Structure dependent negative and positive magnetoresistance of amorphous carbon films

摘要

Amorphous carbon thin films with a negative magnetoresistance (MR) of 13% and a positive MR of 31 % at 2 K under a magnetic field of 7 T were fabricated through chemical vapor deposition (CVD) and pulsed laser deposition (PLD), respectively. Graphitic like carbon and amorphous structures of the thin films were observed by high-resolution transmission electron microscopy and X-ray diffraction. The MR decreases rapidly with the increase in temperature and vanishes after 40 K for the PLD grown sample, whereas for the CVD grown sample, the MR is observed up to 300 K. The negative MR may be due to the ordered graphitic like structures and its mechanism is explained by the weak localization theory for a lower temperature range of 2-50 K and the grain boundary scattering model for a higher temperature range of 50-300 K, whereas the positive MR may be due to its disordered amorphous structure and its mechanism is explained by the Efros-Shklovskii-type variable range hopping model.