Hopping conduction and magnetoresistance of C2N -based nanomaterials synthesized under high pressure

Abstract

The hopping conductivity and magnetoresistance of fullerene C2N samples treated under high pressure at high temperatures were studied in detail. It was revealed that an increase in the synthesis temperature in the range 800 < Tsyn < 1000°C under a pressure psyn = 8 GPa induces a metal-insulator transition in fullerene C2N samples, which is accompanied by a significant (nine orders of magnitude at room temperature) decrease in the electrical resistivity. In the intermediate range 900 < Tsyn < 1000°C, the C2N samples have Mott hopping conductivity and the exponent α in the Mott law ρ(T) ∼ exp[T0/T)α] depends on the synthesis temperature and varies within the range 1/4 < α < 1/2. In the cases α = 1/3 and 1/4, the hopping conduction was found to occur over the anomalously wide temperature range 4.2 < T < 300 K. It was established that an adequate description of the temperature dependence of the magnetoresistance in the C2N samples requires the inclusion of the joint effect of the spin-polarization mechanism and the wave-function shrinkage. A model is discussed relating the change in the character of the hopping conduction in fullerenes to physical nanoscale inhomogeneities.