JP4333531B2 - Magnetic recording medium - Google Patents

Description

  The present invention relates to a magnetic recording medium mounted on a fixed magnetic recording device (HDD) and a manufacturing method thereof. More specifically, the present invention relates to an anisotropic magnetic recording medium using a glass-based material substrate.

In so-called longitudinal magnetic recording media in which magnetization is recorded in parallel in the substrate surface, it is common to use the easy magnetization axis of the magnetic layer oriented in the circumferential direction for recording. A magnetic recording medium in which the residual magnetization (Mrc) in the circumferential direction and the residual magnetization (Mrr) in the radial direction are different is called an anisotropic magnetic recording medium. Generally, the larger the ratio Mrc / Mrr is, the more magnetic the medium becomes. The performance of the recording medium is improved. Hereinafter, Mrc / Mrr is expressed as OR-Mrt.
In a magnetic recording medium using an aluminum-based material as a substrate, anisotropy is obtained by forming circumferential grooves called textures on the substrate surface. In general, NiP plating is performed on an aluminum substrate, and texture processing is performed on the surface thereof to form a circumferential groove, and the difference between the residual magnetization in the circumferential direction and the radial direction of the magnetic layer by the groove. Is generated. Texture processing also has a role of preventing the magnetic recording medium and the magnetic head from coming into contact with each other and wearing when the magnetic head floats and seeks on the magnetic recording medium.

On the other hand, a magnetic recording medium using a substrate made of a conventional glass material has a high hardness of the substrate material itself, a small thermal expansion, and can obtain a difference in residual magnetization between the circumferential direction and the radial direction even after texturing. Therefore, so-called isotropic magnetic recording media are common.
In recent years, the density of magnetic recording media has increased, and the bit size, which is the minimum unit of data written to the magnetic recording media, has become smaller. An isotropic medium using a glass-based substrate has a characteristic that if the bit size is reduced, the resolution is lower and the signal-to-noise ratio (SNR) is worse than an anisotropic magnetic recording medium such as an aluminum-based substrate. It is becoming. In order to obtain characteristics equivalent to those of an anisotropic magnetic recording medium with an isotropic magnetic recording medium, it is necessary to increase the product (Mr · t) of the residual magnetization in the circumferential direction and the film thickness. This is because as a result of increasing the thickness, noise due to the magnetic layer increases. For this reason, in the magnetic recording medium using a glass substrate, various ideas for improving the orientation of the magnetic layer have been proposed. For example, it has been proposed to improve the in-plane orientation of the easy axis of the magnetic layer by oxidizing the surface of the underlayer formed on the substrate (see, for example, Patent Document 1). Although this method is effective for a specific underlayer material, it results in deterioration of properties in other materials. In addition, there has been proposed a method of increasing the coercive force in the circumferential direction by inclining crystal grains constituting the magnetic layer with respect to the substrate surface and directing them in the circumferential direction (see, for example, Patent Document 2). . In this method, a special film forming apparatus is required, and the use efficiency of raw materials at the time of sputtering film formation is reduced. In any of the methods proposed so far, the present situation is that sufficient performance is not obtained.
Japanese Patent Laid-Open No. 10-143865 JP 2002-260208 A

  The present invention has been made in view of the above problems, and provides a magnetic recording medium having a high anisotropy and excellent electromagnetic characteristics in a magnetic recording medium using a glass substrate. With the goal.

The present invention provides a magnetic recording medium having a glass substrate, a seed layer, and a magnetic layer, wherein the glass substrate is textured, and the seed layer is a first seed layer made of a CoTi alloy and a second seed made of a NiNb alloy. A seed layer is laminated.
The texture processing is preferably 25 or more and 60 or less substantially concentric grooves per 1 μm square, and the depth of the substantially concentric grooves is preferably 3 nm or more and 5 nm or less.
The CoTi alloy preferably contains 30 atomic% or more and 50 atomic% or less of Ti.
Further, the NiNb alloy preferably contains Nb at 30 atomic% or more and 50 atomic% or less.

  By configuring the magnetic recording medium as described above, even in a magnetic recording medium using a glass substrate, it can be an anisotropic magnetic recording medium having high anisotropy, and has excellent magnetic characteristics and electromagnetic conversion characteristics. Can be realized. Furthermore, even in a glass substrate having an insulating property, it is possible to use a film forming method in which a bias is applied in the film forming process of each layer.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining a configuration example of a magnetic recording medium of the present invention. In the magnetic recording medium, a seed layer 2, an underlayer 3, a magnetic layer 4 and a protective layer 5 are sequentially laminated on a glass substrate 1. In addition, a lubricating layer 6 is formed on the protective layer 5. The seed layer 2 is configured by laminating a first seed layer 21 and a second seed layer 22.
The material used for the glass substrate 1 can be a normal glass-based material used for magnetic recording media, such as chemically strengthened glass and crystallized glass. A disk shape having a circular hole in the center is preferable, and the diameter of the circular hole in the center, the outer diameter of the substrate, the thickness of the substrate, and the like are appropriately set according to the desired application.

  The glass substrate 1 is textured. Prior to texture processing, it is preferable to polish the glass substrate by polishing it by a conventional method. Ra (center line average roughness) after polishing is preferably 0.2 to 0.5 nm. Texture processing is applied to the substrate whose surface is smoothed to form substantially concentric grooves in the circumferential direction. As the texture processing method, the free abrasive grain method is preferable. Specifically, a work cloth (urethane, polyester, nylon, etc.) that does not contain abrasive grains is pressed against the substrate surface, and polishing slurry (diamond, aluminum oxide, cerium oxide, colloidal silica, silicon carbide, etc.) is applied to the work cloth. ) Is included while rotating the substrate. It is preferable that 25 to 60 concentric grooves in the circumferential direction are formed per 1 μm square on the textured substrate. If the number is less than 25, the desired remanent magnetization anisotropy cannot be obtained. It is preferable that the number of grooves is large, but if it exceeds 60, it becomes difficult to obtain a desired groove depth.

The depth of the groove formed in the substrate is preferably 3 to 5 nm. If the thickness is less than 3 nm, the desired remanent magnetization anisotropy cannot be obtained, and if the depth of the groove is deeper than 5 nm, the error of the magnetic recording medium increases to deteriorate the signal quality and become unusable.
The glass substrate textured in this way is thoroughly washed, and after removing foreign substances on the surface, film formation is performed.
The seed layer 2 is formed by laminating a first seed layer 21 and a second seed layer 22, and obtains desired characteristics of the magnetic recording medium by controlling the crystal orientation and crystal grain size of the layer formed thereon. It is a layer provided for this purpose. By using a CoTi alloy composed of Co and Ti as the first seed layer 21 and a NiNb alloy composed of Ni and Nb as the second seed layer 22, the circumferential residual magnetization is remarkably increased with respect to the radial residual magnetization. The OR-Mrt can be 1.5 or more. These two seed layers are preferably formed by sputtering. The first seed layer is preferably 10 to 20 nm thick, and the second seed layer is preferably 5 to 20 nm thick.

  Since it is preferable to apply a bias when forming each layer, a process for enabling application of a bias is performed after forming the first seed layer. Since the glass substrate is insulative, in order to apply a bias, an electrode for applying a bias (bias electrode) is brought into contact with the first seed layer, but the substrate holder for holding the substrate also serves as the bias electrode. Then, the bias can be applied by changing the holding position of the substrate after the first seed layer is formed. The holding position may be changed by a method of adding a position changing function to the substrate holder. Alternatively, after the first seed layer is formed, the substrate is taken out into the atmosphere and the position where the substrate is supported is changed. It is also possible to use a method of ensuring conductivity between the substrate holder and the substrate holder. By doing so, it is possible to apply a bias even in the subsequent deposition of each layer. When the magnetic recording medium in the process of film formation is taken out into the atmosphere, the characteristics of the magnetic recording medium are usually deteriorated. By using a CoTi alloy as the first seed layer and a NiNb alloy as the second seed layer, Even if the step of taking out into the atmosphere is provided, it is possible to produce a magnetic recording medium without causing deterioration of characteristics.

The CoTi alloy preferably contains 30 atomic% or more and 50 atomic% or less of Ti. When Ti is less than 30 atomic% and Ti exceeds 50 atomic%, OR-Mrt decreases. The NiNb alloy preferably contains 30 atomic% or more and 50 atomic% or less of Nb. When Nb is less than 30 atomic% and Nb exceeds 50 atomic%, OR-Mrt decreases.
The underlayer 3 is used to obtain a magnetic recording medium having desired characteristics by controlling the crystal orientation and crystal grain size of the magnetic layer formed thereon. As a material for the underlayer, Cr or CrMo-based alloy can be used. The underlayer is also preferably formed by sputtering, and the thickness is preferably 5 to 15 nm.
The underlayer 3 can have a multilayer structure of two or more layers. In this case, for example, if the first underlayer is Cr and the second underlayer is CrMo or the like, there is an effect of increasing OR-Mrt and further facilitating the epitaxial growth of the magnetic layer formed on the underlayer. The film thickness when the underlayer is a multilayer is preferably 15 nm or less.

The magnetic layer 4 is formed of a magnetic material mainly containing Co. For example, a CoCr alloy, a CoCrTa alloy, a CoCrPt alloy, a CoCrPtB alloy, a CoCrPtBCu alloy, or the like can be used. The film formation method of the magnetic layer is preferably a sputtering method, and the film thickness is preferably 10 to 25 nm.
Further, the magnetic layer 4 can be composed of two or more layers. For example, if the first magnetic layer is made of a CoCrTa alloy, the second magnetic layer is made of a CoCrPtB alloy, and the third magnetic layer is made of a CoCrPtBCu alloy, the recording density can be improved. When the magnetic layer is a multilayer, the film thickness of the entire magnetic layer is preferably 25 nm or less.
The protective layer 5 is formed to prevent layers below the magnetic layer from being destroyed by contact with the magnetic head. Therefore, it is preferable to use a material having high hardness, and C, CN (carbon nitride), DLC (diamond-like carbon), or the like can be used. The protective layer is formed by sputtering or CVD. The protective layer is preferably thinner in order to improve the characteristics of the magnetic recording medium, and preferably has a thickness of 2 to 5 nm.

In forming the underlayer 3, the magnetic layer 4, and the protective layer 5 described above, it is preferable to apply a DC or RF bias to the substrate.
The lubricating layer 6 is formed for the purpose of reducing friction when the magnetic recording medium and the magnetic head come into contact with each other, and a liquid lubricant such as perfluoropolyether used in a normal magnetic recording medium is used. Can do. The lubricating layer can be formed by a method such as spin coating or dip coating with a liquid lubricant, and the thickness is preferably 1 to 2 nm.

As the glass substrate 1, a chemically strengthened glass substrate (glass substrate manufactured by Asahi Glass Co., Ltd.) having a diameter of 21.6 mm and a plate thickness of 0.381 mm was used, and this was polished to a surface roughness Ra of 0.3 nm. Subsequently, using a non-woven fabric and diamond slurry, texture processing was performed by a floating abrasive grain method, and an average of 60 circumferentially substantially concentric grooves per 1 μm square was formed. The average depth of the grooves was 3 nm.
Subsequently, the glass substrate was thoroughly cleaned and then introduced into a film forming apparatus. First, a CoTi film as the first seed layer 21 was formed on a glass substrate by a DC magnetron sputtering method. Using a sputtering target of Co50Ti (where the number represents atomic%, Ti represents 50 atomic%, and the remainder represents Co. The same applies hereinafter), Ar gas as the sputtering gas, and the gas pressure to 1 Pa Thus, a first seed layer having a thickness of 17 nm was formed. Subsequently, a NiNb film as the second seed layer 22 was formed by a DC magnetron sputtering method. A Ni 50 Nb sputtering target was used, Ar gas was used as the sputtering gas, the gas pressure was 1 Pa, and a second seed layer having a thickness of 15 nm was formed. After the first seed layer is formed, the substrate is taken out into the atmosphere, and the substrate is once removed from the substrate holder. The position where the substrate is held is changed and attached to the substrate holder again to ensure conductivity between the substrate and the substrate holder. Thus, it was possible to apply a bias to the subsequent film formation. By making it possible to apply a bias, the CVD method can be used to significantly improve the characteristics of the magnetic recording medium and to form a protective film.

Thus, the substrate on which the seed layer 2 laminated in two layers is formed on an Ar gas (hereinafter referred to as Ar + 30 wt% O) to which 30 wt% O ₂ is added under a gas pressure of 1 Pa before forming the underlayer 3. Exposure to ₂ gases), and a step of adsorbing oxygen on the surface of NiNb as the second seed layer was performed. Next, the substrate was heated to 270 ° C. with a heater to form an underlayer 3. The underlayer 3 has a three-layer structure, and was formed in the order of a Cr film, a CrMoB film, and a CrMo film. Each film was formed by using a DC magnetron sputtering method using Ar gas as a sputtering gas and a gas pressure of 1 Pa. The Cr film was formed with a film thickness of 3 nm using a sputtering target made of Cr. The CrMoB film was formed with a thickness of 2 nm using a Cr15Mo7B target. The CrMo film was formed with a film thickness of 2 nm using a Cr30Mo target.
Subsequently, the magnetic layer 4 was formed. The magnetic layer 4 has a four-layer structure, and is formed in the order of a CoCrTa film, a Ru film, a CoCrPtB film, and a CoCrPtBCu film. Each film was formed by using a DC magnetron sputtering method using Ar gas as a sputtering gas and a gas pressure of 1 Pa. The CoCrTa film was formed to a thickness of 3 nm using a Co17Cr5Ta sputter target. The Ru film was formed with a film thickness of 0.8 nm using a Ru sputtering target. Next, the substrate was heated again to 270 ° C. with a heater, and then a CoCrPtB film was formed. Using a Co24Cr14Pt8B film target, the substrate was formed to a thickness of 12 nm while applying a DC bias of −300 V to the substrate. Subsequently, a CoCrPtBCu film was formed. Using a target of a Co13Cr11Pt10B4Cu film, the substrate was formed with a film thickness of 8 nm while applying a DC bias of −300 V to the substrate.

Subsequently, a protective layer 5 made of carbon was formed by an RF-CVD method. C ₂ H ₄ gas was introduced and an RF bias of −200 V was applied to the substrate to form a film with a thickness of 3 nm.
Subsequently, a magnetic recording medium was obtained by applying 1.6 nm of a lubricant made of perfluoropolyether to obtain Example 1.

A magnetic recording medium was produced in the same manner as in Example 1 except that Ar + 10 wt% N ₂ gas was used as the sputtering gas for forming the second seed layer, and Example 2 was obtained.

A magnetic recording medium was manufactured in the same manner as in Example 1 except that the thickness of the second seed layer was 10 nm, and Example 3 was obtained.
(Comparative Examples 1-3)
A magnetic recording medium was prepared in the same manner as in Example 1 except that the sputtering target for the first seed layer was Cr, the sputtering gas was Ar + 10 wt% N _2, and the sputtering target for the second seed layer was various materials shown in Table 1. It produced and it was set as Comparative Examples 1-3.
(Comparative Examples 4-6)
Examples except that the sputtering target of the first seed layer was Cr, the sputtering gas was Ar + 10 wt% N ₂ , the sputtering target of the second seed layer was various materials shown in Table 1, and the sputtering gas was Ar + 30 wt% N ₂ A magnetic recording medium was produced in the same manner as in Example 1, and Comparative Examples 4 to 6 were obtained.

  Table 1 shows OR-Mrt of Examples 1 to 3 and Comparative Examples 1 to 6.

第１シード層としてＣｏＴｉを用い、第２シード層としてＮｉＮｂを用いた場合、ガラス基板を用いてもＯＲ−Ｍｒｔが１．５以上と高い値が得られている。
表２に保磁力（Ｈｃｒ）、電磁変換特性として信号対雑音比（ＳＮＲ）を示す。ＳＮＲはスピンスタンドテスタを用いて３５０ｋＦＣＩ（ｋｉｌｏ ｆｌｕｘ ｃｈａｎｇｅ ｐｅｒ ｉｎｃｈ）にて測定を行った。
第１シード層としてＣｏＴｉを用い、第２シード層としてＮｉＮｂを用いてＯＲ−Ｍｒｔを１．５以上とすることにより、保磁力、ＳＮＲが大きく向上することが分かる。

When CoTi is used as the first seed layer and NiNb is used as the second seed layer, a high value of OR-Mrt of 1.5 or more is obtained even when a glass substrate is used.
Table 2 shows signal-to-noise ratio (SNR) as coercive force (Hcr) and electromagnetic conversion characteristics. SNR was measured at 350 kFCI (kilo flux change per inch) using a spin stand tester.
It can be seen that by using CoTi as the first seed layer and NiNb as the second seed layer and setting OR-Mrt to 1.5 or more, the coercive force and SNR are greatly improved.

FIG. 3 is a schematic cross-sectional view for explaining a configuration example of the magnetic recording medium of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Seed layer 21 1st seed layer 22 2nd seed layer 3 Underlayer 4 Magnetic layer 5 Protective layer 6 Lubrication layer

Claims (5)

In a magnetic recording medium having a glass substrate, a seed layer and a magnetic layer,
The glass substrate is textured,
The magnetic recording medium, wherein the seed layer includes a first seed layer made of a CoTi alloy and a second seed layer made of a NiNb alloy.   2. The magnetic recording medium according to claim 1, wherein the texturing is a substantially concentric groove of 25 to 60 per 1 μm square.   The magnetic recording medium according to claim 2, wherein a depth of the substantially concentric groove is 3 nm or more and 5 nm or less.   4. The magnetic recording medium according to claim 1, wherein the CoTi alloy contains 30 atomic% or more and 50 atomic% or less of Ti.   5. The magnetic recording medium according to claim 1, wherein the NiNb alloy contains 30 atomic% or more and 50 atomic% or less of Nb.

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