Potentiodynamic cathodic polarization tests and electrochemical impedance spectra were obtained for magnetic hard disks coated with a layer of diamond-like carbon (DLC) and immersed in aqueous borate buffer (pH8.4) containing 0.1 M NaCl. The log of the cathodic current was linearly related to (Deltaphi-Deltaphi(corr))(1/2) for disks coated with a layer of DLC and polarized between 0.2 and 0.4 V below the corrosion potential. In addition, the low frequency impedance of the disks coated with a layer of DLC decreased by a factor of similar to50 as the potential was decreased from 0.2 to 0.4 V below the corrosion potential. The results were independent of the DLC's thickness (2-5 nm), dopant (H and H + N) and method of deposition (sputtering and ion-beam deposition). The results suggest the presence of a thin (approximate to12-19 Angstrom) charge-denuded layer that forms by a reaction between the DLC and either air or the aqueous solution. At potentials within -0.4 V of the corrosion potential, the kinetics of the electrochemical reduction reactions on DLC-coated hard disks are explained equally well by Schottky emission or quantum mechanical tunneling of electrons through the charge-denuded, reaction product layer. Both charge-transport mechanisms suggest similar remedial actions for decreasing corrosion of the magnetic layer. (C) 2004 The Electrochemical Society.