JPH01199341A - Overwritable magneto-optical recording medium which is controlled on overall exchange power between magnetic layers - Google Patents

Abstract

PURPOSE:To enable overwriting without increasing the film thickness over the entire part by adding a nonmagnetic element to the layer which has the smaller product of the magnetic saturation moment (Ms) and coercive force (Hc), of the 1st and 2nd layers, thereby controlling the exchange bonding force acting between the magnetic layers. CONSTITUTION:The nonmagnetic element is added to the layer which has the smaller Hc.Ms product, of a 1st layer and the 2nd layer 2, by which the exchange coupling force sigma2 is controlled to a prescribed value and the overwritable magneto-optical recording medium having the decreased total film thickness t12 is formed. Namely, there is substantially no increase in sigmaw/HcMs when the nonmagnetic element is added to the layer having the smaller Hc.Ms product before the addition of the nonmagnetic element of the 1st layer 1 and the 2nd layer 2. Although the film thickness (t) of the layer added with said element cannot be reduced, the Hc.Ms product of the layer not added with said element does not change in spite of a decrease in the sigmaw, and therefore, the film thickness (t) can be decreased. The total film thickness t12 is eventu ally decreased as compared with the total thickness before the addition.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an overwritable magneto-optical recording medium in which the exchange coupling force between magnetic layers is controlled.

[Conventional technology]

Recently, efforts have been made to develop optical recording and reproducing methods, recording devices, reproducing devices, and recording media used therein that satisfy various requirements including high density, large capacity, high access speed, and high recording and reproducing speed. Efforts are being made.

Among a wide range of optical recording and reproducing methods, magneto-optical recording and reproducing methods have the greatest appeal due to the unique advantage that information can be erased after being used and new information can be recorded. full of.

The recording medium used in this magneto-optical recording and reproducing method has one or multiple perpendicular magnetization films as a recording layer.
cular magnetic 1ayer or l
ayers). This magnetized film is made of, for example, amorphous GdFe, GdCo, GdFeCo, TbF.
It consists of TbCo, TbPeCo, etc. The recording layer generally has concentric or spiral cane tracks on which information is recorded. Here, in this specification, either "upward J" or "downhard J" is applied to the membrane surface.
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 (B1) with magnetization in the "A direction" and a bit (B,) with magnetization in the "reverse A direction". recorded.

These bits Bt and B* correspond to one and the other of 1.0 of the digital signal, respectively. However, in general, the magnetization of the trailing edge to be recorded is aligned in the "reverse A direction" by applying a strong external magnetic field before recording.

This process is called initialize. Then, a bit (B1) having magnetization in the "A direction" is formed on the trunk. Information is recorded by the presence or absence of this bit CB+) and/or bit length.

Danyujo Seishoko Zahori: In the formation of the bit, the characteristics of the laser, namely its excellent spatial and temporal coherence, are used to advantage, and the diffraction limit, which is determined by the wavelength of the laser light, is almost reached. The beam is narrowed down to an equally small spot. The focused light is irradiated onto the track surface,
Information is recorded by forming bits with a diameter of 1 μm or less in the recording/reproducing layer. In optical recording, recording densities of up to about 10@bit/- can theoretically be achieved. This is because the laser beam condenses into a spot with a diameter almost as small as its wavelength (
This is because it is possible to concen- trate).

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 Hc (co
ersivity) decreases and becomes smaller than the recording magnetic field (Hb). As a result, the magnetization of that part is changed by the recording magnetic field (Hb
), thus forming oppositely magnetized bits.

Ferromagnetic materials and ferrimagnetic materials have different magnetization and temperature dependence of 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.
, where the magnetization (M) becomes zero. Conversely, Hc becomes extremely large near this temperature, and as the temperature deviates from this temperature, Hc drops rapidly. This decreased Hc is
It is overcome by the relatively weak recording magnetic field (Hb).

In other words, recording becomes possible. This recording process is T c
It is called ll@#+ 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, at a predetermined temperature higher than room temperature, a recording magnetic field (Hb) that can overcome the reduced Hc for a magnetic material having a reduced Hc.
Recording is possible by applying .

Figure 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. When the light is converted into linearly polarized light (L, ) and irradiated onto the recording layer (1), the light is either reflected on its surface or
).

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 plane of polarization of the reflected light is rotated by θ degrees for "A direction" magnetization, it is rotated by 10 degrees for "reverse A direction" magnetization. Therefore, the optical analyzer (polarizer)
If the axis of is set perpendicular to a plane tilted to one degree, then
The light reflected from the bit (B,) magnetized in the "reverse A direction" cannot pass through the analyzer, whereas the light reflected from the bit (B1) magnetized in the "A direction" is ( The amount multiplied by sin2θk) wealth passes through the analyzer and is captured by the detector (photoelectric conversion means). As a result, the bit (B1) is magnetized in the “A direction”
appears brighter than the bit (Bo) 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 played.

By the way, conventionally, one magnetic material has been developed that has a low Curie point, allows for good recording, has a high coercive force, has high storage stability, and has a large θk and a high C/N ratio during reproduction (reading). Therefore, a multilayer magneto-optical recording medium was proposed in which the necessary functions were separated and two different magnetic materials were laminated (Japanese Patent Application Laid-open No. 78652/1983). It consists of a two-layer film consisting of a high coercive force layer with a low Curie point and a low coercive force layer with a high Curie point that can be perpendicularly magnetized, and the high coercive force layer and the low coercive force layer are exchange-coupled with each other. . Therefore, information is recorded and stored using a high coercive force layer with a low Kyrie point.
Since the recorded information is transferred to the low coercive force layer, the information is read out in the low coercive force layer which has a high Curie point and a large θ. The layer is a recording auxiliary layer, and the exchange coupling force σ of both layers is σ. Then, a multilayer magneto-optical recording medium that could be overwritten only by optical modulation using differences in the Curie point and coercive force was invented and a patent application was filed (Japanese Patent Application Laid-open No. 175948/1983). I quote, ``I pray.'' In addition, in the specification of the prior application, the exchange coupling force σ. is called the interfacial domain wall energy.

[Explanation of the prior invention]

The overwrite of the prior invention modulates only the light and does not modulate the recording magnetic field. It is difficult to modulate magnetic fields at high speeds. That is, the laser beam used for recording is modulated in a pulsed manner 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, TIIE B
ELLSYSTEM TECHNICAL J
OURNAL, Vol. 62 (1983).

1923-1936.

One of the characteristics of the overwriting of the prior invention is the high and low levels of beam intensity.

That is, when the beam intensity is at a high level, the recording magnetic field (Hb)
The “A direction” magnetization of the recording auxiliary layer (second layer) is changed to “reverse A” by
In order to reverse the direction of this second layer,
A bit having "reverse A direction" magnetization [or "A direction" magnetization] is formed in the recording layer (first layer) by the "reverse A direction" magnetization. When the beam intensity is at a low level, the "A direction" magnetization of the recording auxiliary layer causes the recording/reproducing layer to have "A direction" magnetization [or "
A bit with magnetization in the reverse A direction is formed. The beams are ``two beams in close proximity'', and the leading beam is lit at a low level and is not modulated in principle, thereby always forming a bip in the opposite A direction [or in the A direction]. The previous information is erased. □ The trailing beam is then pulse modulated between the high level and a base level (including zero level) equal to or lower than the lower level, according to the information. It is also possible to form a bip in the direction of A (or in the opposite direction of A) only when the signal is at the level, and record it accordingly.

Example of beam intensity information number 111001111000 In any case, if the necessary high level, low level, and base level are given, the beam Adjust the strength as above (
Modulation is easy for those skilled in the art.

Note that, herein, "A direction" means either upward or downward with respect to the magnetic layer, and the other direction is referred to as "reverse A direction."

Also, here, the expression ΔΔΔ is
When you read OOO outside [] first, the following
Even when ΔΔΔ], we will read OOO outside []. On the other hand, if you select Δ△Δ in [ ] without reading 000 first, you will get the following ΩΩΩA
Also, when grave △ΔΔ], do not read 000 and read ΔΔ in []
Δ shall be read.

Such an overwritable medium is composed of two magnetic layers each having perpendicular magnetic anisotropy, the first layer being a recording layer and the second layer being a recording auxiliary layer.

The medium is roughly divided into a first embodiment a and a second embodiment.

In either embodiment, the recording medium has a personnel structure, which is divided into the following:

The first layer is a recording and reproducing layer that has a high coercive force and a low magnetization reversal temperature at room temperature. The second layer is a recording auxiliary layer having a relatively low coercive force at room temperature (high magnetization reversal temperature) compared to the first layer. Both layers are made of perpendicular magnetization films.

Note that both the first layer and the second layer may themselves be composed of yarn NB.

In the first embodiment, the coercive force of the first layer is HC, that of the second layer is Ict, the Curie point of the first layer is T, that of the second layer is Tea, the room temperature is T1, and a low-level laser is used. The temperature of the recording medium when the beam is irradiated is TL%.If a high-level laser beam is irradiated, TH1 is the coupling magnetic field received by the first layer as Ho, and the coupling magnetic field received by the second layer is H□. The recording medium satisfies the following formula 1 and satisfies formulas 2 to 5 at room temperature.

T11 <Tcr4Tt < TC! 47M-
・・−・=−−−−−−Formula lHc+ > Hc**
l Hot + Howl・−・・・・・・・−・−・−
・−・Formula 2Hc+>H□ ・−・−・−・・−・・
・・−・・−・・・・・・・・−・・−・・−・−
−−−−・−・・・Formula 3Hct>H□・・−・−・
・・−・・・・−・−・−・・・−・−・−・・Listen to the song・
-Curved surface formula 4Hcs+H*t<Hini, l<H
c+ +-H+u-” Conversion 5 In the above formula, the symbol “~” is
In the above formula, the upper row represents A (antip
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.

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.

TL TM Therefore, the initial auxiliary magnetic field (old ni,
), according to Equation 5, only the magnetization of the second layer is reversed without reversing the direction of magnetization of the first layer. Therefore, when an initial auxiliary magnetic field (Hini, ) is applied to the medium before recording, only the second layer is moved in the "A direction". ``Reverse A''
It can be magnetized in the □ direction, which is indicated by a downward blank number. And old n1. Even if becomes zero, according to equation 4,
The magnetization function of the second layer is not reversed again but is maintained as it is.

The following is a conceptual representation of the state in which only the second layer is magnetized in the A-direction j direction by the initial auxiliary magnetic field (formerly ni) until just before recording.

Here, the magnetization direction 1 in the first layer represents the information that has been recorded up to that point.In the following explanation, the direction is unrelated, so it will be indicated by X below, and the above table can be simplified. Therefore, it is expressed as follows.

Here, a high-level laser beam is irradiated to raise the medium temperature to T. Then, since T and I are higher in temperature than the Curie point TCI, the magnetization of the first layer disappears.Furthermore, since T is near the Curie point Tc8, the magnetization of the second layer also completely or almost disappears. Here, a recording magnetic field (Hb) in the "A direction" or "inverse A direction" is applied depending on the type of medium. The recording magnetic field (Hb) may be a stray magnetic field from the medium itself.

To simplify the explanation, the recording magnetic field (Hb
) is applied. Since the medium is moving, the irradiated area quickly moves away from the laser beam and is cooled by air. 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 2N).

Then, when the cooling progresses further and the medium temperature drops slightly below Tcl, 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. The result is 8 (for P type media) or 9 (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 T. Since TL is near the Chierie point 'rc+, the magnetization of the first layer disappears completely or almost completely, but since the temperature is lower than the Curie point TCI, the magnetization of the second layer does not disappear.

Here, the recording magnetic field (Hb) is unnecessary, but it is impossible to turn Hb on and off at high speed (for a short time). Therefore, it is unavoidably left as it is during the high temperature cycle.

However, since Hcm still remains large, the magnetization of the second layer is not reversed by Hb.Since the medium is moving, the irradiated area quickly moves away from the laser beam and is cooled by air. As cooling progresses, the first
The magnetization of the layer appears.

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, by the medium?
(for P type) or 8 (for A type) magnetization appears. 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 magnetization of the first layer, a bit having magnetization points or 8 in opposite directions is formed by the high temperature cycle and the low temperature cycle. 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.

Incidentally, the recording medium is generally disk-shaped, and the medium is rotated during recording. Therefore, the recorded part (bit)
is again acted upon by the old ni during one rotation, and as a result, the magnetization of the second layer is aligned to the original "A direction" charge. However, at room temperature, the magnetization of the second layer does not affect the first layer, so recorded information is retained.

Therefore, if the first layer is irradiated with linearly polarized light, the reflected light contains information, so information is reproduced in the same way as in conventional magneto-optical recording media.

The perpendicular magnetization films constituting the first layer and the second layer are as follows:
The material is selected from the group consisting of (1) ferromagnetic materials and ferrimagnetic materials that have a Curie point but no compensation temperature, and (2) amorphous or crystalline ferrimagnetic materials that have both a compensation temperature and a Curie point.

The above description is of the first embodiment using Curie points. In contrast, the second embodiment utilizes reduced Hc at a predetermined temperature higher than room temperature. The second embodiment uses the temperature T□ at which the first layer is magnetically coupled to the second layer instead of Tcl in the first embodiment, and the temperature Tst at which the second N is reversed by Hb instead of Tc.
If this is used, the explanation will be similar to the first embodiment.

In the second implementation Jldl, the coercive force of the first layer is )Ic+, that of the second layer is Ho, the temperature at which the first layer is magnetically coupled to the second layer is T□, and the magnetization of the second layer is TI is the temperature at which Hb reverses, TI is the room temperature, TL is the temperature of the medium when irradiated with a low-level laser beam, TI is the temperature when irradiated with a high-level laser beam, and is the coupling magnetic field received by the first layer. Ha+, and when the coupling magnetic field received by the second layer is Hllll, the recording medium satisfies the following formula 6 and satisfies formulas 7 to 1 at room temperature.
It satisfies 0.

T * < T * + w; T L < T 64
T N ---------Formula 6Hc+ > Hc
m + l Hat 'i'' Hcx l =-・-・
=−−−−−=Formula 7Hc+ > Hs+ ・・・−・
・・・－・・・・・・・・・・・・・・・・・・・・・
・−・・−・−・・・・−・・・Formula 8HC! ＞
HD! −・−・−・・−・−・・−・・−・・・・
−・・−・・−・・−・−・・−・・−・・Formula 91 (cz+) (at < l old ni, l < Hct±
H111'-""Formula 10 In the above formula, the upper row is A (antiparallel), which will be described later.
This is the case for media of type P (pa
(rallel) type media.

In both the first and second embodiments, both the first layer and the second layer are transition metal (e.g. Fe, Co)-heavy rare earth metal (e.g. G
The recording medium is preferably an amorphous ferrimagnetic material selected from the alloy composition (d+ Tb, Dy, etc.).

Both the first and second layers are made of transition metals - heavy rare earth metals.
l) When selected based on alloy composition, the direction and magnitude of magnetization appearing externally as each alloy are the same as the direction and magnitude of spin of transition metal atoms (hereinafter abbreviated as TM) inside the alloy. 0 determined by the relationship with the spin direction and size of heavy rare earth metal atoms (hereinafter abbreviated as RE). For example, the direction and size of the spin of TM are represented by the dotted line vector ↑, and that of the RE spin is represented by the solid line vector ↑ Represented by
Is the direction and magnitude of magnetization of the entire alloy a double solid line vector? In this case, the vector function is expressed as the sum of vector ↑ and vector ↑. However, among alloys, 7
Due to the interaction between M spin and RE spin, the vector ↑
and vector ↑ are always opposite in direction. Therefore, the sum of self and ↑ or the sum of ↓ and ↑ is that when the strengths of both are equal, the vector of the alloy becomes zero (that is, the magnitude of magnetization appearing externally is zero), and when it becomes zero, The alloy composition of
position). For other compositions, the alloy has a strength equal to the difference in strength between the two spins,
The magnetization of a vector with a vector (original or 8) having a direction equal to the direction of the larger vector appears on the outside. For example, ↑↓ becomes electric, and ↑↓ becomes 8.

When the intensity of each vector of 7M spin and RE spin of a certain alloy composition is large, the alloy composition is
Take the name of the spin with the higher intensity and use OO rich for example R
It is called E Lynch.

For both the first and second layers, the 7M-rich composition and R
E-rich composition. Therefore, if the 1N composition is plotted on the vertical axis and the 2N composition is plotted on the horizontal axis, the types of the medium as a whole 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 rich (171st) 7M rich (1st 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 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 the compensation temperature (Tc,
) is called.

No compensation temperature exists between room temperature and the Curie point for the 7M rich alloy composition. 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.

Classifying the presence or absence of compensation temperature in the first and second layers,
Media are classified into four types. The medium in the first quadrant is
Includes all four types. Regarding the four types,
Draw a ``graph representing the relationship between coercive force and temperature'' as shown below.The thin line is that of the first layer, and the thick line is that of the second layer.

Coercive force Coercive force, L' - Coercive force Coercive force Here, whether RE rich or T for both the first layer and the second layer
Recording media can be classified into the following nine classes by dividing them by whether they have temperature compensation or not.

Table 1 Table 1 (continued) Here, the class 1 recording media shown in Table 1 (P type
(2) The principle of overwriting will be explained in detail by taking as an example a specific medium Nll belonging to quadrant type l).

This medium-1 has the following formula: T@< Tc+es*, I< Tc+ #TL #
Tcoap, z < T ct part T.

have the following relationship. This relationship is shown in 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.
Shows a graph of layers.

T8゜＠In　　T　t29.2 At room temperature T3, the magnetization of the first layer is the same as the initial auxiliary magnetic field.

The condition that only the second layer is inverted without being inverted is given by Equation 12
It is. This medium 11m1 satisfies Equation 12.

Formula 12: % Formula % However, MCI: Coercive force of the first layer 1 (ct: Coercive force of the second layer M3.: Saturation magnetic moment of the first layer
n) Mo: saturation magnetic moment t of second layer: 111th film thickness 1, + second layer film thickness σ1; interfacial domain wall energy (exchange coupling force) (inter
face wall energy) At this time, R
The conditional expression for ial is shown in Equation 15.

Old n1. When the magnetization disappears, the reversed magnetization of the second layer is influenced by the magnetization of the first layer due to exchange coupling force. Still the second
The conditions under which the magnetization of the layer is maintained without reversing are expressed by Equation 13~
14. This medium storm seal satisfies 213-14.

σ− 'l　M、、　t　.

σ- Equation 14: Hc〉□ 2 M■t Equation 15: %Equation % The magnetization of the second layer of the recording medium that satisfies the conditions of Equations 12 to 14 at room temperature satisfies the conditions of Equation 15 immediately before recording. H that satisfies
Ini, for example, the JT for A is aligned (↑↓). At this time, the first layer remains in the recording state (state
).

This state l is maintained until immediately before recording. Here, the recording magnetic field (Hb) is applied in the ↑ direction.

□High-temperature cycle□ Then, when the medium temperature is raised to TL by irradiation with a high-level laser beam, TL becomes the Curie point Tc of the first layer.
Since it is almost equal to I, its magnetization disappears (state 2.)
.

If the irradiation continues further, the temperature of the medium further increases. When the temperature of the medium becomes a little higher than T e O @ e H1 of the second layer, the direction of each spin of RE%TM does not change, but the strength relationship is reversed (↑↓−↑↓)
, Therefore, the magnetization of the second layer is reversed and becomes magnetized in the "reverse A direction" (state 3H).

However, at this temperature) fct is still large, so ↑H
The magnetization of the second layer is not reversed by b. When the temperature further increases and reaches TH, the temperature of the second layer almost reaches the Curie point T'ct, and its magnetization also disappears (54
11>.

When the medium moves out of the laser beam spot area in this state a4II, the temperature of the medium begins to decrease.

When the temperature of the medium drops slightly below To, magnetization occurs at the 211th point. In this case, by ↑Hb? (↓゛) magnetization occurs (like Li5.I), but since the temperature is still higher than Tcl, no magnetization appears in the first layer.

When the temperature of the medium further decreases to below TC6m, 1, the directions of the RE and TM spins do not change, but the magnitude relationship of the intensities reverses (,↑-↓↑).

As a result, the magnetization of the entire alloy is reversed and ? Then, the state changes to "reverse A direction" 8 (state 6N).

In this state a 6 II, the temperature of the medium is higher than T,1, so the magnetization of the first layer remains extinguished. Also, Hc at that temperature! is large, so the magnetization 6 of the second layer is ↑Hb
It will not be reversed.

Then, when the temperature decreases further and falls slightly below TCI,
Magnetization appears in the first layer. At that time, the exchange coupling force from the second layer acts to align the RE spins (↓) and the TM spins (↑), and the temperature of the first layer is T e 6
Since @e is 7 or more, the 7M spin is larger, and therefore, ↑, that is, the previous magnetization appears in the first layer. This state is state 7N.

When the temperature of the medium further decreases from the temperature at this state ML and becomes below T eamp, +, a reversal occurs in the magnitude relationship between the intensities of the 1N RE spin and the 7M spin ( ↓
↑→↓↑ ), as a result, magnetization of 8 appears (state 8
N).

Then, the temperature of the medium eventually decreases from the temperature in state 8H to room temperature. Since I(c+ at room temperature is sufficiently large, the magnetization of the first layer is not reversed by ↑Hb,
The state ML is maintained. In this way, the bit formation for the "reverse A direction" is completed.

□Low-temperature cycle□ On the other hand, a low-level laser beam is irradiated to raise the medium temperature to TL. Then, since TL is almost equal to the Curie point T'c+ of the first layer, its magnetization disappears (
&2L) @ When the medium moves out of the laser beam spot area in this state 2L, the medium temperature starts to decrease.

When the medium temperature drops slightly below the TCI, the RE of the second layer.

The influence of the 7M spin (↑-) extends to each spin in the first layer due to the exchange coupling force, that is, the RE spins (↑) and T
A force acts to align the M spins (4>).

As a result, the first layer has a magnetization of ↑↓, that is, 8, in the recording magnetic field ↑
It emerges by overcoming I(b) (state 13t >, and the temperature in this state is T CO @ +++ 1 or higher, so the 7M spin is larger.

When the medium temperature is further cooled below Tcoae, the magnitude relationship between the RE spin and 7M spin of the first layer is reversed (↑↓−↑↓), similar to the high temperature cycle. As a result, the magnetization of the first layer becomes uniform (shape B 4 L).

This state 4L is maintained even if the medium temperature drops to room temperature. As a result, the bit formation for "A direction" ↑ is completed.

Next, taking as an example the specific media portion 2 belonging to the class 2 recording medium (P type, summer quadrant, type 2) shown in Table 1,
The principle of overwriting will be explained in detail.

This medium 11h2 has the relationship of the following formula 16: % formula %. This relationship can be shown graphically as follows (
Become.

TL Tcase, t 7w At room temperature Tl1l, the magnetization of the first layer is the initial auxiliary magnetic field old ni.

The conditions for only the magnetization of the second layer to be reversed without being reversed are as follows.
This is equation 17. This medium Na2 satisfies Equation 17.
Formula 17: % Formula % where Hcl: coercive force of the first layer HC8F coercive force of the second layer Ml,: saturation magnetic moment of the first layer Mo: saturation magnetic moment of the second layer t1: film thickness of the first layer t8: Film thickness of the second layer σ,: Interfacial domain wall energy At this time, the conditional expression for old ni is expressed by Equation 20.

When Min+ disappears, the reversed magnetization of the second layer is influenced by the magnetization of the first layer due to exchange coupling force. Even so, the conditions under which the magnetization of the second layer is maintained without being reversed again are expressed by formula 18.
~19. This medium 11h2 satisfies Equations 18-19.

Equation 18: Hcl>□ 2Ms+t+ σ- Equation 19: Hcm >□ 2Ms wealth Equation 20: %Equation % The magnetization of the second layer of the recording medium that satisfies the conditions of Equations 17 to 19 at room temperature is maintained until just before recording. H that satisfies the condition of Equation 20
Ini, for example, it is aligned to the "A-oriented" official (↑↓). At this time, the first layer remains in the recording state (state l
).

This state 1 is maintained until immediately before recording. Here, the recording magnetic field (Hb'') is applied in the direction of ↑.

□High-temperature cycle□ Then, when the medium temperature is raised to TL by irradiation with a high-level laser beam, TL becomes the Curie point Tc of the first layer.
Since it is almost equal to I, its magnetization disappears (shape 11ii
2M) - If the irradiation continues further, the temperature of the medium further increases. The temperature of the medium is 2N Tcosp+! When the temperature rises to a slightly higher temperature, the direction of each spin in RESTM does not change, but the strength relationship is reversed (↑↓−↑↓).As a result, the magnetization of the entire alloy is reversed, resulting in the "reverse A direction" The magnetization becomes 8 (state 3N).

However, at this temperature, the Hc dew is still large, so ↑Hb
The magnetization of the second layer is not reversed by the temperature rise further and when it reaches TM, the temperature of the second layer almost reaches the Curie point TCt and its magnetization disappears (state 4°).
.

When the medium moves out of the laser beam spot area in this fourth layer, the temperature of the medium begins to decrease.

When the temperature of the medium drops slightly below To, magnetization occurs in the second layer. In this case, magnetization of electricity (↓↑) occurs due to ↑Hb. However, since the temperature is still higher than Tcl, no magnetization appears in the first layer, and this state is state 5. It is l.

Then, the temperature of the medium further decreases to T. 1. ,! Below, the direction of each spin of RESTM does not change, but the strength relationship is reversed (,7-↓↑).

As a result, the magnetization of the entire alloy is reversed and the magnetization changes from electric to "reverse A direction" (state 6D).

In this state C++, the temperature of the medium is higher than the TCI, so the magnetization of the first layer remains extinguished. Furthermore, since Ic1 (at that temperature) is large, the magnetization of the second layer is not reversed at ↑Hb.

Then, when the temperature further decreases to a little below T'c+, magnetization appears in the first layer. At that time, the exchange coupling force from the second N is between the RE spins (↓) and between the TM spins (↑)
Therefore, in the first layer there are ↓↑, that is, 8
magnetization appears. Is this state a state? It is #+.

Then, the temperature of the medium eventually decreases from the temperature in state 7E to room temperature. Since H(1) at room temperature is sufficiently large, the magnetization of the first layer is not reversed by ↑Hb, and state 7E is maintained. In this way, the bit formation in the "reverse A direction" is completed.

□Low-temperature cycle□ On the other hand, a low-level laser beam is irradiated to raise the medium temperature to TL. Then, since T is almost equal to the Curie point Tel of the first layer, its magnetization disappears (shape Jli2L) - When the medium temperature moves out of the laser beam spot area in this shape J[L, the medium temperature starts to decrease. .

When the medium temperature drops slightly below T'ct, the RE of the second FJ
.

The influence of the 7M spins (↑↓) extends to each spin in the first layer due to exchange coupling force, that is, the RE spins (↑) and T
The force that aligns the M spins works.

As a result, ↑↓, that is, magnetization t appears in the first layer (
Condition B3t) - This condition M3L does not change even if the medium temperature further decreases.
As a result, an "A-oriented" bit is formed in the first layer.

Next, class 3 recording media (P type, ■
The principle of overwriting will be explained in detail by taking as an example a specific medium 11h3 belonging to quadrant type 3).

This medium-3 has the relationship of the following formula 21: % formula %. This relationship is shown in a graph as follows.

TCllllll, lTL TN room temperature T,
The magnetization of the first layer is the initial auxiliary magnetic field old ni.

The condition that only the second layer is inverted without being inverted is given by Equation 22
It is. This medium volume 3 satisfies Equation 22.

Formula 22: %formula% However, Hc+: Coercive force of the first layer HH: Coercive force of second layer M＊+: Saturation magnetic moment of the first layer M,, + saturation magnetic moment of second layer t1: Film thickness of the first layer Wealth: Film thickness of the second layer σw: Interface domain wall energy At this time, the conditional expression for Hint is shown by Expression 25.

If the old ni is null (then the reversed magnetization of the second layer is influenced by the magnetization of the first layer due to the exchange coupling force.
The conditions under which the magnetization of the layer is maintained without reversing are expressed by Equation 23~
24. This medium-3 satisfies Equations 23 and 24.

Equation 23: H,, > − 2M□t1 Equation 24: HCI> − 2M3 suffix Equation 25: %Equation % The magnetization of the second layer of the recording medium that satisfies the conditions of Equations 22 to 24 at room temperature is With the old ni that satisfies the condition of Equation 25 just before, it is aligned to, for example, "A direction J Ii (T,). At this time, the first layer remains in the recorded state (state 1).

This state Ml is maintained until immediately before recording. Here,
! The magnetic field (Hb) is applied in the ↓ direction.

□High-temperature cycle□ Then, when the medium temperature is raised to TL by irradiation with a high-level laser beam, TL becomes the Curie point T' of the first layer.
Since it is almost equal to c+, its magnetization disappears (at 1 m
2m) - When the beam irradiation continues and the temperature of the medium reaches T, I, the magnetization also disappears (Li5N-like) since T is approximately equal to Tel of the second layer.

This state 3. The medium temperature begins to decrease when the medium moves out of the laser beam spot area.

When the temperature of the medium drops slightly below Tc, magnetization occurs in the second layer. In this case, ↓Hb causes magnetization of 8 (↓↑). However, since the temperature is still higher than TCI, no magnetization appears in the first layer, and this state is 84N.

Furthermore, when the medium temperature decreases to a little below Tcl, magnetization appears in the first layer as well. In this case, the magnetization of the second layer extends to the first layer due to exchange coupling force. As a result, a force acts to align the RE spins (↓) and the TM spins (↑). In this case, the medium temperature is still Te ( Since it is above 1SP+1, the 7M spin is larger than the RE spin (, i
), as a result, official magnetization appears in the second layer (state 5
M).

From the temperature in this state 5H, the medium temperature further decreases to T
cost, + or less, the 7M spin of the first layer and RE
The magnitude relationship of the spin intensities is reversed (,↑−↓↑), so the magnetization of the first layer is reversed and becomes magnetized in the “reverse A direction” 8 (shape M 6 N ).

Then, the temperature of the medium eventually reaches Li6. The temperature decreases from I to room temperature. Since the HCI at room temperature is sufficiently large, the magnetization of the first layer is maintained stably.

In this way, the bit formation for the "reverse A direction" is completed.

□Low-temperature cycle□ On the other hand, a low-level laser beam is irradiated to raise the medium temperature to TL. Then, since TL is approximately equal to the Curie point Tel of the first layer, its magnetization disappears. However, at this temperature, the second layer of Hc! is large, so
Its magnetization is not reversed by ↓Hb (state 2L).

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

When the medium temperature drops slightly below the TCI, the RE of the second layer.

The influence of the 7M spin < T = > becomes the first due to the exchange coupling force.
It extends to each spin of the layer, that is, between RE spins (↑),
A force acts to align the TM spins (↓).

As a result, a magnetization of ↑↓, that is, 6, appears in the first layer.

In this case, since the temperature is T well@1.1 or higher, the 7M spin is larger (state 3L).

When the medium temperature further cools below T C6@p+ +, the magnitude relationship between the RE spin and 7M spin of the first layer is reversed (↑↓−↑↓), as in the high temperature cycle, and as a result,
The magnetization of the first layer overcomes ↓Hb and becomes t (state 4.
).

This state of 7Li 4 t is maintained even when the medium temperature drops to room temperature. As a result, bit formation for "A direction" t is completed.

Next, class 4 recording media (P type, ■
The principle of overwriting will be explained in detail by taking as an example a specific medium Na4 belonging to quadrant type 4).

This medium portion 4 has the relationship of the following formula 26: % formula %. This relationship is shown in a graph as follows.

T L T N At room temperature T, the magnetization of the first layer is the initial auxiliary magnetic field old ni.

The condition that only the second layer is inverted without being inverted is expressed by Equation 27.
It is. This medium-4 satisfies Equation 27.

Formula 27: % Formula % Where, Hcl: Coercive force of the first layer Hcm: Coercive force M of the second layer, ,: Saturation magnetic moment of the first layer M■: Saturation magnetic moment of the second layer 1, +1st Thickness of layer t8: Thickness of second Ji σw: Interfacial domain wall energy In this case, the conditional expression of 1lini is expressed by Equation 30.

When Hini disappears, the reversed magnetization of the second layer is influenced by the magnetization of the first layer due to exchange coupling force. Even so, the conditions under which the magnetization of the second layer is maintained without being reversed again are expressed by formula 28.
~29. This medium magnet 4 satisfies Equations 28-29.

σ- Equation 211 Hcl>□ 2M1t+ Equation 29: Hcx>□ 2Msgj Equation 30: % Equation % The magnetization of the second layer of a recording medium that satisfies the conditions of Equations 27 to 29 at room temperature is expressed by Equation 30 immediately before recording. For example, the old ni that satisfies the condition ``A-oriented'' (↑↓) can be aligned. At this time, the first layer remains in the recorded state (state 1)
.

This situation! a1 is held until just before recording. Here, the recording magnetic field (Wb) is applied in the ↓ direction.

□High-temperature cycle□ Then, when the medium temperature is raised to TL by irradiation with a high-level laser beam, TL becomes the Curie point Tc of the first layer.
Since it is almost equal to t, its magnetization disappears (like Jli2
m)- As the beam irradiation continues, the medium temperature further increases to T, l, and since the temperature T, l of the second layer is approximately equal to the Curie point Tcff1, its magnetization also disappears. This is condition a3.
It is I.

When the medium moves out of the laser beam spot area in state 3II, the temperature of the medium begins to decrease.

When the temperature of the medium drops slightly below the Tc atmosphere, magnetization of the second layer appears. In this case, magnetization of 8 (↓↑) appears due to ↓Hb. However, since the temperature is higher than TCI, no magnetization appears in the first layer, and this state is state 4N.

Then, when the medium temperature decreases further and becomes slightly lower than the TCI, magnetization appears in the first layer. At that time, the exchange coupling force from the second layer is between RE spins (↓) and between TM spins (↑
), so a magnetization of ↓↑, that is, 8, appears in the first layer. This state is state 5H.

Then, the temperature of the medium eventually reaches state 5. The temperature decreases from the temperature at 1 to room temperature. Since Hcl at room temperature is sufficiently large, the magnetization of the first layer is maintained stably.

In this way, the bit formation for the "reverse A direction" is completed.

□Low-temperature cycle□ On the other hand, a low-level laser beam is irradiated to raise the medium temperature to TL. Then, since T exceeds the Curie point Tel of the first layer, its magnetization disappears. In this state, Ho is still sufficiently large, so the magnetization type of the second layer will not be reversed by ↓Hb, and this state is state 2.
It is L.

In this state 2L, when the medium moves out of the laser beam spot area, the medium temperature begins to decrease.

When the medium temperature drops slightly below TcI, the RE of the second layer.

The influence of the 7M spins (↑↓) is exerted on each spin in the first layer by the exchange coupling force, that is, the exchange coupling force affects the RE spins (
↑) acts to align the TM spins (↓) (, as a result, in the first layer, ↑↓, that is, old magnetization overcomes ↓Hb and appears. This state is state 11i: JL.

This state 3L is maintained even if the medium temperature drops to room temperature. As a result, the bit formation for the "A direction" direction is completed.

Next, class 5 recording media cA type shown in Table 1・■
Taking as an example a specific medium-5 belonging to quadrant type 3),
The principle of overwriting will be explained in detail.

This medium Na5 has the relationship of the following formula 31: % formula %. This relationship is shown in a graph as follows.

T @@wa-・ITL TII At room temperature Tll, the magnetization of the first layer is the initial auxiliary magnetic field old ni.

The condition that only the second layer is inverted without being inverted is expressed by Equation 32
It is. This medium h5 satisfies Equation 32.

Formula 32: However, the coercive force of the Hc++ first layer H: Coercive force of second layer MB2: Saturation magnetic moment of the first layer M, is the saturation magnetic moment of the second layer t: Film thickness of the first layer t8: Second layer thickness σw: Interface domain wall energy At this time, the conditional expression for Hlni is expressed by Expression 35.

When the old Ni disappears, the reversed magnetization of the second layer is influenced by the magnetization of the first layer due to exchange coupling force. Still the second
The conditions under which the magnetization of the layer is maintained without being reversed again are expressed by Equation 33~
34. This medium-5 satisfies Equations 33 and 34.

σ− 2M,...t.

σ Equation 34: Hcz>□ Msmtt Equation 35: % Equation % The magnetization of the second layer of the recording medium that satisfies the conditions of Equations 32 to 34 at room temperature is H that satisfies the conditions of Equation 35 immediately before recording.
Ini, for example, “A direction”? (, ↑). At this time, the first layer remains in the recorded state (state Jl
it).

This state fll is maintained until immediately before recording. Here, the recording magnetic field (Hb) is applied in the ↓ direction.

□High-temperature cycle□ Then, when the medium temperature is raised to TL by irradiation with a high-level laser beam, TL becomes the Curie point T' of the first layer.
Since it is almost equal to c+, its magnetization disappears (state 2H
).

As the beam irradiation continues, when the temperature of the medium reaches TM, the magnetization of the second layer also disappears (state 3H) since T and I are approximately equal to T'ct.

When the medium deviates from the laser beam spot area in this state Ls*, the medium temperature begins to decrease.

When the temperature of the medium drops slightly below the TCI, the magnetization of the second layer appears. In this case, magnetization of 8 (↑↓) appears due to ↓Hb. However, since the temperature is higher than TCI, no magnetization appears in the first layer, and this state is state 4.

Furthermore, when the medium temperature decreases to a level slightly lower than the TCI, magnetization appears in the first layer as well. In this case, the magnetization of the second layer extends to layer 1 due to exchange coupling force, and as a result, a force acts to align the RE spins (↑) and the TM spins (↓) (in this case, the medium temperature is still T). 2. Since it is more than 1,
7M spin is larger than RE spin (↑↓),
As a result, breath magnetization appears in the second layer (shape 1hi5
．． ) - When the medium temperature further decreases from the temperature of state 5N to below Tcoat1, the magnitude relationship between the intensities of the 1N 7M spin and the RE spin is reversed (↑↓-↑, )
, Therefore, the magnetization of the blind layer is reversed and "directed to A"? The magnetization becomes (state 6N).

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

In this way, the formation of the "A-oriented" bit is completed.

□Low-temperature cycle□ On the other hand, a low-level laser beam is irradiated to raise the medium temperature to TL. Then, since TL is approximately equal to the Curie point Tel of the first layer, its magnetization disappears. However, at this temperature, the Hcl in the second layer is still large, so
The magnetization of the second layer is not reversed by ↓Hb (
Condition 2L).

This state 2. When the beam irradiation ends at , the medium temperature begins to drop. When the medium temperature is slightly lower than the TCI, the influence of the RE and 7M spins (↓↑) in the second layer is exerted on each spin in the first layer due to exchange coupling force.

In other words, RE spins (↓) and TM spins (↑)
As a result, in the first FJ, ↓↑, that is, electric magnetization overcomes ↓Hb and appears.

In this case, since the temperature is higher than T CIn @e+ +, the 7M spin becomes larger (state 3L).

When the medium temperature further decreases to below TCaI6$+j, the magnitude relationship between the RE spin and 7M spin of the iris layer is reversed ( , ↑-t), as in the high temperature cycle, and as a result, the magnetization of the first layer becomes 8. (state a4t) - This state Jff4t is maintained even if the medium temperature drops to room temperature. As a result, the formation of 6 bits in the "reverse A direction" is completed.

Next, class 6 recording media (A type, ■
Taking as an example a specific medium hidden 6 belonging to quadrant type 4),
The principle of overwriting will be explained in detail.

This medium Na6 has the relationship of the following formula 36: % formula %. This relationship is shown in a graph as follows.

T * T c IT c t'r L
T M At room temperature TI, the magnetization of the first layer is the initial auxiliary magnetic field old ni.

The condition that only the second layer is inverted without being inverted is given by Equation 37.
It is. This medium N16 satisfies Equation 37.

Formula 37: However, HH + coercive force of the first layer Hct: Coercive force of second layer M, 1: saturation magnetic moment of the first layer Mo: saturation magnetic moment of second layer tl: Thickness of the first layer t2: Second layer thickness σ,: interfacial domain wall energy At this time, the conditional expression for old ni is shown by Expression 40.

If the old ni is zero, the reversed magnetization of the second layer is influenced by the magnetization of the first II due to the exchange coupling force.Even so, the condition for the magnetization of the second layer to be maintained without being reversed again is given by Equation 38.
~39. This medium N16 satisfies Equations 38-39.

Equation 38i Hcl>□ 2M11tl σ Equation 39: 1(Cl>□ 2Mgg! Dew Equation 40: %Equation % The magnetization of the second layer of the recording medium that satisfies the conditions of Equations 37 to 39 at room temperature is until just before recording. H that satisfies the condition of Equation 40
ini,, for example, “A direction”? (Le ↑). At this time, the first layer remains in the recorded state (state 1).

This state 1 is maintained until immediately before recording. Here, the recording magnetic field (Hb) is applied in the ↓ direction.

□High-temperature cycle□ Then, when the medium temperature is raised to T by irradiation with a high-level laser beam, TL becomes the Curie point of the first layer, Tc.
, so the magnetization disappears (state 2.)
.

As the beam irradiation continues and the medium temperature further increases to T,l, the temperature TN of the second N becomes Tc! Since it is almost equal to
Its magnetization also disappears. This is state 3M.

When the medium deviates from the laser beam spot area in this state a311, the temperature of the medium begins to decrease.

When the temperature of the medium drops slightly below T,8, a second N magnetization appears. In this case, magnetization of a(,i) appears due to ↓Hb. However, since the temperature is higher than T'c+, the first
This state, in which no magnetization appears in the layer, is state 4N.

Then, when the medium temperature decreases further and becomes slightly lower than the TCI, magnetization appears in the first layer. At that time, the exchange coupling force from the second N is between the RE spins (↑) and between the TM spins (↓
), and therefore, in the first layer, ↑↓, that is, electric magnetization overcomes ↓Hb and appears. This state is state 5N.

Then, the temperature of the medium eventually decreases from the temperature in state 5H to room temperature. Since the HCI at room temperature is sufficiently large, the magnetization of the first layer is maintained stably.

In this way, the formation of the "A direction" electric bit is completed.

□Low-temperature cycle□ On the other hand, a low-level laser beam is irradiated to raise the medium temperature to TL. Then, since TL is approximately equal to the Curie point T'ct of the first layer, its magnetization disappears.

In this state, Ho is still sufficiently large, so the magnetization of the second layer is not reversed by ↓Hb, and this state is state 2L.

In this state tfA2L, when the medium deviates from the laser beam spot area, the medium temperature starts to decrease.

When the medium temperature drops slightly below T'ct, the RB of the second layer.

The influence of the 7M spin (↓↑) extends to each spin in the first layer due to the exchange coupling force, and the exchange coupling force is the same as the RE spin ± (↓)
, act to align the TM spins (↑), and as a result, magnetization of ↓↑, that is, 8, appears in layer 1. This condition is like this! It is 13L.

This state 3L is maintained even if the medium temperature drops to room temperature. As a result, the formation of 8 bits 7 in the "reverse A direction" is completed.

Next, class 7 recording media (P type, ■
Taking as an example a specific medium-7 belonging to quadrant type 4),
The principle of overwriting will be explained in detail.

This medium positive 7 has the relationship of the following formula 41: % formula %. This relationship is shown in a graph as follows.

TL T circle At room temperature T, the magnetization of the first layer is the initial auxiliary magnetic field old ni.

The condition that only the second layer is inverted without being inverted is given by Equation 42
It is. This medium circle 7 satisfies equation 42.

Formula 42: % Formula % Where: )ICI: Coercive force Hc of the first layer: Coercive force M31 of the second layer: Saturation magnetic moment M of the first layer, , : Saturation magnetic moment tl of the second layer: 1st In this case, the conditional expression of 1lini is expressed by Equation 45.

When Hini disappears, the reversed magnetization of the second layer is influenced by the magnetization of the first layer due to exchange coupling force. Even so, the condition for the second M magnetization to be maintained without reversing is equation 43.
~44. This medium chamber 7 satisfies Equations 43 and 44.

σChi formula 43: 1(CI>□ 2Ms+tt Formula 44: Hcx>□ 2M, ttFu formula 45; % formula % The magnetization of the second layer of the recording medium that satisfies the conditions of formulas 42 to 44 at room temperature is The old ni satisfies the condition of Equation 45 just before , for example, it is aligned to "J city facing A (↓↑). At this time, the first layer remains in the recorded state (state l)
.

This state a1 is maintained until immediately before recording. Here, the recording magnetic field (Hb) is applied in the ↓ direction.

□High-temperature cycle□ Then, when the medium temperature is raised to TL by irradiating a high-level laser beam, TL becomes the Curie point T0 of the first layer.
Since it is almost equal to , its magnetization disappears (like Jii2M
).

As the beam irradiation continues, the medium temperature further increases to T, and since the temperature T11 of the second N is approximately equal to the Curie point T0, its magnetization also disappears. This is the state JLi 3N
It is.

Moving out of the spot area of the laser beam at this cane BsII, the temperature of the medium begins to decrease.

The temperature of the medium is Tc! When the temperature drops a little further, the magnetization of the second layer appears. In this case, magnetization of 8 (↑↓) appears due to ↓Hb. However, since the temperature is still higher than T'c+, no magnetization appears in the first layer, and this state is state 4N.

Then, when the medium temperature decreases further and becomes slightly lower than Tel, magnetization appears in the first layer. At that time, the second layer (↑↓)
The exchange coupling force acts to align the RE spins (↑) and the TM spins (3), so a magnetization of ↑↓, that is, 8, appears in the first layer. This state is state B5N.

Then, the temperature of the medium eventually decreases from the temperature at RM 5 M to room temperature. Since Ict (at room temperature) is sufficiently large, the magnetization of the first layer is maintained stably.

In this way, the formation of 8 bits in the "reverse A direction" is completed. □Low temperature cycle□ On the other hand, a low level laser beam is irradiated to raise the medium temperature to TL. Then, since TL is approximately equal to the Curie point TCI of the first layer, its magnetization disappears. In this state, ) Ic is still sufficiently large, so the magnetization of the second layer? is not reversed at ↓Hb, and this state is state 2L.

When the medium moves out of the laser beam spot area in this state 2L, the medium temperature begins to decrease.

When the medium temperature drops slightly below Tel, the RE of the second layer.

The influence of the TM spin (↓↑) is exerted on each spin in the first layer by the exchange coupling force, and the exchange coupling force is between the RE spins (↓)
, acts to align the TM spins (↑), and as a result, in the first layer, ↓↑, that is, the previous magnetization overcomes ↓Hb and appears. This state is state 3L.

This state B3L is maintained even if the medium temperature drops to room temperature. As a result, the bit formation for the "A direction" direction is completed.

Next, class 8 recording media (A type, ■
The principle of overwriting will be explained in detail by taking as an example a specific medium N118 belonging to quadrant type 2).

This medium-8 has the relationship of the following formula 46: % formula %. This relationship is shown in a graph as follows.

T L T C11+&$+ l T H room temperature T11
The magnetization of the first layer is the initial auxiliary magnetic field old ni.

The condition that only the second layer is inverted without being inverted is given by Equation 47.
It is. This medium Na9 satisfies the formula 47 at room temperature. (47) where: CI = Coercive force of the first layer 1 (cm: Coercive force of the second layer MSI: Saturation magnetic moment amount of the first layer 8. Saturation magnetic moment tl of the second layer: Thickness t of the first layer: Thickness σw of the second layer: Interfacial domain wall energy At this time, the conditional expression for Min! is expressed by Equation 50.

Old n1. When the magnetization disappears, the reversed magnetization of the second layer is influenced by the magnetization of the first layer due to exchange coupling force. Still the second
The conditions under which the magnetization of the layer is maintained without reversing are expressed by Equation 48~
49. This medium 1lkL8 satisfies Equations 48-49.

σ, 2 M*, t.

σ− Formula 49: Hcm>□ 2M,,t.

Formula 50: % Formula % The magnetization of the second layer of the recording medium that satisfies the conditions of formulas 47 to 49 at room temperature is 1 that satisfies the conditions of formula 50 immediately before recording.
For example, is it “suitable for A”? Aligned to (↑,). At this time, No. 11 remains in the recording state (state 1).

This state l is maintained until immediately before recording. Here, the recording magnetic field (Hb) is applied in the direction of ↑.

□High-temperature cycle□ Then, when the medium temperature is raised to TL by irradiation with a high-level laser beam, TL becomes the Curie point Tc of the first layer.
Since it is almost equal to l, its magnetization disappears (state 2N)
.

Further beam irradiation continues, and the medium temperature increases to T co□,2
When it becomes slightly stronger (when the direction of the RE spin (↑) and 1M spin (3) remains the same, the magnitude relationship of the intensities is reversed (↑↓ −↑↓), and as a result, the magnetization of the second layer is reversed. This results in the "reverse A direction" 6. This state is the shape Li5H.

However, at this temperature) Icm is still large, so the second
The magnetization 8 of the layer is not reversed by ↑Hb.

Suppose that the beam irradiation continues and the medium temperature rises further to T, then T becomes Tc! , the magnetization of the second layer also disappears (state 4N).

When the medium moves out of the laser beam spot area at this state 84M, the medium temperature begins to decrease.

When the medium temperature drops slightly below T, magnetization occurs in the second layer. In this case, due to ↑Hb? A magnetization of (, τ) appears. However, since the temperature is still higher than TCI, no magnetization appears in the first layer, and this state is JLi 5 N.

The medium temperature further decreases to T. When it falls a little below 6M41, the direction of the RE spin (↓) and 1M spin (↑) remains the same, but the strength relationship is reversed (toward -↓), and as a result, the magnetization of the second layer is reversed. "Reverse A direction" 8
becomes. In this state, the magnetization 8 of the second layer will not be reversed by ↑Hb since I(cz is already quite large, and the temperature is still higher than TCI, so the first
The magnetization of the layer has not yet appeared, and this state is state B6H.

Furthermore, when the medium temperature decreases to a little below Tel, magnetization appears in the first layer as well. In this case, the magnetization of the second layer (↓
↑) extends to the first layer due to exchange coupling force.

As a result, RE spins (↓) and TM spins (
↑) works, and as a result, the first layer has ↓? (
? ) magnetization appears (like s'y, > ).

Then, the temperature of the medium eventually decreases from the temperature in the Li 7 II state to room temperature. Since the HCI at room temperature is sufficiently large, the magnetization of the first layer is maintained stably.

In this way, the formation of the "A direction" electric bit is completed.

□Low-temperature cycle□ On the other hand, a low-level laser beam is irradiated to raise the medium temperature to TL. Then, since TL is approximately equal to the Curie point T'ct of the first layer, its magnetization disappears.

However, since Hc of the second layer is still large at this temperature, its magnetization is not reversed by ↑Hb (state a2L).

This situation is W! As the medium moves out of the laser beam spot area at A2L, the medium temperature begins to decrease.

When the medium temperature drops slightly below Tc1, the RE of the second layer.

The influence of the 7M spin (↑↓) extends to each spin in the first layer due to the exchange coupling force, that is, the RE spins (↑), TM
A force acts to align the spins (3).

As a result, magnetization ↑↓, that is, magnetization 8 overcomes ↑Hb and appears in the first layer. This state is state L3t.

This state M3L is maintained even if the medium temperature drops to room temperature. As a result, the formation of 8 bits in the "reverse A direction" is completed.

Next, class 9 recording media shown in Table 1 <A type・■
The principle of overwriting will be explained in detail by taking as an example a specific medium N19 belonging to quadrant type 4).

This medium-9 has the relationship of the following formula 51: % formula %. This relationship is shown in a graph as follows.

At room temperature T, the magnetization of the first layer is the initial auxiliary magnetic field old ni.

The condition for only the second N to be inverted without being inverted by Equation 52 is
It is. This medium-9 satisfies Equation 52.

Formula 52: However, Hol: Coercive force of the first layer HCl: Coercive force of second layer M, 1: saturation magnetic moment of the first layer M38: Saturation magnetic moment of second layer t1: Film thickness of the iris layer t,: second layer thickness σw: Interfacial domain wall energy At this time, the conditional expression for old ni is shown by Expression 55.

H4n1. When the magnetization disappears, the reversed magnetization of the second layer is influenced by the magnetization of the first layer due to exchange coupling force. Even so, the condition for the magnetization of the second layer to be maintained without reversing is given by formula 53.
~54. This medium 11h9 satisfies Equations 53 and 54.

Formula 53: Hcl>□ 2 M,, t.

σ screen Formula 54: Hc*>□ 2 M,! T.

Equation 55: %Equation % The magnetization of the second layer of the recording medium that satisfies the conditions of Equations 52 to 54 at room temperature is, for example, "A direction" due to the old ni that satisfies the conditions of Equation 55 just before recording? (↑.). At this time, the first layer remains in the recorded state (state al)
.

This state B1 is maintained until immediately before recording. Here it is! 3
The magnetic field (Hb) is applied in the ↓ direction.

□High-temperature cycle□ When the medium temperature is raised to TL by irradiation with a high-level laser beam, TL is the Curie point T of the first layer.
Since it is almost equal to c+, its magnetization disappears (state f!1
2N) - As the beam irradiation continues, the medium temperature further increases to T, and since the temperature of the second layer T, is approximately equal to To, the second layer
The magnetization of the layer also disappears. This is state 3.

In this state of JLi3m, the temperature of the medium begins to decrease when the medium is out of the laser beam spot area.

When the temperature of the medium drops slightly below To, the magnetization of the second layer appears. In this case, & (↓↑) magnetization appears due to 'lHb. However, since this temperature is still higher than TCI, no magnetization appears in the first layer, and this state is state 4H.

Then, when the medium temperature decreases further and becomes slightly lower than the TCI, magnetization appears in the first layer. At that time, the second layer (↓↑)
The exchange coupling force acts to align the RE spins (↓) and the TM spins (↑), so ↓↑, that is, electric magnetization overcomes ↓Hb and appears in the first layer. This state is state *5N.

Then, the temperature of the medium eventually decreases from the temperature at the state 1'13i 5 II to room temperature. Since the MCI at room temperature is sufficiently large, the magnetization of the first M is stably maintained.

In this way, the bit formation for the "A-oriented" official is completed.

□Low-temperature cycle□ On the other hand, a low-level laser beam is irradiated to raise the medium temperature to TL. Then, since TL is approximately equal to the Curie point Tcl of the first layer, its magnetization disappears. In this state, HC! is still large enough, the magnetization charge of the second N will not be reversed at ↓Hb. This state is
lQ 2 t.

In this state 2L, when the medium moves out of the laser beam spot area, the medium temperature begins to decrease.

When the medium temperature drops slightly below the TCI, the RE of the second layer.

The influence of the 7M spin (↑ya) extends to each spin in the first layer due to the exchange coupling force, and the exchange coupling force is between the RE spins (↑)
, acts to align the TM spins (↓), and as a result, ↑↓, that is, breath magnetization appears in the first layer. This state is state a3L.

This state 3L is maintained even if the medium temperature drops to room temperature. As a result, the formation of the "reverse A" numbered bit is completed.

[Problem to be solved by the invention]

In order to increase the lifetime of the magnetic layer, it is necessary to form the film in a high vacuum.

However, according to experiments conducted by the present inventors, if the first and second layers are successively deposited in high vacuum, regardless of the order, the exchange coupling force σ between the magnetic layers becomes too large depending on the materials used. There is.

By the way, in an overwritable medium, it is necessary to satisfy σ-Equation 3: HCI>-2M11tl in order to prevent the information in the first layer from being erased by the initialized 2N magnetization, and also Since the initialized magnetization of the second layer cannot be reversed by the magnetization of the first layer, it is necessary to satisfy the following equation 4: Hcm>□2Ms. Therefore, if the exchange coupling force σ is too large, the coercive force HC and the saturation magnetic moment Ms are determined by the material of the magnetic layer, so the film thickness t must be increased.

However, as the total film thickness tag of the first and second layers increases, the heat capacity of the magnetic layer increases, so during recording, a laser beam is irradiated to lower the temperature of the medium to T. Alternatively, when raising the laser beam to TL, the power of the laser beam must be increased, resulting in a problem of poor irradiation efficiency.

Therefore, as a result of intensive research on means for downwardly modifying (controlling) the exchange coupling force σ1 itself regardless of the material of the magnetic layer, we first added a non-magnetic element such as Sis Ge to either or both of the second blind layer and the second layer. It has been found that the exchange coupling force σw can be controlled by the amount added.

However, simply adding a non-magnetic element reduces the exchange coupling force σ1 to t
Even with W control, it was rare to obtain an overwritable medium as designed (problem).

Therefore, an object of the present invention is to design an overwritable magneto-optical recording medium with a large exchange coupling force σ- by adding a non-magnetic element without increasing the total film thickness 111 of the first layer and the second layer. The object of the present invention is to provide a magneto-optical recording medium that can be overwritten as described above.

[Means to solve the problem]

As a result of research, the present inventor found that in media that cannot be overwritten as designed even if the exchange coupling force σ is controlled simply by adding non-magnetic elements, the information in the first layer is initialized. It has been found that the magnetization of the 211th layer which has been erased by the 211th layer or (2) initialized is disturbed by the magnetization of the first layer and becomes a non-initialized state.

Therefore, as a result of further research, it was found that when a nonmagnetic element is added, the exchange coupling force σ- decreases, and at the same time, the product of the coercive force H0 and the saturation magnetic moment) MS also decreases.

Therefore, by transforming Equations 3 and 4, σ− 2Hc, M,, t.

σ- Equation 4/lk: 1>□ 2HctMstl. However, if the decrease in the Hc-MS product exceeds the decrease in σw, 7FgcMs may increase significantly, and in that case, the It has been found that Equations 3 and 4 cannot be satisfied without increasing the total film thickness ttx, and overwriting becomes impossible or incomplete.

However, between the first layer and the second layer, Hc before addition of non-magnetic elements
- When a non-magnetic element is added to the side with a smaller MS product, there is almost no increase in HcMs (see Figure 6). Therefore, although the thickness t of the added layer cannot be made thinner, the layer without the addition is , σ, decreases, Ho・M.

Since the product does not change, it is possible to reduce the film thickness t that satisfies Equation 3 or Equation 4, and as a result, it has been discovered that the total film thickness t+x can be made thinner than before addition, leading to the present invention.

On the other hand, when a non-magnetic element is added to the layer with a smaller Hc-Ms product, the σ-HcM cloud increases significantly (see Figure 8), and therefore the thickness t of the added layer becomes considerably thicker. Otherwise, Equations 3 and 4 would not be satisfied, and as a result, the total film thickness tit could not be made thinner than before addition.

Further, even when it was added to both the first layer and the second layer, the total film thickness tit could not be made thinner than before addition.

Therefore, the present invention controls the exchange coupling force σ- to a predetermined value by adding a non-magnetic element to the first layer or the second layer, whichever has a smaller Hc/Ms product, thereby controlling the total film thickness t1 !
The present invention provides an overwritable magneto-optical recording medium that has a reduced performance.

[Effect]

The magnetic moment of a magnetic material is due to the orbital angular momentum and spin angular momentum of the outer shell electrons of atoms, and the exchange interaction is based on the Pauli principle and the electrostatic relationship between two electrons. By doing so through interaction.

Therefore, when the distance between magnetic atoms becomes long (or when the number of nearest magnetic atoms decreases), the overlap of the wave functions of the electrons of the atoms becomes smaller, and the exchange interaction decreases.

Therefore, the present invention adds a non-magnetic element to the magnetic layer to substantially increase the distance between the magnetic atoms between the eyebrows and reduce the number of nearest magnetic atoms, thereby increasing the exchange interaction. , thereby controlling (reducing) the exchange coupling force σ5.

Examples of non-magnetic elements include Si, Ges 71%
CrhCu, In, etc. are used.

The amount of non-magnetic element added should be at least 0.00 to produce an effect.
Although 5at+s% is preferable, the actual amount to be added should be determined by preliminary experiments to be the amount to be added in accordance with the required predetermined exchange coupling force σ1 and the Hc-Ms product at that time.

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

[Reference Example 1] Using a ternary RF magnetron sputtering device,
A disk-shaped glass substrate with a thickness of 1.2a+s+ and a diameter of 200a+m is placed in the vacuum chamber of the apparatus.

Once the inside of the vacuum chamber was evacuated to 5 x 10-'Pa, argon gas was introduced and the Ar gas pressure was increased to 2 x 10-'Pa.
Sputtering is performed at a deposition rate of about 3 persons/sec while maintaining the temperature at -'Pa.

First target is Tb! . Fe,. Using an alloy (note: subscript numbers are atomic %), a film thickness of tl-50 was formed on the substrate.
1st Ji (recording layer) consisting of 0 dibFe perpendicular magnetization film
form.

Next, while maintaining the vacuum state, target 7) is set as l).
A second Ji (recording auxiliary layer) consisting of a DYFeCoSi perpendicular magnetization film with a film thickness of tz -500 is formed on the first layer by simultaneous sputtering using y□Fes・1COt+, h alloy and Si, which is a nonmagnetic element. form.

In this way, by changing the power applied to the SI target, the amount of St added to the second layer was changed.
A layered magneto-optical recording medium (see FIG. 1) was manufactured.

Then, the product and exchange coupling force σ of the first N of the produced medium and the Hc′Ms product of the second layer are measured, and σ,
The relationship between the 211th Ho·M product and the amount of St added was investigated. The results are shown in FIGS. 5 and 6, and SI
An example in which Ge was added instead of was also measured and is also shown.

As a result, when no element is added, the Hc-Ms product of the first layer is 200,000, and that of the second N is 1.
50.000, and this example is an example in which the Hc-Ms product is added to the smaller one.

As shown in FIG. 6, adding a non-magnetic element to σ- cannot reduce the film thickness of the second layer according to equation 4A, but adding a non-magnetic element as shown in FIG.
Since the thickness decreases, the film thickness t of the first layer can be made thinner according to equation 3A, and the total film thickness tit can be made thinner.

[Reference Example 2] Under the same conditions as Reference Example 1, this time Si or Go was added to the first layer.
Two-layer magneto-optical recording media were manufactured with various additive amounts, with the addition of a non-magnetic element to the second layer and no non-magnetic element added to the second layer.

Then, the 211th Hc-Ms product and exchange coupling force σw of the produced medium and the Hc-M* product of the first layer were measured, and σ
The relationship between w and the Hc-Ms product of the first layer and the amount added was investigated. The results are shown in FIGS. 7 and 8.

As a result, when no element is added, the Hc-M product of the first layer is 200,000, and that of the second layer is 1.
50,000, and this example is an example in which it is added to the one with the larger Hc-Ms product.

As shown in Fig. 8, when a non-magnetic element is added and the value of σ increases, □ increases significantly, and therefore, according to formula 3A, the thickness of the first layer ti must be increased considerably. Therefore, as shown in Figure 7, adding a non-magnetic element lowers σ-, so Equation 4A
Although the film thickness t of the second layer can be reduced by this, the increase in the thickness of the first layer is outweighed by the increase, and in the end, the total film thickness 1+1 cannot be made thinner than before addition.

[Reference Example 3] Under the same conditions as Reference Example 1, the same amount of Si or Ge was added to both the illumination layer and the second layer, and various addition amounts of 211
A magneto-optical recording medium was manufactured.

Then, the exchange coupling force σ5 of the produced medium and the product of each Hc-M of the first layer and the second layer are measured, and σw and the Ho of the first layer are measured.
・We investigated the relationship between the product of M and the amount added. The results are shown in FIG.

σ- In this case, □ is Hc M! for the first layer. As shown in FIG.
As shown in the figure, the film thickness t8 cannot be reduced because it hardly increases, so the total film thickness t,! must be made thicker than Reference Example 2.

〔Example〕

In the same manner as in Reference Example 1, a film thickness of t+''500 Tb was formed on the substrate using a magnetron sputtering apparatus.

Pew. A first layer (recording M) consisting of a perpendicularly magnetized film was formed. The Hc-Ms product of the first layer is 200.000.

Next, while maintaining the vacuum state, a film with a thickness of h- is deposited on the first layer.
1000 people, (DyzaFeab, 5cOzs, t
), h, 5sis, s of perpendicular magnetization film.
The Hc-Ms product of the magnetic layer having the composition of the second layer excluding St was 150,000.

The magnetic properties of the two-layer magneto-optical recording medium belonging to class 8 (A type, quadrant 1, type 2) manufactured in this manner are shown in Table 2 below.

Table 2 ml Tb5eFex.

Rate 2 (DVtsFe4i, @coal i) q
h, 5Sis, s This medium belongs to class 8, so the conditions that this medium should satisfy at room temperature are: 2 Ms+ t I Equation 49: Hc*>□ 2Ms wealth 1°, and when calculating each equation, the following equation is obtained: 47: Left side - 5000 > Right side - 4788 Formula 48: Left side - 5000 > Right side = 4688 Formula 49: Left side - 720>
The right side is −620, which satisfies each equation.

Furthermore, in Equation 50, since the left side -40<1 old at and l<the right side -9688, Equation 50 is satisfied by setting old ni, =2000 0e, for example.

Therefore, this medium is overwritable according to the prior invention.

[Comparative example]

Next, for comparison, a 2N magneto-optical recording medium was manufactured in the same manner as in the example except that no non-magnetic element was added.

The magnetic properties of this medium are shown in Table 3 below.

Table 3 *1 rb,. Fe,.

*2 DV FujiFeah, acOxs, Tomi So, when formulas 47 to 49 are calculated in the same manner as in the example, (a) formula 47:
Left side -5ooo > Right side -8619 (b) Equation 48: Left side -5000 > Right side = 8437 (c) Equation 49: Left side -1
000>Right side=818, and Equations 47 and 48 are not satisfied.

Therefore, in this medium, (a) it is impossible to initialize only the second layer without affecting the first layer, and overwriting is not possible.

To enable overwriting with this magnetic material, the film thickness t1 must be made thicker than 675 to satisfy Equation 48, and the film thickness t must be increased to 681 to satisfy Equation 47. It must be thicker than the human, therefore,
The overall film thickness t1□ is (6B?+1.10
0)÷(400+1+100) #1.2 times or more thicker.

[Reference Example 4: Magneto-optical recording device capable of over'J()] This device is for recording only, and its overall configuration is shown in FIG. 4 (conceptual diagram).

This device basically consists of: (a) rotating means 21 as an example of means for moving the recording medium 20; (C) laser beam light source 23; (d) beam intensity in accordance with the binarized information to be recorded. ,(
1) a high level that provides a medium temperature T suitable for forming either a bit with upward magnetization or a bit with downward magnetization, and (2) a medium suitable for forming the other bit. It consists of a means 24 for modulating the temperature TL in a pulsed manner to a low level; (b, e) an initial auxiliary magnetic field Ni, and a recording magnetic field Hb applying means 25 which also serves as the applying means 22;

As the combined means 22 & 25, here, Hb - old ni, = 2000 0e and the direction of the magnetic field is "direction A" ↑
Uses permanent magnets. The permanent magnets 22 & 25 are rod-shaped and have a length corresponding to the length of the disk-shaped recording medium 20 in the radial direction.

The magnets 22 & 25 are fixedly installed on the recording device,
We will not move it together with the pink-up including the light source 23.

[Reference Example 5 - All-9 () Magneto-Optical Recording] Magneto-optical recording is carried out using the recording apparatus F of Reference Example 4 (see FIG. 4). First, the recording medium (class 8) 20 of the example is moved by the rotating means 21 at a constant linear velocity of 8.5 m and 7 seconds. The medium 20 is irradiated with a laser beam. When this beam is at high level by the means 24: 8.
Ow+11 (on disk), at low level: 4.
It is adjusted to output an output of 4 mW (on disk). The beam is then modulated into pulses according to the information by means 24. Here, the information to be recorded is a signal of frequency I MIX. Therefore, the medium 20 was irradiated with the beam while being modulated at the frequency I MIX. This should have recorded the I MIX signal.

When reproduced with another magneto-optical reproducing device, the C/N ratio is 55 dB.
It was confirmed that this was recorded.

Next, in the already recorded area of the medium 20, this time the frequency 2
The MHz signal was recorded as new information.

When this information was similarly reproduced, new information was reproduced with a C/N ratio of 53 dB. The error rate is 104-1
It was 0-h. At this time, the IMIIz signal (previous information) did not appear at all.

As a result, it was found that overwriting was possible.

Note that under this condition, the temperature of the medium is near H at high level.
-200℃, reaches TL-120℃ at low level.

On the other hand, when recording was performed in the same manner on the medium of the comparative example, overwriting was impossible.

[Effects of the Invention] As described above, the present invention provides an overwritable magneto-optical recording medium with a large exchange coupling force σ, in which a predetermined amount of non-magnetic element is added to the magnetic layer without changing the basic material of the magnetic layer. By adding , the exchange coupling force σ□ can be controlled to a predetermined value depending on the amount added, and as a result, overwriting is possible without increasing the overall film thickness.

In addition, conversely, the range of design of the composition of the first and second layers is expanded,
A great deal of good news can be gained from practical application.

[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 explaining the recording principle of the magneto-optical recording method. FIG. 3 is a conceptual diagram explaining 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 present invention. FIG. 5 shows the amount of non-magnetic element added and the exchange coupling force σ acting between the magnetic layers when the non-magnetic element is added to the layer with the smaller Hc-Ms product. It is a graph showing the relationship between FIG. 6 is a graph cMa showing the relationship between the amount of σ-oil added to the non-magnetic element and □ when the non-magnetic element is added to the layer with the smaller Hc-Ms product. FIG. 7 is a graph showing the relationship between the amount of non-magnetic element added and the exchange coupling force σ acting between the magnetic layers when the non-magnetic element is added to the layer with the larger Ho・M product. . FIG. 8 is a graph cMs showing the relationship between the amount of σ-oil added to the nonmagnetic element and □ when the nonmagnetic element is added to the layer with the larger Hc-Ms product. FIG. 9 is a graph showing the relationship between the amount of the nonmagnetic element added and the exchange coupling force σw acting between the magnetic layers when the nonmagnetic element is added to both the first layer and the second layer. [Explanation of symbols of main parts] L・--1--, laser beam Lp-...Linearly polarized light B1--... Bit B with "A direction" magnetization, -
・・・・・・−・If it has “reverse A direction” magnetization, 7) 1−・−
--- Recording N (first layer) 2 --- One recording auxiliary layer (second layer) S ---
--- Substrate 20 --- Overwritable magneto-optical recording medium 2
1...--Rotating means 22 for rotating the recording medium.
...-Initial auxiliary magnetic field old ni, application means 23--
Laser beam light source 24...--According to the binary information to be recorded, the beam intensity is set to (1) bits with "A direction" magnetization or "
(2) a high level that provides the medium with an appropriate temperature to form one of the bits with magnetization in the "reverse A direction"; and (2) a low level that provides the medium with an appropriate temperature to form the other bit. A means of modulating pulses between

Claims (1)

[Claims] 1. An overwritable magneto-optical recording medium in which at least two magnetic layers having perpendicular magnetic anisotropy are laminated, the first layer being a recording layer and the second layer being a recording auxiliary layer. By adding a non-magnetic element to the first layer or the second layer, whichever has a smaller product of magnetic saturation moment Ms and coercive force Hc, the exchange coupling force σ_w acting between the magnetic layers can be reduced. A recording medium characterized by being controlled to a predetermined value. 2 The amount of the non-magnetic element added is at least 0.5 atm
%, the recording medium according to claim 1. 3 The nonmagnetic element is Si, Ge, Ti, Cr, Cu
The recording medium according to claim 1, wherein the recording medium is In. 4 Point either upward or downward toward the medium as “A”.
When the second layer is oriented in the "A direction" and the other is in the "reverse A direction", just before recording, only the magnetization of the second layer is aligned in the "A direction" by the initial auxiliary magnetic field H, and when a high-level laser beam is irradiated. The "A direction" magnetization of the second layer is reversed to "reverse A direction" by the recording magnetic field, and the "reverse A direction" of this second layer is reversed.
Due to the magnetization, a bit with "reverse A direction" magnetization [or "A direction" magnetization] is formed in the first layer, and when irradiated with a low level laser beam, the "A direction" magnetization of the second layer causes the bit to “A direction” magnetization in the layer [or “reverse A direction” magnetization]
2. A recording medium according to claim 1, wherein a bit is formed. 5 Claims characterized in that the first layer is a magnetic thin film with a high coercive force and a low Curie point at room temperature, and the second layer is a magnetic thin film with a relatively low coercive force and a high Curie point at room temperature. The recording medium described in item 4. 6 The temperature at which the first layer is magnetically coupled to the second layer is T_s_1
When the temperature at which the second layer is reversed by the recording magnetic field is T_s_2, the first layer has a high coercive force at room temperature, the second layer has a relatively low coercive force at room temperature, and T_s_1<T_s_2. The recording medium according to claim 4, characterized in that: 7. The recording medium according to claim 1, wherein the first layer and the second layer are both selected from a transition metal-heavy rare earth alloy composition. 8 A transition metal-heavy rare earth alloy in which the first layer is rich in heavy rare earths and has a compensation temperature between room temperature and the Curie point, and the second layer is a transition metal that is rich in heavy rare earths and has a compensation temperature between room temperature and the Curie point. - made of a heavy rare earth alloy, and the following conditional expression: (1) T_R<T_c_o_m_p_. _1<T_c_
1≒T_L≒T_c_o_m_p_. _2<T_c_2
≒T_H and at room temperature, the following conditional expressions: (2) H_c_1>H_c_2+σ_w/2M_s_1
t_1+σ_w/2M_s_2t_2 (3) H_c_1>σ_w/2M_s_1t_1 (4) H_c_2>σ_w/2M_s_2t_2 (5) H_c_2+σ_w/2M_s_2t_2<|H
ini. The recording medium according to claim 7, which satisfies |<H_c_1−σ_w/2M_s_1t_1. However, T_R: room temperature T_c_o_m_p_. _1: Compensation temperature T_c_o_m_p_ of the first layer. _2: Compensation temperature of the second layer T_c_1: Curie point of the first layer T_c_2: Curie point of the second layer T_L: Temperature of the recording medium when irradiated with a low-level laser beam T_H: Temperature of the recording medium when irradiated with a high-level laser beam Temperature of the recording medium at the time H_c_1: Coercive force of the first layer H_c_2: Coercive force of the second layer M_s_1: Saturation magnetic moment of the first layer M_s_2: Saturation magnetic moment of the second layer t_1: Thickness of the first layer t_2: Film thickness of second layer σ_w: Exchange coupling force Hini. : Initial auxiliary magnetic field 9 The first layer is rich in heavy rare earths and has no compensation temperature between room temperature and the Curie point. The second layer is rich in heavy rare earths and has no compensation temperature between room temperature and the Curie point. made of a transition metal-heavy rare earth alloy having a temperature, and the following conditional expression: (1) T_R<T_c_1≒T_L≒T_c_o_m_
p_. _2<T_c_2≒T_H and at room temperature, each of the following conditional expressions: (2) H_c_1>H_c_2+σ_w/2M_s_1
t_1+σ_w/2M_s_2t_2 (3) H_c_1>σ_w/2M_s_1t_1 (4) H_c_2>σ_w/2M_s_2t_2 (5) H_c_2+σ_w/2M_s_2t_2<|H
ini. The recording medium according to claim 7, which satisfies |<H_c_1−σ_w2M_s_1t_1. However, T_R: room temperature T_c_o_m_p_. _2: Compensation temperature of the second layer T_c_1: Curie point of the first layer T_c_2: Curie point of the second layer T_L: Temperature of the recording medium when irradiated with a low-level laser beam T_H: Temperature of the recording medium when irradiated with a high-level laser beam Temperature of the recording medium at the time H_c_1: Coercive force of the first layer H_c_2: Coercive force of the second layer M_s_1: Saturation magnetic moment of the first layer M_s_2: Saturation magnetic moment of the second layer t_1: Thickness of the first layer t_2: Film thickness of second layer σ_w: Exchange coupling force Hini. : Initial auxiliary magnetic field 10 The first layer is heavy rare earth rich and has a compensation temperature between room temperature and the Curie point.The second layer is heavy rare earth rich and has a compensation temperature between room temperature and the Curie point. is made of a transition metal-heavy rare earth alloy having no _1<T_c_
1≒T_L<T_c_2≒T_H and at room temperature, each of the following conditional expressions: (2) H_c_1>H_c_2+σ_w/2M_s_1
t_1+σ_w/2M_s_2t_2 (3) H_c_1>σ_w/2M_s_1t_1 (4) H_c_2>σ_w/2M_s_2t_2 (5) H_c_2+σ_w/2M_s_2t_2<|H
ini. The recording medium according to claim 7, which satisfies |<H_c_1−σ_w/2M_s_1t_1. However, T_R: room temperature T_c_o_m_p_. _1: Compensation temperature of the first layer T_c_1: Curie point of the first layer T_c_2: Curie point of the second layer T_L: Temperature of the recording medium when irradiated with a low-level laser beam T_H: Temperature of the recording medium when irradiated with a high-level laser beam Temperature of the recording medium at the time H_c_1: Coercive force of the first layer H_c_2: Coercive force of the second layer M_s_1: Saturation magnetic moment of the first layer M_s_2: Saturation magnetic moment of the second layer t_1: Thickness of the first layer t_2: Film thickness of second layer σ_w: Exchange coupling force Hini. : Initial auxiliary magnetic field 11 The first layer is a transition metal-heavy rare earth alloy that is rich in heavy rare earths and has no compensation temperature between room temperature and the Curie point;
The layer is heavy rare earth rich and consists of a transition metal-heavy rare earth alloy that does not have a compensation temperature between room temperature and the Curie point, and the following conditional expression: (1) T_R<T_c_1≒T_L<T_c_2≒T_
H and at room temperature, the following conditional expressions: (2) H_c_1>H_c_2+σ_w/2M_s_1
t_1+σ_w/2M_s_2t_2 (3) H_c_1>σ_w/2M_s_1t_1 (4) H_c_2>σ_w/2M_s_2t_2 (5) H_c_2+σ_w/2M_s_2t_2<|H
ini. The recording medium according to claim 7, which satisfies |<H_c_1−σ_w/2M_s_1t_1. However, T_R: Room temperature T_c_1: Curie point of the first layer T_c_2: Curie point of the second layer T_L: Temperature of the recording medium when irradiated with a low-level laser beam T_H: Record when irradiated with a high-level laser beam Medium temperature H_c_1: Coercive force of the first layer H_c_2: Coercive force of the second layer M_s_1: Saturation magnetic moment of the first layer M_s_2: Saturation magnetic moment of the second layer t_1: Film thickness of the first layer t_2: Second layer Film thickness σ_w: interfacial domain wall energy Hini. : Initial auxiliary magnetic field 12 The first layer is a transition metal-heavy rare earth alloy that is rich in heavy rare earths and has a compensation temperature between room temperature and the Curie point, the second layer is rich in transition metals and has a compensation temperature between room temperature and the Curie point. and the following conditional expression: (1) T_r<T_c_o_m_p_. _1<T_c_
1≒T_L<T_c_2≒T_H and at room temperature, the following conditional expressions: (2) H_c_1>H_c_2+|σ_w/2M_s_
1t_1−σ_w/2M_s_2t_2 | (3) H_c_1>σ_w/2M_s_1t_1 (4) H_c_2>σ_w/2M_s_2t_2 (5) H_c_2+σ_w/2M_s_2t_2<|H
ini. The recording medium according to claim 7, which satisfies |<H_c_1+σ_w/2M_s_2t_2. However, T_R: room temperature T_c_o_m_p_. _1: Compensation temperature of the first layer T_c_1: Curie point of the first layer T_c_2: Curie point of the second layer T_L: Temperature of the recording medium when irradiated with a low-level laser beam T_H: Temperature of the recording medium when irradiated with a high-level laser beam Temperature of the recording medium at the time H_c_1: Coercive force of the first layer H_c_2: Coercive force of the second layer M_s_1: Saturation magnetic moment of the first layer M_s_2: Saturation magnetic moment of the second layer t_1: Thickness of the first layer t_2: Film thickness of second layer σ_w: Exchange coupling force Hini. : Initial auxiliary magnetic field 13 The first layer is a transition metal-heavy rare earth alloy that is rich in heavy rare earths and has no compensation temperature between room temperature and the Curie point;
The layer is made of a transition metal-heavy rare earth alloy that is rich in transition metals and does not have a compensation temperature between room temperature and the Curie point, and the following conditional expression: (1) T_R<T_c_1≒T_L<T_c_2≒T_
H and at room temperature the following conditional expressions: (2) H_c_1>H_c_2+|σ_w/2M_s_
1t_1−σ_w/2M_s_2t_2 | (3) H_c_1>σ_w/2M_s_1t_1 (4) H_c_2>σ_w/2M_s_2t_2 (5) H_c_2+σ_w/2M_s_2t_2<|H
ini. The recording medium according to claim 7, which satisfies |<H_c_1+σ_w/2M_s_2t_2. However, T_R: Room temperature T_c_1: Curie point of the first layer T_c_2: Curie point of the second layer T_L: Temperature of the recording medium when irradiated with a low-level laser beam T_H: Record when irradiated with a high-level laser beam Medium temperature H_c_1: Coercive force of the first layer H_c_2: Coercive force of the second layer M_s_1: Saturation magnetic moment of the first layer M_s_2: Saturation magnetic moment of the second layer t_1: Film thickness of the first layer t_2: Second layer Film thickness σ_w: exchange coupling force Hini. : Initial auxiliary magnetic field 14 The first layer is a transition metal-heavy rare earth alloy that is rich in transition metals and has no compensation temperature between room temperature and the Curie point;
The layer is made of a transition metal-heavy rare earth alloy that is rich in transition metals and does not have a compensation temperature between room temperature and the Curie point, and the following conditional expression: (1) T_R<T_c_1≒T_L<T_c_2≒T_
H and at room temperature, the following conditional expressions: (2) H_c_1>H_c_2+σ_w/2M_s_1
t_1+σ_w/2M_s_2t_2 (3) H_c_1>σ_w/2M_s_1t_1 (4) H_c_2>σ_w/2M_s_2t_2 (5) H_c_2+σ_w/2M_s_2t_2<|H
ini. The recording medium according to claim 7, which satisfies |<H_c_1−σ_w/2M_s_1t_1. However, T_R: Room temperature T_c_1: Curie point of the first layer T_c_2: Curie point of the second layer T_L: Temperature of the recording medium when irradiated with a low-level laser beam T_H: Record when irradiated with a high-level laser beam Medium temperature H_c_1: Coercive force of the first layer H_c_2: Coercive force of the second layer M_s_1: Saturation magnetic moment of the first layer M_s_2: Saturation magnetic moment of the second layer t_1: Film thickness of the first layer t_2: Second layer Film thickness σ_w: exchange coupling force Hini. : Initial auxiliary magnetic field 15 A transition metal-heavy rare earth alloy in which the first layer is rich in transition metals and has no compensation temperature between room temperature and the Curie point;
The layer is heavy rare earth rich and consists of a transition metal-heavy rare earth alloy having a compensation temperature between room temperature and the Curie point, and the following conditional expression: (1) T_R<T_c_1≒T_L≒T_c_o_m_
p_. _2<T_c_2≒T_H and at room temperature, each of the following conditional expressions: (2) H_c_1>H_c_2+|σ_w/2M_s_
1t_1−σ_w/2M_s_2t_2 | (3) H_c_1>σ_w/2M_s_1t_1 (4) H_c_2>σ_w/2M_s_2t_2 (5) H_c_2+σ_w/2M_s_2t_2<|H
ini. The recording medium according to claim 7, which satisfies |<H_c_1−σ_w/2M_s_1t_1. However, T_R: room temperature T_c_o_m_p_. _2: Compensation temperature of the second layer T_c_1: Curie point of the first layer T_c_2: Curie point of the second layer T_L: Temperature of the recording medium when irradiated with a low-level laser beam T_H: Temperature of the recording medium when irradiated with a high-level laser beam Temperature of the recording medium at the time H_c_1: Coercive force of the first layer H_c_2: Coercive force of the second layer M_s_1: Saturation magnetic moment of the first layer M_s_2: Saturation magnetic moment of the second layer t_1: Thickness of the first layer t_2: Film thickness of second layer σ_w: Exchange coupling force Hini. : Initial auxiliary magnetic field 16 The first layer is a transition metal-heavy rare earth alloy that is rich in transition metals and has no compensation temperature between room temperature and the Curie point, the second layer is
The layer is heavy rare earth rich and consists of a transition metal-heavy rare earth alloy that does not have a compensation temperature between room temperature and the Curie point, and the following conditional expression: (1) T_R<T_c_1≒T_L<T_c_2≒T_
H and at room temperature the following conditional expressions: (2) H_c_1>H_c_2+|σ_w/2M_s_
1t_1−σ_w/2M_s_2t_2 | (3) H_c_1>σ_w/2M_s_1t_1 (4) H_c_2>σ_w/2M_s_2t_2 (5) H_c_2+σ_w/2M_s_2t_2<|H
ini. The recording medium according to claim 7, which satisfies |<H_c_1+σ_w/2M_s_1t_1. However, T_R: Room temperature T_c_1: Curie point of the first layer T_c_2: Curie point of the second layer T_L: Temperature of the recording medium when irradiated with a low-level laser beam T_H: Record when irradiated with a high-level laser beam Medium temperature H_c_1: Coercive force of the first layer H_c_2: Coercive force of the second layer M_s_1: Saturation magnetic moment of the first layer M_s_2: Saturation magnetic moment of the second layer t_1: Film thickness of the first layer t_2: Second layer Film thickness σ_w: exchange coupling force Hini. : Initial auxiliary magnetic field