JPH07129946A - Perpendicular magnetic recording medium - Google Patents

Abstract

PURPOSE:To prevent the demagnetization of a medium due to turning, to reduce medium noise, to attain high reproduction output and to obtain a perpendicular magnetic recording medium having high performance and high quality. CONSTITUTION:A soft magnetic underlayer 4 and a perpendicular magnetic recording layer 5 are successively formed on a discoid substrate 1 to obtain a perpendicular magnetic recording medium 10, a hard magnetic underlayer 3 having magnetization whose entire direction is toward the periphery or center of the substrate 1 in the radial direction is interposed between the substrate 1 and the soft magnetic underlayer 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a perpendicular magnetic recording medium, and more particularly to a two-layer film medium having a soft magnetic underlayer.

[0002]

2. Description of the Related Art Perpendicular magnetic recording has attracted attention because it enables higher density recording than in-plane magnetic recording. As a medium used for this, a soft magnetic underlayer formed on a non-magnetic substrate and perpendicular magnetic recording are used. Many studies have been made on a two-layer film medium composed of two layers. By combining such a two-layer film medium with a single pole type head, efficient magnetic recording / reproducing can be performed. Among them, the two-layer film medium having the Co—Zr-based amorphous soft magnetic film as the underlayer can obtain a perpendicular magnetic recording layer having a sharp vertical orientation, and is particularly effective for improving the recording efficiency.

However, when this two-layer film medium is used as a disk-shaped medium, there is a problem that the signal intensity is attenuated by demagnetizing with time simply by rotating the medium after recording the signal. is there. When the medium rotates, this demagnetization phenomenon causes the magnetization of the amorphous soft magnetic underlayer to be easily reversed due to the effect of an external magnetic field such as the earth's magnetism. It is considered that the recorded information on the magnetic recording layer is erased.

Therefore, the applicant of the present application has previously filed Japanese Patent Application No. 4-1.
No. 03490 proposes a method of eliminating demagnetization by forming acicular particles on the soft magnetic underlayer to make the surface uneven. This will be described as a first conventional example. FIG. 3 is a partial cross-sectional view schematically showing the configurations of the perpendicular magnetic recording media of the first conventional example and the second comparative example. In the figure, 21 is a mirror-polished disk-shaped glass substrate, on which glass, for example, Co
A soft magnetic underlayer 24 made of an amorphous thin film containing -Zr is formed. Then, this soft magnetic underlayer 24
A large number of acicular particles 27 are formed on the surface of the. The needle-shaped particles 27 are made of a material that does not easily form a solid solution with the Co—Zr-based alloy that is a constituent material of the soft magnetic underlayer 24, such as Cu or S.
A metal such as n, Zn, Al, Cd, or Pb or a material that easily forms whiskers is used. Then, the perpendicular magnetic recording layer 25 is formed on the acicular particles 27, and the perpendicular magnetic recording layer 2 is formed.
5 has a structure in which a protective layer 26 is formed.

In the perpendicular magnetic recording medium 12 having such a structure, the movement of the magnetic domain wall of the soft magnetic underlayer 24 is suppressed by the presence of the acicular particles 27, so that the soft magnetic underlayer 24 is formed.
The coercive force Hc can be increased to some extent, and the change over time due to the influence of the external magnetic field can be suppressed, and thus the problem of demagnetization can be solved.

Further, the applicant of the present application is further in Japanese Patent Application No. 5-6.
In No. 3528, a method of eliminating demagnetization by providing a carbon layer between the soft magnetic underlayer and the substrate and then performing heat treatment in vacuum was also proposed. This will be described as a second conventional example. FIG. 9 is a partial cross-sectional view schematically showing the structure of the second conventional perpendicular magnetic recording medium. In the figure, 31 is a mirror-polished disk-shaped glass substrate, and a chromium layer 32 having a film thickness of, for example, 50 nm is formed on the glass substrate 31. This chrome layer 32
A carbon layer 37 is formed on the upper surface. This car
A soft magnetic underlayer 34 made of, for example, a Co—Zr—Nb-based amorphous thin film is formed on the Bon layer 37. Then, a perpendicular magnetic recording layer 35 made of, for example, a Co—Cr—Ta-based amorphous thin film is formed on the soft magnetic underlayer 34, and made of SiO ₂ , for example, on the perpendicular magnetic recording layer 35. The protective layer 36 is formed. The perpendicular recording medium 13 having such a structure is heat-treated in a vacuum while applying a rotating magnetic field.

In the perpendicular magnetic recording medium 13 thus obtained, the carbon is diffused into the soft magnetic underlayer 34, so that the crystallization temperature of the soft magnetic underlayer 34 becomes low and the carbon becomes relatively low. Soft magnetic underlayer 34 by low temperature heat treatment
Since the coercive force (Hc) can be increased to an appropriate value by controlling the crystallization of (1), the perpendicular magnetic recording medium 13 that does not cause demagnetization can be obtained.

[0008]

By the way, in any of the methods described above, the coercive force (Hc) of the soft magnetic underlayer is increased to prevent demagnetization caused by rotation of the medium. Increasing the Hc of the soft magnetic underlayer lowers the magnetic permeability μ of the soft magnetic underlayer, which is disadvantageous for obtaining a high reproduction output from the perpendicular recording medium. In addition, in a perpendicular magnetic recording medium composed of a soft magnetic underlayer and a perpendicular magnetic recording layer, a domain wall exists in the soft magnetic underlayer, so that medium noise is generated due to the domain wall.

In view of the above, the present invention prevents the demagnetization of the perpendicular magnetic recording medium due to the rotation of the medium, reduces the medium noise, and makes it possible to obtain a high reproduction output. Therefore, it is an object of the present invention to provide a high-performance and high-quality perpendicular magnetic recording medium.

[0010]

A perpendicular magnetic recording medium of the present invention according to claim 1 is a disk-shaped substrate, a soft magnetic underlayer formed on the substrate, and a soft magnetic underlayer formed on the soft magnetic underlayer. In a perpendicular magnetic recording medium having a perpendicular recording layer
By providing between the substrate and the soft magnetic underlayer a hard magnetic underlayer having a magnetization in which all the magnetization directions are either the outer peripheral direction or the central direction in the radial direction of the substrate, Is achieved.

The perpendicular magnetic recording medium of the present invention according to claim 2 is a disk-shaped substrate, a soft magnetic underlayer formed on this substrate, and a perpendicular magnetic recording layer formed on this soft magnetic underlayer. In a perpendicular magnetic recording medium having a recording layer, between the substrate and the soft magnetic underlayer, all the magnetization directions are either the outer peripheral direction or the center direction in the radial direction of the substrate and the orientation direction is The above object is achieved by providing an in-plane oriented hard magnetic underlayer which is in the plane of the substrate.

The perpendicular magnetic recording medium of the present invention according to claim 3 is a disk-shaped substrate, a soft magnetic underlayer formed on the substrate, and a perpendicular magnetic layer formed on the soft magnetic underlayer. In a perpendicular magnetic recording medium provided with a recording layer, between the substrate and the soft magnetic underlayer, all the magnetizations are either in the radial direction toward the outer periphery or in the center, and the orientation direction is the above-mentioned direction. By providing the radially oriented hard magnetic underlayer in the radial direction, the above object is achieved.

A perpendicular magnetic recording medium according to a fourth aspect of the present invention is the perpendicular magnetic recording medium according to the third aspect, wherein the radially oriented hard magnetic underlayer is Sm (samarium).
The above-mentioned object is achieved by using a Co alloy film containing

[0014]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Example 1 FIG. 1 shows a first example of the perpendicular magnetic recording medium of the present invention.
2 is a partial cross-sectional view schematically showing the configuration of the embodiment of FIG. As shown in FIG. 1, the perpendicular magnetic recording medium 10 includes a mirror-polished disk-shaped glass substrate 1, a chrome layer 2, a hard magnetic underlayer 3 and a soft magnetic layer which are sequentially formed on the glass substrate 1. It is composed of an underlayer 4, a perpendicular magnetic recording layer 5 and a protective layer 6.

A specific manufacturing method of the first embodiment of the present invention will be described below. The respective layers 2, 3, 4, 5, 6 formed on the glass substrate 1 were formed by using a DC magnetron sputtering apparatus as shown in the schematic sectional view of the vicinity of the electrodes in FIG. In this device, for example, Co-Zr
In the lower center part of the target 43 such as -Nb, the first
The rare earth permanent magnet 41 of FIG. 7 and the second rare earth permanent magnet 42 of the target 43 are arranged on the outer peripheral portion below the target 43. The polarities of the first and second rare earth permanent magnets 41 and 42 are shown in FIG. As you can see, they are reversed. In addition, above the target 43, a disk-shaped glass substrate 1 that is mirror-polished is arranged. With this arrangement, the glass substrate 1 has the first and second rare earth permanent magnets 41,
By 42, a magnetic field of about 4 kA / m is always applied in the radial direction. The rare earth permanent magnets 41 and 42 also act as magnetron magnets, and also contribute to focus plasma near the target 43 to form a film at a high rate.

The film forming conditions for this apparatus are as follows: power density 1.0 to 1.0 in Ar atmosphere with gas pressure 0.067 Pa.
2.0 W / cm ² , target-substrate distance 60 m
m, and the substrate temperature was 150 ° C to 250 ° C. The target 43 uses a Co-Cr15-Ta4 at% alloy having a diameter of 203 mm for the hard magnetic underlayer 3, and a Co-Zr7-Nb5 a having a diameter of 203 mm for the soft magnetic underlayer 4.
t% alloy, the same size Co-Cr15-Ta4 at% alloy is used for the perpendicular magnetic recording layer 5, and the protective layer 6 is used.
For the purpose, SiO ₂ of the same size was used.

First, 50 to 100 n of a chromium layer 2 is formed on a mirror-finished soda lime glass substrate 1 having a diameter of 95 mm.
m film thickness and then Co-Cr15-Ta4a
With the t% alloy as the target 43, the hard magnetic underlayer 3 is 25
The film was formed to a thickness of 200 nm to 200 nm. The chrome layer 2 is provided for in-plane orientation of the magnetization of the hard magnetic underlayer 3. In practice, in order to see the film thickness dependence of the hard magnetic underlayer 3 on the recording / reproducing characteristics and the magnetic characteristics, the film thickness of the hard magnetic underlayer 3 is 25 nm, 50 nm, 100 n.
A plurality of samples having respective film thicknesses of m and 200 nm were manufactured.

Then, a soft magnetic underlayer 4 having a thickness of 500 nm is formed using a Co-Zr7-Nb5 at% alloy as a target 43, and a perpendicular magnetic recording layer 5 having a thickness of 75 nm is immediately formed using a Co-Cr15-Ta4 at% alloy as a target 43. did.
By immediately forming a film here, Co-Zr-Nb and Co-Cr-Ta are directly bonded to each other, and the perpendicular magnetic recording layer 5 having a strong vertical orientation is obtained. Finally, as the protective layer 6, Si
O2 was formed to a thickness of 10 nm. After the film formation was completed in this way, heat treatment was performed in a magnetic field. FIG. 8 is a conceptual diagram for explaining heat treatment in a magnetic field, which is one of the manufacturing steps of the perpendicular magnetic recording medium 10. As shown in FIG. 8, in a vacuum atmosphere of 10 ⁻³ Pa or less, at 300 ° C., while rotating the perpendicular magnetic recording medium 10 after film formation in a magnetic field of 24 kA / m around the rotation center axis 9 thereof. The perpendicular magnetic recording medium 10 was obtained by performing heat treatment for 3 hours.

Here, in order to compare the characteristics with the first embodiment, perpendicular magnetic recording media of the first and second comparative examples were manufactured. The perpendicular magnetic recording medium 11 of Comparative Example 1 is configured as shown in FIG. 2, and includes a glass substrate 1, a soft magnetic underlayer 4, a perpendicular magnetic recording layer 5, and a protective layer 6 which are sequentially formed on the glass substrate 1. Consists of. The material and film forming conditions for each of the layers 4, 5 and 6 are the same as in the case of the above-described first embodiment.

The perpendicular magnetic recording medium 12 of Comparative Example 2 is shown in FIG.
The same configuration as the first conventional example shown in FIG. Specifically, the soft magnetic underlayer 24, the perpendicular magnetic recording layer 25, the protective layer 2
The DC magnetron sputtering apparatus having the structure shown in FIG. 7 described above was used for forming or forming 6 and the acicular particles 27. The target 43 is used for the soft magnetic underlayer 24 and has a diameter of 203 mm of Co-Zr7-Nb5 at%.
16 pieces of Cu (7 × 7 × 1 mm) as impurities are arranged on the erosion area on the alloy, and the same size of Co—Cr 15 is used for the perpendicular magnetic recording layer 25.
Using -Ta4 at% alloy, for the protective film 26, SiO ₂ is used in the same size. The substrate 21 has a diameter of 95.
mm soda lime glass with a mirror finish was used.

The film forming conditions are Ar with a gas pressure of 0.067 Pa.
The atmosphere was set, the power density was 1.0 to 2.0 W / cm ² , the distance between the target and the substrate was 60 mm, and the substrate temperature was 150 ° C. First, the soft magnetic underlayer 24 is formed to a thickness of 500 nm on the glass substrate 21, the perpendicular magnetic recording layer 25 is immediately formed to a thickness of 75 nm, and then the protective layer 26 is formed to a thickness of 20 nm. Perpendicular magnetic recording medium 12
Got In addition, when forming the soft magnetic underlayer 24,
Since Cu as an impurity for forming the needle-shaped particles 27 is arranged in the get 43, many Cu needle-shaped particles 27 are formed on the surface of the soft magnetic underlayer 24.

Next, the characteristic evaluation results of these samples (Example 1, Comparative Example 1 and Comparative Example 2) will be described.
First, the recording / reproducing characteristics will be described. The recording / reproducing characteristics of these samples are as follows: track width 8 μm,
A single magnetic pole head having a main magnetic pole thickness of 0.4 μm and a coil winding number of 60 turns is used.
The measurement was performed under the conditions of m / s and head flying height of 80 nm.

Recording and reproducing a rectangular wave signal of 100 kHz,
Oscilloscope - solitary wave by-flops reproduction output E _pp (nV /
(Μm · t · m / s)) was measured. Here, the reproduction output is standardized by the track width (μm), the coil winding number (t), and the linear velocity (m / s). A signal of 6.67 MHz was recorded and reproduced, and the difference between the noise component and the system noise at that time was measured with a spectrum analyzer over a band of 16 MHz to obtain medium noise (μV _rms ).
Also, the ratio between the reproduction output immediately after the perpendicular magnetic recording medium starts rotating and the reproduction output after 2 × 10 ⁴ rotations is demagnetized (dB).
And On the other hand, the magnetic characteristics of the perpendicular magnetic recording medium were evaluated by VSM. For each sample, the MH curve was measured to determine the magnetic permeability μ of the composite layer of the soft magnetic underlayer / hard magnetic underlayer.
Got Table 1 shows the above measurement results.

[0024]

[Table 1]

According to Table 1, the perpendicular magnetic recording medium 10 of Example 1 of the present invention does not have the hard magnetic underlayer 3 as Comparative Example 1.
On the other hand, the reproduction output is the same, but the medium noise is reduced, and as a result, the S / N is improved, and the demagnetization amount is improved to about the measurement limit. Is equivalent to Comparative Example 2 in which Regarding the magnetic permeability, in Example 1 of the present invention, although it was inferior to Comparative Example 1 in which the underlayer consisted only of the soft magnetic underlayer 4, it showed a higher value than Comparative Example 2 in which needle-shaped particles were formed. .

Next, the MH (magnetization) curve of the composite layer of the soft magnetic underlayer / hard magnetic underlayer will be described. FIG. 5 is a graph showing the MH curve of the composite layer of the soft magnetic underlayer 4 / hard magnetic underlayer 3 which constitutes the first embodiment of the perpendicular magnetic recording medium of the present invention, and the horizontal axis represents the applied voltage. The strength of the magnetic field, the vertical axis is the magnetization,
Curves l and m show saturation magnetization curves, and curves n1, n2 and n3 show minor loops. Since the measurement of the MH curve was performed by applying a magnetic field in the in-plane direction of the substrate,
Even if there is the perpendicular magnetic recording layer 5, this perpendicular magnetic recording layer 5
Has a strong anisotropy in the direction perpendicular to the substrate surface, and is known not to affect the measurement results described below.

First, when a magnetic field H which increases in the positive direction is applied to the non-magnetized composite layer, an initial magnetization curve not shown is followed, and the hard magnetic underlayer 3 is positively magnetized in the positive direction. At the magnetic field strength of 500 Oe which is sufficiently saturated, the point A is reached, and the magnetization M is saturated in the positive direction. Next, the applied magnetic field H
The magnetization M follows the curve m and decreases.
When the magnetic field H reaches 0, this time the magnetic field H is increased in the negative direction. When the magnetic field H reaches -Hc (coercive force), the magnetization M becomes zero. Further, when the magnetic field H is increased in the negative direction, the composite layer is magnetized in the negative direction, and reaches the point B when the magnetic field H becomes −H1 (reversal magnetic field).

Next, when the magnetic field is inverted at point B and the magnetic field H is changed in the positive direction, the MH curve draws a minor loop, and the magnetization M changes along the curve n1. Go.
Then, the magnetic field H when the magnetization M becomes 0 is Hm (H
See 1). When the magnetic field H is further changed in the positive direction, it is magnetized in the positive direction, passes through the point C, and the magnetic field H becomes 50
When it reaches 0 Oe, point A is reached again. Repeating this operation, the magnetic field H is decreased from the positive saturation magnetic field to -H2, and when it is changed in the positive direction, the curves n2 and Hm (H2) are decreased, and the magnetic field H is decreased from the positive saturation magnetic field to -H3, and the positive magnetic field is decreased there. By changing the direction, the curves n3 and Hm (H3) are obtained. The magnetic field strength that saturates sufficiently in the negative direction is -500.
It is indicated by point D in Oe.

On the other hand, FIG. 6 shows the MH curve of the soft magnetic underlayer 4 which constitutes the perpendicular magnetic recording medium 12 of the second comparative example. In the figure, the horizontal axis represents the strength of the applied magnetic field, the vertical axis represents the magnetization, the curves r and s represent the saturation magnetization curves, and the curves t1, t2,
t3 represents a minor loop, respectively. The influence on the measurement of the perpendicular magnetic recording layer 25 can be ignored as in the above-described embodiment of the present invention.

First, when a magnetic field H increasing in the positive direction is applied to the soft magnetic underlayer 24 containing the non-magnetized needle-shaped particles 27, the initial magnetization curve not shown in the figure is traced and the magnetization is performed in the positive direction. At 500 Oe, which is a magnetic field strength sufficient to saturate the soft magnetic underlayer 24 in the positive direction, the point reaches the A'point, and the magnetization M is saturated in the positive direction. Next, when the applied magnetic field H is decreased, the magnetization M follows the curve s and decreases. When the magnetic field H reaches 0, this time the magnetic field H is increased in the negative direction. When the magnetic field H reaches -Hc (coercive force), the magnetization M becomes zero. Further, when the magnetic field H is increased in the negative direction, the soft magnetic underlayer 24
Is magnetized in the negative direction and reaches the point B'when the magnetic field H becomes -H1 '(reversal magnetic field).

Next, when the magnetic field is reversed at point B and the magnetic field H is changed in the positive direction, the MH curve draws a minor loop, and the magnetization M changes along the curve t1. Go.
Then, the magnetic field H when the magnetization M becomes 0 is Hm (H
1 '). Hereinafter, the same measurement as in the case of the composite layer of Example 1 described above was performed.

In this way, the relationship between the reversal magnetic field H and the magnetic field Hm (H) at which the magnetization becomes 0 when the reversal magnetic field H is obtained is shown in FIG. Normalized applied (reversal) magnetic field H in the magnetization curve of the formation / hard magnetic underlayer
It is a graph which shows the relationship between / Hc (this Hc is a coercive force) and Hm (H) of a minor loop. In FIG. 4, the thickness of the hard magnetic underlayer 3 of the composite layer is set to 25 nm, 50
The results when the thickness is 100 nm, 100 nm, and 200 nm, and the results of Comparative Example 2 are shown.

FIG. 5 shows the MH curve of Example 1 of the present invention.
Is characteristic in that Hm (H) is negative. This corresponds to the presence of the line in the region where Hm (H) is negative in FIG. In FIG. 5, A,
The directions of magnetization at points B and C are indicated by arrows in a square frame (the upper part is the soft magnetic underlayer 4 and the lower part is the hard magnetic underlayer 3).
At the point B, only the soft magnetic underlayer 4 is inverted in the negative direction and the hard magnetic underlayer 3 is magnetized in the positive direction. Due to the magnetic interaction with the magnetic underlayer 3, the magnetization of the soft magnetic underlayer 4 is returned to the positive direction although the magnetic field is negative at point C.

In FIG. 4, in Example 1 of the present invention, the line extends to the negative region regardless of the film thickness of the hard magnetic underlayer 3, indicating that the magnetic interaction is strong. It should be noted that, as described in detail in the following description of Example 2, the simulation is performed on the composite film of the soft magnetic underlayer / hard magnetic underlayer assuming exchange interaction or magnetostatic coupling between them. The above-mentioned magnetic interaction is confirmed to be an exchange interaction.

That is, as shown in FIG. 5, the apparent Hc
Is about 6 Oe, which is sufficiently large to prevent demagnetization and spike noise, and Hc (soft) of the soft magnetic underlayer 4 itself is much smaller than that. The numerical value can be estimated by FIG. 4 and the formula shown below. That is, in FIG. 4, Hm (H) is changed by the magnetic field H because the residual magnetization of the hard magnetic underlayer 3 is changed, and the horizontal axis is | H | / H.
At the point of c = 1 (Hm (1)), it is considered that there is almost no change in the magnetization of the hard magnetic underlayer 3, and only the magnetization of the soft magnetic underlayer 4 is reversed. When the difference from Hc is only the soft magnetic underlayer 4, the coercive force (Hc (sof
t)). That is, it is expressed by the following equation.

[0036]

[Equation 1]

From this, the Hc (so
ft) is Hc when the hard magnetic underlayer 3 has a thickness of 50 nm or more.
15% (1 Oe) of 40% even at 25 nm
It is evaluated as about (2 to 2.5 Oe), which is a sufficiently small value to maintain the soft magnetic characteristics originally possessed by the soft magnetic underlayer 4. Therefore, as shown in Table 1, the magnetic permeability μ and the reproduction output E _PP maintain high values. On the other hand, in Comparative Example 2 shown in FIG. 6, since Hc of the soft magnetic underlayer 24 itself is high, Hm (H) is almost equal to Hc and the line in FIG. 4 never becomes negative ( In FIG. 6, the arrows in the square frame indicate the directions of magnetization at the points A ', B', C'and D '). Therefore, the soft magnetic properties are impaired, and the magnetic permeability μ is low. Due to this fact and also because Cu is added, the magnetic flux density is lowered and the output is lowered.

In Example 1, in order to magnetize the hard magnetic underlayer on the disk-shaped glass substrate in one direction,
It depends on the magnetic field applied in the radial direction of the substrate at the time of DC magnetron sputtering for forming the hard magnetic underlayer, but the invention is not limited to this.
It goes without saying that magnetization can also be achieved by magnetizing in one direction in the radial direction.

<Embodiment 2> FIG. 10 is a partial sectional view schematically showing the construction of a second embodiment of the perpendicular magnetic recording medium of the present invention. As shown in FIG.
Is composed of a disk-shaped glass substrate 1 which is mirror-polished, and a hard magnetic underlayer 53, a soft magnetic underlayer 4, a perpendicular magnetic recording layer 5 and a protective layer 6 which are sequentially formed on the glass substrate 1. ing.

A concrete manufacturing method of the second embodiment of the present invention will be described below. For forming the layers 53, 4, 5, and 6 formed on the glass substrate 1, the DC magnetron sputtering apparatus having the structure shown in FIG. 7 used for manufacturing the above-described Example 1 was used.

The film forming conditions are gas pressure 0.067 to 0.13.
Power density of 0.5 to 2.0 W / c in Ar atmosphere of Pa
m ² , the target-substrate distance was 60 mm, and the substrate temperature was 150 ° C to 250 ° C. As the target 43 for the hard magnetic underlayer 53, 32 to 48 Sm chips (size: 5 × 5 × 1 mm) are arranged near the erosion area on Co having a diameter of 203 mm. The constructed composite target was used. Also, target 4
3 is a C having a diameter of 203 mm for the soft magnetic underlayer 4.
o-Zr5-Nb4 at% alloy is used, and for the perpendicular magnetic recording layer 5, the same size Co-Cr15-Ta4 at is used.
% SiO _{2 with the} same size as the protective layer 6
It was used.

First, a hard magnetic underlayer 53 having a film thickness of 100 to 200 nm is formed on a mirror-finished soda lime glass substrate 1 having a diameter of 95 mm by using the above Co-Sm composite target as a target 43. did. The composition of Sm in the hard magnetic underlayer 53 varies depending on the number of Sm chips on the composite target, the positional relationship, and the sputtering power, but the obtained Sm composition ratio was 11 to 33 at%.

Then, a soft magnetic underlayer 4 having a thickness of 500 nm was formed with a Co--Zr5 --Nb4 at% alloy as a target 43, and a perpendicular magnetic recording layer 5 having a thickness of 75 nm was immediately formed with a Co--Cr15 --Ta4 at% alloy as a target 43. did.
By immediately forming a film here, Co-Zr-Nb and Co-Cr-Ta are directly bonded to each other, and the perpendicular magnetic recording layer 5 having a strong vertical orientation is obtained. During the film formation, a magnetic field of about 4 kA / m is constantly applied in the radial direction of the substrate 1 by the magnets 41 and 42 of the magnetron, so that the magnetization of the hard magnetic underlayer 53 and the soft magnetic underlayer 4 and The easy axis of magnetization is aligned in the radial direction of the substrate 1. Finally S as the protective layer 6
15 nm of iO ₂ was formed.

After the film formation was completed in this way, Example 1
The same heat treatment in a magnetic field was performed. That is, 10 ^-3 Pa
In the following atmosphere in vacuum, the perpendicular magnetic recording medium 50 is subjected to a heat treatment at 300 ° C. for 3 hours while rotating the film-formed perpendicular magnetic recording medium 50 in the magnetic field of 24 kA / m around the rotation center axis thereof to perform perpendicular magnetic recording. The medium 50 was obtained.

Here, in order to compare the characteristics with the second embodiment, the first embodiment and the third comparative example described above were used. The perpendicular magnetic recording medium of Comparative Example 3 was manufactured separately. A perpendicular magnetic recording medium 51 of Comparative Example 3 is configured as shown in FIG. 11, and includes a glass substrate 1, a soft magnetic underlayer 4, a perpendicular magnetic recording layer 5, and a protective layer 6 which are sequentially formed on the glass substrate 1. Consists of. The material and film forming conditions for each of the layers 4, 5, and 6 are the same as those in the above-described second embodiment.

Next, these samples (Example 2, Example 1)
And the characteristic evaluation result of the comparative example 3) is demonstrated. First, the recording / reproducing characteristics will be described. The recording / reproducing characteristics of these samples were as follows: a track width of 8 μm, a main magnetic pole thickness of 0.4 μm, and a single magnetic pole head having a coil winding number of 60 turns, a disk rotation speed of 2070 rpm, and a linear velocity of 8 m /
The measurement was performed under the conditions of s and head flying height of 80 nm.

Recording and reproducing a rectangular wave signal of 100 kHz,
Oscilloscope - solitary wave by-flops reproduction output E _pp (nV /
(Μm · t · m / s)) was measured. Here, the reproduction output is standardized by the track width (μm), the coil winding number (t), and the linear velocity (m / s). The ratio to Comparative Example 1 is expressed in dB. A signal of 6.67 MHz was recorded and reproduced, and the difference between the noise component and the system noise at that time was measured with a spectrum analyzer over a band of 16 MHz to obtain medium noise (μV _rms ). The ratio to Comparative Example 1 is expressed in dB. The ratio of the solitary-wave reproduction output E _pp to the medium noise was S / N, and the ratio to Comparative Example 3 was expressed in dB. Further, the ratio between the reproduction output immediately after the perpendicular magnetic recording medium was started to rotate and the reproduction output after 2 × 10 ⁴ rotations was the demagnetization amount (dB), and the ratio to Example 1 was expressed in dB. Table 2 shows the above measurement results.

[0048]

[Table 2]

According to Table 2, in the perpendicular magnetic recording medium 50 of Example 2 of the present invention, the reproduction output was increased and the medium noise was decreased as compared with Comparative Example 3 having no hard magnetic underlayer 53. As a result, the S / N is significantly improved to 2.1 dB. The S / N of Example 1 is equivalent to that of Comparative Example 3. The perpendicular magnetic recording medium 50 according to the present invention is improved in demagnetization amount up to the measurement limit level, which is equivalent to Example 1 in which the demagnetization amount is improved.

Next, the magnetic characteristics will be described. The magnetic characteristics of the perpendicular magnetic recording medium were evaluated by VSM.
First, the magnetic characteristics of a single CoSm film will be described. Figure 15
FIG. 4 is a diagram showing an MH curve of a single CoSm film that constitutes the hard magnetic underlayer 53 in Example 2 of the perpendicular magnetic recording medium of the present invention. The measurement results in the radial direction are shown. As can be seen in the figure, the radial MH curve exhibits a squareness ratio of approximately 1, while
The MH curve in the circumferential direction shows a gentle slope. From this, it is understood that the CoSm film is strongly oriented in the radial direction. In addition, the same MH curve was obtained within the range of the composition ratio of Sm of 11 to 33 at%, and the coercive force Hc was 50.
Was in the range of ~ 100 Oe. The CoSm film is manufactured in the same manner as the above-described method for manufacturing the hard magnetic underlayer 53, and the heat treatment in the magnetic field is also performed.

Next, the MH curve of the hard magnetic underlayer / soft magnetic underlayer composite layer will be described. First, the estimation of the MH curve of the composite layer when the CoSm film was used as the hard magnetic underlayer and the CoZrNb film was used as the soft magnetic underlayer was performed by simulation in consideration of magnetic interaction. FIG. 16 shows the CoSm film and Co used in the simulation.
The MH curve of a ZrNb film simple substance is shown. FIG. 17 shows CoS
The MH curve obtained as a result of simulating the composite layer of the m film and the CoZrNb film assuming that there is no magnetic interaction (magnetostatic coupling and exchange coupling) between the CoSm film and the CoZrNb film is shown. . That is, 2 in FIG.
Results are obtained by simply superimposing the curves.

On the other hand, FIG. 18 shows a CoSm film and a CoZrN film.
The MH curve obtained as a result of simulating the composite layer of the b film as having only the magnetic interaction of exchange coupling between the CoSm film and the CoZrNb film is shown. The apparent coercive force Hc is large. Further, FIG. 20 shows an MH curve obtained as a result of simulating a composite layer of a CoSm film and a CoZrNb film assuming that only a magnetic interaction of magnetostatic coupling exists between the CoSm film and the CoZrNb film. Shows. Apparent coercive force H
c indicates a negative value.

The MH curve of the actual composite film is shown in FIG. In FIG. 14, (A) shows an MH curve in the case where there is an intermediate layer between the composite layer of the soft magnetic underlayer / hard magnetic underlayer, which constitutes Example 2 of the perpendicular magnetic recording medium of the present invention. ,
(B) shows the MH curves of the composite layer of the soft magnetic underlayer / hard magnetic underlayer constituting Example 2 of the perpendicular magnetic recording medium of the present invention. In addition, CoS is used as the hard magnetic underlayer.
An m film, a CoZrNb film as a soft magnetic underlayer, and a 2 nm SiO ₂ layer as an intermediate layer were formed in the same manner as in Example 2 described above.

The MH curve shown in FIG. 14A is shown in FIG.
It is similar to the M-H curve shown in FIG.
The magnetic interaction between the CoSm film and the CoZrNb film is cut off. On the other hand, the MH curve shown in FIG.
It is similar to the MH curve shown in FIG.
It can be seen that strong exchange coupling works with the oZrNb film. From the shape of the MH curve shown in FIG. 20,
It can be seen that magnetostatic coupling alone does not act between the CoSm film and the CoZrNb film.

The MH curve of each sample was measured to clarify the relationship between the applied magnetic field of the composite layer of the soft magnetic underlayer / hard magnetic underlayer and the reversal magnetic field of the minor loop corresponding to the magnetic field. did. MH of composite layer of soft magnetic underlayer / hard magnetic underlayer
The (magnetization) curve will be described. First, the minor loop showing the relationship between the applied magnetic field H and the reversal magnetic field Hm obtained for the composite layer shown in FIG. 19 will be described. In FIG. 19, the horizontal axis represents the strength of the applied magnetic field H, the vertical axis represents the magnetization M, and u
Indicates a saturation magnetization curve (part), and v indicates a minor loop. Since the measurement of the MH curve was performed by applying a magnetic field in the in-plane direction of the substrate 1, even if the perpendicular magnetic recording layer 5 was present, the perpendicular magnetic recording layer 5 was perpendicular to the surface of the substrate 1. It has been found that since it has a strong anisotropy, it does not affect the measurement results described below.

First, when a magnetic field H increasing in the positive direction is applied to the non-magnetized composite layer, the initial magnetization curve not shown is followed, and the hard magnetic underlayer is positively magnetized in the positive direction. At the point a, which is a magnetic field strength that is sufficiently saturated, the magnetization M
Is saturated in the positive direction. Next, when the applied magnetic field H is decreased, the magnetization M follows the curve u and decreases. When the magnetic field H reaches 0, this time the magnetic field H is increased in the negative direction. When the magnetic field H reaches −Hc (coercive force) indicated by the point c, the magnetization M
Is 0. Further, when the magnetic field H is increased in the negative direction,
The composite layer is magnetized in the negative direction, and when the magnetic field H becomes -H1, b
Reach the point.

Next, when the magnetic field is inverted at point b and the magnetic field H is changed in the positive direction, the MH curve draws a minor loop, and the magnetization M changes along the curve v. Go. Then, the magnetic field H indicated by the point d when the magnetization M becomes 0
Is calculated as Hm (H1) (Hm is a reversal magnetic field). When the magnetic field H is further changed in the positive direction, it is magnetized in the positive direction and reaches point a again. By repeating this operation, the relationship between the applied magnetic field H and the reversal magnetic field Hm was obtained.

FIG. 12 shows the applied magnetic field H of the composite layer of the soft magnetic underlayer 3 / hard magnetic underlayer 2 when the hard magnetic underlayer 2 is Co-Sm in which the hard magnetic underlayer 2 is radially oriented according to the second embodiment of the present invention. And the reversal magnetic field Hm of the minor loop corresponding to the magnetic field are shown together with the first embodiment. In the second embodiment, Hm shows a constant negative value until H reaches 50 Oe (4 kA / m). This means that when the medium is stored,
It is shown that even if a magnetic field smaller than e is applied in the opposite direction to the magnetization of the hard magnetic underlayer 53, if the magnetic field is returned to 0, the original magnetization state is restored again.

On the other hand, in the composite layer of the soft magnetic underlayer 3 / hard magnetic underlayer 7 of Example 1, Hm changes monotonically with respect to the applied magnetic field H, which is the opposite direction when the medium is stored. If a magnetic field slightly exceeding the coercive force is applied, it will not return to the original magnetized state and there is a risk of demagnetization and spike noise when using the medium (of course, the above-mentioned. As described in Example 1, it is clear that the coercive force itself is much larger than that of the conventional example, and the demagnetization is improved).

Next, the crystallinity of the hard magnetic underlayers 53 and 3 is set to X.
The results of the line analysis method will be described. FIG.
Are Examples 1 and 2 of the perpendicular magnetic recording medium of the present invention.
FIG. 6 is a view showing an X-ray diffraction pattern of the perpendicular magnetic recording medium of FIG. As shown in the figure, in the hard magnetic underlayer 3 of Example 1, clear peaks of bcc-Cr and hcp-CoCrTa were observed, and it was found that they were clearly crystalline. On the other hand, in the hard magnetic underlayer 53 of the second embodiment,
No peaks from CoSm were observed, which indicates that the hard magnetic underlayer 53 is amorphous or microcrystalline. Note that a Cu target was used for diffraction, and in the case of Example 2, in order to confirm the diffraction peak, Example 1 was used.
A target current that is four times that of the target current was applied.

Further, by a scanning electron microscope (SEM), a hard magnetic underlayer 53, which is independently formed on the substrate 1,
As a result of observing the thin film surface of No. 3, clear crystal grains were observed in the hard magnetic underlayer 3 of Example 1, whereas
It was found that crystal grains were not found in CoSm of the hard magnetic underlayer 53 of Example 2 and the surface was smooth.

The magnetic characteristics and the range of the film thickness of the hard magnetic underlayer 53 to be used are determined in relation to the magnetic characteristics and the film thickness of the soft magnetic underlayer 4, and in the curve shown in FIG. The magnetic field at which Hm rises may be set to be sufficiently larger than the external magnetic field, for example, 500 A / m or more.

[0063]

As described above, according to the perpendicular magnetic recording medium of the present invention according to claim 1, the disk-shaped substrate, the soft magnetic underlayer formed on this substrate, and the soft magnetic underlayer. In a perpendicular magnetic recording medium having a perpendicular magnetic recording layer formed on an underlayer, all the magnetization directions between the substrate and the soft magnetic underlayer are the outer peripheral direction or the center direction in the radial direction of the substrate. By providing a hard magnetic underlayer having either magnetization, demagnetization due to rotation of the medium is prevented,
Medium noise can be reduced and high playback output can be obtained.
As a result, a high-performance and high-quality perpendicular magnetic recording medium can be provided.

According to the perpendicular magnetic recording medium of the present invention according to claim 2, a disk-shaped substrate, a soft magnetic underlayer formed on this substrate, and a soft magnetic underlayer formed on this substrate. In a perpendicular magnetic recording medium having a perpendicular magnetic recording layer,
In-plane orientation hard magnetic between the substrate and the soft magnetic underlayer, in which all the magnetization directions are either the outer circumferential direction or the central direction in the radial direction of the substrate and the orientation direction is in the plane of the substrate. By providing the underlayer, demagnetization due to rotation of the medium can be prevented, medium noise can be reduced, and high reproduction output can be obtained, thereby providing a high-performance and high-quality perpendicular magnetic recording medium. Can be done.

According to the perpendicular magnetic recording medium of the third aspect of the present invention, the disk-shaped substrate, the soft magnetic underlayer formed on the substrate, and the soft magnetic underlayer are formed. In a perpendicular magnetic recording medium having a perpendicular magnetic recording layer,
Between the substrate and the soft magnetic underlayer, provided is a radially oriented hard magnetic underlayer in which all the magnetizations are either in the radial direction toward the outer periphery or in the central direction and the orientation direction is the radial direction. As a result, demagnetization due to rotation of the medium can be prevented, medium noise can be reduced, and a high reproduction output can be obtained, whereby a high-performance and high-quality perpendicular magnetic recording medium can be provided.

According to the perpendicular magnetic recording medium of the present invention according to claim 4, the perpendicular magnetic recording medium according to claim 3, wherein the radially oriented hard magnetic underlayer is a Co alloy containing Sm (samarium). By using a film, demagnetization due to rotation of the medium can be prevented, medium noise can be reduced, and high reproduction output can be obtained, thereby providing a high-performance and high-quality perpendicular magnetic recording medium. .

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view schematically showing the configuration of a first embodiment of a perpendicular magnetic recording medium of the present invention.

FIG. 2 is a partial cross-sectional view schematically showing the configuration of a perpendicular magnetic recording medium of a first comparative example.

FIG. 3 is a partial cross-sectional view schematically showing the configurations of perpendicular magnetic recording media of a first conventional example and a second comparative example.

FIG. 4 shows the normalized applied magnetic field H / Hc in the MH curve of the soft magnetic underlayer / hard magnetic underlayer and the H of the minor loop.
It is a graph which shows the relationship with m (H).

FIG. 5 is a graph showing an MH curve of a composite layer of a soft magnetic underlayer / hard magnetic underlayer which constitutes the first embodiment of the perpendicular magnetic recording medium of the present invention.

FIG. 6 is a graph showing an MH curve of a soft magnetic underlayer forming the perpendicular magnetic recording medium of the second comparative example.

FIG. 7 is a schematic cross-sectional view showing a configuration near a target electrode of a DC magnetron sputtering apparatus used for manufacturing a perpendicular magnetic recording medium.

FIG. 8 is a conceptual diagram for explaining heat treatment in a magnetic field, which is one of the manufacturing steps of a perpendicular magnetic recording medium.

FIG. 9 is a partial cross-sectional view schematically showing the configuration of a perpendicular magnetic recording medium of a second conventional example.

FIG. 10 is a partial cross-sectional view schematically showing the configuration of a second embodiment of the perpendicular magnetic recording medium of the present invention.

FIG. 11 is a partial cross-sectional view schematically showing the configuration of a perpendicular magnetic recording medium of a third comparative example.

FIG. 12 shows applied magnetic field H and its magnetic field of a composite layer of a soft magnetic underlayer / hard magnetic underlayer constituting the perpendicular magnetic recording media of the first and second embodiments of the perpendicular magnetic recording medium of the present invention. It is a graph showing the relationship with the switching field Hm of the minor loop.

FIG. 13 is a diagram showing X-ray diffraction patterns of the perpendicular magnetic recording media of the first and second embodiments of the perpendicular magnetic recording medium of the present invention.

FIG. 14 is a graph showing MH curves of the soft magnetic underlayer / hard magnetic underlayer composite layer in the second embodiment of the perpendicular magnetic recording medium of the present invention, with and without an intermediate layer. FIG.

FIG. 15 is an M− of a single CoSm film forming the hard magnetic underlayer 2 in the second embodiment of the perpendicular magnetic recording medium of the present invention.
It is a figure which shows a H curve.

FIG. 16 is a diagram showing MH curves obtained as a result of simulation for each of the soft magnetic underlayer and the hard magnetic underlayer constituting the second embodiment of the perpendicular magnetic recording medium of the present invention.

FIG. 17 shows a magnetic layer between a soft magnetic underlayer and a hard magnetic underlayer of a composite layer of a soft magnetic underlayer / hard magnetic underlayer which constitutes a second embodiment of the perpendicular magnetic recording medium of the present invention. M- obtained as a result of simulating that there is no interaction
It is a figure which shows a H curve.

FIG. 18 shows a soft magnetic underlayer / hard magnetic underlayer composite layer constituting the second embodiment of the perpendicular magnetic recording medium of the present invention, and the soft magnetic underlayer and the hard magnetic underlayer are exchanged with each other. MH obtained as a result of simulating that it has an action
It is a figure which shows a curve.

FIG. 19 is a diagram showing a minor loop for explaining the relationship between an applied magnetic field H and a reversal magnetic field Hm.

FIG. 20 shows a magnetostatic layer between a soft magnetic underlayer and a hard magnetic underlayer of a composite layer of a soft magnetic underlayer / hard magnetic underlayer which constitutes a second embodiment of the perpendicular magnetic recording medium of the present invention. It is a figure which shows the MH curve obtained as a result of simulating as having a bond.

[Explanation of symbols]

 1 Circular Substrate 2 Chromium Layer 3 Hard Magnetic Underlayer 4 Soft Magnetic Underlayer 5 Perpendicular Magnetic Recording Layer 6 Protective Layer 9 Rotation Center Axis 10 Perpendicular Magnetic Recording Medium (Example 1) 11 Perpendicular Magnetic Recording Medium (Comparative Example 1) 12 Perpendicular Magnetic Recording Medium (Conventional Example 1) 13 Perpendicular Magnetic Recording Medium (Conventional Example 2) 21 Glass Substrate 24 Soft Magnetic Underlayer 25 Perpendicular Magnetic Recording Layer 26 Protective Layer 31 Glass Substrate 32 Chrome Layer 34 Soft Magnetic Underlayer 35 Perpendicular Magnetic Recording Layer 36 Protective Layer 37 Carbon Layer 41 First Permanent Magnet 42 Second Rare Earth Permanent Magnet 43 Target 50 Perpendicular Magnetic Recording Medium (Example 2) 51 Perpendicular Magnetic Recording Medium (Comparative Example 1) 53 Hard Magnetic Underlayer

Claims (4)

[Claims] 1. A perpendicular magnetic recording medium comprising a disk-shaped substrate, a soft magnetic underlayer formed on the substrate, and a perpendicular magnetic recording layer formed on the soft magnetic underlayer. A perpendicular magnetic layer characterized in that a hard magnetic underlayer having a magnetization in which all the magnetization directions are either the outer peripheral direction or the central direction in the radial direction of the substrate is provided between the substrate and the soft magnetic underlayer. recoding media. 2. A perpendicular magnetic recording medium comprising a disk-shaped substrate, a soft magnetic underlayer formed on the substrate, and a perpendicular magnetic recording layer formed on the soft magnetic underlayer. Between the substrate and the soft magnetic underlayer, an in-plane oriented hard magnetic layer in which all the magnetization directions are either the outer peripheral direction or the central direction in the radial direction of the substrate and the orientation direction is in the plane of the substrate. A perpendicular magnetic recording medium having a stratum. 3. A perpendicular magnetic recording medium comprising a disk-shaped substrate, a soft magnetic underlayer formed on the substrate, and a perpendicular magnetic recording layer formed on the soft magnetic underlayer. Between the substrate and the soft magnetic underlayer, provided was a radially oriented hard magnetic underlayer in which all the magnetization was either in the radial direction toward the outer periphery or in the central direction, and the orientation was in the radial direction. Perpendicular magnetic recording medium characterized. 4. The perpendicular magnetic recording medium according to claim 3, wherein the radially oriented hard magnetic underlayer is Sm (samarium).
A perpendicular magnetic recording medium comprising a Co alloy film containing