Structure and giant magnetoresistance of carbon-based amorphous films prepared by magnetron sputtering

Pure amorphous carbon (а-C) and Co-doped CoxC1 − x films were prepared on n-Si(100) substrates by dc magnetron sputtering. In Co-C films, the nano-sized amorphous Co particles were homogeneously dispersed in the amorphous cross-linked carbon matrix. The structures of a-C and CoxC1 − x films were investigated by X-ray photoelectron spectroscopy and Raman spectroscopy. The results showed that the a-C films were diamond-like carbon (DLC) films. After doping cobalt into DLC film, the sp3-hybridized carbon content in DLC composite films almost had no change. The as-deposited CoxC1 − x granular films had larger value of magnetoresistance (MR) than the amorphous carbon film. A very high positive MR, up to 15.5% at magnetic field B = 0.8 T and x = 2.5 at.% was observed in a CoxC1 − x granular film with thickness of 80 nm at room temperature when the external magnetic field was perpendicular to the electric current and the film surface. With increase of the film thickness and Co-doped content, the MR decreased gradually. It remains a challenge to well explain the observed MR effect in the CoxC1 − x granular films.