JPH03171454A - Magneto-optic recording medium capable of clear overwriting of tl - Google Patents

Abstract

PURPOSE:To widen the margin of a recording magnetic field, to enable irradiation with an intense beam at the time of reproduction, and to increase the C/N ratio by giving a 1st layer a compensation temperature between room temperature and the Curie point and specifying a coefficient eta at temperature where a low temperature process is initiated. CONSTITUTION:The magneto-optic recording medium consisting of a multi-layered vertical magnetism film is two-layered structure of a recording layer (1st layer) and a recording auxiliary layer (2nd layer) is used. The 1st layer has magnetic barrier energy shown by an equation I and the compensation temperature Tcomp.1 between the room temperature and Curie point Tci, and the coefficient eta defined by equations II and III is >=200(Oe/ deg.C) at the temperature TL where the low-temperature process is initiated. In the equations I - III, Ms1 is the saturated magnetism (gauss) of the 1st layer (recording layer), Hc1 the coercive force (Oe), t1 the film thickness (cm), sigmaw the magnetic barrier energy (erg/cm<2>) generated or ceased as the magnetism of the 1st layer (recording layer) is inverted, and T the medium temperature. Consequently, the margin of the recording magnetic field is wide, the intense laser beam is used at the time of reproduction, and the high C/N ratio is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention enables overwrite (over+write) by modulating the intensity of a light beam without modulating the direction of the recording magnetic field Hb.
) and related to possible magneto-optical recording media.

[Conventional technology]

Developed optical recording and reproducing methods, recording devices, reproducing devices, and recording media used therein that satisfy various requirements, including close-up, high-density, large-scale imaging, high access speeds, and high recording and reproducing speeds. Efforts to do so are under threat.

Among a wide range of optical recording and reproducing methods, magneto-optical recording and reproducing methods are unique in that after information is recorded, it can be erased and new information can be recorded again and again. Because of its advantages, it is full of the greatest charm.

The recording medium used in this magneto-optical recording and reproducing method has one or more perpendicularly magnetized films as a recording layer.
icular magnetic layer or
layers). This magnetized film is made of, for example, amorphous GdPe, GdCo, GdFeCoSTbF.
It consists of e, TbCo, and TbFeCo. The recording layer generally has concentric or spiral tracks on which information is recorded. Here, in this specification, "upward" J
or “either one of the downward J.
One direction is defined as "direction A" and the other direction is defined as "direction A". The information to be recorded is pre-binarized, and this information is made up of two signals: a bit with magnetization in the "A direction" (B1) and a bit with magnetization in the "reverse A direction" (B.). recorded.

These Bisoto B+. Bo corresponds 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.

This process is called initialization (iniLialiZe). Then, a bit (B1) having magnetization in the "A direction" is formed on the track. Information is recorded by the presence or absence of Konohiso l-(B.) and/or bit length.

Principle of bit shape: In the shape of the bit, the characteristics of the laser, i.e. the spatio-temporal coherence, are advantageously used, which is very similar to the diffraction limit determined by the wavelength of the laser light. The beam is narrowed down to a spot as small as possible. The focused light is irradiated onto the track surface,
Information is recorded by forming bits with a diameter of 1 μm or less on the recording layer. In optical recording, recording densities of up to about 108 bits/c& can be theoretically achieved. This is because the laser beam can be concentrated into a spot with a diameter approximately as small as its wavelength.

As shown in FIG. 2, in magneto-optical recording, a laser beam (L) is focused onto a recording layer (1) 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 H c (
coersivity) decreases and becomes smaller than the recording magnetic field (Hb). As a result, the magnetization of that part changes with the recording magnetic field (
Hb). A reversely magnetized bit is thus formed.

The magnetization and temperature dependence of He are different between the ferromagnetic material and the ferrimagnetic material. The Huet magnetic material has 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 compensator degree (
compensation temperature)
, where the magnetization (M) becomes zero. On the other hand, He becomes very large around this temperature, and the salinity increases? Then, Hc decreases rapidly. This decreased +-1
c is overcome by the relatively weak recording magnetic field (1-1b). In other words, it becomes possible to record. This recording process is T. . ■2 1 called writing (compensation tun writing)
．． However, it is not necessary to stick to the Curie point or its vicinity, or the vicinity of the compensation temperature. In short, at a given temperature above room temperature, magnetic 44 It has a reduced Hc.
However, recording is possible by applying a recording magnetic field (Hb) that overcomes the decreased I-1c.

Principle of regeneration FIG. 3 shows the principle of information reproduction based on the magneto-optical effect.

Light is an electromagnetic wave with an electromagnetic field hector usually diverging in all directions in a plane perpendicular to the optical path. The light is converted into linearly polarized light (I. .), and the recording layer (1)
When irradiated with the recording layer (1), the light is either reflected at its surface or transmitted through the recording layer (1).

At this time, the plane of polarization rotates according to the direction of magnetization (M). This rotating phenomenon is called the magnetic Kerr effect or the magnetic Faraday effect.

For example, if the polarization plane of the reflected light is rotated by θk degrees with respect to the "A-direction" magnetization, it will be rotated by 10k degrees with respect to the "reverse A-direction" magnetization. Therefore, the optical analyzer (polarizer)
If you set the axis perpendicular to the plane tilted by -θk degrees,
The light reflected from the bit (BO) magnetized in the reverse A direction cannot pass through the analyzer. In this illusion, ``the light reflected from the hill (B.) magnetized in the direction J of A is transmitted through the analyzer by the amount multiplied by (sin2θk)2, and is captured by the detector (photoelectric conversion means). As a result, Hiso l-(
B. ) appears brighter than Biso1.(Bo), which is magnetized in the "reverse 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 the information is reproduced.

By the way, in order to reuse a recorded medium, (1) the medium is again initialized with an initialization device, or (ii) a removal head similar to a recording head is attached to the recording device, or ( ii) It is necessary to erase the recorded information in advance using a recording device or an erasing device as a preliminary process.

Therefore, in the magneto-optical recording system, it has been thought that over write, in which new information is recorded on the spot regardless of the presence or absence of previously recorded information, is impossible.

However, if you change the direction of the recording magnetic field Hb as necessary,
If it is possible to freely modulate between the "direction" and the "reverse A direction," it will be possible to achieve 1. 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. but,
It is impossible to reverse the direction of a 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, technological progress has been remarkable, and the recording magnetic field Hb has been reduced to O
By modulating the intensity of the irradiated light beam according to the binarized information to be recorded without turning off the recording magnetic field Hb or modulating the direction of the recording magnetic field Hb, the optical magnetism that can be realized A recording method, an overwrite-enabled magneto-optical recording medium used therein, and an overwrite-enabled recording apparatus also used therefor were invented and a patent application was filed (Japanese Patent Laid-Open No. 175948/1983). Hereinafter, this invention will be referred to as the "basic invention."

[Description of basic invention]

One of the features of the basic invention is the use of a magneto-optical recording medium consisting of a multilayer perpendicularly magnetized film having at least a two-layer structure of a recording layer (first layer) and a recording Urasuke layer (second layer). Then, the information is divided into bits with magnetization in the “A direction” and bits with magnetization in the “reverse A direction”.
Bits with magnetization in the first layer (and in some cases, the second layer)
It is recorded in .

The overwriting method according to the basic invention includes (a) moving the recording medium; (b) initial auxiliary magnetic field old n1. By applying
Before recording, leave the magnetization of the first layer as it is and align only the magnetization of the second layer in the "A direction": (C) Irradiate the medium with a laser beam (d) As described above. (e) When the beam is irradiated, a recording magnetic field is applied to the irradiated area; (f) the intensity of the pulsed beam is at a high level; Sometimes “A
It consists of activating either a bit with magnetization in the J direction or a bit with ``reverse A'' magnetization, and activating the other bi-soto when the beam intensity is at a low level.

In the basic invention, when recording, for example, (a) a means for moving the magneto-optical recording medium; (b) an initial auxiliary magnetic field;
Application means; (c) laser beam light source; (d) beam intensity according to the binarized information to be recorded; (
1) A high level that applies a temperature to the medium suitable for forming either a bit with magnetization in the "rA direction" or a bit with magnetization in the "reverse A direction," and (2) the other bit. (e) Overwrite consisting of a recording magnetic field applying means that may also be used as the initial auxiliary magnetic field applying means; Use any available magneto-optical recording device.

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 the means 1 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 SYS
TEM Tl! CHNICAL JOURNAL,
Vol. 62 (1983), 1923-193
6 is explained in detail. Therefore, given the required high and low levels of beam intensity, conventional modulation means can easily be modified with some modification. For those skilled in the art, such modifications will be easy given the high and low levels of beam intensity.

One of the distinctive features of the basic invention is Bee? There are high and low levels of intensity. That is, when the beam intensity is at a high level, the "A direction" magnetization of the recording auxiliary layer (second layer) is reversed to the "reverse A direction" by the recording magnetic field Hb.
e) Form a bit having "reverse A direction" magnetization [or "A direction" magnetization] in the recording layer (first layer) by the "1 reverse A direction" magnetization of this second layer. When the beam intensity is at a low level, the "A-direction" magnetization of the second layer forms a bit with "A-direction" magnetization (or "reverse A-direction" magnetization) in the first layer.

In addition, in this specification, when the expression ○○○ [or △△△] is first read as ○○○ outside [ ], it becomes the following ■danΩ [or Δ△△]
Even in the case of , I will read ○○○ outside of [ ]. On the other hand, when you select and read △△△ in [ ] without reading ○○○ first, the ○O○ [or △△△]
Even when , it is assumed that △△△ in [ ] is read instead of ○○○.

As is well known, 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. When the beam is also used for reproduction, the laser beam may be turned on with an intensity of very low level 1. In the present invention, the intensity of the laser beam may also be set to this very low level 1. However,
The lower leher when forming bi-not is higher than this very low lehenoha. Therefore, for example, the output waveform of the laser beam in the basic invention is as follows.

Example of beam intensity value information 111001111000
Although not specified in the specification of the basic invention, in the basic invention, the recording beam is a low-level laser beam that does not modulate the preceding beam in principle, using two beams in close proximity instead of one. (for tree removal) and a high-level laser beam (for writing) that modulates the trailing beam according to the information.
You can also use it as In this case, the trailing beam is pulse modulated between the high level and the base level (which is the same as or lower than the low level and may have zero output).

The output waveform in this case is as follows.

Example 1 of leading beam trailing beam beam intensity value information 1 1 0 0 1 1 1 1 0 0 0 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 a recording layer (first layer) and a recording auxiliary layer (second layer).

? The first layer is a recording layer that has a high coercive force at room temperature and a low magnetization reversal temperature. The second layer is a recording auxiliary layer which has a lower coercive force at room temperature and a higher magnetization reversal temperature than the first layer. Note that both the first layer and the second layer may themselves be composed of multilayer films. In some cases, a third layer may be present between the first layer and the second layer. Furthermore, there may be no clear boundary between the first layer and the second layer, and one may gradually change to the other.

In the first embodiment, the coercive force of the recording layer (first layer) is
, that of the recording auxiliary layer (second layer) is HC2, the Curie point of the first layer is Tc+, and that of the second layer is T. 2. Set the room temperature to T■,
TL is the temperature of the recording medium when it is irradiated with a low-level laser beam, and T is the temperature when it is irradiated with a high-level laser beam. , the coupling magnetic field received by the first layer is Hl), and the coupling magnetic field received by the second layer is Hl).
In the case of D2, the recording medium satisfies the following formula 1 and satisfies formulas 2 to 5 at room temperature.

T Il< T c+埒T L < T el4 T
o −−−−−− −Formula lH c+ > H Te
l + l H o + 乎H. l 1 -”””””
""Formula 2H c, > H . ．． −−−−−−−1−
−−−−−−−−−Set 3H C l > H [+
1-----------------1 set 4HC2+HD
l<lHini. l<Hc1±H D l-Formula 5
In the above formula, the symbol "Kyo" represents equal or approximately equal. In addition, in the above formula, regarding the composite and jin, the upper row is for A (antiparallel) type media described later, and the lower row is for P (parallel) type media described later.
) type of media. Note that the ferromagnetic medium belongs to the P type.

In other words, the relationship between coercive force and temperature can be expressed graphically as follows. The thin line represents that of the first layer, and the thick line represents that of the second layer.

? L TI+ Therefore, the initial auxiliary magnetic field (Hini) is applied to this recording medium at room temperature.
．． ), according to Equation 5, only the magnetization of the recording auxiliary layer (second layer) is reversed without reversing the direction of magnetization of the recording layer (first layer). Therefore, before recording, the initial auxiliary magnetic field (
Hini. ), only the second layer is turned to "A direction"■
Here, for convenience, the "A direction" is indicated by an upward arrow 8 on the paper of this specification, and the "reverse A direction" can be magnetized to a square (■) indicated by a downward arrow 8. Even if Hini becomes zero, according to equation 4, the magnetization of the second layer is maintained as it is without being reversed again.

A conceptual representation of a state in which only the second layer is magnetized in the "A direction" until immediately before recording by the initial auxiliary magnetic field (Hini.) is as follows.

Here, the magnetization direction 9 in the first layer represents the information recorded up to that point. In the following description, since the direction is not relevant, it will be indicated by X below.

Here, a high-level laser beam is irradiated to raise the medium temperature to TH. Then, since T++ is a temperature higher than the Curie point Tc+, the magnetization of the recording layer (first layer) disappears. Furthermore, TH is the Curie point T. 2, the magnetization of the recording auxiliary layer (second layer) 21 also disappears completely or almost completely. Here, the recording magnetic field (Hb) in "A direction" or "reverse A direction" depending on the type of medium.
Apply. The recording magnetic field (Hb) may be a stray magnetic field from the medium itself. To simplify the explanation, assume that a recording magnetic field (Hb) in the "reverse A direction" 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 second layer is reversed in accordance with Hb and becomes magnetized in the "reverse A direction" (state 2l+).

Then, as the cooling progresses further and the medium temperature drops slightly below Tc+, the magnetization of the first layer appears again. In that case, the direction of magnetization of the first layer is influenced by the direction of magnetization of the second layer due to magnetic coupling (exchange coupling) forces. This results in either 8 (for P type 22 media) or 22 (for A type media) depending on the media.

This state change caused by the high-level laser beam will be referred to as a high-temperature cycle.

Next, a low-level laser beam is irradiated to raise the medium temperature to TL. Since TL is close to the Curie point ToI, the magnetization of the first layer disappears completely or partially, but the magnetization of the second layer does not disappear because it is lower than the Curie point Tel.

It is impossible to turn Hb on and off quickly (in a short period of time). Therefore, it is unavoidable that it remains as it was during the high temperature cycle.

However, since Hc2 remains large, the magnetization of the second layer is not reversed by H11. Since the medium is moving, the irradiated area quickly moves away from the laser beam and is removed. As the process progresses, the magnetization of the first layer appears again. The direction of magnetization that appears is influenced by the direction of magnetization of the second layer due to the magnetic coupling force. As a result, magnetization of 1r (for P type) or 8 (for A type) appears depending on the medium. This magnetization does not change even at room temperature.

This state change caused by the low-level laser beam will be referred to as a low-temperature cycle.

As described above, regardless of the direction of the magnetization of the first layer, tips having magnetization values opposite to each other are formed depending on the high-salt cycle and the low-salt cycle. In other words, overwriting is possible by pulse-modulating the laser beam between high level (high temperature cycle) and low level (low temperature cycle) according to the information.

/ For P type media? The explanation so far has been about a magnetic material assembly in which both the first layer and the second layer have a compensator temperature T ea■ between room temperature and the Curie point. However, if a compensation temperature T co ■ exists, the direction of magnetization is reversed when the compensation temperature T co ■ is exceeded, and the A and P types are reversed, making the explanation that much more complicated. Furthermore, when considered at room temperature, the direction of the recording magnetic field Hb is also opposite to the direction ↓ described on the previous page.

A recording medium is generally disk-shaped, and the medium is rotated during recording. Therefore, the recorded part (bit) is 1
Hini. again while rotating. As a result,
The magnetization of the recording auxiliary layer (second layer) is aligned in the original "A direction" 9. However, at room temperature, the magnetization of the second layer does not affect the recording layer (first layer), so recorded information is retained.

Therefore, if the first layer is irradiated with linearly polarized light, the reflected light contains information, so the information is reproduced in the same way as in conventional magneto-optical recording media. Depending on the combination design of the first and second layers, by applying a reproduction magnetic field HR before reproduction, the information of the first layer may be transferred to the second layer aligned in the original "A direction". method, and without applying the reproduction magnetic field HR, the old nl. In some cases, the information in the first layer is naturally transferred to the second layer as soon as the influence of
Information may be reproduced layer by layer.

Such a recording layer (first layer) and recording auxiliary layer (second layer)
The perpendicularly magnetized film constituting is made of: (1) ferromagnets and ferrimagnetic materials that have no compensation temperature and a Curie point, and (2) amorphous or crystalline ferrimagnetic materials that have both a compensation temperature and a Curie point. selected from the group.

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 He at a predetermined temperature higher than room temperature. In the second embodiment, instead of Tc+ in the first embodiment, the recording layer (l-th layer) is a recording auxiliary layer (
TC2
If the temperature Ts2 at which the second layer is inverted by Hb is used instead of , the explanation will be similar to the first embodiment.

In the second embodiment, the coercive force of the first layer is Hc+, that of the second layer is Hat, the temperature at which the first layer is magnetically coupled to the second layer is T1, and the magnetization of the second layer is Hb. The temperature to be reversed is 7.
52. The temperature of the medium when irradiated with a low-level laser beam is TL, the temperature of the medium when irradiated with a high-level laser beam is TII, and the coupling magnetic field received by the first layer is H. ,, When the coupling magnetic field received by the second layer is HD2, the recording medium satisfies the following formula 6 and satisfies formulas 7 to 1 at room temperature.
This satisfies O.

Ttt<Tll suburbTt<T. 2 埒T)＋
--------- Complete set 6HCI > HC2+ HDI failure
D2 ---------- Complete set 7H c+ > H
o 29 H c t > H o a------------
-------- Complete set 9fIci-1-Hot< Ili
ni. <tlcI:i:Ho+ Formula lO In the above formula, the upper row will be described later for A (
The lower row shows the case of a P (parallel) type medium, which will be described later.

In the second embodiment, during the high temperature process (high mTl+), the magnetization of the second layer does not disappear, but is sufficiently weak. 1st
The magnetization of the layer is absent or sufficiently weak. 1st layer,
Even if a sufficiently weak magnetization remains in both the second layers, the recording magnetic field Hb↓ is sufficiently large, and Hb↓ causes the direction of magnetization of the second layer and possibly the first layer to follow Hb↓.

After this, either immediately or ■ when the laser beam irradiation ceases and cooling progresses and the medium temperature is below TH or when it is far from l'-1b, the second layer is The first layer is influenced to cause the first layer to follow a stable orientation. As a result, the state becomes 31{. If the magnetization of the first layer is originally in a stable direction, it will not change.

On the other hand, when the first
Although neither the magnetization nor the second layer has lost its magnetization, the magnetization of the first layer is sufficiently weak.

Therefore, the direction of magnetization of the first layer is influenced by the magnetization of the second layer, which is greater than the influence of Hb, via σ1. However, since the second layer has sufficient magnetization, the magnetization is not reversed by Hb.

As a result, the state becomes 3L even if Hb↓.

(P type) (A type) In the above explanation, the compensation temperature T6 is between room temperature and the Curie point for both the first layer and the second layer. ．． The formation of a fleeting magnetic material has been explained. However, complementary (1'l rfa degree T H6m
If n exists, the explanation becomes that much more complicated because if it is exceeded, 1) the direction of magnetization will be reversed, and 2) the ASP type will be reversed. Further, the direction of the recording magnetic field Hb is also opposite to the direction when considered at room temperature.

Although not specified in the specification of the basic invention, the initial auxiliary magnetic field old n1. The third layer has the application means in close contact with the second layer.
The second layer of the medium of the present invention may be initialized by the exchange coupling force σW acting on the magnetic layer (perpendicularly magnetized film).

In both the eleventh and second embodiments, a recording layer (i-th layer), a recording auxiliary layer (second layer), a transition metal (e.g. FeCo), a single rare earth metal (e.g. Gd. Tb. DV, etc.) alloy combination is selected. Preferably, the recording medium is an amorphous ferrimagnetic material.

Both the first layer and the second layer are transition metals, heavy rare earth metals,
When selected from alloy compositions, the direction and magnitude of magnetization appearing externally as each alloy are determined by the direction and magnitude and weight of spin of transition metal atoms (hereinafter abbreviated as TM) inside the alloy. It is determined by the relationship between the spin direction and size of rare earth metal atoms (hereinafter abbreviated as RE). For example, TM
The direction and magnitude of the spin of RE are represented by the dotted hector line, the spin of RE is represented by the solid line hector T, and the direction and magnitude of the magnetization of the entire alloy are represented by the double solid line hector combination. At this time, Hector cat is Hector ↑ and Vector ↑
It is expressed as the sum of However, in an alloy, the vector ↑ and the hector T are always in opposite directions due to the interaction between the TM spin and the RE spin. Therefore, when the sum of T or the sum of ↓ and T is equal in strength, the vector of the alloy becomes zero (that is, the magnitude of magnetization appearing externally is zero). The alloy composition when this becomes zero is the compensation composition.
location). For other combinations, the alloy has a strength equal to the difference in strength between the two spins, and a vector 1-le (廿 or 8) with an orientation equal to the direction of the larger vector 1-le. .

The magnetization of this hexle appears on the outside. For example, ↑- becomes 廿, and ↑ko becomes 8.

When the hector strength of the TM spin and the RE spin of a certain alloy composition is greater than the other, the alloy composition is
Taking the name of the spin with greater intensity, ○○lisochi, for example, R
It is called E-Rinochiteru.

For both the first and second layers, the TM-rich composition and R
It can be divided into E-rich groups and groups. Therefore, if the composition of the first layer is plotted on the vertical axis and the composition of the second layer is plotted on the horizontal axis, the overall medium of the basic invention can be classified into the following four quadrants. The P type mentioned above belongs to the I quadrant and ■ quadrant, and the A type belongs to the ■ quadrant and ■ quadrant.

RE litho (first layer) TM rich (first layer) [The intersection of the vertical and horizontal coordinates represents the compensation composition of both layers. 〕on the other hand,
Looking at the change in coercive force due to temperature change, we can see that the Curie point (
Do you say that the coercive force increases to infinity and then decreases again before reaching the temperature at which the coercive force is zero? There are alloy composites with properties. The temperature corresponding to this infinity is the compensation temperature (T.

■． ) is called.

No compensation temperature exists between room temperature and the Curie point in TM-rich alloy compositions. Since a compensation temperature below room temperature is meaningless in magneto-optical recording, in this specification the compensation temperature is defined as a temperature between room temperature and the Curie point.

Classifying the presence or absence of compensation temperature in the first and second layers,
Media are classified into four types. The medium in the second quadrant is
Includes all four types. Regarding the four types,
If you draw a graph representing the relationship between coercive force and degree d, it will look like this: Note that the thin line is that of the first layer, and the thick line is that of the second layer.

Type 1 Coercive force Type 2 Coercive force 37 Type 3 Coercive force Type 4 Coercive force 38 Here, for both the recording layer (1st layer) and recording auxiliary layer (2nd layer), RE or TM Reinoch is used. , and l
lk ll'f i4A Recording media are classified into the following nine classes depending on whether they have summer or not.

Table 1 Table 39 Table (Continued) 40 C Invention or problem to be solved] However, in the medium specifically disclosed in the specification of the basic invention, ■ the possible range of the recording magnetic field Hb is The first problem is that it is narrow, and ■ If we call the formation of marks (currently, hits in the basic invention are called "marks") by low-temperature cycles as erasing, then the laser beam intensity (power) is sufficient to completely erase them. The difference between Pce and the laser beam intensity Prs at which erasure begins during playback (
PceP rs) is large, and therefore a strong beam cannot be irradiated during reproduction, resulting in the second problem of low C/N ratio.

The purpose of the present invention is to solve these problems.

[Means for solving problems]

Therefore, the present invention provides the following advantages: ``At least a first layer (recording layer) and a second layer (auxiliary layer) are laminated, and the direction of magnetization of the second layer can be changed without reversing the direction of magnetization of the first layer. 41 ?Magneto-optical technology that allows overwriting by aligning the magnetization direction either upward or downward before recording, and by modulating the light beam according to the information without modulating the recording magnetic field. In the recording medium, the first layer is between room temperature and the Curie point T.
o1 and has a compensation temperature ToQ■2 between the
000 or more, preferably 4000 or more.

However, E1=2・MS1・H91・t1 (unit: er
g/cIIi) M51: Saturation magnetization of the first layer (recording layer) (
Gauss) H. ．． : Coercive force (Oe)
t1: Film thickness (thickness) σ. is the domain wall energy 42 (unit: erg/af) that is created or destroyed as the magnetization of the i-th layer (recording layer) is reversed.

[Function] The medium of the present invention is not limited to the overwritable medium of the basic invention, but also includes at least the first layer (recording layer) and the second layer.
The layers (recording auxiliary layer) are laminated, and the direction of magnetization of the second layer can be changed to either upward or downward immediately before recording without reversing the direction of magnetization of the first layer. Any magneto-optical recording medium that can be overwritten by aligning the magnetic field and modulating the light beam according to the information without modulating the recording magnetic field may be used. If you use it, you will get results.

This is because in the medium with the above-mentioned η, H near TL
The temperature characteristics (temperature change) of e6pF are shown in Figure 7 or Figure 8 (
Hb in the figure stands sharply, as shown in the recording magnetic field applied to the recording site, and is sensitive to various fluctuations, such as fluctuations in the magnetic properties of materials, fluctuations in film thickness, and fluctuations in thermal conductivity. This is because it becomes clear whether a low-temperature process is possible or not.

η is large and H e6jF and Hb intersect in a wide range?
Since it is possible to increase the Hb margin, the Hb margin becomes wider.

On the other hand, for various fluctuations, T. Since the fluctuation of L becomes smaller, Pce-Prs becomes smaller.

In addition, in the medium of the present invention, the medium temperature TL at which the low-salt cycle occurs is ±15°C (±10°C in a preferable medium, ±5° in a particularly preferable medium) with respect to the compensation temperature Tc0,I of the first layer.
C) will approach or match within. Therefore, in the following explanation, T h6mp. It is sometimes written as l''T L, but in this case, ``suburban'' has the above-mentioned meaning.

Here, the class 1 recording media shown in Table 1 (P type
■Media No. belonging to quadrant type 1). Taking 1 as an example,
The overwrite principle will be explained in detail.

This medium 1 is expressed by the following formula 11. TR <Tea+ip. + Suburbs Tt <Tc+<To≦T
-2 and 2 of formula 1l: Tcomp2 < Tc. The above relationship can be expressed as a graph as follows. Note that the thin line indicates the graph of the first layer, and the thick line indicates the graph of the second layer.

Coercive Force TL The condition for only the second layer to be inverted without being inverted by the magnetic field of the first layer (recording layer) or the initial auxiliary magnetic field old n1 at room temperature TII is Equation 12. This medium no. 1 satisfies formula l2.

Equation 12 σ W σ WH c 1>
H( 2+ +2 Ms+ t 1
2 Ms+ t +47 However, HCI・Previously defined HCI: Second layer coercive force Ms+・previously defined (saturation agnetization
n) M52, saturation magnetic moment t1 of the second layer; t2 defined previously; film thickness σw of the second layer; defined previously At this time, the conditional expression for Hini is expressed by Expression 15.

Hini. When , the magnetization of the first layer and the second layer are mutually influenced by the interfacial domain wall energy. Conditions under which the magnetization of the first layer and the second layer are maintained without being reversed are shown by Equations 13 and 14. This medium Nα1 is expressed by formulas l3-14
satisfy.

σ W Equation 13; Hc+> 2Ms+i+ 48 Equation 14: Hc2> 2Ms+jl At room temperature, the magnetization of the second layer of the recording medium that satisfies the conditions of Equations 12 to 14 is calculated by the following equation 152 Ms+ t just before recording.
For example, "A direction" 0 (1,000) due to the old n1 satisfying 2 2 Ms + j
It can be aligned to At this time, the first layer remains in its previous recording state (state 1a or lb).

[ "Reverse A direction" mark　　　　　　　　　["A direction" mark] ?　■　 indicates a domain wall (hereinafter, similar).

These states 1a and lb are maintained until immediately before recording.

Then, the recording magnetic field Hb is applied in the “A direction”↑49 Suppose that

Note that it is difficult to narrow down the recording magnetic field Hb to the same range as the laser beam irradiation area (spot area), as is the case with general magnetic fields. When the medium is disk-shaped, once recorded information (marks) is rotated once, the old n1. , the state becomes 1a, lb. Then, the laser beam passes adjacent to the laser beam irradiation area (spot area) by one track. At this time, the marks in states la and lb are affected by the recording magnetic field Hb. At that time, state 1 with magnetization in the opposite direction to Hb
If the direction of magnetization of the first layer of the mark a is reversed by Hb, the information recorded just one revolution ago will be erased. The condition under which this must not occur is expressed by the following formula 15: 2: Hc+>Hb + 2Ms+j, and the disk-shaped medium must satisfy conditional formula 50 at room temperature. Conversely, one condition for determining Wb is expressed by 2 in equation 15.

Now, the marks in states 1a and lb finally reach the spot area of the laser beam. As with the prior invention, there are two types of laser beam intensity: low level and high level.

Low-temperature cycle A low-level laser beam is irradiated, and the medium temperature reaches T.
It becomes L. Then, σ>E, ±2M5, ・Hb−t (wherein, if Hini. is positive, then T. m.
．． + When <T L, it is ten and T. . . p. +
＞ T When L, the relationship is 1), and Hb↓
In the presence of
remains as it is.

In this state, when the medium moves out of the spot area of the laser beam, the medium temperature begins to decrease and becomes state 2L, which leads to "direction A" 9.
The mark shape or completed.

When irradiated with a high-level laser beam during a high-temperature cycle, the medium temperature is T e6n+p. l''T rises above L. As a result, state 2. is reached.

Irradiation with a high-level laser beam further increases the medium temperature. Is the medium temperature of the second layer? When the temperature is slightly higher than camp ■, the directions of the RE and TM spins do not change, but the magnitude relationship of their intensities is reversed (↑0 - ↑2). Therefore, the magnetization of the second layer is reversed and becomes magnetized in the "reverse A direction" 6 (state 3, I).

However, at this salinity, HC2 is still large, so ↑Hb
The magnetization of the second layer is not reversed. When the temperature further increases to Tc+, the magnetization of the first layer disappears (state 4H).

As the temperature further increases and reaches To, the temperature of the second layer approaches the Curie point TCI, and MCI becomes smaller.
Is the magnetization of the second layer reversed by ↑Hb? Condition 5 ■).

? When the medium moves out of the laser beam spot area in state 5■, the temperature of the medium begins to decrease.

And the temperature is T. When the value falls slightly below 1, magnetization appears in the first layer. At this time, the interfacial domain wall energy of the second layer acts to align the RE spins (↓) and the TM spins (↑). And the temperature of the first layer is T. . ．． , so the TM spin is larger, and therefore a magnetization of ↓↑, that is, 9, appears in the first layer. This state is state 6. It is.

The direction of each spin in RESTM does not change, but the strength relationship is reversed (↓゜1↓1). As a result, the magnetization of the entire alloy is reversed, and it becomes "reverse A direction" 8 (state 7).
l+).

The temperature of the medium further decreases from the temperature in this state 71, to T. ．． 61 or less, the magnitude relationship between the RE spin and TM spin in the first layer is reversed (4, →
1,1). As a result, magnetization of 8 appears (state 8,,
).

Then, the temperature of the medium eventually decreases from the temperature in the state 8ll to room temperature. Since Hc at room temperature is sufficiently large (see equation 15, 3), the magnetization of the first layer is ↑Hb
The state 8o is maintained without being reversed.

Formula l5-3: Hb <　H　c + 2M51t thus, "Reverse A direction" 8 mark shape or complete do.

56 Next, class 3 recording media (P type, ■
Taking specific medium No. 3 belonging to quadrant type 3) as an example, the principle of O'Herrite will be explained in detail.

This medium no. 3 is expressed by the following formula 21 TR <T(Qml'1-TL<Tct<T++ suburb T
It has a relationship of u. This relationship is shown in a graph as follows.

TL 57 The condition for only the second layer to be reversed without the i-th layer's magnetization being reversed by the initial trapping magnetic field old n at room temperature TR is Equation 22. This medium Nα3 satisfies Equation 22.

Formula 22・ Ha >Hc++ + 2 Ms. t 2Ms+j+ At this time, Hini The conditional expression is shown in Equation 25.

Formula 25 2Ms+t+ 2
M, 1tHini. When σW disappears, the magnetizations of the first layer and the second layer are mutually influenced by σW. Nevertheless, the conditional expression that maintains the magnetization of the first layer and the second layer without reversing is Equation 2
3 to 24. This medium no. 3 is formula 23
~24 are satisfied.

58 Formula 24: Hc+>2Ms+j+ Medium No. that satisfies Formulas 22 to 24 at room temperature. 2nd of 3
The magnetization of the layer is determined by the old nj that satisfies Equation 20 immediately before recording.
, for example, it is aligned to "A direction" 9 (↑↓).

At this time, the first layer remains in the previous recording state (state 1
a or lb).

[“Reverse A direction” mark] [“A direction” mark]?
■ indicates a domain wall (the same applies hereafter).

This state 1aSlb is maintained until immediately before recording.

Here, the recording magnetic field (Hb) is applied in the ↓ direction.

Note that it is difficult to narrow down the recording magnetic field Hb to the same range as the laser beam irradiation area (spot area), as is the case with general magnetic fields. When the medium is in the form of a disk, the information (marks) once recorded will be replaced by the old nI. , the state becomes 1a and lb. Then, the mark is the area irradiated by the laser beam (
spot area). At this time, the marks in states la and lb are affected by the recording magnetic field Hb. At that time, if the direction of magnetization of the first layer of the mark in state 1a, which has magnetization in the opposite direction to Hb, is reversed by Hb, the information recorded just one rotation ago will be erased. The condition under which this should not occur is the following formula No. 25 of 2: σ W Hc+>Hb + 2Ms+t, and medium No. 3 satisfies this equation at room temperature.

Now, the marks in states 1a and lb finally reach the spot area of the laser beam. As with the basic invention, there are two types of laser beam intensity: low level and high level.

A low-temperature cycle low-level laser beam is irradiated, and the medium temperature quickly becomes TL. Then, σ1〉E1±2M,1・Hb−t+ (In the formula, σ is T c6m if Hini. is positive.
p. When l < T L, it is ten and T,. mp.
When l > T L, the relationship is 1), and H
In the presence of b↓, (1) state 1a where there is a domain wall is the first
The layers are inverted and the domain wall disappears, and (2) the state 1b where there is no domain wall remains as it is.

In this state, when the medium moves out of the spot area of the laser beam, the medium temperature begins to decrease and becomes state 2L, which leads to "direction A" 9.
mark formation is completed.

61 High-temperature cycle First, the medium temperature is brought to T by irradiating a high-level laser beam.
When raised to C+, the magnetization disappears (state 21+
).

? When the beam irradiation continues and the temperature of the medium reaches T■, TH becomes T of the second layer. Since it is approximately equal to r, its magnetization also almost disappears (state 3H).

? When the medium moves out of the laser beam spot area in state 3 (2), the medium temperature begins to decrease.

When the temperature of the medium drops slightly below T C 2, magnetization occurs in the second layer. In this case, ↓Hb causes magnetization of 8 (↓↑). However, since the temperature is still higher than To, 62, no magnetization appears in the first layer.

This state State 41.

? Furthermore, when the medium temperature decreases to slightly below Tc1, magnetization appears in the first layer as well. In this case, the magnetization of the second layer affects the first layer due to the exchange coupling force. As a result, a force acts to align the RE spins (top) and the TM spins (''').

In this case, the medium temperature is also T. . ■, 1 or more, so the TM spin is larger than the RE spin (4.7
). As a result, a magnetization of 9 appears in the second layer (shape @5
1-1).

From the temperature in this state 5H, the medium temperature further decreases to T,
. . ,, below, the magnitude relationship between the TM spin and RE spin in the first layer is reversed (↓↑1↓↑). Therefore, the magnetization of the first layer is reversed, and the magnetization becomes convex in the "reverse A direction" (state 61).

Then, the temperature of the medium eventually decreases from the salinity at state 6l+ to room temperature. Since Hc+ at room temperature is sufficiently large, the magnetization of the first layer is maintained stably.

In this way, the "reverse A direction" mark shape is completed.

/ Next, class 5 recording media (A type・■
Media No. belonging to quadrant/type 3). Taking 5 as an example,
The overwrite principle will be explained in detail.

This medium no. 5 is the following formula 3l TR < T . . ,,,1”6 T t < T o
The relationship is ≦TCI≦To2. For the purpose of simplifying the explanation, in the following explanation, T o < T c 1 <
7. Set it to 2. This relationship is shown in a graph as follows.

Coercive force T1 At room temperature TR, the magnetization of the first layer is lower than the initial auxiliary magnetic field old n1. The condition under which only the second layer is inverted without being inverted is Equation 32. This medium no. S satisfies Equation 32.

Formula 32 At this time, Hini. The conditional expression is shown in Equation 35.

When the old and old layers disappear, the magnetizations of the first and second layers are mutually influenced by the interfacial domain wall energy. Even so, the condition that the magnetization of the first layer and the second layer is maintained without reversal is expressed by formula 33.
~34. This medium no. 5 is formula 33-34
satisfy.

σ W 2Ms1t σ W Equation 34: Hc2> 2Ms+t+ The magnetization of the second layer of the recording medium that satisfies the conditions of Equations 32 to 34 at room temperature is expressed by Equation 352 Mst tr just before recording.
The old ni. which satisfies the condition of 2 Ms+t. For example, "A direction" 9 (↓
T). At this time, the first layer remains in the recorded state (state 1a or lb).

These states 1a and lb are maintained until immediately before recording.

It is assumed that the recording magnetic field Hb is applied in the "reverse A direction" ↓.

In addition, when the medium is disk-shaped, the conditions under which the previously recorded mark (especially the mark in state la where the first layer is in the opposite direction to Hb) must not be reversed by Hb when it approaches the Hb applying means are as follows. Equation 35-2: σ W Hb <Hc, -2 M. ．． t, and the disk medium must satisfy this condition at room temperature. Further, the condition under which the initialized second layer is not inverted by Hb when it approaches the Hb applying means is expressed by 3:σ W H b < H c2 2Ms2ta in the following equation 35. Conversely, one of the conditions for determining Hb is Equation 35-2 and Equation 35-3.

Now, the marks in states 1a and lb finally reach the spot area of the laser beam. There are two types of laser beam intensity: low level and high level.

Is the medium irradiated with a low-level laser beam in one low-temperature cycle? degree is T
When it rises to L, (7.>E, ±2Msl-Hb-t (in the formula, shi is T if Hin+. is negative).
When T1, it is 10 and T,. . , > TL), and in the presence of Hb↓, (1) state 1a where there was a domain wall changes to state 1a where the first layer is inverted and the domain wall disappears, and (2) there is no domain wall. The state 1b remains as it is.

In this state, when the medium moves out of the spot area of the laser beam, the medium temperature begins to decrease and becomes state 2, which is the "reverse A direction".
8 mark formation is completed.

When irradiated with a high-temperature cycle high-level laser beam, the medium? The temperature is T. (2) The temperature rises to higher than the sub-suburban temperature T1. As a result, there is no domain wall.

As the beam continues to irradiate, the medium temperature eventually reaches T. rise to Since TH is close to the Curie points of the first layer and the second layer, the coercive force of both layers becomes small. As a result, the medium is as follows (1
) to (3): (1) ? s+t+ Hc++Ms■tr Hc+and
Hb > (2) and (3) and Hb Hb Hb Hb > H c + > HC2- > H c > HC2+? s+ t + +MS+ t 2 σ W 2Ms+t σW 2Ms+t2 σ W 2Ms+t σW 2 Ms■t2 7n- is satisfied. Therefore, the magnetizations of both layers are reversed almost simultaneously and follow the direction of Hb. This is the shape D 2 1-1.

In this state 21, when the medium deviates from the spot 1 region of the laser beam, the medium temperature begins to decrease.

The medium temperature drops to T+am+. When it becomes 1 or less, the P type returns to the original A type. Then, the magnitude relationship between the intensities of the TM spin and RE spin in the first layer is reversed (↑Ko↑.). Therefore, the magnetization of the first layer is reversed, and the direction is "A".
The magnetization becomes 9 (state 3++).

Then, the temperature of the heated medium decreases from the temperature in state 4H to room temperature. H Cl at room temperature is sufficiently large that 4 σ W Hb <H in the following equation 35. Since 1+2Ms+t is satisfied, the magnetization of the first layer is stably maintained in state 3o.

In this way, the mark of the "A-oriented" meeting is stamped on the first layer.

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

[Example - Class 1] Using a ternary RF magnetron sputtering device,
TbFeCo alloy, DyTbFeCo as target
Place 2 pieces of alloy. And thickness 1.2mm, diameter 2
A 00 mm glass substrate is placed into the chamber of the apparatus.

The inside of the chamber of the device is once heated to 7 x 10' Torr.
After evacuating to the following degree of vacuum, Ar gas was
0-3 Torr will be introduced. Then, deposition
sputtering at a speed of about 2 A/sec.

First, a TbFeCo alloy was used as a substrate, and a thickness of 500 mm Tll++. +Fe+oCO+
．． A first layer (recording layer) is formed of a perpendicularly magnetized film of .

Next, while maintaining the vacuum state, target 1.? Gd
DY+ eTb with a thickness of 1700A was formed on the first layer by replacing it with TbFeCo alloy and sputtering in the same way.
Je4■CO3. A second layer (recording auxiliary layer) consisting of a perpendicularly magnetized film is formed.

In this way, class 1 (P type, 1st quadrant, type l
) Belonging to dual-layer magneto-optical recording medium No. 1 is produced.

The manufacturing conditions and characteristics of this medium are shown in Table 2 below. Ms
, He s σ. All values are at 25°C.

74 Table 2 [Comparative Example 1 - Class 8] Similarly to the example, class 8 (A type, quadrant 1,
A two-layer magneto-optical recording medium N (L8) belonging to type 2) is manufactured.

In Table 3, the values of Ms, He, and σ1 are all at 25°C.
This is the value at

Table 3 [Test Example 1] For the medium of the example and the medium of the comparative example, linear velocity v =
5. Rotate at 65 m/sec, increase the recording magnetic field Hb by 1000 e, and at each Hb, ``marks with a mark length of 0.75 μm'' previously formed (recorded) in a high temperature cycle are completely completed in a low temperature cycle. The minimum laser beam intensity required to completely erase the mark and (2) the minimum laser beam intensity necessary to form the mark using the Takaya cycle after complete erasing were measured.

The results are shown in FIG. In Figure 5, ■ indicates the former;
■ indicates the latter. As is clear from FIG. 5, in the medium of the example (solid line graph), the graphs ■ and ■ do not intersect, so the Hb can be set to 12000 e or more, and the margin is wide.

On the other hand, in the comparative example medium (broken line graph), the graphs ■ and ■ intersect at Hb = 5000e, and H
b must be less than 5000 e, and the margin is narrow.

[Test Example 2] (1) On the medium of the example and the medium of the comparative example, marks J with a mark length of 0.75 μm were intermittently recorded (recorded) on predetermined tracks in advance in a high temperature cycle.

(2) Next, for each medium, linear velocity v = 5. 65
Rotate at m/sec, recording magnetic field Hb = 300
A laser beam with an intensity of 1 mw was irradiated onto the "mark" under an application condition of 0e.

(3) For each medium, while changing the track, for each track, change the "mark" shape or (recording) described above (1) and increase the laser beam intensity by 0.1 mW (2
) Irradiation was repeated.

(4) Then, each "mark" was irradiated with a reproduction laser beam to measure the C/N ratio.

(5) The results are shown in FIG. In FIG. 6, when the laser beam intensity is low, the C/N ratio of the medium of the example (solid line graph) is constant at 47 dB, but at a certain value P.
From rs=2.2 mW, it started to decrease suddenly and Pce-3.
It becomes completely zero at 2mW. In other words, the difference (Pce-PrS) between the beam intensity Pce that is completely erased and the beam intensity Prs that starts erasing during playback is the I. OmW
be.

On the other hand, in the comparative example medium (dashed line graph), when the beam intensity is low, the C/N ratio is constant at <47 dB, but drops sharply below a certain value Prs = 2.0 mW. Initially, it becomes completely zero at Pce=3.2 mW. In other words, (PCe-PrS) is 1.2 mW.

From this, it can be understood that in the medium of the embodiment, there is less risk of marks (recordings) being erased even if the beam intensity is increased during reproduction, and therefore the C/N ratio is higher.

In fact, if we take safety into account and take a margin, in this case, 1 to 1
．． It is preferable to reproduce at 5 mW, but in that case,
In this example, the margin of 0.2 mW means that the laser beam intensity during reproduction can be increased by about 10 to 20%, and as a result, it is expected that the C/N ratio will improve by about 2 dB. Ru.

C Effects of the Invention] As described above, according to the present invention, ■ the margin of the recording magnetic field Hb is wide, and the design of the recording medium can be designed more freely;
In addition, (2) a high-intensity laser beam can be used during reproduction, and a higher C/N ratio can be obtained.

4

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing a longitudinal section of an overwritable magneto-optical recording medium according to an embodiment 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 conceptual diagram illustrating the main parts of the overwritable magneto-optical recording device according to the basic invention. 5-8 are graphs. [Explanation of symbols of main parts] Laser beam linearly polarized light Hi-1 with magnetization in the “A direction” Bit recording layer (first layer) with “reverse A direction” magnetization Recording auxiliary layer (second layer) Substrate overwritable Rotating means for rotating the magneto-optical recording medium recording medium Initial auxiliary magnetic field old n1. Applying means Laser beam light source According to the recorded binary information, the beam intensity is 8l degrees.
(2) a high level that provides the medium with a temperature suitable for controlling one of the bits with magnetization; and (2) a low level that provides the medium with a temperature suitable for controlling the other bit. A modulation means that modulates the recording magnetic field Hb in a pulsed manner between

Claims (1)

[Claims] At least a first layer (recording layer) and a second layer (auxiliary layer) are laminated, and the direction of magnetization of the second layer can be changed for recording without reversing the direction of magnetization of the first layer. In a magneto-optical recording medium that can be overwritten by aligning the direction of magnetization to either upward or downward immediately before the recording, and modulating the light beam according to the information without modulating the recording magnetic field, One layer has a compensation temperature T_c_o_m_p_. between room temperature and the Curie point T_c_1. _1, and η defined below is the temperature T_L at which the low-temperature process occurs.
200 (unit: Oe/°C) or more. (Note) η=d/dT | H_c_o_p_y | (T is medium temperature)
H_c_o_p_y=H_c_1(1-σ_W/E_1
)E_1=2・M_S_1・H_c_1・t_1 (unit: erg/cm^2) [M_S_1: Saturation magnetization (Gauss) of the I-th layer (recording layer) H_c_1: Coercive force (Oe) of the I-th layer (recording layer) t_1: Thickness (cm) of the first layer (recording layer)] σ_W is the domain wall energy (unit: erg/cm^2) that is generated or destroyed as the magnetization of the first layer (recording layer) is reversed. It is.