FIELD DEPENDENCE OF MAGNETORESISTIVITY AND HALL COEFFICIENT FOR CARBONS AT VARIOUS TEMPERATURES

Measurements were made at 300°, 78°, 20° and 4·5°K of the dependence of transverse magnetoresistivity (Δρ/ρ) on field intensity (H) for a soft carbon heattreated to temperatures above 2000°C, for a hard carbon heattreated to 2600° and 2800°C and for acceptor-doped soft carbons. Measurements on baked soft and hard carbons were carried out at 1·7° and 4·5°K. In general the shape of the curves of Δρ/ρ vs. H, is such that Δρ/ρ is negative at low H, passes through a minimum and tends to or becomes positive at higher H. The negative part becomes more prominent at low temperature and also becomes greater for lower heat-treatment temperature (HTT) in the range above 2000°C. For baked carbons, the negative Δρ/ρ decreases in absolute value and the magnetoresistance becomes even positive at sufficiently low temperature. Dependence of the Hall coefficient on magnetic field for the soft carbon was measured at various temperatures. An opposite field dependence for HTT 2400° and 3000°C was observed. The lower is the temperature, the more remarkable the field dependence becomes. Some discussion of the effects found is included. © 1969.