Magnetic disk, magnetic disk substrate, and usage of magnetic disk substrate, and method for manufacturing magnetic disk

Abstract

Provided are a magnetic disk that is suitable for use in thermal assist magnetic recording, a magnetic disk substrate, usage of the magnetic disk substrate, and a method for manufacturing the magnetic disk.　The present disclosure pertains to a magnetic disk which has: a substrate having a pair of main surfaces and an outer circumferential end surface; and a magnetic layer having an L10 structure on the pair of main surfaces and the outer circumferential end surface of the substrate. The straightness of the magnetic disk measured under the following measurement condition after heating the magnetic disk under the following heating condition is 90 μm or less. (Heating condition) The magnetic disk is heated such that the surface temperature reaches 600°C from room temperature in 25 seconds, then is heated such that the surface temperature reaches 700°C in 35 seconds, and then is cooled such that the surface temperature reaches room temperature in 120 seconds. (Measurement condition of straightness) By using a surface roughness measurement device, the values of the maximum valley depths Sv are measured in a measurement range of at least 88 mm length in three directions that are different from each other by 120°, and the number-average value of the maximum valley depths Sv are obtained as the value of straightness.

Description

Magnetic disk, magnetic disk substrate, use of magnetic disk substrate, and manufacturing method of magnetic disk

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to magnetic disks, magnetic disk substrates, uses of magnetic disk substrates, and methods of manufacturing magnetic disks.

[0002] With the recent development of computer technology, there is a demand for magnetic recording devices with larger storage capacities and smaller spaces, and for recording media with higher recording densities. To achieve this, it is preferable to use ferromagnetic materials with large magnetocrystalline anisotropy Ku, and L1 ０ FePt, which has an ordered structure of

[0001] , has attracted attention. Because FePt has high magnetic anisotropy, it is possible to reduce the particle diameter to 4 nm. However, as the particle size is reduced, the magnetization reversal field becomes large, exceeding the magnetic field (approximately 1 T) that can be generated by a magnetic head for writing, making writing impossible using current recording methods. To solve this problem, a new magnetic recording method called heat-assisted magnetic recording (HAMR) has been proposed, in which the temperature of the medium is locally raised to near the Curie point (the temperature at which ferromagnetism disappears) only during writing (see, for example, Patent Document 1).

[0003] JP 2011-198455 A

[0004] L1 ０ In order to form a magnetic layer having such a structure on a magnetic disk substrate, for example, a sputtering method is used, but this method has the problem of the magnetic disk substrate deforming due to exposure to high temperatures. For this reason, a magnetic disk that is less likely to deform is desired.

[0005] Therefore, an object of the present disclosure is to provide a magnetic disk, a magnetic disk substrate, a use of the magnetic disk substrate, and a method for manufacturing a magnetic disk that are suitable for use in thermally assisted magnetic recording.

[0006] One embodiment of the present disclosure is a magnetic disk, comprising: a substrate having a pair of main surfaces and an outer peripheral end surface; and an L1 ０and a magnetic layer having a structure, wherein the magnetic disk has a straightness of 90 μm or less when measured under the following measurement conditions after being heated under the following heating conditions.

[0007] One embodiment of the present disclosure relates to a magnetic disk substrate having a pair of main surfaces and an outer peripheral end surface, wherein the magnetic disk substrate is heated under the following heating conditions and then has a straightness of 90 μm or less measured under the following measurement conditions:

[0008] One embodiment of the present disclosure is a method for manufacturing a magnetic disk, comprising: heating a substrate until the substrate surface temperature reaches 600 to 780° C.; ０ The present invention relates to a method for manufacturing a magnetic disk, comprising a step of forming a magnetic layer having a structure, wherein the substrate is a magnetic disk substrate having a pair of main surfaces and an outer peripheral end surface, and after heating the magnetic disk substrate under the following heating conditions, the magnetic disk substrate has a straightness of 90 μm or less as measured under the following measuring conditions.

[0009] (Heating conditions) The magnetic disk is heated from room temperature to 600°C in 25 seconds, then heated to 700°C in 35 seconds, and then cooled to room temperature in 120 seconds. (Straightness measurement conditions) The maximum valley depth Sv is measured in three directions, each 120 degrees apart, over a measurement range of at least 88 mm in length using a surface roughness measuring device, and the number average of the maximum valley depth Sv is determined as the straightness value.

[0010] According to the present embodiment, it is possible to provide a magnetic disk, a magnetic disk substrate, a method for using the magnetic disk substrate, and a method for manufacturing a magnetic disk that are suitable for use in thermally assisted magnetic recording.

[0011] Fig. 1 is a perspective view of the appearance of a magnetic disk according to this embodiment. Fig. 2 is a cross-sectional view of the magnetic disk according to this embodiment. Fig. 3 is a front view showing the measurement points of the straightness of the magnetic disk according to this embodiment. Fig. 4 is a diagram showing a temperature rise program for a heating test.

[0012] Preferred embodiments of the present disclosure will be described with reference to the accompanying drawings (note that in each drawing, components with the same reference numerals have the same or similar configurations). The embodiments described below are intended to facilitate understanding of the present disclosure and are not intended to limit the scope of the present disclosure. The elements of the embodiments, as well as their arrangement, materials, conditions, shape, size, etc., are not limited to those exemplified and can be modified as appropriate. Furthermore, configurations shown in different embodiments can be partially substituted or combined with each other.

[0013] [Magnetic Disk] The magnetic disk according to this embodiment includes a substrate having a pair of main surfaces and an outer peripheral end surface, and an L1 ０ and a magnetic layer having a structure, wherein the magnetic disk has a straightness of 90 μm or less measured under the following conditions after being heated under the following conditions: According to the above configuration, a magnetic disk suitable for use in thermally assisted magnetic recording can be provided.

[0014] (Heating Conditions) The surface temperature of the magnetic disk is heated from room temperature to 600° C. in 25 seconds, then heated to 700° C. in 35 seconds, and then cooled to room temperature in 120 seconds.

[0015] <Straightness> Straightness can be measured by the following method.

[0016] (Conditions for measuring straightness) The maximum valley depth Sv is measured in three directions, each oriented 120 degrees apart, over a measurement range of at least 88 mm in length using a surface roughness measuring device, and the number average value of the maximum valley depth Sv is determined as the straightness value.

[0017] The straightness is measured in a measurement range of at least 88 mm in length. For example, the measurement position on the magnetic disk can be a measurement range on a straight line of 88 mm in length shown by the dotted line in Figure 3. The straightness is measured by measuring the maximum valley depth Sv in three directions that are 120 degrees apart as shown in Figure 3, and the number average of the measured values ​​is taken as the straightness. Note that, as a surface roughness measuring instrument, for example, a product named "Surftest-VS2100" manufactured by Mitutoyo Corporation can be used.

[0018] The magnetic disk according to this embodiment has a straightness of 90 μm or less (hereinafter simply referred to as "straightness after heating"). Having this straightness results in a magnetic disk suitable for use in thermally assisted magnetic recording. The straightness after heating is preferably 80 μm or less, more preferably 70 μm or less, and even more preferably 60 μm or less. The lower limit of the straightness after heating is not particularly limited, but is, for example, 20 μm or more. To achieve this straightness, the above-mentioned range can be achieved, for example, by changing the composition of the magnetic disk material to adjust the glass transition temperature, thermal expansion coefficient, specific elastic modulus, etc., by adjusting the thickness of the magnetic disk, or by changing the manufacturing method (for example, by forming molten glass into a sheet, quenching it to obtain plate glass, and then processing it into the shape of a substrate, or by using a down-draw method when forming it into a sheet).

[0019] Furthermore, the straightness value after heating is also affected by the thickness of the substrate, and the rate of increase in straightness due to a thinner substrate thickness varies depending on the material. It is preferable that the increase in the straightness value after heating is small even when the substrate thickness is reduced. Taking the thickness of the substrate into consideration, the product of the straightness (μm) of the glass substrate after heating and the thickness (mm) of the substrate is preferably 50.0 (μm mm) or less, more preferably 40.0 (μm mm) or less, and even more preferably 35.0 (μm mm) or less.

[0020] The magnetic disk according to this embodiment preferably has a change in straightness between before and after heating under the above conditions (hereinafter simply referred to as "change in straightness") of 10 to 80 μm. By having this straightness, a magnetic disk suitable for use in thermally assisted magnetic recording can be obtained. The change in straightness is preferably 15 to 75 μm, more preferably 15 to 70 μm, even more preferably 15 to 60 μm, and even more preferably 15 to 50 μm.

[0021] The magnetic disk according to this embodiment preferably has a straightness of 30 μm or less before heating (hereinafter also referred to as "straightness before heating"). By having this straightness, a magnetic disk suitable for use in thermally assisted magnetic recording can be obtained. The straightness before heating is preferably 20 μm or less, more preferably 15 μm or less, even more preferably 10 μm or less, and even more preferably 5 μm or less. The lower limit of the straightness before heating is not particularly limited, but is, for example, 1 μm or more.

[0022] FIG. 1 is a perspective view of the appearance of a magnetic disk 21 according to this embodiment. The magnetic disk 21 is annular in shape and has a spindle hole 215. The magnetic disk 21 has main surfaces 216 that face each other. The pair of main surfaces are substantially parallel. Here, substantially parallel means that the parallelism is, for example, 5 μm or less. The magnetic disk 21 has an outer peripheral end surface 217 that connects the pair of main surfaces. The magnetic disk 21 also has an inner peripheral end surface 218 that connects the pair of main surfaces.

[0023] 2 is a cross-sectional view of the magnetic disk 21 according to this embodiment. The magnetic disk 21 includes a substrate 211 and an L1 ０ The magnetic disk 21 includes a magnetic layer 214 containing a magnetic material containing an FePt alloy. The magnetic disk 21 may further include a first underlayer 213 containing MgO. The magnetic disk 21 may also further include a second underlayer 212 containing a Cr alloy.

[0024] The magnetic layer 214 may be a single layer, or may have a multi-layer structure.

[0025] The magnetic disk 21 may have a protective layer 215 and a lubricating layer 216. A soft magnetic layer and a heat sink layer may be added as appropriate.

[0026] The magnetic disk substrate (hereinafter simply referred to as "substrate") according to this embodiment preferably has a thickness of 0.2 to 0.6 mm. The thickness of the substrate is preferably 0.30 to 0.55 mm, more preferably 0.35 to 0.50 mm, and even more preferably 0.41 to 0.45 mm.

[0027] Examples of materials for the substrate include metal materials such as stainless steel, titanium, aluminum, and aluminum alloys, ceramics, and glass. Among these, the substrate is preferably a glass substrate.

[0028] The glass composition of the glass substrate is preferably SiO ２ 55 to 80 mol%, Al ２ O ３ 5 to 25 mol%, B ２ O ３ 0 to 8 mol%, P ２ O ５ 0 to 5 mol % of MO, 5 to 25 mol % of MO (MO is at least one selected from MgO, CaO, SrO and BaO, and the content thereof is the total value of the contents of MgO, CaO, SrO and BaO), and 0 to 15 mol % of M ２ O (M ２ O is Li ２ O, Na ２ O and K ２ At least one selected from Li, O, ２ O, Na ２ O and K ２ The glass composition of the glass substrate may consist of these components.

[0029] The preferred contents of each component in the glass composition of the glass substrate are as follows:

[0030] SiO ２ is a glass network forming component. SiO ２ From the viewpoint of increasing the stability of the glass and improving the meltability during production, the content of is preferably 55 to 80 mol %, more preferably 57 to 75 mol %, and even more preferably 60 to 70 mol %.

[0031] Al ２ O ３ From the viewpoint of improving the heat resistance of the glass and enhancing the stability of the glass, the content of is preferably 5 to 25 mol %, more preferably 10 to 20 mol %, and even more preferably 12 to 18 mol %.

[0032] B２ O ３ is a glass network forming component. ２ O ３ The content is preferably 0 to 8 mol %, more preferably 0 to 1.5 mol %, and even more preferably 0.1 to 0.8 mol %.

[0033] P ２ O ５ The content is preferably 0 to 5 mol %, more preferably 0 to 3 mol %, and even more preferably 0.1 to 3 mol %.

[0034] MO is at least one selected from MgO, CaO, SrO, and BaO, and its content is the total content of MgO, CaO, SrO, and BaO. From the viewpoint of adjusting the Young's modulus, the content of MO is preferably 5 to 25 mol%, more preferably 6 to 20 mol%, and even more preferably 14 to 18 mol%. From the viewpoint of adjusting the Young's modulus, the content of MgO is preferably 3 to 20 mol%, more preferably 4 to 19 mol%, and even more preferably 8 to 18 mol%.

[0035] From the viewpoint of improving productivity, the CaO content is preferably 0 to 10 mol %, more preferably 0 to 8 mol %, and even more preferably 0 to 6 mol %.

[0036] From the viewpoint of reducing the specific gravity of the glass, the content of SrO is preferably 0 to 5 mol %, more preferably 0 to 3 mol %, and even more preferably 0 to 1.5 mol %.

[0037] From the viewpoint of reducing the specific gravity of the glass, the content of BaO is preferably 0 to 5 mol %, more preferably 0 to 4 mol %, and even more preferably 0 to 1.5 mol %.

[0038] M ２ O is Li ２ O, Na ２ O and K ２ At least one selected from Li, O, ２ O, Na ２ O and K ２ The total value of O.２ The O content is preferably 0 to 15 mol %, more preferably 0 to 10 mol %, and even more preferably 0.01 to 9 mol %.

[0039] Li ２ From the viewpoint of improving heat resistance, the O content is preferably 0 to 5 mol %, more preferably 0 to 7 mol %, and even more preferably 0.01 to 6 mol %.

[0040] Na ２ The O content is preferably 0 to 10 mol %, more preferably 0 to 7 mol %, and even more preferably 0.01 to 5 mol %.

[0041] K ２ The O content is preferably 0 to 3 mol %, more preferably 0 to 1 mol %, and even more preferably 0 to 0.3 mol %.

[0042] In the present disclosure, the glass composition is expressed as a glass composition based on oxides. Here, "glass composition based on oxides" refers to a glass composition obtained by converting the glass raw materials into oxides present in the glass after they are all decomposed during melting. The glass composition in the present disclosure can be determined by a method such as ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Quantitative analysis is performed for each element using ICP-AES. The analytical values ​​are then converted into oxide notation. The analytical values ​​obtained by ICP-AES may contain, for example, a measurement error of about ±5% of the analytical value. Therefore, the oxide notation values ​​converted from the analytical values ​​may also contain an error of about ±5%. Furthermore, in the present disclosure, a content of 0 mol% of a constituent component means that the constituent component is substantially absent, and indicates that the content of the constituent component is at or below the impurity level. The level of impurities or less means, for example, less than 0.01 mol %.

[0043] The magnetic disk substrate according to this embodiment has a straightness of 90 μm or less, measured after heating under the above conditions (hereinafter also referred to simply as "straightness after heating"). By having this straightness, a magnetic disk substrate suitable for use in thermally assisted magnetic recording can be obtained. The straightness after heating is preferably 80 μm or less, more preferably 70 μm or less, and even more preferably 60 μm or less. The lower limit of the straightness after heating is not particularly limited, but is, for example, 20 μm or more.

[0044] In the magnetic disk substrate according to this embodiment, the change in straightness between before and after heating under the above conditions (hereinafter simply referred to as "change in straightness") is preferably 80 μm or less. By having this straightness, a magnetic disk substrate suitable for use in thermally assisted magnetic recording can be obtained. The change in straightness is preferably 70 μm or less, more preferably 60 μm or less, even more preferably 50 μm or less, and even more preferably 40 μm or less. The lower limit of the change in straightness is not particularly limited, but is, for example, 20 μm or more.

[0045] The magnetic disk substrate according to this embodiment preferably has a straightness of 50 μm or less before heating (hereinafter also referred to as "straightness before heating"). By having this straightness, a magnetic disk substrate suitable for use in thermally assisted magnetic recording can be obtained. The straightness before heating is preferably 40 μm or less, more preferably 30 μm or less, even more preferably 20 μm or less, and even more preferably 15 μm or less. The lower limit of the straightness before heating is not particularly limited, but is, for example, 20 μm or more.

[0046] The Young's modulus of the substrate is preferably 80 GPa or more, more preferably 80 to 110 GPa, and even more preferably 85 to 105 GPa.

[0047] The glass transition temperature of the substrate is preferably 700°C or higher, more preferably 710 to 850°C, and even more preferably 720 to 840°C.

[0048] The thermal expansion coefficient of the substrate at 100 to 300°C is (unit: × 10 －７ / K) is preferably 10 to 110, more preferably 25 to 98, and even more preferably 30 to 55.

[0049] The specific elastic modulus E / d of the substrate is preferably 31.0×10 ６ m ２ / s ２ More preferably, 31.5×10 ６ m ２ / s ２ or more, preferably 34.0×10 ６ m ２ / s ２ That's all. When the substrate has a specific elastic modulus E / d within this range, impact resistance is further improved. Note that when the substrate has a thickness of 0.51 mm or less, the above-mentioned effect is more pronounced when the specific elastic modulus E / d is within the above-mentioned range. The specific elastic modulus E / d means the value obtained by dividing Young's modulus by specific gravity.

[0050] The magnetic disk 21 includes a magnetic layer 214. The magnetic disk 21 may include, for example, a second underlayer 212 containing a Cr alloy, a first underlayer 213 containing MgO, the magnetic layer 214, a protective layer 215, and a lubricating layer 216, which are stacked on the main surface of a smoothly polished glass substrate in this order from the side closest to the main surface.

[0051] The second underlayer may be made of, for example, a Cr alloy, more specifically, CrTi, CrB, etc. The thickness of the second underlayer may be, for example, 1 to 30 nm.

[0052] The first underlayer may be made of a material containing, for example, Ru or MgO, and preferably contains MgO. By using a first underlayer containing MgO, the L1 ０ The thickness of the first underlayer may be, for example, 5 to 30 nm.

[0053] For example, the first underlayer and the second underlayer are sequentially formed on the main surfaces of the glass substrate by DC (Direct Current) magnetron sputtering in an Ar atmosphere after the glass substrate is introduced into a vacuum-drawn film-forming apparatus.

[0054] The magnetic layer is L1 for ultra-high recording density of the magnetic disk. ０ It is preferable that the magnetic material has a granular structure including magnetic grains containing an FePt alloy and grain boundary portions. The grain boundary portions may contain, for example, C, B, BN, Al ２ O ３ , SiO ２ , TiO ２ , and Cr ２ O ３ The magnetic material contains non-magnetic materials such as ferromagnetic materials and alternating magnetic materials. The granular structure is also called a granular structure. The magnetic material is not limited to ferromagnetic materials, but may be an alternating magnetic material. By using an alternating magnetic material, the influence of an external magnetic field can be eliminated, and the particle diameter of the magnetic material can be set to 10 nm or less, preferably 4 nm or less, and more preferably 2 nm or less, thereby further improving the recording density.

[0055] The magnetic layer is L1 ０ It is preferable that the magnetic layer is made of an FePt-based alloy material. Here, "based" means containing. ０ Examples of the FePt-based alloy material include FePt and FePtAg (FePt alloyed with Ag) containing C (carbon), and FePt and FePtAg (FePt alloyed with Ag) containing Si (silicon). ０ As magnetic materials having the structure, in addition to FePt alloys, CoPt alloys, Nd ２ Fe １４ B. SnCo ５ The magnet may be made of a rare earth magnetic material such as

[0056] The magnetic layer preferably has a composition represented by formula (1): (Fe ｘ Pt １－ｘ ) １－ｚ Ag ｚ -C ｖ ... (1) (Wherein, 0.4<x<0.55, 0≦z<0.2, 0≦v≦50vol% (preferably 30vol%≦v≦50vol%), (Fe ｘ Pt １－ｘ ) １－ｚ Ag ｚis (100-v) vol%.) By making the Fe:Pt composition close to 1:1, L1 ０ Since the order-disorder transformation temperature of the A1 phase is the highest, a high L1 ０ The driving force for ordering is obtained. ０ To promote the ordering of the FePt structure, it is preferable to alloy FePt with Ag. In this case, as described above, it is preferable to include Ag at an atomic ratio of 0 to 20% relative to FePt. The C in the FePt-C layer or FePtAg-C layer phase-separates from the FePt or FePtAg during film growth, forming a nonmagnetic matrix with a granular structure.

[0057] In the magnetic layer, L1 ０ The magnetic particles containing the FePt alloy are preferably island-shaped magnetic particles. The smaller the particle size of the magnetic particles, the better. To obtain magnetic particles with a small particle size, it is sufficient to form a thin film with a thickness of, for example, 20 nm or less.

[0058] When sputtering using an FePt alloy or an FePtAg alloy as the nonmagnetic material constituting the grain boundary portion, an alloy target containing the above material is prepared. In the case of simultaneous sputtering, each target is prepared and film formation is performed simultaneously. Simultaneous sputtering using two targets, an FePt alloy and a compound that forms the nonmagnetic matrix, may also be performed. The volume fraction of the nonmagnetic matrix can be changed by controlling the film formation rate. For example, when forming a film of an FePt alloy containing C, simultaneous sputtering of FePt and C (cosputtering) can be employed. A preferred method is to use an FePt alloy target and a C target, and control the power of the C target during FePt sputtering to change the film formation rate of C, as shown in the examples.

[0059] The thickness of the magnetic layer may be, for example, 1 to 20 nm.

[0060] An auxiliary recording layer may be provided above or below the magnetic layer. By providing an auxiliary recording layer, it is possible to add high heat resistance to the magnetic recording layer in addition to the high density recording properties, low noise, and coercive force control. The composition of the auxiliary recording layer may be, for example, a ferromagnetic alloy containing FePt with an A1 structure. Also, instead of forming a ferromagnetic layer, an L1 structure may be formed by ion irradiation or plasma damage. ０ The coercive force can also be controlled by disordering a portion of the FePt magnetic material having a lattice structure into an A1 structure. The thickness of the auxiliary recording layer is preferably about 0 to 10 nm. The auxiliary recording layer can be formed by, for example, sputtering.

[0061] Furthermore, an exchange coupling control layer may be provided between the magnetic layer and the auxiliary recording layer. By providing the exchange coupling control layer, the strength of the exchange coupling between the granular magnetic layer and the auxiliary recording layer can be controlled, thereby optimizing the recording and reproduction characteristics. For example, Ru or a Ru alloy is used as the exchange coupling control layer. The film thickness of the exchange coupling control layer is preferably about 0 to 10 nm. The exchange coupling control layer can be formed, for example, by sputtering.

[0062] The protective layer is preferably made of a carbon-based material. ２ H ４ The protective layer can be formed by depositing a protective layer using a nitriding agent and then performing a nitriding treatment in the same chamber to introduce nitrogen onto the surface. By providing the protective layer, the magnetic disk surface can be protected from the magnetic head flying over the magnetic disk. The thickness of the protective layer can be, for example, 3 to 7 nm.

[0063] The lubricating layer may contain PFPE (polyfluoropolyether). The lubricating layer can be formed, for example, by applying PFPE (polyfluoropolyether) onto the protective layer by a dip coating method.

[0064] [Magnetic Disk Manufacturing Method] The magnetic disk manufacturing method according to this embodiment includes the steps of: heating a substrate until the substrate surface temperature reaches 600 to 780° C.; ０The method includes a step of forming a magnetic layer having a structure, wherein the substrate is a magnetic disk substrate having a pair of main surfaces and an outer peripheral end surface, and after heating the magnetic disk substrate under the aforementioned heating conditions, the magnetic disk substrate has a straightness of 90 μm or less as measured under the aforementioned measuring conditions.

[0065] In the magnetic layer forming step, it is preferable to form the magnetic layer on the substrate by sputtering. For the sputtering process itself, various devices and conditions, including known ones, can be appropriately adopted. In particular, forming the magnetic layer by DC magnetron sputtering is preferable because it enables uniform film formation.

[0066] In order to form an alloy exhibiting high coercivity, the magnetic disk must have an ordered L1 structure with high uniaxial magnetic anisotropy. ０ In this embodiment, it is preferable to produce an alloy having a highly ordered L1 structure. ０ In order to grow the FePt alloy fine particles having the mold structure in an island shape, it is preferable to maintain the substrate temperature at 650° C. or higher during sputtering film formation.

[0067] For example, simultaneous sputtering may be performed using targets of Fe and Pt that constitute an FePt alloy, or targets of Fe, Pt, and Ag that constitute an FePtAg alloy, or sputtering may be performed using an FePt alloy target or an FePtAg alloy target whose composition has been preliminarily adjusted.

[0068] The alloy target mainly composed of Fe and Pt has a composition in which the Fe and Pt ratio in the magnetic layer to be formed is close to 1:1, specifically, Fe ｘ Pt １－ｘ It is preferable to prepare the film so that x satisfies the condition 0.4<x<0.55. When using separate targets of Fe and Pt, the film formation rate can be made approximately 1:1 by controlling the power input to each target.

[0069] After the magnetic layer formation step, the substrate may be subjected to a heat treatment (annealing treatment) if necessary. In this case, the annealing temperature is preferably 300 to 700°C.

[0070] The present disclosure includes the following embodiments: <1> A magnetic disk, comprising: a substrate having a pair of main surfaces and an outer peripheral end surface; and an L1 ０ and a magnetic layer having a structure, wherein the magnetic disk has a straightness of 90 μm or less when heated under the following heating conditions and then measured under the following measurement conditions: (Heating conditions) The magnetic disk is heated from room temperature to 600°C in 25 seconds, then heated to 700°C in 35 seconds, and then cooled to room temperature over 120 seconds. (Straightness measurement conditions) The maximum valley depth Sv is measured in three directions 120 degrees apart over a measurement range of at least 88 mm using a surface roughness tester, and the number average of the maximum valley depth Sv is calculated as the straightness value. <2> The magnetic disk according to <1>, wherein the change in straightness before and after heating under the heating conditions is 10 to 80 μm. <3> The magnetic disk according to <1> or <2>, wherein the straightness measured under the measurement conditions after heating under the heating conditions is 80 μm or less. <4> The magnetic disk according to any one of <1> to <3>, wherein the change in straightness before and after heating under the heating conditions is 15 to 70 μm. <5> The magnetic layer is L1 ０ The magnetic disk according to any one of <1> to <4>, having a granular structure including magnetic grains containing an FePt-based alloy and grain boundary portions. <6> The magnetic disk according to any one of <1> to <5>, further comprising a first underlayer containing MgO on the pair of main surfaces and the outer peripheral end face of the substrate. <7> The magnetic disk according to any one of <1> to <6>, further comprising a second underlayer containing a Cr alloy on the pair of main surfaces and the outer peripheral end face of the substrate. <8> The magnetic disk according to any one of <1> to <7>, wherein the substrate is a glass substrate. <9> The substrate is made of SiO ２ 55 to 80 mol%, Al ２ O ３ 5 to 25 mol%, B ２ O ３ 0 to 8 mol%, P ２ O ５0 to 5 mol %, MO is 5 to 25 mol % (MO is at least one selected from MgO, CaO, SrO and BaO, and the content is the total value of the contents of MgO, CaO, SrO and BaO), M ２ O from 0 to 15 mol% (M ２ O is Li ２ O, Na ２ O and K ２ At least one selected from Li, O, ２ O, Na ２ O and K ２0. <10> The magnetic disk according to any one of <1> to <9>, wherein the substrate has a thickness of 0.2 to 0.6 mm. <11> The magnetic disk according to any one of <1> to <10>, wherein the substrate has a Young's modulus of 80 GPa or more. <12> The magnetic disk according to any one of <1> to <11>, wherein the substrate has a glass transition temperature of 700°C or more. <13> A magnetic disk substrate having a pair of main surfaces and an outer peripheral end face, wherein the magnetic disk substrate is heated under the following heating conditions, and then the straightness measured under the following measurement conditions is 90 μm or less. (Heating conditions) The surface temperature of the magnetic disk is heated from room temperature to 600°C in 25 seconds, then heated to 700°C in 35 seconds, and then cooled to room temperature over 120 seconds. (Conditions for measuring straightness) The maximum valley depth Sv is measured in three directions differing by 120 degrees using a surface roughness measuring device over a measurement range of at least 88 mm in length, and the number average of the maximum valley depth Sv is calculated as the straightness value. <14> The magnetic disk substrate according to <13>, wherein the change in straightness before and after heating under the heating conditions is 10 to 80 μm. <15> The magnetic disk substrate according to <13> or <14>, wherein the straightness measured under the measurement conditions after heating the magnetic disk under the heating conditions is 80 μm or less. <16> The magnetic disk substrate according to any one of <13> to <15>, wherein the change in straightness before and after heating under the heating conditions is 15 to 70 μm. <17> The magnetic disk substrate according to any one of <13> to <16>, wherein the substrate is made of glass. <18> The substrate is made of SiO ２ 55 to 80 mol%, Al ２ O ３ 5 to 25 mol%, B ２ O ３ 0 to 8 mol %, MO is 5 to 25 mol % (MO is at least one selected from MgO, CaO, SrO and BaO, and the content is the total value of the contents of MgO, CaO, SrO and BaO), M ２ O from 0 to 15 mol% (M ２ O is Li ２ O, Na２ O and K ２ At least one selected from Li, O, ２ O, Na ２ O and K ２ <19> The magnetic disk substrate according to any one of <13> to <18>, wherein the substrate has a thickness of 0.2 to 0.6 mm. <20> The magnetic disk substrate according to any one of <13> to <19>, wherein the substrate has a Young's modulus of 80 GPa or more. <21> The magnetic disk substrate according to any one of <13> to <20>, wherein the substrate has a glass transition temperature of 700°C or more. <22> The magnetic disk substrate according to any one of <13> to <21>, wherein the magnetic disk substrate is for thermally assisted recording. <23> Use of the magnetic disk substrate according to any one of <13> to <22> for manufacturing a magnetic disk for thermally assisted recording. <24> A method for manufacturing a magnetic disk, comprising: heating a substrate until the substrate surface temperature reaches 600 to 780°C, and then ０A method for manufacturing a magnetic disk, comprising a step of forming a magnetic layer having a structure, the substrate being a magnetic disk substrate having a pair of main surfaces and an outer peripheral end surface, wherein the magnetic disk substrate is heated under the following heating conditions, and then the straightness measured under the following measurement conditions is 90 μm or less. (Heating conditions) The magnetic disk is heated from room temperature to 600°C in 25 seconds, then heated to 700°C in 35 seconds, and then cooled to room temperature over 120 seconds. (Straightness measurement conditions) The maximum valley depth Sv is measured in three directions, each oriented 120 degrees apart, over a measurement range of at least 88 mm in length using a surface roughness tester, and the number average of the maximum valley depth Sv is calculated as the straightness value. <25> The method for manufacturing a magnetic disk according to <24>, wherein the change in straightness before and after heating under the heating conditions is 10 to 80 μm. <26> The method for manufacturing a magnetic disk according to <24> or <25>, wherein the straightness of the magnetic disk measured under the measurement conditions after heating under the heating conditions is 80 μm or less. <27> The method for manufacturing a magnetic disk according to any one of <24> to <26>, wherein the change in straightness before and after heating under the heating conditions is 15 to 70 μm.

[0071] The present embodiment will be described in more detail below with reference to examples, but the present embodiment is not limited to the following examples.

[0072] <Straightness> Straightness was measured using a surface roughness measuring instrument (product name "Surftest-VS2100" manufactured by Mitutoyo Corporation). The measurement was performed within a measurement range on a straight line with a length of 88 mm, as shown by the dotted line in Figure 3. Measurement was performed in three directions, each oriented 120 degrees apart, and the number average of the measured values ​​was taken as the straightness.

[0073] <Heating Test> A magnetic disk (substrate) was placed between two ceramic panel heaters, and the substrate was left in place for 60 seconds before being removed. Four cartridge heaters (500 W) were inserted into one ceramic panel (AIN (aluminum nitride)). Two panels were prepared, and the heater panel surfaces were spaced 18 mm apart. A thermocouple (Cerathermo thermocouple, type K, wire diameter φ0.1) was placed on the magnetic disk surface to adjust the panel temperature so that the disk surface reached a predetermined temperature. Non-contact heating was performed in the atmosphere. The magnetic disk was heated to 700°C in 60 seconds, as shown in the graph below, and then removed. As shown in Figure 4, the magnetic disk surface temperature was heated from room temperature to 600°C in 25 seconds, and then heated to 700°C in 35 seconds. The disk was then cooled to room temperature over 120 seconds.

[0074] <Young's Modulus> The Young's modulus E of the substrate was measured based on JIS R1602: 1995. A test piece for measurement was cut out from the magnetic disk 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, and measurement was performed at room temperature.

[0075] <Glass Transition Temperature> Using a thermomechanical analyzer, a graph was created from the amount of change in probe position due to thermal expansion caused by a temperature rise, and the glass transition temperature was read from the change in the slope of the graph.

[0076] <Thermal expansion coefficient at 100 to 300°C> The thermal expansion coefficient of the substrate was determined by measuring a sample cut out from the magnetic disk to have dimensions of 50 mm in length and 10 mm in width, and measuring the amount of change in length in a predetermined temperature range using a thermal dilatometer based on laser interferometry, and this was taken as the average linear expansion coefficient at 100 to 300°C.

[0077] <Specific Gravity> The specific gravity was measured by the Archimedes method.

[0078] <Specific Elastic Modulus E / d> Calculated by dividing Young's modulus by specific gravity.

[0079] (Examples and Comparative Examples) In the examples and comparative examples, the following magnetic disk substrates were prepared with the compositions shown in Table 1, and a heating test was conducted, and the straightness was measured before and after the heating test. The formation of other layers such as a magnetic layer has little effect on the straightness of the magnetic disk substrate after heating, and the straightness of the magnetic disk substrate is directly reflected in the straightness of the magnetic disk. Magnetic disk substrate: diameter 97 mm, inner diameter 25 mm, plate thickness 0.5 mm or 0.43 mm

[0080]

[0081] Thickness t: Thickness of glass substrate (mm) Straightness before heating C1: Straightness before heating (μm) Straightness after heating C2: Straightness after heating (μm) Change in straightness before and after heating dC: Change in straightness C2-C1 (μm) (Magnetic disk substrate) SU-1: Glass substrate (glass transition temperature is 752°C, thermal expansion coefficient at 100 to 300°C is 43 (10 ―７ / K), Young's modulus 90 (GPa), specific elastic modulus 36.1 (10 ６ m ２ / s ２ A glass substrate having a thickness of 0.43 mm was obtained using an alkali-containing glass containing B. The product of the straightness C2 (μm) of the glass substrate after heating and the thickness (mm) of the substrate was 16.3 (μm mm). ２ O ３ The content of MgO and CaO is 0 mol%, and the total content of MgO and CaO is 18.5 mol%, Li ２ The content of O is 1.0 mol%, Na ２ SU-2: Glass substrate (glass transition temperature of 737°C, thermal expansion coefficient of 43 (10 ―７ / K), Young's modulus 93 (GPa), specific elastic modulus 36.8 (10 ６ m ２ / s ２ A glass substrate having a thickness of 0.43 mm was obtained using an alkali-containing glass containing B. The product of the straightness C2 (μm) of the glass substrate after heating and the thickness (mm) of the substrate was 25.4 (μm mm).２ O ３ The content of MgO and CaO is 0.3 mol%, and the total content of MgO and CaO is 16.5 mol%, Li ２ The O content is 0.8 mol%, Na ２ SU-3: Glass substrate (glass transition temperature: 810°C, thermal expansion coefficient at 100 to 300°C: 39 (10 ―７ / K), Young's modulus 83 (GPa), specific elastic modulus 31.4 (10 ６ m ２ / s ２ A glass substrate having a thickness of 0.50 mm was obtained using alkali-free glass formed by down-drawing. The product of the straightness C2 (μm) of the glass substrate after heating and the thickness (mm) of the substrate was 29.5 (μm mm). In addition, in the alkali-free glass used, B ２ O ３ The content of MgO and CaO is 0.8 mol%, and the total content of MgO and CaO is 11.0 mol%, Li ２ O and Na ２ SU-4: Glass substrate (glass transition temperature of 805°C, thermal expansion coefficient of 34 (10 ―７ / K), Young's modulus 83 (GPa), specific elastic modulus 31.5 (10 ６ m ２ / s ２ ) A glass substrate having a thickness of 0.50 mm was obtained using alkali-free glass formed by down-draw. The product of the straightness C2 (μm) of the glass substrate after heating and the thickness (mm) of the substrate was 34.5 (μm mm). SU-5: Glass substrate (glass transition temperature of 710°C, thermal expansion coefficient of 45 (10 ―７ / K), Young's modulus 98 (GPa), specific elastic modulus 38.2 (10 ６ m ２ / s ２) was used to obtain a glass substrate having a thickness of 0.50 mm. The product of the straightness C2 (μm) of the glass substrate after heating and the thickness (mm) of the substrate was 35.0 (μm mm). SU-6: Glass substrate (glass transition temperature of 727°C, thermal expansion coefficient of 45 (10 ―７ / K), Young's modulus 96 (GPa), specific elastic modulus 37.9 (10 ６ m ２ / s ２ A glass substrate having a thickness of 0.43 mm was obtained using an alkali-containing glass containing B. The product of the straightness C2 (μm) of the glass substrate after heating and the thickness (mm) of the substrate was 33.5 (μm mm). ２ O ３ The content of MgO and CaO is 1.5 mol%, and the total content of MgO and CaO is 21.5 mol%, Li ２ The content of O is 0.5 mol%, Na ２ SU-7: Glass substrate (glass transition temperature of 810°C, thermal expansion coefficient of 39 (10 ―７ / K), Young's modulus 83 (GPa), specific elastic modulus 31.4 (10 ６ m ２ / s ２ A glass substrate having a thickness of 0.43 mm was obtained using alkali-free glass formed by down-drawing. The product of the straightness C2 (μm) of the glass substrate after heating and the thickness (mm) of the substrate was 35.7 (μm mm). SU-8: Glass substrate (glass transition temperature of 805°C, thermal expansion coefficient of 34 (10 ―７ / K), Young's modulus 83 (GPa), specific elastic modulus 31.5 (10 ６ m ２ / s ２ ) was down-drawn to obtain a glass substrate having a thickness of 0.43 mm. The product of the straightness C2 (μm) of the glass substrate after heating and the thickness (mm) of the substrate was 37.4 (μm mm). SU-9: Glass substrate (glass transition temperature of 782°C, thermal expansion coefficient of 35 (10 ―７ / K), Young's modulus 85 (GPa), specific elastic modulus 32.8 (10 ６ m ２ / s ２ ) A glass substrate having a thickness of 0.50 mm was obtained using alkali-free glass formed by the float method. The product of the straightness C2 (μm) of the glass substrate after heating and the thickness (mm) of the substrate was 42.5 (μm mm). SU-10: Glass substrate (glass transition temperature of 710°C, thermal expansion coefficient of 45 (10 ―７ / K), Young's modulus 98 (GPa), specific elastic modulus 38.2 (10 ６ m ２ / s ２ ) was used to obtain a glass substrate having a thickness of 0.43 mm. The product of the straightness C2 (μm) of the glass substrate after heating and the thickness (mm) of the substrate was 44.3 (μm mm). SU-11: Glass substrate (glass transition temperature of 782°C, thermal expansion coefficient of 35 (10 ―７ / K), Young's modulus 85 (GPa), specific elastic modulus 32.8 (10 ６ m ２ / s ２ ) A glass substrate having a thickness of 0.43 mm was obtained using alkali-free glass formed by the float method. The product of the straightness C2 (μm) of the glass substrate after heating and the thickness (mm) of the substrate was 51.2 (μm mm). SU-12: Glass substrate (glass transition temperature of 780°C, thermal expansion coefficient of 36 (10 ―７ / K), Young's modulus 84 (GPa), specific elastic modulus 33.1 (10 ６ m ２ / s ２ ) A glass substrate having a thickness of 0.50 mm was obtained using alkali-free glass formed by down-draw. The product of the straightness C2 (μm) of the glass substrate after heating and the thickness (mm) of the substrate was 58.0 (μm mm). SU-13: Glass substrate (glass transition temperature of 780°C, thermal expansion coefficient of 36 (10 ―７ / K), Young's modulus 84 (GPa), specific elastic modulus 33.1 (10 ６ m ２ / s ２) was down-drawn to obtain a glass substrate having a thickness of 0.43 mm. The product of the straightness C2 (μm) of the glass substrate after heating and the thickness (mm) of the substrate was 56.3 (μm mm). SU-14: Glass substrate (glass transition temperature of 691°C, thermal expansion coefficient of 51 (10 ―７ / K), Young's modulus 95 (GPa), specific elastic modulus 36.6 (10 ６ m ２ / s ２ ) was used to obtain a glass substrate having a thickness of 0.50 mm. The product of the straightness C2 (μm) of the glass substrate after heating and the thickness (mm) of the substrate was 138.0 (μm mm). SU-15: Glass substrate (glass transition temperature of 691°C, thermal expansion coefficient of 51 (10 ―７ / K), Young's modulus 95 (GPa), specific elastic modulus 36.6 (10 ６ m ２ / s ２ ) was used to obtain a glass substrate having a thickness of 0.43 mm. The product of the straightness C2 (μm) of the glass substrate after heating and the thickness (mm) of the substrate was 164.7 (μm mm).

[0082] dC x t ２ In magnetic disk substrates with a value of 14 (μm·mm·mm) or less, deformation tends to be less likely to occur even when the plate thickness is reduced.

[0083] The value of C2×t is preferably 34.0 (μm mm) or less. As the substrate thickness decreases, the change in straightness dC before and after heating tends to increase, but in a substrate with a C2×t value of 34.0 (μm mm) or less, the change in straightness dC before and after heating can be made sufficiently small even if the thickness is 0.43 mm or less.

[0084] In addition, the magnetic disk substrates in each example were made of SiO ２ 55 to 80 mol%, Al ２ O ３ 5 to 25 mol%, B ２ O ３ 0 to 8 mol%, P ２ O ５0 to 5 mol % of MO, 5 to 25 mol % of MO (MO is at least one selected from MgO, CaO, SrO and BaO, and the content thereof is the total value of the contents of MgO, CaO, SrO and BaO), and 0 to 15 mol % of M ２ O (M ２ O is Li ２ O, Na ２ O and K ２ At least one selected from Li, O, ２ O, Na ２ O and K ２ The total value of the hydroxybenzoates was 0.

[0085] Furthermore, the magnetic disk substrates of Examples 1, 2, 3, and 6 contain 0 to 15 mol % of M ２ Furthermore, in these magnetic disk substrates, B ２ O ３ The content of B was 0 to 1.5 mol % and the total content of MgO and CaO was 5.0 to 25.0 mol %. ２ O ３ Since the content of is low, the change in straightness dC after heating can be reduced even if the plate thickness is small, which is preferable.

Claims

1. A magnetic disk comprising: a substrate having a pair of main surfaces and an outer peripheral end surface; and an L1 on the pair of main surfaces and the outer peripheral end surface of the substrate. ０ and a magnetic layer having a structure, wherein the magnetic disk has a straightness of 90 μm or less when heated under the following heating conditions and then measured under the following measurement conditions: (Heating conditions) The surface temperature of the magnetic disk is heated from room temperature to 600° C. in 25 seconds, then heated to 700° C. in 35 seconds, and then cooled to room temperature over 120 seconds. (Straightness measurement conditions) The maximum valley depth Sv is measured in three directions, each oriented 120 degrees apart, over a measurement range of at least 88 mm in length using a surface roughness tester, and the number average of the maximum valley depth Sv is calculated as the straightness value.

2. The magnetic disk according to claim 1, wherein the change in straightness before and after heating under said heating conditions is 10 to 80 μm.

3. The magnetic disk according to claim 1, wherein the straightness measured under the measuring conditions after heating the magnetic disk under the heating conditions is 80 μm or less.

4. The magnetic disk according to claim 3, wherein the change in straightness before and after heating under said heating conditions is 15 to 70 μm.

5. The magnetic layer is L1 ０ 2. The magnetic disk according to claim 1, having a granular structure including magnetic grains and grain boundaries containing an FePt-based alloy.

6. The magnetic disk according to claim 5, further comprising a first underlayer containing MgO on the pair of main surfaces and the outer peripheral end surface of the substrate.

7. The magnetic disk according to claim 6, further comprising a second underlayer containing a Cr alloy on the pair of main surfaces and the outer peripheral end surface of the substrate.

8. The magnetic disk according to claim 1, wherein the substrate is a glass substrate.

9. The substrate is made of SiO ２ 55 to 80 mol%, Al ２ O ３ 5 to 25 mol%, B ２ O ３ 0 to 8 mol%, P ２ O ５ 0 to 5 mol %, MO is 5 to 25 mol % (MO is at least one selected from MgO, CaO, SrO and BaO, and the content is the total value of the contents of MgO, CaO, SrO and BaO), M ２ O from 0 to 15 mol% (M ２ O is Li ２ O, Na ２ O and K ２ At least one selected from Li, O, ２ O, Na ２ O and K ２ 9. The magnetic disk according to claim 8, wherein the total value of the SiO 2 and the SiO 2 is O.

10. The magnetic disk according to claim 1, wherein the substrate has a thickness of 0.2 to 0.6 mm.

11. The magnetic disk according to claim 1, wherein the substrate has a Young's modulus of 80 GPa or greater.

12. The magnetic disk according to claim 1, wherein the substrate has a glass transition temperature of 700° C. or higher.

13. A magnetic disk substrate having a pair of main surfaces and an outer peripheral end surface, wherein the magnetic disk substrate is heated under the following heating conditions, and then the straightness measured under the following measurement conditions is 90 μm or less: (Heating conditions) The surface temperature of the magnetic disk is heated from room temperature to 600°C in 25 seconds, then heated to 700°C in 35 seconds, and then cooled to room temperature over 120 seconds. (Straightness measurement conditions) The maximum valley depth Sv is measured in three directions oriented 120 degrees apart using a surface roughness measuring device over a measurement range of at least 88 mm in length, and the number average of the maximum valley depth Sv is calculated as the straightness value.

14. The magnetic disk substrate according to claim 13, wherein the change in straightness before and after heating under said heating conditions is 10 to 80 μm.

15. The magnetic disk substrate according to claim 13, wherein the straightness measured under the measurement conditions after heating the magnetic disk under the heating conditions is 80 μm or less.

16. The magnetic disk substrate according to claim 15, wherein the change in straightness before and after heating under said heating conditions is 15 to 70 μm.

17. The magnetic disk substrate according to claim 13, wherein the substrate is made of glass.

18. The substrate is made of SiO ２ 55 to 80 mol%, Al ２ O ３ 5 to 25 mol%, B ２ O ３ 0 to 8 mol %, MO is 5 to 25 mol % (MO is at least one selected from MgO, CaO, SrO and BaO, and the content is the total value of the contents of MgO, CaO, SrO and BaO), M ２ O from 0 to 15 mol% (M ２ O is Li ２ O, Na ２ O and K ２ At least one selected from Li, O, ２ O, Na ２ O and K ２ 18. The magnetic disk substrate according to claim 17, wherein the total value of the total of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 19. The magnetic disk substrate according to claim 13, wherein the substrate has a thickness of 0.2 to 0.6 mm.

20. The magnetic disk substrate according to claim 13, wherein the substrate has a Young's modulus of 80 GPa or greater.

21. The magnetic disk substrate according to claim 13, wherein the substrate has a glass transition temperature of 700° C. or higher.

22. The magnetic disk substrate according to claim 13, which is for thermally assisted recording.

23. Use of a magnetic disk substrate according to any one of claims 13 to 22 for manufacturing a magnetic disk for thermally assisted recording.

24. A method for manufacturing a magnetic disk, comprising: heating a substrate until the substrate surface temperature reaches 600 to 780°C; ０ A method for manufacturing a magnetic disk, comprising a step of forming a magnetic layer having a structure, the substrate being a magnetic disk substrate having a pair of main surfaces and an outer peripheral end surface, the magnetic disk substrate being heated under the following heating conditions, and then having a straightness of 90 μm or less measured under the following measurement conditions: (Heating conditions) The surface temperature of the magnetic disk is heated from room temperature to 600° C. in 25 seconds, then heated to 700° C. in 35 seconds, and then cooled to room temperature over 120 seconds; (Straightness measurement conditions) The maximum valley depth Sv is measured in three directions, each oriented 120 degrees apart, over a measurement range of at least 88 mm in length using a surface roughness tester, and the number average of the maximum valley depth Sv is calculated as the straightness value.

25. The method for manufacturing a magnetic disk according to claim 24, wherein the change in straightness before and after heating under said heating conditions is 10 to 80 μm.

26. The method for manufacturing a magnetic disk according to claim 24, wherein the straightness of the magnetic disk measured under the measuring conditions after heating under the heating conditions is 80 μm or less.

27. The method for manufacturing a magnetic disk according to claim 26, wherein the change in straightness before and after heating under the heating conditions is 15 to 70 μm.

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