JPH0620324A - Magneto-optical recording medium and recording method by overwriting using the same - Google Patents

Abstract

PURPOSE:To provide a magneto-optical recording medium attaining perfect erasure, having high reliability, withstanding practical use and capable of overwriting. CONSTITUTION:In a magneto-optical recording medium having an exchange coupled two-layered film structure as the structure of the magnetic layer, the film structure is set so that a margin for erasing power is regulated to >=2.5mW. Even if tracking offset, a change in the ambient environment and variation in the characteristics of the medium are caused, overwriting action is stably carried out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overwritable magneto-optical recording medium used in a recording device and a recording method thereof.

[0002]

2. Description of the Related Art As is well known, magneto-optical recording is an optical recording capable of recording, reproducing and erasing information, and has attracted attention because it can achieve high density recording which is far superior to conventional magnetic recording. . In addition to these functions, in recent years, when writing new information on a magneto-optical disk on which information has already been written, a new magneto-optical recording method called an overwrite method of writing while erasing the previous information is proposed. Has been done. This overwritable magneto-optical recording method is roughly classified into a magnetic field modulation method and a light intensity modulation method.

When these two methods are compared, high-speed modulation and high-speed recording are possible and two magneto-optical recording media can be stuck together to form a double-sided recordable disk structure. The latter method is advantageous. As a magneto-optical recording medium for realizing this light intensity modulation method, it is already known in principle as described in, for example, Japanese Patent Laid-Open No. 62-175948. That is, as the magnetic layer used in this type of recording medium, an exchange coupling two-layer film having magnetic coupling is used.

An outline of overwrite will be described below with reference to the drawings. 2 to 5 are explanatory views of a light intensity modulation method using a known exchange coupling two-layer film as a magnetic layer. The magnetic film used for recording is a two-layer film including the auxiliary layer 15 and the recording layer 4. FIG. 2 shows the relationship between the magnetic field, the coercive force, and the temperature. At room temperature Tr, the coercive force 8 of the recording layer 4 is larger than the coercive force 9 of the auxiliary layer 15, and the Curie temperature of the auxiliary layer 15 is high. T ₉ is higher than the Curie temperature T ₈ of the recording layer 4.

In recording, first, as shown in FIG. 3, the magnetization 18 of the auxiliary layer 15 is aligned in the direction of the initialization magnetic field 13 by the initialization magnet 17. The initialization magnet 17 is normally fixed to the disk in the disk device so as to face the disk, is composed of a permanent magnet or a DC electromagnet, and is configured to form a magnetic field with a constant strength and in a constant direction. . Here, the magnitude of the initialization magnetic field 13 is set to be larger than the coercive force 9 of the auxiliary layer 15 at room temperature Tr and smaller than the coercive force 8 of the recording layer 4 as shown in FIG. The direction of the magnetization 19 of the recording layer 4 does not change even when the magnetic field 13 is applied.

When recording information, the intensity of the laser beam is changed under the bias magnetic field 14 of constant intensity shown in FIG.
As shown in, to be recorded "1", based on the digital information of "0", high laser power level (referred to hereinafter P _H) (referred to hereinafter P _L) 23 and the lower laser power level between 24 Modulate with. The bias magnetic field 14 having a constant strength applied at the time of recording is different from the initialization magnetic field 13 in both strength and direction of the magnetic field, but like the initialization magnet 17, the magnet 22 fixed facing the disk of the disk device.
Thereby forming a magnetic field with a constant strength and in a constant direction.

As shown in FIG. 4 (a) or FIG. 5 (a), the laser beam 20 is narrowed down to a predetermined spot diameter by a narrowing lens 21 and is irradiated onto the magnetic film. When the laser beam intensity is P _H, the laser beam 20 as shown in FIG. 2
The region irradiated by the Curie temperature of the auxiliary layer 15 is T ₉
Since the temperature of the recording layer 4 has already exceeded the Curie point T ₈ because it is heated close to it, the magnetization 19 of the recording layer 4 disappears as shown in FIG. 4A. On the other hand, the direction of the magnetization 18 of the auxiliary layer 15 in this temperature region is that the bias magnetic field 14 applied by the magnet 22 is already larger than the coercive force 9 of the auxiliary layer 15 as apparent from FIG. It is oriented in the direction of the bias magnetic field 14 (opposite direction of the initialization magnetic field 13). Then, when the irradiation of the laser beam 20 is finished and the magnetic film is cooled, the magnetization 19 of the recording layer 4 is also generated in the direction of the bias magnetic field 14 as shown in FIG. 4B, and information is recorded.

Next, when the laser light intensity is P _L , as shown in FIG.
As shown in (a), the temperature of the region irradiated with the laser beam 20 is close to the Curie temperature T ₈ of the recording layer 4.
Therefore, the coercive force 9 of the auxiliary layer 15 is larger than that of the bias magnetic field 14 as shown in FIG. As shown in FIG. 5B, when the irradiation of the laser beam is finished and the magnetic film is cooled, the magnetization 19 of the recording layer 4 has a larger exchange coupling force than the magnetization 18 of the auxiliary layer 15 and the bias magnetic field 14. Has a magnetization of the recording layer 4 of 1
9 also faces away from the bias magnetic field 14.

[0009]

However, the above-mentioned prior art is merely a proposal of the principle of overwrite, and in practical use, there are cases where overwriting is impossible due to various factors, and these factors should be removed. Is mandatory. A particularly serious problem is that new information is recorded in the state where the already recorded mark is not completely erased but partially remains even after the overwrite processing is performed, and the reliability is significantly deteriorated.

Therefore, an object of the present invention is to solve such a conventional problem, and a first object thereof is to provide an improved magneto-optical disk which can be practically overwritten. A second object is to provide an improved overwrite recording method.

[0011]

In order to achieve the above object, it is necessary to analyze factors that obstruct overwriting in a magneto-optical recording medium capable of overwriting. What plays the most important role in the operation of the overwrite is the low power level P _L of the modulation power intensity of the laser light. This is because old information is erased by irradiation with P _L and information is recorded by irradiation with P _H at a high power level. To old information and P _L intensity is too small, not erased, too and the recording will be begun size. Therefore, there is some optimum range for P _L.

This range varies greatly depending on the film forming characteristics of the magneto-optical recording medium, the number of revolutions of the medium, the wavelength of the recording laser beam, and the numerical aperture of the objective lens for narrowing the laser beam onto the medium surface. . Therefore, the optimum P _L range cannot be found unless these values are determined. Therefore, as a result of various studies, the inventors of the present application have found that the intended purpose can be achieved by using the configuration described below.

That is, it comprises an optical substrate, a magnetic layer having perpendicular anisotropy provided on the substrate, and a protective layer formed on the magnetic layer, and the magnetic layer has a low Curie temperature and a high coercive force. Exchange-coupled 2 which is composed of a recording layer (first magnetic layer) having the following: and an auxiliary layer (second magnetic layer) having a Curie temperature and a low coercive force relatively higher than those of the magnetic layer.
In a magneto-optical recording medium made of a layer film and capable of overwriting by modulating the power intensity of laser light into two levels, high and low, the line of the area that is actually used for the magneto-optical recording medium. The slowest speed (the innermost side)
At a position, the magneto-optical recording medium is irradiated with a constant intensity unmodulated laser beam based on predetermined recording information to record a band-shaped magnetic domain, and a constant intensity unmodulated laser beam is again irradiated onto the recorded magnetic domain. When the strength is gradually increased, the difference between the power P _{EC at} which the magnetic domain is completely erased and the power P _WS at which the magnetic domain starts to be recorded again becomes at least 2.5 mW or more. A protective layer and, if necessary, a thermal diffusion layer were also formed.

FIG. 7 illustrates this principle. In this figure, the horizontal axis represents the laser power, the vertical axis represents the reproduction output, curve 6 shows the erasing characteristic, and curve 7 shows the recording characteristic. P
_{The L} settable range is between P _EC and P _WS, and P _L is set so that the width of the laser power is at least 2.5 mW or more. The magneto-optical recording medium capable of overwriting according to the present invention is made based on such knowledge.

The protective layer and, if necessary, the thermal diffusion layer formed are usually composed of a non-magnetic film made of a dielectric or metal. Further, the width of the band-shaped magnetic domain to be recorded is 0.6 to 0.9 μm level at the present technical level, but if the technology is further advanced and the recording density is further increased, it can be 0.5 μm or less. Become. Furthermore, "at the position where the linear velocity is the slowest (the innermost position)" means that the innermost peripheral speed of the disc is the slowest, so the disc is driven under the most severe conditions. This is because it was determined that it is appropriate as a condition for evaluating the reliability of.

It is desired that the overwritable magneto-optical recording medium has higher performance than the conventional erasable only magneto-optical recording medium. Therefore, the wavelength of the laser beam used for recording is 833n so that high-density recording can be performed.
A wavelength of m or less is desirable. The wavelength is more preferably 783 nm or less.

Further, it is desired that the numerical aperture of the objective lens is 0.55 or more, preferably 0.6 for high density recording. Further, the size of the magneto-optical recording medium is preferably 5.25 inches or less so that the magneto-optical recording medium can be easily handled and the medium drive can be downsized. For example, it may be 3.5 inches or 2 inches. At this time, in order to increase the data transfer speed, the rotation speed of the magneto-optical recording medium is preferably 2400 rotations per minute or more. For example, by setting the rotation speed to 3600, it is possible to obtain a transfer speed equivalent to that of the magnetic recording medium.

As the recording magnetic domain width described above, it is preferable to record the magnetic domain width of 0.9 μm or less when the laser beam wavelength is 830 nm and the lens numerical aperture is 0.55. It is necessary to reduce the recording magnetic domain width as the laser light wavelength becomes shorter and the lens numerical aperture becomes larger. The current semiconductor laser wavelength is 630 nm, which is the shortest wavelength. Therefore, the recording magnetic domain width may be 0.6 μm. The track pitch provided on the substrate is preferably 1.6 μm or less. For this track pitch, the recording magnetic domain width needs to be 0.9 μm or less. Also, 1.4 μm
For the track pitch of, the magnetic domain width needs to be 0.8 μm or less. However, in any case, in order to obtain a sufficient reproduced signal output, the magnetic domain width must be 0.6 μm or more in the performance of the current output detector.

In order to achieve the overwrite recording method of the magneto-optical recording medium of the present invention, the film forming characteristics of the magneto-optical recording medium, the number of rotations of the medium, the wavelength of the recording laser beam, and further the laser beam on the medium surface. The objective is to control at least one of the numerical apertures of the objective lens for narrowing to the upper limit to a predetermined value and set it in the optimum P _L range.

[0020]

When the non-modulated (so-called direct current) laser light having a constant intensity is irradiated to the magneto-optical recording medium at the innermost position in the area actually used for the magneto-optical recording medium, the information is If the power for completely erasing data is P _EC and the power for starting to record information is P _WS , the range of the erasing power P _L is P _EC and P _WS as described in FIG.
P _WS due to factors such as
The difference between P _EC is required at least 2.5mW or higher.

Factors It should be noted that in actual recording, the length of the recorded mark (magnetic domain) is not uniform depending on the content of information. By the way, in (2,7) RLL modulation recording, the mark length when the bit length is T is 1.5T, 2
There are 6 types of T, 2.5T, 3T, 3.5T and 4T. There is no problem when overwriting a mark having the same length as the recorded mark. However, an attempt to record a short mark on a long mark (magnetic domain), since the mark width in the mark length and proportional, requires high P _L than the minimum P _L required to clear the short mark Become. The longest mark [(2,
7) When recording the shortest mark [1.5T in (2,7) modulation] on 4T in modulation. Assuming such a "worst case", it is necessary to estimate an extra P _L of about 0.3 mW.

Factors It is necessary to be able to surely erase old information even when the light spot passes through the track at a certain position without passing through the center position of the track. Even if it is displaced from the track center position, if P _L having the same power as usual is emitted, old information is erased and left. Since the amount of the unerased portion increases as the track offset amount increases, it is necessary to increase P _L correspondingly. The track offset varies depending on the tracking method and the like. In order to prevent track offset, attempts have been made to provide wobble pits on the medium and improve the tracking method.
Under these circumstances, the track offset is 0.1 μm
There is no problem in practical use if you allow for it. In this case, the unerased portion is most likely to occur when the recording medium is deviated by 0.1 μm to the left with respect to the light spot traveling direction during recording and deviated to the right by 0.1 μm during overwriting. This corresponds to erasing a mark wider than usual by 0.2 μm from a different viewpoint. That is, if P _L is set so that a mark wider by 0.2 μm than a normal mark can always be erased, a track offset of 0.1 μm can be dealt with. The amount of increase in P _L required for this is about 1.
It is 2 mW.

Factors On the other hand, it is necessary to consider that the ambient temperature during recording and overwriting is constantly changing. The ambient temperature when operating the magneto-optical recording medium is specified in ISO (International Standard) as 0 ° C to 50 ° C. Therefore,
The worst situation in the erasing operation is when erasing a mark recorded at 50 ° C at 0 ° C. This is because, when recording is performed with the same power, the mark width is widest when the ambient temperature is 50 ° C. and is narrowest when the ambient temperature is 0 ° C. Therefore, in order to guarantee complete erasing even in the above-mentioned worst case, the P required for overwriting at the same temperature is used.
_An additional 0.5 mW is required more than the _L power.

Factors There are also reasons for having to set P _L higher in the medium itself. It is the variation between media. Even if you are erasing in the P _L of 4mW in some media, 5m in some media
A P _{L of} W may be needed. This is because, when the medium is mass-produced, the Curie temperature of the memory layer and the film thickness are varied, and the ultimate vacuum degree of the sputtering apparatus, which is a manufacturing apparatus, is different between lots. It is unavoidable. If this variation is converted into the power of P _L , it can be estimated to be about 0.5 mW.

As described above, the set value of P _L is,
It is necessary to set 2.5 mW higher in consideration of all the factors. That is, the difference between P _WS and P _EC is 2.5 mW
More is required. In each of the factors (1) to (4), considering the worst case, the laser beam is irradiated at a constant intensity without being modulated. Therefore, at this time, the difference between P _WS and P _EC is 2.5 mW or more. is necessary.
Since P _WS and P _EC are closer to each other as the linear velocity is slower, the difference between P _WS and P _EC is 2.5 mW at the innermost striking position of the area actually used for the magneto-optical recording medium. The above is necessary.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

Example 1 FIG. 1 is a longitudinal sectional view of a magneto-optical recording medium, in which a disk-shaped glass substrate 1 is
An ultraviolet curable resin layer 2 having grooves formed at a pitch of 1.6 μm is provided with a thickness of 30 μm. The following films were sequentially formed on this by sputtering. First, the silicon nitride film 3 was laminated by 850 Å to form a multiple reflection interference film. The sputtering was carried out at a pressure of 10 mTorr using silicon as a target and a mixed gas of argon and nitrogen as a sputtering gas. The refractive index of silicon nitride can be controlled by changing the mixing ratio of nitrogen gas. Here, the nitrogen gas mixing ratio was set to 8% so that the refractive index was 2.1.

Next, as a recording layer 4 (first magnetic layer), a Tb ₂₀ Fe ₇₂ Co ₈ film having a Curie temperature T ₈ of 170 ° C. is 400 Å,
The Curie temperature T _{9 of the} auxiliary layer 15 (second magnetic layer) is 2
Tb ₁₇ Dy ₁₆ Fe ₅₀ Co ₁₇ films at 50 ° C. were laminated in 1500Å. As a target, T on a Fe plate
A composite target in which chips such as b, Dy, and Co were arranged was used. Of course, an alloy target prepared in advance with a predetermined composition may be used. Finally, in order to prevent the magnetic layer from being oxidized and corroded, a silicon nitride film 5 is formed as a protective film.
Was formed. At this time, changing the thickness of the silicon nitride film 5,
The magneto-optical recording medium A is 200 Å, and the magneto-optical recording medium B is
Then it was 2000Å.

The two types of magneto-optical recording media thus completed were rotated at a speed of 2400 rpm, and the recording area was not modulated with a constant intensity at the innermost position (radius 30 mm). 6 mW of laser light was irradiated to form and record a band-shaped magnetic domain having a width of 0.8 μm. At this time, a semiconductor laser with a wavelength of 830 nm and a numerical aperture of 0.55
An optical head composed of the lens is used. When the magneto-optical recording medium rotates and passes under the initialization magnet 17 as schematically shown in FIG. 3, the magnetization direction of the auxiliary layer 15 of the magneto-optical recording medium is aligned with the direction of the initialization magnetic field 13.

Subsequently, a track on which magnetic domains were recorded in a band-like shape was irradiated with a laser beam having a constant intensity, and thereafter the reproduction output at that time was measured with a reproduction power of 1 mW. The result is shown in FIG. In this characteristic diagram, the horizontal axis represents the irradiated laser power (laser light having a constant intensity), and the vertical axis represents the reproduction output. That is, in the magneto-optical recording medium A, as shown by the solid line, erasing is completely performed at 3 mW (= P _EC ), and recording is started at 5 mW (= P _WS ). on the other hand,
In the magneto-optical recording medium B, as shown by the broken line, 4 mW (= P
It has been completely erased by _EC ) and the recording has started from 7.5 mW (= P _WS ).

Therefore, the magneto-optical recording medium A has a margin in the setting range of the erasing power of about 2 mW (= P _WS -P _EC ), and the magneto-optical recording medium B has the erasing power P _L of about 3.5 mW. There is a margin in the setting range.

Using this magneto-optical recording medium, the recording power P _{H is set} to 11 mW, the erasing power P _L is set to 4 mW for the magneto-optical recording medium A and 6 mW for the magneto-optical recording medium B, and 3 MH is set.
The z signal was recorded and then the 5 MHz signal was overwritten. The results are shown in Table 1 below. As is clear from this, in both magneto-optical recording media A and B, when there was no tracking offset, there was no unerased 3MHz signal. However, when a tracking offset of 0.1 .mu.m was intentionally generated to examine the unerased portion, the magneto-optical recording medium B did not remain at all, but the magneto-optical recording medium A had an unerased portion of about 20 dB. .
As described above, since the magneto-optical recording medium B satisfies the condition that the difference between P _WS and P _EC of the present invention is at least 2.5 mW or more, it can be understood that the magneto-optical recording medium B has highly reliable characteristics. See.

In this example, the thickness of the silicon nitride protective film 5 is adjusted as a condition for setting the difference between P _WS and P _EC to be at least 2.5 mW or more.

[0034]

[Table 1]

Example 2 FIG. 9 is a longitudinal sectional view of a magneto-optical recording medium, which is sequentially sputtered on a polycarbonate substrate 10 having a diameter of 3.5 inches and having a track pitch of 1.4 μm. Was formed into a film. First, a polycarbonate substrate was sputter-etched in a vacuum, and then a silicon dioxide film 11 was formed to a thickness of about 50Å. After that, the sputtering apparatus was evacuated to 8 × 10 to ⁷ Torr or less, and then a mixed gas of Ar gas and N ₂ gas was introduced, and
The silicon nitride film 16 is sputtered at a gas pressure of mTorr by using a sintered body of silicon nitride as a target to 800 Å.
Formed.

Next, after vacuum evacuation in the same manner, TbFeCo
An Nb alloy target was sputtered at a gas pressure of 5 mTorr to form TbFe as the recording layer 25 (first magnetic layer).
A CoNb film of 300 Å was formed. After vacuum evacuation in the same manner, a GdTbFeCo alloy target of 5 m
Sputtering was carried out at a gas pressure of Torr, and a GdTbFeCo film as a supplementary layer 26 (second magnetic layer) was laminated in 700 liters. After that, a silicon nitride film as a protective film 27 was laminated by 200Å by the same procedure. Finally, as a thermal diffusion film, Al-T
The i alloy film 28 was laminated and formed. At this time, the thickness of the Al—Ti alloy film is changed so that the magneto-optical recording medium C has a thickness of 400
Å, 1100Å in the magneto-optical recording medium D.

The magneto-optical recording media C and D thus completed are rotated at a speed of 3600 rpm at an ambient temperature of 25 ° C., and the innermost peripheral position (radius 25 m) of the recording area is rotated.
m) is not modulated with constant intensity (DC-like) 7 mW
Was irradiated with the laser beam to form a band-shaped magnetic domain having a width of 0.75 μm and recorded. At this time, an optical head composed of a semiconductor laser having a wavelength of 780 nm and a lens having a numerical aperture of 0.55 is used. When the magneto-optical recording medium rotates and passes under the initialization magnet 17 as schematically shown in FIG. 3, the auxiliary layer 15 (26) of the magneto-optical recording medium is aligned in the direction of the initialization magnetic field 13.

Subsequently, the track on which the magnetic domains are already recorded in the band shape is irradiated with laser light having a constant intensity, and then 1.5
The reproduction output at that time was measured by the reproduction power of mW.
The result is shown in FIG. In this characteristic diagram, the horizontal axis represents the irradiated laser power (laser light having a constant intensity), and the vertical axis represents the reproduction output. That is, in the magneto-optical recording medium C, as shown by the solid line, complete erasing is performed at 3.5 mW (= P _EC ), and recording is started from 5.5 mW (= P _WS ). On the other hand, in the magneto-optical recording medium D, erasing was completely performed at 5 mW (= P _EC ) as shown by the broken line, and 9 m
The record starts from W (= P _WS ). Therefore, the magneto-optical recording medium C has a setting range of subtraction (= P _WS −P _EC ) of 2 mW, and the magneto-optical recording medium D has a setting range of subtraction of 4 mW.

Using this magneto-optical recording medium C, the recording power P _H was set to 8 mW and the erasing power P _L was set to 5 mW, 5 MHz signals were recorded at an ambient temperature of 50 ° C., and then 7 MHz signals were recorded. Overwritten. The same experiment was performed on the magneto-optical recording medium D. At this time, P _H is 12 mW, P _L was set to 7 mW. The results are shown in Table 2 below. As is clear from this, in both the C and D magneto-optical recording media, when there was no tracking offset, and when a tracking offset of 0.1 μm was intentionally generated at 50 ° C., there was no remaining of the 5 MHz signal.

However, when the ambient environment was set to 0 ° C. during recording of the 5 MHz signal, and a tracking offset of 0.1 μm was intentionally produced to examine the remaining erasure, the remaining erasure of about 20 dB occurred in the magneto-optical recording medium C. In the magneto-optical recording medium D, the unerased residue did not occur at all. Thus, it can be understood that the magneto-optical recording medium D has highly reliable characteristics because it satisfies the condition that the difference between P _WS and P _EC of the present invention is at least 2.5 mW or more. See. In this example, the difference between P _WS and P _EC is at least 2.5.
As a condition for setting mW or more, A as a heat diffusion film
The thickness of the l-Ti film is adjusted.

[0041]

[Table 2]

<Embodiment 3> 100 pieces of each of the magneto-optical recording media C and D shown in Embodiment 2 were prepared, P _L and P _H were set to the same values, and 5 MHz was set under a normal room temperature environment. The signal was recorded and then the 7 MHz signal was overwritten. At this time, in the magneto-optical recording medium C, the unerased residue occurred on the eight media, but in the magneto-optical recording medium D, the unerased residue was not seen at all.

[0043]

As described above in detail, according to the present invention, the intended purpose can be achieved. That is, in the overwritable magneto-optical recording medium, the power range required for erasing is set to be at least 2.5 mW or more, so that the mark (magnetic domain) diameter difference, the tracking offset, the ambient environmental temperature fluctuation, the medium It is possible to obtain a highly reliable magneto-optical recording medium in which overwriting is possible without causing unerased characteristics due to variations in characteristics between them.

[Brief description of drawings]

1 is a cross-sectional view of a magneto-optical recording medium according to an embodiment of the present invention. FIG. 2 is a characteristic diagram for explaining the principle of overwrite and showing the relationship between temperature, magnetic field, and coercive force. Figure 3 is a diagram for explaining the principle of overwrite and is an explanatory diagram of initialization. Serve to explain the principles of Figure 4 overwrite, illustration of a high at the time of recording laser power level P _H. FIG. 5 is a diagram for explaining the principle of overwriting, with a low laser power level P _L. FIG. 6 is an explanatory diagram of laser power level modulation (P _L , P _H ) for explaining the principle of overwrite. Figure 7 Erasing a magneto-optical recording medium that enables overwriting,
Explanatory drawing of a recording characteristic and a settable range of P _L. 8 is a characteristic diagram showing erasing and recording characteristics of the magneto-optical recording medium of Example 1. FIG. 9 is a sectional view of a magneto-optical recording medium according to another embodiment of the present invention. 10 is a characteristic diagram showing erasing and recording characteristics of the magneto-optical recording medium of Example 2.

[Explanation of symbols]

1, 10 ... Substrate, 4 ... Recording layer, 3, 5, 16, 27 ... Silicon nitride film, 6 ...
Erasing characteristics, 7 ... recording characteristics,
8 ... Coercive force of recording layer, 9 ... Coercive force of auxiliary layer,
11 ... Silicon dioxide film, 13 ... Initializing magnetic field, 14 ... Bias magnetic field, 1
5, 26 ... Auxiliary layer, 17 ... Initializing magnet, 18, 19 ... Magnetization, 22
… Magnet, 23… High laser power (P _H ), 2
4 ... low laser power (P _L)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shin Miyamoto 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Pref.Inside of Hitachi Media Visual Media Research Laboratories (72) Inventor Keikichi Ando 1-280, Higashi Koikeku, Kokubunji, Tokyo Central Research Laboratory of Hitachi, Ltd. (72) Inventor Go Toda 1-280 Higashi Koikeku, Kokubunji City, Tokyo Metropolitan Institute of Hitachi, Ltd. (72) Atsushi Saito 1-280 1 Higashi Koikeku, Kokubunji, Tokyo Hitachi Ltd. Central Research Laboratory (72) Inventor Masahiro Ojima 1-280, Higashi Koikekubo, Kokubunji, Tokyo Inside Hitachi Central Research Laboratory

Claims (7)

[Claims] 1. An optical substrate, a magnetic layer having perpendicular anisotropy provided on the substrate, and a protective layer formed on the magnetic layer, wherein the magnetic layer has a low Curie temperature and a high coercive force. A two-layer film magnetically exchange-coupled with a recording layer as a first magnetic layer having a magnetic recording medium and an auxiliary layer as a second magnetic layer having a higher Curie temperature and a lower coercive force than the magnetic layer. A magneto-optical recording medium that enables overwriting by modulating the power intensity of laser light into two levels, high and low, and is the innermost of the areas actually used for the magneto-optical recording medium. At the position on the circumferential side, the magneto-optical recording medium is irradiated with a laser beam having a constant intensity which is not modulated on the basis of predetermined recording information to record a band-shaped magnetic domain, and the non-modulated laser beam having a constant intensity is recorded again on the recorded magnetic domain. Irradiate on and its intensity When began to gradually increase, formed by the difference between the power P _WS power P _EC the magnetic domains in which the magnetic domains are completely erased starts being recorded again to form a deposited structure to be at least 2.5mW or higher Magneto-optical recording medium. 2. The difference between the power P _{EC at} which the magnetic domain is completely erased by controlling the composition and thickness of the magnetic layer and the protective layer and the power P _WS at which the magnetic domain starts to be recorded again is at least 2.
The magneto-optical recording medium according to claim 1, wherein the film-forming structure is formed to have a power of 5 mW or more. 3. A thermal diffusion layer is formed on the protective layer, the thickness of which is controlled to control the difference between the power P _{EC at} which the magnetic domain is completely erased and the power P _WS at which the magnetic domain starts to be recorded again. The magneto-optical recording medium according to claim 1, wherein the film forming structure is formed to have a power of at least 2.5 mW or more. 4. The magneto-optical recording medium according to claim 1, wherein when the band-shaped magnetic domain is recorded by irradiating the magneto-optical recording medium with the laser light, the band-shaped magnetic domain width is 0.5 to 0.9 μm. . 5. The magneto-optical recording medium according to claim 1, wherein the magneto-optical recording medium comprises a 3.5 to 5.25 inch disc. 6. An optical substrate, a magnetic layer having perpendicular anisotropy provided on the substrate, and a protective layer formed on the magnetic layer, wherein the magnetic layer has a low Curie temperature and a high coercive force. A two-layer film magnetically exchange-coupled with a recording layer as a first magnetic layer having a magnetic recording medium and an auxiliary layer as a second magnetic layer having a higher Curie temperature and a lower coercive force than the magnetic layer. And a film-forming structure of a magneto-optical recording medium capable of overwriting by modulating the power intensity of the laser beam into two levels, high and low, the rotational speed of the medium, the wavelength of the recording laser beam, and the laser beam. Is set to a predetermined value with at least one of the numerical aperture of the objective lens that narrows down the medium to a predetermined value, and the predetermined recording information is set at the innermost position of the area actually used for the magneto-optical recording medium. Based on a constant intensity unmodulated ray When the magneto-optical recording medium is irradiated with light to record a band-shaped magnetic domain, laser light having a constant intensity and which is not modulated is irradiated onto the recorded magnetic domain again, and when the intensity is gradually increased, the magnetic domain is increased. The method of overwriting recording on a magneto-optical recording medium, wherein the difference between the power P _EC at which data is completely erased and the power P _WS at which the magnetic domain starts to be recorded again is controlled to be at least 2.5 mW or more. 7. The magneto-optical device according to claim 6, wherein the number of revolutions of the medium is at least 2400 revolutions / minute, the wavelength of the laser light is 833 nm or less, and the numerical aperture of the objective lens is at least 0.55 or more. Overwrite recording method for recording medium.