JP2013178855A - Magnetic recording medium and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium capable of lowering a generation rate of read errors and the manufacturing method thereof.SOLUTION: A glass substrate 1G with a magnetic recording layer 20 formed thereon has a concentrically curved shape so as to make one main surface side concave. Since the surface of a magnetic disk can be rotated while maintaining high flatness in the case that the magnetic disk is rotated at a high speed to execute recording and playback by a magnetic head in this way, the generation rate of read errors in the magnetic head can be lowered.

Description

  The present invention relates to a magnetic recording medium suitable as a substrate for an information recording medium such as a hard disk (HDD), particularly a substrate for a heat-assisted recording medium, and a method for manufacturing the same.

  Conventionally, an aluminum alloy has been used as a substrate for an information recording medium such as a hard disk (HDD). However, since aluminum alloys have problems such as being easily deformed and insufficient smoothness of the substrate surface after polishing, glass substrates are now widely used (for example, Patent Documents 1 to 6). .

JP 2010-080025 A JP 2000-169184 A JP 2006-327935 A JP 2006-327936 A JP 2007-161552 A International Publication No. 2009/028570 Pamphlet

  In recent years, in the information recording medium as described above, it is required to set the recording density to an ultra-high density state as the information recording amount increases. Since the magnetic method is used as the recording means, when the recording density is increased, the holding power of the recording becomes weaker, and the recording due to the influence of heat generated during recording is known as so-called “thermal fluctuation”. There was a problem of disappearing.

  As a means for solving such a problem, an information recording means of a system called heat assist recording has been attracting attention. This heat-assisted recording is intended to solve the above-described problems by recording information while heating a substrate for a recording medium with a laser. In such a heat-assisted recording system, a glass substrate is used as a substrate (hereinafter also referred to as “substrate for heat-assisted recording medium”), and a magnetic magnetic recording layer comprising a plurality of layers on the glass substrate ( (Hereinafter simply referred to as “magnetic recording layer”), but for the purpose of densifying the magnetic recording layer, an extremely high temperature of about 550 ° C. is applied during the formation (during film formation). Has special characteristics.

  Further, after the formation of the magnetic recording layer, a post-heating treatment of about 600 ° C. is performed for the purpose of improving the magnetocrystalline anisotropy of the magnetic recording layer.

  Thus, when a high temperature heat treatment is performed, there is a possibility that an asymmetrical deformation (a saddle type or an elliptical type, which will be described later) occurs in the glass substrate of the magnetic recording medium. As a result, it is conceivable that the magnetic recording head collides with the glass substrate when reading the recording information using the magnetic recording head, thereby causing a read error.

  The present invention has been made in view of the current situation as described above, and an object of the present invention is to provide a magnetic recording medium capable of reducing the incidence of read errors and a method for manufacturing the same. is there.

  In the method of manufacturing a magnetic recording medium based on the present invention, a method of manufacturing a magnetic recording medium used for a heat-assisted recording method, the step of preparing a glass substrate having an annular disk shape, and the glass substrate Rough polishing the two main surfaces of the glass substrate, forming a surface reinforcing layer on the two main surfaces of the rough polished glass substrate, polishing amount of the one surface reinforcing layer and the other of the above By subjecting the two surface enhancement layers to a precise polishing treatment so that the polishing amount of the surface enhancement layer is different, the main surface side where the surface enhancement layer on the side with a smaller amount of polishing is located becomes concave. And concentrically curving the glass substrate, and the magnetic recording layer is formed on at least one main surface of the glass substrate while the glass substrate remains concentrically curved toward one main surface side. And a step to be.

  In another embodiment, the magnetic recording layer is formed on the main surface side where the surface enhancement layer on the side where the glass substrate has a large amount of polishing is convex.

In another embodiment, the magnetic recording layer is formed on each of the two main surfaces.
A magnetic recording medium based on the present invention is a magnetic recording medium used for a thermally assisted recording method, and is a glass substrate having an annular disk shape and at least one of two main surfaces of the glass substrate. A planar magnetic recording layer provided on the main surface, and the glass substrate provided with the magnetic recording layer has a concentrically curved shape toward one main surface.

  In another embodiment, the distance between the center portion and the edge portion of the glass substrate in the thickness direction of the glass substrate is 0.1 μm to 3.0 μm.

  In another embodiment, the total value of the distance from the least square plane to the highest point and the distance from the least square plane to the lowest point in one circumferential circumference at a position of 25 mm from the center of the glass substrate is 1. 0 μm or less.

  In another embodiment, the magnetic recording layer is provided on the main surface side where the glass substrate is convex.

  In another embodiment, the magnetic recording layer is provided on each of the two main surfaces.

  According to the magnetic recording medium and the manufacturing method thereof based on the present invention, it is possible to provide a magnetic recording medium and a manufacturing method thereof that can reduce the read error occurrence rate.

1 is a plan view showing a schematic configuration of a thermally-assisted magnetic recording apparatus in an embodiment. 1 is a side view showing a schematic configuration of a heat-assisted magnetic recording apparatus in an embodiment. It is a perspective view which shows the glass substrate used for the magnetic disc in embodiment. 1 is a perspective view showing a magnetic disk in an embodiment. It is a partial expanded sectional view of the other magnetic disc in an embodiment. 1 is a cross-sectional view of a magnetic disk in an embodiment. It is a flowchart which shows the manufacturing process of the magnetic disc in embodiment. It is a partial expanded sectional view of the glass substrate which shows the chemical strengthening process in the manufacturing process of the magnetic disc in embodiment. It is a partial expanded sectional view of the glass substrate in the precision grinding | polishing process in the manufacturing process of the magnetic disc in embodiment. It is a partial expanded sectional view of the glass substrate after giving the precision grinding | polishing process in the manufacturing process of the magnetic disc in embodiment. It is sectional drawing of the other magnetic disc in embodiment. It is a figure which shows the classification of the magnetic disk used in the Example and the comparative example. (A) Schematic diagram showing the internal stress state of a saddle type magnetic disk, (B) Schematic diagram showing the internal stress state of an elliptical magnetic disk, (C) Elliptic magnetism It is a schematic diagram which shows the internal stress state of a disk. “Glass substrate flatness (μm)”, “magnetic disk flatness (μm)”, “circumferential direction TIR (μm)”, and “lead” in Comparative Examples 1 to 2 and Examples 1 to 3 It is a figure which shows the measurement result of "error (%) (those by collision)".

  A magnetic recording medium and a manufacturing method thereof according to the present invention will be described below with reference to the drawings. Note that in the embodiments described below, when referring to the number, amount, and the like, the scope of the present invention is not necessarily limited to the number, amount, and the like unless otherwise specified.

  The same parts and corresponding parts are denoted by the same reference numerals, and redundant description may not be repeated. In addition, it is planned from the beginning to use the structures in the embodiments in appropriate combinations.

(Schematic configuration of the heat-assisted magnetic recording apparatus 2)
First, an example of a schematic configuration of the heat-assisted magnetic recording apparatus 2 will be described with reference to FIGS. 1 is a plan view showing a schematic configuration of the thermally-assisted magnetic recording apparatus 2, FIG. 2 is a side view showing the schematic configuration of the thermally-assisted magnetic recording apparatus 2, and FIG. 3 is a glass substrate used for the magnetic disk 1. 1G is a perspective view showing the magnetic disk 1, FIG. 5 is a partially enlarged sectional view of another magnetic disk 1A, and FIG. 6 is a sectional view of the magnetic disk 1A.

  As shown in FIG. 1, the heat-assisted magnetic recording apparatus 2 includes a magnetic recording head 2D disposed opposite to a magnetic disk 1 for heat-assisted magnetic recording that is a magnetic recording medium that is rotationally driven in the direction of arrow DR1. Yes. Although the shape of the magnetic disk 1 will be described later with reference to FIG. 6, the magnetic disk 1 used in the present embodiment has a shape that is concentrically curved toward one main surface.

  Note that “concentric” means that the height from the center of the magnetic disk 1 is substantially the same in the thickness direction of the substrate at a position where the distance from the center of the magnetic disk 1 is approximately equal (on the circle). It means a shape in which the height is higher than the center side as the distance from the center increases.

  The magnetic recording head 2D is mounted on the tip of the suspension 2C. The suspension 2C is provided so as to be rotatable in the direction of the arrow DR2 (tracking direction) with the support shaft 2A as a fulcrum. A tracking actuator 2B is attached to the support shaft 2A.

  As shown in FIG. 2, the laser beam LB is irradiated on the side facing the magnetic recording head 2D with the magnetic disk 1 interposed therebetween. A portion to be recorded on the magnetic disk 1 is instantaneously heated by the laser beam LB, and data is recorded on the magnetic disk 1 by the magnetic recording head 2D.

  The magnetic particles of the magnetic layer formed on the magnetic disk 1 have a lower holding force as the temperature rises. By heating the magnetic layer with the laser beam LB, even a magnetic layer having a high coercive force at room temperature can be recorded with the normal magnetic recording head 2D, and ultrahigh density recording can be realized.

  Here, the position of the magnetic recording head 2D and the irradiation position of the laser beam LB are configured to face the magnetic disk. However, in order to simplify the configuration and position control of the head, they are provided on the magnetic disk 1. Alternatively, they may be arranged on the same side. In particular, when both surfaces of the magnetic disk 1 are used as recording surfaces, they are arranged on the same side.

(Configuration of magnetic disk 1)
Next, the configuration of the magnetic disk 1 will be described with reference to FIGS. 3 is a perspective view showing a glass substrate 1G used for the magnetic disk 1, and FIG. 4 is a perspective view showing the magnetic disk 1. As shown in FIG.

  As shown in FIG. 3, the glass substrate 1G used for the magnetic disk 1 has an annular disk shape with a hole 11 formed in the center. The glass substrate 1G has an outer peripheral end face 12, an inner peripheral end face 13, a front main surface 14, and a back main surface 15. As an example of the size of the glass substrate 1G, the outer diameter is about 64 mm, the inner diameter is about 20 mm, and the thickness is about 0.8 mm.

  As shown in FIG. 4, in the magnetic disk 1, a magnetic layer 23 is formed on the front main surface 14 of the glass substrate 1G. In the figure, the magnetic layer 23 is formed only on the front main surface 14, but it is also possible to provide the magnetic layer 23 on the back main surface 15 (see FIG. 11).

  As a method for forming the magnetic layer 23, a conventionally known method can be used. For example, a method in which a thermosetting resin in which magnetic particles are dispersed is spin-coated on a substrate, or a method in which sputtering or electroless plating is used. A method is mentioned.

  The film thickness by spin coating is about 0.3 to 1.2 μm, the film thickness by sputtering is about 0.04 to 0.08 μm, and the film thickness by electroless plating is 0.05 to 0.1 μm. From the viewpoint of thinning and densification, film formation by sputtering and electroless plating is preferable.

  The magnetic material used for the magnetic layer 23 is not particularly limited, and a conventionally known material can be used. However, in order to obtain a high coercive force, Co having high crystal anisotropy is basically used, and Ni is used for the purpose of adjusting the residual magnetic flux density. A Co-based alloy or the like to which Cr is added is suitable. In recent years, FePt-based materials have been used as magnetic layer materials suitable for heat-assisted recording.

  In addition, a lubricant may be thinly coated on the surface of the magnetic layer 23 in order to improve the sliding of the magnetic recording head. Examples of the lubricant include those obtained by diluting perfluoropolyether (PFPE), which is a liquid lubricant, with a freon-based solvent.

  Furthermore, you may provide a base layer and a protective layer as needed. The underlayer in the magnetic disk is selected according to the magnetic film. Examples of the material for the underlayer include at least one material selected from nonmagnetic metals such as Cr, Mo, Ta, Ti, W, V, B, Al, and Ni.

  Further, the underlayer is not limited to a single layer, and may have a multi-layer structure in which the same or different layers are stacked. For example, a multilayer underlayer such as Cr / Cr, Cr / CrMo, Cr / CrV, NiAl / Cr, NiAl / CrMo, or NiAl / CrV may be used.

  Examples of the protective layer that prevents wear and corrosion of the magnetic layer 23 include a Cr layer, a Cr alloy layer, a carbon layer, a hydrogenated carbon layer, a zirconia layer, and a silica layer. These protective layers can be formed continuously with an in-line type sputtering apparatus, such as an underlayer and a magnetic film. In addition, these protective layers may be a single layer, or may have a multilayer structure including the same or different layers.

Note that another protective layer may be formed on the protective layer or instead of the protective layer. For example, in place of the protective layer, tetraalkoxylane is diluted with an alcohol-based solvent on a Cr layer, and then colloidal silica fine particles are dispersed and applied, followed by baking to form a silicon oxide (SiO ₂ ) layer. It may be formed.

(Magnetic disk 1A)
FIG. 5 shows an example of the configuration of another magnetic disk 1A. FIG. 5 is a partially enlarged cross-sectional view of another magnetic disk 1A. In this magnetic disk 1A, a magnetic recording layer 20 having a plurality of layers is formed on a glass substrate 1G.

  The magnetic recording layer 20 has a seed (unevenness control) layer 21 made of AlN or the like directly formed on the front main surface 14 of the glass substrate 1G, and a thickness of about 60 nm formed on the seed (unevenness control) layer 21. The underlayer 22, the magnetic layer 23 having a thickness of about 30 nm formed on the underlayer 22, the protective layer 24 having a thickness of about 10 nm formed on the magnetic layer 23, and the protective layer 24 are formed. And a lubricating layer 25 having a thickness of about 0.8 nm.

  The configuration of the magnetic disk 1A is merely an example, and the size of the glass substrate 1G and the configuration of the magnetic recording layer 20 are appropriately changed according to the performance required for the magnetic disk 1A.

(Detailed structure of magnetic disk 1A)
Next, the detailed structure of the magnetic disk 1A when the magnetic recording layer 20 shown in FIG. 5 is employed will be described with reference to FIG. The same applies to the magnetic disk 1 shown in FIG. 4 in which only the magnetic layer 23 is formed as the magnetic recording layer.

  In the magnetic disk 1A in the present embodiment, the glass substrate 1G on which the magnetic recording layer 20 is formed has a concentrically curved shape so as to be concave toward one main surface side. Here, as described above, “concentric” means that from the center of the glass substrate 1G in the thickness direction of the glass substrate 1G at a position where the distance from the center of the glass substrate 1G is substantially equal (on the circle). It means that the height is higher than the center side as the distance from the center increases.

  In the present embodiment, the glass substrate 1G having a distance (h1) between the center portion and the edge portion of the glass substrate 1G in the thickness direction of the glass substrate 1G is 0.1 μm to 3.0 μm. Further, the glass substrate 1G is used in which the TIR (Total Indicator Runout) value for one round in the circumferential direction of the glass substrate 1G is 1.0 μm or less. The TIR value will be described later. The magnetic recording layer 20 is provided on the main surface side where the glass substrate 1G is convex.

(Manufacturing process of glass substrate 1G)
Next, with reference to FIGS. 7 to 11, a method of manufacturing the hard disk magnetic disk 1A according to this embodiment will be described. 7 is a flowchart showing the manufacturing process of the magnetic disk 1A, FIG. 8 is a partially enlarged sectional view of the glass substrate 1G showing the chemical strengthening process in the manufacturing process of the magnetic disk 1A, and FIG. 10 is a partially enlarged sectional view of the glass substrate 1G in the precision polishing step in the manufacturing process, FIG. 10 is a partially enlarged sectional view of the glass substrate 1G after the precision polishing step in the manufacturing process of the magnetic disk 1A, and FIG. It is sectional drawing of the magnetic disc 1B.

  First, in the “glass melting step” of step 10 (hereinafter abbreviated as “S10”, the same applies to step 20 and subsequent steps), the glass material constituting the substrate is melted. Next, in the “press molding step” of S20, the molten glass is poured onto the lower mold and press molded with the upper mold. Thus, the glass substrate 1G having an annular disk shape is prepared.

  As the glass material, aluminosilicate glass, soda lime glass, borosilicate glass, or the like can be used.

  In the “rough polishing step” of S30, the surface of the press-molded glass substrate is polished, and the flatness of the glass substrate is preliminarily adjusted. Next, in the “chemical strengthening step” of S40, surface reinforcing layers are formed on the two main surfaces of the glass substrate 1G.

  As a specific example of the “chemical strengthening step”, a mixed solution of potassium nitrate (60%) and sodium nitrate (40%) is used as the chemical strengthening solution. The chemical strengthening solution is heated to 300 ° C. or higher, the glass substrate 1G is preheated, and immersed in the chemical strengthening solution for about 3 hours to about 4 hours.

  Thus, by immersing in the chemical strengthening solution, lithium ions and sodium ions in the surface layer of the glass substrate 1G are replaced with sodium ions and potassium ions having a relatively large ion radius in the chemical strengthening solution, respectively. The surface of the substrate is strengthened.

  As shown in the cross-sectional view of FIG. 8, the “chemical strengthening step (S40)” has surface reinforcing layers 101A and 101B each having a thickness (t1) of about 10 μm on the two main surfaces of the glass substrate 1G. It is formed. In order to obtain characteristics excellent in flatness and strength of the main surface of the glass substrate 1G, it is preferable to use an aluminosilicate glass for the glass substrate 1G.

  Next, in the “precision polishing step” of S50, the glass substrate 1G is polished. In this “precision polishing step”, a polishing step for adjusting the roughness of the main surface of the glass substrate 1G is performed, and as shown in FIG. 9, the polishing amount of the surface reinforcing layer 101A and the polishing amount of the surface reinforcing layer 101B The glass substrate 1G is polished so as to be different.

  In the present embodiment, the polishing amount (t2) of the surface reinforcing layer 101A is about 2 μm (the remaining thickness (t3) is about 8 μm), and the polishing amount (t4) of the surface reinforcing layer 101B is about 5 μm (the remaining thickness ( t5) was about 5 μm).

  As described above, by polishing the glass substrate 1G so that the polishing amount of the surface reinforcing layer 101A and the polishing amount of the surface reinforcing layer 101B are different, the surface reinforcing layer 101A having a thicker remaining thickness is more suitable. The compressive stress is different from that of the surface reinforcing layer 101B.

  As a result, as shown in FIG. 10, in the glass substrate 1G, the glass substrate 1G is concentrically curved so that the main surface side where the surface enhancement layer 101A on the side where the polishing amount is small is located is concave. The degree of bending is appropriately determined depending on the polishing amount of the surface reinforcing layer 101A and the polishing amount of the surface reinforcing layer 101B.

  In addition, it is also possible to employ | adopt the grinding | polishing process which mainly arranges the roughness of the main surface of the glass substrate 1G between the "rough grinding | polishing process" of S30, and the "chemical strengthening process" of S40.

  Next, in the “cleaning step” of S60, the glass substrate is cleaned. Through the above steps, a glass substrate 1G applicable to a hard disk substrate is obtained.

  Further, in the “film formation step” of S70, the magnetic recording layer 20 is formed on the main surface side where the surface enhancement layer 101B on the side with a large polishing amount where the glass substrate 1G is convex is located. Finally, in the “post heat treatment step” of S80, heat treatment for improving the crystal magnetic field anisotropy is performed. The heating temperature is about 600 ° C. Thus, the magnetic disk (hard disk) 1A is completed.

  The glass substrate 1G has a thickness of about 0.8 mm, whereas the magnetic recording layer 20 has a thickness of about 100 nm. Therefore, the magnetic recording layer 20 affects the curved state of the glass substrate 1G. Never give.

  Further, in the above embodiment, in the “film formation step” of S70, the magnetic recording layer 20 is formed on the main surface side where the surface enhancement layer 101B on the side where the glass substrate 1G has a large amount of polishing becomes convex. Although the case has been described, it is also possible to use a magnetic disk 1B in which the magnetic recording layers 20 are formed on the two main surfaces of the glass substrate 1G as shown in FIG.

  As described above, the glass substrate on which the magnetic recording layer is conventionally formed improves the crystal magnetic anisotropy of the magnetic recording layer after the magnetic recording layer is formed in the “film formation step”. For the purpose, post-heating treatment of about 600 ° C. is performed, and it has been regarded as a problem that asymmetrical bowl-shaped or elliptical deformation occurs in the glass substrate.

  However, in the present embodiment, the glass substrate 1G is concentrically curved toward the one main surface side with respect to the glass substrate 1G in advance before the “film formation step”. As a whole, the rigidity of the glass substrate increases, and even when the post-heating treatment in the “film formation step” is performed, it is possible to prevent the glass substrate from being asymmetrically deformed.

  Further, by concentrically bending the glass substrate 1G toward one main surface, the surface of the magnetic disk can be obtained even when the magnetic disk is rotated at a high speed and recording / reproduction is performed by the magnetic head. Can rotate while maintaining a high flatness, so that it is possible to reduce the incidence of read errors in the magnetic head.

(Example)
Next, examples of the magnetic disk manufactured by the manufacturing method shown in the above embodiment will be described. Ten magnetic disks manufactured by the manufacturing method shown in the above embodiment (hereinafter referred to as the magnetic disk of the example) and magnetic disks manufactured by the conventional manufacturing method (hereinafter referred to as the magnetic disk of the comparative example). .) 10 sheets were prepared.

  The shape of the magnetic disk was measured using an optical interferometer on these 20 magnetic disks in total. The results are shown in FIGS. As the glass substrate, a 2.5-inch glass substrate with a magnetic recording film formed on both surfaces of the glass substrate was used.

  The shape of the magnetic disk can be roughly divided into three types as shown in FIG. FIG. 13A shows a shape called a saddle shape. The lines indicated by dotted lines in the figure are at the same distance from the center of the magnetic disk when viewed in the direction of the height of the magnetic disk (height from the center of the glass substrate 1G in the thickness direction of the glass substrate 1G). A line connecting a certain position. So-called contour lines. In the case of a saddle type magnetic disk, a contour line appears such that the center is located on the edge side of the magnetic disk. In this case, the magnetic disk is in a wavy state.

  FIG. 13B shows a shape called an elliptical shape. In the case of an elliptical magnetic disk, contour lines appear in an elliptical shape when viewed from the center of the magnetic disk. In this case, the magnetic disk is in a state of being rounded into a cylindrical shape. FIG. 13C shows a shape called a concentric circle. In the case of a concentric magnetic disk, contour lines appear concentrically with respect to the center of the magnetic disk. According to a general substrate processing process that does not control the internal stress state of the substrate, these shapes appear randomly depending on the distribution state of the internal stress accumulated in the processing process.

  When the concentric contour lines appear concentrically, the bowl has a shallow bowl shape, and in the thickness direction of the substrate, at the same distance from the center of the glass substrate (on the circle), the center of the glass substrate The height from the center is the same, and the higher the distance from the center, the higher the height from the center side.

  As shown in FIG. 12, the 10 magnetic disks of the example were all (C) concentric circles as a result of the measurement. On the other hand, 10 magnetic disks of the comparative example were (A) saddle type, 4 (B) elliptical type, and (C) concentric type did not exist.

  Next, the occurrence state of the read error was compared between the magnetic disk of the example and the magnetic disk of the comparative example. The result is shown in FIG.

  Of the magnetic disks of the comparative examples, (A) one saddle type and (B) one elliptical type were selected and the following measurements were performed. (A) A saddle type magnetic disk is referred to as Comparative Example 1, and (B) an elliptical magnetic disk is referred to as Comparative Example 2. Further, three of the magnetic disks of the examples were selected and the following measurements were performed. These (C) concentric magnetic disks are referred to as Example 1 to Example 3.

  In the measurement of the magnetic disk, (a) glass substrate flatness (μm), (b) magnetic disk flatness, (c) circumferential TIR value (μm), and (d) read error (due to collision) It was measured. For the determination of concentric circles, (i) the contour lines are concentric with the center of the disc, and (ii) the TIR for one round in the circumferential direction at a position 17 mm from the center and a position 25 mm from the center. Both values were 1.0 μm or less.

  (A) Glass substrate flatness is measured by measuring a glass substrate before forming a magnetic recording film. (B) Magnetic disk flatness and (c) circumferential direction TIR (μm) are measured on the magnetic disk after the magnetic recording film is formed.

  Here, the values of (a) glass substrate flatness, (b) magnetic disk flatness, and (c) circumferential direction TIR are indices representing the flatness of the substrate, from the least-squares plane of the evaluation surface to the highest point. And the total value of the distance from the least square plane to the lowest point.

  (A) Glass substrate flatness and (b) magnetic disk flatness measure the entire surface of the substrate, and the total of the distance to the highest point and the distance to the lowest point on the basis of the least squares plane is the evaluation surface. It is a value measured over the entire surface of. (C) The circumferential direction TIR is a value obtained by measuring one round in the circumferential direction at a position 25 mm from the center.

  When the TIR for one round in the circumferential direction is 1.0 μm or less, it is easy to cope with low flying of the magnetic head and high-speed rotation, and recording / reproduction can be performed stably. If the circumferential direction TIR is larger than 1.0 μm, a recording / reproducing error due to a collision between the magnetic head and the magnetic disk may occur in some cases. Accordingly, the circumferential direction TIR is preferably 1.0 μm or less. Among these, 0.5 μm or less is preferable. (C) The circumferential direction TIR and (b) flatness were measured by an optical interferometer.

  As shown in FIG. 14, (d) the read error in Comparative Example 1 is “32%”, and (d) the read error in Comparative Example 2 is “18%”. (D) The measurement result was “5%” for the read error, and “2%” for the (d) read error in Examples 2 and 3. As a result, it was confirmed that when the magnetic disk in Examples 1 to 3 was used, the read error rate could be reduced.

  There is no significant change between (a) glass substrate flatness and (b) magnetic disk flatness. This means that the shape of the glass substrate formed concentrically in the “precision polishing step” is maintained as it is even during the heat treatment of the magnetic recording film.

  As described above, according to the magnetic disk and the manufacturing method thereof in the present embodiment, it is possible to provide the magnetic disk and the manufacturing method thereof that can reduce the error occurrence rate of information.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1, 1A, 1B magnetic disk, 1G glass substrate, 2 thermally assisted magnetic recording device, 2A support shaft, 2B tracking actuator, 2C suspension, 2D magnetic recording head, 11 holes, 12 outer peripheral end surface, 13 inner peripheral end surface, 14 table Main surface, 15 Back main surface, 20 Magnetic recording layer, 21 Seed (roughness control) layer, 22 Underlayer, 23 Magnetic layer, 24 Protective layer, 25 Lubricating layer, 101A, 101B Surface enhancement layer.

Claims (8)

A method of manufacturing a magnetic recording medium used in a heat-assisted recording method,
Preparing a glass substrate having an annular disk shape;
Rough polishing the two main surfaces of the glass substrate;
Forming a surface enhancement layer on the two major surfaces of the coarsely polished glass substrate;
The surface on the side where the polishing amount is small is obtained by performing precision polishing treatment on the two surface reinforcing layers so that the polishing amount of the one surface reinforcing layer and the polishing amount of the other surface reinforcing layer are different. Curving the glass substrate concentrically so that the main surface side where the reinforcing layer is located is concave; and
The step of forming a magnetic recording layer on at least one main surface of the glass substrate while the glass substrate remains concentrically curved toward one main surface side,
A method for manufacturing a magnetic recording medium.   2. The method of manufacturing a magnetic recording medium according to claim 1, wherein the magnetic recording layer is formed on the main surface side where the surface enhancement layer on the side with a large polishing amount on which the glass substrate is convex is located.   The method of manufacturing a magnetic recording medium according to claim 1, wherein the magnetic recording layer is formed on each of the two main surfaces. A magnetic recording medium used in a heat-assisted recording method,
A glass substrate having an annular disk shape;
A magnetic recording layer having a circular planar shape provided on at least one of the two main surfaces of the glass substrate;
The glass substrate provided with the magnetic recording layer is a magnetic recording medium having a shape that is concentrically curved toward one main surface side.   The magnetic recording medium according to claim 4, wherein a distance between a center portion and an edge portion of the glass substrate in a thickness direction of the glass substrate is 0.1 μm to 3.0 μm.   The total value of the distance from the least square plane to the highest point and the distance from the least square plane to the lowest point in one circumference in the circumferential direction at a position of 25 mm from the center of the glass substrate is 1.0 μm or less. The magnetic recording medium according to claim 4 or 5.   The magnetic recording medium according to claim 4, wherein the magnetic recording layer is provided on the main surface side where the glass substrate is convex.   The magnetic recording medium according to claim 4, wherein the magnetic recording layer is provided on each of the two main surfaces.

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