JP2004259378A - Magnetic disk substrate for perpendicular recording and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic disk substrate for a perpendicular recording, in which a plated layer mass-producible at a low cost is arranged, and to offer a method for satisfactorily polishing this plated layer. <P>SOLUTION: This method includes that the plated layer of Ni-low P capable of plating by an electroless plating is arranged on the magnetic disk substrate for the perpendicular recording, to polish this plated layer of Ni-low P by using an alkaline abrasive of ≥pH8, and also the magnetic disk substrate obtained by the above method is provided. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００７２】
以上、評価１および２より、粗研摩工程においては、Ｎｉ−低Ｐ層を従来の酸性研摩剤で研摩をしても、Ｎｉ−高Ｐ層と同様の表面粗さを得ることができることが示された。したがって最終研摩工程においてのみアルカリ性研摩剤を用いれば、Ｎｉ−低Ｐ層に関しても従来からの一般的な表面粗さ以上の値を得ることができることがわかる。
【００７３】
【発明の効果】
本発明のアルカリ性研摩剤を用いた研摩方法により、基板上に施したＮｉ−低Ｐ層を良好に研摩することが可能となった。これにより、垂直記録用磁気ディスク基板上に無電解めっき法による安価で大量生産できるめっき膜を形成することができ、該めっき膜の超平坦面を達成することが可能となった。また本発明のＮｉ−低Ｐめっき膜は、２元素により構成されており、３元素以上のめっき膜に比べて、よりめっき液が安定し、一定のめっき膜組成に管理することが容易であり、形成されためっき膜の品質も安定しているという利点を有する。
【００７４】
さらに、Ｎｉ−低Ｐ膜の軟磁気特性を利用して、垂直記録用磁気ディスクの基板のめっき膜として形成したＮｉ−低Ｐ層を、同時に裏打ち層としても機能させることができる。
【図面の簡単な説明】
【図１】本発明の垂直記録媒体用磁気ディスク基板のうち、非磁性基体上に初期反応層および軟磁性下地層を形成したディスク基板の断面模式図である。
【図２】本発明の垂直記録媒体用磁気ディスク基板のうち、非磁性基体上に初期反応層、非磁性下地層および軟磁性下地層を形成したディスク基板の断面模式図である。
【図３】本発明による垂直記録媒体用磁気ディスクの構成を示す断面模式図である。
【符号の説明】
１ 非磁性基体
２ 初期反応層
３ 非磁性下地層
４ 軟磁性下地層
１０ 垂直磁気記録用磁気ディスク基板
２０ 非磁性シード層
３０ 磁気記録層
４０ 保護層[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a perpendicular recording magnetic disk substrate used for a fixed magnetic disk storage device and a method of manufacturing the same.
[0002]
[Prior art]
As a technique for realizing a higher density of a magnetic recording medium, a perpendicular magnetic recording system is attracting attention instead of a conventional longitudinal magnetic recording system.
[0003]
In particular, a two-layer perpendicular magnetic recording medium in which a soft magnetic film called a soft magnetic backing layer that easily passes magnetic flux generated from a magnetic head is provided below a magnetic recording layer that plays a role of recording information is generated by a magnetic head. It is known that it is suitable as a perpendicular magnetic recording medium capable of high-density recording because it increases the strength and its magnetic field gradient, improves the recording resolution, and increases the magnetic flux leakage from the medium (for example, see Patent Document 1). 1).
[0004]
Conventionally, as a soft magnetic underlayer, an NiFe alloy, an amorphous alloy mainly composed of Co, or the like is generally used. When these materials are used, a film thickness of 0.1 μm to several μm is required from the viewpoint of recording / reproducing characteristics. Such a relatively thick soft magnetic layer is very difficult to mass-produce inexpensively by the sputtering method used in the production of conventional magnetic recording media, and low cost by electroless plating. Mass production in the country is an issue. To date, the possibility of producing a soft magnetic material film composed of a Ni-Fe-P layer by electroless plating has been disclosed (see, for example, Patent Document 2). However, since the soft magnetic underlayer using the Ni-Fe-P layer is composed of three elements, it is very difficult to control the composition and the like of the plating tank in the electroless plating method. It is difficult to maintain and control. Furthermore, since ferrous sulfate in the components of the plating solution is oxidized when exposed to the air and gradually changes to ferric sulfate, it is difficult to maintain a constant plating solution composition.
[0005]
On the other hand, the applicants studied a plating film that can be mass-produced more stably by electroless plating. As a result, it was found that a Ni-P film having a P concentration of 6 wt% or less (hereinafter, Ni-low P film) is promising. Since the Ni-low P film is composed of two elements, when it is prepared by electroless plating, the plating solution is more stable and easier to control than the plating solution composed of three elements, and the quality is stable. It can be mass-produced stably at low cost. Further, by setting the P concentration to 6% by weight or less, the film can have soft magnetic characteristics that sufficiently function as a soft magnetic underlayer.
[0006]
[Patent Document 1]
JP-B-58-91 [0007]
[Patent Document 2]
JP-A-7-66034
[Problems to be solved by the invention]
By the way, a Ni-P plated aluminum substrate having a P concentration of 12% or more is generally used as a conventional magnetic disk substrate.
[0009]
The magnetic disk device realizes random access by operating the head slightly above a storage medium (disk) that rotates at a high speed, so that the magnetic disk requires an ultra-flat surface, and Ni-P plating The surface needs to be polished. Polishing generally comprises two steps, a rough polishing step using alumina slurry and a final polishing step using colloidal silica. These polishing agents have an etching action in order to achieve both productivity and surface quality. An acidic etchant has been added. A general Ni-P plating layer having a P concentration of 12% or more has high corrosion resistance in an acid solution, and this acidic polishing slurry can be used. However, a substrate coated with Ni-low P plating having a P concentration of 6% or less has low acid resistance, and the surface is eluted unevenly, so that mirror polishing cannot be performed. Further, when the corrosion is severe, there is a problem that Ni phosphate is reprecipitated to form a black film.
[0010]
An object of the present invention is to propose a method of satisfactorily polishing a Ni-low P plating film having a low P concentration, and to satisfactorily polish a magnetic disk substrate for perpendicular recording by the method, thereby making it possible to mass-produce a plating film at low cost. And to provide a magnetic disk substrate for perpendicular recording provided with. Still another object of the present invention is to use a Ni-low P layer on the surface of a magnetic disk substrate polished by the polishing method of the present invention as a backing layer in a perpendicular recording medium.
[0011]
[Means for Solving the Problems]
In order to solve the above problems, the present invention proposes a method for polishing the surface of a perpendicular recording magnetic disk substrate using an alkaline abrasive having a pH of 8 or more.
[0012]
In a preferred embodiment of the present invention, a perpendicular recording magnetic disk substrate plated with Ni and low P having a P concentration of 6 wt% or less can be polished well by the polishing method of the present invention. The required ultra-flat surface can be secured.
[0013]
The present invention also relates to a magnetic disk substrate for perpendicular recording having a Ni-P layer, wherein the Ni-P layer is polished with an alkaline abrasive having a pH of 8 or more. A substrate is provided.
[0014]
In the magnetic disk substrate of the present invention, the Ni-P layer preferably has a P concentration of 6 wt% or less.
[0015]
Further, the present invention provides a magnetic disk for perpendicular recording, wherein the magnetic disk substrate is used as a substrate and at least a magnetic recording layer is provided.
[0016]
As one embodiment of the present invention, in a perpendicular magnetic recording medium having a soft magnetic underlayer and a magnetic recording layer, a Ni-low P having a P concentration of 6 wt% or less on the surface of a magnetic disk substrate polished by the polishing method according to the present invention. Preferably, the plating layer is used as a soft magnetic underlayer in the perpendicular recording medium.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be described.
[0018]
First, the magnetic disk substrate for perpendicular recording according to the present invention will be described. FIGS. 1 and 2 show schematic cross-sectional views of a preferred structure for a magnetic disk substrate. However, these are shown as examples of the magnetic disk substrate for perpendicular recording, and the magnetic disk substrate for perpendicular recording of the present invention is not limited thereto.
[0019]
The disk substrate 10 shown in FIG. 1 has a structure in which a nonmagnetic substrate 1, an initial reaction layer 2, and a soft magnetic underlayer 4 are sequentially laminated.
[0020]
As the nonmagnetic substrate 1, a material used for a substrate of a general perpendicular recording magnetic disk substrate, for example, an aluminum alloy, tempered glass, crystallized glass, or the like is used. Alternatively, a substrate formed by injection molding of polycarbonate, polyolefin, and other plastic resins can be used.
[0021]
Next, the initial reaction layer 2 will be described.
[0022]
In general, a Zn film layer formed by dipping in a zincate solution (a solution containing zinc oxide and an aqueous solution of caustic soda) is used as the initial reaction layer on the substrate 1 using an aluminum alloy. The thickness of the Zn layer is desirably 0.1 to 0.8 μm, but may be out of this range.
[0023]
The initial reaction layer on the non-conductive substrate 1 made of tempered glass, crystallized glass, plastic or the like has a tin chloride solution of 20 to 40 g / l and a hydrochloric acid of 0.1 to 0.5 g / l. In general, an activation treatment for sequentially immersing in a palladium chloride solution to precipitate Pd nuclei on the surface is performed. Note that Ni, Ni-P, Cu, Cr, Fe, Pd, or the like can be formed to have a thickness of 1 nm to 1000 nm by using a physical vapor deposition method such as a sputtering method or an ion plating method.
[0024]
Further, a soft magnetic underlayer 4 composed of a Ni-low P layer is laminated on the initial reaction layer 2 by an electroless plating method. In order to realize the soft magnetic characteristics of the Ni-P plating layer, it is desirable that the P concentration be 6 wt% or less, and the thickness of the Ni-low P be 0.5 μm or more and 7.0 μm or less. When the saturation magnetic flux density [Bs] of the Ni-low P layer was measured with a VSM (vibrating sample magnetometer), the P concentration was 2%, 0.4 T at a film thickness of 1 μm, 6% at a P concentration of 0.15 T at a film thickness of 1 μm. A degree of soft magnetic characteristics can be obtained.
[0025]
As another aspect, in the disk substrate 10 shown in FIG. 2, a nonmagnetic underlayer 3 can be provided between the initial reaction layer 2 and the soft magnetic underlayer. The non-magnetic underlayer 3 can be laminated by an electroless plating method.
[0026]
As the nonmagnetic underlayer 3, a Ni-high P plating layer can be used. The plating layer can be laminated by an electroless plating method. The P concentration of the Ni-high P plating layer is desirably 10 wt% or more and 13 wt% or less. Further, the thickness of the Ni-high P plating layer is preferably from 0 μm to 7 μm.
[0027]
As described above, the Ni-P plating layer can be laminated by an electroless plating method. At this time, the electroless plating solution contains Ni ions, a complexing agent, and a reducing agent. NiSO ₄ , NiCl _2, or the like can be used as the Ni ions. As a complexing agent, general citric acid, tartrate, and the like can be used. As a reducing agent, sodium hypophosphite is generally used, and hydrazine, formaldehyde, sodium borohydride, or the like may be used in combination. The magnetic disk substrate is immersed in a plating bath adjusted to 80 to 95 ° C. with a plating solution containing these, and a Ni-low P plating layer is laminated. An Ni-high P layer which can be provided arbitrarily can also be plated by a method similar to the above-described electroless plating method except that the P concentration is changed.
[0028]
The Ni-P plating layer is desirably laminated by an electroless plating method from the viewpoint of mass production at low cost, but is not limited to this. Depending on required characteristics and the like, physical vapor deposition such as a sputtering method or an ion plating method may be used. Other general film formation methods such as a method can also be used.
[0029]
Next, the surface of the magnetic disk substrate prepared as described above is polished by the polishing method of the present invention.
[0030]
When a plating film with low acid resistance such as a Ni-low P layer is polished with an acidic abrasive, uneven plating on the surface of the plating film, formation of a black film by re-deposition of nickel phosphate due to corrosion, etc. Occurs. However, when polished with an alkaline abrasive according to the present invention, the above problems can be prevented.
[0031]
Therefore, first, abrasives such as silica, colloidal silica, alumina, silicon carbide, zirconia, and diamond are adjusted to pH 8 or more. The particle size of these abrasives is desirably 5 nm or more and 3000 nm or less. For adjusting the pH, a common alkaline solution such as caustic soda may be used. Next, the above-mentioned Ni-low P layer on the surface of the magnetic disk substrate is polished by a double-side polishing machine on which a polishing pad adjusted to pH 8 or higher and a polishing pad are applied. The polishing amount in this step is desirably 100 nm or more and 1000 nm or less, and the surface roughness is desirably Ra = 0.6 nm or less.
[0032]
In the polishing method of the present invention, the Ni-low P plating layer may be optionally subjected to rough polishing before the above-mentioned polishing is performed. In the rough polishing step, the above-described alkaline polishing agent may be used, or a general acidic polishing agent may be used. In the rough polishing step, the above-mentioned Ni-low P layer on the surface of the magnetic disk substrate is polished by a double-sided polishing machine or the like.
[0033]
The polishing method according to the present invention is not limited to a perpendicular recording magnetic disk substrate having a Ni-low P plating layer formed by electroless plating on its surface, but also a perpendicular recording magnetic disk having a pure Ni plating layer formed by electrolytic plating. It is also effective for polishing the substrate surface.
[0034]
Using the magnetic disk substrate polished by the polishing method of the present invention, a magnetic disk for perpendicular recording can be produced. FIG. 3 shows a schematic cross-sectional view of a preferred structure for the magnetic disk of the present invention. However, the magnetic disk shown in FIG. 3 is shown as an example, and the magnetic disk of the present invention is not limited to this.
[0035]
The disk shown in FIG. 3 has a structure in which a nonmagnetic seed layer 20, a magnetic recording layer 30, and a protective layer 40 are sequentially stacked on a disk substrate 10 for a perpendicular magnetic recording medium.
[0036]
The perpendicular magnetic recording medium disk substrate 10 refers to any one of the disk substrates of the present invention shown in FIG. 1 or FIG. 2, which has been polished by the polishing method of the present invention.
[0037]
For the nonmagnetic seed layer 20, a material for preferably controlling the crystal orientation, crystal grain size, and the like of the magnetic recording layer 30 can be used without any particular limitation. For example, if the magnetic recording layer 30 is a perpendicular magnetization film made of a CoCr-based alloy, the nonmagnetic seed layer 20 can be made of a CoCr-based alloy, Ti, or a Ti-based alloy, Ru, or the like. Is a so-called laminated perpendicular magnetic film in which Pt or Pd or the like is laminated with a Co-based alloy or the like, Pt, Pd, or the like can be used for the nonmagnetic seed layer 20. Further, a pre-seed layer, an intermediate layer and the like can be further provided above and below the non-magnetic seed layer 20. The thickness of the nonmagnetic seed layer 20 is preferably 1 to 500 nm.
[0038]
As the magnetic recording layer 30, any material that can perform recording and reproduction as a perpendicular magnetic recording medium can be used. That is, a so-called perpendicular magnetization film such as a film in which Pt or Pd or the like is laminated with the above-described CoCr-based alloy or Co-based alloy can be used. The thickness of the magnetic recording layer 30 is preferably 1 to 50 nm.
[0039]
As the protective layer 40, for example, a thin film mainly composed of carbon is used. After the formation of the protective layer 40, a liquid lubricant layer made of, for example, perfluoropolyether may be applied. The thickness of the protective layer 40 is preferably 1 to 10 nm.
[0040]
The nonmagnetic seed layer 20, the magnetic recording layer 30, and the protective layer 40 can be formed by a method generally used for forming a thin film, such as a sputtering method, a CVD method, a vacuum evaporation method, or a plating method. It is.
[0041]
【Example】
Hereinafter, examples of the present invention will be described.
[0042]
(Example 1)
A 3.5-inch φ Al-5Mg (at%) alloy was used as the non-magnetic substrate, and the substrate was treated with an alkaline cleaning agent (AD-68F, Uemura Kogyo) and an etching agent (AD-101F, Uemura Kogyo). The surface was cleaned by alkali cleaning and acid etching. Next, the step of immersing the substrate in a 30% nitric acid solution and then in a 25% zincate solution was repeated twice. By repeating this step twice, a thin and dense zincate layer, that is, an initial reaction layer is formed, and the adhesion between the substrate and the initial reaction layer is improved. AD-301F-3X manufactured by Uemura Kogyo was used as the zincate.
[0043]
Subsequently, a plating tank using a Ni-high P plating solution having a P concentration of 12.5% (HDX manufactured by Uemura Kogyo) was adjusted to 90 ° C., and the substrate on which the above-described initial reaction tank was laminated was immersed in the plating tank. Then, a Ni-high P layer having a P concentration of 12.5% and a film thickness of 2 μm was formed. Next, a plating tank using a Ni-low P plating solution having a P concentration of 4.5% (Nimden LPX manufactured by Uemura Kogyo) was adjusted to 90 ° C., and the above-mentioned Ni-high P layer was laminated on the plating tank. Was immersed to form a Ni-low P layer having a P concentration of 4.5% and a film thickness of 10 µm, and the total film thickness of the Ni-P layer was 12 µm.
[0044]
Next, the surface of the Ni-low P plating layer on the aluminum substrate was roughly polished and polished to 2 μm. The rough polishing step was performed using a double-sided polishing machine to which an alumina slurry (DISKLITE-1312: manufactured by Fujimi Incorporated) having an average particle diameter of 0.8 μm and pH 3.5 and a pad made of urethane foam were adhered.
[0045]
Further, the above-mentioned substrate having been roughly polished was subjected to final polishing, and polished to 0.5 μm. The final polishing step was performed using a double-sided polishing machine to which a pad made of urethane foam and a colloidal silica having an average particle diameter of 20 nm and a pH of 10 (Snowtex 30: manufactured by Nissan Chemical Industries) was adhered.
[0046]
(Example 2)
Instead of the Ni-low P layer formed in Example 1, a nickel sulfamate solution (nickel sulfamate 400 g / l, boric acid 40 g / l, pH 4.0, 50 ° C.) at a current density of 10 A / dm ² Each layer was formed on an aluminum substrate in the same manner as in Example 1 except that a plating layer was formed by applying pure Ni plating at 10 μm (middle circumference) and the total film thickness was 12 μm, thereby forming an aluminum substrate.
[0047]
Next, the surface of the pure Ni plating layer on the aluminum substrate was polished according to the rough polishing step of Example 1.
[0048]
Further, as a final polishing step, the above-mentioned substrate surface was adjusted to 0.5 μm by using a double-sided polishing machine to which a pad made of colloidal silica (Snowtex C: manufactured by Nissan Chemical) having an average particle diameter of 20 nm and pH 8.5 and urethane foam was adhered. Polished.
[0049]
(Example 3)
Instead of the Ni-low P layer formed in Example 1, an Ni-low P layer having a P concentration of 6.0% and a film thickness of 10.0 μm was formed using an electroless plating solution (Nimden LPR4) manufactured by Uemura Kogyo. Except for this, each layer was formed on an aluminum substrate in the same manner as in Example 1 to form an aluminum substrate.
[0050]
Next, the surface of the Ni-low P plating layer on the aluminum substrate was polished according to the rough polishing step of Example 1.
[0051]
Further, as a final polishing step, the above-mentioned substrate surface was adjusted to 0.5 μm by using a double-sided polishing machine to which a pad made of colloidal silica (Snowtex C: manufactured by Nissan Chemical) having an average particle diameter of 20 nm and pH 8.5 and urethane foam was adhered. Polished.
[0052]
(Example 4)
Instead of the Ni-low P layer formed in Example 1, a Ni-low P layer having a P concentration of 2.0% and a film thickness of 10 μm was formed by using a plating solution manufactured by Okuno Pharmaceutical Co., Ltd. (Top Nicolon LPH). Except for this, each layer was formed on an aluminum substrate in the same manner as in Example 1 to form an aluminum substrate.
[0053]
Next, the surface of the Ni-low P plating layer on the aluminum substrate was polished according to the rough polishing step of Example 1.
[0054]
Furthermore, as a final polishing step, the pH of colloidal silica having an average particle diameter of 20 nm and a pH of 10.0 (Snowtex 30: manufactured by Nissan Chemical Industries) was adjusted with caustic soda, and a slurry having a pH of 11.0 and a pad made of urethane foam were stuck. Using a polishing machine, the above-described substrate surface was polished by 0.5 μm.
[0055]
(Example 5)
Each layer was formed on an aluminum substrate in the same manner as in Example 1, and an aluminum substrate was formed.
[0056]
Next, the surface of the Ni-low P plating layer on the aluminum substrate was polished according to the rough polishing step of Example 1.
[0057]
Furthermore, as a final polishing step, the pH of colloidal silica having an average particle diameter of 20 nm and a pH of 10.0 (Snowtex 30: manufactured by Nissan Chemical Industries) was adjusted with caustic soda, and a slurry having a pH of 11.0 and a pad made of urethane foam were stuck. Using a polishing machine, the above-described substrate surface was polished by 0.5 μm.
[0058]
(Comparative Example 1)
Each layer was formed on an aluminum substrate in the same manner as in Example 1 except that the thickness of the Ni-high P layer was set to 12 μm and the Ni-low P layer was removed, to thereby form an aluminum substrate.
[0059]
Next, the surface of the Ni-high P plating layer on the aluminum substrate was polished according to the rough polishing step of Example 1.
[0060]
Further, as a final polishing step, the above-mentioned substrate surface was adjusted to 0.5 μm by using a double-sided polishing machine to which a pad made of colloidal silica (Snowtex 0: manufactured by Nissan Chemical) having an average particle diameter of 20 nm and pH 3.0 and urethane foam was adhered. Polished.
[0061]
(Comparative Example 2)
Each layer was formed on an aluminum substrate in the same manner as in Example 1, and an aluminum substrate was formed.
[0062]
Next, the surface of the Ni-low P plating layer on the aluminum substrate was polished according to the rough polishing step of Example 1.
[0063]
Further, as a final polishing step, the above-mentioned substrate surface was adjusted to 0.5 μm by using a double-sided polishing machine to which a pad made of colloidal silica (Snowtex 0: manufactured by Nissan Chemical) having an average particle diameter of 20 nm and pH 3.0 and urethane foam was adhered. Polished.
[0064]
(Comparative Example 3)
Each layer was formed on an aluminum substrate in the same manner as in Example 1, and an aluminum substrate was formed.
[0065]
Next, the surface of the Ni-low P plating layer on the aluminum substrate was polished according to the rough polishing step of Example 1.
[0066]
Further, as a final polishing step, the pH of colloidal silica having an average particle size of 20 nm and a pH of 3.0 (Snowtex 0: manufactured by Nissan Chemical) was adjusted using caustic soda, and a slurry having a pH of 5.5 and a urethane foam pad were applied. The surface of the substrate was polished by 0.5 μm using a double-side polishing machine.
[0067]
(Evaluation 1)
In Examples 1 to 5 and Comparative Examples 1 to 3, the surface roughness of the roughly polished disk substrate surface was measured. The surface roughness was measured with a stylus-type roughness meter. Table 1 shows the measurement results. The measured roughness on all the plating layer surfaces showed almost the same results.
[0068]
(Evaluation 2)
In Examples 1 to 5 and Comparative Examples 1 to 3, the surface roughness of the final polished disk substrate surface was measured. Table 1 shows the measurement results. In this measurement, a surface roughness of 10 μm × 10 μm was measured by AFM.
[0069]
As a result of the measurement in Evaluation 2, as shown in Table 1, the surface roughness after polishing the surface of a general plating layer having no Ni-low P layer in Comparative Example 1 using an acidic abrasive was Ra = 0.4 nm. On the other hand, the surface roughness after polishing the plating layers formed of the Ni-low P layers of Examples 1 to 5 using an alkaline abrasive was Ra = 0.3 nm to 0.5 nm. This result was equal to or higher than the surface roughness of a general plating film shown in the polishing result of Comparative Example 1.
[0070]
On the other hand, the surface roughness after polishing the plating films having the Ni-low P layers of Comparative Examples 2 and 3 with an acidic abrasive was Ra = 1.8 nm and Ra = 1.6 nm, respectively. This is a roughness that cannot be used as a substrate. When the plating layer having a low P concentration is polished with an acidic abrasive, the surface of the substrate is roughened due to the corrosion of the layer surface, and the surface of the substrate is roughened, resulting in a surface roughness that cannot be used as a magnetic disk substrate. .
[0071]
[Table 1]

[0072]
As described above, the evaluations 1 and 2 show that in the rough polishing step, even if the Ni-low P layer is polished with a conventional acidic abrasive, the same surface roughness as that of the Ni-high P layer can be obtained. Was done. Therefore, it is understood that the use of an alkaline polishing agent only in the final polishing step can provide a Ni-low P layer with a value higher than the conventional general surface roughness.
[0073]
【The invention's effect】
The polishing method using the alkaline polishing agent of the present invention makes it possible to satisfactorily polish the Ni-low P layer applied on the substrate. Thus, an inexpensive and mass-produced plating film can be formed on the magnetic disk substrate for perpendicular recording by the electroless plating method, and an ultra-flat surface of the plating film can be achieved. Further, the Ni-low P plating film of the present invention is composed of two elements, and the plating solution is more stable than the plating film of three or more elements, and it is easy to control the composition of the plating film to be constant. This has the advantage that the quality of the formed plating film is also stable.
[0074]
Further, by utilizing the soft magnetic properties of the Ni-low P film, the Ni-low P layer formed as a plating film on the substrate of the magnetic disk for perpendicular recording can simultaneously function as a backing layer.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a magnetic disk substrate for a perpendicular recording medium according to the present invention, in which an initial reaction layer and a soft magnetic underlayer are formed on a non-magnetic substrate.
FIG. 2 is a schematic sectional view of a magnetic disk substrate for a perpendicular recording medium according to the present invention, in which an initial reaction layer, a nonmagnetic underlayer, and a soft magnetic underlayer are formed on a nonmagnetic substrate.
FIG. 3 is a schematic sectional view showing a configuration of a magnetic disk for a perpendicular recording medium according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Nonmagnetic base 2 Initial reaction layer 3 Nonmagnetic underlayer 4 Soft magnetic underlayer 10 Magnetic disk substrate for perpendicular magnetic recording 20 Nonmagnetic seed layer 30 Magnetic recording layer 40 Protective layer

Claims (6)

A method for polishing a surface of a magnetic disk substrate for perpendicular recording, wherein the surface of the substrate is polished with an alkaline polishing agent having a pH of 8 or more. 2. The method according to claim 1, wherein the magnetic disk substrate is plated with Ni-P having a P concentration of 6 wt% or less, and the plated layer is polished. A perpendicular recording magnetic disk substrate having a Ni-P layer on a surface, wherein the Ni-P layer is polished with an alkaline abrasive having a pH of 8 or more. 4. The perpendicular recording magnetic disk substrate according to claim 3, wherein the P concentration of the Ni-P layer is 6 wt% or less. 5. A magnetic disk for perpendicular recording, wherein the magnetic disk substrate according to claim 3 or 4 is used as a substrate and at least a magnetic recording layer is provided. In a perpendicular magnetic recording disk having at least a soft magnetic underlayer and a magnetic recording layer, the soft magnetic property of a Ni—P plating layer having a P concentration of 6 wt% or less on the surface of a magnetic disk substrate polished by the method according to claim 2. Use as backing layer.

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