Transport phenomena in polymer-graphite composite materials

The dc electrical resistance of a polymer-graphite composite has been studied in high magnetic fields (<10 T) and at low temperatures for different concentrations of graphite. The resistivity of the composites for the high graphite concentrations was much greater (${>10}^{4}$) than that of pure graphite, and above a critical concentration of graphite a percolative behavior occurred. In addition to the ordinary positive magnetoresistance, an anomalous negative magnetoresistance at low fields was observed in the composite, but not in pure graphite. The data are explained in terms of contact resistances between adjacent graphite particles, with a special emphasis on the bidimensional aspect of graphite.