Magnetoresistance sign change in iron-doped amorphous carbon films at low temperatures

Positive and negative magnetoresistance (MR) is observed in iron-doped amorphous carbon films at low temperatures. The MR of these films changes between positive and negative values by adjusting metallic doping, the temperature and the magnetic field. Wave-function shrinkage and spin-dependent scattering are found to be responsible for these changes. The former contributes to the positive MR, while the latter contributes to the negative one. These two factors compete with each other, resulting in different MR values with opposite signs. The results may be beneficial to carbon-based spintronics.