Strong Temperature Dependence of Magnetoresistance in Co-C Granular Thin Films

Co-C granular thin films with a Co content of 6.4 at.% were deposited at room temperature by co-sputtering. The magnetotransport properties of the thin films were investigated within 2-300 K under magnetic fields up to 90 kOe. A large negative magnetoresistance (MR) of 27.6% was successfully observed at 2 K. As temperature (T) increased, negative MR decreased drastically. Meanwhile, positive MR with an organic MR (OMAR)-like shape emerged in a low magnetic field region. Ordinary MR (OMR) appeared in a high magnetic field region and can be verified by MR ¿ H² fitting. When T reached 10 K, MR became completely positive. The MR effect showed strong temperature dependence. The interesting phenomena may help us gain a new insight into the spin-dependent transport in ferromagnetic metal (FM)/amorphous-carbon (¿-C) system.