JP2008097824A - Vertical magnetic recording medium and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize high thermal stability, noise reduction and cost reduction relating to a vertical magnetic recording medium and a method for manufacturing the same. <P>SOLUTION: A soft magnetic lining layer 2, a base layer 3, a non-magnetic intermediate layer 4, a non-magnetic intermediate layer 4, a magnetic recording layer 5, a protective film 6, and a liquid lubricating layer 7 are successively formed on a non-magnetic substrate 1. The base layer 3 is deposited by using a permalloy-base material, and the non-magnetic intermediate layer 4 is formed by using Ru or an RU-based alloy material. The magnetic recording layer 5 is deposited by using a granular material, formed by adding B<SB>4</SB>C to a magnetic material as a raw material, and at this time, the deposition is performed by maintaining the temperature of the non-magnetic substrate 1 at a normal temperature of substantially the room temperature. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a perpendicular magnetic recording medium mounted on various magnetic recording apparatuses and a manufacturing method thereof.

As a technique for realizing a high density magnetic recording, a perpendicular magnetic recording system is drawing attention in place of the conventional longitudinal magnetic recording system.
Perpendicular magnetic recording media are mainly used for magnetic recording layers of hard magnetic materials, an underlayer for orienting the magnetic recording layer in a desired direction, a protective film for protecting the surface of the magnetic recording layer, and recording on this recording layer. It is composed of a backing layer of a soft magnetic material that plays a role of concentrating the magnetic flux generated by the magnetic head used.
As magnetic recording layer materials for perpendicular media, alloy materials such as CoCrPt and CoCrTa have been mainly used so far. In these alloy materials, Cr, which is a nonmagnetic material, segregates at the crystal grain boundaries, so that individual crystal grains are magnetically separated, and the characteristics necessary for a magnetic recording medium such as high coercive force (Hc) are exhibited. . Such segregation of Cr to the crystal grain boundary has been promoted in the in-plane medium by devising a film forming process such as heating or applying a substrate bias. However, in the case of a vertical medium, the amount of Cr segregation is small even when heating or applying a substrate bias is applied as in the case of the in-plane medium, and this causes a problem that the medium noise becomes high.
As a method for solving this problem, a granular magnetic film in which a nonmagnetic material such as an oxide such as SiO ₂ , Al ₂ O ₃ , Cr ₂ O ₃ or a nitride such as SiN or AlN is added to an alloy material such as CoPt or CoCrPt. Has been proposed (Patent Documents 1 to 3 etc.). For example, in a CoPt—SiO ₂ granular film, the CoPt crystal grains are segregated so as to surround the SiO ₂ , whereby the individual CoPt crystal grains are magnetically separated. As described above, the granular film is characterized in that it does not use phase separation (magnetic phase separation) of the alloy material but adds an amorphous material that is not easily dissolved in the alloy material, such as oxide or nitride.
JP 2001-291230 A Japanese Patent Laid-Open No. 08-083418 International Publication No. 2002/039433

However, it is difficult to completely separate magnetic materials such as CoPt and CoCrPt and nonmagnetic matrix materials such as SiO ₂ and AlN from granular materials using oxide or nitride as a matrix. It is known to mix in magnetic materials. Mixing the matrix material with the magnetic material not only causes deterioration in crystallinity and orientation of the magnetic recording layer, but also causes deterioration in thermal stability due to a decrease in uniaxial anisotropy. Although there are attempts to improve magnetic properties and uniaxial anisotropy by heat treatment, heat treatment that requires a long time is not suitable for mass production, so it is difficult to apply when considering practical application.
In addition, materials such as oxides and nitrides have low conductivity, and even when mixed with alloy materials such as CoPt and CoCrPt, high conductivity cannot be obtained. For this reason, when the granular film is formed by sputtering, it is necessary to use RF sputtering. However, the RF sputtering method is higher in apparatus cost and running cost than the DC sputtering method, and it is desirable to form a film by DC sputtering in consideration of mass production.
Non-oxide or non-nitride granular magnetic films that can be formed by DC sputtering include CoC (Summary of the 21st Annual Conference of the Magnetic Society of Japan, 23 (1997) and CoPtC (IEEE Trans.Mag., 34 , 4). , 1627 (1998)), but the coercive force [Hc] is 80 [kA / m] or less for CoC and about 160 [kA / m] for CoPtC, and sufficient magnetic properties are not obtained. .

  Accordingly, an object of the present invention is to provide a perpendicular magnetic recording medium and a method for manufacturing the same that can solve the above-described problems.

In a granular magnetic film, in order for the nonmagnetic matrix material and the magnetic material to properly phase-separate and obtain sufficient magnetic properties and thermal stability, the nonmagnetic matrix material can form a solid solution or form a compound with the magnetic material. However, it is necessary to precipitate in the grain boundary in an amorphous state. When mass production is considered, it is desirable that the film can be formed by a DC sputtering method from the viewpoint of the stability and cost of the apparatus. However, in order to obtain such a granular magnetic layer material, a nonmagnetic additive can be used. High conductivity is required.
As means for satisfying the above-described conditions and solving the conventional problems, the present inventors have repeatedly studied and formed a film by DC sputtering by using a granular film containing B ₄ C as a nonmagnetic material for the magnetic recording layer. It was found that high magnetic properties and thermal stability can be obtained. It has also been found that when these granular films are used, the noise is lower than that of conventional magnetic recording layers such as CoCrPt and CoCrTa.
In order to achieve the above object based on the above consideration and knowledge, the present inventors have provided a soft magnetic backing layer, an underlayer, an intermediate layer, a magnetic recording layer, a protective film, and a liquid lubricating layer on a nonmagnetic substrate. The perpendicular magnetic recording medium was sequentially stacked, and the magnetic recording layer was a perpendicular magnetic recording medium having a granular structure based on B ₄ C.

Here, the granular structure of the magnetic recording layer may be formed by segregating B ₄ C at a grain boundary.
The underlayer may be made of a permalloy material, and the intermediate layer may be made of Ru or a Ru-based alloy.
In order to achieve the above object, the inventors of the present invention provide a method for manufacturing a perpendicular magnetic recording medium in which a soft magnetic backing layer, an underlayer, an intermediate layer, and a magnetic recording layer are sequentially formed on a nonmagnetic substrate. Then, a perpendicular magnetic recording medium manufacturing method was carried out, in which the magnetic recording layer was formed using a granular material obtained by adding B ₄ C to a magnetic material as a raw material.
Here, the underlayer is formed using a permalloy-based material, the intermediate layer is formed using a Ru or Ru-based alloy material, and the temperature of the nonmagnetic substrate at the time of forming the magnetic recording layer is set to room temperature. The magnetic recording layer can be formed at an ordinary temperature.

As described above, according to the perpendicular magnetic recording medium and the method for manufacturing the same according to the present invention, a granular magnetic recording layer is formed by using a material in which B ₄ C is added as a nonmagnetic additive to a magnetic material. Compared with CoCrPt medium and CoCrPt-SiO ₂ granular medium, high thermal stability can be obtained. In addition, noise can be reduced as compared with conventional alloy materials such as CoCrPt, which leads to improvement of the characteristics of the medium. Further, since the granular magnetic recording layer in the perpendicular magnetic recording medium according to the present invention can be formed by DC sputtering, a conventional granular material such as CoPt—SiO ₂ that cannot be formed only by RF sputtering is used. Compared with this, it is possible to manufacture at a lower cost and to reduce the cost of the medium.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic sectional view of a perpendicular magnetic recording medium according to the present invention.
The perpendicular magnetic recording medium according to the present invention includes a nonmagnetic substrate 1, a soft magnetic backing layer 2, an underlayer 3, a nonmagnetic intermediate layer 4, a magnetic recording layer 5, and a protective layer that are sequentially provided on the nonmagnetic substrate 1. It has a film 6 and a liquid lubricating layer 7.
The nonmagnetic substrate 1 may be various substrates having a smooth surface. For example, an Al alloy plated with NiP, tempered glass, crystallized glass or the like used for a magnetic recording medium can be used. As the soft magnetic backing layer 2, crystalline FeTaC, Sendust (FeSiAl) alloy, etc., or amorphous Co alloy such as CoZrNb, CoTaZr, or the like can be used. The optimum value of the film thickness of the soft magnetic underlayer 2 varies depending on the structure and characteristics of the magnetic head used for recording, but is preferably about 10 nm to 500 nm in view of productivity.
The underlayer 3 is made of a material having an effect of orienting the c-axis of the magnetic recording layer 5 perpendicularly to the film surface. NiFe, NiFeCr, NiFeMo, NiFeNb, NiFeNbMo, nonmagnetic, which are soft magnetic permalloy materials. NiFeCr, Ti, TiCr, Pd, or the like can be used.

The nonmagnetic intermediate layer 4 is made of a material that is nonmagnetic and has an effect of orienting the c-axis of the magnetic recording layer perpendicularly to the film surface, and also has an effect of reducing the initial layer of the magnetic recording layer. Ru-based alloys such as RuC and RuW can be used.
For the magnetic recording layer 5, a granular material obtained by adding B ₄ C to a magnetic material is used. At this time, Co, CoPt, CoCrPt, FePt, or SmCo can be used as the magnetic material. However, the magnetic recording layer 5 may be formed while the temperature of the nonmagnetic substrate 1 when forming the magnetic recording layer 5 is kept at about room temperature, and phase separation can be realized without heat treatment. it can.
Between the soft magnetic backing layer 2 and the nonmagnetic substrate 1, the underlayer and the antiferromagnetic pin layer (both shown in the figure) are used to reduce noise by pinning the magnetization of the soft magnetic backing layer 2 radially outward. (Not shown) can be used.
FIG. 2 is a schematic cross-sectional view of a vertical medium having an antiferromagnetic pinned layer according to the present invention.
For the underlayer 8 for the antiferromagnetic pin layer, a permalloy material such as NiFe, NiFeCr, NiFeB or the like can be used. As the antiferromagnetic pin layer 9, an ordered alloy material such as PtMn or NiMn, FeMn, An irregular alloy material such as IrMn or an oxide material such as NiO can be used. The film thickness of the antiferromagnetic pinned layer 9 varies depending on the combination of the material used and the soft magnetic layer, but is preferably about 1 nm to 30 nm in view of productivity.

For example, a thin film mainly composed of carbon is used as the protective film 6. In addition, various thin film materials generally used as a protective film of a magnetic recording medium may be used.
For the liquid lubricant layer 7, for example, a perfluoropolyether lubricant can be used. In addition, various lubricating materials that are generally used as liquid lubricating layer materials for magnetic recording media may be used.
Each layer laminated on the nonmagnetic substrate 1 can be formed by various film forming techniques usually used in the field of magnetic recording media. For example, a DC magnetron sputtering method, an RF magnetron sputtering method, or a vacuum deposition method can be used to form each layer except the liquid lubricant layer. In addition, for example, a dipping method or a spin coating method can be used for forming the liquid lubricating layer. However, it is not limited to these.

Hereinafter, the perpendicular magnetic recording medium of the present invention will be described in detail with reference to the following examples. However, the present invention is not limited thereto, and various modifications can be made without departing from the scope of the present invention. Needless to say.
[Example 1]
In this example, a nonmagnetic substrate and a soft magnetic CoZrNb backing layer, a soft magnetic NiFeNbB underlayer, a Ru intermediate layer, a CoCrPt-B ₄ C granular magnetic recording layer, a protective film, and a liquid lubricating layer sequentially provided thereon are formed. The present invention relates to a dual-layer perpendicular magnetic recording medium having the same.
A chemically tempered glass substrate (for example, N-10 glass substrate manufactured by HOYA) having a smooth surface is used as the nonmagnetic substrate, and this is introduced into a sputtering apparatus after cleaning, and a CoZrNb amorphous soft magnetic backing layer using a Co8Zr5Nb target. Was deposited to 200 nm. Next, as a base layer, a NiFeNbB base layer having a thickness of 5 nm was formed using a Ni12Fe3Nb3B target, which is a permalloy-based soft magnetic material.
Subsequently, using a Ru target, a 20 nm thick Ru intermediate layer was formed under an Ar gas pressure of 4.0 Pa. Next, a CoCrPt—B ₄ C magnetic recording layer was formed to a thickness of 20 nm using a 92 (Co8Cr15Pt) -8B ₄ C target in which 8 at% of B ₄ C was mixed in a Co10Cr15Pt alloy.

Finally, a protective film 10 nm made of carbon was formed using a carbon target, and then taken out from the vacuum apparatus. All of these film formations except for the Ru intermediate layer film formation were performed under an Ar gas pressure of 0.67 Pa, and all film formations were performed by the DC magnetron sputtering method. Thereafter, a liquid lubricating layer 2 nm made of perfluoropolyether was formed by a dip method to obtain a perpendicular magnetic recording medium.
[Comparative Example 1]
Perpendicular magnetic recording medium using the same method as in Example 1 except that Co20Cr10Pt was used for the magnetic recording layer and that the substrate surface temperature was 280 ° C. using a lamp heater before the magnetic recording layer was formed. Was made.
The coercive force Hc and squareness ratio S of the completed perpendicular magnetic recording medium are determined by the rocking curve method using the magnetic Kerr effect magnetometer and the orientation dispersion (Δθ ₅₀ ) using an X-ray diffractometer, and the crystal grain size and grain boundary width are determined. Evaluation was performed with a transmission electron microscope (TEM). The measurement results are shown in Table 1.
When the magnetic properties are compared, in Example 1, Hc higher than that in Comparative Example 1 (medium manufactured under conventional conditions) is obtained. As can be seen from the difference in grain boundary width evaluated by TEM, This is thought to be because the separation of crystal grains progressed and the interparticle interaction decreased. Further, the squareness ratio S is about 0.9 in Comparative Example 1, whereas it is almost 1 in Example 1. A high squareness ratio means that the signal degradation is small, that is, the thermal stability is high. Therefore, it is understood that the CoCrPt-B ₄ C granular medium is superior in thermal stability compared to the CoCrPt medium. It was.

There is no difference in the orientation dispersion Δ ₅₀ between the granular magnetic film (Example 1) and the CoCrPt magnetic film (Comparative Example 1), and it was confirmed that no deterioration of the orientation occurred even though the nonmagnetic matrix material was mixed. It was done. The difference between the granular medium and the CoCrPt medium is particularly large in the crystal grain size and the grain boundary width. In Example 1 and Comparative Example 1, although the same underlayer and intermediate layer are used, the crystal grain size of the magnetic recording layer is greatly miniaturized. The fact that the crystal grain size is small means that the jaggedness of bit transition is reduced when recording by the head, and is an important index for reducing the noise of the medium.
In addition, the grain boundary width of CoCrPt in Comparative Example 1 is 1 nm, whereas in CoCrPt-B ₄ C (Example 1), the grain boundary width is about twice as large as 2.2 nm. The broadening of the grain boundary width is effective for reducing the magnetic interaction between crystal grains, and the reduction of the magnetic interaction leads to a reduction in noise.
FIG. 3 shows the results of measuring the noise of the media of Example 1 and Comparative Example 1 using a spin stand tester. CoCrPt-B ₄ C (Example 1) is significantly noisy compared to CoCrPt (Comparative Example 1), as expected because the crystal grain size has been refined and the grain boundary width has increased. Was able to be lowered.

As described above, by using CoCrPt—B ₄ C as the magnetic recording layer, a medium having high thermal stability and magnetic characteristics could be obtained. In addition, with the refinement of crystal grains and the increase in grain boundary width, a significant reduction in noise was achieved compared to conventional CoCrPt media.

［実施例２］
本実施例は、非磁性基体と、その上に順次設けられるＴａシード層、非磁性ＮｉＦｅＣｒ下地層、Ｒｕ中間層、ＣｏＣｒＰｔ−Ｂ₄Ｃグラニュラー磁気記録層、保護膜、液体潤滑層とを有する単層垂直磁気記録媒体に関する。
非磁性基体として表面が平滑な化学強化ガラス基体（例えばＨＯＹＡ社製Ｎ−１０ガラス基体）を用い、これを洗浄後スパッタ装置内に導入し、Ｔａターゲットを用いてＴａシード層を５ｎｍ成膜した。次に下地層として、パーマロイ系の非磁性材料であるＮｉ１２Ｆｅ２７Ｃｒターゲットを用いてＮｉＦｅＣｒ下地層を１０ｎｍ成膜した。
引き続いてＲｕターゲットを用いて、Ａｒガス圧４．０Ｐａ下でＲｕ中間層を２０ｎｍ成膜した。次に、Ｃｏ８Ｃｒ１２Ｐｔ合金中にＢ₄Ｃを８ａｔ％混合した、９２（Ｃｏ８Ｃｒ１２Ｐｔ）−８Ｂ₄Ｃターゲットを用いて、ＣｏＣｒＰｔ−Ｂ₄Ｃ磁気記録層を２０ｎｍ成膜した。
最後にカーボンターゲットを用いてカーボンからなる保護膜１０ｎｍを成膜後、真空装置から取り出した。Ｒｕ中間層の成膜を除くこれらの成膜はすべてＡｒガス圧０．６７Ｐａ下で行い、全ての成膜はＤＣマグネトロンスパッタリング法により行なった。その後、パーフルオロポリエーテルからなる液体潤滑層２ｎｍをディップ法により形成し、単層垂直磁気記録媒体とした。

[Example 2]
In this example, a single layer having a nonmagnetic substrate, a Ta seed layer, a nonmagnetic NiFeCr underlayer, a Ru intermediate layer, a CoCrPt-B ₄ C granular magnetic recording layer, a protective film, and a liquid lubricating layer sequentially provided thereon. The present invention relates to a layer perpendicular magnetic recording medium.
A chemically strengthened glass substrate having a smooth surface (for example, N-10 glass substrate manufactured by HOYA) was used as the nonmagnetic substrate, and this was introduced into the sputtering apparatus after cleaning, and a Ta seed layer was formed to a thickness of 5 nm using a Ta target. . Next, a NiFeCr underlayer was formed to a thickness of 10 nm using a Ni12Fe27Cr target, which is a permalloy-based nonmagnetic material.
Subsequently, using a Ru target, a 20 nm thick Ru intermediate layer was formed under an Ar gas pressure of 4.0 Pa. Next, a CoCrPt—B ₄ C magnetic recording layer was formed to a thickness of 20 nm using a 92 (Co8Cr12Pt) -8B ₄ C target in which 8 at% of B ₄ C was mixed in a Co8Cr12Pt alloy.
Finally, a protective film 10 nm made of carbon was formed using a carbon target, and then taken out from the vacuum apparatus. All of these film formations except for the Ru intermediate layer film formation were performed under an Ar gas pressure of 0.67 Pa, and all film formations were performed by the DC magnetron sputtering method. Thereafter, a liquid lubricating layer 2 nm made of perfluoropolyether was formed by a dipping method to obtain a single layer perpendicular magnetic recording medium.

[Example 3]
A single-layer perpendicular magnetic recording medium was produced in the same manner as in Example 2 except that the B ₄ C concentration in the magnetic recording layer was 12 at% and the magnetic recording layer composition was 88 (Co8Cr12Pt) -12B ₄ C.
[Example 4]
A single-layer perpendicular magnetic recording medium was produced in the same manner as in Example 2 except that the B ₄ C concentration in the magnetic recording layer was 16 at% and the magnetic recording layer composition was 84 (Co8Cr12Pt) -16B ₄ C.
[Example 5]
A single-layer perpendicular magnetic recording medium was produced in the same manner as in Example 2 except that the magnetic recording composition was 84 (Co8Cr16Pt) -16B ₄ C in which B ₄ C concentration was mixed at 16 at% in Co 8 Cr 16 Pt.
[Comparative Example 2]
A single-layer perpendicular magnetic recording medium was fabricated in the same manner as in Example 2 except that 92 (Co8Cr12Pt) -8SiO ₂ by RF sputtering was used for the magnetic recording layer.

The coercive force Hc and squareness ratio S of the completed perpendicular magnetic recording medium were evaluated by a sample vibration magnetometer (VSM), and the uniaxial anisotropy constant Ku was evaluated by a magnetic torque meter. The measurement results are shown in Table 2. As for Hc, although it is lower than Comparative Example 2 in Examples 2 to 4, it is higher than that of Comparative Example 2 in Example 5, and is higher than the conventional SiO ₂ granular medium due to the devising of the composition. It can be seen that Hc can be obtained.
A particularly large difference is the uniaxial anisotropy constant Ku. Ku greatly exceeds the comparative example in all the examples shown in Table 2. Particularly, in Example 5, a large Ku of approximately twice that of Comparative Example 2 is obtained. A large Ku indicates that the thermal stability is excellent, and the CoCrPt—B ₄ C media of Examples 2 to 5 have superior thermal stability as compared with the conventional CoCrPt—SiO ₂ media. I understand.
Also, the squareness ratio is about 0.9 in Comparative Example 2, whereas it is almost 1 in the error range in Examples 2 to 5 (lower than 1 due to measurement noise). Although it is clearly 1 on the magnetization curve). The reason why the squareness ratio is high in the CoCrPt—B ₄ C medium is thought to be due to the above-described improvement in Ku.

It is a cross-sectional schematic diagram which shows one Embodiment of the perpendicular | vertical double layer medium based on this invention. It is a cross-sectional schematic diagram which shows another embodiment of the perpendicular | vertical double layer medium based on this invention. It is a characteristic view which shows the linear recording density dependence of the normalized noise which concerns on Example 1 and the comparative example 1 of the perpendicular | vertical double layer medium based on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nonmagnetic base | substrate 2 Soft magnetic backing layer 3 Soft magnetic underlayer 4 Nonmagnetic intermediate | middle layer 5 Magnetic recording layer 6 Protective film 7 Liquid lubricating layer

Claims (6)

On a non-magnetic substrate, a soft magnetic underlayer, an underlayer, an intermediate layer made of Ru or Ru-based alloy, a magnetic recording layer using any of Co, CoPt, CoCrPt, FePt, and SmCo as a magnetic material, a protective film, A perpendicular magnetic recording medium in which liquid lubricant layers are sequentially laminated, wherein the magnetic recording layer has a granular structure based on B ₄ C. 2. The perpendicular magnetic recording medium according to claim 1, wherein the granular structure of the magnetic recording layer is formed by segregating B ₄ C at a grain boundary.   3. The perpendicular magnetic recording medium according to claim 1, wherein the underlayer is made of a permalloy material. On the nonmagnetic substrate, a soft magnetic backing layer, an underlayer, an intermediate layer made of Ru or a Ru-based alloy, and a magnetic recording layer using any one of Co, CoPt, CoCrPt, FePt, and SmCo as a magnetic material are sequentially formed. A method of manufacturing a perpendicular magnetic recording medium, wherein the magnetic recording layer is formed using a granular material obtained by adding B ₄ C to a magnetic material as a raw material.   5. The method of manufacturing a perpendicular magnetic recording medium according to claim 4, wherein the magnetic recording layer is formed by setting the temperature of the nonmagnetic substrate at the time of forming the magnetic recording layer to a room temperature of about room temperature. 6. The method for manufacturing a perpendicular magnetic recording medium according to claim 4, wherein the magnetic recording layer is formed by a DC sputtering method.

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