US3489661A - Electrolytic processes for the production of thin ferromagnetic film - Google Patents

Electrolytic processes for the production of thin ferromagnetic film Download PDF

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US3489661A
US3489661A US536999A US3489661DA US3489661A US 3489661 A US3489661 A US 3489661A US 536999 A US536999 A US 536999A US 3489661D A US3489661D A US 3489661DA US 3489661 A US3489661 A US 3489661A
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iron
electrolyte
alloy
nickel
deposit
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US536999A
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Pierre Georges Henri Chezel
Rene Fernand Victor Girard
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Ind Bull General Electric SA S
Ind Bull General Electric Sa soc
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Ind Bull General Electric SA S
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F10/00—Thin magnetic films, e.g. of one-domain structure
    • H01F10/08—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers
    • H01F10/10—Thin magnetic films, e.g. of one-domain structure characterised by magnetic layers characterised by the composition
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D3/00—Electroplating: Baths therefor
    • C25D3/02—Electroplating: Baths therefor from solutions
    • C25D3/56—Electroplating: Baths therefor from solutions of alloys
    • C25D3/562—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of iron or nickel or cobalt
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
    • H01F41/14—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for applying magnetic films to substrates
    • H01F41/24—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for applying magnetic films to substrates from liquids
    • H01F41/26—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for applying magnetic films to substrates from liquids using electric currents, e.g. electroplating

Definitions

  • This invention relates to thin ferromagnetic films, also called thin ferromagnetic foils or skins, and electrolytic processes for the production of such films.
  • the invention concerns more particularly, but not exclusively, the production of films of this type which are intended to form memory elements having very rapid triggering times in high-capacity magnetic memories.
  • the invention has for one object to adapt such electrolytic processes so that they conform better than hitherto to the various practical requirements, notably in regard to the production of very thin ferromagnetic films or foils which are homogeneous throughout their thickness and in the plane of the film, and which have a weak anisotropy field and a weak coercive field, notably of minimum value, and reduced changes in the direction of easy magnetisation and the strength of the anisotropy field.
  • the invention comprises producing the deposition of a thin film or foil of a ferromagnetic alloy by electrolysis with constant current density at constant temperature and Without agitation, by means of an electrolyte having a high concentration of ions of the constituent metals of the alloy to be deposited, the ratio of the concentrations of the metallic 3,489,661 Patented Jan. 13, 1970 ions of the electrolyte being substantially identical to the ratio of the concentrations of the metallic atoms of the said alloy, and containing a particular quantity of an additive such as thiourea, which displaces the polarisation curves of the deposit of the constituents of the alloy on the said alloy in order that these curves may intersect one another at this current density and at this temperature.
  • an additive such as thiourea
  • the invention comprises other features which will preferably be used at the same time, but which could, where necessary, be used singly and which will hereinafter be more explicitly referred to.
  • the invention concerns more particularly a certain mode of application (that in which it is applied to the preparation of one of the thin layers of a pair of coupled ferromagnetic layers of the type described in the copending patent application of Pierre Georges Henri Chezel et al., Ser. No. 536,997, filed Mar. 24, 1966, hereinafter referred to as the second application), as also certain embodiments of the said features, and it concerns more particularly still, as new industrial products, the thin ferromagnetic films or foils obtained by the aforesaid process, as also the electrolytic installations in which this process is carried out and the devices (magnetic memories and logic or parametric devices) comprising such films.
  • FIGURE 1 illustrates the variation of the iron content of a nickel-iron alloy deposited, as a function of the current density, when an electrolyte is employed which contains nickel and iron sulphates and thiourea, and
  • FIGURE 2 illustrates the displacement of the polarisation curves produced by the addition of thiourea in the case of the deposition of iron on iron, on the one hand, and of nickel on nickel on the other hand.
  • the ferromagnetic properties of certain metal alloys vary in accordance with the proportions of the constitutents. More particularly, the magnetostriction and the anisotropy field vary as a function of the composition of the nickel-iron alloys, as set forth in detail in the said first application.
  • anistropy field is also desirable because this anistropy field is related to the microscopic coercive field and the currents controlling the triggering of a memory element increase with the anisotropy field.
  • the magnetisation is generally oriented in a privileged direction of easy magnetisation by effecting the deposition of the film in the presence of a magnetic field of constant direction, so as to induce a uniaxial anisotropy.
  • a layer is substantially obtained which comprises only one direction of magnetisation, ie only one domain.
  • the real magnetisations are slightly dispersed in direction in relation to the mean direction of the magnetisation, while the anisotropy fields are slightly dispersed in intensity.
  • Bloch lines (along which the orientation of the magnetisation changes within a Neel wall or cross-tie) commence to appear when the thickness exceeds 300 A. Now, the propagation or creep of the Bloch lines is likely to destroy the stored information.
  • These thin films must in addition have a very good homogeneity, so that the sum of the microscopic and macroscopic angular dispersions of the magnetisation is less than two or three degrees, and the microscopic dispersion of the intensity of the anisotropy field is less than two or three percent.
  • Electrolysis has the advantage that its cost is low, but on the other hand it has a number of disadvantages in the previously known methods of application, including notably:
  • the current density on the foils or supports constituting the cathode varies in the course of the electrolysis owing to poor conductivity of the support, so that it is necessary to choose the operating conditions in such manner that the composition of the deposit depends as little as possible upon the current density and upon the thickness of the deposit;
  • the initial deposit has a much higher iron content than the electrolyte, which results in an unequal relative depletion of the nickel and iron ions in the electrolyte in the neighborhood of the electrode, whereby a composition gradient through the thickness is produced; the result of this is that the first layers have not zero magnetostriction, which results, on the one hand, in sensitivity to external stresses and deformations, and on the other hand in the impossibility of obtaining a well-defined direction of the axis of easy magnetisation.
  • This gradient also has the effect of raising the mean anisotropy energy, because the anisotropy energy is minimum with zero magnetostriction level, as indicated in the first application.
  • Fluctuations in composition occur in the plane of the foil, owing to the fluctuations of the activities of the support and the current peak phenomena; especially when they are associated with stresses in the deposit, these fluctuations have the effect of locally deflecting the magnetisation by magnetostriction;
  • the present invention has for its object to obviate the aforesaid disadvantages by effecting the deposition of a film or thin foil of a ferromagnetic alloy, notably of a nickel-iron alloy and more particularly an alloy containing 82-83% of nickel and 18-17% of iron with zero magnetostriction, by electrolysis at constant current density, at constant temperature and without agitation by means of an elecrolyte which has a high concentration of ions of the constituent metals of the deposited alloy, the ratio of the metallic ion concentrations of the electrolyte being substantially identical to the ratio of the metallic atom concentrations of the said alloy, and containing a certain quanity of an additive such as thiourea, which displaces the polarisation curves of the deposit of the constituents of the alloy on the said alloy so that these curves intersect one another at this current density and at this temperature.
  • a ferromagnetic alloy notably of a nickel-iron alloy and more particularly an alloy containing 82-83% of nickel
  • the electrolyte contains the metallic ions in the form of sulphates, the total concentration of sulphates, notably in the case of the deposition of a nickeliron alloy having zero magnetostriction, being several hundred grammes of sulphates per litre of electrolyte.
  • Example 1 As a non-limiting example'of the application of the invention, the following electrolyte was prepared, in which the ratio of the concentrations of ferrous and nickelous ions is identical to that of the aforesaid alloy containing 82-83% of nickel and l8l7% of iron:
  • the electrolysis is carried out on a metallic or metallised support serving as cathode, with constant current density (6.8 Ina/cm?) at constant temperature (28 C. for the indicated quantity of thiourea) and without agitation, the electrolyte being advantageously maintained under an inert atmosphere (nitrogen atmosphere) to avoid oxidation of the iron in the air.
  • Thiourea in addition to having the essential advantage of permitting the production of a deposit having the same metallic composition as the electrolytic bath (for the reasons explained in the following), increases the yield of the electrolysis, which may reach and even exceed 95%, with a resultant considerable lessening of the dangers of pollution of the deposit by hydrogen (this being due to the phenomena of displacement of the polarisation curves of iron, nickel and hydrogen which are discussed in the following with reference to FIGURE 2).
  • One of the essential advantages is that a composition is obtained which is the same throughout the thickness of the layer, substantially without any composition gradient in the direction of the thickness.
  • the composition of the deposit is essentially a function of the current density, the temperature and the thiourea content of the electrolyte. More particularly, there can be obtained from the aforesaid electrolyte, by operating without agitation, at a given temperature and with a given thiourea content, a deposit whose composition varies as a function of the current density from pure nickel to an iron content at least equal to that of the electrolyte.
  • the curve 1 illustrates the variation of the iron content (plotted along the ordinates in percent) of the deposited nickel-iron alloy as a function of the current density i (in ma./cm. plotted along the abscissae) for the aforesaid electrolyte at 28 C.
  • the experimental points noted are represented by crosses 2.
  • FIGURE 1 There are also represented in FIGURE 1 by crosses 3 surrounded by a circle the operating points at which the nickeliron alloy is deposited with zero magnetrostriction, i.e. without relative depletion of the ferrous or nickelous ions in the electrolyte, each of these crosses corresponding to a temperature (in C.) and current density (in ma./cm. couple. It will be seen that the higher the temperature of the bath, the higher the current density must be in order to obtain the alloy with zero magnetostriction.
  • FIGURE 2 there is shown the displacement of the nickel-on-nickel and iron-on-iron polarisation curves under the influence of the addition of thiourea.
  • the polarisatio Ec in millivolts in relation to the reference electrode has been plotted along the abscissae, and the current densities i in ma./cm. has been plotted along the ordinates.
  • the curves 4 and 5 represent the nickel-on-nickel polarisation for an electrolyte without thiourea and for the electrolyte containing 0.500 g. of thiourea per litre, respectively.
  • the curves 6 and 7 represent the iron-on-iron polarisation for an electrolyte without thiourea and with 0.500 g. per litre of thiourea, respectively, the points 8 representing the experimental results.
  • the points 8 representing the experimental results.
  • the essential action of the thiourea is to displace towards one another the curves representing the deposition of iron on a nickel-iron alloy having zero magnetostriction, and of nickel on the same alloy in order that these two curves may intersect one another under certain operating conditions without agitation, i.e. for the temperature-current density couple indicated at 3 (crosses surrounded by a circle) in FIGURE 1.
  • thiourea present in the electrolyte has an influence on the internal stresses in the deposited alloy. Depending upon its concentration, thiourea may produce variable stresses and even stresses of different signs. Consequently, there is an optimum quantity of thiourea to be added to the electrolyte, which depends upon the difference between the crystal meshes of the base metal co nstituting the support and of the deposited alloy, as also the thickness of the deposit.
  • the production of uniformity in the size of the crystals also has the effect of eliminating the contribution of the magnetostriction to the dispersion and it has been found that the presence of thiourea adsorbed on the thin ferromagnetic layer or foil in the course of the preparation produces a perpetual reorientation of the crystal nuclei, which results in a formation of very small crystals which are isotropically distributed, whereby the current peaks are eliminated.
  • FIGURE 1 a level of the iron concentration of the deposit as a function of the current density: the deposit substantially retains the same composition if the current density varies slightly. Applicants investigations have shown that this level, which corresponds to an iron content of the order of 65% for an electrolysis temperature of 28 C. with the electrolyte of the example, corresponds to an iron content of the order of 18-17% (that of the alloy having zero magnetostriction) for a temperature of the order of 60 C. with the same electrolyte.
  • the characteristics of the thin films obtained under the level conditions and under the conditions of the example are the same: zero magnetostriction, minimum anisotropy, homogeneity, etc.; in addition, the magnetic fields necessary for pulse-wise triggering are identical to the necessary static fields.
  • composition of the deposit constituting the thin film substantially does not vary in the direction of the thickness owing to the fact that the electrolyte has the same ferrous and nickelous iron composition as the deposit to be produced;
  • the deposit is well-oriented and the mean anisotropy energy is low
  • the magnetostriction is substantially zero
  • an electrolysis temperature such that the variations of current density result only in an insignificant variation of the composition of the deposit, so that it is possible to eliminate fluctuations of concentration in the plane of the deposit, which fluctuations would tend to increase the dispersion of the direction of easy magnetisation of the deposit and to produce the blocking of the coherent rotation of the magnetisation in pulse operation; in the case of a deposit of a ferromagnetic film on a wire, the variation of the crosssection of the wire, which produces a variation of the current density, does not result in any variation of the composition;
  • Thin magnetic films are obtained in which the ratio of the coercive field to the anisotropy field is at least equal to 1.
  • the process of the invention is applicable to the deposition of alloys both upon plane supports and upon filiform supports.
  • NiSo '7I-I O about 462.5 grams
  • FeSO -7H O about 98.7 grams (0) boric acid about 30 grams
  • sodium lauryl sulphate about 0.420 gram
  • thiourea about 0.25 gram said process further comprising operating at a pH of about 2.5, at a temperature of about 28 C. and at a current density of about 6.8 ma./cm.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electroplating And Plating Baths Therefor (AREA)
  • Thin Magnetic Films (AREA)
  • Electrolytic Production Of Metals (AREA)
US536999A 1965-04-02 1966-03-24 Electrolytic processes for the production of thin ferromagnetic film Expired - Lifetime US3489661A (en)

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FR11756A FR1438564A (fr) 1965-04-02 1965-04-02 Perfectionnements aux procédés électrolytiques de fabrication de pellicules minces ferromagnétiques

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BE (1) BE678663A (el)
DE (1) DE1521007A1 (el)
FR (2) FR1438564A (el)
GB (1) GB1136492A (el)
NL (1) NL6604331A (el)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3645857A (en) * 1969-05-28 1972-02-29 Ferroxcube Corp Method of making plated wire memory element
US11542615B2 (en) * 2017-09-21 2023-01-03 Hymeth Aps Method of producing an electrocatalyst

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2166305A1 (en) * 1972-01-07 1973-08-17 Honeywell Bull Magnetic memory element - with non-destructive read-out
GB2339797A (en) * 1998-07-22 2000-02-09 Telcon Ltd Magnetic alloys

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3032486A (en) * 1958-10-01 1962-05-01 Ncr Co Electrolytic bath for use in electrodeposition of ferromagnetic compositions
US3047475A (en) * 1958-09-25 1962-07-31 Burroughs Corp Method for producing magnetic materials
US3099803A (en) * 1959-07-02 1963-07-30 Bell Telephone Labor Inc Automatic frequency control for tunable oscillators
US3124520A (en) * 1959-09-28 1964-03-10 Electrode
US3239437A (en) * 1960-07-28 1966-03-08 Atomic Energy Authority Uk Methods of depositing magnetic alloy films
US3261711A (en) * 1962-12-17 1966-07-19 Honeywell Inc Electroless plating

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3047475A (en) * 1958-09-25 1962-07-31 Burroughs Corp Method for producing magnetic materials
US3032486A (en) * 1958-10-01 1962-05-01 Ncr Co Electrolytic bath for use in electrodeposition of ferromagnetic compositions
US3099803A (en) * 1959-07-02 1963-07-30 Bell Telephone Labor Inc Automatic frequency control for tunable oscillators
US3124520A (en) * 1959-09-28 1964-03-10 Electrode
US3239437A (en) * 1960-07-28 1966-03-08 Atomic Energy Authority Uk Methods of depositing magnetic alloy films
US3261711A (en) * 1962-12-17 1966-07-19 Honeywell Inc Electroless plating

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3645857A (en) * 1969-05-28 1972-02-29 Ferroxcube Corp Method of making plated wire memory element
US11542615B2 (en) * 2017-09-21 2023-01-03 Hymeth Aps Method of producing an electrocatalyst

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NL6604331A (el) 1966-10-03
DE1521007A1 (de) 1969-08-14
GB1136492A (en) 1968-12-11
FR143854A (el)
FR1438564A (fr) 1966-05-13
BE678663A (el) 1966-09-01

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