JPH05266523A - Magneto-optical recording medium and method for reproducing information from this magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To provide the reproduction-only magneto-optical recording medium which can be increased in recording density by an ultra-resolution method and to provide the ultra-resolution method suitable for reproduction of the recorded information from such magneto-optical recording medium. CONSTITUTION:A first dielectric layer 4, a recording layer 6 consisting of a magnetic material, a second dielectric layer 8 and a reflection layer 10 are successively laminated on a transparent substrate 2. Marks (or pits recessed from the other surface region) which are the assemblage of microruggedness are formed on the surface of the transparent substrate 2 and the information is expressed by these marks (or pits) and are succeeded to the surface shape of the first dielectric layer 4 thereon. The surface shape of the first dielectric layer 4 is reflected in the change in the coercive force of the recording layer 6 thereon. The parts (mark parts) existing on the marks (or pits) of the recording layer 6 has the relatively large coercive force and the other parts (non-mark parts) have the relatively small coercive force.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a magneto-optical recording medium suitable as a read-only information recording medium and a method of reproducing information from this magneto-optical recording medium.

[0002]

2. Description of the Related Art In magneto-optical recording / reproducing, a semiconductor laser is often used as a light source. The laser light emitted from the light source is converged by the lens and focused on the recording medium to concentrate the light energy in a very narrow area.
The area where this energy is concentrated is called a beam spot. When the medium is irradiated with a laser beam having a small output of about 1 mW, the direction of magnetization at the beam spot position can be detected by utilizing the so-called Kerr effect in which the polarization plane of the reflected light rotates depending on the direction of magnetization. Information is reproduced by detecting the magnetization direction of the magnetic domain corresponding to the information. Also,
When a laser beam with a high output of about 5 mW or more is irradiated, the temperature of the beam spot position rises and the coercive force at that position decreases. At this time, by applying a relatively weak magnetic field to the region including the beam spot, a magnetic domain magnetized in the direction of the applied magnetic field can be written at the beam spot position.

Japanese Patent Laid-Open Nos. 3-88156 and 3-97
No. 140 discloses a so-called thermomagnetic super-resolution method for detecting a magnetic domain formed smaller than a beam spot. Normally, if the recording domain is smaller than the beam spot,
A plurality of recording magnetic domains enter the beam spot, and the interference deteriorates the reproduced signal. However, this super-resolution method uses the fact that high-temperature spots are displaced backward from the center of the beam spot to transfer or erase magnetic domains, thereby
It is possible to reproduce by eliminating interference in the magnetic domain.

[0004]

According to the above-mentioned thermomagnetic super-resolution method, the recording exceeding the limit so far is achieved without changing the wavelength of light for determining the size of the beam spot and the numerical aperture of the condenser lens. It is possible to record and reproduce at high density. However, the applicable range of this technique is limited to a magneto-optical recording medium capable of both recording and reproduction. That is, this super-resolution method cannot be applied to a read-only magneto-optical recording medium.

The manufacture of a read-only optical information recording medium is
Usually, it is carried out by a method of using a master disc on which information is recorded by unevenness and transferring the unevenness onto a plastic substrate, which is very suitable for mass production. This read-only recording medium is an important medium for distributing music information, video information, software, etc. Therefore, a super-resolution method applicable to a read-only medium is desired.

Therefore, an object of the present invention is to provide a read-only magneto-optical recording medium capable of increasing the recording density by the super-resolution method, and reproducing recorded information from such a magneto-optical recording medium. It is to provide a super-resolution method suitable for.

[0007]

The magneto-optical recording medium of the present invention comprises a substrate having a surface on which irregularities representing information are formed. A recording layer made of a magnetic material is formed on this substrate. Then, the unevenness of the substrate surface is reflected in the difference in the coercive force in the recording layer depending on the location. That is, in this medium, information is recorded as a difference in coercive force in the recording layer.

In the preferred embodiment, the substrate is a transparent substrate and a first substrate.
And a dielectric layer, and a recording layer is formed thereon. Further thereon, a second dielectric layer and a reflective layer are sequentially formed. On the surface of the transparent substrate, marks, which are a collection of minute concavities and convexities, or pits that are depressed from other surface regions are formed, and information is represented by these marks or pits. The marks or pits on the surface of the substrate are inherited by the surface shape of the first dielectric layer thereabove. The surface shape of the first dielectric layer is reflected in the change in the coercive force of the recording layer thereabove. For example, the portion of the recording layer located on the mark or pit has a relatively large coercive force. , The coercive force of other parts is relatively small.

[0009]

In the production of the medium of the present invention, the method of transferring the irregularities of the master to the substrate by embossing can be used, so the medium of the present invention is easy to mass-produce and is suitable as a read-only medium. Is.

In the medium of the present invention, the recording layer can be magnetized in different directions depending on the location by utilizing the difference in coercive force of the recording layer. That is, the unevenness information of the substrate can be transferred to the recording layer as the magnetization direction information. When the information is thus represented as the magnetization direction of the recording layer, this information can be reproduced by using the super-resolution method.

[0011]

FIG. 1 shows a sectional structure of an embodiment of the magneto-optical recording medium of the present invention.

In FIG. 1, the transparent substrate 2 has a first
Dielectric layer 4, recording layer 6, second dielectric layer 8 and reflective layer 1
0 is sequentially stacked. Here, as an example of the material of each layer, the substrate 2 is a polycarbonate (PC) substrate, the first and second dielectric layers 4 and 8 are SiN layers,
The recording layer 6 is an NdDyFeCo layer, and the reflective layer 10 is A
It is the l-layer. However, the material is not limited to this. For example, for the recording layer 6, TbFe, DyF
e, GdTbFe, GdDyTbFe, TbFeCo,
Light rare earth + heavy rare earth + 10 Fe, NdDyFeCo, GdD
Various rare earth-transition metal alloys such as yTbFeCo can be used.

In this magneto-optical recording medium, information is recorded as unevenness on the surface of the PC substrate 2. That is, FIG.
(A) shows the state of the surface of the PC board 2,
In the same drawing, a hatched area 20 is a recording mark, and this recording mark 20 is formed of a group of minute irregularities as shown in the AA ′ sectional view of FIG. 2 (B).
The portion other than the recording mark 20 is composed of a smooth surface. Such a PC board 2 is produced by using a method suitable for mass production, which is often used for producing a read-only medium, in which a master having information recorded in unevenness is pressed against the PC board to transfer the unevenness. be able to.

A magneto-optical recording medium is manufactured by sequentially stacking the first dielectric layer 4, the recording layer 6, the second dielectric layer 8 and the reflective layer 10 on such a PC substrate 2. However, the specific procedure is as follows, for example.

(1) First, the PC substrate 2 on which the recording marks 20 are formed by the embossing as described above is prepared, and the SiN layer (first dielectric layer) 4 is vapor-deposited on the surface thereof by the RF sputtering method. The sputtering condition at this time is that the surface state of the completed SiN layer 4 is the base PC substrate 2
The conditions are selected such that the area of the recording mark 20 is a collection of minute irregularities and the other area is a smooth surface, reflecting the surface state of the above.

(2) Next, an NdDyFeCo layer (recording layer) 6 is vapor-deposited on the SiN layer 4 by a DC sputtering method. At this time, depending on the difference in the surface state of the underlying SiN layer 4, that is, whether the surface is a fine uneven surface or a smooth surface,
The growth mode of the yFeCo layer 6 is different as described later.
As the sputtering conditions at this time, the conditions are selected so that the difference in the growth pattern is remarkably generated.

(3) Next, on the NdDyFeCo layer 6,
SiN layer (second dielectric layer) by RF sputtering method
8 is vapor-deposited. The sputtering conditions at this time may be the same as those used for forming the second dielectric layer of the known magneto-optical recording medium.

(4) Finally, the Al layer (reflection layer) 10 is formed by the DC sputtering method. The sputtering conditions at this time may be the same as the conditions used for forming the reflective layer of the known magneto-optical recording medium.

By using such a manufacturing method, a portion of the recording layer 6 corresponding to the recording mark 20 of the substrate 2 (hereinafter, referred to as a mark portion) is the other portion (hereinafter, referred to as a mark portion).
The fluctuation of the domain wall energy is larger than that of the non-mark portion). As a result, the marked portion has a property that the domain wall does not easily move, that is, the coercive force is larger than that of the unmarked portion.

The reason for this is presumed as follows.

As described above, the surface of the first dielectric layer 4 formed on the surface of the substrate having the recording marks 20 has the structure shown in FIG.
As shown in (A), the area S corresponding to the recording mark 20
1 is a collection of minute irregularities, and the other region S2 is a flat surface.

NdDyF is formed on the surfaces S1 and S2.
When the recording layer 6 of a rare earth-transition metal alloy such as eCo is formed by sputtering, the growth mode of crystal grains (crystal nuclei) is different between the uneven surface S1 and the smooth surface S2 as shown in FIG. 3B. come.

That is, on the uneven surface S1, the crystal grains do not grow uniformly in the direction perpendicular to the substrate surface, but each crystal grain grows in the direction according to the inclination of the unevenness of the surface. As a result of the growth directions of the crystal grains colliding with each other in the course of this growth, the size of the crystal grains is limited, and the recording layer 6 (mark portion) is formed as a collection of minute crystal grains having random growth directions. ..

On the other hand, on the smooth surface S2, the crystal grains grow uniformly in the direction perpendicular to the substrate surface, and as a collection of relatively large crystal grains having a perpendicular growth direction, the recording layer 6 (non- Mark portion) is formed.

The thin film of rare earth-transition metal alloy as the recording layer 6 has a large perpendicular magnetic anisotropy. Since this perpendicular magnetic anisotropy is closely related to the growth direction of the film, the above-mentioned difference in the growth pattern also affects the perpendicular magnetic anisotropy. That is, if the distribution (fluctuation) in the growth direction is large, the perpendicular magnetic anisotropy energy also has a large fluctuation. Since the domain wall energy is proportional to the one-half power of the perpendicular magnetic anisotropy energy, the fluctuation of the perpendicular magnetic anisotropy energy is reflected in the fluctuation of the domain wall energy.

Therefore, as shown in FIG. 4, the mark part having a large fluctuation in the growth direction has a large fluctuation in the domain wall energy, and the non-mark part having a small fluctuation in the growth direction has a small fluctuation in the domain wall energy.

Such a difference in fluctuation of domain wall energy causes a difference in coercive force between the marked portion and the non-marked portion. That is, in the mark portion where the fluctuation of the domain wall energy is large, once the magnetic domain is formed, in order for the domain wall to move, the peak (see FIG. 4) where the fluctuation of the domain wall energy is high must be crossed. Therefore, in the mark part, the domain wall is less likely to move, that is, the magnetic domain is less likely to be deformed or disappeared, as compared with the non-mark part where the fluctuation of domain wall energy is small. In other words, the marked part has a larger coercive force than the non-marked part.

By utilizing this difference in coercive force, it is possible to magnetize the mark portion and the non-mark portion in opposite directions. That is, the information of the unevenness recorded on the substrate 2 is recorded on the recording layer 6
Can be transferred as information on the magnetization direction. Then, the magnetization direction information can be reproduced by a magneto-optical method utilizing the Kerr effect.

An embodiment of the information reproducing method according to the present invention utilizing this principle will be described with reference to FIG.

In FIG. 5, as the magneto-optical recording medium 100 moves, first, an initializing magnetic field H1 in the direction perpendicular to the substrate surface is first formed.
Inside, and then inside the reversal magnetic field H2 in the opposite direction, and then from the condensing lens 200, a relatively large power (reproducing the recording layer 6 near its Curie temperature or The laser beam is irradiated to the extent that it can be heated more than that). Then, the mark portion is detected at the front portion of the beam spot 300, that is, the information is reproduced.

Assuming that the coercive force of the mark portion 6m of the recording layer 6 at room temperature is Hm and that of the non-mark portion 6n is Hn, the strengths of the initialization and reversal magnetic fields H1 and H2 are H1>Hm> H2. > Hn.

When the medium 100 first passes through the initialization magnetic field H1, both the mark portion 6m and the non-mark portion 6n are magnetized in the direction of the initialization magnetic field H1. Next, when passing through the reversal magnetic field H2, only the magnetization direction of the non-mark portion 6n having a small coercive force is reversed to the direction of the second magnetic field H2, and the magnetization direction of the mark portion 6m having a large coercive force does not change. Thus, the mark portion 6m and the non-mark portion 6n are magnetized in opposite directions.

Next, when passing through the beam spot 300, as shown in FIG. 6, a portion behind the center of the beam spot 300 becomes a high temperature (around the Curie temperature or higher). The magnetization disappears and a loss-of-magnetization region 400 is formed. Since the portion of the beam spot 300 that overlaps with the magnetization loss region 400 acts as a mask that does not contribute to reproduction, substantially only the first half of the beam spot 300 contributes to reproduction.
In this way, reproduction by the super-resolution method becomes possible.

FIG. 7 shows another embodiment of the reproducing method of the present invention.

As shown in FIG. 7, while moving the recording medium 100, first, as in the embodiment of FIG.
Passing through the inside, and thereby the mark portion 6m and the non-mark portion 6
Both n are magnetized in the direction of the initializing magnetic field H1.

Next, the medium 100 is irradiated with the laser beam from the condenser lens 500 and, at the same time, passes through a relatively weak bias magnetic field H3 in the direction opposite to the initialization magnetic field H1.
The laser beam at this time has such power as to heat the recording layer 6 to an appropriate temperature lower than the Curie temperature so that only the non-marked portion 6n having a small coercive force is magnetized by the weak bias magnetic field H3. , This is Figure 5
It is smaller than the laser beam power of the embodiment. When receiving this laser beam irradiation, the temperature of the recording layer 6 rises,
At this time, due to the action of the bias magnetic field H3, the non-mark portion 6
Only the magnetization of n is reversed. On the other hand, the magnetization direction of the mark portion 6m having a large coercive force does not change. Thus, in the beam spot 600, the mark portion 6m and the non-mark portion 6n are magnetized in opposite directions.

8 to 11 show this beam spot 60.
The state of magnetization within 0 is shown.

In FIG. 8, when a high temperature region is generated behind the center of the beam spot 600 and a non-mark portion having a small coercive force enters this high temperature region, the magnetization direction is reversed according to the bias magnetic field H3 and the magnetization reversal region 700 is formed. Is formed at the rear. Next, as shown in FIG. 9, when the mark portion 6 approaches the high temperature region, the magnetization direction is not reversed only in the mark portion 6m because the coercive force is high. Next, as shown in FIG.
The mark portion 6m includes the magnetization reversal region 700 and the beam spot 6.
When entering the overlapping area with 00, the mark portion 6m is detected as a magneto-optical signal. At this time, the area other than the magnetization switching area 700 in the beam spot 600 does not contribute to reproduction as a mask. Next, as shown in FIG. 11, when the preceding mark portion 6m leaves the beam spot 600 and the succeeding mark portion 6m enters the overlapping region of the magnetization reversal region 700 and the beam spot 600, the preceding mark portion 6m.
The subsequent mark portion 6m is detected without causing interference with. Thus, the reproduction by the super-resolution method is performed in the overlapping region of the beam spot 600 and the magnetization reversal region 700.

FIG. 12 shows another embodiment of the magneto-optical recording medium according to the present invention.

In FIG. 12, the first substrate is formed on the transparent substrate 22.
The dielectric layer 24, the recording layer 26, the second dielectric layer 28, and the reflective layer 30 are sequentially stacked. For each layer, the same material as in the embodiment of FIG. 1 can be used.

As shown in FIG. 13, a small hole (hereinafter, referred to as a pit) 40 depressed from another surface portion (hereinafter, referred to as a land) 50 is formed on the surface of the substrate 22, and the pit 40 is recorded information. Carry. The bottom surface of the pit 40 and the land 50 are preferably smooth surfaces. Pit 4
The depth of 0 may be several tens of nm. The substrate 22 having such pits 40 can be easily mass-produced by a known method in which a master is pressed against the substrate 22 to transfer irregularities.

A first dielectric layer 24, a recording layer 26, a second dielectric layer 28 and a reflective layer 30 are sequentially laminated on the substrate 22 having the pits 40 in the same manner as in the embodiment of FIG. As a result, the recording medium of FIG. 12 can be manufactured. In this recording medium, the pits 40 and the lands 50 on the substrate 22 are
Is inherited by the surface shape of the first dielectric layer 24, which affects the growth mode of the crystal grains of the recording layer 26.

That is, as shown in FIG. 14A, in the mark portion 26m and the non-mark portion 26n which grow on the smooth surface of the first dielectric layer 24, crystal grains grow one-dimensionally in the direction perpendicular to the smooth surface. To do. On the other hand, the mark portion 26m and the non-mark portion 2
At the boundary with 6n, since the growth is performed on the step, the crystal grains grow three-dimensionally. As a result, this boundary is
Coercive force is large compared to other parts, and domain wall energy
Becomes smaller. Therefore, as shown in FIG.
The domain structure that creates the domain wall at the boundary becomes stable. And
The mark portion 26m surrounded by the boundary portion having a small domain wall energy has a larger coercive force than the non-mark portion 26n. By utilizing this characteristic, the information represented by the pit 40 can be transferred to the recording layer 26.

Utilizing this, the same reproducing method as the reproducing method described above for the medium of FIG. 1 can be applied to the recording medium of FIG.

The first method is shown in FIG.

While moving, the recording medium 800 first passes through the initializing magnetic field H1, then passes through the reversing magnetic field H2, and then is irradiated with a laser beam from the condenser lens 200. Here, the power of the laser beam is set to the recording layer 2
It has a power capable of heating 6 to a temperature near or above its Curie temperature. If the coercive force of the mark portion 26m at room temperature is Hm and that of the non-mark portion 26n is Hn, the intensities of the initialization and reversal magnetic fields H1 and H2 are selected so that H1>Hm>H2> Hn. ing.

By this reproducing method, it is possible to reproduce by the super-resolution method based on the same principle as the reproducing method of FIG. 5 for the medium of FIG. 1 already described.

FIG. 16 shows the second reproducing method.

The recording medium 800 first passes through an initializing magnetic field H1 similar to that shown in FIG. 15, and then is irradiated with a laser beam from the condenser lens 500 under a relatively weak bias magnetic field H3. Here, the laser beam has such power as to heat the recording layer 26 to an appropriate temperature lower than the Curie temperature so that only the non-marked portion 26n having a small coercive force is magnetized by the weak bias magnetic field H3. , Which is smaller than the power of the laser beam in FIG.

By this reproducing method, it is possible to reproduce by the super-resolution method according to the same principle as the reproducing method of FIG. 7 for the medium of FIG.

[0051]

As described above, according to the present invention,
It is possible to provide a read-only magneto-optical recording medium that can be reproduced by the super-resolution method, and a reproduction method by the super-resolution method applied to the medium.

[Brief description of drawings]

FIG. 1 is a sectional view showing the structure of an example of a magneto-optical recording medium of the present invention.

2A and 2B are a perspective view and a cross-sectional view showing a surface of a substrate of the magneto-optical recording medium of FIG.

FIG. 3 is a cross-sectional view showing how the recording layer of the magneto-optical recording medium of FIG. 1 grows.

FIG. 4 is a diagram showing a domain wall energy distribution state of a marked portion and a non-marked portion of the recording layer of FIG.

5 is a diagram showing an embodiment of a reproducing method of the present invention applied to the magneto-optical recording medium of FIG.

FIG. 6 is an explanatory view of the principle of the reproducing method of FIG.

FIG. 7 is a diagram showing another embodiment of the reproducing method of the present invention applied to the magneto-optical recording medium of FIG.

FIG. 8 is an explanatory view of the principle of the reproducing method of FIG.

9 is an explanatory diagram of the principle of the reproducing method of FIG. 7.

FIG. 10 is an explanatory view of the principle of the reproducing method of FIG.

11 is an explanatory view of the principle of the reproducing method of FIG.

FIG. 12 is a sectional view showing the structure of another embodiment of the magneto-optical recording medium of the present invention.

13 is a perspective view and a sectional view showing the surface of the substrate of the magneto-optical recording medium of FIG.

FIG. 14 is a cross-sectional view showing how the recording layer of the magneto-optical recording medium of FIG. 12 grows and how domain walls are formed.

15 is a diagram showing an embodiment of the reproducing method of the present invention applied to the magneto-optical recording medium of FIG.

16 is a diagram showing another embodiment of the reproducing method of the present invention applied to the magneto-optical recording medium of FIG.

[Explanation of symbols]

 2, 22 Transparent substrate 4, 24 First dielectric layer 6, 26 Recording layer 6m, 26m Mark part 6n, 26n Non-mark part 8,28 Second dielectric layer 10, 30 Reflective layer

Claims (5)

[Claims] 1. A substrate having a surface on which irregularities representing information are formed, and a recording layer made of a magnetic material formed on the substrate, wherein the irregularities on the surface of the substrate are the coercive force in the recording layer. And a recording layer in which the information is recorded as a difference in the coercive force in the recording layer depending on the location. 2. The medium according to claim 1, wherein the surface of the substrate is composed of a mark region and a region outside the mark, and the mark region is a collection of minute irregularities,
The area outside the mark is a smooth surface, so that the portion of the recording layer on the mark area has a larger coercive force than the portion on the area outside the mark. recoding media. 3. The medium according to claim 1, wherein the surface of the substrate is composed of pits and lands, the pits are surrounded by the lands, and the boundary between them is composed of a step, whereby the recording layer is formed. The magneto-optical recording medium, wherein the portion on the pit has a larger coercive force than the portion on the land. 4. The information represented by the mark portion is reproduced from an information recording medium having a recording layer composed of a mark portion having a first coercive force and a non-mark portion having a second coercive force. A method of applying a constant direction initialization magnetic field having a strength greater than the first and second coercive forces to the medium to magnetize both the marked portion and the non-marked portion in a fixed direction; After the application of the initializing magnetic field, a reversal magnetic field having an intermediate strength between the first and second coercive forces and in a direction opposite to the initializing magnetic field is applied to the medium, and the mark portion and the non-magnetic field are applied. In the process of reversing the magnetization direction of only one of the mark parts, and after applying the reversal magnetic field, by irradiating the medium with a light beam while moving the medium, a high temperature region is formed at a position behind the center in the beam spot. Generate Magneto-optically detecting the process in which the magnetization of both the mark portion and the non-mark portion is erased in this high temperature region, and the presence or absence of the mark portion in the region other than the high temperature region in the beam spot. Process,
An information reproducing method comprising: 5. The information represented by the mark portion is reproduced from an information recording medium having a recording layer composed of a mark portion having a first coercive force and a non-mark portion having a second coercive force. A method of applying a constant direction initialization magnetic field having a strength greater than the first and second coercive forces to the medium to magnetize both the marked portion and the unmarked portion in a fixed direction; After applying the initialization magnetic field, a process of irradiating the medium with a light beam while moving the medium to generate a high temperature region at a position behind the center in the beam spot, and the initialization to the high temperature region Applying a bias magnetic field in the direction opposite to the magnetic field to reverse the magnetization direction of only one of the mark part and the non-mark part in this high temperature region; and in the high temperature region in the beam spot. And a step of magneto-optically detecting the presence or absence of the mark portion that enters the information reproducing method.