JP4944471B2 - Magnetic disk and manufacturing method thereof - Google Patents

Description

  The present invention relates to a magnetic disk mounted on a magnetic disk device such as a hard disk drive (hereinafter abbreviated as HDD) and a method for manufacturing the same.

  The magnetic disk is a magnetic recording medium mounted on a magnetic disk device such as an HDD. The HDD has at least a magnetic disk and a magnetic head, and information is recorded on and reproduced from the magnetic disk by the magnetic head.

  This type of magnetic disk is formed by forming layers such as an underlayer, a magnetic layer, a protective layer, and a lubricating layer in this order on a substrate.

  The underlayer is a layer formed to control the grain orientation of the magnetic layer, and has a function of controlling the easy magnetization direction of the magnetic layer in the in-plane direction of the disk or the normal direction of the disk. Have.

  The underlayer also has a function of controlling the grain size of the magnetic layer. The underlayer exhibits the effect of reducing the grain size of the magnetic layer and improving, for example, the signal noise intensity ratio (SN ratio) of the magnetic recording medium and the magnetostatic characteristics.

  As a technique regarding the underlayer, for example, a technique described in Patent Document 1 can be cited. In the technique described in Patent Document 1, it is preferable to use an underlayer having a B2 crystal structure such as NiAl or FeAl.

  As another technique related to the underlayer, for example, Patent Document 2 discloses a technique of inserting a CrTi alloy layer between a substrate and the underlayer.

  On the other hand, Patent Documents 3 and 4 disclose techniques for improving the sliding durability of the protective layer. In these techniques, a DLC (diamond-like carbon) protective layer is formed as a protective layer, and a bias voltage is applied in this protective layer forming step. The sliding durability of the protective layer is improved by improving the bias voltage so that it can be stably applied. This is because when the bias voltage at the time of forming the protective layer changes, the amount of hydrogen contained in the surface of the protective layer that affects the wear resistance changes, which adversely affects the sliding durability of the protective layer.

  Patent Document 5 discloses a technique for improving the mechanical characteristics and magnetic characteristics of a substrate. This technique is characterized in that silicon is used as a substrate and the electrical resistance is lowered by doping a group III element or a group V element during the crystal growth of single crystal silicon. A bias is applied to the silicon substrate. The magnetic recording layer is formed by the applied sputtering method.

US Patent No. 5,800,931 US Pat. No. 5,789,056 JP 2002-319125 A JP 2004-273030 A JP-A-8-167134

  By the way, the amount of stored information required for the HDD has been dramatically increased. Recently, information recording density has been required to exceed 60 gigabits per square inch or over 60 gigabits. Various developments including the above-mentioned technology have been made to meet such demands for higher recording density. However, improvement of the S / N ratio is indispensable for increasing the recording density, so that a sufficient S / N ratio is achieved. Has become difficult.

  Further, it is required to achieve a sufficient S / N ratio even when information is recorded / reproduced at a high recording density of 700 kfci or higher as the linear recording density.

  The first object of the present invention is to provide a low noise magnetic disk capable of achieving such a high recording density.

  The second object of the present invention is to provide a magnetic disk having magnetic anisotropy suitable for achieving such a high recording density.

  A third object of the present invention is to provide a magnetic disk suitable for mounting on an HDD that records and reproduces at a high linear recording density.

  A fourth object of the present invention is to provide a magnetic disk suitable for mounting on an HDD that records and reproduces at a surface recording density of 60 gigabits per square inch or exceeding 60 gigabits.

  The present invention can include the following configurations.

(Configuration 1)
When a glass disk substrate is provided with at least an underlayer, a magnetic layer containing a CoCr alloy, and a protective layer, the residual magnetization in the circumferential direction of the disk is Mrc and the residual magnetization in the radial direction of the disk is Mrr. A method of manufacturing a magnetic disk having a magnetic anisotropy ratio Mrc / Mrr, which is a ratio of residual magnetization in the circumferential direction and residual magnetization in the radial direction of the disk, exceeding 1, wherein the underlayer is formed on the glass disk substrate After the underlayer is formed, the first magnetic layer and the second magnetic layer are formed as the magnetic layer so that the first magnetic layer is on the underlayer side, and the first magnetic layer is formed. A method of manufacturing a magnetic disk , wherein a bias of −150 V or less is applied during film formation, and the underlayer includes a first underlayer made of CrW and a second underlayer made of CrMn .

(Configuration 2)
A method of manufacturing a magnetic disk according to Configuration 1, wherein a nonmagnetic layer and a stabilization layer are formed between the underlayer and the first magnetic layer.

(Configuration 3)
A method of manufacturing a magnetic disk according to any one of Configurations 1 and 2, wherein at least one of the first magnetic layer and the second magnetic layer and the stabilization layer are made to react with each other via the nonmagnetic layer. A method of manufacturing a magnetic disk, comprising ferromagnetic coupling.

(Configuration 4)
A magnetic disk manufacturing method according to any one of Structures 1 to 3, wherein a bias voltage applied during film formation of the first magnetic layer is −150 V or lower and −600 V or higher. Production method.

(Configuration 5)
A method of manufacturing a magnetic disk according to any one of Structures 1 to 4, wherein the Cr content of the first magnetic layer is greater than the Cr content of the second magnetic layer. Method.

(Configuration 6)
A method of manufacturing a magnetic disk according to any one of Structures 1 to 5, wherein the Cr content of the first magnetic layer is 20 at% or more and 35 at% or less.

(Configuration 7)
A method of manufacturing a magnetic disk according to any one of Structures 1 to 6, wherein the Cr content of the second magnetic layer is less than 20 at%.

(Configuration 8)
A magnetic disk manufactured by a method of manufacturing a magnetic disk according to any one of configurations 1 to 7.

  According to the present invention, a magnetic disk for high recording density having a high SN ratio can be provided using a glass substrate. This is because the underlayer formed on the glass substrate acts so as to contribute to the induction of magnetic anisotropy, and as a result, the magnetized particles cooperate with the energy by the bias applied when the first magnetic layer is formed. It is considered that the film is formed so as to face the circumferential direction of the disk.

  In the magnetic disk according to the present invention, an amorphous glass substrate, a crystallized glass substrate, or the like can be used as the glass substrate. It is particularly preferable to use an amorphous glass substrate.

  As the glass composition, aluminosilicate glass is particularly preferable.

  In the magnetic disk according to the present invention, a circumferential texture is formed on a glass substrate. An underlayer is formed on this glass substrate, and then a magnetic layer is formed. As the underlayer, after forming an adhesion layer such as CrTi having good adhesion to the glass substrate, a W-containing alloy layer such as CoW or CrW is formed. With this configuration, the anisotropy due to the texture formed on the glass substrate can be induced to the upper layer, and a magnetic disk having high magnetic anisotropy can be produced. In the present invention, the present invention is more effective when applied to a magnetic disk having a magnetic anisotropy ratio Mrc / Mrr of more than 1, preferably 1.5 or more.

  In the magnetic disk according to the present invention, the magnetic layer is made of a material containing CoCr, and is preferably composed of two or more layers including the first and second magnetic layers.

  In the magnetic disk according to the present invention, a stabilizing layer made of a CoCrTa alloy or the like and a nonmagnetic layer made of a Ru material are formed between the underlayer and the first magnetic layer formed on the underlayer side. Preferably it is done.

  CoCrPtTa, CoCrPtB, CoCrPtBTa, and CoCrPtBCu can be used for the first magnetic layer formed on the underlayer side. The Cr content in the first magnetic layer is preferably 20 at% or more and 35 at% or less, more preferably 22 at% to 30 at%. Further, a DC bias is applied to the glass substrate during the formation of the first magnetic layer formed on the underlayer side. This is because noise is reduced by applying a bias. When the Cr content is less than 20 at%, the effect of bias application is not so much seen, and when it is more than 35 at%, it becomes non-magnetic. Further, when the bias voltage is larger than −150V, the effect of bias application is not so much seen. When the bias voltage is smaller than −600V, the impact resistance of the glass substrate is affected.

  Next, a second magnetic layer is formed on the first magnetic layer. CoCrPtTa, CoCrPtB, CoCrPtBTa, and CoCrPtBCu can also be used for the second magnetic layer, but the Cr content of the second magnetic layer is preferably smaller than the Cr content of the first magnetic layer, particularly less than 20 at%. It is preferable that This is to increase the resolution at a high recording density.

  In the magnetic disk according to the present invention, a configuration in which the magnetic layer has an AFC (Antiferro coupling) structure (antiferromagnetic coupling structure) can also be used. In this case, the magnetic layer is configured to include the above-described nonmagnetic layer, and two or more magnetic layers including the first and second magnetic layers may be formed between the nonmagnetic layer and the protective layer. preferable.

  Further, in the magnetic disk according to the present invention, a glass substrate on which substantially regular streak grooves along the circumferential direction of the disk can be used.

  Next, an embodiment of the present invention will be described with reference to FIG.

  In the magnetic disk 10 of FIG. 1, an underlayer 2, a magnetic layer 3, a protective layer 4, and a lubricating layer 5 are sequentially formed on a glass substrate 1 in contact therewith.

  On the glass substrate 1, a circumferential texture that induces magnetic anisotropy in the circumferential direction is formed in the magnetic layer 3.

  The underlayer 2 is formed by contacting an amorphous underlayer 2a and body-centered cubic underlayers 2b and 2c. As described above, it is preferable to form an adhesion layer made of CrTi or the like having good adhesion to the glass substrate 1 between the glass substrate 1 and the amorphous base layer 2a.

  The magnetic layer 3 is formed by contacting a stabilization layer 3a that functions as a magnetic layer, a nonmagnetic layer 3b that functions as a spacer layer, a first magnetic layer 3c, and a second magnetic layer 3d. The stabilization layer 3a, the first magnetic layer 3c, and the second magnetic layer 3d are exchange-coupled antiparallel through the nonmagnetic layer 3b. The stabilizing layer 3a and the nonmagnetic layer 3b may be omitted.

  This will be specifically described below.

Example 1
The glass substrate 1 is a 2.5-inch type chemically strengthened glass substrate obtained by melting amorphous aluminosilicate glass and subjecting the glass disk obtained by direct pressing to shape processing, grinding, polishing, and chemical strengthening. is there.

Incidentally, aluminosilicate glass in Example 1 _SiO 2: 63.6 _{wt%, Al} 2 O 3: 14.2 _wt%, Na 2 O: 10.4 _wt%, Li 2 O: 5.4 wt%, This is an aluminosilicate glass having a composition of ZrO ₂ : 6.0% by weight and SB ₂ O ₃ : 0.4% by weight.

  After chemical strengthening, a circumferential texture was formed on the main surface using a single-wafer tape texture device and diamond slurry.

  The fine morphology of the main surface of the obtained glass substrate 1 was observed using an AFM (atomic force microscope). When an area of 5 μm square was observed, it was confirmed that textures composed of regular streaks were arranged along the circumferential direction of the disk. The surface roughness was a smooth surface with Rmax of 4.81 nm and Ra of 0.42 nm. The surface roughness was calculated according to Japanese Industrial Standard (JIS) based on the observed shape of AFM.

  Next, using a single wafer stationary facing film formation method, film formation was sequentially performed in an Ar gas atmosphere by DC magnetron sputtering.

  The underlayer 2a is an amorphous W-containing alloy layer made of CrW (Cr: 50 at%, W: 50 at%), and was formed in an Ar gas atmosphere so as to have a film thickness of 100 Å.

  The body-centered cubic base layer 2b was made of CrMn (Cr: 80 at%, Mn: 20 at%), and was formed to have a film thickness of 100 angstroms. The body-centered cubic base layer 2c was made of CrMo (Cr: 80 at%, Mo: 20 at%), and was formed to have a film thickness of 100 angstroms.

  By these underlayers, the easy axis of magnetization is controlled to be aligned within the disk surface in the film forming process of the magnetic layer 3, and grain coarsening can be prevented.

  The stabilization layer 3 a is a ferromagnetic alloy layer having a hcp crystal structure of CoCrTa (Co: 85 at%, Cr: 10 at%, Ta: 5 at%), and was formed to have a film thickness of 30 Å.

  The nonmagnetic layer 3b is a nonmagnetic Ru metal layer having an hcp crystal structure, and was formed to have a thickness of 7 Å so that antiferromagnetic exchange coupling can be induced.

  The first magnetic layer 3c is a magnetic layer formed to be a main component of magnetic recording, and has an hcp crystal structure of CoCrPtB (Co: 59 at%, Cr: 24 at%, Pt: 11 at%, B: 6 at%). The film was formed so as to have a film thickness of 150 Å. During the formation of the first magnetic layer 3c, a DC bias of −350 V was applied to the glass substrate 1.

  The second magnetic layer 3d is a magnetic layer formed to be a main body of magnetic recording, and CoCrPtBCu (Co: 57 at%, Cr: 14 at%, Pt: 11 at%, B: 13 at%, Cu: 5 at%) The ferromagnetic alloy layer having the hcp crystal structure was formed so as to have a film thickness of 150 Å.

  The thickness of the magnetic layer 3 is 337 angstroms.

  The protective layer 4 is a protective layer made of hydrogenated carbon, and was formed in a mixed atmosphere of Ar and hydrogen so as to have a film thickness of 30 angstroms. The protective layer 4 is a layer for protecting the magnetic layer from the impact of the magnetic head.

  A polymer compound made of PFPE (perfluoropolyether) was applied to the surface of the disk after the above film formation by a dip method to form a lubricating layer 5 having a thickness of 10 Å. The lubricating layer 5 is a layer for reducing the impact of the magnetic head.

  The magnetic disk 10 obtained as described above was examined for the orientation of the Co alloy using XRD (X-ray diffraction), and it was found that the (110) plane was oriented in the in-plane direction. That is, it was confirmed that the easy axis of magnetization of the magnetic layer was oriented in parallel in the plane.

  Next, the electromagnetic conversion characteristics of the magnetic disk 10 were evaluated. The evaluation method is as follows.

  Using a GMR head with a magnetic head flying height of 12 nm, recording / reproducing output and medium noise at a linear recording density of 700 kfci were measured. The SN ratio was calculated from the ratio of the reproduction output and noise at this time.

The results are as shown in Table 1 below.

  In Table 1, in addition to Example 1 in which the Cr content of the first magnetic layer 3c is 24 at%, the Cr content of the second magnetic layer 3d is 14 at%, and the bias voltage is −350 V, Example 2 to Example 10 are shown. The results up to are shown. All of Examples 2 to 10 are the same except for the three conditions of the Cr content of the first magnetic layer 3c, the Cr content of the second magnetic layer 3d, and the bias voltage.

  In Example 2, the Cr content of the first magnetic layer 3c was 26 at%, the Cr content of the second magnetic layer 3d was 14 at%, and the bias voltage was −350 V. In Example 3, the Cr content of the first magnetic layer 3c was The amount is 28 at%, the Cr content of the second magnetic layer 3 d is 14 at%, and the bias voltage is −350V.

  In Example 4, the Cr content of the first magnetic layer 3c was 32 at%, the Cr content of the second magnetic layer 3d was 14 at%, and the bias voltage was −350 V. In Example 5, the Cr content of the first magnetic layer 3c was used. The amount is 35 at%, the Cr content of the second magnetic layer 3 d is 14 at%, and the bias voltage is −350V.

  In Example 6, the Cr content of the first magnetic layer 3c was 24 at%, the Cr content of the second magnetic layer 3d was 12 at%, and the bias voltage was −350 V. In Example 7, the Cr content of the first magnetic layer 3c was The amount is 24 at%, the Cr content of the second magnetic layer 3 d is 16 at%, and the bias voltage is −350V.

  In Example 8, the Cr content of the first magnetic layer 3c was 24 at%, the Cr content of the second magnetic layer 3d was 18 at%, and the bias voltage was −350 V. In Example 9, the Cr content of the first magnetic layer 3c was The amount is 24 at%, the Cr content of the second magnetic layer 3 d is 14 at%, and the bias voltage is −200 V.

  In Example 10, the Cr content of the first magnetic layer 3c is 24 at%, the Cr content of the second magnetic layer 3d is 14 at%, and the bias voltage is −500V.

  Further, in order to investigate the reliability of the magnetic disk 10, an LUL (load unload) durability test was performed using an LUL (load unload) type HDD (hard disk drive). Usually, in the case of a magnetic disk for LUL (load / unload) system, it is required to endure the number of LUL times of 400,000 or more continuously. As a result of the test, in any of Examples 1 to 10, the magnetic disk 10 was able to endure 600,000 times of LUL without failure. When the magnetic disk 10 was removed from the HDD after the test and observed, no abnormality such as film peeling was observed.

  In any of Examples 1 to 10, an improved S / N ratio is shown compared to the comparative example described later. That is, the bias voltage applied during the formation of the first magnetic layer 3c is preferably −150 V or less and −600 V or more, and the Cr content of the first magnetic layer 3c is preferably 20 at% or more and 35 at% or less. Further, the Cr content of the second magnetic layer 3d is preferably less than 20 at%.

  The reason why the above results are obtained is considered as follows.

  1. As a result of the underlayer 2 formed on the glass substrate 1 acting so as to contribute to the induction of magnetic anisotropy, the magnetized particles cooperate with the energy by the bias applied when the first magnetic layer 3c is formed. The film is formed so as to face the circumferential direction of the disk.

  2. When the magnetic layer 3 has an AFC structure, the first magnetic layer 3c has a great influence on exchange coupling with the stabilization layer 3a. In the first magnetic layer 3c, each magnetized particle in the circumferential direction greatly affects the improvement of the SN ratio, and the SN ratio is further improved by the AFC structure with the stabilization layer 3a.

  3. The Cr content in the first magnetic layer 3c is within the range of 20 at% or more and 35 at% or less, and if it is contained in a large amount, the SN ratio tends to be improved because the magnetization direction of the bit depends on the Cr content. The changing part (magnetization transition region) is clear.

  Table 1 further shows the test results of Comparative Example 1 to Comparative Example 8 which were carried out in the same manner as in the above example.

(Comparative Example 1)
A magnetic disk of Comparative Example 1 was manufactured. Comparative Example 1 is a similar magnetic disk produced by the same manufacturing method as Example 1 except that the bias of Example 1 was not applied.

(Comparative Example 2)
Next, a magnetic disk of Comparative Example 2 was manufactured. Comparative Example 2 is the same magnetic disk produced by the same manufacturing method as in Example 1 except that the Cr content of the first magnetic layer of Example 1 was 18 at%.

(Comparative Example 3)
Next, a magnetic disk of Comparative Example 3 was manufactured. Comparative Example 3 is a similar magnetic disk produced by the same manufacturing method as Comparative Example 2 except that no bias was applied.

(Comparative Example 4)
Next, a magnetic disk of Comparative Example 4 was manufactured. Comparative Example 4 is a similar magnetic disk produced by the same manufacturing method as in Example 1 except that the Cr content of the first magnetic layer of Example 1 was 38 at%.

(Comparative Example 5)
Next, a magnetic disk of Comparative Example 5 was manufactured. Comparative Example 5 is a similar magnetic disk by the same manufacturing method as Comparative Example 4 except that no bias was applied.

(Comparative Example 6)
Next, a magnetic disk of Comparative Example 6 was manufactured. Comparative Example 6 is the same magnetic disk manufactured by the same manufacturing method as in Example 1 except that the Cr content of the second magnetic layer of Example 1 was changed to 22 at%.

(Comparative Example 7)
Next, a magnetic disk of Comparative Example 7 was manufactured. Comparative Example 7 is a similar magnetic disk manufactured by the same manufacturing method as in Example 1 except that the bias voltage in Example 1 was set to −100V.

(Comparative Example 8)
Next, a magnetic disk of Comparative Example 8 was manufactured. Comparative Example 8 is a similar magnetic disk produced by the same manufacturing method as in Example 1 except that the bias voltage in Example 1 was set to -650V. In the test of Comparative Example 8, the substrate was deformed during bias application, and the magnetic characteristics could not be measured.

  As apparent from the above description, according to the present invention, it is possible to provide a low noise magnetic disk for high recording density having excellent characteristics in SN ratio.

It is sectional drawing of the magnetic disc by the Example of this invention.

Explanation of symbols

1 Glass substrate 2 Underlayer 3 Magnetic layer

Claims (3)

A glass disk substrate having a circumferential texture is provided with at least an underlayer, a magnetic layer containing a CoCr alloy, and a protective layer. The residual magnetization in the circumferential direction of the disk is Mrc and the residual magnetization in the radial direction of the disk is A magnetic disk manufacturing method in which the magnetic anisotropy ratio Mrc / Mrr, which is the ratio of the residual magnetization in the circumferential direction of the disk to the residual magnetization in the radial direction of the disk when Mrr, is greater than 1.
Forming the underlayer on the glass disk substrate, and forming the first magnetic layer and the second magnetic layer as the magnetic layer after forming the underlayer so that the first magnetic layer is on the underlayer side To form a film,
Of the first magnetic layer and the second magnetic layer, a DC bias is applied only during the formation of the first magnetic layer , and the bias voltage is −150 V or less, −600 V. And above
The underlayer includes an amorphous first underlayer made of CrW, a body-centered cubic second underlayer made of CrMn, and a body-centered cubic third underlayer made of CrMo ,
The Cr content of the first magnetic layer is 20 at% or more and 35 at% or less,
A method of manufacturing a magnetic disk, wherein the Cr content of the second magnetic layer is 12 at% or more and less than 20 at%.   2. The method of manufacturing a magnetic disk according to claim 1, wherein a nonmagnetic layer and a stabilizing layer are formed between the underlayer and the first magnetic layer. 3. The magnetic disk according to claim 2 , wherein at least one of the first magnetic layer and the second magnetic layer and the stabilization layer are antiferromagnetically coupled via the nonmagnetic layer. Production method.

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