JP2002032909A - Substrate for magnetic recording medium, magnetic recording medium, method for manufacturing substrate for magnetic recording medium and method for manufacturing magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a glass substrate which permit low floating height and to enhance recording density by realizing micronization and reduction of dispersion of crystalline particle sizes of a layer film-deposited on the substrate. SOLUTION: In the substrate for a magnetic recording medium, having concentric circle-shaped grooves formed on its principal surface, the height of its concentric circle-shaped ruggedness is specified to be a height not to have magnetic anisotropy in a circumferential direction when at least a magnetic layer is formed on the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a substrate for a magnetic recording medium and a method for manufacturing the same. Further, the present invention relates to a magnetic recording medium and a method for manufacturing the same.

[0002]

2. Description of the Related Art With the increase in capacity of magnetic disk storage devices, the technology of each component constituting the device, such as the performance of magnetic recording media and magnetic heads and the speed of recording / reproducing channels, has been improved. I have. To improve the performance of a magnetic disk storage device, it is important to improve the recording density, and it is essential to improve the magnetic recording medium and the magnetic head that are directly involved in recording and reproduction. In particular, where the magnetic recording medium is concerned, the PW50 and the medium S / N, which greatly affect the high recording density, are improved, and the spacing between the magnetic head and the magnetic layer of the magnetic recording medium is reduced.

In a magnetic recording medium comprising an underlayer, a magnetic layer, a protective layer, and a lubricating layer, high PW50 characteristics and high S / N are achieved by increasing the coercive force of the magnetic layer as the recording layer, miniaturizing crystal grains, and so on. It is necessary to reduce dispersion. In order to increase the coercive force, refine the crystal grains, and reduce the dispersion, the lattice constants of the underlayer and the magnetic layer are matched (high coercive force), or the crystal grains of the magnetic layer are interposed between the substrate and the underlayer. There are methods such as interposing a seed layer to be miniaturized (miniaturization of crystal grains and reduction of dispersion), and high recording density is being promoted every day by high PW50 characteristics and high S / N.

In order to reduce spacing, which is another major solution to the increase in recording density, it is necessary to reduce the flying height of the magnetic head. When the flying height is reduced, the thickness of the magnetic layer is 100 n in the current magnetic recording medium.
Since it is less than m, the smoothness of the substrate directly affects the flying height of the magnetic head. Therefore, it is important to increase the smoothness of the substrate for a magnetic recording medium. For example, at a recording density of 25 Gbit / inch ^2, it is necessary to realize a flying height of 6 nm or less. At this time, the smoothness of the magnetic recording medium substrate is required to have a maximum height Rmax = 3 nm or less. Under such demands, the glass substrate as the substrate material can be easily smoothed by polishing.
Increasingly, it is receiving attention as a substrate for magnetic recording media.

Usually, a glass substrate for a magnetic recording medium is manufactured by shaping the glass substrate into a predetermined shape for a magnetic recording medium, lapping the flatness within a predetermined range, and a polishing step for improving the smoothness. It is produced through. In the case of a chemically strengthened glass substrate, an ion exchange process is performed to strengthen the glass substrate. The ion exchange treatment is a method of exchanging alkali ions on the outermost surface of a glass substrate with alkali ions having a larger atomic radius to stress the substrate surface and strengthen the substrate. For magnetic recording media using a glass substrate, at least an underlayer, a magnetic layer, and a protective layer are formed by sputtering on the glass substrate produced by the above steps, and a lubricating layer is applied to reduce friction with a magnetic head. It is produced by doing.

[0006]

As described above, in order to improve the recording density, the flying height of the magnetic head has been reduced. However, when the flying height is 6 nm or less, the magnetic head flies in a region close to contact with the substrate surface, and there is a high possibility that minute and minute projections and dirt (contamination) on the substrate surface become a serious problem. For example, there is a concern about hindrance in reducing the flying height and loss of reliability after manufacturing the magnetic recording medium due to contamination. Further, in general, there is a concern about a temporal change of the surface of the glass substrate from the production of the glass substrate to the injection of the sputter. For example, in the case of a chemically strengthened glass substrate, as described in JP-A-8-124153, a chemically strengthened glass substrate subjected to an ion exchange treatment has a high concentration of ion-exchanged alkali ions on the outermost surface and changes with time. It has been pointed out that there is a possibility that the magnetic recording medium may be eluted, which may impair the reliability of the magnetic recording medium.

Further, in order to improve the recording density of a magnetic recording medium, it is necessary to reduce (decrease) the PW50 value and to increase the medium S / N. In particular, MR
In a magnetic head (MR head) using a (magnetoresistive) element, since the output is small due to sensitivity, the medium noise Nm
It is necessary to reduce (noise due to medium) to achieve high S / N. Therefore, it is necessary to further increase the coercive force, refine the crystal grains, and reduce the dispersion. In order to reduce the size of the magnetic crystal grains and reduce the dispersion, it is necessary to reduce the size and the dispersion of the crystal grain size of the underlayer which affects the growth of the crystal grains of the magnetic layer.

Further, as a method of reducing the crystal grain size of the underlayer, a method of using a layer called a seed layer having the same crystal structure as the underlayer and having fine crystal grains as the underlayer of the underlayer. Is also disclosed in JP-A-9-259418. As described above, from the property that the thin film grows epitaxially (the thin film to be formed grows while reflecting the crystal state of the lower layer), the control of the crystal grains of the magnetic layer for improving the recording density is performed as an underlayer of each layer. This largely depends on the growth of the crystal grains of the layer to be formed. In other words, it can be said that the layer formed directly above the substrate greatly affects the growth of the magnetic crystal grains.Controlling the crystal growth of the layer directly above the substrate by the substrate greatly increases the recording density. It is considered to contribute.

In view of such circumstances, the present invention provides a 6 nm
Realize the roughness of the glass substrate that enables the following flying height,
In addition, a method for manufacturing a highly reliable magnetic recording medium is provided, and further, the crystal shape of a layer formed on the glass substrate is reduced in size and dispersion is reduced by the surface shape of the glass substrate. Accordingly, it is an object of the present invention to provide a method for improving the recording density.

[0010]

The present invention has the following arrangement. (Structure 1) In a magnetic recording medium substrate having a concentric groove formed on a main surface, the height of the concentric unevenness increases in a circumferential direction when at least a magnetic layer is formed on the substrate. A substrate for a magnetic recording medium having a size without anisotropy.

(Structure 2) When at least a magnetic layer is formed on the substrate, an external magnetic field is applied in a circumferential direction and a radial direction at an arbitrary position on the magnetic recording medium, and the coercive force in the circumferential direction is reduced. When the ratio (Hc1 / Hc2) of the coercive forces Hc1 and Hc2 when Hc1 and the coercive force in the radial direction are Hc2 is defined as magnetic anisotropy, the magnetic anisotropy is 0.90 to 0.90.
1. The substrate for a magnetic recording medium according to Configuration 1, wherein the substrate is 1.10. (Structure 3) The substrate for a magnetic recording medium according to Structure 1 or 2, wherein the height of the concentric unevenness is 3 nm or less. (Arrangement 4) The concentric concavo-convex shape has a radial width of 20
4. The substrate for a magnetic recording medium according to any one of Configurations 1 to 3, wherein the substrate has a thickness of not less than 60 nm and not more than 60 nm.

(Structure 5) The magnetic recording medium substrate according to any one of structures 1 to 4, wherein the magnetic recording medium substrate is made of glass. (Structure 6) A magnetic recording medium characterized in that at least a magnetic layer is formed on a main surface of the magnetic recording medium substrate according to any one of Structures 1 to 5. (Structure 7) In a manufacturing method for manufacturing a substrate for a magnetic recording medium by polishing a main surface of a disk-shaped substrate, a polishing liquid containing an abrasive is supplied to both main surfaces after polishing the main surface of the disk-shaped substrate. A method for manufacturing a substrate for a magnetic recording medium, comprising: bringing a polishing tape into contact with a main surface of the disc-shaped substrate that rotates about the center of the disc-shaped substrate.

(Structure 8) The abrasive has an average particle diameter of 1.0.
The method for producing a substrate for a magnetic recording medium according to Configuration 7, wherein the thickness is not more than μm. (Structure 9) The method for manufacturing a substrate for a magnetic recording medium according to structure 7 or 8, wherein the abrasive does not cause a chemical reaction with the material of the substrate. (Structure 10) The abrasive includes diamond abrasive grains, alumina abrasive grains, colloidal silica abrasive grains, zirconia oxide abrasive grains,
10. The method for manufacturing a substrate for a magnetic recording medium according to Configuration 9, wherein the method comprises at least one selected from silicon carbide abrasive grains.

(Structure 11) The method for manufacturing a substrate for a magnetic recording medium according to any one of structures 7 to 10, wherein a polishing amount (gap) of the repolishing is 5 to 30 nm. (Structure 12) The method of manufacturing a magnetic recording medium substrate according to any one of structures 7 to 11, wherein the substrate is made of glass. (Constitution 13) In the method for manufacturing a glass substrate for a magnetic recording medium for polishing and smoothing the main surface of a glass substrate subjected to a chemical strengthening treatment, the thickness of the glass to be polished and reduced is 5 to 30 nm for each polished surface. A method for producing a glass substrate for a magnetic recording medium, comprising: (Structure 14) A method for manufacturing a magnetic recording medium, comprising forming at least a magnetic layer on the main surface of the magnetic recording medium substrate according to any one of Structures 7 to 13.

By forming concentric irregularities on the main surface of the substrate for a magnetic recording medium as in Configuration 1, the crystal grains of the film formed on the substrate are refined and the crystal grain size is reduced. Since the dispersion is reduced, a high S / N ratio is obtained. This is because the concentric asperities formed on the substrate cause the concentric grooves (concave) to promote the miniaturization of the crystal grain size and the reduction in dispersion during the crystal growth of the film formed thereon, and the concentric circles. It is considered that an effect of suppressing disturbance of crystal grains in a direction perpendicular to the direction of the irregularities is provided.

The concentric unevenness is the height of the unevenness having no anisotropy in the circumferential direction when at least the magnetic layer is formed on the substrate. This is because concentric concavo-convex portions are used to promote the refinement of crystal grains during the initial growth of a thin film crystal formed on a substrate for a magnetic recording medium and to reduce the dispersion of crystal grain sizes. This is for distinguishing from the effect obtained by the sexual medium. An anisotropic medium refers to a magnetic recording medium in which the coercive force in the circumferential direction is always greater than the coercive force in the radial direction. Here, having no circumferential magnetic anisotropy means that an external magnetic field is applied in a circumferential direction and a radial direction at an arbitrary position on a magnetic recording medium, and the coercive force in the circumferential direction is Hc1. When the ratio (Hc1 / Hc2) of the coercive forces Hc1 and Hc2 when the coercive force in the radial direction is Hc2 is defined as magnetic anisotropy, it indicates a state of 1.10 or less.

Specifically, as described in Configuration 2, when at least a magnetic layer is formed on a substrate, an external magnetic field is applied in a circumferential direction and a radial direction at an arbitrary position on a magnetic recording medium, and When the coercive force in the circumferential direction is Hc1 and the coercive force in the radial direction is Hc2, the ratio of coercive forces Hc1 and Hc2 (H
When c1 / Hc2) is defined as magnetic anisotropy, it refers to a state where the value is 0.90 to 1.10. Preferably,
0.95 to 1.05, more preferably 0.98 to 1.
02.

Further, as in Configuration 3, the height of the concentric unevenness is preferably 3 nm or less. If it exceeds 3 nm, it is difficult to achieve a flying height of 6 nm or less, and high-density recording and reproduction cannot be performed. Preferably, 2.5n
m or less, more preferably 2 nm or less. Further, as in Configuration 4, the concentric concavo-convex radial width in the radial direction is preferably from 20 nm to 60 nm. If it exceeds 60 nm, the effect of controlling the crystal grain size by the concentric unevenness is lost. If it is less than 20 nm, the crystal grains become too fine, and the PW50 characteristics deteriorate. Therefore, preferably 2
5 nm or more and 50 nm or less, more preferably 25 nm
It is desirable that the thickness be at least 40 nm.

The material of the substrate used in the present invention is not particularly limited. For example, glass (including glass-ceramic (crystallized glass)), ceramic, silicon, carbon, titanium, aluminum, and other metallic substrates may be used. Among them, glass as described in Configuration 5 is preferable in terms of smoothness and hardness. The glass type of the glass is not particularly limited. Examples include aluminosilicate glass, borosilicate glass, aluminoborosilicate glass, soda lime glass, chemically strengthened glass, crystallized glass, and the like.
Further, as described in Configuration 6, by forming at least a magnetic layer on the substrate described in any one of Configurations 1 to 5 to form a magnetic recording medium, the S / N is improved and the flying height is 6 nm or less. Is obtained.

After the main surface of the disk-shaped substrate is polished as in Configuration 7, while the polishing liquid containing an abrasive is supplied to both main surfaces of the disk-shaped substrate, the center of the disk-shaped substrate is set at the center axis. By bringing the polishing tape into contact with the main surface of the rotating disk-shaped substrate and re-polishing the substrate, the variation in quality of each substrate is small, and a substrate having concentric unevenness can be stably manufactured. The polishing tape ensures that a new surface always contacts the main surface of the substrate at a certain speed. The material and width of the polishing tape to be used are not particularly limited. Examples of the type of the polishing tape include flocking, woven fabric, non-woven fabric, and polyurethane. Especially, a textile tape is preferable. The material is not limited in terms of easy formation of concentric irregularities and smoothness. Examples of the material include polyester and nylon. The width of the polishing tape is appropriately adjusted depending on the size of the substrate. Specifically, it is 5 to 40 mm. In addition, the feed speed of the polishing tape, the load of the polishing tape on the substrate, and the pressure are also appropriately adjusted according to the smoothness and the concentric concavo-convex shape. For example, the feed speed of the polishing tape is 1 to 10 mm / sec.
It is. Preferably, 2 mm / sec is desirable. Also, the weight and pressure of the polishing tape are appropriately adjusted according to the smoothness. For example, the weight is 0.5 to 5 kg. Preferably, about 1.5 kg is desirable. The pressure is
It is a 4.5~45g / mm ^2. The surface roughness of the substrate before re-polishing is preferably 8 nm or less in Rmax. This is because the polishing amount (gap) is 10 nm or less. Polish amount 1
The reason for setting the thickness to 0 nm or less will be described later.

Further, as in Configuration 8, the average particle size of the abrasive is preferably 1.0 μm or less. When the average particle size of the abrasive exceeds 1.0 μm, the surface roughness of the substrate is Rmax and 3n
This is because smoothness of m or less cannot be realized. Preferably not more than 0.5 μm, more preferably 0.25 μm
The following is desirable. However, if the average particle size is too small, the polishing rate is reduced and the production efficiency is reduced. Therefore, the average particle size is preferably limited to about 0.125 μm.

Further, as in the configuration 9, it is desirable that the abrasive does not cause a chemical reaction with the material of the substrate. This is because it is difficult to remove abrasives that cause a chemical reaction with the substrate material by scrubbing with a neutral detergent. Here, that no chemical reaction occurs means a state in which the material of the substrate and the abrasive are not adsorbed by a chemical bond. Specific abrasives include, as in Configuration 10, diamond abrasive grains, alumina abrasive grains,
Colloidal silica abrasives, oxidized zirconia abrasives, silicon carbide abrasives and the like can be mentioned. Abrasives are smooth,
It is appropriately selected according to the concentric uneven shape. Among them, when the substrate is glass, polycrystalline diamond abrasive grains having a small particle size distribution are desirable from the viewpoint of stable polishing and texturing. When these abrasives are used, they are not limited to one type, and two or more types of abrasives may be mixed and used.

Further, as in the configuration 11, the polishing amount (clearance) of the repolishing is preferably 5 to 30 nm. If it is less than 5 nm, protrusions and dirt on the substrate surface cannot be sufficiently removed, and 3n
This is not preferable because a smoothness of m or less cannot be obtained. Also,
If the thickness exceeds 30 nm, polishing with a tape is not preferable because the processing time becomes longer and the surface roughness obtained by the influence of heat due to the longer processing time varies. Further, as described in Structure 12, by using glass as the material of the substrate, there is an advantage in manufacturing that the substrate can have high smoothness and flatness, and undulation and the like are small.

Further, as in the structure 13, the thickness of the glass to be polished and removed from the glass substrate subjected to the chemical strengthening treatment is set to 5 to 30 nm for each polished surface. Here, examples of the polishing method include a batch-type polishing method, a method using a tape-type texture device, and the like. In the batch type polishing method, since a large amount is polished at a time, the polishing conditions for each substrate are not stable and delicate control is difficult. Therefore, when a hard polishing agent is used, Pit, Scrat
Channels are easy to enter and smoothness cannot be improved. The use of a tape-type texturing device is preferable because the polishing can be always performed with a new tape surface and an abrasive, so that stable polishing can be performed. By forming at least a magnetic layer on the substrate of any one of the constitutions 7 to 13 as in the constitution 14, a magnetic recording medium having a high recording density corresponding to high-density recording / reproducing can be obtained, and the magnetic characteristic S / N can be manufactured with a stable magnetic recording medium. The magnetic recording medium has at least a magnetic layer formed on a substrate.

The magnetic layer preferably contains Co and Pt having high coercive force as main components. An alloy containing Co and Pt as main components is made of Co + P from the viewpoint of obtaining a sufficient coercive force.
It is desirable that t be 70% or more. Also, Co and P
In consideration of coercive force, medium noise, and cost, the ratio of t is preferably Pt (at%) / Co (at%) and is 0.05 or more and 0.2 or less. The components other than Co and Pt are not particularly limited, but for example, Cr, Ta, Ni,
Si, B, O, N, Nb, Mn, Mo, Zn, W, P
One, or two or more of b, Re, V, Sm, and Zr can be used as appropriate. The addition amount of these elements is
It is appropriately determined in consideration of the electromagnetic conversion characteristics and the like, and it is usually desirable that the content be 30% or less.

In addition to the magnetic layer 5, for example, a seed layer 2, an underlayer 3, an intermediate layer 4,
It can have a protective layer 6, a lubricating layer 7, and the like. Known seed layers, underlayers 2, intermediate layers 3, protective layers 6, and lubricating layers 7 can be used as they are. The seed layer 2 is generally made of a material having a small crystal grain size and uniform crystal grains. The underlayer 3 and the intermediate layer 4 formed on the seed layer 2 make the crystal grains of the magnetic layer 5 fine. It is provided for the purpose of improving the crystal growth while maintaining. A typical material for the seed layer 2 is NiAl
B2 type crystal structure materials such as alloys, CrTi
Alloys and CrNi alloys. Note that the seed layer 2 may be stacked to improve the crystal growth.

It is preferable that the underlayer 3 is made of a material that can provide a high coercive force. The underlayer 3 is one layer or two
It can be composed of layers or more. As the underlayer 3,
For example, a CrMo alloy, a CrV alloy, a CrW alloy, or the like can be used. As described above, by using a Cr alloy, the lattice spacing between the magnetic layer 5 and the underlayer 3 is well matched, so that the easy axis of magnetization of the magnetic layer 5 is easily oriented in the plane. As a result, the in-plane coercive force increases, and when the coercive force is adjusted to the coercive force when Cr is used, the thickness of the underlayer can be reduced, so that the electromagnetic conversion characteristics are improved.

The intermediate layer 4 is provided between the underlayer 3 and the magnetic layer 5.
Preferably, the magnetic layer 5 is formed at a position in contact with the magnetic layer 5.
Is provided for the purpose of improving the orientation of the C-axis. Middle layer 4
Is a non-magnetic material, and its crystal system is desirably matched to the crystal system of the magnetic layer 5. The protective layer 6 is provided for protecting the magnetic layer 5 from being broken by contact sliding of the head.
It is provided on. The protective layer 6 can be composed of one layer or two or more layers. As the protective layer 6, for example,
Examples thereof include a silicon oxide film, a carbon film, a zirconia film, hydrogenated carbon, a hydrogenated carbon nitride film, a carbon nitride film, a silicon nitride film, and a SiC film. The protective layer 6
Can be provided by a known film formation method such as a sputtering method. The lubricating layer 7 is provided for the purpose of reducing the resistance due to sliding contact with the head, and for example, perfluoropolyether or the like is generally used.

[0029]

Embodiments of the present invention will be described in more detail with reference to the following examples. [Embodiments 1 and 2] As shown in FIG. 1, a glass substrate 1 for a magnetic recording medium according to the present embodiment is a substrate obtained by polishing and concentrically texture a chemically strengthened aluminosilicate glass. The magnetic recording medium of this embodiment using the glass substrate 1 is a magnetic disk in which a seed layer 2, an underlayer 3, an intermediate layer 4, a magnetic layer 5, a protective layer 6, and a lubricating layer 7 are sequentially laminated. The glass substrate 1 has Rmax = 7 nm, Ra
Polishing and concentric texture processing are performed on a chemically reinforced aluminosilicate glass that has been mirror-polished to about = 0.8 nm using a tape-type texture device.

FIG. 2 is a schematic diagram of a tape-type texture device used in this embodiment. The tape-type texturing device used in the present example rotated the glass substrate fixed to the spindle, supplied the abrasive to the tape from the slurry dropping port, and wound both main surfaces of the glass substrate around the roller. A circumferential groove is formed on the main surface of the glass substrate by being sandwiched between the tapes. The roller around which the tape is wound is rotating at a constant rotational speed, so that a new surface of the tape always contacts the glass substrate.

The glass substrate is centered on the fulcrum a in FIG.
The glass substrates are pinched by moving plate-like members fixed to the shafts of the rollers. At this time, the force (load) applied to the glass substrate is determined by the force of a spring stretched between the plate-shaped members. Loading is performed by measuring the tension of the spring at the time of processing with a tensiometer attached to one surface of the spring. When producing the glass substrate 1, a woven tape was used as the tape, and a slurry in which polycrystalline diamond having an average particle size of 0.125 μm was dissolved in a dispersant was used as the hard abrasive.

The other processing conditions of the texturing apparatus were as follows: Example 1: processing weight 1.4 kg processing pressure 12 g / mm ² substrate rotation speed 1000 rpm tape feed speed 2 mm / sec processing time 30 sec For Example 2, the processing load was 1.4 kg, the processing pressure was 12 g / mm ² , the number of substrate rotations was 500 rpm, the tape feed rate was 2 mm / sec, and the processing time was 30 seconds. Then, in a washing tank containing a weak alkaline detergent,
After rubbing (scrub cleaning) with a Velklin cloth, ultrasonic cleaning and drying were performed. The seed layer 2 is made of N
It is made of an iAl thin film (thickness: 500 angstroms). The NiAl thin film was composed of Ni: 50 at%, A
1: 50 at%.

The underlayer 3 is made of a CrMo thin film (thickness: 300).
Angstrom) to improve the crystal structure of the magnetic layer. In addition, this CrMo thin film is C
r: 90 at%, Mo: 10 at%. The intermediate layer 4 is made of a CoCr thin film (thickness: 30 angstroms). This CoCr thin film is made of Co:
The composition ratio is 65 at% and Cr: 35 at%.

The magnetic layer 5 is made of a CoPtCrTa alloy and has a thickness of 200 angstroms. The contents of Co, Pt, Cr, and Ta in this magnetic layer are as follows. That is, Co: 73 at%, Pt: 7 at%,
Cr: 18 at%, Ta: 2 at%. Protective layer 6
Is for preventing the magnetic layer from deteriorating due to contact with the magnetic head, and is made of hydrogenated carbon having a thickness of 50 Å, and provides wear resistance. The lubricating layer 7 is made of a liquid lubricant of perfluoropolyether, and this film alleviates the contact with the magnetic head. The thickness is 9 Å.

The magnetic recording media of Comparative Examples 1 and 2 are magnetic disks manufactured by using a glass substrate which has not been polished and concentrically textured before manufacturing the magnetic recording medium of the present invention. Comparative Example 1 and Comparative Example 2 are glass substrates having different substrate surface roughnesses Rmax and Ra. The magnetic recording medium of Comparative Example 1 had Rmax = 2.95 nm, Ra
= 0.26 nm, Comparative Example 2 has Rmax = 7.10 nm,
This is a magnetic disk manufactured using a glass substrate having a roughness of about Ra = 0.84 nm.
Same as

Table 1 shows the surface roughness of the substrate with respect to the glass substrate of Example 1 and the flying height of the magnetic head measured on the magnetic disk manufactured using the glass substrate of Example 1.
The results of coercive force, residual magnetization, medium noise, and glide inspection are listed. The definition of each parameter and the measurement method for each measurement are shown below.

Surface Roughness of Substrate The obtained glass substrate was subjected to an atomic force microscope (AFM) (trade name: Nan, manufactured by Digital Instruments Co., Ltd.).
The surface roughness (Rmax, Ra) was measured using o Scope. Considering the correlation with the resolution, the measurement time, and the flying height of the head, the measurement range is 5 μm □, the number of samplings is 256 dots in a 5 μm visual field (0.02 μm per dot).
m measurement interval).

Magnetic Head Flying A touch-down height (TDH) was measured as an index for measuring the magnetic head flying capacity of the magnetic recording medium. T
DH is a method in which the flying height of a flying head is sequentially reduced, the flying height at which the flying head starts to come into contact with the magnetic disk is determined, and the flying height capability of the magnetic disk is measured. In order to reduce the flying height of the head, a method of reducing the number of rotations is adopted because the head floats due to the rotation of the magnetic disk.
In addition, the measurement radius performed in this example is 22 mm.

Coercive force A sample of 8 mmφ is cut out from the magnetic disk for measuring the coercive force, and the maximum applied magnetic field is measured in the circumferential direction and the radial direction of the substrate in the film plane using a vibrating sample magnetometer (VSM). 10
A magnetic field was applied as kOe, and the coercive force (Oe) was determined.

Medium noise: A magnetic resistance type (M)
R) A head was attached, and medium noise (μVrms) was measured. The MR head is a thin film head having a flying height of 0.018 μm, and has a relative speed of 9.77 m with respect to the magnetic disk.
/ S, the recording / reproducing output at a linear recording density of 430 kfci (a linear recording density of 430,000 bits per inch) was measured. Also, a carrier frequency of 82.3 MHz
Then, the measurement spectrum was set to 98.76 MHz, and the noise spectrum at the time of signal recording and reproduction was measured by a spectrum analyzer. The thin film head used for this measurement was written /
0.85 / 0.6μ track width on reading side
m, and the magnetic head gap length is 0.15 / 0.14 μm.

Glide Inspection The glide inspection is an inspection in which the head is levitated above the surface of the magnetic disk with a constant flying height and the head and the magnetic disk are collided while changing the radial position of the head.
Causes of collision include protrusions on the magnetic disk surface,
The inspection is on the glass substrate and the surface of the magnetic disk. This is performed for detecting a protrusion, a dent, or the like. The detection of the collision at this time was performed by detecting the vibration at the time of the collision using an AE sensor (a sensor that converts the vibration into a voltage) attached to the base of the head arm.

With respect to the 100 magnetic disks of Examples 1 and 2 and Comparative Example 1, the head was floated at a flying height of 6 nm in the radius area of the data zone of the magnetic disk (the area on the magnetic disk for recording and reproduction). Move the position of the head,
The presence or absence of collision between the head and the magnetic disk was examined. Table 1 shows the number of magnetic disks that did not collide among the 100 disks of each of the tested examples. The radius inspected in the present embodiment is from 12.0 mm to 32.0 mm.

[0043]

[Table 1]

According to the results of Examples 1 and 2 in Table 1, by introducing a re-polishing step using a tape using a slurry before producing a magnetic recording medium, it has a concentric texture, Rmax = 3 nm, and Ra = Since TDH could be reduced to 0.3 nm or less, TDH could be suppressed to 6 nm or less. In addition, the results of the glide inspection are shown in Example 1 and Example 1.
As a result, the number of magnetic disks having no collision was larger in the magnetic disk No. 2 than in the magnetic disk of Comparative Example 1. The difference between the magnetic disk manufacturing processes of Examples 1 and 2 and Comparative Example 1 was the presence or absence of a re-polishing process before film formation. As a result, it is considered that the ratio of the colliding magnetic disks was reduced. Therefore, by the re-polishing treatment of the glass substrate before manufacturing the magnetic recording medium according to the present invention, a low flying height of the magnetic head can be realized, and a magnetic disk with high production stability and high reliability can be obtained.

Further, the magnetic recording media of Examples 1 and 2
The medium noise is smaller than the magnetic recording media of Comparative Examples 1 and 2. This is because the concentric texture formed on the glass substrate reduces the crystal grain size of the seed layer formed on the substrate and forms crystal grains with less dispersion, and furthermore, the underlayer grown epitaxially on the seed layer. It is considered that the crystal grain size of the magnetic layer was small and dispersion was suppressed.

The magnetic recording media of Examples 1 and 2 had substantially the same coercive force when a magnetic field was applied in the circumferential and radial directions. Generally, a magnetic recording medium manufactured using an Al / NiP substrate with a concentric texture is called an anisotropic medium, and a magnetic field is applied in a circumferential direction and a radial direction in a magnetic disk film surface. The coercive force at the time is different, and the coercive force in the circumferential direction becomes higher than the coercive force in the radial direction, resulting in a high coercive force. However, the magnetic recording medium of Example 1 in which a glass substrate is provided with a concentric texture has substantially the same coercive force when a magnetic field is applied in the circumferential direction and the radial direction (generally referred to as an isotropic medium). Al / Ni
In a form different from the effect of the anisotropic medium using the P substrate, it can be said that the magnetic recording medium of this embodiment achieves a high coercive force.

Example 3 and Comparative Example 4 Confirmation of the Effect of Concentric Texture In Example 3, a glass substrate 1 manufactured under the same conditions as in Example 1 was used.
The disk has a seed layer thickness of 500 Å. FIG. 3 is an electron micrograph SEM surface photograph of the seed layer surface of Example 3. The seed layer used in the present embodiment is the same as the seed layer used in the first embodiment. Comparative Example 3 includes the glass substrate used in Comparative Example 2,
The same seed layer as in Example 3 was formed to a thickness of 500 Å.

FIG. 4 shows an SEM surface photograph of the seed layer surface. Table 2 shows the crystal grain size of the seed layer calculated from the SEM surface photograph. As shown in Table 2, forming a concentric texture on the glass substrate has a smaller crystal grain size,
In addition, it shows that the crystal grain growth of the seed layer with less dispersion is promoted. Here, the variance is a half value width of a normal distribution when the crystal grain size of a crystal grain within a predetermined area is measured and the distribution of the crystal grain size is plotted, and indicates the variation of the crystal grain size. Therefore, the concentric texture on the surface of the glass substrate in this embodiment promotes crystal growth with a small grain size of the seed layer and little dispersion, and furthermore, the crystal grain size of the underlayer and the magnetic layer for epicapital growth. Can be reduced and dispersion can be suppressed. As a result, medium noise can be reduced and good electromagnetic conversion characteristics can be obtained. This is a value in Table 1 and supports the result of the medium noise.

[0049]

[Table 2]

[Examples 4 to 7, Reference Example 1] In fabricating the glass substrate 1 of this example, a woven tape was used as a tape, and polycrystalline diamond was dissolved in a dispersant as a hard abrasive. This was performed using a slurry. The average grain size of the polycrystalline diamond used in this example is 0.1 μm
(Example 4), 0.125 μm (Example 5), 0.5 μm
m (Example 6), 1.0 μm (Example 7), 1.2 μm
(Comparative Example 5). Other processing conditions of the texture device were as follows: processing load 1.0 kg processing pressure 9 g / mm ² substrate rotation speed 1000 rpm tape feed speed 2 mm / sec processing time 30 sec. The magnetic recording medium using the glass substrate 1 has the same seed layer 2, underlayer 3, magnetic layer 5,
This is a magnetic disk in which a protective layer 6 and a lubricating layer 7 are sequentially laminated.

In contrast to Examples 4 to 7 and Comparative Example 5, the surface of the glass substrate 1 was 0.5 μm square by AFM.
And the width of the concentric texture groove was determined from the cross-sectional profile in the direction (radial direction) perpendicular to the texture direction in the substrate plane with respect to the texture direction. Table 3 shows Examples 4 to 7
In addition, the width of the texture groove in the glass substrate of Comparative Example 5 in which the concentric texture was not attached and the value of the medium noise of each magnetic recording medium were placed.

[0052]

[Table 3]

From the results shown in Table 3, it can be seen that as the width of the concentric texture groove is increased, the medium noise becomes worse. If the width of the texture groove exceeds 60 nm, the medium noise of the magnetic recording medium without the concentric texture is almost the same, so that the effect of the concentric texture on the medium noise is lost. Therefore, the width of the concentric texture groove is preferably 60 nm or less.

The weight and polished thickness of the tape with respect to the substrate;
Example 8 Relationship between Surface Roughness of Substrate Surface In fabricating the glass substrate 1 of this example, a woven tape was used as the tape, and polycrystalline having an average particle size of 0.125 μm was used as the hard abrasive. This was performed using a slurry in which diamond was dissolved in a dispersant. In this embodiment, the processing weight is 0 kg, 0.50 kg, 0.75 kg,
1.00kg, 1.20kg, 1.4kg, 1.5kg
The other texture devices were set as follows: substrate rotation speed 1000 rpm tape feed speed 2 mm / sec processing time 30 sec. FIG. 3 shows the polishing thickness (the thickness of the polished glass surface in the present invention) and the surface roughness Rmax of the substrate surface with respect to the processing load.

As shown in FIG. 3, as the processing load increases, the polishing thickness monotonically increases, and Rmax decreases accordingly. However, when the polishing thickness is about 6 nm, R
The decrease in max is slow and the polishing thickness is at most 10 n
It can be seen that if it exceeds m, the surface roughness of the substrate will not substantially change. Further, it can be seen that if the polishing thickness is less than 3 nm, sufficient smoothness cannot be obtained. Although not shown in FIG. 3, it was confirmed that when the processing time was increased and the polished thickness exceeded 30 nm, the surface roughness varied due to the influence of heat due to the processing. In addition, the measurement of the polishing thickness was performed on a glass substrate.
A polished portion and a non-polished portion were formed, and the step in the boundary area was measured using an interference type surface profiler (WYKO).

[0056]

According to the present invention, in the step before sputtering, the surface of a glass substrate is polished again with a polishing thickness of 5 to 30 nm to provide a glass substrate with a floating height of 6 nm or less and high reliability. Further, by providing a concentric texture having a groove width of 60 nm or less, the seed layer on the glass substrate has a small crystal grain size, promotes growth with small dispersion, and has a magnetic characteristic of low medium noise. A magnetic recording medium can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a film structure of a magnetic disk.

FIG. 2 is a schematic diagram of a tape-type texture device.

FIG. 3 is a diagram showing a relationship between a polishing thickness and a surface roughness of a substrate surface with respect to a processing load.

FIG. 4 is a SEM surface photograph of the seed layer surface of Example 3.

FIG. 5 is an SEM surface photograph of the surface of a seed layer of Comparative Example 3.

Continuation of the front page (72) Inventor Hiroshi Tomiyasu 2-7-5 Nakaochiai, Shinjuku-ku, Tokyo F-term in Hoya Corporation (reference) 5D006 BB07 CB04 CB07 DA03 FA09 5D112 AA02 AA05 AA24 BA03 GA02 GA13 GA14

Claims (14)

[Claims] 1. A magnetic recording medium substrate having a concentric groove formed on a main surface thereof, wherein the height of the concentric irregularities is such that when at least a magnetic layer is formed on the substrate, the height in the circumferential direction is increased. A substrate having no magnetic anisotropy. 2. When at least a magnetic layer is formed on the substrate, an external magnetic field is applied in a circumferential direction and a radial direction at an arbitrary position on a magnetic recording medium, and a coercive force in a circumferential direction is Hc1, If the ratio (Hc1 / Hc2) of the coercive forces Hc1 and Hc2 when the coercive force in the radial direction is Hc2 is defined as magnetic anisotropy, the magnetic anisotropy is 0.90 to 1.10.
2. The substrate for a magnetic recording medium according to claim 1, wherein: 3. The substrate for a magnetic recording medium according to claim 1, wherein the height of the concentric unevenness is 3 nm or less. 4. The radial width of the concentric unevenness is:
The substrate for a magnetic recording medium according to claim 1, wherein the substrate has a thickness of 20 nm or more and 60 nm or less. 5. The substrate for a magnetic recording medium according to claim 1, wherein the substrate for a magnetic recording medium is made of glass. 6. A magnetic recording medium, wherein at least a magnetic layer is formed on a main surface of the magnetic recording medium substrate according to claim 1. Description: 7. A method for manufacturing a substrate for a magnetic recording medium by polishing a main surface of a disk-shaped substrate, wherein after polishing the main surface of the disk-shaped substrate, a polishing liquid containing an abrasive is applied to both main surfaces. A method for manufacturing a substrate for a magnetic recording medium, wherein a polishing tape is brought into contact with a main surface of the disk-shaped substrate which rotates about the center of the disk-shaped substrate as a central axis while supplying the same, and re-polishing is performed. 8. The method according to claim 7, wherein the abrasive has an average particle size of 1.0 μm or less. 9. The method for manufacturing a substrate for a magnetic recording medium according to claim 7, wherein the abrasive does not cause a chemical reaction with the material of the substrate. 10. The abrasive according to claim 1, wherein the abrasive is at least one selected from diamond abrasive grains, alumina abrasive grains, colloidal silica abrasive grains, zirconia oxide abrasive grains, and silicon carbide abrasive grains. 10. The method for producing a magnetic recording medium substrate according to item 9. 11. The polishing amount (gap) of said repolishing is 5
The method for manufacturing a substrate for a magnetic recording medium according to any one of claims 7 to 10, wherein the thickness is from 30 to 30 nm. 12. The method of manufacturing a magnetic recording medium substrate according to claim 7, wherein the substrate is made of glass. 13. A method for manufacturing a glass substrate for a magnetic recording medium, wherein the main surface of a glass substrate subjected to a chemical strengthening treatment is polished and smoothed, wherein the glass thickness to be polished and reduced is 5 to 30 n per polished surface.
m. A method for producing a glass substrate for a magnetic recording medium, the method comprising: 14. A method for manufacturing a magnetic recording medium, comprising: forming at least a magnetic layer on a main surface of the substrate for a magnetic recording medium according to claim 7. Description: