Role of particle size on the magnetoresistance of nano-crystalline graphite

We report on microstructure and magnetotransport behavior of ball milled graphite to investigate the effect of particle size on magnetoresistance (MR) in graphite. The observed results show, large values of resistivity and a negative temperature coefficient of resistivity indicating non-metallic, semiconductor nature of the compacts. As the milling time increases, the resistivity value increase which is attributed to the particle size differences of the samples. Graphite exhibits the positive MR at room temperature as well as at low temperatures (4 K). 600 °C annealed samples exhibit less resistivity compared to as-milled samples due to the grain growth during annealing but show large MR values compared to as-milled sample.