Hopping Conductivity Spectroscopy of Carbon Nanocluster Materials

Procedure of the hopping conductivity ρ∼exp[(T 0/T)α] and magnetoresistance data analysis, which takes into account spin‐polarization contribution and allows finding correct parameters of the localized states, is suggested. This general approach was checked for the nanocluster material synthesized under high (up to 8 GPa) pressure of carbon SWNT mat containing 5% Ni. Experiments for the temperature/field domain 1.8–300 K/70 kOe have confirmed theoretical results, including universal magnetoresistance scaling ln[ρ(H)/ρ(0)] = (T 0/T)α F(H/T). It is found that the interaction with magnetic impurities renormalizes the electron magnetic moment: μ≈0.7μB. In conclusion, a possible way of creation of the carbon nanocluster material with colossal magnetoresistance is suggested.