Magnetic Recording Medium and Magnetic Storage Device

Abstract

An object of the present invention is to provide a magnetic recording medium and a magnetic storage device capable of having excellent electromagnetic conversion characteristics. The magnetic recording medium according to the present invention includes a substrate, a base layer, and a magnetic layer containing an alloy having an L10-type crystal structure, which are laminated in this order. The base layer contains MgO, and the magnetic layer has at least three or more layers. When the three magnetic layers are, in order from the substrate side, a first magnetic recording layer, a second magnetic recording layer, and a third magnetic recording layer, the Curie temperature Tc of the second magnetic recording layer is lower than the Curie temperature Tc of the first magnetic recording layer and the third magnetic recording layer, respectively, and the degree of the decrease is in the range of 30K to 100K. The average particle size of the bottom surface of the magnetic particles constituting the first magnetic recording layer is smaller by 15% or more than the average particle size of the bottom surface of the magnetic particles constituting the second magnetic recording layer and the third magnetic recording layer, respectively.

Description

Technical Field

[0001] The present invention relates to a magnetic recording medium and a magnetic storage device. Background Art

[0002] Generally, a magnetic recording medium includes a base layer, a magnetic layer, and a protective layer laminated in sequence on a substrate. As a method of recording magnetic information on the magnetic recording medium, there are a heat-assisted recording method or a microwave-assisted recording method in which a laser or microwave is irradiated onto the magnetic recording medium to locally reduce the coercive force for recording magnetic information. The heat-assisted recording method and the microwave-assisted recording method can achieve a areal recording density of 2 Tbit / inch 2 level, and thus, with the miniaturization, thinning, and high recording density of the magnetic recording medium, a next-generation magnetic recording method capable of increasing the storage capacity has been studied.

[0003] As a magnetic recording medium that can be used in the heat-assisted recording method, for example, a magnetic recording medium is disclosed which is composed of a substrate, a plurality of base layers formed on the substrate, and a magnetic layer mainly composed of an alloy having an L10 structure. The plurality of base layers include a NiO base layer and an orientation control layer (for example, refer to Patent Document 1). In this magnetic recording medium, the orientation control layer includes a base layer formed of an alloy having a BCC structure and a base layer such as MgO having an NaCl structure, and the NiO base layer is oriented in the (100) direction.

[0004] As the magnetic layer of the magnetic recording medium, when using an FePt alloy having an L10 structure, the (001) plane is used as the crystal orientation plane of the magnetic layer. In order to orient the FePt alloy in the (001) direction, generally, MgO that has been oriented in the (100) direction is often used as the base layer. That is, since the lattice integrality between the (100) plane of MgO and the (001) plane of the FePt alloy is high, by forming a magnetic layer containing the FePt alloy on top of the MgO layer, it is easy to orient the FePt alloy in the (001) direction. In addition, in the magnetic recording medium of Patent Document 1, in order to also orient the NiO base layer in the (100) direction, MgO is used as the base layer of the orientation control layer.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-26368 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] Here, the lattice constant of MgO is 0.42 nm. In contrast, that of FePt is 0.39 nm. Therefore, when epitaxially growing an FePt film on an MgO film, there is a slight lattice mismatch, and tensile stress is generated in the FePt film. The tensile stress generated in this FePt film acts in the direction of enlarging the FePt particles. As a result, the magnetic particles enlarge, reducing the electromagnetic conversion characteristics of the magnetic recording medium and highly likely impairing the high recording density of the magnetic recording medium. In addition, the larger the contact area of the particles that are further enlarged, the more easily they are subjected to large stress, so they are more likely to be further enlarged, and the deviation of the crystal grain size becomes larger, thus highly likely reducing the electromagnetic conversion characteristics of the magnetic recording medium.

[0010] An object of one method of the present invention is to provide a magnetic recording medium capable of having excellent electromagnetic conversion characteristics.

[0011] Method for solving the problem

[0012] The magnetic recording medium according to one method of the present invention includes a substrate, a base layer, and a magnetic layer containing an alloy having an L10-type crystal structure, which are laminated in sequence. The base layer contains MgO, and the magnetic layer has at least three or more layers. When the three magnetic layers are, in order from the substrate side, a first magnetic recording layer, a second magnetic recording layer, and a third magnetic recording layer, the Curie temperature Tc of the second magnetic recording layer is lower than that of the first magnetic recording layer and the third magnetic recording layer, respectively, and the degree of lowering is in the range of 30 K to 100 K. The average particle size of the bottom surface of the magnetic particles constituting the first magnetic recording layer is 15% or more smaller than that of the bottom surface of the magnetic particles constituting the second magnetic recording layer and the third magnetic recording layer, respectively.

[0013] Effect of the invention

[0014] According to one method of the present invention, excellent electromagnetic conversion characteristics can be achieved. Description of the drawings

[0015] Figure 1 A cross-sectional view showing an example of the structure of the magnetic recording medium according to the present embodiment.

[0016] Figure 2 A TEM photograph showing an example of the cross-section of the magnetic recording medium 1 according to the present embodiment.

[0017] Figure 3 A perspective view showing an example of a magnetic storage device using the magnetic recording medium according to the present embodiment.

[0018] Figure 4 A schematic diagram showing an example of a magnetic head.

[0019] Explanation of symbols

[0020] 1. 101 Magnetic recording medium

[0021] 10. Substrate

[0022] 20. Base layer

[0023] 30. Magnetic layer

[0024] 31. First magnetic recording layer

[0025] 32. Second magnetic recording layer

[0026] 33. Third magnetic recording layer

[0027] 100. Magnetic storage device Detailed implementation mode

[0028] Hereinafter, the implementation modes of the present invention will be described in detail. In addition, for ease of understanding of the description, the same reference numerals are assigned to the same components in the respective drawings, and redundant descriptions are omitted. In addition, the scales of the respective components in the drawings are sometimes different from the actual ones. 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.

[0029] [Magnetic recording medium]

[0030] Figure 1 FIG. is a cross-sectional view showing an example of the configuration of the magnetic recording medium according to the present embodiment. As Figure 1 shown, the magnetic recording medium 1 is laminated in order from the substrate 10 side and includes a substrate 10, a base layer 20, and a magnetic layer 30.

[0031] In addition, in this specification, the thickness direction (vertical direction) of the magnetic recording medium 1 is set as the Z-axis direction, and the lateral direction (horizontal direction) orthogonal to the thickness direction is set as the X-axis direction. The magnetic layer 30 side in the Z-axis direction is set as the +Z-axis direction, and the substrate 10 side is set as the -Z-axis direction. In the following description, for convenience of explanation, the +Z-axis direction is referred to as up or upper, and the -Z-axis direction is referred to as down or lower, but this does not represent a general up and down relationship.

[0032] Figure 1 FIG. shows only the base layer 20 and the magnetic layer 30 above the substrate 10, but the magnetic recording medium 1 is also below the substrate 10 and includes a base layer 20 and a magnetic layer 30 laminated in order from the substrate 10 side.

[0033] The magnetic recording medium 1 has a base layer 20 and a magnetic layer 30 on both the upper and lower surfaces of the substrate 10. Information can be recorded on both surfaces (double-sided recording) of the substrate 10, but only one of the upper or lower surfaces of the substrate 10 may have the base layer 20 and the magnetic layer 30, and information can be recorded on only one side (single-sided recording) of the substrate 10.

[0034] The material constituting the substrate 10 can be used without particular limitation as long as it is a material that can be used for the magnetic recording medium. Examples of the material constituting the substrate 10 include Al alloys such as AlMg alloy, soda glass, aluminosilicate glass, amorphous glass, silicone, titanium, ceramics, sapphire, quartz, resin, etc. Among these, glasses such as Al alloy, crystalline glass, and amorphous glass are preferred.

[0035] When manufacturing the magnetic recording medium 1, the substrate 10 is sometimes heated to a temperature of 500 °C or higher. Therefore, as the substrate 10, for example, a heat-resistant glass substrate with a softening temperature of 500 °C or higher, preferably 600 °C or higher, is preferably used.

[0036] The base layer 20 is provided above the substrate 10. The base layer 20 includes a layer containing MgO.

[0037] The layer containing MgO contains MgO, is preferably substantially formed of MgO, and more preferably formed only of MgO. The term "substantially" means that in addition to MgO, it may contain inevitable impurities that may inevitably be contained during the manufacturing process.

[0038] In the present embodiment, since the base layer 20 is preferably in direct contact with the first magnetic recording layer 31, the (100) plane of MgO and the (001) plane of the magnetic alloy having an L10 structure included in the first magnetic recording layer 31 are easily lattice integrated, and thus the crystal orientation of the magnetic alloy can be improved.

[0039] The base layer 20 preferably contains an NaCl-type compound. Examples of the NaCl-type compound include TiO, NiO, TiN, TaN, HfN, NbN, ZrC, HfC, TaC, NbC, TiC, etc., in addition to MgO, and two or more types can be used in combination.

[0040] If the base layer 20 can orient the magnetic particles having an L10 structure included in the magnetic layer 30 in the (001) plane, it can be a multilayer structure including other layers.

[0041] The magnetic layer 30 is disposed above the base layer 20. The magnetic layer 30 is sequentially stacked from the base layer 20 side and includes a first magnetic recording layer 31, a second magnetic recording layer 32, and a third magnetic recording layer 33. In addition, the magnetic layer 30 may be composed of the first magnetic recording layer 31, the second magnetic recording layer 32, and the third magnetic recording layer 33. Further, the magnetic layer 30 may further include one or more magnetic layers other than the first magnetic recording layer 31, the second magnetic recording layer 32, and the third magnetic recording layer 33.

[0042] The magnetic layer 30 contains magnetic particles having an L10 structure. That is, the first magnetic recording layer 31, the second magnetic recording layer 32, and the third magnetic recording layer 33 included in the magnetic layer 30 contain magnetic particles having an L10 structure.

[0043] By making the average particle diameter of the bottom surface portion of the magnetic particles constituting the first magnetic recording layer 31 smaller by 15% or more, more preferably in the range of 30% to 60%, respectively, than the average particle diameter of the bottom surface portion of the magnetic particles constituting the second magnetic recording layer 32 and the third magnetic recording layer 33, it is possible to prevent the hypertrophy of the magnetic particles and reduce the magnitude of the deviation of the average particle diameter of the bottom surface portion of the magnetic particles.

[0044] Here, the average particle diameter of the bottom surface portion of the magnetic particles refers to the average particle diameter in the interface portion under the magnetic particles. That is, the particles constituting the base layer 20, the first magnetic recording layer 31, the second magnetic recording layer 32, and the third magnetic recording layer 33 grow epitaxially, so these particles become continuous columnar crystals. In this columnar crystal, the average particle diameter of the interface portion between the base layer 20 and the first magnetic recording layer 31 is made the average particle diameter of the bottom surface of the magnetic particles constituting the first magnetic recording layer 31. The average particle diameter of the interface portion between the first magnetic recording layer 31 and the second magnetic recording layer 32 is the average particle diameter of the bottom surface of the magnetic particles constituting the second magnetic recording layer 32. The average particle diameter of the interface portion between the second magnetic recording layer 32 and the third magnetic recording layer 33 is the average particle diameter of the bottom surface of the magnetic particles constituting the third magnetic recording layer 33.

[0045] In addition, in the present embodiment, the average particle diameter of the bottom surface portion of the magnetic particles is measured using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). For example, in the case of observing the cross section of the magnetic recording layer using a TEM, since the electron beam penetrates 10 nm or more, the depth information of the cross section can be obtained. By analyzing this cross section information, the average particle diameter of the magnetic particles can be measured.

[0046] The Curie temperature Tc of the second magnetic recording layer 32 is lower than the respective Curie temperatures Tc of the first magnetic recording layer 31 and the third magnetic recording layer 33, and the degree of the decrease is in the range of 30 K to 100 K. As described above, the volume of the magnetic particles constituting the first magnetic recording layer 31 is smaller than that of the first magnetic recording layer 31 and the second magnetic recording layer 32, and thus the magnetic characteristics of the first magnetic recording layer 31 are weaker than those of the third magnetic recording layer 33 in contact with the second magnetic recording layer 32. In the present embodiment, by making the Curie temperature Tc of the second magnetic recording layer 32 decrease to a certain extent within a specified range compared with the respective Curie temperatures Tc of the first magnetic recording layer 31 and the third magnetic recording layer 33, it is possible to function in a manner of enhancing the magnetic characteristics of the first magnetic recording layer 31. As a result, the magnetic characteristics of the first magnetic recording layer 31 become stronger, and the noise caused by the first magnetic recording layer 31 can be reduced.

[0047] Figure 2 This is a TEM photograph showing an example of the cross section of the magnetic recording medium 1 according to the present embodiment. Figure 2 The magnetic recording medium shown has a structure in which a base layer 20 containing MgO, a first magnetic recording layer 31, a second magnetic recording layer 32, a third magnetic recording layer 33, and a protective layer 40 are sequentially stacked on a substrate 10. Figure 2 Among the three dashed lines in, starting from the lower side in the figure, they respectively represent the average particle diameter of the bottom surface portion of the magnetic particles constituting the first magnetic recording layer 31, the average particle diameter of the bottom surface portion of the magnetic particles constituting the second magnetic recording layer 32, and the average particle diameter of the bottom surface portion of the magnetic particles constituting the third magnetic recording layer 33. Since the compositions of the materials constituting the first magnetic recording layer 31, the second magnetic recording layer 32, and the third magnetic recording layer 33 are different, the respective boundary positions can be discriminated by the difference in contrast in the TEM photograph. It can be confirmed that the average particle diameter of the bottom surface portion of the magnetic particles constituting the first magnetic recording layer 31 is smaller than the average particle diameter of the bottom surface portion of the magnetic particles constituting the second magnetic recording layer 32 and the average particle diameter of the bottom surface portion of the magnetic particles constituting the third magnetic recording layer 33.

[0048] As a method of making the average particle diameter of the bottom surface portion of the magnetic particles constituting the first magnetic recording layer 31 smaller than that of the magnetic particles constituting the second magnetic recording layer 32 and the third magnetic recording layer 33 in the range of 5% to 40% respectively, for example, there is a method of using a sputtering method for forming the first magnetic recording layer 31 and applying a positive bias potential to the substrate 10. In the sputtering method, the target is set to a negative potential, and sputtering particles such as Ar are made to carry a positive charge to impact the target at high speed, knocking out target particles from the target surface and depositing them on the substrate surface. Here, if a positive bias potential is applied to the substrate, the kinetic energy of the sputtering particles decreases and the mobility decreases, and at the same time, the mobility of the target particles knocked out from the target also decreases, thereby reducing the particle diameter of the magnetic particles.

[0049] The film thickness of the first magnetic recording layer 31 is preferably from 0.4 nm to 1.5 nm, more preferably from 0.5 nm to 1.0 nm, and still more preferably from 0.6 nm to 0.8 nm. If the film thickness of the first magnetic recording layer 31 is within the above preferred range, the tensile stress generated at the interface between the first magnetic recording layer 31 and the second magnetic recording layer 32 can be tolerated, and thus the first magnetic recording layer 31 can exhibit magnetic properties.

[0050] In addition, in the present embodiment, the film thickness of the first magnetic recording layer 31 is the length in the direction perpendicular to the main surface of the first magnetic recording layer 31. For example, the film thickness of the first magnetic recording layer 31 is the thickness measured at an arbitrary position in the cross section of the first magnetic recording layer 31. When several places are measured at arbitrary positions in the cross section of the first magnetic recording layer 31, it can be set as the average value of the thicknesses at these measured places.

[0051] The film thickness of the second magnetic recording layer 32 is preferably from 0.8 nm to 3.0 nm, more preferably from 1.0 nm to 2.5 nm, and still more preferably from 1.2 nm to 2.0 nm. If the film thickness of the second magnetic recording layer 32 is within the above preferred range, the tensile stress generated at the interface between the second magnetic recording layer 32 and the first magnetic recording layer 31 or the third magnetic recording layer 33 can be tolerated, and thus the second magnetic recording layer 32 can exhibit magnetic properties.

[0052] The film thickness of the third magnetic recording layer 33 is preferably 3 nm or more. More preferably, it is from 3.5 nm to 10.0 nm, and still more preferably from 4.5 nm to 6.0 nm. If the film thickness of the third magnetic recording layer 33 is within the above preferred range, the tensile stress generated at the interface between the third magnetic recording layer 33 and the second magnetic recording layer 32 can be tolerated, and thus the third magnetic recording layer 33 can exhibit magnetic properties.

[0053] By making the film thicknesses of the first magnetic recording layer 31, the second magnetic recording layer 32, and the third magnetic recording layer 33 within the above preferred ranges, the action of the tensile stress generated at the interfaces between the respective magnetic recording layers can be tolerated, and thus the electromagnetic conversion characteristics of the magnetic recording medium 1 are improved.

[0054] As the magnetic particles having an L10 structure included in the magnetic layer 30, for example, FePt alloy particles, CoPt alloy particles, etc. can be used. The crystalline magnetic anisotropy constant (Ku) of the FePt alloy is 7×10 6 J / m 3 Hereinafter, the Ku of the CoPt alloy is 5×10 6 J / m 3 Hereinafter, they are all 1×10 6 J / m 3Materials with a high Ku value on a large scale (high Ku materials). Therefore, an FePt alloy or a CoPt alloy is included in the magnetic layer 30, so that in a state where thermal stability is maintained, the magnetic particles constituting the magnetic layer 30 can be refined to a particle size of, for example, 6 nm or less.

[0055] In addition, the magnetic layer 30 may have a granular structure including grain boundary portions.

[0056] When the magnetic layer 30 has a granular structure, the content of the grain boundary portions in the magnetic layer 30 is preferably in the range of 25 vol% to 50 vol%, and more preferably in the range of 35 vol% to 45 vol%. By making the content of the grain boundary portions in the magnetic layer 30 within the above-preferred range, the anisotropy of the magnetic particles included in the magnetic layer 30 can be improved.

[0057] Here, the grain boundary portions can use carbides, nitrides, oxides, borides, etc. As specific examples thereof, BN, B4C, C, MoO3, GeO2, etc. can be cited.

[0058] The magnetic particles included in the magnetic layer 30 are preferably c-axis oriented with respect to the substrate 10, that is, (001) plane orientation. The method of making the magnetic particles included in the magnetic layer 30 c-axis oriented with respect to the substrate 10 is not particularly limited. For example, a method of epitaxially growing the magnetic layer 30 along the c-axis using the base layer 20 can be used.

[0059] The magnetic recording medium 1 preferably further has a protective layer 40 on the magnetic layer 30. The protective layer 40 has a function of protecting the magnetic recording medium 1 from damage caused by contact between the magnetic recording medium 1 and a magnetic head, etc.

[0060] As the protective layer 40, for example, a hard carbon film, etc. can be cited.

[0061] As a method for forming the protective layer 40, for example, an RF-CVD (Radio Frequency-Chemical Vapor Deposition) method of decomposing a hydrocarbon gas (source gas) using high-frequency plasma for film formation; an IBD (Ion Beam Deposition) method of ionizing the source gas using electrons emitted from a filament for film formation; an FCVA (Filtered Cathodic Vacuum Arc) method of forming a film using a solid carbon target without using a source gas, etc. can be cited.

[0062] The thickness of the protective layer 40 is preferably 1 nm to 6 nm. If the thickness of the protective layer 40 is 1 nm or more, the flying characteristics of the magnetic head become good, and the magnetic spacing becomes small, and the SNR of the magnetic recording medium 1 is improved.

[0063] The magnetic recording medium 1 may further have a lubricant layer 50 on the protective layer 40.

[0064] Examples of the wetting agent include fluororesins such as perfluoropolyether.

[0065] The magnetic recording medium 1 according to the present embodiment includes a substrate 10, a base layer 20, and a magnetic layer 30 laminated in this order. The base layer 20 contains MgO, and the magnetic layer 30 includes a first magnetic recording layer 31, a second magnetic recording layer 32, and a third magnetic recording layer 33 laminated in this order from the substrate 10 side. Moreover, in the magnetic recording medium 1, the Curie temperature Tc of the second magnetic recording layer 32 is lower than the Curie temperature Tc of the first magnetic recording layer 31 and the third magnetic recording layer 33, respectively, and the degree of the decrease is in the range of 30 K to 100 K. The average particle diameter of the bottom surface portion of the magnetic particles constituting the first magnetic recording layer 31 is smaller by 15% or more than the average particle diameter of the bottom surface portion of the magnetic particles constituting the second magnetic recording layer 32 and the third magnetic recording layer 33, respectively. Since the average particle diameter of the bottom surface portion of the magnetic particles constituting the first magnetic recording layer 31 is smaller by 15% or more than the average particle diameter of the bottom surface portion of the magnetic particles constituting the second magnetic recording layer 32 and the third magnetic recording layer 33, respectively, only in this portion, the magnetic characteristics of the first magnetic recording layer 31 are generally lower than the magnetic characteristics of the second magnetic recording layer 32 and the third magnetic recording layer 33. In the present embodiment, the second magnetic recording layer 32 has a smaller Curie temperature Tc than the first magnetic recording layer 31 and the third magnetic recording layer 33 only in a specified range to a certain extent. Therefore, the magnetic characteristics of the second magnetic recording layer 32 can act in a manner of enhancing the first magnetic recording layer 31 and the third magnetic recording layer 33. Therefore, even if the magnetic characteristics of the first magnetic recording layer 31 are lower than those of the second magnetic recording layer 32 and the third magnetic recording layer 33 that are directly or indirectly in contact therewith, the magnetic characteristics of the first magnetic recording layer 31 can be improved by the second magnetic recording layer 32 and the third magnetic recording layer 33. As a result, the magnetic characteristics of the first magnetic recording layer 31 are enhanced, and the noise caused by the first magnetic recording layer 31 can be reduced. As a result, the magnetic recording medium 1 can exhibit excellent electromagnetic conversion characteristics.

[0066] The electromagnetic conversion characteristics of the magnetic recording medium 1 can be evaluated by SNR (signal / noise ratio (S / N ratio)). The smaller the SNR of the magnetic recording medium, the more excellent the electromagnetic conversion characteristics of the magnetic recording medium 1 can be evaluated. The measurement of SNR is not particularly limited. For example, it can be performed using a read / write analyzer RWA1632 and a rotary test stand S1701MP (both manufactured by GUZIK).

[0067] The magnetic recording medium 1 can contain magnetic particles in each magnetic recording layer in a state where the average particle diameter of the bottom surface portion of the magnetic particles constituting the first magnetic recording layer 31 is smaller than that of the magnetic particles constituting the second magnetic recording layer 32 and the third magnetic recording layer 33 within a range of 30% to 60%. Even if the size of the magnetic particles constituting the first magnetic recording layer 31 becomes smaller than that of the second magnetic recording layer 32 and the third magnetic recording layer 33 within the above range, the magnetic characteristics of the first magnetic recording layer 31 are enhanced, and the noise caused by the first magnetic recording layer 31 can be reduced. Thus, the magnetic recording medium 1 can exhibit excellent electromagnetic conversion characteristics.

[0068] The magnetic recording medium 1 can make the film thickness of the first magnetic recording layer 31 be 0.4 nm to 1.5 nm. Thus, the magnetic recording medium 1 can fully exhibit the magnetic characteristics of the first magnetic recording layer 31, and therefore can surely exhibit excellent electromagnetic conversion characteristics.

[0069] The magnetic recording medium 1 can make the film thickness of the second magnetic recording layer 32 be 0.8 nm to 3.0 nm. Thus, the magnetic recording medium 1 can fully exhibit the magnetic characteristics of the second magnetic recording layer 32, and therefore can surely exhibit excellent electromagnetic conversion characteristics.

[0070] The magnetic recording medium 1 can make the film thickness of the third magnetic recording layer 33 be 3 nm or more. Thus, the magnetic recording medium 1 can fully exhibit the magnetic characteristics of the third magnetic recording layer 33, and therefore can surely exhibit excellent electromagnetic conversion characteristics.

[0071] In the magnetic recording medium 1, the magnetic layer 30 can contain at least one of an FePt alloy and a CoPt alloy having an L10 structure. Both the FePt alloy and the CoPt alloy are high Ku materials on the order of 1×10 6 J / m 3 scale. Therefore, by using at least one of the FePt alloy and the CoPt alloy as the material constituting the magnetic layer 30, the magnetic particles constituting the magnetic layer 30 can be refined, for example, until the particle diameter becomes 6 nm or less while maintaining the thermal stability. Thus, when using a heat-assisted recording method or a microwave-assisted recording method as a recording method, the magnetic layer 30 can have a coercive force of several tens of kOe at room temperature, and magnetic information can be easily recorded on the magnetic layer 30 by the recording magnetic field of a magnetic head.

[0072] [Magnetic storage device]

[0073] A magnetic storage device using the 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 the magnetic recording medium according to this embodiment. In addition, here, the case where magnetic information is recorded on the magnetic recording medium by using a heat-assisted recording method in the magnetic storage device will be described.

[0074] The magnetic storage device according to this embodiment can have, for example: a magnetic recording medium driving unit for rotating the magnetic recording medium according to this embodiment; a magnetic head provided with a near-field light generating element at the front end; a magnetic head driving unit for moving the magnetic head; and a recording / reproducing signal processing unit.

[0075] In addition, the magnetic head is a magnetic head for thermally assisted recording, and has, for example, a laser generating unit for heating the magnetic recording medium and a waveguide for guiding the laser generated by the laser generating unit to the near-field light generating element.

[0076] Figure 3 FIG. is a perspective view showing an example of a magnetic storage device using the magnetic recording medium according to this embodiment. As Figure 3 shown, 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 the front end, a magnetic head driving unit 104 for moving the magnetic head 103, and a recording / reproducing signal processing unit 105. The magnetic recording medium 101 uses the magnetic recording medium 1 according to the above-described embodiment.

[0077] Figure 4 FIG. is a schematic diagram showing an example of the magnetic head 103. As Figure 4 shown, the magnetic head 103 has a recording head 110 and a reproducing head 120.

[0078] 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 as a laser generating unit, and a waveguide 116 for transmitting the laser L generated by the LD 114 to the near-field light generating element 115.

[0079] The reproducing head 120 has a shield 121 and a reproducing element 122 sandwiched by the shield 121.

[0080] As Figure 3 shown, the magnetic storage device 100 mounts the central portion of the magnetic recording medium 101 on the rotating shaft of the spindle motor, and while the magnetic head 103 floats and moves onto the surface of the magnetic recording medium 101 rotated and driven by the spindle motor, information is written to or read from the magnetic recording medium 101.

[0081] The magnetic storage device 100 according to this embodiment can increase the recording density of the magnetic recording medium 101 by using the magnetic recording medium 1 according to this embodiment, thereby improving the recording density.

[0082] In addition, in a magnetic storage device, a magnetic head for microwave-assisted recording may be used instead of the magnetic head for heat-assisted recording, with the magnetic head 103.

[0083] Example

[0084] Hereinafter, examples and comparative examples will be shown to specifically describe the embodiments, but the embodiments are not limited to these examples and comparative examples.

[0085] <Manufacture of Magnetic Recording Medium>

[0086] [Example 1]

[0087] A magnetic recording medium was manufactured by the following method.

[0088] On a glass substrate, as a base layer, a Cr-50 at% Ti alloy layer with a thickness of 100 nm and a Co-27 at% Fe-5 at% Zr-5 at% B alloy layer with a thickness of 30 nm were sequentially formed. Next, after heating the glass substrate to 250 °C, a Cr layer with a thickness of 10 nm and an MgO layer with a thickness of 5 nm were sequentially formed. Next, after heating the glass substrate to 450 °C, as the first magnetic recording layer, FePt-40 mol% C was formed to a thickness of 1 nm while applying a bias potential of +10 V to the substrate. Next, after heating the glass substrate to 630 °C, as the second magnetic recording layer, FePt 5 at% Rh-40 mol% C was formed to a thickness of 2 nm. Next, as the third magnetic recording layer, an FePt-16SiO2 layer with a thickness of 3 nm was formed. Next, as a protective layer, a carbon film with a thickness of 3 nm was formed, thereby manufacturing a magnetic recording medium according to Example 1.

[0089] [Examples 2 to 11, Comparative Examples 1-1 to 1-5]

[0090] In Example 1, at least one or more of the materials constituting the first magnetic recording layer, the second magnetic recording layer, and the third magnetic recording layer were changed as shown in Table 1, and except for this, the same operations as in Example 1 were performed to manufacture the magnetic recording media of Examples 2 to 11 and Comparative Examples 1-1 to 1-5.

[0091] [Comparative Examples 2-1 to 2-4]

[0092] In Example 1, the temperature of the glass substrate during the film formation of the first magnetic recording layer was 650 °C, and no bias potential was applied during the film formation of the first magnetic recording layer. Except for this, the same operations as in Example 1 were performed to manufacture the magnetic recording media of Comparative Examples 2-1 to 2-4.

[0093] [Comparative Example 3-1]

[0094] In Example 1, the materials constituting the magnetic layer were changed as shown in Table 1, and no bias potential was applied during the film formation of the first magnetic recording layer. Otherwise, the process was the same as in Example 1 to fabricate a magnetic recording medium.

[0095] The cross-sections of the magnetic recording media of the respective Examples and Comparative Examples produced were observed by TEM, and the average particle diameter of the bottom surfaces of the magnetic particles constituting the first magnetic recording layer, the average particle diameter of the bottom surfaces of the magnetic particles constituting the second magnetic recording layer, and the average particle diameter of the bottom surfaces of the magnetic particles constituting the third magnetic recording layer were measured. The respective measurement results are shown in Table 1.

[0096] <Evaluation of Magnetic Recording Medium>

[0097] (Electromagnetic Conversion Characteristics)

[0098] Using the read / write analyzer RWA1632 and the rotary test bench S1701MP manufactured by GUZIK Co., Ltd. in the United States, the SNR (signal / noise ratio (S / N ratio)) was evaluated as the electromagnetic conversion characteristics of the magnetic recording media of the respective Examples and Comparative Examples produced.

[0099] [Table 1]

[0100]

[0101] From Table 1, in Examples 1 to 11, the SNR was 6.2 or more. On the other hand, in Comparative Examples 1-1 to 1-5, 2-1 to 2-4, and 3-1, the SNR was 5.8 or less.

[0102] Thus, the magnetic recording media of Examples 1 to 11 are different from the magnetic recording media of Comparative Examples 1-1 to 1-5, 2-1 to 2-4, and 3-1. The Curie temperature Tc of the second magnetic recording layer 32 is lower than the Curie temperature Tc of the first magnetic recording layer 31 and the third magnetic recording layer 33, respectively, and the degree of the decrease is in the range of 30K to 100K. The average particle diameter of the bottom surfaces of the magnetic particles constituting the first magnetic recording layer 31 is 15% or more smaller than the average particle diameter of the bottom surfaces of the magnetic particles constituting the second magnetic recording layer 32 and the third magnetic recording layer 33. Thus, it can be said that the magnetic recording medium 1 can reduce the particle diameter of the magnetic particles included in the magnetic layer 30, and thereby can exhibit excellent electromagnetic conversion characteristics.

[0103] As described above, the embodiments have been described, but the above embodiments are presented as examples, and the present invention is not limited to 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 gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the invention described in the claims and its equivalents.

Claims

1. A magnetic recording medium which sequentially stacks a substrate, a base layer, and a magnetic layer containing an alloy having an L10-type crystal structure. The base layer contains MgO. The magnetic layer has at least three or more layers. When the three magnetic layers are the first magnetic recording layer, the second magnetic recording layer, and the third magnetic recording layer in order from the substrate side, the Curie temperature Tc of the second magnetic recording layer is lower than that of the first magnetic recording layer and the third magnetic recording layer respectively, and the degree of the decrease is in the range of 30K to 100K. The average particle size of the bottom surface of the magnetic particles constituting the first magnetic recording layer is smaller than that of the bottom surface of the magnetic particles constituting the second magnetic recording layer and the third magnetic recording layer by 15% or more respectively. The first magnetic recording layer, the second magnetic recording layer, and the third magnetic recording layer have a granular structure, and the content of the grain boundary portion in each magnetic recording layer is in the range of 35% to 45% by volume. A bias potential is applied during the film formation of the first magnetic recording layer.

2. The magnetic recording medium according to claim 1, wherein the average particle size of the bottom surface of the magnetic particles constituting the first magnetic recording layer is 30% to 60% smaller than that of the bottom surface of the magnetic particles constituting the second magnetic recording layer and the third magnetic recording layer.

3. The magnetic recording medium according to claim 1 or 2, wherein the film thickness of the first magnetic recording layer is 0.4nm to 1.5nm.

4. The magnetic recording medium according to any one of claims 1 to 3, wherein the film thickness of the second magnetic recording layer is 0.8nm to 3.0nm.

5. The magnetic recording medium according to any one of claims 1 to 4, wherein the film thickness of the third magnetic recording layer is 3nm or more.

6. The magnetic recording medium according to claim 1, wherein the base layer is in direct contact with the first magnetic recording layer.

7. A magnetic storage device which includes the magnetic recording medium according to any one of claims 1 to 6.

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