US3682604A - Memory element and method of making protective coating therefor - Google Patents

Memory element and method of making protective coating therefor Download PDF

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Publication number
US3682604A
US3682604A US51194A US3682604DA US3682604A US 3682604 A US3682604 A US 3682604A US 51194 A US51194 A US 51194A US 3682604D A US3682604D A US 3682604DA US 3682604 A US3682604 A US 3682604A
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United States
Prior art keywords
nickel
alloy
film
magnetic
wire
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Expired - Lifetime
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US51194A
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English (en)
Inventor
Rene Fernand Victor Girard
Hubert Lucien Louis Baton
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Bull General Electric NV
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Bull General Electric NV
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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
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/72—Protective coatings, e.g. anti-static or antifriction
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12708—Sn-base component
    • Y10T428/12722—Next to Group VIII metal-base component
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/12—All metal or with adjacent metals
    • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
    • Y10T428/12771—Transition metal-base component
    • Y10T428/12861—Group VIII or IB metal-base component
    • Y10T428/12944—Ni-base component

Definitions

  • This invention relates to improved protective coatings for thin magnetic films.
  • the ability to utilize thin magnetic films for fast memories, of reduced size and of large storage capacity, results from the fact that such films are capable of assuming different stable magnetic states and of transferring from one state to the other in a very short time, of the order of a few nanoseconds, by undergoing a reversal of the magnetization.
  • These films are usually obtained by depositing a ferromagnetic material on a substrate by electrolytic means or by evaporation under vacuum, the deposition occurring in the presence of an orienting magnetic field in order to provide a uniaxial anisotropy of magnetization; i.e., a direction, termed the easy axis, along which, when the orienting field is removed, the magnetization of the film remains preferentially oriented.
  • the ferromagnetic materials most commonly employed for these films consist generally either of binary alloys of iron and nickel or of nickel and cobalt, or of ternary alloys of iron, nickel and cobalt. These alloys may also contain, on occasion, other materials such as aluminium, silicon, manganese, titanium, etc.
  • the magnetic material After the magnetic material has been deposited on its substrate, it is necessary to protect it to conserve its magnetic properties, not only against the oxidizing action of the air, but against the corrosive action of humidity and of various acids which are found, even though in very small proportions, in the atmosphere.
  • a protective layer of insulating material For this purpose, various insulating materials have been utilized, among which are, for example, polyethylene terephthalate, varnish, and synthetic resins.
  • these materials have the disadvantage of not being thermally stable. Therefore, there is the danger that these materials no longer provide effective protection for the ferromagnetic material when, after accidental heating, they undergo plastic deformation or volatilize more or less rapidly.
  • these insulating materials possess only a relatively low mechanical resistance, but they ultimately impair, sooner or later, the magnetic properties of the ferromagnetic film on which they are deposited, because of chemical interactions which take place between these materials and the film. Consequently, to avoid the ferromagnetic material not being provided suflicient protection after a certain time because of the progressive deterioration of the protective coating under the action of heat, even the relatively low heat which is always produced during normal operation of the memory, it has been found preferable for assuring the protection of the film to utilize certain metals which present relatively high melting temperatures and practically no reaction to atmospheric agents. Such metals include, for example, chromium, gold, platinum and rhodium.
  • Rhodium being a relatively good conductor of electricty, supports the flow of eddy currents when, under the action of magnetic fields generated by current pulses in control conductor pairs of the film, the magnetization in the film turns to align itself in the direction of the resultant applied magnetic field.
  • the rhodium layer supports eddy currents.
  • This eddy current eifect increases in significance with the thickness of the protective conductive layer, and, therefore, is an important factor, because to assure efiective protection it is necessary to cover the film with a substantially thick layer of rhodium, of the order of a few microns.
  • the readout signals induced by the rotation of the magnetization of the film distorted but, in addition, the amplitude of these signals is substantially reduced, whereby costl amplifiers must be added to permit effective triggering of the switching circuits to which these readout signals are applied.
  • the single figure shows curves representing the variation of the proportion of nickel in the nickel-tin alloy deposit, as a function of the current density and temperature of the electrolytic bath employed for obtarmng this alloy.
  • the layer of nickel and tin alloy which is provided, in accordance with in the invention, for protecting magnetic film is applied on a film for which the substrate constitutes a cylindrical conductive wire of small diameter.
  • this alloy of nickel and tin can also be applied on a magnetic film deposited on any form of substrate, for example a plane substrate.
  • This alloy of nickel and tin on a magnetic film is deposited by electrolytic means, which permits for obtaining a protective coating uniformly distributed over all the surface of the magnetic film.
  • the layer when a magnetic film is coated with a layer of protective material, it is necessary that the layer have a thickness sulficient to assure adequate protection of the film.
  • the material forming the protective layer is constituted of a metal or a good conductive alloy, this requirement is more difiicult to realize since, above a certain thickness of the layer, particularly troublesome eddy currents begin to appear at the time of switching of the film, causing heating which ultimately alters the magnetic properties of the film and substantially reduces the amplitude of the readout signals.
  • the power dissipated by eddy currents is proportional to the square of the thickness of the protective layer and inversely proportional to the electrical resistivity of the material of which the layer is constituted.
  • this alloy of nickel and tin which contains 29% to 37% of nickel has the advantage of conserving the same physical state up to high temperatures, of the order of 400 C. Because of such good thermal stability, a magnetic film which is covered with a layer of this alloy remains effectively protected, even if, in the course of normal operation, considerable inadvertent heating is produced.
  • this nickel-tin alloy presents a very great hardness which permits it to strongly resist penetration and friction.
  • the hardness defined here is the Vickers hardness, which is measured by the progressive driving into the material, under a load P expressed in kilograms, of a diamond indenter, of pyramidal form perpendicular to a square base.
  • the value H of this hardness is given by the relation:
  • d designates the length, expressed in millimeters of the diagonal of the pyramidal indentation.
  • this Vickers hardness which varies with the content of nickel in the ,alloy, remains between 400 and 700.
  • the substrate of the magnetic film is constituted of a cylindrical wire of beryllium-copper, coated with a layer of copper of a few microns thickness.
  • This wire microns in diameter and of great length, traverses from one end to the other an electrolysis tank containing a bath adapted for depositing on the substrate a thin film of ferromagnetic material.
  • the bath consists, for example, of an aqueous solution of salts of iron and nickel, providing for depositing on the wire an alloy of iron and nickel containing about 18% iron.
  • the wire is moved through the tank by a suitable driving arrangement which provides for pulling the wire at a constant velocity. In the example described, this velocity is of the order of 10 meters per hour.v
  • the wire covered with is magnetic film is subjected to a rinsing, and then enters another electrolysis tank containing a bath of which the composition will be indicated hereinafter, this latter bath being intended for forming on the wire a protective coating of nickel-tin alloy containing 29% to 37% of nickel.
  • this latter bath being intended for forming on the wire a protective coating of nickel-tin alloy containing 29% to 37% of nickel.
  • the wire is completely immersed in the bath.
  • the wire is utilized as the cathode and is surrounded by an anode of nickel of appropriate form, which provides for assuring a practically constant current density along all of the immersed length of the wire.
  • the electrolysis solution which is utilized for providing this protective layer has the following composition:
  • the value of the pH is adjusted by the addition of ammonia or hydrochloric acid in the electrolytic solution. This solution is employed at a constant temperature, the value remaining between substantially 55 C. and 70 C.
  • the nickel-tin alloy is electro-deposited on the wire with a constant density current having a value which will be specified hereinafter.
  • curves 1, 3, and 4 represent the variation of the proportion of nickel in the deposited nickel-tin alloy, as a function of the current density 1', for the above-mentioned electrolyte when the temperatures of the bath are respectively 55 C., 60 C. and 70 C.
  • the protective layer of electro'deposited nickeltin alloy have a thickness between 5,000 angstroms and a few microns, in order that the magnetic film is effective- 1y protected and that eddy currents are suppressed.
  • the electrolytic depositing of the alloy on the magnetic film take place during a precisely determined interval, which must be less as the value of the current density utilized is increased.
  • the object of these experiments was to determine the quantity of electricity required for obtaining a protective layer of thickness satisfying the requirement indicated above. It was determined that to obtain such thickness a quantity of electricity of between about 0.05 and 0.1 coulombs per centimeter of length of wire must be provided. In the example being considered, because the relative change in diameter of the wire produced by depositing the protective layer is negligible, the product obtained by multiplying the current density, expressed in milliamperes per square centimeter, by the time of electrolysis, expressed in seconds, must be between about 1250 and 2500 millicoulombs per square centimeter. Since the values of current density for obtaining the nickeltin alloy possessing the desired properties are known, it is simple to determine the duration of the electrolytic deposition.
  • the operation takes place at a temperature of 60 C.
  • a current density greater than ma./cm. must be employed. If, for this temperature, a current density equal of 20 ma./cm. is selected, it is necessary that the duration of the alloy deposition operation be between about 62 seconds and 125 seconds.
  • the accompanying figure shows that if the coating operation takes place under these conditions; i.e., at 60 C. and with a current density of 20 ma./cm. the nickel-tin alloy deposited on the magnetic film contains about 34.5% of nickel.
  • the electrolysis process described for depositing the nickel-tin alloy provides for obtaining a coating uniformly distributed over all the surface of the magnetic film.
  • Automatic regulation of the thickness of the deposited layer occurs because the resistance of the nickel-tin alloy is relatively high, whereby points on the magnetic film which become covered with even a very thin coating of the nickel-tin alloy present a much higher resistance to the electrolysis current than points on film not yet covered by the alloy.
  • this protective coating is of very low cost. Furthermore, not only does this protective coating not alter the magnetic properties of the film on which it is deposited but further, it does not disturb the structure of the film when, after having been covered with its protective layer, the magnetic coated wire is introduced into an oven in order to be subjected to the well-known operation of annealing for stabilizing its magnetic properties. It has been verified, moreover, that this nickel-tin alloy which contains 29% to 37% of nickel, is virtually not attacked when it is subjected to the action of air, of oxygen, of water, of strong bases such as sodium or potassium hydroxide, or of strong acids such as sulfuric or nitric acid.
  • a coated memory element comprising;
  • a conductive substrate in the form of a length of cylindrical wire a conductive substrate in the form of a length of cylindrical wire
  • a process for producing a memory element having a conductive substrate with a thin magnetic film deposited thereon which includes the steps of:
  • a conductive substrate in the form of a cylindrical wire having a magnetic film consisting of about 18% iron with the remainder essentially nickel supported thereon,
  • said magnetically-protective 7 8 layer being an alloy consisting of between 29% and 3,077,285 2/ 1963 Budininkas 29-196.6 XR 37% nickel with the remainder essentially tin. 3,077,421 2/1963 Budininkas 29-1966 XR References Cited GERALD L. KAPLAN, Primary Examiner UNITED STATES PATENTS 5 US. Cl. X.R.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Chemically Coating (AREA)
  • Electroplating Methods And Accessories (AREA)
  • Thin Magnetic Films (AREA)
US51194A 1969-07-02 1970-06-30 Memory element and method of making protective coating therefor Expired - Lifetime US3682604A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
FR6922276A FR2051927A5 (de) 1969-07-02 1969-07-02

Publications (1)

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US3682604A true US3682604A (en) 1972-08-08

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US51194A Expired - Lifetime US3682604A (en) 1969-07-02 1970-06-30 Memory element and method of making protective coating therefor

Country Status (5)

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US (1) US3682604A (de)
DE (1) DE2031446A1 (de)
FR (1) FR2051927A5 (de)
GB (1) GB1311330A (de)
NL (1) NL170679C (de)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3884116A (en) * 1971-12-15 1975-05-20 Midwest Chrome Process Company Screw threaded fastening means and like products
US3973920A (en) * 1974-08-22 1976-08-10 Fuji Photo Film Co., Ltd. Magnetic recording medium
US3975076A (en) * 1972-12-06 1976-08-17 Matsushita Electric Industrial Co., Ltd. Receptacle for printed circuit board
US4365769A (en) * 1980-01-14 1982-12-28 Tdk Electronic Co., Ltd. Magnetic tape cassette
US4678722A (en) * 1984-11-13 1987-07-07 Uri Cohen Record member with metallic antifriction overcoat
US4923574A (en) * 1984-11-13 1990-05-08 Uri Cohen Method for making a record member with a metallic antifriction overcoat

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3884116A (en) * 1971-12-15 1975-05-20 Midwest Chrome Process Company Screw threaded fastening means and like products
US3975076A (en) * 1972-12-06 1976-08-17 Matsushita Electric Industrial Co., Ltd. Receptacle for printed circuit board
US3973920A (en) * 1974-08-22 1976-08-10 Fuji Photo Film Co., Ltd. Magnetic recording medium
US4365769A (en) * 1980-01-14 1982-12-28 Tdk Electronic Co., Ltd. Magnetic tape cassette
US4678722A (en) * 1984-11-13 1987-07-07 Uri Cohen Record member with metallic antifriction overcoat
US4923574A (en) * 1984-11-13 1990-05-08 Uri Cohen Method for making a record member with a metallic antifriction overcoat

Also Published As

Publication number Publication date
DE2031446A1 (de) 1971-01-14
FR2051927A5 (de) 1971-04-09
NL7008985A (de) 1971-01-05
GB1311330A (en) 1973-03-28
NL170679C (nl) 1982-12-01
NL170679B (nl) 1982-07-01

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