Magnetic recording medium, manufacturing method of magnetic recording medium, and magnetic recording device

Abstract

To provide a magnetic recording medium which stably maintains a state in which a granular magnetic layer has a granular structure formed therein and further improves areal recording density.SOLUTION: A magnetic recording medium 1 has a substrate 10, an underlayer 20, a first magnetic layer 30, and a second magnetic layer 40 in this order, in which the first magnetic layer includes magnetic particles having L10 structures, the second magnetic layer has a granular structure having magnetic particles having L10 structures and a grain boundary portion containing hexagonal boron nitride, a (111) surface of the magnetic particles contained in the first magnetic layer is covered by the boron nitride at a boundary surface with the second magnetic layer, the magnetic particles contained in the second magnetic layer are epitaxially grown from a (001) surface of the magnetic particles contained in the first magnetic layer, and the magnetic particles contained in the first magnetic layer and the magnetic particles contained in the second magnetic layer are columnar crystals penetrating the first magnetic layer and the second magnetic layer, respectively.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a magnetic recording medium, a method for manufacturing a magnetic recording medium, and a magnetic storage device. [Background technology]

[0002] In recent years, the thermally assisted recording method or microwave assisted recording method, in which near-field light or microwaves are irradiated onto a magnetic recording medium to locally heat it, thereby reducing the coercive force and recording, has achieved a data rate of 2 Tbit / inch. 2 It is attracting attention as a next-generation recording method that can achieve a high surface recording density.

[0003] By using such an assisted recording magnetic head, it is easy to record on a magnetic recording medium with a coercive force of several tens of kOe at room temperature. As the magnetic particles contained in the magnetic layer of the magnetic recording medium, for example, magnetic particles with a high magnetocrystalline anisotropy constant (Ku) are used. Magnetic particles with a high magnetocrystalline anisotropy constant (Ku) can be made fine while maintaining thermal stability, and increase the coercive force at room temperature.

[0004] As an example of magnetic particles with a high magnetocrystalline anisotropy constant (Ku), there is an Fe-Pt alloy particle (Ku: up to 7×10 6 J / m 3 ), Co-Pt alloy particles (Ku: up to 5 × 10 6 J / m 3 Magnetic particles having an L10 structure such as ZnO 2 , ZnO 3 , and ZnO 4 , are known.

[0005] As an example of a magnetic layer using magnetic particles having an L10 structure, Non-Patent Document 1 discloses a magnetic layer with a granular structure in which FePt magnetic particles having an L10 structure are covered with layers of hexagonal boron nitride. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] BSD Ch. S. Varaprasad et al., AIP Advances, 13, 035002(2023) Summary of the Invention [Problem to be solved by the invention]

[0007] Here, it is desired to further improve the areal recording density of the magnetic recording medium. In order to further improve the areal recording density of the magnetic recording medium, it is important to further reduce the grain size of the magnetic particles contained in the magnetic layer and to further increase the anisotropy of the magnetic particles.

[0008] As such a magnetic layer, a granular-structure magnetic layer containing FePt magnetic grains oriented in the (001) direction in an L10 structure and hexagonal boron nitride at the grain boundaries (hereinafter referred to simply as an “FePt-hBN granular magnetic layer”) has been proposed.

[0009] Hexagonal boron nitride has a layered structure in which (001) planes are stacked in parallel, but since grain boundaries are easily formed between FePt magnetic particles, the particle size of the FePt magnetic particles can be reduced. Moreover, since hexagonal boron nitride has low reactivity with FePt magnetic particles, it does not inhibit the ordering of the magnetic particles. It is preferable that such hexagonal boron nitride is formed so that its (001) plane surrounds the side surface of the FePt magnetic particles.

[0010] However, in the magnetic layer having a granular structure, such as the conventional FePt-hBN granular magnetic layer, the magnetic grains and the grain boundary part are easily separated from each other and are often layered, and the granular structure is not formed. Also, the grain boundary part components such as BN are often not crystallized sufficiently and are in an amorphous state. Therefore, even if a magnetic layer having a granular structure (granular magnetic layer) is used, there is a problem that the surface recording density of the magnetic recording medium may not be improved.

[0011] An object of one aspect of the present invention is to provide a magnetic recording medium in which a granular magnetic layer stably maintains a state in which a granular structure is formed therein, and in which the areal recording density is further improved. [Means for solving the problem]

[0012] The above objectives can be achieved by:

[0013] (1) A magnetic recording medium having a substrate, an underlayer, a first magnetic layer, and a second magnetic layer, in that order; the first magnetic layer includes magnetic grains having an L10 structure; the second magnetic layer has a granular structure having magnetic grains with an L10 structure and grain boundaries containing hexagonal boron nitride; the (111) faces of the magnetic grains included in the first magnetic layer are covered with boron nitride at the interface with the second magnetic layer; the magnetic grains included in the second magnetic layer are epitaxially grown from the (001) planes of the magnetic grains included in the first magnetic layer; A magnetic recording medium, wherein the magnetic grains contained in the first magnetic layer and the magnetic grains contained in the second magnetic layer are columnar crystals penetrating the first magnetic layer and the second magnetic layer, respectively. (2) the boron nitride covering the (111) faces of the magnetic grains contained in the first magnetic layer is hexagonal boron nitride; 2. The magnetic recording medium according to claim 1, wherein the (001) plane of the hexagonal boron nitride is parallel to the (111) plane. (3) The magnetic recording medium according to (1) or (2), wherein the hexagonal boron nitride in the grain boundary portion is formed such that the (001) plane of the hexagonal boron nitride surrounds the side surfaces of the magnetic grains contained in the second magnetic layer. (4) The magnetic recording medium according to any one of (1) to (3), wherein the magnetic particles having an L10 structure contained in the first magnetic layer and the second magnetic layer are FePt alloy particles. (5) A method for producing a magnetic recording medium according to any one of (1) to (4), comprising the steps of: A method for producing the magnetic recording medium according to claim 1 or 2, comprising the steps of: The manufacturing method includes a step of forming a boron 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. (6) A magnetic storage device having the magnetic recording medium according to any one of (1) to (4). Effect of the Invention

[0014] According to one aspect of the present invention, it is possible to provide a magnetic recording medium in which the granular magnetic layer stably maintains a state in which a granular structure is formed therein, and in which the areal recording density is further improved.

[0015] According to another aspect of the present invention, it is possible to provide a method for manufacturing a magnetic recording medium in which a granular magnetic layer stably maintains a state in which a granular structure is formed therein, thereby further improving the areal recording density.

[0016] According to another aspect of the present invention, a magnetic storage device with a high recording capacity can be provided. [Brief description of the drawings]

[0017] [Figure 1] 1 is a cross-sectional view showing an example of a layer structure of a magnetic recording medium according to an embodiment of the present invention. [Diagram 2] 1A and 1B are schematic cross-sectional views illustrating crystal growth during the formation of a first magnetic layer and a second magnetic layer, where (a) is a schematic cross-sectional view showing conventional crystal growth, and (b) is a schematic cross-sectional view showing crystal growth in an embodiment of the present invention. [Diagram 3] FIG. 1 is a perspective view showing an example of a magnetic storage device according to an embodiment of the present invention. [Figure 4] FIG. 4 is a schematic diagram showing the magnetic head of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, the embodiments of the present invention will be described with reference to the drawings. Note that the drawings used in the following description may show characteristic parts in an enlarged scale for the sake of convenience in order to make the characteristics easier to understand, and the dimensional ratios of each component may not necessarily be the same. In addition, in this specification, "to" indicating a numerical range means that the numerical values ​​before and after it are included as the lower and upper limits, unless otherwise specified.

[0019] [Magnetic recording media] An example of the layer structure of the magnetic recording medium according to this embodiment is shown in Fig. 1. As shown in Fig. 1, the magnetic recording medium 1 includes a substrate 10, an underlayer 20, a first magnetic layer 30, and a second magnetic layer 40, which are laminated in this order.

[0020] The substrate 10 may be a substrate generally used for the magnetic recording medium 1. For example, a heat-resistant glass substrate having a softening temperature of 500° C. or higher, preferably 600° C. or higher, is preferably used as the substrate 10. The substrate 10 can also be used in cases where it is heated to a temperature of 500° C. or higher when the magnetic recording medium 1 is manufactured.

[0021] The material constituting the underlayer 20 is not particularly limited as long as it is capable of orienting the magnetic grains having the L10 structure contained in the first magnetic layer 30 and the second magnetic layer 40 in the (001) plane.

[0022] The underlayer 20 may have a multi-layer structure.

[0023] The underlayer 20 preferably comprises a NaCl type compound.

[0024] Examples of NaCl type compounds include MgO, TiO, NiO, TiN, TaN, HfN, NbN, ZrC, HfC, TaC, NbC, TiC, etc. These may be used alone or in combination of two or more.

[0025] The first magnetic layer 30 includes magnetic grains having an L10 structure.

[0026] Examples of magnetic grains having an L10 structure that constitute the first magnetic layer 30 include FePt alloy grains, CoPt alloy grains, etc. The FePt alloy grains and CoPt alloy grains are magnetic grains that have an L10 structure and are oriented in the (001) direction.

[0027] The magnetic grains contained in the first magnetic layer 30 are columnar crystals having a shape penetrating the first magnetic layer 30 .

[0028] The particle size of the magnetic particles contained in the first magnetic layer 30 is not particularly limited as long as the particles are columnar, and may be, for example, 3 nm to 7 nm in equivalent circle diameter. The average particle size of the magnetic particles contained in the first magnetic layer 30 can be measured by observation with a planar transmission electron microscope.

[0029] The aspect ratio of the magnetic grains contained in the first magnetic layer 30 depends on the thickness of the first magnetic layer 30, but for example, when the height (t) of a columnar grain is the equivalent circle diameter (D), t / D may be 0.1 to 1.5. The aspect ratio is the value obtained by dividing the longest axis by the shortest axis of a magnetic grain. The aspect ratio of a magnetic grain is obtained by dividing the grain height of the magnetic grain measured by observing with a cross-sectional transmission electron microscope by the average grain size of the magnetic grain measured by observing with a planar transmission electron microscope.

[0030] The center-to-center distance between the magnetic particles contained in the first magnetic layer 30 is preferably 4.0 nm to 8.0 nm. The center-to-center distance between the magnetic particles contained in the first magnetic layer 30 is more preferably 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 preferred range, the first magnetic layer 30 can contain magnetic particles with small particle sizes.

[0031] The center distance between magnetic particles refers to the distance between the centers of gravity of adjacent magnetic particles. The center distance between magnetic particles can be measured, for example, by calculating the center distance between the centers of gravity of adjacent magnetic particles from a surface observation image obtained by a scanning electron microscope (SEM).

[0032] The second magnetic layer 40 is a magnetic layer (granular magnetic layer) having a granular structure including magnetic grains having an L10 structure and grain boundary portions, and the grain boundary portions contain hexagonal boron nitride.

[0033] Examples of the magnetic grains having the L10 structure that constitute the second magnetic layer 40 include FePt alloy grains and CoPt alloy grains.

[0034] The magnetic grains contained in the second magnetic layer 40 are columnar crystals having a shape penetrating the second magnetic layer 40, similar to the magnetic grains contained in the first magnetic layer 30.

[0035] The particle size of the magnetic particles contained in the second magnetic layer 40 is not particularly limited as long as they are columnar, similar to the magnetic particles contained in the first magnetic layer 30, and may be, for example, 3 nm to 7 nm in equivalent circle diameter. The average particle size of the magnetic particles contained in the second magnetic layer 40 can be measured by the same method as that of the magnetic particles contained in the first magnetic layer 30.

[0036] The aspect ratio of the magnetic particles contained in the second magnetic layer 40 depends on the thickness of the second magnetic layer 40, similar to the aspect ratio of the magnetic particles contained in the first magnetic layer 30, and may be, for example, t / D=1.2 to 2.5. The aspect ratio is calculated by t / D, where t is the height of a columnar particle and D is the equivalent circle diameter. The aspect ratio of the magnetic particles contained in the second magnetic layer 40 can be measured by the same method as that for measuring the aspect ratio of the magnetic particles contained in the first magnetic layer 30.

[0037] The hexagonal boron nitride contained in the grain boundary portion has a layered structure in which (001) planes are stacked approximately parallel to each other, and since it is easy to form a grain boundary portion between the hexagonal boron nitride and the magnetic grains contained in the second magnetic layer 40, the grain size of the magnetic grains contained in the second magnetic layer 40 can be reduced. In addition, since hexagonal boron nitride has low reactivity with magnetic grains having an L10 structure, it does not hinder the ordering of the magnetic grains contained in the second magnetic layer 40. Therefore, it is preferable that the hexagonal boron nitride is formed so that its (001) plane surrounds the side surfaces of the magnetic grains contained in the second magnetic layer 40.

[0038] It was difficult to stably form such a granular magnetic layer using conventional methods. In other words, because the reactivity between the magnetic alloy and boron nitride is low, the two often become separated layers during film formation, and the granular structure is not formed. In addition, boron nitride often becomes amorphous without crystallizing.

[0039] The present inventors have discovered that by forming the magnetic layer into a two-layer structure of a first magnetic layer 30 and a second magnetic layer 40 from the substrate 10 side, and by epitaxially growing the magnetic grains of the second magnetic layer 40 from the magnetic grains of the first magnetic layer 30, the granular structure of the second magnetic layer 40 can be stably formed.

[0040] In this case, the magnetic grains on the growth surface of the first magnetic layer 30 form a (111) surface in addition to a (001) surface, so that when the second magnetic layer 40 is formed, crystal growth proceeds in a direction perpendicular to the (111) surface, and the magnetic grains of the second magnetic layer 40 become coarse. In order to prevent the magnetic grains of the second magnetic layer 40 from becoming coarse, in this embodiment, the (111) surface of the first magnetic layer 30 is covered with boron nitride, so that the magnetic grains of the second magnetic layer 40 can be prevented from becoming coarse. This point will be described in detail with reference to FIG. 2.

[0041] 2A and 2B are schematic cross-sectional views for explaining crystal growth during the formation of the first magnetic layer 30 and the second magnetic layer 40, in which (a) is a schematic cross-sectional view showing crystal growth during the formation of the conventional first magnetic layer 30 and the second magnetic layer 40, and (b) is a schematic cross-sectional view showing crystal growth during the formation of the first magnetic layer 30 and the second magnetic layer 40 of the present embodiment. As shown in FIG. 2A, the growth surface 311A ​​of the magnetic grains 31 constituting the first magnetic layer 30 having the L10 structure formed on the substrate 10 includes a (001) surface 311B parallel to the substrate 10 and a (111) surface 311C inclined at about 35° toward the growth surface 311A ​​side (lower side in FIG. 2) with respect to the (001) surface 311B. When the second magnetic layer 40 (dashed line portion) is formed on the (111) surface 311C, the magnetic grains 41 of the second magnetic layer 40 also grow in the direction perpendicular to the (111) surface 311C of the magnetic grains 31, causing the grain size of the magnetic grains 41 to become coarse.

[0042] 2(b), in this embodiment, the (111) faces 311C of the magnetic grains 31 of the first magnetic layer 30 are covered with a boron nitride layer 50. This prevents the magnetic grains 41 of the second magnetic layer 40 (dashed line portion) from becoming coarse, and the magnetic grains 41 of the second magnetic layer 40 are epitaxially grown on the (001) faces 311B of the magnetic grains 31 of the first magnetic layer 30 to form columnar crystals that penetrate the first magnetic layer 30 and the second magnetic layer 40, thereby allowing the magnetic grains 31, 41 to maintain a fine grain size.

[0043] In this embodiment, the boron nitride layer 50 is a layer containing boron nitride, preferably contains 50 atomic % or more of boron nitride, and most preferably is composed only of boron nitride. Moreover, the boron nitride layer 50 is not a continuous film, but a film partially penetrating between the magnetic particles 31 and the magnetic particles 41.

[0044] In this embodiment, the boron nitride layer 50 covering the (111) faces 311C of the magnetic grains 31 included in the first magnetic layer 30 is preferably made of hexagonal boron nitride, and the (001) faces 50A of this hexagonal boron nitride are preferably approximately parallel to the (111) faces 311C. This can reliably suppress the growth of the magnetic grains 41 of the second magnetic layer 40 from the (111) faces 311C of the magnetic grains 31 of the first magnetic layer 30.

[0045] In this embodiment, it is preferable to form the hexagonal boron nitride grain boundary portion 42, which is the grain boundary portion of the second magnetic layer 40, so that its (001) face 42A surrounds the side surface 411 of the magnetic grain 41 included in the second magnetic layer 40. This prevents the magnetic grain 41 of the second magnetic layer 40 from growing laterally and becoming coarse, thereby making it possible to reduce the grain size of the magnetic grain 41.

[0046] The hexagonal boron nitride grain boundary portion 42 contains hexagonal boron nitride, preferably contains 50 atomic % or more of hexagonal boron nitride, and most preferably is composed only of hexagonal boron nitride.

[0047] In this embodiment, the boron nitride layer 50 covering the (111) faces 311C of the magnetic grains 31 contained in the first magnetic layer 30 is preferably formed with its (001) face 50A substantially parallel to the (111) face 311C of the magnetic grains 31, and the hexagonal boron nitride grain boundary portion 42, which is the grain boundary portion of the second magnetic layer 40, is preferably formed with its (001) face 42A surrounding the side of the magnetic grains 41 contained in the second magnetic layer 40. Therefore, it is preferable that the hexagonal boron nitride grain boundary portion 42 is formed so that the crystal orientation gradually changes at the interface 42B with the boron nitride layer 50.

[0048] The content of the hexagonal boron nitride grain boundary parts 42 in the second magnetic layer 40 is preferably within a range of 25 volume % to 50 volume %, and more preferably within a range of 35 volume % to 45 volume %. When the content of the hexagonal boron nitride grain boundary parts 42 in the second magnetic layer 40 is within a range of 25 volume % to 50 volume %, the coercivity HcJ of the magnetic recording medium 1 and the anisotropy of the magnetic grains 31, 41 contained in the first magnetic layer 30 and the second magnetic layer 40 can be increased.

[0049] The method for measuring the content of hexagonal boron nitride grain boundary portion 42 in second magnetic layer 40 is not particularly limited, and any general method for measuring the volume within a grain can be used. For example, the content can be determined by elemental analysis of the grain boundary portion using TEM-EELS.

[0050] In this embodiment, the first magnetic layer 30 may also have a granular structure, similar to the second magnetic layer 40. In this case, the content of the grain boundary part in the first magnetic layer 30 may be the same as that of the second magnetic layer 40.

[0051] [Method of manufacturing magnetic recording media] An example of a method for manufacturing the magnetic recording medium 1 will be 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 a boron nitride layer by sputtering boron 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 boron nitride layer. That is, the magnetic recording medium 1 includes a step of forming a boron nitride layer 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, and is manufactured by providing a boron nitride layer between the first magnetic layer 30 and the second magnetic layer 40. By using such a manufacturing method, the (111) face 311C of the magnetic grains 31 on the growth surface of the first magnetic layer 30 can be covered with the boron nitride layer 50, so that the magnetic grains 41 of the second magnetic layer 40 can be prevented from becoming coarse.

[0052] The method for manufacturing the magnetic recording medium 1 can selectively form a film of boron nitride only on the (111) faces 311C of the magnetic grains 31 by appropriately selecting the sputtering conditions of boron nitride. Furthermore, the method for manufacturing the magnetic recording medium 1 can form the film such that the (001) faces 50A of the boron nitride layer 50 are approximately parallel to the (111) faces 311C of the magnetic grains 31.

[0053] Such a film formation method may, for example, use a discharge gas pressure of 2 Pa or less, use RF discharge, set the target surface potential to 50 V to 200 V, and perform post-film formation heating (post-annealing) at a temperature approximately 100° C. higher than the film formation temperature.

[0054] Alternatively, after forming a boron nitride layer 50 so as to cover the entire surface of the magnetic grain 31, the surface may be etched to remove only the hexagonal boron nitride precipitated on the (001) face 311B of the magnetic grain 31, so that the hexagonal boron nitride covers only the (111) face 311C.

[0055] When RF discharge is used for sputtering deposition of boron nitride, the plasma has a greater effect on the substrate 10 than when DC discharge is used, and nitrogen generated by separation from boron nitride during sputtering is more easily taken into the substrate. Since nitrogen is a gas at the deposition temperature of 400° C. or higher, the nitrogen tends to degas from the surfaces of the magnetic particles 31 when the post-annealing temperature after deposition is increased. In this case, metallic boron generated by nitrogen separation from boron nitride during sputtering of boron nitride migrates into the interior of the magnetic particles 31 of the first magnetic layer 30 when the magnetic particles 31 are sputtered, but is also precipitated on the surface by post-annealing. Nitrogen that tends to degas from the surfaces of the magnetic particles 31 recombines with boron precipitated on the surfaces of the magnetic particles 31, making it easier to form hexagonal boron nitride.

[0056] The magnetic grains 31, 41 contained in the first magnetic layer 30 and the second magnetic layer 40 form columnar crystals, so it is preferable to enhance the c-axis orientation, that is, the (001) plane orientation, relative to the substrate 10.

[0057] Examples of a method for orienting the magnetic grains 31, 41 contained in the first magnetic layer 30 and the second magnetic layer 40 in the c-axis direction with respect to the substrate 10 include a method of epitaxially growing the first magnetic layer 30 and the second magnetic layer 40 in the c-axis direction using an underlayer 20.

[0058] Another magnetic layer may be provided under the first magnetic layer 30 or on the second magnetic layer 40. The newly provided another magnetic layer preferably contains magnetic grains having an L10 structure, similar to the first magnetic layer 30. In addition, the magnetic grains preferably form columnar crystals together with the magnetic grains 31 and 41.

[0059] Therefore, by using the manufacturing method of the magnetic recording medium 1, the magnetic recording medium 1 shown in FIG. 1 can be obtained.

[0060] The magnetic recording medium 1 preferably further comprises a protective layer on the first magnetic layer 30 and the second magnetic layer 40 .

[0061] The protective layer may be, for example, a hard carbon film.

[0062] Methods for forming the protective layer include, for example, RF-CVD (Radio Frequency-Chemical Vapor Deposition) method, in which a film is formed by decomposing a hydrocarbon gas (raw material gas) using high frequency plasma, IBD (Ion Beam Deposition) method, in which a film is formed by ionizing a raw material gas using electrons emitted from a filament, and FCVA (Filtered Cathodic Vacuum Arc) method, in which a film is formed by using a solid carbon target without using a raw material gas.

[0063] The thickness of the protective layer is preferably 1 nm to 6 nm. If the thickness of the protective layer is 1 nm or more, the floating characteristics of the magnetic head are improved, and if it is 6 nm or less, the magnetic spacing is small, and the SNR (signal / noise ratio (S / N ratio)) of the magnetic recording medium 1 is improved.

[0064] In this specification, the thickness of the protective layer refers to the length in the direction perpendicular to the main surface of the protective layer. The thickness of the protective layer is, for example, the thickness measured at any point on the cross section of the protective layer. When the thickness is measured at several points on the cross section of the protective layer, the average value of the thicknesses at these measurement points may be used. The same measurement method as that for the thickness of the protective layer can be used for other layers.

[0065] The magnetic recording medium 1 may further have a lubricant layer on the protective layer.

[0066] The lubricant layer can be formed by using a liquid lubricant layer. The liquid lubricant is preferably one that is chemically stable, has low friction, and has low adsorption. For example, the liquid lubricant can be a fluororesin-based lubricant such as a perfluoropolyether-based lubricant that contains a compound having a perfluoropolyether structure.

[0067] The thickness of the lubricant layer is not particularly limited, but may be, for example, 1 nm to 3 nm.

[0068] In addition, the magnetic recording medium 1 may include any layer as appropriate, in addition to the protective layer and the lubricant layer. For example, the magnetic recording medium 1 may include an adhesion layer, a soft magnetic underlayer, an orientation control layer, etc., between any of the layers of the substrate 10, the underlayer 20, and the first magnetic layer 30, as necessary. The soft magnetic underlayer may include, for example, a first soft magnetic layer, an intermediate layer, and a second soft magnetic layer. The orientation control layer may be one layer, or may be two or more layers (for example, a first orientation control layer, a second orientation control layer, etc.). Materials for forming the adhesion layer, the soft magnetic underlayer, the orientation control layer, etc. may be general materials used for magnetic recording media.

[0069] Thus, the magnetic recording medium 1 has the substrate 10, the underlayer 20, the first magnetic layer 30 and the second magnetic layer 40 in this order, the first magnetic layer 30 includes magnetic grains 31 having an L10 structure, the second magnetic layer 40 is a granular magnetic layer including magnetic grains 41 having an L10 structure and hexagonal boron nitride grain boundary portions 42, and the hexagonal boron nitride grain boundary portions 42 include hexagonal boron nitride. The (111) face 311C of the magnetic grain 31 is covered with boron nitride at the interface with the second magnetic layer 40, and the magnetic grain 41 grows epitaxially from the (001) face 311B of the magnetic grain 31. Furthermore, the magnetic grains 31 and 41 are formed to be columnar crystals penetrating the first magnetic layer 30 and the second magnetic layer 40. Therefore, the particle diameter of the magnetic particles 31 and 41 is small and minute, and the magnetic particles 31 and 41 are formed continuously in one direction in a columnar shape.

[0070] The magnetic recording medium 1 can enhance anisotropy by reducing the particle size of the magnetic grains 31 and 41 contained in the first magnetic layer 30 and the second magnetic layer 40, respectively, and by containing the magnetic grains 31 and 41 in a state in which they are continuously connected in the same direction. Therefore, the magnetic recording medium 1 can stably maintain a 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.

[0071] Since the magnetic recording medium 1 has the above-mentioned characteristics, even if a thermally assisted recording method or a microwave assisted recording method is used as the recording method, the first magnetic layer 30 and the second magnetic layer 40 have high recording density, so that magnetic information can be sufficiently recorded on the first magnetic layer 30 and the second magnetic layer 40 by the recording magnetic field of a magnetic head. Therefore, the magnetic recording medium 1 can be suitably used in a magnetic recording and reproducing device having an even higher recording density.

[0072] [Magnetic storage device] A magnetic storage device including the magnetic recording medium according to the present embodiment will be described. The magnetic storage device according to the present embodiment is not particularly limited in form as long as it has the magnetic recording medium according to the present embodiment. Here, the magnetic storage device will be described as recording magnetic information on the magnetic recording medium using a thermally assisted recording method.

[0073] The magnetic storage device of this embodiment may have, for example, a magnetic recording medium driving unit that drives and rotates the magnetic recording medium of this embodiment, a magnetic head having a near-field light generating element at its tip, a magnetic head driving unit that drives and moves the magnetic head, and a recording / playback signal processing system.

[0074] The magnetic head is a thermally assisted recording type magnetic head and has, for example, a laser light generating unit that generates laser light to heat the magnetic recording medium, and a waveguide that guides the laser light generated from the laser light generating unit to a near-field light generating element.

[0075] Fig. 3 shows a perspective view of an example of a magnetic storage device using the magnetic recording medium according to this embodiment. As shown in Fig. 3, the magnetic storage device 100 can have 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 tip, a magnetic head driving unit 104 for moving the magnetic head 103, and a recording / reproducing signal processing unit 105. The magnetic recording medium 1 described above is used as the magnetic recording medium 101.

[0076] 4 is a schematic diagram of an example of the magnetic head 103. As shown in FIG.

[0077] 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 from the LD 114 to a near-field light generating element 115.

[0078] The reproducing head 120 has a shield 121 and a reproducing element 122 sandwiched between the shield 121 .

[0079] As shown in FIG. 3, in the magnetic storage device 100, the center of a magnetic recording medium 101 is attached to the rotating shaft of a spindle motor, and information is written to or read from the magnetic recording medium 101 while a magnetic head 103 floats and runs above the surface of the magnetic recording medium 101, which is rotated by the spindle motor.

[0080] In the magnetic storage device 100 according to this embodiment, by using the magnetic recording medium 1 as the magnetic recording medium 101, the surface recording density of the magnetic recording medium 101 can be increased, and therefore the recording capacity of the magnetic recording medium 101 can be increased.

[0081] The magnetic storage device may use a microwave-assisted recording type magnetic head for the magnetic head 103 instead of the thermally-assisted recording type magnetic head.

[0082] As described above, the embodiment has been described, but the above embodiment is presented as an example, and the present invention is not limited to the above embodiment. The above embodiment can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims. EXAMPLES

[0083] The embodiments will be described in more detail below with reference to examples and comparative examples, but the embodiments are not limited to these examples and comparative examples.

[0084] <Manufacture of magnetic recording media> Example 1 On a glass substrate, 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 were sequentially formed as underlayers by sputtering. Next, the glass substrate was heated to 250°C, and a 10 nm thick Cr layer and a 5 nm thick MgO layer were sequentially formed by sputtering. Next, the glass substrate was heated to 450°C, and a 0.5 nm thick (Fe-48 at% Pt-5 at% B) alloy layer (first magnetic layer) was formed by sputtering.

[0085] Then, a 0.5 nm-thick boron nitride film was deposited as a (111) surface coating layer by RF sputtering under the following deposition conditions: target surface potential 100 V, deposition rate 0.08 nm / sec, and post-annealing temperature 100°C higher than the deposition temperature.

[0086] Thereafter, an etching process was carried out in an argon atmosphere of 0.5 Pa at 7 W.

[0087] This resulted in a structure in which the (111) faces of the magnetic grains in the magnetic layer were covered with hexagonal boron nitride, and the (001) faces of this hexagonal boron nitride were approximately parallel to the (111) faces of the magnetic grains.

[0088] Then, a 13 nm thick (Fe-49 at% Pt)-40 volume% hexagonal boron nitride layer (second magnetic layer) was formed by sputtering, followed by a 3 nm thick carbon film as a protective layer to produce a magnetic recording medium.

[0089] Table 1 shows the composition and coating conditions of the first magnetic layer and the composition of the second magnetic layer.

[0090] (Examples 2 to 7, Comparative Examples 1 to 8) A magnetic recording medium was produced in the same manner as in Example 1, except that the coating conditions for the first magnetic layer were changed to those shown in Table 1.

[0091] <Evaluation of magnetic recording media> The magnetic recording media manufactured in each of the examples and comparative examples were evaluated. The evaluation consisted of checking the coating state of the (111) faces of the magnetic grains in the first magnetic layer and the crystallinity of the hexagonal boron nitride hBN, and measuring the coercive force Hc of the magnetic recording media and the center-to-center distance between the magnetic grains in the first magnetic layer.

[0092] (Covering state of the (111) faces of the magnetic particles in the first magnetic layer) The coating state of the (111) faces of the magnetic particles in the first magnetic layer was evaluated by observing the cross section of the magnetic recording medium using a transmission electron microscope (manufactured by Hitachi High-Technologies).

[0093] (Crystallization of hexagonal boron nitride (hBN)) The crystallinity of the hexagonal boron nitride (hBN) of the first magnetic layer was evaluated by observing the cross section of the magnetic recording medium using a transmission electron microscope (Hitachi High-Technologies Corporation) and observing the lattice fringes. When a crystalline material is observed with an electron microscope, lattice fringes can be observed at the lattice spacing, so the crystallinity of the hexagonal boron nitride (hBN) of the first magnetic layer can be confirmed by observing the cross section of the magnetic recording medium with a transmission electron microscope and observing the lattice fringes. If the crystallinity of the hexagonal boron nitride (hBN) is good, it can be evaluated that the state in which a granular structure is formed inside the second magnetic layer is stably maintained, and the second magnetic layer functions as a granular magnetic layer.

[0094] (Coercive force Hc of magnetic recording medium) The coercive force Hc of the magnetic recording medium was evaluated by measuring the Kerr rotation angle when a laser beam (wavelength 408 nm) was irradiated onto the main surface of the magnetic recording medium using a superconducting Kerr measuring device (manufactured by NeoArc). The coercive force Hc reflects the crystallinity of the magnetic particles in the first magnetic layer and the second magnetic layer, and it is considered that the coercive force Hc decreases when the crystal structure of the first magnetic layer and the second magnetic layer is disturbed. Therefore, it can be evaluated that the higher the coercive force Hc, the higher the crystallinity of the first magnetic layer and the second magnetic layer, and the more the areal recording density can be improved.

[0095] (Center-to-center distance between magnetic particles in the first magnetic layer) The center distance between the magnetic particles in the first magnetic layer was obtained by calculating the center distance between the centers of gravity of adjacent magnetic particles in the first magnetic layer from the surface observation image obtained by SEM. It can be evaluated that the smaller the center distance between the magnetic particles, the smaller the grain size of the magnetic particles. Therefore, it can be evaluated that the smaller the center distance between the magnetic particles in the first magnetic layer, the smaller the grain size of the magnetic particles in the first magnetic layer, and the more the surface recording density can be improved. In addition, when evaluating the grain size of the magnetic particles, an argon etching process was performed for 1 minute to remove the carbon protective film on the surface of the magnetic recording medium.

[0096] Table 1 shows the evaluation results of the coverage state of the (111) faces of the magnetic grains in the first magnetic layer and the crystallinity of hexagonal boron nitride hBN, as well as the measurement results of the coercive force Hc of the magnetic recording medium and the center-to-center distance between the magnetic grains in the first magnetic layer.

[0097] [Table 1]

[0098] From Table 1, it was confirmed that the magnetic recording medium of each embodiment has a high coercive force Hc. Therefore, if the (111) face of the magnetic grain of the first magnetic layer is covered with hexagonal boron nitride hBN and the crystallinity of hexagonal boron nitride hBN is improved, the grain size of the magnetic grain contained in the first magnetic layer and the second magnetic layer can be reduced, and the second magnetic layer can maintain the state in which a granular structure is formed therein and function as a granular magnetic layer. Therefore, it can be said that the magnetic recording medium of each embodiment has a high surface recording density, and therefore can have a high recording capacity when used in a magnetic storage device. [Explanation of symbols]

[0099] 1, 101 Magnetic recording media 10 Substrate 20 Base layer 30 First magnetic layer 31, 41 magnetic particles 40 Second magnetic layer 42 Hexagonal boron nitride grain boundary (grain boundary) 50 Boron nitride layer 100 Magnetic storage device 311A Growth aspect 42A, 50A, 311B (001) plane 311C (111) side

Claims

1. A substrate, an underlayer, a first magnetic layer, and a second magnetic layer, in that order; The first magnetic layer is L1 ０ The magnetic particles have a structure, The second magnetic layer is L1 ０ and a granular structure having a grain boundary portion containing hexagonal boron nitride, the (111) faces of the magnetic grains included in the first magnetic layer are covered with boron nitride at the interface with the second magnetic layer; the magnetic grains included in the second magnetic layer are epitaxially grown from the (001) planes of the magnetic grains included in the first magnetic layer, A magnetic recording medium, wherein the magnetic grains contained in the first magnetic layer and the magnetic grains contained in the second magnetic layer are columnar crystals penetrating the first magnetic layer and the second magnetic layer, respectively.

2. the boron nitride covering the (111) faces of the magnetic grains contained in the first magnetic layer is hexagonal boron nitride; 2. The magnetic recording medium according to claim 1, wherein the (001) plane of the hexagonal boron nitride is parallel to the (111) plane.

3. 3. The magnetic recording medium according to claim 1, wherein the hexagonal boron nitride in the grain boundary portion is formed such that the (001) plane of the hexagonal boron nitride surrounds the side surfaces of the magnetic grains contained in the second magnetic layer.

4. The L1 included in the first magnetic layer and the second magnetic layer ０ 3. The magnetic recording medium according to claim 1, wherein the magnetic particles having the structure are FePt alloy particles.

5. A method for producing the magnetic recording medium according to claim 1 or 2, comprising the steps of: The manufacturing method includes a step of forming a boron 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.

6. 10. A magnetic storage device comprising the magnetic recording medium according to claim 1.

Images