Field Dependence of Magnetoresistance in No-binder Soft Carbons at 77°K

The dependence of magnetoresistance on magnetic field is investigated at 77°K for soft carbons prepared from Texas petroleum coke (no-binder) by heat treatments in the range 1400°–3000°C. For specimens heat treated at temperatures between 1400° and 2200°C, the magnetoresistance is negative; its absolute value increases monotonically with increasing heat treatment temperature (HTT) and with increasing magnetic field. For specimens heat treated between 2400° and 2450°C, the magnetoresistance is negative and tends to saturate at higher fields. The absolute value becomes larger for lower HTT. Specimens heat treated between 2400° and 2450°C show a magnetoresistance which is negative at low fields, passes through minimum and becomes greater for lower HTT. For specimens with HTT≥2570°C, no negative magnetoresistance is observed even at low fields. Some discussion of the effects found is included.