JPH0733581B2 - Electroless plating bath - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention provides a magnetic recording medium used for so-called perpendicular recording, in which recording is performed by magnetization in the film thickness direction of the magnetic recording medium (magnetic film). It relates to an electrolytic plating bath.

(Prior Art) Conventionally, in a magnetic recording device such as a general magnetic disk device or a magnetic tape device, recording has been performed by magnetizing in the longitudinal direction of the magnetic recording medium. There is a drawback that the demagnetizing field is increased to cause the decay and rotation of the residual magnetization, and the reproduction output is significantly reduced. Therefore, a perpendicular recording method has been proposed in which the demagnetizing field decreases as the recording density increases, and a CoCr sputtered film that is easy to magnetize in the direction perpendicular to the film thickness has been proposed as a magnetic recording medium suitable for this perpendicular recording. (Japanese Patent Laid-Open No. 52-13470
No. 6). After that, as such a perpendicular recording medium, CoC
r In addition to sputtered films, Co alloy films such as CoM and CoCrM (M is the third element) by dry film forming methods such as sputtering and vapor deposition,
Fe alloy films, Os-added ferrite films, Ba ferrite films, etc. have been developed, but when these films are produced by a dry film forming method, there is a problem in mass productivity because they are performed in a vacuum system.

Therefore, there has been developed a method of manufacturing a perpendicular recording medium by an electroless plating method which is excellent in mass productivity by improving such manufacturing problems. The plating bath used in this method is
Electroless CoMnP plating bath (JP-A-57-140869), electroless CoNiMnP plating bath (JP-A-58-058267), electroless
CoNiMnReP plating bath (JP-A-60-103181), electroless
A CoNiReP plating bath (Japanese Patent Laid-Open No. 61-003316) has been found. In order to have perpendicular anisotropy in a cobalt alloy magnetic film, it is necessary to orient mainly the c-axis of hcpCo (hexagonal crystal) vertically to the substrate, but in these baths, CoP or CoNiP plating baths are used for Mn. Alternatively, a soluble salt such as Re may be added to add CoMnP, CoNiMnP, CoNiMnReP, CoNiReP
Good vertical orientation is obtained by using an alloy film such as.

Generally, the conditions that make the magnetization easy in the direction perpendicular to the film surface are: the media anisotropic energy Ku, the film-specific perpendicular anisotropy energy K⊥, and the shape anisotropy energy 2πMs ² (Ms is saturation magnetization). Then K⊥> 2πMs ² or Ku = K⊥
There is a relationship of −2πMs ² > 0. (This is between the perpendicular anisotropy field Hk of the medium and the maximum demagnetizing field of 4πMs.
This is the same as having a relationship of Hk> 4πMs. It is not always necessary to satisfy this condition in the perpendicular recording medium, but it can be said that the larger the value of Ku or Hk, the better the medium characteristics. In order to obtain high density recording, it is usually preferable that the Hk value is at least about 2.0 kOe.

On the other hand, in order to obtain a large reproduction output, it is desirable to increase the Ms value. In other words, IEE Transaction on Magnetics (IEEE Transaction o
n Magnetics) According to Mag-18, No. 2, pp. 769-771, Ms <(3 / 4π) Hc (⊥) (Hc (⊥) is the perpendicular coercive force of the medium). The reproduction output value is said to be proportional to Ms. Also, in the above literature, Ms ≧ (3/4
In the case of π) Hc (⊥), the reproduction output is said to be proportional to Hc (⊥). Therefore, to increase the playback output, Hc
It is necessary to increase (⊥) and increase Ms within the range of having sufficient perpendicular magnetic anisotropy. In practice, the value of Hc (⊥) is limited by the type of magnetic head used or the recording conditions, so it is desirable to select an appropriate Hc (⊥) value according to the required recording density and output.

(Problems to be solved by the invention) By using the above electroless CoMnP plating bath or electroless CoNiMnP plating bath, the c-axis of hcpCo hexagonal crystal is vertically oriented to the substrate, and a maximum Hc (⊥) of about 2.1 kOe is obtained. CoMnP and CoNiM
A magnetic film of nP can be obtained, but the magnetic film thus obtained is
The perpendicular magnetic anisotropy was insufficient for the Ms value, which was not preferable as a perpendicular recording medium. Therefore, CoMnP and CoNiMnP
By co-depositing Re on the magnetic layer, the perpendicular magnetic anisotropy was improved and a perpendicular magnetic film was obtained, but Ms was 150-350emu /
It was difficult to obtain Hc (⊥) larger than 1.4 kOe. That is, there has been a demand for a perpendicular recording medium having sufficient perpendicular magnetic anisotropy (large Hk value) while maintaining a large Hc (⊥) value and Ms value for higher output. Then either of these was insufficient.

An object of the present invention is to provide an electroless plating bath for improving a conventional problem and producing a magnetic recording medium having excellent characteristics as a perpendicular recording medium.

(Means for Solving the Problems) The electroless plating bath according to the present invention contains cobalt ions and nickel ions, contains at least a reducing agent for the metal ions as an additive, and has a tartaric acid group as a complexing agent for the metal ions. And an aqueous solution containing a malonic acid group, a glycolic acid group and a malic acid group, to which zinc ions in a concentration range of 0.01 to 0.10 mol / l are added.

The main components of the electroless plating bath used in the present invention include cobalt ion, nickel ion and zinc ion, hypophosphite, tartaric acid group, malonic acid group, glycolic acid group and malic acid group. Additives such as pH buffers, brighteners, leveling agents, stimulants, pinhole inhibitors, and surfactants may be used as long as the purpose and effect are not impaired.

Cobalt ion, nickel ion, zinc ion, cobalt, nickel or zinc sulfate, chloride, acetate,
It is supplied by dissolving a soluble salt such as an organic acid salt in an electroless plating bath. The cobalt ion concentration is 0.
A range of 0005 to 1.5 mol / l is used, preferably 0.00
Used in the range of 2 to 0.2 mol / l. The concentration of nickel ion is used in the range of 0.001 to 2 mol / l, preferably 0.01 to 0.25 mol / l. Cobalt as a metal ion used in the present invention, cobalt as a main component, a small amount of Be, Mg, Al, Ru, Si, Fe, Sr, Y, Zr,
Nb, Cd, In, Sb, Ta, Ir, Hg, Tl, Nb, Gd, Tb, Ti, V, Cr, Cu, Ga, Ge,
Mn, W, Mo, Rh, Pd, Ag, Au, Pt, Sn, Te, Ba, Ce, Sm, Os, Pb, Re, Bi
And the like may be contained in a range that does not affect the effect of the present invention, and these ions are supplied by the respective soluble salts.

As the reducing agent, hypophosphite is used in the range of 0.005 to 0.9 mol / l, preferably 0.05 to 0.3 mol / l. Since hypophosphite is used as the reducing agent, P is co-deposited in the obtained plated film. In the CoNiZnP film formed by the electroplating method, P is likely to be co-deposited, and the P content is 4 to 8% by weight (JP-A-59-48904). However, in the electroless plating method, a large amount of P is co-deposited. Difficult and the P content is low. The plating film which can obtain good perpendicular magnetic anisotropy by the electroless plating bath has a P content of 0.1 to 3.8% by weight, preferably 1.5 to 3.5% by weight.

Examples of complexing agents include glycolic acid groups such as glycolic acid, sodium glycolate, ethyl glycolate, methyl glycolate, cobalt glycolate, nickel glycolate, and malic acid, sodium malate, potassium malate, diethyl malate, and the like. Malic acid groups are used. As the glycolic acid group, glycolic acid or a soluble salt of glycolic acid is used in the range of 0.001 to 3 mol / l, preferably 0.1 to 1.75 mol / l. The malic acid group is
Malic acid or a soluble salt of malic acid is used in the range of 0.001 to 1 mol / l, preferably in the range of 0.1 to 0.75 mol / l.

In addition, as the complexing agent, soluble salts of malonic acid and tartaric acid are used in a concentration range of 0.1 to 1.5 mol / l.

Ammonium salts, carbonates, organic acid salts, etc. are used as the pH buffer, and ammonium sulfate, ammonium chloride,
It is preferable to use boric acid or the like. Concentration range is 0.01-3m
ol / l, preferably 0.03 to 1 mol / l is used.

As a pH adjuster, ammonia, caustic alkali as NaOH, LiOH, KOH, RbOH, CsOH, FrOH, Be (OH) ₂ , Mg (OH) ₂ , C
Metal hydroxides such as a (OH) ₂ , Sr (OH) ₂ , Ba (OH) ₂ and Ra (OH) ₂ are used alone or in combination of two or more. It is also possible to use ammonia and caustic together.

Usually, the plating solution before adding a bath without adding a pH adjuster is in a neutral or acidic range, and the pH is adjusted to alkaline by adding the hydroxide. Acids such as hydrochloric acid, sulfuric acid, nitric acid, and acetic acid are used to lower the pH when the pH exceeds the required level. The pH range used is between 6 and 14.5, preferably between 8.0 and 11.0.

(Function) A typical perpendicular recording medium by electroless plating is CoNiMnRe
It is a P film. Mn has a function of vertically aligning the c-axis of hcpCo (hexagonal crystal) with the substrate. Re has the function of maintaining perpendicular magnetic anisotropy and effectively lowering Ms. Ni has the role of preventing the precipitation rate from decreasing when eutectoiding Re. P is co-deposited at the same time in the electroless plating of hypophosphorous acid reduction. This is CoNiMn
It is considered to be the role of each component of the ReP film, but it is preferable not to use Re, which has a problem in bath management and reduces Mn and Ms. Electroless plating thermodynamically causes a plating reaction that can occur anywhere in a plating bath solution to proceed at a substantially reaction rate on a highly active substrate surface, and to prevent the reaction from progressing in a solution, the solution components are It has been adjusted. Further, the control of the plating reaction also changes the plating film structure and film characteristics. Mn and Re are involved in the film structure and properties, but Mn and Re
This is because the addition of a soluble salt of Re affects the plating reaction on the substrate surface. Therefore, it was thought that it would be unnecessary to use Mn or Re depending on the appropriate combination of other added metals that affect the plating reaction and complexing agents that are important solution components. However, since the relationship between the complexing agent and the orientation of the deposited alloy film, the magnetic properties, etc. has not been clarified, until the present invention, as a result of extensive and extensive studies conducted experimentally, various complexing agents Among them, it was found that a combination of glycolic acid group and malic acid group can be applied for this purpose. Furthermore, as a result of examining the effect of various added metals other than Mn and Re, it was revealed that zinc is co-deposited on the CoNiP film by the addition of a soluble salt of zinc, which improves perpendicular magnetic anisotropy and increases Hc (⊥). Became.

The present invention has been brought about by obtaining such knowledge.

Next, the present invention will be specifically described with reference to Examples and Comparative Examples.

(Example 1) A non-magnetic NiP layer was plated on an aluminum alloy substrate, the surface was mirror-polished, and the following plating bath was used thereon to obtain a film thickness of 0.1.
A CoNiZnP alloy magnetic film having a thickness of 05 to 1.0 μm was formed.

Plating bath (1) Bath composition Cobalt sulfate 0.07mol / l Nickel sulfate 0.17mol / l Zinc sulfate 0.04mol / l Sodium hypophosphite 0.2mol / l Ammonium sulfate 0.5mol / l Sodium tartrate 0.25mol / l Sodium malonate 0.75mol / l Sodium malate 0.02mol / l Glycolic acid 1.0mol / l Plating condition Bath temperature 80 ℃ Plating bath pH 9.15 (pH adjusted with ammonia water at room temperature) Magnetic properties of the magnetic film thus obtained Meter and magnetic torque meter. MH of this magnetic film
The loop had a shape peculiar to the perpendicular magnetic anisotropic film in which the vertical loop surrounded the in-plane loop. Hc (⊥) is 3.15 kOe, Ms is 6
10emu / cc, Hk had a large value of 8.6 kOe. The torque curves obtained by the magnetic anisotropy energy measurement all showed clear uniaxial anisotropy and had a positive anisotropy energy Ku value (eg, 7.5 × 10 ⁴ erg / c at a film thickness of 0.25 μm).
c).

Next, the structure of the magnetic film, which is considered to be the cause of exhibiting such characteristics, was examined by X-ray diffraction and electron beam diffraction. In X-ray diffraction, only sharp peaks due to diffraction from the (002) plane, which indicates that the c-axis of hcpCo (hexagonal crystal) is oriented perpendicular to the substrate surface, are recognized, which corresponds to diffraction from other lattice planes. No peak was observed. The electron beam diffraction results also revealed that the hcpCo structure had a c-axis oriented perpendicularly to the substrate surface and exhibited a higher orientation than the thin film having a film thickness of 0.05 μm. That is, it was clarified that the magnetic film obtained in this example exhibits perpendicular magnetic anisotropy and has preferable characteristics as a perpendicular recording medium.

(Example 2) A magnetic film was produced in the same procedure as in Example 1, but in this example, the concentration of zinc sulfate was 0 to 0 in the plating bath (1).
The CoNiZnP alloy magnetic film was formed by changing the range of 0.2 mol / l.

Magnetic properties of the magnetic film thus obtained (saturation magnetization Ms
Table 1 shows the results of measuring (⊥), anisotropic magnetic field Hk, and coercive force Hc (⊥).

When the zinc sulfate concentration is 0 mol / l, Hk is 4.7 kOe and Hc (⊥) is
It was 1.40 kOe. Hk and Hc with increasing zinc sulfate concentration
(⊥) increased. Hk at a zinc sulfate concentration of 0.01 mol / l
(⊥) increased to 6.4 kOe and Hc (⊥) increased to 1.76 kOe, 0.04 mol
With / l, Hk reached 8.6 kOe and Hc (⊥) reached 3.15 kOe, which was the maximum value.
At higher concentrations, Hk and Hc (⊥) decrease and zinc sulfate concentration increases.
At 0.175 mol / l, Hk decreased to 1.9 kOe and Hc (⊥) decreased to 0.74 kOe. Further, as shown in the table, in the plating bath of the present invention, Ms does not decrease sharply even if the perpendicular magnetic anisotropy increases, and the zinc sulfate concentration becomes 0.175 mol / l and 500 emu / cc.
Fell to a value below. For Hc (⊥), Hk is 2.
It was possible to change in a considerably wide range in the film of 0 kOe or more. The MH loop of the magnetic film obtained in the concentration range of zinc sulfate up to 0.10 mol / l had a shape peculiar to the perpendicular magnetic anisotropy film in which the vertical loop surrounded the in-plane loop. In X-ray diffraction of these magnetic films, only sharp peaks due to diffraction from the (002) plane were observed, and peaks corresponding to diffraction from other lattice planes were not observed. The electron beam diffraction results also revealed that the c-axis was composed of the hcpCo structure oriented perpendicularly to the substrate surface and exhibited high crystallinity and orientation.

That is, the magnetic film obtained in this example has a large Hc (⊥)
Has a sufficient perpendicular magnetic anisotropy (large Hk value) while maintaining the Ms value and a large Ms value, and has various characteristics preferable as a perpendicular recording medium, and the magnetic characteristics can be controlled by changing the zinc sulfate concentration. It became clear.

(Example 3) A magnetic film was prepared by the same procedure as in Example 1, but in this example, in the plating bath (2) shown below, the concentration of zinc acetate was in the range of 0 to 0.2 mol / l. The CoNiZnP alloy magnetic film was formed by changing.

Plating bath (2) Cobalt sulfate 0.05mol / l Nickel sulfate 0.13mol / l Zinc acetate 0.1 ~ 0.2mol / l Sodium hypophosphite 0.17mol / l Ammonium sulfate 0.41mol / l Sodium potassium tartrate 0.15mol / l Sodium malonate 0.55mol / l Sodium malate 0.01mol / l Sodium glycolate 1.1mol / l Plating condition Bath temperature 78 ℃ Plating bath pH 9.4 (pH adjustment with ammonia water at room temperature) Magnetic properties of magnetic film (saturation) Magnetization Ms
Table 2 shows the results of measuring (⊥), anisotropic magnetic field Hk, and coercive force Hc (⊥).

When the zinc acetate concentration is 0 mol / l, Hk is 3.9 kOe and Hc (⊥) is
It was 1.06 kOe. Hk and Hc with increasing zinc acetate concentration
(⊥) increased. Hk at a zinc acetate concentration of 0.01 mol / l
(⊥) increased to 6.1 kOe, Hc (⊥) increased to 1.77 kOe, 0.04 mol
With / l, Hk reaches 7.8 kOe and Hc (⊥) reaches 2.55 kOe, which is the maximum value.
Hk and Hc (⊥) decreased at higher concentrations. When the zinc acetate concentration is 0.15 mol / l, Hk is 1.9 kOe and Hc (⊥) is 0.81 kOe.
And greatly decreased. In addition, as shown in the table, in the plating bath of the present invention, Ms does not decrease sharply even when the perpendicular magnetic anisotropy increases, and the zinc acetate concentration becomes 0.15 mol / l and 400 emu / cc.
Fell to a value below. For Hc (⊥), Hk is 2.
It was possible to change in a considerably wide range in the film of 0 kOe or more. The MH loop of the magnetic film obtained in the concentration range of zinc acetate up to 0.10 mol / l had a shape peculiar to the perpendicular magnetic anisotropy film in which the vertical loop surrounded the in-plane loop. In X-ray diffraction of these magnetic films, only sharp peaks due to diffraction from the (002) plane were observed, and peaks corresponding to diffraction from other lattice planes were not observed. The electron beam diffraction results also revealed that the c-axis was composed of the hcpCo structure oriented perpendicularly to the substrate surface and exhibited high crystallinity and orientation.

That is, the magnetic film obtained in this example has a large Hc (⊥)
Has a sufficient perpendicular magnetic anisotropy (large Hk value) while maintaining the Ms value and a large Ms value, and has various characteristics preferable as a perpendicular recording medium, and the magnetic characteristics can be controlled by changing the zinc acetate concentration. It became clear.

In addition, the electroless plating bath used in the above examples is
Compared to a four-element or five-element multi-element alloy electroless plating bath containing Mn or Re, bath management is easy and remarkably stable, and a magnetic film having excellent characteristics as a perpendicular recording medium can be produced with good reproducibility. I was able to. Anisotropy field of 2.0 kOe or more when making many media from plating baths of the same capacity
When the plating treatment from the beginning of plating where the Hk value is obtained to a value of 2.0 kOe or less is taken as the bath life, the bath life of the electroless plating bath according to the present invention is 10 compared to the conventional multi-component alloy electroless plating bath. It was more than doubled.

(Effects of the Invention) As described above, according to the present invention, at least cobalt ions, nickel ions and zinc ions are contained as metal ions, and a reducing agent for at least the metal ions is contained as an additive, and By using an electroless plating bath containing at least a glycolic acid group and a malic acid group as a metal ion complexing agent, a CoNiZnP film having excellent properties as a perpendicular recording medium can be stably prepared.

Claims (1)

[Claims] 1. A cobalt ion and a nickel ion, at least the reducing agent for the metal ion as an additive, and a tartaric acid group, a malonic acid group, a glycolic acid group, and malic acid as a complexing agent for the metal ion. An electroless plating bath for producing a magnetic recording medium used for perpendicular recording, which is an aqueous solution containing a group and to which zinc ions in a concentration range of 0.01 to 0.10 mol / l are added.