JPH08147682A - Magnetic disk and substrate for magnetic disk and recording and reproduction method - Google Patents

Abstract

PURPOSE: To reduce the floating height of a head by providing long projections and short projections in a contact start and stop CSS region, increasing the number of the long projections in the vicinity of a recording region and increasing the number of the short projections in the vicinity of an inner circumference. CONSTITUTION: The range of 21 to 18mm of a radius from the center of a magnetic disk is adopted as a CSS region and 20 pieces of long projections are formed per the length of 1mm in a radial direction in which the ratio of the major axis and the short axis of the cross section of a bottom part is 3. The intensity of a laser is changed within the range of 60 to 105mW, thereby changing the height of the projections within the range of 5 to 30nm. Short projections are formed within the range of 20 to 19mm from the center of the magnetic disk, and the intensity of a laser is changed within the range of 95 to 220mW, thereby changing the height of the projections within the range of 30 to 70nm. Further, in the stop position of a magnetic head within the range of 19 to 18mm of a radius from the center of the magnetic disk, the short projections are formed, and the height of the projections is made so as to be the constant height of about 70nm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic disk such as a hard disk used in an apparatus for a magnetic recording medium, a substrate for the magnetic disk, and a recording / reproducing method, and more particularly to a medium surface of a magnetic head while maintaining good CSS characteristics. The present invention relates to a magnetic disk, a magnetic disk substrate, and a recording / reproducing method capable of simultaneously improving sticking characteristics to the magnetic head and lowering the flying height of the magnetic head.

[0002]

2. Description of the Related Art Normally, writing / reading of information to / from a hard disk is performed via a magnetic head, and at that time, the hard disk rotates at high speed to levitate the magnetic head. A hard disk is a substrate surface of a disk or a Ni provided on the substrate surface for improving magnetic characteristics.
On a base layer made of a non-magnetic material such as P plating, mechanical polishing is performed in a circumferential direction of a magnetic disk in a substantially concentric manner to leave a processing mark (hereinafter, referred to as mechanical texture).

With the recent increase in the amount of information and the demand for smaller and lighter devices, a hard disk has a high linear recording density and a high track density, and the area per bit becomes smaller. Scratch scratches due to texture have a high probability of causing an error when reading information. Therefore, a method has been proposed in which only the CSS area on the inner circumference of the magnetic disk is mechanically textured and the data recording area is left as it is. However, in this case, the surface of the data recording area is higher than the surface of the CSS area. However, there is a problem in that it is difficult to make the step have a smooth slope, and the magnetic head crashes when seeking.

Also, a method of making a texture pattern by a laser has been proposed in place of such a mechanical texture. Examples of laser textures are disclosed in US Pat. Nos. 5,062,021 and 5,108,781, and Nd-YAG strong pulse laser light is used to generate N.
By locally melting the iP layer, the concave hole formed by melting and the molten NiP around the hole are raised by surface tension and solidified to form a diameter of 2.5.
A large number of crater-shaped irregularities consisting of a rim portion of ~ 100 μm are made, and the ring-shaped convex rim makes CSS with a magnetic head.
Attempts to improve the properties have been proposed.

When this method is used, the CS of the magnetic disk is
It is possible to texture only the S area. However, even in this case, in order to prevent sticking of the magnetic head, the protrusion height in the CSS region needs to be a certain height or more, and the glide height increases by the height of the protrusion. . Therefore, since the glide height of the medium is defined by the glide height of the CSS area, the head flying height becomes excessive in the data recording area, and the recording density cannot be sufficiently increased. It was

[0006]

Therefore, the stable flying height of the magnetic head in the data recording area of the magnetic disk can be made sufficiently low as defined by the glide of the data recording area, and in the CSS area. It is desired to stop the magnetic head on a protrusion having an appropriate height so that sticking does not occur.

[0007]

The present invention has been made for the purpose of fully utilizing the performance of such a magnetic disk for high density recording. The first gist of the present invention is to provide a non-magnetic substrate on a non-magnetic substrate. In a magnetic recording medium having at least an underlayer and a magnetic layer, the magnetic head on the magnetic layer side surface of the non-magnetic substrate or the underlayer is in contact start and stop (C
The CSS area for performing SS) has long protrusions and short protrusions. The proportion of long protrusions is large in the CSS area near the data recording area, and the proportion of short protrusions in the CSS area near the inner circumference of the disc. And the height of the protrusions gradually decreases toward the data recording area.

A second aspect of the present invention is a magnetic disk substrate having an underlayer on a nonmagnetic substrate, wherein the magnetic head on the magnetic layer side surface of the nonmagnetic substrate or the underlayer makes contact start and stop. (CSS) has long protrusions and short protrusions in the CSS area, and the proportion of long protrusions is large in the CSS area near the data recording area.
In the CSS area near the inner circumference of the disk, the ratio of short projections is large, and the height of the projections gradually decreases toward the data recording area.
Exist in.

Further, a third aspect of the present invention is a recording / reproducing method of reading / writing data from / to a magnetic disk by a magnetic head by a contact start and stop (CSS) system, wherein the magnetic disk is a non-magnetic substrate or an underlayer. The magnetic head on the surface of the magnetic layer has long protrusions and short protrusions in the CSS area for performing contact start and stop (CSS), and the proportion of long protrusions is large in the CSS area near the data recording area. In the CSS area near the inner circumference of the disk, a large number of short protrusions are used, and the height of the protrusion is gradually reduced toward the data recording area. In the CSS area near the area, the magnetic head drops to the magnetic disk and floats from the magnetic disk. Was carried out, in the CSS region near the peripheral portion discs large proportion of the short projections consists in recording and reproducing method, characterized in that for stationary magnetic head.

Hereinafter, the present invention will be described in detail. In the present invention, a magnetic disk having a large proportion of long protrusions in the CSS area (landing area of the magnetic head) near the data recording area on the surface of the magnetic disk is used, and when the magnetic head performs CSS on this magnetic disk, The descent of the magnetic head to the magnetic disk and the levitating from the magnetic disk are performed in the CSS area with a large proportion of long protrusions, the magnetic head is moved to the data recording area or the CSS area as the magnetic disk rotates at low speed, and The final stationary position of the head is C near the inner circumference of the disk where the protrusion height is high.
It is characterized by being an SS area.

The magnetic head may be moved to the CSS area in the vicinity of the inner peripheral portion of the disk where the projection height is high, immediately before the magnetic head is stopped, as long as the magnetic head is not sticking. In the magnetic disk of the present invention, as the non-magnetic substrate, usually a substrate made of silicon or aluminum alloy is preferably used, but a metal substrate made of copper, titanium or the like, a ceramic substrate or the like can also be used. Generally, the material of the non-magnetic substrate is preferably one having a small surface reflectance and a small thermal diffusivity in view of the relationship between heat generation by laser irradiation and heat dissipation by heat conduction.

The underlayer is usually made of a nonmagnetic material, preferably a NiP alloy layer, and is usually formed by an electroless plating method or a sputtering method. The thickness is preferably 50 to 20,000 nm, particularly preferably 100.
˜15,000 nm. An intermediate layer such as a Cr layer or a Cu layer is preferably provided between the magnetic layer and the underlayer, and the thickness thereof is usually 20 to 200 nm, preferably 50 to 100 nm.

The magnetic layer provided on the underlayer or the intermediate layer is
Usually, Co-P, Co-Ni-P, Co-Ni-Cr,
Co-Ni-Pt, Co-Cr-Ta, Co-Cr-P
A ferromagnetic alloy thin film such as t, Co—Cr—Ta—Pt alloy is formed by a method such as electroless plating, electroplating, sputtering, or vapor deposition, and its film thickness is usually 30 to 70 n.
m.

A protective layer is usually provided on the magnetic layer. As the protective layer, vapor deposition, sputtering, plasma CVD,
A carbon film, a hydrogenated carbon film, a carbide film such as TiC, SiC, etc., by a method such as ion plating or a wet method,
SiN, TiN, etc. nitride films, etc., SiO, AlO, ZrO
An oxide film or the like is formed. Of these, a carbon film and a hydrogenated carbon film are particularly preferable. A lubricant layer is usually provided on the protective layer.

A preferred method for producing the magnetic recording medium used in the present invention is to rotate a magnetic disk substrate provided with an underlayer made of a non-magnetic material such as NiP while rotating the surface of the magnetic disk substrate along the circumferential direction. Then, a method of forming projections on the surface by irradiating an energy beam or the like whose output is accurately controlled is cited. Examples of the energy beam include pulse lasers, electron beams, X-rays, and the like, and among them, pulse lasers are preferably used. Further, the magnetic disk substrate does not need to be provided with the above-mentioned underlayer. Further, instead of rotating the magnetic disk substrate, a pulse laser may be scanned on the magnetic disk substrate. next,
After providing an intermediate layer as needed, a magnetic layer is provided on the magnetic disk substrate, and a protective layer is usually formed to produce the magnetic disk of the present invention.

The mechanism of formation of protrusions has not been fully clarified yet, but it is considered as follows. The locally overheated spot portion on the non-magnetic substrate or underlayer irradiated with the pulsed laser is partially melted, and the molten portion is moved by the rotation of the substrate or the scanning of the energy beam. At the portion where the beam first hits, the temperature then drops and a temperature gradient occurs.
Generally, in a molten liquid, the surface tension is higher on the low temperature side, and due to this difference in surface tension, the beam is first irradiated and melted, and then the low temperature part takes up the liquid of the melted part later and rises. . Therefore, a recess is formed in the last melted portion. That is, in this case, a recess is often provided at the rear of the projection in the scanning direction of the energy beam. Whether the protrusion is long or short depends on the time width of the pulse. That is, when the pulse width is long, it becomes a long protrusion, and when it is short, it becomes a short protrusion. Here, the long protrusion means a protrusion having a ratio of the long axis to the short axis of the bottom cross section of 2 or more, and the short protrusion means a protrusion having a ratio of the long axis to the short axis of the bottom cross section of less than 2. That is.

In the present invention, the scanning direction of the energy beam is not limited to the scanning direction of the energy beam on the stationary magnetic disk substrate, but the energy beam is kept stationary and the irradiation is performed while the magnetic disk substrate is rotated. It also means the direction of rotation of the magnetic disk substrate. Depending on the conditions, such as when the scanning speed of the energy beam or the rotation speed of the magnetic disk substrate is slow or when the power of the energy beam is large, there may be a case where a recess is formed around the protrusion due to thermal contraction. Although this phenomenon has not been fully clarified, the locally heated spot expands, but the surrounding area is cold and difficult to deform, so the heated and expanded part is immediately cooled by the outside air and remains as a protrusion. It is considered that this is because the periphery of the protrusion is depressed due to thermal contraction.

The height of the protrusions can be freely controlled by adjusting the intensity of the laser, the average irradiation time thereof, and the linear velocity of the disk, and the density of the protrusions can be determined by the number of protrusions per revolution,
It can be freely controlled by adjusting the irradiation interval of the pulsed laser in the radial direction and the condition for controlling the height of the protrusion. Laser intensity is usually 20-500m
W, average irradiation time is 0.05 to 100 μsec, laser spot diameter is 0.2 to 4 μm, and substrate linear velocity is 0.8.
-15 m / sec is preferable. Here, the average irradiation time indicates the irradiation time of the laser required to form one protrusion. However, when a spiral mountain-shaped projection is formed, the energy beam is continuously oscillated while being scanned in the radial direction.

The protrusion has a maximum protrusion height of 200 nm.
The gradient of the protrusion height in the radial direction from the data recording area of the magnetic disk to the inner peripheral portion is preferably 0.0001 or less. Further, the protrusion density is usually preferably 10 ² to 10 ⁶ pieces / mm ² . Projection density may become difficult to support the lower surface magnetic head only projections due to the influence of such undulation of the substrate is less than 10 ² / mm ^2, making the projection beyond 10 ⁶ / mm ² protrusions each other It may be difficult to make the heights of the protrusions uniform due to the interference of. In addition, CS near the inner circumference of the disk
In the S region (particularly the magnetic head stop position), the existence density of protrusions having a height of 30 nm or more is 1 to 100 / mm.
It is preferably ² .

The height of the protrusion is determined by JIS surface roughness (B060
1-1982), the height of the protrusion when the center line of the roughness curve is used as a reference. The density of protrusions is not the average density of the entire medium but the density per unit area of the protrusions. The magnetic disk of the present invention is
The CSS area has long projections and short projections, the CSS area near the data recording area has a large proportion of long projections, and the CSS area near the inner circumference of the disk has a large proportion of short projections. The height of the protrusion is gradually reduced toward the data recording area. Long protrusions and short protrusions may be mixed in the CSS area, only long protrusions exist in the CSS area near the data recording area, and only short protrusions exist in the CSS area near the inner circumference of the disc. You may separate and exist.

When the magnetic recording device is stopped, the magnetic head is placed in the CSS area near the inner circumference of the disk where the short protrusions are present at a high ratio, the protrusion height is relatively high, and the sticking is small. There is. When the drive is started, the magnetic head moves to a CSS area near the data recording area in which the long protrusions are relatively high and the height of the protrusions is relatively low as the disk rotates. This part will stick if the magnetic head stops on the medium, but the frictional force in the sliding state is sufficiently small, and the long protrusions have a large top area compared to the short protrusions. It has excellent wear resistance.

When the number of rotations of the magnetic disk reaches a specified high-speed rotation, the magnetic head floats completely away from the magnetic disk and can freely move on the data recording area. When the magnetic recording device is driven, normally when the magnetic head is not sought on the data recording area, the magnetic head has a relatively low protrusion height in case of emergency such as power failure. It is desirable to wait in the CSS area near the area. Therefore, it is desired that the CSS area near the data recording area has a glide height almost equal to that of the data recording area.

When the driving magnetic recording apparatus is stopped, first, the magnetic head is usually moved to a CSS area near the data recording area where the protrusion height is relatively low. After that, when the number of rotations of the medium is decreased to lower the flying height of the magnetic head and the bottom of the magnetic head starts to hit the protrusion, the magnetic head is relatively high in the protrusion height, near the inner circumference of the disk. Move to and stop the CSS area.

When the CSS region is textured with an energy beam, it is preferable to use a magnetic disk substrate whose entire surface is mechanically textured in the circumferential direction with low glide. This is because when the height and density of the projections formed by the energy beam are small, that is, even when the substrate and the magnetic head are partially in contact with each other, compared to the case where a simply polished substrate is used,
This is because sticking is unlikely to occur and the friction coefficient is also small. Further, in this case, the conditions for producing the laser texture can be widened, which is particularly preferable for mass production.

[0025]

EXAMPLES Next, the present invention will be described more specifically by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist. Examples 1 and 2 and Comparative Examples 1 to 3 An aluminum substrate coated with a NiP underlayer having a diameter of 90 mm was mechanically textured in the circumferential direction to obtain a substrate having a surface roughness Ra of 2 nm or less in the data recording area and the CSS area. It was used as a magnetic disk substrate.

Next, an argon pulse laser whose intensity was accurately controlled as shown in Table 1 was irradiated on the CSS region of the NiP layer under the conditions shown in Table 1 to form protrusions. Then, by a sputtering method, a Cr intermediate layer (film thickness 100 nm) and Co- were sequentially formed on the magnetic disk substrate.
A Cr-Ta alloy magnetic film (film thickness 50 nm) and a carbon protective film (film thickness 20 nm) are formed, and then a fluorine-based liquid lubricant ("DOL-" manufactured by Monte Edison Co., Ltd. is prepared by an immersion method.
2000 ") was applied to a film thickness of 2 nm to prepare a magnetic disk.

Further, in Comparative Example 3, a magnetic disk was manufactured by the same process as in Example 1 except that a substrate having a NiP layer having a CSS region with a mechanical texture and a surface roughness Ra of about 2 nm was used. It was made. Table 1 shows the conditions when the protrusions were formed on the magnetic disk substrates manufactured in Example 1 and Comparative Examples 1 to 3 (the linear velocity of the rotated substrate, the intensity of the irradiated laser, the average irradiation time of the laser, the laser). The numerical aperture (NA) of the objective lens used for condensing is shown. The spot diameter at which 84% of the irradiated laser energy is concentrated is 1.22
It is represented by × λ / NA. Table 1 shows the average protrusion density of the formed protrusions, the average protrusion height, and the cross-sectional area of the portion 1 nm lower than the protrusion tips. The cross-sectional area shown in Table-1 is
The area of a figure surrounded by contour lines at a height 1 nm lower than the tip of the protrusion is shown.

[0028]

[Table 1] Table 1 -------------------------------------- Substrate Laser Average Average Average Average Average Projection Protrusion Objective velocity Linear velocity Strength Radiation time Evoked height Elevated cross-sectional area Open area (mm / sec) (mW) (μsec) (pieces / mm ² ) (nm) (μm ² ) (NA) −−−−− −−−−−−−−−−−−−−−−−−−−−−−−−−−−−− Example 1 Short protrusion 1714 95 to 220 1.25 9260 30 to 70 0.38 to 0.08 0.6 Long protrusion 1714 60 to 105 1.25 − 5 to 30 − 0.6 Example 2 Maximum protrusion 1714 220 1.25 80 70 0.08 0.6 Comparative example 1 Maximum protrusion 1714 62 1.25 9260 5 0.38 0.6 Comparative example 2 Maximum protrusion 1714 200 1.25 9260 56 0.08 0.3 COMPARATIVE EXAMPLE 3 Mechanical Texture -----------------------------------------------------

In the first embodiment, the range of radius 21 to 18 mm from the center of the magnetic disk is set as the CSS region, and the range of radius 21 to 20 mm on the outer side has a ratio of the major axis to the minor axis of the bottom cross section of 3. 20 shaku protrusions were formed per 1 mm in the radial direction. By changing the laser intensity in the range of 60 to 105 mW, the height of the protrusion was changed to about 5 to 30 nm.

Surface shape measuring device "ZY" by laser interference
Figure 1 shows the long protrusions made by GO ”(manufactured by Zygo, USA)
2A shows a cross-sectional shape passing through the tops of the projections along the laser scanning direction, and FIG. 2B shows a cross-sectional shape of the projections in a direction (radial direction) perpendicular thereto. Short projections were similarly formed within a radius of 20 to 19 mm from the center of the magnetic disk. By changing the laser intensity to 95 to 220 mW, the protrusion height was changed to about 30 to 70 nm.

Further, the radius 19 to the center of the magnetic disk is
At the magnetic head stop position within the range of 18 mm, short protrusions were similarly formed so that the protrusion height was a constant height of about 70 nm. Fig. 3 shows the shape of short protrusions made by "ZYGO".
4C shows a cross-sectional shape passing through the tops of the projections along the laser scanning direction, and FIG. 4D shows a cross-sectional shape of the projections in a direction (radial direction) perpendicular thereto.

In the second embodiment, at the magnetic head stop position within a radius of 19 to 18 mm from the center of the magnetic disk, 80 convex protrusions having a protrusion height of about 70 nm / mm ^{2 are formed.}
A protrusion was formed in exactly the same manner as in Example 1 except that the above was adopted. Table 2 shows the static friction coefficient (initial stiction) of these disks before CSS test and the frictional force after CSS 20,000 times. In the CSS test, a thin film head (slider material: Al ₂ O ₃ TiC) having a head flying height of 1.6 μinch and a loadgram of 6 gf was used. The flying stability of the magnetic head was evaluated by using a glide tester to evaluate the flying stability of the magnetic head when seeking between the data recording area and the CSS area. The stable flying height of the CSS region is 1.1 μ inch in Comparative Example 1 and about 2.7 μ inch in Comparative Example 2,
In Comparative Example 3 including only the mechanical texture, the value was 1.0 μ inch. It is believed that the glide height of Example 1 varies continuously between 1.1 and 2.7 μin in the CSS region.

In the magnetic disks obtained in Examples 1 and 2, the friction between the magnetic head and the protrusion at the stationary position of the magnetic head is not a problem because the relative speed is small.
Since the contact area between the tip of the protrusion and the magnetic head is made extremely small, sticking does not occur at all even when stopped for a long time. As described above, the magnetic head stopped on the protrusion having a sufficiently high height gradually moves to the outside of the magnetic disk at the same time as the rotation of the medium, and reaches the stable rotation speed (5,400 rpm) of the magnetic disk. Has a radius of 18-2
Move to the position of 0 mm and levitate.

On the contrary, when the magnetic head stops, the radius of the magnetic head is 2
When it is in the range of 0 to 21 mm, the rotation speed of the medium is reduced until the magnetic head and the long protrusions on the magnetic disk come into contact with each other.
After that, before the medium is stopped, the magnetic head is moved to a region where a sufficiently high protrusion having a radius of 19 to 18 mm is formed. Here, the stickion of Example 1 and Example 2 and the frictional force after 20,000 times are values at a position of a radius of 19 to 18 mm from the center of the magnetic disk.

[0035]

[Table 2] Table-2 -------------------------------------- (Frictional coefficient) Friction force after 20,000 times of initial stiction CSS −−−−−−−−−−−−−−−−−−−−−−−−−−−−− Example 1 0.12 3 gf Example 2 0.11 3 gf Comparative Example 1 4.41 36 gf Comparative Example 2 0.12 Head crash Comparative example 3 5.19 Adsorption drive stop (750 times) -------------------------------

As is clear from Table 2, the mechanical texture alone (Comparative Example 3) and the magnetic disk having a laser projection of 5 nm (Comparative Example 1) had no stickion and frictional force values. It is enough. In addition, C with laser
The protrusion having a protrusion height of 56 nm formed in the entire SS region (Comparative Example 2) has a better sticktion, but a low-flying magnetic head hits the protrusion during seek, causing a head crash. Will end up.

On the other hand, it can be seen that the CSS in the magnetic disk (Examples 1 and 2) in which the protrusion height is continuously changed in the CSS area has low sticking and does not cause head crash. In the second embodiment in which the protrusion density is low at the magnetic head stationary position,
Even in head parking every 2000 times in the S test, the stiction value is almost the same as the initial stiction value.

When only the short protrusion is used as the contact portion with the magnetic head, the tip of the protrusion is worn, but in the present invention, the protrusion shape of the contact portion at the time of high speed rotation with the magnetic head is the long protrusion. Therefore, the durability is extremely high.

[0039]

According to the present invention, the flying height of the magnetic head in the data recording area can be made sufficiently low, and sticking does not occur when the magnetic head is stopped. The device can be developed.
Moreover, since the long protrusion is formed on the sliding portion of the protrusion of the magnetic head, a magnetic disk having extremely high durability can be obtained, which is very useful in industry.

[Brief description of drawings]

FIG. 1 is a view showing a shape of a long protrusion of the present invention observed by a surface shape measuring device.

FIG. 2 is a diagram showing a cross-sectional shape (a) of the projection of FIG. 1 which passes through the top of the projection along the laser scanning direction and a cross-sectional shape (b) perpendicular to the laser scanning direction (radial direction). .

FIG. 3 is a view showing a shape of a short protrusion of the present invention observed by a surface shape measuring device.

FIG. 4 is a diagram showing a cross-sectional shape (c) of the protrusion of FIG. 3 that passes through the top of the protrusion along the laser scanning direction and a cross-sectional shape (d) of a direction (radial direction) perpendicular to the laser scanning direction. .

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsunori Mochida 1000 Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa Mitsubishi Chemical Corporation Yokohama Research Institute

Claims (8)

[Claims] 1. In a magnetic recording medium having at least an underlayer and a magnetic layer on a nonmagnetic substrate, a CSS area in which a magnetic head on the magnetic layer side surface of the nonmagnetic substrate or the underlayer performs contact start and stop (CSS). C has a long protrusion and a short protrusion in the vicinity of the data recording area.
The SS area has a large proportion of long projections, the CSS area near the inner peripheral portion of the disc has a large proportion of short projections, and the height of the projection gradually decreases toward the data recording area. Magnetic disk. 2. The long protrusion is a protrusion having a ratio of the major axis to the minor axis of the bottom cross section of 2 or more, and the short protrusion is a protrusion having a ratio of the major axis to the minor axis of the bottom cross section of less than 2. Item 1. The magnetic disk according to Item 1. 3. The magnetic according to claim 1, wherein the maximum height of the protrusion is 200 nm or less, and the gradient of the protrusion height in the radial direction from the data recording area of the magnetic disk toward the inner peripheral portion is 0.0001 or less. disk. 4. A magnetic disk substrate having an underlayer on a non-magnetic substrate, wherein the magnetic head on the magnetic layer side surface of the non-magnetic substrate or the underlayer extends to a CSS area for performing contact start and stop (CSS). It has long protrusions and short protrusions, and the proportion of long protrusions is large in the CSS area near the data recording area.
A magnetic disk substrate characterized in that a large proportion of short protrusions are present in the area, and the height of the protrusions gradually decreases toward the data recording area. 5. A recording / reproducing method of reading / writing data from / to a magnetic disk by a magnetic head by a contact start and stop (CSS) method, wherein a magnetic head is a non-magnetic substrate or a magnetic head on the surface of a magnetic layer of an underlayer. The CSS area for performing contact start and stop (CSS) has long protrusions and short protrusions. In the CSS area near the data recording area, the proportion of long protrusions is high, and in the CSS area near the inner circumference of the disc. Is a magnetic disk in which the proportion of short protrusions is large and the height of the protrusions gradually decreases toward the data recording area. In the CSS area near the data recording area where the proportion of long protrusions is large, a magnetic head is used. Drop to and levitate from the magnetic disk, and there are many short protrusions. A recording / reproducing method characterized in that the magnetic head is made to stand still in the CSS area near the inner peripheral portion of the disk. 6. The long protrusion is a protrusion having a ratio of a long axis to a short axis of the bottom cross section of 2 or more, and the short protrusion is a protrusion having a ratio of the long axis to the short axis of the bottom cross section of less than 2. The recording / reproducing method according to claim 6. 7. The magnetic disk has a maximum protrusion height of 20.
8. The recording / reproducing method according to claim 6, wherein the projection height gradient in the radial direction from the outer peripheral portion to the inner peripheral portion of the magnetic disk is 0 nm or less and 0.0001 or less. 8. The recording / reproducing method according to claim 6, wherein the magnetic head is made to stand still in a CSS region in which the existence density of short protrusions having a height of 30 nm or more is 1 to 100 / mm ^2. .