Effects of saccharin and thiourea on sulfur inclusion and coercivity of electroplated soft magnetic CoNiFe film

During the course of our recent work performed to develop an electroplated CoNiFe ternary alloy with high saturation magnetic flux density and low coe rcivity for use in magnetic recording heads, it was observed that two commo n sulfur-containing additives, saccharin and thiourea, behave differently w ith respect to the dependence of sulfur inclusion and coercivity of the all oy film on the additive concentration in the plating bath. To understand th e cause of this difference, scanning tunneling microscopy (STM) was perform ed, using Au(111) as the substrate, to examine the structure of the adsorbe d layers of the additive molecules. The result revealed that the nature of adsorption is fundamentally different for the two different additives; i.e. , the adsorption of saccharin is physical and reversible, whereas thiourea undergoes irreversible chemisorption. This finding is consistent with the k nown behaviors of the two additives in the electroplating of nickel. In thi s paper the different effects of saccharin and thiourea in the electrodepos ition of CoNiFe alloy are interpreted based on the STM results and relevant information available in the literature on the electrodeposition of nickel . (C) 1999 The Electrochemical Society. S0013-4651(98)12-087-6. All rights reserved.