Electrodeposition of soft-magnetic cobalt-molybdenum coatings containing low molybdenum percentages

Electrodeposition of cobalt-molybdenum alloys has been optimised to obtain coatings that show low coercivity and high saturation magnetisation. For this purpose, low molybdenum percentages were required (less than or equal to 10%). Solutions containing a fixed sodium citrate concentration (0.2 mol dm(-3)) and variable concentrations of CoSO4 and Na2MoO4 were tested. 0.1 mol dm(-3) CoSO4 + 0.005 mol dm(-3) Na2MoO4 or 0.3 mol dm(-3) CoSO4 + 0.012 mol dm(-3) Na2MoO4 solutions, both at pH 4, were useful to obtain Co-Mo coatings of several microns with a molybdenum percentage less than or equal to 10%, although higher process efficiency was obtained from the second solution. These coatings showed a fluffy morphology and a close-packed hexagonal structure (hcp) with (1 1 0) + (1 0 0) preferred orientation. These films exhibited a soft magnetic behaviour and their coercivity (H-c) was clearly lower than that corresponding to pure-cobalt deposits and they maintained, moreover, high saturation magnetisation (M-s). (C) 2004 Published by Elsevier B.V.