JPH04214247A - Four-layered film structure magneto-optical recording medium capable of being overwritten - Google Patents

Abstract

PURPOSE:To have good overwriting characteristics even if the recording layer is thinned and to attain high recording sensitivity even if the entire magnetic layer is thinned by using a TbDyFeSi-based alloy for the recording layer. CONSTITUTION:A W layer 2 consisting of a perpendicular magnetization film of Tb9Dy18Co28Si3, etc., having 200Angstrom thickness t2 is formed on an M layer 1. A TbFe-based alloy as the fourth target is firstly sputtered in vacuum, and a TbCo-based alloy as the fifth target is finally sputtered also in vacuum. An I layer 3 consisting of the perpendicular magnetization film of Tb27Co73 having 500Angstrom thickness t4 is formed on an S layer 4 in this way. In this case, when the recorded information is reproduced with a magneto-optical recording and reproducing device, the information is reproduced at the C/B ratio of 50dB, and the fact that the perfect overwriting has been performed is confirmed.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides two methods for recording the intensity of a light beam without modulating the direction and intensity of the recording magnetic field Hb.
Overwrite (overwrite) is possible by simply modulating according to the value information.
The present invention relates to a magneto-optical recording medium which has a four-layer film structure in principle and which is capable of writing.

0002

2. Description of the Related Art Recently, optical recording and reproducing methods, recording devices, reproducing devices, and recording media used therefor satisfy various demands including high density, large capacity, high access speed, and high recording and reproducing speed. Efforts are being made to develop. Among a wide range of optical recording and reproducing methods, the magneto-optical recording and reproducing method has the unique advantage of being able to record information, erase it, and record new information again and again. Because of this, it is full of the greatest charm.

The recording medium used in this magneto-optical recording and reproducing method has a perpendicular magnetic film consisting of one layer or multiple layers as a recording layer.
tic layer or layers). This magnetized film is made of, for example, amorphous GdFe or GdC.
o, GdFeCo, TbFe, TbCo, TbFeCo
Consists of etc. A perpendicularly magnetized film generally has concentric or spiral tracks on which information is recorded. There are two types of tracks: explicit and implicit. Here, in this specification, "upward" or "downward" with respect to the membrane surface is used.
rd)'' is defined as the ``A direction'' and the other as the ``reverse A direction.'' The information to be recorded is pre-binarized, and this information is divided into bits with magnetization in the "A direction" (B
1) and a bit (B0) with magnetization in the "reverse A direction". These bits B1, B0
correspond to one and the other of digital signals 1 and 0, respectively. However, the magnetization of the track to be recorded is generally aligned in the "reverse A direction" by applying a strong external magnetic field before recording. Then, a bit (B1) having magnetization in the "A direction" is formed on the track. Information is expressed by the presence or absence of this bit (B1) and/or bit length. Incidentally, recently, bits are sometimes called marks.

Principle of bit formation: In the formation of bits, the characteristics of the laser, namely its excellent spatial and temporal coherence, are advantageously used, almost the same as the diffraction limit determined by the wavelength of the laser light. The beam is narrowed down to an extremely small spot. The focused light is irradiated onto the track surface, and information is recorded by forming bits with a diameter of 1 μm or less on the perpendicularly magnetized film. In optical recording, recording densities of up to about 108 bits/cm3 can theoretically be achieved. This is because the laser beam can be concentrated into a spot with a diameter almost as small as its wavelength.

As shown in FIG. 2, in magneto-optical recording, a laser beam (L) is focused onto a perpendicularly magnetized film (MO) and heated. During this time, a recording magnetic field (Hb) in a direction opposite 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). A reversely magnetized bit is thus formed.

[0006] Ferromagnetic materials and ferrimagnetic materials differ in the temperature dependence 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 below the Curie point.
n temperature ) Tcomp. , where the magnetization (M) becomes zero. Conversely, Hc becomes extremely large near that temperature, and as the temperature deviates from that temperature, Hc drops rapidly. This decreased Hc
is overcome by the relatively weak recording magnetic field (Hb). In other words, recording becomes possible. This recording process is Tcomp. This is called writing (compensation point writing).

However, it is not necessary to be particular about the Curie point or its vicinity, or the vicinity of the compensation temperature. In short, recording is possible by applying a recording magnetic field (Hb) that can overcome the reduced Hc to a magnetic material having a reduced Hc at a predetermined temperature higher than room temperature. However, it is impossible to set Hb so high that it would reverse the magnetization of the perpendicularly magnetized film (MO) in a region that has not yet reached a predetermined temperature higher than room temperature (the Hc in this region has the original high Hc).

Principle of reproduction: FIG. 3 shows the principle of information reproduction based on the magneto-optical effect. Light is an electromagnetic wave with an electromagnetic field vector that typically diverges in all directions in a plane perpendicular to the optical path. The light is converted into linearly polarized light (Lp) and perpendicularly magnetized film (MO)
When irradiated with a perpendicularly magnetized film (MO), the light is reflected from the surface or transmitted through the perpendicularly magnetized film (MO). At this time, the plane of polarization rotates according to the direction of magnetization M. This rotating phenomenon is caused by the magnetic Kerr effect or magnetic Faraday.
day) called the effect.

For example, if the polarization plane of the reflected light is "direction A"
If it is rotated by θk degrees with respect to magnetization, it will be in the "reverse A direction"
It rotates by -θk degrees with respect to magnetization. Therefore, if the axis of the optical analyzer (polarizer) is set perpendicular to a plane tilted by -θk degrees, the bit (B
0) cannot pass through the analyzer. On the other hand, for the light reflected from the bit (B1) magnetized in the "A direction", the amount multiplied by (sin2θk)2 is transmitted through the analyzer and the detector (
photoelectric conversion means). As a result, the bit (B1) magnetized in the "A direction" appears brighter than the bit (B0) magnetized in the "opposite A direction" and generates a stronger electrical signal at the detector. The electrical signal from this detector is modulated according to the recorded information, so
Information is reproduced.

By the way, in order to reuse a recorded medium, (1) either initialize the medium again with an initialization device, or
or (2) it is necessary to install an erasing head similar to the recording head in the recording device, or (3) it is necessary to erase the recorded information in advance using a recording device or an erasing device as a preliminary process.

[0011] Therefore, in the magneto-optical recording system, until now,
Overwriting, which allows new information to be recorded on the spot regardless of the presence or absence of previously recorded information, was considered impossible. However, if you change the direction of the recording magnetic field Hb to "A" as necessary,
If it is possible to freely modulate between the "A direction" and the "Reverse A direction", overwriting will become possible. however,
It is impossible to modulate the direction of the recording magnetic field Hb at high speed. For example, if 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 amount of current at such high speed.

However, with remarkable progress in technology, the intensity of the irradiated light beam can be adjusted according to the binarized information to be recorded without modulating the intensity of the recording magnetic field Hb (including ON and OFF) or the direction of the recording magnetic field Hb. A magneto-optical recording method that allows overwriting by just modulation, an overwritable magneto-optical recording medium used therein, and an overwritable recording device used therefor were invented and a patent application was filed. JP-A-62-175948=DE
3,619,618). Hereinafter, this invention will be referred to as the "basic invention".
I quote.

[Description of the basic invention] The basic invention includes a recording/reproducing layer (herein referred to as a memory layer or M layer) basically consisting of a perpendicularly magnetizable magnetic thin film, and a perpendicularly magnetizable magnetic thin film. (herein referred to as the "recording layer" or W layer), both layers are exchange-coupled, and the direction of magnetization of the M layer does not change at room temperature. An overwritable multilayer magneto-optical recording medium in which only the magnetization of the magnetic field can be directed in a predetermined direction is used.

[0014] Then, information is expressed and recorded by bits having magnetization in the "A direction" and bits having magnetization in the "reverse A direction" in the M layer (and possibly in the W layer). In this medium, the W layer is formed by an external means (e.g. initial auxiliary magnetic field Hi).
ni. ), the direction of magnetization of the M layer can be aligned in the "A direction", and at that time, the magnetization direction of the M layer does not reverse, and furthermore, the magnetization of the W layer, which was once aligned in the "A direction", The direction of magnetization does not reverse even when receiving the exchange coupling force from the M layer, and conversely, the direction of magnetization of the M layer does not reverse even when receiving the exchange coupling force from the W layer aligned in the "A direction". .

The W layer has a lower coercive force HC and a higher Curie point TC than the M layer. According to the recording method of the basic invention, the magnetization direction of the W layer of the recording medium is aligned in the "A direction" by external means before recording. In this specification, this action is specifically referred to as "initialization".
ze)". This initialization is specific to overwritable media.

[0016] Then, the medium is irradiated with a pulse-modulated laser beam according to the binarized information. The intensity of the laser beam has a high level PH and a low level PL.
This corresponds to high and low levels of pulses. This low level is higher than the playback level PR which illuminates the medium during playback. As is already known, even when not recording, a laser beam may be turned on at a <very low level>, for example in order to access a predetermined recording location on a medium. This <very low level> is also at playback level P.
The level is the same as or similar to R. Therefore, for example,
The output waveform of the laser beam in the basic invention is as shown in FIG.

[0017]Although not specified in the specification of the basic invention, in the basic invention, the recording beam is not one but two closely spaced beams, and the leading beam is, in principle, not modulated. It may be a high-level laser beam (for erasing) and a high-level laser beam (for writing) that modulates the trailing beam according to the information. In this case, the trailing beam is pulse modulated between a high level and a base level (which is the same as or lower than the low level and may have zero power). The output waveform in this case is shown in FIG. 5, for example.

A recording magnetic field Hb whose direction and intensity are not modulated acts on the portion of the medium irradiated with the beam. Hb
cannot be narrowed down to the same size as the beam irradiated area (spot area), and the area where Hb acts is:
It is much larger than the spot area. When a low-level beam is irradiated, the M layer is exposed to either an “A-oriented” bit (B1) or a “reverse A-oriented” bit (B1), regardless of the magnetization direction of the previous bit.
One of the "direction" bits (B0) is formed.

When a high-level beam is irradiated, another bit is formed in the M layer regardless of the magnetization direction of the previous bit. Overwriting is now complete.

In the basic invention, the laser beam is modulated in pulses according to the information to be recorded. However, this itself is also performed in conventional magneto-optical recording, and means for modulating the beam intensity in a pulsed manner according to the binary information to be recorded is a known means. For example, THE BELL
SYSTEM TECHNICAL JOUR
NAL, Vol. 62 (1983), 1923 -
1936. Therefore, given the required high and low levels of beam intensity, conventional modulation means can be readily obtained with only some modifications. For those skilled in the art, such modifications will be easy given the high and low levels of beam intensity.

One of the characteristics of the basic invention is that
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 to the "reverse A direction" by the recording magnetic field Hb or other external means (
reverse), and the "reverse A direction" magnetization of this W layer causes the M layer to have "reverse A direction" magnetization [or "A direction" magnetization]
form a bit with When the beam intensity is at a low level, the magnetization direction of the W layer remains the same as in the initial state, and the action of the W layer (this action is transmitted to the M layer through exchange coupling force) causes the M layer to be in the "A direction". Form a bit with magnetization [or "reverse A direction" magnetization].

[0022] In this specification, ○○○ [or △△△]
The expression, when you first read ○○○ outside [ ], also when you read ○○○ [or △△△] below, it also reads [
] I decided to read ○○○ outside. In contrast, first ○
If you select and read △△△ in [ ] without reading ○○, the following ○○○ [or △△△] will also be read as ○.
Instead of reading ○○, read △△△ in [ ].

The medium used in the basic invention is roughly divided into a first embodiment and a second embodiment. In either embodiment, the recording medium has a multilayer structure including an M layer and a W layer. The M layer is a magnetic layer that has a high coercive force and a low magnetization reversal temperature at room temperature. The W layer is a magnetic layer that has a relatively low coercive force at room temperature and a high magnetization reversal temperature compared to the M layer. In addition, M
Both the layer and the W layer may themselves be composed of multilayer films. In some cases, a third layer (for example, a layer for adjusting the exchange coupling force σW) may be present between the M layer and the W layer. Furthermore, there may be no clear boundary between the M layer and the W layer, and one may gradually change to the other.

In the first embodiment, the coercive force of the M layer is HC1
, that of the W layer is HC2, the Curie point of the M layer is TC1, W
TC2 is that of the layer, TR is the room temperature, TL is the temperature of the recording medium when irradiated with a laser beam of low level PL,
The coupling magnetic field received by the M layer is HD1 (HD1 is σW
is calculated by dividing the M layer saturation magnetic moment MS by the product of the M layer thickness t), and the coupling magnetic field received by the W layer is HD2 (HD2 is calculated by dividing σW by the W layer saturation magnetic moment MS).
and the film thickness t of the W layer), the recording medium satisfies the following equation 1 and also satisfies equations 2 to 5 at room temperature.

[0025] TR <TC1≒TL <TC2≒TH……Formula 1
HC1>HC2+｜HD1−(±HD2)｜……
Formula 2 HC1>HD1 …………………………………
…Formula 3HC2>HD2 …………………………………
Formula 4HC2+HD2<|Hini. |<HC1±HD
1 -- Formula 5 In the above formula, the symbol "≒" represents equal or almost equal (approximately ±20°C). In addition, in the above formula, regarding the compound ±, the upper row is A (antipara
llel) type medium, and the lower row shows the case of a P (parallel) type medium, which will be described later. Note that the ferromagnetic medium belongs to the P type.

That is, if the relationship between coercive force and temperature is expressed graphically, it will generally look like the one 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, only the magnetization of the W layer is reversed without reversing the direction of magnetization of the M layer. Therefore, before recording, an external means acts on the medium (for example, an initial auxiliary magnetic field Hini.).
When , only the W layer is ``A direction'' --- Here, ``A direction'' is indicated by an upward arrow ↑ on the paper of this specification for convenience, and ``reverse A direction'' is indicated by a downward arrow ↓. show------
It can be magnetized to −. And Hini. Even if becomes zero, according to Equation 4, the magnetization ↑ of the W layer is maintained as it is without being reversed again.

[0027] Conceptually, the state in which only the W layer is magnetized in the "A direction" ↑ by external means before recording is as follows:
It becomes Figure 7. In FIG. 7, the magnetization direction* in the M layer represents the information recorded up to that point. In the following explanation, since the orientation is not relevant, this is indicated by X for simplification, and FIG. 7 can be shown as state 1 in FIG. 8.

Here, a high-level laser beam is irradiated to raise the medium temperature to TH. Then, T
Since H 2 has a temperature higher than the Curie point TC1, the magnetization of the M layer disappears. Furthermore, since TH is near the Curie point TC2, the magnetization of the W layer also disappears completely or almost completely. here,
A recording magnetic field Hb in the "A direction" or "inverse A direction" is applied depending on the type of medium. Hb may be a stray magnetic field from the medium itself. To simplify the explanation, “reverse A direction”↓
Assume that a recording magnetic field Hb of is applied. Since the medium is moving, the irradiated area quickly moves away from the laser beam and cools down. When the temperature of the medium decreases in the presence of Hb, the magnetization of the W layer is reversed in accordance with Hb and becomes magnetized in the "reverse A direction" (state 2 in FIG. 8).

Then, the cooling progresses further and the medium temperature reaches T.
When the temperature drops slightly below C1, the magnetization of the M layer appears again. In that case, due to the magnetic coupling (exchange coupling) force, the direction of magnetization of the M layer is influenced by the W layer and becomes a predetermined direction. As a result, a "reverse A direction" ↓ bit (in the case of a P type medium) or a "A direction" ↑ bit (in the case of an A type medium) is formed in the M layer depending on the type of medium. This state is shown in Figure 8.
State 3 (P type) or state 4 (A type).

[0030] This state change caused by the high-level laser beam will be referred to herein as a high-temperature cycle. Next, a laser beam at a low level PL is irradiated to raise the medium temperature to TL. Since TL is near the Curie point TC1, the magnetization of the M layer completely or almost disappears, but since the temperature is lower than the Curie point TC2, the magnetization of the W layer does not disappear. This state is shown as state 5 in FIG. Although the recording magnetic field Hb is not required here, it is impossible to turn Hb on and off at high speed (for a short period of time). Therefore, it is unavoidable that it remains as it was during the high temperature cycle.

[0031] However, since HC2 is still large,
The magnetization ↑ of the W layer is not reversed by Hb. Since the medium is moving, the irradiated area quickly moves away from the laser beam and cools down. As cooling progresses,
Magnetization appears in the M layer again. The direction of magnetization that appears is influenced by the W layer due to the magnetic coupling force and becomes a predetermined direction. As a result, depending on the type of media, the bit (P
type media) or the “reverse A direction” ↓ bit (A
type of media) is formed in the M layer. This magnetization does not change even at room temperature. This state is state 6 (P type) or state 7 (A type) in FIG.

[0032] This change in state due to the low-level laser beam will be referred to herein as a low-temperature cycle.

As explained above, regardless of the magnetization direction of the M layer before recording, by selecting the high temperature cycle and the low temperature cycle, the bits in the "reverse A direction" ↓ and
Bits of “A direction” ↑ can be freely formed in the M layer. In other words, overwriting is possible by pulse-modulating the laser beam between a high level (high temperature cycle) and a low level (low temperature cycle) according to the information. Please refer to FIG. 9. The magnetization states in FIG. 9 are all depicted at room temperature or as the result when the temperature returns to room temperature.

In the above explanation, both the M layer and the W layer have a compensation temperature Tcomp. between room temperature and the Curie point. We have explained the magnetic material composition that has no. However, the compensation temperature Tcom
p. exists, and if it is exceeded, ■ the direction of magnetization will be reversed.In reality, the direction of each sublattice magnetization of RE and TM will not change, but their magnitude relationship will be reversed, so the overall The direction of magnetization as (alloy) is reversed.
Since the A and P types are reversed, the explanation becomes that much more complicated. In this case, the direction of the recording magnetic field Hb is also
When considered at room temperature, the direction is the opposite of the explanation on the previous page. In other words, H in the same direction as the magnetization direction ↑ of the initialized W layer
Apply b.

[0035] The recording medium is generally disk-shaped, and the medium is rotated during recording. Therefore, the recorded portions (bits) are stored again after recording by external means such as Hini. As a result, the magnetization of the W layer returns to the original "A direction" ↑
It can be aligned to However, at room temperature, the magnetization of the W layer does not affect the M layer, so recorded information is retained.

If the M layer is irradiated with linearly polarized light, the reflected light contains information, so information is reproduced in the same manner as in conventional magneto-optical recording media. The perpendicularly magnetized films constituting such M and W layers are: (1) ferromagnetic materials and ferrimagnetic materials that do not have a compensation temperature but have a Curie point, and (2) ferrimagnetic materials that have both a compensation temperature and a Curie point. Selected from the group consisting of amorphous or crystalline.

The above description is of the first embodiment in which the Curie point is used as the magnetization reversal temperature. In contrast, the second embodiment utilizes reduced Hc at temperatures below the Curie point. In the second embodiment, the temperature TS1 at which the M layer is magnetically coupled to the W layer is used instead of TC1 in the first embodiment, and the temperature TS2 at which the W layer is reversed by Hb is used instead of TC2. , will be explained similarly to the first embodiment.

In the second embodiment, the coercive force of the M layer is set to HC1.
, that of the W layer is HC2, the temperature at which the M layer is magnetically coupled to the W layer is Ts1, the temperature at which the magnetization of the W layer is reversed by Hb is TS2, the room temperature is TR, and a laser beam of low level PL is irradiated. The temperature of the medium when TL is high level P
When irradiated with a laser beam of H, it is TH,M
The coupling magnetic field received by the layer is HD1 (HD1 is calculated by dividing σW by the product of the M layer saturation magnetic moment MS and the M layer thickness t), and the coupling magnetic field received by the W layer is HD2 (H
D2 is calculated as the quotient of σW divided by the product of the W layer saturation magnetic moment MS and the W layer thickness t), then the recording medium satisfies Equation 6 below and satisfies Equations 7 to 7 at room temperature. 10.

TR <Ts1≒TL <Ts2≒TH ………Formula 6HC1>HC2+|HD1−(±HD2)|……Formula 7HC1>HD1 …………………………………Formula 8
HC2>HD2──………………………………Formula 9HC
2+HD2<|Hini. |<HC1±HD1──Formula 10 In the above equation, for compound ±, the upper row is A(anti
The lower row shows the case of a P (parallel) type medium.

In the second embodiment, at high temperature TH, W
The magnetization of the layer has not disappeared but is sufficiently weak, and the magnetization of the M layer has disappeared or is sufficiently weak. Even if sufficiently weak magnetization remains in both the M layer and the W layer, the recording magnetic field Hb ↓ is sufficiently large, so Hb ↓ can cause the direction of magnetization of the W layer and possibly the M layer to follow Hb ↓. . This state is state 2 in FIG. After this, either immediately or ■ when the laser beam irradiation stops and cooling progresses and the medium temperature drops below TH or when it moves away from Hb, the W layer influences the M layer via σW and the M layer The direction of magnetization of the layer follows a stable direction. As a result, Figure 1
0 state 3 (P type) or state 4 (A type).

On the other hand, at low temperature TL, not only the W layer but also the M layer does not lose its magnetization. However, that of the M layer is relatively small. In this case, in the case of the P type, there are two types of bit states, state 5 and state 6 in FIG. 10, and in the case of the A type, there are two types of bit states, state 7 and state 8 in FIG. In states 6 and 8, an interfacial domain wall (indicated by a thick line ━) is generated between the M layer and the W layer, and the state is somewhat unstable (metastable). State 1 indicates any of states 5 to 8. Immediately before the medium part in this state comes to the laser beam irradiation position,
b Receives the impression of ↓. Nevertheless, this state 6 or state 8 is maintained. This is because the W layer has sufficient magnetization at room temperature, so the magnetization is not reversed by Hb↓. In addition, the memory layer in state 8, where the direction is opposite to Hb ↓, is affected by the exchange coupling force σW from the W layer, which is greater than the effect of Hb ↓, and because it is a P type, the direction of magnetization is maintained in the same direction as the W layer. be done.

Shortly thereafter, state 6 or state 8 is irradiated with a low level laser beam. Therefore, the medium temperature increases. Correspondingly, the coercivity of both layers decreases. However, since the W layer has a high Curie point, the coercive force H
The decrease in C2 is small and is not affected by Hb ↓, and the magnetization direction "A direction" ↑ at the time of initialization is maintained. On the other hand, although the M layer has a low Curie point, the medium temperature is still lower than the Curie point Tc1 of the M layer, so the coercive force HC1 remains. However, since HC1 is small, the W layer is affected by ■Hb ↓ and ■exchange coupling force σw from the W layer.
(For P-types, the force that forces them to move in the same direction) In this case, the latter is stronger, and for P type, the formula: Hc1+Hb <σw /2Ms1t
Equation 1: Hc2<σw /2Ms2t2 (
Note: In the formula, the right side of the inequality sign is σw and 2Ms1t, respectively.
1 or 2 (means the fraction divided by 2Ms2t2)
Two equations are satisfied simultaneously. For type A, the formula:
Hc1-Hb <σw /2Ms1t1 formula:
Hc2<σw /2Ms2t2 (Note: In the formula, the right side of the inequality sign represents σw as 2Ms1t1 or 2Ms2, respectively.
(meaning the fraction divided by t2) are simultaneously satisfied. The lowest temperature at which these equations are simultaneously satisfied is called TLS. In other words, the lowest temperature at which the domain wall in state 6 or state 8 disappears is TLS.

As a result, state 6 transitions to state 9, and state 8 transitions to state 10. On the other hand, state 5 where there is no domain wall originally
is the same as state 9, and state 7, which originally has no domain wall, is the same as state 10, so in the end, the previous state (for P type, state 5 or 6, for A type, state 7 or 8) State 9 (
A bit of state 10 (P type) or state 10 (A type) is formed.

This state does not change even when the medium temperature decreases and returns to room temperature because the bit stops being irradiated with the laser beam or moves out of the irradiation position. This figure 10 state 9 (P type) or state 10 (
A type) is state 6 (P type) or state 7 (A type) in Figure 8.
type). It will be understood that this allows a low temperature cycle to be achieved without increasing the medium temperature to the Curie point TC1 of the M layer.

In fact, even in the case of the first embodiment in which the low temperature cycle is carried out at TC1 or higher, the medium temperature passes through TLS on the way to rise from room temperature to TC1, so at that time, in the case of P type, the state changes from state 6 to state 9. If the transition to is type A, a transition from state 8 to state 10 occurs. Thereafter, the state reaches TC1 and becomes state 5 in FIG. In the above explanation, both the M layer and the W layer have a compensation temperature Tcomp between room temperature and the Curie point. We have explained the magnetic material composition that has no. However, the compensation temperature Tcomp. If , if exceeded, ① the direction of magnetization will be reversed and ② the A and P types will be reversed, so the explanation becomes that much more complicated. Furthermore, the direction of the recording magnetic field Hb is also opposite to that considered at room temperature.

[0046] In both the first and second embodiments, the M layer and the W layer are made of a transition metal (for example, Fe, Co) - a heavy rare earth metal (
For example, a recording medium that is an amorphous ferrimagnetic material selected from an alloy composition such as Gd, Tb, Dy, etc. is preferable.

Both the M layer and the W layer contain transition metals (tra
heavy rare earth metals
When selected from the alloy composition (virare earth metal), the direction and magnitude of the magnetization that appears externally as each alloy depends on the transition metal atoms (T
It is determined by the relationship between the direction and magnitude of the sublattice magnetization of M) and the direction and magnitude of the sublattice magnetization of the heavy rare earth metal atom (RE). For example, the direction and magnitude of the sublattice magnetization of TM are represented by vectors indicated by dotted arrows, those of the RE sublattice magnetization are represented by vectors indicated by solid arrows, and the direction and magnitude of magnetization of the entire alloy are represented by white lines. It is represented by the vector shown by the arrow. At this time, the white arrow (vector) is the dotted arrow (vector)
and a solid arrow (vector). However, in alloys, the dotted line arrow (vector) and the solid line arrow (
vector), the direction is always opposite. Therefore, the dotted arrow (vector) and the solid arrow (vector)
When the strengths of both are equal, the vector of the alloy becomes zero (that is, the magnitude of the external magnetization is zero). The alloy composition when this becomes zero is the compensation composition (com
(pensation composition). For other compositions, the alloy has an intensity equal to the difference in intensity between both sublattice magnetizations, and an open arrow (
vector).

Therefore, the magnetization vector of the alloy is represented by a dotted line vector and a solid line vector adjacent to each other, as shown in FIG. 11, for example. There are four states of sublattice magnetization in RE and TM, and these are shown in (1A) to (1A) in FIG.
4A). The magnetization vectors (white arrows) of the alloy in each state are shown corresponding to (1B) to (4B) in FIG. 12. For example, when the RE vector is large compared to the TM vector, the state of sublattice magnetization is shown in (1A) and the magnetization vector of the alloy is shown in (1B).

When either the strength of the TM vector or the RE vector of a certain alloy composition is large, the alloy composition is named ○○ rich, for example, RE
Called rich. For both M and W layers,
It can be divided into TM-rich compositions and RE-rich compositions. Therefore, if we take the composition of the M layer on the vertical axis and the composition of the W layer on the horizontal axis, the types of the medium of the basic invention as a whole are shown in Figure 13.
It can be classified into four quadrants as shown below. The P type mentioned above belongs to the 1st and 3rd quadrants, and the A type belongs to the 2nd and 4th quadrants.

On the other hand, when looking at changes in coercive force with respect to temperature changes, there are alloy compositions that have the characteristic that the coercive force increases to infinity and then decreases again before reaching the Curie point (the temperature at which the coercive force is zero). . The temperature corresponding to this infinite temperature is called the compensation temperature (Tcomp.). At temperatures lower than the compensation temperature, the RE vector (solid arrow) is larger than the TM vector (dotted arrow), so it can be said to be TM rich, and the opposite is true at temperatures higher than the compensation temperature. Therefore, it can be said that the compensation temperature of the alloy of compensation composition is at room temperature.

Conversely, in a TM-rich alloy composition, no compensation temperature exists between room temperature and the Curie point. Since a compensation temperature below room temperature is meaningless in magneto-optical recording, the compensation temperature in this specification refers to a temperature between room temperature and the Curie point.

Media are classified into four types, Type 1 to Type 4, based on the presence or absence of compensation temperature in the M layer and W layer. Quadrant 1 media includes all four types. Therefore, if both the M layer and the W layer are classified into RE-rich or TM-rich, and whether they have compensation temperature or not, recording media are classified into nine classes in Table 1 shown in FIG. 14.

[Description of Class 8-2] Medium No. 8 belonging to the class 8 recording medium (A type, 4 quadrant, type 2) shown in Table 1 (FIG. 14). Taking 8-2 as an example, the overwriting principle will be explained in detail.

[0054] This medium No. 8-2 is the following formula 46-2:
The relationship is TR < TL < TH ≦Tc1≦Tc2. For the purpose of simplifying the explanation, TH < TC1 < Tc2 in the following explanation. Also, Tcomp. 2 may be lower than, equal to, or higher than TL and TC1, but for the purpose of simplifying the explanation, in the following description, TL < Tcomp. 2<
Let it be TC1. This relationship is shown in a graph as shown in FIG. 15.

[0055] At room temperature TR, the magnetization of the M layer is equal to the initial auxiliary magnetic field H.
ini. The conditions for only the W layer to be inverted without being inverted by

[0056]

[Math 1]

Equation 47 is shown below. This medium no. 8-
2 satisfies Equation 47 at room temperature. At this time, Hini.
The conditional expression is shown in Equation 50. Hini. When , the magnetization of the M layer and the W layer are mutually influenced by the interfacial domain wall energy. However, the conditions for the magnetization of the M layer and W layer to be maintained without reversal are as follows:

[0058]

[Math 2]

Equation 48 shown in

[0060]

[Math 3]

It is expressed by Equation 49 shown below. This medium no.
8-2 satisfies Equations 48-49. Formulas 47-49 at room temperature
The magnetization of the W layer of a recording medium that satisfies the conditions of

[0062]

[Math 4]

Hini. which satisfies the condition of Equation 50 shown in
For example, it is directed toward "A" ↑. in this case,
The medium temperature is now room temperature and Tcomp. Since the spin state of the W layer is lower than 2, the spin state of the W layer is shown as (1A) in FIG. The M layer remains in its previous recorded state, so the magnetization state is shown as state 1 or 2 in FIG. States 1 and 2 are maintained until immediately before recording. It is assumed that the recording magnetic field Hb is applied in the "A direction" ↑.

[0064] When the medium is disk-shaped, the conditions under which the bit recorded just one rotation ago (particularly the bit in state 1 where the M layer has magnetization in the opposite direction to Hb) must not be reversed by Hb are as follows:

[0065]

[Math 5]

The disk medium must satisfy this conditional expression at room temperature. Conversely, one condition for determining the magnitude of Hb is Equation 50
It is shown in 2.

Now, the bits 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.

-------Low-temperature cycle--A low level laser beam is irradiated to raise the medium temperature to TLS. Then,

[0069]

[Math 6]

##EQU50#3 is satisfied, and state 2 in FIG. 16 transitions to state 3. On the other hand, since state 1 in FIG. 16 remains as it is, it becomes the same state 3. When moving out of the laser beam spot area in state 3, the medium temperature begins to decrease. State 3 is maintained even if the medium temperature drops to room temperature because HC1 is sufficiently large (see 2 in Equation 50). As a result, a "reverse A direction" ↓ bit is formed in the M layer.

--------High-temperature cycle ------------When a high-level laser beam is irradiated, the medium temperature first decreases to a low temperature T.
Rise to LS. As a result, the state 4 is the same as the state 3 in FIG. 16 of the low temperature cycle.

[0072] By irradiating with a high-level laser beam,
The medium temperature increases further. When the medium temperature is Tcomp. When it exceeds 2, it shifts from A type to P type. At the same time W
The orientations of the RE spins (solid arrows) and TM spins (dotted arrows) of the layer do not change, but the magnitude relationship of the intensities is reversed, and the spin state shifts from (1A) to (2A) in FIG. 12. As a result, the magnetization of the W layer is reversed and becomes the "reverse A direction" shown in FIG. 12 (2B). This state is state 5 in FIG. However, since HC2 is still large at this temperature, the magnetization ↓ of the W layer is not reversed by ↑Hb.

[0073] As the beam irradiation continues, the medium temperature eventually rises further and reaches TH. Then, the medium temperature is M layer,
Since it is close to the Curie point of the W layer, the coercive force of both layers becomes small. As a result, the medium

[0074]

[Math 7]

Formula (1) shown below, or

[0076]

[Math. 8]

Formula (2) shown below, or

[0078]

[Math. 9]

2 shown in any one of formula (3) shown in
Satisfy two relational expressions at the same time. Therefore, the magnetizations of both layers are reversed almost simultaneously and follow the direction of ↑Hb. This is state 6 in FIG. When moving out of the laser beam spot area in state 6, the medium temperature begins to decrease. When the medium temperature is Tcomp. When it falls below 2, it returns from the P type to the original A type. At the same time, the directions of the RE spins (solid arrows) and TM spins (dotted arrows) of the W layer remain the same, but the strength relationship is reversed, and the spin state is as shown in (4A) in Figure 12.
Shift to (3A). As a result, the magnetization of the W layer is reversed and becomes the "reverse A direction" shown in FIG. 12 (3B). In this state, since HC2 has already become considerably large, the magnetization ↓ of the W layer is not reversed by ↑Hb. This is state 7 in FIG.

Eventually, the temperature of the medium decreases from the temperature in state 7 to room temperature. However, state 7 remains unchanged. In this way, a bit "A direction" ↑ is formed in the M layer.

[0081] The above explanation is based on the two-layer film of the M layer and the W layer, but if it has such a two-layer film, it is possible to overwrite even a medium containing a multilayer film of three or more layers. Become. In particular, in the above explanation, the initial auxiliary magnetic field Hi is used as an external means.
ni. Although the basic invention has been described using the external means, any specific example of such external means may be used. In other words, it is sufficient that the magnetization of the W layer is oriented in a predetermined direction before recording.

Therefore, as an external means, Hini. Instead, an invention was invented that utilized the exchange coupling force from the initialization layer. This utilization invention has international publication number WO90/0
This invention is described in claim 3 of the specification published in International Publication No. 2400. This International Publication Patent Publication was published on March 8, 1990. This utilization invention is also published in the Japanese magazine “OPTRONICS”
1990 No. 4, pp. 227-231. Next, the invention utilizing this invention will be explained.

[Description of the utilized invention] State 1 in FIG. 17 shows the configuration of the medium of the utilized invention.

[0084] This medium consists of a substrate and a magnetic film formed on the substrate, which basically has a four-layer structure. This magnetic film is, in order,
An M layer made of a perpendicularly magnetizable magnetic thin film, a W layer made of a perpendicularly magnetizable magnetic thin film, a switch layer (hereinafter referred to as S layer) made of a perpendicularly magnetizable magnetic thin film, and a perpendicularly magnetizable magnetic thin film. In principle, it has a four-layer structure with an initialization layer (hereinafter referred to as the I layer) consisting of (the S layer may be omitted in some cases).
Consisting of

[0085] In the above-mentioned International Publication Patent 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 the first magnetic layer. It is called a fourth magnetic layer (see claim 3). In places other than this third term, the names of the third magnetic layer and the fourth magnetic layer are reversed, which seems to be a typo. Also, the magazine “OP”
In "TRONICS", the S layer is called the control layer.Recently, in Japanese academic societies, it is often called the memory layer, "recording layer", switch layer, and initialization layer, so in this specification, it is called the "control layer". I will follow this.

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

However, in the process of high-temperature cycles (for example, near TH), the magnetization reversal of the W layer must occur, and in that case, the influence from the I layer must be so small that it can be ignored. As the temperature rises, W
This is advantageous because the exchange coupling force σw24 between the layer and the I layer becomes smaller. However, even in TH, if sufficient σw24 remains, an S layer is required between the W layer and the I layer. If the S layer is a non-magnetic material, σw24
becomes zero or very small. However, at temperatures somewhere below TH and up to room temperature, σw24 must be large for initialization of the W layer. At this time, the S layer must provide an apparently sufficiently large exchange coupling force between the W layer and the I layer. For this purpose, the S layer needs to be a magnetic material. Therefore, at relatively low temperatures, the S layer
It becomes a magnetic material and gives an apparently sufficiently large exchange coupling force σw24 between the W layer and the I layer, and at a relatively high temperature it becomes a nonmagnetic material and gives an apparently large exchange coupling force σw24 between the W layer and the I layer. This provides zero or very small exchange coupling force σw24. Therefore, the S layer is called the switch layer.

Next, the principle of four-layer film overwriting will be explained using FIG. 17. This explanation is a typical example; there are other examples. For example, if any of the layers has Tcomp. between room temperature and the Curie point. The explanation becomes more complex. The white arrows in FIG. 17 indicate the direction of magnetization of each layer. The state before recording is either state 1 or state 2. Focusing on the M layer, state 1 is a bit ``A-oriented'' (B1), state 2 is a bit ``reverse A-oriented'' (B0), and there is an interfacial domain wall (thick line) between the M layer and the W layer. ━
) and is in a somewhat unstable state (metastable).

----------Low temperature cycle---When the bits in state 1 and state 2 are irradiated with a laser beam to raise the temperature, the magnetization of the S layer disappears first. Therefore,
State 1 transitions to state 3, and state 2 transitions to state 4. When the temperature further increases and reaches the TLS, the magnetization of the M layer becomes weaker, and the effect via the exchange coupling force from the W layer becomes stronger. As a result, the magnetization of the M layer in state 4 is reversed and at the same time the interlayer domain wall disappears. This is state 5. Since the bit in state 3 originally has no domain wall between layers, it remains in state 5.
to move to.

[0090] Here, when the laser beam irradiation stops or the bit moves away from the irradiation position, the temperature of the bit in state 5 begins to decrease, and eventually changes to state 1 via state 3. This is the low temperature cycle. Note that when the temperature further rises from state 5 and exceeds the Curie point of the M layer, the magnetization disappears and state 6 is reached. Here, when the laser beam irradiation stops or the bit moves away from the irradiation position, the temperature of the bit in state 6 begins to decrease, and eventually reaches a temperature slightly lower than the Curie point of the M layer. Then, magnetization appears in the M layer. The direction of this magnetization is affected by the exchange coupling force from the W layer, and becomes a direction that is stable with respect to the direction of magnetization of the W layer (a direction in which no domain wall is generated between the layers). Here, since it is the P type, state 5 is reproduced. The temperature decreases further and accordingly, state 3 occurs and then the state 1 bit occurs. This process is another example of low temperature cycling.

----------- High temperature cycle ----- When the bits in states 1 and 2 are irradiated with a laser beam to increase their temperature, they pass through state 5 and change to state 6. As the temperature further increases, the coercive force of the W layer decreases significantly. Therefore, the magnetization is reversed by the recording magnetic field Hb↓. This is state 8.

[0092] Here, when the laser beam irradiation stops or the medium moves away from the irradiation position, the medium temperature starts to decrease. Eventually, the medium temperature becomes slightly lower than the Curie point of the M layer. Then, magnetization appears in the M layer. The direction of this magnetization is
Under the effect of the exchange coupling force from the W layer, the magnetization direction becomes stable with respect to the direction of magnetization of the W layer (an orientation in which a domain wall does not occur between the layers). Here, since it is a P type, state 9 appears.

[0093] When the temperature further decreases, magnetization appears in the S layer, and as a result, the W layer and I layer become magnetically (by exchange coupling force)
be combined. As a result, the direction of magnetization of the W layer becomes a direction that is stable with respect to the direction of magnetization of the I layer (a direction in which no domain wall is generated between the layers). Here, since it is of P type, the magnetization of the W layer is reversed to 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, producing state 2 bits.

This is the high temperature cycle.

Note that when the temperature further increases after state 8 appears due to the recording magnetic field Hb↓, the temperature eventually exceeds the Curie point of the W layer. Then, state 7 appears. Here, when the laser beam irradiation stops or moves away from the irradiation position, the medium temperature starts to decrease. Eventually, the medium temperature becomes slightly lower than the Curie point of the W layer. Then,
Magnetization appears in the W layer. The direction of this magnetization is determined by the recording magnetic field Hb
Follow the direction below. As a result, state 8 appears.

[0096] When the temperature further decreases, bits in state 2 are formed through state 9. This process is another example of high temperature cycling.

−−−−−−Overwrite−−−−−−−− As described above, the bit (B1) in state 1 is formed in the M layer in the low temperature cycle, and the bit (B1) in state 1 is formed in the M layer in the high temperature cycle, regardless of the previous recording state. M
A state 2 bit (B0) is formed in the layer. Therefore, overwriting is possible.

[0098]

[Problem to be Solved by the Invention] The "overwritable magneto-optical recording medium with a four-layer film structure that does not require an initializing magnetic field Hini." according to the utilization invention is superior to the medium with a two-layer film structure according to the basic invention. , the thickness of the entire magnetic layer is thick.

Therefore, the first problem with this medium is that the recording sensitivity is low. Therefore, the present inventor attempted to manufacture and evaluate a medium in which the thickness of each layer was forcibly reduced. However, these media had the following drawbacks: (1) The C/N ratio was low, or (2) the overwriting was not good. In addition, if the overwriting is not good, it means that even though new information has been recorded, when playing back,
This means that the previous information is included in the reproduced information.

Therefore, attempts to improve the recording sensitivity by forcibly reducing the thickness of each layer failed. If the recording sensitivity is low, the intensity of the semiconductor laser used as the light source is currently not very high, which causes the following secondary problems. In other words, when recording, the linear velocity of the medium cannot be made very high, so the data (
(information) causes a secondary problem of low transfer speed.

An object of the present invention is to improve the recording sensitivity in an overwritable magneto-optical recording medium that basically has a four-layer structure.

[0102]

Means for Solving the Problems By the way, the thickest layer in the medium of the invention is the W layer. The material composition of the W layer of the invention that has been reported so far is GdDyFeCo. As a result of intensive research, the present inventor has found that by using TbDyFeCoSi as the material composition of the W layer, which is the thickest film, in the medium of the utilization invention, the W layer can be replaced without impairing the overwrite characteristics and the C/N ratio. The present inventors have discovered that the film thickness of the magnetic layer can be significantly reduced, and therefore the film thickness of the entire magnetic layer can be reduced, and as a result, the recording sensitivity is improved, and the present invention has been completed.

Therefore, the present invention provides an M layer consisting of a perpendicularly magnetizable magnetic thin film; a W layer consisting of a perpendicularly magnetizable magnetic thin film; an S layer consisting of a perpendicularly magnetizable magnetic thin film; The M layer and the W layer are exchange-coupled, and the magnetization direction of the M layer is not changed at room temperature, but only the magnetization of the W layer is set in a predetermined direction. This is an overwritable magneto-optical recording system that basically has a four-layer film structure in which the W and I layers are exchange-coupled via the S layer at a temperature below the Curie point of the S layer. The present invention provides a magneto-optical recording medium characterized in that the W layer is made of a TbDyFeCoSi alloy thin film.

[0104]

[Operation] The composition ratio of the TbDyFeCoSi system, which is a feature of the present invention, is (TbvDy100-v) x (FewCo100-w)
When expressed as ySiz, the following range is preferable.

v=0 to 50 atom% y=65 to 75 atom% w=
50 to 90 atomic% z=0.1 to 5 atomic% x=
25 to 32 atom % In particular, the following range is even more preferable. v=20-50 atom% y=67-75 atom%w
=60 to 80 atomic% z=0.1 to 3 atomic%x
= 25 to 30 atomic % In the medium of the invention (W layer = GdDyFeCo), when the thickness of the W layer was made thinner than 1300 Å, overwriting could not be performed satisfactorily. In contrast, the medium of the present invention (
The overwriting of the W layer (TbDyFeCoSi system) was good even when the W layer thickness was at least 200 Å.

[0106] Therefore, the film thickness of the W layer is 200 to 120
0 Å is preferred. Further, when the Curie points of the M layer, W layer, S layer, and I layer are respectively TC1, TC2, TC3, and TC4 in this order, it is preferable that the relationship TC3≦TC1<TC2<TC4 holds true.

The material composition of the M layer is TbFeCo or Tb
DyFeCo type is preferred. The material composition of the S layer is TbF
e, TbFeCo, DyFe or DyFeCo systems are preferred. The material composition of the I layer is TbCo, TbFeCo, T
bGdCo or TbGdFeCo systems are preferred. below,
The present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto.

[0108]

[Example 1] First, a 1.2-inch thick resin was equipped with a groove material resin (so-called 2P resin) layer with a large number of concentric grooves (called pre-grooves) formed on the surface for tracking purposes.
A disk-shaped glass substrate of mm was prepared. The substrate was placed in a vacuum chamber of a sputtering device equipped with four target sources. Once inside the vacuum chamber, 5×10
After evacuating to -5 Pa, while rotating the above board,
Introduce argon (Ar) gas and increase the Ar gas pressure to 2
The pressure was maintained at ×10 −1 Pa.

[0109] First, a Si target was used as the first target. Reactive sputtering was performed while introducing N2 gas into the chamber in addition to Ar gas. As a result, silicon nitride (Si3
A protective layer consisting of N4) was provided to a thickness of 700 Å. Next, the introduction of N2 gas was stopped, and sputtering was performed in Ar gas using a TbFeCo alloy as a second target. As a result, an M layer consisting of a perpendicularly magnetized film having a thickness t1 of 500 Å and a composition of Tb24Fe72Co4 was formed on the protective layer. This M layer is RE rich.

Subsequently, while maintaining the vacuum state, simultaneous sputtering was performed using a TbDyFeCo alloy as the third target and the first target (Si). At this time, adjust the sputtering power to increase the amount of Si added by 3
It was set as atm%. As a result, a film thickness t2 is formed on the M layer.
is 200 Å and the composition is Tb9Dy18Fe42Co2
A W layer consisting of a perpendicularly magnetized film of 8Si3 was formed. This W
The layer is RE rich.

Furthermore, while maintaining the vacuum state, sputtering was performed using a TbFe alloy target as a fourth target. As a result, an S layer consisting of a perpendicularly magnetized film having a thickness t3 of 100 Å and a composition of Tb21Fe29 was formed on the W layer. This S layer is TM rich. Further, while maintaining the vacuum state, sputtering was performed using a TbCo alloy target as a fifth target. As a result, a film thickness t4 is formed on the S layer.
An I layer consisting of a perpendicularly magnetized film having a thickness of 500 Å and a composition of Tb27Co73 was formed. This I layer is RE rich.

Finally, while maintaining the vacuum state, the first
Using a target, measure the thickness in the same way as for the protective layer above.
A second protective layer of 700 Å of Si3N4 was formed over the I layer. The vertical cross-sectional structure of the overwritable magneto-optical recording medium thus obtained is shown in FIG. in fact,
Thereafter, a protective glass plate is bonded onto the second protective layer using an adhesive.

[Evaluation Test] First, by applying an external magnetic field (permanent magnet) of 6 kOe or more to the medium of the example, the W layer, S layer, and I layer were
The magnetization direction of the layer was aligned in the "A direction".

[0114] Next, the medium was rotated at a constant linear velocity of 11.3 m/sec using a magneto-optical recording/reproducing device, and the first reference information was recorded by irradiating the medium with a laser beam having a wavelength of 830 nm. At this time, the intensity of the laser beam was set to PH = 8.5 mW (on disk) at high level, and PL = 3.5 mW (on disk) at low level.
k), and a frequency of 7.5 MHz (first
reference information). The high level pulse width is 4
It was set to 5 nsec.

[0115] When the recorded information is reproduced, the C/N ratio=
It was played back at 50dB. This confirmed that the first reference information was recorded. Next information is 2.8MHz
(second reference information), and recorded in the same manner in the area of this medium where the first reference information was recorded. When the information recorded in this way was reproduced and the obtained reproduced signal was analyzed with a spectrum analyzer, the reproduced signal was 7.5M.
It contained no Hz information at all, only 2.8 MHz information. The C/N ratio was 50 dB.

[0116] This indicates that complete overwriting has been performed.

[0117]

[Example 2] In the same manner as in Example 1, M
Layer: Tb12Dy12Fe65Co11 (film thickness
500 Å) W layer: Tb14Dy14Fe48Co21
Si3 (film thickness 200 Å) S layer: Tb20Fe80
(Film thickness 100 Å) I layer: Tb
20Gd5Co75 (film thickness 500Å)
A magneto-optical recording medium was manufactured by laminating the following. Each layer is RE rich.

[0118] When this medium was evaluated according to the evaluation test described above, this medium showed almost the same characteristics as the medium of Example 1.

[0119]

[Effects of the Invention] As described above, according to the present invention, the W layer has T
By using the bDyFeCoSi alloy, it is possible to obtain a magneto-optical recording medium with good overwriting even if the thickness of the W layer is reduced. As a result, the medium of the present invention has the advantage that the entire magnetic layer has a thin film thickness, and therefore has high recording sensitivity.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing a vertical cross section of a medium according to Example 1 of the present invention.

FIG. 2 is a conceptual diagram illustrating the recording principle of the magneto-optical recording method.

FIG. 3 is a conceptual diagram illustrating the reproduction principle of the magneto-optical recording method.

FIG. 4 is a waveform diagram of a laser beam when overwriting according to the basic invention.

FIG. 5 is a waveform diagram of a laser beam when overwriting is performed with two beams according to the basic invention.

FIG. 6 shows M of an overwritable magneto-optical recording medium.
It is a graph showing the relationship between coercive force and temperature for the W layer.

FIG. 7 is a conceptual diagram showing the magnetization directions of the M layer and the W layer.

FIG. 8 is an explanatory diagram showing changes in the magnetization directions of the M layer and the W layer.

FIG. 9 is an explanatory diagram showing how the magnetization directions of the M layer and the W layer change as a result of low-temperature cycles and high-temperature cycles for P-type media and A-type media. All conditions are shown at room temperature.

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

FIG. 11 is an explanatory diagram for comparing a vector (solid arrow) indicating the sublattice magnetization of a rare earth (RE) atom and a vector (dotted line arrow) indicating the sublattice magnetization of a transition metal (TM) atom. It is.

FIG. 12 is an explanatory diagram showing the relationship between the vector of sublattice magnetization and the vector (white arrow) indicating the direction of magnetization of the alloy.

FIG. 13 is an explanatory diagram explaining that overwritable media are divided into four categories (quadrant 1 to quadrant 4) when the M layer and W layer are divided into RE rich and TM rich, respectively. be.

FIG. 14 is a table (Table 1) explaining that when the medium of the basic invention is classified from various viewpoints, it is ultimately classified into nine classes, Class 1 to Class 9.

FIG. 15 is an overwritable magneto-optical recording medium N.
o. 8-2 is a graph showing the relationship between coercive force and temperature for the M layer and the W layer.

FIG. 16 shows medium No. 8-2 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 No. 8-2. FIG.

FIG. 17 is an explanatory diagram illustrating the overwriting principle of the overwritable magneto-optical recording medium having a four-layer film structure according to the invention.

[Explanation of symbols of main parts] L……Laser beam Lp
……Linearly polarized light B1 ……Bit B0 with “A direction” magnetization ……”
Bit MO having magnetization in the "reverse A direction"... Perpendicular magnetization film S... Substrate P... Groove resin layer 1... Memory layer (M layer) 2... Recording layer (W layer) 3 ......Switch layer (S layer) 4...Initialization layer (I layer) 5...Protection layer

Claims (6)

[Claims] [Claim 1] A memory layer consisting of a perpendicularly magnetizable magnetic thin film, and a "recording layer" consisting of a perpendicularly magnetizable magnetic thin film.
, a switch layer made of a perpendicularly magnetizable magnetic thin film, and an initialization layer made of a perpendicularly magnetizable magnetic thin film are laminated in this order, and the memory layer and "recording layer" are exchange-coupled and are It is possible to keep the magnetization of the recording layer in a predetermined direction without changing the direction of magnetization of the memory layer, and the recording layer and initialization layer can be switched at a temperature below the Curie point of the switch layer. In an overwritable magneto-optical recording medium that basically has a four-layer film structure in which exchange coupling is provided through layers, the "recording layer" is made of TbDyFeCo.
A magneto-optical recording medium comprising a Si-based alloy thin film. [Claim 2] The film thickness of the "recording layer" is 200 to 200.
2. The overwritable magneto-optical recording medium according to claim 1, characterized in that it has a thickness of 1200 Å. 3. Curie points of the memory layer, "recording layer", switch layer, and initialization layer are sequentially set to TC1, TC2,
The overwritable magneto-optical recording medium according to claim 1, characterized in that, when TC3 and TC4, the following relationship holds: TC3≦TC1<TC2<TC4. 4. The memory layer is made of TbFeCo
2. The overwritable magneto-optical recording medium according to claim 1, wherein the overwritable magneto-optical recording medium is made of a TbDyFeCo alloy thin film. 5. The switch layer is made of TbFe, T
The overwritable magneto-optical recording medium according to claim 1, characterized in that it is made of bFeCo, DyFe or DyFeCo alloy thin film. 6. The initialization layer includes TbCo, Tb
2. The overwritable magneto-optical recording medium according to claim 1, wherein the overwritable magneto-optical recording medium is made of a FeCo, TbGdCo or TbGdFeCo alloy thin film.