Magnetotransport properties of undoped amorphous carbon films

Anomalous positive magnetoresistance (MR) up to 36% was observed at 2 K and 12 T in the undoped amorphous carbon (a-C) film deposited on glass substrate by pulsed laser deposition at 500 °C. There is no tendency of saturation of MR with increase of the magnetic field. The MR decreases as the measurement temperature increases from 2 to 80 K, and could hardly be observed above 80 K. As the deposition temperature grows from 300 to 600 °C, the disorder degree of the a-C film decreases, and the value of MR also decreases, indicating that the lower disorder degree results in a smaller MR. The mechanism of this MR could be ascribed to the wave function shrinkage. It could help to understand the MR phenomenon in amorphous material systems.