Influence of current density on crystalline structure and magnetic properties of electrodeposited Co-rich CoNiW alloys

• Production of crystalline or amorphous Co-rich CoNiW alloys by electrodeposition.
• Dependence of current density on the crystalline structure and magnetic properties of CoNiW alloys.
• Structural transitions evidenced by X-ray diffractometry.
• The Co-rich CoNiW alloys are magnetically soft.

The influence of current density, at the interval 5–100 mA cm−2, on the structural and magnetic properties of electrodeposited (Co100−xNix)100−yWy alloys (x = 23–33.5 at. % Ni, y = 1.7–7.3 at. % W) was studied from a glycine-containing bath. W-content decreases with the increase of the current density magnitude. X-ray data have shown stabilization of hexagonal close packed, face centered cubic or a mixture of these structures by modulating the applied cathodic current density, for values lower than 50 mA cm−2. Two structural phase transitions were observed: one from hexagonal close packed to face centered cubic structural transition occurring for a current density of 20 mA cm−2, and another one, from cubic crystalline phase to amorphous state, which happens for values higher than 50 mA cm−2. These structural phase transitions seem to be associated with the W-content as well as average crystalline grain sizes that reduce with increasing the current density value. The grain size effect may explain the face centered cubic stabilization in Co-rich CoNiW alloys, which was initially assumed to be basically due to H-adsorption/incorporation. Magnetic properties of Co-rich CoNiW alloys are strongly modified by the current density value; as a result of the changes on the W-content and their structural properties.