JP2006309926A - Perpendicular magnetic recording medium, and magnetic recording and reproducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a perpendicular recording medium and a magnetic recording and reproducing apparatus capable of recording and reproduction of information with high recording density by reviewing the function of magnetic anisotropy of a soft magnetic underlayer. <P>SOLUTION: A soft magnetic underlayer has a large negative perpendicular magnetic anisotropic energy Ku<SP>⊥</SP>perpendicular to a substrate surface. For example, a hexagonal Co-Ir alloy naturally has a negative crystal magnetic anisotropic energy Ku<SP>grain</SP>along its C axis, so when the C axis is oriented in parallel to the substrate surface, the substrate surface has properties of strong magnetization because of Ku<SP>⊥</SP>=-2πMs<SP>2</SP>-Ku<SP>grain</SP>. Further, the magnetization direction can freely be changed in the substrate surface, so there are the advantages that a magnetic wall is not apt to move in the surface and the possibility of generation of a spike noise etc., accompanying magnetic wall movement is small. Therefore, the direction of easy axis of a magnetization of the soft magnetic underlayer of the perpendicular magnetic recording medium can be controlled relatively easily and reliably. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a perpendicular magnetic recording medium used in a hard disk device or the like and a magnetic recording / reproducing apparatus using the perpendicular magnetic recording medium.

  In the perpendicular magnetic recording method, the demagnetizing field in the vicinity of the magnetization transition region, which is the boundary between recording bits, is achieved by orienting the easy axis of the magnetic recording layer that has been oriented in the in-plane direction of the medium in the perpendicular direction of the medium. Therefore, the higher the recording density, the more stable the magnetic field and the higher the resistance to thermal fluctuation, so that the method is suitable for improving the surface recording density.

  Further, when a backing layer made of a soft magnetic material is provided between the substrate and the perpendicular magnetic recording layer, it functions as a so-called perpendicular two-layer medium, and high recording ability can be obtained. At this time, the soft magnetic underlayer plays a role of refluxing the recording magnetic field from the magnetic head, so that the recording / reproducing efficiency can be improved.

  Generally, a perpendicular magnetic recording medium is provided with a backing layer (nonmagnetic film) on a substrate, an underlayer film in which the easy axis of magnetization of the magnetic layer is oriented perpendicular to the substrate surface, a perpendicular magnetic recording layer made of a Co alloy, and a protective layer. It is composed in the order. However, in recent years, it has been found that there is WATE (Wide Area / Adjacent Track Erasure) as a problem of the perpendicular magnetic recording medium. WAIT is a problem peculiar to the perpendicular magnetic recording medium. When a signal is recorded on a certain track, the signal is demagnetized over a wide area of several μm from the recorded track. A method for improving mainly the structure of the backing layer and magnetic anisotropy has been proposed (for example, see Patent Document 1).

It is also said that it is particularly effective to align the direction of the easy magnetization axis of the soft magnetic underlayer with the substrate radial direction. As a method for realizing this, there is a method of forming a backing layer in a magnetic field in the radial direction, or the backing layer is a laminated structure of a soft magnetic film and an antiferromagnetic film, and the spin direction is aligned in a certain direction. A method has been proposed (see, for example, Patent Document 2 and Patent Document 3).
In addition, there is an in-plane magnetic recording medium as an example using an alloy composition similar to that of the present invention (see, for example, Patent Document 4). In this example, the film thickness of the CoIr-based layer is thin and c-axis orientation is not performed.
In addition, a perpendicular magnetic recording medium in which a porous material is filled with a functional material although Ir is used for the soft magnetic material portion is also known (see, for example, Patent Document 5). Further, a perpendicular magnetic recording medium using Ir as a dividing layer of a soft magnetic layer is also known (see, for example, Patent Document 6).
Japanese Patent Laid-Open No. 58-166531 Japanese Patent Laid-Open No. 06-103553 US Patent Application Publication No. 2002/0028357 JP 2003-132515 A JP 2004-237429 A JP 2003-203326 A

The following problems arise when the soft magnetic underlayer of the perpendicular magnetic recording medium is formed in a magnetic field.
(1) It is difficult to uniformly control the magnetic field in the radial direction.
(2) The magnetic field is reduced at the inner periphery of the substrate.
In the future, when the size of the medium is further reduced, it is estimated that (2) will be a big problem.
In addition, when a backing layer is simply provided as described above, it is very difficult to form a uniform easy axis in the radial direction, and there is a magnetic recording medium that can solve this problem and can be easily manufactured. It is requested.
In addition, even when the easy magnetization axis is controlled with the above various ideas, the WAIT phenomenon may occur due to the fact that a slight perpendicular magnetization component remains in the soft magnetic underlayer film. It is believed that.
The present invention has been made in view of the above circumstances, and provides a perpendicular magnetic recording medium and a magnetic recording / reproducing apparatus capable of recording / reproducing high-density information by reviewing the function of the magnetic anisotropy of the backing layer. With the goal.

In order to solve the above-mentioned problems, the present invention is listed below.
(1) A perpendicular magnetic recording medium having at least a soft magnetic backing layer and a perpendicular magnetic recording layer on a nonmagnetic substrate, wherein the soft magnetic backing layer having a saturation magnetization of Ms (emu / cc) is formed on the medium surface. A perpendicular magnetic recording medium having a negative value smaller than −2πMs ² as perpendicular magnetic anisotropy energy Ku ^⊥ (erg / cc),
(2) The soft magnetic underlayer is made of a material having a negative uniaxial crystal magnetic anisotropy energy Ku ^grain , and its hard axis is oriented in a direction perpendicular to the substrate surface (1). The perpendicular magnetic recording medium according to the description,
(3) The perpendicular magnetic recording medium according to (1) or (2), wherein the soft magnetic underlayer is made of an alloy mainly containing Co and Ir.
(4) The perpendicular magnetic recording according to any one of (1) to (3), wherein an Ir content of the alloy of Co and Ir forming the soft magnetic underlayer is 5 atomic% or more and 20 atomic% or less. Medium,

(5) Any one of (1) to (4), comprising a two-dimensional hexagonal close-packed lattice plane or a crystalline underlayer having a cubic lattice plane oriented parallel to the substrate surface under the soft magnetic underlayer. Perpendicular magnetic recording medium according to
(6) The perpendicular magnetic recording medium according to any one of (1) to (5), wherein the nonmagnetic substrate is a disk-shaped substrate having a radius of 28 mm or less,
(7) A magnetic recording / reproducing apparatus comprising a perpendicular magnetic recording medium and a magnetic head for recording / reproducing information on / from the perpendicular magnetic recording medium, wherein any one of the perpendicular magnetic recording media (1) to (6) A magnetic recording / reproducing apparatus, which is a perpendicular magnetic recording medium according to claim 1,
Each invention is provided.

  According to the present invention, there is provided a perpendicular magnetic recording medium in which the easy axis of magnetization of the soft magnetic underlayer is oriented in the in-plane direction of the substrate, and domain wall movement is unlikely to occur, and the risk of occurrence of WATE phenomenon, spike noise, etc. is small. be able to.

In the present invention, a material having a negative value of the magnetocrystalline anisotropy energy Ku ^{grain in the} direction perpendicular to the substrate surface is used for the soft magnetic underlayer. An example of such a material is a Co—Ir alloy. In the case of Co—Ir, the crystal structure has a hexagonal close-packed structure, and has the property that the magnetocrystalline anisotropy energy Ku ^grain <0 with respect to the C-axis direction.
A material whose magnetocrystalline anisotropy energy Ku ^grain <0 with respect to the C axis is in a direction perpendicular to the C axis, and therefore in the substrate plane when the C axis is perpendicular to the substrate plane. It has the property of strongly magnetizing. Therefore, the vertical magnetic anisotropy Ku ^⊥ of the soft magnetic underlayer becomes -2πMs ² -Ku ^grain becomes smaller than conventional Ku ^⊥ which soft magnetic backing layer had. For this reason, the soft magnetic underlayer is magnetized in the in-plane direction of the substrate with a stronger force than before, so the possibility that the WAIT phenomenon occurs due to the magnetization component in the direction perpendicular to the plane is significantly reduced.

The contents of the present invention will be specifically described.
As already described, in the perpendicular magnetic recording medium, control of the magnetic anisotropy and easy magnetization axis direction of the soft magnetic underlayer is extremely important in the medium design. In particular, in order to suppress the WATE (Wide Area / Adjacent Track Erasure) phenomenon and the spike noise phenomenon that is said to accompany the movement of the magnetic domain of the soft magnetic layer, the direction of the easy axis of magnetization of the soft magnetic layer is oriented in the substrate plane. In addition, it is said that a device such as providing a ferromagnetic film called a pinned layer under the soft magnetic backing layer to make the domain wall of the soft magnetic layer difficult to move is said to be necessary.
The present invention intends to solve the problems caused by the soft magnetic underlayer of these perpendicular magnetic recording media by appropriately selecting a soft magnetic material.

FIG. 1 shows an example of the first embodiment of the magnetic recording medium of the present invention. A magnetic recording medium 10 shown here includes a soft magnetic backing layer 4, an orientation control layer 5, and perpendicular magnetic recording on a nonmagnetic substrate 1 via a pinned layer 2 and a nonmagnetic underlayer 3. The layer 6, the protective layer 7, and the lubricating layer 8 are sequentially formed.
As the nonmagnetic substrate, a metal substrate made of a metal material such as aluminum or an aluminum alloy may be used, or a nonmetal substrate made of a nonmetal material such as glass, ceramic, silicon, silicon carbide, or carbon may be used. .
Examples of the glass substrate include amorphous glass and crystallized glass. As the amorphous glass, general-purpose soda lime glass and aluminosilicate glass can be used. Further, as the crystallized glass, lithium-based crystallized glass can be used.
As the nonmagnetic substrate, a glass substrate or a silicon substrate is particularly preferable.

The nonmagnetic substrate preferably has an average surface roughness Ra of 0.8 nm or less, preferably 0.5 nm or less from the viewpoint of being suitable for high recording density recording with a low flying head.
Further, it is preferable that the surface micro-waviness (Wa) is 0.3 nm or less (more preferably 0.25 nm or less) from the viewpoint of being suitable for high recording density recording with a low flying head.
It is preferable that the average surface roughness Ra of the textured substrate after the treatment is 0.1 nm or more and 0.8 nm or less. When the thickness is less than 0.1 nm, the effect of the textured groove becomes insufficient, and the magnetic anisotropy of the backing layer deviates from the groove, which is not preferable. If it exceeds 0.8 nm, the flying height of the magnetic head cannot be made sufficiently small, which is not preferable. Further, it is not preferable because the SNR is lowered due to the deterioration of the orientation of the perpendicular magnetic recording layer.

In the present invention, a pinning layer and / or a base layer may be provided, and even if one or both of these layers are not provided, there is no influence on the effect of the invention. Absent. The present invention is characterized in that the magnetocrystalline anisotropy energy Ku ^grain of the soft magnetic underlayer has a negative value. For example, when Co—Ir is used as the soft magnetic layer material, the C axis of the dense hexagonal crystal structure is used. Must be oriented in a direction perpendicular to the substrate surface. An underlayer may be provided for the purpose of controlling the crystal orientation. In this case, the underlying layer itself often has a dense hexagonal crystal structure, and Ti, Ru, etc. are conceivable.
It has been found that a soft magnetic backing layer is particularly suitable when the magnetocrystalline anisotropy energy Ku ^grain with respect to an axis perpendicular to the substrate surface takes a negative value.
Here, the method of determining the magnetocrystalline anisotropy energy Ku ^grain was as follows. That is, a thin film of a soft magnetic backing layer material is formed on a substrate, a small piece of the sample is applied to a torque meter, and a 2θ component of a perpendicular magnetic torque curve obtained by rotating a magnetic field in a plane orthogonal to the substrate field saturation extrapolation value was defined as the perpendicular magnetic anisotropy energy Ku ^⊥.
Also, the c-axis (uniaxial symmetry axis) of the soft magnetic backing layer is oriented in a direction perpendicular to the film surface of the material with uniaxial magnetocrystalline anisotropy, the relationship between Ku ^⊥ = -2πMs ² -Ku ^grain Using this, the uniaxial anisotropic energy Ku ^grain was calculated.
Generally known to work strong demagnetizing field in the direction perpendicular to the film plane, the value of Ku ^⊥ at that time, when the saturation magnetization of the sample was Ms, the -2πMs ^2. The soft magnetic backing layer according to the present invention, when a representative of the assumed Ku ^⊥ = -2πMs 2 + ^X value of Ku ^⊥ this case, refers to those properties such as X takes a negative value.
In the case of a conventional soft magnetic underlayer, the value of X is almost a small positive value due to the presence of defects and impurities. In the present invention however, by the value of X is negative, it is possible to direct the magnetization force of the large │Ku ^⊥ │ toward the substrate surface. In addition, since the direction in which the magnetization is directed in the substrate plane becomes more stable, the possibility that the magnetization is shaken due to the influence of the external environment can be reduced.
When Ku ^を takes a negative value, the magnetization state of the material is most energetically stable when the magnetization direction is the in-plane direction of the substrate. Therefore, such a soft magnetic film tends to be magnetized by itself in the in-plane direction of the substrate without requiring any special device.

From the above guidelines, the present inventors have found that a Co—Ir alloy film exhibits extremely suitable properties as a material for a soft magnetic underlayer of a perpendicular magnetic recording medium.
That is, in a region where the Ir content is 5 atomic% or more, the magnetocrystalline anisotropy energy Ku ^{⊥ with} respect to the C-axis direction of the Co—Ir alloy takes a negative value, and exhibits properties suitable for the use of the present invention. . However, since the saturation magnetic flux magnetization Ms decreases as the Ir addition amount increases, it is necessary to control the concentration to match the purpose.
The substrate temperature when depositing Co—Ir is preferably in the range from room temperature to about 400 ° C.

The coercive force Hc of the soft magnetic underlayer is 30 (Oe) or less, preferably 10 (Oe) or less, more preferably 1 (Oe) or less. Note that 1 (Oe) is about 79 A / m.
The saturation magnetic flux density Bs of the soft magnetic underlayer is 0.6T or more, preferably 1T or more.
The thickness of the soft magnetic film constituting the soft magnetic backing layer is 20 nm to 120 nm, preferably 20 nm to 100 nm, and more preferably 20 nm to 60 nm.
Further, in the Co—Ir alloy thin film included in the present invention, the film thickness at which the magnetization mode changes from the Nehru domain wall structure to the Bloch domain wall structure (hereinafter referred to as domain wall critical film thickness) corresponds to the change in the atomic ratio of Co. It has been confirmed that it changes with this. That is, when the Ir concentration is fixed to a certain value within the range of 5 atomic% or more and 20 atomic% or less, the Co—Ir alloy thin film is gradually increased in thickness to increase the boundary of the domain wall at a certain thickness. Magnetization mode changes from Nail type to Bloch type. In general, the Neel magnetic field is considered to be preferable for suppressing the WATE phenomenon, but the Bloch magnetic field structure may be advantageous in terms of suppressing medium noise. The film thickness should be determined in consideration of these facts.
As a method for forming the soft magnetic film, a sputtering method can be used.
The soft magnetic backing layer may have a sandwich structure of a soft magnetic film and a Ru film or Re film. This is because the soft magnetic film and the Ru film or the Re film are provided and set to a predetermined thickness so that the soft magnetic film can be antiferromagnetically coupled. At this time, by setting the film thickness of Ru or Re to be generally 0.3 nm to 1.5 nm, preferably 0.5 nm to 1.2 nm, the WAIT phenomenon which is a problem peculiar to vertical media can be prevented. It can be improved further.

The orientation control layer is for controlling the orientation and crystal size of the perpendicular magnetic recording layer provided on the orientation control layer together with the underlayer. The material used for the orientation control layer preferably has a hexagonal close-packed structure (hcp structure) or a face-centered cubic structure (fcc structure), and Pt, Pd, NiCr, NiFeCr, Mg, and the like can be used. If the structure is other than the hcp structure or the fcc structure (for example, a body-centered cubic structure (bcc structure) or an amorphous structure), the orientation of the perpendicular magnetic recording layer becomes insufficient, resulting in a decrease in SNR and a decrease in coercive force. Since it occurs, it is not preferable.
The orientation control layer 5 is formed of two layers, a seed layer 5-1 and an intermediate layer 5-2. For example, Pd is suitable as the material used for the seed layer 5-1. The material used for the intermediate layer 5-2 is particularly preferably Ru. The thickness of the orientation control layer is preferably 30 nm or less. If the thickness of the orientation control layer exceeds 30 nm, the distance between the magnetic head and the soft magnetic backing layer at the time of recording / reproducing is increased, which is not preferable because the OW characteristics and the resolution of the reproduced signal are lowered.

The perpendicular magnetic recording layer 5 has an easy axis of magnetization perpendicular to the substrate surface. Constituent elements include at least Co, Pt, and oxide, and Cr, B, Cu, Ta, and Zr can be added for the purpose of improving SNR characteristics.
Examples of the oxide constituting the perpendicular magnetic recording layer include SiO ₂ , SiO, Cr ₂ O ₃ , CoO, Ta ₂ O ₃ , and TiO ₂ . The volume ratio of the oxide is preferably 15 to 40% by volume. If the volume ratio of the oxide is less than 15% by volume, the SNR characteristic becomes insufficient, which is not preferable. When the volume ratio of the oxide exceeds 40% by volume, it is not preferable because a coercive force sufficient for a high recording density cannot be obtained.
In addition, a perpendicular magnetic recording medium material such as a Co / Pt · Co / Pd artificial lattice system, an FePt · FePd ordered alloy system, or an RE-TM system can be used.
The nucleation magnetic field (-Hn) of the perpendicular magnetic recording layer is preferably 1.5 (kOe) or more. -Hn of less than 1.5 (kOe) is not preferable because thermal fluctuation occurs.
The thickness of the perpendicular magnetic recording layer is preferably 6 to 18 nm. When the thickness of the perpendicular magnetic recording layer is within this range, it is preferable because a sufficient output can be secured and the OW characteristics do not deteriorate.
The perpendicular magnetic recording layer can have a single layer structure, or can have a structure of two or more layers made of materials having different compositions.

The protective layer prevents corrosion of the perpendicular magnetic recording layer and prevents damage to the surface of the medium when the magnetic head comes into contact with the medium. Conventionally known materials can be used, for example, C, SiO ₂ , ZrO ₂ can be used. What is included can be used. The thickness of the protective layer is preferably 1 nm or more and 5 nm or less because the distance between the head and the medium can be reduced, which is desirable from the viewpoint of high recording density.

  A conventionally known material such as perfluoropolyether, fluorinated alcohol, fluorinated carboxylic acid or the like is preferably used for the lubricating layer.

  FIG. 2 shows an example of a magnetic recording / reproducing apparatus using the magnetic recording medium. The magnetic recording / reproducing apparatus shown here includes a magnetic recording medium 10, a medium driving unit 11 that rotationally drives the magnetic recording medium 10, a magnetic head 12 that records and reproduces information on the magnetic recording medium 10, a head driving unit 13, And a recording / reproducing signal processing system 14. The recording / reproducing signal processing system 14 can process the input data and send the recording signal to the magnetic head 12, or can process the reproducing signal from the magnetic head 12 and output the data.

Hereinafter, an example is shown and the operation effect of the present invention is clarified. However, the present invention is not limited to the following examples.
(Example 1)
After cleaning the glass substrate (Ohara's crystallized substrate TS10-SX, diameter 2.5 inches), the substrate is housed in a film formation chamber of a DC magnetron sputtering apparatus (Anelva C-3010), and an ultimate vacuum is reached. The film formation chamber was evacuated until the ^pressure reached 1 × 10 ⁻⁵ Pa. A Ti film as a base layer was formed to 7 nm on this substrate. A Ru film was formed thereon with a thickness of 3 nm, and an 88Co-12Ir (Ir; 12 atom%) soft magnetic film was further formed thereon with a thickness of 20 nm to form a soft magnetic backing layer having a two-layer structure.
On top of this, a Pd seed layer was formed by sputtering, a Ru intermediate layer was formed by 20 nm, a CoCrPt—SiO ₂ perpendicular magnetic recording layer was formed by 10 nm, and a C film was formed by 5 nm as a protective layer. Next, a lubricating layer made of perfluoropolyether was formed by a dipping method to obtain a perpendicular magnetic recording medium.

(Comparative Example 1)
On the other hand, using the same substrate and method as in Example 1, 91Co-5Zr-4Nb (Co content 91 at%, Zr content 5 at%, Nb as a first soft magnetic film to be a soft magnetic underlayer on the substrate) The content was 4 at%) 60 nm, the Ru film was 0.8 nm, and the second soft magnetic film was 91 Co-5Zr-4Nb.
After forming the soft magnetic backing layer, the Pd seed layer was 6 nm, the Ru intermediate layer was 20 nm, the CoCrPt—SiO ₂ perpendicular magnetic recording layer was 10 nm, and the C film was formed as a protective layer with a thickness of 5 nm, as in Example 1. .
Next, a lubricating layer made of perfluoropolyether was formed by a dipping method to obtain a perpendicular magnetic recording medium. The direct magnetic recording medium thus obtained was used as a comparative example.

Subsequently, WAIT measurement was performed on the perpendicular magnetic recording media of the examples and comparative examples. The evaluation method is as follows.
(1) A basic pattern of 156 kfci is recorded over the medium surface ± 6 μm.
(2) The average output of each track is measured over all tracks to obtain a track profile in the initial state.
(3) Select one middle track and record a 937 kfci signal 10,000 times repeatedly.
(4) Measure the track profile again and compare with the initial state.
The track profiles of the example and the comparative example thus obtained are shown in FIGS. 3 and 4, respectively.
Table 1 shows values of the magnetocrystalline anisotropy energy Ku ^grain , the output attenuation width in the tracking profile, the perpendicular magnetic anisotropy Ku ^⊥ and −2πMs ² with respect to the C axis.

  From the results shown in Table 1, it is clear that the perpendicular magnetic recording medium according to the present invention has an effect of suppressing the WATE phenomenon.

(Example 2 to Example 6, Comparative Example 2 to Comparative Example 6)
Next, a perpendicular magnetic recording medium was manufactured using the same process as in Example 1 and Comparative Example 1 using a silicon substrate having a radius of 22 mm as the substrate. However, when film formation was performed in the sputtering apparatus, a total of five substrates were set and film formation was performed simultaneously. That is, five sheets of the same process as in Example 1 and five sheets of the same process as in Comparative Example 1 were produced. The arrangement of the substrate during the film formation is shown in FIG.
Samples according to Example 1 are referred to as Examples 2 to 6, and samples according to Comparative Example 1 are referred to as Comparative Examples 2 to 6.
These samples were also subjected to WAIT measurement in the same manner as in Example 1 and Comparative Example 1. It was compared whether or not there was a difference in how the WAIT phenomenon occurred between five media having different positional relationships with respect to the target. The results are shown in Table 2.

From the results of Table 2, in Examples 2 to 6 according to the present invention, no WAIT phenomenon was observed regardless of the substrate arrangement. This suggests that, regardless of the direction of the magnetic field to which the substrate is exposed, the direction of the magnetic field, the direction of the target, etc., if the crystal structure of the soft magnetic backing layer can be controlled, the easy axis direction can be strongly directed in the substrate plane. it seems to do.
In one comparative example 2 to comparative example 6, the WAIT phenomenon is observed, and it is recognized that the intensity may vary depending on the substrate position. This is presumably because the soft magnetic properties of the backing soft magnetic layer are influenced by the magnetron magnetic field on the back of the target, the incident angle of sputtered particles from the target, and the like.

(Example 7)
Two targets can be rotated, and a crystallized glass substrate is set in a vacuum chamber of a magnetron sputtering apparatus (Anelva C-3010) capable of mixed sputtering film formation using two types of target materials. The inside of the chamber was evacuated until the ultimate vacuum was 1 × 10 ⁻⁵ Pa. As target materials, pure Co and pure Ir were set.
First, the crystallized glass substrate was heated to 350 ° C. using a lamp heater. Next, a Ti film was formed in a thickness of 7 nm and a Ru film was formed in a thickness of 3 nm, and then Co _100-x Ir _x was formed in a thickness of 20 nm by using simultaneous rotation of Co and Ir. At this time, x was changed by adjusting the discharge outputs of Co and Ir.
Further, a C protective film was formed on the top of the sample.
The crystal magnetic anisotropy energy Ku ^grain was measured for Co _100-x Ir _x having various compositions thus obtained. As described above, a magnetic torque meter was used for the measurement. Moreover, the composition obtained by changing the discharge output of two targets was calculated | required using the fluorescent X ray analysis. These measurement results are summarized in Table 3. _{Incidentally,} Ar partial pressure at the time of forming the _{Co 100-x} Ir x alloy film was examined for two types of 3.0Pa and 0.6 Pa.

Based on the results shown in Table 3, the relationship between Ir concentration and Ku ^grain is graphed and shown in FIG.
In the present invention, Ku ^grain needs to be negative. Although the behavior of Ku ^grain changes depending on the Ar gas partial pressure during film formation, it was found that the range of Ir concentration of 5 at% to 30 at% is most suitable based on the above results.

(Examples 8 to 12, Comparative Example 8 to Comparative Example 12)
For five types of substrates having different diameters, perpendicular magnetic recording media were prepared using the same method as in Example 1 and Comparative Example 1, and their WAIT characteristics were measured.
There are five types of substrate sizes of 95 mm in diameter (Example 8), 65 mm (Example 9), 48 mm (Example 10), 28 mm (Example 11), and 22 mm (Example 12). Samples were made and evaluated. Examples using Co—Ir as the backing magnetic layer material were Examples 8 to 12, and those using Co—Zr—Nb as the backing magnetic layer material were Comparative Examples 8 to 12. Table 4 shows the measurement results.

  When the soft magnetic underlayer material is Co—Zr—Nb, the WAIT phenomenon is more prominent when the substrate diameter is small. Therefore, it can be said that the present invention is more valuable when a substrate having a diameter of 28 mm or less is used.

It is a figure which shows the cross-section of the perpendicular magnetic recording medium of this invention. It is a figure which shows the structure of the perpendicular magnetic recording / reproducing apparatus of this invention. 2A and 2B are diagrams showing a track profile of a perpendicular magnetic recording medium according to Example 1, where FIG. 5A shows an initial state, and FIG. 5B shows a state after recording 10,000 times. It is a figure which shows the track profile of the perpendicular magnetic recording medium concerning the comparative example 1, (a) shows an initial state, (b) shows the state after 10,000 times recording. It is a figure explaining arrangement | positioning of the board | substrate at the time of film-forming, Comprising: (a) is a front view, (b) shows a top view. It is a diagram showing the relationship between Ir concentration and Ku ^⊥ in Example 7.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Nonmagnetic board | substrate, 2 ... Pinning layer, 3 ... Underlayer, 4 ... Soft magnetic backing layer, 5 ... Orientation control layer, 6... Perpendicular magnetic recording layer, 7... Protective layer, 8... Lubricating layer, 10... Magnetic recording medium, 11. ... Magnetic head, 13... Head drive unit, 14... Recording / reproducing signal system, 20.

Claims (7)

A perpendicular magnetic recording medium having at least a soft magnetic backing layer and a perpendicular magnetic recording layer on a nonmagnetic substrate, wherein the soft magnetic backing layer having a saturation magnetization of Ms (emu / cc) is perpendicular to the medium surface. A perpendicular magnetic recording medium having a negative value smaller than −2πMs ² as magnetic anisotropy energy Ku ^⊥ (erg / cc). The soft magnetic underlayer is made of a material having negative uniaxial crystal magnetic anisotropy energy Ku ^grain , and its hard axis of magnetization is oriented in a direction perpendicular to the substrate surface. 2. The perpendicular magnetic recording medium according to 1.   3. The perpendicular magnetic recording medium according to claim 1, wherein the soft magnetic underlayer is made of an alloy mainly composed of Co and Ir.   The vertical content according to any one of claims 1 to 3, wherein an Ir content of an alloy of Co and Ir forming the soft magnetic underlayer is 5 atomic percent or more and 30 atomic percent or less. Magnetic recording medium.   5. The crystalline underlayer having a two-dimensional hexagonal close-packed lattice plane or a cubic lattice plane oriented parallel to the substrate surface under the soft magnetic backing layer. 6. 2. The perpendicular magnetic recording medium according to claim 1.   The perpendicular magnetic recording medium according to claim 1, wherein the nonmagnetic substrate is a disk-shaped substrate having a radius of 28 mm or less. A magnetic recording / reproducing apparatus comprising a perpendicular magnetic recording medium and a magnetic head for recording / reproducing information on the perpendicular magnetic recording medium, wherein the perpendicular magnetic recording medium is defined in any one of claims 1 to 6. A magnetic recording / reproducing apparatus comprising the perpendicular magnetic recording medium described above.

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