High spin polarization induced by the interface hybridization in Co/C composite films

Co/C composite films with 10 at.% Co were fabricated by facing-target sputtering and postannealed in vacuum at 300–650 °C for 1.5 h. Co nanoparticles are dispersed in amorphous carbon matrix and Co–C compounds exist at the interface between Co nanoparticles and carbon matrix. Negative magnetoresistance was observed in the Co/C films and its maximum value of −19% was measured at 3.98 × 106 A/m and 5 K for the as-deposited film. Besides cotunneling effect, higher interfacial spin polarization, which is probably induced by the hybridization between Co 3d and C 2p electrons and consequently the preferred d-electron conduction and interfacial spin-filtering effect, also contributes to the large negative magnetoresistance. Postannealing treatment damages the interface hybridization, and thus leads to the disappearance of the higher interfacial spin polarization and large negative magnetoresistance.