Relations between degree of graphitization and galvanomagnetic properties of pyrolytic carbons and cokes Original Research Article

The relations between degree of graphitization (P1) and galvanomagnetic properties [maximum magnetoresistance (Δϱϱ)max, Hall coefficient RH and electrical resistivity ϱ] were investigated for pyrolytic carbons and cokes treated at different temperatures. With increasing heat treatment temperature, sign changes from negative to positive in (Δϱϱ)max and from positive to negative in RH took place at P1 ~0.5, irrespective of the specimen. Such a phenomenon implies that electronic conduction in these specimens changes from a one-carrier type to a two-carrier type when the three-dimensional graphitic stacking order becomes predominant in the volume fraction. Galvanomagnetic parameters as a function of P1 depend considerably on the texture of the carbon materials. However, a positive value of (Δϱϱ)max was observed as a unique function of the crystallite size of the hexagonal carbon layers (La), independent of the specimen. The absolute value of RH was strongly affected by the degree of orientation of the hexagonal layers.