JPH08981B2 - Electroless plating bath - Google Patents

Description

TECHNICAL FIELD The present invention relates to a plating bath for producing a magnetic recording medium used for so-called perpendicular recording, in which recording is performed by magnetization in the film thickness direction of a magnetic recording medium (magnetic film). It is a thing.

(Prior Art) Conventionally, in a magnetic recording device such as a general magnetic disk device and a magnetic tape device, recording has been performed by magnetizing in the longitudinal direction of a magnetic recording medium. There is a drawback that the demagnetizing field in the medium is increased to cause attenuation and rotation of the residual magnetization, and the reproduction output is significantly reduced. Therefore, the demagnetizing field becomes smaller as the recording density increases, and a perpendicular recording method capable of high density recording and a CoCr sputtered film as a recording medium suitable for this perpendicular recording have been proposed (Japanese Patent Laid-Open No. 52-134706). Gazette). After that, as such a perpendicular recording medium, in addition to the CoCr sputtered film, CoM and CoC by a dry film-forming method such as sputtering and vapor deposition.
Co alloy films such as rM (M is the third element), Fe alloy films, Os-added ferrite films, Ba ferrite films, etc. have been developed. However, when these films are produced by the dry film forming method, they are in a vacuum system. Therefore, there is a problem in mass productivity.

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 includes an electroless CoMnP plating bath (JP-A-57-140869),
An electroless CoNiMnP plating bath (JP-A-58-058267) and an electroless CoNiMnReP plating bath (JP-A-60-103181) have 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) vertically to the substrate.
Alternatively, add Mn to the CoNiP plating bath to remove CoMnP, CoNiMn
Good vertical orientation was obtained by using an alloy film such as P. Furthermore, the magnetic properties were improved by adding Re to CoNiMnP.

However, the medium characteristics are closely related to the film structure and the film composition, and it is not easy to control the structure and composition of the multi-component alloy film to obtain good medium characteristics. For this reason, simplification of the alloy system has been investigated. First, tartronic acid is c of Co
It has been found that it is an extremely effective complexing agent for axially vertical alignment, and it has become possible to achieve vertical alignment without using Mn in the CoNiMnReP film (Japanese Patent Laid-Open No. 61-003316). However, since tartronic acid is expensive, CoNiP perpendicular medium films have been obtained by an electroless plating bath characterized by containing glycolic acid and malic acid without using tartronic acid (13th Japan Applied Magnetics). Academic Conference Lectures, 294 pages, November 24, 1989).

Generally, the conditions that make the magnetization easy in the direction perpendicular to the film surface are: the anisotropy energy of the medium is Ku, the perpendicular anisotropy energy of the film is K⊥, and the shape anisotropy energy is 2πMs ² (Ms is saturation magnetization). Then K⊥> 2πMs ² or Ku = K
It means that there is a relation of ⊥-2πMs ² > 0. (this is,
This is similar to the fact that there is a relationship of Hk> 4πMs between the perpendicular anisotropy magnetic field Hk of the medium and the maximum demagnetizing field value 4πMs. )
The perpendicular recording medium does not necessarily have to satisfy this condition, but it can be said that the larger the value of Ku or Hk, the better the medium characteristics. To obtain high density recording,
Usually, it is 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 Transac
tion on Magnetics) Volume Mag-18, No. 2, 769-771
According to the page, the reproduction output value is Ms under the condition of Ms <(3 / 4π) Hc (⊥) (Hc (⊥) is the coercive force in the perpendicular direction of the medium).
It is said to be proportional to. In the above literature, Ms ≧
In the case of (3 / 4π) Hc (⊥), the reproduction output is said to be proportional to Hc (⊥). Therefore, in order to increase the reproduction output, it is necessary to increase Hc (⊥) and increase Ms within a range having sufficient perpendicular magnetic anisotropy. In practice, Hc (⊥) depends on the type of magnetic head used or recording conditions.
Since the value of is limited, it is desirable to be able 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 CoNiP plating bath, a simplified alloy-based perpendicular recording medium can be obtained as compared with conventional alloy films such as CoNiMnP, CoNiMnReP, and CoNiReP. However, since the characteristics obtained by the multi-component alloy film are obtained by the simplified alloy film, the control of the plating reaction becomes more important. For this reason, the bath system was complicated and the plating bath was more difficult to control. That is, in the above electroless CoNiP plating bath,
Although it is characterized by containing at least glycolic acid and malic acid as complexing agents, it is not easy to obtain medium characteristics with good reproducibility when glycolic acid is used in the plating bath. Therefore, there has been a demand for a simplified electroless CoNiP plating bath that does not require the use of glycolic acid.

The object of the present invention is to improve the conventional problems, to have excellent characteristics as a perpendicular recording medium, and to have an appropriate Hc (⊥) value.
It is to provide an electroless plating bath capable of producing a CoNiP film with good reproducibility and stability.

(Means for Solving the Problems) The electroless plating bath of the CoNiP perpendicular recording medium according to the present invention contains cobalt ions and nickel ions as metal ions, and contains at least hypophosphorous acid or hypophosphite as an additive. An electroless plating bath containing a reducing agent for the metal ions of one or more species, which contains a tartaric acid group, a malonic acid group and a malic acid group as a complexing agent for the metal ions,
The malic acid group concentration is in the range of 0.3 to 1.0 mol / l.

The main components of the electroless plating bath used in the present invention include at least cobalt ions and nickel ions as metal ions, and an aqueous solution containing at least a reducing agent for the metal ions as an additive, as a complexing agent for the metal ions. Although it contains a malonic acid group, a tartaric acid group, and a malic acid group, the addition of a pH buffer, a brightening agent, a leveling agent, an stimulant, a pinhole inhibitor, a surfactant, etc. is included within the scope of the object and effect of the present invention Agents may be used.

Cobalt ions and nickel ions are supplied by dissolving soluble salts such as cobalt or nickel sulfates, chlorides and acetates in an electroless plating bath. The cobalt ion concentration used is in the range of 0.0015 to 1 mol / l, preferably 0.02 to 0.15 mol / l. The concentration of nickel ions is in the range of 0.01 to 1 mol / l, preferably 0.03 to 0.2 mol / l.

As a reducing agent, hypophosphorous acid or hypophosphite 1
Seed or more, 0.01 ~ 0.6 mol / l, preferably 0.07 ~ 0.35 mol /
Used in the l range.

As a complexing agent, malonic acid or sodium malonate, malonic acid groups such as ethyl malonate, methyl malonate and tartaric acid or sodium tartrate, ammonium tartrate, potassium sodium tartrate, potassium ammonium tartrate,
Tartaric acid groups such as diethyl tartrate and malic acid groups such as malic acid, sodium malate, potassium malate and ethyl malate are used. As the malonic acid group, malonic acid or a soluble salt of malonic acid is used in the range of 0.05 to 1.7 mol / l, preferably 0.2 to 0.9 mol / l. As the tartaric acid group, tartaric acid or a soluble salt of tartaric acid is used in the range of 0.01 to 1.2, preferably 0.05 to 0.6 mol / l. The malic acid group contains 0.3% of malic acid or a soluble salt of malic acid.
Used in the range of ~ 1 mol / l. In order to obtain a CoNiP perpendicular recording medium without using glycolic acid, it is necessary to use malic acid groups in this concentration range in combination with malonic acid groups and tartaric acid groups.

Ammonium salts, carbonates, organic acid salts and the like are used as the pH buffering agent, and ammonium sulfate, ammonium chloride, boric acid and the like are preferably used. Concentration range is 0.01
~ 3 mol / l, preferably 0.03 to 1 mol / l is used.

As a pH adjuster, ammonia or caustic 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 7.5 and 12.5, preferably between 8.0 and 11.0.

(Function) As a plating bath for producing a CoNiP perpendicular recording medium, a simplified electroless CoNiReP plating bath having a bath system is preferable to an electroless CoNiMnReP plating bath. Conventionally, a special complexing agent called tartronic acid has been used in order to orient the c-axis of hcpCo (hexagonal crystal) vertically to the substrate without using Mn and obtain excellent characteristics as a perpendicular recording medium.
It is believed that this is because tartronic acid played an important role in maintaining a favorable complex state for the c-axis vertical orientation of Co. Therefore, it was thought that it would not be necessary to use Re in addition to Mn depending on the combination of appropriate complexing agents. However, since the relationship between the complexing agent and the orientation of the deposited alloy film has not been clarified, the results of extensive and extensive experimental studies up to the present invention showed that malonic acid groups , A combination of tartaric acid groups and malic acid groups was found to be applicable for this purpose. The concentration range of malic acid group is particularly important, and it is necessary to set it to 0.3 to 1 mol / l. At present, the relationship between the complexing agent and the film structure / magnetic properties has not been theoretically elucidated, so that the action of the malic acid group, which is an important complexing agent, cannot be fully explained. However, considering the results after the inventors discovered a suitable bath, malic acid CH ₂ CH (OH) (COOH) ₂ was found to be tartronic acid CH (which has the action of vertically aligning the Co crystals of the magnetic film. OH) (COO
H) close structural in which CH ₂ was increased to _2. Also, both are OH
It is a carboxylic acid having both a group and a COOH group. It is speculated that such structural characteristics of the complexing agent may be due to this action.

The present invention has been made by obtaining such knowledge.

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

Example 1 A non-magnetic Ni-P layer was plated on an aluminum alloy substrate, the surface was mirror-polished, and then the following plating bath was used to form a film thickness.
A CoNiP alloy magnetic film of 0.06 to 1.0 μm was formed.

Plating bath (1) Bath composition Cobalt sulfate 0.065 mol / l Nickel sulfate 0.17 mol / l Sodium hypophosphite 0.25 mol / l Ammonium sulfate 0.5 mol / l Sodium tartrate 0.2 mol / l Sodium malonate 0.7 mol / l Sodium malate 0.7 mol / l Plating condition Bath temperature 80 ° C pH 9.5 of plating bath (pH adjusted with ammonia water at room temperature) The magnetic properties of the magnetic film thus obtained were measured using a vibrating sample magnetometer and a magnetic torque meter. Of this magnetic film
The MH loop had a shape peculiar to the perpendicular magnetic anisotropic film in which the vertical loop surrounded the in-plane loop. Hk is 6.1 kOe, saturation magnetization Ms
Had a large value of 610 emu / cc. The torque curves obtained by the magnetic anisotropy energy measurement all showed clear uniaxial anisotropy and had a positive anisotropy energy Ku value (for example, 6.5 × 10 ⁴ erg / cc at a film thickness of 0.25 μm). ).

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) is oriented perpendicular to the substrate surface, were observed, and diffraction from other lattice planes was observed. No peak corresponding to was observed. The electron diffraction results also revealed that the c-axis is composed of a hcpCo structure oriented vertically to the substrate surface and exhibits a higher orientation than the thin film having a film thickness of 0.06 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 prepared by the same procedure as in Example 1, but
In this example, the concentration of sodium malate in the plating bath (1) was changed in the range of 0 to 1.1 mol / l to form a CoNiP alloy magnetic film.

Magnetic properties of the magnetic film thus obtained (anisotropic magnetic field Hk,
The results of measuring the coercive force Hc (⊥)) are shown in Fig. 1.

When the sodium malate concentration is 0 mol / l, Hk is 0.55 kO
It was e, and the MH loop of the magnetic film and the film could be easily magnetized in-plane according to the torque measurement. 0.3 mol / l sodium malate
When added, Hk became 3.8 kOe, and it was confirmed that MH loop of the magnetic film and the tendency to change to a film in which perpendicular magnetization was easy were observed by torque measurement. Hk further increases with increasing sodium malate concentration and progresses to the perpendicular magnetization film. Hk reaches a maximum value of 6.25 kOe at a sodium malate concentration of 0.6 mol / l. At higher concentrations, Hk decreases to 1.0 mol / l, which is 3.6 kOe. Further, in the plating bath of the present invention, even if the perpendicular magnetic anisotropy is increased,
Ms did not decrease sharply and maintained a large value of 550 to 630 emu / cc. Hc (⊥) could be changed in a wide range of about 860 to 1750 Oe in the film with Hk of 3.5 kOe or more. Sodium malate concentration is 0.3-1.0
In the mol / l range, the MH loop of the obtained magnetic film is
The vertical loop had a shape unique to the perpendicular magnetic anisotropy film surrounding the in-plane loop. In X-ray diffraction of these magnetic films, (00
2) Only sharp peaks due to diffraction from the plane were observed, and no peaks corresponding to diffraction from other lattice planes were observed. The electron 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, it was revealed that the magnetic film obtained in this example exhibits perpendicular magnetic anisotropy and has various characteristics preferable as a perpendicular recording medium.

Example 3 A magnetic film was prepared in the same procedure as in Example 1, but
In this example, a CoNiP alloy magnetic film was formed using the following plating bath.

Plating bath (2) Cobalt chloride 0.05 mol / l Nickel chloride 0.15 mol / l Sodium hypophosphite 0.16 mol / l Ammonium chloride 0.35 mol / l Sodium tartrate 0.35 mol / l Sodium malonate 0.8 mol / l Sodium malate 0 1.3 mol / l Plating conditions Bath temperature 83 ℃ pH of plating bath 9.3 (pH adjustment with ammonia water at room temperature) Magnetic properties of the magnetic film thus obtained (anisotropic magnetic field Hk,
The results of measuring the coercive force Hc (⊥)) are shown in Fig. 2.

When sodium malate concentration is 0 mol / l, Hk is 0.6 kOe
Therefore, the MH loop of the magnetic film and the film could be easily magnetized in-plane according to the torque measurement. When 0.3 mol / l of sodium malate was added, Hk became 2.2 kOe, and it was confirmed that the MH loop of the magnetic film and the tendency to change to a film with easy perpendicular magnetization were obtained by torque measurement. As the sodium malate concentration increases, Hk further increases and advances to the perpendicular magnetization film. Sodium malate concentration
Hk reaches a maximum of 5.55 kOe at 0.7 mol / l. At higher concentrations, Hk decreases to 2.0 kOe at 1.0 mol / l. Further, in the plating bath of the present invention, Ms did not decrease sharply even if the perpendicular magnetic anisotropy increased, and a large value of 500 to 600 emu / cc was maintained. Hc (⊥) could be changed in a fairly wide range of about 500 to 1500 Oe in the film with Hk of 2.0 kOe or more. Sodium malate concentration is 0.4 ~ 0.9mol / l
In the range, the MH loop of the obtained magnetic film had a shape peculiar to the perpendicular magnetic anisotropy film in which the perpendicular 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. Also, from the electron diffraction result, the c-axis was vertically aligned with the substrate surface.
It was revealed that it is composed of hcpCo structure and exhibits high crystallinity and orientation.

That is, it was revealed that the magnetic film obtained in this example exhibits perpendicular magnetic anisotropy and has various characteristics preferable as a perpendicular recording medium.

In addition, the electroless plating bath used in the above examples is easy to manage and is extremely excellent in stability as compared with the conventional electroless plating bath using a glycolic acid group as a complexing agent, and as a perpendicular recording medium. A magnetic film having excellent characteristics could be produced with good reproducibility. When a large number of media are produced from plating baths of the same capacity, the plating treatment amount until the anisotropic magnetic field Hk value of 2.0 kOe or more obtained at the beginning of plating becomes a value of 2.0 kOe or less is the bath life. The bath life of the electroless plating bath was increased by 5 times or more as compared with the conventional electroless plating bath using a glycolic acid group.

(Effects of the Invention) As described above in the embodiments, according to the present invention, Co
In an electroless plating bath for producing a NiP magnetic film, a reducing agent for the metal ion containing at least cobalt ion and nickel ion as metal ions and at least one kind of hypophosphorous acid or hypophosphite as an additive. Containing a tartaric acid group, a malonic acid group and a malic acid group as a complexing agent of the metal ion, and changing the concentration of the malic acid group in the range of 0.3 to 1.0 mol / l, thereby maintaining and controlling the plating bath. It becomes easier to maintain a large Hk value and Hc
The value of (⊥) can be changed in a wide range, and a large number of magnetic films having excellent characteristics as a perpendicular recording medium can be stably manufactured.

[Brief description of drawings]

1 is a diagram showing the relationship between the sodium malate concentration of the electroless plating bath of the present invention obtained in Example 2 and Hk and Hc (⊥) of the obtained CoNiP magnetic film, and FIG. FIG. 7 is a similar view in Example 3.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-58-58270 (JP, A) JP-A-61-15985 (JP, A) JP-A-61-231176 (JP, A) JP-A-63- 83281 (JP, A)

Claims (1)

[Claims] 1. A metal ion containing cobalt ion, nickel ion, an additive containing at least one or more hypophosphorous acid or hypophosphite reducing agent for the metal ion, and a complex of the metal ion. An electroless plating bath containing a tartaric acid group, a malonic acid group and a malic acid group as an agent, wherein the concentration of the malic acid group is in the range of 0.3 to 1.0 mol / l. Electrolytic plating bath.