Magnetoresistance studies of polymer nanotube/wire pellets and single polymer nanotubes/wires

Abstract

Conductivity and magnetoresistance (MR) measurements on pellets of conducting polyaniline and polypyrrole nanotubes/wires are presented. A transition from small negative MR to large positive MR was measured below 60 K. The positive and negative MR has been discussed in terms of a wavefunction shrinkage effect and a quantum interference effect on hopping conduction. In addition, further studies show that the MR of single polymer nanotubes/wires is very small even at 2 K (MR<5% at 10 T) compared with that of the pellets (40%–100% at 10 T), and no evident and stable negative MR is observed above 50 K. The results indicate that the MR in the bulk pellet samples made of polymer nanotubes/wires is dominated by a random network of inter-fibril contacts.

Synthesis, electrical and magnetotransport properties of polypyrrole-MWCNT nanocomposite

“…Therefore, the competition of these two (wave function shrinkage and forward interference) effects is responsible for change in the sign and magnitude of magnetoconductivity of the PPy-MWCNT composites. In addition, we note that the magnitude of the positive magnetoconductance is much smaller than that of the negative magnetoconductance, which may reflect that the quantum interference effect is much weaker than the wave function shrinkage effect of the samples whose localization length is comparatively small [58]. Therefore, the predominance of wave function shrinkage effect over forward interference effect is indicated by the observed decrement of magnetoconductivity of the investigated samples.…”

A Review on Electronic Transport Properties of Individual Conducting Polymer Nanotubes and Nanowires

“…9a), and MR ~ 90% (3K) for the polyaniline nanotubes' pellet (Fig. 9b, Long et al, 2006a). In addition, when the temperature increases, the magnetoresistance of the single nanotube/wire becomes smaller and close to zero.…”

“…Whereas highly conductive polyacetylene films usually show a negative magnetoresistance at low temperatures, which is mainly attributed to the weak localization effects (Menon et al, 1998;Kozub et al, 2002). Up to date, only a few papers have reported the magnetoresistance of polymer nanotubes/wires (Kim et al, 1999;Kozub et al, 2002;Long et al, 2006aLong et al, , 2006cLong et al, & 2009c. Fig.…”

“…The magnetoresistance curves for different temperatures of (a) a single polyaniline nanotube and (b) a pellet of polyaniline nanotubes. (Long et al, 2006a) Long et al reported that the magnetoresistance of single polyaniline nanotube and single PEDOT nanowire is positive below 10 K and increases as H 2 up to 9 T. Typically, a positive magnetoresistance is expected for hopping conduction, because applying a magnetic field results in a contraction of the overlap of the localized state wavefunctions and thus an increase in the average hopping length. This corresponds to a positive magnetoresistance at sufficiently low temperatures.…”

“…The reason for this weak magnetoresistance effect in individual polymer nanotube/wire is possibly due to the elimination of inter-nanotube/wire contacts, small size and, relatively high conducitivity of individual polymer nanotube/wire. Long et al, 2006a) …”