JP2009238325A - Method for manufacturing perpendicular magnetic recording medium, and perpendicular magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a perpendicular magnetic recording medium which has sufficient durability, moisture resistance and contamination-proof nature, and is also equipped with a suitable lubricous layer holding an R/W property. <P>SOLUTION: A method for manufacturing a perpendicular magnetic recording medium 100 which includes a magnetic recording layer 122, medium protective layer 126 and a lubricous layer 128 on a substrate 110 in this order, is characterized by including: a measurement process which measures surface free energy by variously changing film thickness of the lubricous layer; a linear approximation process for deriving a linear function which approximates a relation between film thickness when the measured surface free energy does not reach a minimum value and the surface free energy; and a film thickness determination process for obtaining a film thickness T when the linear function reaches the minimum value of the surface free energy. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a perpendicular magnetic recording medium mounted on a perpendicular magnetic recording type HDD (hard disk drive) or the like, and a perpendicular magnetic recording medium.

  Various information recording techniques have been developed with the recent increase in information processing capacity. In particular, the surface recording density of HDDs using magnetic recording technology continues to increase at an annual rate of about 100%. Recently, an information recording capacity exceeding 160 GB has been demanded for a 2.5-inch diameter magnetic disk used for HDDs and the like, and in order to meet such a demand, per square inch. It is required to realize an information recording density exceeding 250 GBit.

  In recent years, a perpendicular magnetic recording type magnetic disk (perpendicular magnetic recording disk) has been proposed in order to achieve a high recording density in a magnetic disk used for an HDD or the like. In the conventional in-plane magnetic recording method, the easy axis of magnetization of the magnetic recording layer is aligned in the plane direction of the substrate surface, but in the perpendicular magnetic recording method, the easy magnetization axis is adjusted to be aligned in the direction perpendicular to the substrate surface. ing. In the perpendicular magnetic recording method, the demagnetizing field (Hd) increases and the coercive force Hc improves as the magnetic grains become finer than the in-plane recording method, and the thermal fluctuation phenomenon can be suppressed. It is suitable for.

  Conventional magnetic recording magnetic disks are made of a substrate such as aluminum or glass, a magnetic recording layer for performing magnetic recording, and a carbon medium protective layer (carbon protective layer) and lubrication for the purpose of ensuring the reliability of the magnetic disk. It consists of layers.

  With the recent increase in recording density, the flying height between the magnetic head and the disk is decreasing. For example, a technique called DFH (Dynamic Flying Height) has been developed as one technique for stabilizing the control of the flying height of the magnetic head and further reducing the flying height (for example, Non-Patent Document 1). According to DFH, a heater element is embedded in a magnetic head, and the heater element generates heat during operation of the magnetic head. The heat causes the magnetic head to thermally expand and slightly protrude toward the magnetic disk. Thereby, the magnetic spacing, which is a magnetic gap between the magnetic head and the main surface of the magnetic disk, can be reduced only at that time. That is, DFH is a technology that can reduce the flying height of a magnetic head from a magnetic disk.

  Although such a DFH head can further reduce the flying height, the MR element is mounted on the magnetic head, and there is a problem that a head crash failure and a thermal asperity failure are caused as inherent failures. Further, even if these failures are not caused, it is assumed that intermittent contact between the magnetic head and the disk will increase in the future.

  Therefore, there is an increasing demand for reducing the friction coefficient on the surface of the lubricating layer. This is required to reduce the damage to the magnetic head and disk and improve the durability when contact occurs, and to reduce the wear of the carbon medium protective layer (carbon protective layer) as much as possible. Because.

In addition, the environment in which the HDD device is employed is extremely severe, such as high temperature and high humidity, as represented by mounting on a passenger car (on-vehicle). In such an environment, the contamination (contamination) of the disk is serious, and it is important to deal with a highly active carbon protective layer.
Meijin, “Mobile 2.5-inch HDD”, magazine FUJITSU, Fujitsu Limited, January 2007, Vol. 58, No. 1, p. 10-15

  However, if the lubricating layer is too thick for the purpose of improving durability, moisture resistance and contamination resistance, the R / W characteristics (read / write characteristics) cannot be maintained. Thus, durability and R / W characteristics are in a trade-off relationship. Therefore, it is necessary to achieve the purpose such as durability while ensuring the R / W characteristic with the smallest possible film thickness.

  However, in conventional lubricant development, since the lubricating layer itself is very thin, whether or not the carbon protective layer is covered with a lubricating layer having a sufficient thickness to protect the carbon protective layer from damage. It was very difficult to evaluate.

  In view of such problems, the present invention provides a method for producing a perpendicular magnetic recording medium having a suitable lubricating layer having sufficient durability, moisture resistance, and contamination resistance and having R / W characteristics, and An object of the present invention is to provide a perpendicular magnetic recording medium.

  In order to solve the above problems, the inventors have found that when the lubricating layer has an insufficient film thickness (coating is insufficient), the property of the medium protective layer under the lubricating layer appears on the main surface of the medium, and the surface is free. We focused on the energy becoming high. That is, the high surface free energy means that the film thickness is insufficient, the durability, moisture resistance and contamination resistance are insufficient, and the friction coefficient is also high.

  On the other hand, the surface free energy gradually decreases when the lubricating layer is thickened, but it was also noted that the surface free energy does not increase when a certain film thickness is exceeded. That is, after the properties of the medium protective layer appearing on the main surface have completely disappeared, there is no point in increasing the thickness of the lubricating layer. On the other hand, the R / W characteristics are reduced by the increased thickness of the lubricating layer. I paid attention to it.

  In order to solve the above problems, a typical configuration of the present invention is a method for manufacturing a perpendicular magnetic recording medium comprising a magnetic recording layer, a medium protective layer, and a lubricating layer in this order on a substrate. A measurement process that measures surface free energy by various changes, a linear approximation process that derives a linear function that approximates the relationship between the surface free energy and the film thickness at which the measured surface free energy does not reach the minimum value, and linear And a film thickness determining step for obtaining a film thickness when the function reaches the minimum value of the surface free energy.

  According to said structure, it is possible to obtain | require the minimum film thickness of the lubricating layer required for the surface free energy of a lubricating layer to reach the minimum value. Accordingly, it is possible to manufacture a perpendicular magnetic recording medium that has sufficient durability, moisture resistance, and contamination resistance, has a high friction coefficient, and maintains R / W characteristics that are in a trade-off relationship.

  In the measurement step, the surface free energy may be measured using a contact angle method. This is because if the surface free energy is high, the film thickness is insufficient, the durability, moisture resistance and contamination resistance are insufficient, and the degree of coating can be evaluated such that the friction coefficient is high. In addition, the contact angle method is suitable for measuring the surface free energy of a very thin layer such as a lubricating layer of a perpendicular magnetic recording medium.

  In the linear approximation step, a linear function may be derived using a least square method. This is because it is suitable as a method for deriving a straight line that approximates the relationship between the film thickness and the surface free energy.

The lubricating layer may be perfluoropolyether. Perfluoropolyether is a fluorinated synthetic oil based on C—F ₂ with O in between, is excellent in heat resistance and chemical resistance, and has a high viscosity index.

  Another typical configuration of the present invention is a perpendicular magnetic recording medium having a magnetic recording layer, a medium protective layer, and a lubricating layer in this order on a substrate. The film thickness of the lubricating layer reaches the minimum surface free energy. A linear function that approximates the relationship between the various free film thicknesses and the surface free energy is the film thickness when the minimum value of the surface free energy is reached.

  The components corresponding to the technical idea in the method for manufacturing the perpendicular magnetic recording medium and the description thereof can be applied to the perpendicular magnetic recording medium.

  As described above, according to the present invention, in a perpendicular magnetic recording medium with a low flying height such as adopting DFH, durability, moisture resistance, and contamination resistance are sufficient, and the friction coefficient is kept low. In addition, it is possible to manufacture a perpendicular magnetic recording medium including a lubricating layer that can also maintain R / W characteristics in a trade-off relationship with them.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiments are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

(Embodiment)
An embodiment of a method for manufacturing a perpendicular magnetic recording medium according to the present invention will be described. FIG. 1 is a diagram illustrating the configuration of a perpendicular magnetic recording medium 100 according to the present embodiment. A perpendicular magnetic recording medium 100 shown in FIG. 1 includes a disk substrate 110 as a substrate, an adhesion layer 112, a first soft magnetic layer 114a, a spacer layer 114b, a second soft magnetic layer 114c, a pre-underlayer 116, and a first underlayer 118a. , A second underlayer 118b, a nonmagnetic granular layer 120, a first magnetic recording layer 122a, a second magnetic recording layer 122b, a continuous layer 124, a medium protective layer 126, and a lubricating layer 128. The first soft magnetic layer 114a, the spacer layer 114b, and the second soft magnetic layer 114c together constitute the soft magnetic layer 114. The first base layer 118a and the second base layer 118b together constitute the base layer 118. The first magnetic recording layer 122a and the second magnetic recording layer 122b together constitute the magnetic recording layer 122.

  As the disk substrate 110, a glass disk obtained by forming amorphous aluminosilicate glass into a disk shape by direct pressing can be used. The type, size, thickness, etc. of the glass disk are not particularly limited. Examples of the material of the glass disk include aluminosilicate glass, soda lime glass, soda aluminosilicate glass, aluminoborosilicate glass, borosilicate glass, quartz glass, chain silicate glass, or glass ceramic such as crystallized glass. It is done. The glass disk is subjected to grinding, polishing, and chemical strengthening sequentially to obtain a smooth non-magnetic disk base 110 made of a chemically strengthened glass disk.

  Note that aluminum may be used as the disk base 110 instead of glass.

  On the disk substrate 110, a film is sequentially formed from the adhesion layer 112 to the continuous layer 124 by a DC magnetron sputtering method, and the medium protective layer 126 can be formed by a CVD method. Thereafter, the lubricating layer 128 can be formed by dip coating.

  Hereinafter, the configuration and manufacturing method of each layer will be described. In this embodiment, an in-line film forming method with high productivity is used.

  The adhesion layer 112 is an amorphous underlayer, which is formed in contact with the disk substrate 110 and has a function of increasing the peel strength between the soft magnetic layer 114 formed on the disk substrate 110 and the disk substrate 110. It has a function of miniaturizing and homogenizing the crystal grain of each layer to be formed. When the disk substrate 110 is made of amorphous glass, the adhesion layer 112 is preferably an amorphous alloy film so as to correspond to the amorphous glass surface.

  The adhesion layer 112 can be selected from, for example, a CrTi amorphous layer, a CoW amorphous layer, a CrW amorphous layer, a CrTa amorphous layer, and a CrNb amorphous layer. Among these, a CrTi alloy film is particularly preferable because it forms an amorphous metal film containing microcrystals. The adhesion layer 112 may be a single layer made of a single material, or may be formed by laminating a plurality of layers. For example, a CoW layer or a CrW layer may be formed on the CrTi layer. These adhesion layers 112 are preferably formed by sputtering with a material containing carbon dioxide, carbon monoxide, nitrogen, or oxygen, or the surface layer is exposed with these gases.

  The soft magnetic layer 114 is a layer that temporarily forms a magnetic path during recording in order to pass magnetic flux in a direction perpendicular to the recording layer in the perpendicular magnetic recording method. The soft magnetic layer 114 is provided with AFC (Antiferro-magnetic exchange coupling) by interposing a nonmagnetic spacer layer 114b between the first soft magnetic layer 114a and the second soft magnetic layer 114c. Can be configured. As a result, the magnetization direction of the soft magnetic layer 114 can be aligned along the magnetic path (magnetic circuit) with high accuracy, and the vertical component of the magnetization direction is extremely reduced, so that noise generated from the soft magnetic layer 114 is reduced. Can do. The compositions of the first soft magnetic layer 114a and the second soft magnetic layer 114c include a Co-based alloy such as CoTaZr, a Co-Fe based alloy such as CoCrFeB, and a Ni-Fe such as a [Ni-Fe / Sn] n multilayer structure. A system alloy or the like can be used.

  The pre-underlayer 116 is a non-magnetic alloy layer, and acts to protect the soft magnetic layer 114 and the easy magnetization axis of the hexagonal close packed structure (hcp structure) included in the underlayer 118 formed thereon is a disk. A function for aligning in the vertical direction is provided. The pre-underlayer 116 preferably has a (111) plane of a face-centered cubic structure (fcc structure) parallel to the main surface of the disk substrate 110. Further, the pre-underlayer 116 may have a configuration in which these crystal structures and amorphous are mixed. The material of the front ground layer can be selected from Ni, Cu, Pt, Pd, Zr, Hf, Nb, and Ta. Furthermore, it is good also as an alloy which contains these metals as a main component and contains any one or more additional elements of Ti, V, Ta, Cr, Mo, and W. For example, NiW, CuW, or CuCr can be suitably selected.

  The underlayer 118 has an hcp structure, and has a function of growing a Co hcp crystal of the magnetic recording layer 122 as a granular structure. Therefore, the higher the crystal orientation of the underlayer 118, that is, the more the (0001) plane of the crystal of the underlayer 118 is parallel to the main surface of the disk substrate 110, the more the orientation of the magnetic recording layer 22 is improved. Can do. Ru is a typical material for the underlayer, but in addition, it can be selected from RuCr and RuCo. Since Ru has an hcp structure and the lattice spacing of crystals is close to Co, a magnetic recording layer containing Co as a main component can be well oriented.

  When the underlayer 118 is made of Ru, a two-layer structure made of Ru can be obtained by changing the gas pressure during sputtering. Specifically, when forming the second base layer 118b on the upper layer side, the Ar gas pressure is set higher than when forming the first base layer 118a on the lower layer side. When the gas pressure is increased, the free movement distance of the plasma ions to be sputtered is shortened, so that the film formation rate is reduced and the crystal orientation can be improved. Further, by increasing the pressure, the size of the crystal lattice is reduced. Since the size of the Ru crystal lattice is larger than that of the Co crystal lattice, if the Ru crystal lattice is made smaller, it approaches that of Co, and the crystal orientation of the Co granular layer can be further improved.

The nonmagnetic granular layer 120 is a nonmagnetic granular layer. A nonmagnetic granular layer is formed on the hcp crystal structure of the underlayer 118, and the granular layer of the first magnetic recording layer 122a is grown thereon, so that the magnetic granular layer can be grown from the initial growth stage (rise). Has the effect of separating. The composition of the nonmagnetic granular layer 120 can be a granular structure by forming a grain boundary by segregating a nonmagnetic substance between nonmagnetic crystal grains made of a Co-based alloy. In particular, CoCr—SiO ₂ and CoCrRu—SiO ₂ can be preferably used, and Rh (rhodium), Pd (palladium), Ag (silver), Os (osmium), Ir (iridium), Au (in addition to Ru) Gold) can also be used. A nonmagnetic substance is a substance that can form a grain boundary around magnetic grains so that exchange interaction between magnetic grains (magnetic grains) is suppressed or blocked, and is cobalt (Co). Any non-magnetic substance that does not dissolve in solution can be used. Examples thereof include silicon oxide (SiOx), chromium (Cr), chromium oxide (CrO ₂ ), titanium oxide (TiO ₂ ), zircon oxide (ZrO ₂ ), and tantalum oxide (Ta ₂ O ₅ ).

The magnetic recording layer 122 has a columnar granular structure in which a nonmagnetic substance is segregated around magnetic grains of a hard magnetic material selected from a Co-based alloy, an Fe-based alloy, and a Ni-based alloy to form a grain boundary. It is a magnetic layer. By providing the nonmagnetic granular layer 120, the magnetic grains can be continuously epitaxially grown from the granular structure. In the present embodiment, the first magnetic recording layer 122a and the second magnetic recording layer 122b having different compositions and film thicknesses are used. The first magnetic recording layer 122a and the second magnetic recording layer 122b are all non-magnetic materials such as oxides such as SiO ₂ , Cr ₂ O ₃ , TiO ₂ , B ₂ O ₃ , Fe ₂ O ₃ , BN, etc. Nitride and carbides such as B ₄ C ₃ can be preferably used.

  The continuous layer 124 is a layer (also referred to as a continuous layer) that is magnetically continuous in the in-plane direction on the magnetic recording layer 122 having a granular structure. The continuous layer 124 is not always necessary, but by providing it, in addition to the high density recording property and low noise property of the magnetic recording layer 122, the reverse domain nucleation magnetic field Hn is improved, the heat-resistant fluctuation property is improved, and the overwrite property is improved. Can be improved.

  The continuous layer 124 may not be a single layer but may be a CGC structure (Coupled Granular Continuous) that forms a thin film (continuous layer) exhibiting high perpendicular magnetic anisotropy and high saturation magnetization MS. The CGC structure is an exchange energy control layer comprising a magnetic recording layer having a granular structure, a thin film coupling control layer made of a nonmagnetic material such as Pd or Pt, and an alternating laminated film in which thin films of CoB and Pd are laminated. It can consist of.

  The medium protective layer 126 can be formed by forming a carbon film by a CVD method while maintaining a vacuum. The medium protective layer 126 is a protective layer for protecting the perpendicular magnetic recording layer from the impact of the magnetic head. In general, carbon deposited by the CVD method has improved film hardness as compared with that deposited by the sputtering method, so that the magnetic recording layer 122 can be more effectively protected against the impact from the magnetic head. The outermost surface of the medium protective layer 126 was subjected to nitrogen treatment.

  The medium protective layer 126 may be formed by an FCVA (Filtered Cathodic Vacuum Arc) method or an IBD (Ion Beam Deposition) method instead of the CVD method.

  The lubricating layer 128 can be formed of PFPE (perfluoropolyether) by dip coating. PFPE has a long chain molecular structure and binds with high affinity to N atoms on the surface of the medium protective layer 126. Due to the action of the lubricating layer 128, even if the magnetic head comes into contact with the surface of the perpendicular magnetic recording medium 100, damage or loss of the medium protective layer 126 can be prevented.

  More specifically, Fomblin Z (“fomblin” is a registered trademark) -based lubricant (Fomblin Z DOL, Fomblin Z TETRAOL, etc.) was used as the material of the lubricating layer 128. FIG. 2 is a view showing a chemical structural formula of Fomblin Z-based lubricant that can be used as the lubricating layer of FIG. The molecular weight (typically 1000 to 2000) is determined by the number of two types of main chain units (n, m and subscripted parts) contained in the lubricant molecule.

  FIG. 3 is a diagram for explaining the principle of the measurement process for measuring the surface free energy using the contact angle method in order to determine the film thickness of the lubricating layer of FIG. 3A to 3C schematically show the cross-sectional shape of the droplet 140 placed on the solid 130, and the droplet 140 and the solid 130 are in contact with each other at an angle θ. This angle θ is referred to as a contact angle. The smaller the contact angle θ as shown in FIG. 3C, the more hydrophilic the surface of the solid 130 is, and the better the “wetting”. On the contrary, as the contact angle is larger as shown in FIG. 3A, the surface of the solid 130 has water repellency and “wetting” is worse.

When the surface energy of the solid 130 is γ _S , the surface energy of the droplet 140 is γ _L , and the interface energy between the solid / liquid is γ _SL , the following equation (1) is established.
cos θ = (γ _S −γ _L ) / γ _SL (1)
In other words, the smaller the contact angle θ, the larger cos θ, and the better the “wetting”, the larger the surface energy γ _S of the solid 130 becomes. However, an active surface having a large surface energy γ _S means that the free energy component in the surface energy, that is, the surface free energy is also high. That is, the property of the medium protective layer 126 under the lubricating layer 128 appears on the main surface of the medium, and the surface free energy is high, and the coating (film thickness) with the lubricating layer 128 is insufficient.

  The film thickness of the lubricating layer 128 is determined as follows. Fomblin Z-based lubricant has a molecular weight determined according to a purification method, and applies the purified lubricant to a magnetic disk. FIG. 4 is a graph showing the results of measuring the surface free energy using the contact angle method of FIG. 3 while varying the film thickness of the lubricating layer of FIG.

  As shown in FIG. 4, when the lubricating layer 128 is gradually thickened, the surface free energy does not decrease even if the lubricating layer 128 is thickened. Therefore, a linear function approximating the relationship between the film thickness at which the measured surface free energy has not reached the minimum value and the surface free energy was derived using the least square method (linear approximation step). However, the method of determining the approximate linear function is not limited to the least square method. Further, in the present embodiment, although a linear function is derived, an approximation with a higher order function may be derived.

  Next, the film thickness T when the linear function reaches the minimum value of the surface free energy was determined (film thickness determination step). This film thickness T can be said to be the minimum film thickness that can minimize the surface free energy, that is, can maximize the durability, moisture resistance, and contamination resistance. By forming such a lubricating layer having the minimum necessary film thickness T, it is possible to prevent the R / W characteristics from being reduced unnecessarily. When the film thickness is made larger than the film thickness T, the R / W characteristic is deteriorated due to the spacing loss between the head and the media.

  According to said structure, it is possible to make the film thickness of the lubrication layer 128 into the minimum film thickness T required for the surface free energy to reach the minimum value. The film thickness T may be determined according to various lubricants (difference in composition, molecular weight, etc.), process conditions (bake, tape conditions), and the like. Accordingly, it is possible to manufacture a perpendicular magnetic recording medium that has sufficient durability, moisture resistance, and contamination resistance, has a high friction coefficient, and maintains R / W characteristics that are in a trade-off relationship.

  Through the above manufacturing process, the perpendicular magnetic recording medium 100 can be obtained. The effectiveness of the present invention will be described below using examples and comparative examples.

(Example)
On the disk substrate 110, a film was formed in order from the adhesion layer 112 to the continuous layer 124 in an Ar atmosphere by a DC magnetron sputtering method using a film forming apparatus that was evacuated. The adhesion layer 112 was made of CrTi. In the soft magnetic layer 114, the composition of the first soft magnetic layer 114a and the second soft magnetic layer 114c was CoCrFeB, and the composition of the spacer layer 114b was Ru. The composition of the pre-underlayer 116 was a NiW alloy having an fcc structure. For the underlayer 118, the first underlayer 118a was formed with Ru under high pressure Ar, and the second underlayer 118b was formed with Ru under low pressure Ar. The composition of the nonmagnetic granular layer 120 was nonmagnetic CoCr—SiO ₂ . The composition of the magnetic recording layer 122 was as shown in FIG. The composition of the continuous layer 124 was CoCrPtB. The medium protective layer 126 was formed using C ₂ H ₄ and CN by a CVD method, and the outermost surface of the medium protective layer was subjected to nitrogen treatment. The lubricating layer 128 was formed using PFPE by a dip coating method. After film formation, heat treatment was performed at a constant temperature.

  The manufactured perpendicular magnetic recording medium 100 was subjected to a load / unload test for 1 week in a high-temperature and high-humidity condition in a drive and a fixed-point levitation test for 2 weeks. After that, when the lubricant adhering to the head was observed, it was found that there was intermittent magnetic head / disk contact, but there was no head crash failure or thermal asperity failure. That is, it was confirmed that the durability, moisture resistance, and contamination resistance were sufficient. In addition, no particular problem was found in the R / W characteristics, which are these contradictory characteristics.

  Although the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such examples. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  For example, although a perpendicular magnetic recording type disk is used in this embodiment, the present invention can also be used for a longitudinal magnetic recording type disk.

  The present invention can be used as a method for manufacturing a perpendicular magnetic recording medium mounted on a perpendicular magnetic recording type HDD (hard disk drive) or the like and as a perpendicular magnetic recording medium.

It is a figure explaining the structure of the perpendicular magnetic recording medium concerning embodiment. It is a figure which shows the chemical structural formula of Fomblin Z type | system | group lubricant used as a lubricating layer of FIG. It is a figure explaining the principle which measures surface free energy using a contact angle method in order to determine the film thickness of the lubricating layer of FIG. FIG. 4 is a graph showing the results of measuring the surface free energy using the contact angle method of FIG. 3 while varying the film thickness of the lubricating layer of FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Perpendicular magnetic recording medium 110 ... Disk base | substrate 112 ... Adhesion layer 114a ... 1st soft magnetic layer 114b ... Spacer layer 114c ... 2nd soft magnetic layer 116 ... Pre-underlayer 118 ... Underlayer 118a ... First underlayer 118b ... First 2 Underlayer 120 ... Non-magnetic granular layer 122 ... Magnetic recording layer 122a ... First magnetic recording layer 122b ... Second magnetic recording layer 124 ... Continuous layer 126 ... Medium protective layer 128 ... Lubrication layer

Claims (5)

In a method for manufacturing a perpendicular magnetic recording medium comprising a magnetic recording layer, a medium protective layer, and a lubricating layer in this order on a substrate,
A measurement step of measuring the surface free energy by variously changing the thickness of the lubricating layer;
A linear approximation step for deriving a linear function that approximates the relationship between the surface free energy and the film thickness at which the measured surface free energy does not reach the minimum value;
A film thickness determining step for determining a film thickness when the linear function reaches the minimum value of surface free energy;
A method of manufacturing a perpendicular magnetic recording medium.   2. The method of manufacturing a perpendicular magnetic recording medium according to claim 1, wherein in the measuring step, the surface free energy is measured using a contact angle method.   3. The method of manufacturing a perpendicular magnetic recording medium according to claim 1, wherein, in the linear approximation step, the linear function is derived using a least square method.   The method of manufacturing a perpendicular magnetic recording medium according to claim 1, wherein the lubricating layer is perfluoropolyether (PFPE). In a perpendicular magnetic recording medium comprising a magnetic recording layer, a medium protective layer, and a lubricating layer in this order on a substrate,
The film thickness of the lubricating layer is the film thickness when a linear function approximating the relationship between various film thicknesses that do not reach the minimum value of the surface free energy and the surface free energy reaches the minimum value of the surface free energy. A perpendicular magnetic recording medium.

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