Effect of magnetic field on Mott's variable-range hopping parameters in multiwall carbon nanotube mat

• Published in: Journal of physics. Condensed matter 2012-06, Vol.24 (24), p.245602-245602
• Main Authors: Arya, Ved Prakash, Prasad, V, Anil Kumar, P S
• Format: Article
• Language: English
• Subjects: Condensed matter; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic transport in multilayers, nanoscale materials and structures; Exact sciences and technology; Hopping (conductivity); Localization; Magnetic fields; Magnetic properties and materials; Magnetic properties of nanostructures; Materials science; Multi wall carbon nanotubes; Nanoscale materials and structures: fabrication and characterization; Nanotubes; Physics; Position (location); Three dimensional; Two dimensional
• ISSN: 0953-8984; 1361-648X
• DOI: 10.1088/0953-8984/24/24/245602

We report the temperature and magnetic field dependence of the conductivity of multiwall carbon nanotube mat in the temperature range 1.4-150 K and in magnetic fields up to 10 T. It is observed that charge transport in this system is governed by Mott's variable-range hopping of three-dimensional type in the higher temperature range and two-dimensional type in the lower temperature range. Mott's various parameters, such as localization length, hopping length, hopping energy and density of states at the Fermi level are deduced from the variable-range hopping fit. The resistance of the sample decreases with the magnetic field applied in the direction of tube axis of the nanotubes. The magnetic field gives rise to delocalization of states with the well-known consequence of a decrease in Mott's T0 parameter in variable-range hopping. The application of magnetic field lowers the crossover temperature at which three-dimensional variable-range hopping turns to two-dimensional variable-range hopping. The conductivity on the lower temperature side is governed by the weak localization giving rise to positive magnetoconductance. Finally, a magnetic field-temperature diagram is proposed showing different regions for different kinds of transport mechanism.