JP2014081980A - Method for manufacturing magnetic recording medium and magnetic recording medium manufactured by this method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a magnetic recording medium which is excellent in both surface flatness and magnetic characteristics.SOLUTION: The method for manufacturing a magnetic recording medium includes the steps of: forming a ground layer on a nonmagnetic substrate; exposing the surface of the ground layer to oxygen; and forming a magnetic recording layer on the surface of the ground layer exposed to oxygen. The ground layer contains CrN having a NaCl type crystal structure, and the magnetic recording layer is composed of regular alloy.

Description

  The present invention relates to a method for manufacturing a magnetic recording medium. More specifically, the present invention relates to a method of manufacturing a magnetic recording medium used for a storage device for information equipment such as a computer. The present invention also relates to a magnetic recording medium obtained by such a manufacturing method.

  As a technique for realizing high density magnetic recording, a perpendicular magnetic recording system is adopted. The perpendicular magnetic recording medium includes at least a magnetic recording layer formed of a hard magnetic material, and optionally includes a soft magnetic underlayer, an underlayer, a protective layer, and the like. Here, the soft magnetic underlayer is formed of a soft magnetic material and plays a role of concentrating the magnetic flux generated by the magnetic head on the magnetic recording layer. The underlayer is used to orient the magnetic recording layer in a desired direction. The protective layer is a layer that protects the surface of the magnetic recording layer.

As a material for forming a magnetic recording layer of a perpendicular magnetic recording medium, a granular magnetic film in which a nonmagnetic material such as SiO ₂ or TiO ₂ is added to an alloy material such as CoCrPt or CoCrTa has been proposed (for example, Patent Documents). 1-3). For example, in a CoCrPt—SiO ₂ granular magnetic film, non-magnetic SiO ₂ segregates so as to surround the periphery of CoCrPt magnetic crystal grains, and each CoCrPt magnetic crystal grain is magnetically separated by non-magnetic SiO ₂ . It is separated.

  In recent years, there has been an urgent need to further reduce the recording density of perpendicular magnetic recording media by reducing the grain size of magnetic crystal grains in the granular magnetic film. On the other hand, the reduction in the grain size of the magnetic crystal grains reduces the thermal stability of the recorded magnetization. Therefore, in order to compensate for the decrease in thermal stability due to the reduction in the grain size of the magnetic crystal grains, it is required to form the magnetic crystal grains in the granular magnetic film using a material having higher crystal magnetic anisotropy. Yes.

As a material having such a high crystal magnetic anisotropy, are known L1 ₀ type ordered alloy, various manufacturing methods L1 ₀ type ordered alloy thin film has been proposed (e.g., Patent Documents 4-8 reference).

On the other hand, in a magnetic recording medium, a nonmagnetic substrate made of aluminum or glass is used from the viewpoint of strength and impact resistance. When forming an L1 ₀ type ordered alloy on the surface of such a non-magnetic substrate, undercoat layer is important. This is because, in order to give high crystal magnetic anisotropy, the crystal of the L1 _0- based ordered alloy needs to be (001) -oriented (the [001] axis of the crystal is perpendicular to the substrate surface). . Therefore, in general, L1 ₀ type rules high lattice matching with a suitable lattice misfit with respect to alloy MgO, SrTiO ₃ is used as an underlying layer.

  There are also known magnetic recording media in which the material of the underlayer and the formation method thereof are variously changed according to the purpose.

  For example, in Patent Document 9, a single layer or a multilayer substrate, an in-plane non-oriented and out-of-plane oriented microcrystal film deposited on the substrate, and individual base microcrystals of the base microcrystalline film are individually provided. Nanoparticle devices comprising local epitaxy nanoparticles are disclosed. It is disclosed that TiN, VN, ZrN, NbN, HfN, TaN, ThN nitride, MgO, CaO, SrO, and BaO oxides are used as the base microcrystalline film. Furthermore, it is also disclosed that in the manufacture of nanoparticle devices, after the base microcrystalline film is formed, FePt or CoPt is deposited without exposure to the atmosphere, thereby allowing local epitaxial growth.

In Patent Document 10, a first soft magnetic underlayer formed on a rigid substrate directly or via an adhesive layer, and a second soft magnetic underlayer formed on the first soft magnetic underlayer via a nonmagnetic intermediate layer. A soft magnetic underlayer, a low thermal conductivity intermediate layer made of an oxide formed on the second soft magnetic underlayer, and a crystal grain size formed on the low thermal conductivity intermediate layer directly or via a crystal orientation control layer a control layer formed of a composition which is formed directly or via a crystal orientation-control and low thermal conductivity intermediate layer on the crystal grain diameter control layer, take the L1 ₀ structure at the stage of progress in ordering is expected A granular recording layer mainly composed of Fe-Pt alloy or Co-Pt alloy, a cap layer made of Fe-Pt alloy or Co-Pt alloy formed on the granular recording layer, and formed on the cap layer. Perpendicular magnetic recording with protective layer A recording medium is disclosed. It is also disclosed that a Cr—MB alloy layer to which at least one element selected from the group M consisting of Ti, Mo, and W is added as the crystal grain size control layer is provided.

  Patent Document 11 discloses a magnetic recording medium including a base, an underlayer including a CrN film, and a magnetic recording layer.

JP 2001-291230 A Japanese Patent Laid-Open No. 08-083418 International Publication No. 2002/039433 Pamphlet Japanese Patent No. 3318204 Japanese Patent No. 3010156 JP 2001-101645 A Japanese Patent Application Laid-Open No. 2004-178753 Special table 2010-503139 International Publication No. 2005/022565 Pamphlet JP 2009-158054 A US Patent Application Publication No. 2009/142621

However, when conventional MgO and SrTiO ₃ are used as the material for the underlayer, the surface flatness of the magnetic recording layer may be extremely deteriorated. In addition, although magnetic recording media using a material that is not an oxide for the underlayer are also known as in References 9 to 11, it has been clarified that the recording media satisfy both surface flatness and magnetic characteristics. Not. Since both the surface flatness and the magnetic characteristics are major factors that influence the performance of the magnetic recording medium, there is still a need for a method for manufacturing a magnetic recording medium excellent in these characteristics.

  Accordingly, an object of the present invention is to provide a method of manufacturing a magnetic recording medium that is excellent in both surface flatness and magnetic characteristics.

  In order to achieve the above object, a method for manufacturing a magnetic recording medium according to the present invention includes a step of forming an underlayer on a nonmagnetic substrate, a step of exposing the surface of the underlayer to oxygen, and the underlayer exposed to oxygen. Forming a magnetic recording layer on the surface of the substrate, wherein the underlayer contains CrN having an NaCl type crystal structure, and the magnetic recording layer is made of an ordered alloy.

  In such a magnetic recording medium manufacturing method, it is preferable that the oxygen gas exposure amount is 60 to 500 Langmuir in the step of exposing the surface of the underlayer to oxygen.

  The present invention includes a magnetic recording medium obtained by such a method of manufacturing a magnetic recording medium.

  According to the method of the present invention, a magnetic recording medium excellent in both surface flatness and magnetic characteristics can be produced.

1A and 1B are schematic cross-sectional views showing a method for manufacturing a magnetic recording medium 100 of the present invention, where FIG. 1A shows a step of forming a base layer 104 on a nonmagnetic substrate 102, and FIG. 2B shows oxygen exposure of the surface of the base layer 104; (C) shows the step of forming the magnetic recording layer 106 on the surface of the underlayer 105 exposed to oxygen.

<Method of manufacturing magnetic recording medium>
The method for producing a magnetic recording medium of the present invention comprises a step of forming a base layer on a nonmagnetic substrate, a step of exposing the surface of the base layer to oxygen, and a magnetic recording layer on the surface of the base layer exposed to oxygen. The underlayer includes CrN having an NaCl type crystal structure, and the magnetic recording layer is made of a regular alloy.

  Below, the manufacturing method of the magnetic recording medium of this invention is demonstrated in detail according to drawing. The following example is merely an example of the present invention, and those skilled in the art can change the design as appropriate.

  1A and 1B are schematic cross-sectional views showing a method for manufacturing a magnetic recording medium 100 of the present invention. FIG. 1A shows a process of forming an underlayer 104 on a nonmagnetic substrate 102, and FIG. A step of exposing the surface to oxygen is shown. (C) shows a step of forming the magnetic recording layer 106 on the surface of the underlayer 105 exposed to oxygen. Below, each process is explained in full detail.

[Step 1]
Step 1 is a step of forming a base layer 104 on the nonmagnetic substrate 102 as shown in FIG.

(Preparation of non-magnetic substrate 102)
As the nonmagnetic substrate 102, tempered glass, crystallized glass, or the like that is usually used for magnetic recording media can be used.

  The nonmagnetic substrate 102 is preferably washed before forming the underlayer 104. Cleaning can be performed by a scrub method using a brush, a high-pressure water jet method, a dipping method in an acid or alkaline detergent, or the like, and ultrasonic waves can be applied during these cleaning operations. Further, after the cleaning, ultraviolet irradiation can be further performed.

(Formation of underlayer 104)
The underlayer 104 is made of a material containing CrN according to any method and conditions known in the art such as sputtering (including DC magnetron sputtering, RF magnetron sputtering), CVD, and vacuum deposition. Can be formed.

  For example, in the case of using a sputtering method, the underlayer 104 containing CrN having an NaCl type crystal structure can be formed using a CrN target in an inert gas atmosphere such as Ar.

Alternatively, the base layer 104 containing CrN having an NaCl type crystal structure can be formed by performing sputtering in a N ₂ atmosphere diluted with an inert gas such as Ar using a Cr target instead of the CrN target. . When such a forming method is applied, it is necessary to appropriately select the concentration of N ₂ gas diluted with an inert gas and the gas pressure. This is because a crystal state in which Cr having a bcc structure and hexagonal Cr ₂ N, which is not suitable as a structure for epitaxially growing a magnetic recording layer (for example, an FePt layer), is not generated in CrN having an NaCl type crystal structure. is there. For this reason, it is preferable that the N ₂ gas concentration is 20 to 30% by volume and the gas pressure is 0.5 to 4 Pa.

  The CrN contained in the underlayer 104 is preferably CrN having an NaCl type crystal structure from the viewpoint of remarkably improving the surface roughness of the magnetic recording medium as compared with the case of using conventional MgO. Strictly speaking, the ratio of Cr atoms to N atoms is 1: 1, but it may be in the vicinity of 1: 1 in consideration of lattice defects and the like.

  In order to confirm whether the underlayer 104 has a NaCl-type crystal structure, it can be confirmed using, for example, an X-ray diffractometer.

  The thickness of the underlayer 104 is not particularly limited, but is preferably 10 nm to 20 nm because it is desirable that it is thick from the viewpoint of orientation and thin from the viewpoint of productivity.

(Arbitrary layer formation)
An arbitrary layer (not shown) generally used for a magnetic recording medium may be further formed between the nonmagnetic substrate 102 and the underlayer 104. Non-limiting examples of optional layers include adhesion layers, pre-seed layers, orientation control layers, thermal control layers, soft magnetic layers, and the like.

  Any layer can be formed from the materials making up the layer using any methods and conditions known in the art.

  For example, the adhesion layer is made of a conventionally used material such as a Cr-containing alloy such as a CrTi alloy, such as a sputtering method (including a DC magnetron sputtering method, an RF magnetron sputtering method), a vacuum deposition method, a CVD method, or the like. It can be formed using conventional methods.

  The pre-seed layer is made of a conventional material such as a Cr-containing alloy such as a CrRu alloy, or a conventional method such as a sputtering method (including a DC magnetron sputtering method, an RF magnetron sputtering method), a vacuum deposition method, a CVD method, or the like. It can be formed using a method.

  The orientation control layer is formed of a conventionally used material such as a Ni alloy using a conventional method such as sputtering (including DC magnetron sputtering, RF magnetron sputtering), vacuum deposition, or CVD. be able to.

  The heat control layer is made of a conventionally used material such as a Cu alloy or an Ag alloy by using a conventional method such as a sputtering method (including a DC magnetron sputtering method, an RF magnetron sputtering method, etc.), a vacuum evaporation method, a CVD method, or the like. Can be formed.

[Step 2]
Step 2 is a step of exposing the surface of the base layer 104 to oxygen as shown in FIG.

  Oxygen exposure can be performed by exposing oxygen gas alone or a mixed gas obtained by diluting oxygen with an inert gas to the surface of the base layer 104 of the laminate 110 obtained in step 1. Here, a rare gas or the like can be used as the inert gas.

From the viewpoint of dramatically improving the magnetic properties of the magnetic recording medium, it is preferable that the oxygen gas exposure amount on the surface of the underlayer 104 is 60 to 500 Langmuir. Here, 1 Langmuir means the amount of oxygen exposed to the surface of the base layer 104 when the laminate 110 is held for 1 second under 1.33 × 10 ⁻⁴ Pa (1 × 10 ⁻⁶ torr). Moreover, when performing oxygen exposure using the mixed gas of an inert gas and oxygen, a process is set based on the exposure amount only of an oxygen gas component. For example, in this specification, oxygen exposure at 100 Langmuir using an oxygen mixed gas diluted with Ar means that oxygen gas is exposed at 100 Langmuir.

[Step 3]
Step 3 is a step of forming a magnetic recording layer 106 on the surface of the underlayer 105 exposed to oxygen, as shown in FIG.

The magnetic recording layer 106 is made of an ordered alloy. From the viewpoint of having a crystal magnetic anisotropy high as ordered alloy, L1 ₀ type ordered alloy is particularly preferred.

  The magnetic material of the ordered alloy is not particularly limited, but it is preferable to use FePt because the formation temperature can be further lowered. From the viewpoint of ensuring the separation of magnetic grains, an alloy obtained by adding carbon to the FePt alloy is used. Particularly preferred.

  The magnetic recording layer 106 is made of a conventionally used material such as the above materials, and is known in the art such as sputtering (including DC magnetron sputtering, RF magnetron sputtering, etc.), CVD, and vacuum deposition. It can be formed by any method and conditions that have been described.

(Arbitrary layer formation)
On the magnetic recording layer 106, an arbitrary layer (not shown) normally used in the magnetic recording medium 100 may be further formed. Non-limiting examples of optional layers include protective layers, liquid lubricant layers, and the like.

  Any layer can be formed from the materials making up the layer using any methods and conditions known in the art.

For example, the protective layer can be formed using carbon (such as diamond-like carbon), ZrO _{2, or} SiO ₂ . The protective layer can be generally formed using a sputtering method (including a DC magnetron sputtering method, an RF magnetron sputtering method, etc.), a vacuum deposition method, a CVD method, or the like.

  The liquid lubricant layer can be formed using a perfluoropolyether liquid lubricant or the like. The liquid lubricant layer can be formed using any coating method known in the art such as a dip coating method or a spin coating method.

  As described in detail above, according to the method of the present invention, a magnetic recording medium excellent in both surface flatness and magnetic characteristics can be produced. Therefore, the magnetic recording medium of the present invention can be applied to various information device storage devices such as computers.

  The effects of the present invention are demonstrated below by examples. The following examples are merely representative examples for explaining the present invention, and do not limit the present invention in any way.

<Formation of magnetic recording medium>
Example 1
First, a chemically strengthened glass substrate 102 having a diameter of 65 mm and a plate thickness of 0.635 mm was prepared. This was cleaned to a level where there was no problem even if it was introduced into the vacuum apparatus, and introduced into the vacuum apparatus. Next, a CrTi film having a thickness of 4 nm was formed as an adhesion layer on the substrate by a DC magnetron sputtering method using a Cr ₅₀ Ti ₅₀ target. Further, a CrRu film having a thickness of 10 nm was formed as a pre-seed layer on the adhesion layer by a DC magnetron sputtering method using a Cr ₉₀ Ru ₁₀ target. Next, the Cr target was discharged by DC magnetron sputtering in an N ₂ atmosphere diluted with Ar (N ₂ gas concentration: 20 vol%, gas pressure: 1 Pa) to form a CrN film with a thickness of 10 nm as an underlayer. Got the body. It was confirmed by X-ray diffraction using PW3040 / 60 manufactured by Philips that the underlayer had a NaCl-type crystal structure.

  Next, after heating the laminated body to 450 ° C., an oxygen mixed gas diluted with Ar (oxygen gas concentration 10 volume%, gas pressure 0.013 Pa) was used, and the oxygen gas exposure amount on the surface of the underlayer was 60 Langmuir. Oxygen exposure was performed until the result was obtained to obtain a laminate after exposure to oxygen.

The laminated body after the oxygen exposure is quickly transferred into the sputtering apparatus, and a FePt-C film is formed at 5 nm as a magnetic recording layer by a DC sputtering method using a (Fe ₅₀ Pt ₅₀ ) -20 volume% C alloy target, The substrate was held in vacuum until the substrate temperature dropped to near room temperature. Finally, a diamond-like carbon (DLC) film was formed at 2.5 nm as a protective layer on the magnetic recording layer by CVD to obtain a magnetic recording medium.

(Example 2)
A magnetic recording medium of Example 2 was obtained under the same conditions as Example 1 except that the surface of the underlayer was exposed to oxygen with 100 Langmuir instead of 60 Langmuir.

(Example 3)
A magnetic recording medium of Example 3 was obtained under the same conditions as Example 1 except that the surface of the underlayer was exposed with 200 Langmuir instead of 60 Langmuir.

(Example 4)
A magnetic recording medium of Example 4 was obtained under the same conditions as in Example 1 except that the surface of the underlayer was exposed with 500 Langmuir instead of 60 Langmuir.

(Example 5)
A magnetic recording medium of Example 5 was obtained under the same conditions as in Example 1 except that the surface of the underlayer was exposed to 1,000 Langmuir instead of 60 Langmuir.

(Example 6)
A magnetic recording medium of Example 6 was obtained under the same conditions as in Example 1 except that the surface of the underlayer was exposed with 2,000 Langmuir instead of 60 Langmuir.

(Comparative Example 1)
A magnetic recording medium of Comparative Example 1 was obtained under the same conditions as in Example 1 except that the surface of the underlayer was not exposed to oxygen.

(Comparative Example 2)
A comparative example under the same conditions as in Example 1 except that a CrN film was formed at 10 nm as the underlayer and the surface of the underlayer was exposed to oxygen with an oxygen mixed gas instead of forming an MgO film at 10 nm as the underlayer. 2 magnetic recording media were obtained.

<Evaluation items>
(Smoothness of magnetic recording media)
For each of the magnetic recording media of Examples 1 to 6 and Comparative Examples 1 and 2, the surface roughness Ra of the magnetic recording medium was measured with a 1 × 1 μm field of view using an atomic force microscope (Nanoscope V manufactured by Beco). It was measured. A probe made of Si was used. The results are shown in Table 1.

  It was found that all of the magnetic recording media of Examples 1 to 6 in which the CrN film was formed as the underlayer had a surface roughness of 0.6 nm and a very smooth surface.

  On the other hand, the magnetic recording medium of Comparative Example 2 in which the MgO film was formed had a surface roughness of 1.0 nm, and was very inferior in smoothness compared to the magnetic recording medium of the present invention. As a result, the magnetic recording medium of Comparative Example 2 has a high contact risk between the magnetic head and the medium surface when the magnetic head is flying, and lacks reliability.

(Magnetic properties of magnetic recording media)
As an item for evaluating the magnetic characteristics of the magnetic recording medium, the coercive force Hc and the inclination α of the magnetization curve were adopted from the viewpoint of magnetic grain separability.

  About each magnetic recording medium of Examples 1-6 and Comparative Examples 1-2, the coercive force Hc of the magnetic recording medium was measured with a maximum applied magnetic field of 20 kOe using a vibrating sample magnetometer (manufactured by Tamagawa Kogyo Co., Ltd.). The coercive force Hc is calculated by adding, on the + magnetic field and -magnetic field sides, a magnetic field in which a function obtained by linearly approximating two points before and after the magnetization curve crosses the X axis (zero magnetization) (total of four points) crosses the X axis. Obtained by averaging. In addition, the inclination α of the magnetization curve was obtained by multiplying the inclination of the approximate function by 4π, which was also calculated on the + magnetic field side and the − magnetic field side and added and averaged. The results are shown in Table 2. The magnetization characteristics of the magnetic recording medium are better as the value of the coercive force Hc is larger and the inclination α of the magnetization curve is smaller.

  The magnetic recording media of Examples 1 to 6 in which the surface of the underlayer was exposed to oxygen had a higher coercive force Hc and an equal or smaller slope α of the magnetization curve than Comparative Example 1 in which oxygen exposure was not performed. From this, it was found that the magnetic characteristics of the magnetic recording medium are more excellent.

  The reason why the magnetic properties are improved when the surface of the underlayer is exposed to oxygen is that the exposed oxygen is adsorbed on the surface of the underlayer and the adsorbed oxygen is used as a nucleus to grow FePt particles constituting the magnetic recording layer, or This is probably because the growth of the grain boundary C layer occurs.

  Further, the magnetic recording media of Examples 1 to 4 in which the oxygen gas exposure amount on the surface of the underlayer is 60 to 500 Langmuir are compared with those in Examples 5 and 6 in which the exposure amount is 1,000 Langmuir or more. Since the value of Hc is larger and the slope α of the magnetization curve is smaller, it can be said that the magnetization characteristics are more excellent. In particular, in the magnetic recording media of Examples 2 to 4 in which the oxygen gas exposure amount to the surface of the underlayer is 100 to 500 Langmuir, as in Comparative Example 2 in which the MgO film is formed as the underlayer, extremely excellent magnetization characteristics are obtained. Had.

  When the oxygen exposure amount on the surface of the underlayer is 1,000 Langmuir or more, the magnetization characteristics tend to decrease. FePt or C constituting the magnetic recording layer is trapped at a large number of locations on the surface of the underlayer. This is considered to be caused by insufficient separation of the FePt phase and the C phase because atomic diffusion (migration) on the surface of the underlayer is inhibited.

  As described above, according to the method of the present invention, it has been clarified that a magnetic recording medium excellent in both surface flatness and magnetic characteristics can be manufactured.

DESCRIPTION OF SYMBOLS 100 Magnetic recording medium 102 Nonmagnetic base | substrate 104 Underlayer 105 Underlayer exposed to oxygen 106 Magnetic recording layer

Claims (3)

Forming an underlayer on the nonmagnetic substrate;
Exposing the surface of the underlayer to oxygen;
Forming a magnetic recording layer on the surface of the underlayer exposed to oxygen;
Including
The underlayer includes CrN having a NaCl-type crystal structure;
A method for manufacturing a magnetic recording medium, wherein the magnetic recording layer is made of an ordered alloy.   2. The method of manufacturing a magnetic recording medium according to claim 1, wherein, in the step of exposing the surface of the underlayer to oxygen, an oxygen gas exposure amount is 60 to 500 Langmuir.   A magnetic recording medium manufactured by the method according to claim 1.

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