Disc for information recording medium

Abstract

The information recording medium disk of the embodiment is a disk with a thickness of 0.51 mm or less. The disk includes a substrate and a recording layer. The substrate has one main surface, another main surface, and a sidewall connecting the two main surfaces. In the disk, the amount of thermal expansion is the radial thermal expansion of the disk when the temperature is increased by 5°C within a temperature range of -30°C to 70°C. The change in thermal expansion in the circumferential direction of the disk, calculated with a diameter of 95 mm, is less than 0.3 μm. The ratio of the change in thermal expansion of the disk within the temperature range of -30°C to 70°C to the rate of thermal expansion is 1.1 × 10⁻⁶. 4 Below μm·K.

Description

Technical Field

[0001] This invention relates to discs for information recording media. Background Technology

[0002] With the rise of cloud computing in recent years, a large number of hard disk drives (HDDs) have been used in cloud-oriented data centers to increase storage capacity. HDDs, as storage media, use a disk (hereinafter also called a disk) that is an information recording medium with a magnetic layer on a ring-shaped substrate. To increase the storage capacity of HDDs, in addition to reducing the thickness of the disk and increasing the number of disks mounted, it is preferable to increase the recording density of the magnetic layer of the disk.

[0003] To increase the recording density of the magnetic layer, shingled magnetic recording (SMR) is a known recording method for increasing recording density in the track width direction. In SMR, data is recorded by overlapping portions of previously recorded tracks in a shingled manner, thereby narrowing the track width and increasing the recording density. Additionally, energy-assisted magnetic recording (EAMR), represented by heat-assisted magnetic recording (HAMR) and microwave-assisted magnetic recording (MAMR), is known as a recording method that increases recording density by increasing the density of magnetic particles. In EAMR, the number of magnetic particles is reduced to decrease the bit size. During data recording, energy is applied to the magnetic particles to reduce coercivity, thereby assisting in magnetization reversal and increasing the recording density. Due to the small size of the magnetic particles, the track width is also narrowed in EAMR. Furthermore, SMR and EAMR can be used together.

[0004] Within an HDD, the ambient temperature around the disk changes due to its high-speed rotation (see Patent Document 1). If the ambient temperature rises, the disk thermally expands, causing the tracks to extend outwards. Therefore, during data writing and reading, the read / write head may be positioned radially off-center relative to the tracks, exceeding permissible limits, which can easily lead to errors. In Shingled Magnetic Recording (SMR) and Energy-Assisted Magnetic Recording (EAMR), the track width is narrow, and correspondingly, the permissible offset of the read / write head relative to the tracks (track deviation tolerance) is small, making write or read errors (R / W errors) more likely. Furthermore, from the viewpoint of increasing recording capacity, while improving the positioning accuracy based on servo information from the narrower tracks, it may be impossible to tolerate disk shape changes caused by temperature variations. Therefore, it is preferable to minimize the thermal expansion of the disk with temperature changes, and from the viewpoint of ensuring disk quality, a low rate of thermal expansion is required over a wide temperature range.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2008-4139 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] However, it is known that even when the thermal expansion rate of a disk is within a specified range, the magnitude of the thermal expansion rate varies depending on the circumferential position of the disk. If there is a deviation in the thermal expansion rate in the circumferential direction, the circular track shape will be distorted when the disk undergoes thermal expansion, potentially causing data to be written to other tracks or preventing continuous data reading from a single track. The greater the thermal expansion and the greater the distortion of the track shape, the more significant this phenomenon may occur at the outer periphery of the disk. In particular, in disks that record data using shingled magnetic recording (SMR) and / or energy-assisted magnetic recording (EAMR), the narrow track width means that even small distortions in track shape can increase the frequency of R / W errors due to this phenomenon. Furthermore, if the disk thickness is reduced to increase the number of disks, the resulting flutter is more likely, and it is foreseeable that even small distortions in track shape will further increase the frequency of R / W errors.

[0010] Therefore, the object of the present invention is to provide a thin information recording medium disk capable of suppressing the occurrence of errors in writing or reading information on the information recording medium disk.

[0011] Methods for solving problems

[0012] This disclosure includes the following methods.

[0013] Method 1

[0014] A disk for recording information, with a thickness of 0.51 mm or less, is characterized in that... The information recording medium disk includes a substrate and a recording layer. The substrate has one main surface and another main surface, and also has a sidewall surface connecting the two main surfaces. The thermal expansion is the radial thermal expansion of the disk when the temperature rises by 5°C within a temperature range of -30°C to 70°C. With the diameter of the disk set to 95 mm, the calculated change in thermal expansion in the circumferential direction of the disk is less than 0.3 μm. The ratio of the change in thermal expansion of the disk within the temperature range of -30℃ to 70℃ to the coefficient of thermal expansion is 1.1 × 10⁻⁶. 4 Below μm·K.

[0015] Method 2

[0016] A disk for recording information, with a thickness of 0.51 mm or less, is characterized in that... The information recording medium disk includes a substrate and a recording layer. The substrate has one main surface and another main surface, and also has a sidewall surface connecting the two main surfaces. The thermal expansion is the radial thermal expansion of the disk when the temperature rises by 5°C within a temperature range of -30°C to 70°C. With the diameter of the disk set to 95 mm, the calculated change in thermal expansion in the circumferential direction of the disk is less than 0.3 μm. The thermal expansion coefficient CTE of the disk used in the range of -30℃ to 70℃ is [×10]. -6 / K], the change in thermal expansion VTE [μm], and the Young's modulus E [GPa] and density d [g / cm] of the disk. 3 The ratio of E / d[×10] 6 m 2 / s 2 The value of CTE×(E / d) / CTE is 3.0×10⁻⁶. 5 [m 3 ·K / s 2 ]the following.

[0017] Method 3

[0018] According to claim 1, the information recording medium disk, wherein, The thermal expansion coefficient CTE of the disk used in the range of -30℃ to 70℃ is [×10]. -6 / K], the change in thermal expansion VTE [μm], and the Young's modulus E [GPa] and density d [g / cm] of the disk. 3 The ratio of E / d[×10] 6 m 2 / s 2 The VTE×(E / d) / CTE represented by [] is 2.6×10 5 [m 3 ·K / s 2 ]the following.

[0019] Method 4

[0020] The information recording medium disk according to method 1 or 2, wherein... The recording layer has a magnetic layer with a circumferential recording area formed on at least the main surface of the substrate. The track width in the recording area for reading the recorded information is less than 60 nm, and the change in thermal expansion is smaller than the track width.

[0021] Method 5

[0022] The information recording medium disk according to method 4, wherein... The information recording medium disk is used as a hard disk drive for reading and writing information on the magnetic layer via shingled magnetic recording.

[0023] Method 6

[0024] The information recording medium disk according to method 4, wherein... Information is recorded in the magnetic layer using energy-assisted magnetic recording.

[0025] Method 7

[0026] The information recording medium disk according to method 1 or 2, wherein... The change in thermal expansion is less than 0.040 μm. The substrate is made of glass, expressed as a molar percentage based on oxides, wherein the glass contains 55% to 80% SiO2, 5% to 25% Al2O3, and 0% to 8% B2O3; the glass contains at least one of MgO, CaO, SrO, and BaO, with a total content of 10% to 25%; and the glass contains at least one of Li2O, Na2O, and K2O, with a total content of 0.001% to 5.0%.

[0027] Method 8

[0028] The information recording medium disk according to method 1 or 2, wherein... The change in thermal expansion is less than 0.20 μm. The substrate has a substrate body made of aluminum alloy and a nickel alloy film disposed on the surface of the substrate body. The aluminum alloy contains at least one of Fe, Mn, and Ni, with a total content of 3.0% to 8.0% by mass, or the aluminum alloy contains more than 3.0% by mass of Si, and the remainder of the aluminum alloy consists of Al and unavoidable impurities.

[0029] Method 9

[0030] The information recording medium disk according to method 8, wherein... In the cross-section of the substrate body, the longest diameter of the particles containing metals other than Al precipitated in the substrate body is less than 5 μm.

[0031] Method 10

[0032] The information recording medium disk according to method 9, wherein... In the cross-section of the substrate body, the number density of particles with a longest diameter of 0.1 to 3 μm is 50 particles / mm. 2 above.

[0033] Method 11

[0034] The information recording medium disk according to method 8, wherein... The thickness of the membrane is less than 7.5 μm. Attached Figure Description

[0035] Figure 1 This is a diagram showing the external shape of an information recording medium disk according to one embodiment.

[0036] Figure 2 It is a diagram illustrating the key points of measuring the change in thermal expansion of a hard disk.

[0037] Figure 3 This is a schematic cross-sectional view illustrating the coarse particles precipitated on the substrate of the disk. Detailed Implementation

[0038] The following is a detailed description of the information recording medium disk used in the implementation method.

[0039] In the following description, a disk that records information on a magnetic film formed on the main surface of a substrate will be used as an example of an information recording medium.

[0040] Figure 1 The external shape of disk 1 according to the embodiment is shown. This embodiment includes the first embodiment and the second embodiment described below.

[0041] (First Implementation)

[0042] The thickness of disk 1 is 0.51 mm or less. By making the thickness of disk 1 0.51 mm or less, the number of HDDs that can be mounted on disk 1 can be increased, thereby increasing the storage capacity of the HDD. The thickness of disk 1 is preferably 0.50 mm or less, 0.48 mm or less, 0.46 mm or less, 0.45 mm or less, 0.43 mm or less, 0.42 mm or less, 0.40 mm or less, 0.38 mm or less, 0.35 mm or less, 0.32 mm or less, 0.30 mm or less, 0.28 mm or less, 0.25 mm or less, 0.22 mm or less, 0.20 mm or less, or 0.18 mm or less. There is no particular limitation on the lower limit of the thickness of disk 1, for example, it is 0.15 mm. In addition, the thickness of the magnetic film of disk 1 is extremely thin, about 100 nm or less, so the thickness of the magnetic film can be ignored in the thickness of disk 1.

[0043] The disk 1 includes a substrate 3 and a magnetic film (not shown). The substrate 3 is an annular plate with an inner hole 1a. The substrate 3 has a main surface 3a and another main surface 3b, and also has sidewalls 3c and 3d connecting the two main surfaces 3a and 3b. The main surfaces 3a and 3b are opposite each other and parallel to each other. The sidewall 3c is located at the outer peripheral end of the substrate 3, and the sidewall 3d is located at the inner peripheral end of the substrate 3.

[0044] Thermal expansion is the radial thermal expansion of disk 1 when the temperature rises by 5°C within a temperature range of -30°C to 70°C. The change in thermal expansion in the circumferential direction of disk 1, calculated with a diameter of 95mm (the magnitude of the deviation, hereinafter also referred to as the change in thermal expansion VTE), is less than 0.3μm. During operation, the temperature inside the HDD, due to the high-speed rotation of disk 1, falls within a temperature range of approximately 5°C (typically 55-60°C) within the range of -30°C to 70°C. By limiting the change in thermal expansion in the circumferential direction (VTE) in this temperature range to less than 0.3μm, during data reading or writing, the reader or writer mounted on the read / write head can be easily positioned within the allowable radial offset range (track deviation tolerance) relative to the target track of disk 1, thus easily suppressing R / W errors.

[0045] The track deviation tolerance is typically set to a range of no more than 10% of the track width radially to both sides of the target track. From the perspective of increasing recording capacity, there is a demand to improve the positioning accuracy of the read / write head based on servo information, leading to a trend of further reducing track width to utilize high positioning accuracy. If the head deviation exceeds the track deviation tolerance, an error will occur, potentially requiring repeated attempts to read or write data by the HDD controller (retry). If repeated retries fail to eliminate the error, the HDD's inherent function of correctly reading or writing information will be compromised, compromising its reliability. Therefore, the radial elongation of the disk due to thermal expansion within the operating temperature range of the HDD is preferably minimized. However, even if the radial elongation of the disk as a whole due to thermal expansion is small, if the elongation deviates circumferentially from the disk, indicating anisotropy in thermal expansion, the shape of the circular tracks will distort during thermal expansion, potentially resulting in the inability to continuously read data from one track or write data to other tracks. Regarding the distortion of track shape, for example, due to the different elongations of the disk in two mutually orthogonal directions within the main surface of the disk, the track shape may become elliptical. The thermal expansion of the disk, manifested as cumulative radial elongation, is greater at the outer periphery, resulting in greater track shape distortion. Therefore, the aforementioned phenomenon may occur significantly at the outer periphery of the disk. In particular, in disks where track widths narrow with increasing recording density, deviations from the permissible track width can be extremely narrow, reaching several nanometers. Therefore, even small track shape distortions can increase the frequency of R / W errors due to this phenomenon. Furthermore, if the disk thickness is reduced to increase the number of disks mounted, the result is increased flutter, and it is foreseeable that even small track shape distortions will further increase the frequency of R / W errors.

[0046] The change in thermal expansion, VTE, is calculated as the difference between the maximum and minimum values ​​of thermal expansion at multiple locations circumferentially around the center of disk 1. The thermal expansion is measured at three or more points equally spaced circumferentially. In the disk, thermal expansion occurs in the diametrical direction, and the amount of thermal expansion in the circumferential direction deviates due to differences in substrate material orientation and residual stress distribution. In this regard, the multiple circumferential locations for calculating the thermal expansion of disk 1 are three points (120° intervals) circumferentially spaced apart, preferably six points (60° intervals), and more preferably twelve points (30° intervals), and the values ​​of the coefficient of thermal expansion (average linear expansion coefficient) measured at these locations are used for calculation. Figure 2 A diagram illustrating the procedure for measuring the change in thermal expansion (VTE) of disk 1 is shown. Figure 2In the measurement procedure shown, the sample S is a portion located at three circumferential positions (sample S) that are 120 degrees apart from each other around the center O of disk 1.

[0047] As shown in the figure, the sample S is preferably cut into a long strip along the radial direction. The size of the sample S on disk 1 is not particularly limited; for example, it can be cut radially with a length of 10 mm to 12 mm and a width of 5 mm to 6 mm (length in the direction orthogonal to the radial direction). The average coefficient of linear expansion α is determined by measuring the sample S cut from various circumferential positions using a thermomechanical analysis apparatus within a temperature range of -30°C to 70°C.

[0048] The thermal expansion at each circumferential location of the measured object is the thermal expansion when the disk temperature rises by 5°C within a temperature range of -30°C to 70°C, for example, the expansion when the disk temperature changes from 55°C to 60°C. The calculation is performed using the average linear expansion coefficient α of each sample S measured at each circumferential location, with the diameter of disk 1 set to 95 mm. By calculating the thermal expansion of disk 1 with a diameter of 95 mm, the change in thermal expansion VTE can be compared between disks of different diameters, allowing for a comparison of the degree of anisotropy in thermal expansion. The reason for assuming a diameter of 95 mm for calculating the thermal expansion is that disks with a diameter of 95 mm or larger can have a larger magnetic layer area, thus being widely used to increase the storage capacity of HDDs. On the other hand, the thermal expansion of disk 1 at the outer periphery of disk with a diameter of 95mm or more increases, and the distortion of the track caused by the anisotropy of thermal expansion also increases. Therefore, from the viewpoint of suppressing the generation of errors in HDD during operation, it is effective to limit the change in thermal expansion VTE calculated by setting the diameter of disk 1 to 95mm.

[0049] The thermal expansion when the diameter of disk 1 is set to 95mm is calculated according to the following formula.

[0050] ΔL=α(T2-T1)L

[0051] (In the formula, ΔL represents the thermal expansion [mm], and α represents the average linear expansion coefficient (hereinafter also referred to as the linear expansion coefficient) [×10] -6 [K], T1 is 55℃, T2 is 60℃, L is 95mm.

[0052] The coefficient of linear expansion α is represented by the gradient of the thermal expansion of sample S relative to the temperature change of the linear expansion curve obtained in the temperature range of -30 to 70°C. The linear expansion curve is a curve showing the relationship between the temperature obtained when sample S is heated at a constant rate of 5°C or less per minute (e.g., 4°C per minute) and the elongation of sample S. Furthermore, when determining the coefficient of linear expansion, it is preferable not to subject sample S to prior heat treatment for the measurement. This is because if prior heat treatment is performed, the difference in the coefficient of linear expansion α obtained from the linear expansion curve between the circumferential positions of the object being measured becomes smaller, making it impossible to accurately evaluate the anisotropy of thermal expansion. The coefficient of linear expansion, except for the points described in this specification, conforms to Japanese Industrial Standard JIS Z2285:2003 or R3102:1995.

[0053] The change in thermal expansion VTE is preferably less than 0.2 μm.

[0054] The ratio of the change in thermal expansion VTE of disk 1 to the coefficient of thermal expansion CTE (hereinafter also referred to as VTE / CTE) in the temperature range of -30℃ to 70℃ is 1.1 × 10⁻⁶. 4 Below μm·K. According to the inventors' research, even if the change in thermal expansion (VTE) of disk 1 is small, if its magnitude is large relative to the coefficient of thermal expansion (CTE), the error suppression effect is not sufficient. For example, disks with a small CTE are suitable as disks with narrow track widths and high recording density, but high recording density disks require high positioning accuracy of the read / write head, so sometimes even if the change in thermal expansion (VTE) is small, the error suppression effect is not sufficient. According to the disk 1 of the first embodiment, by limiting the ratio VTE / CTE within the range of -30°C to 70°C, a sufficient error suppression effect can be obtained. Furthermore, in this specification, the coefficient of thermal expansion (CTE) is the average value of the average coefficient of linear expansion obtained by measuring multiple circumferential positions of disk 1 within a temperature range of -30°C to 70°C. The average coefficient of linear expansion within the temperature range of -30°C to 70°C is generally set as an indicator to ensure the quality of disk 1. As described above, the average coefficient of linear expansion is expressed as the ratio of the change in length of disk 1 to a specified temperature change, and refers to the average slope of the linear expansion curve within a specified temperature range.

[0055] Furthermore, the influence of the magnetic film on the change in thermal expansion VTE and the coefficient of thermal expansion CTE is negligible. Therefore, the change in thermal expansion VTE and the coefficient of thermal expansion CTE can be determined using a substrate 3 on which no magnetic film is formed.

[0056] The preferred ratio of VTE / CTE is 1.0 × 10⁻⁶. 4 Below μm·K, 0.8×10 4 Below μm·K.

[0057] There is no particular limit to the lower limit of VTE / CTE, for example, it can be 0.1 × 10⁻⁶. 4 μm·K.

[0058] The thermal expansion coefficient CTE of disk 1 in the range of -30℃ to 70℃ is preferably 0.5×10⁻⁶. -6 / K or higher and 25×10 -6 / K or less. The thermal expansion coefficient CTE of the disk 1 is within the above range, which can make the thermal expansion of the disk 1 converge within a specified range, and can predict in advance the expansion of the substrate within the ambient temperature of the HDD's use environment. Therefore, the width of the track when recording servo information can be designed so that the HDD's read / write head is positioned on the target track of the disk 1.

[0059] As described above, the disk 1 includes a magnetic film. The magnetic film on the main surface of the substrate 3 comprises, for example, an adhesion layer, a base layer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricating layer, stacked sequentially from the side closest to the main surface. The adhesion layer, base layer, and magnetic layer are formed sequentially on the main surface of the substrate 3 by, for example, introducing the substrate 3 into a vacuum-sealed film-forming apparatus and using DC (Direct Current) magnetron sputtering in an Ar atmosphere. For example, CrTi can be used as the adhesion layer, and for example, a material containing Ru or MgO can be used as the base layer. Furthermore, a soft magnetic layer and a heat dissipation layer may be appropriately added. After the magnetic layer is formed, for example, a protective layer can be formed using C2H4 via CVD (Chemical Vapor Deposition), followed by nitriding treatment to introduce nitrogen into the surface within the same chamber. Then, for example, PFPE (polyfluoropolyether) is coated onto the protective layer by dip coating, thereby forming a lubricating layer. In this way, the disk 1 can be manufactured. The magnetic film can be formed only on at least the main surface of the substrate 3, or it can be formed on the sidewalls.

[0060] To further improve the recording density of disk 1, the magnetic layer preferably comprises a magnetic material with high magnetic anisotropy energy. From this perspective, Fe-Pt based magnetic materials or Co-Pt based magnetic materials are preferred examples. "Based on" refers to materials containing the previously described elements. For information on magnetic recording layers containing such magnetic materials and methods for forming such layers, please refer to paragraph 0074 of WO2011 / 019010A1 and the embodiments described in that publication. Disk 1 having such a magnetic layer is suitable as a disk for mounting on an HDD that performs magnetic recording using energy-assisted magnetic recording (EAMR). In energy-assisted recording, the recording method assisted by near-field light or the like to reverse magnetization is called heat-assisted magnetic recording (HAMR), and the recording method assisted by microwaves is called microwave-assisted magnetic recording (MAMR). For details on these methods, please refer to paragraph 0075 of WO2011 / 019010A1. Furthermore, conventional CoPtCr based materials can also be used as the magnetic material for forming the magnetic layer.

[0061] The disk 1 according to the first embodiment described above can suppress the occurrence of errors in writing or reading information to the disk 1, and can ensure the reliability of the HDD.

[0062] (Second Implementation)

[0063] The disk 1 of the second embodiment is constructed in the same way as the disk 1 of the first embodiment, except that it replaces the disk in the disk 1 of the first embodiment where the VTE / CTE is in the range described above so that the VTE×(E / d) / CTE is in the specified range as described below.

[0064] In the disk 1 of the second embodiment, the thermal expansion coefficient CTE[×10] of the disk 1 in the range of -30°C to 70°C is used. -6 / K], the change in thermal expansion VTE [μm], and the Young's modulus E [GPa] and density d [g / cm] of disk 1. 3 The ratio of E / d[×10] 6 m 2 / s 2 The VTE×(E / d) / CTE represented by [] is 3.0×10 5 [m 3 ·K / s 2The following is a summary of the present invention. According to the inventors' research, sometimes even if the value of the change in thermal expansion VTE of disk 1 is small, if its magnitude is large relative to the specific elastic modulus E / (E / d), the error suppression effect is not sufficient. According to the disk 1 of the second embodiment, by limiting VTE×(E / d) / CTE within the range of -30°C to 70°C, a sufficient error suppression effect can be obtained. To increase the number of disks loaded into the hard disk drive housing, disk 1 preferably uses a Young's modulus E [GPa] and a specific elastic modulus E / d [×10⁻¹⁰]. 6 m 2 / s 2 The material is large. Therefore, it is possible to reduce the deformation of the disk 1 under external stress at a specified temperature. However, the larger the Young's modulus E [GPa], the greater the thermal stress generated in the disk 1 due to temperature changes. That is, when shape changes accompanying temperature changes are constrained or when there is a temperature distribution, thermal expansion is restricted, thereby generating internal energy not used for expansion as thermal stress (compressive stress or tensile stress). The disk 1 is stacked with multiple sheets constrained on the inner periphery of the disk by spacers while mounted within the hard disk drive housing. Furthermore, if the material orientation in the circumferential direction of the disk 1 and the distribution of internal stress are generated, a portion of the thermal expansion accompanying temperature changes is constrained, thereby generating thermal stress. Thermal stress is related to Young's modulus E [GPa] and the coefficient of thermal expansion CTE [×10]. -6 The values ​​are proportional to / K], therefore these values ​​are the main cause of the circumferential deviation in thermal expansion. Thus, if Young's modulus E [GPa] and specific elastic modulus E / d [×10] are used according to the thinning of disk 1, 6 m 2 / s 2 Larger materials result in greater thermal stress and exacerbate circumferential deviations in thermal expansion, thus increasing the frequency of errors. According to the inventors' research, by adjusting the range of (E / d) / CTE to achieve a balance with the change in thermal expansion VTE, a sufficient error suppression effect can be obtained. Furthermore, the magnitude of CTE / (E / d) is correlated with the ease with which flutter occurs during high-speed rotation of the disk 1. According to the second embodiment, it is believed that the effect of suppressing error generation by suppressing distortion of the track shape caused by the anisotropy of thermal expansion can be balanced with the effect of suppressing error generation by suppressing flutter.

[0065] The Young's modulus E of disk 1 can be measured based on the Japanese Industrial Standard JIS R1602-1995. The test piece used for measurement can be a cuboid cut from disk 1 with a length of 50 mm, a width of 10 mm, and a thickness equal to that of disk 1, and the measurement is performed at room temperature. Since the influence of the magnetic film on the Young's modulus E and density d of disk 1 is negligible, the Young's modulus E and density d of substrate 3 can be set as the Young's modulus E and density d of disk 1.

[0066] The upper limit of VTE×(E / d) / CTE is preferably 2.9×10 5 [m 3 ·K / s 2 ]、2.6×10 5 [m 3 ·K / s 2 ].

[0067] There is no particular limit to the lower limit of VTE×(E / d) / CTE, for example, it can be 0.5×10. 5 m 3 ·K / s 2 .

[0068] To improve shock resistance and further suppress flutter of disk 1 during high-speed rotation, the E / d of disk 1 is preferably 27 × 10⁻⁶. 6 m 2 / s 2 The above is preferred, with 27.5×10 being more desirable. 6 m 2 / s 2 Above, 30×10 6 m 2 / s 2 Above, 34×10 6 m 2 / s 2 Above, 35×10 6 m 2 / s 2 That's all. There are no specific restrictions on the lower limit of the E / d ratio; for example, it could be 26.5 × 10⁻⁶. 6 m 2 / s 2 Furthermore, there is no particular limit to the upper limit of E / d, for example, it can be 40 × 10⁻⁶. 6 m 2 / s 2 .

[0069] From the viewpoint of improving the ratio E / d, the Young's modulus E of disk 1 is preferably 74.0 GPa or higher, and more preferably 75.0 GPa or higher, 81.0 GPa or higher, 85.0 GPa or higher, 90.0 GPa or higher, or 96.0 GPa or higher.

[0070] On the other hand, sometimes, even if the Young's modulus E is high, if the density is high, the vibration will increase due to the weight of the disk 1 itself. Therefore, in the substrate body 3e (refer to...) Figure 3 In the case of an aluminum alloy disk, the density d of disk 1 is preferably 2.90 g / cm³. 3 Below and 2.65g / cm 3 The above is further optimized to 2.80 g / cm³. 3 Below and 2.71g / cm 3 In the case that the substrate 3 is made of glass, the density d of the disk 1 is preferably 2.65 g / cm³. 3 Below and 2.45g / cm 3 The above is further preferred to be 2.60 g / cm³. 3 Below and 2.50g / cm 3 above.

[0071] The disk 1 according to the second embodiment described above can suppress the occurrence of errors in writing or reading information to the disk 1, and can ensure the reliability of the HDD.

[0072] The disk 1 in the first and second embodiments preferably has additional structures as follows.

[0073] In the magnetic layer of disk 1, multiple recording areas (tracks) are formed concentrically in a circular pattern when servo information is written by a servo track writer. Disk 1 is suitable for a track width (radial length) where the width of the area holding the recorded information and used for data reading by the read / write head (hereinafter referred to as track width) is 60 nm or less, and further 50 nm or less. There is no particular limitation on the lower limit of the track width, but it is, for example, 5 nm, preferably 20 nm. The magnetic particles forming the magnetic layer are formed on the substrate with reduced particle size according to the recording method used, such as perpendicular magnetic recording (PMR) or energy-assisted magnetic recording (EAMR), thereby increasing the recording density of the magnetic layer. In particular, in energy-assisted magnetic recording (EAMR), the magnetic particles are reduced in order to reduce the bit size. When recording data, energy is added to the magnetic particles to reduce coercivity, thereby assisting in magnetization reversal and increasing the recording density. However, since the magnetic particles are small, the track width is also narrowed in energy-assisted magnetic recording (EAMR). From the viewpoint of further increasing the recording density of the magnetic layer, shingled magnetic recording (SMR) is preferred. In SMR, when recording data, the track spacing is narrowed by overlapping with a portion of the previously recorded track, thereby increasing the track density (TPI) and thus improving the recording density. In this invention, the track width in SMR refers to the track spacing, which is the radial length of the recording area that is not covered by adjacent tracks and is capable of reading data within the track width where data has been written. The track width in SMR is, for example, 55 nm or less, preferably 50 nm or less, more preferably 45 nm or less, and even more preferably 40 nm or less. Thus, when the track width is narrow, the allowable deviation of the read / write head from the track also becomes narrower. Therefore, as described above, when distortion of the shape of the disk tracks occurs due to the anisotropy of thermal expansion, even if the size of the distortion is small, the frequency of R / W errors increases. However, according to disk 1, in addition to limiting the change in thermal expansion VTE (preferably, the change in thermal expansion VTE is smaller than the track width), the ratio VTE / CTE or VTE×(E / d) / CTE is limited as described above, thus suppressing the generation of R / W errors. Therefore, disk 1 is suitable for HDDs that read and write information to the magnetic layer using shingled magnetic recording (SMR) or for recording information to the magnetic layer using energy-assisted magnetic recording (EAMR).

[0074] The substrate 3 of the disk 1 is preferably made of a material whose change in thermal expansion (VTE) is less than 0.3 μm and whose VTE / CTE ratio is 1.1 × 10⁻⁶. 4 Below μm·K, or VTE×(E / d) / CTE is 3.0×10 5 m 3·K / s 2 the following.

[0075] Preferred materials for substrate 3 include glass containing, in molar percentages based on oxides, 55%–80% SiO2, 5%–25% Al2O3, 0%–8% B2O3, and at least one of MgO, CaO, SrO, and BaO, totaling 10%–25%, and at least one of Li2O, Na2O, and K2O, totaling 0.001%–5.0%. Glass with this composition not only facilitates the fabrication of substrate 3 but also excels in improving the heat resistance and rigidity of disk 1.

[0076] In the disk 1 with substrate 3 made of the aforementioned glass, the change in thermal expansion (VTE) is 0.040 μm or less, preferably 0.040 μm or less, more preferably 0.030 μm or less, or 0.025 μm or less. Since the coefficient of thermal expansion (CTE) of the glass is low, in order to limit the ratio VTE / CTE or VTE×(E / d) / CTE to the aforementioned range, the change in thermal expansion (VTE) is preferably 0.040 μm or less. This improves the effect of suppressing R / W errors. The disk 1 with a change in thermal expansion (VTE) of 0.040 μm or less exhibits minimal distortion of the tracks due to thermal expansion during HDD operation, making it suitable as a disk with narrow track width and suitable for magnetic recording via shingled magnetic recording (SMR) or energy-assisted magnetic recording (EAMR).

[0077] Furthermore, glass sheets produced by methods such as the draw-out process or float glass process, which continuously form molten glass into long strips, sometimes exhibit anisotropic thermal expansion due to residual stress deviations caused by the different cooling rates between the drawing direction of the molten glass and its orthogonal width direction during forming. Therefore, the glass sheet used for substrate 3 is preferably a glass sheet whose residual stress generation is reduced by managing the cooling rate during the production of long strip glass sheets using methods such as the draw-out process or float glass process. More preferably, the produced glass sheet is a glass sheet whose change in thermal expansion has been adjusted to a specified range through annealing treatment.

[0078] From the viewpoint of ensuring heat resistance during heat treatment of the magnetic layer, the preferred glass transition temperature (Tg) of the glass used for the substrate 3 is 700°C or higher, more preferably 740°C or higher, and even more preferably 770°C or higher and 782°C or higher. The heat treatment temperature for obtaining the L10 structure of the magnetic layer most suitable for energy-assisted magnetic recording (EAMR) sometimes exceeds 600°C or even reaches 700°C or higher. By performing heat treatment at such high temperatures, the irregular structure of the magnetic layer is regularized.

[0079] According to one embodiment, the substrate 3 has a substrate body 3e made of aluminum alloy (see reference). Figure 3 ) and a nickel alloy film 3f disposed on the surface of the substrate body 3e (refer to Figure 3 ).

[0080] As a preferred material for the substrate body 3e, an aluminum alloy containing at least one of Fe, Mn, and Ni, with a combined content of 3.0% to 8.0% by mass, or containing more than 3.0% by mass of Si, with the remainder of the aluminum alloy consisting of Al and unavoidable impurities. Such an aluminum alloy composition is excellent in improving the rigidity of the disk 1.

[0081] In the disk 1 whose substrate body 3e is made of the aforementioned aluminum alloy, the change in thermal expansion is preferably 0.20 μm or less, more preferably 0.15 μm or less. The aluminum alloy has a relatively high coefficient of thermal expansion (CTE), therefore, in order to limit the ratio VTE / CTE or VTE×(E / d) / CTE within the aforementioned range, the change in thermal expansion VTE is preferably 0.20 μm or less. This improves the effect of suppressing R / W errors. The disk 1 with a change in thermal expansion VTE of 0.20 μm or less is suitable as a disk for magnetic recording using a perpendicular recording method (PMR) known as conventional magnetic recording (CMR) because the distortion of the tracks due to thermal expansion during HDD operation is small.

[0082] The nickel alloy film 3f is necessary to form a smooth surface on the surface of the aluminum alloy substrate body 3e for forming the magnetic layer, and helps to improve the rigidity of the disk 1 by assisting the rigidity of the substrate 3. On the other hand, if the thickness of the nickel alloy film is increased, internal strain is generated, which becomes the cause of deviation in the circumferential thermal expansion of the disk. Therefore, it is preferable that the thickness of the polished nickel alloy film 3f formed on the surface of the aluminum alloy substrate body 3e is 7.5 μm or less, more preferably 7.0 μm or less, 6.0 μm or less, and even more preferably 5.5 μm or less. There is no particular limitation on the lower limit of the thickness of the nickel alloy film 3f, for example, it is 0.05 μm, preferably 3.0 μm. Here, the thickness of the nickel alloy film 3f is the thickness on one main surface, and the value is measured at an inner position at least 10 mm away from the outer perimeter sidewall. Nickel-phosphorus (NiP) alloy is preferably used as the nickel alloy. In nickel-phosphorus (NiP) alloy films, to prevent magnetization caused by heating during disk manufacturing, it is preferable to use a NiWP-based coating containing tungsten (W) in the range of 10% to 30% by mass, or a NiPMo-based coating containing molybdenum (Mo) in the range of 0.1% to 10% by mass.

[0083] The aluminum alloys described above may also contain elements that are unavoidable impurities other than those mentioned above. Examples of such elements include Ti, B, and Ga, and their content, when each element is 0.10% by mass or less, and the total content is 0.30% by mass or less, will not impair the effectiveness of the present invention.

[0084] Other preferred materials for the substrate body 3e include aluminum alloys containing 0.5% to 8.0% by mass of Mg.

[0085] The aluminum alloy sheet that becomes the material of the substrate 3e is made by rolling an aluminum alloy ingot. The rolled part is wound into a coil and then stretched again when drawn out, and punched into a shape with a specified outer and inner diameter to produce a ring-shaped substrate. In the rolled part, the deviation of residual stress due to the difference between the elongation in the rolling direction and the transverse direction orthogonal to it may have anisotropy of thermal expansion. Therefore, for the substrate of the substrate 3 made of aluminum alloy sheet, it is preferable to use a substrate that has been treated as follows: after the substrate of the substrate 3 is stacked with spacers, it is subjected to heat treatment in a continuous heating furnace at 420°C for 30 minutes, thereby reducing the change in thermal expansion VTE.

[0086] Figure 3 A schematic cross-sectional view illustrating coarse particles 5 precipitated on the substrate 3 of the disk 1 is shown.

[0087] According to one embodiment, in the cross-section of the aluminum alloy substrate body 3e, the precipitated particles in the substrate body 3e are particles containing metals other than Al (e.g., particles composed of Al-Fe intermetallic compounds), and their size preferably has a longest diameter of 5 μm or less. The precipitated particles may also contain Al. Components other than Al contained in the aluminum alloy sometimes become coarse particles and precipitate during the rolling process. When coarse particles 5 with a longest diameter greater than 5 μm exist in the cross-section of the substrate body 3e, the dispersion of the intermetallic compounds within the substrate body 3e may be poor, and the number density of intermetallic compound particles with a longest diameter of 0.1 μm to 3 μm may be less than 50 particles / mm². 2 It is easy to have a population density of 50 per mm. 2 The surrounding area exhibits a radial difference in thermal expansion. The presence of these coarse particles 5 is considered one of the reasons for the anisotropy of thermal expansion. Therefore, from the viewpoint of reducing the change in thermal expansion VTE, it is preferable that coarse particles 5 are absent; that is, it is preferable that the longest diameter of the particles (precipitated particles) containing metals other than Al precipitated in the substrate body 3e is 5 μm or less, preferably 3 μm or less or 1 μm or less, and the number density of intermetallic compound particles with a longest diameter of 0.1 μm to 3 μm is preferably 50 particles / mm. 2The above is preferred to be 100 pieces / mm. 2 The above. The metals other than Al constituting the precipitated particles include at least one of the above-mentioned elements contained in the aluminum alloy, excluding Si: Fe, Mn, and Ni.

[0088] The determination of the longest diameter and the calculation of the number density of the precipitated particles are preferably performed using a radial cross-section at a location where the circumferential position of the disk 1, where the coefficient of thermal expansion (CTE) is measured, exhibits the highest CTE. Such a substrate cross-section is highly likely to contain coarse particles 5, and is therefore suitable for determining the presence or absence of coarse particles 5. The determination of the longest diameter and the calculation of the number density can be performed using an image of the substrate cross-section at the same circumferential position as the sample S. The longest diameter of the particles can be, for example, a reflectance electron image of a SEM photograph of a cross-section of the substrate 3, denoted as the maximum length of the particles in the image (…). Figure 3 (The double arrows in the image). The determination that the longest diameter of particles containing metals other than Al is 5 μm or less is preferably based on an area of ​​0.04 mm² in the cross-section of the substrate body 3e. 2 The area is taken as the object. The particle number density is calculated, for example, as the average of the number densities of each of the multiple (e.g., more than 3) regions selected from the above image of the cross-section of substrate 3.

[0089] In the disk 1 of the first embodiment, VTE×(E / d) / CTE is preferably 2.6×10⁻⁶. 5 [m 3 ·K / s 2 ]the following.

[0090] Disk 1 preferably meets the standard of a nominal diameter of 3.5 inches or 2.5 inches. For example, the outer diameter of disk 1 with a nominal diameter of 3.5 inches is 95 mm to 100 mm (e.g., 95 mm, 97 mm), and the diameter of the inner hole 1a is 24 mm to 26 mm (e.g., 25 mm). For example, the outer diameter of disk 1 with a nominal diameter of 2.5 inches is 65 mm to 70 mm (65 mm, 67 mm), and the diameter of the inner hole 1a is 19 mm to 21 mm (e.g., 20 mm).

[0091] Disk 1 is made as follows, for example.

[0092] When fabricating a disk 1 with a glass substrate 3, firstly, a circular substrate is formed by scribing or core extraction of the glass sheet, and chamfered surfaces are formed on the inner and outer peripheral end faces of the circular substrate. Next, the main surface of the substrate with the chamfered surfaces is ground. In the grinding process, a grinding component with fixed abrasive grains formed into a sheet shape or a slurry containing free abrasive grains is used to grind the main surface of the circular substrate. Next, the main surface of the substrate with the ground main surface is polished. In the polishing process, a slurry containing free abrasive grains with a particle size smaller than the free abrasive grains used in the grinding process and a polishing pad are used for polishing. The polishing process is preferably performed in multiple steps, using abrasive grains of different sizes or polishing pads of different hardness.

[0093] In the case of fabricating a disk 1 with a substrate body 3e made of aluminum alloy, firstly, a circular ring-shaped substrate is punched from an aluminum alloy sheet, annealed by heating at a specified temperature and time, and then the main surface is machined and the end faces are shaped to form the substrate body 3e. Annealing can be performed after the machining of the end faces and the main surface. In the end face shaping, the end faces are ground or machined into a specified shape using tools such as a forming lathe tool or a single-edged lathe tool.

[0094] Then, a nickel alloy coating is formed on the surface of the aluminum alloy substrate 3e with a thickness of, for example, 0.5 μm to 12 μm. Next, the main surface of the substrate 3 is ground. From the viewpoint of balancing improved surface quality and increased productivity, the grinding process is preferably performed in a multi-stage process, similar to the grinding of the glass substrate 3.

[0095] An attachment layer, a base layer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricating layer are sequentially stacked on the main surface of the substrate 3 as described above to form a magnetic film, thereby manufacturing the disk 1.

[0096] (Experimental Example)

[0097] To investigate the performance of disk 1, various substrates and disks of different specifications were manufactured.

[0098] (Substrate fabrication)

[0099] Following the above-described procedure, a circular substrate cut from an aluminum alloy sheet is annealed, and the main surface is machined and the end face is shaped to form the substrate body. A 9μm thick NiP film is formed by electroless plating to cover the entire surface. End face grinding, polishing, first grinding, and second grinding are then performed to produce a substrate with a specified NiP film thickness (Examples 1, 5, Comparative Examples 1-3). The substrate of Example 5 is further annealed in a furnace at 200°C for 30 minutes.

[0100] In addition, following the above-described principles, a substrate with a circular shape was made from a glass sheet, and end face grinding, polishing, first grinding, and second grinding were performed to produce a substrate (Examples 2-4, Comparative Examples 4 and 5). Among them, the substrate of Example 2 was further subjected to annealing in a furnace at 700°C for 4 hours.

[0101] The dimensions of the fabricated substrate are as follows.

[0102] • Outer diameter 97mm, inner diameter 25mm, plate thickness 0.44mm (Examples 1 and 4), wherein the thickness of the polished NiP film in Example 1 is 5.3μm.

[0103] • Outer diameter 97 mm, inner diameter 25 mm, plate thickness 0.5 mm (Examples 2, 3, 5, Comparative Examples 2-5), wherein the thickness of the NiP film after polishing in Example 5 and Comparative Examples 2 and 3 is 8.0 μm.

[0104] • Outer diameter 96 mm, inner diameter 25 mm, plate thickness 0.635 mm (Comparative Example 1), the thickness of the NiP film after polishing is 8.0 μm.

[0105] The composition of the materials used in the substrate body or substrate and the manufacturing method of the glass plate are described below.

[0106] • An aluminum alloy containing 0.1% by mass of Mg, 0.05% by mass of Si, 1.2% by mass of Fe, 1.2% by mass of Mn, 1.95% by mass of Ni, 0.2% by mass of Cr, 0.2% by mass of Ti, and 0.2% by mass of Zr (Example 1)

[0107] • Alkali-free glass produced by the down-drawing method (Example 2, Comparative Example 5)

[0108] To obtain glass with the specified composition, SiO2, Al2O3, Al(OH)3, B2O3, HBO3, MgO, Mg(OH)2, MgCO3, CaCO3, SrCO3, BaCO3, ZnO, Li2CO3, Na2CO3, K2CO3, TiO2, and ZrO2 were used as starting materials, weighed in quantities of 300g to 1500g, and thoroughly mixed to form a batch. This batch was placed in a platinum crucible and melted in air at a temperature of 1400℃ to 1600℃ for approximately 3 to 8 hours. After melting, the molten glass was poured into a carbon mold with a rectangular concave portion measuring 200mm (length) × 200mm (width) × 20mm (depth). After naturally cooling to the glass transition temperature, the mold was immediately placed in an annealing furnace and held for 1 hour. The resulting glass was then naturally cooled to room temperature within the furnace (Examples 3, 4, and Comparative Example 4).

[0109] • In Example 3, the glass contains, in molar percentage, more than 80% of SiO2, B2O3 and / or Al2O3, and 10% to 20% of RO (R is at least one selected from Mg, Ca, Zn, Sr and Ba), 0% to 1% of R'2O (R' is at least one selected from Li, Na and K), and the total content of the above components is 98% or more.

[0110] • In Example 4, the glass contains, in molar percentage, more than 70% of SiO2, B2O3 and / or Al2O3, and 15% to 25% of RO (R is at least one selected from Mg, Ca, Zn, Sr and Ba), 1% to 10% of R'2O (R' is at least one selected from Li, Na and K), and the total content of the above components is more than 98%.

[0111] • Comparative Example 4 is a glass that, in molar percentage, contains more than 70% of SiO2 and B2O3 and / or Al2O3 in total, and contains 1% to 10% of RO (R is at least one selected from Mg, Ca, Zn, Sr and Ba), 15% to 25% of R'2O (R' is at least one selected from Li, Na and K), and the total content of the above components is more than 98%.

[0112] • Aluminum alloys containing 3.0% to 40.0% by mass of Si (Example 5, Comparative Example 3)

[0113] • An aluminum alloy containing 1.60% by mass of Mg, 0.05% by mass of Si, 0.70% by mass of Fe, 0.30% by mass of Mn, 1.83% by mass of Ni, 0.15% by mass of Cr, 0.25% by mass of Cu, and 0.01% by mass of Zn (Comparative Example 1)

[0114] • An aluminum alloy containing 3.0% by mass or more of Mg and less than 0.1% by mass of Ni, Fe, Mn, and Si (Comparative Example 2)

[0115] The magnetic film has a negligible effect on the following properties; therefore, the substrate fabricated as described above was used to measure or calculate these properties as characteristics of the disk. The measurement results are shown in Tables 1 and 2.

[0116] (Coefficient of thermal expansion, CTE)

[0117] For the substrates of the embodiments and comparative examples, in accordance with the above-described principles, for the samples cut at three circumferential positions at 120-degree intervals, the linear expansion coefficient of each sample was determined using a thermomechanical analysis device based on the TMA method, based on the change in length within the temperature range of -30 to 70°C, and the average of the three linear expansion coefficients was taken as the thermal expansion coefficient CTE within the range of -30 to 70°C.

[0118] (Change in thermal expansion, VTE)

[0119] Using the coefficient of linear expansion obtained from measuring each sample within a temperature range of -30 to 70°C, the thermal expansion of the substrate at a length of 95 mm when the temperature changes to 55 to 60°C is calculated, and the difference between the maximum and minimum values ​​is taken as the change in thermal expansion, VTE.

[0120] (Compared to VTE / CTE)

[0121] Calculate VTE / CTE using the change in thermal expansion VTE and the coefficient of thermal expansion CTE.

[0122] (Compared to E / d)

[0123] The ratio E / d is calculated using the Young's modulus E and density d of the disk obtained according to the above method.

[0124] (VTE×(E / d) / CTE)

[0125] Calculate VTE×(E / d) / CTE using the change in thermal expansion VTE, E / d, and the coefficient of thermal expansion CTE.

[0126] Furthermore, in the embodiments and comparative examples, multiple substrates were fabricated, and disks were fabricated using substrates other than the substrates on which the above characteristics were measured and calculated, and the effect of suppressing error occurrence was investigated.

[0127] (Disk creation)

[0128] On the main surface of the substrates in the embodiments and comparative examples, a magnetic film (thickness 30 nm or less) containing a magnetic layer was formed according to the above-described procedure to fabricate a disk. In Examples 1, 5, and Comparative Examples 1 to 3, a magnetic layer containing the above-described CoPtCr-based material was formed. In Examples 2 to 4, and Comparative Examples 4 and 5, a magnetic layer containing the above-described Fe-Pt-based magnetic material was formed. In Examples 2 to 4, and Comparative Examples 4 and 5, in order to obtain a magnetic layer with an L10 structure, a heat treatment based on preheating of the substrate was performed at 630°C for 5 seconds.

[0129] (Confirmation test of error suppression effect)

[0130] The fabricated disk was assembled into an HDD with an internal temperature sensor, and the effect of suppressing errors was investigated.

[0131] When writing servo signals to the disk using a servo track writer, for Examples 1 and 5, and Comparative Examples 1 to 3, tracks for magnetic recording using conventional magnetic recording (CMR) were formed. The track width was 60 nm. For Examples 2 to 4, and Comparative Examples 4 and 5, tracks for magnetic recording using heat-assisted magnetic recording (HAMR) were formed. The track width was 50 nm.

[0132] The manufactured HDD was placed in a chamber equipped with a cooling device to maintain the temperature inside the chamber at 20–25°C, and data was written to the disk. The disks of Examples 1 and 5, and Comparative Examples 1–3 were magnetically recorded using conventional magnetic recording (CMR), while the disks of Examples 2–4, and Comparative Examples 4 and 5 were magnetically recorded using heat-assisted magnetic recording (HAMR).

[0133] The HDD with data written to it was removed from the chamber, and the data was read. The number of retries required to achieve a successful read was investigated. Cases with fewer than 2 retries were rated A, cases with 3 to 10 retries were rated B, and cases with more than 10 retries were rated C. The results are shown in Table 1. Furthermore, during the read operation, the temperature inside the HDDs of both the examples and comparative examples was within the range of 55 to 60°C.

[0134] [Table 1]

[0135] As can be seen from the comparison between the examples and the comparative examples, if the change in thermal expansion VTE is less than 0.3 μm, and further, the VTE / CTE ratio is 1.1 × 10⁻⁶, then the thermal expansion is significantly reduced. 4 Below μm·K, or VTE×(E / d) / CTE is 3.0×10 5 [m 3 ·K / s 2 The following results in fewer retries until a correct read is performed, demonstrating excellent error suppression.

[0136] For Example 1 and Comparative Example 1, the reflected electron image of the substrate along the radial thickness direction of the substrate was observed at the circumferential position where the average linear expansion coefficient α was highest among multiple circumferential positions where the linear expansion coefficient was measured. The result was that, in Example 1, for every 0.04 mm... 2 In Example 1, there were no coarse particles with a longest diameter exceeding 5 μm. In contrast, in Comparative Example 1, there were coarse particles with a longest diameter exceeding 5 μm. Furthermore, in Example 1, the intermetallic compound exhibited good dispersibility, with a particle number density of 50 particles / mm for intermetallic compound particles with a longest diameter of 0.1 μm to 3 μm. 2In contrast, in Comparative Example 1, the number density of intermetallic compound particles with a longest diameter of 0.1 μm to 3 μm was less than 50 particles / mm. 2 On the other hand, compared to Comparative Example 1, the change in thermal expansion (VTE) in Example 1 was smaller, but the coefficient of thermal expansion (CTE) in the range of -30 to 70°C was larger. Therefore, it is believed that the absence of coarse particles with a longest diameter exceeding 5 μm helps to reduce the values ​​of VTE / CTE and VTE×(E / d) / CTE. Furthermore, in Comparative Example 1, the NiP thickness was 8.0 μm, compared to 5.3 μm in Example 1. It is believed that the NiP film has a smaller effect on internal strain, which helps to reduce the change in thermal expansion (VTE) and the value of VTE / CTE.

[0137] The information recording medium disk of the present invention has been described in detail above. However, the present invention is not limited to the above embodiments and examples. Various improvements or modifications can be made without departing from the spirit of the present invention.

[0138] The information recording medium disk of the present invention is not limited to a magnetic disk. For example, it can also be a disk (high-voltage dielectric recording medium) that has a high-voltage dielectric layer (recording layer) on the main surface of the substrate and can repeatedly record information by changing the polarization of the high-voltage dielectric.

[0139] Label Explanation

[0140] 1: Information recording medium, disk; 1a: Inner hole; 3: Substrate; 3a, 3b: Main surfaces; 3c, 3d: Sidewall surface; 3e: Substrate body; 5: Coarse particles.

Claims

1. A disk for recording information, the thickness of which is 0.51 mm or less, characterized in that, The information recording medium disk includes a substrate and a recording layer. The substrate has one main surface and another main surface, and also has a sidewall surface connecting the two main surfaces. The thermal expansion is the radial thermal expansion of the disk when the temperature rises by 5°C within a temperature range of -30°C to 70°C. With the diameter of the disk set to 95 mm, the calculated change in thermal expansion in the circumferential direction of the disk is less than 0.3 μm. The ratio of the change in thermal expansion of the disk within the temperature range of -30℃ to 70℃ to the coefficient of thermal expansion is 1.1 × 10⁻⁶. 4 Below μm·K.

2. A disk for recording information, the thickness of which is 0.51 mm or less, characterized in that, The information recording medium disk includes a substrate and a recording layer. The substrate has one main surface and another main surface, and also has a sidewall surface connecting the two main surfaces. The thermal expansion is the radial thermal expansion of the disk when the temperature rises by 5°C within a temperature range of -30°C to 70°C. With the diameter of the disk set to 95 mm, the calculated change in thermal expansion in the circumferential direction of the disk is less than 0.3 μm. The thermal expansion coefficient CTE of the disk used in the range of -30℃ to 70℃ is [×10]. -6 / K], the change in thermal expansion VTE [μm], and the Young's modulus E [GPa] and density d [g / cm] of the disk. 3 The ratio of E / d[×10] 6 m 2 / s 2 The value of CTE×(E / d) / CTE is 3.0×10⁻⁶. 5 [m 3 ·K / s 2 ]the following.

3. The information recording medium disk according to claim 1, wherein, The thermal expansion coefficient CTE of the disk used in the range of -30℃ to 70℃ is [×10]. -6 / K], the change in thermal expansion VTE [μm], and the Young's modulus E [GPa] and density d [g / cm] of the disk. 3 The ratio of E / d[×10] 6 m 2 / s 2 The VTE×(E / d) / CTE represented by [] is 2.6×10 5 [m 3 ·K / s 2 ]the following.

4. The information recording medium disk according to claim 1 or 2, wherein, The recording layer has a magnetic layer with a circumferential recording area formed on at least the main surface of the substrate. The track width in the recording area for reading the recorded information is less than 60 nm, and the change in thermal expansion is smaller than the track width.

5. The information recording medium disk according to claim 4, wherein, The information recording medium disk is used as a hard disk drive for reading and writing information on the magnetic layer via shingled magnetic recording.

6. The information recording medium disk according to claim 4, wherein, Information is recorded in the magnetic layer using energy-assisted magnetic recording.

7. The information recording medium disk according to claim 1 or 2, wherein, The change in thermal expansion is less than 0.040 μm. The substrate is made of glass, expressed as a molar percentage based on oxides, wherein the glass contains 55% to 80% SiO2, 5% to 25% Al2O3, and 0% to 8% B2O3; the glass contains at least one of MgO, CaO, SrO, and BaO, with a total content of 10% to 25%; and the glass contains at least one of Li2O, Na2O, and K2O, with a total content of 0.001% to 5.0%.

8. The information recording medium disk according to claim 1 or 2, wherein, The change in thermal expansion is less than 0.20 μm. The substrate has a substrate body made of aluminum alloy and a nickel alloy film disposed on the surface of the substrate body. The aluminum alloy contains at least one of Fe, Mn, and Ni, with a total content of 3.0% to 8.0% by mass, or the aluminum alloy contains more than 3.0% by mass of Si, and the remainder of the aluminum alloy consists of Al and unavoidable impurities.

9. The information recording medium disk according to claim 8, wherein, In the cross-section of the substrate body, the longest diameter of the particles containing metals other than Al precipitated in the substrate body is less than 5 μm.

10. The information recording medium disk according to claim 9, wherein, In the cross-section of the substrate body, the number density of particles with a longest diameter of 0.1 to 3 μm is 50 particles / mm. 2 above.

11. The disk for information recording medium according to claim 8, wherein, The thickness of the membrane is less than 7.5 μm.

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