The resistivity $\rho \mathrm{}\left(T\right)\mathrm{}$ and magnetoresistance (MR) $(\Delta \rho /\rho )$ of an entangled single-wall carbon-nanotube network are investigated. The temperature dependence of the resistivity shows a negative $d\rho /dT$ from $T=4.3\mathrm{}–300\hspace{0.5em}\mathrm{K}$ with no resistivity minimum, which is fitted well to the two-dimensional variable-range-hopping (VRH) $\left(\rho \mathrm{}\right(T)={\rho }_0\exp [{(T}_0{/T)}^{1/3}\left]\right)$ formula with $T_0=259.2\mathrm{}\hspace{0.5em}\mathrm{K}.$ The MR shows a negative $H^2$ behavior at low magnetic field. At $T<~3.8\hspace{0.5em}\mathrm{K}$ and high magnetic field, the negative MR becomes positive. The positive MR tends to be saturated for $H>\mathrm{}10\mathrm{}\hspace{0.5em}\mathrm{T}.$ The negative MR with a positive upturn can be decomposed into a positive contribution from the two-dimensional spin-dependent VRH and a negative contribution from the two-dimensional weak localization, with some contribution of the Ni impurities in the sample found with the transmission electron microscope and by energy dispersive spectrometer analysis.

• Received 22 April 1998

DOI:https://doi.org/10.1103/PhysRevB.58.16064