Magnetic recording medium and magnetic recording device

Abstract

This magnetic recording medium comprises at least a magnetic recording layer having an (001) oriented L10 structure, a pinning layer, and a carbon protective layer layered, in this order, on a nonmagnetic substrate, and has a nonmagnetic layer, which is formed from an oxide, disposed between the pinning layer and the carbon protective layer.

Description

Magnetic recording medium and magnetic recording device

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

[0002] In recent years, in the field of magnetic recording media such as hard disk drives (HDDs), assisted recording methods such as thermally assisted recording and microwave assisted recording, which record by irradiating the magnetic recording media with near-field light or microwaves, have achieved data rates of 2 Tbit / inch. ２ It is attracting attention as a next-generation recording method that can achieve a high surface recording density.

[0003] In magnetic recording media using the assisted recording method, writing is performed by locally reducing the coercivity of the magnetic recording medium using laser light or microwaves irradiated from a magnetic head. It is known that when the coercivity recovers immediately after writing, magnetization reversal occurs in some of the magnetic particles that make up the bit around the written bit, and the parts where magnetization reversal occurs become noise when reading.

[0004] In order to suppress such noise, for example, an assisted magnetic recording medium has been disclosed in which the difference between the Curie temperature of the magnetic material constituting the pinning layer and the Curie temperature of the magnetic material constituting the magnetic layer is set to 200 K or more, thereby pinning the magnetization reversal of the magnetic particles (see, for example, Patent Document 1).

[0005] The pinning layer is often formed using a material that has a smaller saturation magnetization Ms and magnetic anisotropy constant Ku than the magnetic layer, but energy such as thermal energy generated during the formation of the carbon protective layer formed on the pinning layer can cause the material that makes up the pinning layer to diffuse into the magnetic layer, resulting in a deterioration in the magnetic properties of the assisted magnetic recording medium.

[0006] Therefore, in order to suppress the deterioration of magnetic properties, a magnetic recording medium for a thermally assisted recording method has been disclosed in which a first lower protective layer formed on top of the magnetic recording layer uses an element selected from the group consisting of Si, Al, and Cu as its main component (see, for example, Patent Document 2).

[0007] Japanese Patent No. 7011477 Japanese Patent No. 5556979

[0008] However, the magnetic recording medium for thermally assisted recording disclosed in Patent Document 2 has a problem in that it is not possible to sufficiently prevent the deterioration of magnetic properties.

[0009] An object of the present invention is to provide a magnetic recording medium that can suppress the deterioration of magnetic properties and maintain excellent magnetic properties.

[0010] In order to achieve the above object, the present invention employs the following configuration: (1) A (001)-oriented L1 ０ (2) A magnetic recording medium comprising a magnetic recording layer having a structure, a pinning layer, and a carbon protective layer laminated at least in this order, and a non-magnetic layer made of an oxide between the pinning layer and the carbon protective layer. (3) The magnetic recording medium according to (1), wherein the non-magnetic layer contains ZnO in a range of 40 to 100 atomic %. (4) The magnetic recording medium according to (2), wherein the non-magnetic layer contains ZnO in a range of 40 to 80 atomic % and SiO ２ (4) A magnetic recording device comprising the magnetic recording medium according to any one of (1) to (3).

[0011] The present invention can provide a magnetic recording medium that can suppress the deterioration of magnetic properties and maintain excellent magnetic properties.

[0012] 1 is a cross-sectional view showing an example of a layer configuration of a magnetic recording medium according to an embodiment of the present invention; 2 is a cross-sectional view showing an example of a structure of a pinning layer of a magnetic recording medium according to an embodiment of the present invention; 3 is a cross-sectional view showing another example of a structure of a pinning layer of a magnetic recording medium according to an embodiment of the present invention; 4 is a perspective view showing an example of a magnetic recording and reproducing device to which a magnetic recording medium according to an embodiment of the present invention is applied;

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this specification, unless otherwise specified, the term "to" indicating a range of values ​​means that the values ​​before and after it are included as the lower and upper limits. Furthermore, when a unit is specified for only the upper limit of a range of values ​​expressed by "to," it means that the lower limit is also expressed in the same unit.

[0014] 1 is a cross-sectional view showing an example of the layer structure of a magnetic recording medium according to this embodiment. As shown in Fig. 1, the magnetic recording medium 1 includes a non-magnetic substrate 10, an underlayer 20, a magnetic recording layer 30, a pinning layer 40, a non-magnetic layer 50, a carbon protective layer 60, and a lubricant layer 70 stacked in this order on the non-magnetic substrate 10.

[0015] The non-magnetic substrate 10 may be a metal substrate made of a metal material such as aluminum or an aluminum alloy, or a non-metal substrate made of a non-metal material such as glass, ceramics, silicon, silicon carbide, or carbon. The non-magnetic substrate 10 may also be a laminate in which a NiP layer or a NiP alloy layer is formed on the surface of such a metal or non-metal substrate.

[0016] The underlayer 20 is provided on the upper surface of the non-magnetic substrate 10 and has the effect of enhancing the crystal orientation of the magnetic recording layer 30 formed on the underlayer 20. The underlayer 20 includes a first underlayer 21 and a second underlayer 22 stacked in this order. Note that the number of layers of the first underlayer 21 and the second underlayer 22 stacked is not particularly limited.

[0017] The first underlayer 21 preferably contains at least one of Cr and W, more preferably consists essentially of at least one of Cr and W, and even more preferably consists only of at least one of Cr and W. In this specification, "substantially" means that in addition to Cr and W, it may also contain inevitable impurities that may be inevitably contained during the manufacturing process. The combined content of Cr and W may be any amount that is effective in enhancing the crystal orientation of the magnetic recording layer 30, and is, for example, preferably 80 atomic % or more, more preferably 90 atomic % or more, even more preferably 95 atomic % or more, and most preferably 100 atomic % of the elements constituting the first underlayer 21.

[0018] The second underlayer 22 preferably contains MgO, more preferably consists essentially of MgO, and even more preferably consists only of MgO. The MgO content may be any amount that is effective in enhancing the crystal orientation of the magnetic recording layer 30. For example, the MgO content of the elements constituting the second underlayer 22 is preferably 80 atomic % or more, more preferably 90 atomic % or more, even more preferably 95 atomic % or more, and most preferably 100 atomic %.

[0019] The first underlayer 21 and the second underlayer 22 can be formed by using a general film formation method such as DC sputtering or RF sputtering.

[0020] The thickness of the first underlayer 21 is not particularly limited, and may be, for example, 1 to 100 nm.

[0021] The thickness of the second underlayer 22 is not particularly limited, and may be, for example, 1 to 10 nm.

[0022] The lattice misfit between the first underlayer 21 and the second underlayer 22 is preferably 10% or less. If the lattice misfit is 10% or less, the effect of improving the crystal orientation of the magnetic recording layer 30 can be reliably achieved. Examples of a structure for reducing the lattice misfit between the first underlayer 21 and the second underlayer 22 to 10% or less include (100)-oriented Cr, W, and MgO. To ensure the (100) orientation, the first underlayer 21 may be formed using Cr or an alloy with a bcc structure containing Cr as the main component (e.g., CrMn, CrMo, CrW, CrV, CrTi, and CrRu), or may be formed using an alloy with a B2 structure (e.g., RuAl and NiAl).

[0023] The magnetic recording layer 30 is provided on the upper surface of the underlayer 20. The magnetic recording layer 30 has a thickness of L1 ０ It is preferable that the alloy contains an alloy having a L1 type crystal structure. ０ More preferably, the alloy essentially consists of an alloy having a L1 type crystal structure. ０ It is more preferable that the alloy is composed solely of an alloy having the L1 type crystal structure. ０The alloy having the L1 crystal structure has a (001) orientation. ０ Alloys having the crystalline structure can have a high magnetic anisotropy constant Ku. Examples of such alloys include FePt-based alloys and CoPt-based alloys.

[0024] The magnetic recording layer 30 is formed by L1 ０ In order to promote ordering of the alloy having the L1 type crystal structure, it is preferable to perform a heat treatment. ０ Ag, Au, Cu, Ni, etc. may be added to the alloy having the crystalline structure.

[0025] L1 contained in the magnetic recording layer 30 ０ The crystal grains of the alloy having the L1 crystal structure are preferably magnetically separated. ０ Magnetic particles 31 having a crystalline structure and containing Fe or Co as a main component, and SiO ２ , TiO ２ , Cr ２ O ３ , Al ２ O ３ , Ta ２ O ５ , ZrO ２ , Y ２ O ３ , CeO ２ , GeO ２ , MnO, TiO, ZnO, B ２ O ３ It is preferable that the magnetic recording layer 30 has a grain boundary material 32 containing one or more additive substances selected from the group consisting of C, B, and BN. The grain boundary material 32 is present between the magnetic grains 31, and it is preferable that the magnetic grains 31 and the grain boundary material 32 are present separately within the magnetic recording layer 30. This more reliably separates the exchange coupling between the crystal grains within the magnetic recording layer 30, and further increases the signal-to-noise ratio (SNR) of the magnetic recording layer 30.

[0026] The magnetic recording layer 30 may have a multi-layer structure of two or more layers. In this case, the types of the additive substances contained in the grain boundary material 32 of each magnetic recording layer 30 may be different.

[0027] The thickness of the magnetic recording layer 30 is not particularly limited, but is preferably 1 to 20 nm. A thickness of the magnetic recording layer of 1 nm or more makes it possible to obtain sufficient reproduction output, and a thickness of 20 nm or less makes it possible to suppress enlargement of crystal grains. Note that when the magnetic recording layer 30 has a multi-layer structure, the thickness of the magnetic recording layer 30 refers to the total thickness of all layers.

[0028] In this specification, the thickness of the magnetic recording layer 30 refers to the length in the direction perpendicular to the main surface of the magnetic recording layer 30. The thickness of the magnetic recording layer 30 may be, for example, the thickness measured at an arbitrary location on the cross section of the magnetic recording layer 30, or may be the average value of measurements measured at several arbitrary locations. Hereinafter, the definition of thickness is similarly defined for other members.

[0029] The pinning layer 40 is preferably provided on the upper surface of the magnetic recording layer 30 in contact with the magnetic recording layer 30. The pinning layer 40 is preferably formed of a magnetic material having a Curie temperature 200 K or more higher than that of the material forming the magnetic recording layer 30. This allows the magnetization reversal of the magnetic grains 31 contained in the magnetic recording layer 30 to be pinned by the pinning layer 40, thereby reducing magnetic recording noise.

[0030] Examples of magnetic materials that can be used for the pinning layer 40 include Co, CoPt, CoB, CoSi, CoC, CoNi, CoFe, CoPtB, CoPtSi, CoPtC, CoGe, Co, oxides, nitrides, and carbides thereof, and carbon. By using the above-mentioned magnetic materials, the pinning layer 40 can have a granular structure that includes magnetic grains such as Co, CoPt, CoB, CoSi, CoC, CoNi, CoFe, CoPtB, CoPtSi, CoPtC, and CoGe, and at least one component selected from the group consisting of oxides, nitrides, carbides, and carbon, which is included in the grain boundaries between the magnetic grains.

[0031] The oxide is, for example, SiO ２ , Cr ２ O ３ , TiO ２ , B ２ O ３, GeO ２ , MgO, Ta ２ O ５ , CoO, Co ３ O ４ , FeO, Fe ２ O ３ and Fe ３ O ４ At least one oxide selected from the group consisting of:

[0032] Nitrides include BN and Si ３ N ４ , SiOxNy (x>0 and y>0), TiN, ZrN, AlN, TaN, Ta ２ N, CrN, Cr ２ N, GaN and Mg ３ N ２ At least one nitride selected from the group consisting of:

[0033] Carbides include TiC, SiC, ZrC, and B ４ C, WC, VC, Al ４ C ３ , HfC, Mo ２ At least one carbide selected from the group consisting of C, NbC, and TaC can be used.

[0034] The preferred thickness of the pinning layer 40 may be adjusted to any appropriate thickness depending on the magnetic material of the pinning layer 40, the constituent material and thickness of the magnetic recording layer 30, the particle size distribution of the magnetic grains 31 that constitute the magnetic recording layer 30, etc. The thickness of the pinning layer 40 is preferably 0.5 to 5 nm, for example. If the thickness of the pinning layer 40 is 0.5 nm or more, a higher pinning effect can be obtained, and if it is 5 nm or less, noise from the pinning layer 40 can be suppressed.

[0035] The nonmagnetic layer 50 is formed on the upper surface of the pinning layer 40. Examples of materials used to form the nonmagnetic layer 50 include ZnO and SiO. ２ , Ga ２ O ３ , Al ２ O ３ , In ２ O ３ and ZrO ２These oxides can be prevented from penetrating into the structure of the pinning layer 40. These oxides may be used alone or in combination of two or more.

[0036] In magnetic recording media with a pinning layer, the structure of the magnetic material of the pinning layer is destroyed by sputtering and etching, which are performed when forming a carbon protective layer on the pinning layer, and the saturation magnetization Ms of the magnetic recording medium decreases. For example, even if a nonmagnetic layer is formed on the surface of the pinning layer to protect the pinning layer, an alloy such as Si or Al cannot suppress the decrease in saturation magnetization Ms of the magnetic recording medium.

[0037] The inventors believed that if the nonmagnetic layer were made of an alloy such as Si or Al, the metallic bonds of the metal lattice in the alloy would easily be broken by the energy generated when forming the carbon protective layer, and the constituent elements would penetrate into the alloy structure of the pinning layer, destroying the structure of the pinning layer and resulting in a deterioration of the magnetic properties of the magnetic recording medium. The inventors discovered that by using an oxide that forms an ionic or covalent bond stronger than a metallic bond as the material for the nonmagnetic layer 50, the oxide would not penetrate into the pinning layer 40, and even when energy is applied, such as when forming the carbon protective layer, the constituent elements of the nonmagnetic layer 50 would be prevented from penetrating into the alloy structure of the pinning layer 40, preventing the destruction of the structure of the pinning layer 40 and thereby suppressing a deterioration in the magnetic properties of the magnetic recording medium 1.

[0038] The oxide in the nonmagnetic layer 50 preferably contains ZnO.

[0039] The content of oxides contained in the non-magnetic layer 50 can be adjusted appropriately depending on the type and number of oxides contained in the non-magnetic layer 50, and is preferably, for example, 40 to 100 atomic %.

[0040] Oxide materials generally have poor wettability and spreadability on alloys, so when the nonmagnetic layer 50 is formed using an oxide material, the nonmagnetic layer 50 tends to have a shape as shown in FIG. 2 . That is, the nonmagnetic layer 50 is formed so as to be approximately uniform along the surface shape of the pinning layer 40, and is unlikely to be preferentially formed in the recesses of the uneven surface of the pinning layer 40 on the magnetic recording layer 30. Therefore, the uneven surface of the pinning layer 40 tends not to be flattened by the nonmagnetic layer 50. Among the above oxides, ZnO has good wettability and spreadability on the alloy that constitutes the pinning layer 40, so it is likely to be preferentially formed in the recesses of the uneven surface of the pinning layer 40. Therefore, as shown in FIG. 3 , the nonmagnetic layer 50 is thought to be formed so as to fill the recesses of the uneven surface of the pinning layer 40. The non-magnetic layer 50 is stacked on the pinning layer 40 so that the size of the irregularities on its surface is smaller than the size of the irregularities on the surface of the pinning layer 40, and the surface of the non-magnetic layer 50 is flattened, so that the non-magnetic layer 50 has high surface smoothness.

[0041] The oxide composition of the non-magnetic layer 50 is a combination of ZnO in the range of 40 to 80 atm % and SiO ２ It is preferable that the content of the element be in the range of 10 to 60 atm %.

[0042] ZnO contained in the non-magnetic layer 50 penetrates from the recesses of the pinning layer 40 through the grain boundary material 32 of the magnetic recording layer 30 into the magnetic grains 31, and may connect the separated magnetic grains 31 of the magnetic recording layer 30 together, which may cause fluctuations in the coercivity of the magnetic recording layer 30. In contrast, the oxides ZnO and SiO contained in the non-magnetic layer 50 ２ By forming the non-magnetic layer 50 with the composition of SiO ２ can be limited to penetrating up to the grain boundary material 32 of the magnetic recording layer 30, so that the magnetic grains 31 can be maintained in a state of being separated from each other. By maintaining the separation between the magnetic grains 31, fluctuations in the coercivity of the magnetic recording layer 30 are suppressed.

[0043] The thickness of the nonmagnetic layer 50 may be adjusted to any appropriate thickness, and is preferably, for example, 0.5 to 2 nm. If the thickness of the nonmagnetic layer 50 is 0.5 nm or more, the magnetic recording layer 30 and the pinning layer 40 can be protected from the energy of forming a protective film, etc., and if the thickness is 2 nm or less, the magnetic head and the magnetic recording layer 30 can be spaced apart, preventing a decrease in recording density.

[0044] The carbon protective layer 60 is formed on the upper surface of the nonmagnetic layer 50. There are no particular limitations on the method for forming the carbon protective layer 60, and a general film formation method can be used. The carbon protective layer 60 can be formed by, for example, RF-CVD (Radio Frequency-Chemical Vapor Deposition), which forms a film by decomposing a source gas made of hydrocarbons using high-frequency plasma, IBD (Ion Beam Deposition), which forms a film by ionizing a source gas with electrons emitted from a filament, or FCVA (Filtered Cathodic Vacuum Arc), which forms a film using a solid C target without using a source gas.

[0045] The thickness of the carbon protective layer 60 is not particularly limited, but is preferably set to, for example, 1 to 6 nm. By setting the thickness of the carbon protective layer 60 to 1 nm or more, it is possible to suppress deterioration of the flying characteristics of the magnetic head, and by setting the thickness of the carbon protective layer 60 to 6 nm or less, it is possible to suppress an increase in magnetic spacing loss and suppress a decrease in the SNR of the magnetic recording medium 1.

[0046] The lubricant layer 70 is formed on the upper surface of the carbon protective layer 60. The method for forming the lubricant layer 70 is not particularly limited, and a general film-forming method can be used. The lubricant layer 70 can be formed, for example, by applying a lubricant film composition containing a perfluoropolyether-based fluororesin to the upper surface of the carbon protective layer 60 using a method such as immersion, and then drying the composition.

[0047] As described above, the magnetic recording medium 1 includes a magnetic recording layer 30, a pinning layer 40, a non-magnetic layer 50, and a carbon protective layer 60 on a non-magnetic substrate 10, with the non-magnetic layer 50 being made of an oxide. By having the above-described configuration, the magnetic recording medium 1 is able to prevent the constituent elements contained in the non-magnetic layer 50 from penetrating into the alloy structure of the pinning layer 40 due to energy generated when, for example, forming the carbon protective layer 60 on the pinning layer 40, thereby maintaining the structure of the pinning layer 40. Therefore, the magnetic recording medium 1 is able to prevent deterioration of the magnetic properties of the magnetic recording medium 1, and therefore is able to maintain excellent magnetic properties.

[0048] In addition, in the magnetic recording medium 1, the magnetic recording layer 30 has a (001)-oriented L1 ０ The magnetic anisotropy constant Ku can be increased due to the presence of the crystalline structure, and the magnetic recording medium 1 can therefore have excellent magnetic properties.

[0049] In the magnetic recording medium 1, the nonmagnetic layer 50 preferably contains ZnO at a ratio of 40 to 100 atomic %. This allows the nonmagnetic layer 50 to be stacked on the pinning layer 40 with the surface irregularities of the pinning layer 40 kept smaller than those of the pinning layer 40, thereby improving surface smoothness. Therefore, when the magnetic recording medium 1 is used in a magnetic recording device such as a hard disk drive, it is possible to reduce the amount of floating noise detected by the magnetic head of the magnetic recording device.

[0050] In the magnetic recording medium 1, the non-magnetic layer 50 contains ZnO in the range of 40 to 80 atm % and SiO ２ It is preferable that the non-magnetic layer 50 contains, as an oxide, SiO in addition to ZnO. ２ Even when the magnetic recording medium 1 includes the nonmagnetic layer 50, the nonmagnetic layer 50 can be stacked on the pinning layer 40 with the unevenness of the surface of the pinning layer 40 kept smaller than that of the pinning layer 40, thereby improving the surface smoothness. Therefore, when the magnetic recording medium 1 is used in a magnetic recording device, it is possible to reduce the amount of floating noise detected by the magnetic head of the magnetic recording device.

[0051] Because the magnetic recording medium 1 has the above-described characteristics, even when an assisted recording method such as a thermally assisted recording method or a microwave assisted recording method is used as the recording method, the magnetic recording layer 30 can maintain high magnetic properties and have a high recording density, so that magnetic information can be sufficiently recorded on the magnetic recording layer 30 by the recording magnetic field of a magnetic head. Therefore, the magnetic recording medium 1 can be suitably used in a magnetic storage device using an assisted recording method.

[0052] (Magnetic Recording Apparatus) A magnetic recording apparatus including the magnetic recording medium according to this embodiment will be described. The magnetic recording apparatus according to this embodiment is not particularly limited in form as long as it includes the magnetic recording medium according to this embodiment.

[0053] 4 is a perspective view showing an example of a magnetic recording device that uses the magnetic recording medium according to this embodiment. As shown in FIG. 4, the magnetic recording device 100 includes a perpendicular magnetic recording medium 101, a medium drive unit 102 that rotates the perpendicular magnetic recording medium 101, a magnetic head 103 that records and reproduces information on the perpendicular magnetic recording medium 101, a head drive unit 104 that moves the magnetic head 103 relative to the perpendicular magnetic recording medium 101, and a recording / reproducing signal processing system 105. The perpendicular magnetic recording medium 101 is the magnetic recording medium 1 shown in FIG. 1 above. The recording / reproducing signal processing system 105 processes data input from an external source and sends a recording signal to the magnetic head 103, and processes a reproduction signal from the magnetic head 103 and sends the data to the outside.

[0054] In the magnetic recording device 100, the perpendicular magnetic recording medium 101 uses the magnetic recording medium 1, which improves the magnetic characteristics of the perpendicular magnetic recording medium 101 and increases the recording density. Therefore, the magnetic recording device 100 can have a high recording density.

[0055] The present embodiment will be described in more detail below by way of examples, but the present embodiment is not limited to these examples.

[0056] <Preparation of Magnetic Recording Media> [Example 1] A 30 nm thick Co-27 atm % Fe-5 atm % Zr-5 atm % B alloy layer and a 100 nm thick Cr-50 at % Ti alloy layer were sequentially formed as soft magnetic underlayers on a glass substrate having an outer diameter of 3.5 inches using a sputtering method. Next, the glass substrate was heated to 250°C, and then a 10 nm thick Cr layer serving as a first underlayer and a 5 nm thick MgO layer serving as a second underlayer were sequentially formed as soft magnetic underlayers using a sputtering method. Next, the glass substrate was heated to 450°C, and a 0.67 nm thick FePt-20 vol % AlN layer (first magnetic layer) and a 4 nm thick FePt-38 vol % BN layer (second magnetic layer) were sequentially formed as magnetic recording layers. Next, a 1.2 nm thick (80Co20Pt)-28.8 vol% SiO ２ and a non-magnetic layer of 40 atm% ZnO-20 atm% Ga with a thickness of 2 nm. ２ O ３ -40atm%SiO ２ Both were formed in this order using a sputtering method. Next, a 3 nm carbon protective layer was formed using an RF-CVD method, and then a 1 nm perfluoropolyether lubricant layer was formed using a coating method, thereby obtaining a magnetic recording medium.

[0057] (Thickness of Non-Magnetic Layer) The thickness of the non-magnetic layer was measured by XRR (X'Pert MRD, manufactured by Malvern Panalytical) and calculated using the value calculated from the formation rate of sputtering.

[0058] [Examples 2 to 15, Comparative Examples 1 to 4] In Example 1, the composition, thickness, presence or absence of oxides, ZnO ratio and SiO ２ A magnetic recording medium was produced in the same manner as in Example 1, except that the ratio of was changed to that shown in Table 1.

[0059] The composition, thickness, presence or absence of oxide, ZnO ratio, and SiO of the non-magnetic layer of the magnetic recording medium produced in each Example and Comparative Example. ２ The ratios are shown in Table 1.

[0060] <Evaluation of magnetic recording medium characteristics> As the characteristics of the magnetic recording media produced in each example and comparative example, the difference dMs in saturation magnetization Ms of the magnetic recording medium, the average number of irregularities on the magnetic recording medium, and the difference dHc in coercivity Hc of the magnetic recording medium were calculated, and the magnetic characteristics and noise level of the magnetic head were evaluated.

[0061] [Calculation of difference dMs in saturation magnetization Ms] For each example and comparative example, a magnetic recording medium without a non-magnetic layer was fabricated, i.e., a magnetic recording medium having an underlayer, a Cr layer, an MgO layer, a magnetic recording layer, a carbon protective layer, and a lubricant layer laminated in this order on a glass substrate. Using a Squid-VSM measuring device (MPMS3, manufactured by Quantum Design), the saturation magnetization Ms1 of the fabricated magnetic recording medium and the saturation magnetization Ms2 of the magnetic recording medium without a non-magnetic layer were measured, and the difference dMs in saturation magnetization was calculated using the following formula (1). Note that the saturation magnetizations Ms1 and Ms2 of the magnetic recording medium were measured for the saturation magnetizations of the first magnetic layer and the second magnetic layer constituting the magnetic recording layer. When the difference dMs in saturation magnetization was -0.01 emu / cm ３ If the value was equal to or greater than this, the saturation magnetization Ms of the magnetic recording medium was evaluated as being good. dMs = saturation magnetization Ms1 of magnetic recording medium - saturation magnetization Ms2 of magnetic recording medium without non-magnetic layer (1)

[0062] [Calculation of the average number of irregularities on the magnetic recording medium] For each example and comparative example, ten magnetic recording media were prepared, and a floating test was performed on the ten magnetic recording media using an HDD RQ tester (RQ7800, manufactured by Hitachi High-Tech Corporation). The average number of irregularities on each magnetic recording medium was calculated. The floating test involved bringing a magnetic head into contact with the magnetic recording medium, floating it 90 mW above the magnetic recording medium, and rotating the magnetic recording medium at 12 m / s. The number of times a voltage of 600 mV or more was detected by the AE sensor on the magnetic head was counted. It was assumed that when a voltage of 600 mV or more was detected, there were irregularities on the magnetic recording medium that would cause a large noise level in the magnetic head. The number of times a voltage of 600 mV or more was detected was taken as the number of irregularities on the magnetic recording medium. The noise level of the magnetic head was evaluated based on the average number of irregularities on the ten magnetic recording media. The smaller the average number of irregularities, the fewer irregularities there are on the magnetic recording medium, the lower the noise level of the magnetic head, and the more reliable the magnetic recording medium is for long-term use.

[0063] [Calculation of the difference dHc in coercive force Hc] As in the above [Calculation of the difference dMs in saturation magnetization Ms], a magnetic recording medium without a non-magnetic layer was produced. Using a superconducting Kerr magnetometer (BH-810-HM7, manufactured by NeoArc Corporation), the coercive force Hc1 of the produced magnetic recording medium and the coercive force Hc2 of the magnetic recording medium without a non-magnetic layer were measured, and the coercive force difference dHc was calculated using the following formula (2). When the coercive force difference dHc was -2.0 kOe to 2.0 kOe, the coercive force Hc of the magnetic recording medium was evaluated as good. dHc = coercive force Hc1 of magnetic recording medium - coercive force Hc2 of magnetic recording medium without a non-magnetic layer (2)

[0064]

[0065] From Table 1, in each example, dMs is -0.008 emu / cm ３ As described above, the saturation magnetization Ms of the magnetic recording media of each example was −0.010 emu / cm compared to a magnetic recording medium without a non-magnetic layer. ３ On the other hand, in Comparative Examples 1 to 3, the difference dMs in saturation magnetization Ms was −0.066 emu / cm ３Therefore, it was confirmed that the inclusion of an oxide in the non-magnetic layer can suppress a decrease in the saturation magnetization Ms of the magnetic recording layer.

[0066] Furthermore, in Examples 1 to 13, the average number of irregularities on the magnetic recording media at which a voltage of 600 mV or more was detected was 0.9 or less. Therefore, it was confirmed that when the non-magnetic layer is formed containing 40 to 100 atomic % of ZnO, the noise level of the magnetic head is kept low, and a highly reliable magnetic recording medium can be obtained.

[0067] Furthermore, in Examples 1 to 11, the difference in coercive force dHc was −1.88 to 0.09 kOe. Therefore, when the nonmagnetic layer contains ZnO in the range of 40 to 80 atm % and SiO ２ It has been confirmed that when the magnetic recording medium is formed with a content of ZnO in the range of 10 to 40 atm %, the coercivity Hc of the magnetic recording medium can be said to be good. This is thought to be because ZnO can prevent the magnetic grains contained in the magnetic recording layer from bonding to each other.

[0068] Therefore, it was confirmed that the non-magnetic layer provided between the pinning layer and the carbon protective layer is made of an oxide, which suppresses the deterioration of the magnetic properties of the magnetic recording medium and enables excellent magnetic properties to be maintained. Therefore, since the magnetic recording media of each example can maintain excellent magnetic properties, when used in a magnetic storage device, the magnetic storage device can maintain a high recording density.

[0069] Although the embodiments have been described above, they 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, or modifications can be made without departing from the spirit of the invention. The above embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as set forth in the claims.

[0070] This application claims priority based on Japanese Patent Application No. 2024-104886, filed with the Japan Patent Office on June 28, 2024, the entire contents of which are incorporated herein by reference.

[0071] REFERENCE SIGNS LIST 1 magnetic recording medium 10 non-magnetic substrate 20 underlayer 21 first underlayer 22 second underlayer 30 magnetic recording layer 31 magnetic grains 32 grain boundary material 40 pinning layer 50 non-magnetic layer 60 carbon protective layer 70 lubricant layer 100 magnetic recording device 101 perpendicular magnetic recording medium 103 magnetic head

Claims

1. (001) oriented L1 ０ 1. A magnetic recording medium comprising: a magnetic recording layer having a structure; a pinning layer; and a carbon protective layer laminated at least in this order; and a non-magnetic layer made of an oxide between the pinning layer and the carbon protective layer.

2. The magnetic recording medium according to claim 1, wherein the non-magnetic layer contains ZnO at a ratio of 40 to 100 atomic %.

3. The non-magnetic layer contains ZnO in the range of 40 to 80 atomic % and SiO ２ 3. The magnetic recording medium according to claim 2, wherein the content is in the range of 10 to 60 atomic %.

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

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