Effect of impurities on the electric conductivity and magnetoresistance in carbon nanotubes

Temperature and magnetic field dependences of electric resistivity of carbon nanotubes both of the as-received material and of material chemically cleaned of impurities have been investigated. It has been shown that the temperature dependence of the electric resistivity of the studied powders of carbon nanotubes may be well described in the framework of 3D hopping conductivity with a variable hop length in a wide temperature range (5–250 K for the as-received nanotubes and 5–189 K for nanotubes after chemical treatment). Magnetoresistance of the as-received and chemically treated carbon nanotubes at temperatures of 5, 77, and 250 K has been shown to decrease with increasing magnetic field intensity.