Charge transport and magnetic properties of coaxial composite fibrils of polypyrrole/multiwall carbon nanotubes at low temperature

We report the low temperature electrical and magnetic properties of polypyrrole (PPy)/multiwall carbon nanotube (MWNT) coaxial composite fibrils synthesized by the electro-polymerization method. The iron-filled MWNTs were first grown by chemical vapor deposition of a mixture of liquid phase organic compound and ferrocene by the one step method. Then the PPy/MWNT fibrils were prepared by the electrochemical polymerization process. Electron microscopy studies reveal that PPy coating on the surface of nanotube is quite uniform throughout the length. The temperature dependent electrical resistivity and magnetization measurements were done from room temperature down to 5 and 10 K, respectively. The room temperature resistivity (ρ) of PPy/MWNT composite fibril sample is ∼3.8 Ωcm with resistivity ratio [R5 K/R300 K] of ∼300, and the analysis of ρ(T) in terms of reduced activation energy shows that resistivity lies in the insulating regime below 40 K. The resistivity varies according to three dimensional variable range hopping mechanism at low temperature. The magnetization versus applied field (M–H loop) data up to a field of 20 kOe are presented, displaying ferromagnetic behavior at all temperatures with enhanced coercivities ∼680 and 1870 Oe at room temperature and 10 K, respectively. The observation of enhanced coercivity is due to significant dipolar interaction among encapsulated iron nanoparticles, and their shape anisotropy contribution as well.

► Multifunctional polypyrrole/MWNTs coaxial composite fibrils are fabricated via the two step process.
► Polypyrrole coaxially attached onto MWNT surface to form novel structure of fibrils.
► Resistivity ratio [R5 K/R300 K] for fibril is ∼300 whereas for MWNT it is less than 2.
► Fibrils follow 3D VRH model whereas MWNTs display metallic behavior.
► Hc of fibrils ∼680 Oe is more than MWNTs ∼488 Oe at 300 K due to dipolar interaction and shape anisotropy.