Room-temperature magnetoresistance in a-C:Co/Si system

Three types of a-C:Co/Si samples were fabricated using the pulsed laser deposition:Co2-C98/Si with Co dispersed in the a-C film,Co2-C98/Si with Co segregated at the interface,and a-C/Co/Si with Co continuously distributed at the a-C/Si interface.Both types of Co2-C98/Si samples had the positive bias-voltage-dependent magnetoresistance(MR) at 300 K,and all MRs had saturated behavior.The study on the electrotransport properties indicated that the MR appeared in the diffusion current region,and the mechanism of MR was proposed to be that the applied magnetic field and local random magnetic field caused by the superparamagnetic Co particles modulate the ratio of singlet and triplet spin states,resulting in the MR effect.In addition,the very different physical and structural properties of all samples revealed that Co played a crucial role in the room-temperature positive MR of a-C:Co/Si system.