High-field magnetoresistance measurements on highly ordered graphite fibers

Abstract

High-field magnetoresistance measurements are shown to provide a sensitive characterization technique for graphite fibers with such a high degree of crystalline perfection that conventional characterization techniques are insensitive, including x-ray linewidth measurements, intensity of disorder-induced features in the Raman spectra, and lattice fringe images observed with high-resolution electron microscopy techniques. Specific results are reported for pristine and intercalated benzene-derived fibers heat treated to 2900, 3300, and 3500°C. The magnitude of the magnetoresistance ($\frac{\Delta \rho }{{\rho }_0}$) is sensitive to the degree of crystalline order, and the angular dependence of $\frac{\Delta \rho }{{\rho }_0}$ is sensitive to the cross-sectional structure arrangement, which is found to be faceted. Complementary characterization techniques, including Debye-Scherrer x-ray diffraction, resistivity, and first- and second-order Raman-spectroscopy measurements, are also applied to the same set of heat-treated and intercalated fibers. Of significance is the lowest resistivity air-stable intercalated fiber (∼7 μΩ cm) that has been achieved.