Shubnikov-de Haas oscillations results indicate that at least a relevant part of the carrier densities measured in graphite is not intrinsic.