Mechanism of Saccharin Transformation to Metal Sulfides and Effect of Inclusions on Corrosion Susceptibility of Electroplated CoFe Magnetic Films

Abstract

The electroplated magnetic alloys ͑1.0T Ni 80 Fe 20 , 1.6T Ni 45 Fe 55 , 2.4T Co 40 Fe 60 ͒, obtained in the presence of saccharin, and sputtered magnetic alloys of the same composition showed dramatically different corrosion properties at pH 5.9. The higher corrosion susceptibility of electroplated magnetic alloys, known for many years, was generally attributed to sulfur inclusions into the deposit. However, there was no direct evidence of the structure of sulfur-containing molecules included in deposit. We have analyzed electroplated, EP-CoFe, and sputtered, SP-CoFe, magnetic films using electrochemical, secondary ion mass spectroscopy, X-ray photoelectron spectroscopy ͑XPS͒, and high-pressure liquid chromatography ͑HPLC͒ techniques. The analysis of electroplated CoFe films obtained in the presence of saccharin revealed saccharin, benzamide, o-toluenbenzamide ͑HPLC͒ and metal sulfides ͑XPS͒ in EP-CoFe deposit. The proposed mechanism for saccharin transformation to metal sulfides involves four steps: ͑i͒ a reductive cleavage of C-S bond in saccharin giving rise to benzamido sulfinate, ͑ii͒ a desulfurization step leading to benzamide and sulfur dioxide, ͑iii͒ an electrochemical reduction of sulfur dioxide to hydrogen sulfide, and ͑iv͒ a reaction between H 2 S and M +2 ͑M = CO, Fe͒ to metal sulfides. The higher corrosion susceptibility of EP-CoFe magnetic alloys than SP-CoFe magnetic alloys is discussed in terms of the mechanism of sulfur-assisted corrosion.Saccharin is an additive that has been widely used for more than three decades in the industry for electrodeposition of magnetic alloys such as 1.0T NiFe, 1 1.6T NiFe, 2 and 1.8T CoNiFe, 3-5 used as writer materials in the recording heads. It has been reported that saccharin reduces tensile stress, 1,6 grain size, 6 roughness, 7 and coercivity 1-6 of magnetic materials. However, it is also known that electroplated magnetic films in the presence of saccharin show higher corrosion susceptibility than magnetic films deposited without saccharin or sputtered by vacuum deposition. [8][9][10][11] The higher corrosion susceptibility of electroplated magnetic alloys was generally attributed to sulfur inclusions into the deposit. Notably, the sulfur in the deposit was associated with saccharin present in the plating bath but there was no direct evidence about the structure of the sulfurcontaining molecules included in the deposit.The CoFe magnetic alloys with 50-70% Fe have the highest magnetic moment of 2.4 Tesla 12 and can be obtained electrochemically in the presence of saccharin as an organic additive. Such CoFe alloy has also very high corrosion susceptibility and when used as a writer element in recording heads it can have detrimental effects on performance. Attempts were made to electrodeposit 2.4T CoFe alloys without additives 13 or by replacing saccharin with another organic additive. 14-16 However, replacing saccharin is a difficult task. It is very often a trade-off between good corrosion resistance on one side, and high stress, roughness, grain size, and coer...

Controlled Electrodeposition and Magnetic Properties of Co35Fe65Nanowires with High Saturation Magnetization

“…30 However, magnetic alloys prepared by electrodeposition in the presence of saccharin show very poor corrosion resistance due to sulfur-induced corrosion. 30 Many efforts are being made to find a non-saccharin additive which will improve corrosion properties. Unfortunately, some complexing organic non-saccharin additives in electrodeposition of TM alloys, caused more than 40% decrease of B s -value due to the incorporation of oxygen compounds into the deposit.…”

“…33 The effect of MA concentration on the saturation magnetization was examined using 400-500 nm thick CoFe films deposited on six inch round alumina coated AlTiC wafers using 100 nm Ru seed layers. The CoFe films deposited using a standard paddle configuration 30 with a 1000 Oe external magnetic field and pulse current densities of i on = 15 mA/cm 2 (t on = 2.5 s), i off = 0.0 mA/cm 2 (t off = 1.0 s). The uniformity of CoFe films, defined as Sigma/Mean thickness x 100, was optimized to ∼2% by changing the ratio of holder/wafer current densities.…”

Role of p-Hydroxybenzhydrazide Additive in Electrodeposition of Thin NiP Film Used as a Nonmagnetic Spacer in Laminated (CoFe/NiP) Nano Structures

“…The origin of oxygen is from organic compounds present in plating solution and from NiOH, Ni(OH) 2 and NiO, which are formed possibly through mechanism discussed in a our recent paper. 30 The total amount of light elements present as "impurities" is much higher in Ni (4.23 at. %) than in Ni 78 P 22 film (0.276 at.…”

“…Notably, we have found that the molecules of organic additives and their reduction products were incorporated into the deposit by dissolution of deposit and HPLC analysis of the obtained solution. 30,31 The origin of S, Cl, and B comes from anions present in electrolytes which are presumably complexed with Ni +2 ions forming neutral salts. The origin of oxygen is from organic compounds present in plating solution and from NiOH, Ni(OH) 2 and NiO, which are formed possibly through mechanism discussed in a our recent paper.…”

Deposition Technologies

“…Additives and surfactants are widely employed in the electrochemical deposition practice for controlling the microstructure, resulting in grain refinement, causing leveling and brightening, and reducing internal stress [147,148]. Tabakovic et al report that examples of organic additives are saccharin and sodium lauryl sulfate (NaLS) [156].…”