Magnetic recording medium, method for manufacturing magnetic recording medium, and magnetic storage device

Abstract

The purpose of the present invention is to provide a magnetic recording medium which stably maintains a state in which a granular magnetic layer forms a granular structure therein, and which improves the surface recording density. The magnetic recording medium has a substrate, an underlayer, a first magnetic layer, and a second magnetic layer in this order, the first magnetic layer including magnetic particles having an L10 structure, and the second magnetic layer including magnetic particles having an L10 structure and having a granular structure including a grain boundary portion of hexagonal boron nitride. The (111) plane of the magnetic particles contained in the first magnetic layer is covered with an alloy of VN, Si3N4, YN, or TiN at the interface with the second magnetic layer, and the magnetic particles contained in the second magnetic layer are epitaxially grown from the (001) plane of the magnetic particles contained in the first magnetic layer. The magnetic particles contained in the first magnetic layer and the magnetic particles contained in the second magnetic layer are each columnar crystals penetrating the first magnetic layer and the second magnetic layer.

Description

Technical Field

[0001] This disclosure relates to magnetic recording media, methods for manufacturing magnetic recording media, and magnetic storage devices. Background Technology

[0002] In recent years, thermal-assisted recording and microwave-assisted recording methods, which involve irradiating the magnetic recording medium with near-field light or microwaves to locally heat it, thereby reducing the coercivity and recording the data, have emerged as methods capable of achieving 2Tbit / inch recording speeds. 2 The next generation of recording methods, characterized by high surface density, has attracted attention.

[0003] If a magnetic head using this auxiliary recording method is employed, it is possible to easily record on magnetic recording media with a coercivity of tens of kOe at room temperature. Furthermore, the magnetic particles contained in the magnetic layer of the magnetic recording medium can, for example, be magnetic particles with a high crystalline magnetic anisotropy constant (Ku). Magnetic particles with a high crystalline magnetic anisotropy constant (Ku) can be miniaturized while maintaining thermal stability, thereby increasing the coercivity at room temperature.

[0004] As magnetic particles with high crystal magnetic anisotropy constant (Ku), for example, Fe-Pt alloy particles (Ku: maximum 7 × 10⁻⁶) are known to have an anisotropy constant of 7 × 10⁻⁶. 6 J / m 3 Co-Pt alloy particles (Ku: maximum 5×10⁻⁶) 6 J / m 3 Magnetic particles with an L10 structure, such as )

[0005] As a magnetic layer that uses magnetic particles with an L10 structure, for example, Non-Patent Document 1 discloses a granular magnetic layer in which FePt magnetic particles with an L10 structure are surrounded by a layer of hexagonal boron nitride.

[0006] Existing technical documents

[0007] Non-patent literature

[0008] Non-Patent Literature 1: BSD Ch. S. Varaprasad et al., “FePt-BN granular HAMRmedia with high grain aspect ratio and high L1 ordering on corning Lotus” TM NXTglass”, AIP Advances, Volume 13, Issue 3, 035002(2023)

[0009] Here, it is desirable to further increase the areal recording density of the magnetic recording medium. In order to further increase the areal recording density of the magnetic recording medium, it is important to further reduce the particle size of the magnetic particles contained in the magnetic layer, while further improving the anisotropy of the magnetic particles.

[0010] As such a magnetic layer, a magnetic layer with FePt magnetic particles oriented in the (001) direction in the L10 structure and a granular structure containing hexagonal boron nitride at the grain boundary was proposed (hereinafter referred to as "FePt-hBN granular magnetic layer").

[0011] Hexagonal boron nitride has a layered structure with (001) planes stacked parallel to each other, but grain boundaries are easily formed between FePt magnetic particles, thereby reducing the particle size of the FePt magnetic particles. Furthermore, hexagonal boron nitride has low reactivity with FePt magnetic particles, thus not compromising the normalization of the magnetic particles. Moreover, such hexagonal boron nitride is preferably formed such that its (001) planes surround the sides of the FePt magnetic particles.

[0012] However, in conventional FePt-hBN granular magnetic layers, the magnetic particles and grain boundaries tend to separate into layers, often failing to produce a granular structure. Furthermore, the grain boundary components, such as BN, are often not fully crystallized and remain amorphous. Therefore, even when using magnetic layers with a granular structure (also called granular magnetic layers), there is sometimes a problem where the planar recording density of the magnetic recording medium is not improved. Summary of the Invention

[0013] The purpose of this disclosure is to provide a magnetic recording medium that stably maintains the granular magnetic layer in a granular structure within the interior, thereby further improving the surface recording density.

[0014] Methods for solving problems

[0015] The above objectives can be achieved through the following methods.

[0016] (1) A magnetic recording medium having, in sequence, a substrate, a base layer, a first magnetic layer, and a second magnetic layer,

[0017] The first magnetic layer mentioned above contains magnetic particles with an L10 structure.

[0018] The second magnetic layer described above comprises magnetic particles with an L10 structure and a granular structure having grain boundaries containing hexagonal boron nitride.

[0019] The (111) facets of the magnetic particles contained in the first magnetic layer are covered at the interface with the second magnetic layer by any alloy of VN, Si3N4, YN, or TiN.

[0020] The magnetic particles contained in the second magnetic layer are epitaxially grown from the (001) face of the magnetic particles contained in the first magnetic layer.

[0021] The magnetic particles contained in the first magnetic layer and the magnetic particles contained in the second magnetic layer are each columnar crystals that penetrate the first magnetic layer and the second magnetic layer.

[0022] (2) According to the magnetic recording medium described in (1), the magnetic particles with an L10 structure contained in the first magnetic layer and the second magnetic layer are FePt alloy particles.

[0023] (3) A method for manufacturing a magnetic recording medium, wherein the magnetic recording medium sequentially comprises a substrate, a base layer, a first magnetic layer, and a second magnetic layer.

[0024] The first magnetic layer mentioned above contains magnetic particles with an L10 structure.

[0025] The second magnetic layer described above comprises magnetic particles with an L10 structure and a granular structure having grain boundaries containing hexagonal boron nitride.

[0026] The (111) facets of the magnetic particles contained in the first magnetic layer are covered at the interface with the second magnetic layer by any alloy of VN, Si3N4, YN, or TiN.

[0027] The magnetic particles contained in the second magnetic layer are epitaxially grown from the (001) face of the magnetic particles contained in the first magnetic layer.

[0028] The magnetic particles contained in the first magnetic layer and the magnetic particles contained in the second magnetic layer are each columnar crystals that penetrate the first magnetic layer and the second magnetic layer, respectively.

[0029] The manufacturing method includes, between the step of forming the first magnetic layer by sputtering and the step of forming the second magnetic layer by sputtering, a step of forming a layer of any alloy of VN, Si3N4, YN, or TiN by sputtering.

[0030] (4) A magnetic storage device having the magnetic recording medium described in (1) or (2).

[0031] The effects of the invention

[0032] According to one aspect of this disclosure, a magnetic recording medium is provided that can stably maintain the state in which the granular magnetic layer has formed a granular structure, thereby further improving the surface recording density.

[0033] According to other aspects of this disclosure, a method for manufacturing a magnetic recording medium is provided that can stably maintain the state in which the granular magnetic layer has formed a granular structure, thereby further improving the surface recording density.

[0034] Furthermore, magnetic storage devices with high recording capacity can be provided according to other methods of this disclosure. Attached Figure Description

[0035] Figure 1 This is a cross-sectional view illustrating an example of the layer structure of a magnetic recording medium according to an embodiment of the present disclosure.

[0036] Figure 2 The cross-sectional schematic diagrams illustrating the crystal growth during the formation of the first magnetic layer and the second magnetic layer are shown below. (a) is a cross-sectional schematic diagram showing conventional crystal growth, and (b) is a cross-sectional schematic diagram showing crystal growth according to the embodiment of the present disclosure.

[0037] Figure 3 An angle view illustrating an example of a magnetic storage device according to an embodiment of this disclosure.

[0038] Figure 4 To indicate Figure 3 A schematic diagram of the magnetic head. Detailed Implementation

[0039] Hereinafter, this specific embodiment will be described with reference to the accompanying drawings. Furthermore, in order to facilitate understanding of the features, the accompanying drawings used in the following description sometimes show enlarged portions of the features, and the dimensions and proportions of each component may not be the same. In addition, in this specification, the tilde “~” indicating a numerical range means, unless otherwise specified, that the numerical values ​​described before and after it are the lower and upper limits. When only the unit of the upper limit value is described in the numerical range indicated by “~”, the lower limit value also uses the same unit.

[0040] [Magnetic recording media]

[0041] Figure 1 This illustrates an example of the layer configuration of a magnetic recording medium according to an embodiment of the present disclosure (hereinafter, sometimes referred to as this embodiment). Figure 1 As shown, the magnetic recording medium 1 is provided with a substrate 10, a base layer 20, a first magnetic layer 30 and a second magnetic layer 40, which are stacked in sequence.

[0042] The substrate 10 can be a commonly used substrate in the magnetic recording medium 1. For example, a heat-resistant glass substrate with a softening temperature of 500°C or higher, and more preferably 600°C or higher, is preferred as the substrate 10. It can be used even when the substrate 10 is heated to a temperature of 500°C or higher during the manufacture of the magnetic recording medium 1.

[0043] As for the material constituting the base layer 20, there are no particular limitations as long as the magnetic particles with L10 structure contained in the first magnetic layer 30 and the second magnetic layer 40 can be oriented in the (001) plane.

[0044] The base layer 20 can have a multi-layer structure.

[0045] The base layer 20 preferably contains a NaCl-type compound.

[0046] Examples of NaCl-type compounds include MgO, TiO, NiO, TiN, TaN, HfN, NbN, ZrC, HfC, TaC, NbC, and TiC. These can be used individually or in combination with two or more.

[0047] The first magnetic layer 30 contains magnetic particles with an L10 structure.

[0048] Examples of magnetic particles with an L10 structure constituting the first magnetic layer 30 include FePt alloy particles and CoPt alloy particles. FePt alloy particles and CoPt alloy particles are magnetic particles oriented in the (001) direction of the L10 structure.

[0049] The magnetic particles contained in the first magnetic layer 30 are columnar crystals with a shape that extends through the first magnetic layer 30.

[0050] The particle size of the magnetic particles contained in the first magnetic layer 30 is not particularly limited if they are columnar; for example, it can be 3 to 7 nm in diameter equivalent to a circle. Alternatively, the particle size of the magnetic particles contained in the first magnetic layer 30 can be the average particle size of the magnetic particles as determined by observation using a plane transmission electron microscope. When the magnetic particles are spherical, their diameter is used; when they are elliptical, the midpoint between their minor and major axes is used; and when they are amorphous, the midpoint between their short and long sides is used to determine the particle size distribution. The average particle size obtained based on the determined particle size distribution can be used as the average particle size and set as the particle size of the magnetic particles.

[0051] The aspect ratio of the magnetic particles contained in the first magnetic layer 30 depends on the thickness of the first magnetic layer 30. For example, when the height t of the magnetic particle is equal to the equivalent circle diameter D, the aspect ratio (t / D) of the magnetic particle can be 0.1 to 1.5. Furthermore, the aspect ratio refers to the value obtained by dividing the longest axis by the shortest axis in the magnetic particle. The aspect ratio of the magnetic particle is calculated by dividing the particle height, as measured using a cross-sectional transmission electron microscope, by the average particle size, as measured using a planar transmission electron microscope.

[0053] The center-to-center distance between the magnetic particles contained in the first magnetic layer 30 is preferably 4.0 to 9.0 nm. More preferably, the center-to-center distance between the magnetic particles contained in the first magnetic layer 30 is 8.8 nm or less, and even more preferably 8.6 nm or less. If the center-to-center distance between the magnetic particles contained in the first magnetic layer 30 is within the above-mentioned preferred range, then the first magnetic layer 30 can contain magnetic particles with small particle sizes.

[0054] Furthermore, the center-to-center distance between magnetic particles refers to the distance between the centers of mass of adjacent magnetic particles. The center-to-center distance between magnetic particles can be determined, for example, by calculating the distance between the centers of mass of adjacent magnetic particles from a surface observation image obtained using a scanning electron microscope (SEM).

[0055] The second magnetic layer 40 is a granular magnetic layer containing magnetic particles with an L10 structure and grain boundaries containing hexagonal boron nitride, also known as hexagonal boron nitride grain boundaries.

[0056] Examples of magnetic particles constituting the second magnetic layer 40 and having an L10 structure include, for example, FePt alloy particles and CoPt alloy particles.

[0057] The magnetic particles contained in the second magnetic layer 40 are the same as those contained in the first magnetic layer 30, and are columnar crystals with a shape that extends through the second magnetic layer 40.

[0058] The particle size of the magnetic particles contained in the second magnetic layer 40 is the same as that of the magnetic particles contained in the first magnetic layer 30. If they are columnar, there is no particular limitation; for example, the equivalent circle diameter can be 3 to 7 nm. In addition, the average particle size of the magnetic particles contained in the second magnetic layer 40 can be determined using the same method as that used for the magnetic particles contained in the first magnetic layer 30.

[0059] The aspect ratio of the magnetic particles contained in the second magnetic layer 40 is the same as that of the magnetic particles contained in the first magnetic layer 30, and depends on the thickness of the second magnetic layer 40. For example, the aspect ratio of the magnetic particles can be 1.2 to 2.5. Furthermore, the aspect ratio of the magnetic particles is calculated from t / D when the height of the magnetic particles is t and the equivalent circle diameter is D. The aspect ratio of the magnetic particles contained in the second magnetic layer 40 can be measured using the same method as that used to measure the aspect ratio of the magnetic particles contained in the first magnetic layer 30.

[0060] The hexagonal boron nitride contained in the grain boundary portion has a layered structure with its (001) planes stacked approximately parallel to each other. Since grain boundaries are easily formed between the magnetic particles contained in the second magnetic layer 40, the particle size of the magnetic particles contained in the second magnetic layer 40 can be reduced. Furthermore, the hexagonal boron nitride has low reactivity with magnetic particles having an L10 structure, thus not compromising the normalization of the magnetic particles contained in the second magnetic layer 40. Therefore, the hexagonal boron nitride is preferably formed such that its (001) plane surrounds the side surfaces of the magnetic particles contained in the second magnetic layer 40.

[0061] In previous methods, it was difficult to stably form such granular magnetic layers. Specifically, the magnetic alloy has low reactivity with boron nitride, resulting in layers that separate during film formation, often failing to form a granular structure. Furthermore, boron nitride often fails to crystallize and becomes amorphous.

[0062] The inventors of this disclosure have discovered that by making the magnetic layer a two-layer structure of a first magnetic layer 30 and a second magnetic layer 40 extending from the substrate 10 side, magnetic particles of the second magnetic layer 40 can be epitaxially grown from the magnetic particles of the first magnetic layer 30, thereby enabling the stable formation of a granular structure of the second magnetic layer 40.

[0063] In this case, in addition to the (001) surface, the (111) surface is also formed among the magnetic particles on the growth surface of the first magnetic layer 30. As a result, during the formation of the second magnetic layer 40, crystal growth occurs in the direction perpendicular to the (111) surface, leading to coarsening of the magnetic particles in the second magnetic layer 40. To prevent the coarsening of the magnetic particles in the second magnetic layer 40, in this embodiment, the (111) surface of the first magnetic layer 30 is covered with an alloy containing any nitride of VN, Si3N4, YN, or TiN, thereby suppressing the coarsening of the magnetic particles in the second magnetic layer 40. Figure 2 Let me explain this in detail.

[0064] Figure 2 (a) is a cross-sectional schematic diagram illustrating the crystal growth during the formation of the first magnetic layer 30 and the second magnetic layer 40, and shows a conventional cross-sectional schematic diagram of the crystal growth during the formation of the first magnetic layer 30 and the second magnetic layer 40. Figure 2 (b) is a cross-sectional schematic diagram showing the crystal growth during the formation of the first magnetic layer 30 and the second magnetic layer 40 in this embodiment. Figure 2 As shown in (a), in the growth surface 311A ​​of the magnetic particles 31 constituting the first magnetic layer 30 with the L10 structure formed on the substrate 10, a (001) surface 311B parallel to the substrate 10 is formed, and the (001) surface 311B is formed on the side opposite to the growth surface 311A. Figure 2The (111) surface 311C is inclined at about 35° on the middle and lower sides. If a second magnetic layer 40 (dashed part) is formed on the (111) surface 311C, the magnetic particles 41 of the second magnetic layer 40 grow in the direction perpendicular to the (111) surface 311C of the magnetic particles 31, thereby increasing the particle size of the magnetic particles 41.

[0065] On the other hand, in this embodiment, Figure 2 As shown in (b), the (111) facet 311C of the magnetic particles 31 in the first magnetic layer 30 is covered with a layer 50 of any alloy of VN, Si3N4, YN, or TiN. This suppresses the coarsening of the magnetic particles 41 in the second magnetic layer 40 (dashed portion). By epitaxially growing the magnetic particles 41 in the second magnetic layer 40 on the (001) facet 311B of the magnetic particles 31 in the first magnetic layer 30, columnar crystals are formed in which the magnetic particles 31 and 41 penetrate the first magnetic layer 30 and the second magnetic layer 40, thereby maintaining a fine particle size for the magnetic particles 31 and 41.

[0066] In this embodiment, the layer 50 of any alloy of VN, Si3N4, YN, or TiN is a layer comprising an alloy formed from any nitride of VN, Si3N4, YN, or TiN. Preferably, it comprises at least 50% of any alloy of VN, Si3N4, YN, or TiN, and most preferably, it is composed solely of any alloy of VN, Si3N4, YN, or TiN. Furthermore, the layer 50 of any alloy of VN, Si3N4, YN, or TiN is not a continuous film, but a film that partially penetrates between the magnetic particles 31 and 41.

[0067] The hexagonal boron nitride grain boundary 42 of the second magnetic layer 40 contains hexagonal boron nitride, preferably containing more than 50 atomic% hexagonal boron nitride, and most preferably composed of only hexagonal boron nitride.

[0068] The content of hexagonal boron nitride grain boundaries 42 in the second magnetic layer 40 is preferably in the range of 25 to 50 vol%, more preferably in the range of 35 to 45 vol%. When the content of hexagonal boron nitride grain boundaries 42 in the second magnetic layer 40 is in the range of 25 to 50 vol%, the anisotropy of the coercivity Hc of the magnetic recording medium 1 and the magnetic particles 31 and 41 contained in the first magnetic layer 30 and the second magnetic layer 40 can be improved.

[0069] There is no particular limitation on the method for determining the content of hexagonal boron nitride grain boundaries 42 in the second magnetic layer 40. Common methods for determining the volume of particles can be used, for example, elemental analysis of the grain boundaries can be performed using TEM-EELS.

[0070] Furthermore, in this embodiment, the first magnetic layer 30, like the second magnetic layer 40, can also have a granular structure. In this case, the content of grain boundaries in the first magnetic layer 30 can be the same as that in the second magnetic layer 40.

[0071] [Method for manufacturing magnetic recording media]

[0072] Here is an example of a method for manufacturing a magnetic recording medium 1. The method includes: a step of forming a first magnetic layer 30 by sputtering; a step of forming a layer 50 of any alloy of VN, Si3N4, YN, or TiN by sputtering on the main surface of the first magnetic layer 30; and a step of forming a second magnetic layer 40 by sputtering on the main surface of the layer 50 of any alloy of VN, Si3N4, YN, or TiN. That is, the magnetic recording medium 1 includes a step of forming a layer 50 of any alloy of VN, Si3N4, YN, or TiN by sputtering between the step of forming the first magnetic layer 30 by sputtering and the step of forming the second magnetic layer 40 by sputtering, thereby manufacturing the magnetic recording medium 1 by providing a layer 50 of any alloy of VN, Si3N4, YN, or TiN between the first magnetic layer 30 and the second magnetic layer 40. By using such a manufacturing method, it is possible to cover the (111) surface 311C of the magnetic particles 31 on the growth surface of the first magnetic layer 30 with a layer 50 of any alloy of VN, Si3N4, YN or TiN, thereby suppressing the coarsening of the magnetic particles 41 in the second magnetic layer 40.

[0073] Examples of such film-forming methods include using a discharge gas pressure of less than 2 Pa, employing RF discharge to achieve a target surface potential of 50–200 V, and then heating (post-annealing) the film to raise its temperature by 100°C compared to the initial film-forming temperature. Additionally, the gas atmosphere can be an inert gas atmosphere such as nitrogen or argon.

[0074] Furthermore, after forming a layer 50 of any alloy of VN, Si3N4, YN or TiN covering the entire surface of the magnetic particles 31, its surface is etched to remove only the VN, Si3N4, YN or TiN alloy precipitated on the (001) surface 311B of the magnetic particles 31. The VN, Si3N4, YN or TiN alloy only covers the (111) surface 311C, and only the layer 50 of any alloy of VN, Si3N4, YN or TiN is provided on the (111) surface 311C.

[0075] In the etched surface of any alloy of VN, Si3N4, YN, or TiN, the nitrogen contained in any of these alloys is easily separated, subsequently filling the nitrogen defects in the hexagonal boron nitride grain boundaries 42 of the second magnetic layer 40. Therefore, the peak position obtained by chemical composition analysis of the hexagonal boron nitride grain boundaries 42 using X-ray photoelectron spectrometry (XPS) can be shifted to near 191 eV, the source of the hexagonal boron nitride nitride as a nitride. The nitrided hexagonal boron nitride grain boundaries 42 exhibit better crystallinity, facilitating the separation of magnetic particles and columnar growth of the hexagonal boron nitride.

[0076] The magnetic particles 31 contained in the first magnetic layer 30 and the magnetic particles 41 contained in the second magnetic layer 40 form columnar crystals, thus preferably improving the orientation of the c-axis relative to the substrate 10, i.e., the orientation of the (001) plane.

[0077] As a method for aligning the magnetic particles 31 contained in the first magnetic layer 30 and the magnetic particles 41 contained in the second magnetic layer 40 relative to the substrate 10 along the c-axis, for example, a method of epitaxially growing the first magnetic layer 30 and the second magnetic layer 40 along the c-axis using a substrate layer 20 can be cited.

[0078] Other magnetic layers may be further disposed below the first magnetic layer 30 or on the second magnetic layer 40. These newly disposed magnetic layers, like the first magnetic layer 30, preferably contain magnetic particles having an L10 structure. Furthermore, these magnetic particles preferably form columnar crystals with magnetic particles 31 and 41.

[0079] Therefore, by using the manufacturing method of magnetic recording medium 1, a result is obtained. Figure 1 The magnetic recording medium 1 shown.

[0080] The magnetic recording medium 1 preferably has a protective layer on the first magnetic layer 30 and the second magnetic layer 40.

[0081] As a protective layer, for example, hard carbon film can be cited.

[0082] Methods for forming a protective layer include, for example, the following: RF-CVD (Radio Frequency-Chemical Vapor Deposition) method, which decomposes hydrocarbon gas (raw material gas) using high-frequency plasma and forms a film; IBD (Ion Beam Deposition) method, which uses electrons emitted from a filament to ionize the raw material gas and form a film; and FCVA (Filtered Cathodic Vacuum Arc) method, which does not use a raw material gas but uses a solid carbon target to form a film.

[0083] The thickness of the protective layer is preferably 1 to 6 nm. If the thickness of the protective layer is 1 nm or more, the levitation characteristics of the magnetic head become better. If it is less than 6 nm, the magnetic spacing becomes smaller and the SNR (signal-to-noise ratio, also known as S / N ratio) of the magnetic recording medium 1 is improved.

[0084] Furthermore, in this specification, the thickness of the protective layer refers to its length in the direction perpendicular to the main surface of the protective layer. For example, the thickness of the protective layer can be the thickness measured at any location within a cross-section of the protective layer. If multiple measurements are taken at any location within a cross-section of the protective layer, the thickness can be the average of the thicknesses at those locations. Other layers can also be measured using the same method as the protective layer thickness.

[0085] The magnetic recording medium 1 may further have a lubricant layer on top of the protective layer.

[0086] The lubricant layer can be formed using a liquid lubricant layer. Among liquid lubricants, chemically stable, low-friction, and low-adsorption liquid lubricants are suitable. Examples of liquid lubricants include, for instance, perfluoropolyether-based lubricants containing compounds having a perfluoropolyether structure, and fluoropolymer-based lubricants.

[0087] The thickness of the lubricant layer is not particularly limited; for example, it can be 1 to 3 nm.

[0088] Furthermore, the magnetic recording medium 1 may contain any appropriate layers other than the protective layer and the lubricant layer. For example, the magnetic recording medium 1 may, as needed, have an adhesive layer, a soft magnetic substrate layer, an alignment control layer, etc., between any of the substrate 10, the base layer 20, and the first magnetic layer 30. The soft magnetic substrate layer may, for example, be composed of a first soft magnetic layer, an intermediate layer, and a second soft magnetic layer. The alignment control layer may be one layer, or two layers (e.g., a first alignment control layer, a second alignment control layer, etc.) or more. The materials used to form the adhesive layer, the soft magnetic substrate layer, the alignment control layer, etc., can be general materials used in magnetic recording media.

[0089] Thus, the magnetic recording medium 1 sequentially comprises a substrate 10, a base layer 20, a first magnetic layer 30, and a second magnetic layer 40. The first magnetic layer 30 contains magnetic particles 31 having an L10 structure, and the second magnetic layer 40 is a granular magnetic layer containing magnetic particles 41 having an L10 structure and hexagonal boron nitride grain boundaries 42, wherein the hexagonal boron nitride grain boundaries 42 contain hexagonal boron nitride. Furthermore, the interface between the (111) facet 311C of the magnetic particles 31 and the second magnetic layer 40 is covered by any alloy of VN, Si3N4, YN, or TiN, and the magnetic particles 41 are epitaxially grown from the (001) facet 311B of the magnetic particles 31. Further, the magnetic particles 31 and 41 are formed in a columnar manner, becoming columnar crystals penetrating the first magnetic layer 30 and the second magnetic layer 40. Therefore, the particle size of the magnetic particles 31 and 41 becomes small and minimal, and the magnetic particles 31 and 41 are continuously formed columnarly in one direction.

[0090] The magnetic recording medium 1 can reduce the particle size of the magnetic particles 31 and 41 contained in the first magnetic layer 30 and the second magnetic layer 40, while containing the magnetic particles 31 and 41 continuously connected in the same direction, thereby improving anisotropy. Thus, the magnetic recording medium 1 stably maintains the state in which a granular structure is formed inside the second magnetic layer 40, and can stably contain the second magnetic layer 40 as a granular magnetic layer, thereby further improving the areal recording density.

[0091] By possessing the aforementioned characteristics, the magnetic recording medium 1 exhibits high recording density in both the first magnetic layer 30 and the second magnetic layer 40, even when using heat-assisted recording or microwave-assisted recording methods. Therefore, magnetic information can be sufficiently recorded in both the first magnetic layer 30 and the second magnetic layer 40 using the recording magnetic field of the magnetic head. Consequently, the magnetic recording medium 1 is further suitable for use in magnetic recording and playback devices with high recording density.

[0092] [Magnetic storage device]

[0093] This describes a magnetic storage device (also called a "magnetic recording reproduction device") equipped with the magnetic recording medium described in this embodiment. The magnetic storage device described in this embodiment is not particularly limited in form if it has the magnetic recording medium described in this embodiment. Furthermore, this description focuses on the case where the magnetic storage device uses a heat-assisted recording method to record magnetic information on the magnetic recording medium.

[0094] The magnetic storage device according to this embodiment may include, for example, a magnetic recording medium driving unit that drives the magnetic recording medium according to this embodiment to rotate; a magnetic head having a near-field light generating element provided at its front end; a magnetic head driving unit that drives the magnetic head to move; and a recording and playback signal processing system.

[0095] The magnetic head is a heat-assisted recording head, for example, having a laser generating section that generates laser light and heats the magnetic recording medium, and a waveguide that guides the laser light generated by the laser generating section to a near-field light generating element.

[0096] Figure 3 A perspective view showing an example of a magnetic storage device using the magnetic recording medium described in this embodiment. Figure 3 As shown, the magnetic storage device 100 may include: a magnetic recording medium 101; a magnetic recording medium driving unit 102 for rotating the magnetic recording medium 101; a magnetic head 103 having a near-field light generating element at its front end; a magnetic head driving unit 104 for moving the magnetic head 103; and a recording and playback signal processing unit 105. The magnetic recording medium 101 uses the aforementioned magnetic recording medium 1.

[0097] Figure 4 An example of the magnetic head 103 is shown schematically. Figure 4 As shown, the magnetic head 103 has a recording head 110 and a playback head 120.

[0098] The recording head 110 has a main magnetic pole 111, an auxiliary magnetic pole 112, a coil 113 that generates a magnetic field, a laser diode (LD) 114 that generates laser light, and a waveguide 116 that guides the laser light L generated by the LD 114 to the near-field light generating element 115.

[0099] The regeneration head 120 has a shield 121 and a regeneration element 122 held by the shield 121.

[0100] Figure 3 As shown, the magnetic storage device 100 mounts the center of the magnetic recording medium 101 to the rotating shaft of the spindle motor, and writes or reads information relative to the surface of the magnetic recording medium 101, which is driven by the rotation of the spindle motor, while moving the magnetic head 103 upward.

[0101] The magnetic storage device 100 of this embodiment uses the magnetic recording medium 101, thereby increasing the surface recording density of the magnetic recording medium 101 and thus increasing the recording capacity of the magnetic recording medium 101.

[0102] In addition, in the magnetic storage device, the magnetic head 103 can be replaced by a magnetic head with microwave-assisted recording instead of a magnetic head with heat-assisted recording.

[0103] As described above, the embodiments have been illustrated, but these embodiments are merely examples and do not limit the present invention. The embodiments described above can be implemented in various other ways, and various combinations, omissions, substitutions, modifications, etc., can be made without departing from the spirit of the present invention. The embodiments described above and their variations are included within the scope and spirit of the invention, and are included within the scope of the invention as described in the claims and its equivalents.

[0104] Example

[0105] The following examples further illustrate this embodiment in detail, but this embodiment is not limited to these examples and comparative examples.

[0106] <Manufacturing of Magnetic Recording Media>

[0107] (Example 1)

[0108] On a glass substrate, as a base layer, a 100 nm thick Cr-50at%Ti alloy layer and a 30 nm thick Co-27at%Fe-5at%Zr-5at%B alloy layer are sequentially formed by sputtering. Next, the glass substrate is heated to 250°C, and a 10 nm thick Cr layer and a 5 nm thick MgO layer are sequentially formed by sputtering. Then, the glass substrate is heated to 450°C, and a 0.5 nm thick (Fe-48at%Pt-5at%B) alloy layer (first magnetic layer) is formed by sputtering.

[0109] Then, a VN layer with a thickness of 0.2 nm was formed as the coating layer of the (111) face using RF sputtering. The film formation conditions were such that the target surface potential was 100 V, the film formation rate was 0.08 nm / s, and the post-annealing temperature was 100 °C higher than the film formation temperature.

[0110] Then, etching was performed at 7W under an argon atmosphere of 0.5 Pa.

[0111] Thus, a structure is made in which the (111) face of the magnetic particles of the first magnetic layer is covered by a VN layer.

[0112] Then, using sputtering, a 13 nm thick (Fe-49at%Pt)-40 vol% hexagonal boron nitride layer (the second magnetic layer) was sequentially formed. Next, as a protective layer, a 3 nm thick carbon film was formed to fabricate the magnetic recording medium.

[0113] The composition and coating conditions of the first magnetic layer and the composition of the second magnetic layer are shown in Table 1.

[0114] (Examples 2-26, Comparative Examples 1-12)

[0115] The coating conditions of the first magnetic layer were changed to those shown in Table 1. Otherwise, the magnetic recording medium was fabricated in the same manner as in Example 1.

[0116] <Evaluation of Magnetic Recording Media>

[0117] Evaluations were conducted on the magnetic recording media manufactured by each embodiment and each comparative example. The evaluation included confirmation of the coating state of the (111) facet of the magnetic particles in the first magnetic layer using any alloy of VN, Si3N4, YN, or TiN, and the crystallinity of hexagonal boron nitride (also known as hBN), as well as the determination of the coercivity Hc of the magnetic recording medium and the center distance between the magnetic particles in the first magnetic layer.

[0118] (The coating state of the magnetic particles of the first magnetic layer using any alloy of VN, Si3N4, YN or TiN on the (111) facet)

[0119] The coating condition of the magnetic particles in the first magnetic layer (111) was evaluated by observing the cross-section of the magnetic recording medium using a transmission electron microscope (HD2300, Hitachi High-Tech). Furthermore, when the film thickness of any of the VN, Si3N4, YN, or TiN alloys was inconsistent, and the magnetic particles were interconnected, the coating quality was considered deteriorated.

[0120] (Crystallization of hexagonal boron nitride)

[0121] The crystallinity of the hexagonal boron nitride in the first magnetic layer was evaluated using a transmission electron microscope (HD2300, Hitachi High-Tech). The cross-section of the magnetic recording medium was observed, and the crystallinity was assessed by observing the lattice texture and the peak positions in the XPS spectrum obtained during chemical composition analysis. When crystalline materials are observed with an electron microscope, the lattice texture can be observed at crystalline intervals. By observing the cross-section of the magnetic recording medium with a transmission electron microscope, observing the lattice texture, and confirming the peak positions in the XPS spectrum, the crystallinity of the hexagonal boron nitride in the first magnetic layer can be confirmed. If a peak of 191 eV originating from hexagonal boron nitride is observed in the XPS spectrum, the crystallinity of the hexagonal boron nitride can be considered good. If the hexagonal boron nitride has good crystallinity, it stably maintains a granular structure within the second magnetic layer, and the second magnetic layer can be evaluated as functioning as a granular magnetic layer.

[0122] (Center-to-center distance between magnetic particles in the first magnetic layer)

[0123] The center-to-center distance between magnetic particles in the first magnetic layer is calculated from the surface observation image obtained by SEM, using the distance between the centroids of adjacent magnetic particles in the first magnetic layer (in nm). A smaller center-to-center distance indicates a smaller particle size. Therefore, a smaller center-to-center distance in the first magnetic layer results in a smaller particle size, which is considered beneficial for increasing surface recording density. Furthermore, a center-to-center distance of 9.5 nm or less in the first magnetic layer is considered good. For evaluating the particle size, an argon etching process for 1 minute is performed to remove the carbon protective film on the surface of the magnetic recording medium.

[0124] (The coercivity Hc of the magnetic recording medium)

[0125] The coercivity Hc of magnetic recording media was evaluated using a superconducting Kerr measuring apparatus (BH-810-HM7, Neoark Corporation) by measuring the Kerr rotation angle (in kOe) when a laser (wavelength 408 nm) irradiates the main surface of the magnetic recording medium. The coercivity Hc reflects the crystallinity of the magnetic particles in the first and second magnetic layers. It is believed that if the crystal structure of the first and second magnetic layers is disordered, the coercivity Hc decreases. Therefore, a higher coercivity Hc indicates higher crystallinity in the first and second magnetic layers, which can be considered as a potential for increasing surface recording density. A coercivity Hc of 32.5 kOe or higher is considered good.

[0126] The evaluation results of the crystallinity of hexagonal boron nitride, the coating state of the (111) plane of the magnetic particles in the first magnetic layer using any layer of VN, Si3N4, YN, or TiN, and the measurement results of the center distance between the magnetic particles in the first magnetic layer and the coercivity Hc of the magnetic recording medium are shown in Table 1. In addition, in Table 1, the 191 eV peak from hexagonal boron nitride is represented as "hBN peak" as a measure of the crystallinity of hexagonal boron nitride.

[0127] [Table 1]

[0128]

[0129] [Table 2]

[0130]

[0131] [Table 3]

[0132]

[0133] As can be confirmed from Tables 1-3, compared with the magnetic recording media of the comparative examples, the hexagonal boron nitride in the first magnetic layer of each embodiment has good crystallinity, and even if the center distance between the magnetic particles in the first magnetic layer is less than 9.0 nm, it can still exert a coercive force of more than 32 kOe Hc. In addition, in the comparative examples, especially Comparative Examples 2 and 8, the center distance between the magnetic particles in the first magnetic layer is as high as 10.5 nm or more. Therefore, the bit size of the magnetic recording medium cannot be reduced, and thus the areal recording density of the magnetic recording medium cannot be increased.

[0134] Therefore, it has been confirmed that if the (111) facet of the magnetic particles in the first magnetic layer is coated with a layer of any alloy of VN, Si3N4, YN, or TiN, the first magnetic layer can maintain its granular structure and function as a granular magnetic layer even if the particle size of the magnetic particles contained in the first and second magnetic layers becomes smaller, thereby further improving the planar recording density. Therefore, the magnetic recording media of each embodiment have a high planar recording density, and thus, by using them in a magnetic storage device, can achieve a high recording capacity.

[0135] Explanation of symbols

[0136] 1,101 Magnetic Recording Media

[0137] 10 substrates

[0138] 20 basal layer

[0139] 30 First magnetic layer

[0140] 31, 41 Magnetic particles

[0141] 40 Second magnetic layer

[0142] 42 Hexagonal boron nitride grain boundary (grain boundary)

[0143] Layers of any alloy of 50VN, Si3N4, YN, or TiN

[0144] 100 magnetic storage devices

[0145] 311A growth surface

[0146] 42A, 50A, 311B (001) face

[0147] 311C (111) surface

Claims

1. A magnetic recording medium, comprising, in sequence, a substrate, a base layer, a first magnetic layer, and a second magnetic layer. The first magnetic layer contains magnetic particles with an L10 structure. The second magnetic layer comprises magnetic particles with an L10 structure and a granular structure containing hexagonal boron nitride grain boundaries. The (111) facets of the magnetic particles contained in the first magnetic layer are covered at the interface with the second magnetic layer by any alloy of VN, Si3N4, YN, or TiN. The magnetic particles contained in the second magnetic layer are epitaxially grown from the (001) face of the magnetic particles contained in the first magnetic layer. The magnetic particles contained in the first magnetic layer and the magnetic particles contained in the second magnetic layer are each columnar crystals that penetrate the first magnetic layer and the second magnetic layer.

2. The magnetic recording medium according to claim 1, The magnetic particles with an L10 structure contained in the first magnetic layer and the second magnetic layer are FePt alloy particles.

3. A method for manufacturing a magnetic recording medium, wherein the magnetic recording medium sequentially comprises a substrate, a base layer, a first magnetic layer, and a second magnetic layer. The first magnetic layer contains magnetic particles with an L10 structure. The second magnetic layer comprises magnetic particles with an L10 structure and a granular structure containing hexagonal boron nitride grain boundaries. The (111) facets of the magnetic particles contained in the first magnetic layer are covered at the interface with the second magnetic layer by any alloy of VN, Si3N4, YN, or TiN. The magnetic particles contained in the second magnetic layer are epitaxially grown from the (001) face of the magnetic particles contained in the first magnetic layer. The magnetic particles contained in the first magnetic layer and the magnetic particles contained in the second magnetic layer are each columnar crystals that penetrate the first magnetic layer and the second magnetic layer. The manufacturing method includes, between the step of forming the first magnetic layer by sputtering and the step of forming the second magnetic layer by sputtering, a step of forming a layer of any alloy of VN, Si3N4, YN, or TiN by sputtering.

4. A magnetic storage device having the magnetic recording medium as described in claim 1 or 2.

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