JP2017027642A - Perpendicular magnetic recording medium and magnetic recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a perpendicular magnetic recording medium having a protective layer configured to increase surface smoothness, to reduce thickness, and to enhance binding power of a lubricant layer.SOLUTION: In a perpendicular magnetic recording medium formed by laminating a perpendicular magnetic layer, a protective layer, and a lubricant layer in this order on a non-magnetic substrate, the protective layer includes a graphene and/or a graphene laminate and amorphous carbon. The protective layer and the lubricant layer are provided in contact with each other. A boundary surface between the protective layer and the lubricant layer includes nitrogen.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a perpendicular magnetic recording medium and a magnetic recording / reproducing apparatus.

  In recent years, in the field of magnetic recording media used for hard disk drives (HDD) and the like, the recording density has continued to grow at a phenomenal rate. One of key technologies for improving the recording density is a technique for controlling sliding characteristics between a magnetic head and a magnetic recording medium.

  That is, contact sliding of the magnetic head on the magnetic recording medium is unavoidable, including accidental cases, so the problem regarding tribology between the magnetic head and the magnetic recording medium is fatal. As a technical problem, it is now possible to improve the wear resistance and sliding resistance of a magnetic recording medium by forming a protective layer on the magnetic layer of the magnetic recording medium. It has become a major pillar for securing.

  Various materials have been proposed as the material constituting the protective layer, but carbon is mainly employed from the comprehensive viewpoints such as film forming properties and durability. The hardness, density, dynamic friction coefficient, etc. of the protective layer are very important because they are reflected in the L / UL characteristics (load / unload characteristics) with the magnetic head in the magnetic recording medium.

  On the other hand, in order to improve the recording density of the magnetic recording medium or improve the read / write speed, the flying height (flying height) of the magnetic head is reduced or the rotational speed of the magnetic recording medium is increased. It is preferable. Therefore, in order to cope with accidental contact of the magnetic head, the protective layer is required to have sliding resistance and flatness, and the recording loss is reduced by reducing the spacing loss between the magnetic recording medium and the magnetic head. In order to increase the thickness, the thickness of the protective layer is required to be as thin as possible.

  The carbon film used for the protective layer of the magnetic recording medium is formed by sputtering, CVD, ion beam evaporation or the like.

  Patent Document 1 discloses a magnetic medium for magnetic data recording having a plurality of magnetic grains and a plurality of layers of graphitic carbon formed on each of the plurality of magnetic grains. At this time, graphitic carbon is composed of graphite, graphene (single monolayer of graphite), nanotube (graphene sheet wound in a cylindrical shape), fullerene (graphene wound in a closed shape such as a sphere) And other forms).

Patent Document 2 discloses FePt / graphene for use in hard disks.
Patent Document 3 discloses a method for forming graphene at a low temperature.
Non-Patent Document 1 describes nitrogen doping of graphene in which carbon atoms constituting graphene are replaced with nitrogen atoms.

JP 2013-101742 A Special table 2013-536141 gazette Special table 2013-530124 gazette

ACS NANO, Vol. 4, no. 4, pp. 1790-1798, 2010

  Efforts to improve the protective layer of magnetic recording media are continuing. Currently, a hydrogenated amorphous carbon film is mainly used as a protective layer of a magnetic recording medium. The hydrogenated amorphous carbon film is characterized by high surface smoothness and relatively high hardness. On the other hand, since the hydrogenated amorphous carbon film has an amorphous structure, there is a problem that the film has a wide range of characteristics and the surface smoothness varies depending on the film forming conditions. Further, since the surface of the hydrogenated amorphous carbon film is basically water-repellent, it is difficult to apply a lubricant. For this reason, the hydrogenated amorphous carbon film requires modification of the surface such as nitridation and oxidation, which has been an obstacle to thinning the protective layer.

  An object of one embodiment of the present invention is to provide a perpendicular magnetic recording medium that uses graphene and has a protective layer that has high surface smoothness and can be thinned.

  According to one aspect of this embodiment, a perpendicular magnetic layer, a protective layer, and a lubricant layer are formed on a nonmagnetic substrate in the order of the perpendicular magnetic layer, the protective layer, and the lubricant layer. In the recording medium, the protective layer includes graphene and / or a stack of graphene and amorphous carbon, the protective layer and the lubricant layer are provided in contact with each other, and the interface between the protective layer and the lubricant layer is nitrogen. It is characterized by including.

  According to one embodiment of the present invention, a perpendicular magnetic recording medium having a protective layer having a high surface smoothness, a thin film thickness, and a high binding force of a lubricant layer can be provided. An apparatus can be provided.

Sectional view showing an example of a perpendicular magnetic recording medium The block diagram which shows an example of the film-forming apparatus which forms the protective layer in this Embodiment The figure which shows an example of the Raman spectrum of the protective layer of FIG. Configuration diagram showing an example of a magnetic recording / reproducing apparatus

  Next, the form for implementing this invention is demonstrated with drawing.

  FIG. 1 shows an example of a perpendicular magnetic recording medium according to an embodiment of the present invention.

  In the perpendicular magnetic recording medium 31, a soft magnetic layer 21, an intermediate layer 22, a perpendicular magnetic layer 23, a protective layer 24, and a lubricant layer 25 are sequentially laminated on both surfaces of a nonmagnetic substrate 20. In the present invention, the protective layer 24 and the lubricant layer 25 are provided in contact with each other.

  The intermediate layer 22 may be nonmagnetic or magnetic (ferromagnetic).

  The perpendicular magnetic layer 23 has an easy axis of magnetization oriented perpendicularly to the surface of the nonmagnetic substrate 20. In addition, the perpendicular magnetic layer 23 preferably has a hexagonal close-packed (hcp) structure, and a layer having a (0002) crystal plane oriented parallel to the nonmagnetic substrate 20 is preferably laminated. Further, the uppermost layer of the perpendicular magnetic layer 23 preferably includes polycrystalline grains, and the polycrystalline grains preferably include a CoCr-based alloy, a CoPt-based alloy, a CoCrPt-based alloy, or a CoPtCr-based alloy.

  The CoCrPt-based alloy has a higher Cr composition ratio than Pt, and the CoPtCr-based alloy has a higher Pt composition ratio than Cr.

  The content of Cr in the CoCr-based alloy is usually 14 to 24 atomic%.

  The content of Pt in the CoPt base alloy is usually 8 to 22 atomic%.

  The CoCrPt-based alloy usually has a Cr content of 14 to 24 atomic% and a Pt content of 8 to 22 atomic%.

  The CoPtCr-based alloy usually has a Pt content of 8 to 22 atomic% and a Cr content of 7 to 21 atomic%.

  These alloys contain one or more elements selected from B, Ta, Mo, Cu, Nd, W, Nb, Sm, Tb, Ru, Re, and Mn within a range of 1 to 10 atomic%. May be.

The vertical magnetic layer 23 of the present invention is preferably a magnetic layer containing an L1 ₀ structure has a (001) FePt based alloy or CoPt based alloy took orientation. Then, in order to promote the ordering of the alloy having an L1 ₀ structure of the magnetic layer, the substrate temperature during the formation of the magnetic layer is preferably set to 600 ° C. or higher. In addition, to reduce the ordering temperature, the alloy having an L1 ₀ structure, Ag, Au, Cu, may be added to Ni or the like. In this case, the substrate temperature when forming the perpendicular magnetic layer can be reduced to about 400 to 500 ° C.

The protective layer 24 is formed in contact with the uppermost layer of the perpendicular magnetic layer 23 and contains graphene and / or a stack of graphene and amorphous carbon. At this time, the graphene and / or graphene laminate is (0002) crystal plane of the individual hcp structure polycrystalline grains, or of L1 ₀ structure (001) is parallel coupled to the crystal surface. Such a structure is specified by a Raman spectrum described later.

  Here, since graphene generally has a film forming temperature of 600 ° C. or higher, it is difficult to apply it to the manufacture of a magnetic recording medium. Further, the graphene laminate is peelable like graphite.

  However, since the polycrystalline grains contained in the uppermost layer of the perpendicular magnetic layer 23 of the present invention have catalytic activity, the protective layer 24 including graphene and / or a stack of graphene can be formed at a temperature lower than 600 ° C. it can. Furthermore, since the protective layer 24 contains amorphous carbon together with graphene and / or a graphene stack, the surface of the protective layer 24 can be smoothed and peeling of the graphene stack can be reduced.

  In addition, graphene has a slow deposition rate when a conventional film forming method is used, which makes it difficult to apply graphene to a magnetic recording medium.

  In the present invention, as a method for forming the protective layer 24, a raw material gas containing carbon is introduced into a decompressed film forming chamber, and the filament-shaped cathode electrode heated by energization of the gas, and an anode provided therearound A method can be employed in which ionization is performed between the electrode and the electrode, and the ionized gas is accelerated and irradiated onto the surface of the deposition substrate. Accordingly, graphene and / or a stack of graphene and a layer containing amorphous carbon can be formed on the surface of the deposition substrate at a high speed at a low substrate temperature.

  Hereinafter, the protective layer 24 of the present invention will be described in detail with reference to the drawings. In addition, in the drawings used in the following description, in order to make the features easy to understand, there are cases where the portions that become the features are enlarged for convenience, and the dimensional ratios of the respective components are not always the same as the actual ones. . In addition, the materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to them, and can be appropriately changed and implemented without changing the gist thereof.

  First, an example of an apparatus for forming the protective layer 24 to which the present invention is applied will be described.

  FIG. 2 is a schematic configuration diagram schematically showing an apparatus for forming the protective layer 24 of the present invention.

  A protective layer 24 forming apparatus 10 shown in FIG. 2 is a film forming apparatus using an ion beam evaporation method, and can be decompressed and can hold a substrate D in the film forming chamber 101 having a side wall and a film forming chamber 101. And an ion source 104 that irradiates an ion beam toward a substrate D held by the holder 102. Yes.

  Here, the central axis C coincides with the irradiation direction of the ion beam (the direction in which the central portion of the ion beam travels). When the ion source is arranged symmetrically with respect to the central axis of the film formation chamber 101, the central axis C coincides with the central axis of the film formation chamber 101.

  Further, the ion source 104 shown in FIG. 2 includes a filament-like cathode electrode 104a and an anode electrode 104b disposed around the cathode electrode 104a. The protective layer 24 forming apparatus shown in FIG. 2 includes a first power source 106 that heats the cathode electrode 104a by energization, a second power source 107 that generates a discharge between the cathode electrode 104a and the anode electrode 104b, and a cathode A third power source 108 for providing a potential difference between the electrode 104a or the anode electrode 104b and the substrate D is provided.

  FIG. 2 shows a state where the substrate D is held by the holder 102.

  The side wall is preferably cylindrical, but is not limited to a cylindrical shape.

  The film forming chamber 101 is hermetically configured by a chamber wall 101a, and can be evacuated inside through an exhaust pipe 110 connected to a vacuum pump (not shown).

  The first power source 106 is an AC power source connected to the cathode electrode 104 a and supplies power to the cathode electrode 104 a when the protective layer 24 is formed. The first power source 106 is not limited to an AC power source, and a DC power source may be used.

  The second power source 107 is a DC power source in which the negative electrode side is connected to the cathode electrode 104a and the positive electrode side is connected to the anode electrode 104b, and discharge is generated between the cathode electrode 104a and the anode electrode 104b when the protective layer 24 is formed. Cause it to occur.

  The third power source 108 is a DC power source in which the + electrode side is connected to the anode electrode 104 b and the − electrode side is connected to the holder 102, and the anode electrode 104 b and the substrate D held by the holder 102 are formed when the protective layer 24 is formed. A potential difference is applied between them. The third power supply 108 may have a configuration in which the + electrode side is connected to the cathode electrode 104a.

  In the present invention, although depending on the size of the substrate D, when the protective layer 24 is formed on a disk-shaped substrate having an outer diameter of 3.5 inches, the voltage of the first power supply 106 is in the range of 10 to 200 V, The current is preferably set in the range of 5 to 50 A by direct current or alternating current. For the second power source 107, the voltage is preferably set in the range of 50 to 300 V, and the current is preferably set in the range of 10 to 5000 mA. For the power supply 108, it is preferable to set the voltage in the range of 30 to 500V and the current in the range of 10 to 200mA.

  When the protective layer 24 is formed on the surface of the substrate D using the protective layer 24 forming apparatus having the above-described configuration, the film formation chamber 101 is evacuated through the exhaust pipe 110 and is introduced into the film formation chamber 101 through the introduction pipe 103. A raw material gas G containing carbon is introduced. This raw material gas G is discharged between the thermal plasma of the cathode electrode 104 a heated by the supply of electric power from the first power source 106 and the cathode electrode 104 a and the anode electrode 104 b connected to the second power source 107. It is excited and decomposed by the plasma generated by the above and becomes an ionized gas (carbon ion). Then, the carbon ions excited in the plasma collide with the surface of the substrate D while accelerating toward the substrate D which has been set to a negative potential by the third power source 108.

  In the protective layer 24 forming apparatus shown in FIG. 2, the protective layer 24 is formed only on one side of the substrate D. However, the protective layer 24 is formed on both sides of the substrate D. Is also possible. In this case, an apparatus configuration similar to that in the case where the protective layer 24 is formed only on one surface of the substrate D may be disposed on both sides of the substrate D in the film formation chamber 101.

  In the method for forming the protective layer 24 to which the present invention is applied, as the raw material gas G containing carbon, for example, a gas containing hydrocarbon can be used. As the hydrocarbon, it is preferable to use one kind or two or more kinds of low carbon hydrocarbons among lower saturated hydrocarbons, lower unsaturated hydrocarbons, and lower cyclic hydrocarbons. Here, the term “lower” refers to a case of 1 to 10 carbon atoms.

  Among these, methane, ethane, propane, butane, octane, etc. can be used as the lower saturated hydrocarbon. On the other hand, as the lower unsaturated hydrocarbon, isoprene, ethylene, propylene, butylene, butadiene and the like can be used. On the other hand, as the lower cyclic hydrocarbon, benzene, toluene, xylene, styrene, naphthalene, cyclohexane, cyclohexadiene, or the like can be used.

  The ratio of the graphene and / or the graphene laminated body contained in the protective layer 24 and the amorphous carbon can be controlled by, for example, the amount of hydrogen radicals contained in the plasma formed by the source gas. That is, hydrogen radicals can etch amorphous carbon, but their etching power is higher for amorphous carbon than graphene and / or a stack of graphene. For this reason, when the amount of hydrogen contained in the source gas is increased, the ratio of graphene and / or the stack of graphene contained in the protective layer 24 is increased, and when the amount of hydrogen contained in the source gas is reduced, the protective layer 24 The proportion of amorphous carbon contained is increased.

  In addition, the ratio of graphene and / or a graphene stack included in the protective layer 24 and amorphous carbon may be controlled by the temperature of the nonmagnetic substrate 20 when the protective layer 24 is formed. In general, when the temperature of the nonmagnetic substrate 20 is high, the ratio of graphene and / or a stack of graphene included in the protective layer 24 increases, and when the temperature of the nonmagnetic substrate 20 is low, the amorphous layer included in the protective layer 24. The proportion of carbon increases.

  FIG. 3 shows an example of the Raman spectrum of the protective layer 24. FIG. 3 also shows a Raman spectrum of an amorphous carbon film (a DLC film containing hydrogen).

In the Raman spectrum of the protective layer 24, the graphene near 1585 cm ⁻¹ and / or the G band related to the sp ² bond stretching vibration of the graphene laminate, and the six-membered graphene and / or graphene laminate near 2700 cm ⁻¹ A 2D band related to a ring structure and a D band related to amorphization of graphene in the vicinity of 1350 cm ⁻¹ are observed. That is, in the Raman spectrum of the protective layer 24, the G band and the 2D band indicating the presence of the graphene and / or the graphene stack are seen, while the D band and the broad peaks superimposed on the D band and the G band are seen. . This is because the protective layer 24 includes graphene and / or a graphene stack and amorphous carbon, and the graphene and / or graphene stack includes individual hcp structures of polycrystalline grains constituting the perpendicular magnetic layer 23. It is shown that they are bonded in parallel to the (0002) crystal plane of the crystal or the (001) crystal plane of the L1 ₀ structure.

  On the other hand, the Raman spectrum of the amorphous carbon film shows a broad signal because the film has an amorphous structure. For this reason, the film quality of the amorphous carbon film is likely to change depending on the film formation conditions, and thereby the smoothness of the film surface varies, which affects the wear resistance, sliding resistance, and corrosion resistance of the protective layer.

  On the other hand, since the protective layer 24 includes crystalline graphene and / or a stack of graphene and amorphous carbon, a smooth surface is realized, and stable wear resistance, sliding resistance, and corrosion resistance can be obtained. . That is, the unevenness that can be generated from amorphous carbon is not more than the thickness of the atomic layer (about 0.3 nm), so that the surface smoothness of the perpendicular magnetic recording medium 31 on which the protective layer 24 is formed can be improved.

The graphene and / or the graphene stack included in the protective layer 24 has an individual hcp structure of polycrystalline grains in which the surface of the six-membered ring constituting the graphene and / or the graphene stack is included in the perpendicular magnetic layer 23 ( 0002), or having an L1 ₀ structure (001) parallel coupled with the crystal plane to that structure. When the protective layer 24 is formed, the catalytic activity of the CoCr-based alloy, CoPt-based alloy, CoCrPt-based alloy, CoPtCr-based alloy, FePt-based alloy, or CoPt-based alloy is used. At this time, it is presumed that the graphene and / or the graphene laminate is electronically bonded to Co, Fe, and Pt. Therefore, the surface of the six-membered rings constituting the graphene and / or graphene laminate is polycrystalline grains of individual hcp structure contained in the perpendicular magnetic layer 23 (0002), or the L1 ₀ structure (001) Bonding in parallel with the crystal plane. As a result, the protective layer 24 and the perpendicular magnetic layer 23 including graphene and / or a stack of graphene are firmly bonded.

In the present invention, in the Raman spectrum of the protective layer 24, the peak height of the 2D band according to six-membered ring structure of graphene and / or graphene laminate around 2700 cm ^-1 and (2D), graphene and near 1585 cm ^-1 The ratio (2D / G) to the peak height (G) of the G band related to the stretching vibration of the sp ² bond of the graphene laminate is in the range of 0.4 to 5.

  It is known that the ratio of the peak height of the 2D band and the G band of the Raman spectrum indicates the number of layers of the graphene stack (for example, Ferrari, AC et al. Raman spectrum of graphene and graphene layers. Phys. Rev. Lett. 97, 187401 (2006). That is, when the peak height of the 2D band is larger than the peak height of the G band, it is a graphene single layer, and when the peak height of the 2D band is the same as the peak height of the G band, When the number of layers is approximately two and the peak height of the 2D band is smaller than the peak height of the G band, the number of layers of the graphene stack is three or more, and the specific number of layers is 2D band And the ratio of the peak height of the G band.

  Since the protective layer 24 of the present invention includes amorphous carbon in graphene, high smoothness of the surface can be obtained by setting 2D / G within the range of 0.4 to 5. That is, when 2D / G is 1 or less, graphene becomes a multilayer film and the sliding resistance of the protective layer 24 is lowered. However, by including amorphous carbon in the protective layer 24, the sliding resistance of the protective layer 24 is improved. Can be made. Further, when 2D / G is higher than 1, the number of layers of the graphene laminate decreases and the surface unevenness increases, but the amorphous carbon is included in the protective layer 24 to prevent the graphene unevenness and to protect the protective layer 24. The smoothness can be improved.

  On the other hand, when 2D / G is smaller than 0.4, the amount of graphene contained in the protective layer 24 decreases, and the effect of using graphene decreases. On the other hand, when 2D / G is larger than 5, the ratio of the amorphous carbon is lowered, so that the surface irregularities are increased, and the smoothing effect by the amorphous carbon is lowered.

  In the present invention, the following method can be used to control 2D / G of the protective layer. That is, empirically, 2D / G also tends to increase when the flow rate of the source gas into the protective layer deposition chamber is increased. Further, when the reaction pressure in the film formation chamber is increased, 2D / G also tends to increase. Further, when the ratio of hydrogen atoms to carbon atoms contained in the source gas is increased, 2D / G also tends to increase.

  The uppermost layer of the perpendicular magnetic layer 23 preferably has a non-granular structure. Thereby, at the interface between the perpendicular magnetic layer 23 and the protective layer 24, a CoCr-based alloy, a CoPt-based alloy, a CoCrPt-based alloy, a CoPtCr-based alloy, a FePt-based alloy, or a CoPt that is firmly bonded to graphene and / or a stack of graphene. By increasing the area ratio occupied by the base alloy, the adhesion between the protective layer 24 and the perpendicular magnetic layer 23 can be improved.

  The non-granular structure magnetic layer is composed of magnetic particles of a CoCr-based alloy, CoPt-based alloy, CoCrPt-based alloy, CoPtCr-based alloy, FePt-based alloy, or CoPt-based alloy, and around the magnetic particles. In addition, it refers to a structure that does not contain oxides, nitrides, carbides and the like that separate the magnetic particles.

  In addition, in order to realize isolation and refinement of polycrystalline grains, oxides such as Cr, Si, Ta, Al, and B, nitrides, carbides, and the like other than the uppermost layer of the perpendicular magnetic layer 23 are added, A granular structure is preferred.

  In the graphene laminate, graphene is preferably laminated within a range of 2 to 10 layers, and more preferably graphene is laminated within a range of 4 to 6 layers. As a result, the graphene laminate is protected by amorphous carbon and is less likely to be peeled off. In addition, the wear resistance, sliding resistance, and corrosion resistance of the graphene laminate are easily utilized.

  In the present invention, nitrogen is contained in the interface between the protective layer 24 and the lubricant layer 25.

  Here, since the surface of the amorphous carbon film conventionally used as a protective layer is basically water-repellent, the surface is nitrided and oxidized to form a lubricant layer by applying a lubricant. Etc. have been modified. In order to modify the surface by nitridation, oxidation or the like, a certain degree of film thickness is required, which has been an obstacle to making the protective layer thinner. Although it is possible to dope the amorphous carbon film with nitrogen, it has an amorphous structure, which causes deterioration and instability of the film quality and reduces the wear resistance, sliding resistance and corrosion resistance of the protective layer. It was.

  On the other hand, the graphene contained in the protective layer 24 of the present invention contains a nitrogen atom so as to substitute a carbon atom while maintaining a six-membered ring structure as disclosed in Non-Patent Document 1. Therefore, the wettability of the protective layer 24 to the lubricant when forming the lubricant layer 25 can be improved without reducing the crystallinity of graphene and / or the graphene laminate. That is, since the nitrogen atoms contained in the protective layer 24 are bonded to a polar group, for example, a hydroxyl group, contained in the lubricant layer 25, it can be firmly bonded to the lubricant layer 25 to the protective layer 24 of the present invention.

  The protective layer 24 can also incorporate nitrogen atoms into the amorphous carbon contained in the protective layer 24. Thereby, the wettability with respect to the lubricant of the protective layer 24 when forming the lubricant layer 25 can be improved without reducing the crystallinity of the graphene and / or the graphene laminate.

  In the present invention, the nitrogen content at the interface between the protective layer 24 and the lubricant layer 25 is preferably in the range of 5 atomic% to 90 atomic%. As described above, since the protective layer 24 of the present invention can incorporate nitrogen atoms into the carbon atom position of graphene or inside the amorphous carbon, it can incorporate nitrogen atoms in a wide concentration range into the protective layer 24. . Therefore, the nitrogen concentration in the protective layer 24 can be set according to the type of lubricant used for the lubricant layer 25, and the bonding force (bonded ratio) between the protective layer 24 and the lubricant layer 25 can be freely controlled. It becomes possible. In other words, for lubricants with a small number of polar groups, it is possible to increase the nitrogen concentration on the surface of the protective layer to supplement the bonding force between the protective layer and the lubricant layer, and for lubricants with a large number of polar groups. The nitrogen concentration on the surface of the protective layer can be lowered, and the bonding force between the protective layer and the lubricant layer can be lowered to increase free rubes (a highly fluid lubricant that does not bind to the protective layer).

  In the present invention, a known method can be used as a method for containing nitrogen at the interface between the protective layer 24 and the lubricant layer 25, that is, a method for containing nitrogen in the surface layer of the protective layer 24. It is preferable to use a method of containing nitrogen in the carbon raw material and a method of injecting nitrogen ions into the surface layer of the protective layer 24. In particular, it is preferable to employ a method in which after forming the protective layer 24 of carbon or hydrogenated carbon, nitrogen ions are implanted only into the surface thereof, or a method of nitriding by exposing the surface of the protective layer 24 to nitrogen plasma.

  In the present invention, the content of nitrogen at the interface between the protective layer 24 and the lubricant layer 25 is within the range of 5 atomic% to 90 atomic%. This content is contained in the carbon raw material in the above-described method. This can be achieved by controlling the concentration of nitrogen, the amount of nitrogen ions implanted, the exposure time to nitrogen plasma, and the nitrogen plasma density.

  The material constituting the nonmagnetic substrate 20 is not particularly limited, but Al alloy such as Al, Al-Mg alloy, soda glass, aluminosilicate glass, crystallized glass, amorphous glass, silicon, titanium, ceramics, Various resins are listed. Among these, glass such as Al alloy and crystallized glass, and silicon are preferable.

  The arithmetic average roughness (Ra) of the nonmagnetic substrate 20 is usually 1 nm or less, preferably 0.5 nm or less, and more preferably 0.1 nm or less.

  The material constituting the soft magnetic layer 21 is not particularly limited, but FeCo-based alloys (for example, FeCoB, FeCoSiB, FeCoZr, FeCoZrB, FeCoZrBCu), CoFe alloys, FeTa-based alloys (for example, FeTaN, FeTaC), and Co-based alloys. (For example, CoTaZr, CoZrNB, CoB) and the like.

  Examples of the material constituting the intermediate layer 22 include Ru.

  The perpendicular magnetic layer 23 can be formed by sequentially laminating a magnetic layer having a granular structure and a magnetic layer having a non-granular structure.

A material constituting the magnetic layer having the granular structure is not particularly limited, and examples thereof include 70Co-5Cr-15Pt-10SiO ₂ alloy.

  A material constituting the magnetic layer having a non-granular structure is not particularly limited, and examples thereof include a 70Co-15Cr-15Pt alloy.

  An orientation control layer may be formed between the soft magnetic layer 21 and the intermediate layer 22.

  The material constituting the orientation control layer is not particularly limited, and examples thereof include Pt, Pd, NiCr alloy, NiFeCr alloy, and NiW alloy.

  The thickness of the perpendicular magnetic layer 23 is usually 3 to 20 nm, and preferably 5 to 15 nm.

  The thickness of the perpendicular magnetic layer 23 is preferably set to a certain value or more in order to obtain a certain value or more during reproduction. However, since various parameters representing the recording / reproducing characteristics usually deteriorate as the output increases, the thickness of the perpendicular magnetic layer 23 is preferably set in accordance with the configuration of the magnetic recording / reproducing apparatus. That is, the perpendicular magnetic layer 23 is preferably formed so as to obtain sufficient head input / output according to the type of magnetic alloy used and the laminated structure.

  The lubricant layer 25 can be formed by applying a lubricant.

  The lubricant is not particularly limited, and examples thereof include fluorinated liquid lubricants such as perfluoroether (PFPE) and solid lubricants such as fatty acids.

  The method for applying the lubricant is not particularly limited, and examples thereof include a dipping method and a spin coating method.

  The thickness of the lubricant layer 25 is usually 1 to 4 nm.

  The perpendicular magnetic recording medium 31 uses a known in-line film forming apparatus to sequentially transport the nonmagnetic substrate 20 between a plurality of film forming chambers, while soft magnetic layer 21, intermediate layer 22, and perpendicular magnetic layer 23. Further, the protective layer 24 and the lubricant layer 25 can be sequentially laminated.

  FIG. 4 shows an example of a magnetic recording / reproducing apparatus.

  The magnetic recording / reproducing apparatus 30 includes a perpendicular magnetic recording medium 31, a medium driving unit 32 that rotationally drives the perpendicular magnetic recording medium 31, a magnetic head 33, a head driving unit 34 that drives the magnetic head 33, and recording / reproducing signal processing. A system 35 is provided. The magnetic head 33 records information on the perpendicular magnetic recording medium 31 and reproduces information recorded on the perpendicular magnetic recording medium 31. The recording / reproducing signal processing system 35 processes input data and transmits a recording signal to the magnetic head 33, processes the reproducing signal transmitted from the magnetic head 33, and outputs data.

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to the examples.

(Examples and Comparative Examples)
The perpendicular magnetic recording medium 31 (see FIG. 1) was manufactured as follows.

  First, an amorphous glass substrate having an outer diameter of 2.5 inches was prepared as the nonmagnetic substrate 20.

Next, the soft magnetic layer 21, the intermediate layer 22, and the perpendicular magnetic layer 23 were sequentially formed on both surfaces of the nonmagnetic substrate 20 mounted on the carrier using an in-line type film forming apparatus C3010 (manufactured by Canon Anelva). Here, in the soft magnetic layer 21, a CoFe alloy layer (70Co-30Fe) having a thickness of 30 nm, a Ru layer having a thickness of 5 nm, and a CoFe alloy layer (70Co-30Fe) having a thickness of 30 nm are sequentially stacked. . The intermediate layer 22 is formed by sequentially laminating a NiW alloy layer (90Ni-10W) having a thickness of 7 nm and a Ru layer having a thickness of 20 nm. Furthermore, perpendicular magnetic layer 23, CoPtCr-based alloy layer (70Co-15Pt-5Cr-10SiO 2) and a thickness of CoCrPt-based alloy layer of the non-granular structure of 6nm a granular structure having a thickness of 6nm (64Co-20Cr-15Pt -1B) are sequentially stacked. Here, the CoCrPt-based alloy layer having the granular structure and the CoCrPt-based alloy layer having the non-granular structure have a hexagonal close-packed structure, and the (0002) crystal plane is oriented in parallel to the nonmagnetic substrate 20.

  Next, the protective layer 24 was formed on the perpendicular magnetic layer 23 using the film forming apparatus shown in FIG. Specifically, the film forming chamber 101 has a cylindrical shape with an outer diameter of 180 mm and a length of 250 mm, and the material of the chamber wall constituting the film forming chamber 101 is SUS304. In the film forming chamber 101, a coiled cathode electrode 104a made of tantalum having a length of about 30 mm and a cylindrical anode electrode 104b surrounding the cathode electrode 104a are provided. The anode electrode 104b is made of SUS304, has an outer diameter of 140 mm, and a length of 40 mm. The distance between the cathode electrode 104a and the nonmagnetic substrate was 160 mm. Then, a raw material gas containing carbon is introduced into the film forming chamber 101 having a reduced pressure, and a discharge is performed between the filament-shaped cathode electrode 104a heated by energization of the gas and the anode electrode 104b provided therearound. Ionized.

Ethylene was used as the source gas. As for the film formation conditions of the protective layer 24, the gas flow rate, reaction pressure, and film formation time are changed as shown in Table 1, the cathode power is 800 W, the voltage between the cathode electrode 104a and the anode electrode 104b is 75V, and the current is The ion acceleration voltage was 200 V, 180 mA, the substrate temperature was 550 ° C., and the thickness of the protective layer 24 to be deposited was 1 nm.

  Thereafter, the surface layer portion of the protective layer 24 was nitrided. That is, the supply of the source gas was stopped and the film formation chamber was evacuated for 2 seconds. Next, nitrogen was supplied at a gas flow rate of 2 SCCM and a reaction pressure of 5 Pa into the film formation chamber. The cathode power was set to 128 W (AC16V, 8A). Further, the surface layer portion of the protective layer 24 was irradiated with nitrogen ions formed from nitrogen gas at a voltage between the cathode electrode and the anode electrode of 75 V, a current of 1000 mA, an ion acceleration voltage of 200 V and 90 mA, and a treatment time of 1 second. .

  The protective layer 24 was analyzed in two stages before and after the nitriding treatment of the surface layer portion.

  Before the nitriding treatment of the protective layer, analysis was performed using a Raman spectroscope (manufactured by Tokyo Instruments). In the Raman spectroscope, a highly sensitive cooled CCD detector (manufactured by ANDOR Technology) and a diffraction grating having a groove number of 1200 / nm and a blaze wavelength of 500 nm were used. 2D / G of the obtained protective layer is shown in Table 1. Since both 2D band and G band are seen, the protective layer contains graphene and amorphous carbon, and graphene constitutes the perpendicular magnetic layer It was confirmed to be parallel to the individual (0002) crystal planes of the polycrystalline grains.

Further, by using the AFM, _{R max} of the surface of the protective layer (measurement area is 5μm square) were evaluated as denseness. In the protective layers of Examples 1 to 6, there was a tendency for R _{max to} increase with an increase in 2D / G, but the smoothness was able to withstand practical use as a magnetic recording / reproducing apparatus. Further, the protective layer of Comparative Example 1 had a low film density. Further, the protective layer of Comparative Example 2 had a high surface undulation, and uncoated portions were observed in some places.

  After the nitriding treatment of the protective layer, the composition of the outermost surface was measured by XPS (ESCA). As a result, nitridation at a concentration of about 40 atomic% was performed on the outermost surface of any protective layer. And the tendency for nitriding to advance easily was seen, so that the value of (2D / G) was small.

  Next, using a dipping device, tetraol (average molecular weight: 1800) is applied onto the protective layer 24 after nitriding to form a lubricant layer 25 having a thickness of 1.4 nm, and perpendicular magnetic recording is performed. Medium 31 was obtained.

The bonded ratio of the obtained perpendicular magnetic recording medium 31 was measured. The bonded ratio is obtained by immersing the magnetic recording medium after forming the lubricant layer in a fluorocarbon solvent for 5 minutes, measuring the absorbance around 1270 cm ⁻¹ before and after immersion in the same position of the same medium by ESCA, and percentage of the ratio. ((Absorbance after immersion / absorbance before immersion) × 100). Vertrel XF (trade name, manufactured by Mitsui DuPont Fluoro Chemical Co., Ltd.) was used as the fluorocarbon solvent. The evaluation results of the bonded ratio are shown in Table 1, and there was a tendency that the bonded ratio of the lubricant layer increased as nitridation of the protective layer surface progressed.

  The perpendicular magnetic recording media obtained in the examples withstood practical use as a magnetic recording / reproducing apparatus.

DESCRIPTION OF SYMBOLS 20 Nonmagnetic board | substrate 21 Soft magnetic layer 22 Intermediate | middle layer 23 Perpendicular magnetic layer 24 Protective layer 25 Lubricant layer 30 Magnetic recording / reproducing apparatus 31 Perpendicular magnetic recording medium 32 Medium drive part 33 Magnetic head 34 Head drive part 35 Recording / reproduction signal processing system

Claims (7)

In a perpendicular magnetic recording medium in which a perpendicular magnetic layer, a protective layer, and a lubricant layer are formed on a nonmagnetic substrate in the order of the perpendicular magnetic layer, the protective layer, and the lubricant layer.
The protective layer includes graphene and / or a stack of graphene and amorphous carbon,
The protective layer and the lubricant layer are provided in contact with each other,
The perpendicular magnetic recording medium according to claim 1, wherein an interface between the protective layer and the lubricant layer contains nitrogen.   2. The perpendicular magnetic recording medium according to claim 1, wherein a nitrogen content at an interface between the protective layer and the lubricant layer is in a range of 5 atomic% to 90 atomic%. The Raman spectrum of the protective layer includes graphene near 2700 cm ⁻¹ and / or the peak height (2D) of the 2D band related to the six-membered ring structure of the graphene laminate, and graphene and / or graphene near 1585 cm ⁻¹ . The ratio (2D / G) with the peak height (G) of the G band related to the sp ² bond stretching vibration of the laminate is in the range of 0.4-5. 2. A perpendicular magnetic recording medium according to 1.   4. The perpendicular magnetic recording medium according to claim 1, wherein the graphene stack is formed by stacking graphene in a range of 2 to 10 layers. 5. The uppermost layer of the perpendicular magnetic layer includes polycrystalline grains,
The polycrystalline grains include a CoCr-based alloy, a CoPt-based alloy, a CoCrPt-based alloy, or a CoPtCr-based alloy,
The protective layer is in contact with the uppermost layer of the perpendicular magnetic layer, and includes graphene and / or a stack of graphene, and amorphous carbon.
5. The perpendicular magnetic recording according to claim 1, wherein the graphene and / or the graphene laminate is parallel to individual (0002) crystal planes of the polycrystalline grains. 6. Medium. The uppermost layer of the perpendicular magnetic layer includes polycrystalline grains,
The polycrystalline grains include FePt based alloy or CoPt-based alloy having an L1 ₀ structure,
The protective layer is in contact with the uppermost layer of the perpendicular magnetic layer, and includes graphene and / or a stack of graphene, and amorphous carbon.
5. The perpendicular magnetic recording according to claim 1, wherein the graphene and / or the graphene laminate is parallel to each (001) crystal plane of the polycrystalline grains. 6. Medium. The perpendicular magnetic recording medium according to any one of claims 1 to 6,
A magnetic head for recording information on the perpendicular magnetic recording medium and reproducing the information recorded on the perpendicular magnetic recording medium;
A magnetic recording / reproducing apparatus comprising:

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