Magnetic recording medium and magnetic recording / recovery device

Abstract

To provide highly reliable magnetic recording media and magnetic recording / recovery devices. [Solution] A magnetic recording medium having a magnetic layer on a non-magnetic substrate, wherein the height is 0.1 nm or more and 1.5 nm or less, and the width is 1 μm or more and 15 μm or less, and the location of the defect portion having a non-periodic convex shape is specified, or there is no defect portion having a non-periodic convex shape, or the amount of non-periodic convex shape is below a reference value.

Description

Technical Field

[0001] The present disclosure relates to a magnetic recording medium and a magnetic recording and reproducing apparatus.

Background Art

[0002] Magnetic recording and reproducing apparatuses typified by hard disk drives (HDDs) are widely used as external storage devices for information processing apparatuses such as computers. In recent years, they are also used as recording apparatuses for moving images and as large-capacity storage in data centers.

[0003] A magnetic recording medium mounted in an HDD is generally manufactured by sequentially forming an underlayer, a magnetic layer, a protective layer, a lubricating layer, etc. on the surface of a substrate made of an aluminum alloy, a glass substrate, or the like. The manufactured magnetic recording medium is evaluated by a glide inspection, a certification inspection, and HDIs (Head Disk Interface sensor) inspection. A magnetic recording medium that has passed the glide inspection, the certification inspection, and the HDIs inspection is guaranteed to have no defective portions, or the amount of defective portions present is guaranteed to be below a reference value, or the location of the defective portions is specified and then shipped.

[0004] As a method for evaluating a conventional magnetic recording medium, for example, a method for evaluating the surface characteristics of a magnetic recording medium using a signal caused by a thermal asperity phenomenon due to contact between a magnetic head having an MR element and protrusions generated on the surface of the magnetic recording medium is disclosed (see Patent Document 1). The thermal asperity phenomenon refers to a phenomenon in which when an MR element provided in a magnetic head comes into contact with protrusions on the surface of a magnetic recording medium, a rapid temperature rise occurs in the read element due to the contact heat, and the electrical resistance value of this read element fluctuates.

[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. That is, 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. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 10-105908 [Patent Document 2] Japanese Patent Publication No. 2008-146803 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] This disclosure aims to provide a highly reliable magnetic recording medium. [Means for solving the problem]

[0008] The means to solve the aforementioned problem are as follows: <1> A magnetic recording medium having a magnetic layer on a non-magnetic substrate, The location of the non-periodic convex defect on the surface of the magnetic recording medium is identified. The aforementioned convex shape is characterized by having a height of 0.1 nm to 1.5 nm and a width of 1 μm to 15 μm. <2> A magnetic recording medium having a magnetic layer on a non-magnetic substrate, The surface of the magnetic recording medium does not have any defects having a non-periodic convex shape. The aforementioned convex shape is characterized by having a height of 0.1 nm to 1.5 nm and a width of 1 μm to 15 μm. <3> A magnetic recording medium having a magnetic layer on a non-magnetic substrate, The amount of non-periodic convex shapes on the surface of the magnetic recording medium is below a reference value, The aforementioned convex shape is characterized by having a height of 0.1 nm to 1.5 nm and a width of 1 μm to 15 μm. <4> The amount of the defect or the protrusion is determined based on the output signal obtained by scanning the surface of the magnetic recording medium with an inspection head having a thermoresistive element. <1> from <3> It is a magnetic recording medium described in any of the following. <5> <1> from <4> A magnetic recording and reproduction device characterized by comprising a magnetic recording medium described in any of the above, and a magnetic head for recording and reproducing information on the magnetic recording medium. [Effects of the Invention]

[0009] According to embodiments of this disclosure, a highly reliable magnetic recording medium can be provided. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view illustrating the mechanism by which the substrate deforms. [Figure 2] This graph schematically shows the signals output from a thermoresistive element during certification testing and HDIs testing of magnetic recording media. [Figure 3] This is a schematic diagram showing an example of an inspection apparatus for inspecting magnetic recording media in this disclosure. [Figure 4] This graph shows an example of an output signal obtained by scanning an inspection head having a thermoresistive element when inspecting the magnetic recording medium of this disclosure using an inspection device. [Figure 5] It is a schematic cross-sectional view showing an example of a magnetic recording medium manufactured by the method for manufacturing a magnetic recording medium of the present disclosure. [Figure 6] It is a schematic perspective view showing an example of the structure of a magnetic recording and reproducing apparatus of the present disclosure. [Figure 7] It is an example of an AFM observation image of a magnetic recording medium in an embodiment.

Mode for Carrying Out the Invention

[0011] The present inventors have discovered that, in conventional HDIs inspections, among the signals output in a state where the thermal resistance element and the magnetic recording medium are non-contact, there are signals different from those 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.

[0012] The present inventors investigated the cause of the generation of this signal and found that it is caused by 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 deformation of the substrate are diverse, but the main causes are as follows.

[0013] Inevitable impurities contained near the surface of the substrate react with surrounding substances and expand in volume due to heating of the substrate during film formation. It is considered that deformation of the substrate occurs due to the film being pushed up as the volume of the inevitable impurities expands. Note that inevitable impurities are impurities that unavoidably混入 from raw materials and the manufacturing process. This will be described in detail using FIG. 1.

[0014] [FIG. 1] 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. 1(b) is a schematic cross-sectional view showing an example of the state of the substrate 14 after the thin film 12 is formed.

[0015] As shown in Figure 1(a), we assume that unavoidable impurities 11 are present near the surface of the substrate 14. Since the surface 10 of the substrate 14 is polished to a smooth finish, the area containing the unavoidable impurities 11 is flat and without any steps compared to the surrounding area. When the substrate 14 is heated to form a thin film 12 on the surface 10 of the substrate 14, the unavoidable impurities 11 expand in volume according to their own coefficient of thermal expansion, or by reacting with the surrounding material, or by crystallizing. As a result, the thin film 12 is pushed up, which may cause protrusions 13 to form on the surface of the thin film 12. Note that the location of the protrusions 13 and the location of the unavoidable impurities 11 approximately coincide in a plan view of the substrate 14.

[0016] The example shown in Figure 1 illustrates the case where the unavoidable impurity 11 appears on the surface 10 of the substrate 14, but the same applies when the unavoidable impurity 11 is located inside the substrate 14 and near the surface 10 of the substrate 14.

[0017] The inventors have found that, in addition to the presence of unavoidable impurities 11, factors that cause the surface of the substrate 14 to deform after heating and form protrusions 13 on the surface of the magnetic recording medium include aggregation of additive elements, segregation of additive elements, and processing strain. Specific causative materials include aluminum alloy substrates, crystallized glass substrates, amorphous glass substrates, and ceramic substrates. Other causative materials include amorphous NiP-based plating films and other plating films applied to the substrate surface.

[0018] Further investigation by the inventors revealed that the protrusions 13 that appear on the surface of the magnetic recording medium have a height of 0.1 nm to 1.5 nm and a width of 1 μm to 15 μm. Magnetic recording media having such protrusions 13 may not be rejected as defective products in the manufacturing process because the protrusions 13 do not come into contact with the thermoresistive element during glide testing, certify testing, and HDIs testing. This can lead to the following problems (1) to (3).

[0019] (1) Unlike the output signals caused by the undulations, the output signals caused by the protrusions lack periodicity and appear superimposed on the output signals caused by the undulations, thus degrading the electromagnetic conversion characteristics of the magnetic recording medium and making signal processing in HDDs difficult.

[0020] (2) The protrusions may grow significantly even after the product has been manufactured. For example, laser heating in heat-assisted HDDs may cause the protrusions to grow even larger, potentially leading to contact between the magnetic head and the protrusions.

[0021] (3) Since the protrusions are generated during the deposition of magnetic films and the like, strain is introduced into the film, which may cause delamination of the film on magnetic recording media in the future.

[0022] Regarding problem (1), we will explain it in detail using Figure 2.

[0023] [Figure 2] 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 both a 170 μm period and a 50 μm period. 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.

[0024] 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.

[0025] 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.

[0026] 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 HDDs difficult.

[0027] 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.

[0028] The magnetic recording medium described herein has been proposed in view of the above circumstances and provides a highly reliable magnetic recording medium.

[0029] The details of the present invention are described below.

[0030] (Magnetic recording medium) The magnetic recording medium as the first embodiment in this disclosure is a magnetic recording medium having a magnetic layer on a non-magnetic substrate, wherein the location of a non-periodic convex defect portion on the surface of the magnetic recording medium is identified, and the convex shape 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.

[0031] A magnetic recording medium as a second embodiment in this disclosure is a magnetic recording medium having a magnetic layer on a non-magnetic substrate, wherein the surface of the magnetic recording medium does not have any non-periodic convex defect portions, and the convex shapes have 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.

[0032] A magnetic recording medium as a third embodiment in this disclosure is a magnetic recording medium having a magnetic layer on a non-magnetic substrate, wherein the amount of non-periodic convex shapes on the surface of the magnetic recording medium is less than or equal to a reference value, and the convex shapes have 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.

[0033] 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 the non-magnetic substrate.

[0034] The magnetic recording medium as the first embodiment, the magnetic recording medium as the second embodiment, and the magnetic recording medium as the third embodiment in this disclosure may be collectively referred to as "magnetic recording medium."

[0035] The magnetic recording medium of this disclosure may include other components as necessary.

[0036] In the magnetic recording medium of this disclosure, it is preferable that the amount of a non-periodic convex defect or convex shape is identified based on an output signal obtained by scanning the surface of the magnetic recording medium with an inspection head having a thermoresistive element.

[0037] The magnetic recording medium of this disclosure makes it possible to identify defective portions having a non-periodic convex shape. Magnetic recording mediums in which defective portions are detected are either removed from the manufacturing line, the amount of defective portions in the magnetic recording medium is identified, or the location of the defective portions in the magnetic recording medium is identified. In other words, the magnetic recording medium of this disclosure guarantees that the magnetic recording medium is free of defects, or that the amount of defective portions in the magnetic recording medium is below a certain value, or that the location of the defective portions in the magnetic recording medium is identified, thus enabling the shipment of highly reliable and high-quality products.

[0038] The magnetic recording medium of this disclosure, when applied to a magnetic recording and playback device, can suppress the generation of noise signals, enhance the electromagnetic conversion characteristics of the magnetic recording medium, and facilitate signal processing in the magnetic recording and playback device.

[0039] The magnetic recording medium described herein makes it possible to eliminate magnetic recording mediums with potentially growing defects or to identify the location of such defects in a commercially available magnetic recording and playback device. Therefore, it is possible to reduce the risk of film delamination occurring on the magnetic recording medium and to identify the location of such risk, thereby providing a highly reliable magnetic recording and playback device.

[0040] <Defective part> The defective portion has a non-periodic convex shape. This convex shape has a height of 0.1 nm to 1.5 nm and a width of 1 μm to 15 μm.

[0041] As mentioned above, it is preferable that the convex shape is formed during the manufacturing process of the magnetic recording medium.

[0042] 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.

[0043] 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.

[0044] The height and width of the convex shape are defined by the following measurement method. (1) In AFM measurement, the measurement is performed in a quadrilateral region (preferably 50 μm) that includes the entire convex shape and also includes a flat region of at least 10 μm or more around it. (2) Extract the profile of the cross-section of the convex shape that passes through the position of the vertex of the convex shape. (3) A flat region of at least 10 μm or more around the convex shape of the obtained cross-sectional profile is used as the baseline (preferably 15 μm). (4) Using the baseline obtained in (3) as a reference, the length to the vertex of the convex shape of the cross-sectional profile is defined as the "height of the convex shape". (5) Using the baseline obtained in (3) as a reference, the length of the base of the convex shape is defined as the "width of the convex shape".

[0045] Defects with a non-periodic convex shape are identified based on an output signal obtained by scanning the surface of a magnetic recording medium with an inspection head having a thermoresistive element in a non-contact manner. This signal is 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 thermoresistive element and the convex defect.

[0046] As long as the magnetic recording medium to be inspected has a magnetic layer on a non-magnetic substrate, there are no restrictions on the type and number of layers stacked, and they can be appropriately selected according to the purpose.

[0047] Herein, the present disclosure will be described in detail with reference to the drawings. However, the embodiments shown below are illustrative examples for the purpose of realizing the technical concept of the present disclosure and are not limited to those described below, and may be modified as appropriate without departing from the gist of the present disclosure.

[0048] 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.

[0049] Furthermore, the following description uses terms to indicate specific directions or positions as needed (e.g., "up," "down," "side," "top surface," "bottom surface," "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 excessively limit the technical scope of the invention. For example, if "top surface" is mentioned, the invention must not always be used in a way that it faces upwards.

[0050] <Inspection equipment> [Figure 3] Figure 3 is a schematic diagram showing an example of an inspection apparatus for inspecting the magnetic recording medium of this disclosure.

[0051] The inspection device 41 shown in Figure 3 comprises 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.

[0052] 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.

[0053] The HDI sensor unit functions as a thermoresistive element whose physical properties, such as resistance, change as the temperature rises, and can output a signal resulting from the phenomenon of the resistance value of the thermoresistive element changing.

[0054] Examples of thermoresistive elements that can be used 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."

[0055] The inspection device 41 may also have a laser heating mechanism 40 for non-contact heating of the measurement area when the magnetic recording medium 42 is used in a heat-assisted manner.

[0056] 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.

[0057] The inspection device 41 may be used in conjunction with the certify inspection and HDIs inspection in the manufacturing process of the magnetic recording medium 42, or it may be provided separately from the certify inspection and HDIs inspection.

[0058] [Figure 4] Figure 4 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 of the present disclosure using an inspection device. Specifically, Figure 4(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 4(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 4(a). Both signals shown in Figure 4(a) and Figure 4(b) 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 between the thermoresistive element and the surface of the magnetic recording medium via air.

[0059] In the graphs shown in Figures 4(a) and 4(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. Specifically, the height of the convex shape is indicated by the signal intensity on the vertical axis in Figure 4, 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 4, 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.

[0060] As shown in Figure 4(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 4(a).

[0061] Here, of the three convex-shaped signals 21 in Figure 4(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.

[0062] 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 in the magnetic recording media. In other words, undulations on the surface of the non-magnetic substrate are affected by the thin film surface formed on it, and as a result appear on the surface of the magnetic recording media.

[0063] Since the undulations on the surface of non-magnetic substrates used in magnetic recording media often 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.

[0064] Figure 4(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 4(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 this 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.

[0065] As described above, the inspection of the magnetic recording medium according to this disclosure preferably identifies defective portions having a non-periodic convex shape based on an output signal from which signals caused by undulations on the surface of the magnetic recording medium have been removed.

[0066] <Method for manufacturing magnetic recording media> The method for manufacturing a magnetic recording medium according to this disclosure is a method for manufacturing a magnetic recording medium having a magnetic layer on a non-magnetic substrate, and may include a magnetic recording medium formation step and an inspection step, and may also include other steps as necessary.

[0067] There are no particular restrictions on the magnetic recording media manufactured by the manufacturing method of the magnetic recording media, and they can be appropriately selected according to the purpose. Examples include conventional magnetic recording media, magnetic recording media used in the heat-assisted method, and magnetic recording media used in the microwave-assisted method.

[0068] In the method for manufacturing a magnetic recording medium described in this disclosure, a magnetic recording medium used in a heat-assisted method will be specifically described below with reference to Figure 5.

[0069] [Figure 5] Figure 5 is a schematic cross-sectional view showing an example of a magnetic recording medium manufactured by the manufacturing method of the magnetic recording medium described herein.

[0070] The magnetic recording medium shown in Figure 5 has a soft magnetic layer 2, an underlayer 3, a perpendicular magnetic layer 4, and a protective layer 5 sequentially laminated on both main surfaces of a non-magnetic substrate 1. Although Figure 5 shows a configuration in which each layer is laminated on both sides of a non-magnetic substrate 1, the magnetic recording medium may also consist of a configuration in which each layer is laminated on only one side of the non-magnetic substrate 1.

[0071] The shape of the magnetic recording medium is not particularly limited as long as it can be applied to a magnetic recording and playback device, and can be appropriately selected according to the purpose. For example, a disc shape with a central hole can be used.

[0072] <<Magnetic recording medium formation process>> The magnetic recording medium formation process is a process of heating a non-magnetic substrate 1 to form a magnetic layer. 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.

[0073] 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.

[0074] <<<Soft magnetic layer formation process>>> The soft magnetic layer formation process of this disclosure is a process of forming a soft magnetic layer 2 on a non-magnetic substrate 1.

[0075] -Nonmagnetic substrate 1- There are no particular restrictions on the non-magnetic substrate 1, and it can be appropriately selected according to the purpose. Examples include metal substrates and non-metallic substrates.

[0076] --Non-metallic substrate-- Examples of non-metallic substrates include those made of non-metallic materials such as glass.

[0077] Examples of glass substrates include SiO2-Al2O3-R2O-based chemically strengthened glass, SiO2-Al2O3-Li2O-based glass ceramics, and SiO2-Al2O3-MgO-TiO2-based glass ceramics. Note that R represents at least one element selected from among the alkali metal elements.

[0078] Among these glass substrates, SiO2-Al2O3-MgO-CaO-Li2O-Na2O-ZrO2-Y2O3-TiO2-As2O3-type chemically strengthened glass, SiO2-Al2O3-Li2O-Na2O-ZrO2-As2O3-type chemically strengthened glass, SiO2-Al2O3-MgO-ZnO-Li2O-P2O5-ZrO2-K2O-Sb2O3-type glass ceramics, SiO2-Al2O3-MgO-CaO-BaO-TiO2-P2O5-As2O3-type glass ceramics, and SiO2-Al2O3-MgO-CaO-SrO-BaO-TiO2-ZrO2-Bi2O3-Sb2O3-type glass ceramics are preferred.

[0079] --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.

[0080] 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.

[0081] 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.

[0082] In addition to Mg and Cr as additive elements, the aluminum alloy substrate may also contain one or more elements selected from the group consisting of Si, Zn, Mn, Ti, Cr, V, Zr, Mo, and Co.

[0083] Unavoidable impurities include, for example, B and P.

[0084] 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.

[0085] Among these non-magnetic substrates, 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] Examples of targets containing materials that form a soft magnetic layer include soft magnetic alloys such as FeCo alloys, CoZrNb alloys, and CoTaZr alloys.

[0090] <<<Underlayer formation process>>> The underlying layer formation process described herein is a process of forming an underlying layer 3 on a soft magnetic layer 2. The sub-layer formation process may include a first sub-layer formation process in which a first sub-layer is formed on the soft magnetic layer 2, a second sub-layer formation process in which a second sub-layer is formed on the first sub-layer, and a third sub-layer formation process in which a third sub-layer is formed on the second sub-layer.

[0091] 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.

[0092] 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.

[0093] In the first sublayer formation process, there are no particular restrictions on the material used to form the first sublayer, 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] <<<Perpendicular magnetic layer formation process>>> The perpendicular magnetic layer formation process of this disclosure is a process of forming a perpendicular magnetic layer 4 on a base layer 3.

[0098] 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.

[0099] 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.

[0100] There are no particular limitations on the target material that forms the perpendicular magnetic layer 4, and it can be appropriately selected depending on the purpose. For example, a target containing an alloy having an L10 structure can be used.

[0101] Examples of alloys having an L10 structure include alloys containing Fe or Co and Pt, etc. Specific examples of alloys having an L10 structure include FePt alloys and CoPt alloys.

[0102] In the perpendicular magnetic layer formation process, it is preferable to include a heating step in which the non-magnetic substrate 1, soft magnetic layer 2, underlayer 3, and 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, high-frequency waves, and electromagnetic waves such as microwaves can be used.

[0103] If the perpendicular magnetic layer 4 contains an FePt alloy having an L10 structure, it is preferable to heat it to a high temperature of 400°C or higher to order it.

[0104] <<<Protective layer formation process>>> The protective layer formation step of this disclosure is a step of forming a protective layer 5 on a perpendicular magnetic layer 4.

[0105] 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.

[0106] 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.

[0107] <<<Liquid Lubricant Layer Formation Process>>> The liquid lubricant layer formation step of this disclosure is a step of forming a liquid lubricant layer on the protective layer 5.

[0108] 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.

[0109] <<<<Burning Process>>> The burnishing process described herein is a process of burnishing the surface of a laminate with an abrasive material. Specifically, it is a process of pressing a tape containing an abrasive material (abrasive tape) against the surface of the laminate and rubbing it.

[0110] <<Inspection Process>> The inspection process involves inspecting the magnetic recording medium obtained by the magnetic recording medium formation process using the inspection apparatus for inspecting magnetic recording media described above.

[0111] The inspection process may include, in addition to the inspection method using the inspection device for inspecting the magnetic recording medium described above, glide inspection, certify inspection, and HDIs inspection.

[0112] <<<Glide Inspection>>> Glide inspection is an inspection for checking the presence or absence 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 is a protrusion on the surface of the magnetic recording medium that is higher than the floating height (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, a magnetic recording medium detected to have high protrusions on its surface by glide inspection is excluded from the manufacturing process as a defective product.

[0113] For magnetic recording media that pass the glide inspection, certification inspection and HDIs inspection are carried out.

[0114] <<<Certification Inspection>>> Certification inspection is an inspection for confirming the defects and quality of the electromagnetic conversion characteristics of a magnetic recording medium. In the certification inspection, for a magnetic recording medium, after recording a predetermined signal using a magnetic head in the same way as recording and playing back in a normal HDD, the signal is played back, and the electromagnetic conversion characteristics are evaluated from the obtained playback signal.

[0115] <<<HDIs Inspection>>> HDIs inspection is an inspection for checking the presence or absence of convex defects and concave defects in a magnetic recording medium. By checking what kind of convex defects and concave defects exist on the surface of the magnetic recording medium, the data read / write performance and the reliability of the magnetic recording medium are evaluated.

[0116] The inspection method using the inspection apparatus for inspecting the above-mentioned magnetic recording medium is preferably carried out in conjunction with the HDIs inspection.

[0117] The inspection process described in this disclosure does not necessarily require inspection of the entire area of ​​the magnetic recording medium. A common practice in magnetic recording medium inspection methods 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 medium, thereby providing a sufficient understanding of its overall characteristics. The accuracy increases as the proportion of the area evaluated increases.

[0118] 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.

[0119] 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.

[0120] (Magnetic recording and playback device) The magnetic recording and playback apparatus of this disclosure comprises a magnetic recording medium and a magnetic head for recording and playback of information on the magnetic recording medium, and may include other components as needed. Since the magnetic recording medium is the same as described above (magnetic recording medium), redundant descriptions are omitted.

[0121] [Figure 6] Figure 6 is a schematic perspective view showing an example of the structure of the magnetic recording and playback apparatus of this disclosure.

[0122] The magnetic recording and playback device 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 that rotates 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 that moves 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 device shown in Figure 6, further improvements in reliability can be achieved by using a magnetic recording medium 30 that has been judged to pass the inspection method for magnetic recording media of this disclosure. [Examples]

[0124] The following are examples of the present invention, but the scope of the present invention is not limited to these examples.

[0125] A magnetic recording medium with an outer diameter of 3.5 inches, used in a heat-assisted system, was manufactured using the method described below.

[0126] A heat-resistant glass substrate was used as the non-magnetic substrate.

[0127] 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.

[0128] A glide test was performed on the obtained magnetic recording media using a glide tester equipped with a piezoelectric element head. The glide height of the head (the distance between the head and the surface of the magnetic recording media, assuming no surface defects) was set to 10 nm, and magnetic recording media with large protrusions on the surface were excluded.

[0129] One hundred magnetic recording media that passed glide testing were prepared, and each magnetic recording media was subjected to HDIs testing 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 higher 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 test.

[0130] Next, a second HDIs inspection was performed on the 96 magnetic recording media that passed the initial inspection, under modified conditions. Specifically, the glide height remained unchanged, and an 800kHz-10MHz bandpass filter was used to remove signals caused by undulation from the output signal from the thermoresistive element of the inspection head, extracting only signals corresponding to non-periodic convex shapes (height between 0.1nm and 1.5nm, and width between 1μm and 15μm). Among the extracted signals, those without defects of 400mV or more in absolute value were deemed to pass. 91 magnetic recording media passed the initial inspection.

[0131] 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.

[0132] 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 then checked. It was confirmed that the SNR of the passing products improved by an average of 0.3%.

[0133] For magnetic recording media that passed the second HDIs test, a third HDIs test was performed under modified conditions. Specifically, the track pitch was set to 1 μm, and the magnetic recording media was evaluated from the inner 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.

[0134] As described above, this disclosure has been explained based on specific embodiments, but these embodiments are merely examples, and this disclosure is not limited to the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, additions, modifications, etc., are possible without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of symbols]

[0135] 1...Nonmagnetic substrate 2...Soft magnetic layer 3…base layer 4...Perpendicular magnetic layer 5…Protective layer 30…Magnetic recording media 31…Media drive unit 32… Magnetic head 33... Head drive unit 34…Recording and playback signal processing system

Claims

1. A magnetic recording medium having a magnetic layer on a non-magnetic substrate, The location of the non-periodic convex defect on the surface of the magnetic recording medium is identified. The aforementioned convex shape is characterized by 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, in a magnetic recording medium.

2. A magnetic recording medium having a magnetic layer on a non-magnetic substrate, The surface of the magnetic recording medium does not have any defects having a non-periodic convex shape. The aforementioned convex shape is characterized by 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, in a magnetic recording medium.

3. A magnetic recording medium having a magnetic layer on a non-magnetic substrate, The amount of non-periodic convex shapes on the surface of the magnetic recording medium is below a reference value, The aforementioned convex shape is characterized by 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, in a magnetic recording medium.

4. The magnetic recording medium according to any one of claims 1 to 3, wherein the amount of the defect or the protruding shape is identified based on an output signal obtained by scanning the surface of the magnetic recording medium with an inspection head having a thermosensitive resistance element.

5. A magnetic recording and reproduction device comprising a magnetic recording medium according to any one of claims 1 to 3, and a magnetic head for recording and reproducing information on the magnetic recording medium.

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