Origin of the negative magneto-resistance in carbons and its relation with the degree of graphitization

University of Electro-Communications, 14, hojimacho, Chofu-shi, Tokio, Japon.

Abstract

Negative magneto-resistance in poorly graphitized carbons can be observed at liquid nitrogen temperature or even higher. This peculiar phenomenon is studied with pyrolytic carbon (P.G.) as a model material. It is concluded that the negative magneto-resistance is caused by a change of the carrier concentration induced by the magnetic field. The incentive for the change of the carrier concentration in poorly graphitized materials, which is not only quite unusual among all substances but also is hardly observed in graphite Loo, lies in the two-dimensionality of the electronic structure of the materials. Theoretical curves calculated on this conjecture (almost two-dimensional model) reproduce the experimental results fairly well.