Nonmagnetic substrate for magnetic recording medium and method for manufacturing magnetic recording medium

Abstract

Provided is a nonmagnetic substrate for a magnetic recording medium in which inspection of the magnetic recording medium identifies that there are no non-periodic convex shapes on the surface of the magnetic recording medium, the nonmagnetic substrate for a magnetic recording medium being characterized in that: the magnetic recording medium has a magnetic layer on a non-magnetic substrate; and in the inspection of the magnetic recording medium, defect portions, which are identified on the basis of output signals obtained by using an inspection head having a thermal resistive element to scan the surface of the non-magnetic substrate for the magnetic recording medium, the surface having a magnetic layer formed under heating conditions at or below a guaranteed temperature, have a non-periodic convex shape having a height of 0.1-1.5 nm and a width of 1-15 μm.

Description

Non-magnetic substrate for magnetic recording media and method for manufacturing magnetic recording media

[0001] This disclosure relates to a non-magnetic substrate for magnetic recording media and a method for manufacturing magnetic recording media.

[0002] Magnetic recording and playback devices, such as hard disk drives (HDDs), are widely used as external storage devices for information processing equipment such as computers. In recent years, they have also been used as video recording devices and high-capacity storage in data centers.

[0003] Magnetic recording media used in HDDs are generally manufactured by sequentially forming an underlayer, magnetic layer, protective layer, and lubricating layer on the surface of a substrate made of aluminum alloy and glass substrate. The manufactured magnetic recording media are evaluated by glide testing, certify testing, and HDIs (Head Disk Interface sensor) testing. Magnetic recording media that have undergone glide testing, certify testing, and HDIs testing are shipped only after it is guaranteed that there are no defects, the amount of defects is below a standard value, or the location of defects has been identified.

[0004] Conventional methods for evaluating magnetic recording media include, for example, a method for evaluating the surface characteristics of a magnetic recording media using signals resulting from the thermal asperity phenomenon caused by contact between a magnetic head having an MR element and protrusions generated on the surface of the magnetic recording media (see Patent Document 1). The thermal asperity phenomenon refers to the phenomenon in which, when an MR element provided on a magnetic head comes into contact with a protrusion on the surface of a magnetic recording media, the heat generated by the contact causes a rapid temperature rise in the reading element, and the electrical resistance value of this reading element changes.

[0005] Other conventional evaluation methods for magnetic recording media include, for example, a method in which the surface of the magnetic recording media is scanned using a thermoresistive element, and signals caused by long-period undulations of wavelength 40 μm or longer on the surface of the magnetic recording media are separated from the signal output from the thermoresistive element, and protrusions on the surface of the magnetic recording media are detected from the separated signal (see Patent Document 2). The signals caused by undulations from the thermoresistive element are output by heat transfer mediated by air between the inspection head and the surface of the magnetic recording media. In other words, it is presumed that the signals caused by undulations from the thermoresistive element are output when the thermoresistive element and the surface of the magnetic recording media are not in contact.

[0006] Japanese Unexamined Patent Publication No. 10-105908 Japanese Unexamined Patent Publication No. 2008-146803

[0007] One aspect of this disclosure aims to provide a highly reliable non-magnetic substrate for magnetic recording media.

[0008] The means for solving the above problem are as follows: <1> A non-magnetic substrate for a magnetic recording medium, which is identified by inspection of the magnetic recording medium as not having a periodic convex shape on its surface, wherein the magnetic recording medium has a magnetic layer on the non-magnetic substrate, and in the inspection of the magnetic recording medium, the defect portion identified based on the output signal obtained by scanning the surface of the non-magnetic substrate for a magnetic recording medium having a magnetic layer formed under heating conditions below a guaranteed temperature with a thermosensitive resistance element has a periodic convex shape with a height of 0.1 nm or more and a width of 1 μm or more and 15 μm or less. <2> A non-magnetic substrate for a magnetic recording medium, wherein, by inspection of the magnetic recording medium, the amount of non-periodic convex shapes on the surface is identified as being below a standard value, wherein the magnetic recording medium has a magnetic layer on the non-magnetic substrate, and in the inspection of the magnetic recording medium, the defect portion identified based on the output signal obtained by scanning the surface of the non-magnetic substrate for a magnetic recording medium having a magnetic layer formed under heating conditions below a guaranteed temperature with a thermosensitive resistance element has a non-periodic convex shape with a height of 0.1 nm or more and a width of 1 μm or more and 15 μm or less. <3> A method for manufacturing a magnetic recording medium, comprising a step of forming a magnetic recording medium by heating a non-magnetic substrate for a magnetic recording medium at a temperature below a guaranteed temperature, wherein the non-magnetic substrate for the magnetic recording medium is identified by inspection of the magnetic recording medium as not having a periodic convex shape on its surface, the magnetic recording medium has a magnetic layer on the non-magnetic substrate, and in the inspection of the magnetic recording medium, the defect portion identified based on the output signal obtained by scanning the surface of the non-magnetic substrate for the magnetic recording medium, which has a magnetic layer formed on its surface under heating conditions below a guaranteed temperature, with a thermosensitive resistance element, has a periodic convex shape with a height of 0.1 nm or more and a width of 1 μm or more and 15 μm or less.<4> A method for manufacturing a magnetic recording medium, comprising a step of forming a magnetic recording medium by heating a non-magnetic substrate for a magnetic recording medium at a temperature below a guaranteed temperature, wherein the non-magnetic substrate for the magnetic recording medium is identified by inspection of the magnetic recording medium as having an amount of non-periodic convex shapes on its surface that is below a standard value, the magnetic recording medium has a magnetic layer on the non-magnetic substrate, and in the inspection of the magnetic recording medium, the defect portion identified based on the output signal obtained by scanning the surface of the non-magnetic substrate for the magnetic recording medium, which has a magnetic layer formed on its surface under heating conditions below a guaranteed temperature, with a thermosensitive resistance element, has a non-periodic convex shape with a height of 0.1 nm or more and a width of 1 μm or more and 15 μm or less.

[0009] According to one aspect of this disclosure, a highly reliable non-magnetic substrate for magnetic recording media can be provided.

[0010] This is a schematic cross-sectional view illustrating the mechanism of deformation of the substrate. This is a schematic graph showing the signals output from the thermoresistive element during certification and HDIs testing of a magnetic recording medium. This is a schematic cross-sectional view showing an example of a magnetic recording medium manufactured by the magnetic recording medium forming process in an embodiment of this disclosure. This is a schematic diagram showing an example of an inspection apparatus for performing inspection of a magnetic recording medium manufactured in an embodiment of this disclosure. This is a graph showing an example of an output signal obtained by scanning an inspection head having a thermoresistive element when a magnetic recording medium manufactured according to an embodiment of this disclosure is inspected using the inspection apparatus. This is a schematic perspective view showing an example of a magnetic recording and playback apparatus using a magnetic recording medium manufactured by the magnetic recording medium manufacturing method according to an embodiment of this disclosure. This is an example of an AFM observation image of a magnetic recording medium in an embodiment.

[0011] The following describes the forms for implementing this disclosure. In this specification, unless otherwise specified, the "~" indicating a numerical range means that the numbers before and after it are included as the lower and upper limits. Furthermore, if only the upper limit of a numerical range represented by "~" has a unit specified, it means that the lower limit also has the same unit.

[0012] The present inventors have discovered that, in conventional HDIs inspections, among the signals output in a state where the thermoresistive element and the magnetic recording medium are non-contact, there is a signal different from that caused by the undulations on the surface of the magnetic recording medium. When analyzing this signal, it was found that the signal has a height comparable to that of the undulations, the width is close to the lower limit value of the undulations, has no periodicity like the undulations, and appears superimposed on the signal caused by the undulations.

[0013] When the present inventors investigated the cause of the generation of this signal, they found that it is due to the deformation of the substrate that occurs in the manufacturing process of the magnetic recording medium, particularly in the film-forming process. The reasons for the occurrence of substrate deformation are diverse, but the main causes are as follows.

[0014] The inevitable impurities contained near the surface of the substrate react with surrounding substances and expand in volume due to the heating of the substrate during film formation. It is considered that the deformation of the substrate occurs due to the film being pushed up along with the volume expansion of the inevitable impurities. Note that the inevitable impurities are impurities that unavoidably mix in from raw materials and the manufacturing process. This will be described in detail using FIG. 1.

[0015] FIG. 1 is a schematic cross-sectional view for explaining the mechanism by which the substrate is deformed. Specifically, FIG. 1(a) is a schematic cross-sectional view showing an example of the state of the substrate 14 before the thin film 12 is formed, and FIG. ](b) is a schematic cross-sectional view showing an example of the state of the substrate 14 after the thin film 12 is formed.

[0016] As shown in FIG. 1(a), assume a case where inevitable impurities 11 are contained near the surface of the substrate 14. Since the surface 10 of the substrate 14 is smoothly polished, the portion containing the inevitable impurities 11 is also flat without a step with respect to the surroundings. When heating the substrate 14 to form the thin film 12 on the surface 10 of the substrate 14, the inevitable impurities 11 expand in volume according to their own coefficient of thermal expansion, or react with surrounding substances, or expand in volume by crystallization. Then, since the thin film 12 is pushed up, convex portions 13 may occur on the surface of the thin film 12. Note that the position of the convex portions 13 and the position where the inevitable impurities 11 are contained substantially coincide in a plan view of the substrate 14.

[0017] In the example shown in FIG. 1, the case where the inevitable impurity 11 appears on the surface 10 of the substrate 14 is shown. However, the same applies to the case where the inevitable impurity 11 exists inside the substrate 14 and in the vicinity of the surface 10 of the substrate 14.

[0018] As a result of the study by the present inventors, factors causing the surface of the substrate 14 to be deformed post - factum by heating and forming the convex portion 13 on the surface of the magnetic recording medium include, in addition to the inclusion of the inevitable impurity 11, aggregation of additive elements, segregation of additive elements, and processing strain, etc. Specific causative materials include aluminum alloy substrates, crystallized glass substrates, amorphous glass substrates, and ceramic substrates, etc. Further, as causative materials, in addition to these, plating films such as amorphous NiP - based plating films applied to the substrate surface are also included.

[0019] As a result of further study by the present inventors, it was found that the convex portion 13 generated on the surface of the magnetic recording medium has a height of 0.1 nm or more and 1.5 nm or less, and a width of 1 μm or more and 15 μm or less. A magnetic recording medium having such a convex portion 13 may not be excluded from the manufacturing process as a defective product because the convex portion 13 does not come into contact with the thermal resistance element in the glide inspection, the certification inspection, and the HDIs inspection. Then, the following problems (1) to (3) may occur.

[0020] (1) The output signal caused by the convex portion is different from the output signal caused by the waviness, has no periodicity, and appears superimposed on the output signal caused by the waviness. Therefore, it deteriorates the electromagnetic conversion characteristics of the magnetic recording medium and makes signal processing in the HDD difficult.

[0021] (2) The convex portion may grow significantly even after the product is commercialized. For example, due to laser heating in a heat assist type HDD, the convex portion may grow even larger, and there is a possibility that the magnetic head and the convex portion come into contact with each other.

[0022] (3) Since the convex portion is generated during the film formation of the magnetic film or the like, strain is introduced into the film, which may cause film peeling in the magnetic recording medium in the future.

[0023] Regarding the problem of (1), it will be described in detail using FIG. 2.

[0024] Figure 2 is a schematic graph showing the signals output from a thermoresistive element during HDIs inspection of a magnetic recording medium. Specifically, Figure 2(a) is an example of an output signal from a magnetic recording medium with a period of 170 μm. Figure 2(b) is an example of an output signal from a magnetic recording medium with a period of 50 μm. Figure 2(c) is an example of an output signal from a magnetic recording medium with periods of 170 μm and 50 μm. Figure 2(d) is an example of an output signal when a signal 21 from a 10 μm wide protrusion is superimposed on the signal in Figure 2(c). Note that all signals from Figure 2(a) to Figure 2(d) are signals output due to a phenomenon in which the resistance value of the thermoresistive element of the inspection head changes due to temperature changes caused by heat transfer mediated by air between the inspection head (thermoresistive element) and the surface of the magnetic recording medium.

[0025] In the graph shown in Figure 2, the horizontal axis represents time and corresponds to the surface shape of the magnetic recording medium in the circumferential direction. The vertical axis represents signal intensity, and its absolute value corresponds to the magnitude of the surface relief of the magnetic recording medium.

[0026] Periodic output signals, as shown in Figures 2(a) to 2(c), become easier to filter and remove by identifying their period. Furthermore, periodic output signals often possess specific frequency components, and by designing appropriate bandstop and bandpass filters, noise components can be effectively removed. Additionally, signal processing techniques such as Fourier transforms can be used to separate and remove periodic output components in the frequency domain.

[0027] As shown in Figure 2(d), the non-periodic output signal 21 often lacks specific frequency components, making it difficult to remove. Therefore, signals containing the irregularly appearing output signal 21, as shown in Figure 2(d), make signal processing in the HDD difficult.

[0028] Furthermore, the non-periodic output signal 21 is superimposed on the signal caused by undulation, as shown in Figures 2(a) to 2(c), which can increase the signal intensity and degrade the electromagnetic conversion characteristics of the magnetic recording medium.

[0029] The non-magnetic substrate for magnetic recording media according to the embodiment of this disclosure (hereinafter sometimes simply referred to as "this embodiment") has been proposed in view of the above circumstances and provides a highly reliable non-magnetic substrate for magnetic recording media.

[0030] The following describes in detail the non-magnetic substrate for magnetic recording media and the method for manufacturing the magnetic recording media according to this embodiment.

[0031] (Non-magnetic substrate for magnetic recording medium) The non-magnetic substrate for magnetic recording medium according to the first embodiment of the present disclosure is a non-magnetic substrate for magnetic recording medium which is identified by inspection of the magnetic recording medium as not having a periodic convex shape on its surface, wherein the magnetic recording medium has a magnetic layer on the non-magnetic substrate, and in the inspection of the magnetic recording medium, the defect portion identified based on the output signal obtained by scanning the surface of the non-magnetic substrate for magnetic recording medium having a magnetic layer formed under heating conditions below a guaranteed temperature with a thermosensitive resistance element has a periodic convex shape with a height of 0.1 nm or more and a width of 1 μm or more and a width of 1 μm or more and a width of 15 μm or less.

[0032] The specific guaranteed temperatures in this disclosure are as follows: For non-magnetic substrates for magnetic recording media used in conventional magnetic recording media, the guaranteed temperature is preferably 300°C and more preferably 400°C. For non-magnetic substrates for magnetic recording media used in heat-assisted magnetic recording media, the guaranteed temperature is preferably 700°C, more preferably 800°C, even more preferably 850°C, and particularly preferably 900°C. For non-magnetic substrates for magnetic recording media used in microwave-assisted magnetic recording media, the guaranteed temperature is preferably 300°C and more preferably 400°C.

[0033] A non-magnetic substrate for a magnetic recording medium according to a second embodiment of the present disclosure is a non-magnetic substrate for a magnetic recording medium in which the amount of non-periodic convex shapes on the surface is identified as being below a reference value by inspection of the magnetic recording medium, wherein the magnetic recording medium has a magnetic layer on the non-magnetic substrate, and in the inspection of the magnetic recording medium, the defect portion identified based on the output signal obtained by scanning the surface of the non-magnetic substrate for a magnetic recording medium having a magnetic layer formed on its surface under heating conditions below a guaranteed temperature with a thermosensitive resistance element has a non-periodic convex shape having a height of 0.1 nm or more and 1.5 nm or less and a width of 1 μm or more and 15 μm or less.

[0034] In this disclosure, the specific reference values ​​for the amount of non-periodic convex shapes present are preferably 1,000, more preferably 500, even more preferably 100, and particularly preferably 0 per face of a non-magnetic substrate for magnetic recording media.

[0035] The non-magnetic substrate for magnetic recording media according to the first embodiment and the non-magnetic substrate for magnetic recording media according to the second embodiment of this disclosure may be collectively referred to as "the non-magnetic substrate for magnetic recording media according to this embodiment."

[0036] In this disclosure, the "non-magnetic substrate for magnetic recording media having a magnetic layer formed on its surface under heating conditions below a guaranteed temperature" may be referred to as a "magnetic recording media" for convenience.

[0037] The non-magnetic substrate for the magnetic recording medium according to this embodiment may include other components as needed.

[0038] According to the non-magnetic substrate for magnetic recording media of this embodiment, it is possible to identify defective portions having a non-periodic convex shape in a magnetic recording media having the non-magnetic substrate for magnetic recording media. Magnetic recording media in which defective portions are detected are either removed from the manufacturing line, the amount of defective portions in the magnetic recording media is identified, or the location of the defective portions in the magnetic recording media is identified. In other words, according to the non-magnetic substrate for magnetic recording media of this embodiment, it is guaranteed that there are no defective portions in the magnetic recording media, or that the amount of defective portions in the magnetic recording media is below a standard value, or the location of the defective portions in the magnetic recording media is identified, making it possible to ship highly reliable and high-quality products.

[0039] According to the non-magnetic substrate for magnetic recording media of this embodiment, by applying a magnetic recording media having the non-magnetic substrate to a magnetic recording and playback device, the generation of noise signals can be suppressed, the electromagnetic conversion characteristics of the magnetic recording media can be improved, and signal processing in the magnetic recording and playback device can be facilitated.

[0040] According to the non-magnetic substrate for magnetic recording media of this embodiment, in a magnetic recording and playback device equipped with a magnetic recording media having a non-magnetic substrate for magnetic recording media, it is possible to eliminate magnetic recording media having potentially growing defective portions or to identify the location of such defective portions. Therefore, the risk of film peeling of the magnetic recording media is reduced, and the location of such risk can be identified, thereby providing a highly reliable magnetic recording and playback device.

[0041] <Method for inspecting magnetic recording media> The method for inspecting magnetic recording media using a non-magnetic substrate for magnetic recording media according to this embodiment is a method for determining whether the surface of the non-magnetic substrate for magnetic recording media does not have aperiodic convex shape, or whether the amount of aperiodic convex shape on the surface of the non-magnetic substrate for magnetic recording media is below a reference value. Specifically, a defective portion is identified based on an output signal obtained by scanning the surface of a non-magnetic substrate for magnetic recording media having a magnetic layer formed on its surface under heating conditions below a guaranteed temperature with an inspection head having a thermosensitive resistance element. The method for inspecting magnetic recording media may include other steps as necessary.

[0042] <<Defective Area>> The defective area has a non-periodic convex shape. The convex shape has a height of 0.1 nm to 1.5 nm and a width of 1 μm to 15 μm.

[0043] The height of the convex shape is 0.1 nm or more and 1.5 nm or less, preferably 0.5 nm or more and 1.0 nm or less. In this specification, "height of the convex shape" refers to the maximum height of the convex shape when viewed from the cross-sectional direction with respect to the surface of the magnetic recording medium.

[0044] The width of the convex shape is 1 μm or more and 15 μm or less, preferably 5 μm or more and 13 μm or less. In this specification, "width of the convex shape" refers to the maximum length of the convex shape when viewed from the cross-sectional direction in the planar direction of the magnetic recording medium.

[0045] The height and width of the convex shape are defined by the following measurement method: (1) In AFM measurement, the measurement is taken over a quadrilateral region (preferably 50 μm) that includes the entire convex shape and a flat region of at least 10 μm around it. (2) A cross-sectional profile of the convex shape is taken, passing through the position of the apex of the convex shape. (3) A flat region of at least 10 μm around the convex shape of the obtained cross-sectional profile is taken as the baseline (preferably 15 μm). (4) Using the baseline obtained in (3) as a reference, the length from the cross-sectional profile to the apex of the convex shape is taken as the "height of the convex shape". (5) Using the baseline obtained in (3) as a reference, the length of the bottom surface of the convex shape is taken as the "width of the convex shape".

[0046] As mentioned above, it is preferable that the convex shape is formed during the manufacturing process of the magnetic recording medium.

[0047] <<Inspection Target>> In the inspection method for magnetic recording media according to this embodiment, the inspection target is a non-magnetic substrate for magnetic recording media having a magnetic layer formed on its surface under heating conditions below the guaranteed temperature. There are no restrictions on the type and number of each layer to be stacked, and they can be appropriately selected according to the purpose.

[0048] In this embodiment, the step of forming a non-magnetic substrate for a magnetic recording medium having a magnetic layer formed on its surface under heating conditions below a guaranteed temperature may be referred to as the "magnetic recording medium formation step."

[0049] <<<Magnetic Recording Medium Formation Process>>> The magnetic recording medium formation process is a process of forming a magnetic layer on a non-magnetic substrate for magnetic recording medium by heating it at a temperature below the guaranteed temperature.

[0050] The magnetic recording medium formation process may include a soft magnetic layer formation process, a base layer formation process, a perpendicular magnetic layer formation process, a protective layer formation process, a liquid lubricant layer formation process, and a varnish process.

[0051] There are no particular limitations on the heating process in the magnetic recording medium formation process, and heating processes used in known film formation methods can be appropriately adopted. Examples include heating processes performed before and after the process of forming a thin film by sputtering (sputtering method), and heating processes for laminates of thin films including a non-magnetic substrate. These heating processes are intended to improve and enhance the crystal structure of the thin film, repair defects, relieve stress, promote diffusion processes, accelerate chemical reactions, improve the adhesion of the thin film, promote surface diffusion, accelerate interfacial reactions, and form specific phases.

[0052] There are no particular restrictions on the magnetic recording medium manufactured by the magnetic recording medium formation process, and it can be appropriately selected according to the purpose. Examples include conventional magnetic recording media, magnetic recording media used in heat-assisted methods, and magnetic recording media used in microwave-assisted methods.

[0053] In this embodiment, a magnetic recording medium used in a heat-assisted method will be described below in detail with reference to Figure 3 as an example of a magnetic recording medium manufactured by the magnetic recording medium formation process. The embodiments shown below are illustrative examples to embody the technical concept of this disclosure and are not limited to those described below. They can be modified as appropriate without departing from the gist of this disclosure.

[0054] Furthermore, the dimensions, materials, shapes, numbers, and relative arrangements of the components described in the embodiments are merely illustrative examples and not intended to limit the scope of this disclosure unless otherwise specified. Note that the size and positional relationships of the components shown in each drawing may be exaggerated for clarity. Also, in the following description, the same name and reference numeral indicate the same or identical components, and detailed explanations are omitted as appropriate. To avoid overly complex drawings, schematic diagrams may be used with some elements omitted, or end views showing only the cross-section may be used as cross-sectional views.

[0055] Furthermore, the following description uses terms to indicate specific directions or positions as needed (e.g., "up," "down," "side," "top," "bottom," "side," "X," "Y," "Z," and other terms including these terms). However, the use of these terms is solely to facilitate understanding of the invention with reference to the drawings, and the meaning of these terms does not unduly limit the technical scope of this disclosure. For example, if "top" is mentioned, the invention must not always be used in a way that it faces upwards.

[0056] Figure 3 is a schematic cross-sectional view showing an example of a magnetic recording medium manufactured by the magnetic recording medium forming process in this embodiment. In the magnetic recording medium shown in Figure 3, a soft magnetic layer 2, an underlayer 3, a perpendicular magnetic layer 4, and a protective layer 5 are sequentially laminated on both main surfaces of a non-magnetic substrate 1 for magnetic recording medium. Although Figure 3 shows the layers laminated on both sides of the non-magnetic substrate 1 for magnetic recording medium, the magnetic recording medium may also have the layers laminated on only one side of the non-magnetic substrate 1 for magnetic recording medium.

[0057] As for the shape of the magnetic recording medium, there is no particular limitation as long as it can be applied to a magnetic recording / reproducing apparatus, and it can be appropriately selected according to the purpose. For example, a disk shape having a center hole can be mentioned.

[0058] <<<<Soft magnetic layer forming step>>>> The soft magnetic layer forming step of the present disclosure is a step of forming a soft magnetic layer 2 on a non-magnetic substrate 1 for a magnetic recording medium.

[0059] - Non-magnetic substrate for magnetic recording medium - There is no particular limitation on the non-magnetic substrate 1 for a magnetic recording medium, and it can be appropriately selected according to the purpose. For example, a metal substrate and a non-metal substrate can be mentioned.

[0060] - - Non-metal substrate - - As the non-metal substrate, for example, those formed of a non-metal material such as glass can be mentioned.

[0061] As the glass substrate, for example, SiO ３ - Al ２ O ３ - R ２ O-based chemically strengthened glass, SiO ２ - Al ２ O ３ - Li ２ O-based glass ceramics and SiO ２ - Al ２ O ３ - MgO - TiO ２ - based glass ceramics and the like can be mentioned. Here, R represents at least one or more selected from alkali metal elements.

[0062] Among these glass substrates, SiO ２ - Al ２ O ３ - MgO - CaO - Li ２ O - Na ２ O - ZrO ２ - Y ２ O ３ - TiO ２ - As ２ O ３ - based chemically strengthened glass, SiO ２ - Al ２ O ３ - Li ２ O - Na ２ O - ZrO ２-As ２ O ３ Chemically strengthened glass, SiO ２ - Al ２ O ３ -MgO-ZnO-Li ２ O-P ２ O ５ -ZrO ２ -K ２ O-Sb ２ O ３ Glass ceramics, SiO ２ - Al ２ O ３ -MgO-CaO-BaO-TiO ２ -P ２ O ５ -As ２ O ３ Glass ceramics and SiO ２ - Al ２ O ３ -MgO-CaO-SrO-BaO-TiO ２ -ZrO ２ -Bi ２ O ３ -Sb ２ O ３ Glass-ceramic materials are preferred.

[0063] --Metal Substrate-- Examples of metal substrates include those made of metallic materials such as aluminum alloys. An aluminum alloy substrate may contain, for example, additive elements including Mg and Cr, with the remainder being Al, and may also contain unavoidable impurities.

[0064] In aluminum alloy substrates, Mg has the function of improving mechanical strength. There are no particular restrictions on the Mg content, and it can be appropriately selected depending on the purpose, but it is preferable that it be 2% by mass or more and 7% by mass or less of the total weight of the aluminum alloy substrate.

[0065] In aluminum alloy substrates, Cr has the function of improving strength at high temperatures and improving extrusion processing. There are no particular restrictions on the Cr content, and it can be appropriately selected depending on the purpose, but it is preferable that it be 0.02% by mass or more and 0.3% by mass or less of the total amount of the aluminum alloy substrate.

[0066] In addition to Mg and Cr as additive elements, the aluminum alloy substrate may contain one or more elements selected from the group consisting of Si, Zn, Mn, Ti, Cr, V, Zr, Mo, and Co.

[0067] Unavoidable impurities include, for example, B and P.

[0068] NiP-based alloy layers may be formed on the surfaces of metal and non-metallic substrates. The NiP-based alloy layers can be formed, for example, by plating and sputtering.

[0069] Among these non-magnetic substrates for magnetic recording media, heat-resistant glass substrates with a softening temperature of 500°C or higher and aluminum alloy substrates with heat-resistant plating such as NiMoP are preferred, and heat-resistant glass substrates with a softening temperature of 600°C or higher are more preferred.

[0070] There are no particular restrictions on the method for forming the soft magnetic layer 2, and it can be appropriately selected according to the purpose. For example, general film deposition methods such as sputtering can be used.

[0071] There are no particular restrictions on the sputtering method, and it can be appropriately selected depending on the purpose. Examples include DC (Direct Current) sputtering, DC magnetron sputtering, and RF (Radio Frequency) sputtering.

[0072] When using the sputtering method as the method for forming the soft magnetic layer 2, it is preferable to use a target containing the material for forming the soft magnetic layer.

[0073] Examples of targets containing materials that form a soft magnetic layer include soft magnetic alloys such as FeCo-based alloys, CoZrNb-based alloys, and CoTaZr-based alloys.

[0074] <<

[0075] There are no particular restrictions on the method for forming the underlayer 3, and it can be appropriately selected according to the purpose. For example, general film deposition methods such as sputtering can be used.

[0076] When using the sputtering method as the method for forming the base layer 3, it is preferable to use a target that contains the material for forming the base layer.

[0077] In the first subsoil formation process, there are no particular restrictions on the material used to form the first subsoil, and it can be appropriately selected according to the purpose. For example, a Cr alloy in which a bcc alloy mainly composed of Cr is (100) oriented can be used.

[0078] In the second sublayer formation process, there are no particular restrictions on the material used to form the second sublayer, and it can be appropriately selected according to the purpose. For example, a W alloy in which a bcc alloy mainly composed of W is (100) oriented can be used.

[0079] In the third subsoil formation process, there are no particular restrictions on the material used to form the third subsoil; it can be appropriately selected according to the purpose. Examples include NaCl-type compounds. Examples of NaCl-type compounds include MgO.

[0080] It is preferable to include a heating step before and after each of the first, second, and third subsoil formation steps. The heating temperature at this time is preferably 150°C or higher, and more preferably 200°C or higher.

[0081] <<<<Perpendicular Magnetic Layer Formation Process>>>> The perpendicular magnetic layer formation process is a process of forming a perpendicular magnetic layer 4 on the base layer 3.

[0082] There are no particular restrictions on the method for forming the perpendicular magnetic layer 4, and it can be appropriately selected according to the purpose. For example, general film deposition methods such as sputtering can be used.

[0083] When using the sputtering method as the method for forming the perpendicular magnetic layer 4, it is preferable to use a target that contains the material for forming the perpendicular magnetic layer.

[0084] There are no particular limitations on the target material that forms the perpendicular magnetic layer 4, and it can be appropriately selected according to the purpose, for example, L1 ０ Examples include targets containing alloys with a specific structure.

[0085] L1 ０ Examples of alloys with a structure include alloys containing Fe or Co and Pt, etc. L1 ０ Specific examples of alloys with a structure include FePt-based alloys and CoPt-based alloys.

[0086] In the perpendicular magnetic layer formation process, it is preferable to include a heating step in which the non-magnetic substrate 1 for magnetic recording media, the soft magnetic layer 2, the underlayer 3, and the perpendicular magnetic layer 4 are heated in a laminated state, from the viewpoint of improving the crystal orientation of the perpendicular magnetic layer 4. As the heating means at this time, known methods such as halogen lamps, lasers, LEDs, electromagnetic waves such as high frequency and microwaves can be used.

[0087] L1 ０ If the FePt alloy has a structure, it is preferable to heat it to a high temperature of 400°C or higher to regularize it.

[0088] <<<<Protective layer formation process>>>> The protective layer formation process is the process of forming a protective layer 5 on the perpendicular magnetic layer 4.

[0089] There are no particular restrictions on the method for forming the protective layer 5, and general film deposition methods can be used. Examples include the RF-CVD (Radio Frequency-Chemical Vapor Deposition) method, which decomposes a hydrocarbon source gas with a high-frequency plasma to form a film; the IBD (Ion Beam Deposition) method, which ionizes the source gas with electrons emitted from a filament to form a film; and the FCVA (Filtered Cathodic Vacuum Arc) method, which uses a solid carbon target to form a film without using a source gas.

[0090] It is preferable to include a heating step before the protective layer formation step. The heating temperature at this step is preferably 150°C or higher, and more preferably 200°C or higher.

[0091] <<<<<Liquid Lubricant Layer Formation Process>>>> The liquid lubricant layer formation process is a process of forming a liquid lubricant layer on the protective layer 5.

[0092] The liquid lubricant layer can be formed by applying a fluorine-based lubricant such as a perfluoropolyether using methods such as the dip method and the spin coating method.

[0093] <<

[0094] In this embodiment, the method for inspecting the magnetic recording medium may include glide testing, certify testing, and HDIs testing.

[0095] <<Glide Inspection>> Glide inspection is an inspection to check for the presence of protrusions on the surface of a magnetic recording medium. When recording and playing back a magnetic recording medium using a magnetic head, if there are protrusions on the surface of the magnetic recording medium that are taller than the levitation amount (the distance between the medium and the magnetic head), the magnetic head may collide with the protrusion, causing damage to the magnetic head or defects in the magnetic recording medium. Therefore, magnetic recording mediums that are detected to have tall protrusions on their surface through glide inspection are removed from the manufacturing process as defective products.

[0096] Magnetic recording media that pass the glide test undergo a certify test and an HDIs test.

[0097] <<Certify Test>> The Certify test is an inspection to verify the defects and quality of the electromagnetic conversion characteristics of a magnetic recording medium. In the Certify test, a predetermined signal is recorded on the magnetic recording medium using a magnetic head, similar to the recording and playback in a normal HDD, and then the signal is reproduced. The electromagnetic conversion characteristics are then evaluated from the obtained reproduced signal.

[0098] <<HDIs Testing>> HDIs testing is a test that checks for the presence or absence of convex and concave defects in magnetic recording media. By checking what kinds of convex and concave defects exist on the surface of the magnetic recording media, HDIs testing evaluates the data read / write performance and the reliability of the magnetic recording media.

[0099] In this embodiment, it is preferable that the magnetic recording medium inspection method be performed in conjunction with the HDIs inspection.

[0100] In this embodiment, the inspection method for magnetic recording media does not necessarily require inspection of the entire area of ​​the magnetic recording media. A common practice for inspecting magnetic recording media is to evaluate an area that includes 3% or more, more preferably 5% or more, of the inner, middle, and outer circumferences of the magnetic recording media, thereby providing a sufficient understanding of its overall characteristics. The accuracy increases as the proportion of the area evaluated increases.

[0101] For a 2.5-inch diameter magnetic recording medium, the positions of the inner circumference, middle circumference, and outer circumference at the radial position are approximately 15 mm for the inner circumference, approximately 24 mm for the middle circumference, and approximately 33 mm for the outer circumference.

[0102] For a 3.5-inch diameter magnetic recording medium, the positions of the inner circumference, middle circumference, and outer circumference at the radial position are approximately 20 mm for the inner circumference, approximately 31.5 mm for the middle circumference, and approximately 43 mm for the outer circumference.

[0103] In this embodiment, the inspection method for the magnetic recording medium can be carried out by an inspection device.

[0104] <<Inspection Apparatus>> Figure 4 is a schematic diagram showing an example of an inspection apparatus for performing inspection of magnetic recording media manufactured in this embodiment.

[0105] The inspection device 41 shown in Figure 4 includes a rotating mechanism 43 for rotating the magnetic recording medium 42, an inspection head 50 positioned opposite the measurement area of ​​the magnetic recording medium 42, and an inspection head drive mechanism 60 for driving the inspection head 50 via a suspension 70.

[0106] The inspection head 50 includes a magnetic writing unit 51 that magnetizes the measurement area without contact, a magnetic reading unit 52 that reads the leakage magnetic field of the measurement area without contact, and an HDI sensor unit.

[0107] The HDI sensor unit functions as a thermoresistive element whose physical properties, such as resistance, change with increasing temperature, and can output signals caused by thermal asperity phenomena.

[0108] Examples of thermoresistive elements include MR elements that utilize the magnetoresistance (MR) effect, GMR elements that utilize the giant magnetoresistance (GMR) effect, and TMR elements that utilize the tunnel magnetoresistance (TuMR) effect. In this specification, MR elements, GMR elements, and TMR elements may be referred to as "magnetoresistive elements."

[0109] The inspection device 41 may also have a laser heating mechanism 40 that heats the measurement area non-contact when the magnetic recording medium 42 is used in a heat-assisted manner.

[0110] The inspection head 50 can adjust the height of the thermoresistive element relative to the surface of the magnetic recording medium 42 by changing the rotation speed (movement speed) of the magnetic recording medium 42. Furthermore, the inspection head 50 can also adjust the height of the thermoresistive element relative to the surface of the magnetic recording medium 42 by causing expansion or contraction of the area around the thermoresistive element due to the heat generated by a heater located near the thermoresistive element.

[0111] The inspection device 41 may be used in combination with the certify inspection and HDIs inspection in the magnetic recording medium formation process, or it may be provided separately from the certify inspection and HDIs inspection.

[0112] Figure 5 is a graph showing an example of an output signal obtained by scanning an inspection head having a thermoresistive element when inspecting a magnetic recording medium manufactured according to this embodiment using an inspection device. Specifically, Figure 5(a) is an example of a signal in which three convex signals 21 with a width of 10 μm are superimposed on a signal 53 having undulations with a period of 170 μm and undulations with a period of 50 μm. Figure 5(b) is an example of a signal obtained by filtering out the signal 53 having undulations with a period of 170 μm and undulations with a period of 50 μm from the signal in Figure 5(a).

[0113] Note that both signals shown in Figure 5(a) and Figure 5(b) are signals output due to a phenomenon in which the resistance value of the thermoresistive element of the inspection head changes due to a temperature change caused by heat transfer between the thermoresistive element and the surface of the magnetic recording medium via air.

[0114] In the graphs shown in Figures 5(a) and 5(b), the horizontal axis represents time and corresponds to the surface shape of the magnetic recording medium in the circumferential direction. The vertical axis represents signal intensity, and its absolute value corresponds to the magnitude of the surface relief.

[0115] In other words, the height of the convex shape is indicated by the signal intensity on the vertical axis in Figure 5, and the higher the convex shape, the larger the negative potential. The width of the convex shape is indicated by time on the horizontal axis in Figure 5, and the larger the width of the convex shape, the larger the time interval. The width of the convex shape is calculated from the relative speed of the inspection head on the surface of the magnetic recording medium.

[0116] As shown in Figure 5(a), the undulation signal 53 on the surface of the magnetic recording medium has periodicity, while the convex signal 21 does not. Therefore, it is easy to identify the convex signal 21 from the signals in Figure 5(a).

[0117] Here, of the three convex-shaped signals 21 in Figure 5(a), the leftmost signal 21 has a higher signal strength than signal 53 and is easy to identify, but the rightmost signal 21 is difficult to identify because it is buried in the signal strength of signal 53. Therefore, in order to facilitate the identification of all convex shapes, it is preferable to remove signals caused by undulations on the surface of the magnetic recording medium from the output signal from the thermoresistive element.

[0118] Most of the undulations that appear on the surface of magnetic recording media are caused by undulations on the surface of the non-magnetic substrate used for the magnetic recording media. In other words, undulations on the surface of the non-magnetic substrate for the magnetic recording media are influenced by the thin film surface formed on it, and as a result appear on the surface of the magnetic recording media.

[0119] Since the undulations on the surface of non-magnetic substrates for magnetic recording media mostly have wavelength components of 10 μm to 1 mm, it is preferable to remove periodic signals of 10 μm to 1 mm from the output signal from the thermoresistive element.

[0120] Figure 5(b) shows a signal in which three convex-shaped signals 21 with a width of 10 μm are superimposed on a stable amplitude signal 54. In the signal in Figure 5(b), it is even easier to identify all of the convex-shaped signals 21. This is because signals caused by swells repeat at a constant period, and by identifying that period, filtering and other removal techniques become easier to apply. Also, signals caused by swells often have specific frequency components, and can be effectively removed by designing appropriate bandstop filters and bandpass filters. Furthermore, it is also effective to use signal processing techniques such as Fourier transforms to separate periodic noise components in the frequency domain and effectively remove signals caused by swells.

[0121] As described above, the inspection method for a magnetic recording medium manufactured according to this embodiment preferably identifies a defect portion having a non-periodic convex shape based on the output signal from which signals caused by undulations on the surface of the magnetic recording medium have been removed.

[0122] Figure 6 is a schematic perspective view showing an example of a magnetic recording and playback apparatus using a magnetic recording medium manufactured by a method for manufacturing a magnetic recording medium according to an embodiment of the present disclosure. The magnetic recording and playback apparatus shown in Figure 6 comprises a magnetic recording medium 30, a rotational drive unit (a medium drive unit that drives the magnetic recording medium in the recording direction) 31 for rotationally driving the magnetic recording medium 30, a magnetic head 32 that performs recording and playback operations on the magnetic recording medium 30, a head drive unit (a head moving means that moves the magnetic head relative to the magnetic recording medium) 33 for moving the magnetic head 32 in the radial direction of the magnetic recording medium 30, and a recording and playback signal processing system (a recording and playback signal processing means) 34 for inputting signals to the magnetic head 32 and playing back output signals from the magnetic head 32.

[0123] In the magnetic recording and playback apparatus shown in Figure 6, further improvements in reliability can be achieved by using a magnetic recording medium 30 having a non-magnetic substrate for magnetic recording media according to this embodiment.

[0124] (Method for Manufacturing Magnetic Recording Media) The method for manufacturing a magnetic recording media according to this embodiment includes a magnetic recording media forming step in which a non-magnetic substrate for a magnetic recording media according to this embodiment is heated at a temperature below the guaranteed temperature to form a magnetic layer, and may include other steps as needed. The magnetic recording media forming step is the same as the <<<Magnetic Recording Media Forming Step>>> described above, so the details are omitted.

[0125] The embodiment will be described in more detail below with reference to examples, but this embodiment is not limited to the following examples.

[0126] (Manufacturing of magnetic recording media) A magnetic recording media with an outer diameter of 3.5 inches, used in a heat-assisted method, was manufactured using the method described below.

[0127] A heat-resistant glass substrate was used as the non-magnetic substrate for the magnetic recording medium.

[0128] Using the sputtering method, a Cr-50at%Ti alloy layer with an average thickness of 100 nm and a Co-27at%Fe-5at%Zr-5at%B alloy layer with an average thickness of 30 nm were sequentially formed. Next, after heating the non-magnetic substrate to 200°C, a Cr layer with an average thickness of 10 nm and an MgO layer with an average thickness of 5 nm were sequentially formed using the sputtering method. Next, after heating the non-magnetic substrate to 400°C, a (Fe-49at%Pt)-40 volume% hexagonal boron nitride layer (magnetic layer) with an average thickness of 13 nm was sequentially formed using the sputtering method. Finally, the non-magnetic substrate was heated to 200°C to form a carbon film with an average thickness of 3 nm as a protective layer.

[0129] (Evaluation of magnetic recording media by glide testing) The obtained magnetic recording media were subjected to glide testing using a glide tester equipped with a piezoelectric element head, with the glide height of the head (the distance between the head and the surface of the magnetic recording media assuming no surface defects) set to 10 nm, in order to exclude magnetic recording media with large protrusions on the surface.

[0130] (Evaluation of magnetic recording media by HDIs inspection) <First HDIs inspection> 100 magnetic recording media that passed the glide inspection were prepared, and each magnetic recording media was subjected to HDIs inspection using an inspection head equipped with a thermoresistive element. Specifically, the glide height (height from the surface of the magnetic recording media to the thermoresistive element) was set to 1.5 nm, and a recording media was considered to have passed if the signal output from the thermoresistive element of the inspection head was 500 mV or more in absolute value and there were no defects. The track pitch during inspection was set to 20 μm, and the magnetic recording media was evaluated from the inner circumference to the outer circumference. This corresponds to evaluating 5% of the entire area of ​​the magnetic recording media. 96 magnetic recording media passed the inspection.

[0131] <Second HDIs Inspection> Next, a second HDIs inspection was performed on the 96 magnetic recording media that had passed, under modified conditions. Specifically, the glide height was not changed, and a bandpass filter from 800 kHz to 10 MHz was used to remove signals caused by undulation from the output signal from the thermoresistive element of the inspection head, and to extract only signals corresponding to non-periodic convex shapes (height of 0.1 nm to 1.5 nm and width of 1 μm to 15 μm). Among the extracted signals, those without defects of 400 mV or more in absolute value were deemed to pass. 91 magnetic recording media passed the inspection.

[0132] When the defective areas of the magnetic recording media that failed the second HDIs inspection were observed using an AFM (Atomic Force Microscope), a non-periodic convex shape (with a height of 0.1 nm to 1.5 nm and a width of 1 μm to 15 μm) was observed on the surface of the magnetic recording media. An example of the observed image is shown in Figure 7. The convex part in Figure 7 had a height of 0.68 nm and a width of 13.52 μm. It was determined that all of the convex shapes of the magnetic recording media that failed the second HDIs inspection were caused by bulging of the substrate during film deposition.

[0133] The signal-to-noise ratio (SNR) of magnetic recording media that passed the second HDIs test and those that failed the second HDIs test were compared. SNR was measured using a spin stand tester with a magnetic head equipped with a laser spot heating mechanism. The current supplied to the laser diode was adjusted so that the recording track width (MWW), defined as the half-width of the reproduced signal waveform, was 70 nm, and the SNR was checked. It was confirmed that the SNR of the passing products improved by an average of 0.3%.

[0134] <Third HDIs Test> A third HDIs test was performed on magnetic recording media that had passed the second HDIs test, with modified conditions. Specifically, the track pitch was set to 1 μm, and the magnetic recording media was evaluated from the inner circumference to the outer circumference. This is equivalent to evaluating the entire area of ​​the magnetic recording media, and all magnetic recording media passed the test.

[0135] As described above, embodiments of this disclosure have been explained, but these embodiments are provided as examples only and do not limit this disclosure. The embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, or modifications are possible without departing from the spirit of the invention. The embodiments and their variations are included in the scope or spirit of the invention and are included in the scope of the invention and its equivalents as described in the claims.

[0136] This application claims priority based on Japanese Patent Application No. 2024-227901, filed with the Japan Patent Office on 24 December 2024, and incorporates all the contents of the said application.

[0137] 1...Non-magnetic substrate 2...Soft magnetic layer 3...Underlayment 4...Perpendicular magnetic layer 5...Protective layer 30...Magnetic recording medium 31...Rotation drive unit 32...Magnetic head 33...Head drive unit 34...Recording / playback signal processing system

Claims

1. A non-magnetic substrate for a magnetic recording medium, which is identified by inspection of the magnetic recording medium as not having a periodic convex shape on its surface, wherein the magnetic recording medium has a magnetic layer on the non-magnetic substrate, and in the inspection of the magnetic recording medium, the defect portion identified based on the output signal obtained by scanning the surface of the non-magnetic substrate for a magnetic recording medium having a magnetic layer formed under heating conditions below a guaranteed temperature with a thermosensitive resistance element has a periodic convex shape with a height of 0.1 nm or more and a width of 1 μm or more and 15 μm or less.

2. A non-magnetic substrate for a magnetic recording medium, wherein, by inspection of the magnetic recording medium, the amount of non-periodic convex shapes on its surface is identified as being below a standard value, wherein the magnetic recording medium has a magnetic layer on the non-magnetic substrate, and in the inspection of the magnetic recording medium, the defect portion identified based on the output signal obtained by scanning the surface of the non-magnetic substrate for a magnetic recording medium having a magnetic layer formed under heating conditions below a guaranteed temperature with a thermal resistance element has a non-periodic convex shape with a height of 0.1 nm or more and a width of 1 μm or more and 15 μm or less.

3. A method for manufacturing a magnetic recording medium, comprising a step of forming a magnetic recording medium by heating a non-magnetic substrate for a magnetic recording medium at a temperature below a guaranteed temperature, wherein the non-magnetic substrate for the magnetic recording medium is identified by inspection of the magnetic recording medium as not having a periodic convex shape on its surface, the magnetic recording medium has a magnetic layer on the non-magnetic substrate, and in the inspection of the magnetic recording medium, the defect portion identified based on the output signal obtained by scanning the surface of the non-magnetic substrate for the magnetic recording medium, which has a magnetic layer formed on its surface under heating conditions below a guaranteed temperature, with a thermosensitive resistance element, has a periodic convex shape with a height of 0.1 nm to 1.5 nm and a width of 1 μm to 15 μm.

4. A method for manufacturing a magnetic recording medium, comprising a step of forming a magnetic recording medium by heating a non-magnetic substrate for a magnetic recording medium at a temperature below a guaranteed temperature, wherein the non-magnetic substrate for the magnetic recording medium is identified by inspection of the magnetic recording medium as having an amount of non-periodic convex shapes on its surface that is below a standard value, the magnetic recording medium has a magnetic layer on the non-magnetic substrate, and in the inspection of the magnetic recording medium, the defect portion identified based on the output signal obtained by scanning the surface of the non-magnetic substrate for the magnetic recording medium, which has a magnetic layer formed on its surface under heating conditions below a guaranteed temperature, has a non-periodic convex shape with a height of 0.1 nm or more and a width of 1 μm or more and 15 μm or less.

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