Information recording medium disk

Abstract

An information recording medium disk according to an embodiment of the present invention is a disk having a plate thickness of 0.51 mm or less. The disk comprises a substrate and a recording layer, and the substrate has one main surface and another main surface and has a side wall surface connecting both main surfaces. In the disk, the amount of change in the thermal expansion amount in the radial direction of the disk when the temperature is increased 5°C in the temperature range of -30°C to 70°C is 0.3 μm or less in the circumferential direction of the disk, the thermal expansion amount being calculated on the basis of the diameter of the disk being 95 mm, and the ratio of the amount of change in the thermal expansion amount to the coefficient of thermal expansion of the disk in the temperature range of -30°C to 70°C is 1.1 × 104 μm·K or less.

Description

Information recording medium disc

[0001] The present invention relates to an information recording medium disc.

[0002] With the recent rise of cloud computing, many hard disk drives (HDDs) are being used in cloud data centers to increase storage capacity. HDDs use information recording medium disks (hereinafter also referred to as magnetic disks) with a magnetic layer on a circular substrate as the storage medium. In order to increase the storage capacity of HDDs, it is preferable to make the magnetic disks thinner and increase the number of magnetic disks installed, as well as to increase the recording density of the magnetic layers of the magnetic disks.

[0003] Shingled magnetic recording (SMR) is a known recording method for increasing the recording density in the track width direction to increase the recording density of the magnetic layer. In SMR, when recording data, each new track is recorded overlapping a portion of the previously recorded track, like a tile roof, thereby narrowing the track width and increasing the recording density. Another recording method that increases the recording density by increasing the density of magnetic particles is energy-assisted magnetic recording (EAMR), represented by thermally assisted magnetic recording (HAMR) and microwave-assisted magnetic recording (MAMR). In EAMR, magnetic particles are made smaller to reduce the bit size, and when recording data, energy is applied to the magnetic particles to reduce their coercivity, thereby assisting magnetization reversal and increasing the recording density. Because the magnetic particles are small, the track width is also narrow in EAMR. It is possible to use both SMR and EAMR.

[0004] In HDDs, the environmental temperature around the magnetic disk changes due to the high-speed rotation of the magnetic disk (see Patent Document 1). As the environmental temperature rises, the magnetic disk thermally expands, causing the tracks to expand toward the outer periphery. This leads to errors when writing or reading data, as the magnetic head is radially misaligned beyond the allowable range relative to the track. In single-mode magnetic recording (SMR) and energy-assisted magnetic recording (EAMR), the track width is narrow, and the allowable amount of misalignment of the magnetic head relative to the track (off-track tolerance) is small, making write or read errors (read / write errors) more likely to occur. On the other hand, even if the positioning accuracy of the magnetic head based on servo information relative to the narrower tracks is increased in order to increase recording capacity, temperature-related changes in the shape of the magnetic disk may become unacceptable. Therefore, it is preferable for the thermal expansion of the magnetic disk with temperature changes to be as small as possible. To ensure the quality of the magnetic disk, a low thermal expansion coefficient over a wide temperature range is required.

[0005] Japanese Patent Application Laid-Open No. 2008-4139

[0006] However, it has been found that even when the thermal expansion coefficient of a magnetic disk is within a predetermined range, the magnitude of the thermal expansion coefficient may vary depending on the circumferential position on the magnetic disk. Variations in the thermal expansion coefficient along the circumferential direction can cause the circular tracks to become distorted when the magnetic disk thermally expands, resulting in data being written to other tracks or the inability to read data continuously from one track. The amount of thermal expansion of a magnetic disk is greater toward the outer periphery, resulting in greater distortion of the track shape, and this phenomenon is likely to occur more prominently at the outer periphery of the magnetic disk. In particular, magnetic disks that record data using shingled magnetic recording (SMR) and / or energy-assisted magnetic recording (EAMR) have narrow track widths, so even slight distortion of the track shape can increase the frequency of R / W errors due to this phenomenon. Furthermore, if disk thickness is reduced to increase the number of disks mounted, making fluttering more likely to occur, it is expected that even slight distortion of the track shape will further increase the frequency of R / W errors.

[0007] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a thin information recording medium disc that can suppress the occurrence of errors when writing or reading information to or from the information recording medium disc.

[0008] The present disclosure includes the following aspects: Aspect 1: A disk for an information recording medium having a thickness of 0.51 mm or less, comprising a substrate and a recording layer, each having one main surface and the other main surface, and a sidewall surface connecting the two main surfaces, wherein the amount of thermal expansion of the disk in the radial direction when the temperature is increased by 5°C in a temperature range of -30°C to 70°C, the amount of change in the amount of thermal expansion calculated assuming a diameter of the disk is 95 mm, is 0.3 μm or less in the circumferential direction of the disk, and the ratio of the amount of change in the amount of thermal expansion to the coefficient of thermal expansion of the disk in the temperature range of -30°C to 70°C is 1.1 x 10 4 1. A disk for information recording medium, characterized in that the surface roughness is 1 μm·K or less.

[0009] Aspect 2: A disk for information recording media having a thickness of 0.51 mm or less, comprising a substrate and a recording layer having one main surface and the other main surface and further having a sidewall surface connecting both main surfaces, wherein the amount of thermal expansion of the disk in the radial direction when the temperature is increased by 5°C in a temperature range of -30°C to 70°C, the amount of change in the amount of thermal expansion calculated assuming a diameter of the disk is 95 mm, over the circumferential direction of the disk is 0.3 μm or less, and the coefficient of thermal expansion CTE [×10 -6 / K], the change in the thermal expansion amount VTE [μm], and the Young's modulus E [GPa] and density d [g / cm 3 ] to the ratio E / d [×10 6 m 2 / s 2 ], VTE × (E / d) / CTE is 3.0 × 10 5 [m 3 ・K / s 2 ] or less.

[0010] Aspect 3: The thermal expansion coefficient CTE of the disk at −30° C. to 70° C. [×10 -6 / K], the change in the thermal expansion amount VTE [μm], and the Young's modulus E [GPa] and density d [g / cm 3 ] to the ratio E / d [×10 6 m 2 / s 2 ], VTE × (E / d) / CTE is 2.6 × 10 5 [m 3 ・K / s 2 2. The information recording medium disk according to claim 1, wherein the recording layer has a magnetic layer on at least a main surface of the substrate, the magnetic layer having a circumferential recording area formed thereon, the recording area having a track width for reading recorded information of 60 nm or less, and the change in the amount of thermal expansion is smaller than the track width.

[0011] Aspect 5: The disk for an information recording medium according to aspect 4, which is used in a hard disk drive in which information is read from and written to the magnetic layer by shingled magnetic recording.

[0012] Aspect 6: The disk for an information recording medium according to aspect 4, wherein information is recorded on the magnetic layer by an energy-assisted magnetic recording method.

[0013] Aspect 7 The disk for an information recording medium according to Aspect 1 or 2, wherein the change in thermal expansion is 0.040 μm or less, and the substrate is made of glass containing, in mole percentages based on oxides, 55 to 80% SiO2, 5 to 25% Al2O3, and 0 to 8% B2O3, and at least one of MgO, CaO, SrO, and BaO, the total content of which is 10 to 25%, and at least one of Li2O, Na2O, and KO, the total content of which is 0.001 to 5.0%.

[0014] Aspect 8 The disk for an information recording medium according to Aspect 1 or 2, wherein the change in the amount of thermal expansion is 0.20 μm or less, and the substrate has: a substrate body made of an aluminum alloy; and a nickel alloy film provided on the surface of the substrate body, and the aluminum alloy contains at least one of Fe, Mn, and Ni, the total content of which is 3.0 to 8.0 mass %, or contains Si in excess of 3.0 mass %, with the remainder consisting of Al and unavoidable impurities.

[0015] Aspect 9: The disk for an information recording medium according to Aspect 8, wherein, in a cross section of the substrate body, the longest diameter of particles containing a metal other than Al precipitated in the substrate body is 5 μm or less. Aspect 10: In a cross section of the substrate body, the number density of particles having a longest diameter of 0.1 to 3 μm among the particles is 50 particles / mm 2 Aspect 11: The information recording medium disc according to aspect 8, wherein the thickness of the film is 7.5 μm or less.

[0016] The present invention relates to a method for measuring the amount of change in the amount of thermal expansion of a magnetic disk, and a method for measuring the amount of change in the amount of thermal expansion of a magnetic disk.

[0017] The information recording medium disc according to the embodiment will be described in detail below.

[0018] In the following description, a magnetic disk for recording information on a magnetic film formed on the main surface of a substrate will be used as an example of an information recording medium disk. Figure 1 shows the external shape of a magnetic disk 1 according to an embodiment. This embodiment encompasses the first and second embodiments described below.

[0019] (First embodiment) The thickness of the magnetic disk 1 is 0.51 mm or less. By making the thickness of the magnetic disk 1 0.51 mm or less, the number of magnetic disks 1 that can be mounted in a HDD can be increased, thereby increasing the storage capacity of the HDD. The thickness of the magnetic 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. The lower limit of the thickness of the magnetic disk 1 is not particularly limited, but is, for example, 0.15 mm. The thickness of the magnetic film of the magnetic disk 1 is extremely thin, about 100 nm or less, so the thickness of the magnetic film can be ignored in the thickness of the magnetic disk 1 .

[0020] The magnetic disk 1 includes a substrate 3 and a magnetic film (not shown). The substrate 3 is a circular plate having an inner hole 1a. The substrate 3 has one main surface 3a and the other main surface 3b, and further has sidewall surfaces 3c and 3d connecting the two main surfaces 3a and 3b. The main surfaces 3a and 3b are a pair of surfaces parallel to each other. The sidewall surface 3c is located at the outer circumferential edge of the substrate 3, and the sidewall surface 3d is located at the inner circumferential edge of the substrate 3.

[0021] The amount of thermal expansion of the magnetic disk 1 in the radial direction when the temperature is increased by 5°C within a temperature range of -30°C to 70°C, calculated assuming a diameter of the magnetic disk 1 of 95 mm, is measured. The amount of change (the magnitude of variation; hereinafter, also referred to as the amount of change in thermal expansion VTE) in the circumferential direction of the magnetic disk 1 is 0.3 μm or less. The temperature inside an operating HDD is in a temperature range of about 5°C (typically 55 to 60°C) within the temperature range of -30°C to 70°C due to the high speed rotation of the magnetic disk 1. By limiting the amount of change in thermal expansion VTE in the circumferential direction within this temperature range to 0.3 μm or less, when reading or writing data, the reader or writer mounted on the magnetic head is more likely to be positioned within the allowable range of radial deviation (off-track allowance) relative to the target track on the magnetic disk 1, making it easier to suppress the occurrence of R / W errors.

[0022] The off-track tolerance is typically set within a range of 10% of the track width on both sides of the target track in the radial direction. To increase recording capacity, there is a demand for higher accuracy in positioning the magnetic head using servo information, and the track width tends to become even smaller by utilizing high positioning accuracy. If the magnetic head deviation exceeds the off-track tolerance, an error occurs, and the HDD controller may repeatedly perform a process (retry) to retry reading or writing. If the error is not resolved even after repeated retries, the HDD's original function of correctly reading or writing recorded information is impaired, and the reliability of the HDD cannot be ensured. Therefore, it is preferable that the radial expansion of the magnetic disk due to thermal expansion within the temperature range of an operating HDD be as small as possible. However, even if the radial expansion of the magnetic disk as a whole is small, if the expansion varies circumferentially around the magnetic disk and anisotropy of thermal expansion exists, the circular track shape may be distorted when the magnetic disk thermally expands, resulting in a phenomenon in which data cannot be read continuously from one track or data is written to another track. Such distortion of the track shape may occur, for example, due to the difference in the amount of expansion of the magnetic disk between two perpendicular directions within the main surface of the magnetic disk, resulting in the track shape becoming elliptical. The amount of thermal expansion of the magnetic disk is greater at the outer periphery of the magnetic disk, where the radial expansion is cumulative, and the distortion of the track shape is also greater, so the above-mentioned phenomenon may occur more prominently at the outer periphery of the magnetic disk. In particular, in magnetic disks where the track width has narrowed as recording density has increased, the off-track tolerance is extremely narrow, reaching the range of a few nanometers, so even a slight distortion in the shape of the track causes this phenomenon to occur, increasing the frequency of R / W errors.Furthermore, if the thickness of the disk is reduced in order to increase the number of disks mounted, making fluttering more likely to occur, it is expected that the frequency of R / W errors will increase even further, even if the distortion in the shape of the track is slight.

[0023] The change in thermal expansion (VTE) is calculated as the difference between the maximum and minimum values ​​of the thermal expansion at multiple positions around the center of the magnetic disk 1 in the circumferential direction. The thermal expansion is measured at three or more positions equally spaced around the circumferential direction. Thermal expansion occurs in the radial direction of the magnetic disk, and variations in the thermal expansion occur in the circumferential direction due to differences (distribution) in the material orientation and residual stress of the substrate. In this regard, the multiple positions around the circumferential direction of the magnetic disk 1 for determining the thermal expansion are three positions (120° intervals), preferably six positions (60° intervals), and more preferably twelve positions (30° intervals) equally spaced from one another in the circumferential direction, and the thermal expansion coefficient (average linear expansion coefficient) measured at these positions is used for calculation. Figure 2 illustrates a method for measuring the change in thermal expansion (VTE) of the magnetic disk 1. In the measurement method shown in Figure 2, the measurement targets are portions (samples S) located at three circumferential positions spaced 120° apart from one another around the center O of the magnetic disk 1.

[0024] As shown in the figure, the sample S is preferably cut into a strip shape along the radial direction. The dimensions of the sample S on the magnetic disk 1 are not particularly limited, but for example, the sample S is cut out to a length of 10 to 12 mm in the radial direction and a width of 5 to 6 mm (length in the direction perpendicular to the radial direction). The sample S cut out from each position in the circumferential direction is measured using a thermomechanical analyzer in a temperature range of -30°C to 70°C to determine the average linear expansion coefficient α.

[0025] The amount of thermal expansion at each circumferential position to be measured is the amount of thermal expansion when the temperature of the magnetic disk rises by 5°C in a temperature range of -30°C to 70°C, for example, the amount of expansion when the temperature of the magnetic disk is changed from 55°C to 60°C, and is calculated using the average linear expansion coefficient α of each sample S measured at each circumferential position, assuming a diameter of the magnetic disk 1 of 95 mm. By calculating the amount of thermal expansion of the magnetic disk 1 assuming a diameter of 95 mm, it is possible to compare the amount of change in thermal expansion VTE between magnetic disks of different diameters and compare the degree of anisotropy of thermal expansion. The reason for calculating the amount of thermal expansion assuming a diameter of the magnetic disk 1 of 95 mm is that magnetic disks with a diameter of 95 mm or more are widely used because they can provide a magnetic layer over a wide area and increase the storage capacity of HDDs. On the other hand, for magnetic disks with a diameter of 95 mm or more, the amount of thermal expansion of the magnetic disk 1 is large at the outer periphery, and the distortion of the tracks due to the anisotropy of thermal expansion is also large. Therefore, limiting the change in the amount of thermal expansion VTE calculated assuming that the diameter of the magnetic disk 1 is 95 mm is effective from the perspective of suppressing the occurrence of errors within the HDD during operation.

[0026] Specifically, the amount of thermal expansion when the diameter of the magnetic disk 1 is set to 95 mm is calculated according to the following formula: ΔL=α(T2-T1)L (where ΔL is the amount of thermal expansion [mm], α is the average linear expansion coefficient (hereinafter simply referred to as the linear expansion coefficient) [×10 -6 / K], where T1 is 55°C, T2 is 60°C, and L is 95 mm. The linear expansion coefficient α is expressed as the gradient of the thermal expansion of sample S relative to the temperature change from -30 to 70°C on the linear expansion curve obtained by measurement in the temperature range of -30 to 70°C. The linear expansion curve is a curve showing the relationship between temperature and elongation of sample S when sample S is heated at a constant rate of 5°C per minute or less (e.g., 4°C per minute). It is preferable not to perform a pre-heat treatment on sample S when measuring the linear expansion coefficient. This is because performing a pre-heat treatment on sample S reduces the difference in the linear expansion coefficient α obtained from the linear expansion curve between the circumferential positions being measured, making it impossible to accurately evaluate the anisotropy of thermal expansion. Except for the points described herein, the linear expansion coefficient is determined in accordance with Japanese Industrial Standards JIS Z2285:2003 or R3102:1995.

[0027] The change in thermal expansion VTE is preferably 0.2 μm or less.

[0028] The ratio of the change in thermal expansion VTE to the thermal expansion coefficient CTE of the magnetic disk 1 in the temperature range of −30° C. to 70° C. (hereinafter also referred to as the ratio VTE / CTE) is 1.1×10 4μm·K or less. According to the inventor's research, even if the value of the change in thermal expansion (VTE) of the magnetic disk 1 is small, if its magnitude is large relative to the coefficient of thermal expansion (CTE), the error suppression effect may be insufficient. For example, a magnetic disk with a small coefficient of thermal expansion (CTE) is suitable for a magnetic disk with a narrow track width and high recording density. However, since a magnetic disk with a high recording density requires high positioning accuracy of the magnetic head, the error suppression effect may be insufficient even if the change in thermal expansion (VTE) is small. According to the magnetic disk 1 of the first embodiment, a sufficient error suppression effect can be achieved by limiting the ratio VTE / CTE from −30°C to 70°C to the above range. Note that, in this specification, the coefficient of thermal expansion (CTE) is the average value of the average linear expansion coefficients obtained by measuring multiple circumferential positions on the magnetic disk 1 in a temperature range of −30°C to 70°C. The average linear expansion coefficient in the temperature range of −30°C to 70°C is generally considered an index for guaranteeing the quality of the magnetic disk 1. As described above, the average coefficient of linear expansion is expressed as the ratio of the change in length of the magnetic disk 1 to a predetermined change in temperature, and means the average slope of the linear expansion curve within a predetermined temperature range.

[0029] Since the influence of the magnetic film on the change in thermal expansion VTE and the coefficient of thermal expansion CTE is negligible, the change in thermal expansion VTE and the coefficient of thermal expansion CTE can be determined using a substrate 3 on whose surface no magnetic film is formed.

[0030] The ratio VTE / CTE is preferably 1.0×10 4 μm・K or less, 0.8×10 4 μm·K or less.

[0031] The lower limit of the ratio VTE / CTE is not particularly limited, but is, for example, 0.1 × 10 4 μm·K.

[0032] The coefficient of thermal expansion (CTE) of the magnetic disk 1 at temperatures between −30° C. and 70° C. is preferably 0.5×10 -6 / K or more, 25×10 -6 / K or less. A magnetic disk 1 having a coefficient of thermal expansion CTE within the above range can keep the amount of thermal expansion of the magnetic disk 1 within a predetermined range, and also makes it possible to predict the amount of expansion of the substrate within the operating temperature range of the HDD, making it possible to design the width of the track when recording servo information so that the magnetic head of the HDD is positioned at the target track on the magnetic disk 1.

[0033] As described above, the magnetic disk 1 includes a magnetic film. The magnetic film includes at least an adhesive layer, an underlayer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricating layer, which are stacked on the main surface of the substrate 3 in this order, starting from the surface. The adhesive layer, underlayer, and magnetic layer are sequentially deposited on the main surface of the substrate 3 by DC (Direct Current) magnetron sputtering in an Ar atmosphere, for example, by placing the substrate 3 in a vacuum-evacuated film-forming apparatus. The adhesive layer may be made of, for example, CrTi, and the underlayer may be made of a material containing, for example, Ru or MgO. A soft magnetic layer and a heat sink layer may also be added as appropriate. After the magnetic layer is formed, a protective layer is formed using, for example, C2H4 by CVD (Chemical Vapor Deposition), followed by a nitriding process in the same chamber to introduce nitrogen into the surface. A lubricating layer can then be formed by applying, for example, PFPE (polyfluoropolyether) to the protective layer by dip coating. In this manner, the magnetic disk 1 can be fabricated. The magnetic film needs to be formed on at least the main surface of the substrate 3, and may also be formed on the sidewall surface.

[0034] To further increase the recording density of the magnetic disk 1, the magnetic layer preferably contains a magnetic material with high magnetic anisotropy energy. From this perspective, preferred magnetic materials include Fe—Pt-based magnetic materials and Co—Pt-based magnetic materials. The term "based" refers to the inclusion of the elements previously described. For a magnetic recording layer containing such a magnetic material and a method for forming the same, see paragraph 0074 of WO 2011 / 019010 A1 and the examples therein. A magnetic disk 1 having such a magnetic layer is suitable as a magnetic disk to be mounted in a HDD that performs magnetic recording using energy-assisted magnetic recording (EAMR). Among energy-assisted recording methods, a recording method that assisted magnetization reversal by irradiation with near-field light or the like is called thermally-assisted magnetic recording (HAMR), and a recording method that assisted magnetization reversal by microwaves is called microwave-assisted magnetic recording (MAMR). For details on these, see paragraph 0075 of WO 2011 / 019010 A1. As the magnetic material for forming the magnetic layer, a conventional CoPtCr-based material may be used.

[0035] According to the magnetic disk 1 of the first embodiment described above, it is possible to suppress the occurrence of errors when writing or reading information to or from the magnetic disk 1, and it is possible to ensure the reliability of the HDD.

[0036] (Second embodiment) The magnetic disk 1 of the second embodiment is a magnetic disk in which, instead of the ratio VTE / CTE being in the above range in the magnetic disk 1 of the first embodiment, the ratio VTE×(E / d) / CTE described below is in a predetermined range, and except for this point, is configured in the same way as the magnetic disk 1 of the first embodiment.

[0037] The magnetic disk 1 of the second embodiment has a thermal expansion coefficient CTE [×10 -6 / K], the change in thermal expansion VTE [μm], and the Young's modulus E [GPa] and density d [g / cm 3 ] to the ratio E / d [×10 6 m 2 / s 2 ], VTE × (E / d) / CTE is 3.0 × 105 [m 3 ・K / s 2 ] or less. According to the study by the present inventors, even if the value of the change in thermal expansion amount VTE of the magnetic disk 1 is small, if its magnitude is large relative to the ratio CTE / (E / d), the error suppression effect may be insufficient. With the magnetic disk 1 of the second embodiment, by limiting VTE×(E / d) / CTE at -30°C to 70°C within the above range, a sufficient error suppression effect can be obtained. In order to increase the number of disks that can be mounted in a hard disk drive housing, the magnetic disk 1 is required to have Young's modulus E [GPa] and specific elastic modulus E / d [×10 6 m 2 / s 2 ] is preferably used. This allows for reduced deformation of the magnetic disk 1 due to external stress at a given temperature. However, the greater the Young's modulus E [GPa], the greater the thermal stress generated in the magnetic disk 1 due to temperature changes. In other words, when thermal expansion is restricted in cases where shape changes due to temperature changes are constrained or there is a temperature distribution, the energy not used for expansion generates internally as thermal stress (compressive stress or tensile stress). Multiple magnetic disks 1 are stacked in a hard disk drive housing, with the inner periphery of the disk constrained via spacers. Furthermore, if there is material orientation or internal stress distribution in the circumferential direction of the magnetic disk 1, part of the thermal expansion due to temperature changes is constrained and generates thermal stress. Thermal stress is determined by the Young's modulus E [GPa] and the coefficient of thermal expansion CTE [×10 -6 / K], these values ​​are factors that promote variations in the amount of thermal expansion in the circumferential direction. Thus, as the magnetic disk 1 becomes thinner, the Young's modulus E [GPa] and the specific elastic modulus E / d [×10 6 m 2 / s 2

[0033] When a material with a large CTE / CTE ratio is used, thermal stress increases, promoting circumferential variations in thermal expansion, resulting in a higher frequency of errors. The inventors' studies have shown that a sufficient error suppression effect can be achieved by adjusting the range of (E / d) / CTE and balancing it with the change in thermal expansion, VTE. The magnitude of the ratio CTE / (E / d) correlates with the likelihood of fluttering occurring when the magnetic disk 1 rotates at high speed. According to the second embodiment, it is believed possible to achieve a balance between the effect of suppressing error occurrence by suppressing distortion of the track shape due to anisotropy of thermal expansion and the effect of suppressing error occurrence by suppressing fluttering.

[0038] The Young's modulus E of the magnetic disk 1 can be measured in accordance with Japanese Industrial Standard JIS R1602-1995. A test piece for measurement is cut from the magnetic disk 1 as a rectangular parallelepiped having a length of 50 mm, a width of 10 mm, and a thickness the same as the plate thickness of the magnetic disk 1, and measurement can be performed at room temperature. Since the influence of the magnetic film on the Young's modulus E and density d of the magnetic disk 1 is negligible, the Young's modulus E and density d of the substrate 3 can be taken as the Young's modulus E and density d of the magnetic disk 1.

[0039] 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 ].

[0040] The lower limit of VTE×(E / d) / CTE is not particularly limited, but is, for example, 0.5×10 5 m 3 ・K / s 2 is.

[0041] The E / d of the magnetic disk 1 is preferably 27×10 to improve the shock resistance and further suppress fluttering of the magnetic disk 1 when rotated at high speed. 6 m 2 / s 2 More preferably, it is 27.5×10 6 m 2 / s2 That's it, 30 x 10 6 m 2 / s 2 That's it, 34 x 10 6 m 2 / s 2 That's it, 35 x 10 6 m 2 / s 2 The lower limit of the ratio E / d is not particularly limited, but may be, for example, 26.5×10 6 m 2 / s 2 Furthermore, the upper limit of the ratio E / d is not particularly limited, but is, for example, 40×10 6 m 2 / s 2 From the viewpoint of increasing the ratio E / d, the Young's modulus E of the magnetic disk 1 is preferably 74.0 GPa or more, and more preferably 75.0 GPa or more, 81.0 GPa or more, 85.0 GPa or more, 90.0 GPa or more, or 96.0 GPa or more. On the other hand, even if the Young's modulus E is high, if the density is high, the weight of the magnetic disk 1 itself may cause large vibrations. Therefore, the density d of the magnetic disk 1 is set to 2.90 g / cm when the substrate body 3e (see FIG. 3) is made of an aluminum alloy. 3 Below 2.65g / cm 3 Further, 2.80 g / cm 3 Below 2.71g / cm 3 When the substrate 3 is made of glass, the density is preferably 2.65 g / cm 3 Below 2.45g / cm 3 Further, 2.60 g / cm 3 Below 2.50g / cm 3 It is preferable that this is equal to or greater than this.

[0042] According to the magnetic disk 1 of the second embodiment described above, it is possible to suppress the occurrence of errors when writing or reading information to or from the magnetic disk 1, and it is possible to ensure the reliability of the HDD.

[0043] The magnetic disks 1 of the first and second embodiments each preferably have the following additional configuration.

[0044] When servo information is written by a servo track writer, multiple circumferential recording areas (tracks) are formed concentrically on the magnetic layer of the magnetic disk 1. The magnetic disk 1 is suitable when the width (radial length) of the track, within which the recorded information is held and used for data reading by the magnetic head (hereinafter referred to as track width), is 60 nm or less, and even 50 nm or less. The lower limit of the track width is not particularly limited, but is, for example, 5 nm, preferably 20 nm. The magnetic particles forming the magnetic layer can be formed on a substrate with reduced particle size depending on the recording method used, such as perpendicular magnetic recording (PMR) or energy-assisted magnetic recording (EAMR), to increase the recording density of the magnetic layer. In particular, in energy-assisted magnetic recording (EAMR), magnetic particles are made smaller to reduce the bit size, and when recording data, energy is applied to the magnetic particles to reduce the coercivity, thereby assisting magnetization reversal and increasing the recording density. However, due to the small magnetic particles, the track width is narrow even in energy-assisted magnetic recording (EAMR). Furthermore, from the viewpoint of increasing the recording density of the magnetic layer, it is preferable to use shingled magnetic recording (SMR) in combination. In shingled magnetic recording (SMR), when recording data, the track pitch is narrowed by overlapping a portion of the previously recorded track, thereby increasing the track density (TPI), thereby increasing the recording density. In the present invention, the track width in shingled magnetic recording (SMR) refers to the track pitch, which is the radial length of the recording area where data is written and not overwritten by adjacent tracks, from which data can be read. The track width in shingled magnetic recording (SMR) is, for example, 55 nm or less, preferably 50 nm or less, preferably 45 nm or less, and more preferably 40 nm or less. Such a narrow track width also reduces the off-track tolerance of the magnetic head. Therefore, as described above, when distortion of the track shape of the magnetic disk occurs due to anisotropy of thermal expansion, even a slight amount of distortion increases the frequency of R / W errors.However, with the magnetic disk 1, the change in thermal expansion VTE is limited (preferably the change in thermal expansion VTE is smaller than the track width), and the ratio VTE / CTE or VTE×(E / d) / CTE is limited as described above, so that the occurrence of R / W errors is suppressed. Therefore, the magnetic disk 1 is suitable for use in HDDs in which information is read and written to the magnetic layer by shingled magnetic recording (SMR), or when information is recorded to the magnetic layer by energy-assisted magnetic recording (EAMR).

[0045] The substrate 3 of the magnetic disk 1 has a thermal expansion change VTE of 0.3 μm or less, and a ratio VTE / CTE of 1.1×10 4 μm·K or less, or VTE×(E / d) / CTE is 3.0×10 5 m 3 ・K / s 2 It is preferable that the material be made of the following materials:

[0046] A preferred material for the substrate 3 is glass containing, in mole percentages based on oxides, 55-80% SiO2, 5-25% Al2O3, and 0-8% BO3, at least one of MgO, CaO, SrO, and BaO, with a total content of 10-25%, and at least one of Li2O, Na2O, and KO, with a total content of 0.001-5.0%. Glass with this composition is excellent in that it allows the substrate 3 to be easily fabricated, and also in that it can enhance the heat resistance and rigidity of the magnetic disk 1.

[0047] In a magnetic disk 1 whose substrate 3 is made of the above-mentioned glass, the change in thermal expansion VTE is 0.040 μm or less, preferably 0.040 μm or less, and more preferably 0.030 μm or less, or 0.025 μm or less. Since glass has a relatively low coefficient of thermal expansion CTE, in order to limit the ratio VTE / CTE or VTE×(E / d) / CTE to the above range, the change in thermal expansion VTE is preferably 0.040 μm or less. This enhances the effect of suppressing the occurrence of R / W errors. A magnetic disk 1 whose change in thermal expansion VTE is 0.040 μm or less has extremely small track distortion due to thermal expansion during HDD operation, and is therefore suitable as a magnetic disk with a narrow track width, and is suitable as a magnetic disk for magnetic recording using shingled magnetic recording (SMR) or energy-assisted magnetic recording (EAMR).

[0048] Glass sheets produced by methods such as the down-draw method and the float method, in which molten glass is continuously formed into a long glass sheet, may have variations in residual stress due to differences in the cooling rate between the drawing direction of the molten glass during forming and the width direction perpendicular to the drawing direction, and may have anisotropic thermal expansion. Therefore, the glass sheet used for the substrate 3 is preferably one in which the cooling rate is controlled during the production of a long glass sheet by the down-draw method, the float method, or the like, to reduce the occurrence of residual stress, and further preferably one in which the produced glass sheet is adjusted by annealing so that the change in thermal expansion falls within a predetermined range.

[0049] The glass transition point (Tg) of the glass used for the substrate 3 is preferably 700° C. or higher, more preferably 740° C. or higher, and even more preferably 770° C. or higher, or 782° C. or higher, from the viewpoint of ensuring heat resistance when the magnetic layer is subjected to heat treatment. ０ The temperature of the heat treatment to obtain the magnetic layer with this structure may exceed 600° C. and reach 700° C. or more. By performing heat treatment at such a high temperature, the disordered structure of the magnetic layer is made into an ordered structure.

[0050] According to one embodiment, the substrate 3 has a substrate body 3e (see FIG. 3) made of an aluminum alloy and a nickel alloy film 3f (see FIG. 3) provided on the surface of the substrate body 3e. A preferred material for the substrate body 3e is an aluminum alloy containing at least one of Fe, Mn, and Ni, with a total content of 3.0 to 8.0 mass %, or containing more than 3.0 mass % Si, with the balance being Al and unavoidable impurities. Aluminum alloys with such compositions are advantageous in that they can increase the rigidity of the magnetic disk 1.

[0051] In a magnetic disk 1 whose substrate body 3e is made of the above-mentioned aluminum alloy, the change in thermal expansion is preferably 0.20 μm or less, and more preferably 0.15 μm or less. Because the thermal expansion coefficient CTE of the above-mentioned aluminum alloy is relatively high, in order to limit the ratio VTE / CTE or VTE×(E / d) / CTE to the above range, the change in thermal expansion VTE is preferably 0.20 μm or less. This enhances the effect of suppressing the occurrence of R / W errors. A magnetic disk 1 whose change in thermal expansion VTE is 0.20 μm or less has small track distortion due to thermal expansion during HDD operation, and is therefore suitable as a magnetic disk for magnetic recording using perpendicular magnetic recording (PMR), also known as conventional magnetic recording (CMR).

[0052] The nickel alloy film 3f is necessary for forming a smooth surface on the surface of the aluminum alloy substrate body 3e for forming a magnetic layer, and also contributes to increasing the rigidity of the magnetic disk 1 by supplementing the rigidity of the substrate 3. On the other hand, increasing the thickness of the nickel alloy film generates internal strain, causing variations in the amount of thermal expansion in the circumferential direction of the disk. Therefore, the thickness of the nickel alloy film 3f formed on the surface of the aluminum alloy substrate body 3e after polishing is preferably 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. The lower limit of the thickness of the nickel alloy film 3f is not particularly limited, but is, for example, 0.05 μm, preferably 3.0 μm. Here, the thickness of the nickel alloy film 3f is the thickness on one main surface, measured at a position at least 10 mm inward from the outer peripheral sidewall surface. A nickel-phosphorus (NiP) alloy is preferably used as the nickel alloy. For the nickel phosphorus (NiP) alloy film, in order to prevent magnetization due to heating during magnetic disk manufacturing, NiWP-based plating containing tungsten (W) in the range of 10 to 30 mass % or NiPMo-based plating containing molybdenum (Mo) in the range of 0.1 to 10 mass % is preferably used.

[0053] The aluminum alloy may contain elements other than those mentioned above that are unavoidable impurities, such as Ti, B, and Ga. The effects of the present invention are not impaired as long as the content of each element is 0.10% by mass or less, and the total content is 0.30% by mass or less.

[0054] Another preferred material for the substrate body 3e is an aluminum alloy containing 0.5 to 8.0 mass % of Mg.

[0055] The aluminum alloy plate material used for the substrate body 3e is produced by rolling an aluminum alloy ingot. The produced rolled material is wound into a coil, stretched again as it is drawn out, and punched into a shape with a predetermined outer diameter and inner diameter to produce a ring-shaped base material. The rolled material may have variations in residual stress due to differences in elongation between the rolling direction and the transverse direction perpendicular to the rolling direction, which may result in anisotropy of thermal expansion. Therefore, the base material for the substrate 3 produced from the aluminum alloy plate material is preferably one that has been stacked with spacers between them and then heat-treated in a continuous heating furnace at 420°C for 30 minutes to reduce the change in thermal expansion (VTE).

[0056] 3 shows a schematic cross-sectional view illustrating coarse particles 5 precipitated on the substrate 3 of the magnetic disk 1. According to one embodiment, in the cross section of the aluminum alloy substrate body 3e, the precipitated particles precipitated in the substrate body 3e are particles containing a metal other than Al (for example, particles made of an Al-Fe intermetallic compound), and the size of the particles preferably has a longest diameter of 5 μm or less. The precipitated particles may contain Al. Components other than Al contained in the aluminum alloy may precipitate as coarse particles during the rolling process. When coarse particles 5 with a longest diameter greater than 5 μm are present in the cross section of the substrate body 3e, the dispersibility of the intermetallic compound within the substrate body 3e is poor, and the number density of intermetallic compound particles with a longest diameter of 0.1 to 3 μm is 50 particles / mm 2 The number density may be less than 50 pieces / mm 2 The presence of such coarse particles 5 is also considered to be one of the causes of anisotropy in thermal expansion. Therefore, from the viewpoint of reducing the change in thermal expansion VTE, it is preferable that no coarse particles 5 are present, that is, that the longest diameter of particles (precipitated particles) containing metals other than Al precipitated in the substrate body 3e is 5 μm or less, and that the number density of intermetallic compound particles having a longest diameter of 0.1 to 3 μm is 50 particles / mm 2 It is preferable that the number of particles is 100 or more per mm. 2The metal other than Al constituting the precipitated particles includes at least one of Fe, Mn, and Ni, excluding Si, from among the elements contained in the aluminum alloy.

[0057] The determination of the longest diameter of the precipitated particles and the calculation of the number density are preferably performed on a radial cross section passing through the circumferential position showing the highest CTE among multiple positions in the circumferential direction of the magnetic disk 1 where the CTE was measured. Such a substrate cross section is 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 determined, for example, by using a backscattered electron image of an SEM photograph of the cross section of the substrate 3, and taking the maximum length of the particles in the image (double arrow in Figure 3). The determination that the longest diameter of particles containing metals other than Al is 5 μm or less can be performed by measuring an area of ​​0.04 mm2 of the cross section of the substrate main body 3e. 2 The particle number density is calculated as the average value of the particle number densities in a plurality of (for example, three or more) regions selected from the image of the cross section of the substrate 3.

[0058] In the magnetic disk 1 of the first embodiment, VTE×(E / d) / CTE is 2.6×10 5 [m 3 ・K / s 2 ] or less.

[0059] The magnetic disk 1 preferably meets the standard of a nominal diameter of 3.5 inches or 2.5 inches. The outer diameter of a magnetic disk 1 with a nominal diameter of 3.5 inches is, for example, 95 to 100 mm (e.g., 95 mm, 97 mm), and the diameter of the inner hole 1a is, for example, 24 to 26 mm (e.g., 25 mm). The outer diameter of a magnetic disk 1 with a nominal diameter of 2.5 inches is, for example, 65 to 70 mm (65 mm, 67 mm), and the diameter of the inner hole 1a is, for example, 19 to 21 mm (e.g., 20 mm).

[0060] The magnetic disk 1 is manufactured, for example, as follows. When manufacturing a magnetic disk 1 in which the substrate 3 is made of glass, first, a glass plate is scribed or cored to produce a circular-shaped base material, and chamfered surfaces are formed on the inner and outer peripheral end surfaces of the circular-shaped base material. Next, the main surfaces of the base material with the chamfered surfaces are ground. In the grinding process, the main surfaces of the circular-shaped base material are ground using a grinding member in the form of a sheet of fixed abrasive grains, or a slurry containing free abrasive grains. Next, the main surfaces of the base material whose main surfaces have been ground are polished. In the polishing process, polishing is performed using a polishing pad and a slurry containing free abrasive grains with a smaller grain size than the free abrasive grains used in the grinding process. It is preferable that the polishing process be divided into multiple processes and performed using abrasive grains with different grain sizes or polishing pads with different hardnesses.

[0061] When manufacturing a magnetic disk 1 having an aluminum alloy substrate body 3e, a circular ring-shaped blank is first punched out of an aluminum alloy plate, heated for a predetermined temperature and time, and annealed. The main surfaces are then cut and the end faces are shaped to produce the substrate body 3e. Annealing may be performed after processing the end faces and main surfaces. The end faces are shaped by grinding or cutting the end faces into a predetermined shape using a tool such as a forming tool or a single tool. A nickel alloy plating film is then formed on the surface of the aluminum alloy substrate body 3e to a thickness of, for example, 0.5 to 12 μm. The main surfaces of the substrate 3 are then polished. From the perspective of achieving both improved surface quality and improved productivity, the polishing process preferably involves a multi-stage polishing process, similar to that used for polishing a glass substrate 3.

[0062] The magnetic disk 1 is manufactured by sequentially laminating an adhesive layer, an underlayer, a magnetic layer (magnetic recording layer), a protective layer, and a lubricating layer on the main surface of the substrate 3 prepared as described above to form a magnetic film.

[0063] (Experimental Example) In order to investigate the effect of the magnetic disk 1, various substrates and magnetic disks with different specifications were fabricated.

[0064] (Substrate Preparation) In the manner described above, a circular-shaped base material punched from an aluminum alloy plate was annealed, and the main surfaces were cut and the edge surfaces were shaped to produce a substrate body. A 9 μm thick NiP film was formed by electroless plating to cover the entire surface, followed by edge polishing, grinding, first polishing, and second polishing to produce a substrate with a predetermined NiP film thickness (Examples 1 and 5, Comparative Examples 1 to 3). The substrate of Example 5 was further annealed in a furnace at 200°C for 30 minutes. Separately, a circular-shaped base material was prepared from a glass plate in the manner described above, and edge polishing, grinding, first polishing, and second polishing were performed to produce a substrate (Examples 2 to 4, Comparative Examples 4 and 5). The substrate of Example 2 was further annealed in a furnace at 700°C for 4 hours.

[0065] The dimensions of the fabricated substrates are as follows: outer diameter 97 mm, inner diameter 25 mm, thickness 0.44 mm (Examples 1 and 4), of which the thickness of the NiP film after polishing in Example 1 was 5.3 μm; outer diameter 97 mm, inner diameter 25 mm, thickness 0.5 mm (Examples 2, 3, 5, Comparative Examples 2 to 5), of which the thickness of the NiP film after polishing in Example 5 and Comparative Examples 2 and 3 was 8.0 μm; outer diameter 96 mm, inner diameter 25 mm, thickness 0.635 mm (Comparative Example 1), thickness of the NiP film after polishing was 8.0 μm

[0066] The compositions of the materials used in the produced substrate bodies or substrates and the methods for producing the glass plates are as follows: Aluminum alloy containing 0.1 mass% Mg, 0.05 mass% Si, 1.2 mass% Fe, 1.2 mass% Mn, 1.95 mass% Ni, 0.2 mass% Cr, 0.2 mass% Ti, and 0.2 mass% Zr (Example 1) Alkali-free glass produced by the down-draw method (Example 2, Comparative Example 5) In order to obtain glass of the specified composition, 300 to 1500 g of starting materials such as SiO2, Al2O3, Al(OH)3, BO, HBO, MgO, Mg(OH), MgCO3, CaCO3, SrCO3, BaCO3, ZnO, Li2CO3, Na2CO3, K2CO3, TiO2, and ZrO2 were weighed out and thoroughly mixed to form a blended batch, which was then placed in a platinum crucible and melted in air at a temperature of 1400 to 1600°C for approximately 3 to 8 hours to form a glass.After melting, the molten glass was poured into a carbon mold having a rectangular parallelepiped recess measuring 200 mm (length) × 200 mm (width) × 20 mm (depth), allowed to cool to the glass transition temperature, and then immediately placed in an annealing furnace, where it was held for 1 hour and then allowed to cool to room temperature in the furnace to obtain the glass (Examples 3, 4, and Comparative Example 4). Example 3 is a glass containing, in mol%, a total amount of more than 80% of SiO2, B2O3, and / or Al2O3, as well as 10 to 20% of RO (R is at least one selected from Mg, Ca, Zn, Sr, and Ba) and 0 to 1% of R'2O (R' is at least one selected from Li, Na, and K), with the total content of the above components being 98% or more. Example 4 is a glass containing, in mol%, more than 70% in total of SiO2, B2O3 and / or Al2O3, as well as 15 to 25% RO (R is at least one selected from Mg, Ca, Zn, Sr, and Ba) and 1 to 10% R'2O (R' is at least one selected from Li, Na, and K), with the total content of the above components being 98% or more. Comparative Example 4 is a glass containing, in mol%, more than 70% in total of SiO2, B2O3, and / or Al2O3, as well as 1 to 10% RO (R is at least one selected from Mg, Ca, Zn, Sr, and Ba) and 15 to 25% R'2O (R' is at least one selected from Li, Na, and K), with the total content of the above components being 98% or more. - Aluminum alloy containing 3.0 to 40.0 mass% Si (Example 5, Comparative Example 3) - Aluminum alloy containing 1.60 mass% Mg, 0.05 mass% Si, 0.70 mass% Fe, 0.30 mass% Mn, 1.83 mass% Ni, 0.15 mass% Cr, 0.25 mass% Cu, and 0.01 mass% Zn (Comparative Example 1) - Aluminum alloy containing 3.0 mass% or more Mg, and with the contents of Ni, Fe, Mn, and Si all less than 0.1 mass% (Comparative Example 2).

[0067] Since the influence of the magnetic film on the following characteristics is negligible, the following characteristics were measured or calculated using the substrate prepared above and used as the magnetic disk characteristics. The measurement results are shown in Tables 1 and 2.

[0068] (Coefficient of thermal expansion CTE) For each of the substrates of the examples and comparative examples, samples were cut out at three circumferential positions at 120 degree intervals in the manner described above, and the linear expansion coefficient of each sample was determined from the change in length in the temperature range of -30 to 70°C using a thermomechanical analyzer using the TMA method. The average value of the three linear expansion coefficients was taken as the coefficient of thermal expansion CTE in the temperature range of -30 to 70°C.

[0069] (Change in thermal expansion VTE) Using the linear expansion coefficient in the temperature range of -30 to 70°C obtained by measuring each sample, the amount of thermal expansion of the substrate over a length of 95 mm when the temperature was changed from 55 to 60°C was calculated, and the difference between the maximum and minimum values ​​was taken as the change in thermal expansion VTE.

[0070] (Ratio VTE / CTE) VTE / CTE was calculated using the amount of change in thermal expansion VTE and the coefficient of thermal expansion CTE.

[0071] (Ratio E / d) The ratio E / d was calculated using the Young's modulus E and density d of the magnetic disk obtained in the above manner.

[0072] (VTE×(E / d) / CTE) VTE×(E / d) / CTE was calculated using the amount of change in thermal expansion VTE, E / d, and the coefficient of thermal expansion CTE.

[0073] In addition, multiple substrates were prepared for each of the examples and comparative examples, and magnetic disks were prepared using substrates different from those used for measuring and calculating the above characteristics, and the effect of suppressing error occurrence was investigated.

[0074] (Magnetic Disk Fabrication) A magnetic film (thickness 30 nm or less) including a magnetic layer was formed on the main surface of the substrate of each of the examples and comparative examples in the same manner as described above, to fabricate magnetic disks. In Examples 1 and 5 and Comparative Examples 1 to 3, a magnetic layer including the CoPtCr-based material was formed. In Examples 2 to 4 and Comparative Examples 4 and 5, a magnetic layer including the Fe—Pt-based magnetic material was formed. In Examples 2 to 4 and Comparative Examples 4 and 5, L1 ０ To obtain the magnetic layer of the structure, the substrate was heat-treated by preheating at 630° C. for 5 seconds.

[0075] (Test to confirm error suppression effect) The manufactured magnetic disk was incorporated into an HDD equipped with an internal temperature sensor, and the effect of suppressing the occurrence of errors was investigated. When writing servo signals to the magnetic disk using a servo track writer, tracks for magnetic recording using conventional magnetic recording (CMR) were formed for Examples 1 and 5 and Comparative Examples 1 to 3. The track width was 60 nm. For Examples 2 to 4 and Comparative Examples 4 and 5, tracks for magnetic recording using thermally assisted magnetic recording (HAMR) were formed. The track width was 50 nm.

[0076] The fabricated HDDs were placed in a chamber equipped with a cooling device, and data was written to the magnetic disks while the temperature inside the chamber was maintained at 20-25°C. Magnetic recording was performed using conventional magnetic recording (CMR) on the magnetic disks of Examples 1 and 5 and Comparative Examples 1-3, while magnetic recording was performed using thermally assisted magnetic recording (HAMR) on the magnetic disks of Examples 2-4 and Comparative Examples 4 and 5. The HDDs with data written to the magnetic disks were removed from the chamber, and the data was read. The number of retries required to correctly read the data was measured. A retries of 2 or less were evaluated as A, 3-10 retries were evaluated as B, and more than 10 retries were evaluated as C. The results are shown in Table 1. During the reading process, the temperature inside the HDDs was within the range of 55-60°C in both the Examples and Comparative Examples.

[0077]

[0078] Comparing the examples and comparative examples, the change in thermal expansion VTE was 0.3 μm or less, and the ratio VTE / CTE was 1.1×10 4 μm·K or less, or VTE×(E / d) / CTE is 3.0×10 5 [m 3 ・K / s 2 ] or less, the number of retries required to perform a correct read is small, and it can be seen that the error suppression effect is excellent.

[0079] For Example 1 and Comparative Example 1, a backscattered electron image was observed using an SEM of a cross section in the thickness direction of the substrate along the radial direction, which passed through the circumferential position where the average linear expansion coefficient α was the highest among the multiple circumferential positions where the linear expansion coefficient was measured. In Example 1, 2 In Example 1, no coarse particles with a maximum diameter exceeding 5 μm were present, whereas in Comparative Example 1, coarse particles with a maximum diameter exceeding 5 μm were present. Furthermore, in Example 1, the dispersibility of the intermetallic compound was good, and the number density of intermetallic compound particles with a maximum diameter of 0.1 to 3 μm was 50 particles / mm 2 In contrast, in Comparative Example 1, the number density of intermetallic compound particles having a maximum diameter of 0.1 to 3 μm was 50 particles / mm 2 The results were less than 100%. On the other hand, Example 1 had a smaller change in thermal expansion VTE than Comparative Example 1, but a larger thermal expansion coefficient CTE at -30 to 70°C. From these results, it is believed that the absence of coarse particles with a longest diameter exceeding 5 μm contributes to reducing the values ​​of the ratio VTE / CTE and VTE×(E / d) / CTE. Furthermore, the thickness of the NiP in Comparative Example 1 was 8.0 μm, while that in Example 1 was 5.3 μm, which means that the effect of internal strain due to the NiP film was small and contributes to reducing the values ​​of the change in thermal expansion VTE and the ratio VTE / CTE.

[0080] Although the information recording medium disk of the present invention has been described in detail above, the present invention is not limited to the above-mentioned embodiments and examples, and various improvements and modifications may be made without departing from the spirit of the present invention. The information recording medium disk of the present invention is not limited to a magnetic disk, but may be, for example, a disk (ferroelectric recording medium) that has a ferroelectric layer (recording layer) on the main surface of a substrate and that can repeatedly record information by changing the polarization of the ferroelectric.

[0081] REFERENCE SIGNS LIST 1 Information recording medium disc 1a Inner hole 3 Substrate 3a, 3b Main surfaces 3c, 3d Side wall surfaces 3e Substrate body 5 Coarse particles

Claims

1. A disk for an information recording medium having a thickness of 0.51 mm or less, comprising a substrate having one main surface and the other main surface, and further having side wall surfaces connecting both main surfaces and a recording layer, wherein the change amount over the circumferential direction of the thermal expansion amount in the radial direction of the disk when the temperature is increased by 5 ° C in the temperature range of -30 ° C to 70 ° C, calculated with the diameter of the disk being 95 mm, is 0.3 μm or less, and the ratio of the change amount of the thermal expansion amount to the thermal expansion rate of the disk at -30 ° C to 70 ° C is 1.1 × 10 4 μm·K or less, a disk for an information recording medium, characterized by this.

2. A disk for an information recording medium having a plate thickness of 0.51 mm or less, comprising a substrate having one main surface and the other main surface, and further having side wall surfaces connecting both main surfaces and a recording layer, the change amount over the circumferential direction of the thermal expansion amount in the radial direction of the disk when the temperature is increased by 5 ° C in the temperature range of -30 ° C to 70 ° C, calculated with the diameter of the disk being 95 mm, is 0.3 μm or less, the coefficient of thermal expansion CTE [× 10 -6 / K], the change amount VTE [μm] of the thermal expansion amount, and the ratio E / d [× 10 3 of the Young's modulus E [GPa] and the density d [g / cm 6 m 2 / s 2 of the disk represented by VTE × (E / d) / CTE is 3.0 × 10 5 [m 3 ·K / s 2 or less, a disk for an information recording medium, characterized by this.

3. The coefficient of thermal expansion CTE [×10 -6 / K] of the disk at -30°C to 70°C, the change amount VTE [μm] of the thermal expansion amount, and the ratio E / d [×10 3 of the Young's modulus E [GPa] and the density d [g / cm 6 m 2 / s 2 of the disk, where VTE × (E / d) / CTE represented thereby is 2.6 × 10 5 [m 3 ·K / s 2 or less. The disk for an information recording medium according to claim 1.

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

5. The disk for an information recording medium according to claim 4, which is used in a hard disk drive in which information is read and written to the magnetic layer by single magnetic recording.

6. The disk for an information recording medium according to claim 4, in which information is recorded in the magnetic layer by an energy-assisted magnetic recording method.

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

8. The change amount of the thermal expansion amount is 0.20 μm or less, and the substrate has a substrate body made of an aluminum alloy and a nickel alloy film provided on the surface of the substrate body. The aluminum alloy contains at least one of Fe, Mn, and Ni, and the total content thereof is 3.0 to 8.0% by mass, or contains more than 3.0% by mass of Si, and the balance is composed of Al and inevitable impurities. The disk for an information recording medium according to claim 1 or 2.

9. 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 5 μm or less. The disk for an information recording medium according to claim 8.

10. In the cross-section of the substrate body, the number density of particles having a longest diameter of 0.1 to 3 μm among the particles is 50 particles / mm 2 or more, and the disk for an information recording medium according to claim 9.

11. The thickness of the film is 7.5 μm or less. The disk for an information recording medium according to claim 8.

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