SynopsisWe have made quantitative estimates of some of the energetic factors to be considered in packaging of double-stranded DNA in virus particles. Numerical calculations were made using parameters appropriate for T4 bacteriophage. The unfavorable factors, and the Gibbs free energies per mole virus a t 20°C associated with them, are bending, 1.5 X lo3 kcal/mol; conformational restriction upon condensation, 5.1 X lo2 kcal/mol; polyelectrolyte repulsion, 2.1 X lo5 kcal/mol; and melting or kinking, 6.9 X lo3 kcal/mol. These must be counterbalanced in the assembled phage by noncovalent bonding interactions between protein subunits in the phage-head shell; by interactions between the DNA and polyvalent cations, especially putrescine and spermidine; and perhaps by repulsive excluded volume and electrostatic interactions between the DNA and acidic polypeptides. Indeed, a rough estimate of the standard free energy of interaction between T4 DNA and the putrescine and spermidine contained in the head is -2.1 X lo5 kcal/mol. In the absence of the other two sources of stabilization, each head protein subunit must contribute about 210 kcal/mol of binding energy.

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...

The properties of soft magnetic CoNiFe films electrodeposited in the presence of saccharin and sodium lauryl sulfate additives were studied in terms of their thickness and substrate dependence. Auger depth profile analysis of the elemental composition in CoNiFe films electrodeposited over different substrates ͑Pd 90 Ni 10 , 1.0 T NiFe, Cu͒ demonstrate that the average composition at the substrate interface and bulk deposited films remains constant. X-ray diffraction ͑XRD͒ measurements reveal the existance of mixed fcc ϩ bcc phase with larger amounts of bcc crystallites near the substrate side of the films, i.e., at the lower thickness. XRD and transmission electron microscopy measurements revealed a larger grain size at the CoNiFe/substrate interface. The measured average stress is both substrate-and thickness-dependent. The easy-axis coercivity, H c , follows the Neel's relation H c ϭ ct n ͑t is the thickness and c is a constant͒. It was found that the value of the exponent n is substrate dependent. Mechanisms related to the coercivity of CoNiFe films deposited over different substrates ͑1.0 T NiFe, Cu, Pd 90 Ni 10 , high magnetic moment CoNiFe͒ are discussed in terms of material properties of these magnetic films.An increase in recording media coercivity leads to an increase in the required saturation magnetization, B s , of the pole materials beyond those of conventionally used magnetic materials ͑1.0 T Ni 80 Fe 20 or 1.6 T Ni 45 Fe 55 ͒ in the magnetic recording head. Since the coercivity of media is a measure of the field required to reverse the magnetic orientation of a bit, the recording head must generate a higher magnetic field to write effectively on the high coercivity media. Electrochemically prepared soft, high magnetic moment ͑HMM͒ materials offer advantages such as higher rate of deposition, easier control of small features, and lower cost of the processing when compared to sputtered films. 1 Efforts to find alternatives to NiFe and still have HMM typically involve alloying them with Co. It has been shown recently that soft CoNiFe films with B s ϭ 1.6-2.1 T and H c less than 2 Oe can be obtained in the presence of different organic additives. [2][3][4][5][6][7][8][9][10][11] The effect of deposit thickness has been thoroughly investigated in the case of NiFe alloys. 12,13 A composition gradient has been found with higher Fe content in the deposit in the beginning of electrolysis. The composition gradient may also affect the crystalline structure and orientation of the films leading to the change in magnetic and mechanical properties with thickness of the deposited alloy. Importantly, the design of the recording head often requires that the same magnetic material be deposited in several layers differing in their thickness.To our knowledge there is only one paper published recently 3 in which the composition and magnetic properties of electrodeposited CoNiFe films from electrolytes without additives was examined as a function of film thickness. It is the purpose of the present communication to study ...

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...

Enhancement of current for solutions, containing Ni+2, Fe+2, and H+ ions, has been observed by linear sweep voltammetry and chronoamperometry when a magnetic field of 0.1 T was applied parallel to the cathode. The current enhancement in a magnetic field was attributed to the convection near the electrode surface induced by the Lorentz force. There is a decrease of the Fe content in NiFe films by approximately 4% obtained with applied magnetic field. It was also demonstrated that the applied magnetic field affects the magnetic properties, crystalline structure and/or texture, stress, and surface roughness of NiFe films. © 2003 The Electrochemical Society. All rights reserved.