JPH06103629A - Overwritable magneto-optical recording method for improving data discrimination and magneto-optical recorder used therefor - Google Patents

Abstract

PURPOSE:To enhance C/N and to improve data discrimination by shaping beam intensity to a specified waveform and irradiating it at the time of recording to an overwritable magneto-optical recording medium. CONSTITUTION:A multilayer magneto-optical recording medium composed of a memory layer (M layer) and a writing layer (W layer) for which the nagmetization of the W layer is facing in a prescribed direction is rotated and is irradiated with laser beams pulse-modulated corresponding to binarized information to be recorded. At the time of rising from a low level PL to a high level PH for the intensity of the laser beams, a premark previously formed by the beams at PH is lowered below a limit value PLmin deletable with the laser beams of DC lighting. Then, after rising to PH and forming a mark, pulse waveform is shaped so as to return to PL. Thus, the premark is almost completely deleted and the data discrimination is improved.

Description

Detailed Description of the Invention

[0001]

INDUSTRIAL APPLICABILITY The present invention is directed to irradiating a laser beam while modulating the pulse according to the binary information to be recorded without modulating the direction and intensity of the recording magnetic field Hb.
The present invention relates to an overwritable magneto-optical recording method and an overwritable magneto-optical recording device used therefor. In particular, the present invention relates to a good recording method and recording apparatus for data discrimination.

Overwriting refers to the act of recording new information without erasing the previous information. In this case, the previous information when reproduced should not be reproduced.

[0003]

2. Description of the Related Art Recently, an optical recording / reproducing method satisfying various requirements including high density, large capacity, high access speed, and high recording / reproducing speed, and a recording apparatus, reproducing apparatus and recording medium used therefor. Efforts are being made to develop. Among a wide range of optical recording / reproducing methods, the magneto-optical recording / reproducing method has a unique advantage that information can be recorded and then erased, and new information can be recorded again and again. For being full of the greatest attraction.

A recording medium used in this magneto-optical recording / reproducing method has a perpendicular magnetic layer (perpendicular magnetic layer or layers) consisting of one layer or multiple layers as a layer for recording. This magnetic film is made of, for example, amorphous GdFe or Gd.
It is composed of Co, GdFeCo, TbFe, TbCo, TbFeCo and the like. The perpendicular magnetic film generally has concentric or spiral tracks, and information is recorded on the tracks. There are two types of tracks, explicit and implicit. [Explicit Track] The magneto-optical recording medium has a disk shape. In a disc having explicit tracks, tracks for recording information are formed in a spiral shape or a concentric circle shape when viewed in a direction perpendicular to the disk plane. There is a groove for tracking and separation between two adjacent tracks. Conversely, the space between the grooves is called a land. In reality, the land and groove are reversed on the front and back of the disc. Therefore, looking at the disk in the same way as the beam enters, the front side is called a groove and the back side is called a land. Since the perpendicularly magnetized film is formed over both the groove and the land, the groove portion may be the track or the land portion may be the track. There is no particular relationship between the width of the groove and the width of the land.

In order to form such a land and groove,
Generally, a substrate has a land formed in a spiral or concentric shape on the surface and a groove sandwiched between two adjacent lands. A thin perpendicular magnetic film is formed on such a substrate. As a result, the perpendicular magnetization film has lands and grooves. [Mark] In the present specification, “upward (upwar
d) "or" downward "
Orientation "and the other is defined as" reverse A orientation ". The information to be recorded is binarized in advance, and this information is "A direction".
Are recorded with two signals: a mark (B ₁ ) having the magnetization of _No. 2 and a mark (B ₀ ) having the magnetization of the “reverse A direction”. These marks B ₁ and B ₀ correspond to either one or the other of the digital signals 1 and 0, respectively. However, generally, the magnetization of the track to be recorded is aligned in the "reverse A direction" by applying a strong external magnetic field before recording. In the old sense, the act of aligning the directions of magnetization is "initialization ^* (init
ialize ^* ) ”. Then, a mark (B ₁ ) having "A direction" magnetization is formed on the track. The information is
It is expressed by the presence or absence of this mark (B ₁ ) and / or the mark length. Incidentally, the mark has been called a pit or a bit in the past, but recently it is called a mark. [Principle of mark formation] In the formation of marks, the characteristic of the laser, that is, the excellent coherence in terms of space and time (coheren
ce) is advantageously used to focus the beam into a spot as small as the diffraction limit determined by the wavelength of the laser light. The focused light is applied to the track surface, and information is recorded by forming marks with a diameter of 1 μm or less on the perpendicular magnetization film. In optical recording, recording densities up to about 10 ⁸ marks / cm ² can theoretically be achieved. This is because the laser beam can be concentrated into a spot with a diameter as small as about its wavelength.

As shown in FIG. 4, in magneto-optical recording, a laser beam (L) is focused on a perpendicular magnetization film (MO) and heated. Meanwhile, a recording magnetic field (Hb) in the opposite direction to the initialized ^* direction is externally applied to the heated portion. Then, the coercive force Hc (coersivity) of the locally heated portion decreases and becomes smaller than the recording magnetic field (Hb). As a result, the magnetization of that portion is aligned in the direction of the recording magnetic field (Hb). In this way, the oppositely magnetized mark is formed.

Ferromagnetic materials and ferrimagnetic materials have different temperature dependences of magnetization and Hc. Ferromagnetic materials have Hc that decreases near the Curie point, and recording is performed based on this phenomenon. Therefore, it is referred to as Tc writing (Curie point writing). On the other hand, ferrimagnetic materials have a compensation temperature T below the Curie point.
_comp. , where the magnetization (M) is zero. On the contrary, Hc becomes very large near that temperature, and when it deviates from that temperature, Hc drops sharply. This lowered Hc is defeated by the relatively weak recording magnetic field (Hb). That is, recording becomes possible. This recording process is called T _comp. Writing (compensation point writing).

However, it is not necessary to stick to the Curie point or its vicinity and the compensation temperature. In short, recording is possible by applying a recording magnetic field (Hb) that defeats the lowered Hc to the magnetic material having the lowered Hc at a predetermined temperature higher than room temperature. However, the perpendicular magnetization film (Mc in the region where Hc in this region has the original high Hc) that has not reached a predetermined temperature higher than room temperature (M
Too high Hb that reverses the magnetization of (O) is not possible. [Principle of Reproduction] FIG. 5 shows the principle of information reproduction based on the magneto-optical effect. Light is an electromagnetic wave having an electromagnetic field vector that is normally divergent in all directions on a plane perpendicular to the optical path. When the light is converted into linearly polarized light (L _p ) and applied to the perpendicular magnetic film (MO), the light is reflected on its surface or transmitted through the perpendicular magnetic film (MO). At this time, the polarization plane rotates according to the direction of the magnetization M. This rotating phenomenon is due to the magnetic Kerr effect or magnetic Faraday.
y) Called the effect.

For example, if the plane of polarization of the reflected light is "A direction"
Rotation of θ k degrees with respect to magnetization causes rotation of −θ k degrees with respect to "reverse A direction" magnetization. Therefore, if the axis of the optical analyzer (polarizer) is set perpendicular to the plane inclined by -θk, the light reflected from the mark (B ₀ ) magnetized in the "inverse A direction" will pass through the analyzer. I can't. On the other hand, the mark (B ₁ ) magnetized in "A direction"
The amount of light reflected from is multiplied by (sin2θk) ² and passes through the analyzer, and is captured by a detector (photoelectric conversion means). As a result, the mark (B ₁ ) magnetized in the "A direction" appears brighter than the mark (B ₀ ) magnetized in the "reverse A direction", and generates a strong electric signal in the detector. Therefore, the electrical signal from this detector is
The information is reproduced because it is modulated according to the recorded information.

By the way, in order to reuse the recorded medium, (1) initialize the medium again ^* initialize it with the device ^* , or
Or (2) it is necessary to add an erasing head similar to the recording head to the recording device, or (3) it is necessary to erase the recorded information in advance by using the recording device or the erasing device as a pre-stage process. Therefore, in the magneto-optical recording system, it has hitherto been impossible to perform overwriting capable of recording new information on the spot regardless of the presence or absence of recorded information.

However, if the direction of the recording magnetic field Hb can be freely modulated between "A direction" and "reverse A direction" as required, overwriting becomes possible. However, it is impossible to modulate the direction of the recording magnetic field Hb at high speed. For example, when the recording magnetic field Hb is a permanent magnet, it is necessary to mechanically reverse the direction of the magnet. However, it is impossible to reverse the direction of the magnet at high speed. Even when the recording magnetic field Hb is an electromagnet, it is impossible to modulate the direction of a large-capacity current at such a high speed.

However, the technological progress is remarkable, and the intensity of the irradiation light beam should be recorded without modulating the intensity of the recording magnetic field Hb (including ON and OFF) or without modulating the direction of the recording magnetic field Hb. A magneto-optical recording method capable of overwriting, a magneto-optical recording medium capable of being overwritten, and an overwritable recording apparatus also employed therefor have been invented only by modulating in accordance with binary information. A patent application has been filed (JP-A-62-175948 = DE3,619,61)
8A1 = US patent pending Ser. No. 453,255). Hereinafter, this invention is referred to as a "basic invention". [Description of Basic Invention] In the basic invention, "a recording / reproducing layer basically composed of a magnetic thin film capable of perpendicular magnetization
(In this specification, this recording / reproducing layer is referred to as a memory layer memory
layer or M layer) and a recording auxiliary layer reference layer composed of a magnetic thin film capable of perpendicular magnetization (in this specification, this recording auxiliary layer is a writing layer writing layer or W).
Layers), both layers are exchange-coupled, and
An overwritable multi-layered magneto-optical recording medium capable of keeping only the magnetization of the W layer in a predetermined direction without changing the magnetization direction of the M layer at room temperature is used.

Then, the information is represented and recorded by the mark having the "A direction" magnetization and the mark having the "reverse A direction" magnetization in the M layer (and also in the W layer in some cases).
In this medium, the W layer has an external means (for example, an initial auxiliary magnetic field Hin.
By i.), the direction of the magnetization can be aligned in the “A direction”. Moreover, at that time, the magnetization direction of the M layer is not reversed, and further, the magnetization direction of the W layer once aligned in the “A direction” is not reversed even when the exchange coupling force from the M layer is received. On the contrary, the magnetization direction of the M layer is not reversed even when receiving the exchange coupling force from the W layer aligned in the “A direction”.

The W layer has a lower coercive force H _C and a higher Curie point T _C than the M layer. According to the recording method of the basic invention, only the magnetization direction of the W layer of the recording medium is aligned in the “A direction” by external means before recording. This act is specifically referred to herein as "initialize". This "initialization" is unique to overwritable media.

Then, the medium is irradiated with a laser beam pulse-modulated according to the binarized information. The intensity of the laser beam has a high level P _H and a low level P _L , which correspond to the high level and low level of the pulse. This low level is higher than the reproduction level P _R that illuminates the medium during reproduction. As is already known, the laser beam may be turned on at a <very low level> even when recording is not performed, for example, to access a predetermined recording position on the medium. This <very low level> is also the same as or close to the reproduction level P _R. Therefore, for example, the output waveform of the laser beam in the basic invention is as shown in FIG.

Although not specified in the specification of the basic invention, in the basic invention, the recording beam is not a single beam but two beams which are close to each other, and in principle, does not modulate the preceding beam. A level laser beam (for erasing) may be used, and a trailing beam may be a high level laser beam (for writing) that is modulated according to information. In this case, the trailing beam is pulse-modulated between a high level and a base level (equal to or lower than the low level and may have zero output). The output waveform in this case is, for example, as shown in FIG.
Shown in.

A recording magnetic field Hb whose direction and intensity are not modulated acts on the medium irradiated with the beam. Hb is
It cannot be narrowed down to the same size as the irradiated portion of the beam (spot region), and the region where Hb acts is much larger than the spot region. When illuminated by a low level beam, M is independent of the direction of magnetization of the previous mark.
One of the "A-oriented" mark (B ₁ ) and the "reverse A-oriented" mark (B ₀ ) is formed on the layer.

When a high level beam is irradiated, the other mark is formed on the M layer regardless of the magnetization direction of the previous mark. This completes the overwrite. In the basic invention, the laser beam is pulse-modulated according to the information to be recorded. However, this is also done in the conventional magneto-optical recording, and it should be recorded.
The means for pulse-modulating the beam intensity according to the digitized information is a known means. For example, THE BELL SYSTEM TECHN
ICAL JOURNAL, Vol. 62 (1983), 1923 -1936. Therefore, given the required high and low levels of beam intensity, they are readily available with some modifications to conventional modulation means. For those skilled in the art, such modification would be easy given the high and low levels of beam intensity.

One of the features of the basic invention is
There are high and low levels of beam intensity. That is, when the beam intensity is at a high level, the "A direction" magnetization of the W layer is reversed (reverse A direction) by the recording magnetic field Hb or other external means (re
verse), and the "reverse A direction" magnetization of the W layer forms a mark having "reverse A direction" magnetization (or "A direction" magnetization) in the M layer. When the beam intensity is low, the magnetization direction of the W layer is the same as in the "initialized" state, and
By the action of the layer (this action is transmitted to the M layer through the exchange coupling force), the M layer is magnetized "A direction" [or "reverse A direction"].
Magnetization] is formed.

In the present specification, ○○○ [or △△△]
With the expression, when XX outside [] is read first, XX outside [] will be read also in the following XX [or ΔΔΔ ]. On the contrary, ○○○
If you select and read the △△△ one in [] without reading, you can also read △ ○ △ in [] without reading ○○○ even in the following ○○○ [or △△△ ] Should be read.

The medium used in the basic invention is roughly classified into a first embodiment and a second embodiment. In any of the embodiments, the recording medium has a multilayer structure including an M layer and a W layer. The M layer is a magnetic layer having a high coercive force and a low magnetization reversal temperature at room temperature. The W layer is a magnetic layer having a lower coercive force and a higher magnetization reversal temperature at room temperature than the M layer. Both the M layer and the W layer may themselves be composed of a multilayer film. In some cases, a third layer (for example, an adjustment layer for the exchange coupling force σ _W ) may be present between the M layer and the W layer.
See JP-A-64-50257 and JP-A-1-273248. Furthermore, there is no clear boundary between the M layer and the W layer, and it is possible to gradually change from one to the other.

In the first embodiment, the coercive force of the M layer is H _C1 ,
The W layer has H _C2 , the M layer has a Curie point T _C1 , the W layer has T _C2 , the room temperature is T _R , and the temperature of the recording medium when irradiated with a low-level P _L laser beam is T _L , When a high-level P _H laser beam is irradiated, it is T _H , and the coupling magnetic field received by the M layer is H _D1 (H _D1 is σ _W multiplied by the product of the M layer saturation magnetic moment M _S and the M layer thickness t). Is calculated by dividing the coupling magnetic field received by the W layer by H _D2 (where H _D2 is σ _W divided by the product of the W layer saturation magnetic moment M _S and the W layer thickness t). , The recording medium is
And satisfying formulas 2 to 5 at room temperature.

T _R <T _C1 ≈T _L <T _C2 ≈T _H ………… Equation 1 H _C1 > H _C2 + | HD ₁ − (± HD ₂ ) | ……… Equation 2 H _C1 > HD ₁ ……………………………………… Formula 3 H _C2 > H _D2 ………………………………… Formula 4 H _C2 + H _D2 <| Hini. | <H _C1 ± H _D1 ──Equation 5 In the above equation, the symbols “≈” are equal or almost equal (±
20 ° C). Further, in the above formula, the composite ± is for the case of the A (antiparallel) type medium described below in the upper stage, and is for the case of the P (parallel) type medium described below in the lower stage. The ferromagnetic medium belongs to the P type.

That is, the relationship between the coercive force and the temperature is generally represented by a graph as shown in FIG. The thin line represents that of the M layer, and the thick line represents that of the W layer. Therefore, when an external means such as an initial auxiliary magnetic field (Hini.) Is applied to this recording medium at room temperature, according to Equation 5, the magnetization direction of the M layer is not reversed and W
Only the magnetization of the layer is reversed. Therefore, when an action (for example, an initial auxiliary magnetic field Hini.) Is exerted on the medium before recording, only the magnetization of the W layer can be aligned in the “A direction”. That is, "initialization". In the following description, the “A direction” is indicated by an upward arrow ↑ and the “reverse A direction” is indicated by a downward arrow ↓ for convenience sake. And Hin
Even if i. disappears, the magnetization ↑ of the W layer is maintained as it is without being re-inverted according to the equation (4).

A conceptual representation of a state in which only the magnetization of the W layer is aligned in the "A direction" ↑ before recording by an external means ----- "initialized" state --- 9 In FIG. 9, the magnetization direction ^* in the M layer represents the information recorded up to that point. In the following description, since there is no relation to the orientation, if this is shown by X and is simplified, FIG. 9 can be shown as state 1 in FIG. 10.

Here, the medium temperature is raised to T _H by irradiating a high level laser beam. Then T _H
Is higher than the Curie point T _C1 , the magnetization of the M layer disappears. Furthermore, since T _H is near the Curie point T _C2 , the magnetization of the W layer disappears completely or almost. Here, the recording magnetic field Hb of "A direction" or "reverse A direction" is applied according to the type of medium. Hb may be a stray magnetic field from the medium itself. In order to simplify the explanation, it is assumed that the recording magnetic field Hb in the "reverse A direction" ↓ is applied. Since the medium is moving, the irradiated portion is immediately moved away from the laser beam and cooled. When the temperature of the medium is lowered in the presence of Hb, the magnetization of the W layer is reversed according to Hb to become "inverse A direction" ↓ magnetization (state 2 in FIG. 10).

Then, the cooling is further advanced, and the medium temperature becomes T
_When it is slightly lower than _C1, the magnetization of the M layer appears again. In that case, due to the magnetic coupling (exchange coupling) force, the magnetization direction of the M layer is influenced by the W layer and becomes a predetermined direction. As a result, depending on the type of medium, an "inverse A direction" ↓ mark (for P type medium) or an "A direction" ↑ mark (for A type medium) is formed in the M layer. This state is shown in Figure 1.
0 state 3 (P type) or state 4 (A type).

The change of state due to this high level laser beam will be referred to as a high temperature cycle here. Next, the medium temperature is raised to T _L by irradiating a low-level P _L laser beam. Since T _L is near the Curie point T _C1, the magnetization of the M layer disappears at all or almost disappears, but since it is lower than the Curie point T _C2 , the magnetization of the W layer does not disappear. This state is shown as state 5 in FIG. Here, the recording magnetic field Hb is unnecessary, but Hb at high speed (short time)
It is impossible to turn on and off. Therefore, it is unavoidable that it remains as it was during the high temperature cycle.

However, since H _C2 is still large, H
The magnetization ↑ of the W layer is not reversed by b. Since the medium is moving, the irradiated portion is immediately moved away from the laser beam and cooled. As cooling progresses, magnetization again appears in the M layer. The direction of magnetization that appears is a predetermined direction due to the influence of the W layer due to the magnetic coupling force. As a result, depending on the type of medium, "A direction" ↑ mark (for P type medium) or "reverse A direction" ↓ mark (for A type medium) is formed in the M layer. This magnetization does not change even at room temperature. This state is shown in Figure 10, State 6 (P type).
Alternatively, it is the state 7 (A type).

The change of state caused by the low-level laser beam will be referred to as a low temperature cycle here. As described above, regardless of the magnetization direction of the M layer before recording, by selecting the high temperature cycle and the low temperature cycle, the mark of "reverse A direction" ↓ and the mark of "A direction" ↑ can be obtained. It can be freely formed on the M layer. That is, overwriting is possible by modulating the laser beam in a pulse shape between a high level (high temperature cycle) and a low level (low temperature cycle) according to information. See FIGS. 11 and 12. In FIG. 11 and FIG. 12, P type and A are respectively
All types of media are depicted as a result of room temperature or back to room temperature.

In the above description, the magnetic material composition in which there is no compensation temperature T _comp. Between the room temperature and the Curie point for both the M layer and the W layer has been described. However, if the compensation temperature T _comp. Exists, the direction of the magnetization is reversed when the temperature exceeds the temperature _{T-- comp.} Is reversed, the direction of the magnetization as a whole (alloy) is reversed -----
The explanation becomes more complicated because the A and P types are reversed. In this case, the direction of the recording magnetic field Hb is also opposite to the direction ↓ described in the previous page when considered at room temperature. That is, Hb having the same direction as the magnetization direction ↑ of the “initialized” W layer is applied.

The recording medium is generally disc-shaped, and the medium is rotated during recording. Therefore, the recorded portion (mark) is again subjected to the action of external means such as Hini. After recording, and as a result, the magnetization of the W layer is aligned in the original “A direction” ↑. That is, the W layer is “initialized”. But,
At room temperature, the influence of the magnetization of the W layer does not affect the M layer,
Therefore, the recorded information is retained.

Therefore, when the M layer is irradiated with linearly polarized light, the reflected light contains information, so that the information is reproduced as in the conventional magneto-optical recording medium. The perpendicularly magnetized films forming the M layer and the W layer are amorphous or crystalline of a ferromagnetic material having no Curie point and having a Curie point.
It is selected from the group consisting of an amorphous or crystalline ferrimagnetic material having no Curie point without a compensation temperature and an amorphous or crystalline ferrimagnetic material having both a compensation temperature and a Curie point. The above description is for the first embodiment using the Curie point as the magnetization reversal temperature. On the other hand, the second embodiment utilizes Hc lowered at a temperature lower than the Curie point. The second embodiment uses the temperature T _S1 at which the M layer is magnetically coupled to the W layer in place of T _{C1 in} the first embodiment, and the temperature T _S2 at which the W layer inverts at Hb instead of T _C2. Is used in the same manner as in the first embodiment.

In the second embodiment, the coercive force of the M layer is H _C1 ,
Let W _C2 be that of the W layer, T _s1 be the temperature at which the M layer is magnetically coupled to the W layer, T _{S2 be} the temperature at which the magnetization of the W layer is reversed at Hb, T _{R be} the room temperature, and T _{L be} the low level. the temperature of the medium when irradiated with a laser beam T _L, it T _H when irradiated with a laser beam of high level P _H, the coupling magnetic field M layer receives H _D1 (H _D1 is the sigma _W of the M layer Saturation magnetic moment M _S
Is calculated by the quotient divided by the product of M and the film thickness t of the M layer), and the coupling magnetic field received by the W layer is H _D2 (where H _D2 is σ _W is the W layer saturation magnetic moment M _S and the W layer thickness t). (Calculated by the quotient divided by the product of and), the recording medium satisfies the following expression 6 and also satisfies the expressions 7 to 10 at room temperature.

T _R <T _s1 ≈T _L <T _s2 ≈T _H ………… Equation 6 H _C1 > H _C2 + | HD ₁ − (± HD ₂ ) | …… Equation 7 H _C1 > HD ₁ ……………………………………… Formula 8 H _C2 > H _D2 ─ …………………………………… Formula 9 H _C2 + H _D2 <| Hini. | <H _C1 ± H _D1 ──Equation 10 In the above equation, for composite ±, the upper row is A (antiparalle
The case of the l) type medium, and the lower case is the case of the P (parallel) type medium.

In the second embodiment, at high temperature T _H , the magnetization of the W layer has not disappeared, but is sufficiently weak, and the magnetization of the M layer has disappeared or is sufficiently weak. The recording magnetic field Hb ↓ is sufficiently large even if a sufficiently weak magnetization remains in both the M layer and the W layer, so that the Hb ↓ can cause the magnetization direction of the W layer and, in some cases, the M layer to follow the Hb ↓. . This state is state 2 in FIG. Immediately thereafter, or when the laser beam irradiation is stopped and the cooling progresses and the medium temperature falls below T _H or moves away from Hb, the W layer is σ _W.
To affect the M layer through the magnetic field to make the magnetization direction of the M layer follow a stable direction. As a result, the state becomes the state 3 (P type) or the state 4 (A type) in FIG.

On the other hand, at low temperature T _L , the W layer is of course M
The layers have not lost their magnetization. However, that of the M layer is relatively small. In this case, there are two kinds of mark states, that is, state 5 and state 6 in FIG. 13 for the P type, and state 7 and state 8 in FIG. 13 for the A type. In the states 6 and 8, the interface domain wall (indicated by the thick line ━) is formed between the M layer and the W layer, and the state is somewhat unstable (metastable). State 1 indicates any of states 5 to 8. Just before the medium part in this state reaches the irradiation position of the laser beam,
Hb ↓ is applied. Nevertheless, this state 6 or state 8 is retained. Because the W layer has a sufficient magnetization at room temperature, the magnetization is not reversed by Hb ↓. In addition, the memory layer in the state 8 whose direction is opposite to Hb ↓ has a larger exchange coupling force σ from the W layer than the influence of Hb ↓.
_Under the influence of W, the magnetization direction is maintained in the same direction as the W layer because of the P type.

Shortly thereafter, the state 6 or the state 8 is irradiated with a low level laser beam. Therefore, the medium temperature rises. Along with that, the coercive force of both layers decreases.
However, since the W layer has a high Curie point, the coercive force H
The decrease of _C2 is small, it does not lose to Hb ↓, and the magnetization direction "A direction" ↑ when "initialized" is maintained. On the other hand, although the M layer has a low Curie point, since the medium temperature is still lower than the Curie point T _{c1 of the} M layer, the coercive force H _C1 remains. However, since H _C1 is small, the influence of Hb ↓ on the W layer and the influence via the exchange coupling force σ _w from the W layer (in the case of the P type, the force trying to turn in the same direction)
Receive. In this case, the latter is stronger, and two equations of 2: H _c1 + Hb <(σ _w / 2M _S1 t ₁ ) 3 of equation 10: H _c2 + Hb> (σ _w / 2M _S2 t ₂ ) are obtained. At the same time satisfied. The lowest temperature at which these equations are satisfied simultaneously is called T _LS . In other words, the minimum temperature at which the domain wall in state 6 or state 8 disappears is T _LS .

As a result, the state 6 shifts to the state 9 and the state 8 shifts to the state 10. On the other hand, since the state 5 without the domain wall is the same as the state 9 and the state 7 without the domain wall is the same as the state 10, after all, the previous state (in the case of the P type, the state 5 or 6 or A In the case of the type, regardless of the state 7 or 8), irradiation of the low level beam forms the mark of the state 9 (P type) or the state 10 (A type).

This state does not change even when the medium temperature is lowered and the temperature is returned to room temperature because the laser beam irradiation of the mark is stopped or the mark is removed from the irradiation position thereafter. This FIG. 13 state 9 (P type) or state 10 (A
Type) is state 6 (P type) or state 7 (A in FIG. 10).
Type). It will be appreciated that this allows a low temperature cycle to be achieved without raising the medium temperature to the Curie point T _C1 of the M layer.

In fact, also in the case of the first embodiment in which the low temperature cycle is carried out at T _C1 or more, since the medium temperature passes through T _LS on the way from room temperature to T _C1 , at that time, in the case of the P type, the state 6 The transition from state 8 to state 9 occurs in the case of type A, the transition from state 8 to state 10 respectively. After that, T _C1 is reached and the state 5 shown in FIG. 10 is established. The above description has explained the magnetic material composition in which there is no compensation temperature T _comp. Between the room temperature and the Curie point for both the M layer and the W layer.
However, if the compensating temperature T _comp. Exists, the direction of the magnetization is reversed when the compensating temperature T _comp. Is exceeded, and the A and P types are reversed, and the explanation becomes complicated accordingly. Further, the direction of the recording magnetic field Hb is also opposite to the direction when considered at room temperature.

In both the first and second embodiments, the M layer and the W layer are made of a transition metal (eg Fe, Co) -heavy rare earth metal (eg G).
d, Tb, Dy, etc.) A recording medium which is an amorphous ferrimagnetic material selected from alloy compositions is preferable. Both the M layer and the W layer are transition metal-heavy rare earth metal (heavy metal).
When selected from the alloy composition, the direction and magnitude of the magnetization appearing externally as each alloy is the direction and magnitude of the sublattice magnetization of the transition metal atom (TM) inside the alloy and the heavy rare earth metal. It is determined by the relationship with the direction and magnitude of the sublattice magnetization of the atom (RE). For example, the direction and magnitude of the sublattice magnetization of TM is represented by a vector indicated by a dotted arrow, the direction of the sublattice magnetization of RE is represented by a vector indicated by a solid line arrow, and the orientation and magnitude of the entire alloy are outlined. It is represented by the vector indicated by the arrow. At this time, the white arrow (vector) is a dotted arrow (vector) and the solid arrow (vector)
It is expressed as the sum of and. However, in the alloy, due to the interaction between the TM sublattice magnetization and the RE sublattice magnetization, the dotted arrow (vector) and the solid arrow (vector) always have opposite directions. Therefore, the sum of the dotted arrows (vectors) and the solid arrows (vectors) makes the alloy vector zero (that is, the magnitude of the magnetization appearing outside) when the two have the same intensity. The alloy composition when it reaches zero is called the compensation composition. For any other composition, the alloy has an intensity equal to the intensity difference of both sublattice magnetizations and has a hollow arrow (vector) with an orientation equal to the orientation of the larger vector.

Therefore, the magnetization vector of the alloy is written adjacent to the vector of the dotted line and the vector of the solid line, for example, as shown in FIG. The sublattice magnetization states of RE and TM are roughly classified into four states, which are shown in (1A) to (4A) of FIG. The magnetization vector (open arrow) of the alloy in each state is shown in correspondence with (1B) to (4B) of FIG. For example, if the RE vector is larger than the TM vector,
The state of sublattice magnetization is shown in (1A), and the magnetization vector of the alloy is shown in (1B).

When the strength of either the TM vector or the RE vector of a certain alloy composition is large, the alloy composition takes the name of the one with the larger strength and is XX rich, for example, RE.
Called rich. For both M and W layers,
It is divided into TM-rich composition and RE-rich composition.
Therefore, when the composition of the M layer is plotted on the ordinate and the composition of the W layer is plotted on the abscissa, the types of the medium of the basic invention as a whole are shown in FIG.
It can be classified into the four quadrants shown in. In FIG. 16, the intersection of the coordinates shows the compensation composition of both layers. P mentioned above
The type belongs to the first and third quadrants shown in FIG. 16, and the type A belongs to the second and fourth quadrants.

On the other hand, looking at the change in coercive force with respect to temperature change, there is an alloy composition having a characteristic that the coercive force temporarily increases to infinity and then drops before reaching the Curie point (temperature at which coercive force is zero). . The temperature corresponding to this infinity is called the compensation temperature (T _comp. ). At a temperature lower than the compensation temperature, the RE vector (solid line arrow) is larger than the TM vector (dotted line arrow), so it can be said that it is TM rich, and vice versa at a temperature higher than the compensation temperature. Therefore, it can be said that the compensation temperature of the alloy having the compensation composition is at room temperature.

On the contrary, the compensation temperature does not exist between room temperature and the Curie point in the TM-rich alloy composition. Since the compensation temperature below room temperature is meaningless in magneto-optical recording, the compensation temperature in this specification means that it exists between room temperature and the Curie point. Classifying the presence or absence of the compensation temperature of the M layer and the W layer, the medium is type 1
Are classified into four types. In Type 1, both the M layer and the W layer have a compensation temperature. In the type 2, the M layer has no compensation temperature and the W layer has compensation temperature. Type 3 is M
The layer has a compensation temperature and the W layer has no compensation temperature. In Type 4, both the M layer and the W layer have no compensation temperature. One-quadrant media includes all four types. Therefore, for both the M layer and the W layer, it is classified as RE rich or TM rich,
Moreover, the recording media are classified into 9 classes shown in FIG. [Explanation of Class 1-1] Class 1 shown in FIG. 20 here
The overwrite principle will be described in detail by taking as an example the medium No. 1-1 belonging to the recording medium (P type, 1 quadrant, type 1).

[0047] The medium No.1-1, the following equation _{11: T R <T comp.1 <} T L <T H ≦ T C1 ≦ T c2 and 2 of Formula _11: T comp.2 <relation T _C1 Have. In the present specification, “=” in “≦” means that they are equal or almost equal (± 20 ° C. or so). For the purpose of simplifying the explanation, the following explanation is T _H <T _C1 <T _c2
Those having the relationship of will be described. T _comp.2 is T
_It may be higher than, equal to, or lower than _L , but for the purpose of simplifying the explanation, in the following explanation, T _L <T _comp.2
And FIG. 17 is a graph showing the above relationship. The thin line shows the graph of the M layer, and the thick line shows the graph of the W layer.

At room temperature T _R , the magnetic field of the M layer is the initial auxiliary magnetic field Hin.
The condition that only W layer is inverted without being inverted by i.

[0049]

[Equation 1]

Equation 12 is expressed as This medium No.1-1
Satisfies Equation 12. However, H _C1 : Coercive force of M layer H _C2 : Coercive force of W layer M _S1 : Saturation magnet moment of M layer
ization) M _S2 : saturation magnetic moment of W layer t ₁ : thickness of M layer t ₂ : thickness of W layer σ _w : domain wall energy = exchange coupling force (interface w
all energy) At this time, the conditional expression of Hini. is expressed by Expression 15 shown in Expression 4. When the Hini. Disappears, the magnetizations of the M layer and the W layer are affected by the exchange coupling force. Nevertheless, the conditions under which the magnetizations of the M layer and W layer are maintained without being inverted are shown by equations 13-14. This medium No. 1-1 satisfies equations 13-14.

[0051]

[Equation 2]

[0052]

[Equation 3]

The magnetization of the W layer of the recording medium satisfying the conditions of equations 12 to 14 at room temperature should be measured by the time immediately before recording.

[0054]

[Equation 4]

Hini. That satisfies the expression 15 shown in FIG. At this time, the M layer remains in the previous recording state. This state is state 1 or state 2 in FIG.
Indicated by either. This will be described with reference to FIG. The states 1 and 2 are held until just before recording.
Then, the recording magnetic field Hb is applied in the “A direction” ↑.

It is difficult to limit the recording magnetic field Hb to the same range as the irradiation area (spot area) of the laser beam, as is the case with general magnetic fields. When the medium is a disc, once the recorded information (mark) is rotated once, it is changed to state 1 or state 2 under the influence of Hini. After that, the mark passes near a laser beam irradiation region (spot region). At this time, the marks in state 1 and state 2 are affected by the approach to the recording magnetic field Hb applying means. In this case, if the magnetization direction of the M layer of the mark in the state 2 having the magnetization opposite to Hb is reversed by Hb, the information just recorded one rotation before disappears. The conditions that should not be so are

[0057]

[Equation 5]

It is expressed by 2 of the equation 15 shown in FIG. The disk-shaped medium No. 1-1 needs to satisfy the condition (2) of conditional expression 15 at room temperature. Conversely, one condition that determines Hb is
It is shown by 2 in Expression 15. The marks in states 1 and 2 finally reach the spot area of the laser beam. There are two types of laser beam intensity, low level and high level, as in the basic invention.

----- Low Temperature Cycle ---- When a low level laser beam is irradiated, the medium temperature rises above T _comp.1 . Then, from P type to A
Move to type. Although the directions of the RE and TM spins of the M layer do not change, the magnitude relationship of the intensity is (3A) in FIG.
To reverse (4A). Therefore, the magnetization of the M layer is as shown in FIG.
Invert from (3B) to (4B). As a result, the mark in state 1 shown in FIG. 18 shifts to state 3, and the mark in state 2 changes to state 4.
Move to.

Following the irradiation of the laser beam, the medium temperature eventually becomes T _LS . Then, the two in Equation 10 and the one in Equation 10
3 are satisfied at the same time. As a result, even if Hb ↑ exists, the mark in state 4 in FIG. 18 transits to state 5. On the other hand, the mark of state 3 in FIG. 18 is 10 even if Hb ↑ is present.
Since 2 and 3 in Eq. 10 are satisfied at the same time, keep the same condition. That is, the state 3 only changes to the same state as the state 5 in FIG.

In this state, when the laser beam deviates from the spot area, the medium temperature starts to drop. Medium temperature is T
_When it cools down to below _comp.1, it returns from the A type to the original P type. Then, the magnitude relationship between the RE spin and the TM spin of the M layer is reversed from (2A) to (1A) in FIG. for that reason,
The magnetization of the M layer is reversed from (2B) to (1B) in FIG. As a result, the mark in the state 5 in FIG. 18 shifts to the state 6 (the magnetization of the M layer is in the “A direction” ↑). This state 6 is maintained even if the medium temperature drops to room temperature. In this way, the mark of “A direction” ↑ is formed on the M layer.

----- High Temperature Cycle ---- When a high level laser beam is irradiated, the medium temperature rises to a low temperature T _L via T _comp.1 . As a result, the state 7 is the same as the state 5 in FIG. Irradiation with a high level laser beam further raises the medium temperature. When the medium temperature exceeds T _comp.2 of the W layer, the A type shifts to the P type. Then, although the directions of the RE and TM spins of the W layer do not change, the magnitude relationship between the strengths is (1A) to (2A) in FIG.
Reverse to. Therefore, the magnetization of the W layer is reversed from (1B) to (2B) in FIG. As a result, the magnetization of the W layer is
The direction will be ↓. This is state 8 in FIG.

However, since H _C2 is still large at this temperature, the magnetization of the W layer is not reversed by ↑ Hb. When the temperature further rises to T _H , the coercive force of the M layer and the W layer becomes small because the temperature is close to the Curie point. As a result, the medium is

[0064]

[Equation 6]

(1) or

[0066]

[Equation 7]

(2) or

[0068]

[Equation 8]

The two expressions (3) shown in (3) are simultaneously satisfied. Therefore, the magnetizations of both layers are reversed almost at the same time and follow the direction of Hb ↑. This state is state 9. In this state, when the laser beam deviates from the spot area, the medium temperature starts to drop. When the medium temperature becomes T _{comp. 2} or less, the P type shifts to the A type. Then, although the directions of the spins of RE and TM do not change, the magnitude relationship of the strength is reversed from (4A) to (3A) in FIG. Therefore, the magnetization of the W layer is reversed from (4B) to (3B) in FIG. As a result, the magnetization of the W layer becomes “inverse A direction” ↓.
This is state 10 in FIG. In state 10, the medium is

[0070]

[Equation 9]

4 of Expression 15 shown in is satisfied. Therefore, W
Even if Hb ↑ acts on the layer, it does not reverse. When the temperature of the medium further decreases from the temperature in this state 10,
_When it becomes _comp.1 or less, it returns from the A type to the original P type. Then, the magnitude relation between the intensity of the RE spin and the intensity of the TM spin of the M layer is reversed from (4A) to (3A) in FIG. Therefore, the magnetization of the M layer is reversed from (4B) to (3B) in FIG.
As a result, the magnetization of the M layer becomes “inverse A direction” ↓. This state is state 11 in FIG.

Eventually, the temperature of the medium drops from the temperature in state 11 to room temperature. Since H _C1 at room temperature is sufficiently large (see 5 in Equation 15), the magnetization ↓ of the M layer is not inverted by ↑ Hb, and the state 11 is maintained.

[0073]

[Equation 10]

In this way, the mark of "inverse A direction" ↓ is formed on the M layer. [Explanation of Selected Invention] The above explanation has been made on the two-layer film of the M layer and the W layer. With such a two-layer film, overwriting is possible even with a multilayer film of three or more layers. In particular,
In the above description, the external means called the initial auxiliary magnetic field (Hini.) Is used. However, in the basic invention, the external means is Hin
It is not limited to i. In short, by the time before recording, the magnetization of the W layer is oriented in a predetermined direction, that is,
It just needs to be "initialized". Therefore, instead of Hini. As an external means, an initialization layer (intializing laye
An invention was made using r). Japanese journal "OPTRONICS"
See No. 4, 1990, pages 227-231. More detailed information is WO / 90/2400 (PCT / JP89 / 863) published on Mar. 8, 1990. Hereinafter, this invention is referred to as a selected invention.

The state 1 of FIG. 19 shows the structure of the medium used in the selection invention. This medium is composed of a substrate and a magnetic film basically having a four-layer structure formed on the substrate. This magnetic film comprises, in order, an M layer made of a vertically magnetizable magnetic thin film, a W layer made of a vertically magnetizable magnetic thin film, and a switching layer (hereinafter, S layer) made of a vertically magnetizable magnetic thin film.
A layer is abbreviated) and an "initializing" layer (hereinafter abbreviated as I layer) composed of a perpendicularly magnetizable magnetic thin film has a four-layer structure in principle (the S layer may be omitted).

In the International Publication, the M layer is the first magnetic layer, the W layer is the second magnetic layer, the S layer is the third magnetic layer (see claim 3), and the I layer is It is called the fourth magnetic layer (see claim 3). At points other than the third term, the names of the third magnetic layer and the fourth magnetic layer are opposite to each other, which seems to be a mistaken writing. Also, the magazine "OPTRONIC"
In S ", the S layer is called the control layer.

In this four-layer structure medium, the M layer and the W layer are exchange-coupled, and it is possible to direct only the magnetization of the W layer to a predetermined direction without changing the magnetization direction of the M layer at room temperature. You can
Moreover, the W layer and the I layer are S at a temperature below the Curie point of the S layer.
Exchange coupled through the layers. The I layer has the highest Curie point and does not lose its magnetization even when irradiated with a high level laser beam. The I layer always holds the magnetization in a predetermined direction, and this serves as means for repeatedly performing "initialization" of the W layer in preparation for the next recording each time recording is performed. Therefore, I
The layer is called the "initialization" layer.

However, in the course of the high temperature cycle (for example, near T _H ), the magnetization reversal of the W layer must occur, and in that case, the influence from the I layer must be small so that it can be ignored. It is advantageous that the exchange coupling force σ _w24 between the W layer and the I layer becomes smaller as the temperature becomes higher. However, even at T _H , when sufficient σ _w24 remains, an S layer is required between the W layer and the I layer. If the S layer is a non-magnetic material, σ _w24 is zero or very small. However, at some temperature below T _H to room temperature, σ _w24 must be large due to the “initialization” of the W layer. At that time, the S layer must give an apparently sufficiently large exchange coupling force between the W layer and the I layer. For that purpose, the S layer needs to be magnetic. Therefore, the S layer becomes a magnetic material at a relatively low temperature and becomes W.
Apparently sufficiently large exchange coupling force σ between layer I and layer I
_w24 , which becomes a non-magnetic material at a relatively high temperature, and gives an apparent zero or very small exchange coupling force σ _w24 between the W layer and the I layer. Therefore, the S layer is referred to as a switching layer.

Next, the principle of the four-layer film overwrite will be described with reference to FIG. This description is a typical example, and there are other examples. For example, the explanation becomes more complicated if any one of the layers has T _comp. Between room temperature and the Curie point. In FIG. 19, white arrows indicate the magnetization directions of the layers. The state before recording is either state 1 or state 2. Focusing on the M layer, the state 1 is the “A-oriented” mark (B ₁ ), and the state 2 is the “reverse A-oriented” mark (B ₀ ).
And the domain wall between the M layer and the W layer (indicated by a bold line ━)
And is in a somewhat unstable state (metastable).

------------- Low Temperature Cycle ---------- When the laser beam is applied to the marks in state 1 and state 2 to raise the temperature, the magnetization of the S layer first disappears. Therefore, the state 1 shifts to the state 3, and the state 2 shifts to the state 4. When the temperature further rises to reach T _LS , the magnetization of the M layer becomes weak and the action via the exchange coupling force from the W layer becomes strong. As a result, the magnetization of the M layer in state 4 is reversed, and at the same time, the domain wall between layers disappears. This is state 5. Since the mark in state 3 originally has no domain wall between layers, the state is directly shifted to state 5.

Here, when the irradiation of the laser beam stops or moves away from the irradiation position, the temperature of the mark in the state 5 starts to drop, and then the mark in the state 5 goes to the state 1 through the state 3. This is the low temperature cycle. When the temperature further rises from the state 5 and exceeds the Curie point of the M layer, the magnetization disappears and the state 6 is established. Here, when the irradiation of the laser beam stops or moves away from the irradiation position, the temperature of the mark in state 6 starts to decrease, and eventually the Curie point of the M layer reaches a slightly lower temperature. Then, magnetization appears in the M layer. The direction of this magnetization is W
A direction that is stable with respect to the magnetization direction of the W layer due to the action via the exchange coupling force from the layers (direction that does not cause domain walls between layers)
Becomes Since the type is P type here, state 5 is reproduced. The temperature drops further, and accordingly state 3 occurs, followed by the state 1 mark. This process is another example of a low temperature cycle.

---------- High Temperature Cycle ------------- FIG. 19 When the laser beam is applied to the marks in the states 1 and 2 to raise the temperature, the state 5 is changed as described above. After that, the state 6 is reached. When the temperature further rises, the coercive force of the W layer drops significantly. Therefore, the magnetization is inverted by the recording magnetic field Hb ↓. This is state 8.

Here, when the irradiation of the laser beam stops or moves away from the irradiation position, the medium temperature starts to decrease.
Eventually, the medium temperature falls slightly below the Curie point of the M layer.
Then, magnetization appears in the M layer. The direction of this magnetization is
Due to the action via the exchange coupling force from the W layer, the orientation becomes stable with respect to the magnetization direction of the W layer (direction in which no domain wall is generated between layers). Since the type is P type here, the state 9 appears.

When the temperature further decreases, magnetization appears in the S layer, and as a result, the W layer and the I layer are magnetically coupled (by an exchange coupling force). As a result, the magnetization direction of the W layer is stable with respect to the magnetization direction of the I layer (direction in which no domain wall is generated between layers). Since it is of P type here, the magnetization of the W layer is inverted in the “A direction”, and as a result, an interface domain wall is generated between the M layer and the W layer. This state is maintained even at room temperature, and the mark of state 2 is generated.

This is a high temperature cycle. When the temperature further rises after the state 8 appears due to the recording magnetic field Hb ↓, the temperature eventually exceeds the Curie point of the W layer. Then, the state 7 appears. Here, when the irradiation of the laser beam stops or moves away from the irradiation position, the medium temperature starts to decrease. Eventually, the medium temperature falls slightly below the Curie point of the W layer. Then, magnetization appears in the W layer. The direction of this magnetization follows the direction of the recording magnetic field Hb ↓. As a result, the state 8 appears.

When the temperature is further lowered, the mark of state 2 is formed through state 9. This process is another example of a high temperature cycle. ---------- Overwrite -------- As mentioned above, the mark (B ₁ ) of the state 1 is formed in the M layer in the low temperature cycle and the M layer in the high temperature cycle regardless of the previous recording state. A mark (B ₀ ) of the state 2 is formed at. Therefore,
Overwriting is possible.

[0087]

However, the existing overwritable recording methods have a problem that the data discrimination is not sufficient. In order to solve this problem, the present inventors have used the device shown in FIG.
It has been proposed to try to form marks by the recording method as shown in (2) and (3) (Japanese Patent Application No. 4-33221). This is that the overwritable medium is pulse-modulated between the high level P _H and the low level P _L according to the binarized information, the medium is irradiated with the laser beam according to this, and the recording magnetic field is generated at the laser beam irradiation position. When applying a mark to form a mark,
As shown in (1) of FIG. 2, when the beam intensity is raised from the low level P _L to the high level P _H , once the limit value P _Lmin (the mark formed at the high level P _H is turned on by DC lighting). This is a method in which the laser beam is lowered to a level below the minimum low level P _L which can be erased and then rises to P _H. As another method, as shown in (2) of FIG. 2, when the beam intensity is lowered from the high level P _H to the low level P _L , the limit value P
We proposed a method to reduce the value to below _Lmin and then to restore it to the low level P _L. Further, a shaping method in which the shaping methods of (1) and (2) in FIG. 2 are added is proposed. this is,
As shown in (3) of FIG.
When launching from _L to the high level P _H, once reduced to below the limit value P _Lmin, then shaping as launch to the high level P _H, and the beam intensity, a high level P _H to the low level P _L When shutting down, once the limit value P
_We also proposed a method of lowering it below _Lmin and then shaping it back to the low level P _L.

In the method as described above, if the amount of decrease when the value is decreased to the limit value P _Lmin or less and the duration thereof is lengthened, the data discriminability deteriorates. As shown in (1) of FIG. 21, the waveform of the reproduced signal when P _LB = 0 below P _Lmin is set is shown in (2). As can be seen from the above, the waveform of the reproduction signal shows a dim waveform indicating that the premark is not completely erased.
FIG. 22 shows edge intervals measured in the case of setting P _LB = 0 and FIG. 23 shows P _LB = 3.0, and shows the measured data in the form of a frequency table. The appearance frequency of the edge interval is n
It is expressed as 11 mountains centered on Tu (n = 6 to 16). It can be said that the more the mountains are separated, the higher the data discrimination is (the better) because there is no variation in the edge interval. Figure 2
Comparing 2 with (2) in FIG. 23, it can be seen that the peak separation becomes unclear and the data discriminability deteriorates when _PLB is further reduced.

Further, the conventional techniques have a problem that the power margin is small. Now, consider the high level P _H and the low level P _L with reference to FIG. Theoretically, P _L is lower than P _H. That is, P _L
When P and P _H are regarded as variables, P _L and P _H must be selected from the lower right region of the line P _L = P _H shown in FIG. Also, if P _L is too high, a high temperature cycle occurs, so P _L must be lower than a predetermined value P _Lmax . On the contrary, if P _H is too low, a high temperature cycle does not occur, so P _H must be higher than a predetermined limit value P _Hth .
In this case, P _Lmax has the same value as P _Hth, and both are shown as P _Hth in FIG. Furthermore, the higher P _H is,
Since the mark B ₁ (or B ₀ ) formed by P _H becomes thicker, when the mark is erased by P _L (the other mark B ₀ (or B ₁ ) is formed), in order to avoid the unerased portion, , P _L must also be high. Therefore,
When P _L and P _H are regarded as variables, P _L = a · shown in FIG.
From the region on the upper left of the line of P _H (a is a constant), P _L and P _H
Must be selected. In summary, P _L and P
_H must be selected as a value of a point existing in a triangular area formed by the three points A, B and C shown in FIG. In this case, C / N is different by a point selecting (P _L, P _H). When the same C / N is plotted, as shown in FIG. 24, the curves R ₁ and R ₂ , which are close to parabolas,
R ₃ ... etc. are obtained. Since a too low C / N is not practical, a predetermined C / N (here, curve R ₁ ) or more is required. Therefore, the actual P _L and P _H are shown in FIG.
The intersection of the triangular area formed by the three points A, B, and C shown in (3) and the area surrounded by the curve R ₁ (the overlapping area ...
-Hunting part of Fig. 24). In practice, more conditions are added, but in this specification, the power margin of P _L and P _H is defined by this product set.

The conventional technology has a problem that the power margin is small. Therefore, the magneto-optical recording device used for this purpose requires extremely precise and accurate control of the laser that determines P _L and P _H, which causes a problem that a sophisticated and expensive control circuit is required. It was Naturally, P _L and P _H must be changed even under ambient temperature conditions. Conversely, considering the case of using a magneto-optical recording device that does not have a sophisticated and expensive control circuit, the range in which the variation in recording sensitivity (related to P _L and P _H ) between individual media is acceptable. It is also narrow, which causes a problem that the yield rate of the recording medium is lowered.

In addition, since extremely high precision and accuracy are required for controlling the laser, there is a further problem that the incidence of defective products of the magneto-optical recording device increases and the productivity decreases. In order to solve these problems, the present inventors have proposed to use the apparatus shown in FIG. 3 to form marks by the recording method shown in (4) of FIG. 2 (Japanese Patent Application No. 3-234674). ). This is to increase the power of the pulse waveform at the start of P _H and then form the mark by performing waveform shaping so as to lower the power waveform to expand the power margin. However, even with this method, the discriminability of the data was not sufficient.

The object of the present invention is to solve these problems,
It is to obtain a good reproduction signal for data discrimination by further increasing C / N.

[0093]

For this reason, the present invention provides, for the first time, "" consisting of at least two layers, a memory layer and a writing layer, and both layers being exchange-bonded to each other. Prepare the overwritable multi-layered magneto-optical recording medium in which the magnetization of the writing layer can be set to the specified direction without changing the direction of the magnetization and the magnetization of the writing layer is actually set to the specified direction. ; rotates the medium; it is irradiated with a laser beam to the medium; the intensity of the laser beam, in accordance with binary information to be recorded, pulsing modulated between a high level P _H and the low level P _L ; and applying a recording magnetic field to the irradiation position of the laser beam; in overwritable magneto-optical recording method comprising, Ma formed by a beam of high level P _H before When defining the phrase Puremaku, it is defined as a limit value P _Lmin the minimum low level P _L can be erased by irradiating a laser beam of this Puremaku DC lighting, the intensity of the laser beam, from the low level P _L High level P
When launching the _H, once reduced to below the limit value P _Lmin, then raised to the high level P _H, When the formation of the mark is initiated by the high level P _H, the formation of marks by reducing the intensity of the laser beam A good method of data discrimination (claim 1), characterized in that it continues and, after mark formation, returns to a low level P _L.

Secondly, the present invention relates to "" It is composed of at least two layers of a memory layer and a writing layer, and both layers are exchange-coupled with each other. Preparing an overwritable multilayer magneto-optical recording medium in which the magnetization of the layers can be oriented in a predetermined direction and the magnetization of the writing layer is actually oriented in a predetermined direction; rotating the medium; Irradiating the medium with a laser beam; pulse-modulating the intensity of the laser beam between a high level P _H and a low level P _L according to the binary information to be recorded; and at the irradiation position of the laser beam. applying a recording magnetic field; in overwritable magneto-optical recording method comprising, a mark formed by a beam of high level P _H is defined as Puremaku before When defining a limit value P _Lmin the minimum low level P _L can be erased by the Puremaku irradiating a laser beam of DC lighting, the intensity of the laser beam, the low level P _L from the high level P
Raised to _H, When the formation of the mark by the high level P _H is started, continuing the formation of marks by reducing the intensity of the laser beam, after the mark formation, temporarily reduced to below the limit value P _Lmin, then low level P A good method of data discrimination (claim 2), characterized by returning to _L.

Thirdly, ““ The magnetization of the writing layer is composed of at least two layers of the memory layer and the writing layer, and both layers are exchange-coupled with each other, and the magnetization direction of the writing layer is not changed at room temperature. Preparing an overwritable multilayer magneto-optical recording medium which can be oriented in a predetermined direction and in which the magnetization of the writing layer is actually in a predetermined direction; rotating the medium; Irradiating the beam; 3 pulse-modulating the intensity of the laser beam between the high level P _H and the low level P _L according to the binary information to be recorded; and a recording magnetic field at the irradiation position of the laser beam. It applied to; in overwritable magneto-optical recording method comprising, a mark formed by a beam of high level P _H is defined as Puremaku before, the flop When defining a minimum low level P _L can be erased by irradiating a laser beam having a DC lighting marks the limit value P _Lmin, the laser intensity of the beam, the high level P from a low level P _L
When launching the _H, once reduced to below the limit value P _Lmin, then raised to the high level P _H, When the formation of the mark is initiated by the high level P _H, the formation of marks by reducing the intensity of the laser beam continuing, after the mark formation, when fall to the low level P _L, once reduced to below the limit value P _Lmin, then and returning to the low level P _L, good method of data discrimination (claim 3 )"I will provide a.

Fourth, "rotating means for magneto-optical recording medium; laser beam light source; laser beam intensity is pulse-modulated between high level P _H and low level P _{L in} accordance with binary information to be recorded. In an overwritable magneto-optical recording device comprising a light source drive circuit and recording magnetic field applying means, a mark previously formed by a beam of high level P _H is defined as a premark, and this premark is irradiated with a laser beam for DC lighting. When the minimum low level P _L that can be erased by the above is defined as a limit value P _Lmin , the intensity of the laser beam is
When rising from _L to high level P _H , once lower to below the limit value P _Lmin , then rise to high level P _H ,
When the mark formation is started at the high level P _H , the intensity of the laser beam is reduced to continue the mark formation, and after the mark formation, a pulse waveform shaping circuit for returning to the low level P _L is added. , A magneto-optical recording device (claim 4).

Fifth, "rotating means for magneto-optical recording medium; laser beam light source; laser beam intensity is pulse-modulated between high level P _H and low level P _L according to binary information to be recorded. In an overwritable magneto-optical recording device comprising a light source drive circuit and recording magnetic field applying means, a mark previously formed by a beam of high level P _H is defined as a premark, and this premark is irradiated with a laser beam for DC lighting. When the minimum low level P _L that can be erased by the above is defined as a limit value P _Lmin , the intensity of the laser beam is
Raised from _L to the high level P _H, When the formation of the mark is initiated by the high level P _H, continuing the formation of marks by reducing the intensity of the laser beam, after the mark formation, temporarily reduced to below the limit value P _Lmin , And then a pulse waveform shaping circuit for returning to a low level P _L ; are provided. A magneto-optical recording device (claim 5) "is provided.

Sixth, "rotating means for magneto-optical recording medium; laser beam light source; laser beam intensity is pulse-modulated between a high level P _H and a low level P _L according to binary information to be recorded. In an overwritable magneto-optical recording device comprising a light source drive circuit and recording magnetic field applying means, a mark previously formed by a beam of high level P _H is defined as a premark, and this premark is irradiated with a laser beam for DC lighting. When the minimum low level P _L that can be erased by the above is defined as a limit value P _Lmin , the intensity of the laser beam is
When rising from _L to high level P _H , once lower to below the limit value P _Lmin , then rise to high level P _H ,
When the mark formation is started by the high level P _H , the intensity of the laser beam is reduced to continue the mark formation, and when the mark is formed and then the mark is lowered to the low level P _L , it is temporarily lowered to the limit value P _Lmin or less. , And then returning to a low level P _{L. A} magneto-optical recording device (claim 6) characterized by the addition of a pulse waveform shaping circuit;

Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto.

[0100]

[Embodiment 1 ... Description of magneto-optical recording apparatus according to claim 4] FIG. 3 is a conceptual diagram showing a main configuration of a magneto-optical recording apparatus according to the present embodiment. This device also serves as a reproducing device, and mainly includes a motor (rotating means 6) for rotating the magneto-optical recording medium (D), a laser beam light source (2), and binary information to be recorded for the intensity of the laser beam. Accordingly, the light source drive circuit (1) for pulse-modulating between the high level P _H and the low level P _L , the recording magnetic field applying means (H on the magnetic film of the medium
b = 300 O _e permanent magnet 11), pulse waveform shaping circuit (1
0), and initial auxiliary magnetic field applying means (Hi on the magnetic film of the medium
ni. = 3 kO _e permanent magnet 12). Hb and Hin
i. Have the same orientation. Here, the shaping circuit (10)
As shown in (1) of FIG. 1 for the pulse waveform, when the beam intensity is raised from the low level P _L to the high level P _H , the beam intensity is once lowered to below the limit value P _Lmin and then to the high level P _H. After the start-up and the formation of the mark by the high level P _H , the intensity of the laser beam is lowered and the formation of the P _HB mark is continued. After that, when the formation of the mark is completed, the intensity of the laser beam is lowered to the low level P _L again.

The medium rotated by the rotating means (6) is
It is "initialized" by passing over the magnet (12). "Initialization"
The formed W layer next comes to the irradiation position of the laser beam. When using a medium having an I layer, the magnet (1
2) is unnecessary. The beam emitted from the light source (2) is pulse-modulated by the light source drive circuit (1) according to the binary information to be recorded. Conventional pulse waveforms are shown in FIG.
As shown in (3), when the mark is formed at the high level P _H , the intensity of the laser beam is kept at a constant value until the formation of the mark is completed. On the other hand, the pulse waveform of this embodiment is shaped by the shaping circuit (10) as shown in (1) of FIG.

The beam emitted from the light source (2) is collimated through the collimator lens (3) and then collimated, and then reflected by the beam splitter (4). The reflected beam is collected by the objective lens (5) and focused on the medium (D). The record is basically over. In the case of reproduction, the medium (D) is irradiated with a non-modulated (DC-lighted) laser beam having a reduced intensity as in recording. Then, the light reflected from the medium is incident on the beam splitter (4) through the objective lens (5), the light transmitted therethrough is condensed by the condenser lens (7), and then the detector (9).
Incident on. At this time, the state of rotation (+ θk and −θk) of the plane of polarization is converted into a change in light intensity through an analyzer (polarizer) placed between the condenser lens (7) and the detector (9). As a result, the recorded information on the medium (D) read as the rotation of the plane of polarization is converted into a change in light intensity.
The change in light intensity is converted into the intensity of an electric signal by the detector (9). This is reproduction.

[0103]

[Embodiment 2 ... Description of magneto-optical recording apparatus according to claim 5] This apparatus is different from the magneto-optical recording apparatus in the first embodiment only in the shaping circuit. Here, the shaping circuit (10) lowers the intensity of the laser beam to P _{HB when the} mark formation is started at the high level P _H , as shown in the pulse waveform of (2) of FIG. Continue forming marks. After that, when the mark formation is completed, the intensity of the laser beam is once set to the limit value P _Lmin.
It is reduced to the following and shaped so as to return to the low level P _L.

[0104]

[Embodiment 3 ... Description of magneto-optical recording apparatus according to claims 4 and 5] This apparatus is different from the first embodiment only in the shaping circuit. Here, the shaping circuit (10) temporarily raises the limit value P _Lmin when raising the beam intensity from the low level P _L to the high level P _H as shown in (3) of FIG.
After that, shaping is performed so as to rise to a high level P _H , and mark formation is started. When the mark formation is started, the intensity of the laser beam is reduced to continue the formation of the _PHB mark. After that, when the mark formation is completed, the intensity of the laser beam is once reduced to below the limit value P _Lmin to a low level P _L. Format to return.

[0105]

[Example 4 ... Explanation of magneto-optical recording] (1) Preparation of medium (class 1): diameter 130 mm, thickness 1.2 m
A substrate is prepared in which a 0.03 mm-thick 2P resin layer is formed on an m 2 glass disk. For 2P resin layer, radius r = 30 ~
A large number of concentric tracking grooves are formed in an area of 60 mm. The groove has a depth h of 700 Å, a groove width w of 0.5 μm and a pitch of 1.6 μm. The following 6 layers are formed on the 2P resin layer by sputtering. 700 Å thick silicon nitride as protective layer, 250 Å thick Tb as M layer
₂₃ Fe ₇₂ Co ₅ (Note: The numbers in the subscripts are atomic%; the same applies below),
Gd ₂₃ Fe ₇₂ Co _{5 with} a thickness of 100 Å as the exchange coupling force adjustment layer,
Dy ₂₈ Fe ₃₆ Co _{36 with} a thickness of 500 Å as a W layer, a silicon nitride thin film with a thickness of 100 Å as a protective layer, and a thickness as a protective layer
Six layers of 700 Å silicon nitride thin film. Finally, the protective substrate is adhered on the protective layer to complete the medium. The protective substrate is of the same type as the glass disc used for the substrate.

By applying a magnetic field of 23 kOe in the A direction to this medium, the magnetizations of both the M layer and the W layer in the entire medium are aligned in the A direction ("initialized"). (2) Information to be recorded: The information to be recorded is standard information. In the standard information, the value H and the value L are the unit time Tu (23.9 n
(Sec), which is information that switches every 3 to 8 times. Integer n
Then, the value H (irradiation of the laser beam of high level P _H ) continues for n · Tu is represented as nL, and here, the standard information is as follows.

[0107] 3H3L3H4L3H5L3H6L3H7L3H8L 4H3L4H4L4H5L4H6L4H7L4H8L 5H3L5H4L5H5L5H6L5H7L5H8L 6H3L6H4L6H5L6H6L6H7L6H8L 7H3L7H4L7H5L7H6L7H7L7H8L 8H3L8H4L8H5L8H6L8H7L8H8L 3H3L6H8L Incidentally, the last 3H3L6H8L is such that the total information is added as a convenience to be an integral multiple of 16T. The value H corresponds to high-level irradiation writing with a laser beam.

(3) Measurement of P _Hth The above medium (D) is rotated at 3600 rpm. Radius on it
Record by irradiating a laser beam at the position of r = 30mm. The information to be recorded has a sufficiently long pulse length and T ₈ is selected as standard information. At this time, P _L is set sufficiently low, P _H is changed variously, recording is repeated, and reproduction is performed each time recording is performed. As a result, if reproduction is confirmed even with a weak signal during reproduction, it is considered that a mark with P _H has been formed, and the lowest value of P _H at that time P _Hth
And As a result, the above medium (D) has P _Hth = 6.0 m
It was W.

[0109] (4) Measurement equation of _{P Lmin: P Lmin = a ·} P H (a is a constant) to measure the "a" in. "Initialized" above medium (D)
Rotate at 3600 rpm. Then, irradiate a laser beam at a position of radius r = 30 mm for recording. The information to be recorded is standard information T ₈ having the largest pulse width. At this time,
Set P _L sufficiently low and set P _H from 6.0 mW to 16 m
Recording is repeated with various changes up to W, and is reproduced each time recording is performed. Thus, after confirming the recording, the P _L is increased, and the beam of the increased P _L is irradiated with the DC lighting (that is, without modulation) to erase the recorded standard information. Then, the reproduction is performed again to see whether or not the data has been completely erased. _{Find the} lowest P _Lmin required for complete erasure. This P _Lmin changes according to P _H. Therefore, the positions of P _H and P _Lmin for each recording are plotted on the XY coordinates where the vertical axis is P _L and the horizontal axis is P _H. As a result, for the method of forming a mark by the laser beam intensity during irradiation of a conventional high-level P _H constant a = 0.5, for the embodiment of the present invention was obtained straight line a = 0.4.

(5) Recording (1), (2), (3) and (4) of FIG. 2 are waveforms of conventional standard information, and (1), (2) and (3) of FIG. 7 is a waveform shaped by the shaping circuits of Examples 1, 2, and 3. Here, P _H was 7.8 mW and P _L was 4.2 mW. Further, such _{PHB of the} present invention is 6.0 mW. At this time, P _Lmin is 0.5 (=
a) × P _H = 3.9 mW, 3.1 mW in the case of this embodiment. Furthermore, T _LBT = 3Tu (71.7 nSec), T _LBL = 2T
u (47.8 nSec) and P _LB = 0.5 mW.

Conventional Example The above medium (D) was rotated at 3600 rpm and the radius r = 30 m.
Arbitrary information is recorded by irradiating a laser beam to the position m. After that, using a conventional recording device, the waveform is shaped as shown in (1), (2), (3), and (4) of FIG. 2, and the standard information is overwritten.

Example 1 The above medium (D) was rotated at 3600 rpm and the radius r = 30 mm.
Arbitrary information is recorded by irradiating a laser beam at the position. After that, the standard information is overwritten after waveform shaping (Example 1 = see (1) of FIG. 1) using the recording apparatus of Example 1.

Example 2 The above medium (D) was rotated at 3600 rpm and the radius r = 30 mm.
Arbitrary information is recorded by irradiating a laser beam at the position. After that, using the recording apparatus of the second embodiment, the waveform is shaped (second embodiment = see (2) of FIG. 1), and then the standard information is overwritten.

Example 3 The above medium (D) was rotated at 3600 rpm and the radius r = 30 mm.
Arbitrary information is recorded by irradiating a laser beam at the position. After that, using the recording apparatus of the third embodiment, the waveform is shaped (third embodiment = see (3) in FIG. 1) and then the standard information is overwritten.

Evaluation The standard information recorded in each is reproduced magneto-optically,
The waveform is shaped, the clock is extracted, and the waveform is binarized, and 10 ⁶ windows (a in FIG. 25) indicating the deviation between the edge position of the reproduced waveform and the clock are collected and plotted in the histogram of FIG. In the figure, the ratio of the window to the clock cycle was measured as the window margin. The larger the window margin, the higher (the better) the data discrimination is.

The window margins of Example 1, Example 2, and Example 3 of FIG. 26, which are waveform-shaped according to the present invention, are different from those of Conventional Example 1, Conventional Example 2, and Conventional Example 3 in which the waveform is shaped by the conventional method. Shows a large value, and the data discrimination is very good.

[0117]

[Embodiment 5] The waveform shaping according to the present invention is not limited to the above embodiment, but may be the examples shown in FIGS. 27 to 32, for example.
The four examples of (1) and (2) in FIG. 27 and (1) and (2) in FIG. 30 are examples in which the waveform is not rectangular but the corners are rounded. The four examples in FIGS. 28 and 29 are examples in which the waveform oscillates at the positions P _H , P _HB , P _L , and P _LB when the pulse rises. The four examples of FIGS. 31 and 32 are examples in which the waveform oscillates at the positions of P _L , P _LB , and P _HB when the pulse falls.

[0118]

As described above, according to the present invention, even if the value of P _L is brought close to 0, the premark is almost completely erased, and no mark remains unerased. With this, C / N
Can be further improved, and since the premarks can be erased almost completely, the discriminability of data becomes high (better).

[Brief description of drawings]

FIG. 1 is a waveform diagram of information to be recorded according to an embodiment of the present invention.

FIG. 2 is a waveform diagram of conventional information to be recorded.

FIG. 3 is a conceptual diagram showing a main configuration of a magneto-optical recording apparatus according to an example.

FIG. 4 is a conceptual diagram illustrating a recording principle of a magneto-optical recording method.

FIG. 5 is a conceptual diagram for explaining the reproducing principle of the magneto-optical recording method.

FIG. 6 is a waveform diagram of a laser beam when overwriting according to the basic invention.

FIG. 7 is a waveform diagram of a laser beam when overwriting with two beams according to the basic invention.

FIG. 8 shows M of an overwritable magneto-optical recording medium.
It is a graph which shows the relationship between coercive force and temperature about a layer and a W layer.

FIG. 9 is a conceptual diagram showing the magnetization directions of the M layer and the W layer.

FIG. 10 is an explanatory diagram showing changes in the magnetization directions of the M layer and the W layer.

FIG. 11 is a low temperature cycle for P-type media,
It is explanatory drawing which shows how the direction of magnetization of M layer and W layer changes as a result of a high temperature cycle. Both show the state at room temperature.

FIG. 12 is a low temperature cycle for Type A media,
It is explanatory drawing which shows how the direction of magnetization of M layer and W layer changes as a result of a high temperature cycle. Both show the state at room temperature.

FIG. 13 is an explanatory diagram showing changes in the magnetization directions of the M layer and the W layer.

FIG. 14 is an explanatory diagram for comparing a vector indicating a sublattice magnetization of a rare earth (RE) atom (solid arrow) with a vector indicating a sublattice magnetization of a transition metal (TM) atom (dotted arrow). Is.

FIG. 15 is an explanatory diagram showing the relationship between the vector of sublattice magnetization and the vector (open arrow) indicating the direction of magnetization of the alloy.

FIG. 16 is an explanatory diagram illustrating that, when the M layer and the W layer are divided into RE-rich and TM-rich, respectively, the overwritable medium is divided into four classifications (quadrants 1 to 4). is there.

FIG. 17 is an overwritable magneto-optical recording medium N.
o. 3 is a graph showing the relationship between coercive force and temperature for 1-1 M layer and W layer.

FIG. 18 is a conceptual diagram showing how the magnetization directions of the M layer and the W layer change as a result of the low temperature cycle and the high temperature cycle for the medium of medium No. 1-1.

FIG. 19 is an explanatory diagram for explaining the overwriting principle of the overwritable magneto-optical recording medium having a four-layer film structure according to the selected invention.

FIG. 20 is an explanatory diagram illustrating that when the medium of the basic invention is classified from various viewpoints, the medium is eventually classified into nine classes, class 1 to class 9.

FIG. 21 is a conventional waveform diagram of information to be recorded and its reproduction signal.

FIG. 22 is a graph showing a conventional waveform diagram of information to be recorded and data for data discrimination.

FIG. 23 is a graph showing a waveform diagram of other information to be recorded and data of data discrimination according to the related art.

FIG. 24 is an explanatory diagram illustrating a power margin.

FIG. 25 is a histogram for measuring a wind margin.

FIG. 26 is a table comparing the window margins of reproduced signals from the conventional information waveform and the information waveform of the example.

FIG. 27 is a waveform chart of information to be recorded in Example 5.

FIG. 28 is a waveform diagram of information to be recorded in Example 5.

FIG. 29 is a waveform diagram of information to be recorded in Example 5.

FIG. 30 is a waveform diagram of information to be recorded in Example 5.

FIG. 31 is a waveform diagram of information to be recorded in Example 5.

FIG. 32 is a waveform diagram of information to be recorded in Example 5.

[Explanation of symbols]

L ・ ・ ・ ・ Laser beam Lp ・ ・ ・ ・ ・ ・ Linear polarized light B ₁・ ・ ・ ・ ・ ・ Mark with magnetization in "A direction" B ₀・ ・ ・ ・ "Inverse A direction" Magnetized mark S ··· Substrate MO ··· Perpendicular magnetic film (magneto-optical recording layer) a ··· Wind 1 ··· Optical drive circuit 2 ･ ･ ･ Light source 3 ･ ･ ･ Collimator lens 4 ･ ･ ･ Beam splitter 5 ･ ･ ･ Objective lens 6 ･ ･ ･ Rotating unit 7 ································································· Pulse waveform circuit 11 ········ ·····permanent magnet

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] November 2, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Fig. 21

[Correction method] Change

[Correction content]

FIG. 21 is a conventional waveform diagram of information to be recorded and a photograph of an oscilloscope waveform of its reproduction signal.

Claims (6)

[Claims] 1. A magnetic recording medium comprising at least two layers of a memory layer and a writing layer, both layers being exchange-coupled, and the magnetization of the writing layer is kept in a predetermined direction at room temperature without changing the magnetization direction of the memory layer. Can be directed to
Actually, the magnetization of the lighting layer is oriented in a predetermined direction
Preparing an overwritable multi-layered magneto-optical recording medium; rotating the medium; irradiating the medium with a laser beam; increasing the intensity of the laser beam to a high level P according to the binary information to be recorded. pulse modulated between _H and the low level P _L; and applying a recording magnetic field to the irradiation position of the laser beam; in overwritable magneto-optical recording method comprising, by the beam of a high level P _H before When the formed mark is defined as a premark, and the minimum low level P _L that can be erased by irradiating a laser beam of DC lighting with this premark is defined as a limit value P _Lmin , the intensity of the laser beam is defined as a low level. when launching from P _L to the high level P _H, once reduced to below the limit value P _Lmin, then raised to the high level P _H, the high level P _H
A good method for data discrimination, characterized in that the intensity of the laser beam is reduced to continue the mark formation when the mark formation is started by, and the mark is formed and then returned to the low level P _L. 2. A magnetic recording medium comprising at least two layers of a memory layer and a writing layer, both layers being exchange-coupled, and the magnetization of the writing layer is kept in a predetermined direction at room temperature without changing the magnetization direction of the memory layer. Can be directed to
Actually, the magnetization of the lighting layer is oriented in a predetermined direction
Preparing an overwritable multi-layered magneto-optical recording medium; rotating the medium; irradiating the medium with a laser beam; increasing the intensity of the laser beam to a high level P according to the binary information to be recorded. pulse modulated between _H and the low level P _L; and applying a recording magnetic field to the irradiation position of the laser beam; in overwritable magneto-optical recording method comprising, by the beam of a high level P _H before When the formed mark is defined as a premark, and the minimum low level P _L that can be erased by irradiating a laser beam of DC lighting with this premark is defined as a limit value P _Lmin , the intensity of the laser beam is defined as a low level. raised from P _L to the high level P _H, When the formation of the mark is initiated by the high level P _H, Ma lowering the intensity of the laser beam A good method for data discrimination, which is characterized in that the formation of the mark is continued, and after the mark is formed, the mark is once lowered to a limit value P _Lmin or less and then returned to the low level P _L. 3. A magnetic recording medium comprising at least two layers of a memory layer and a writing layer, both layers being exchange-coupled, and the magnetization of the writing layer having a predetermined direction at room temperature without changing the magnetization direction of the memory layer. Can be directed to
Actually, the magnetization of the lighting layer is oriented in a predetermined direction
Preparing an overwritable multi-layered magneto-optical recording medium; rotating the medium; irradiating the medium with a laser beam; increasing the intensity of the laser beam to a high level P according to the binary information to be recorded. pulse modulated between _H and the low level P _L; and applying a recording magnetic field to the irradiation position of the laser beam; in overwritable magneto-optical recording method comprising, by the beam of a high level P _H before When the formed mark is defined as a premark, and the minimum low level P _L that can be erased by irradiating a laser beam of DC lighting with this premark is defined as a limit value P _Lmin , the intensity of the laser beam is defined as a low level. when launching from P _L to the high level P _H, once reduced to below the limit value P _Lmin, then raised to the high level P _H, the high level P _H
When the mark formation is started by, the intensity of the laser beam is reduced to continue the mark formation, and after the mark formation, when the mark is lowered to the low level P _L , it is once lowered to the limit value P _Lmin or less, and then to the low level. A good method of data discrimination, characterized by returning to P _L. 4. A rotating means of a magneto-optical recording medium; a laser beam light source; a light source drive circuit for pulse-modulating a laser beam intensity between a high level P _H and a low level P _L according to binary information to be recorded. In the overwritable magneto-optical recording device comprising: and a recording magnetic field applying means, a mark previously formed by a beam of high level P _H is defined as a premark, and the premark is irradiated with a laser beam for DC lighting. When the minimum erasable low level P _L is defined as a limit value P _Lmin , when the laser beam intensity is raised from the low level P _L to a high level P _H , the intensity is once lowered to a limit value P _Lmin or less, then raised to the high level P _H, the high level P _H
When the formation of the mark is started by the above, a pulse waveform shaping circuit for reducing the intensity of the laser beam to continue the formation of the mark and returning to the low level P _L after the mark formation is added. apparatus. 5. A rotating means for a magneto-optical recording medium; a laser beam light source; a light source drive circuit for pulse-modulating a laser beam intensity between a high level P _H and a low level P _L according to binary information to be recorded. In the overwritable magneto-optical recording device comprising: and a recording magnetic field applying means, a mark previously formed by a beam of high level P _H is defined as a premark, and the premark is irradiated with a laser beam for DC lighting. When the minimum low level P _L that can be erased is defined as the limit value P _Lmin , the intensity of the laser beam is raised from the low level P _L to the high level P _H , and when the mark formation is started by the high level P _H. continues the formation of marks by reducing the intensity of the laser beam, after the mark formation, temporarily reduced to below the limit value P _Lmin, then path back to the low level P _L Scan waveform shaping circuit; characterized in that the addition of the magneto-optical recording apparatus. 6. A rotating means for a magneto-optical recording medium; a laser beam light source; a light source driving circuit for pulse-modulating a laser beam intensity between a high level P _H and a low level P _L according to binary information to be recorded. In the overwritable magneto-optical recording device comprising: and a recording magnetic field applying means, a mark previously formed by a beam of high level P _H is defined as a premark, and the premark is irradiated with a laser beam for DC lighting. When the minimum erasable low level P _L is defined as a limit value P _Lmin , when the laser beam intensity is raised from the low level P _L to a high level P _H , the intensity is once lowered to a limit value P _Lmin or less, then raised to the high level P _H, the high level P _H
When the mark formation is started by, the intensity of the laser beam is reduced to continue the mark formation, and after the mark formation, when the mark is lowered to the low level P _L , it is once lowered to the limit value P _Lmin or less, and then to the low level. A magneto-optical recording device, characterized in that a pulse waveform shaping circuit; which is returned to P _L is added.