Organic Additives in the Electrochemical Preparation of Soft Magnetic CoNiFe Films

Abstract

High moment soft magnetic films are essential for thin-film recording heads to meet the future trends in high-density magnetic recording. An increase in recording media coercivity (H c ) requires a soft material for the write head poles of higher saturation magnetic flux density (B s ) beyond that of available conventional materials. The soft magnetic materials are considered to have a low H c value, i.e., the critical field strength required to reverse the direction of magnetization. Electrochemically prepared CoNiFe films, 1-9 CoFe based films, 10-12 sputtered Fe-based nanocrystalline films, 13,14 and Fe-N based films 15,16 are the candidates for this purpose. Electrochemical preparation of soft magnetic films offers advantages such as higher rates of deposition, easier control of small features, and a less costly process. 17 Electrodeposition of iron alloys exhibits a phenomenon known as anomalous codeposition which is characterized by the anomaly that the less noble metal deposits preferentially. 18 An explanation of the mechanism of anomalous codeposition for NiFe alloy has been proposed by Dahms and Croll. 19 According to them anomalous codeposition is closely related to an increase in hydroxide concentration at the interface due to the hydrogen evolution reaction. Preferential formation of ferrous hydroxide on the cathode surface inhibits the rate of nickel deposition, while simultaneously allowing the deposition of iron. Romankiw and co-workers 19 suggested that trace amounts of Fe ϩ3 in solution causes precipitation of Fe(OH) 3 and that such film accounts for the selective discharge. The importance of adsorbed metal hydroxyl ions (MOH ϩ ) as an electroactive species, responsible for anomalous codeposition, was stressed by Grande and Talbot. 20,21 This is in accordance with earlier studies of elemental deposition of nickel and iron. 22,23 Maltosz 24 proposed a two-step mechanism for NiFe electrodeposition of bivalent cations involving competitive potential-dependent adsorption of monovalent intermediate ions. Hesammi and Tobias 25 assumed that both bivalent metal ions and also metal hydroxyl ions are the electroactive species. A recent modeling study of NiFe under current-pulse operating conditions by Schultz and Pritzker 26 proposed that surface pH is not a critical factor and that metal deposition occurs via bivalent metal cations rather than metal hydroxyl ions. Sasaki and Talbot 27 extensively studied the electrodeposition of binary alloys and found the following order of anomalous codeposition Co/Ni > Fe/Ni > Fe/Co.In a general way, the type of nucleation and deposition kinetics are sensitive to the presence of organic additives in the plating bath. The influence of organic additives on FeNi codeposition were extensively studied. 28-31 However, only recently has a theoretical explanation been offered by Yin 32,33 to describe the electrodeposition of NiFe alloys in the presence of saccharin, Sacc, as an organic additive. In the electrochemical preparation of soft CoNiFe films the common additives li...

Electrodeposited CoNiFeP Soft-Magnetic Films for High-Frequency Applications

“…Several approaches have been undertaken to increase resistivity, including the incorporation of sulphur [4], [5] and carbon [6] into the deposits. The available literature suggests that small elements such as S and C go to the grain boundaries and hence increase resistivity by enhancing electronic scattering between grains.…”

Influence of Additive Adsorption on Properties of Pulse Deposited CoFeNi Alloys

“…The bath chemistry and additive content in the electrodeposition experiments have been well described previously on several occassions 6,7,11 . The background solution was a modified Watt's electrolyte containing H 3 BO 3 and NH 4 Cl as buffers, and the pH of the solution was adjusted with diluted HCl.…”

“…It is obvious that the highest content of S and C in the deposi observed for the pulse currents where the corresponding potential of the CoFeNi surface is in the range where the maximum adsorption and coverage of additives on the CoFeNi surface occurs (Figure 9b and Figure 5) 35 . The source of the elementary S, and C in deposit can be directly connected to the molecular structure of Saccharin and SLS 6 . T main source of the S in the deposit is probably the adsorbed Saccharin on the CoFeNi surface.…”

“…Besides a commonly seen action of leveling and brightening of the deposit, the benefit of additives in plating bath was usually attributed to improvement in the grain size and the crystal structure of the deposit 2,3 , stress reduction 4 , suppression of hydrogen evolution 4 , and improved corrosion resistance of the deposit 5 . Recently, it was demonstrated that the appropriate choice of the additives and bath chemistry could substantially improve the magnetic properties of the CoFeNi films 2,6,7,8,9 . Magnetically very soft CoFeNi alloys with coercivity less than 2 Oe and high magnetic moment (>1.8T) were produced leading to substantial breakthrough in electrodeposited magnetic head core materials used for high density magnetic recording 2,7,9 .…”

Thermal Synthesis of Nanocrystalline (Co<SUB>x</SUB>Ni<SUB>1-x</SUB>)<SUB>y</SUB>Fe<SUB>1-y</SUB> KOVAR Alloy through Gaseous Reduction of Mixed Oxides

“…NiCoFe ternary alloys, rich in Co, have been reported with higher saturation magnetic flux density and lower coercivity than Permalloy (Ni 80 Fe 20 ), which can be used to develop more sensitive thin film magnetic heads for high-density recording. [6][7][8][9][10][11][12][13][14][15][16][17][18][19] Also, NiCoFe ternary alloys, rich in Fe, have also been noted for their low thermal expansion property. Commercial applications of these alloys include microwave guides, spacecraft optics, laser housings, and printed wired boards.…”