JP2002304788A - Magneto-optical recording medium and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magneto-optical recording medium and a method for manufacturing the medium in which magnetic field modulation overwriting is possible, high CNR characteristics and power margin characteristics are obtained even when the medium is formed by using a MO target with low magnetic permeability, and the productivity can be improved. SOLUTION: The magneto-optical recording medium has a magnetic recording layer in which the magnetization state varies by applying an external magnetic field accompanied with the irradiation of recording light and the medium changes the polarization state of the reproducing light entering from a first face side of the magnetic recording layer. The magnetic recording layer is formed by sputtering by using a target having <=2.0 magnetic permeability. The proportion of the terbium (Tb) content in the target ranges from 24.5 to 25.5 atom.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a magneto-optical recording medium and a method for manufacturing the same, and more particularly, to a magneto-optical recording medium compatible with a magnetic field modulation overwrite method and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, in the field of information recording, researches on optical recording systems have been conducted in various places. This optical recording system records and reproduces information using a laser beam, and as an optical recording medium using the optical recording system,
2. Description of the Related Art A read-only digital audio disc (so-called compact disc), an optical video disc (so-called laser disc (registered trademark)), and the like are widely used.

On the other hand, magneto-optical recording media have been developed and commercialized as writable optical recording media in which a user can repeatedly record and erase information. As such a magneto-optical recording medium, a mini disk (MD) is widely used.

[0004] Mini discs can easily record music and the like as consumer recording equipment, and are excellent in portability.
It is used in a variety of applications, from home use to automotive use. With the expansion of the market scale, the price of the recording medium has also decreased, and it is desired that the productivity of the manufacturer be improved.

[0005] A magneto-optical recording medium such as a mini disk has a magnetic recording layer formed of a magnetic thin film having an easy axis of magnetization in a direction perpendicular to the film surface and having a large magneto-optical effect on a transparent substrate. The magnetic recording layer is laminated together with the reflective layer and the dielectric layer to form a recording unit. Further, a protective film is provided on the recording unit.

Various materials have been studied as magneto-optical recording materials constituting the magnetic recording layer, but Tb-Fe-Co
Based alloys are currently the mainstream. Amorphous rare earths other than Tb, specifically, gadolinium (G
Heavy rare earths such as d) and dysprosium (Dy) and light rare earths such as neodymium (Nd) can be used for the magnetic recording layer. For example, Gd-Fe-Co, Gd-Fe,
Tb-Fe, Gd-Tb-Fe, Nd-Dy-Fe-C
O and the like are known as amorphous rare earth-transition metal alloy-based magneto-optical recording materials.

The magnetic recording layer of a magneto-optical recording medium is often formed by sputtering. According to a vapor phase method such as sputtering or vapor deposition, an amorphous film of the above-described alloy is formed. Hereinafter, a target used when the magnetic recording layer is formed by sputtering is particularly referred to as an MO (magneto-optical) target.

Generally, the rare earth element and the 3d transition metal do not form a solid solution with each other, but form an intermetallic compound at a plurality of specific composition ratios. Therefore, even if the composition of the MO target is the same, the abundance ratio of the intermetallic compound phase and the rare earth element single phase and / or the transition metal single phase in the MO target, the presence or absence of these single phases, the intermetallic compound The characteristics of the MO target vary depending on the particle size of the phase, the particle size of the single phase, the type of the intermetallic compound, and the like.

For example, Japanese Unexamined Patent Publication No. Sho 62-70550 discloses an MO target containing 30 to 50% by weight of a rare earth such as Tb and an iron group metal such as Fe or Co. An MO target having a mixed structure of a compound and a simple substance of an iron group metal is disclosed. On the other hand,
JP-A-3-274774 discloses rare earth elements such as Tb.
An MO target containing 0 atomic% and a transition metal such as Fe or Co, which has a mixed structure of a rare earth-transition metal intermetallic compound and a rare earth element alone is disclosed.

[0010] According to [Example] of JP-A-63-274664, the sample No. As No. 2, a Tb—Fe—Co alloy target having a composition of 48.5% by weight of Tb, 44.2% by weight of Fe, and 7.2% by weight of Co is formed. As a comparative example, an MO target described in JP-A-62-70550 was formed. This composition had 48.6% by weight of Tb, 43.8% of Fe, and 7.60% of Co.
1% by weight. Thus, the sample No. Although the target composition can be considered to be the same in the comparative example and the comparative example, the magnetic permeability of the target is different from each other. The magnetic permeability of No. 2 is 0.65 as a relative value.

[0011] In addition to the magnetic permeability, target characteristics such as bending strength, oxygen content, and density change in accordance with the existence state of the rare earth and the transition metal in the alloy as described above.
Therefore, even if the composition of the MO target is the same,
The characteristics of MO targets are not always the same. When a magnetic recording layer is formed using MO targets having different characteristics, differences occur in the coercive force, film quality uniformity, and the like of the magnetic recording layer, which also affects the recording / reproducing characteristics of the magneto-optical recording medium.

The MO target can be manufactured by various methods such as melting casting and powder sintering. When forming an MO target by powder sintering, Fe powder,
Not only single element powder such as Co powder, but also alloy powder such as Fe-Co alloy powder, Tb-Fe alloy powder, and Tb ₄ O
It is also possible to use metal oxide powder such as ₇ powder. It is possible to control the composition and structure of the MO target according to the MO target manufacturing method, the processing conditions in each manufacturing process, and the like.

Conventional MO targets and / or methods for producing the same are described in, for example, JP-A-64-25977, JP-A-64-25977, and JP-A-6-257054. −129964
JP, JP-A-129965, JP-A-4-325
No. 670 and JP-A-8-302463.

[0014] Of the above publications,
Patent Document 4 discloses a target characterized in that the metal structure is composed of a rare earth metal single phase and a rare earth transition metal alloy phase. Japanese Patent Application Laid-Open No. 1-129965 discloses that the metal structure is composed of a rare earth metal single phase and a rare earth transition metal alloy phase, and the main composition of the target is Gd, Tb, Db.
A target characterized by containing at least one heavy rare earth element of y and at least one transition metal of Fe and Co is disclosed.

It is described that these targets have low magnetic permeability, and sufficient leakage magnetic flux can be obtained even if the targets are made thick. According to Example 1 of JP-A-1-129965, the composition is Tb ₂₂ Fe _70.2 Co _7.8 atom%.
And a target having a magnetic permeability of 3 was obtained.

Japanese Patent Application Laid-Open No. 4-325670 discloses F
e, discloses a method of manufacturing a target in which a suitable alloy powder having a lower maximum magnetic permeability than that of pure Co metal powder is mixed and sintered or the like is mixed. According to the embodiment of JP-A-4-325670, for example, when a target having a composition of Tb ₂₃ Fe _3.85 Co _73.15 is formed using Fe and Co powders, the maximum magnetic permeability is 35, but the same The maximum magnetic permeability is reduced to 17 when a target having the following composition is formed using Fe ₃₀ Co ₇₀ powder and Co powder.

JP-A-8-302463 discloses 15
An MO target is disclosed, in which an alloy powder composed of a rare earth metal of up to 30 atom% and a balance transition metal has a target structure sintered substantially in the form of an alloy powder. In Example 1 of JP-A-8-302463, Tb 26 atom%, Fe 68 atom
It is described that an MO target having a relative magnetic permeability of 2 was obtained by pulverizing an alloy ingot having a composition of 6% and 6 atom% of Co and performing hot isostatic pressing (HIP) sintering.

[0018]

Since the Tb-Fe-Co alloy used as the MO target is a magnetic material,
When the magnetic recording layer is formed by magnetron sputtering, particularly when the MO target has a high magnetic permeability,
When the target is thick, the leakage magnetic flux on the surface of the MO target becomes small.

When the leakage flux is small, magnetron discharge is less likely to occur. As a result, the sputtering efficiency decreases, and the film forming speed decreases. In addition, the uniformity of the film quality of the formed magnetic recording layer is apt to decrease. In order to increase the film formation rate by increasing the leakage magnetic flux, it is necessary to make the MO target thinner. However, when the MO target is made thinner, the ratio of the usable portion per MO target, that is, the MO target,
Target usage efficiency is reduced.

As described above, with the widespread use of magneto-optical recording media such as mini-discs, there is a strong demand for lowering the price of magneto-optical recording media. Generally, since amorphous rare earths are expensive, it is desired to improve the use efficiency of the MO target and reduce the cost of raw materials.

As a method of increasing the use efficiency of the MO target, there are a method of increasing the thickness of the MO target and a method of increasing the diameter of the MO target. When the MO target diameter is increased, magnetic recording layers can be formed on a plurality of magneto-optical recording media by one sputtering, but the film quality of the magnetic recording layers tends to be non-uniform. Also, when the diameter of the MO target is increased, it becomes difficult to obtain an MO target having a uniform composition depending on the method of manufacturing the MO target.

To increase the film formation rate by increasing the leakage magnetic flux without reducing the thickness of the MO target, reduce the permeability of the MO target or adjust the arrangement of the magnets in the cathode, etc. It is necessary to change the distance between the film and the film formation surface. However, when the permeability of the MO target is reduced, there arises a problem that disk characteristics represented by CNR (carrier noise ratio) characteristics and power margin characteristics are reduced.

In particular, when a magnetic field modulation method is adopted as an overwrite method for a magneto-optical recording medium instead of a conventionally widely used optical modulation method, disk characteristics higher than those of a magneto-optical recording medium for an optical modulation method are adopted. Is required. According to the light modulation method, by aligning the magnetization of the entire track in one direction, all the information of one track is erased, and then the information is written again. Therefore, it is difficult for the optical modulation method to increase the data transfer speed.

On the other hand, the magnetic field modulation system is a direct overwrite system in which new information is written and information recorded so far is erased. Therefore, it is possible to increase the data transfer speed. To record information by the magnetic field modulation method, it is necessary to modulate the applied magnetic field at a high speed. However, since it is difficult to generate a large alternating magnetic field, a magneto-optical recording material capable of recording with a low applied magnetic field is desired.

As a material recordable in a low magnetic field, for example, an amorphous Gd-Dy-Fe-Co alloy film or the like has been proposed. However, by shortening the distance between the magnetic recording layer and the magnetic head, an optical modulation method has been proposed. It is also possible to apply a frequently used amorphous Tb-Fe-Co alloy film to the magnetic field modulation method.

As described above, if the permeability of the MO target is reduced without reducing the thickness of the MO target, the film quality of the magnetic recording layer is reduced, and the CNR characteristics and the power margin characteristics of the magneto-optical recording medium become insufficient. In particular, when the magnetic field modulation overwrite method is adopted, it is necessary to sufficiently enhance the disk characteristics.

In order to compensate for a decrease in disk characteristics due to the use of an MO target having a low magnetic permeability and to improve signal characteristics, a guide groove (groove) for an optical guide is formed.
Adjustment of the thickness of the dielectric layer has been performed. Grooves are usually
Width of the same or less than the laser wavelength (0.6 to
1.0 μm), and are provided spirally or concentrically over the entire surface of the disk.

When a dielectric layer having a refractive index higher than the refractive index of the substrate is formed on an optical recording medium or a magneto-optical recording medium, the apparent Kerr rotation angle is enhanced by the effects of multiple reflection and interference (enhancement). effect). However,
At a film thickness at which the Kerr rotation is maximized, the reflectance is minimized.

At present, it is difficult to obtain a disk characteristic which can sufficiently cope with the magnetic field modulation overwriting method by the above method. As described above, conventionally, various MO targets and methods for manufacturing the same have been proposed. However, the permeability and target composition of the MO target which can optimize the disk characteristics and improve the productivity of the magneto-optical recording medium are improved. Not disclosed.

The present invention has been made in view of such problems, and accordingly, the present invention is capable of magnetic field modulation overwriting, and has a high CNR characteristic even when formed using an MO target having a low magnetic permeability. It is another object of the present invention to provide a magneto-optical recording medium capable of obtaining a power margin characteristic and improving productivity, and a method of manufacturing the same.

[0031]

In order to achieve the above-mentioned object, a magneto-optical recording medium of the present invention has a magnetic recording layer whose magnetization state changes by application of an external magnetic field accompanied by irradiation of recording light. A magneto-optical recording medium for changing a polarization state of a reproduction light incident from a first surface side of a magnetic recording layer, wherein the magnetic recording layer is a layer formed by sputtering using a target having a magnetic permeability of 2.0 or less. The target has a Tb content in the range of 24.5 to 25.5 atom%.

[0032] The magneto-optical recording medium of the present invention preferably has a reflection film for reflecting recording light and reproduction light on the second surface side of the magnetic recording layer. The magneto-optical recording medium of the present invention preferably has a light-transmitting substrate on the first surface of the magnetic recording layer via a first dielectric layer. The magneto-optical recording medium of the present invention is preferably provided on the second surface of the magnetic recording layer,
It has the reflection film via a second dielectric layer. The magneto-optical recording medium of the present invention further preferably further includes a protective film on the reflective film. Preferably, said target comprises a transition metal. More preferably, said target comprises Fe and Co.

Preferably, recording of information on the magnetic recording layer is performed by changing the direction of an external magnetic field while continuously irradiating the recording light, and the magnetization of the magnetic recording layer is aligned in one direction. The information can be recorded both when the information is recorded and when the information is not aligned in one direction. Alternatively, preferably, recording of information on the magnetic recording layer is performed by applying a DC magnetic field while intermittently irradiating the recording light, and when the magnetization of the magnetic recording layer is aligned in one direction. Can record information.

Preferably, the magnetic recording layer has a magnetic permeability of 5.0 or more and a Tb content of 2.0 to 2.0 from the above range.
3.0 atom% lower, 22.0 to 23.0 atom%
Recording / equivalent to the second magnetic recording layer formed by sputtering using the second target in the range of
Has reproduction characteristics.

According to the magneto-optical recording medium of the present invention, even when the target is thickened, the main characteristics of the magneto-optical recording medium, namely, the CNR characteristic and the power margin characteristic do not deteriorate. Therefore, the signal quality is stabilized, and magnetic field modulation overwriting is possible. Further, compared to a conventional magneto-optical recording medium formed using a target having a high magnetic permeability, the use efficiency of raw materials is higher, so that cost can be reduced.

In order to achieve the above object, the magneto-optical recording medium of the present invention has a first magnetic recording layer whose magnetization state changes by application of an external magnetic field accompanied by irradiation of recording light. What is claimed is: 1. A magneto-optical recording medium for changing a polarization state of reproduction light incident from a first surface side of a magnetic recording layer, wherein the first magnetic recording layer is formed by sputtering using a first target having a predetermined magnetic permeability. Wherein the first magnetic recording layer is equal to or more than a second magnetic recording layer formed by sputtering using a second target having a higher magnetic permeability than the first target. The first target and the second target have recording and reproducing characteristics, and the first target and the second target include a rare earth element and a transition metal, and the first target and the second target
The target has a rare earth element content in a range higher than the rare earth element content of the second target.

Accordingly, even when an amorphous rare earth-transition metal alloy-based magneto-optical recording material such as Gd-Tb-Fe containing rare earth other than Tb such as Gd or Dy is formed by magnetron sputtering, The thickness of the target can be increased without deteriorating the characteristics. Therefore, the signal quality of the magneto-optical recording medium can be stabilized, and the manufacturing cost can be reduced.

To achieve the above object, a method for manufacturing a magneto-optical recording medium according to the present invention comprises a step of forming a first dielectric layer on a light-transmitting substrate, and a step of forming a first dielectric layer on the first dielectric layer. , The magnetic permeability is 2.0 or less, and the Tb content is 24.5-25.
Forming a magnetic recording layer by magnetron sputtering using a target in the range of 5 atom%, forming a second dielectric layer on the magnetic recording layer, and forming a second dielectric layer on the second dielectric layer. Forming a reflective film;
Forming a protective film on the reflective film.

According to the method of manufacturing a magneto-optical recording medium of the present invention, it is possible to manufacture a magneto-optical recording medium having high CNR characteristics and power margin characteristics by increasing the thickness of a target. Since the target can be made thicker, it is possible to increase the use efficiency of the raw material and reduce the production cost.

[0040]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a magneto-optical recording medium and a method for manufacturing the same according to the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of the magneto-optical recording medium of the present embodiment. The magneto-optical recording disk 1 shown in FIG. 1 has a structure in which a first dielectric layer 3, a magnetic recording layer 4, a second dielectric layer 5, a reflective film 6, and a protective film 7 are sequentially laminated on a disk substrate 2. Having. When information is recorded on the magneto-optical disk 1, the recording layer 4 is irradiated with laser light L from the disk substrate 2 side, and at the same time, a magnetic field is applied by the magnetic head 8. In FIG. 1, FL indicates a condenser lens (the same applies to FIGS. 2 and 3).

When reproducing information recorded on the magneto-optical disk 1, the recording layer 4 is irradiated with laser light from the disk substrate 2 side with a lower laser power than during recording. The laser light L incident on the magneto-optical recording disk 1 is
The light is reflected by the reflection film 6 and is detected by a light receiver provided on the disk substrate 2 side (laser side) of the magneto-optical recording disk 1.

In the sputtering for forming the magnetic recording layer 4 of the magneto-optical recording disk 1 of this embodiment, the magnetic permeability is 2.0 or less and the Tb content is 24.5 to 25.5.
An MO target of atom% is used. This M
The O target contains Fe and Co, which are transition metals, in addition to Tb. Fe content is, for example, 65 to 70 atom%.
Before and after, the Co content is, for example, 10 atom% or less.

Since the Tb-Fe-Co alloy is easily oxidized, titanium (Ti), aluminum (Al), vanadium (V),
Niobium (Nb), tantalum (Ta), chromium (Cr),
At least one of molybdenum (Mo), tungsten (W), palladium (Pd), and platinum (Pt) may be added in a small amount. Specifically, the MO target is, for example, 1 to 4 atom% of Cr or 0.5% of Nb.
Approximately 3 atom% may be contained. In addition to the above, an impurity element such as calcium (Ca) which is inevitably mixed in the process of manufacturing the MO target may be included.

Conventionally, a magnetic recording layer of a magneto-optical recording disk applied to the magnetic field modulation overwrite method uses an MO target having a magnetic permeability of 5.0 or more and a Tb content of about 22.5%. It was formed by sputtering. MO with low permeability without changing Tb content
When the magnetic recording layer is formed using the target, the disk characteristics of the magneto-optical recording medium deteriorate.

Using an MO target having a magnetic permeability of 2.0 or less, the magnetic recording layer 4 of the magneto-optical recording disk 1 of this embodiment is used.
When the magnetic recording layer of the magneto-optical recording disk is formed using an MO target having a magnetic permeability of 5.0 or more, the Tb content of the MO target composition is 2.0 to 2.0.
3.0 atom% higher. Thereby, the magnetic permeability is 5.0.
It is possible to obtain disk characteristics equal to or higher than the case where the above MO target is used. The magnetic recording layer 4 is formed with a thickness of, for example, about 15 to 25 nm.

Next, the magneto-optical recording disk 1 of the present embodiment
Each layer other than the magnetic recording layer 4 constituting the above will be specifically described. As shown in FIG. 1, the laser beam L is transmitted during recording / reproducing, as shown in FIG. 1, so that the disc substrate 2 is desirably transparent to light for recording / reproducing, for example, light having a wavelength of 780 nm.

Specific examples of the material of the disk substrate 2 include transparent resins such as polycarbonate, acrylic resin, amorphous polyolefin, and styrene resin, and glass. On the side of the disk substrate 2 where the laser light L is incident, a groove for light guide is formed in a spiral or concentric shape on the entire surface, for example, with a width (0.6 to 1.0 μm) which is about the same as or smaller than the laser wavelength. Is provided.

First dielectric layer 3 and second dielectric layer 5
Is provided for the purpose of improving CNR characteristics and preventing corrosion and oxidation of the magnetic recording layer 4. As described above, Tb−
Since the Fe—Co alloy is easily oxidized, the dielectric layers 3 and 5 are formed on the surface of the magnetic recording layer 4. The thickness of the first dielectric layer 3 may be generally 30 to 100 nm, and the thickness of the second dielectric layer 5 may be generally 5 to 100 nm.

As a material of each of the dielectric layers 3 and 5, for example, an oxide, a nitride or a mixture thereof, specifically, silicon oxide (SiO), silicon nitride (SiN), aluminum nitride (AlN _x ), oxide Yttrium (Y ₂ O
₃ ), aluminum oxide (Al ₂ O ₃ ), zinc sulfide (Z
Although nS), SiAlON, Tb-added SiO _{2 and the} like can be used, SiN _x is mainly used.

When the first dielectric layer 3 having a higher refractive index than the refractive index of the disk substrate 2 is formed, the apparent Kerr rotation angle is enhanced by the effects of multiple reflection and interference (enhancement effect). At a film thickness at which the Kerr rotation is maximized, the reflectance is minimized, but the CNR characteristics can be improved.

As a material of the reflection film 6, a metal is used.
Specific examples include Al, Au, Ag, and Cu, alloys containing at least one of these, and materials obtained by adding an appropriate amount of an element such as Ni, Ti, Cr, Co, or Pd to these metals or alloys. . It is preferable to provide a protective film 7 made of an ultraviolet curable resin or the like on the surface of the reflective film 6. The thickness of the protective film 7 is preferably 5 to 20 μm.

In particular, when the magnetic head is the magneto-optical recording disk 1
In the case of using a recording device of a sliding type that makes contact with one surface of the recording medium, the protective film 7 is indispensable. Although there is a non-contact type recording device in which the distance between the surface of the protective film 7 and the magnetic head is several μm (for example, about 2 to 4 μm), in the following Examples and Comparative Examples, the magneto-optical recording disk is Since the present invention was applied to a recording apparatus of the type, a protective film 7 was formed.

The magneto-optical recording medium of the present embodiment can be applied to a magnetic field modulation overwrite method. FIG.
FIG. 2 is a diagram showing the principle of the magnetic field modulation overwrite method. In FIG. 2, the magneto-optical recording disk 1 shown in FIG.
Only the disk substrate 2 and the magnetic recording layer 4 are shown.

As shown in FIG. 2, a continuous wave laser beam L is used as a recording beam, and the laser beam L is focused on one point on the magnetic recording layer 4 of the magneto-optical recording disk 1. Thereby, only the portion irradiated with the laser beam L is locally heated to the Curie temperature or higher. In this case, alternating magnetic field corresponding to the input signal S _M from the magnetic head 8 is applied, the information is recorded. Incidentally, LS is a semiconductor laser, S _L denotes an input signal to oscillate the laser (Fig. 3 as well).

The magnetic field modulation system is a direct overwrite system in which new information is written and at the same time the previously recorded information is erased. Therefore, if the magnetization is not reversed exactly in accordance with the applied magnetic field, old information can be left unerased, which becomes a noise source.

In the case of the magnetic field modulation method, it is necessary to modulate the applied magnetic field at a high speed. However, since it is difficult to generate a large alternating magnetic field, the distance between the magnetic recording layer 4 and the magnetic head 8 is minimized. It is necessary to slide the magnetic head 8 on the magneto-optical recording disk 1 or to use a magneto-optical recording material that can be recorded with a low magnetic field.

At the time of reproducing information, the laser power is made lower than at the time of recording so that magnetization reversal does not occur. For example,
When a laser beam having a wavelength of 780 nm is used, the recording laser power is 4.55 mW and the bias magnetic field is 200O.
e, and the laser power during reproduction is 0.6 mW.

The magneto-optical recording medium of the present embodiment is suitably used for a magnetic field modulation overwrite system, but can also be applied to a general-purpose optical modulation writing system. FIG. 3 is a diagram illustrating the principle of the light modulation method. As shown in FIG. 3, as the recording light, modulated laser beam L is used in accordance with the input signal S _L. Laser light L is applied to magneto-optical recording disk 1
At one point on the magnetic recording layer 4. A DC magnetic field is applied from the magnetic head 8.

Only the portion irradiated with the laser beam L is locally heated to the Curie temperature or higher, and information is recorded.
In the case of the light modulation method, by aligning the magnetization of the entire track in one direction, all the information of one track is erased,
Information is written again.

Hereinafter, disk characteristics of the magneto-optical recording medium of the present invention will be described based on examples and comparative examples. (Example 1) A magneto-optical recording disk having the structure shown in FIG. 1 was manufactured by the following procedure. First, using a polycarbonate resin, an outer diameter of 64 mm and a thickness of 1.2 were obtained by an injection molding method.
mm transparent disk substrate 2 was produced. Next, a silicon nitride film is formed by sputtering using Si as a target in an Ar atmosphere in the presence of N ₂ gas,
Of the dielectric layer 3.

Next, the magnetic recording layer 4 was formed by sputtering using an MO target in an Ar atmosphere. At this time, an MO target having a thickness of 12 mm, a magnetic permeability of 1.5 and a Tb content of 25 atom% was used. The Tb content is 2.5% larger than the Tb content of 22.5% at which good disk characteristics can be obtained with an MO target having a magnetic permeability of 5.5 (see Comparative Example 1 described later).

After forming the magnetic recording layer 4, a silicon nitride film was formed by sputtering using Si as a target in an Ar atmosphere in the presence of a N ₂ gas to form a second dielectric layer 5. Next, in an Ar atmosphere, Al-
The reflection film 6 was formed by sputtering using a Ti alloy as a target. Next, an ultraviolet-curable resin was applied by a spin coating method, and was cured by irradiation with ultraviolet light to form a protective film 7.

The characteristics of the magneto-optical recording disk manufactured as described above were measured using an optical media standard evaluation device.
The CNR characteristics were measured at a laser wavelength of 780 nm, a numerical aperture (NA) of 0.45, and a recording laser power of 4.55 m.
W, reproducing laser power 0.6 mW, bias magnetic field 10
The test was performed under the condition of 0 Oe. The standard value of the bias magnetic field of the magneto-optical recording disk of this specification is 200 Oe.
By measuring the bias magnetic field at 100 Oe, recording characteristics in a critical region of a low magnetic field (limit region where writing is possible) were evaluated.

The power margin characteristics were measured under the conditions of a laser wavelength of 780 nm, a numerical aperture (NA) of 0.45, a reproduction laser power of 0.6 mW, and a bias magnetic field of 200 Oe. During recording, the laser power was varied from 2.5 mW to 7 mW based on 4.55 mW.

As the laser power during recording is increased from 4.55 mW, the number of errors increases. Error count is 2
When the laser power when the number of lasers reaches 20 is Pw _max (unit is mW), (Pw _max -4.55) /4.5
5 expressed as a percentage was defined as a plus-side power margin Pw (+).

Similarly, the recording laser power was set to 4.55.
As the number of errors decreases, the number of errors increases. The laser power when the number of errors reaches 220 is Pw
_min (unit is mW), (Pw _min -4.5
5) /4.55 expressed as a percentage was defined as a negative power margin Pw (-).

The CNR characteristics and the power margin P of the magneto-optical recording disk of Example 1 measured by such a method.
Table 1 shows w (+) and Pw (-). Here, the target value of the CNR characteristic was set to 47.5 dB or more, and the target value of the power margin characteristic was set to 27% or more on both the plus side and the minus side.

[0068]

[Table 1]

As shown in Table 1, according to the magneto-optical recording disk of Example 1, the CNR characteristics and the power margin P
Target values were achieved for both w (+) and Pw (-). Further, the thickness of the MO target is 12 mm, and the usage efficiency of the MO target is high.

Example 2 The thickness of the magnetic recording layer 4 was
2 mm, permeability 2.0, Tb content 25.5 atom%
A magneto-optical recording disk was manufactured in the same manner as in Example 1 except that the MO target was used. As shown in Table 1, according to the magneto-optical recording disk of Example 2, the CNR
The target values were achieved for both the characteristics and the power margins Pw (+) and Pw (−). Further, the thickness of the MO target is 12 mm, and the usage efficiency of the MO target is high.

Example 3 The magnetic recording layer 4 was formed with a thickness of 1
2 mm, magnetic permeability 1.5, Tb content 24.5 atom%
A magneto-optical recording disk was manufactured in the same manner as in Example 1 except that the MO target was used. As shown in Table 1, according to the magneto-optical recording disk of Example 3, the CNR
The target values were achieved for both the characteristics and the power margins Pw (+) and Pw (−). Further, the thickness of the MO target is 12 mm, and the usage efficiency of the MO target is high.

When the magnetic recording layer 4 is formed using an MO target having a magnetic permeability of 2.0 or less and a Tb content of 26 atom% or more, the magnetic recording layer 4 is heated to a temperature higher than the Curie temperature by irradiating a laser beam to cause magnetization reversal. Can not be caused. Therefore, information could not be recorded and data could not be obtained.

(Comparative Example 1) The thickness of the magnetic recording layer 4 was
A magneto-optical recording disk was produced in the same manner as in Example 1 except that an MO target having a thickness of 5.5 mm, a magnetic permeability of 5.5, and a Tb content of 22.5 atom% was used. The magneto-optical recording disk of Comparative Example 1 is a disk on which magnetic field modulation overwriting is possible, and has a CNR equivalent to this magneto-optical recording disk.
A magneto-optical recording disk having characteristics and power margins Pw (+) and Pw (-) can be regarded as having sufficient characteristics for magnetic field modulation overwriting.

The magneto-optical recording disks of Examples 1 to 3 have CNR characteristics and power margin characteristics almost equal to or higher than those of the magneto-optical recording disk of Comparative Example 1, and are suitable for the magnetic field modulation overwriting method. I can say. Comparative Example 1
In Example 1, the thickness of the MO target is 7 mm, whereas in Examples 1 to 3, the thickness of the MO target is 12 mm. Therefore, the magneto-optical recording disks of Examples 1 to 3 according to the present invention have a high use efficiency of the MO target, which is advantageous for cost reduction.

(Comparative Example 2) The thickness of the magnetic recording layer 4 was
2 mm, permeability 6.0, Tb content 25.0 atom%
A magneto-optical recording disk was manufactured in the same manner as in Example 1 except that the MO target was used. As shown in Table 1, according to the magneto-optical recording disk of Comparative Example 2, the CNR
Both the characteristics and the power margins Pw (+) and Pw (-) were below the target values.

The MO target of Comparative Example 2 is different from the MO target of Example 1 only in the magnetic permeability, but has the same Tb content and the same target thickness. From Example 1 and Comparative Example 2, it can be seen that when the permeability of the MO target is different, the desirable range of the Tb content is different.

Comparative Example 3 The thickness of the magnetic recording layer 4 was
2mm, magnetic permeability 2.5, Tb content 25.0 atom%
A magneto-optical recording disk was manufactured in the same manner as in Example 1 except that the MO target was used. As shown in Table 1, according to the magneto-optical recording disk of Comparative Example 3, the CNR
Both the characteristics and the power margins Pw (+) and Pw (-) were below the target values.

The MO target of Comparative Example 3 was different from the MO targets of Example 1 and Comparative Example 2 only in the magnetic permeability.
The b content and target thickness are the same. Example 1,
From Comparative Examples 2 and 3, the Tb content was 25 atom
At m%, it can be seen that the target value is achieved if the permeability of the MO target is 1.5, and is lower than the target value if the permeability is 2.5 or more.

(Comparative Example 4) The magnetic recording layer 4 was formed with a thickness of 1
2mm, magnetic permeability 2.5, Tb content 24.0 atom%
A magneto-optical recording disk was manufactured in the same manner as in Example 1 except that the MO target was used. As shown in Table 1, according to the magneto-optical recording disk of Comparative Example 4, the CNR
Both the characteristics and the power margins Pw (+) and Pw (-) were below the target values.

Comparative Example 5 The thickness of the magnetic recording layer 4 was
2mm, magnetic permeability 2.5, Tb content 26.0 atom%
A magneto-optical recording disk was manufactured in the same manner as in Example 1 except that the MO target was used. As shown in Table 1, according to the magneto-optical recording disk of Comparative Example 5, the CNR
Both the characteristics and the power margins Pw (+) and Pw (-) were below the target values.

Comparative Examples 3 to 5 differ only in the Tb content of the MO target, and have the same magnetic permeability and target thickness. In the case of a magnetic permeability of 1.5, the Tb content is 24.5 atoms.
% And the target value are achieved at both 25 atom% (see Examples 1 and 3). In the case of the magnetic permeability of 2, the target value was achieved at a Tb content of 25.5 atom% (see Example 2).

On the other hand, when the magnetic permeability was 2.5 as shown in Comparative Examples 3 to 5, the Tb content was 24 atom%,
The target value is not achieved at atom% and 26 atom%. Therefore, in the case of a magnetic permeability of 2.5, 24-26 ato
It is expected that the target value cannot be achieved in the range of m%, or that the target value is achieved only with a very limited Tb content. From the above, in the present invention, the upper limit of the permeability of the MO target is set to 2.0.

(Comparative Example 6) The magnetic recording layer 4 was formed with a thickness of 1
2mm, magnetic permeability 2.5, Tb content 22.5 atom%
A magneto-optical recording disk was manufactured in the same manner as in Example 1 except that the MO target was used. As shown in Table 1, according to the magneto-optical recording disk of Comparative Example 4, the CNR
Both the characteristics and the power margins Pw (+) and Pw (-) were below the target values.

Comparative Example 6 is similar to Comparative Example 1 corresponding to the standard and M
The magnetic permeability is lowered without changing the Tb content of the O target. By reducing the magnetic permeability, the thickness of the MO target can be increased from 7 mm in Comparative Example 1 to 12 mm, but the target value of the disk characteristics is not achieved. Comparative Example 1 and Comparative Example 6 also suggest that if the permeability of the MO target is different, the desired range of the Tb content is different.

As described above, by setting the permeability and Tb content of the MO target within the ranges shown in the present invention, even when the MO target is thickened, the magneto-optical recording medium having high CNR characteristics and power margin characteristics can be obtained. Is obtained.
According to the magneto-optical recording medium of the present embodiment, since the deterioration of the CNR characteristic and the power margin is prevented, the signal quality is stabilized, and the magnetic field modulation overwriting can be performed. In addition, compared to the conventional method of manufacturing a magneto-optical recording medium using an MO target having a high magnetic permeability, the MO target can be made thicker, so that the use efficiency of raw materials is increased, the manufacturing cost is reduced, and the productivity is improved. It becomes possible.

The embodiments of the magneto-optical recording medium and the method of manufacturing the same according to the present invention are not limited to the above description. For example,
Gd-Tb-F containing rare earth other than Tb such as Gd and Dy
The present invention can be applied to a case where an amorphous rare earth-transition metal alloy-based magneto-optical recording material such as e is formed by magnetron sputtering.

In this case, the MO target having a low magnetic permeability and a high rare earth element content is compared with the MO target having a predetermined disk characteristic and a magnetic permeability and a rare earth element content.
By using the target, it is possible to increase the thickness of the MO target without deteriorating the disk characteristics. In addition, various changes can be made without departing from the spirit of the present invention.

[0088]

According to the magneto-optical recording medium of the present invention, even when a magnetic recording layer is formed using an MO target having a low magnetic permeability, a decrease in CNR characteristics and power margin characteristics is prevented. According to the method for manufacturing a magneto-optical recording medium of the present invention, the magnetic recording layer of the magneto-optical recording medium capable of magnetic field modulation overwriting can be formed using a thick MO target, so that productivity can be improved. Becomes

[Brief description of the drawings]

FIG. 1 is a sectional view of a magneto-optical recording medium according to the present invention.

FIG. 2 is a schematic diagram showing the principle of a magnetic field modulation overwrite method for a magneto-optical recording medium.

FIG. 3 is a schematic view showing the principle of a light modulation writing method for a magneto-optical recording medium.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magneto-optical recording disk, 2 ... Disk substrate, 3 ... First
4 ... magnetic recording layer, 5 ... second dielectric layer, 6
... reflection film, 7 ... protective film, 8 ... magnetic head.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 11/105 531 G11B 11/105 531P 546 546B 553 553F 5/02 5/02 T

Claims (12)

[Claims] 1. A magneto-optical layer having a magnetic recording layer whose magnetization state is changed by application of an external magnetic field accompanied by irradiation of recording light, wherein the magneto-optical layer changes a polarization state of reproduction light incident from a first surface side of the magnetic recording layer. In a recording medium, the magnetic recording layer is a layer formed by sputtering using a target having a magnetic permeability of 2.0 or less, and the target has a terbium (Tb) content of 24.5.
A magneto-optical recording medium in the range of ２５25.5 atom%. 2. The magneto-optical recording medium according to claim 1, further comprising a reflection film for reflecting recording light and reproduction light on the second surface side of the magnetic recording layer. 3. The magneto-optical recording medium according to claim 2, further comprising a light-transmitting substrate on said first surface of said magnetic recording layer via a first dielectric layer. 4. The magneto-optical recording medium according to claim 3, wherein said reflection film is provided on said second surface of said magnetic recording layer via a second dielectric layer. 5. The magneto-optical recording medium according to claim 4, further comprising a protective film on said reflection film. 6. The method of claim 1, wherein said target comprises a transition metal.
A magneto-optical recording medium according to claim 1. 7. The magneto-optical recording medium according to claim 6, wherein said target contains iron (Fe) and cobalt (Co). 8. Recording of information on the magnetic recording layer is performed by changing the direction of an external magnetic field while continuously irradiating the recording light, and the magnetization of the magnetic recording layer is aligned in one direction. 2. The magneto-optical recording medium according to claim 1, wherein information can be recorded both when and when the information is not aligned in one direction. 9. Recording of information on the magnetic recording layer is performed by applying a DC magnetic field while intermittently irradiating the recording light, and when the magnetization of the magnetic recording layer is aligned in one direction. 2. The magneto-optical recording medium according to claim 1, wherein information can be recorded. 10. The magnetic recording layer has a magnetic permeability of at least 5.0 and a Tb content of 2.0 to 3.0 atm from the above range.
2. The light according to claim 1, which has recording / reproducing characteristics equal to or higher than that of a second magnetic recording layer formed by sputtering using a second target in a range of 22.0 to 23.0 atom%, which is lower by om%. Magnetic recording medium. 11. A first magnetic recording layer whose magnetization state is changed by application of an external magnetic field accompanied by irradiation of recording light, wherein polarized light of reproduction light incident from a first surface side of said first magnetic recording layer. A magneto-optical recording medium that changes state, wherein the first magnetic recording layer is a layer formed by sputtering using a first target having a predetermined magnetic permeability, wherein the first magnetic recording layer Has a recording / reproducing characteristic equal to or higher than that of a second magnetic recording layer formed by sputtering using a second target having a higher magnetic permeability than the first target; The second target is
A magneto-optical recording medium comprising a rare earth element and a transition metal, wherein the content of the rare earth element in the first target is higher than the content of the rare earth element in the second target. 12. A step of forming a first dielectric layer on a light-transmissive substrate, wherein the first dielectric layer has a magnetic permeability of 2.0 or less;
A step of forming a magnetic recording layer by magnetron sputtering using a target having a Tb content in the range of 24.5 to 25.5 atom%, and a step of forming a second dielectric layer on the magnetic recording layer. A method of manufacturing a magneto-optical recording medium, comprising: forming a reflective film on the second dielectric layer; and forming a protective film on the reflective film.