Durability of CoCr film on a conventional 3.5 inch FDD was studied. The durability is improved by a graphite-like amorphous carbon protective layer (0.02 μm) prepared by DC magnetron sputtering. Ar plasma treatment prior to the carbon layer sputtering further improves the durability, up to 107passes. The improved durability of the Ar plasma treatment is mainly due to the enhanced adhesion between CoCr / carbon interface by eliminating the oxidized layer on the CoCr surface. Corrosion resistance was also tested under two environments (1) at 25°C 75 %RH containing 1ppm SO 2 for 3 days (2) at 60°C 90%RH for 3 days after NaCl mist spray. The carbon layer exihibits greater resistance even for low Cr content.