Technical Article Direct & Pulse Current Electrodeposition Of Iron Group Thin Film Alloys Containing Vanadium by M. Schwartz, C. Arcos & K. Nobe* Direct current (DC) and pulse current (PC) electrode- tion (Bs), low coercivity (Hc), near zero magnetostriction position of binary and ternary alloys of the iron group (λ) and high permeability (µ).3 (IG) metals and vanadium are discussed. 90 Co/10 Fe Electrodeposited Permalloy (80 Ni/20 Fe) fi lms have alloy compositions with substitutional additions of such desirable magnetic properties and have been used desirable small amounts of V (~2%) were obtained; exclusively as pole material in thin fi lm heads for digital Co-Ni-V and Ni-Fe-V alloys were also deposited. recording.4 However, projections of higher storage density The effects of complexer, pH and current density on and output performance for recording applications show deposit composition and cathode current effi ciency that soft magnetic materials superior to Permalloy are (CCE) are discussed and compared to deposition of required.2 Thus, considerable effort has been directed to binary alloys of the iron group only. Impedance mea- the development of materials similar to Permalloy but with surements indicate greater corrosion resistance for higher magnetic saturation, higher permeability and higher ternary Co-Fe-V alloys than for binary Co-Fe alloys. resistivity.5,6 Crude magnetic measurements show approximately Since the discovery of the giant magnetoresistance two times greater “relative magnetic moments” for (GMR) effect in 1988, i.e., the change in electrical resis- Co-Fe-V deposits than for deposits from typical Ni-Fe tance in response to an applied magnetic fi eld, it has (Permalloy) solutions. attracted considerable attention.7 GMR reading heads sig- nifi cantly increase the capability to read high areal density Electroplating of metals and alloys plays an important computer disks. GMR fi lms in non-volatile memory chips role in the manufacture of magnetic data storage devices. can provide information retention even with the power Preparation of these metallic thin fi lms by electrodeposi- off. Sensors based on GMR materials can be applied to tion processes is much more suitable for mass produc- automotive components, such as anti-lock brakes and the tion and much less costly than by vacuum deposition regulation of crank-shaft speeds, raising fuel economy and processes.1 Electrodeposition processes are essentially lowering exhaust emissions.8 As indicated above, electro- continuous while vacuum deposition processes require deposition offers many advantages over physical vapor signifi cant down time. Furthermore, energy requirements deposition (PVD) technologies. Ross9 and Schwarzacher are substantially less for electrochemical processes com- and Lashmore10 reviewed the feasibility and advances in the pared to vacuum processes.2 Therefore, if magnetic thin fabrication of electrodeposited GMR materials and fi lms (IG fi lms of superior magnetic properties can be produced metals and alloys sandwiched with non-magnetic metals, by electrodeposition, substantial energy savings (over an e.g., Cu or Ag) with properties equivalent to PVD fi lms. order of magnitude compared to vacuum technologies) can Liao obtained 90 Co/10 Fe thin fi lm electrodepos- be achieved, contributing to further decline in manufactur- its having zero magnetostriction and a Bs twice that of ing costs for data storage units. Permalloy (80 Ni/20 Fe), making it a promising thin fi lm The recording head cores of magnetic storage devices head material for use with future higher coercivity record- are fabricated from materials which have soft magnetic ing digital disks.5 In spite of these properties, the 90 Co/10 properties and are characterized by high magnetic satura- Fe alloys do not satisfy all the mechanical and physical requirements for thin fi lm heads because of poor corrosion resistance, brittleness and low resistivity. Because these shortcomings need to be overcome before Co-Fe alloys Nuts & Bolts: can be used as thin fi lm heads, considerable industrial What This Paper Means to You research has been devoted to this problem.11,12 It has been reported that the addition of 2% vanadium Plated coatings are very important in the manufacture of mag- to bulk equiatomic Co-Fe alloys has little effect on their netic storage devices. Direct and pulse current plating of alloys of the iron group metals (iron, nickel and cobalt) with vanadium are studied here. The addition of vanadium in the alloy coating * Corresponding Author: gives us fi lms that allow higher recording capacities and memory Dr. Ken Nobe chips that retain information, even with the power turned off. The Chemical Engineering Department results of an extensive study of the deposition of these alloys… School of Engineering and Applied Science how the operating factors alter the composition and proper- University of California, Los Angeles P. O. Box 951592 ties… are given. In addition to the magnetic effects, they show Los Angeles, CA 90095-1592 improved corrosion resistance. E-mail: [email protected] 46 Plating & Surface Finishing • June 2003 0239 46 5/16/03, 10:19:34 AM magnetic properties, but substantially increases electrical resistiv- ity.13 On the other hand, bulk Co-Fe alloys with 4 to 15% vanadium Table 1 produce alloys with high coercivity. These permanent magnetic Effect of pH & Current Density on Co-Fe-V materials are known as Vicalloys.14 & Co-Fe Alloy Compositions Development and applications of Permendur (50 Co/50 Fe), V- Permendur (49 Co/49 Fe/2 V) and Supermendur (high purity 49 A. Co-Fe-V Alloys Co/49 Fe/2 V) prepared by metallurgical methods date back to over CD CD Co Fe V CCE pH 50 years ago. The technological importance of these Co-Fe alloys A/dm2 A/ft2 at% at% at% % was based on their high magnetic saturation (B ), high permeabil- 0.53 4.92 85.8 14.0 0.2 75.6 s 5.5 ity (µ), low magnetocrystalline anisotropy and low coercivity (Hc), 1.02 9.48 89.0 10.7 0.3 76.4 which made these alloys attractive as soft magnetic materials.15 0.55 5.11 87.4 11.4 1.3 67.6 6.5 Supermendur has superior properties because of its high purity; at 1.08 10.03 89.0 10.2 0.8 76.4 room temperature it has the highest known Bs (2.4 T) and a low Hc 0.55 5.11 89.9 8.2 1.8 59.8 7.0 (0.2 Oe). 1.03 9.57 90.8 7.2 2.0 55.8 Bulk Supermendur’s high temperature properties and high 0.53 4.92 92.6 5.1 2.4 55.8 7.5 magnetic saturation values enable substantial weight and size 1.02 9.48 92.4 5.1 2.4 63.9 reductions and make it suitable for applications such as in high NOTES: CCE = Cathode current effi ciency. speed aircraft electric generators and high temperature magnetic Solution composition: 0.3M CoCl2, 0.033M FeSO4, 0.17M VOSO4, 0.25M components. The addition of about 4% Ni to bulk Co-Fe-V ternary Na3C6H5O7, 0.1M H3BO3, 1.0M NH4Cl, pH adjusted with NH4OH, room alloys restricts grain growth and enhances ductility and strength temperature. with heat treatment over a wide temperature range.16 Also, corro- sion resistance will be increased. Furthermore, thin fi lms of this B. Co-Fe Alloys alloy show promise for use in components of micromotors. CD CD Co Fe CCE pH In addition to these properties, the incorporation of small quan- A/dm2 A/ft2 at% at% % tities of vanadium to Co-Fe alloys has three important potential 0.55 5.11 88.8 11.2 88.5 5.5 effects. The resistivity of the alloys will be increased, brittleness 1.05 9.75 90.2 9.8 90.3 15,16 minimized, and mechanical strength increased considerably. 0.53 4.92 90.9 9.1 78.7 15 7.5 Also, the Curie temperature (Tc) approaches 1000°C (1832°F). 1.02 9.48 91.6 8.4 71.0 Magnetic properties which are sensitive to the microstructure of NOTES: Solution composition: 0.3M CoCl2, 0.033M FeSO4, 0.17M 17 the fi lm are affected by preparation methods. Although Co-Fe-V Na3C6H5O7, 0.1M H3BO3, 1.0M NH4Cl, pH adjusted with NH4OH, fi lms prepared by vacuum sputtering have poor soft magnetic prop- room temperature. erties (e.g., high coercivity) making them unsuitable for thin fi lm 18 heads, electroplated fi lms often have better magnetic properties [VO(H O) ]+2 complex. The vanadium content reached a maximum than sputtered ones.19 This has been observed for Permalloy thin 2 5 (30%) as the CoSO4/VOSO4 solution ratios, prepared by mixing fi lm heads where the output voltage of electroplated heads is 20% 0.5M solutions containing 30 g/L H BO , increased to 14/6 and 20 3 3 greater than that of sputtered thin fi lm heads. decreased as the ratio increased further. At a 1:1 ratio, the deposit Israel and Meites, citing various investigators, report that attempts contained 51.7% Co, 24% V and 5.6% B. to electrodeposit metallic vanadium from aqueous solutions on solid We have been conducting studies in our laboratory to assess the 21 cathodes have not been successful. They suggested that one of the effi cacy of pulse plating iron group alloys25-27 and incorporating contributing factors was the comparative low hydrogen overvoltage small amounts of vanadium to iron group metals to produce binary of vanadium. Russian investigators, however, reported codeposition and ternary magnetic thin fi lm alloys.28-29 of various V-binary alloys with Fe, Co, Zn and Cr, for which they provided solution formulations, operating conditions and resulting claimed deposit contents, with references.22-24 Experimental Kunaev reported electrodeposition of Fe-V alloys (5–12% V) A power supply** was used to provide direct current (DC) and pulse current (PC) waveforms.