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 structure is formed in a granular magnetic layer, and which further improves the surface recording density. A magnetic recording medium according to the present invention has a substrate, an underlayer, a first magnetic layer, and a second magnetic layer in this order, the first magnetic layer containing 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 by aluminum nitride 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 included in the first magnetic layer and the magnetic particles included in the second magnetic layer are each columnar crystals penetrating the first magnetic layer and the second magnetic layer.

Description

TECHNICAL FIELD

[0001] The present application relates to a magnetic recording medium, a manufacturing method of a magnetic recording medium, and a magnetic storage device. BACKGROUND

[0002] In recent years, a heat-assisted recording method or a microwave-assisted recording method in which a near-field light or a microwave is irradiated to a magnetic recording medium to locally heat, thereby reducing a coercive force and recording, has been attracting attention as a next-generation recording method capable of realizing a high areal recording density of 2 Tbit / inch 2 or more.

[0003] If a magnetic head using such an assisted recording method is used, it is possible to easily record a magnetic recording medium having a coercive force of several tens of kOe at room temperature. Also, as the magnetic particles included in the magnetic layer of the magnetic recording medium, for example, magnetic particles having a high crystalline magnetic anisotropy constant (Ku) are used. The magnetic particles having a high crystalline magnetic anisotropy constant (Ku) can be miniaturized while maintaining a state of thermal stability, and the coercive force at room temperature is increased.

[0004] As the magnetic particles having a high crystalline magnetic anisotropy constant (Ku), for example, magnetic particles having an L10 structure such as Fe-Pt alloy particles (Ku: maximum 7 x 10 6 J / m 3 ), Co-Pt alloy particles (Ku: maximum 5 x 10 6 J / m 3 ) are known.

[0005] As the magnetic layer using the magnetic particles having an L10 structure, for example, a granular structure magnetic layer in which the periphery of FePt magnetic particles having an L10 structure is covered with a layered substance of hexagonal boron nitride is disclosed in Non-Patent Literature 1.

[0006] PRIOR ART DOCUMENTS

[0007] NON-PATENT LITERATURE

[0008] Non-Patent Literature 1: B. S. D. Ch. S. Varaprasad et al., AIP Advances, 13, 035002 (2023) SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] 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 diameter of the magnetic particles included in the magnetic layer while further increasing the anisotropy of the magnetic particles.

[0011] As such a magnetic layer, a magnetic layer in which FePt magnetic particles oriented in the (001) direction in an L10 structure and a granular structure including hexagonal boron nitride at the grain boundary portion are combined (hereinafter, referred to as "FePt-hBN granular magnetic layer") is proposed.

[0012] Hexagonal boron nitride is a layered structure in which (001) planes are accumulated in parallel, but is likely to form a grain boundary portion between FePt magnetic particles, whereby the particle diameter of the FePt magnetic particles can be reduced. In addition, hexagonal boron nitride has low reactivity with FePt magnetic particles, and thus does not impair the standardization of the magnetic particles. Furthermore, such hexagonal boron nitride is preferably formed so as to surround the side surface of the FePt magnetic particles with its (001) plane.

[0013] However, in the conventional FePt-hBN granular magnetic layer, a layered structure in which the magnetic particles and the grain boundary portion are separated from each other is likely to be formed, and the granular structure is not likely to be formed. In addition, the component of the grain boundary portion such as BN is not sufficiently crystallized, and is likely to be in an amorphous state. Therefore, even if a magnetic layer having a granular structure (also referred to as a granular magnetic layer) is used, there is a problem in that the improvement in the areal recording density of the magnetic recording medium is not always achieved.

[0014] An object of one embodiment of the present application is to provide a magnetic recording medium that stably maintains a state in which a granular magnetic layer forms a granular structure inside and further improves the areal recording density.

[0015] Method for solving the problem

[0016] The above object can be achieved by the following.

[0017] (1) A magnetic recording medium including a substrate, a base layer, a first magnetic layer, and a second magnetic layer in this order,

[0018] the first magnetic layer includes magnetic particles having an L10 structure,

[0019] the second magnetic layer includes magnetic particles having an L10 structure and a granular structure including a grain boundary portion including hexagonal boron nitride,

[0020] a (111) plane of the magnetic particles included in the first magnetic layer is covered with aluminum nitride at an interface with the second magnetic layer,

[0021] the magnetic particles included in the second magnetic layer are epitaxially grown from a (001) plane of the magnetic particles included in the first magnetic layer,

[0022] the magnetic particles included in the first magnetic layer and the magnetic particles included in the second magnetic layer are each a columnar crystal that penetrates the first magnetic layer and the second magnetic layer.

[0023] (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.

[0024] The method for manufacturing the magnetic recording medium described in (3)(1) or (2),

[0025] The manufacturing method described above includes a step of forming an aluminum nitride layer by sputtering between the step of forming the first magnetic layer by sputtering and the step of forming the second magnetic layer by sputtering.

[0026] (4) A magnetic storage device having the magnetic recording medium described in (1) or (2).

[0027] The effects of the invention

[0028] According to one aspect of the present invention, 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.

[0029] According to other aspects of the present invention, 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.

[0030] Furthermore, according to other aspects of the present invention, magnetic storage devices with high recording capacity can be provided. Attached Figure Description

[0031] 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 invention.

[0032] 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 an embodiment of the present invention.

[0033] Figure 3 This is a perspective view illustrating an example of a magnetic storage device according to an embodiment of the present invention.

[0034] Figure 4 To indicate Figure 3 A schematic diagram of the magnetic head. Detailed Implementation

[0035] 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.

[0036] [Magnetic recording media]

[0037] Figure 1 This illustrates an example of the layer structure of the magnetic recording medium involved in 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.

[0038] 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.

[0039] 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.

[0040] The base layer 20 can have a multi-layer structure.

[0041] The base layer 20 preferably contains a NaCl-type compound.

[0042] 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.

[0043] The first magnetic layer 30 contains magnetic particles with an L10 structure.

[0044] 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.

[0045] The magnetic particles contained in the first magnetic layer 30 are columnar crystals with a shape that extends through the first magnetic layer 30.

[0046] The particle size of the magnetic particles contained in the first magnetic layer 30 is not particularly limited if it is columnar; for example, it can be 3 to 7 nm in diameter equivalent to a circle. Furthermore, the average particle size of the magnetic particles contained in the first magnetic layer 30 can be determined by observation using a plane transmission electron microscope.

[0047] 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 columnar particles is equal to the equivalent circle diameter (D), it can be t / D = 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 particles. The aspect ratio of the magnetic particles 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.

[0048] The center-to-center distance between the magnetic particles contained in the first magnetic layer 30 is preferably 4.0 to 8.0 nm. More preferably, the center-to-center distance between the magnetic particles contained in the first magnetic layer 30 is 7.8 nm or less, and even more preferably 7.6 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.

[0049] 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).

[0050] The second magnetic layer 40 is a granular magnetic layer containing magnetic particles with an L10 structure and grain boundaries, the grain boundaries containing hexagonal boron nitride.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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, it can be t / D = 1.2 to 2.5. Furthermore, the aspect ratio is calculated as t / D of the height (t) of the columnar particle and the equivalent circle diameter (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.

[0055] 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.

[0056] 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.

[0057] The inventors of this application 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, the 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.

[0058] 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 aluminum nitride, thereby suppressing the coarsening of the magnetic particles in the second magnetic layer 40. Figure 2 Let me explain this in detail.

[0059] 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 2 The (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.

[0060] 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 an aluminum nitride layer 50. Thus, by suppressing the coarsening of the magnetic particles 41 in the second magnetic layer 40 (dashed portion), the magnetic particles 41 in the second magnetic layer 40 are epitaxially grown on the (001) facet 311B of the magnetic particles 31 in the first magnetic layer 30, making the magnetic particles 31 and 41 columnar crystals penetrating both the first and second magnetic layers 30, thereby maintaining a fine particle size.

[0061] In this embodiment, the aluminum nitride layer 50 is a layer containing aluminum nitride, preferably containing more than 50 atomic percent aluminum nitride, and most preferably composed of only aluminum nitride. Furthermore, the aluminum nitride layer 50 is not a continuous film, but a film that partially penetrates between the magnetic particles 31 and 41.

[0062] The hexagonal boron nitride grain boundary 42 contains hexagonal boron nitride, preferably containing more than 50 atomic% hexagonal boron nitride, and most preferably consisting of only hexagonal boron nitride.

[0063] The content of hexagonal boron nitride grain boundary 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 boundary 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, 41 contained in the first magnetic layer 30 and the second magnetic layer 40 can be improved.

[0064] 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.

[0065] 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.

[0066] [Manufacturing methods for magnetic recording media]

[0067] An example of a method for manufacturing a magnetic recording medium 1 is described. The method for manufacturing the magnetic recording medium 1 includes: a step of forming a first magnetic layer 30 by sputtering; a step of forming an aluminum nitride layer 50 by sputtering aluminum nitride 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 aluminum nitride layer 50. That is, the magnetic recording medium 1 is manufactured by sputtering an aluminum nitride layer 50 between the step of forming the first magnetic layer 30 and the step of forming the second magnetic layer 40, thereby providing the aluminum nitride layer 50 between the first magnetic layer 30 and the second magnetic layer 40. By using such a manufacturing method, the (111) surface 311C of the magnetic particles 31 on the growth surface of the first magnetic layer 30 can be covered with the aluminum nitride layer 50, and the coarsening of the magnetic particles 41 in the second magnetic layer 40 can be suppressed.

[0068] 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.

[0069] In addition, after forming an aluminum nitride layer 50 covering the entire surface of the magnetic particles 31, its surface is etched to remove only the aluminum nitride precipitated on the (001) surface 311B of the magnetic particles 31. The aluminum nitride only covers the (111) surface 311C, and only the aluminum nitride layer 50 is provided on the (111) surface 311C.

[0070] In the etched surface of aluminum nitride, the nitrogen in aluminum nitride is easily separated, and then effectively fills the nitrogen defects in the hexagonal boron nitride grain boundaries 42 of the second magnetic layer 40. Therefore, the XPS peak of the hexagonal boron nitride grain boundaries 42 can be shifted to the vicinity of 191 eV, which is a nitride. The nitrided hexagonal boron nitride grain boundaries 42 exhibit better crystallinity, facilitating the separation of magnetic particles and columnar growth of hexagonal boron nitride.

[0071] The magnetic particles 31, 41 contained in the first magnetic layer 30 and the second magnetic layer 40 form columnar crystals, thus preferably improving the orientation relative to the c-axis of the substrate 10, i.e., the orientation of the (001) plane.

[0072] As a method for aligning the magnetic particles 31, 41 contained in the first magnetic layer 30 and 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.

[0073] 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.

[0074] Therefore, by using the manufacturing method of magnetic recording medium 1, one can obtain... Figure 1 The magnetic recording medium 1 shown.

[0075] The magnetic recording medium 1 preferably has a protective layer on the first magnetic layer 30 and the second magnetic layer 40.

[0076] As a protective layer, for example, hard carbon film can be cited.

[0077] 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.

[0078] 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) of the magnetic recording medium 1 is improved.

[0079] 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.

[0080] The magnetic recording medium 1 may further have a lubricant layer on top of the protective layer.

[0081] 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.

[0082] The thickness of the lubricant layer is not particularly limited; for example, it can be 1 to 3 nm.

[0083] 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.

[0084] 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 aluminum nitride, 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 scarce, and the magnetic particles 31 and 41 are continuously formed in a columnar manner oriented in one direction.

[0085] 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.

[0086] 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.

[0087] [Magnetic storage device]

[0088] This description covers a magnetic storage device incorporating the magnetic recording medium described in this embodiment. The form of the magnetic storage device described in this embodiment is not particularly limited if it incorporates 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 onto the magnetic recording medium.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] The regeneration head 120 has a shield 121 and a regeneration element 122 held by the shield 121.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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. These embodiments 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.

[0099] Example

[0100] The following examples and comparative examples further illustrate the implementation methods, but the implementation methods are not limited to these examples and comparative examples.

[0101] <Manufacturing of Magnetic Recording Media>

[0102] (Example 1)

[0103] On a glass substrate, as a base layer, a 100 nm thick Cr-50 at% Ti alloy layer and a 30 nm thick Co-27 at% Fe-5 at% Zr-5 at% 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. Next, the glass substrate is heated to 450 °C, and a 0.5 nm thick (Fe-48 at% Pt-5 at% B) alloy layer (first magnetic layer) is formed by sputtering.

[0104] Then, an aluminum nitride 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.

[0105] Then, etching was performed at 7W under an argon atmosphere of 0.5 Pa.

[0106] Thus, a structure is made in which the (111) face of the magnetic particles of the first magnetic layer is covered with an aluminum nitride layer.

[0107] 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.

[0108] The composition and coating conditions of the first magnetic layer and the composition of the second magnetic layer are shown in Table 1.

[0109] (Examples 2-7, Comparative Examples 1-8)

[0110] 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.

[0111] <Evaluation of Magnetic Recording Media>

[0112] Evaluations were conducted on the magnetic recording media manufactured using the various embodiments and comparative examples. The evaluation included confirmation of the coating state of the (111) facets of the magnetic particles in the first magnetic layer using the aluminum nitride layer and the crystallinity of the 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.

[0113] (The coating state of the aluminum nitride layer on the (111) face of the magnetic particles in the first magnetic layer)

[0114] The cross-section of the magnetic recording medium was evaluated by observing the (111) facet of the magnetic particles in the first magnetic layer using a transmission electron microscope (HD2300, Hitachi High-Tech). Furthermore, when the aluminum nitride layer thickness varied and the magnetic particles were interconnected, the coating quality was assessed as deteriorated.

[0115] (Crystallization of hexagonal boron nitride)

[0116] The crystallinity of the hexagonal boron nitride in the first magnetic layer was evaluated by observing the cross-section of the magnetic recording medium using a transmission electron microscope (HD2300, manufactured by Hitachi High-Tech). If the crystallinity of the material is observable using an electron microscope, and a lattice texture can be observed at the lattice intervals, then the crystallinity of the hexagonal boron nitride in the first magnetic layer can be confirmed by observing the lattice texture in the cross-section of the magnetic recording medium using a transmission electron microscope. 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.

[0117] (The coercivity Hc of the magnetic recording medium)

[0118] The coercivity Hc of the magnetic recording medium was evaluated using a superconducting Kerr measurement device (BH-810-HM7, Neoark). The Kerr rotation angle was measured when a laser (wavelength 408 nm) irradiated 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. (Center-to-center distance between magnetic particles in the first magnetic layer)

[0119] The center-to-center distance between magnetic particles in the first magnetic layer is obtained by calculating the center-to-center distance between the centroids of adjacent magnetic particles in the first magnetic layer from surface observation images obtained by SEM. A smaller center-to-center distance indicates a smaller particle size. Therefore, a smaller center-to-center distance in the first magnetic layer indicates a smaller particle size, which can improve the surface recording density. Furthermore, for evaluating the particle size, an argon etching process is performed for 1 minute to remove the carbon protective film on the surface of the magnetic recording medium.

[0120] The coating state of the (111) face of the magnetic particles in the first magnetic layer, the evaluation results of the crystallinity of the hexagonal boron nitride, the coercivity Hc of the magnetic recording medium, and the measurement results of the center distance between the magnetic particles in the first magnetic layer are shown in Table 1.

[0121] [Table 1]

[0122]

[0123] As confirmed by Table 1, the magnetic recording media of each embodiment possesses a high coercivity Hc. Therefore, by coating the (111) facet of the magnetic particles in the first magnetic layer with aluminum nitride, the particle size of the magnetic particles contained in the first and second magnetic layers can be reduced. This confirms that the second magnetic layer maintains a granular structure within it and can function as a granular magnetic layer. Therefore, it can be said that the magnetic recording media of each embodiment has a high areal recording density, thereby enabling a high recording capacity when used in a magnetic storage device.

[0124] Explanation of symbols

[0125] 1. 101 Magnetic Recording Medium

[0126] 10 substrate

[0127] 20 basal layer

[0128] 30 First magnetic layer

[0129] 31, 41 magnetic particles

[0130] 40 Second magnetic layer

[0131] 42 Hexagonal boron nitride grain boundary (grain boundary)

[0132] 50 aluminum nitride layers

[0133] 100 Magnetic storage devices

[0134] 311A growth surface

[0135] 42A, 50A, 311B(001) surfaces

[0136] 311C(111) surface

Claims

1. A magnetic recording medium having, in order, a substrate, a base layer, a first magnetic layer, and a second magnetic layer, the first magnetic layer containing magnetic particles having an Ll 0 structure, the second magnetic layer having magnetic particles having an Ll 0 structure, and a granular structure having a grain boundary portion containing hexagonal boron nitride, a (111) plane of the magnetic particles contained in the first magnetic layer is covered with aluminum nitride at an interface with the second magnetic layer, the magnetic particles contained in the second magnetic layer are epitaxially grown from a (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 that extend through the first magnetic layer and the second magnetic layer.

2. The magnetic recording medium according to claim 1, the magnetic particles having an Ll 0 structure contained in the first magnetic layer and the second magnetic layer are FePt alloy particles.

3. A method of manufacturing the magnetic recording medium according to claim 1 or 2, the manufacturing method includes a step of forming an aluminum nitride layer by sputtering between a step of forming the first magnetic layer by sputtering and a step of forming the second magnetic layer by sputtering.

4. A magnetic storage device having the magnetic recording medium according to claim 1 or 2.

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