DE1521007A1 - Process for the production of thin ferromagnetic coatings by electrolysis - Google Patents

Description

Process for the production of thin ferromagnetic coatings by electrolysis

The invention relates to thin ferromagnetic coatings, also called thin ferromagnetic platelets or films; since their application to such coatings, what storage elements with very short magnetization reversal times in magnetic storage devices with large capacities, apparently of the greatest interest, the invention relates in particular, but not exclusively, to such Coatings or plates »

The invention aims in particular to create electrolytic tables Processes which better than the current ones correspond to the various requirements of practice, in particular

Dr Ha / Ma

special

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special what the achievement of very thin ferromagnetic Coatings or platelets that are homogeneous both in the direction of their thickness and in the plane of the platelets are and a low anisotropy field and a low Coercive feud value, especially the minimum values, as well low scatter in the easy direction of magnetization and for the intensity of the anisotropy field.

The ferromagnetic substances, especially in the form essential designs relating to thin coatings, in particular those required for understanding the invention Comments regarding the easy direction of magnetization and the anisotropy field are in the German Patent No. (official file number of

Registration) concerning "thin ferromagnetic

On the other hand, as is well known, the coercive field of a ferromagnetic material with a hysteresis loop is the absolute value of the magnetic field necessary to cancel the magnetization. This is the macroscopic coercive field. There is also a microscopic " Coercive field ¹¹ , which represents the field which is used to reverse the magnetization in the domains of the ferromagnetic material

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must be overcome (the domains are also in of the aforementioned German patent specification).

The invention basically consists in the fact that one > thin train or a thin plate from a ferrotnagnetic Alloy by electrolysis at constant current density, at constant temperature and without movement by means of an electrolyte with a high concentration of constituents of the alloy to be deposited Metal ions precipitated, the concentration ratio of the metal ions of the electrolyte being essentially is equal to the concentration ratio of metal atoms of the alloy and the electrolyte is a certain amount an additive, e.g.! thiourea, which contains the polarization curves of the precipitation of the alloy components on this alloy shifts so that at this current density and at this temperature these curves intersect.

In addition to this basic rule, the invention also encompasses certain ones other measures, preferably at the same time come into use, but also if necessary can be applied separately and those below are explained in more detail.

The 909833/1111

The invention relates in particular to a particular form of application (in the manufacture of one of the thin layers of a pair of coupled ferrcraagnetic layers of the

German patent specification no (official file number

of the registration.) concerning "Coupled

thin ferromagnetic layers with different Coercive fields and a magnetostriction of about zero and method for their production "described type) as well as certain embodiments of this application; the invention also relates in particular to the new technical one Products representing thin ferromagnetic coatings obtained by the specified process or Platelets as well as the electrolysis devices and the Devices (magnetic memories and logical or parametric devices) using such coatings or plates contain.

The invention is illustrated in the following description Connection with the drawing, which, however, only explains exemplary embodiments, better understandable.

Fig. 1 of the drawing shows the change in iron content the precipitated Niokel-iron alloy in Dependence on the current density when using a nickel sulfate, Electrolyte containing iron sulfate and thiourea.

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the

Fig. 2 shows the effects caused by the addition of thiourea Shift of the polarization curves once in the pail of the precipitation of iron on iron and for another time from Kiekel to nickel.

According to the invention and in particular according to its preferred Embodiments and individual features for Production of thin ferromagnetic ^ plates, Layers or coatings, one goes as follows or in analogous way. ,

Before a more detailed description of the method according to the invention, let us summarize those for a storage element ferromagnetic platelets used are generally required Discussed properties and general difficulties encountered with electrodeposition oppose such platelets or coatings.

Me ferromagnetic properties of certain metal alloys, in particular of alloys of nickel and iron, optionally with the addition of cobalt depending on the proportions of the components; in particular, the magnetostriction and the anisotropy depth vary in Depending on the composition of the nickel-iron alloys, as described in more detail in the first mentioned German patent specification no. ...... (official file number the registration ............) is described.

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Pure

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For numerous applications, especially for magnetic storage elements, the production of coatings or platelets is of interest, the magnetic properties of which hardly depend on the stresses exerted on the platelet, ie one wants to obtain platelets with a magnetostriction coefficient of zero or a low value. As is known, the alloys of the "Permalloy" type made from 82 to 83 % nickel and 18 to 17% iron not only have a magnetostriction of zero, but at the same time also have a minimum value of the anisotropy field.

The reduction in the anisotropy field is also therefore of interest because this anisotropy field is connected to the microscopic coercive field and the control currents of the magnetic reversal of a storage element increase with the anisotropy field.

Finally, it should be remembered that one usually uses the Orienting magnetization in a preferred easy magnetization direction by turning the coating or the Applies platelets in the presence of a magnetic field with a constant direction, so that one in the direction of only one Axis anisotropy is generated. To this Way you get practically to a layer with a single direction of magnetization, i.e. a single direction

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Domain: The directions of the actual magnetizations are slightly scattered with respect to the mean direction of magnetization, while the anisotropic fields in their Scatter intensity slightly.

To achieve a correct information recording and in particular the maintenance of the information after repeated inquiries or malfunctions it has been found that platelets with a very small thickness, namely less than 300 &, would be very advantageous because Bloch lines (along which the direction of magnetization changes inside a Neel wall or "crosstye") 'on to-, start kicking when the thickness exceeds 300 Å; the The progression or creeping of Bloch lines is endangered the stored information.

These thin coatings or platelets should also have a very good homogeneity, so that the sum of the microscopic and macroscopic angular scattering of the magnetization is less than 2 or 3 degrees and the microscopic scattering of the intensity of the anisotropy field is less than 2 or 3 % . It is also extremely desirable to prevent the formation of zones (always few, but always disturbing) in a thin coating, in which the direction and size of the anisotropy

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strongly deviate from the mean direction in the field; these This is because zones can generate dynamic blocking fields when interrogated using high-frequency pulses (The existence of such zones requires the application of a much stronger magnetic field than that due to the central one Anisotropy to achieve the actual total rotation of the magnetization by a short field pulse in the On the order of tens of nanoseconds in the difficult one. Direction of magnetization has been calculated).

Several processes for the production of ferromagnetic coatings or platelets have already been proposed to date, in particular vacuum evaporation, cathodic sputtering (Sputtering), the anodic atomization (ion plating) which was only recently introduced by the American Atomic Energy Commission revised in the Sandia laboratory chemical decomposition in the gas phase and finally electrolysis.

Electrolysis has the advantage of a low cost price, however, has certain disadvantages over the earlier known methods, in particular the following:

- The

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- The current density on the plates forming the cathode " or carriers varies as a result of electrolysis

poor conductivity of the carrier, which leads to ι

Choice of procedural conditions compels in which the The composition of the precipitate depends as little as possible on the current density and the thickness of the precipitate;

• At the same time as the precipitation of iron and nickel, a certain amount develops on the electrodes Hydrogen; this gas adversely affects the magnetic properties of the deposited alloy; one meets this is usually done by using an increased current density, since the amount of hydrogen released is with decreases with increasing current density;

especially in the case of the precipitation of a nickel-iron alloy the precipitate initially has a much higher iron content than the electrolyte, so that the electrolyte near the electrode is unevenly applied Nickel and iron ions become depleted, resulting in a change in composition in the direction of thickness; from it it follows that the first layers do not have zero magnetostriction, which is a sensitivity against external stress effects and deformations and, on the other hand, the impossibility of achieving them a certain direction of the axis of the light magnetic

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tization

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tation has the consequence; this change in composition also causes an increase in the mean anisotropy energy, since the anisotropy energy for the composition corresponding to magnetostriction zero is minimal, as in the first mentioned German patent specification no (official file number the registration ......) is specified; man

tries in practice a precipitation with a concentration as regular as possible in the direction of the thickness to achieve (so that the lowest possible magnetostriction and average anisotropy are obtained), by keeping the electrolyte moving to make up for its relative depletion; Unfortunately However, such a movement of the electrolyte reduces the homogeneity of the magnetic properties in the Level of precipitation destroyed;

Fluctuations in the composition result in the direction of the platelet or the coating due to fluctuations in activity of the wearer and current peak phenomena; these fluctuations, especially when using them Voltages connected in the precipitate cause a local deflection of the magnetization by magnetostriction;

- it

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- It is difficult to obtain crystals with a homogeneous shape and an isotropic distribution of these crystals is difficult, however, the presence of large crystals and a non-isotropic distribution cause a local deflection of the magnetization due to anisotropy energy or magnetocrystalline energy.

Indeed, the main disadvantage resides in the usual Electrolysis ensures that the relative metal contents in the electrolyte and the alloy to be applied are different are: This results in the formation of involuntary and uncontrolled changes in the composition of the applied alloy in the direction of the thickness and, consequently, the formation of a precipitate having no minimal anisotropy.

The invention eliminates the disadvantages listed above and enables the application of a thin plate or coating of a ferromagnetic alloy, in particular a nickel-iron alloy and above all an alloy of 82 to 85 # nickel and 18 to 17 $> iron, by electrolysis at constant current density, at constant temperature and without agitation using an electrolyte with a high concentration of constituents forming the alloy applied

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Metal ions j is the concentration ratio of the metal ions of the electrolyte is approximately equal to the concentration ratio of the metal atoms of the alloy and the electrolyte still contains a certain amount of an additive, e.g. thiourea, which the polarization curves of the alloy components applied to the alloy shifts in such a way that for this current density and this temperature sioh intersect the curves.

The electrolyte preferably contains the metal ions in the form of sulfates, the total concentration increasing Sulphates, especially for the application of a nickel-iron alloy, several hundred grams of sulphates per liter Electrolyte.

example

According to an exemplary, non-limiting embodiment of the invention, the following electrolyte is produced in which the concentration ratio of iron and nickel ions is the same as that of the alloy of 82 to 83 Jt of nickel and 18 to 17 % of iron:

Nickel sulfate

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Nickel Sulphate NiSO ^, 7H ₂ O 462.5 Iron Sulphate FeSO., 7H ₂ O 98.7

Boric acid H ₃ BO ₅ (buffer) 30

Sodium laurine sulphate (wetting agent) 0.420

Thiourea (regulator) 0.250

pH value 2.5

The quantities are given in grams per liter of electrolyte.

The electrolysis takes place on a metallic or metallized carrier serving as a cathode at a constant current density (6.8 mA / om), at a constant current density. To the oxidation of iron to prevent temperature (28 ⁰ C -for the specified Thioharnstoffmenge) and without movement, wherein the electrolyte is maintained advantageously under an inert atmosphere (nitrogen) in the air. The anodic oxidation of iron is prevented by using an anode compartment separated from the cathode compartment by a diaphragm, which contains an iron and nickel-free electrolyte (sodium sulfate and boric acid at a pH of 2.5).

The high molarity of nickel and iron salts is limited the harmful diffusion effects across the electrolyte in the range of the current densities used

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The thiourea not only has the essential advantage that it (for the reasons explained below) enables a precipitate to be obtained with the same metal composition as the electrolyte bath , but it also increases the yield in electrolysis, which can reach and even exceed 95 which results in a considerable reduction in the risk of contamination of the precipitate by hydrogen (this is due to the shift phenomena in the folarization curves of iron, nickel and hydrogen, which will be discussed below with reference to FIG. 2).

One of the main advantages is that you get a composition that is in the direction of The thickness of the layer remains the same with practically no change in the direction of this bead.

The composition of the precipitate is essentially a function of the current density, the temperature and the Thiourea content8 of the electrolyte. In particular, on the basis of what has been described above Electrolyte, in an operation performed with static electrolyte, at a given temperature and one given thiourea content a precipitate is obtained,

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its composition depending on the current density from pure nickel to at least one Iron content of the electrolyte varies with the same iron content.

In FIG. 1, curve 1 shows the change in the iron content (plotted on the ordinate in percent) of the deposited nickel-iron alloy as a function of the current density i (in mA / cm , plotted on the abscissa) for the aforementioned electrolyte at 28 ⁰ O; the experimentally obtained values are shown by cross 2.

From Fig. 1 it can be seen that for a current density of about 6.8 mA / cm (ie that mentioned above) the alloy of 82 to 83% nickel and 18 to 17 $> iron with a magnetostriction of zero and a minimum value of Anisotropy field, based on an equal concentration ratio of iron and nickel ions in the electrolyte, is obtained, ie there is no relative depletion of the electrolyte in one of the two types of ions. The analyzes have shown that the above alloy composition was obtained from the first 50 α, that is, during the precipitation period for which the influence of the surface finish of the support, in particular due to the epitaxial phenomenon, is essential 909833/1111

lion is. By the way, we know that the final properties of the finished precipitation largely depend on those of the first layers.

If you work under these "conditions, that is, with static electrolyte at 28 ⁰ G and a current density of 6.8 mA / cm and with a thiourea content of 0.250 g / liter of electrolyte, a precipitate is obtained at the end, the composition of which in the direction of the Thickness does not vary.

In FIG. 1, crosses surrounded by a circle indicate the points at which there is a nickel-iron alloy with zero magnetostriction, i.e. without relative depletion of the electrolyte in iron or nickel ions precipitates, with each of these crosses an assigned temperature (in 0) and current density (in mA / cm) is equivalent to. It is found that the higher the bath temperature, the greater the current density required to achieve it of the alloy with zero magnetostriction.

In Pig. 2 is the shift in the polarization curves from nickel to nickel and from iron to iron below the Influence of thioureas shown. In FIG. 2, the abscissa is the polarization -Ec in millivolts

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relative to a reference electrode and plotted on the ordinate the current densities i in mA / cm. Curves 4 and 5 illustrate the polarization of nickel on nickel for an electrolyte containing no thiourea and for an electrolyte containing 0.500 g of thiourea per liter, respectively. In the same W _e ise the curves 6 and 7 show the polarization of iron to iron for a no thiourea-containing electrolyte and a 0.500 g per liter of thiourea-containing electrolyte, wherein the points 8 "show the test results It represents a shift to the left, ie , according to the positive potentials, solid under the influence of the thiourea (ie one arrives at a curve drawn in dashed lines, corresponding to a thiourea-free electrolyte, to a curve drawn in solid lines, corresponding to the electrolyte containing the thiourea). As can be seen, the curve of the precipitation of iron on iron is shifted much less towards the positive potentials (shift of curve 6 to curve 7) than that of nickel on nickel (shift of curve 4 to curve 5) f which possibly the the re-establishment of the concentration ratios in the precipitated alloy explained.

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In fact, the main effect of thioureas is to shape the curves of the deposition of iron on the iron-nickel alloy with zero magnetostriction and nickel on this same alloy to shift in such a mutual relationship that these two curves differ under certain operating conditions overlap when the electrolyte is at rest, i.e. for those in Pig. 1 by those surrounded by a circle Crosses 3 marked, assigned temperatures and current densities *

It was also found that the amount of thiourea contained in the electrolyte exerts an influence on the internal stresses in the deposited alloy. The thiourea can "depending on its concentration, produce different tensions, even with different signs. Therefore, there is an optimal amount of thiourea to be added to the electrolyte, which depends on the difference between the crystal lattices of the base metal constituting the carrier and the deposited alloy and on the thickness of the precipitate. One should therefore when alloys other than the voret "bend, for example, mentioned alloy of 82-83 i" Nickel and 18 to 17 ft will be reflected Sisen, before the ssususetzende the electrolyte Thioharnstoffmenge

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determine so that the proportion of magnetostriction in the scatter is very low.

The homogenization of the crystal size also effects an elimination of the contribution of magnetostriction to the scattering and it was found that the presence of on the thin ferromagnetic layer or the Thiourea adsorbed on the platelet causes constant reorientation of the platelet during manufacture Crystal nuclei and thus the formation of very small and isotropically distributed crystals causes what the current peaks eliminated.

With the electrolyte described in the above example, at 28 ^° C. and a current density of 6.8 mA / cm with an electrolysis yield of over 95%, the desired composition of 82 to 83 # nickel and 18 to 17% of solvents is obtained first 50 S with the following magnetic properties for a layer thickness between 150 and 250 Å:

Anisotropy field: 2.5 Örsted

Coercive field: 2.5 Örsted

Microscopic angular spread: 2 °

Macroscopic angular spread: 1 °

In 909833/1 1 1 1

The presence of sulfur was found in this coating (the sulfur comes from the thiourea).

1 shows a step in the iron concentration of the precipitate as a function of the current density fixed: The composition of the precipitate remains roughly the same with slight changes in the current density. Tests have shown that this paragraph, which has an iron content of the order of 65% at a Electrolysis temperature of 28 G with the electrolyte specified in the example corresponds to an iron content of about 18 to 17% (that of the alloy with zero magnetostriction) for a temperature of about 60 G with the same Electrolyte.

It can be useful under these conditions too work to avoid the compositional fluctuations due to fluctuations in current density.

The properties of those under those corresponding to the paragraph Conditions and thin sheets or coatings obtained under the conditions of the example are the same: Magnetostriction zero, anisotropy minimal, homogeneity, etc .; In addition, the ones required for pulse unmagnetization Magnetic fields identical to the required static fields.

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As a result, regardless of the embodiment chosen, there is always a method of making thinner ferromagnetic coatings or platelets, the implementation thereof is sufficiently explained above, and which compared to the earlier electrolysis processes, in which an electrolyte with a different metal composition than that of the deposit was used, numerous precursors, in particular has the following:

the composition of the precipitate forming the thin coating or platelet varies in direction the thickness practically not because the electrolyte has the same composition of nickel and iron ions as the precipitation to be achieved;

- the precipitation is well oriented and the mean anisotropy energy is low}

the magnetostriction is essentially zero;

- in particular, very thin, homogeneous layers (less than 300 Å thick) with magnetostriction can be used precipitate from zero and with a minimum value of anisotropy;

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BATH ORIGINAL

• If necessary, you can choose such a control system that the ooh fluctuations of the otro-id pay only an insignificant change in the situation. set ζ απ / of the precipitation, whereby the accounts tration .-; - fluctuations in the: ibene des Nieders-i-iia ^ s ^: iaö _h "e: i:. ^r : old; can; these fluctuations would · Lie incline.-have the stray; ^T der leiohcen Ma; η '-.- ■; je ^ .n ^ sr L-i'\;; · ιη .; des Iiiodersohl-u * s to ver ^ röss ^ rn and -.- Lne nLookierur: - the coherently; s Drer.un.:T the i-Ia ^ ^nec; s ': rinr be.' _ In; UL3-be ^ rubbed to bev / lrken ;.. in? all of a Y. '(-lersci ^ .a ;; se! r. ^ .; fθΓΓΟΉ'-ι .-'η-'ίtischen coating au *; a wire conditional '■. ILe change of the wire length: s, w = i "He's a change in the current density results in: ^" η ^ other mz of the composition;

the tensions in the songwriting will direct the presence of an exact amount of thiourea; vn 1er corresponding to a magnetostriction of Hull Z .isar; .T.er-3et; iung 7o. "- would be different, from including Liehen uncertainties and no scatter compared to the desired easier. .Ia-" net is .

thin magnetic coatings are obtained, for which the Ratio of coercive field / anisotropy field at least equals 1.

I'ie

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BATH ORIGINAL

The invention is of course not limited to those described above Embodiments or limited to the special features specified above, but encompasses all possible embodiments which arise for the person skilled in the art.

In particular, without departing from the scope of the invention, not only other nickel-iron alloys than those with an iron content of 18 to M ° />, but also alloys other than nickel-iron alloys could be applied using the process according to the invention, in particular binary or ternary alloys of Fe, Ni, Go, Mo, by replacing the nickel and iron ions in the sulphates of the example with the ions of the desired alloy and changing the amount of the additive (thiourea); In addition, the method according to the invention is suitable for applying alloys both to flat supports and to thread-like or wire-like supports.

Claims

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BATH

Claims (7)

Patent claims 1) Process for the production of a thin, homogeneous coating from a ferromagnetic alloy, characterized in that the coating is electrolysed at a certain constant current density, a certain constant temperature and without moving the electrolyte using a Electrolyte applies, which has a high concentration of ions of the metals of the alloy to be applied has that the concentration ratio of the metal ions of the electrolyte is approximately equal to the concentration ratio of the metal atoms of the alloy and the electrolyte also contains an additive, e.g. thiourea, which defines the polarization curves of the precipitation of the alloy components on the alloy can shift so that with a suitable amount of this addition these curves cut at the given current density and temperature. 2) Method according to claim 1, characterized in that that the electrolyte is kept under an inert atmosphere, in particular a nitrogen atmosphere will. 21 9 0 9 8 3 3/1111 1521-07 3) Method according to one of the preceding claims, characterized in that the electrolyte is metal sulfate contains in a total amount of several hundred grams per liter. 4) Method according to one of the preceding claims, characterized in that the electrolyte is nickel and iron sulfate and about 0.250 g thiourea per liter and that the concentrations of iron and Jtickel ions give a ratio of about 82/18. 5) Method according to one of the preceding claims, characterized in that an anode compartment and a Cathode compartment are used, which are separated from one another by a diaphragm, and that the Anode compartment contains an electrolyte free of the metals forming the alloy to be deposited, in particular an electrolyte based on sodium sulfate and boric acid with a pH value of about 2.5. 6) Method according to one of the preceding claims, characterized in that an electrolyte with about the following composition per liter is used: 909833/1 1 1 1 (a) NiSO ₄ , VH ₉ O 462.5 g (b) FeSO ₄ , 7H ₂ O 98.7 g (c) boric acid 30 g (d) Sodium Laurine Sulphate 0.420 g (e) thiourea 0.25 g and that the process conditions are approximately as follows are: (f) pH 2.5 (g) temperature 28 ⁰ C (h) Current density 6.8 mA / cm 7) According to one of the preceding claims, sulfur-containing, homogeneous, thin ferromagnetic Coating characterized by a coefficient of magnetostriction of about zero and a minimum value of the anisotropy field. ίο 8t SSM Ή Blank page