Electrodeposited cobalt-molybdenum magnetic materials

Cobalt-molybdenum (Co-Mo) induced electrodeposition has been studied from a sulphate + citrate bath on carbon electrodes, under conditions near to neutral pH. Crack-free homogeneous deposits with a low percentage of molybdenum can be easily obtained from low molybdate concentrations applying low deposition potentials or current densities. The formation of this kind of deposit is related to Q(ox)/Q(red) around 1 in the voltarnmetric/stripping experiments. Moreover, percentages of molybdenum up to 60% can be obtained from high molybdate concentrations but, in this case, the deposits show cracks. The formation of these cracked deposits can be predicted from the observed distortions in the j-t and E-t deposition transients. Coatings with a partially amorphous structure, or with a crystalline structure of nanometric crystal size, are obtained. The magnetisation results show that the saturation magnetisation gradually decreases when the percentage of molybdenum increases in the deposit. Simultaneously, a clear decrease of the coercitivity is observed from the lowest percentage of molybdenum with respect to the value of pure cobalt coatings. (C) 2001 Elsevier Science B.V. All rights reserved.