Magnetoresistance, Electrical Conductivity, and Hall Effect of Glassy Carbon

摘要

These properties of glassy carbon heat treated for three hours between 1200 and 2700 exp 0 C were measured from 3 to 300 exp 0 K in magnetic fields up to 5 tesla. The magnetoresistance was generally negative and saturated with reciprocal temperature, but still increased as a function of magnetic field. The maximum negative magnetoresistance measured was 2.2% for 2700 exp 0 C material. Several models based on the negative magnetoresistance being proportional to the square of the magnetic moment were attempted; the best fit was obtained for the simplest model combining Curie and Pauli paramagnetism for heat treatments above 1600 exp 0 C. Positive magnetoresistance was found only in less than 1600 exp 0 C treated glassy carbon. The electrical conductivity, of the order of 200 (ohm-cm) exp -1 at room temperature, can be empirically written as sigma = A + Bexp(-CT/sup -1/4) - DT/sup -1/2. The Hall coefficient was independent of magnetic field, insensitive to temperature, but was a strong function of heat treatment temperature, crossing over from negative to positive at about 1700 exp 0 C and ranging from -0.048 to 0.126 cm exp 3 /coul. The idea of one-dimensional filaments in glassy carbon suggested by the electrical conductivity is compatible with the present consensus view of the microstructure. (ERA citation 08:051728)