JPS63148446A - Magneto-optical recording medium capable of over-write - Google Patents

Abstract

PURPOSE:To realize an over-write mode where an instantaneous recording action is possible by holding the bits of 1st and 2nd layers which are formed with the beams of low levels regardless of the influence of a recording magnetic field. CONSTITUTION:When a beam intensity has a high level, both the 1st layer (recording layer) 1 and the 2nd layer (auxiliary recording layer) 2 are magnetized at level 0 or a low level by the radiation heat of the laser beam. Thus the temperature of a recording medium drops as the medium gets further away from a beam spot. In this cooling (heat dissipation) process, a bit having the magnetization of 'direction A' is formed at the layer 2 due to a recording magnetic field (Hb). Then in the following cooling process, a bit having the magnetization of 'adverse direction A' is formed at the layer 2 with reverse. Then a bit having the magnetization of 'adverse direction A' or 'direction A' is formed to the layer 1 in the following process owing to the influence of the 'adverse direction A' of the layer 2. In such a way, an over-write mode is secured and furthermore the same information are recorded to both layers 1 and 2. Thus the linear polarized light irradiates the layer 1 or 2 and the information can be reproduced from the reflected light of said polarized light.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to overwrite.
The present invention relates to a possible magneto-optical recording medium, an overwritable magneto-optical recording method using the same, a recording device, and a reproducing method.

[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 a+agnetic 1ayer or
1ayers). This magnetized film is made of, for example, amorphous GdFe, GdCo5GdFeCo, TbF
It consists of TbCo, TbFeCo, etc. The recording layer generally has concentric or spiral tracks on which information is recorded. Here, in this specification, either "upward J" or "downward J" with respect 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 (B,) with magnetization in the "A direction" and a bit (BO) with magnetization in the "opposite A direction". recorded.

These bins) B+ and Bo correspond to one and the other of 1.0 of the digital signal, respectively. However, the magnetization of the track to be recorded is generally aligned in the "reverse A direction" by applying a strong external magnetic field before recording.

This process is initialization (in itialize)
It is called. Then, a bit (B1) having magnetization in the "A direction" is formed on the track. The information is this bit (
B+) and/or bit length.

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 layer. In optical recording, recording densities of up to about 10@bit/- can theoretically be achieved.

This is because the laser beam can spread all the way to a spot with a diameter almost as small as its wavelength.
This is because it is possible to entrate).

As shown in FIG. 2, in magneto-optical recording, a laser beam (L) is focused onto the recording layer (1).

Mix it up and heat it up. 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 (coers iv ity) of the locally heated portion decreases and becomes smaller than the recording magnetic field (Hb). As a result, the magnetization of that portion is aligned with the direction of the recording magnetic field (Hb), thus forming an oppositely magnetized bit.

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 (
compensation te+5perature
), where the magnetization (M) becomes zero. Conversely, He becomes extremely large near this temperature, and when the temperature deviates from this temperature, Hc decreases rapidly. This reduced Hc is overcome by a relatively weak recording magnetic field (Hb). In other words, recording becomes possible. This recording process is T
CO@e, called write (compensation point write).

However, there is no need 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, the recording magnetic field (Hb
'), recording is possible.

Playback ■Pleasure: FIG. 3 shows the principle of information reproduction based on the magneto-optical effect.

Light is an electromagnetic wave with a TL magnetic field vector that is typically diverging in all directions in a plane perpendicular to the optical path. When the light is converted into linearly polarized light and irradiated onto the recording layer (1), the light is either reflected on its surface or the recording layer (
1).

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

For example, if the 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 the plane of 10 degrees, then
The light reflected from the bit (Bo) 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)2 is applied to the analyzer by i3 and captured by the detector (photoelectric conversion means). As a result, a bit magnetized in the “A direction” (B
, ) appears brighter than the nose (Bo) when magnetized in the "reverse A direction" and generates a strong electrical signal at the detector. The electrical signal from this detector is modulated according to the recorded information, thus reproducing the information.

[Problem that the invention seeks to solve]

By the way, in order to reuse a recorded medium, it is necessary to (i) initialize the medium again with an initialization device, or (ii) provide the recording device with an erasing head similar to the recording head, or (iii) ) It is necessary to erase the recorded information in advance using a recording device or an erasing device as a preliminary process.

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

However, if the direction of the recording magnetic field (Hb) can be freely changed between the "A direction" and the "reverse A direction" as necessary, overwriting becomes possible. However, it is impossible to change the direction of the recording magnetic field (Hb) at high speed. For example, if the means for applying the magnetic field (Hb) described above is a permanent magnet, the direction of the magnet may be mechanically reversed. There is a need. However, it is impossible to reverse the direction of the magnet at high speed. Even when the recording magnetic field (Hb) applying means is an electromagnet, it is impossible to change the direction of a large amount of current at such high speed.

[Means for solving problems]

The present inventors have invented an overwritable disk-shaped multilayer magneto-optical recording medium, an overwritable recording method, a recording device thereof, and a method of reproducing overwritten information based on a new principle.

The present invention first provides the following recording medium.

"In an overwritable disk-shaped multilayer magneto-optical recording medium in which a first layer having perpendicular magnetic anisotropy is a recording layer and a second layer having perpendicular magnetic anisotropy is a recording auxiliary layer, the first layer The magnetization of the second layer does not change at room temperature even when a recording magnetic field in the "A direction", which is either upward or downward, is applied; Under a magnetic field, the magnetization is aligned in the "A direction" at room temperature, and a laser beam modulated according to the information to be recorded is irradiated, and when the intensity of the beam is at a high level, the radiant heat of the beam damages the first and second layers. When both magnetizations become zero or weak, and then the beam disappears and cooling begins, a bit with “A direction” magnetization is formed in the second layer under the influence of the recording magnetic field during the cooling process, which is further During the cooling process, a bit is reversed and has "reverse A direction" magnetization, and as the cooling progresses further, the first layer becomes "reverse A direction" [or " Even if a bit with magnetization in the "A direction" is formed, and then the "reverse A direction" magnetization of the second layer is reversed to the "A direction" due to the influence of the "A direction" recording magnetic field, the influence of the recording magnetic field is As soon as it disappears, it is reversed again under the influence of the magnetization of the first layer and becomes "reverse A direction", and when the intensity of the beam is at a low level, only the magnetization of the first layer becomes zero or weak due to the radiant heat of the beam. Then, when the beam disappears and cooling begins,
In the cooling process, bits with magnetization in the A direction (or inverse A direction) are formed in the first layer due to the influence of the magnetization in the second layer, and the first WI formed by the low-level beam A recording medium characterized in that the bits in the second layer are retained whether or not they are subsequently influenced by a recording magnetic field.''The first layer has a higher coercive force at room temperature than the second layer and has a Curie The first layer is a transition metal-rich or heavy rare earth-rich magnetic thin film selected from a transition metal-heavy rare earth metal alloy composition, and the second layer has a lower coercive force at room temperature than the first layer. the second layer has a compensation temperature that is the same as or near the Curie point of the first layer, and the second layer has a high Curie point;
The layer is a heavy rare earth rich magnetic thin film selected from a transition metal-heavy rare earth metal alloy composition.

Second, the present invention provides the following overwritable magneto-optical recording method.

"In a recording method for overwrite recording on an overwritable disk-shaped multilayer magneto-optical recording medium, (a) the following medium is used as the medium; the first layer having perpendicular magnetic anisotropy is the recording layer In an overwritable disk-shaped multilayer magneto-optical recording medium in which a second layer having perpendicular magnetic anisotropy is used as a recording auxiliary layer, the first layer has a higher coercive force at room temperature than the second layer and has a Curie and the first layer is a transition metal-rich or heavy rare earth-rich magnetic thin film selected from a transition metal-heavy rare earth metal alloy composition, and the second layer has a coercive force at room temperature compared to the first layer. the second layer has a compensation temperature equal to or near the Curie point of the first layer, and the second layer has a heavy rare earth selected from a transition metal-heavy rare earth metal alloy composition. (b) moving said medium; (c) moving said medium; (c) moving said medium; (c) moving said medium;
(d) Irradiating the medium with a laser beam; (e) irradiating the medium with a laser beam; (d) irradiating the medium with a laser beam;
) Modulating the beam intensity in a pulsed manner according to the binarization information G to be recorded; (f) Applying a recording magnetic field to a portion of the medium irradiated with the beam; Axis) When the intensity of the beam is at a high level At this time, first, the radiant heat of the beam makes the magnetization of both the first and second layers zero or weak, and then when the beam disappears and cooling begins, the recording magnetic field causes the 2N to be in the "A direction" during the cooling process. A bit with magnetization is formed, and as it is further cooled, it is reversed to form a bit with "reverse A direction" magnetization, and as the cooling progresses further, the second layer's "reverse A direction" magnetization is formed. Due to the influence of magnetization, a bit with "reverse A direction" [or "A direction"] magnetization is formed in the 11th layer, and then the "reverse A direction" magnetization of the second layer is changed to "reverse A direction" magnetization due to the influence of the "A direction" recording magnetic field. Even if it is reversed to the direction A, as soon as the influence of the recording magnetic field disappears, the first
Under the influence of the magnetization of the layer, it is reversed again and becomes ``reverse A direction'', and when the intensity of the beam is at a low level, first the magnetization of only the first layer is reduced to zero or weak by the radiation heat of the beam, and then the beam disappears. When cooling begins, the second layer "
Bits with magnetization in the "A direction" (or "reverse A direction") are formed in the first layer under the influence of magnetization in the "A direction", and the bits in the first and second layers formed by the low-level beam are thus: After that, the recording method is retained whether or not it is influenced by a recording magnetic field. Thirdly, the present invention provides the following overwritable magneto-optical recording device.

"In an overwritable magneto-optical recording device, this device includes (a) means for moving an overwritable magneto-optical recording medium; a first layer having perpendicular magnetic anisotropy as a recording layer; In an overwritable disk-shaped multilayer magneto-optical recording medium having an anisotropic second J! as a recording auxiliary layer, the first layer has a higher coercive force and a lower Curie point at room temperature than the second layer. , and the first layer is a transition metal-rich or heavy rare earth-rich magnetic thin film selected from a transition metal-heavy rare earth metal alloy composition, and the second layer has a lower coercive force at room temperature than the first layer and has a Curie point. is high, the second layer has a compensation temperature equal to or near the Curie point of the 1N, and the second layer is a heavy rare earth-rich magnetic GI film selected from a transition metal-heavy rare earth metal alloy composition. Medium that is characterized by certain things (b) The following Hb
recording magnetic field applying means; (c) laser beam light source; (d) beam intensity according to the binary information to be recorded;
) a high level that provides the medium with an appropriate temperature to form either a bit with upward magnetization or a bit with downward magnetization; and (2) a high level that provides the medium with an appropriate temperature to form the other bit. An overwritable recording device comprising: means for modulating a low level in a pulsed manner;

However, in the compound; ±), the upper row shows the case where the first layer is rich in transition metals, and the lower row shows the case where the first layer is rich in heavy rare earth elements. The symbols used have the following meanings.

HCI: Coercive force of the first layer HCI: Coercive force of the second layer M3. : Saturation magnetic moment of the first layer M31 : Saturation magnetic moment of the second layer t, : Thickness of the first layer t2 : Thickness of the second layer σ, : Interfacial domain wall energy Hb : Recording magnetic field"Fourthly, the present invention provides the following playback method.

``A reproduction method in which a laser beam is irradiated to the second layer of an overwritable multilayer magneto-optical recording medium that has been overwritten by the following recording method.

The following medium is used as the medium; an overwritable disk-shaped multilayer in which the first layer having perpendicular magnetic anisotropy is the recording layer and the second layer having perpendicular magnetic anisotropy is the recording auxiliary layer. In the magneto-optical recording medium, the first layer has a higher coercive force and a lower Curie point at room temperature than the second layer, and the first layer is a transition metal phosphor selected from a transition metal-heavy rare earth metal alloy composition. or a heavy rare earth-based magnetic thin film, the second layer has a lower coercive force and a higher Curie point at room temperature than the first layer, and the second layer has a compensation temperature equal to or near the Curie point of the first N. and the second Jit is a heavy rare earth-rich magnetic thin film selected from a transition metal-heavy rare earth metal alloy composition.

(b) moving the medium; (c) moving the medium in either an upward or downward direction;
(d) irradiating the medium with a laser beam; (e) irradiating the medium with a laser beam; (e) aligning only the magnetization of the second layer in the "A direction" at room temperature immediately before recording; (f) Applying a recording magnetic field to a portion of the medium irradiated with the beam; (g) When the intensity of the beam is at a high level, first The radiant heat of the beam makes the magnetization of both the first and second layers zero or weak,
Next, when the beam disappears and cooling begins, a bit with "A direction" magnetization is formed in the second layer due to the influence of the recording magnetic field during the cooling process, and this bit is reversed during the further cooling process and becomes "reverse A direction". ” A bit with magnetization is formed, and as the cooling progresses further, a bit with magnetization in the “reverse A direction” (or “A direction”) is formed in the first layer due to the influence of the “reverse A direction” magnetization in the second layer. Even if the "reverse A direction" magnetization of the second layer is reversed to "A direction" due to the influence of the "A direction" recording magnetic field, as soon as the influence of the recording magnetic field disappears, the first
Under the influence of the magnetization of the layer, it is reversed again and becomes "inverted A direction", and when the intensity of the beam is at a low level, first the magnetization of the first layer is reduced to zero or weak by the radiation heat of the beam, and then the beam disappears. When cooling begins, the second layer "
Bits with magnetization in the A direction (or in the opposite A direction) are formed in the first layer under the influence of the magnetization in the A direction, and the bits in the first and second layers formed by the low-level beam are A recording method characterized by: being retained whether or not it is influenced by a post-recording magnetic field; [Operation] In the present invention, the laser beam is modulated in a pulsed manner according to the information to be recorded. However, this is also done in conventional magneto-optical recording, and there are known means for modulating the beam intensity in a pulsed manner according to the binary information to be recorded.For example, TIIE BELL SYST
EM TECI! NICAL JOURNAL.

Vol. 62 (1983), 1923-1936.

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

That is, when the beam intensity is at a high level, if the magnetization of both the first layer (recording layer) and the second layer (recording auxiliary N) is reduced to zero or weakly by the radiant heat of the laser beam, then the beam spot The medium temperature decreases as it deviates from the
During the cooling (cooling) process, the recording magnetic field (Hb) causes the second
A bit with "A direction" magnetization is formed at 7W, which is reversed in the further cooling process.
A bit with magnetization in the "reverse A direction" is formed, and in the process of further cooling, the first layer has "reverse A direction" magnetization [or "A direction" magnetization] due to the influence of the "reverse A direction" in the second layer. A bit is formed.

When the beam intensity is at a low level, the magnetization of only the first layer (recording layer) is reduced to zero or weakly by the radiant heat of the laser beam, and then the medium temperature decreases as it moves away from the beam spot. During the cooling process, a bit having "A-direction" magnetization (or "reverse A-direction" magnetization) is formed in the first layer due to the influence of the "A-direction" magnetization of the second layer.

Given the necessary high and low levels, it is possible to modulate the beam strength according to the present invention by only partially modifying the modulation means described in the above-mentioned documents, etc.
Easy for those skilled in the art.

In addition, in this specification, the expression [is △Δ△] means that when you first read ○○○ outside of [], the following ΩΩΩ''
In case of a, a), we will also read OOO outside []. On the other hand, without reading OOO first, ΔΔΔ in []
When you select and read it, the following 000 (is Δ
ΔΔ], ΔΔΔ in () is read without reading OOO.

As is already known, even when no recording is being performed, the laser beam may be turned on at a very low level of 0, for example in order to access a predetermined recording location on the medium. Further, when the laser beam is used for reproduction, the laser beam may be turned on at a very low level of intensity.In the present invention, the intensity of the laser beam may also be set to this very low level of 0. However, the low level when forming the bit is higher than this very low level, so, for example, the output waveform of the laser beam in the present invention is as follows.

In addition, in the present invention, the laser beams are "two beams in close proximity", and the leading beam is lit at a low level and is not modulated in principle, so that the laser beam is always in the "A direction" [or the "reverse A direction"]. By pulse-modulating the trailing beam according to the information between a high level and a level lower than the low level (including zero level), the previous information is erased. Facing A only when level
Alternatively, it is also possible to form a bip in the direction of "reverse A" and record it accordingly.

Example of beam intensity information signal 111001111000 Here, for convenience, "direction A" is referred to as an upward arrow in the paper of this specification. The "reverse A direction" is indicated by a downward arrow a.

A recording magnetic field (Hb) is essentially necessary during recording, but it cannot be narrowed down to a minute area like a laser beam spot.

Therefore, a leakage magnetic field from the recording magnetic field applying means extends before and after the spot position of the laser beam (ie, before and after recording) as shown in FIG.

This leakage magnetic field is actively utilized in the present invention. Therefore, in the recording medium of the present invention, only the second layer is magnetized in the "A direction" by this recording magnetic field (Hb) until immediately before recording. This state can be expressed conceptually as follows.

In the medium of the present invention, both the first layer and the second layer contain transition metals (tra
heavy rare earth metals (heavy rare earth metals)
avyrare earth metal) alloy composition, and the second layer has a compensation temperature.

In this case, the direction and magnitude of magnetization appearing externally as each alloy are determined by the direction and magnitude of spin of transition metal atoms (hereinafter abbreviated as TM) inside the alloy and heavy rare earth metal atoms (hereinafter abbreviated as TM). For example, the direction and magnitude of the spin of TM are represented by the dotted line vector ↑, and the spin of RE is represented by the solid line vector T, and the magnetization of the entire alloy is What is the direction and magnitude of the double solid vector? In this case, expressed as a vector? is expressed as the sum of vector ↑ and vector ↑. However, in the alloy, the directions of the vector ↑ and the vector T are always opposite due to the interaction between the 7M spin and the RE spin. Therefore, harmony with ↑ or ↓
The sum of and ↑ means that when the strengths of both are equal, the alloy vector is zero (that is, the magnitude of external magnetization is zero)
become.

The alloy composition when this becomes zero is the compensation composition (compe
For other compositions, the alloy has an intensity equal to the difference in intensity between the two spins, and a vector (or 8) with a direction equal to the direction of the larger vector. The magnetization of this vector appears outside 0 For example, ↑↓
becomes official, and courtesy becomes a.

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, ○○ Lynch For example, R
It is called E-lift.

For both the first layer and the second N, the 7M-rich composition and R
E-rich composition. Therefore, if we take the composition of the first layer on the vertical axis and the composition of the second layer on the horizontal axis, we get the following 4.
Can be classified into quadrants.

RE Lift (1st layer) 7M Rich (1st layer) [The intersection of the vertical and horizontal coordinates represents the compensation composition of both layers.] The medium of the present invention is divided into the ■quadrant (P type) and ■quadrant (A type). In the medium of the present invention, an exchange coupling force acts between the first layer and the second layer, and the first layer is not magnetized in the high temperature state (the second layer is not magnetized, for example, in the "A direction"). When there is a magnetizer,
As cooling (cooling) further progresses and the temperature decreases, magnetization also appears in the 111th layer, but at that time, the iris layer is influenced by the magnetization of the 21st layer due to exchange coupling force, and the iris layer becomes a second layer in the carbonate layer. The case where the same "A direction" magnetization point appears, and the 21st! There are two types of cases in which "reverse A direction" magnetization 8, which is opposite to the above, appears. Here, the former medium is called P type, and the latter medium is called A type.

In the medium of the present invention, the first layer may be 7M-rich or RE-rich; if it is 7M-rich, it will be in the ■ quadrant (type A), and if it is RE-rich, it will be in the ■ quadrant (type A). Quadrant (becomes P-taifuri.

On the other hand, when looking at changes in coercive force with respect to temperature changes, there are alloy compositions that have the characteristic that the coercive force increases to infinity and then decreases again before reaching the Curie point (the temperature at which the coercive force is zero). The temperature corresponding to this infinity is the compensation temperature (
Tc, , , ).

The second layer has a compensation temperature above room temperature, but the first layer may have a compensation temperature above room temperature.
The media of the present invention are also classified into those in which the first layer does not have a compensation temperature (type I) and those in which it does have a compensation temperature (type 2).
The rich ■quadrant (A type) media is only type 2, R
Both types I and 2 exist in the E-rich I elephant III (P type). If you draw a "graph representing the relationship between coercive force and temperature" for types I and 2 media, it will be as follows. Note that the thin line is that of the first layer, and the thick line is that of the second layer.
It is that of layers.

Type I Coercive Force Coercive Force In all types of the media of the present invention, the first layer has a sufficiently large coercive force MCI that the magnetization is not reversed by the recording magnetic field at room temperature, and the Curie point T'c+ is lower than that of the second layer. The second layer is an RE lift and has a compensation temperature Tco at or near the Curie point of the first layer.
ap,! It is a layer with a high Curie point. Furthermore, the second N
At room temperature, when there is a recording magnetic field Hb, the direction of magnetization is aligned in the direction of the container, and when there is no substantial effect of Hb, it is influenced by each spin in the first layer (due to exchange coupling force). while T, has a small coercive force such that each spin of the second layer can be oriented in the same direction as that of the first layer (i.e. transfer of magnetization is possible). Around 1112, the coercive force is so large that the magnetization cannot be reversed by Hb) (c
It has z.

Expressing the above in a formula, it becomes as follows.

(IITR< T c+z7LzT camp, z
< TM + TCZ (In this formula, there is no difference in magnitude between T and 'fez, but both are T cl x T L
~T Ci) @ 9 + 1. 〉 Then, at room temperature, Msztz However, in the composite;
It is a Lynchian medium (P type, I quadrant), and the symbols used have the following meanings.

T: Room temperature TL + Temperature of the recording medium when irradiated with a low-level laser beam TH: Temperature of the recording medium when irradiated with a high-level laser beam Tel: Curie point of the first layer TB: Temperature of the recording medium when irradiated with a high-level laser beam Curie point T come, z: Compensation temperature Hc of the second layer: Coercive force Hcz of the second layer: Coercive force MH of the second layer: Saturation magnetic moment Mst of the second layer Mst: Saturation magnetic moment t of the second layer : Film thickness of the first layer t! : Thickness of the second layer σw : Interfacial domain wall energy Hb : Recording magnetic field A hysteresis curve at room temperature is as follows for a P type medium (I quadrant, first layer is RE lift).

Note that the square between the first layer and the second layer is an interfacial domain wall, and the thick line in the hysteresis curve is the hysteresis curve of the second layer biased by exchange coupling force. The magnitude of Hb may be within the range indicated by → in the figure, but a value close to the left end is preferable.

The hysteresis curve at room temperature for A type media (I quadrant, first layer is TM Lynch) is as follows.

Note that the □ between the 11th layer and the 2nd layer is an interfacial domain wall, and the thick line in the hysteresis curve is the 2N hysteresis curve biased by the exchange coupling force. The magnitude of Hb may be within the range indicated by → in the figure, but a value close to the left end is preferable.

Note that both the first layer and the second layer may each have a multilayer structure, or may have a non-uniform structure in which there is no clear boundary between the two layers and one gradually changes from one to the other.

Here, the recording principle of the present invention will be explained in detail regarding the P type medium.

Is this medium magnetized in "A direction" or its bit? , and the "reverse" magnetization or its bits are represented by 8.
The state after the previous recording is conceptually in the following state of flail.

(a) (b) And write t! The magnetic field applying means cannot narrowly apply a magnetic field to a minute area like a laser beam spot, and as shown in Figure 4, Hb leaks before and after that, causing damage to the first and second layers. This Hb
continues to be applied up to the beam spot position.

Therefore, for example, the second layer, which is affected by the recording magnetic field Hb in the "A direction" ↑, remains in the "A direction" until just before recording. It becomes a magnetized state. This state can be expressed conceptually as state 2.

(a) (b) Note that the thick line - indicates an interfacial domain wall (the same applies below).

□High-temperature cycle□ Here, the medium temperature is first raised to TL by irradiating a high-level laser beam. Then, since TL is almost equal to the Curie point TCI of the first layer, state 2 (a),
(b) In both cases, the magnetization of the first layer disappears.

On the other hand, for the second layer, the compensation temperature T, is close. ae, *
Therefore, if the temperature continues to rise and exceeds Tcast+t, a significant change will occur in the magnetization state. In other words, T
Magnetization in "A direction" before ellIII'+1? (↑Eng) exceeds T C61j D + Z, RE, T
Although the direction of each M spin does not change, the magnitude relationship of the intensities is reversed (↑4−↑′,). Therefore, the magnetization of the second layer is reversed and becomes magnetization 8 in the "reverse A direction."

This results in state 38.

At this temperature, )Ici is still large, so the magnetization 8 of the second layer is not reversed by ↑Hb.

However, when the temperature further increases and reaches T, HCl becomes smaller and is reversed by ↑Hb. This state is B
4. It is I.

TII is a little higher, so the temperature rises further and H
c! may become zero. In that case, the next time the medium leaves the spot area of the laser beam, the medium will naturally cool down (cooling process) and its temperature will drop, but at that time, when it drops a little, it will follow ↑Hb. Magnetization in the opposite direction appears, resulting in the shape [411].

In any case, when the medium temperature further deviates from the laser beam spot region and exceeds T C (1@e* 1), the same change as before occurs. That is, Tcoa
Magnetization in “A direction” after p+g? (↓τ) is T C6
When 1111H is exceeded, the RE and TM spin directions do not change, but the strength relationship is reversed (,!→↓↑
), therefore, the magnetization of the second layer is reversed and becomes magnetization 8 in the "reverse A direction". This is state 5N.

Note that at this temperature, HCt is sufficiently large so that it is not reversed by Hb.

Then, when the medium cools down a little further, the medium temperature drops below the TCI, and magnetization appears in the first layer. At this time, the exchange coupling force from the second layer acts to align the RE spins (↓) and the TM spins (↑), and as a result, (↓↑), that is, a magnetization of 8 appears.

This state is state B6H.

At this temperature, the coercive force 1 (ct) of the second layer is larger than ↑Hb, so it is not reversed, and the magnetization of the first layer is not reversed and the state 6N is maintained because the effect of the exchange coupling force is larger than Hb.

Then, when the medium temperature further decreases, Hol rapidly increases and becomes unaffected by Hb. On the other hand, HCt
becomes smaller, so only the second Fm is inverted by ↑Hb, resulting in the shape B7H.

This state continues up to room temperature (but as the medium rotates and eventually moves away from the recording magnetic field applying means, the influence of Hb disappears).
However, this time, due to conditional expression (3), the magnetization of the second layer is reversed again due to the exchange coupling force, resulting in a state B8. become.

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

□Low temperature cycle□ A low-level laser beam is irradiated to raise the medium temperature to TL. Since TL is near the Curie point Tel, the state a2
In both (a) and (b), the magnetization of the first layer disappears.

On the other hand, for the second layer, the compensation temperature T C011D is nearby.
Since H1 exists, if the temperature continues to rise, TL may or may not exceed T C6@p H1 to some extent.

(1) When exceeded: In this case, a significant change occurs in the magnetization state of the second layer. In other words, is the magnetization in the “A direction” before Tco*p+wealth? (↑、
) exceeds T C6 @ e + R, the direction of each RE%TM spin does not change, but the strength relationship is reversed (↑0−↑↓). Therefore, the magnetization of the second layer is reversed, The magnetization number is in the "reverse A direction".

As a result, state a3L (1) is obtained.

(2) Case where it does not exceed: In this case, the direction of magnetization of the second layer is Jlt2
This is the state B3L (2).

In any case, at this temperature Hc! is large, so ↑Hb
Not affected by

Next, when the medium temperature falls outside the laser beam spot region, the change will be different depending on whether TL slightly exceeds T tO@e+ Z or not.

(1) When exceeding: The magnetization of the second layer is
From magnetization 8 (cage) of “direction”, T e 011 D H2
Once it is exceeded, the RE and TM spin directions do not change, but
The strength relationship is reversed (↑↓−↑ya), so the magnetization of the second layer is reversed and the magnetization is in the "A direction"? become.

This is state a4t(1).

(2) If it does not exceed - In this case, the direction of magnetization of the second layer is as follows.

State 3L is the same as (2), which is state 7Li4L (
2).

Therefore, if TL exceeds T C@ @ P H1 a little but does not exceed it, and the medium temperature decreases a little, state 4L (1
), the same state will occur as shown in (2).

From this state, as the medium temperature moves further away from the laser beam spot region, the medium temperature decreases further, and when the medium temperature decreases slightly below Tc1, magnetization appears in the first layer.

At this time, the exchange coupling force from the second layer is between the RE spins (↑
), which acts to align the TM spins (↓), resulting in the appearance of (↑↓), that is, electric magnetization. This state is state 5L.

This state continues up to room temperature and remains the same even when the medium rotates and eventually moves away from the recording magnetic field applying means and the influence of Hb disappears.

Although the above description has been made regarding a medium in which the first layer does not have a compensation temperature, a certain medium can also be described in substantially the same way.

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

Note that in the low-temperature cycle, the recording magnetic field (Hb) is not required, but Hb is turned on at high speed (for a short time).

Since it is impossible to turn it off, it is forced to remain as it was during the high temperature cycle.

As explained above, regardless of the direction of magnetization of the first layer, both the first layer and the second layer are magnetized in the "A direction" due to the high temperature cycle and the low temperature cycle. The bit with "reverse A direction" magnetization: is formed. 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. The information remains in both the second and second layers.

Note that, as described above, the leading beam may be constantly turned on at a low level to perform erasing in a low-temperature cycle, the trailing beam may be pulse-modulated according to information, and recording may be performed in a high-temperature cycle when the trailing beam is at the high level.

Next, the recording principle of the present invention will be explained in detail regarding the A type medium.

If the "rA direction" magnetization or its bit is represented by t, and the "reverse" magnetization or its bit is represented by 8, then in the state after the previous recording, conceptually the next state l is reached. It has become.

(a) (b) As described above, the recording magnetic field applying means cannot apply a magnetic field focused on a minute area like a laser beam spot, and as shown in Figure 4, Also H
b leaks and exerts Hb on the first and second layers, and this Hb continues to be applied up to the beam spot position.

Therefore, for example, the second layer affected by the recording magnetic field Hb in the "A direction" ↑ will remain in the "A direction" until just before recording. It becomes a magnetized state. This state can be expressed conceptually as state 2.

□High-temperature cycle□ Here, a high-level laser beam is irradiated to first raise the medium temperature to TL. Then, since TL is almost equal to the Curie point TCI of the first layer, state H2 (a),
(b) In both cases, the magnetization of the g-th layer disappears.

On the other hand, for the second layer, the compensation temperature Te1l@P,
! Therefore, the temperature continues to rise and TCO#j+
Beyond t, significant changes in the magnetization state occur. In other words, T. Me,! Magnetization in front of “A direction”? (↑ya)
When exceeding Teat, z, the RE and TM spin directions do not change, but the magnitude relationship of the intensities is reversed (↑
↓→↑↓), therefore, the magnetization of the second layer is reversed and becomes magnetization 8 in the "reverse A direction."

As a result, state 3. Becomes I.

At this temperature, )(cz is still large, so the magnetization 6 of the second layer is not reversed by ↑Hb.

However, when the temperature rises further and reaches TH, 1 (ct
becomes smaller and is inverted by ↑Hb. This state is state 411.

T, or a little higher (because of that, the temperature rises further and HC
t may become zero. In that case, the next time the medium leaves the spot area of the laser beam, the medium will naturally cool down (cooling process) and the temperature will drop, but at that time, when the temperature decreases a little, it will reach ↑Hb. Magnetization in the same direction appears, and shape B
4. become.

In any case, as we move further out of the laser beam spot region, the medium temperature decreases, and as we cross T co□, fog, the same changes as before occur. In other words, when the magnetization t (, ↑) in the "A direction" after Teat, t exceeds T co □, 8, the RE and TM spin directions do not change, but the strength relationship is reversed ( ↓↑ -↓↑), therefore, the magnetization of the 2311th magnet is reversed and becomes magnetized in the "reverse A direction." This is state 5H.

Then, when it cools down a little further, the medium temperature drops below TcI, and at that time, magnetization appears in the 1N. At this time, the exchange coupling force from the second layer acts to align the RE spins (↓) and the TM spins (↑), resulting in (,?) In other words? magnetization appears.

This state is state 6N.

At this temperature, the coercive force HCI of the second Ji is greater than ↑Hb, so it is not reversed, and the magnetization of the first layer is not reversed and state 6, I is maintained because the effect of the exchange coupling force is greater than Hb.

Then, when the medium temperature further decreases, the MCI increases rapidly and becomes unaffected by Hb. On the other hand) (c
Since x becomes small, only the second layer is inverted by ↑Hb and becomes the state 't, l.

This state continues up to room temperature, but as the medium rotates and eventually moves away from the recording magnetic field applying means, the influence of Hb disappears.

However, this time, due to conditional expression (3), the magnetization of the second layer is reversed again due to the exchange coupling force, resulting in state 8. become.

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

□Low-temperature cycle□ A low-level laser beam is irradiated to raise the medium temperature to T. TL is near the Curie point TcI, so state a2
In both (a) and (b), the magnetization of the first layer disappears.

On the other hand, for the second layer, the compensation temperature Tcosp+1
Therefore, if the temperature continues to rise and TL becomes somewhat T.
c, MPHI may or may not be exceeded.

(1) When exceeded: In this case, a significant change occurs in the magnetization state of the second layer. In other words, T. 1. ．． Magnetization in “A direction” before 2? (↑↓
), when Ttome* is exceeded, the RE and TM spin directions do not change, but the strength relationship is reversed ( ↑
↓→↑↓), therefore, the magnetization of the second layer is reversed and becomes magnetization a in the "reverse A direction."

This results in state 3L (1).

(2) Case where it does not exceed: In this case, the direction of magnetization of the second layer is the same as state 2, which is the state fi! 3t (2).

In any case, at this temperature) (cx is large, so ↑H
Not affected by b.

Next, when the medium temperature falls outside the spot region of the laser beam, the change will be different depending on whether TL slightly exceeds Tceat,g or not.

(1) When exceeded: The magnetization of the second layer changes from the magnetization 8 (↑↓) in the "reverse A direction" after T C (1M 9.1) to T9°1., O.
Although the RE and TM spin directions do not change, the strength relationship is reversed (↑knee 18), so the magnetization of the second layer is reversed and becomes a magnetization point in the "A direction."

This is shape B4L (1).

(2) When not exceeding: In this case, the direction of magnetization of the second layer is state 3L.
This is the state aii4L (2), which is the same as (2).

Therefore, even if TL slightly exceeds T Ca @ p + 1, it will not exceed it (and if the medium temperature decreases slightly, the state B4L (
The same state occurs as shown in 1) and (2).

From this state, as the medium temperature moves further away from the laser beam spot region, the medium temperature decreases further, and when it decreases slightly below T'c+, magnetization appears in the first layer.

At this time, the exchange coupling force from the second layer (T4) acts to align the RE spins (↑) and the TM spins (↓). As a result, (↑↓) that is, the magnetization of 8 is opposed to tHb. Appear. This state is state 5L.

This state continues up to room temperature and remains the same even when the medium rotates and eventually moves away from the recording magnetic field applying means and the influence of Hb disappears.

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

Note that in the low-temperature cycle, the recording magnetic field (Hb) is not required, but Hb is turned on at high speed (for a short time).

Since it is impossible to turn it off, it is forced to remain as it was during the high temperature cycle.

As described above, regardless of the direction of magnetization of the first H, bits having magnetization in opposite directions are formed by the high temperature cycle and the low temperature cycle, that is, the & bit and the official bit.

? 8 As a result, 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.

Of course, as described above, the leading beam may be constantly turned on at a low level to perform erasing in a low-temperature cycle, the trailing beam may be pulse-modulated according to information, and recording may be performed in a high-temperature cycle when the trailing beam is at a high level.

Dwarf A! 6: Input of P type ↓ ↓ No CHb') (No Hb) One of A Eve ↓ ↓ (No Hb) (No Hb) As described above, according to the present invention, information is stored in both the first layer and the second layer. is recorded and stored, so if either the first or second layer is irradiated with linearly polarized light, the reflected light contains information, so the information can be reproduced in the same way as with conventional magneto-optical recording media. be done.

However, the Curie point of the second layer is higher, and the magnetic materials currently available for the second layer have a larger Bekar rotation angle θk than the first layer, so it is better to reproduce the C from the second layer. /N ratio is high (preferable).

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

(Example 1 - A type magneto-optical recording medium) Using a dual electron beam heating vacuum evaporation apparatus, the evaporation sources shown in Table 2 below were placed at two locations. .

A disk-shaped glass substrate with a thickness of 1.2 mm and a diameter of 200 a+m is set in the chamber of the apparatus. The chamber of the device is once evacuated to a vacuum level of 1 x 10" Torr or less. After that, the vacuum level is reduced to 1 to 2 x 10-&
The vapor deposition is carried out at a deposition rate of about 3 Torr/second, thereby depositing a G of 1500 Torr on the substrate.
dzsFeseCOtz (Note: Subscript numbers are atomic%
) is formed. Subsequently, a vacuum state was maintained. Replace the evaporation source. Then perform another evaporation and deposit 300 TbtaFe on top of the second layer. A first layer (recording layer) of b is formed.

Both the first and second layers are perpendicular magnetization films.

In this way, a disk-shaped two-layer magneto-optical recording medium 1 of type A, quadrant 1, type 2 in which the first layer was TM-rich was manufactured.

The manufacturing conditions and characteristics of this medium are shown in Table 1 below.

Table 1 This medium has TL = 140°C, TH = 180°C (
(see Example 4), then the following formula (1): % formula % is satisfied.

Moreover, formula (2): % formula % is satisfied. Furthermore, formula (3): σiHcz-100e <=1690e'1M
5ztz is satisfied, so when the influence of the recording magnetic field disappears, the second
The magnetization of the layer is influenced by the first layer, and the information in the first layer is eventually transferred to the second layer.

Furthermore, in equation (4), since σ5 Msztz σW +−161230e 2M□t1, the recording magnetic field Hb may be set to, for example, 2000e.

(Example 2 - P type magneto-optical recording medium) 2
Using the original RF magnetron sputtering equipment, place two targets as shown in Table 2 below.

A disk-shaped glass substrate with a thickness of 1.2 m+w and a diameter of 200 a+m is placed in the chamber of the apparatus.

The inside of the chamber of the device is once heated to 7 X 1O-7 Torr.
, after evacuation to the following vacuum degree, Ar gas was evacuated to 5×1O
-3 Torr.

Introduce. Sputtering is then performed at a deposition rate of about 2 layers/second, thereby forming a second layer of Gdz@Pe5oCO*z with a thickness of 1500 layers on the substrate. Next, while maintaining the vacuum state,
Change target. Then, sputtering is performed again to form a τbzllPev with a thickness of 300 people on the second FI.
Form the first layer b. Both the first layer and the second layer are perpendicular magnetization films.

In this way, a two-layer magneto-optical recording medium 2 in which the first layer was RE glitch P type, quadrant type 2, was manufactured.

The manufacturing conditions and characteristics of this disk-shaped medium are shown in Table 2 below.

Table 2 This medium has T+ = 140°C, T, = 180°C (
(see Example 5), then the following formula (1): % formula % is satisfied.

In addition, formula (2): % formula % (1 is satisfied.Furthermore, formula (3): σ-Hcz=100e<=1690e'1
M,,t.

Since the following is satisfied, when the influence of the recording magnetic field Hb disappears, the magnetization of the second layer is influenced by the first layer, and information in the first layer is eventually transferred to the second layer.

Further, in equation (4), since σy σ−−=80310e 2M□1°, the recording magnetic field Hb may be set to, for example, 2000e.

(Embodiment 3 - Magneto-optical recording and reproducing apparatus) This apparatus is capable of recording and reproducing, and its overall configuration is shown in FIG. 5 (conceptual diagram).

This device basically consists of: (a) Rotating means 21 for the recording medium 20; (b) Laser beam light source 23 which also serves as a linearly polarized light source; (c) Beam intensity is adjusted according to the binarized information to be recorded. (
1) A high level that provides a medium temperature T8 suitable for forming either a bit with upward magnetization or a bit with downward magnetization, and (2) a medium temperature suitable for forming the other bit. (d) 13m field Hb applying means 25; (e) Receiving the reflected light of the linearly polarized light irradiated to the second layer and detecting the reflected light contained in the reflected light; an optical analyzer 30 and a detector 31 constituting a reproducing means for reproducing the information in the form of an electrical signal;
: Consists of.

Here, as the recording magnetic field Hb applying means 25, the output is Zo.
o Use an electromagnet whose magnetic field direction is "A direction" ↑ at Oe. The electromagnet 25 is a fixed rod-shaped member having a length approximately corresponding to the length of the disk-shaped medium in the radial direction. The electromagnet 25 is connected to a recording head (
I decided not to move it together with the pink amplifier. That way, the big amplifier will be lighter and faster access will be possible. Also, this one! During playback, the magnet 25 is de-energized to stop its function.

(Example 4 -------... Magneto-optical recording/reproduction)
Magneto-optical recording and reproduction are performed using the recording and reproducing apparatus of Example 3 (see FIG. 5). First, the recording medium 20 of Example 1 (F&11) is moved by the rotating means 21 at a constant linear velocity of 8.5 m/sec.

A laser beam is irradiated onto the medium 20 from the substrate side (that is, from the second layer side). This beam is
When the level is high due to 4: 7,1 mTpj (ondi
sk), low level: 5.7 d (on disk)
) is adjusted so that the output is output. The beam is then modulated into pulses according to the information by means 24.

Here, the information to be recorded is a signal with a frequency of IMI+2. Therefore, the medium 20 was irradiated with the beam while being modulated at the frequency IMIIz. This should have recorded an IMHz signal.

Therefore, using the same device, we set the recording magnetic field Hb to zero (it can be weakened to the extent that there is no practical problem without making it zero), and irradiated the laser beam from the substrate side (that is, from the second layer side) for reproduction. I did it. However, the beam intensity was set to 1-disk (□n disk) by means 24. As a result, an IMHz signal was reproduced with a C/N ratio of -59 dB.

Next, a recording magnetic field was similarly applied to the already recorded area of the medium 20, and this time a signal with a frequency of 2 MH2 was recorded as new information. If this information is reproduced in the same way, the C/N ratio -
New information was reproduced at 58 dB.

At this time, all of the 1Ml1z signal (previous information) did not appear.

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

Note that under this condition, the temperature of the medium reaches T = 180°C at the high level and JTL - 140°C at the low level.

(Example 5 --- Magneto-optical recording/reproduction) Example 4
Magneto-optical recording and reproduction were carried out in the same manner as above.

Example 2 A laser beam is irradiated onto the (Na2) medium 20 from the substrate side (that is, from the second layer side). This beam is at high level by the means 24: 7.1 m
lA (on disk), at low level: 5.7 m
It is adjusted to output an output of W (ondisk). The beam is then modulated into pulses according to the information by means 24. Here, the information to be recorded is recorded at frequency I
It was set as the M112 signal. Therefore, the beam frequency l M
The medium 20 was irradiated while modulating at Hz. This would have recorded an I MHz signal.

Therefore, using the same device, we set the recording magnetic field Hb to zero (it can be weakened to the extent that there is no practical problem with zero) and irradiated the laser beam from the substrate side (that is, from the second layer side). Played. However, the beam intensity was set to IImW (on disk) by means 24, and as a result, a signal of 1Ml (z) was reproduced with a C/N ratio of 59dB.

Next, in the previously recorded area of the medium 20, a signal with a frequency of 3 MIIz was recorded as new information in the same way, this time with a recording magnetic field Hb = 2000 s. When this information was similarly reproduced, new information was reproduced with a C/N ratio of -57 dB. At this time, the I Ml2 signal (previous information) did not appear at all.

As a result, it was found that overwriting was possible. In addition, under these conditions, when the temperature of the medium is at a high level: '
r, -t80℃, low level: 'r, reaches -140℃.

〔Effect of the invention〕

As described above, according to the present invention, overwriting is possible and the same information is recorded in both the first layer and the second layer.
Information may be reproduced from the reflected light.

Currently, the material for the second layer has a higher Curie point than the material for the first Ji (which allows for stronger linearly polarized light to be irradiated during reproduction, resulting in a higher C/N ratio) and a larger θk. When reproducing from the first layer, the C ratio becomes higher than when reproducing from the first layer.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram illustrating a vertical cross section of a disk-shaped multilayer magneto-optical recording medium according to the present invention. FIG. 2 is a conceptual diagram illustrating the recording principle of the magneto-optical recording method. FIG. 3 is a conceptual diagram illustrating the reproduction principle of the magneto-optical recording method. FIG. 4 is a conceptual diagram illustrating that when recording on a recording medium according to the present invention, the recording magnetic field Hb extends both in front and behind the laser beam spot. The black hunting part is illuminated by a spot and heated by radiant heat. FIG. 5 is a conceptual diagram showing the overall configuration of a magneto-optical recording and reproducing apparatus according to a third embodiment of the present invention. [Explanation of symbols of main parts] L-... Laser beam t, p...-Linearly polarized light B1-... Bit B having "A direction" magnetization,
・−・・−Bit 1 with “reverse A direction” magnetization−・
--- Recording layer 2 --- Recording auxiliary layer 20 --- Overwritable magneto-optical recording medium 20a --- Substrate 21 --- Recording medium Rotating means 22 for rotating the
......Missing number 23...Laser beam light source 24, which also serves as a linearly polarized light source...According to the disulfide information to be recorded, adjust the beam intensity to (1) rA direction'' magnetization bit with 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. Pulse modulating means 25...- Recording magnetic field Hb applying means 26...
... Collimator lens 27 --- One objective lens 28 --- Missing number 29 --- Beam splinter 30 --- Analyzer

Claims (1)

[Claims] 1. An overwritable disk-shaped multilayer magneto-optical recording medium in which a first layer having perpendicular magnetic anisotropy is a recording layer and a second layer having perpendicular magnetic anisotropy is a recording auxiliary layer. The magnetization of the first layer does not change at room temperature even when a recording magnetic field in the "A direction", which is either upward or downward, is applied, and the magnetization of the second layer does not change in the "A direction". At room temperature under a recording magnetic field,
The magnetization is aligned in the A direction, and a laser beam modulated according to the information to be recorded is irradiated, and when the intensity of the beam is at a high level, the magnetization of both the first and second layers becomes zero or weak due to the radiant heat of the beam. Then, when the beam disappears and cooling begins, a bit with "A direction" magnetization is formed in the second layer due to the influence of the recording magnetic field during the cooling process, and this is reversed during the further cooling process and becomes "reverse". A bit with magnetization in the "A direction" is formed, and as cooling progresses further, a bit with magnetization in the "reverse A direction" [or "A direction"] in the first layer due to the influence of the "reverse A direction" magnetization in the second layer. is formed, and then, even if the "reverse A direction" magnetization of the second layer is reversed to "A direction" due to the influence of the "A direction" recording magnetic field, as soon as the influence of the recording magnetic field disappears, the first layer Under the influence of the magnetization, it is re-inverted and becomes the "reverse A direction", and when the intensity of the beam is at a low level, only the magnetization of the first layer becomes zero or weak due to the radiant heat of the beam, and then the beam disappears and cooling continues. When it starts,
During the cooling process, bits with magnetization in the "A direction" (or "reverse A direction") are formed in the first layer due to the influence of the "A direction" magnetization in the second layer. A recording medium characterized in that bits in the first layer and the second layer are retained whether or not they are subsequently influenced by a recording magnetic field. 2 The first layer has a higher coercive force and a lower Curie point at room temperature than the second layer, and the first layer has transition metal-rich or heavy rare earth-rich magnetism selected from a transition metal-heavy rare earth metal alloy composition. The second layer is a thin film, and the second layer has a lower coercive force and a higher Curie point at room temperature than the first layer, and the second layer has a compensation temperature that is the same as or near the Curie point of the first layer. 2. The overwritable disk-shaped multilayer magneto-optical recording medium according to claim 1, wherein the second layer is a heavy rare earth-rich magnetic thin film selected from a transition metal-heavy rare earth metal alloy composition. 3 The first layer and the second layer satisfy the following conditional expression: (1) T_R<T_C_1≒T_L≒T_c_o_m_
p_. _2<T_H, T_C_2 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_2<(σ_W/2M_S_2t_2) (4)
H_C_2+(σ_W/2M_S_2t_2)<|Hb
The overwritable disk multilayer magneto-optical recording medium according to claim 2, which satisfies |<H_C_1±(σ_W/2M_S_1t_1). However, for composite (■;±), the upper row shows the case where the first layer is rich in transition metals, and the lower row shows the case where the first layer is rich in heavy rare earth elements. The symbols used have the following meanings. T_R: Room temperature 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 T_C_1: Curie point of the first layer T_C_2: Curie of the second layer Point T_c_o_m_p_. _2: Second layer compensation 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: Film thickness of the second layer σ_W: Interfacial domain wall energy Hb: Recording magnetic field 4. The overwritable multilayer magneto-optical recording medium according to claim 3, wherein the second layer is made of a GdFeCo alloy. 5. In a recording method for overwriting an overwritable disk-shaped multilayer magneto-optical recording medium, (a) the following medium is used as the medium; the first layer having perpendicular magnetic anisotropy is the recording layer; In an overwritable disk-shaped multilayer magneto-optical recording medium in which a second layer having perpendicular magnetic anisotropy is used as a recording auxiliary layer, the first layer has a higher coercive force at room temperature than the second layer and has a Curie the first layer is a transition metal-rich or heavy rare earth-rich magnetic thin film selected from a transition metal-heavy rare earth metal alloy composition, and the second layer has a coercive force at room temperature that is lower than that of the first layer. the second layer has a compensation temperature that is the same as or near the Curie point of the first layer, and the second layer has a high Curie point;
A medium characterized in that it is a heavy rare earth-rich magnetic thin film selected from a transition metal-heavy rare earth metal alloy composition. (b) moving the medium; (c) moving the medium in either an upward or downward direction;
(d) irradiating the medium with a laser beam; (e) irradiating the medium with a laser beam; (e) irradiating the medium with a laser beam; (d) irradiating the medium with a laser beam; (f) Applying a recording magnetic field to a portion of the medium irradiated with the beam; (g) When the intensity of the beam is at a high level, first The radiant heat of the beam makes the magnetization of both the first and second layers zero or weak,
Next, when the beam disappears and cooling begins, a bit with "A direction" magnetization is formed in the second layer due to the influence of the recording magnetic field during the cooling process, and this bit is reversed during the further cooling process and becomes "reverse A direction". When a bit with magnetization is formed and further cooling progresses, the first bit becomes
A bit with “reverse A direction” [or “A direction”] magnetization is formed in the layer, and then the “reverse A direction” magnetization in the second layer is reversed to “A direction” under the influence of the “A direction” recording magnetic field. However, as soon as the influence of the recording magnetic field disappears, it is reversed again due to the influence of the magnetization of the first layer and becomes ``reverse A direction.'' When the intensity of the beam is at a low level, the radiant heat of the beam is first The magnetization of only the first layer is reduced to zero or weak, and then, when the beam disappears and cooling begins, the second layer's magnetization increases during the cooling process.
Due to the influence of magnetization in the ``A direction'', the first layer has ``A direction'' [or ``reverse A direction''.
A bit having a magnetization in the direction "] is formed, and the bit of the first layer and the second layer thus formed is retained whether or not it is influenced by a recording magnetic field thereafter. recording method. 6 The first layer and the second layer satisfy the following conditional expression: (1) T_R<T_C_1≒T_L≒T_c_o_m_
p_. _2<T_H, T_C_2 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_2<(σ_W/2M_S_2t_2) (4)
H_C_2+(σ_W/2M_S_2t_2)<|Hb
The recording method according to claim 5, which satisfies |<H_C_1±(σ_W/2M_S_1t_1). However, for composite (■;±), the upper row shows the case where the first layer is rich in transition metals, and the lower row shows the case where the first layer is rich in heavy rare earth elements. The symbols used have the following meanings. T_R: Room temperature 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 T_C_1: Curie point of the first layer T_C_2: Curie of the second layer Point T_c_o_m_p_. _2: Second layer compensation 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: Film thickness of the second layer σ_W: Interfacial domain wall energy Hb: Recording magnetic field 7 The laser beam consists of two closely spaced beams, a leading beam and a trailing beam, the leading beam does not modulate its intensity at the low level in principle, and the trailing beam does not modulate its intensity at the low level. 6. The recording method according to claim 5, wherein the intensity is pulse-modulated at the high level according to the information. 8. A reproducing method for reproducing by irradiating a laser beam onto the second layer of an overwritable multilayer magneto-optical recording medium that has been overwritten by the following recording method. (a) The following medium is used as the medium; an overwritable disk in which a first layer having perpendicular magnetic anisotropy is a recording layer and a second layer having perpendicular magnetic anisotropy is a recording auxiliary layer. In the multilayer magneto-optical recording medium, the first layer has a higher coercive force and a lower Curie point at room temperature than the second layer, and the first layer has a transition metal-heavy rare earth metal alloy composition selected from a transition metal-heavy rare earth metal alloy composition. The second layer is a metal-rich or heavy rare earth-rich magnetic thin film, and the second layer has a lower coercive force and a higher Curie point at room temperature than the first layer, and the second layer has a Curie point that is the same as or near the Curie point of the first layer. has a compensation temperature, and the second layer is
A medium characterized in that it is a heavy rare earth-rich magnetic thin film selected from a transition metal-heavy rare earth metal alloy composition. (b) moving the medium; (c) moving the medium in either an upward or downward direction;
(d) irradiating the medium with a laser beam; (e) recording the beam intensity; (d) irradiating the medium with a laser beam; (e) recording the beam intensity; (f) Applying a recording magnetic field to a portion of the medium irradiated with the beam; (g) When the intensity of the beam is at a high level, first the radiant heat of the beam The magnetization of both the first layer and the second layer is set to zero or weak,
Next, when the beam disappears and cooling begins, a bit with "A direction" magnetization is formed in the second layer due to the influence of the recording magnetic field during the cooling process, and this bit is reversed during the further cooling process and becomes "reverse A direction". When a bit with magnetization is formed and further cooling progresses, the first bit becomes
A bit with “reverse A direction” [or “A direction”] magnetization is formed in the layer, and then the “reverse A direction” magnetization in the second layer is reversed to “A direction” under the influence of the “A direction” recording magnetic field. However, as soon as the influence of the recording magnetic field disappears, it is reversed again due to the influence of the magnetization of the first layer and becomes ``reverse A direction.'' When the intensity of the beam is at a low level, the radiant heat of the beam is first The magnetization of only the first layer is reduced to zero or weak, and then, when the beam disappears and cooling begins, the second layer's magnetization increases during the cooling process.
Due to the influence of magnetization in the ``A direction'', the first layer has ``A direction'' [or ``reverse A direction''.
A bit having magnetization in the direction "] is formed, and the bit of the first layer and the second layer thus formed is retained whether or not it is influenced by the recording magnetic field thereafter; Recording method. 9 The first layer and the second layer meet the following conditional expression: (1) T_R<T_C_1≒T_L≒T_c_o_m_
p_. _2<T_H, T_C_2 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_2<(σ_W/2M_S_2t_2) (4)
H_C_2+(σ_W/2M_S_2t_2)<|Hb
The recording method according to claim 8, which satisfies |<H_C_1±(σ_W/2M_S_1t_1). However, for composite (■;±), the upper row shows the case where the first layer is rich in transition metals, and the lower row shows the case where the first layer is rich in heavy rare earth elements. The symbols used have the following meanings. T_R: Room temperature 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 T_C_1: Curie point of the first layer T_C_2: Curie of the second layer Point T_c_o_m_p_. _2: Second layer compensation 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: Film thickness of the second layer σ_W: Interfacial domain wall energy Hb: Recording magnetic field 10 In an overwritable magneto-optical recording device,
This device includes (a) means for rotating an overwritable disk-shaped multilayer magneto-optical recording medium; (b) means for applying a recording magnetic field of the following Hb; (c) a laser beam light source; (d) binarized information to be recorded. The beam intensity is determined according to (1
) a high level that provides the medium with an appropriate temperature to form either a bit with upward magnetization or a bit with downward magnetization; and (2) a high level that provides the medium with an appropriate temperature to form the other bit. An overwritable recording device comprising: means for modulating a low level in a pulsed manner; Note H_C_2+(σ_W/2M_S_2t_2)<|Hb
|<H_C_1±(σ_W/2M_S_1t_1) However, for composite (■;±), the upper row shows the case where the first layer is rich in transition metals, and the lower row shows the case where the first layer is rich in heavy rare earths. has the following meaning. 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: Thickness of the second layer σ_W: Interfacial domain wall energy Hb: Recording magnetic field 11 The laser beam consists of two closely spaced beams, a leading beam and a trailing beam, the leading beam does not modulate its intensity at the low level in principle, and the trailing beam does not modulate its intensity at the low level. 11. The recording apparatus according to claim 10, wherein the intensity is pulse-modulated at the high level according to the information. 12 The first layer and the second layer meet the following conditional expression: (1) T_
R<T_c_1≒T_L≒T_c_o_m_p_. ＿２
<T_H, T_c_2 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_2<(σ_W/2M_S_2t_2) (4)
H_C_2+(σ_W/2M_S_2t_2)<|Hb
The recording device according to claim 10, which satisfies |<H_C_1±(σ_W/2M_S_1t_1). However, for composite (■;±), the upper row shows the case where the first layer is rich in transition metals, and the lower row shows the case where the first layer is rich in heavy rare earth elements. The symbols used have the following meanings. T_R: Room temperature 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 T_C_1: Curie point of the first layer T_C_2: Curie of the second layer Point T_c_o_m_p_. _2: Second layer compensation 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: Film thickness of the second layer σ_W: Interfacial domain wall energy Hb: Recording magnetic field 13 Claim 11, which can also be used for reproduction, characterized in that the recording magnetic field applying means can be changed to zero or an output smaller than the following Hb during reproduction. Recording device as described in section.