JP2009099162A - Perpendicular magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium achieving both reduction in track width and increase in S/N ratio considered to be incompatible with each other, thereby increasing recording density. <P>SOLUTION: In the perpendicular magnetic recording medium 100 including at least a soft magnetic layer 14, an orientation control layer 16, an underlayer 18 made of ruthenium and a magnetic recording layer 22 for recording a signal deposited in this order on a disk base body 1, the orientation control layer 16 is made of a Cu alloy. As the track width of the perpendicular magnetic recording medium 100 is reduced, the S/N ratio is increased. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

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

  In recent years, a perpendicular magnetic recording type magnetic disk (perpendicular magnetic recording disk) has been proposed in order to achieve a high recording density in a magnetic disk used for an HDD or the like. In the conventional in-plane magnetic recording method, the easy axis of magnetization of the magnetic recording layer is aligned in the plane direction of the substrate surface, but in the perpendicular magnetic recording method, the easy magnetization axis is adjusted to be aligned in the direction perpendicular to the substrate surface. ing. The perpendicular magnetic recording method is more suitable for increasing the recording density because the thermal fluctuation phenomenon can be more suppressed during high-density recording than the in-plane recording method.

Conventionally, CoCrPt—SiO ₂ or CoCrPt—TiO ₂ has been widely used as the magnetic recording layer, Co forms crystals of an hcp structure (hexagonal close-packed crystal lattice), and Cr and SiO ₂ (or TiO ₂ ) segregate. To form grain boundaries. By using such a material, SiO ₂ (or TiO ₂ ) is segregated around ferromagnetic Co, so that it is easy to form physically independent fine Co particles and to easily achieve a high recording density.

  In order to improve the crystal orientation of the magnetic recording layer, an underlayer is generally provided. Ti, V, Zr, Hf, and the like are known for the underlayer, but as shown in Patent Document 1, Ru (ruthenium) is currently mainstream. Ru has an hcp structure, effectively improves the perpendicular orientation of the easy axis of the magnetic recording layer containing Co (cobalt) as a main component, increases the coercive force Hc, and secures a predetermined S / N ratio and resolution. This is because it is known that high recording density can be achieved.

  It is known that even if the material of the underlayer is the same, the function of the film varies depending on the pressure of the atmospheric gas in the film forming process. Patent Document 2 proposes a configuration having a ruthenium-containing layer formed in a high-pressure argon atmosphere and a ruthenium-containing layer formed in a low-pressure argon atmosphere as an underlayer for the perpendicular magnetic layer. In Patent Document 2, a layer containing ruthenium formed in a low-pressure argon atmosphere (around 1 Pa) has an effect that the magnetic layer is highly oriented, and ruthenium formed in a high-pressure argon atmosphere (about 6 Pa to 10 Pa). It is stated that the layer containing the element has the effect that the magnetic layer becomes fine particles.

  As described above, it is effective to make the magnetic grains finer in order to increase the recording density. However, if the magnetic grains are excessively miniaturized, the number of atoms constituting the magnetic grains becomes too small, and the thermal fluctuation phenomenon becomes a problem as in the case of the in-plane magnetic recording medium. In order to avoid this thermal fluctuation problem, the following methods have been adopted so far.

In other words, an orientation control layer is provided below the underlayer, and the material or film configuration of the orientation control layer is optimized to promote the alignment of crystal grains in the underlayer and indirectly in the crystal orientation of the magnetic recording layer. This is a method for improving the coercive force by improving. The material of the orientation control layer can be selected from various materials such as Ni (nickel), Pt (platinum), and Pd (palladium).
Japanese Patent Laid-Open No. 7-334832 JP 2002-197630 A

  Incidentally, there is a method of narrowing the track width in accordance with the request for improvement of the recording density as described above. In general, when the track width is narrowed, the magnetic bit volume contributing to the reproduction output is reduced, Since the amount of noise from the track end portion is relatively increased, generally the S / N ratio of the recording medium is deteriorated.

  Therefore, according to the present invention, it is possible to simultaneously obtain both characteristics which have been considered to be contradictory, that is, to improve the S / N ratio at the same time as the track width is narrowed, thereby enabling high recording density. The purpose is to provide a medium.

  In order to solve the above problems, the inventors have intensively studied, and in order to improve the crystal orientation of the magnetic recording layer having the hcp structure, the nonmagnetic underlayer having the hcp structure, which is the basis of the growth, is important. It was noticed that the crystal state of the nonmagnetic underlayer was greatly affected by the underlying orientation control layer. The present invention has been completed by further research.

  That is, according to the typical configuration of the present invention, at least a soft magnetic layer, an orientation control layer, a ruthenium underlayer, and a magnetic recording layer for recording signals are formed in this order on the disk substrate. In the magnetic recording medium, the orientation control layer is made of a Cu alloy, whereby the S / N ratio is improved as the track width of the perpendicular magnetic recording medium is narrowed.

  This is because when the orientation control layer is made of a Cu alloy, a special effect that the S / N ratio is improved as the track width is narrowed.

  The Cu alloy may be selected from CuCr (copper-chromium alloy), CuW (copper-tungsten alloy), or CuTi (copper-titanium alloy). This is because an alloy containing copper as a main component can achieve an improvement in recording density without increasing the thickness of the underlayer.

  The film thickness of the orientation control layer is preferably 8 to 12 nm. The reason why the S / N ratio is improved as the track width becomes smaller is because of the range of the track width.

  The underlayer is preferably composed of a first underlayer and a second underlayer that have different gas pressures when forming ruthenium by sputtering.

  When the orientation control layer is made of a Cu alloy, even if the underlayer has the two-layer structure as described above, the magnetic recording layer is highly oriented without increasing the thickness of each underlayer, and This is because a layer containing ruthenium formed in a high-pressure argon atmosphere (about 3 Pa to 10 Pa) has an effect that the magnetic recording layer becomes fine particles.

  According to the present invention, the crystal orientation of the magnetic recording layer is improved without increasing the space between the recording / reproducing head and the soft magnetic layer, and a high S / N ratio is maintained even when the magnetic grains are miniaturized. A magnetic recording medium capable of maintaining the magnetic force Hc and increasing the recording density can be provided.

  Next, an embodiment of a perpendicular magnetic recording medium according to the present invention will be described in detail with reference to the accompanying drawings. In the figure, elements not directly related to the present invention are not shown. Similar elements are denoted by the same reference numerals. Note that dimensions, materials, and other specific numerical values shown in the following embodiments are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified.

  FIG. 1 is a diagram for explaining the configuration of a perpendicular magnetic recording medium according to this embodiment. The perpendicular magnetic recording medium 100 shown in FIG. 1 includes a disk substrate 1, an adhesion layer 12, a first soft magnetic layer 14a, a spacer layer 14b, a second soft magnetic layer 14c, an orientation control layer 16, a first underlayer 18a, and a second base layer. The underlayer 18b, the first magnetic recording layer 22a, the second magnetic recording layer 22b, the continuous layer 24, the medium protective layer 28, and the lubricating layer 30 are formed. The first soft magnetic layer 14a, the spacer layer 14b, and the second soft magnetic layer 14c together constitute the soft magnetic layer 14. The first base layer 18a and the second base layer 18b together constitute the base layer 18. The first magnetic recording layer 22a and the second magnetic recording layer 22b together constitute the magnetic recording layer 22.

  First, an amorphous aluminosilicate glass was formed into a disk shape by direct pressing to produce a glass disk. The glass disk was ground, polished, and chemically strengthened in order to obtain a smooth nonmagnetic disk substrate 1 made of a chemically strengthened glass disk.

  On the obtained disk substrate 1, a film is formed in order from the adhesion layer 12 to the continuous layer 24 by a DC magnetron sputtering method in an Ar atmosphere by using a film forming apparatus that is evacuated, and the medium protective layer 28. Was formed by CVD. Thereafter, the lubricating layer 30 was formed by dip coating. Note that it is also preferable to use an in-line film forming method in terms of high productivity.

  The adhesion layer 12 was formed using a Ti alloy target so as to be a 10 nm Ti alloy layer. By forming the adhesion layer 12, the adhesion between the disk substrate 1 and the soft magnetic layer 14 can be improved, so that the soft magnetic layer 14 can be prevented from peeling off. As a material of the adhesion layer 12, for example, a CrTi alloy can be used.

  The soft magnetic layer 14 includes AFC (Antiferro-magnetic exchange coupling) by interposing a nonmagnetic spacer layer 14b between the first soft magnetic layer 14a and the second soft magnetic layer 14c. It was configured as follows. As a result, the magnetization direction of the soft magnetic layer 14 can be aligned along the magnetic path (magnetic circuit) with high accuracy, and the perpendicular component of the magnetization direction is extremely reduced, so that noise generated from the soft magnetic layer 14 is reduced. Can do. Specifically, the composition of the first soft magnetic layer 14a and the second soft magnetic layer 14c was CoFeTaZr, and the composition of the spacer layer 14b was Ru (ruthenium).

  The orientation control layer 16, which is a feature of this embodiment, has a function of promoting alignment of crystal grain orientations of the underlayer 18. This will be described later.

  The underlayer 18 has an hcp structure, and the crystal of the hcp structure of the magnetic recording layer 22 can be grown as a granular structure. Therefore, the higher the crystal orientation of the underlayer 18 is, the more the orientation of the magnetic recording layer 22 can be improved. The material of the underlayer can be selected from RuCr and RuCo in addition to Ru. Ru has an hcp structure and can satisfactorily orient a magnetic recording layer containing Co as a main component.

  The underlayer 18 has a two-layer structure made of Ru. When forming the second base layer 18b on the upper layer side, the Ar gas pressure is set higher than when forming the first base layer 18a on the lower layer side. When the gas pressure is increased, the mean free path of the sputtered particles is shortened, so that the film formation rate is decreased and the crystal orientation can be improved. Further, by increasing the pressure, the size of the crystal lattice is reduced. Since the size of the Ru crystal lattice is larger than that of the Co crystal lattice, if the Ru crystal lattice is made smaller, it approaches that of Co, and the crystal orientation of the Co granular layer can be further improved.

The first magnetic recording layer 22a uses a hard magnetic target made of CoCrPt containing chromium oxide (Cr ₂ O ₃ ) as an example of a nonmagnetic material, and has an hcp crystal structure of ₂ nm CoCrPt—Cr ₂ O _3. Formed. Nonmagnetic substances segregate around magnetic substances to form grain boundaries, and magnetic grains (magnetic grains) form a granular structure in which grain boundaries made of nonmagnetic substances are formed between crystal grains grown in a columnar shape. did. The magnetic grains were epitaxially grown continuously from the granular structure of the underlayer.

The second magnetic recording layer 22b, using a hard magnetic target made of CoCrPt containing titanium oxide as an example of a non-magnetic material (TiO _2), to form a hcp crystal structure of CoCrPt-TiO ₂ of 10 nm. Also in the second magnetic recording layer 22b, the magnetic grains formed a granular structure.

In the present embodiment, the first magnetic recording layer 22a and the second magnetic recording layer 22b are different materials (targets), but the present invention is not limited to this, and the same composition and type may be used. Examples of the nonmagnetic material for forming the nonmagnetic region include silicon oxide (SiO _x ), chromium (Cr), chromium oxide (CrO _x ), titanium oxide (TiO ₂ ), zircon oxide (ZrO ₂ ), and oxide. An example is tantalum (Ta ₂ O ₅ ).

  The continuous layer 24 forms a CGC structure (Coupled Granular Continuous) by forming a thin film (continuous layer) magnetically continuous in the plane direction exhibiting high perpendicular magnetic anisotropy on the granular magnetic layer. Thereby, in addition to the high density recording property and low noise property of the granular layer, the high heat resistance of the continuous film can be added.

  The medium protective layer 28 is formed by depositing carbon by CVD while maintaining a vacuum and including diamond-like carbon. The medium protective layer 28 is a protective layer for protecting the perpendicular magnetic recording layer from the impact of the magnetic head. In general, carbon deposited by the CVD method has improved film hardness compared to that deposited by the sputtering method, so that the perpendicular magnetic recording layer can be protected more effectively against the impact from the magnetic head. In the CVD method, the film hardness can be improved by increasing the bias voltage.

  The lubrication layer 30 was formed of PFPE (perfluoropolyether) by dip coating. The thickness of the lubricating layer 30 is about 1 nm.

(Orientation control layer)
The above-described orientation control layer, which is a feature of this embodiment, will be described in further detail. In the present embodiment, as already described, at least the soft magnetic layer 14, the orientation control layer 16, the ruthenium underlayer 18 and the magnetic recording layer 22 for recording signals are formed in this order on the disk substrate. A perpendicular magnetic recording medium 100 is formed.

  The orientation control layer 16 is made of a Cu alloy, whereby the S / N ratio is improved as the track width of the perpendicular magnetic recording medium is narrowed.

  This is because, when the orientation control layer 16 is made of a Cu alloy, a special effect that the S / N ratio is improved as the track width becomes narrower is obtained.

  The Cu alloy may be selected from CuCr (copper-chromium alloy), CuW (copper-tungsten alloy), or CuTi (copper-titanium alloy). This is because an alloy containing copper as a main component can achieve an improvement in recording density without increasing the thickness of the underlayer 18.

  The film thickness of the orientation control layer 16 is preferably 8 to 12 nm. As shown in FIG. 2 to be described later, it is this track width range that shows the behavior that the S / N ratio is improved as the track width is reduced.

  The underlayer 18 may be composed of a first underlayer 18a and a second underlayer 18b that have different gas pressures during ruthenium film formation by sputtering.

  When the orientation control layer 16 is made of a Cu alloy, even if the underlayer has the two-layer structure as described above, the magnetic recording layer is highly oriented without increasing the thickness of each underlayer, In addition, the layer containing ruthenium formed in a high-pressure argon atmosphere (about 3 Pa to 10 Pa) has an effect that the magnetic recording layer 22 becomes fine particles.

(Evaluation)
FIG. 2 is a graph showing the behavior of the recording medium when the material of the orientation control layer 16 in FIG. 1 is variously changed. FIG. 2A is a graph showing the relationship between the film thickness of the orientation control layer 16 and the track width. A value McW (Magnetic core Width) indicating the track width is the sum of the recording track width MWW (Magnetic Write Width) and the recording blur (erase width).

  According to FIG. 2A, the film thickness of the orientation control layer 16 is preferably 8 to 12 nm. This is because, in a range where the track width is larger than 8 nm, a special effect that the S / N ratio is improved as the track width becomes smaller is obtained. The upper limit of 12 nm is for preventing an excessively large space between the recording / reproducing head and the soft magnetic layer 14 that enables smooth recording by forming a magnetic path during recording.

  FIG. 2B is a graph showing the relationship between the track width and the SN ratio when the orientation control layer material is a NiW (nickel-tungsten) alloy, and FIG. 2C is the orientation control layer material Cu. It is a graph which shows the relationship between the track width at the time of setting it as a system alloy, and SN ratio.

  Comparing FIGS. 2B and 2C, as described above, when a Cu-based alloy is used as the orientation control layer, the SN ratio is improved as the track width is narrowed.

  Presumably, it is presumed that by using a Cu alloy as the orientation control layer, the particle size dispersion of the magnetic particles, and thus the coercive force Hc of each magnetic particle, is suppressed. When the coercive force dispersion of the individual magnetic particles is suppressed, noise due to the magnetization reversal portion of the on-track portion is reduced. Further, since writing blur is also suppressed at the track end, noise is reduced. As a result, even if the track width is reduced, the noise at the on-track and the track end can be reduced, so it is considered that the S / N ratio can be improved.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

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

It is a figure explaining the structure of the magnetic recording medium which concerns on this embodiment. It is a graph which shows the behavior of a recording medium when the raw material of the orientation control layer of FIG. 1 is changed variously.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Disc base | substrate 12 ... Adhesion layer 14 ... Soft magnetic layer 14a ... 1st soft magnetic layer 14b ... Spacer layer 14c ... 2nd soft magnetic layer 16 ... Orientation control layer 18 ... Underlayer 18a ... 1st underlayer 18b ... 2nd Underlayer 22 ... magnetic recording layer 22a ... first magnetic recording layer 22b ... second magnetic recording layer 24 ... continuous layer 24a ... first continuous layer 24b ... second continuous layer 28 ... medium protective layer 30 ... lubricating layer

Claims (4)

In a perpendicular magnetic recording medium in which at least a soft magnetic layer, an orientation control layer, a ruthenium underlayer, and a magnetic recording layer for recording a signal are formed in this order on a disk substrate.
The orientation control layer is made of a Cu alloy,
Accordingly, the S / N ratio is improved as the track width of the perpendicular magnetic recording medium is narrowed.   2. The perpendicular magnetic recording according to claim 1, wherein the Cu alloy is selected from CuCr (copper-chromium alloy), CuW (copper-tungsten alloy), or CuTi (copper-titanium alloy). Medium.   The perpendicular magnetic recording medium according to claim 1, wherein the orientation control layer has a thickness of 8 to 12 nm.   The perpendicular magnetic recording medium according to claim 1, wherein the underlayer includes a first underlayer and a second underlayer that have different gas pressures during ruthenium film formation by sputtering.

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