JPS622629B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION 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 direction of the film thickness of the magnetic recording medium.

Conventionally, in magnetic recording devices such as general magnetic disk devices and magnetic tape devices, recording is performed by horizontally magnetizing a magnetic film formed on a substrate using a ring-shaped magnetic head. However, in recording using horizontal magnetization, as the wavelength of the recording signal becomes shorter, that is, as the recording density increases, the demagnetizing field within the medium increases, causing attenuation and rotation of the residual magnetization, and the reproduction output decreases. The disadvantage is that it is significantly reduced. To solve this problem, a perpendicular recording method was proposed in which the demagnetizing field becomes smaller as the wavelength becomes shorter.A magnetic film suitable for this perpendicular recording has an axis of easy magnetization perpendicular to the film surface. A sputtered Co-Cr alloy film has been proposed. It has been reported that this perpendicular magnetization recording method is superior to the conventional recording method using horizontal magnetization in high-density recording. However, when producing a Co-Cr alloy film using the sputtering method, there are problems with mass production because it is performed in a vacuum system, and there is a problem in that the substrate temperature increases due to sputtering, which limits the substrate material that can be used. .

The purpose of the present invention is to solve these manufacturing problems by using an electroless plating method that is excellent in mass productivity and that can be manufactured at a temperature below the softening temperature of not only metal substrates but also commonly used organic resin substrates. An object of the present invention is to provide an electroless plating bath for producing a magnetic film having an axis of easy magnetization in a direction perpendicular to the film surface.

A feature of the present invention is that an electroless plating bath containing at least a metal ion, a metal ion reducing agent, a PH buffer, a PH regulator, and a complexing agent for the metal ion (1)
Cobalt ion (Co ²⁺ ) of 0.1 mol/or more and nickel ion (Ni ²⁺ ) of 0.1 mol/more as metal ions, (2) Contains at least a pyrophosphate group as a complexing agent for metal ions, and plating bath temperature is 55-75
The PH was adjusted to a range of 8.0 to 10.0 at 65°C, which made it possible to orient the axis of easy magnetization of the magnetic film in a direction perpendicular to the film surface.

As cobalt ions (Co ²⁺ ) and nickel ions (Ni ²⁺ ) used as metal ions in the present invention, soluble salts of cobalt and nickel such as sulfates, sulfamates, chlorides, and acetates can be prepared using an electroless method. It is supplied by dissolving it in a soaking bath. The concentration of cobalt ion is 0.1mol/
The above range is used, but as the cobalt ion concentration increases, the plating bath gradually becomes unstable, and especially when the cobalt ion concentration exceeds 0.2 mol/min, cobalt hydroxide precipitates in a short period of time, significantly shortening the bath life. decreases significantly. Therefore, from the viewpoint of crystallinity, there is no need to set an upper limit, but for practical purposes,
Preferably, the cobalt ion concentration is 0.1-0.2 mol/
is within the range of Also, the concentration of nickel ions is
A range of 0.1 mol/or more is used, but if the nickel ion concentration is 0.4 mol/or more, the plating particles tend to abnormally precipitate in the plating bath, thereby reducing the bath life. Therefore, from the viewpoint of crystallinity, it is not necessary to set a particular upper limit, but it is practically preferable that the nickel ion concentration is 0.1 to 0.4 mol/
is within the range of

As a reducing agent for metal ions, hypophosphorous acid groups such as sodium hypophosphite or potassium hypophosphite are generally used.

Ammonium salts, carbonates, organic acid salts, etc. are generally used as PH buffers.

As a pH regulator, ammonia water or a combination of ammonia water and a caustic alkali such as sodium hydroxide and potassium hydroxide is generally used to increase the pH. Generally, sulfuric acid, sulfamic acid, hydrochloric acid,
Acids such as acetic acid are used, and with these PH regulators,
The pH of the plating bath is always 8.0 to 10.0 based on 65℃.
adjusted to.

Pyrophosphate group as a complexing agent for metal ions
Supplied by pyrophosphate or soluble salts of pyrophosphate. Furthermore, in addition to pyrophosphate groups, inorganic or organic acids, such as boric acid groups, amino acid groups, malonic acid groups, malic acid groups, succinic acid groups, gluconic acid groups, or their soluble salts may be used in combination as complexing agents. good.

The present inventor has disclosed that regarding an ammonia alkaline electroless Co-Ni-P plating bath containing a pyrophosphate group,
FIGS. 1 and 2 are graphs showing the results of investigating the crystallinity of plated films deposited by varying the cobalt ion (Co ²⁺ ) and nickel ion (Ni ²⁺ ) concentrations. Figure 1 shows the cobalt ion (Co ²⁺ ) and nickel ion (Ni ²⁺ ) concentrations and the resulting Co−
This is a graph showing the relationship between the crystallinity of the Ni--P plated film. In the figure, the easy axis of magnetization (C
The region where the easy axis of magnetization is oriented in-plane, the region where the easy axis of magnetization is isotropically oriented in the plane and in the vertical direction, or the region where the easy axis of magnetization is weakly oriented in the vertical direction, and the region where the easy axis of magnetization is strongly oriented vertically. Figure 2 also shows the relationship between the nickel ion (Ni ²⁺ ) concentration at a plating film thickness of 5μ and the Co(002) surface of the resulting plating film, when the cobalt ion (Co ²⁺ ) concentration in the plating bath is taken as a parameter. It is a graph showing the relationship between X-ray diffraction intensity, and the second
The figure shows that when the cobalt ion (Co ²⁺ ) and nickel ion (Ni ²⁺ ) concentrations are both 0.1 mol/or higher, the Co (002) plane of the resulting plated film develops extremely strongly. .

That is, an ammonia alkaline electroless Co-Ni-P containing a pyrophosphate group as a complexing agent for metal ions.
As a result of a detailed study of the influence of the plating bath composition and conditions on the crystal structure of the plating film deposited in the plating bath, it was found that pyrophosphate groups exist in the plating bath and the plating bath temperature is in the range of 55 to 75℃. , the cobalt ion (Co ²⁺ ) and nickel ion (Ni ²⁺ ) concentrations in the plating bath were both 0.1 mol/
above (region in Figure 1), the crystals of the precipitated plated film develop selectively and strongly on the Co (002) plane, and α
- It was newly discovered that the easy axis of magnetization (C axis) of Co hexagonal crystals is highly oriented in the direction perpendicular to the film surface. At this time, if even one of the above conditions is lacking, the resulting plated film will have weaker development of the Co (002) plane and weaker vertical orientation of the axis of easy magnetization.
Or, the object of the present invention cannot be satisfied due to orientation in the in-plane direction.

When the concentration of cobalt ions (Co ²⁺ ) and nickel ions (Ni ²⁺ ) in the plating bath is less than 0.1 mol/min, the perpendicular orientation of the easy axis of magnetization of the plating film crystals weakens, and even the internal orientation do. In addition, if there is no pyrophosphate group in the plating bath and the plating bath temperature is 55 to 75°C, the plating film will hardly precipitate, or even if it does, the rate of precipitation is extremely slow; The crystals are oriented on the Co(100) plane. On the other hand, when the plating bath temperature is 55°C or lower, almost no plating is deposited, and when it is 75°C or higher, Co of the plating film crystals is deposited.
Development to the (002) plane is extremely reduced. In addition, the effect of plating bath pH is not as great as metal ion concentration and plating bath temperature, but when considering a plating bath temperature of 65℃ as a standard, if the pH is not adjusted to 8.0 to 10.0, Since precipitation occurs and the plating bath becomes unstable, it is not a useful plating bath.

Conventionally, Co-Ni-
It is known that a P-plated film can be obtained (see Metal Surface Technology Association Journal VOI31 No. 3 1980). However, in order to obtain a perpendicularly magnetized film by electroless plating,
Co-Ni-Mn-P (see Abstracts of the 65th Academic Conference of the Metal Surface Technology Society, pages 136-137) and Co-Ni-Mn
In addition to Co, Ni, and P, other metals such as Mn and Re are added, such as -Re-P (see Abstracts of the 66th Academic Conference of the Metal Surface Technology Society, pages 8 to 9), and the temperature of the plating bath is increased. Excellent perpendicular magnetization characteristics could not be obtained unless the temperature was set at 80°C or higher. The electroless plated film obtained from the plating bath of the present invention basically consists of Co,
Excellent perpendicular magnetization characteristics can be obtained from the three elements Ni and P, and the plating bath temperature is as low as 55 to 75°C, making it extremely easy to control the plating bath conditions. .

The features of the electroless Co--Ni--P plating bath according to the present invention will be explained below using examples.

Example 1 A copper substrate with an electroless NiP plating film on the surface,
A Co--Ni--P film (film thickness: 5 μm) was formed thereon using the following plating bath composition and plating conditions.

Plating bath composition Cobalt sulfate 0.13 mol/ Nickel sulfate 0.13 mol/ Sodium hypophosphite 0.2 mol/ Ammonium sulfate 0.5 mol/ Sodium pyrophosphate 0.4 mol/ Plating conditions Plating bath PH9.0 (NH ₄ OH at 65℃) Plating bath temperature was 65° C. At this time, the plating deposition rate was about 0.16 mg/cm ² /min, and it took about 28 minutes to obtain a film thickness of 5 μm. FIG. 3 shows the results of X-ray diffraction carried out to examine the crystal structure of the deposited plating film. It can be seen that in the obtained Co-Ni-P plated film crystal, the Co (002) plane grows extremely strongly, and the crystal C axis is strongly oriented in the direction perpendicular to the film surface. When the rocking curve of the (002) plane was measured, its half-value width △θ
The dispersion angle of ₅₀ was approximately 9.5°C. The results of measuring the vertical and horizontal magnetization hysteresis characteristics of the plated film using a vibrating magnetometer (VSM) are shown in the fourth section.
As shown in the figure.

Example 2 A Co--Ni--P film (film thickness: 5 μm) was formed using the following plating bath composition in the same manner as in Example 1.

Plating bath composition Cobalt sulfate 0.14mol/ Nickel sulfate 0.28mol/ Sodium hypophosphite 0.2mol/ Ammonium sulfate 0.5mol/ Sodium pyrophosphate 0.4mol/ Boric acid (anhydrous) 0.1mol/ Plating conditions Plating bath PH9.0 (PH fine adjustment with NH ₄ OH at 65℃) Plating bath temperature 65℃ The plating deposition rate at this time was about 0.15mg/cm ² /min, and it took about 30 minutes to obtain a film thickness of 5μ. . The crystal structure of the deposited plating film is Co(002) as in Example 1.
The surface grew extremely strongly, and the crystal C axis was strongly oriented in the direction perpendicular to the film surface. At this time, Co
The dispersion angle of the half-value width Δθ ₅₀ of the rocking curve of the (002) plane was approximately 9.0°. The magnetization hysteresis characteristics of the plated film were similar to those in Example 1.

Example 3 A Co--Ni--P film (film thickness: 5 μm) was formed using the following plating bath composition in the same manner as in Example 1.

Plating bath composition Cobalt sulfate 0.15mol/ Nickel sulfate 0.13mol/ Sodium hypophosphite 0.2mol/ Ammonium sulfate 0.5mol/ Sodium pyrophosphate 0.4mol/ Sodium malonate 0.1mol/ Plating conditions Plating bath PH9.0 (65 Plating bath temperature: ₆₅ ° C. The plating deposition rate at this time was about 0.14 mg/cm ² /min, and it took about 32 minutes to obtain a film thickness of 5 μm. The crystal structure of the deposited plating film is Co(002) as in Example 1.
The plane grew extremely strongly and was strongly oriented in the direction perpendicular to the crystal C axis and the film plane. At this time Co (002)
The dispersion angle of the half-width Δθ ₅₀ of the rocking curve of the surface was approximately 9.0°. The magnetization hysteresis characteristics of the plated film were similar to those in Example 1.

As mentioned above, in Examples 1 to 3, Co obtained from the accumulating bath described in the claims of the present invention
The C-axis of the -Ni-P film is oriented perpendicular to the substrate, and the magnetization hysteresis property indicates that it can be used in a magnetic recording medium for perpendicular magnetization recording.

In addition, although the case of a metal substrate was described in the example, when an organic resin substrate such as polyester or polyimide film is used, palladium is vapor-deposited on the surface of the film in advance to make it catalytically active, and then plated under the same plating conditions as in the example. As a result, a Co--Ni--P film in which the C-axis of the α-Co hexagonal crystal was vertically oriented was obtained as in the example.

As shown in the examples above, according to the present invention,
The axis of easy magnetization of a magnetic film serving as a magnetic recording medium can be oriented in a direction perpendicular to the film surface.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the cobalt ion (Co ²⁺ ) and nickel ion (Ni ²⁺ ) concentrations and the crystallinity of the resulting Co--Ni--P plated film. A region where the easy axis of magnetization is oriented in-plane; the figure shows a region where the easy axis of magnetization is isotropically oriented in the plane and in the perpendicular direction, or a region where the easy axis is weakly oriented in the perpendicular direction; a region where the easy axis of magnetization is strongly oriented vertically in the figure. , are the scope of the claims of the present invention. Figure 2 shows the relationship between the nickel ion (Ni ²⁺ ) concentration at a plating film thickness of 5 μm and the Co of the resulting plating film, when the cobalt ion (Co ²⁺ ) concentration in the plating bath is taken as a parameter.
This is a graph showing the relationship between the X-ray diffraction intensity of the (002) plane. Figure 3 shows the electroless
An example of an X-ray diffraction curve of a Co-Ni-P plated film. Figure 4 shows magnetization hysteresis curves in the vertical direction (solid line) and horizontal direction (broken line) with respect to the film surface of the electroless Co--Ni--P plated film obtained by the present invention, and the demagnetization field correction is performed. It is something that has not been done yet.

Claims (1)

[Claims] 1. In an electroless plating bath containing at least metal ions, a reducing agent for metal ions, a PH buffer, a PH regulator, and a complexing agent for the metal ions as constituent elements of the plating bath, (1) 0.1 mol/ml as metal ions; or more cobalt ions (Co ²⁺ ) and 0.1 mol/or more nickel ions (Ni ²⁺ ), (2) at least a pyrophosphate group as a complexing agent for metal ions, and the plating bath temperature is 55 to 75°C. Electroless Co-Ni characterized by having a pH adjusted to a range of 8.0 to 10.0 at 65℃.
- P eye bath.