石墨是准二维半金属材料 ,然而在通常细晶粒、无取向的石墨中并没有发现很大的磁电阻效应 .在高度取向的石墨中发现了巨大的正磁电阻效应 ,在 8.15T的外磁场中 ,4 2 ,3 0 0K温度下的磁电阻分别高达 853 0 0 %和 4950 % .生产这一巨磁电阻效应的机制除正常磁电阻效应外 ,可能源于磁场诱导的类金属 绝缘体的转变 Graphite is a quasi-two-dimensional semimetallic material, however, no significant magnetoresistance effect is found in the normally fine grained, non-oriented graphite.High positive magnetoresistance effects were found in the highly oriented graphite at 8.15T In the external magnetic field, the magnetoresistance at the temperatures of 42 and 30 K are as high as 85,300% and 4950%, respectively. The mechanism of producing this giant magneto-resistance effect may be derived from a magnetic field-induced metal-insulator Change