Magnetic recording medium substrate, magnetic recording medium, and magnetic storage device

Abstract

The present invention is directed to providing a magnetic recording medium substrate having high heat resistance. The magnetic recording medium substrate includes an aluminum alloy substrate and a nickel alloy film disposed on at least one main surface of the aluminum alloy substrate, wherein the nickel alloy film comprises 0.5 wt% to 3 wt% Mo, 11 wt% to 15 wt% P, and 0.0001 wt% to 0.001 wt% Fe.

Description

Technical Field

[0001] The present invention relates to a magnetic recording medium substrate, a magnetic recording medium, and a magnetic storage device. Background Art

[0002] As substrates for magnetic recording media (magnetic recording medium substrates), aluminum substrates, glass substrates, etc. are widely used. Among them, when an aluminum substrate is used as a magnetic recording medium substrate, a non-magnetic film such as a NiP alloy film is formed on the surface of the aluminum substrate in order to improve the surface hardness and rigidity of the magnetic recording medium substrate.

[0003] As a substrate for a magnetic recording medium having a non-magnetic film formed on an aluminum substrate, there is disclosed, for example, a substrate for a magnetic recording medium having an amorphous Ni-P-Mo alloy film having a composition of 85.2 to 89.1 weight % nickel, 10.7 to 13 weight % phosphorus, and 0.2 to 1.8 weight % molybdenum formed on a non-magnetic base (for example, refer to patent document 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 2848103 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] Here, with the recent miniaturization, thinning, and high recording density of magnetic recording media, as the next generation magnetic recording media capable of increasing storage capacity, 1Tbit / inch 2 Auxiliary magnetic recording media with high-level areal recording density are attracting attention. These auxiliary magnetic recording media have a magnetic layer formed on the surface of a magnetic recording medium substrate, made of an alloy with an L10 crystal structure, such as an FePt alloy or a CoPt alloy. Forming the magnetic layer on the surface of the magnetic recording medium substrate requires heating the substrate to a temperature exceeding 300°C.

[0009] However, in the technology of Patent Document 1, when the Ni-P-Mo alloy film is heated at a temperature higher than 300°C, it can be said that the composition of the Ni-P-Mo alloy film is easily changed and the heat resistance is insufficient. Therefore, there is a high possibility that the number of slight expansions generated on the surface of the Ni-P-Mo alloy film increases, the surface ripples increase, or the surface smoothness of the Ni-P-Mo alloy film decreases. If the surface smoothness of the magnetic recording medium substrate is low, there is a problem that the magnetic head and the magnetic recording medium become easily in contact when the magnetic storage device is used.

[0010] One aspect of the present invention has been made in view of such circumstances, and an object of the present invention is to provide a magnetic recording medium substrate having high heat resistance.

[0011] Methods for solving problems

[0012] A magnetic recording medium substrate according to one embodiment of the present invention comprises an aluminum alloy substrate and a nickel alloy film provided on at least one main surface of the aluminum alloy substrate, wherein the nickel alloy film contains 0.5 wt% to 3 wt% Mo, 11 wt% to 15 wt% P, and 0.0001 wt% to 0.001 wt% Fe.

[0013] Effects of the Invention

[0014] According to one aspect of the present invention, a magnetic recording medium substrate having high heat resistance can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a perspective view showing an example of a magnetic recording medium substrate according to an embodiment of the present invention.

[0016] Figure 2 It is a partial cross-sectional view showing an example of a magnetic recording medium substrate.

[0017] Figure 3 This is a perspective view showing an example of a grinding disc that can be used in the grinding process.

[0018] Figure 4 It is a schematic cross-sectional view showing an example of an auxiliary magnetic recording medium according to an embodiment of the present invention.

[0019] Figure 5 It is a perspective view showing an example of a magnetic storage device according to an embodiment of the present invention.

[0020] Figure 6 To express Figure 5 Schematic diagram of an example of a magnetic head.

[0021] Figure 7 This is a graph showing the measurement of swelling with a height of 1 nm or more that occurs on the substrate surface. DETAILED DESCRIPTION

[0022] The following describes the embodiments of the present invention in detail. To facilitate understanding of the description, identical components are denoted by the same reference numerals in the accompanying drawings, and duplicate descriptions are omitted. Furthermore, the proportions of the components in the accompanying drawings may differ from the actual values. In this specification, a wavy line "to" indicating a numerical range includes the preceding and following numerical values ​​as lower and upper limits unless otherwise specified.

[0023] <Magnetic Recording Medium Substrates>

[0024] A magnetic recording medium substrate according to an embodiment of the present invention will be described. Figure 1 1 is a perspective view showing an example of a magnetic recording medium substrate according to the present embodiment. Figure 2 FIG. 1 is a partial cross-sectional view showing an example of a substrate for a magnetic recording medium. Figure 1 and Figure 2 As shown, the magnetic recording medium substrate 1 according to this embodiment includes an aluminum alloy substrate for magnetic recording medium (hereinafter referred to as "aluminum alloy substrate") 11 and a nickel alloy film 12 formed on the surface of the aluminum alloy substrate 11. The magnetic recording medium substrate 1 is formed in a circular plate shape and has an opening in its center portion when viewed from above.

[0025] [Aluminum alloy substrate]

[0026] The aluminum alloy substrate 11 contains additive elements including Mg and Cr, and the remainder of Al, and may contain unavoidable impurities.

[0027] Mg improves the mechanical strength of the aluminum alloy substrate 11. The Mg content is preferably 2 to 7 wt%, more preferably 3.5 to 5.0 wt%. Within this preferred range, the Mg content strengthens the material at high temperatures, facilitating hot extrusion and other processing. Furthermore, since the decrease in ductility and toughness is suppressed, extrusion processing can be performed reliably.

[0028] Cr improves strength at high temperatures and facilitates extrusion processing. The Cr content is preferably 0.02wt% to 0.3wt%, more preferably 0.05wt% to 0.25wt%. If the Cr content is within this preferred range, the high-temperature strength effect can be achieved and extrusion processing is facilitated.

[0029] The aluminum alloy substrate 11 may contain, as additional elements, at least one selected from the group consisting of Zn, Mn, Ti, Cr, V, Zr, Mo, and Co, in addition to Mg and Cr. The aluminum alloy substrate 11 may contain 0.01 wt% to 0.5 wt% of Zn, and may further contain 0.01 wt% to 0.5 wt% of at least one of Mn, Ti, Cr, V, Zr, Mo, and Co in addition to Zn.

[0030] Inevitable impurities are impurities that are inevitably mixed in from raw materials and manufacturing processes, and examples include B, P, etc. In this embodiment, for example, as inevitable impurities, when B and P are included, B may be included in an amount of less than 0.01 wt%, and P may be included in an amount of less than 0.1 wt%.

[0031] The aluminum alloy substrate 11 is formed in a disk shape and has an opening at its center in a plan view.

[0032] The aluminum alloy substrate 11 is preferably capable of being housed in a standardized magnetic storage device (hard disk drive), etc. Therefore, the diameter, opening, and thickness of the aluminum alloy substrate are appropriately and arbitrarily selected according to the size of the magnetic storage device, etc.

[0033] The diameter of the aluminum alloy substrate 11 is preferably, for example, 53 mm to 97 mm. The aluminum alloy substrate 11 is used for a magnetic recording medium of a magnetic storage device. The magnetic recording medium needs to be able to be accommodated in a standardized magnetic storage device, that is, a 2.5-inch magnetic storage device, a 3.5-inch magnetic storage device, etc. For example, in a 2.5-inch magnetic storage device, a magnetic recording medium with a maximum diameter of approximately 67 mm is used, and in a 3.5-inch magnetic storage device, a magnetic recording medium with a maximum diameter of approximately 97 mm is used. Therefore, if the diameter of the aluminum alloy substrate 11 is 53 mm to 97 mm, it can be accommodated in any standardized magnetic storage device.

[0034] The inner diameter of the opening of the aluminum alloy substrate 11 is preferably 19 mm to 26 mm. The opening of the magnetic recording medium substrate 1 is where the drive shaft of the magnetic storage device is inserted. If the inner diameter of the opening of the magnetic recording medium substrate 1 is 19 mm to 26 mm, the drive shaft of any standardized magnetic storage device can be inserted.

[0035] The thickness of the aluminum alloy substrate 11 is preferably 0.2 mm to 0.9 mm. In a magnetic storage device, in order to increase the recording capacity, it is effective to increase the number of magnetic recording media housed in the housing. For example, in a conventional 3.5-inch magnetic storage device, a maximum of 5 magnetic recording media with a thickness of 1.27 mm can be housed. However, if 6 or more magnetic recording media can be housed, the recording capacity can be increased. Therefore, if the thickness of the aluminum alloy substrate 11 is 0.2 mm to 0.9 mm, multiple magnetic recording media can be housed in the housing of the magnetic storage device.

[0036] (Method for Manufacturing Aluminum Alloy Substrate)

[0037] The aluminum alloy substrate 11 can be manufactured using a known method. For example, the aluminum alloy substrate 11 can be manufactured by a method comprising the following steps: a casting step of producing an aluminum alloy ingot, a rolling step of rolling the aluminum alloy ingot into a plate shape to obtain an aluminum alloy plate, and a processing step of forming the aluminum alloy plate into the aluminum alloy substrate 11.

[0038] In the casting process, the aluminum alloy material with adjusted composition is heated and melted to cast the aluminum alloy, thereby producing an aluminum alloy ingot.

[0039] As a method for casting aluminum alloys, for example, known methods used for casting aluminum alloy ingots, such as direct chill casting (DC casting) and continuous casting (CC), can be used. DC casting is a method of casting aluminum alloy ingots by pouring molten aluminum alloy into a mold and then directly contacting the mold with cooling water. CC casting is a method of continuously pouring molten aluminum alloy into a mold and rapidly cooling it within the mold.

[0040] In the rolling process, the aluminum alloy ingot obtained in the above-mentioned casting process is rolled into a plate shape to obtain an aluminum alloy plate.

[0041] The rolling method is not particularly limited, and hot rolling and cold rolling can be used. The rolling conditions are not particularly limited, and conventional conditions for rolling aluminum alloy ingots can be employed.

[0042] In the processing step, the aluminum alloy plate material obtained in the rolling step is processed and formed into the aluminum alloy substrate 11 .

[0043] First, the aluminum alloy sheet obtained in the rolling process is punched into a disc shape to obtain an aluminum alloy disc. Next, the aluminum alloy disc is heated at 300°C to 500°C for 0.5 to 5 hours for annealing. Annealing relaxes the inherent strain in the aluminum alloy disc, allowing the rigidity of the resulting aluminum alloy substrate to be adjusted to an appropriate range.

[0044] Then, the surface and end surface of the annealed aluminum alloy disk are cut using a cutting tool, thereby obtaining a disk-shaped aluminum alloy substrate 11 having a predetermined size and an opening at the center.

[0045] As the cutting tool, for example, a diamond cutter can be used.

[0046] In addition, in the processing step, annealing can be performed after cutting.

[0047] [Nickel alloy coating]

[0048] As described above, the nickel alloy film 12 is formed on the surface of the aluminum alloy substrate 11. That is, the nickel alloy film 12 is formed on both main surfaces (the upper surface and the lower surface) and the end surfaces of the aluminum alloy substrate 11. Alternatively, the nickel alloy film 12 may be formed on only one main surface.

[0049] The nickel alloy film 12 has the function of increasing the hardness of the surface of the magnetic recording medium substrate 1 , thereby increasing the strength of the magnetic recording medium substrate 1 , and also flattening the surface of the magnetic recording medium substrate 1 .

[0050] The nickel alloy film 12 is a NiMoP alloy plating film containing Mo, P, and Fe as additives, with the remainder being Ni. Forming the nickel alloy film 12 from the NiMoP alloy plating film can improve the hardness and flatness of the surface of the magnetic recording medium substrate 1.

[0051] The nickel alloy film 12 may contain one or more of Cr, Zn, Ba, Pb, etc. in addition to Mo, P, and Fe as additive elements. These additive elements may be contained in an amount of less than 0.001 wt%.

[0052] The nickel alloy film 12 may contain inevitable impurities in addition to the added components and the remainder of Ni.

[0053] The Mo content is 0.5 wt% to 3 wt%, more preferably 0.5 wt% to 1.5 wt%. If the Mo content is less than 0.5 wt%, the heat resistance of the nickel alloy film 12 decreases. On the other hand, if the Mo content exceeds 3 wt%, the amorphization of the nickel alloy film 12 is hindered. If the Mo content is 0.5 wt% to 3 wt%, the heat resistance of the nickel alloy film 12 can be improved and the amorphization of the nickel alloy film 12 can be promoted.

[0054] The P content is 11 wt% to 15 wt%, more preferably 12 wt% to 13 wt%. If the P content is less than 11 wt%, the amorphization of the nickel alloy film 12 is hindered. On the other hand, if the P content exceeds 15 wt%, the heat resistance of the nickel alloy film 12 is reduced. If the P content is 11 wt% to 15 wt%, the amorphization of the nickel alloy film 12 is promoted while improving the heat resistance.

[0055] The Fe content is 0.0001wt% to 0.001wt%, more preferably 0.0002wt% to 0.0005wt%. When the Fe content is less than 0.0001wt%, the heat resistance of the nickel alloy film 12 cannot be improved. On the other hand, if the Fe content exceeds 0.001wt%, the crystallization of the nickel alloy film 12 proceeds excessively, the tiny expansion generated on the substrate surface becomes larger, and it becomes easy to form a large number of expansions with a height of more than 1nm. If the Fe content is 0.0001wt% to 0.001wt%, the heat resistance of the nickel alloy film 12 can be further improved. The inventors believe that the reason is as follows. That is, the Mo in the nickel alloy film 12 is mainly combined with Fe through the combination with oxygen. Therefore, when the magnetic layer of the magnetic recording medium is formed on the surface of the magnetic recording medium substrate 1, even if it is heated at a temperature exceeding 300°C, the diffusion of Mo into the nickel alloy film 12 can be suppressed. Thus, the crystallization of the NiMoP alloy constituting the nickel alloy film 12 can be suppressed, thereby reducing the magnetization of the NiMoP alloy accompanying heating and suppressing the increase in the saturation magnetic flux density of the nickel alloy film 12. In addition, if the NiMoP alloy constituting the nickel alloy film 12 is crystallized, the surface of the nickel alloy film 12 will undergo slight expansion, and the slight surface ripples (tiny surface ripples) will tend to become larger. The magnetic recording medium substrate 1 of this embodiment can suppress the crystallization of the NiMoP alloy constituting the nickel alloy film 12, thereby reducing the slight expansion on the surface of the nickel alloy film 12 and suppressing the slight surface ripples to be small. In addition, the slight surface ripples can be measured by a well-known measuring device such as an atomic force microscope (AFM).

[0056] In this embodiment, after heating the magnetic recording medium substrate 1 at 320°C for 20 minutes, the surface of the nickel alloy film 12 is preferably expanded by 1 nm or more, with a height of less than 0.060 cells / cm 2 , more preferably 0.050 pieces / cm 2 The heating may be performed in a vacuum or in a non-vacuum environment.

[0057] The thickness of the nickel alloy film 12 is preferably 5 μm to 20 μm, more preferably 10 μm to 17 μm. By setting the thickness of the nickel alloy film within the above preferred range, the hardness of the nickel alloy film 12 can be increased, thereby improving the strength of the magnetic recording medium substrate 1. Furthermore, since the surface irregularities of the aluminum alloy substrate 11 can be absorbed, the surface of the nickel alloy film 12 is smoothed, thereby suppressing chatter vibration. Furthermore, the magnetic recording medium substrate 1 can be made lighter.

[0058] [Method for manufacturing a magnetic recording medium substrate]

[0059] The manufacturing method of the magnetic recording medium substrate 1 involved in this embodiment is described. The manufacturing method of the magnetic recording medium substrate 1 involved in this embodiment includes: a film forming step of forming a nickel alloy film 12 on an aluminum alloy substrate 11 by a plating method, and a grinding step of grinding the surface of the aluminum alloy substrate with the nickel alloy film.

[0060] (Film Forming Step)

[0061] A nickel alloy film 12 is formed on the surface of the aluminum alloy substrate 11 by plating.

[0062] As the plating method, a known plating method can be used, and an electroless plating method is preferably used.

[0063] First, a Mo salt is added to a NiP plating solution to prepare a NiMoP plating solution.

[0064] As the NiP plating solution, for example, a plating solution containing nickel sulfate as a nickel source and hypophosphite as a phosphorus source can be used.

[0065] As the Mo salt, sodium molybdate, potassium molybdate, ammonium molybdate, or the like can be used.

[0066] Next, an Fe salt is added to the NiMoP plating solution to prepare a plating solution for forming a NiMoP-based alloy plating film.

[0067] As the Fe salt, ferric acetate, ferric sulfate, ammonium ferric sulfate, or the like can be used.

[0068] The thickness of the nickel alloy film 12 can be adjusted by plating conditions such as the pH and temperature of the NiMoP alloy plating solution and the immersion time (plating time) of the aluminum alloy substrate 11 in the NiMoP alloy plating solution.

[0069] The pH of the plating solution for forming a NiMoP alloy plating film is preferably 5.0 to 8.6. When the pH is 5.0 to 8.6, the nickel alloy film 12 containing Mo, P, and Fe in an amorphous state within Ni can be stably formed.

[0070] The temperature of the plating solution for forming the NiMoP-based alloy plating film is preferably 70° C. to 100° C., more preferably 85° C. to 95° C. When the temperature is 70° C. to 100° C., it is possible to suppress variations in the growth of the nickel alloy film 12 , and stably form the nickel alloy film 12 with suppressed thickness variations.

[0071] The plating time is preferably 90 minutes to 150 minutes. If the plating time is 90 minutes to 150 minutes, the nickel alloy film 12 can be sufficiently grown to a thickness within the range of 5 μm to 20 μm.

[0072] The aluminum alloy substrate with the nickel alloy plated film is preferably subjected to a heat treatment. This can further increase the hardness of the nickel alloy film 12 and further improve the rigidity (Young's modulus) of the magnetic recording medium substrate 1. The heating temperature is preferably 300°C or higher.

[0073] (Grinding process)

[0074] The surface of the aluminum alloy substrate on which the nickel alloy plating film is formed, obtained by the plating process, is ground. In order to achieve both smooth and less damaged surface quality and improved productivity, the grinding process preferably adopts a multi-stage grinding method having two or more grinding steps using multiple independent grinding discs. For example, the following steps are performed: a rough grinding step in which a first grinding disc is used to grind while supplying a grinding liquid containing aluminum oxide abrasive grains; and a finishing grinding step in which a second grinding disc is used to grind while supplying a grinding liquid containing colloidal silica abrasive grains after washing the ground aluminum alloy substrate.

[0075] Figure 3 : is a perspective view showing an example of a grinding disc that can be used in a grinding process. Figure 3 As shown, the first grinding wheel 30A (the second grinding wheel 30B) includes a pair of upper and lower fixed plates 31 and 32. A plurality of aluminum alloy substrates 1A having nickel alloy plated films are sandwiched between the pair of fixed plates 31 and 32. The pair of fixed plates 31 and 32 are rotated in opposite directions in the axial direction, so that both surfaces of the aluminum alloy substrates 1A having nickel alloy plated films can be ground by the grinding pads 33 provided on the pair of fixed plates 31 and 32.

[0076] By grinding the surface of the aluminum alloy substrate 1A on which the nickel alloy plating film is formed, Figure 1 and Figure 2 As shown, the magnetic recording medium substrate 1 according to this embodiment is obtained.

[0077] Thus, the magnetic recording medium substrate 1 includes an aluminum alloy substrate 11 and a nickel alloy film 12, wherein the nickel alloy film 12 contains 0.5wt% to 3wt% of Mo, 11wt% to 15wt% of P, and 0.0001wt% to 0.001wt% of Fe. By containing 0.0001wt% to 0.001wt% of Fe, the diffusion of Mo contained in the nickel alloy film 12 can be suppressed even when the magnetic recording medium substrate 1 is heated at a temperature exceeding 300°C, thereby suppressing the crystallization of the nickel alloy film 12 and reducing the magnetization of the nickel alloy film 12 accompanying heating. As a result, the magnetic recording medium substrate 1 can reduce the saturation magnetic flux density to, for example, less than 0.500 gauss. In addition, the saturation magnetic flux density can be measured using a known measuring device such as a vibrating sample magnetometer (VSM).

[0078] Furthermore, by heating the magnetic recording medium substrate 1 at a temperature exceeding 300°C, the height of minute surface ripples generated on the surface of the magnetic recording medium substrate 1 can be reduced, and the number of expansions can be reduced. When the magnetic recording medium substrate 1 is used in a magnetic recording medium, in order to achieve a high recording density of the magnetic recording medium, it is necessary to make the flying height relative to the magnetic recording medium of the magnetic head very small when used in a magnetic storage device. Therefore, it is important to improve the smoothness of the surface of the magnetic recording medium substrate 1. The magnetic recording medium substrate 1 can reduce the height of minute surface ripples generated on the surface and reduce the number of expansions, thereby improving the recording density of the magnetic recording medium.

[0079] Therefore, even when heated at temperatures exceeding 300°C, the magnetic recording medium substrate 1 can reduce magnetization, reduce the height of minute surface ripples, and reduce the density of expansion, thereby achieving high heat resistance. Furthermore, the density of expansion can be determined using known methods, for example, by analyzing images obtained using an AFM.

[0080] Therefore, the magnetic recording medium substrate 1 can have high heat resistance suitable for manufacturing auxiliary magnetic recording media that need to be heated to high temperatures (e.g., 320° C.) during manufacturing, and can be suitably used as a magnetic recording medium substrate used for auxiliary magnetic recording media.

[0081] After heating the magnetic recording medium substrate 1 at 320° C. for 20 minutes, the height of the surface ripples on the surface of the nickel alloy film 12 can be reduced to 0.100 nm or less. As a result, the magnetic recording medium substrate 1 can further improve the surface smoothness of the nickel alloy film 12, thereby increasing the recording density of a magnetic recording medium using the magnetic recording medium substrate 1.

[0082] The magnetic recording medium substrate 1 can be heated at 320° for 20 minutes to reduce the number of expansions of the nickel alloy film 12 with a height of 1 nm or more to less than 0.050 per cm. 2 Thus, the magnetic recording medium substrate 1 can further improve the smoothness of the surface of the nickel alloy film 12 , and thus the recording density of the magnetic recording medium using the magnetic recording medium substrate 1 can be increased.

[0083] Magnetic Recording Media

[0084] A magnetic recording medium to which the magnetic recording medium substrate according to this embodiment is applied will be described. In addition, in this embodiment, the case where the magnetic recording medium is an auxiliary magnetic recording medium will be described, but other magnetic recording media can also be applied in the same manner.

[0085] The auxiliary magnetic recording medium has 1Tbit / inch 2 The auxiliary magnetic recording medium is irradiated with near-field light, microwaves, etc. to locally assist the surface and reduce the coercive force of the auxiliary magnetic recording medium, thereby performing writing.

[0086] Figure 4 1 is a schematic cross-sectional view showing an example of an auxiliary magnetic recording medium to which the magnetic recording medium substrate 1 according to this embodiment is applied. Figure 4 As shown, the auxiliary magnetic recording medium 40 includes the magnetic recording medium substrate 1 , a seed layer 41 , a first underlayer 42 , a second underlayer 43 , a magnetic layer 44 , a protective layer 45 , and a lubricant layer 46 stacked in this order from the magnetic recording medium substrate 1 side.

[0087] The seed layer 41, the first underlayer 42, and the second underlayer 43 are preferably lattice-matched with the magnetic layer 44. This further improves the (001) orientation of the magnetic layer 44.

[0088] For example, (100)-oriented Cr, W, MgO, etc. can be used as the seed layer 41, the first underlayer 42, and the second underlayer 43. By forming the seed layer 41, the first underlayer 42, and the second underlayer 43 from (100)-oriented Cr, W, MgO, etc., and forming these layers into a multilayer structure, the lattice mismatch between the seed layer 41, the first underlayer 42, and the second underlayer 43 can be reduced to 10% or less.

[0089] In order to ensure that the first base layer 42 and the second base layer 43 are (100) oriented, a Cr layer with a bcc structure or a Cr alloy layer with Cr as the main component, or an alloy layer with a B2 structure can be further formed under the seed layer 41, the first base layer 42 or the second base layer 43.

[0090] Examples of the Cr alloy forming the Cr alloy layer include Cr—Mn alloy, Cr—Mo alloy, Cr—W alloy, Cr—V alloy, Cr—Ti alloy, and Cr—Ru alloy.

[0091] Examples of the alloy having a B2 structure include Ru-Al alloy and Ni-Al alloy.

[0092] Furthermore, in order to improve lattice matching with the magnetic layer 44 , an oxide may be added to at least one of the seed layer 41 , the first underlayer 42 , and the second underlayer 43 .

[0093] Examples of the oxide include oxides of one or more metals selected from the group consisting of Ni, Cr, Mo, Nb, Ta, V, and W. Among these, preferred metal oxides include NiO, CrO, Cr2O3, CrO3, MoO2, MoO3, Nb2O5, Ta2O5, V2O3, VO2, WO2, WO3, and WO6.

[0094] The oxide content in at least one of the seed layer 41, first underlayer 42, and second underlayer 43 is preferably within a range of 2 mol% to 30 mol%, and more preferably within a range of 10 mol% to 25 mol%. If the oxide content in at least one of the seed layer 41, first underlayer 42, and second underlayer 43 is within this preferred range, the (001) orientation of the magnetic layer 44 can be further improved, and the (100) orientation of at least one of the seed layer 41, first underlayer 42, and second underlayer 43 can be further improved.

[0095] The material forming the first underlayer 42 may be, for example, a CoTi alloy containing 50 at % Ti and the remainder Co. The thickness of the first underlayer 42 is preferably 30 nm to 100 nm, more preferably about 50 nm.

[0096] NiO, for example, can be used as a material forming the second underlayer 43. The thickness of the second underlayer 43 is preferably 3 nm to 10 nm, and more preferably about 5 nm.

[0097] As a method for forming the seed layer 41 , the first underlayer 42 , and the second underlayer 43 , a known method such as sputtering can be used.

[0098] The magnetic layer 44 is provided on the second underlayer 43 , includes an alloy having an L10 type crystal structure, and is a (001) oriented magnetic film.

[0099] An alloy having an L10 structure has a high magnetic anisotropy constant Ku. Examples of alloys having an L10 structure include Fe-Pt alloys and Co-Pt alloys.

[0100] In order to promote ordering of the alloy having the L10 structure of the magnetic layer 44 , it is preferable to perform a heat treatment when forming the magnetic layer 44 .

[0101] The crystal grains of the alloy having an L10 structure included in the magnetic layer 44 are preferably magnetically isolated. Therefore, the magnetic layer 44 preferably further includes one or more substances selected from the group consisting of SiO2, TiO2, Cr2O3, Al2O3, Ta2O5, ZrO2, Y2O3, CeO2, GeO2, MnO, TiO, ZnO, B2O3, C, B, and BN. This can more reliably disrupt exchange bonding between the crystal grains, further improving the signal-to-noise ratio (SNR) of the auxiliary magnetic recording medium 40.

[0102] Specifically, the magnetic layer 44 can use, for example, a (Fe-45at%Pt)-8mol%SiO2-4mol%Cr2O3 alloy (an alloy containing 8mol%SiO2, 4mol%Cr2O3, and the remainder (45at%Pt, and the remainder Fe)).

[0103] The average particle size of the magnetic grains included in the magnetic layer 44 is preferably 10 nm or less from the viewpoint of increasing recording density. Generally, when the average particle size of the magnetic grains is smaller, the magnetic layer 44 is more susceptible to thermal fluctuations immediately after magnetic information is written.

[0104] The average particle size of the magnetic particles can be determined using TEM images. For example, the particle sizes (equivalent circle diameters) of 200 magnetic particles can be measured from the TEM images, and the particle size at the cumulative value of 50% can be used as the average particle size. The average grain boundary width of the magnetic particles is preferably 0.3 nm to 2.0 nm.

[0105] The magnetic layer 44 may have a multilayer structure. Preferably, the magnetic layer 44 is formed by stacking two or more layers containing one or more substances selected from the group consisting of SiO2, TiO2, Cr2O3, Al2O3, Ta2O5, ZrO2, Y2O3, CeO2, GeO2, MnO, TiO, ZnO, B2O3, C, B, and BN, with each layer containing a different substance.

[0106] The thickness of the magnetic layer 44 is preferably 1 nm to 20 nm, more preferably 3 nm to 15 nm. If the thickness of the magnetic layer 44 is within this preferred range, the reproduction output can be improved while suppressing the enlargement of the crystal grains. If the magnetic layer 44 has a multilayer structure, the thickness of the magnetic layer 44 refers to the total thickness of all layers.

[0107] As a method for forming the magnetic layer 44 , similarly to the seed layer 41 , the first underlayer 42 , and the second underlayer 43 , a known method such as sputtering can be used.

[0108] The protective layer 45 is provided in contact with the magnetic layer 44 to protect the magnetic layer 44 .

[0109] As a material forming the protective layer 45 , a carbon material such as diamond-like carbon (DLC) can be used.

[0110] As a method for forming the protective layer 45, for example, there can be cited an RF-CVD (radio frequency chemical vapor deposition) method in which a raw material gas formed of hydrocarbons is decomposed by high-frequency plasma to form a film; an IBD (ion beam deposition) method in which electrons emitted from a cathode ionize the raw material gas to form a film; and an FCVA (filtered cathode vacuum arc) method in which a solid carbon target is used to form a film without using a raw material gas.

[0111] The thickness of the protective layer 45 is not particularly limited, but is preferably 1 nm to 6 nm. If the thickness of the protective layer 45 is within this range, the flying characteristics of the magnetic head can be improved, and the increase in magnetic gap loss can be suppressed, thereby suppressing the reduction in SNR of the auxiliary magnetic recording medium.

[0112] The protective layer 45 may be formed of a single layer or a plurality of layers.

[0113] The lubricant layer 46 is provided on the protective layer 45 to prevent contamination of the auxiliary magnetic recording medium 40 , reduce the friction of the magnetic head of the magnetic recording and reproducing device sliding on the auxiliary magnetic recording medium 40 , and improve the durability of the auxiliary magnetic recording medium 40 .

[0114] The lubricant layer 46 includes, for example, perfluoropolyether-based fluororesin, aliphatic hydrocarbon-based resin, etc. The lubricant layer 46 can be formed using, for example, a lubricating film composition including perfluoropolyether-based fluororesin, aliphatic hydrocarbon, etc.

[0115] The auxiliary magnetic recording medium 40 according to this embodiment uses the magnetic recording medium substrate 1 described above, thereby reducing magnetization, lowering the height of minute surface ripples, and reducing the density of surface expansion, thereby achieving high recording density.

[0116] <Magnetic Storage Device>

[0117] A magnetic storage device using the magnetic recording medium according to this embodiment will be described. Figure 5 The case of the auxiliary magnetic recording medium 40 shown will be described.

[0118] The magnetic storage device according to this embodiment may include, for example, a magnetic recording medium drive unit for rotating an auxiliary magnetic recording medium, a magnetic head having a near-field light generating element at its tip, a head drive unit for moving the magnetic head, and a recording and reproducing signal processing unit.

[0119] Furthermore, the magnetic head includes, for example, a laser generating section for heating the auxiliary magnetic recording medium and a waveguide for conducting the laser light generated from the laser generating section to the near-field light generating element.

[0120] Figure 5 1 is a perspective view showing an example of a magnetic storage device using the magnetic recording medium according to this embodiment. Figure 5 As shown, the magnetic storage device 50 includes an auxiliary magnetic recording medium 40 , a magnetic recording medium driving unit 51 for rotating the auxiliary magnetic recording medium 40 , a magnetic head 52 , a head moving unit 53 for moving the magnetic head 52 , and a recording and reproducing signal processing unit 54 .

[0121] Figure 6 An example of the magnetic head 52 is shown. Figure 6 As shown, the magnetic head 52 includes a recording head 61 and a reproducing head 62 .

[0122] The recording head 61 includes a main magnetic pole 611 , an auxiliary magnetic pole 612 , a coil 613 for generating a magnetic field, a laser diode (LD) 614 as a laser generating unit, and a waveguide 616 for transmitting laser light L generated by the LD 614 to a near-field light generating element 615 .

[0123] The reproduction head 62 includes a reproduction element 622 held by a shield 621 .

[0124] like Figure 5 As shown, the magnetic storage device 50 installs the center portion of the auxiliary magnetic recording medium 40 on the rotating axis of the spindle motor, and while floating the magnetic head 52 to the surface of the auxiliary magnetic recording medium 40 that is driven by the spindle motor, writes or reads information on the auxiliary magnetic recording medium 40.

[0125] The magnetic storage device 50 according to this embodiment uses the auxiliary magnetic recording medium 40 according to this embodiment, thereby enabling the auxiliary magnetic recording medium 40 to have a higher recording density, thereby improving the recording density.

[0126] Example

[0127] Hereinafter, although an Example and a comparative example are shown and embodiment is specifically described, embodiment is not limited to these Examples and comparative examples.

[0128] <Manufacturing of aluminum alloy substrates>

[0129] Al lumps, Mg, Mn, Cr, Si, Fe, and Zn were prepared. The raw materials used for the Al lumps, Mg, Mn, Cr, Si, Fe, and Zn had a purity of 99.9 wt% or higher.

[0130] An aluminum alloy material was weighed so that the raw materials of each element prepared would have a composition after casting of Al-4.0wt%Mg-0.5wt%Mn-0.1wt%Cr-0.2wt%Si-0.3wt%Fe-0.2wt%Zn (Mg content: 4wt%, Mn content: 0.5wt%, Cr content: 0.1wt%, Si content: 0.2wt%, Fe content: 0.3wt%, Zn content: 0.2wt%, and the remainder Al). The aluminum alloy material was dissolved in the atmosphere at 820°C and an aluminum alloy ingot was produced using a direct chill casting method (DC casting method). The casting temperature was 700°C and the casting speed was 80 mm / min.

[0131] The obtained aluminum alloy ingot was then homogenized by holding it at 520° C. for 10 hours and then rolled to produce an aluminum alloy plate having a thickness of 1.2 mm.

[0132] The obtained aluminum alloy plate was punched into a 97 mm diameter disk with a central opening and then annealed at 380°C for 1 hour. The surface and end faces of the aluminum alloy disk were then turned using a diamond tool to obtain an aluminum alloy substrate with a diameter of 96 mm and a thickness of 0.8 mm.

[0133] <Example 1>

[0134] [Fabrication of a Magnetic Recording Medium Substrate]

[0135] (Production of Nickel Alloy Film)

[0136] The aluminum alloy substrate is immersed in a NiMoP-based plating solution, and a non-electrolytic plating method is used to form a Ni-0.9wt% Mo-12.4wt% P-0.0003wt% Fe (Mo content 0.9wt%, P content 12.4wt%, Fe content 0.0003wt%, and the remainder Ni) film as a NiMoP-based plating film on the surface of the aluminum alloy substrate.

[0137] A NiMoP-based plating solution containing nickel sulfate, sodium hypophosphite, sodium molybdate, and iron (II) acetate was used, with sodium citrate and sodium borate added as appropriate, to produce a NiMoP-based plated film of the aforementioned composition. The pH of the NiMoP-based plating solution was adjusted to 6, and the plating temperature was adjusted to 90°C during formation of the NiMoP-based plated film. The aluminum alloy substrate was immersed in the NiMoP-based plating solution for 2 hours.

[0138] Next, the aluminum alloy substrate having the NiMoP-based plated film formed thereon was heated at 300° C. for 3 minutes to obtain an aluminum alloy substrate having a NiMoP-based plated film having a thickness of 10 μm.

[0139] (Grinding)

[0140] As a grinding disc, a three-stage grinding machine with a pair of upper and lower fixed plates was used to grind the surface of an aluminum alloy substrate with a NiMoP-based plated film to produce a substrate for a magnetic recording medium. At this time, a velvet pad (made by Filwel) was used as the grinding pad. In addition, aluminum oxide abrasive grains with a D50 of 0.5 μm were used for grinding in the first stage, colloidal silica abrasive grains with a D50 of 30 nm were used for grinding in the second stage, and colloidal silica abrasive grains with a D50 of 10 nm were used for grinding in the third stage. In addition, the grinding time was 5 minutes at each stage.

[0141] [Evaluation of heat resistance]

[0142] The obtained magnetic recording medium substrate was heated at 320°C in a vacuum for 20 minutes, and the saturation magnetic flux density of the magnetic recording medium substrate, the minute surface ripples in the wavelength band of 20μm to 100μm, and the density of expansions with a height of more than 1nm on the surface of the magnetic recording medium substrate were measured. Based on these measurement results, the heat resistance of the magnetic recording medium substrate was evaluated. The heat resistance of the magnetic recording medium substrate was evaluated when the saturation magnetic flux density was less than 0.10 gauss, the minute surface ripples were less than 0.100nm, and the density of expansions was 0.040 pieces / cm 2 In the following cases, the heat resistance of the magnetic recording medium substrate was judged to be excellent and was rated as ○. When the saturation magnetic flux density exceeded 0.10 gauss, the micro surface ripples exceeded 0.100 nm, and the density of the expanded particles exceeded 0.040 particles / cm 2 If at least any one of the above conditions is present, the heat resistance of the magnetic recording medium substrate is judged to be poor and is rated as ×. Table 1 shows the measurement results of the saturation magnetic flux density, the density of micro surface waviness and expansion, and the evaluation results of the heat resistance of the magnetic recording medium substrate.

[0143] (Saturation flux density)

[0144] The saturation magnetic flux density of the magnetic recording medium substrate was measured by VSM.

[0145] (Small surface ripples)

[0146] The minute surface waviness of the surface of the magnetic recording medium substrate in the wavelength range of 20 μm to 100 μm was measured by AFM.

[0147] (Expanded density)

[0148] The density of the expansion with a height of 1 nm or more that appeared on the surface of the magnetic recording medium substrate was measured by AFM image analysis. Figure 7 middle.

[0149] <Examples 2 to 7, Comparative Examples 1 to 6>

[0150] In Example 1, the same operation as in Example 1 was carried out except that the composition of the NiMoP-based plated film was changed as shown in Table 1. The measurement results are shown in Table 1.

[0151] [Table 1]

[0152]

[0153] As shown in Table 1, in Examples 1 to 7, the saturation magnetic flux density of the magnetic recording medium substrate is less than 0.60 Gauss, the micro surface ripples are less than 0.10 μm, and the density of the expansion with a height of 1 nm or more is 0.050 pieces / cm 2 On the other hand, in Comparative Examples 1 to 6, the saturation magnetic flux density of the magnetic recording medium substrate was 0.70 Gauss or more, the micro surface ripples were 0.11 μm or more, and the density of the expansions with a height of 1 nm or more was 0.060 pieces / cm 2 above.

[0154] It was confirmed that the magnetic recording medium substrates of Examples 1 to 7, unlike the magnetic recording medium substrates of Comparative Examples 1 to 6, had a NiMoP-based plated film composition of 0.5 to 3 wt% Mo, 11 to 12.4 wt% P, and 0.0001 to 0.001 wt% Fe. This reduced the saturation magnetic flux density, the density of minute surface ripples, and the density of swelling with a height of 1 nm or greater, thereby improving heat resistance. Therefore, it can be said that the magnetic recording medium substrates of this embodiment can be effectively used as auxiliary magnetic recording media.

[0155] While the embodiments have been described above, they are provided as examples and the present invention is not limited thereto. The embodiments described above can be implemented in various other forms, and various combinations, omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are intended to be within the scope and spirit of the invention, and are also intended to be within the scope of the invention as set forth in the claims and their equivalents.

[0156] Explanation of symbols

[0157] 1 Magnetic recording medium substrate

[0158] 1A Aluminum alloy substrate with nickel alloy plating film

[0159] 11 Aluminum alloy substrates for magnetic recording media (aluminum alloy substrates)

[0160] 12 Nickel alloy coating

[0161] 40 Auxiliary magnetic recording medium

[0162] 44 Magnetic layer

[0163] 50 Magnetic storage device (hard disk drive).

Claims

1. A magnetic recording medium substrate comprising: an aluminum alloy substrate; and a nickel alloy film provided on at least one main surface of the aluminum alloy substrate. The nickel alloy film contains 0.5 wt% to 3 wt% of Mo, 11 wt% to 15 wt% of P, and 0.0001 wt% to 0.001 wt% of Fe. After heating at 320° C. for 20 minutes, the height of the surface waviness appearing on the surface of the nickel alloy film is 0.100 nm or less. After heating at 320°C for 20 minutes, the surface of the nickel alloy film has less than 0.060 pieces / cm2 of expansion with a height of 1 nm or more. 2 .

2. A magnetic recording medium comprising: The magnetic recording medium substrate according to claim 1; and A magnetic layer is provided on the surface of the magnetic recording medium substrate on the side where the nickel alloy film is formed, and includes a FePt alloy having an L10 type crystal structure or a CoPt alloy having an L10 type crystal structure. 3 . A magnetic storage device comprising the magnetic recording medium according to claim 2 .

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