Negative to Positive Magnetoresistance transition in Functionalization of Carbon nanotube and Polyaniline Composite

Electrical resistivity and magnetoresistance(MR) in polyaniline(PANI) with carbon nanotube(CNT) and functionalized carbon nanotube(fCNT) composites have been studied for different weight percentage down to the temperature 4.2K and up to magnetic field 5T. Resistivity increases significantly in composite at low temperature due to functionalization of CNT compare to only CNT. Interestingly transition from negative to positive magnetoresistance has been observed for 10wt% of composite as the effect of disorder is more in fCNT/PANI. This result depicts that the MR has strong dependency on disorder in the composite system. The transition of MR has been explained in the basis of polaron-bipolaron model. The long range Coulomb interaction between two polarons screened by disorder in the composite of fCNT/PANI, increases the effective on-site Coulomb repulsion energy to form bipolaron which leads to change the sign of MR from negative to positive.Comment: 5 pages, 8 figures; typos adde

Tuning spin one channel to exotic orbital two-channel Kondo effect in ferrimagnetic composites of LaNiO3 and CoFe2O4

We report the tuning from spin one channel (1CK) to orbital two-channel Kondo (2CK) effect by varying CoFe2O4 (CFO) content in the composites with LaNiO3 (LNO) along with the presence of ferrimagnetism. Although there is no signature of resistivity upturn in case of pure LNO, all the composites exhibit a distinct upturn in the temperature range 30-80 K. For composite with lower percentage of CFO (10 %), the electron spin plays the key role in the emergence of resistivity upturn which is affected by external magnetic field. On the other hand, when the CFO content is increased (15%), the upturn shows strong robustness against high magnetic field (14 T) and a crossover in temperature variation from lnT to T^1/2 at the Kondo temperature, indicating the appearance of orbital 2CK effect. The orbital 2CK effect is originated due to the scattering of conduction electrons from the structural two-level systems which is created at the interfaces between the two phases (LNO and CFO) of different crystal structures as well as inside the crystal planes. A negative magnetoresistance (MR) is observed at low temperature (< 30 K) for composites containing both lower (10 %) and higher percentage (15 %) of CFO. We have analyzed the negative MR using Khosla and Fisher semi-empirical model based on spin dependent scattering of conduction electrons from localized spins.Comment: 14 pages including supplementary materials and 12 figure

Effect of chemical functionalization on charge transport of multiwall carbon nanotube

We have studied the effect of chemical functionalization on charge transport property of multiwall carbon nanotube (MWNT) down to the temperature 4.2 K and magnetic field up to 5 T. The resistivity ratio (rho(r) = rho(T)/rho(100 K)]) increases with the increment of degree of functionalization at low temperature as the effect of inclusion of disorder in the samples. The variation of resistivity with temperature has been explained by 3D variable range hopping model and Coulomb gap Efros-Shklovskii model, and the result shows that higher degree of functionalization enhances the disorder induced electron-electron interaction. For all the measured temperature and degree of functionalization, MWNTs show negative magnetoresistance. Negative magnetoresistance has been explained by 3D weak localization model

Tuning magnetoresistance and electrical resistivity by enhancing localization length in polyaniline and carbon nanotube composites

We report low temperature electrical resistivity and magnetoresistance (MR) measurements of conducting polyaniline (PANI) and multiwalled-carbon nanotube (MWCNT) composites. We have used an in-situ oxidative polymerization method to synthesize hydrochloric acid-doped PANI composites with MWCNT weight percentages of 0, 5, 10 and 15. The temperature dependence of resistivity is studied from room temperature to 4.2K and analysed by a Mott variable range hopping (VRH) model. The resistivity increases from 1.1 x 10 -3 m at 300K to 65.75 m at 4.2 K, almost four orders of the magnitude change with temperature for pure PANI. Whereas the PANI composite with 15% MWCNTs shows less variation from 4.6x10 -4 to 3.5x10 -2 m. The huge change in resistivity is due to the localization of charge carriers in the presence of disorder. At 4.2K MR shows transition from positive to negative with higher MWCNT loading. Samples with 5 and 10% MWCNTs show positive MR, whereas the 15% MWCNT loaded sample shows negative MR. The positive and negative MR are discussed in terms of the wave function shrinkage effect and quantum interference effect on VRH conduction

Evaluation of Treatment Techniques for Utilising Acid Mine Water in Agriculture

Acid mine water was treated with fly ash zeolite (FAZ), followed by different active chemicals to know its suitability for crops. Acid mine drainage (AMD) was obtained from Gorbi abandoned opencast mines of Singrauli, Northern Coalfields (NCL), India. The AMD was treated with 20 g/l dosing of fly ash zeolite, followed by different precipitating chemicals, using different doses of Ba(OH)2, BaCO3 and Ca(OH)2. The doses of 1.0 g/l Ba(OH)2, 1.5 g/l BaCO3 and 0.5 g/l Ca(OH)2 were used. The treatment with FAZ, followed by 1.0 g/l of Ba(OH)2, converted the water quality of AMD to the permissible level. The electrical conductivity (EC), percentage of sodium and metals found at the permissible level indicated the suitability of mine water for agriculture use. AMD treated directly with 1.0 g/l of Ba(OH)2 was found unsuitable for agriculture use. The treatment with FAZ and followed by BaCO3 (1.5 g/l) explained that the water quality was not at the permissible level and unsuitable for agriculture use. AMD treated directly with 1.5 g/l of BaCO3 was also found unsuitable for agriculture. The treatment with FAZ, and followed by 0.5 g/l dosing of Ca(OH)2, also showed water quality not at the permissible level. The conductivity, total salt content (as TDS) and sulfate values increased or decreased minimally, and there was an increase in the concentrations of total hardness and calcium hardness in the final treated mine water. The direct dosing with 0.5 g/l of Ca(OH)2 made AMD unsuitable for agriculture use. Treatment with 20 g/l FAZ followed by 1.0 g/l of Ba(OH)2 produced the treated AMD suitable for agriculture use

Dynamics of Spin Crossover Molecular Complexes

We review the current understanding of the time scale and mechanisms associated with the change in spin state in transition metal-based spin crossover (SCO) molecular complexes. Most time resolved experiments, performed by optical techniques, rely on the intrinsic light-induced switching properties of this class of materials. The optically driven spin state transition can be mediated by a rich interplay of complexities including intermediate states in the spin state transition process, as well as intermolecular interactions, temperature, and strain. We emphasize here that the size reduction down to the nanoscale is essential for designing SCO systems that switch quickly as well as possibly retaining the memory of the light-driven state. We argue that SCO nano-sized systems are the key to device applications where the “write” speed is an important criterion