Features of the Electrochemical Deposition of Films from a Triple System of CoNiFe

DOI: http://dx.doi.org/10.24018/ejers.2021.6.2.2081 Vol 6 | Issue 2 | February 2021 19 Abstract — The nature of phenomena that occurs in the electrolyte during the electrochemical deposition of CoNiFe films and the mechanism leading to the difference in the relative content of elements in the electrolyte and film was clarified. This clarification was obtained with the help of a spectrophotometric study of chloride electrolytes and the electrochemical deposition of CoNiFe films at 70 °C. An experimental study of the absorption spectra and the pH values of the FeCl2, NiCl2 and CoCl2 salt solutions at concentrations of 0.005 to 1 mol/l showed the complex nature of the ionformation balance in single-component and mixed solutions and the dependence of ion formation on acidic and alkaline additives. The deposited CoNiFe film was made from a chloride electrolyte with a component content ratio of 1:1:1 at both high (0.5 mol/l) and low (0.006 mol\l) concentrations of each component. The content of each component in the film after the electrochemical deposition of the three component solution (FeCl2, CoCl2, and NiCl2 at equal concentrations) did not correspond to the composition of the electrolyte. The mechanism for the abnormal deposition of Co, Fe, Ni occurred due to the incomplete ionization of atoms and the differences in the mobility of ions. The magnetic susceptibility of the films formed in the triple CoNiFe system was higher than that of a permalloy. Therefore, the triple system shows promise for use in magnetic field converters.


I. INTRODUCTION
There are a large number of publications with research results that show the widespread use of a CoNiFe ternary alloy in microelectronic products and in magnetic memory with a high packing density. A CoNiFe electrochemical coating is used in many technological fields to reduce corrosion and wear in magnetic and electrical devices and to create electrocatalytic materials. Compared to "dry" processes, electrochemical deposition provides a more uniform coating with few defects and allows, if necessary, the ability to increase the thickness of the films without causing mechanical stress.
Magnetometric microsystems use thick (up to 100 μm) CoNiFe films obtained by electrolytic deposition from a sulfate electrolyte with the following concentrations in mol/l: Co -0.053; Ni -0.18 or 0.09, 0.107, 0.132, and 0.18; and Fe -0.012 -0.06 or 0.36 with ammonium and boric acid complexing agents [1]. The use of saccharin and lauryl sulfate can ensure adhesion and decrease mechanical In [2], the authors presented the use of a sulfate electrolyte, without sulfur-containing organic additives, to manufacture thin Co65Ni12Fe23 magnetic films, with a relatively high magnetization saturation field (2.1 T), low coercive force (1.2 Oe) and high resistance (21 μOhm · cm). However, these films had high mechanical stresses and an insufficiently high resistance to operate at frequencies above 100 MHz. Thus, the difference in magnetic properties is associated both with the composition of a film and with the difference in the structure of a film from that of the bulk material.
The deposition of FeCoNi films during pulsed feeding changes the ratio of impurities due to the competition between two phenomena of anomalous codeposition. With short pulses, iron enrichment and the limited diffusion of iron ions occur, while with long pulses, nickel enrichment occurs [3]. Soft magnetic properties for these films have been obtained and show a force Hc of ~ 1 Oe, a magnetic permeability μ of 1000 and a magnetization saturation BS of 2.15 T.
Despite a large number of articles describing technology for the electrochemical deposition of a CoNiFe ternary system, there are still a number of unresolved problems, which are primarily associated with the effect of anomalous metal deposition.
Soft magnetic CoNiFe films were obtained by electrochemical deposition from a sulfate electrolyte with the addition of ammonium chloride and boric acid [4]. The composition of the precipitation was compared with the composition of the bath and the deposition conditions in the potential and current modes. Depending on the current density at the cathode, the composition of the films changed despite the composition of the electrolyte remaining the same, as shown in Fig. 1.
FeCoNi films were deposited by the electrochemical method from a sulfate chloride electrolyte [5] containing: NiSO4-0.304 mol/l, NiCl2-0.084 mol/l, CoSO4-0.1 mol/l, FeSO4-0.036 mol/l, H3BO3-20 g/l, stabilizer-2 g/l, tartaric acid-4 g/l, bleach-4 g/l, and wetting agent and tartaric acid additives-0.1 g/l. The optimum conditions for obtaining high-quality films of Fe15.6-20.6Co43.8-61.9Ni22.5-40 were a current density of 4 A/dm 2 , a temperature of 40 °C, a pH of 2.3-3.2, tartaric acid concentrations of 8-12 g/l, and Co 2+ /Ni 2+ molar ratios of 0.26-0.4. The composition of the film depended on the current density, electrolyte temperature, and pH. The ratio of the content of elements in the electrolyte and the film was observed -CRL for Fe, Co=3, and Ni=0.5. The concentrations of cobalt and iron in the precipitate were larger than their concentrations in the electrolyte, while nickel showed the opposite result.
The above indicated that the dependence of the composition of a film of a ternary alloy does not allow one to obtain a desired film composition that corresponds to the composition of the electrolyte. As seen from the literature review, electrolyte compositions with a component concentration from 0.01 to 1 mol/l have been used to obtain CoNiFe films.
In this work, to clarify the nature of the chemical phenomena occurring in the electrolyte when obtaining CoNiFe films, which is observed by the difference in the relative elemental content between the electrolyte and film, spectrophotometric studies of chloride electrolytes and the electrochemical deposition of CoNiFe films from a chloride electrolyte with an equal 1:1:1 molar concentration of Co:Ni:Fe were carried out at a temperature of 70 °C; the experience of the congruent deposition of NiFe permalloy was also taken into account [6], [7]. The aim of this study is to determine the effect of ion charges in the electrolyte on the composition of the film.

II. STUDY OF THE SPECTRA AND PH OF SALT SOLUTIONS
The absorption spectra at room temperature of solutions at a component concentration of 0.005 to 1 mol/l were studied [8] from 315 to 1050 nm in 1-cm cells on a B-1100 spectrophotometer. Fig. 2, 3, and 4 show optical spectra with absorption peaks at specific wavelengths for the following aqueous solutions: FeCl2 -345 and 975 nm, NiCl2 -395 nm and a double peak at 655 and 720 nm, and CoCl2 -525 nm.
The dependence of the logarithm of intensity of the absorption peaks (A) for single-component solutions of FeCl2·4H2O -345 nm and 965 nm, NiCl2 6H2O -395 nm and 725 nm, and CoCl2 6H2O -525 nm from solution concentrations (C) in a range of 0.005-0.96 mol/l are presented in Figure 5.
The optical absorption spectra of aqueous FeCl2 solutions, with absorption peaks at wavelengths of 345 and 975 nm, are the most intense compared with the peaks of nickel and cobalt. This result indicates that iron had the lowest ionization energy. The absorption peak at a wavelength of 345 nm decreases linearly at a concentration of 0.05 mol/l. At a low concentration, the slope of A(C) dependence decreases. Furthermore, the absorption peak at a wavelength of 975 nm decreases nonlinearly when the electrolyte concentration is less than 0.2 mol/l. This absorption peak is also present at a low intensity for solutions of NiCl2 and CoCl2 and changes when HCl is added to the electrolyte, which means that this peak is associated with the formation of chloride ions. The dependence A(C) of the intensity of the cobalt peak at a wavelength of 525 nm, as shown in Fig. 3, shows barely any change in its slope and is 5 times smaller than the peak of iron absorption at a wavelength of 345 nm.
The A(C) dependence for nickel at a wavelength of 395 nm, as shown in Fig. 4, is very close to the A(C) dependence of a CoCl2 solution at a wavelength of 525 nm in terms of the intensities of absorption peaks. The A(C) dependences for nickel at a wavelength of 725 nm and iron at a wavelength of 965 nm are also very similar in that the slope changes at 0.2 mol/l; however, the absorption intensity of the nickel chloride solution is 2 times lower than the iron chloride solution.  The observed nonlinear dependence of the intensities of absorption peaks on the solution concentration for nickel and iron in Fig. 5 indicates the dependence of atomic ionization on the electrolyte concentration. Fig. 6 shows the optical absorption spectra of aqueous solutions after mixing all three components. Lines 1-4 in Fig. 6 show that a mixed electrolyte, where the concentration of each component (CoCl2, NiCl2, FeCl2) is 0.48 mol/l, has the same absorption peaks as the peaks observed for each component separately; additionally, the addition of boric acid and saccharin barely changes the spectrum. The spectrum of the solution after the addition of 4 mmol/l HCl decreased the absorption intensity over the entire optical range because the electrolyte is purified from the colloidal hydroxide particles. Lines 5-7 in Fig. 6 show that the electrolyte consisting of a mixture of CoCl2, NiCl2, and FeCl2 at a concentration of 0.0074 moll/l has the same absorption peaks as the peaks observed for each component separately, and the addition of boric acid and saccharin barely changes the spectrum. Moreover, the absorption intensity is much lower due to a 64-fold decrease in concentration.

III. HYDROGEN INDEX OF COCL2, NICL2, FECL2 SOLUTIONS
In the CoCl2, NiCl2, and FeCl2 solutions, the pH was measured using a Testo 206 meter [8]. The dependence of pH on the concentration of one-component solutions over a concentration range of 0.01 -1 mol/l is shown in Fig. 7. At a concentration of 1 mol/l, dissolving NiCl2 exhibits a pH=5.8, CoCl2 exhibits a pH=4.7, and FeCl2 exhibits a pH=2.7. The pH value characterizes the ion balance: the concentrations of hydrogen and hydroxyls, which in turn determines the acidity or alkalinity of water. Consequently, the hydrolysis of ferric chloride decreases the concentration of hydrogen during the dissociation of water the most and increases the hydroxyl amount.
Changes in pH during the dilution of a solution are not monotonic, but there are local peaks that appear along with changes in slope, thereby showing some dependence. This result means that a decrease in the concentration of impurities is accompanied by a change in the degree of ionization and the charge values of ions. The presence of local peaks is dependent on different salt concentrations: NiCl2 -0.5 mol/l, CoCl2 -0.03 mol/l, and FeCl2 - Prior to the peaks, the dependence of pH on salt concentration are linear. After the peaks, there is practically no dependence of pH on the concentration of NiCl2 and CoCl2 salts, but for FeCl2 salt, there is a change; however, this change is at a slower rate than that in the linear section. Table 1 presents the results of calculating the pH of the three-component electrolyte in which the concentration of each component was from 0.01 to 1 mol/l. The calculation was carried out by summing the concentrations of hydrogen ions in the CoCl2, NiCl2, FeCl2 solutions, in accordance with the measured pH values shown in Fig. 7 for the singlecomponent solutions. The hydrolysis of iron chloride increases the concentration of hydrogen and decreases the hydroxyl amount, i.e., this hydrolysis increases the acidity of the solution more than the hydrolysis of the other two salts. In fact, the hydrolysis of iron chloride determines the pH of the mixed electrolyte over the entire range of component concentrations from 0.01 to 1 moll/l of a ternary electrolyte with equal concentrations of all three salts of CoCl2, NiCl2, and FeCl2.  The pH values of the CoNiFe ternary electrolyte obtained experimentally and in the calculation, based on the pH values of the one-component solutions of FeCl2·4H2O, NiCl2·6H2O, and CoCl2·6H2O salts, almost completely coincide at low solution concentrations, while at a concentration of 1 mol/l, the calculated values are 10% higher than the experimental values. We can assume that each of the salts provides its own independent contribution to the hydrogen index, i.e., the change in the concentration of hydrogen ions regardless of the presence of other salts.
An experimental study of the absorption spectra and the pH of the FeCl2, NiCl2, and CoCl2 salt solutions at a concentration of up to 1 mol/l shows the complex nature of the formation of ionic balance in the single and mixed solutions and the dependence of this balance on the acidic and alkaline additives.

IV. ELECTROCHEMICAL DEPOSITION OF THE CONIFE FILMS
For the deposition of CoNiFe films, a chloride electrolyte with a component content ratio of 1:1:1 was used. To improve the deposition process, the following was added to the electrolyte: boric acid H3BO3 and sodium saccharinity hydrate C7H4NaNO3S·2Н2О. A film of this electrolyte was deposited in an electrochemical installation with a 2-liter galvanic bath and a graphite anode. The nickel ring electrode of the cathode was in contact with a metallized silicon wafer and was placed vertically. Rectangular regions of a permalloy film (0.5×1.0 mm 2 ) were obtained through a photoresist mask on a silicon wafer surface (diameter of 100 mm) metallized with NiCr and Ni layers along with containing a SiO2 sublayer.
The following characteristics of the obtained films were measured: the film thickness and content of the Fe, Co, Ni components; and the magnetic properties of the films, namely, the saturation of magnetization and coercive force. The thicknesses of the deposited films were measured using an MSA-500 microsystem analyzer. The study of the magnetic characteristicscoercive force and magnetizationwas carried out with plates and an instrument for monitoring magnetic parameters. The compositions of the films were studied using a PhilipsXL 40 energy dispersive X-ray microanalyzer. For the deposition of CoNiFe films with a weak electrolyte, the composition of the film without additives is closest to the relative electrolyte composition.
At a high electrolyte concentration of the three component solutions (CoCl2, NiCl2, and FeCl2 at a concentration of 0.48 mol/l for each component), electrochemical deposition was carried out at a cathode current density of 8.2 mA/cm 2 , a temperature of 70 °C and with additives of 20 g/l boric acid and 3 g/l saccharin.
The compositions of films obtained from the three component solutions (FeCl2, CoCl2, NiCl2) with additives is presented as a histogram in Fig. 9. According to the data in the figure, the content of the components is very different from the composition of the electrolyte without additives. The boric acid, saccharin, and hydrochloric acid additives decrease the content of iron and cobalt and increase the content of nickel. A three-fold increase in the deposition time to 90 minutes with sample 20 increased the iron and cobalt contents and decreased the nickel content; therefore, the composition of the film depends on the deposition time. A feature of the FeCl2 salt is the oxidation of ferrous iron to a trivalent state. The chemical powder initially has a light yellow-green color. With prolonged storage, rusty inclusions of ferric oxides appear. In a solution of such a chemical, the absorption of light increases with the addition of boric acid over the entire measured range of light lengths on hydroxide and boric acid complexes. When filtering a solution with oxidized iron chloride, rust particles remain on the filter.
The density of electric current flowing through the surface of the substrate on the cathode and its effect on the composition of the films was checked by electrochemical deposition from an electrolyte with a concentration of 0.5 mol/l for each component along with the addition of boric acid, saccharin and hydrochloric acid. This test was conducted at cathode current densities of 5-20 mA/cm 2 and a temperature of 70 °C; additionally, the solution of iron chloride was filtered. The dependence of the composition on current density is shown in Fig. 10. The relative contents of the Co, Ni, and Fe components in the film differ from the electrolyte composition (with a content of 33.3% for each component) and varies greatly depending on the current density from 5 to 20 mA/cm 2 . With an increase in the current density from 5 to 15 mA/cm 2 in the CoNiFe film, the iron content increases from 8.9 to 41.3%, while at a current density of 20 mA/cm 2 , it remains at the same level of 42.35%. With an increase in the current density from 5 to 15 mA/cm 2 in the CoNiFe film, the nickel content decreases from 38.5 to 7.9%, while at a current density of 20 mA/cm 2 , it remains at the same level of 7.85%. The actual change in the content of iron and nickel at a current density of 10 mA/cm 2 changes the cobalt content in the overall balance to 60.8%. At a current density of 5, 15, and 20 mA/cm 2 , the cobalt content has close values of 50.6, 50.8, and 49.8%, respectively.
The general character of the C(J) dependence, along with the observations of a high cobalt concentration, a decrease in nickel concentration, and an increase in iron concentration with increasing current density coincides with the data of [5], despite the difference in the composition of the two electrolytes and the difference in the current density range. The difference in anions has an insignificant effect; therefore, the change in the composition of the films from the current density is determined by the Co, Ni, and Fe cations.
The relative content of the Fe, Co, Ni components in the film differs from the composition of the electrolyte and varies greatly depending on the current density. It is difficult to select a mode that ensures the reproduction of the electrolyte composition in the deposited film.
The plot of the film composition in a current range of 15-20 mA/cm 2 has an almost constant value, which makes it possible to set the concentrations of the components in the electrolyte to provide the desired composition in the film.
In this regard, the weighting coefficients of the components in the film are determined: kCo = CoS (2)  The distribution of values of coercive force and specific values of saturation of magnetic induction depending on the composition of the ternary CoNiFe alloy in films obtained by electrochemical deposition from a chloride electrolyte is presented in Fig. 11. For comparison [9], [10], Fig. 12 and 13 show the thickness-normalized magnetization and the derivative of the normalized magnetization of the Co43.1Ni 35.3Fe21.6 (1) and Ni81.6Fe18.4 (2) films depending on the applied magnetic field. The steepness of the magnetization line of the ternary system is 1.7 times higher, which allows us to consider the promising use of a ternary system in magnetic field converters. The scatter of the saturation values of magnetization flux and coercive force is large in accordance with the scatter of the compositions of the films.    In works on the electrochemical deposition of iron, nickel and cobalt, these metals in the electrolyte are considered divalent ions, in accordance with the valency of the metalforming salt. However, the ion charge in the electrolyte has not been studied, despite atoms being ionized during stepwise electrolytic dissociation and hydrolysis in water in accordance with the ionization energy of the electronic levels of salts. The incomplete dissociation of salts in the electrolyte has a significant effect on the rate of

A. Ionic Water Balance
Water dissociates very weakly into H2O ↔ H + + OHions. The equilibrium between water molecules and ions is strongly biased toward the formation of molecules [11]. At a constant temperature, the product of the concentrations of hydrogen and hydroxyl ions is a constant value for water and weak aqueous solutions. At a temperature of 25 °C, the ionic product of water [H + ] · [OH -] = 10 -14 g-ion/l, where pH = -log [H + ] and H + is the concentration of hydrogen ions in gram-ion/l. Additionally, salt additions alter the pH. The following are the pH ranges for each type of medium: an acidic medium 10 -1 <[H + ]> 1.10 -7 -pH <7, a neutral medium [H + ] = [OH -] = 1.10 -7 -pH = 7, and an alkaline medium 1.10 -7 <[H + ] < 1.10 -14 -pH> 7. The ion concentration is calculated by the hydrogen index from the ionic product of water. The electrolyte with a pH=5 has a hydrogen concentration of 10 -5 g-ion/l and a concentration of hydroxide ions of 10 -9 g-ion/l.

B. Dissociation of Salts in Aqueous Solution
Water molecules have a large dipole moment, even during the crystallization of salts, for instance, when forming complexes of hydrates of FeCl2·4H2O, NiCl2·6H2O, and CoCl2·6H2O salts. Molecules of salt dissociate in water, and a weak electrolyte forms [11]. During hydrolysis of the salt, the salt ions bind to hydrogen H + or hydroxyl OH _ ions. According to the Le Chatelier principle, a decrease in the concentration of ions should lead to the further decomposition of water molecules into ions. If one of the ions participates in the formation of the electrolyte, then the other ion accumulates in the solution and changes the pH of the medium. Therefore, to enhance the hydrolysis of salt, the solution must be diluted and heated [11]. According to the law of active masses, when one of the hydrolysis products is introduced into the solution, the hydrolysis of the salt decreases. Upon removal of the hydrolysis product, the hydrolysis of the salt increases.

D. Faraday Law
The content of the main components in the sediment during electrochemical deposition is associated with the Faraday law through the electrochemical equivalent, where m is the mass of the deposited metal released per unit area of the electrode, J is the current density at the cathode, and τ is the time of the electrochemical deposition process.
The electrochemical equivalent is expressed by the formula: where M is the atomic mass of the metal, n is the metal valency is the ion charge, F is the Faraday number, and M/n is the equivalent mass that is calculated as 26.8 A/h.
The current density and time are external parameters of the deposition process, and the electrochemical equivalent is a property of the composition and temperature of the electrolyte, cathode material, and current density, all of which determine the current cathode output and the content of components in the precipitate. The composition of the electrolyte determines the formation of metal ions. To increase the cathode yield, complexing additives were introduced into the electrolyte.
K= 100/(Р1/К1 + Р2/К2 + Р3/К3), The electrochemical equivalent for alloys is determined by the above formula: P1, P2, P3 -the content of the alloy components, % and K1, K2, K3the electrochemical equivalents of the components. For practical use, it is convenient to use electrochemical equivalents, namely, the volumetric Kob = K/ρ [mm 3 /A·h] and linear Wedge = Kob/S = K/ρS [mm/A·h] per 1 cm 2 of surface, where ρ is the metal density and S is the surface area of the deposition [11]. Table 2 shows the electrochemical equivalents for iron, cobalt and nickel, as well as those calculated for the permalloy and three-component CoNiFe alloy with an equal content of components.
The content of the basic elements in the chloride electrolyte for the electrochemical deposition of CoNiFe can be changed, and the deposition rate can be controlled but not above the limit determined by the electrochemical equivalent. Electrolyte additives alter the chemical reactions in the electrolyte and the ion charges. Furthermore, the electrochemical equivalent depends on the charge of the metal ion deposited on the cathode. In [12], ionic equilibria in the FeCl2 electrolyte were considered according to the results of the thermodynamic calculations of equilibrium constants, as well as equations of mass and charge balance. Then, the resulting charge of ions was compared for compliance with the pH value. It was shown that an FeCl2 solution with a concentration of up to 4 mol/l at room temperature contained a high number of singly charged ions (Fe 2+ Cl -) + , few Fe 2+ ions, few neutral molecules, and very few hydroxide ions (Fe 2+ OH -) + .
These data refute the notion commonly accepted in electrochemical deposition of the complete dissociation of salts in an electrolyte. An increase in the concentration of FeCl2 or the addition of hydrochloric acid to the solution increases the content in the electrolyte of singly charged ions (Fe 2+ Cl -) + and neutral molecules of FeCl2 0 , while decreasing the number of doubly charged Fe 2+ ions. At a low salt concentration in the solution, almost identical concentrations of Fe 2+ and (Fe 2+ Cl -) + ions are obtained.
It was shown in [13] that in solutions of CoCl2 and NiCl2 with a concentration of 1 mol/l at room temperature, the almost complete dissociation of salts occurs. The quantity of singly charged CoCl + and NiCl + ions in a mixed solution was 10 times less than that of doubly charged Co 2+ and Ni 2+ ions and a thousand times less than that of neutral chloride molecules. In a mixed solution, the concentration of singly charged cobalt CoCl + ions decreased by 30%, and singly charged nickel ions NiCl + increased by 30%. For singly charged ions, a manifestation of the mutual influence of impurities on the ion balance, as well as the presence of hydrochloric acid, was noticeable.

F. Partial Ion Currents
The value of the potential difference between the cathode and the anode determines the electric field strength in the electrolyte, which determines the speed of ions and the current density in the interelectrode space. J = q n u E, where q is the electron charge, n is the concentration of ions with different charges, u is the mobility of ions, E is the electric field in the space between the anode and cathode, and u E is the speed of ions.
The sum of the currents in each section of the region between the cathode and anode is constant due to the condition of current continuity. The deposition of ions at the cathode fixes the composition of the current. J = q E [(n u)‹(FeCl) + › + (n u)‹Fe 2+ › + (n u)‹(CoCl) + › + (n u)‹Co 2+ › + (n u)‹(NiCl) + › + (n u)‹Ni 2+ ›] In an electrolyte containing three components, the difference in the charge of ions and their mobility determines the difference in the partial current density for each of the components in the form of singly charged and doubly charged ions.
As a result of the difference in the partial currents of the components, differences arise in the mass transfer, discharge of ions at the cathode, and formation of a precipitate.
The chemical composition of an electrolytic alloy formed on a cathode during the joint discharge of ions of two metals can be determined [14] by the ratio of the partial recovery currents of the individual components according to the following equation: where Me, i, and z are the metal concentration in the alloy (atomic fraction or percent), partial current and metal valence, respectively.
With changing electrolysis conditions, the ratio of currents i1/i2 does not remain constant, which determines the dependence of the alloy composition on various parameters. The nature of the influence of individual factors depends on the kinetic region in which the joint discharge occurs in the electrochemical kinetics region or in the diffusion region.
Using the dependences of the partial currents on the potential, equations are obtained that determine the dependence of the alloy composition on the potential and the required ratio of the concentrations of each component in the solution.

G. Electrode Polarization Potential
The deviation of the electrode potential from the stationary (equilibrium) value observed during current transmission is called the polarization (overvoltage) of the electrode.
In [15], the mechanism of electrodeposition of nickel, iron, and their mixture with a sulfide electrolyte was studied. As shown in Fig. 15, the nickel reduction potential of -0.75 V was more positive than iron -0.92 V and the mixed solution of -0.88 V, i.e., this result had an indeterminate meaning. However, in a joint discharge, the reduction rate of nickel ions was much lower than that of iron. The potential for cobalt reduction was -0.42 V, which was the most positive; therefore, the deposition of cobalt was least limited by the formation of a double charged layer on the cathode. The rate of the joint reduction of nickel and iron ions has an average value between their separate values, but the result does not add up. At temperatures above 90 °C, the reduction rate of nickel ions is higher than that of iron ions. In this case, the polarization curves show a nickel reduction potential that is -0.59 V more positive than iron -0.7 V. The reduction potential does not cause the abnormal deposition at high temperature to change to the normally predominant nickel deposition.

H. Consequence
The analysis of the factors determining the change in the composition of films with a change in the current density shows that there is an obvious connection with the change in the mass transfer of ions in the electrolyte. A low nickel concentration is determined by its main contribution of nickel to the partial current of ions with a double charge and the low mobility of Ni 2+ ions. High concentrations of cobalt and iron are associated with the high mobility of singly charged ions (Co 2+ Сl -) + , (Fe 2+ Сl -) + and an increase in their speed with an increasing electric field in the interelectrode space.
In addition to the type of ions, the mass transfer depends on the viscosity of the solution, which increases with increasing concentrations of the components and decreases with increasing temperature [16]. The electrolyte can be stirred mechanically by means of a magnetically driven stirrer, by the rotation or reciprocating motion of the cathode, and by ultrasonic action, thereby leading to a change in the mass transfer of ions and a decrease in the threshold voltage at which current growth begins. In [17], potential-current density curves were presented, and these curves showed that mixing the electrolyte increased the limiting current and concentration polarization.

VII. CONCLUSION
The choice of a chloride electrolyte with a ratio of СNi/СNi/СCo = 1/1/1, the development of technology for the preparation of an electrolyte and the deposition process at a temperature of 70 °C allowed us to confirm the mechanism behind the abnormal deposition of Co, Fe, Ni. The results pointed to the difference in the ionization of iron, cobalt and nickel. Films were obtained without mechanical stresses, and these films contained a uniform structure and high magnetic parameters without the need for a high annealing temperature. The chosen method of deposition with a chloride electrolyte, while taking into account the ion charge, allowed us to obtain reproducible electrochemical deposition of CoNiFe films with a small coercive force.
Electrochemical deposition was carried out at the temperature of 70°С from chloride electrolyte with component ratio CNi/CFe/CCo = 1/1/1. A review of the literature [1]- [5], [18]- [50] shows that none of the researchers used this method of research.