Magnetoresistance of an entangled single-wall carbon-nanotube network

Abstract

The resistivity $\ensuremath{\rho}(T)$ and magnetoresistance (MR) $(\ensuremath{\Delta}\ensuremath{\rho}/\ensuremath{\rho})$ of an entangled single-wall carbon-nanotube network are investigated. The temperature dependence of the resistivity shows a negative $d\ensuremath{\rho}/dT$ from $T=4.3--300 \mathrm{K}$ with no resistivity minimum, which is fitted well to the two-dimensional variable-range-hopping (VRH) $(\ensuremath{\rho}(T)={\ensuremath{\rho}}_{0}\mathrm{exp}[{(T}_{0}{/T)}^{1/3}])$ formula with ${T}_{0}=259.2 \mathrm{K}.$ The MR shows a negative ${H}^{2}$ behavior at low magnetic field. At $Tl~3.8 \mathrm{K}$ and high magnetic field, the negative MR becomes positive. The positive MR tends to be saturated for $Hg10 \mathrm{T}.$ 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.