Tunable positive magnetoresistance effect of Co-doped amorphous carbon films
Jiang, YC; Wu, ZP; Bao, W; Xu, SJ; Gao, J
Gao, J (reprint author), Univ Hong Kong, Dept Phys, Hong Kong, Hong Kong, Peoples R China.
Co-doped amorphous carbon (a-C:Co) films were deposited on n-type Si substrates by pulsed-laser deposition method. A positive magnetoresistance (PMR) effect has been observed after Co doped into a-C films. Such a PMR is tuned by the bias voltage and reaches a peak at a particular voltage, as observed from the Current-voltage relations of the a-C:Co/Si junctions at various magnetic fields. MR-H characteristics were further studied at the temperatures of 65 K, which showed that under the reverse electric field the a-C:Co/Si junctions had a colossal PMR (over 100%). Raman spectra results demonstrate that Co doping favors the formation of graphitic sp(2) sites. The mechanism of the PMR effect is attributed to the interactions between the applied magnetic field and Co ions, which leads to the transition from sp(2) sites to sp(3) sites and increase the resistance. (C) 2012 American Institute of Physics. [doi: 10.1063/1.3675180]
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