Substrate for magnetic recording medium, method for manufacturing substrate for magnetic recording medium, magnetic recording medium, and magnetic storage device

Abstract

A substrate for a magnetic recording medium according to the present disclosure has, on the surface of a steatite sintered body, a heat-resistant film composed of an alloy of at least one selected from the group consisting of SiO2, SiC, Si3N4, and Al2O3.

Description

Substrate for magnetic recording medium, method for manufacturing a substrate for magnetic recording medium, magnetic recording medium, and magnetic storage device.

[0001] This disclosure relates to a substrate for a magnetic recording medium, a method for manufacturing a substrate for a magnetic recording medium, a magnetic recording medium, and a magnetic storage device.

[0002] In recent years, magnetic recording media used in magnetic storage devices (hereinafter also referred to as "hard disk drives") have seen remarkable improvements in recording density. Furthermore, with the recent development of the internet network and the expansion of big data utilization, the amount of data stored in data centers continues to increase. Due to space limitations in data centers, there is a need to increase the storage capacity per hard disk drive.

[0003] To increase the storage capacity per standardized hard disk drive, attempts are being made to increase the storage capacity per magnetic recording medium, and to increase the number of magnetic recording media that can be placed inside the drive case.

[0004] As an attempt to increase the storage capacity per magnetic recording medium, the use of assisted recording media is attracting attention. When using assisted recording media, the surface of the assisted recording media is locally assisted by irradiating it with near-field light and microwaves, thereby reducing the coercivity of the assisted recording media and enabling writing.

[0005] In the assisted recording medium, the magnetic layer is L1 ０ FePt alloy or L1 having a type crystal structure ０ CoPt alloys with a specific crystal structure are used, but in order to form these magnetic layers, the substrate temperature needs to be raised to 400°C or higher.

[0006] Furthermore, increasing the number of magnetic recording media that can be housed inside the drive case requires thinning the circuit board, but this makes the magnetic recording media prone to fluttering. Fluttering is the rattling of the magnetic recording media that occurs when it is rotated at high speed, and if the fluttering becomes large, stable reading and writing in the hard disk drive becomes difficult.

[0007] Therefore, in order to suppress the fluttering of the magnetic recording medium, as a material for the substrate of the magnetic recording medium, for example, a material having a high specific elasticity, that is, a value obtained by dividing the Young's modulus of glass by the density of glass is disclosed to be used (see, for example, Patent Document 1).

[0008] Japanese Patent Application Laid-Open No. 2015-26414

[0009] Here, the demand for increasing the storage capacity of hard disk drives does not stop, and higher heat resistance and specific elastic modulus are required for the substrate of the magnetic recording medium than ever. In addition, in order to ensure substitutability with the conventionally used substrate for magnetic recording media, a manufacturing cost equivalent to that of the conventional substrate for magnetic recording media is required.

[0010] One aspect of the present disclosure has been made in view of such circumstances, and an object thereof is to provide a substrate for a magnetic recording medium having high heat resistance and specific elastic modulus and suppressed manufacturing cost.

[0011] In order to solve the above problems, the present disclosure provides the following configuration. [1] A substrate for a magnetic recording medium having a heat-resistant film made of any one or more alloys selected from the group consisting of SiO, SiC, SiN, and AlO on the surface of a steatite sintered body. [2] A method for manufacturing a substrate for a magnetic recording medium, in which a heat-resistant film is formed on the surface of a plate-shaped steatite sintered body using a liquid precursor. [3] The method for manufacturing a substrate for a magnetic recording medium according to [2], wherein the heat-resistant film contains any one or more alloys selected from the group consisting of SiO, SiC, SiN, and AlO. [4] The substrate for a magnetic recording medium according to [1], and a magnetic layer provided on the substrate for a magnetic recording medium, wherein the magnetic layer is an FePt alloy having an L1-type crystal structure or L1 ２ , SiC, Si ３ N ４ and Al ２ O ３ having a heat-resistant film made of any one or more alloys selected from the group consisting of. [2] A method for manufacturing a substrate for a magnetic recording medium, in which a heat-resistant film is formed on the surface of a plate-shaped steatite sintered body using a liquid precursor. [3] The method for manufacturing a substrate for a magnetic recording medium according to [2], wherein the heat-resistant film contains any one or more alloys selected from the group consisting of SiO, SiC, SiN, and AlO. [4] The substrate for a magnetic recording medium according to [1], and a magnetic layer provided on the substrate for a magnetic recording medium, wherein the magnetic layer is an FePt alloy having an L1-type crystal structure or L1 ２ , SiC, Si ３ N ４ and Al ２ O ３ having a heat-resistant film made of any one or more alloys selected from the group consisting of. [4] The substrate for a magnetic recording medium according to [1], and a magnetic layer provided on the substrate for a magnetic recording medium, wherein the magnetic layer is an FePt alloy having an L-type crystal structure or L ０ type crystal structure or L1 ０A magnetic recording medium comprising a CoPt alloy having a type crystal structure. [5] A magnetic storage device having the magnetic recording medium described in [4].

[0012] According to one aspect of this disclosure, a substrate for magnetic recording media can be provided that has high heat resistance and specific modulus, and has reduced manufacturing costs.

[0013] According to one aspect of this disclosure, a method for manufacturing a magnetic recording medium substrate that has high heat resistance and specific modulus of elasticity can be provided, which allows for the production of such substrates at a lower manufacturing cost.

[0014] According to one aspect of this disclosure, by using a magnetic recording medium substrate with high heat resistance and specific modulus, fluttering can be reduced, thereby providing a magnetic recording medium and magnetic storage device that can be read and written stably. Furthermore, according to one aspect of this disclosure, by using a magnetic recording medium substrate with reduced manufacturing costs, a magnetic recording medium and magnetic storage device with even lower manufacturing costs can be provided.

[0015] This is an exploded perspective view showing an example of a grinding machine used in the lapping process. This is an explanatory diagram showing an example of a method for carrying out the inner and outer circumference grinding process. This is an explanatory diagram showing an example of a method for carrying out the inner circumference polishing process. This is an explanatory diagram showing an example of a method for carrying out the outer circumference polishing process. This is an explanatory diagram showing an example of a method for carrying out the primary polishing process. This is a cross-sectional view showing an example of a magnetic recording medium manufactured using a substrate for a magnetic recording medium according to an embodiment of this disclosure. This is a perspective view showing an example of a magnetic storage device equipped with a magnetic recording medium according to an embodiment of this disclosure.

[0016] Hereinafter, a magnetic recording medium substrate according to an embodiment of the present disclosure (hereinafter sometimes simply referred to as "this embodiment") will be described in detail. For ease of understanding, the same reference numerals are used for the same components in each drawing, and redundant explanations are omitted. Also, the scale of each component in the drawings may differ from the actual scale. In this specification, the "~" indicating a numerical range means that the values ​​written before and after it are included as the lower and upper limits, unless otherwise specified. Furthermore, if only the unit is specified for the upper limit of a numerical range represented by "~", it means that the lower limit also has the same unit.

[0017] <Magnetic Recording Medium Substrate> The magnetic recording medium substrate according to this embodiment has a donut-shaped disc with an opening in the center. A magnetic recording medium can be manufactured by sequentially laminating a magnetic layer, a protective layer, a lubricating film, etc., on the magnetic recording medium substrate. In a hard disk drive using this magnetic recording medium, the center of the magnetic recording medium is attached to the rotation axis of a spindle motor and rotated, and information is written to or read from the magnetic recording medium while a magnetic head levitates and travels on the surface of the magnetic recording medium.

[0018] The substrate for the magnetic recording medium according to this embodiment is a steatite sintered body (MgO・SiO ２ ) and a heat-resistant film provided on the surface of the steatite sintered body.

[0019] Steatite sintered bodies are mainly made of talc (talc, Mg ３ Si ４ O １０ (OH) ２ It mainly consists of magnesium oxide (MgO) and silica (SiO2). ２ The ceramic material contains steatite. Steatite sintered bodies have properties such as electrical insulation, heat resistance, and mechanical strength, and are therefore widely used as electrical components or insulators. Therefore, by using steatite sintered bodies, thin sheets that can be processed into substrates for magnetic recording media can be easily obtained. Thus, the substrate for magnetic recording media according to this embodiment can be manufactured at a low cost by reducing manufacturing costs by including steatite sintered bodies.

[0020] Furthermore, the density (ρ) of the steatite sintered body is approximately 2.7 g / cm³. ３ The Young's modulus (E) is approximately 125 GPa, and the specific modulus (E / ρ) is approximately 46 GPa·cm. ３ The ρ of an aluminum alloy substrate, which has been conventionally used as a substrate for magnetic recording media, is approximately 2.8 g / cm³. ３ E is approximately 75 GPa, and E / ρ is approximately 27 GPa·cm. ３ The melting point is approximately 600°C. The ρ of the glass substrate is approximately 2.5 g / cm³. ３ E is approximately 80 GPa, and E / ρ is approximately 32 GPa·cm. ３The ratio of the material to the mass (E / ρ) is 1 / g, and the melting point (softening point) is approximately 780°C. Comparing the steatite sintered body with the magnetic recording medium substrate, the steatite sintered body is superior in both E / ρ and melting point. Therefore, by including the steatite sintered body, the magnetic recording medium substrate according to this embodiment can suppress fluttering when the magnetic recording medium is rotated at high speed using the magnetic recording medium substrate according to this embodiment. The specific modulus of elasticity (E / ρ) of the magnetic recording medium substrate is, as described above, the value obtained by dividing the Young's modulus (E) of the magnetic recording medium substrate by its density (ρ).

[0021] The heat-resistant film is provided on the surface of the steatite sintered body, and SiO ２ SiC, Si ３ N ４ and Al ２ O ３ It has one or more alloys selected from the group consisting of the following. That is, the heat-resistant film is SiO ２ SiC, Si ３ N ４ or Al ２ O ３ It may be composed of SiO ２ SiC, Si ３ N ４ and Al ２ O ３ It may be composed of two or more of these types. Since the steatite sintered body is made by sintering powder, fine voids tend to form inside the sintered body. If these voids appear on the surface of the steatite sintered body, the smoothness of the substrate for magnetic recording media may be impaired. In addition, the voids in the steatite sintered body may cause cracks to form, which may reduce the mechanical strength of the substrate for magnetic recording media.

[0022] The magnetic recording medium substrate according to this embodiment has a heat-resistant film on the surface of the steatite sintered body, which fills the voids on the surface of the steatite sintered body and improves the surface smoothness of the magnetic recording medium substrate. Furthermore, the magnetic recording medium substrate according to this embodiment can suppress the occurrence of cracks in the steatite sintered body, thereby increasing the mechanical strength of the magnetic recording medium substrate. In addition, the heat-resistant film is SiO ２ SiC, Si ３ N４ or Al ２ O ３ By including this component, the heat resistance can be enhanced, thus improving the heat resistance of the substrate for magnetic recording media.

[0023] Here, the heat resistance temperature is specifically required to be above the heating temperature of the substrate for the magnetic recording medium during the manufacturing process of the magnetic recording medium. ０ FePt alloy or L1 having a type crystal structure ０ When a CoPt alloy having a type crystal structure is used, the heat resistance temperature is 400°C or higher, preferably 500°C or higher. Depending on the atmosphere, SiO ２ The heat resistance temperature of is approximately 1000°C, while the heat resistance temperature of SiC is approximately 1500°C. ３ N ４ The heat resistance temperature is approximately 1000°C, Al ２ O ３ Its heat resistance temperature is approximately 1500°C.

[0024] The magnetic recording medium substrate according to this embodiment can increase the number of magnetic recording media that can be housed in a standardized hard disk drive case by processing the steatite sintered body to a predetermined size. Therefore, the magnetic recording medium substrate according to this embodiment can be formed to fit into a standardized hard disk drive case, such as a 2.5-inch hard disk drive case or a 3.5-inch hard disk drive case, by including a steatite sintered body processed to a predetermined size. For a 2.5-inch hard disk drive, the size of the magnetic recording medium substrate according to this embodiment may be a disc-shaped substrate with a maximum diameter of about 67 mm and an inner diameter of about 20 mm, while for a 3.5-inch hard disk drive, it may be a disc-shaped substrate with a maximum diameter of about 97 mm and an inner diameter of about 25 mm.

[0025] The thickness of the substrate for the magnetic recording medium according to this embodiment is 1.27 mm or less, preferably 0.8 mm or less, and more preferably 0.5 mm or less.

[0026] In this specification, the thickness of a magnetic recording medium substrate refers to the length perpendicular to the main surface of the magnetic recording medium substrate. The thickness of a magnetic recording medium substrate may be, for example, the thickness measured at any point in the cross-section of the magnetic recording medium substrate, or it may be the average of several measurements taken at any point. Hereafter, the definition of thickness will be the same for other components.

[0027] [Method for Manufacturing a Magnetic Recording Medium Substrate] A method for manufacturing a magnetic recording medium substrate will be described.

[0028] (Manufacturing of Steatite Sintered Bodies) First, the manufacturing method for steatite sintered bodies will be explained. The manufacturing method for steatite sintered bodies is not particularly limited and can be manufactured using general manufacturing methods.

[0029] The main raw material used in the manufacture of steatite sintered bodies is talc (Mg ３ Si ４ O １０ (OH) ２ ), kaolin (Al ２ Si ２ O ５ (OH) ４ ), feldspar (KAlSi ３ O ８ Powders such as ) and magnesium oxide (MgO) are used.

[0030] These raw materials are mixed in appropriate proportions and combined until nearly uniform. The raw materials can be mixed using a ball mill or kneader.

[0031] Subsequently, the mixed powder is formed into a plate. Forming methods include compression molding, extrusion molding, or casting. Compression molding involves placing the powder into a mold and compressing it under high pressure. Extrusion molding uses an extruder to push the mixed powder into the desired shape. Casting involves injecting a slurry-like mixture into a mold and drying it to form the product.

[0032] After being formed into a sheet shape, the molded product is dried to remove moisture. Drying is usually done using air drying or a drying oven.

[0033] Subsequently, the dried molded body is fired at a high temperature. The firing temperature is usually within the range of 1200 to 1400°C.

[0034] This firing process decomposes the talc, forming a steatite sintered body.

[0035] The sintered steatite body, after firing, is processed by machining or surface finishing to achieve the specified dimensions.

[0036] (HIP treatment) It is preferable to perform hot isostatic pressing (HIP) on the steatite sintered body that has been processed into a plate shape to a predetermined size. Applying HIP treatment to the steatite sintered body provides the following effects, and the steatite sintered body can be used more suitably as a substrate for magnetic recording media.

[0037] Increased density: Because HIP treatment is performed under high temperature and high pressure, minute voids and defects within the sintered body are compressed, increasing its density. This improves the mechanical strength and durability of the steatite sintered body.

[0038] Improvement of mechanical properties: HIP treatment improves the mechanical properties of steatite sintered bodies, such as toughness, hardness, compressive strength, and tensile strength.

[0039] Improved homogeneity: Defects or inhomogeneities within the steatite sintered body are corrected during processing, improving the overall homogeneity of the steatite sintered body. This results in consistently higher quality steatite sintered bodies.

[0040] Improved fatigue resistance: By reducing defects in steatite sintered bodies, the fatigue resistance of steatite sintered bodies is improved, allowing them to withstand long-term use.

[0041] Pore ​​closure: The HIP treatment closes the pores inside the steatite sintered body, improving airtightness and reducing degassing during sputter deposition.

[0042] Improved chemical stability: Because steatite sintered bodies are processed in a high-temperature, high-pressure environment, their chemical stability is improved, and their resistance to corrosion and oxidation is enhanced.

[0043] In order to obtain the above-mentioned effects, the HIP treatment of steatite sintered bodies is preferably performed with a treatment temperature in the range of 1200 to 1400°C, a treatment pressure in the range of 100 to 200 MPa, and a treatment time in the range of 1 to 4 hours.

[0044] (Formation of a heat-resistant film on the surface of a steatite sintered body) On the surface of a HIP-treated steatite sintered body, SiO ２ SiC, Si ３ N ４ and Al ２ O ３ A heat-resistant film is formed, consisting of one or more alloys selected from the group consisting of SiO. ２ SiC, Si ３ N ４ or Al ２ O ３ It may be formed with SiO ２ SiC, Si ３ N ４ and Al ２ O ３ It may be formed by including two or more of these types.

[0045] On the surface of the steatite sintered body, SiO ２ SiC, Si ３ N ４ and Al ２ O ３ As a method for forming a heat-resistant film made of one or more alloys selected from the group consisting of the above, a method of forming a heat-resistant film using a liquid precursor is used. Among general methods for forming thin films, the method of forming a heat-resistant film using a liquid precursor is simple and can be carried out at low cost.

[0046] As a method for forming a heat-resistant film using a liquid precursor, for example, spin coating, dip coating, spray coating, etc. can be mentioned. Note that spin coating is a method of dropping a liquid precursor onto a steatite sintered body and forming a uniform film using a spin coater. Dip coating is a method of forming a thin film by immersing a steatite sintered body in a liquid precursor and pulling it out. Spray coating is a method of spraying a liquid precursor onto a steatite sintered body using an airbrush or a spray nozzle, etc.

[0047] As the liquid precursor, when the heat-resistant film is a SiO ２ film, for example, tetraethoxysilane (TEOS, chemical formula: Si(OC ２ H ５ ) ４ ) or methylsilsesquioxane (MSQ, chemical formula: (CH ３ SiO ３／２ ) n), etc. can be mentioned. In any case, by firing the liquid precursor at 800 °C or lower after coating, a heat-resistant film made of SiO ２ can be formed on the surface of the steatite sintered body.

[0048] As the liquid precursor for forming a heat-resistant film made of SiC, for example, polysilazane-based precursors such as polymethylsilazane or silanols can be mentioned. In any of these cases, by coating the liquid precursor on the surface of the steatite sintered body and then firing it at 800 °C or higher, a heat-resistant film made of SiC can be formed on the surface of the steatite sintered body.

[0049] For the liquid precursor for forming a film of Si ３ N ４ for example, polysilazane-based precursors such as polydimethylsilazane and aminosilanes can be mentioned. In any of these cases, after coating the liquid precursor, by firing it at 800 °C or higher in an ammonia (NH ３ ) or nitrogen (N ２ ) atmosphere, a film of Si ３ N ４ can be formed on the surface of the steatite sintered body.

[0050] Al ２ O ３ As a liquid precursor for forming a heat-resistant film composed of, for example, aluminum alkoxide such as aluminum isopropoxide, or aluminum acetylacetonate and the like can be mentioned. In any of these cases, after coating the liquid precursor on the surface of the steatite sintered body and firing at 800 ° C or lower, on the surface of the heat-resistant film composed of the steatite sintered body, Al ２ O ３ A heat-resistant film composed of can be formed.

[0051] (Surface processing) After forming a heat-resistant film on the surface of the steatite sintered body, surface processing of the substrate for the magnetic recording medium is performed. Here, the substrate for the magnetic recording medium to be surface-processed is also referred to as a "workpiece".

[0052] ((Lapping process)) In the surface processing of the workpiece, the surface of the workpiece is smoothly ground (lapping process).

[0053] An example of the grinding machine used in the lapping process is shown in FIG. 1. As shown in FIG. 1, in the lapping process, the surface of the workpiece is smoothly ground (also referred to as "lapping") by the grinding machine 20. The grinding machine may be a grinding device or a lapping machine capable of grinding the surface of the workpiece.

[0054] An example of the grinding machine used in the lapping process is shown in FIG. 1. As shown in FIG. 1, the grinding machine 20 includes a holder (also referred to as a "carrier") 21 that holds a plurality of workpieces in an opening, a lower platen 22A on which the workpiece is placed, and an upper platen 22B for applying pressure required for pressing and grinding the workpiece from above.

[0055] Here, a tooth portion 221A is provided on the outer peripheral portion of the lower platen 22A, and a sun gear 222A is provided substantially at the center of the lower platen 22A.

[0056] The outer circumference of the holder 21 is provided with teeth 211. The teeth 211 mesh with both the teeth 221A of the lower platen 22A and the sun gear 222A. In addition, the lower platen 22A and the upper platen 22B have rotating shafts 223A and 223B installed approximately at the center of the lower platen 22A and the upper platen 22B, respectively, for rotating the lower platen 22A and the upper platen 22B.

[0057] The lower platen 22A and the lower platen 22A are embedded with abrasive material for grinding the surface of the workpiece. For grinding the workpiece, aluminum oxide (also called "alumina"), diamond, silicon carbide (also called "silicon carbide"), or cerium oxide can be used. The particle size and particle size distribution of the abrasive material can be appropriately selected according to the surface shape of the workpiece before or after grinding. In addition, during grinding, a coolant such as water may be supplied to the lower platen 22A and the lower platen 22A as appropriate.

[0058] For example, epoxy resin reinforced with aramid fibers or glass fibers can be used as the material for the holder 21.

[0059] The thickness of the holder 21 is preferably made thinner than the finished thickness of the workpiece during the lapping process, so as not to come into contact with the upper platen 22B and hinder grinding when grinding the surface of the workpiece during the lapping process.

[0060] When operating the grinding machine 20, the upper rotating shaft 223B in Figure 1 is rotated in one direction around its axis, and the upper platen 22B is rotated in the same direction. In addition, the rotating shaft 223A located at the bottom of Figure 1 is rotated around its axis in the opposite direction to the rotation of the rotating shaft 223B, and the lower platen 22A is rotated around its axis in the same direction as the rotating shaft 223A. As a result, the teeth 221A of the lower platen 22A and the central sun gear 222A also rotate in the same direction as the rotating shaft 223A.

[0061] In this way, by rotating the lower platen 22A and the upper platen 22B, the holder 21 that meshes with the teeth 221A of the lower platen 22A and the sun gear 222A performs a so-called planetary motion, which is a combination of rotation and revolution. Similarly, the workpiece fitted into the holder 21 also performs a planetary motion. This makes it possible to grind the workpiece with greater precision and speed.

[0062] ((Inner and outer circumference grinding process)) After grinding the surface of the workpiece to a smooth finish, the inner and outer surfaces of the openings in the workpiece are roughly ground (inner and outer circumference grinding process).

[0063] Figure 2 shows an example of how to perform the internal and external grinding process. As shown in Figure 2, in the internal and external grinding process, the inner and outer surfaces 13 of the opening 12 of the workpiece 10 are ground as an example of rough grinding. In this embodiment, the inner and outer surfaces 13 of the opening 12 are ground simultaneously. Specifically, the opening 12 provided in the center of the workpiece 10 is ground with the inner grinding wheel 31, and the outer surface 13 of the workpiece 10 is ground with the outer grinding wheel 32. At this time, the inner and outer surfaces 13 of the opening 12 of the workpiece 10 are sandwiched between the inner grinding wheel 31 and the outer grinding wheel 32 and processed simultaneously. This makes it easier to ensure the concentricity of the inner and outer diameters of the workpiece 10.

[0064] In this embodiment, the inner grinding wheel 31 and the outer grinding wheel 32 have a wavy surface. Therefore, in addition to grinding the inner and outer surfaces 13 of the opening 12 of the workpiece 10, chamfering of the edges of the opening 12 and the outer surface 13 can also be performed.

[0065] ((Inner Circumference Polishing Process)) After grinding the inner and outer surfaces of the workpiece opening, the inner surface of the workpiece opening is polished to a smooth finish (inner circumference polishing process).

[0066] An example of how to carry out the inner circumference polishing process is shown in Figure 3. As shown in Figure 3, in the inner circumference polishing process, the inner surface of the opening 12 of the workpiece 10 that was ground in the inner and outer circumference grinding process shown in Figure 2 is further polished to make it smoother.

[0067] Specifically, first, the workpieces 10 are stacked and set in a holder (not shown). Then, a brush 41 is inserted into the center of the opening 12 of the workpiece 10 set in the holder. Then, while pouring polishing fluid into the opening 12 of the workpiece 10, the brush 41 is rotated at high speed to polish the inner circumferential surface of the opening 12 of the workpiece 10. In this embodiment, since a brush 41 is used for polishing, the inner circumferential surface of the opening 12 of the workpiece 10 is polished, and the chamfered portion of the edge of the opening 12, which was performed in the inner and outer circumference grinding process described above, can also be polished in the same way.

[0068] The brush 41 is not particularly limited and can be any brush capable of polishing the inner circumferential surface of the opening 12 of the workpiece 10.

[0069] As an abrasive solution, for example, a slurry dispersion made by dispersing alumina abrasive particles in water can be used.

[0070] ((Outer surface polishing process)) After polishing the inner surface of the workpiece opening to make it smooth, the outer surface of the workpiece is polished to make it smooth (outer surface polishing process).

[0071] An example of how to carry out the outer perimeter polishing process is shown in Figure 4. As shown in Figure 4, in the outer perimeter polishing process, the outer perimeter surface 13 of the workpiece 10 that was ground in the inner and outer perimeter grinding process shown in Figure 3 is polished to make it even smoother.

[0072] Specifically, first, the workpiece 10 is stacked by passing the jig 51 through the opening 12 of the workpiece 10, and the workpiece 10 is set in the jig 51. Then, while pouring polishing liquid onto the outer circumferential surface 13 of the workpiece 10, the brush 52 is brought into contact with the workpiece 10 stacked on the jig 51 and rotated at high speed. This allows the outer circumferential surface 13 of the workpiece 10 to be polished. In this embodiment, since the brush 52 is used for polishing, the outer circumferential surface 13 of the workpiece 10 is polished, and the chamfered portion of the edge of the outer circumferential surface 13, which was performed in the inner and outer circumferential grinding process described above, can also be polished in the same way.

[0073] The brush 52 is not particularly limited and can be any brush capable of polishing the outer circumferential surface 13 of the workpiece 10.

[0074] As for the polishing solution, similar to the inner circumference polishing process, a slurry dispersion can be used, for example, a slurry obtained by dispersing alumina in water.

[0075] ((Primary Polishing Process)) After polishing the outer surface of the workpiece to a smooth finish, the surface of the workpiece is polished to a smooth finish (primary polishing process).

[0076] An example of how to perform the primary polishing process is shown in Figure 5. As shown in Figure 5, in the primary polishing process, the surface 11 of the workpiece 10 that was ground in the lapping process shown in Figure 1 is polished (also called "polishing") using a polishing machine 60 to further increase its smoothness. The polishing machine can be any polishing device or polishing machine capable of polishing the surface of the workpiece to a smooth finish.

[0077] The polishing machine 60 may have a configuration substantially the same as that of the grinding machine 20 shown in Figure 1. That is, the polishing machine 60 comprises a lower platen 61A on which the workpiece 10 is placed, and an upper platen 61B for applying the necessary pressure to press down on the workpiece 10 from above and perform polishing, and may have a holder for holding multiple workpieces in the opening. The lower platen 61A and the upper platen 61B have the same configuration as the lower platen 22A and the upper platen 22B of the grinding machine 20 shown in Figure 1, so the details are omitted.

[0078] The workpiece 10 is placed on the lower platen 61A of the polishing machine 60 using, for example, a holder 21 (see Figure 1), and the surface 11 of the workpiece 10 is polished by rotating the upper platen 22B and the lower platen 22A.

[0079] In the primary polishing process, the materials used for polishing the workpiece differ from those used in the lapping process described above. In the primary polishing process, the workpiece can be polished using, for example, a hard polishing cloth made of urethane, and a polishing solution in which abrasive material is dispersed in water to form a slurry.

[0080] As abrasive materials, for example, granular alumina, diamond, silicon carbide, or cerium oxide can be used.

[0081] The particle size and particle size distribution of the abrasive material can be appropriately selected according to the surface shape of the workpiece before or after polishing.

[0082] (Second polishing process) The surface of the workpiece 10, which was polished in the first polishing process shown in Figure 5, is subjected to precision polishing and further polishing to achieve the final surface finish (second polishing process).

[0083] In the secondary polishing process, the surface of the workpiece 10 can be precisely polished using the polishing machine 60 shown in Figure 5, which was used in the primary polishing process.

[0084] In the secondary polishing process, precision polishing can be performed using, for example, a suede-like soft polishing cloth and a polishing solution made by dispersing colloidal silica or the like in a dispersion medium such as water to form a slurry.

[0085] (Final Cleaning) After precision polishing the surface of the workpiece, any dirt such as abrasives used in the series of processes described above is removed (final cleaning).

[0086] This yields a substrate for magnetic recording media.

[0087] For cleaning, methods such as chemical cleaning using detergents (chemicals) combined with ultrasound can be used.

[0088] <Magnetic Recording Medium> The magnetic recording medium comprising a substrate for a magnetic recording medium according to this embodiment includes a magnetic layer, and the magnetic layer is L1 ０ FePt alloy or L1 having a type crystal structure ０ The material includes a CoPt alloy having a specific crystal structure. A magnetic recording medium equipped with a substrate for magnetic recording media according to this embodiment can be used, for example, as an assist recording medium.

[0089] Figure 6 is a cross-sectional view showing an example of a magnetic recording medium manufactured using a magnetic recording medium substrate according to this embodiment. As shown in Figure 6, as an example of a magnetic recording medium, the assist recording medium 100 is provided by sequentially laminating a base layer 102, a magnetic layer 103, a protective layer 104, and a liquid lubricant layer 105 on both main surfaces of a disc-shaped magnetic recording medium substrate 101 having a central hole, in this order from the magnetic recording medium substrate 101 toward the liquid lubricant layer 105. The magnetic recording medium substrate 101 consists of a steatite sintered body 101A and a surface of the steatite sintered body 101A different from the steatite sintered body 101A with SiO ２ SiC, Si ３ N ４ or Al ２ O ３ It has a heat-resistant film 101B made of the following material.

[0090] The assist recording medium 100 may also have a base layer 102, a magnetic layer 103, a protective layer 104, and a liquid lubricant layer 105 only on the upper or lower surface of the magnetic recording medium substrate 101.

[0091] (Method for Manufacturing Magnetic Recording Media) Magnetic recording media can be manufactured using a general method for manufacturing magnetic recording media. The method for manufacturing magnetic recording media will be explained using the case where the magnetic recording media is the assist recording media 100 shown in Figure 6 as an example. Note that the magnetic recording media substrate 101 used in the manufacture of the assist recording media 100 is the magnetic recording media substrate according to the embodiment described above, so the details of the manufacturing method of the magnetic recording media substrate 101 will be omitted.

[0092] In the method for manufacturing a magnetic recording medium, a soft magnetic layer is formed on the prepared magnetic recording medium substrate 101 (soft magnetic layer formation step).

[0093] For forming the soft magnetic layer, general film deposition methods such as sputtering (sputtering method) can be used.

[0094] In the sputtering method, a target containing the material that forms the soft magnetic layer can be used.

[0095] As a target containing the material for forming the soft magnetic layer, for example, soft magnetic alloys such as FeCo-based alloys, CoZrNb-based alloys, and CoTaZr-based alloys can be used.

[0096] Sputtering methods that can be used include DC sputtering, DC magnetron sputtering, and RF sputtering.

[0097] Next, a base layer 102 is formed on top of the soft magnetic layer (base layer formation step).

[0098] The process of forming the base layer 102 may include a process of forming a first base layer, a process of forming a second base layer, and a process of forming a third base layer.

[0099] In the process of forming the first sublayer, for example, a Cr alloy in which a bcc alloy mainly composed of Cr is (100) oriented can be used as the material for forming the first sublayer.

[0100] In the process of forming the second sublayer, as the material for forming the second sublayer, for example, a W alloy in which a bcc alloy mainly composed of W is (100) oriented can be used.

[0101] In the process of forming the third sublayer, a material such as an NaCl-type compound can be used to form the third sublayer. For example, MgO can be used as an NaCl-type compound.

[0102] Next, a magnetic layer 103 is formed on the base layer 102 (magnetic layer formation step).

[0103] A target containing the material for forming the magnetic layer 103 is, for example, L1 ０ A target containing an alloy with a structure can be used. L1 ０ As alloys having a structure, for example, alloys containing Fe or Co and Pt can be used, and specifically, FePt-based alloys or CoPt-based alloys can be used.

[0104] Next, the magnetic layer 103 is heated while it is laminated on the magnetic recording medium substrate 101, the soft magnetic layer, and the underlayer 102 to improve the crystal orientation of the magnetic layer 103 (heating step).

[0105] L1 ０ To establish a regular structure in an FePt alloy, heat treatment at a high temperature of 400°C or higher is necessary. Known methods can be used for heat treatment, such as heating using electromagnetic waves including halogen lamps, lasers, LEDs, high-frequency waves, or microwaves.

[0106] Since the magnetic recording medium substrate 101 according to this embodiment has high heat resistance, it can be suitably used in the manufacture of magnetic recording media, including a substrate heating process at high temperatures.

[0107] Next, a protective layer 104 is formed on the magnetic layer 103 (protective layer formation step).

[0108] As the material for forming the protective layer 104, a material commonly used as a protective layer for magnetic recording media may be used.

[0109] The method for forming the protective layer 104 is not particularly limited, but general deposition methods such as the RF-CVD (Radio Frequency-Chemical Vapor Deposition) method, which decomposes a hydrocarbon source gas with a high-frequency plasma to form the film, the IBD (Ion Beam Deposition) method, which ionizes the source gas with electrons emitted from a filament to form the film, and the FCVA (Filtered Cathodic Vacuum Arc) method, which forms the film using a solid carbon target without using a source gas, can be used.

[0110] Furthermore, a liquid lubricant layer 105 is formed on the surface of the protective layer 104 using a general coating method (liquid lubricant layer formation step).

[0111] As the material for forming the liquid lubricant layer 105, a liquid lubricant commonly used as a liquid lubricant layer in magnetic recording media may be used.

[0112] As a result, the assist recording medium 100 can be manufactured.

[0113] In a magnetic storage device equipped with a manufactured assist recording medium, the center of the assist recording medium is attached to the rotation axis of a spindle motor, and a magnetic head levitates and travels over the surface of the assist recording medium, which is rotated by the spindle motor, while writing or reading information from the assist recording medium.

[0114] The assist recording medium 100 uses a magnetic recording medium substrate 101, which has high heat resistance and specific modulus of elasticity, thereby reducing fluttering when used in a magnetic storage device. Therefore, the assist recording medium 100 can perform stable reading and writing.

[0115] Furthermore, since the assist recording medium 100 has an inexpensive magnetic recording medium substrate 101 that reduces manufacturing costs, it can be manufactured at a reduced cost.

[0116] <Magnetic Storage Device> An example of a magnetic storage device equipped with a magnetic recording medium according to this embodiment is shown in Figure 7. As shown in Figure 7, the magnetic storage device 200 comprises a magnetic recording medium 201, a medium drive unit 202 that drives the magnetic recording medium 201 in the recording direction, a magnetic head 203 consisting of a recording unit and a playback unit, a head movement unit 204 that moves the magnetic head 203 relative to the magnetic recording medium 201, and a recording / playback signal processing unit 205 that processes recording / playback signals from the magnetic head 203. The magnetic recording medium 201 is an assist recording medium 100 shown in Figure 7 as an example of a magnetic recording medium according to this embodiment.

[0117] Generally, in magnetic storage devices, the magnetic recording medium is rotated at high speeds of 5000 rpm or more. If the mechanical properties of the magnetic recording medium are poor, fluttering increases, making stable reading difficult in magnetic storage devices.

[0118] The magnetic recording medium 201 is composed of an assist recording medium 100, which includes a magnetic recording medium substrate 101. Since the magnetic recording medium substrate 101 has high heat resistance and specific modulus, it can reduce fluttering in the magnetic recording medium 201 in the magnetic storage device 200. Therefore, the magnetic storage device 200 can perform stable reading and writing of the magnetic recording medium 201.

[0119] Furthermore, the magnetic recording medium 201 is composed of an assist recording medium 100, and the assist recording medium 100 includes a substrate 101 for the magnetic recording medium. Since the substrate 101 for the magnetic recording medium can be manufactured at a low cost by reducing manufacturing costs, the magnetic recording medium 201 can be manufactured at an even lower cost. Therefore, the magnetic storage device 200 can be manufactured at an even lower cost by using the magnetic recording medium 201.

[0120] The effects of this embodiment will be described in more detail below with reference to examples, but this embodiment is not limited to the following examples.

[0121] <Manufacturing of substrates for magnetic recording media> A sintered steatite plate manufactured by Nishimura Ceramics Co., Ltd. was processed into a donut-shaped disc (workpiece) with a thickness of 1 mm, an outer diameter of 97 mm, an inner diameter of 25 mm, and an opening approximately in the center.

[0122] Next, the processed workpieces were subjected to HIP treatment. The HIP treatment was carried out in an air atmosphere at a temperature of 1300°C, a pressure of 150 MPa, and a holding time of 2 hours, after which the workpieces were slowly cooled.

[0123] Subsequently, silica (SiO₂) is applied to the surface of the workpiece using a spin-on-glass (SOG) process with tetraethoxysilane (TEOS). ２ A film of TEOS was formed. Specifically, after washing the workpiece with acetone and drying it, a 10% TEOS solution diluted with ethanol was dropped onto the center of the workpiece, and TEOS was spin-coated onto both sides of the workpiece using a spin coater at a rotation speed of 2000 rpm and a rotation time of 30 seconds. After drying the workpiece, it was fired. The firing was performed in air at a temperature of 700°C, a heating rate of 5°C / min, and a firing time of 30 minutes. After firing, the workpiece was slowly cooled.

[0124] Next, the workpieces were subjected to grinding. Specifically, using the grinding apparatus shown in Figure 1, multiple workpieces held in the opening of the carrier plate were moved in a planetary motion, and both main surfaces of the multiple workpieces were ground for 5 minutes using grinding pads provided on the upper and lower grinding plates.

[0125] A diamond grinding wheel (product name: Trizact, manufactured by Sumitomo 3M) was used as the grinding pad. The outer dimensions of the protrusions on the diamond grinding wheel were 2.6 mm square, the height was 2 mm, the spacing between adjacent protrusions was 1 mm, and the average particle size of the diamond abrasive grains was 6 μm. The diamond abrasive grain content in the protrusions was approximately 15% by volume. An acrylic resin was used as a binder.

[0126] Furthermore, a 4-way double-sided grinding machine (Model 16B, manufactured by Hamai Sangyo Co., Ltd.) was used for the grinding process, with a platen rotation speed of 30 rpm and a processing pressure of 110 g / cm². ２ The grinding fluid used when performing grinding with the grinding machine was water, and the amount of material removed from each side of the workpiece was approximately 100 μm.

[0127] In the lapping process, which smooths the surface of the workpiece, a lapping machine equipped with an inner and outer grinding wheel was used. A laminate was prepared by stacking multiple workpieces with spacers in between, aligning their central holes, and the inner grinding wheel was inserted into the central hole of the workpiece in the prepared laminate. While rotating the laminate of workpieces with the inner grinding wheel inserted into the central hole around its axis, the workpiece was clamped radially between the inner grinding wheel inserted into the central hole and the outer grinding wheel positioned on the outer circumference. While rotating the inner and outer grinding wheels in the opposite direction to the laminate, the inner end face of the workpiece was ground with the inner grinding wheel, and the outer end face of the workpiece was ground with the outer grinding wheel. At this time, the inner and outer grinding wheels used contained 80 volume% diamond abrasive grains with an average particle size of 10 μm, and a nickel alloy was used as a binder. Then, grinding was performed for 30 seconds with the rotation speed of the inner grinding wheel set to 1200 rpm and the rotation speed of the outer grinding wheel set to 600 rpm.

[0128] Next, in the inner circumference polishing process, a polishing machine equipped with an inner circumference polishing brush was used. While dripping polishing fluid onto the inner circumference polishing brush, the laminate was rotated around its axis, and the inner circumference polishing brush inserted into the central hole of the workpiece was moved up and down while rotating in the opposite direction to the workpiece, thereby polishing the inner circumference end surface of the workpiece. At this time, a nylon brush was used for the inner circumference polishing brush, and an alumina slurry was used as the polishing fluid. Polishing was then performed for 10 minutes at a rotation speed of 300 rpm for the inner circumference polishing brush.

[0129] Next, in the polishing process, a two-stage, four-way double-sided polishing machine (Model 11B, manufactured by System Seiko Co., Ltd.) equipped with a pair of upper and lower base plates was used to polish the surface of the workpiece.

[0130] In this process, a suede-type polishing pad (manufactured by Fillel) was used. For the first polishing stage, an aqueous solution was used containing alumina abrasive grains with a D50 of 0.5 μm, along with a chelating agent and an oxidizing agent, adjusted to an acidic pH of 1.5. For the second polishing stage, an aqueous solution was used containing colloidal silica abrasive grains with a D50 of 30 nm, along with a chelating agent and an oxidizing agent, adjusted to an acidic pH of 1.5. The polishing time for each stage was set to 5 minutes.

[0131] The processing pressure between the lower and upper whetstones is 110 g / cm². ２ The rotation speed of the lower and upper grinding wheels was set to 20 rpm, with a polishing amount of approximately 1.5 μm in the first stage of grinding and approximately 0.5 μm in the second stage of grinding.

[0132] Based on the above, a substrate for magnetic recording media was manufactured.

[0133] The heat resistance of the manufactured magnetic recording medium substrate was evaluated based on its melting point, which is 1300°C. Furthermore, the specific modulus of elasticity (E / ρ) of the magnetic recording medium substrate is 46 GPa·cm. ３ The value is / g. The specific modulus of elasticity (E / ρ) of the magnetic recording medium substrate is the value obtained by dividing the Young's modulus (E) of the magnetic recording medium substrate by its density (ρ). Table 1 shows the heat resistance and specific modulus of elasticity of the magnetic recording medium substrate.

[0134] <Manufacturing of Assist Recording Media> [Example 1] Next, an assist recording media was manufactured as a magnetic recording media using the manufactured magnetic recording media substrate. First, a 50 nm thick Co-50at%Ti {Ti content 50 at%, remainder Co} film was formed on the manufactured magnetic recording media substrate, and then heated to 200°C to form a first underlayer. Next, a 5 nm thick NiO film was formed on the first underlayer, and then heated to 520°C to form a second underlayer. Next, a 12 nm thick (Fe-45at%Pt-5at%Ag)-8mol%SiO film was formed on the second underlayer as a magnetic layer. ２ -4 mol% Cr ２ O ３ {SiO ２ Content of 8 mol%, Cr ２ O ３ After forming a film containing 4 mol% of [a specific material], with the remainder being an alloy of 45 at% Pt, 5 at% Ag, and the remainder Fe, a DLC film with a thickness of 3 nm was formed as a protective layer. Subsequently, a 12 Å thick perfluoropolyether was applied to the surface of the DLC film as a liquid lubricant layer using a dip method to manufacture an assisted recording medium.

[0135] [Comparative Examples 1 and 2] Assist recording media were manufactured in the same manner as in Example 1, except that glass or an aluminum alloy was used as the material for the magnetic recording medium substrate. Table 1 shows the heat resistance and specific modulus of the magnetic recording medium substrates made using glass or an aluminum alloy in each comparative example.

[0136] <Evaluation of Assist Recording Media> The assist recording media of each example and comparative example were rotated at 10,000 rpm, and the fluttering occurring on the outermost surface of the assist recording media was measured using a He-Ne laser displacement meter. The measurement results are shown in Table 1.

[0137]

[0138] Table 1 shows that the assist recording medium of Example 1 exhibited reduced fluttering compared to the assist recording mediums of each comparative example. Therefore, it can be said that by using a magnetic recording medium substrate with improved heat resistance and specific modulus, the assist recording medium can reduce fluttering and thus enable stable reading and writing.

[0139] Furthermore, since the assisted recording medium of Example 1 can reduce fluttering, it can be effectively used as a medium for an assisted recording hard disk drive. Therefore, by providing the assisted recording medium with a magnetic recording medium substrate that has high heat resistance and specific modulus, it is possible to manufacture an assisted recording hard disk drive that can perform stable reading and writing.

[0140] As described above, embodiments of this disclosure have been explained, but these embodiments are presented as examples only and do not limit this disclosure. The embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, or modifications are possible without departing from the spirit of the invention. The embodiments and their variations are included in the scope or spirit of the invention and are included in the scope of the invention and its equivalents as described in the claims.

[0141] This application claims priority based on Japanese Patent Application No. 2024-227857, filed with the Japan Patent Office on December 24, 2024, and incorporates all the contents of the said application.

[0142] 10 Workpiece 12 Opening 13 Outer surface 20 Grinding machine 21 Holder 22A, 61A Lower platen 22B, 61B Upper platen 31 Inner grinding wheel 32 Outer grinding wheel 41, 52 Brush 51 Jig 60 Polishing machine 100 Assist recording medium 101 Substrate for magnetic recording medium 101A Steatite sintered body 101B Heat-resistant film 102 Underlayer 103 Magnetic layer 104 Protective layer 105 Liquid lubricant layer 200 Magnetic storage device (hard disk drive) 221A Teeth 222A Sun gear 223A, 223B Rotating shaft

Claims

1. On the surface of the steatite sintered body, SiO ２ SiC, Si ３ N ４ and Al ２ O ３ A substrate for a magnetic recording medium having a heat-resistant film made of one or more alloys selected from the group consisting of the following.

2. A method for manufacturing a substrate for a magnetic recording medium, comprising forming a heat-resistant film on the surface of a steatite sintered body processed into a plate shape using a liquid precursor.

3. The heat-resistant film is SiO ２ , SiC, Si ３ N ４ and Al ２ O ３ The method for manufacturing a substrate for a magnetic recording medium according to claim 2, comprising any one or more alloys selected from the group consisting of.

4. A magnetic recording medium substrate according to claim 1, and a magnetic layer provided on the magnetic recording medium substrate, wherein the magnetic layer is L1 ０ FePt alloy or L1 having a type crystal structure ０ A magnetic recording medium containing a CoPt alloy having a type crystal structure.

5. A magnetic storage device having the magnetic recording medium described in claim 4.

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