Magnetic properties of CoNi films have been drastically modified by alloy electrodeposition from solutions containing a redox cationic surfactant (4-butylazobenzene-4-(oxyethyl)trimethylammoniumiodide-AZTMAI). Electrodeposition in presence of AZTMAI allows preparing CoNi coatings evolving to hard-magnetic behaviour. A gradual increase of CoNi films coercivity accompanied by a decrease of remanence and susceptibility was observed by increasing AZTMAI concentration. CoNi electrodeposition process has been modified by the presence of AZTMAI in the bath. The redox behaviour of the cationic surfactant synthesised in our laboratory was studied in the CoNi electrolytic bath revealing that additive reduces during cobalt-nickel electrodeposition. Cobalt-rich CoNi deposits obtained in the presence of AZTMAI were uniform and compact, showing acicular morphology and hcp structure with [10.0] + [11.0] orientation. The changes in crystalline structure of deposits were the responsible of magnetic properties modification. (c) 2006 Elsevier B.V. All rights reserved.