Band engineering magneto-resistance effect in Co:a-C films

Co-doped amorphous carbon (Co:a-C) films, which comprise a homogeneously mixed carbon matrix phase with approximately 5 at.% cobalt, were deposited on quartz glass by radio frequency magnetron sputtering. A bias-dependent positive magnetoresistance (PMR) with a peak at a particular voltage was observed. The electronic structures were examined by ultraviolet photoelectron spectroscopy and X-ray absorption near edge spectroscopy. The spectroscopic results reveal that Co doping promotes the graphitization in the a-C matrix and the 3d orbital of Co is hybridized with sp2 states (DOSs) in the Co:a-C. The PMR effect is related to the modulation of the DOS of the Co:a-C films at the Fermi level by Zeeman splitting.