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 in which a state in which a granular structure is formed inside a granular magnetic layer is stably maintained, and in which the surface recording density is further improved. The 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 including magnetic particles having an L10 structure, and the second magnetic layer including magnetic particles having an L10 structure and a granular structure having a grain boundary portion including hexagonal boron nitride. The (111) plane of the magnetic particles contained in the first magnetic layer is covered by boron nitride on 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 columnar crystals penetrating the first magnetic layer and the second magnetic layer, respectively.

Description

Technical Field

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

[0002] In recent years, heat-assisted recording and microwave-assisted recording methods, which use near-field light or microwaves to locally heat a magnetic recording medium and reduce its coercivity, have become popular as a method that can achieve 2Tbit / inch. 2 The next generation recording method with high surface recording density is attracting attention.

[0003] If such an auxiliary recording head is used, it is possible to easily record on a magnetic recording medium having a coercive force of several tens of kOe at room temperature. Furthermore, as magnetic particles contained in the magnetic layer of the magnetic recording medium, for example, magnetic particles with a high crystal magnetic anisotropy constant (Ku) are used. Magnetic particles with a high crystal magnetic anisotropy constant (Ku) can be miniaturized while maintaining thermal stability, thereby increasing the coercive force 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 J / m 3 ), Co-Pt alloy particles (Ku: maximum 5×10 6 J / m 3 ) and the like having a magnetic particle with an L10 structure.

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

[0006] [Prior art literature]

[0007]

Non-patent literature

[0008] [Non-patent document 1] BSD Ch. S. Varaprasad et al., AIP Advances, 13, 035002 (2023) Summary of the invention

[0009] [Problems to be solved by the invention]

[0010] Here, it is desired to further improve the surface recording density of the magnetic recording medium. In order to further improve the surface recording density of the magnetic recording medium, it is important to further reduce the particle size of the magnetic grains contained in the magnetic layer and further improve the anisotropy of the magnetic grains.

[0011] As such a magnetic layer, a granular magnetic layer having FePt magnetic grains oriented in the (001) direction in an L10 structure and hexagonal boron nitride at the grain boundaries (hereinafter simply referred to as "FePt-hBN granular magnetic layer") has been proposed.

[0012] Hexagonal boron nitride has a layered structure stacked parallel to the (001) plane, and a grain boundary is easily formed between FePt magnetic particles, thereby reducing the particle size of the FePt magnetic particles. In addition, hexagonal boron nitride has low reactivity with FePt magnetic particles, so it does not hinder the regularization of magnetic particles. Moreover, such hexagonal boron nitride is preferably formed so that its (001) plane surrounds the side of the FePt magnetic particle.

[0013] However, FePt-hBN is often a layered material in which FePt and hBN are separated in the vertical direction, and often does not have a granular structure in which hBN surrounds FePt magnetic particles. In addition, the components of the grain boundary portion such as BN are not fully crystallized and are often in an amorphous state. Therefore, there is the following problem: even if a magnetic layer (granular magnetic layer) with a granular structure is used, it is sometimes impossible to seek to increase the surface recording density of the magnetic recording medium.

[0014] An object of one embodiment of the present invention is to provide a magnetic recording medium in which a granular magnetic layer is stably maintained in a state in which a granular structure is formed inside and the surface recording density is further improved.

[0015]

Methods to solve the problem

[0016] The above objectives can be achieved in the following ways.

[0017] (1) A magnetic recording medium comprising, in order, a substrate, an underlayer, a first magnetic layer, and a second magnetic layer,

[0018] The first magnetic layer contains magnetic particles having an L10 structure.

[0019] The second magnetic layer includes magnetic grains having an L10 structure and a granular structure having a grain boundary portion containing hexagonal boron nitride.

[0020] 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.

[0021] 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.

[0022] The magnetic grains included in the first magnetic layer and the magnetic grains included in the second magnetic layer are columnar crystals penetrating the first magnetic layer and the second magnetic layer, respectively.

[0023] (2) The magnetic recording medium according to (1), wherein the boron nitride covering the (111) planes of the magnetic grains included in the first magnetic layer is hexagonal boron nitride,

[0024] The (001) plane of the hexagonal boron nitride is parallel to the (111) plane.

[0025] (3) In the magnetic recording medium according to (1) or (2), the hexagonal boron nitride in the grain boundary portion is formed so that the (001) plane of the hexagonal boron nitride surrounds the side surfaces of the magnetic grains included in the second magnetic layer.

[0026] (4) In the magnetic recording medium according to any one of (1) to (3), the magnetic grains having the L10 structure included in the first magnetic layer and the second magnetic layer are FePt alloy grains.

[0027] (5) A method for producing a magnetic recording medium, which is the method for producing a magnetic recording medium according to any one of (1) to (4),

[0028] The manufacturing method includes a step of forming a boron 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.

[0029] (6) A magnetic storage device comprising the magnetic recording medium according to any one of (1) to (4).

[0030] [Effects of the invention]

[0031] According to one embodiment of the present invention, it is possible to provide a magnetic recording medium in which a granular magnetic layer is stably maintained in a state in which a granular structure is formed inside and the surface recording density is further improved.

[0032] According to another aspect of the present invention, it is possible to provide a method for producing a magnetic recording medium in which the granular magnetic layer stably maintains a state in which the granular structure is formed inside and the surface recording density is further improved.

[0033] Furthermore, 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

[0034]

Figure 1

[0035]

Figure 2

[0036]

Figure 3

[0037]

Figure 4

[0038] Hereinafter, the present specific embodiment will be described with reference to the accompanying drawings. In addition, the drawings used in the following description may be enlarged to show the characteristic parts for convenience in order to make the characteristics easier to understand, and the size ratios of the components are not necessarily the same. In addition, in this specification, "~" indicating a numerical range means that the numerical values ​​recorded before and after it are included as the lower limit and upper limit unless otherwise specified.

[0039] [Magnetic recording media]

[0040] Figure 1 An example of the layer structure of the magnetic recording medium involved in this embodiment is shown in FIG. Figure 1 As shown, 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 stacked in this order.

[0041] The substrate 10 may be a substrate generally used in 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. When manufacturing the magnetic recording medium 1, the substrate 10 may be heated to a temperature of 500° C. or higher.

[0042] The material constituting the base layer 20 is not particularly limited as long as the magnetic grains having the L10 structure included in the first magnetic layer 30 and the second magnetic layer 40 can be oriented in the (001) plane.

[0043] The base layer 20 may have a multi-layer structure.

[0044] The base layer 20 preferably contains a NaCl type compound.

[0045] Examples of the NaCl type compound include MgO, TiO, NiO, TiN, TaN, HfN, NbN, ZrC, HfC, TaC, NbC, and TiC, etc. These may be used alone or in combination of two or more.

[0046] The first magnetic layer 30 includes magnetic grains having an L10 structure.

[0047] Examples of the magnetic grains having the L10 structure constituting the first magnetic layer 30 include FePt alloy grains and CoPt alloy grains. The FePt alloy grains and CoPt alloy grains are magnetic grains oriented in the (001) direction in the L10 structure.

[0048] The magnetic grains included in the first magnetic layer 30 are columnar crystals having a shape penetrating the first magnetic layer 30 .

[0049] The particle size of the magnetic particles contained in the first magnetic layer 30 is not particularly limited as long as they are columnar, and may be, for example, 3 nm to 7 nm in terms of circle equivalent diameter. The average particle size of the magnetic particles contained in the first magnetic layer 30 can be measured by observation using a planar transmission electron microscope.

[0050] The aspect ratio of the magnetic particles contained in the first magnetic layer 30 depends on the thickness of the first magnetic layer 30, but when expressed as the height (t) of the columnar particles and the equivalent circle diameter (D), for example, t / D = 0.1 to 1.5. In addition, the aspect ratio refers to the value of the longest axis divided by the shortest axis in the magnetic particles. The aspect ratio of the magnetic particles is obtained by dividing the particle height of the magnetic particles measured by cross-sectional transmission electron microscopy by the average particle diameter of the magnetic particles measured by planar transmission electron microscopy.

[0051] The center distance between the magnetic particles contained in the first magnetic layer 30 is preferably 4.0 nm to 8.0 nm. The center distance between the magnetic particles contained in the first magnetic layer 30 is more preferably 7.8 nm or less, and further preferably 7.6 nm or less. If the center distance between the magnetic particles contained in the first magnetic layer 30 is within the above preferred range, the first magnetic layer 30 may contain magnetic particles with a small particle size.

[0052] 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 is 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).

[0053] The second magnetic layer 40 is a magnetic layer (granular magnetic layer) having a granular structure including magnetic grains having an L10 structure and a grain boundary portion, and the grain boundary portion contains hexagonal boron nitride.

[0054] Examples of the magnetic grains having the L10 structure constituting the second magnetic layer 40 include FePt alloy grains and CoPt alloy grains.

[0055] The magnetic grains included in the second magnetic layer 40 are columnar crystals having a shape penetrating the second magnetic layer 40 , similarly to the magnetic grains included in the first magnetic layer 30 .

[0056] The particle size of the magnetic particles contained in the second magnetic layer 40 is the same as the magnetic particles contained in the first magnetic layer 30. There is no particular limitation on the particle size of the magnetic particles contained in the second magnetic layer 40 if they are columnar. For example, the particle size may be 3 nm to 7 nm in terms of circle equivalent diameter. In addition, 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.

[0057] The aspect ratio of the magnetic grains contained in the second magnetic layer 40 is the same as the aspect ratio of the magnetic grains contained in the first magnetic layer 30. Although it depends on the thickness of the second magnetic layer 40, it can be, for example, t / D = 1.2 to 2.5. In addition, the aspect ratio is expressed as the height (t) of the columnar grain and the equivalent circle diameter (D), and is obtained by t / D. The aspect ratio of the magnetic grains contained in the second magnetic layer 40 can be measured by the same method as the method for measuring the aspect ratio of the magnetic grains contained in the first magnetic layer 30.

[0058] The hexagonal boron nitride contained in the grain boundary portion has a layered structure stacked approximately in parallel with the (001) plane, and is easy to form a grain boundary portion between the magnetic grains contained in the second magnetic layer 40, so that the particle size of the magnetic grains contained in the second magnetic layer 40 can be reduced. In addition, the reactivity of hexagonal boron nitride with magnetic grains having an L10 structure is low, so it does not hinder the regularization of the magnetic grains contained in the second magnetic layer 40. Therefore, the hexagonal boron nitride is preferably formed so that its (001) plane surrounds the side surfaces of the magnetic grains contained in the second magnetic layer 40.

[0059] In the past, it was difficult to stably form such a granular magnetic layer. In other words, the magnetic alloy and boron nitride have low reactivity, so the two often become separate layers during film formation, rather than a granular structure. In addition, boron nitride often becomes amorphous instead of crystallized.

[0060] 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 starting from the substrate 10 side, the magnetic grains of the second magnetic layer 40 are epitaxially grown from the magnetic grains of the first magnetic layer 30, so that the granular structure of the second magnetic layer 40 can be stably formed.

[0061] At this time, the magnetic grains in the growth plane of the first magnetic layer 30 have a (111) plane in addition to the (001) plane. Therefore, when the second magnetic layer 40 is formed, crystal growth in a direction perpendicular to the (111) plane will be performed, and the magnetic grains of the second magnetic layer 40 will be coarsened. In order to prevent the magnetic grains of the second magnetic layer 40 from coarsening, in this embodiment, the (111) plane of the first magnetic layer 30 is covered with boron nitride, so that the coarsening of the magnetic grains of the second magnetic layer 40 can be suppressed. In this regard, Figure 2 Provide detailed explanation.

[0062] Figure 2 1 and 2 are cross-sectional schematic diagrams for explaining crystal growth when the first magnetic layer 30 and the second magnetic layer 40 are formed. (a) is a cross-sectional schematic diagram showing crystal growth when the first magnetic layer 30 and the second magnetic layer 40 are formed in the conventional manner. Figure 2 (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 this embodiment. Figure 2 As shown in FIG. 2 , on the growth surface 311A ​​of the magnetic grain 31 constituting the first magnetic layer 30 having the L10 structure formed on the substrate 10, a (001) surface 311B parallel to the substrate 10 and a (001) surface 311B facing the growth surface 311A ​​relative to the (001) surface 311B are formed. Figure 2 In the figure, the (111) surface 311C is inclined at about 35 degrees (lower side). If 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 will also grow in the direction perpendicular to the (111) surface 311C of the magnetic grains 31, so that the grain size of the magnetic grains 41 is coarsened.

[0063] On the other hand, in this embodiment, if Figure 2 As shown in (b), the (111) surface 311C of the magnetic grains 31 of the first magnetic layer 30 is covered with a boron nitride layer 50. As a result, the coarsening of the magnetic grains 41 of the second magnetic layer 40 (dashed line portion) is suppressed, and the magnetic grains 41 of the second magnetic layer 40 are epitaxially grown on the (001) surface 311B of the magnetic grains 31 of the first magnetic layer 30, so that the magnetic grains 31, 41 are columnar crystals that penetrate the first magnetic layer 30 and the second magnetic layer 40, thereby maintaining the fine grain size of the magnetic grains 31, 41.

[0064] In this embodiment, the boron nitride layer 50 is a layer containing boron nitride, preferably containing 50 atomic % or more of boron nitride, and most preferably only consisting of boron nitride. In addition, the boron nitride layer 50 is not a continuous film, but a film partially penetrated between the magnetic particles 31 and the magnetic particles 41.

[0065] In this embodiment, the boron nitride layer 50 covering the (111) plane 311C of the magnetic grains 31 included in the first magnetic layer 30 is made of hexagonal boron nitride, and it is preferred that the (001) plane 50A of the hexagonal boron nitride is substantially parallel to the (111) plane 311C. Thus, the growth of the magnetic grains 41 of the second magnetic layer 40 starting from the (111) plane 311C of the magnetic grains 31 of the first magnetic layer 30 can be strongly suppressed.

[0066] In this embodiment, the hexagonal boron nitride grain boundary portion 42 as the grain boundary portion of the second magnetic layer 40 is preferably formed so that its (001) plane 42A surrounds the side surface 411 of the magnetic grain 41 included in the second magnetic layer 40. As a result, the lateral growth and coarsening of the magnetic grain 41 of the second magnetic layer 40 are suppressed, and the grain size of the magnetic grain 41 can be reduced.

[0067] 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 consists of only hexagonal boron nitride.

[0068] In the present embodiment, the boron nitride layer 50 covering the (111) plane 311C of the magnetic grain 31 included in the first magnetic layer 30 is preferably formed so that its (001) plane 50A is substantially parallel to the (111) plane 311C of the magnetic grain 31, and the hexagonal boron nitride grain boundary portion 42 as the grain boundary portion of the second magnetic layer 40 is formed so that its (001) plane 42A surrounds the side surface of the magnetic grain 41 included in the second magnetic layer 40. Therefore, the hexagonal boron nitride grain boundary portion 42 is preferably formed so that the crystal orientation gradually changes at the interface 42B with the boron nitride layer 50.

[0069] The content of the hexagonal boron nitride grain boundary portion 42 in the second magnetic layer 40 is preferably in the range of 25 volume % to 50 volume %, and more preferably in the range of 35 volume % to 45 volume %. When the content of the hexagonal boron nitride grain boundary portion 42 in the second magnetic layer 40 is in the range of 25 volume % to 50 volume %, the coercive force 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 improved.

[0070] The method for measuring the content of the hexagonal boron nitride grain boundary portion 42 in the second magnetic layer 40 is not particularly limited, and a general volume measurement method in particles can be used. For example, the content can be determined by performing elemental analysis of the grain boundary portion using TEM-EELS.

[0071] In this embodiment, the first magnetic layer 30 may also have a granular structure similarly to the second magnetic layer 40 . In this case, the content of the grain boundary portion in the first magnetic layer 30 may be the same as that in the second magnetic layer 40 .

[0072] [Method for producing magnetic recording medium]

[0073] An example of a method for manufacturing the magnetic recording medium 1 is described. The method for manufacturing the magnetic recording medium 1 includes a step of forming the 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 the second magnetic layer 40 by sputtering on the main surface of the boron nitride layer. That is, the magnetic recording medium 1 is manufactured by including 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 the boron nitride layer is provided between the first magnetic layer 30 and the second magnetic layer 40. By using such a manufacturing method, the (111) planes 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 coarsening of the magnetic grains 41 of the second magnetic layer 40 can be suppressed.

[0074] The method for manufacturing the magnetic recording medium 1 can selectively form a film of boron nitride only on the (111) plane 311C of the magnetic grain 31 by appropriately selecting the sputtering conditions of boron nitride. In addition, the method for manufacturing the magnetic recording medium 1 can form a film in such a manner that the (001) plane 50A of the boron nitride layer 50 is substantially parallel to the (111) plane 311C of the magnetic grain 31.

[0075] As such a film forming method, for example, a discharge gas pressure of less than 2 Pa is used, RF discharge is used, the target surface potential is 50V to 200V, and post-film forming heating (post-annealing) is performed to increase the temperature by about 100°C relative to the temperature during film formation.

[0076] Alternatively, after forming the boron nitride layer 50 so as to cover the entire surface of the magnetic particle 31, the surface may be etched to remove only the hexagonal boron nitride precipitated on the (001) surface 311B of the magnetic particle 31, so that the hexagonal boron nitride only covers the (111) surface 311C.

[0077] When RF discharge is used in the sputtering film formation of boron nitride, the influence of plasma on the substrate 10 is greater than when DC discharge is used, and the nitrogen separated from the boron nitride during sputtering is easily absorbed by the substrate. Nitrogen is a gas at a film forming temperature of 400°C or above, so if the post-annealing temperature after film formation is increased, nitrogen will be degassed from the surface of the magnetic grains 31. At this time, nitrogen is separated from the boron nitride during the sputtering of the boron nitride, and the metal boron thus produced migrates inside the grains during the sputtering of the magnetic grains 31 of the first magnetic layer 30, but similarly, it is precipitated from the surface due to the post-annealing. The nitrogen degassed from the surface of the magnetic grains 31 is recombined with the boron precipitated on the surface of the magnetic grains 31, thereby easily forming hexagonal boron nitride.

[0078] The magnetic grains 31 and 41 included in the first magnetic layer 30 and the second magnetic layer 40 form columnar crystals, and therefore the c-axis orientation, that is, the (001) plane orientation relative to the substrate 10 is improved, which is preferable.

[0079] Examples of a method for c-axis-orienting the magnetic grains 31 and 41 included in the first magnetic layer 30 and the second magnetic layer 40 include a method of epitaxially growing the first magnetic layer 30 and the second magnetic layer 40 in the c-axis direction using the base layer 20 .

[0080] Another magnetic layer may be further provided below the first magnetic layer 30 or above the second magnetic layer 40. The newly provided other magnetic layer preferably contains magnetic grains having an L10 structure similarly to the first magnetic layer 30. In addition, the magnetic grains preferably form columnar crystals with the magnetic grains 31 and 41.

[0081] Therefore, by using the method for manufacturing the magnetic recording medium 1, it is obtained Figure 1 The magnetic recording medium 1 is shown.

[0082] The magnetic recording medium 1 preferably further includes a protective layer on the first magnetic layer 30 and the second magnetic layer 40 .

[0083] As the protective layer, a hard carbon film or the like can be mentioned, for example.

[0084] As methods for forming a protective layer, for example, there can be cited the RF-CVD (radio frequency chemical vapor deposition) method of decomposing hydrocarbon gas (raw gas) using high-frequency plasma to form a film, the IBD (ion beam deposition) method of ionizing the raw gas to form a film using electrons emitted from a filament, and the FCVA (filtered cathode vacuum arc) method of forming a film using a solid carbon target without using a raw gas.

[0085] The protective layer thickness is preferably 1 nm to 6 nm. If the protective layer thickness is 1 nm or more, the floating characteristics of the magnetic head are good, and if it is 6 nm or less, the magnetic pitch is reduced and the SNR (signal / noise ratio (S / N ratio)) of the magnetic recording medium 1 is improved.

[0086] In addition, 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 when measuring an arbitrary position in the cross section of the protective layer. When measuring a plurality of arbitrary positions in the cross section of the protective layer, the thickness may be the average value of the thicknesses at these measured positions. The same measurement method as the thickness of the protective layer can also be used for other layers.

[0087] The magnetic recording medium 1 further has a lubricant layer on the protective layer.

[0088] The lubricant layer can be formed by a liquid lubricant layer. Liquid lubricants are preferably chemically stable, low-friction, and low-adsorbent. Examples of liquid lubricants include fluororesin lubricants such as perfluoropolyether lubricants containing compounds having a perfluoropolyether structure.

[0089] The thickness of the lubricant layer is not particularly limited, and may be, for example, 1 nm to 3 nm.

[0090] In addition, the magnetic recording medium 1 may contain any layer in addition to the protective layer and the lubricant layer. For example, the magnetic recording medium 1 may have an adhesive layer, a soft magnetic base layer, an orientation control layer, etc. in any layer or between any layers in the substrate 10, the base layer 20, and the first magnetic layer 30 as required. The soft magnetic base layer, for example, may be composed of a first soft magnetic layer, an intermediate layer, and a second soft magnetic layer. The orientation control layer may be one layer or two layers (for example, a first orientation control layer, a second orientation control layer, etc.) or more. The materials forming the adhesive layer, the soft magnetic base layer, the orientation control layer, etc. may be general materials used in magnetic recording media.

[0091] Thus, the magnetic recording medium 1 has the substrate 10, the base layer 20, the first magnetic layer 30 and the second magnetic layer 40 in this order, the first magnetic layer 30 contains the magnetic grains 31 having the L10 structure, and the second magnetic layer 40 is a granular magnetic layer containing the magnetic grains 41 having the L10 structure and the hexagonal boron nitride grain boundary portion 42, and the hexagonal boron nitride grain boundary portion 42 contains hexagonal boron nitride. In addition, the interface between the (111) plane 311C of the magnetic grain 31 and the second magnetic layer 40 is covered with boron nitride, and the magnetic grain 41 is epitaxially grown from the (001) plane 311B of the magnetic grain 31. Furthermore, the magnetic grains 31 and 41 are formed as columnar crystals that penetrate the first magnetic layer 30 and the second magnetic layer 40. Therefore, the particle size of the magnetic grains 31 and 41 is small and fine, and the magnetic grains 31 and 41 are continuously formed in a columnar shape in one direction.

[0092] The magnetic recording medium 1 can improve anisotropy by reducing the particle diameters of the magnetic grains 31 and 41 contained in the first magnetic layer 30 and the second magnetic layer 40, respectively, and including the magnetic grains 31 and 41 in a state of continuous connection 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 stably includes the second magnetic layer 40 as a granular magnetic layer, thereby further improving the surface recording density.

[0093] Since the magnetic recording medium 1 has the above-mentioned characteristics, even if a heat-assisted recording method or a microwave-assisted recording method is used as a recording method, the first magnetic layer 30 and the second magnetic layer 40 have a high recording density, so that magnetic information can be fully recorded on the first magnetic layer 30 and the second magnetic layer 40 by the recording magnetic field of the magnetic head. Therefore, the magnetic recording medium 1 can be appropriately used in a magnetic recording and reproducing device with a higher recording density.

[0094] [Magnetic storage device]

[0095] A magnetic storage device having a magnetic recording medium according to the present embodiment is described. If the magnetic storage device according to the present embodiment has a magnetic recording medium according to the present embodiment, the form is not particularly limited. In addition, the following case is described here, in which the magnetic storage device records magnetic information into the magnetic recording medium using a thermally assisted recording method.

[0096] The magnetic storage device involved in this embodiment may have a magnetic recording medium driving unit that drives the magnetic recording medium involved in this embodiment to rotate, a magnetic head with a near-field light generating element provided on the front end, a magnetic head driving unit that drives the magnetic head to move, and a recording and reproducing signal processing system.

[0097] The magnetic head is a heat-assisted recording type magnetic head, and has, for example, a laser generating unit for generating laser light to heat the magnetic recording medium, and a waveguide for guiding the laser light generated from the laser generating unit to the near-field light generating element.

[0098] Figure 3 FIG. 2 is a perspective view showing an example of a magnetic storage device using the magnetic recording medium according to the present 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 the front end, a magnetic head driving unit 104 for moving the magnetic head 103, and a recording and reproducing signal processing unit 105. The magnetic recording medium 101 uses the magnetic recording medium 1 described above.

[0099] Figure 4 An example of the magnetic head 103 is schematically shown. Figure 4 As shown, the magnetic head 103 includes a recording head 110 and a reproducing head 120 .

[0100] The recording head 110 has a main magnetic pole 111 , an auxiliary magnetic pole 112 , a coil 113 for generating a magnetic field, a laser diode (LD) 114 for generating laser light, and a waveguide 116 for guiding the laser light L generated by the LD 114 to a near-field light generating element 115 .

[0101] The reproducing head 120 includes baffles 121 and a reproducing element 122 sandwiched between the baffles 121 .

[0102] like Figure 3 As shown, in the magnetic storage device 100, the center portion of the magnetic recording medium 101 is installed on the rotating axis of the spindle motor. On the surface of the magnetic recording medium 101 driven by the spindle motor, the head 103 floats and operates while writing or reading information from the magnetic recording medium 101.

[0103] The magnetic storage device 100 according to the present embodiment can improve the surface recording density of the magnetic recording medium 101 by using the magnetic recording medium 1 in the magnetic recording medium 101 , and thus can improve the recording capacity of the magnetic recording medium 101 .

[0104] Furthermore, in the magnetic storage device, the magnetic head 103 may be a magnetic head of a microwave-assisted recording method in addition to a magnetic head of a thermal-assisted recording method.

[0105] The above embodiments are described as examples, and the present invention is not limited by the above embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, changes, etc. can be made without departing from the scope of the gist of the invention. These embodiments and their variations, while belonging to the scope or gist of the invention, also belong to the invention recorded in the scope of the patent claim and its equivalent scope.

[0106] [Example]

[0107] Hereinafter, the embodiment will be described in more detail with reference to Examples and Comparative Examples, but the embodiment is not limited to these Examples and Comparative Examples.

[0108] <Manufacturing of magnetic recording media>

[0109] (Example 1)

[0110] On the glass substrate, as a base layer, a 100nm thick Cr-50at%Ti alloy layer and a 30nm thick Co-27at%Fe-5at%Zr-5at%B alloy layer were formed in sequence by sputtering. Next, after the glass substrate was heated to 250°C, a 10nm thick Cr layer and a 5nm thick MgO layer were formed in sequence by sputtering. Next, after the glass substrate was heated to 450°C, a 0.5nm thick (Fe-48at%Pt-5at%B) alloy layer (first magnetic layer) was formed by sputtering.

[0111] Then, as a (111) surface covering layer, a 0.5 nm thick boron nitride film was formed by RF sputtering. The film forming conditions were a target surface potential of 100 V, a film forming rate of 0.08 nm / sec, and a post-annealing temperature increased by about 100°C relative to the film forming temperature.

[0112] Then, etching was performed in an argon atmosphere of 0.5 Pa and 7 W.

[0113] As a result, the (111) planes of the magnetic grains in the magnetic layer are covered with hexagonal boron nitride, and the (001) planes of the hexagonal boron nitride are structured to be substantially parallel to the (111) planes of the magnetic grains.

[0114] Then, a 13 nm thick (Fe-49 at% Pt)-40 volume% hexagonal boron nitride layer (second magnetic layer) was formed by sputtering. Next, a 3 nm thick carbon film was formed as a protective layer to produce a magnetic recording medium.

[0115] Table 1 shows the composition and coating conditions of the first magnetic layer and the composition of the second magnetic layer.

[0116] (Examples 2 to 7, Comparative Examples 1 to 8)

[0117] A magnetic recording medium was produced in the same manner as in Example 1 except that the covering conditions of the first magnetic layer were changed to the covering conditions shown in Table 1.

[0118] <Evaluation of Magnetic Recording Media>

[0119] The magnetic recording media produced in each embodiment and each comparative example were evaluated. The evaluation included confirmation of the coverage of the (111) plane of the magnetic grains of the first magnetic layer and the crystallinity of the hexagonal boron nitride hBN, and measurement of the coercive force Hc of the magnetic recording medium and the center distance between the magnetic grains of the first magnetic layer.

[0120] (Covering State of (111) Surfaces of Magnetic Grains in the First Magnetic Layer)

[0121] The coverage state of the (111) planes of the magnetic grains of 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 Corporation, HD-2300).

[0122] (Crystallinity of hexagonal boron nitride hBN)

[0123] The crystallinity of the hexagonal boron nitride hBN of the first magnetic layer is evaluated by observing the cross section of the magnetic recording medium with a transmission electron microscope (manufactured by Hitachi High-Technologies, HD-2300) and observing the lattice fringes. When a crystalline material is observed with an electron microscope, lattice fringes can be observed from the lattice spacing. Therefore, by observing the cross section of the magnetic recording medium with a transmission electron microscope and observing the lattice fringes, the crystallinity of the hexagonal boron nitride hBN of the first magnetic layer can be confirmed. If the crystallinity of the hexagonal boron nitride hBN is good, it can be evaluated that the state of forming a granular structure inside the second magnetic layer is stably maintained, and the second magnetic layer functions as a granular magnetic layer.

[0124] (Coercive force Hc of magnetic recording medium)

[0125] The coercive force Hc of the magnetic recording medium is evaluated by measuring the Kerr rotation angle when a laser (wavelength 408 nm) is irradiated to the main surface of the magnetic recording medium using a superconducting Kerr measuring device (manufactured by NEOARK, BH-810HM7). It can be considered that the coercive force Hc reflects the crystallinity of the magnetic grains of the first magnetic layer and the second magnetic layer. If the crystal structure of the first magnetic layer and the second magnetic layer is disordered, the coercive force Hc will decrease. Therefore, the higher the coercive force Hc, the higher the crystallinity of the first magnetic layer and the second magnetic layer, and it can be evaluated that the surface recording density can be improved.

[0126] (Center distance between magnetic particles in the first magnetic layer)

[0127] The center distance between the magnetic particles of the first magnetic layer can be obtained as follows: from the surface observation image obtained by SEM, the center distance between the centers of gravity of adjacent magnetic particles of the first magnetic layer is calculated. It can be evaluated that the smaller the center distance between the magnetic particles, the smaller the particle size of the magnetic particles. Therefore, the smaller the center distance between the magnetic particles of the first magnetic layer, the smaller the particle size of the magnetic particles of the first magnetic layer, and the more it can be evaluated that the surface recording density can be improved. In addition, when evaluating the particle size of the magnetic particles, in order to remove the carbon protective film on the surface of the magnetic recording medium, an argon etching process is performed for 1 minute.

[0128] Table 1 shows the evaluation results of the coverage of the (111) planes of the magnetic grains of the first magnetic layer and the crystallinity of the hexagonal boron nitride hBN, as well as the measurement results of the coercive force Hc of the magnetic recording medium and the center distance between the magnetic grains of the first magnetic layer.

[0129]

Table 1

[0130]

[0131] From Table 1, it can be confirmed that the magnetic recording medium of each embodiment has a high coercive force Hc. Therefore, the (111) plane of the magnetic grains of the first magnetic layer is covered with hexagonal boron nitride hBN. If the crystallinity of hexagonal boron nitride hBN is good, the particle size of the magnetic grains contained in the first magnetic layer and the second magnetic layer can be reduced, and it can be confirmed that the second magnetic layer maintains the state of forming a granular structure inside it and can 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 can have a high recording capacity by using it in a magnetic storage device.

[0132] [Reference Signs]

[0133] 1,101 Magnetic Recording Media

[0134] 10 substrate

[0135] 20 Basal layer

[0136] 301st magnetic layer

[0137] 31, 41 Magnetic particles

[0138] 40 2nd magnetic layer

[0139] 42 Hexagonal boron nitride grain boundary (grain boundary)

[0140] 50 Boron Nitride Layer

[0141] 100 Magnetic storage device

[0142] 311A Growth surface

[0143] 42A, 50A, 311B (001) surface

[0144] 311C(111)

Claims

1. A magnetic recording medium comprising a substrate, an underlayer, a first magnetic layer and a second magnetic layer in this order, The first magnetic layer contains magnetic particles having an L10 structure. The second magnetic layer includes magnetic grains having an L10 structure 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. The magnetic grains included in the first magnetic layer and the magnetic grains included in the second magnetic layer are columnar crystals penetrating the first magnetic layer and the second magnetic layer, respectively.

2. The magnetic recording medium according to claim 1, wherein the boron nitride covering the (111) planes of the magnetic grains included in the first magnetic layer is hexagonal boron nitride, The (001) plane of the hexagonal boron nitride is parallel to the (111) plane. 3 . The magnetic recording medium according to claim 1 , wherein the hexagonal boron nitride in the grain boundary portion is formed so that the (001) plane of the hexagonal boron nitride surrounds the side surfaces of the magnetic grains included in the second magnetic layer. 4 . The magnetic recording medium according to claim 1 , wherein the magnetic grains having the L10 structure contained in the first magnetic layer and the second magnetic layer are FePt alloy grains.

5. A method for producing a magnetic recording medium, the method for producing a magnetic recording medium according to claim 1 or 2, The manufacturing method includes a step of forming a boron 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. 6 . A magnetic storage device comprising the magnetic recording medium according to claim 1 .

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