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 (⩽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 ⩽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 (Hc) was clearly lower than that corresponding to pure-cobalt deposits and they maintained, moreover, high saturation magnetisation (Ms).