Surface modification of exchange-coupled Co/NiOx magnetic bilayer by bias sputtering

We have investigated the effect of bias voltage on sheet resistance, surface roughness and surface coverage of Co/NiOx magnetic bilayer. In addition, interface topography and corrosion resistance of the Ta/Co/Cu/Co/NiOx/Si(1 0 0) system have been studied for Co layers deposited at an optimum bias voltage. Atomic force microscopy (AFM) and four point probe sheet resistance (Rs) measurement have been used to determine surface and electrical properties of the sputtered Co layer at different bias voltages ranging from 0 to 80 V. The Co/NiOx bilayer exhibits a minimum surface roughness and low sheet resistance value with a maximum surface coverage at Vb ¼ 60 V resulted in a slight increase of magnetic resistance and its sensitivity for the Co/Cu/Co/NiOx/Si(1 0 0) magnetic multilayers, as compared with the same magnetic multilayers containing unbiased Co layers. The presence of Ta protection layer improves the corrosion resistance of the multilayers by three orders of magnitude in a humid environment.