Magnetic recording medium and magnetic storage device

Abstract

The present invention provides a magnetic recording medium that improves electromagnetic conversion characteristics even when used in a heat-assisted recording method. [Solution] The magnetic recording medium 1 comprises a first underlayer 20, a second underlayer 30, a magnetic layer 40, and a protective layer 50. The magnetic layer has a thickness of 10 to 25 nm and contains magnetic particles having an L10 structure. The magnetic particles have a vertical thermal conductivity of 10 to 20 W / (m·K), a planar thermal conductivity of 1 to 10 W / (m·K), and a ratio of vertical thermal conductivity to planar thermal conductivity of 2 or more. The magnetic layer contains 0.1 to 2 atomic percent of additive elements such as Rh. The content of additive elements in the region from the top surface of the magnetic layer up to 2.5 nm is 5 atomic percent or less, and the content of additive elements in the region from the bottom surface of the magnetic layer up to 5 nm is 50 to 95 atomic percent. The thickness of the first underlayer is 10 nm or more, the average thermal conductivity in the region from the top surface of the first underlayer up to 10 nm is 100 W / (m·K) or more, and the second underlayer contains ionic crystals.

Description

Technical Field

[0001] The present disclosure relates to a magnetic recording medium and a magnetic storage device.

Background Art

[0002] In recent years, assist recording methods such as a heat assist recording method or a microwave assist recording method, which locally heat a magnetic recording medium by irradiating it with near-field light or microwaves to reduce the coercive force for recording, have attracted attention as next-generation recording methods that can achieve a high areal recording density of about 2 Tbit / inch. 2 With such a magnetic head for an assist recording method, it is possible to easily record on a magnetic recording medium having a coercive force of several tens of kOe at room temperature. And, as the magnetic particles contained in the magnetic layer of the magnetic recording medium, for example, magnetic particles having a high crystalline magnetic anisotropy constant (Ku) are used. Magnetic particles having a high crystalline magnetic anisotropy constant (Ku) can be miniaturized while maintaining thermal stability and increase the coercive force at room temperature.

[0003] As magnetic particles having a high crystalline magnetic anisotropy constant (Ku), for example, Fe-Pt alloy particles having a maximum crystalline magnetic anisotropy constant (Ku) of 7×10

[0004] J / m 6 and Co-Pt alloy particles having a maximum crystalline magnetic anisotropy constant (Ku) of 5×10 3 J / m 6 and magnetic particles having an L10 structure such as these are known. 3 And, in a heat assist magnetic recording medium having two magnetic layers containing magnetic particles having a high crystalline magnetic anisotropy constant (Ku), for example, Patent Document 1 discloses that the Curie temperature of the first magnetic layer is made lower than the Curie temperature of the second magnetic layer.

[0005] And, in a heat assist magnetic recording medium having two magnetic layers containing magnetic particles having a high crystalline magnetic anisotropy constant (Ku), for example, Patent Document 1 discloses that the Curie temperature of the first magnetic layer is made lower than the Curie temperature of the second magnetic layer.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2010-108571 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In thermally assisted magnetic recording media (hereinafter sometimes simply referred to as "thermally assisted magnetic recording media"), recording is performed by locally heating the magnetic layer using near-field light emitted from a laser, thereby reducing the coercivity of the magnetic layer. However, during heating, the heat from the laser light diffuses into the surroundings, creating a temperature difference in the depth direction of the magnetic layer. This temperature difference causes disturbances in the rotation of magnetic spins in the depth direction of the magnetic layer, leading to a deterioration in the electromagnetic conversion characteristics of thermally assisted magnetic recording media.

[0008] Furthermore, in order to increase the areal recording density of a heat-assisted magnetic recording medium, it is necessary to increase the thickness of the magnetic layer in order to secure the volume of the magnetic material that constitutes one bit, which further exacerbates the deterioration of the electromagnetic conversion characteristics of the heat-assisted magnetic recording medium.

[0009] One aspect of this disclosure aims to provide a magnetic recording medium that can improve electromagnetic conversion characteristics even when used in a heat-assisted recording method. [Means for solving the problem]

[0010] The above objectives can be achieved by the configuration shown below. [1] A thermally assisted recording magnetic recording medium comprising a substrate, a first underlayer, a second underlayer, a magnetic layer, and a protective layer, stacked in this order, The thickness of the magnetic layer is in the range of 10 to 25 nm. The magnetic layer comprises magnetic particles having an L10 structure. The magnetic particles have a vertical thermal conductivity in the range of 10 to 20 W / (m·K), a planar thermal conductivity in the range of 1 to 10 W / (m·K), and a ratio of vertical thermal conductivity to planar thermal conductivity of 2 or more. The magnetic layer contains, as an additive element, at least one element selected from the group consisting of Rh, Ir, Ru, and Pd. The amount of the additive element added is within the range of 0.1 to 2 atomic percent of the total magnetic layer. The content of the additive element in the region of the magnetic layer from the surface facing the protective layer up to 2.5 nm is 5 atomic percent or less of the total magnetic layer. The content of the additive element in the region of the magnetic layer from the surface facing the second underlayer up to 5 nm is within the range of 50 to 95 atomic percent of the entire magnetic layer. The thickness of the first underlayer is 10 nm or more, and the average thermal conductivity of the first underlayer in the region 10 nm from the surface facing the magnetic layer is 100 W / (m·K) or more. The second underlying layer is a magnetic recording medium containing ionic crystals with a thickness in the range of 0.5 to 15 nm. [2] The magnetic recording medium according to [1], wherein the magnetic particles having the L10 structure contained in the magnetic layer are FePt alloy particles. [3] The magnetic recording medium according to [1] or [2], wherein the ionic crystal is MgO. [4] A magnetic storage device having a magnetic recording medium described in any one of [1] to [3]. [Effects of the Invention]

[0011] According to one aspect of this disclosure, a magnetic recording medium can be provided that can improve electromagnetic conversion characteristics even when used in a heat-assisted recording method.

[0012] According to one aspect of this disclosure, a magnetic storage device with increased recording capacity can be provided by using a magnetic recording medium that can improve electromagnetic conversion characteristics even when used in a heat-assisted recording method. [Brief explanation of the drawing]

[0013] [Figure 1] This is a cross-sectional view showing an example of the layer configuration of a magnetic recording medium according to the present disclosure. [Figure 2]It is a perspective view showing an example of a magnetic storage device according to an embodiment of the present disclosure. [Figure 3] It is a schematic diagram showing the magnetic head of FIG. 2.

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments for carrying out the present disclosure will be described with reference to the drawings. In the drawings used in the following description, for the sake of clarity of the features, the characteristic parts may be shown enlarged for convenience, and the dimensional ratios of each component are not necessarily the same. Also, in this specification, "~" indicating a numerical range means including the numerical values described before and after it as the lower limit value and the upper limit value, unless otherwise specified. Also, when only the unit of the upper limit value is described in the numerical range represented by "~", it means that the lower limit value is also in the same unit.

[0015] [Magnetic Recording Medium] An example of the layer structure of a magnetic recording medium according to an embodiment of the present disclosure (hereinafter sometimes simply referred to as "this embodiment") is shown in FIG. 1. As shown in FIG. 1, the magnetic recording medium 1 according to this embodiment is an assist recording type magnetic recording medium including a substrate 10, a first underlayer 20, a second underlayer 30, a magnetic layer 4 and a protection layer 50 laminated in this order.

[0016] In the magnetic recording medium 1, the thickness of the magnetic layer 40 is in the range of 10 to 25 nm, and the magnetic layer 40 contains magnetic particles having an L10 structure. The vertical thermal conductivity of the magnetic particles contained in the magnetic layer 40 is in the range of 10 to 20 W / (m·K), the planar thermal conductivity is in the range of 1 to 10 W / (m·K), and the ratio of vertical thermal conductivity to planar thermal conductivity (anisotropy) is 2 or more. Furthermore, the magnetic layer 40 contains at least one element selected from the group consisting of Rh, Ir, Ru, and Pd as an additive element, and the amount of the additive element is in the range of 0.1 to 2 atomic percent (atomic percent means "at%") of the total magnetic layer 40. Furthermore, the content of additive elements in the region of the magnetic layer 40 from the surface facing the protective layer 50 up to 2.5 nm is 5 atomic percent or less of the total magnetic layer 40, and the content of additive elements in the region of the magnetic layer 40 from the surface facing the second underlayer 30 up to 5 nm is in the range of 50 to 95 atomic percent of the total magnetic layer 40. In addition, the thickness of the first underlayer 20 is 10 nm or more, the average thermal conductivity in the 10 nm thick region of the first underlayer 20 on the magnetic layer 40 side is 100 W / (m·K) or more, and the second underlayer 30 contains ionic crystals with a thickness in the range of 0.5 to 15 nm.

[0017] The magnetic recording medium 1, having the configuration described above, can improve electromagnetic conversion characteristics even when used in a heat-assisted recording method. As a result, the magnetic recording medium 1 can further improve its areal recording density.

[0018] Furthermore, by having the above-described configuration, the magnetic recording medium 1 can suppress deterioration of electromagnetic conversion characteristics and improve electromagnetic conversion characteristics even when the magnetic layer 40 is made thicker.

[0019] The signal-to-noise ratio (SNR) can be measured using common measurement methods, such as a spin stand manufactured by Guzik.

[0020] Details of the magnetic recording medium 1 will be described below.

[0021] As mentioned above, in general, heat-assisted magnetic recording media record data by locally heating the magnetic layer using near-field light emitted from a laser, thereby reducing the coercivity of the magnetic layer. However, the heating ability of near-field light attenuates in the depth direction of the magnetic layer, resulting in a temperature difference in the depth direction of the magnetic layer. This temperature difference then causes disturbances in the rotation of magnetic spins in the depth direction of the magnetic layer.

[0022] The inventors investigated, through experiments and calculations, the conditions under which disturbances in the rotation of magnetic spins in the depth direction of the magnetic layer are not generated during laser heating. As a result, the inventors found the following:

[0023] The first point is that when the magnetic layer 40 is heated to a maximum temperature of 650K, the magnetic layer 40 is designed so that the temperature difference between the hottest and coldest parts of the magnetic layer 40 is within the range of 50 to 150K, and the interfacial thermal resistance between the first base layer 20 and the second base layer 30 is set to 1 × 10⁻¹⁰ -10 ~1 × 10 -8 (m 2 The first point is that in order for the magnetic layer 40, the first underlayer 20, and the second underlayer 30 to achieve the configuration described in the first point, the thickness of the magnetic layer 40 should be in the range of 10 to 25 nm, the vertical thermal conductivity of the magnetic particles contained in the magnetic layer 40 should be in the range of 10 to 20 W / (m·K), and the planar thermal conductivity should be in the range of 1 to 10 W / (m·K). Furthermore, the ratio (anisotropy) of the vertical thermal conductivity to the planar thermal conductivity of the magnetic particles should be 2 times or more. In addition, the thickness of the first underlayer 20 should be 10 nm or more, and the average thermal conductivity in the 10 nm thick region on the magnetic layer 40 side should be 100 W / (m·K) or more. The second underlayer 30 should have a structure that includes ionic crystals with a thickness in the range of 0.5 to 15 nm.

[0024] Furthermore, the inventors focused on the fact that Rh, Ir, Ru, and Pd can be used as additive elements that have the effect of lowering the Curie temperature of the magnetic layer 40. These additive elements are added in a range of 0.1 to 2 atomic percent of the entire magnetic layer. The content of the additive elements in the region from the surface of the magnetic layer 40 facing the protective layer 50 (i.e., the surface of the magnetic layer 40 on the protective layer 50 side, which is the upper surface of the magnetic layer 40 in Figure 1) up to 2.5 nm is set to 5 atomic percent or less of the entire magnetic layer 40. The content of the additive elements in the region from the surface of the magnetic layer 40 facing the second underlayer 30 (i.e., the surface of the magnetic layer 40 on the second underlayer 30 side, which is the lower surface of the magnetic layer 40 in Figure 1) up to 5 nm is set to a range of 50 to 95 atomic percent of the entire magnetic layer 40. As a result, it was found that even when the magnetic layer 40 is made thicker, a magnetic recording medium 1 can be obtained in which the disorder of the rotation of magnetic spins in the depth direction of the magnetic layer 40 is reduced when laser heating is performed.

[0025] For example, if 0.1 to 2 atomic percent of Rh is added as an additive element to the entire magnetic layer 40, then less than 5 atomic percent of the total Rh in the magnetic layer 40, for example, less than 0.005 to 0.1 atomic percent, will be contained in the region 2.5 nm from the surface of the magnetic layer 40 facing the protective layer 50. Within the range of 50 to 95 atomic percent of the total Rh in the magnetic layer, for example, less than 0.05 to 1.9 atomic percent, will be contained in the region 5 nm from the surface of the magnetic layer 40 facing the second underlayer 30. The remaining Rh will be contained in the other regions of the magnetic layer 40 (i.e., the regions excluding the region 2.5 nm from the surface of the magnetic layer 40 facing the protective layer 50 and the region 5 nm from the surface of the magnetic layer 40 facing the second underlayer 30).

[0026] Here, when magnetic particles having an L10 structure are used in the magnetic layer 40, according to the inventors' studies, the change in Curie temperature when Rh or Ir is included in the magnetic layer 40 is approximately 10 K / atomic percent. The change in Curie temperature when Ru is included in the magnetic layer 40 is approximately 12 K / atomic percent. The change in Curie temperature when Pd is included in the magnetic layer 40 is approximately 3.7 K / atomic percent.

[0027] In the example described above, where 0.1 to 2 atomic percent of Rh is added to the entire magnetic layer 40, the Curie temperature gradient in the depth direction of the magnetic layer 40 is in the range of 0.05 to 1 K / nm, which is a suitable gradient for the Curie temperature of the magnetic particles having an L10 structure contained in the magnetic layer 40. For example, when the magnetic particles having an L10 structure are FePt alloy particles, the Curie temperature of FePt alloy particles is 750 K, and the Curie temperature of CoPt alloy particles is 840 K. When magnetic particles having an L10 structure are used in the magnetic layer 40, by setting the Curie temperature gradient in the depth direction of the magnetic layer 40 to the range of 0.05 to 1 K / nm, the disturbance of the rotation of magnetic spins in the depth direction of the magnetic layer 40 during laser heating can be reduced.

[0028] This is also true when Ir, Ru, or Pd are used as the additive element instead of Rh. Specifically, when Ir is used as the additive element, the Curie temperature gradient in the depth direction of the magnetic layer is in the range of 0.05 to 1 K / nm. When Ru is used as the additive element, the Curie temperature gradient in the depth direction of the magnetic layer is in the range of 0.06 to 1.2 K / nm. When Pd is used as the additive element, the Curie temperature gradient in the depth direction of the magnetic layer is in the range of 0.02 to 0.4 K / nm. In all cases of the element, the disturbance of the rotation of magnetic spins in the depth direction of the magnetic layer 40 can be reduced during laser heating.

[0029] As described above, the magnetic layer 40 can be divided into three regions: a region 2.5 nm from the surface facing the protective layer 50, a region 5 nm from the surface facing the second underlayer 30, and the remaining region, depending on the amount of added additive elements. However, it is not necessary to form the magnetic layer 40 as a three-layer structure corresponding to these three regions. For example, each of the three regions may be formed as a multilayer structure, or all three regions may have a gradient composition by gradually changing the amount of added additive elements.

[0030] The vertical and planar thermal conductivity of magnetic particles can be measured using known methods such as the time-domain thermoreflectance (TDTR) method.

[0031] The content of the additive elements in the region from the surface of the magnetic layer 40 facing the protective layer 50 up to 2.5 nm is 5 atomic percent or less of the total magnetic layer 40, preferably 4.8 atomic percent or less, more preferably 4.6 atomic percent or less, and even more preferably 4.5 atomic percent or less.

[0032] In this embodiment, the content of additive elements in the region from the surface of the magnetic layer 40 facing the protective layer 50 up to 2.5 nm can be measured using an analytical instrument that measures the desired content of general elements. For example, the content of additive elements can be measured by etching the magnetic layer 40 in its depth direction and measuring it by XPS. Alternatively, the content of additive elements can be measured using EDS or the like at the relevant location observed by TEM in the cross-section of the magnetic layer 40.

[0033] The content of the additive elements in the region from the surface of the magnetic layer 40 facing the second underlayer 30 up to 5 nm is in the range of 50 to 95 atomic percent of the total magnetic layer 40, preferably 53 to 90 atomic percent, more preferably 55 to 80 atomic percent, and even more preferably 56 to 70 atomic percent.

[0034] In this embodiment, the content of additive elements in the region from the surface of the magnetic layer 40 facing the second underlayer 30 up to 5 nm can be measured using the same method as the content of additive elements in the region from the surface of the magnetic layer 40 facing the protective layer 50 up to 2.5 nm.

[0035] The thickness of the magnetic layer 40 is in the range of 10 to 25 nm, preferably in the range of 12 to 23 nm, more preferably in the range of 15 to 20 nm, and even more preferably in the range of 16 to 18 nm.

[0036] In this specification, the thickness of the magnetic layer 40 refers to the length of the magnetic layer 40 in the direction perpendicular to the main surface. The thickness of the magnetic layer 40 may be, for example, the thickness measured at any point in the cross-section of the magnetic layer 40, or it may be the average of several measurements taken at any point. Hereafter, the definition of thickness will be the same for other components.

[0037] The concentration gradient of the added element from the surface of the magnetic layer facing the second underlayer (bottom surface) to the surface of the magnetic layer facing the protective layer (top surface) is preferably 0.60 to 2.50 atomic % / nm, more preferably 0.63 to 2.00 atomic % / nm, and even more preferably 0.65 to 1.50 atomic % / nm. If the concentration gradient of the added element is 0.60 to 2.50 atomic % / nm, the disturbance of the rotation of magnetic spins in the depth direction of the magnetic layer 40 can be further reduced during laser heating.

[0038] The concentration gradient of the added elements can be calculated, for example, by XPS while etching the surface of the magnetic layer 40 in the depth direction.

[0039] The magnetic layer 40 contains magnetic particles having an L10 structure. Examples of magnetic particles having an L10 structure included in the magnetic layer 40 include FePt alloy particles and CoPt alloy particles. Preferably, the FePt alloy particles and CoPt alloy particles are magnetic particles oriented in the (001) direction with an L10 structure. By using such magnetic particles, it becomes easy to double or more the anisotropy of the thermal conductivity in the direction perpendicular to the plane direction.

[0040] Here, when FePt is oriented in the (001) direction in an L10 structure, the vertical thermal conductivity is approximately 11.9 W / (m·K) and the planar thermal conductivity is approximately 4.0 W / (m·K). When CoPt is oriented in the (001) direction in an L10 structure, the vertical thermal conductivity is approximately 13.0 W / (m·K) and the planar thermal conductivity is approximately 4.3 W / (m·K). Note that even if Rh or other elements in the range of 0.1 to 2 atomic percent are added to the magnetic layer, the amount added is so small that the thermal conductivity hardly changes.

[0041] It is preferable that the magnetic particles contained in the magnetic layer 40 be columnar crystals having a shape that penetrates the magnetic layer 40. By making the magnetic particles such columnar crystals, it becomes easy to double or more the anisotropy of the thermal conductivity in the direction perpendicular to the plane direction.

[0042] The vertical thermal conductivity of the magnetic particles contained in the magnetic layer 40 is in the range of 10 to 20 W / (m·K), preferably 11 to 18 W / (m·K), more preferably 11.5 to 17 W / (m·K), and even more preferably 11.8 to 16 W / (m·K).

[0043] The thermal conductivity in the planar direction of the magnetic particles contained in the magnetic layer 40 is in the range of 1 to 10 W / (m·K), preferably 2 to 8 W / (m·K), more preferably 3 to 7 W / (m·K), and even more preferably 4 to 6 W / (m·K).

[0044] The ratio of the perpendicular thermal conductivity to the planar thermal conductivity of the magnetic particles contained in the magnetic layer 40 indicates the anisotropy of the magnetic particles. The ratio is 2 times or more, preferably 2.2 times or more, more preferably 2.5 times or more, and even more preferably 3.0 times or more.

[0045] The first underlayer 20 preferably contains Ag, Au, Al, Cu, Rh, Mo, or W as its main components. The thermal conductivity of each material is shown in Table 1. In the case of alloys, the thermal conductivity can be determined, for example, by converting the thermal conductivity of each material constituting the alloy by volume ratio.

[0046] [Table 1]

[0047] The thickness of the first underlayer 20 is 10 nm or more, preferably 13 nm or more, more preferably 15 nm or more, and even more preferably 20 nm or more. The upper limit of the thickness of the first underlayer 20 is not particularly limited, but may be 100 nm or less, 80 nm or less, or 60 nm or less.

[0048] The average thermal conductivity in the region 10 nm from the surface facing the magnetic layer 40 of the first underlayer 20 is 100 W / (m·K) or higher, preferably 120 W / (m·K) or higher, more preferably 130 W / (m·K) or higher, and even more preferably 135 W / (m·K) or higher. The upper limit of the above average thermal conductivity may be 500 W / (m·K) or lower, and may also be 450 W / (m·K) or lower.

[0049] The second underlayer 30 contains ionic crystals with a thickness in the range of 0.5 to 15 nm. Preferably, the second underlayer 30 contains an NaCl-type compound as the ionic crystal. Examples of NaCl-type compounds include MgO, TiO, NiO, TiN, TaN, HfN, NbN, ZrC, HfC, TaC, NbC, and TiC. These may be used individually or in combination of two or more.

[0050] As the material constituting the second underlayer 30, it is particularly preferable to use a material other than an ionic crystal that can orient the magnetic particles having an L10 structure contained in the magnetic layer 40 in the (001) plane.

[0051] The second sublayer 30 may have a multilayer structure.

[0052] The thickness of the ionic crystal is in the range of 0.5 to 15 nm, preferably 1 to 13 nm, more preferably 3 to 12 nm, and even more preferably 5 to 10 nm.

[0053] The substrate 10 may be a substrate commonly used for magnetic recording media 1. Preferably, the substrate 10 is a heat-resistant glass substrate with a softening temperature of 500°C or higher, preferably 600°C or higher. It can also be used when the substrate 10 is heated to a temperature of 500°C or higher during the manufacturing of the magnetic recording media 1.

[0054] Examples of protective layers 50 include a hard carbon film.

[0055] Examples of methods for forming the protective layer 50 include the RF-CVD (Radio Frequency-Chemical Vapor Deposition) method, which involves decomposing hydrocarbon gas (source gas) with high-frequency plasma to form a film; the IBD (Ion Beam Deposition) method, which involves ionizing the source gas with electrons emitted from a filament to form a film; and the FCVA (Filtered Cathodic Vacuum Arc) method, which involves forming a film using a solid carbon target without using a source gas.

[0056] The thickness of the protective layer 50 is preferably 1 to 6 nm. If the thickness of the protective layer 50 is 1 nm or more, the levitation characteristics of the magnetic head will be good, and if it is 6 nm or less, the magnetic spacing will be reduced, and the SNR (signal-to-noise ratio (S / N ratio)) of the magnetic recording medium 1 will be improved.

[0057] The magnetic recording medium 1 may further have a lubricant layer on the protective layer 50.

[0058] The lubricant layer can be formed using a liquid lubricant layer. Liquid lubricants that are chemically stable, have low friction, and low adsorption are preferably used. Examples of liquid lubricants include fluororesin-based lubricants such as perfluoropolyether-based lubricants containing compounds with a perfluoropolyether structure.

[0059] The thickness of the lubricant layer is not particularly limited, but may be, for example, 1 to 3 nm.

[0060] In addition to the first underlayer 20, the second underlayer 30, the magnetic layer 40, and the protective layer 50, the magnetic recording medium 1 may also include any other layers as appropriate. For example, the magnetic recording medium 1 may include an adhesion layer, a soft magnetic underlayer, etc., between the substrate 10 and the first underlayer 20 as needed. The soft magnetic underlayer may consist of, for example, a first soft magnetic layer, an intermediate layer, and a second soft magnetic layer. The materials used to form the adhesion layer, soft magnetic underlayer, etc., can be general materials used for magnetic recording media.

[0061] [Magnetic storage device] A magnetic storage device equipped with a magnetic recording medium according to this embodiment will be described. The form of the magnetic storage device according to this embodiment is not particularly limited as long as it has a magnetic recording medium according to this embodiment. Here, we will describe the case in which the magnetic storage device records magnetic information on the magnetic recording medium using a heat-assisted recording method.

[0062] The magnetic storage device according to this embodiment may include, for example, a magnetic recording medium drive unit that drives and rotates the magnetic recording medium according to this embodiment, a magnetic head provided with a near-field light generating element at its tip, a magnetic head drive unit that drives and moves the magnetic head, and a recording / reproduction signal processing system.

[0063] The magnetic head is a heat-assisted recording magnetic head, and for example, it has 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.

[0064] Figure 2 shows a perspective view of an example of a magnetic storage device using a magnetic recording medium according to this embodiment. As shown in Figure 2, the magnetic storage device 100 may include a magnetic recording medium 101, a magnetic recording medium drive unit 102 for rotating the magnetic recording medium 101, a magnetic head 103 equipped with a near-field light generating element at its tip, a magnetic head drive unit 104 for moving the magnetic head 103, and a recording / reproduction signal processing unit 105. The magnetic recording medium 101 is the magnetic recording medium 1 described above.

[0065] Figure 3 schematically shows an example of a magnetic head 103. As shown in Figure 3, the magnetic head 103 has a recording head 110 and a playback head 120.

[0066] The recording head 110 includes 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 from the LD 114 to the near-field light generating element 115.

[0067] The playback head 120 has a shield 121 and a playback element 122 sandwiched between the shields 121.

[0068] As shown in Figure 3, the magnetic storage device 100 has the center of the magnetic recording medium 101 attached to the rotation axis of the spindle motor, and the magnetic head 103 levitates and travels on the surface of the magnetic recording medium 101, which is rotated by the spindle motor, while writing or reading information to or from the magnetic recording medium 101.

[0069] In this embodiment, the magnetic storage device 100 can increase the recording capacity of the magnetic recording medium 101 by using the magnetic recording medium 1 as the magnetic recording medium 101, thereby increasing the areal recording density of the magnetic recording medium 101.

[0070] As described above, embodiments have been explained, but these embodiments are presented as examples only, and the present disclosure is not limited by these embodiments. The above embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, or modifications are possible without departing from the spirit of the invention. The above embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Examples]

[0071] The embodiment will be described in more detail below with reference to examples and comparative examples, but the embodiment is not limited to these examples and comparative examples.

[0072] <Manufacturing of magnetic recording media> (Example 1) On a glass substrate, a 100 nm thick layer of 50 atoms %Cr-50 atoms %Ti alloy and a 30 nm thick layer of 63 atoms %Co-27 atoms %Fe-5 atoms %Zr-5 atoms %B alloy were sequentially formed as underlayers by sputtering. Next, after heating the glass substrate to 250°C, a 40 nm thick Mo layer was sequentially formed as the first underlayer, and a 5 nm thick MgO layer as the second underlayer, by sputtering. Next, after heating the glass substrate to 450°C, a 2 nm thick layer of 94 atoms %FePt-5 atoms %Rh-1 atom %BN alloy was sequentially formed as the first magnetic layer, and a 10 nm thick layer of 99 atoms %FePt-1 atom %BN alloy was sequentially formed as the second magnetic layer, by sputtering. Finally, a 3 nm thick carbon film was formed as a protective layer to fabricate a magnetic recording medium.

[0073] Tables 2 to 4 show the composition (material and thickness) and properties (thermal conductivity) of the first substrate, the composition (material and thickness) of the second substrate, the composition (layer structure and thickness) and properties (vertical thermal conductivity, horizontal thermal conductivity, and anisotropy) of the magnetic layer, and the composition of the additive elements included in the magnetic layer. The composition of the additive elements includes the material, total content, content of the additive elements in the region from the surface of the magnetic layer facing the protective layer up to 2.5 nm, content of the additive elements in the region from the surface of the magnetic layer facing the second substrate up to 5 nm, and the concentration gradient of the additive elements.

[0074] The thickness of the first and second sublayers, the thermal conductivity of the first sublayer, the vertical thermal conductivity, horizontal thermal conductivity, and anisotropy of the magnetic layer, the content of additive elements in the region from the surface (top) of the magnetic layer facing the protective layer up to 2.5 nm, and the content of additive elements and the concentration gradient of additive elements in the region from the surface (bottom) of the magnetic layer facing the second sublayer up to 5 nm were measured as follows.

[0075] (Thickness of the first and second subsoil layers) The thicknesses of the first and second subsoil layers were measured by observing the cross-sections of the first and second subsoil layers using a TEM.

[0076] (Thermal conductivity of the first subsoil layer) The thermal conductivity of the first subsoil layer was measured using the TDTR method.

[0077] (Perpendicular thermal conductivity, horizontal thermal conductivity, and anisotropy of the magnetic layer) The vertical and horizontal thermal conductivity of the magnetic layer was measured using the TDTR method. The anisotropy of the magnetic layer is the ratio of the perpendicular thermal conductivity to the planar thermal conductivity, and was calculated by dividing the perpendicular thermal conductivity of the magnetic layer by the planar thermal conductivity (perpendicular thermal conductivity / planar thermal conductivity).

[0078] (Content of additive elements in the region from the surface (top surface) of the magnetic layer facing the protective layer up to 2.5 nm, and content of additive elements in the region from the surface (bottom surface) of the magnetic layer facing the second underlayer up to 5 nm) The content of additive elements in the region from the top surface of the magnetic layer up to 2.5 nm and in the region from the bottom surface of the magnetic layer up to 5 nm was measured by XPS.

[0079] (Concentration gradient of added elements) The concentration gradient of the added elements was measured by XPS while etching the magnetic layer in the depth direction.

[0080] Table 4 shows that the content of the additive elements in the region from the top surface of the magnetic layer up to 2.5 nm was smaller than the content of the additive elements in the region from the bottom surface of the magnetic layer up to 5 nm. However, the additive elements were observed even though the second magnetic layer was formed with the composition shown in Table 3. Therefore, it was confirmed that the additive elements in the magnetic layer diffused from the bottom surface to the top surface of the magnetic layer.

[0081] (Examples 2-13, Comparative Examples 1-8) A magnetic recording medium was fabricated in the same manner as in Example 1, except that the composition (material and thickness) and properties (thermal conductivity) of the first substrate, the composition (material and thickness) of the second substrate, the composition (layer structure and thickness) and properties (vertical thermal conductivity, horizontal thermal conductivity, and anisotropy) of the magnetic layer, and the composition of the additive elements included in the magnetic layer were changed to the conditions shown in Tables 2 to 4. In Tables 2 to 4, the lightly hatched areas indicate values ​​outside the range of this embodiment.

[0082] <Evaluation of electromagnetic conversion characteristics (SNR) of magnetic recording media> The electromagnetic conversion characteristics (SNR) of the magnetic recording media manufactured in each example and comparative example were evaluated using a spin stand manufactured by Guzik. The evaluation results are shown in Table 4.

[0083] [Table 2]

[0084] [Table 3]

[0085] [Table 4]

[0086] Tables 2-4 show that the SNR of the magnetic recording media in each example was 10.5 dB or higher, while the SNR of the magnetic recording media in each comparative example was 9.8 dB or lower. This confirms that the magnetic recording media in each example can exhibit a higher SNR even when the magnetic layer is thickened to 12 nm or more, compared to the magnetic recording media in each comparative example.

[0087] Therefore, it has been confirmed that the magnetic recording medium according to this embodiment can improve electromagnetic conversion characteristics even when used in a heat-assisted recording method. Consequently, the magnetic recording medium according to this embodiment has a high areal recording density when used as a heat-assisted magnetic recording medium, and therefore can have a high recording capacity when used in a magnetic storage device. [Explanation of Symbols]

[0088] 1.101 Magnetic recording media 10 circuit boards 20. The first sublayer 30. Second sublayer 40 Magnetic layer 50 protective layer 100 Magnetic storage devices

Claims

1. A thermally assisted recording magnetic recording medium comprising a substrate, a first underlayer, a second underlayer, a magnetic layer, and a protective layer, stacked in this order, The thickness of the magnetic layer is in the range of 10 to 25 nm. The magnetic layer is L1 ０ It contains magnetic particles having a structure, The magnetic particles have a vertical thermal conductivity in the range of 10 to 20 W / (m·K), a planar thermal conductivity in the range of 1 to 10 W / (m·K), and a ratio of vertical thermal conductivity to planar thermal conductivity of 2 or more. The magnetic layer contains, as an additive element, at least one element selected from the group consisting of Rh, Ir, Ru, and Pd. The amount of the additive element added is within the range of 0.1 to 2 atomic percent of the total magnetic layer. The content of the additive element in the region of the magnetic layer from the surface facing the protective layer up to 2.5 nm is 5 atomic percent or less of the total magnetic layer. The content of the additive element in the region of the magnetic layer from the surface facing the second underlayer up to 5 nm is within the range of 50 to 95 atomic percent of the entire magnetic layer. The thickness of the first underlayer is 10 nm or more, and the average thermal conductivity of the first underlayer in the region 10 nm from the surface facing the magnetic layer is 100 W / (m·K) or more. The second underlying layer is a magnetic recording medium containing ionic crystals with a thickness in the range of 0.5 to 15 nm.

2. The L1 included in the magnetic layer ０ The magnetic recording medium according to claim 1, wherein the structured magnetic particles are FePt alloy particles.

3. The magnetic recording medium according to claim 1 or 2, wherein the ionic crystal is MgO.

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

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