Magnetic properties and magnetoresistance of CoxC1−x granular films prepared by magnetron sputtering

Amorphous CoxC1−x granular films were prepared on n-Si(100) substrate by dc magnetron sputtering. The effects of Co concentration, film thickness and annealing temperature on the magnetic properties and magnetoresistance (MR) were investigated. After annealing at 500°C for 0.5 hour, the Co(002) peak of the CoxC1−x (x>2.5 at.%) films was observed, but cracks appeared in the films. Saturation magnetization Ms increased steadily with the increase of Co concentration from 2.5 at.% to 50 at.% and also increased with annealing temperature from room temperature to 400°C. The coercivity of CoxC1−x films was less than 180 Oe. The as-deposited Co2.5C97.5 granular films with 80 nm thickness showed a highly positive MR, up to 15.5% at a magnetic field of 0.8 T, observed at T=300 K when the external magnetic field was perpendicular to the film surface. With increasing film thickness and annealing temperature, the value of MR was found to decrease gradually and changed from positive to negative. The MR effect of the CoxC1−x granular films can be explained by p-n heterojunction theory and interface scattering effect.