Microstructure and magnetic properties of Co-C nanogranular films

Nanogranular films of Co-C were fabricated by DC magnetron sputtering at high (30 mTorr) and low (5 mTorr) pressures with Co concentration controlled at about 40 at%. The granular morphology of the as-deposited film remains unchanged, and is altered, respectively, for 30 and 5 mTorr upon annealing. At annealing temperature Ta≥500 deg. C, the phase is changed from hexagonal closed-pack (HCP) Co to faulted HCP Co plus FCC Co for 30 mTorr, and to Co2C for 5 mTorr. Both the grain size and the coercivity increase with increase in Ta for 30 mTorr. The largest Hc=381 Oe is obtained at Ta=600 deg. C. Different microstructures and magnetic properties of the films made at the high and low pressures are compared and discussed