JP2009116932A - Vertical magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium with high recording density having higher coercive force Hc and an SN ratio than a vertical magnetic recording medium having a single sub-base layer. <P>SOLUTION: The vertical magnetic recording medium 100 is provided with at least a soft magnetic layer 14, a sub-base layer 16, a base layer 18 made of ruthenium and a magnetic recording layer 22 recording a signal which are deposited in this order on a disk substrate 1. The sub-base layer 16 contains a first sub-base layer 16a made of a Cu alloy and a second sub-base layer 16b made of NiW. The first and the second sub-base layers 16a and 16b may be deposited in random order. <P>COPYRIGHT: (C)2009,JPO&amp;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 intermediate layer is provided below the under layer, and the material or film structure of the intermediate layer is optimized to promote the alignment of crystal grains in the under layer and indirectly improve the crystal orientation of the magnetic recording layer. This is a method for improving the coercive force. The material of the intermediate 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

  By the way, when the recording density is improved, the electromagnetic conversion characteristics (hereinafter abbreviated as “electric characteristics”, for example, SN ratio) are improved while enhancing the magnetostatic characteristics (hereinafter abbreviated as “static characteristics”, for example, coercive force Hc). Need to be increased. This is because even if the recording density is increased by improving the coercive force Hc, if the SN ratio is lowered, the performance as a recording medium is not improved.

  Accordingly, an object of the present invention is to provide a magnetic recording medium capable of improving the recording density by improving the coercive force Hc and increasing the SN ratio.

  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 influenced by the underlying intermediate layer. The present invention has been completed by further research.

  That is, according to a typical configuration of the present invention, a perpendicular magnetic layer in which at least a soft magnetic layer, an intermediate layer, a ruthenium underlayer, and a magnetic recording layer for recording a signal are formed in this order on a disk substrate. In the recording medium, the intermediate layer is composed of a first intermediate layer made of a Cu alloy and a second intermediate layer made of NiW.

  The coercive force Hc is improved when the second intermediate layer located above is CuX (X is a predetermined metal), and the SN ratio is improved when the second intermediate layer is NiW. The first and second intermediate layers may be out of order. This is because, regardless of which substance is located above, both the coercive force Hc and the SN ratio are improved by a synergistic effect as compared with the case of a single layer.

  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 total film thickness of the intermediate layer is preferably 5 to 12 nm. This is because the intermediate layer composed of two layers of CuX and NiW can achieve a particularly large coercive force Hc within the range of the total film thickness as compared with the intermediate layer of the CuX single layer. The upper limit of 12 nm is also 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.

  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 first or second intermediate layer is made of a Cu alloy, the magnetic recording layer is highly oriented without increasing the thickness of each underlayer, even if the underlayer has the two-layer structure as described above. This is because the layer containing ruthenium formed in a high-pressure argon atmosphere (about 6 Pa to 10 Pa) exhibits the effect that the magnetic recording layer becomes fine particles.

  According to the present invention, it is possible to provide a magnetic recording medium having a high recording density in which both the coercive force Hc and the SN ratio are increased as compared with a perpendicular magnetic recording medium having a single intermediate layer.

  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. A 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 intermediate layer 16, a first underlayer 18a, and a second lower layer. The base layer 18 b, the first magnetic recording layer 22 a, the second magnetic recording layer 22 b, the continuous layer 24, the medium protective layer 28, and the lubricating layer 30 are configured. 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 intermediate layer 16, which is a feature of the present embodiment, has a function of promoting alignment of crystal grain orientation 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.

(Middle layer)
The above-described intermediate layer, which is a feature of the present embodiment, will be further described in detail. In the present embodiment, as already described, at least the soft magnetic layer 14, the intermediate layer 16, the underlayer 18 made of ruthenium, and the magnetic recording layer 22 for recording signals are formed in this order on the disk substrate. This is a perpendicular magnetic recording medium 100. The intermediate layer 16 is sometimes referred to as an orientation control layer or a seed layer. If the intermediate layer 16 is located further below the base layer 18, its function and composition are not limitedly interpreted by its name.

  The intermediate layer 16 includes a first intermediate layer 16a made of a Cu alloy and a second intermediate layer 16b made of NiW.

  The coercive force Hc is improved when the second intermediate layer 16b located above is CuX (X is a predetermined metal), and the SN ratio is improved when the second intermediate layer 16b is NiW. The first and second intermediate layers 16a and 16b may be out of order. This is because, regardless of which substance is located above, both the coercive force Hc and the SN ratio are improved as compared with the case of a single layer.

  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 total film thickness of the intermediate layer 16 (the sum of the film thickness of the first intermediate layer 16a and the film thickness of the second intermediate layer 16b) is preferably 5 to 12 nm. This is because, as shown in FIG. 4 to be described later, the intermediate layer composed of two layers of CuX and NiW can achieve a particularly large coercive force within the range of the total film thickness as compared with the intermediate layer of the CuX single layer.

  The upper limit of 12 nm is also 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.

  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 first intermediate layer 16a or the second intermediate layer 16b is made of a Cu alloy, even if the underlayer has the two-layer structure as described above, the magnetic recording layer can be made high without increasing the thickness of each underlayer. This is because the layer containing ruthenium formed in the high-pressure argon atmosphere (about 3 Pa to 10 Pa) has the effect that the magnetic recording layer becomes fine particles.

(Evaluation)
FIG. 2 is a graph showing the relationship between the film thickness of the intermediate layer (single layer) and the coercive force Hc. According to FIG. 2, both the NiW intermediate layer and the Cu-based alloy intermediate layer reach the peak of the coercive force Hc as the film thickness increases. FIG. 2 shows the coercive force of each single-layer intermediate layer. The total film thickness of the intermediate layer 16 when the NiW intermediate layer and the Cu-based alloy are the first and second intermediate layers 16a and 16b. Is considered to be 3 to 12 nm.

  FIG. 3 is a graph showing the relationship between the film thickness of the intermediate layer (single layer) and the S / N ratio. According to FIG. 3, the intermediate layer of the NiW single layer reaches a peak of S / N ratio at 8 nm, and the intermediate layer of the single layer made of Cu-based alloy reaches a peak of S / N ratio at a film thickness of 3 nm. Yes. FIG. 3 shows the S / N ratio of a single intermediate layer. The total intermediate layer 16 when the NiW intermediate layer and the Cu-based alloy are the first and second intermediate layers 16a and 16b are shown. If the film thickness is also about 3 to 12 nm, it is considered that a good S / N ratio can be obtained.

  FIG. 4 is a graph showing the relationship between the coercive force Hc and the total film thickness of the intermediate layer of the CuTi single layer to be compared and the intermediate layer composed of two layers of CuTi and NiW. In this graph, the NiW film thickness of the intermediate layer composed of two layers is a constant 5.5 nm, and the total film thickness is changed by changing the film thickness of CuTi. Compared to the CuTi single layer, two layers of CuTi and NiW can clearly obtain a higher coercive force Hc at the same total film thickness of 5 nm or more.

  On the other hand, the upper limit of 12 nm is a point where the reversal of the coercive force Hc is likely to occur as shown in FIG. In addition, as described above, this is also 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.

  As a conclusion in view of FIG. 4, it is considered that the total film thickness of the intermediate layer 16 composed of two layers is preferably 5 to 12 nm. However, as estimated from FIGS. 2 and 3, it may be 3 to 12 nm. In the intermediate layer 16 having such a film thickness, the coercive force Hc is improved when the second intermediate layer 16b located above is CuX (X is a predetermined metal), and the second intermediate layer 16b is made of NiW. In some cases, the signal to noise ratio is improved. The first and second intermediate layers 16a and 16b may be out of order. This is because, regardless of which substance is located above, both the coercive force Hc and the SN ratio are improved by a synergistic effect as compared with the case of a single layer.

  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 relationship between the film thickness of an intermediate | middle layer (single layer), and the coercive force Hc. It is a graph which shows the relationship between the film thickness of an intermediate | middle layer (single layer), and S / N ratio. It is a graph which shows the relationship between the total film thickness of the intermediate | middle layer of the CuTi single layer which is a comparison object, and the intermediate | middle layer which consists of two layers of CuTi and NiW, and the coercive force Hc.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Disk base | substrate 12 ... Adhesion layer 14 ... Soft magnetic layer 14a ... 1st soft magnetic layer 14b ... Spacer layer 14c ... 2nd soft magnetic layer 16 ... Intermediate | middle layer 16a ... 1st intermediate | middle layer 16b ... 2nd intermediate | middle layer 18 ... Bottom Base layer 18a ... first underlayer 18b ... second underlayer 22 ... magnetic recording layer 22a ... first magnetic recording layer 22b ... second magnetic recording layer 24 ... 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 intermediate layer, an underlayer made of ruthenium, and a magnetic recording layer for recording a signal are formed in this order on a disk substrate.
The perpendicular magnetic recording medium according to claim 1, wherein the intermediate layer includes a first intermediate layer made of a Cu alloy and a second intermediate layer made of NiW.   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 total thickness of the intermediate layer is 5 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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