JPH0773518A - Overwritable magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a high C/N value even in the case of high-density recording by providing the magneto-optical recording medium having four layers of magnetic layers, of which the reading out layer is GdFeCo and the ratio of Gd therein is 23.5 to 25.5 (atm.%). CONSTITUTION:This magneto-optical recording medium is constituted by forming guide grooves for tracking by a UV curing resin on, for example, a glass substrate 1 and laminating a first protective layer 3, an R layer 4, an M layer 5, an I layer 6, a W layer 7 and a second protective layer 8 by sputtering thereon. The first and second protective layers are formed of dielectric substances, such as silicon nitride (Si3N4), Al2O3 and SiO2. The M layer, the I layer and the W layer are composed of magnetic materials of amorphous RE-TM alloys, such as GdFe, GdCo, Gd, FeCo, TtFe, TrCo and TrFeCo.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overwritable magneto-optical recording medium. Overwrite
Is the act of recording new information without erasing the previous information. In this case, when played back, the previous information should not be played back. The "overwrite" referred to in the present specification means, in particular, without modulating the direction and intensity of the recording magnetic field Hb,
Overwriting is performed simply by irradiating the laser beam while modulating the pulse according to the information to be recorded.

[0002]

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

A recording medium used in this magneto-optical recording / reproducing method has a perpendicular magnetic anisotropy composed of one layer or multiple layers as a layer for storing recording (perpendicular magnetic layeror).
layers: hereinafter referred to as perpendicular magnetic anisotropic film). This perpendicular magnetic anisotropy film is, for example, amorphous GdFe or GdC.
o, GdFeCo, TbFe, TbCo, TbFeCo, etc. The perpendicular magnetic anisotropic film generally has concentric or spiral tracks, and information is recorded on the tracks. There are two types of tracks, explicit and implicit. [Explicit Track] The magneto-optical recording medium has a disk shape. In a disc having explicit tracks, tracks for recording information are formed in a spiral shape or a concentric circle shape when viewed in a direction perpendicular to the disk plane. There is a groove for tracking and separation between two adjacent tracks. The space between the grooves is called a land. In reality, the relationship between the land and the groove is reversed on the front and back of the disc. Therefore, when the disk is viewed from the same direction as the beam enters, the front side is called a groove and the back side is called a land. Since the perpendicular magnetic anisotropy film is formed on the entire surface of the groove and the land, the groove portion may be a track or the land portion may be a track.
There is no particular relationship between the width of the groove and the width of the land.

As described above, generally, the substrate has a land formed in a spiral or concentric shape on the surface and a groove sandwiched between two adjacent lands. A thin perpendicular magnetic anisotropic film is formed on such a substrate. As a result, the perpendicular magnetic anisotropic film has lands and grooves. [Mark] In the present specification, “upward (upwar
Either "d)" or "downward" is defined as "A direction" and the other is defined as "reverse A direction".

The information to be recorded is binarized in advance, and this information has a mark (B ₁ ) having a magnetization in "A direction".
Then, two signals of the mark (B ₀ ) having the magnetization in the “reverse A direction” are recorded. These marks B ₁ and B ₀ correspond to either one or the other of the digital signals 1 and 0, respectively. However, generally, the magnetization of the track to be recorded is aligned in the "reverse A direction" by applying a strong external magnetic field before recording. Act to align the magnetization direction is referred to as the "initialization ^* (initialize ^*)" in the old sense. A mark (B ₁ ) having "A direction" magnetization on the track
To form. Information is the presence or absence of this mark (B ₁ ), position,
It is represented by the front end position, rear end position, mark length, etc. of the mark. Particularly, a method in which the edge position of the mark represents information is called mark length recording. The mark has been called a pit or a bit in the past, but recently it is called a mark.

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

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

However, the technological progress is remarkable, and the intensity of the irradiation light beam should be recorded without modulating the intensity of the recording magnetic field Hb (including ON and OFF) or without modulating the direction of the recording magnetic field Hb. A magneto-optical recording method capable of overwriting, a magneto-optical recording medium capable of being overwritten, and an overwritable recording apparatus also employed therefor have been invented only by modulating in accordance with binary information.
Patent application filed (JP-A-62-175948 = DE3,619,618A1)
= US patent pending Ser. No. 453,255). Hereinafter, this invention is referred to as a "basic invention". [Explanation of Basic Invention] In the basic invention, "a recording / reproducing layer basically consisting of a magnetic thin film capable of perpendicular magnetization (in this specification, this recording / reproducing layer is referred to as a memory layer Memory layer
Or a M layer) and a recording auxiliary layer reference layer (in this specification, this recording auxiliary layer is referred to as a recording layer Writing layer or a W layer) including a magnetic thin film capable of perpendicular magnetization.
Both layers are exchange-coupled, and
An overwritable multi-layered magneto-optical recording medium capable of keeping only the magnetization of the W layer in a predetermined direction without changing the magnetization direction of the M layer at room temperature is used.

Information is represented and recorded by a mark having an "A direction" magnetization and a mark having an "inverse A direction" magnetization in the M layer (and also in the W layer in some cases).
In this medium, the W layer has an external means (for example, an initial auxiliary magnetic field Hin.
By i.), the direction of the magnetization can be aligned in the “A direction”. Moreover, at that time, the magnetization direction of the M layer is not reversed, and further, the magnetization direction of the W layer once aligned in the “A direction” is not reversed even when the exchange coupling force from the M layer is received. On the contrary, the magnetization direction of the M layer is not reversed even when receiving the exchange coupling force from the W layer aligned in the “A direction”. And
The W layer has a lower coercive force Hc and a higher Curie point Tc than the M layer.

According to the recording method of the basic invention, only the magnetization direction of the W layer of the recording medium is aligned in the "A direction" by external means before recording. This act is specifically referred to herein as "initialize". This "initialization"
Is peculiar to an overwritable medium. Then, the medium is irradiated with the laser beam pulse-modulated according to the binarized information. The intensity of the laser beam has a high level P _H and a low level P _L , which correspond to the high level and low level of the pulse. This low level is higher than the reproduction level P _R that illuminates the medium during reproduction. As already known, even when recording is not performed, a laser beam is used to access a predetermined recording position on the medium, for example.
Very low level> may illuminate. This <very low level> is also the same as or close to the reproduction level P _R.

For example, "initialization" for "A"
When the medium subjected to e) ”is irradiated with a laser beam of a low level P _L , the temperature of the medium is increased and the coercive force Hc _{1 of the} M layer is increased.
Becomes very small or extremely zero. It becomes zero when the temperature of the medium is equal to or higher than the Curie point of the M layer. At this time, the coercive force Hc ₂ of the W layer is sufficiently large,
It is not reversed by the recording magnetic field Hb in the "reverse A direction".
Then, the force of the W layer reaches the M layer via the exchange coupling force. M
Layers and W layers are generally composed of heavy rare earth metals (heavyrareearthmeta).
l: Hereinafter, abbreviated as RE) -transition metal:
Hereinafter, abbreviated as TM). The exchange coupling force is
Force to align RE magnetic moments of both layers and TM of both layers
It consists of forces that align the magnetic moments. In the alloy, the sublattice magnetization of RE and the sublattice magnetization of TM have opposite directions, and the direction of the larger sublattice magnetization determines the direction of magnetization of the alloy. When both sublattice magnetizations are equal, the composition is called a compensation composition, and the temperature is called a compensation temperature. The TM sublattice magnetization is stronger above the compensation temperature, and the RE sublattice magnetization is stronger below the compensation temperature.

There are two types of marks before irradiation with a laser beam: a state in which an interface domain wall exists between the M layer and the W layer, and a state in which there is no interface wall. The existing mark does not match the mark to be formed by the low level P _L laser beam. The mark that does not exist corresponds to the mark that is to be formed by the laser beam of low level P _L. In the former case, the temperature of the M layer rises when the P _L beam is irradiated. Therefore, the coercive force Hc ₁ of the M layer becomes very small. At this time, as a result of the force of the W layer reaching the M layer via the exchange coupling force, the magnetization of the M layer having a very small coercive force Hc ₁ is determined in a predetermined direction (eg, ""Adirection"). As a result, a mark having no interface domain wall (target mark) is formed between the M layer and the W layer.

Even if the temperature of the M layer rises a little higher and the magnetization of the M layer becomes zero (Tc ₁ or more), the temperature of the medium naturally decreases when the irradiation of the laser beam is stopped and the Curie is reached. It is slightly lower than the point Tc ₁ . Then, magnetization appears in the M layer. At this time, similarly, the force of the W layer reaches the M layer via the exchange coupling force. Therefore, the magnetization appearing in the M layer has a predetermined direction (for example, “A
Direction "). From this state, the temperature returns to room temperature, but the predetermined orientation is maintained. However, in the middle of returning to room temperature, M layer or W
When a layer has a compensation temperature, the magnetization direction of that layer reverses when each is exceeded. This process gives the same mark in the latter case and is called the cold process or cold cycle.

On the other hand, for example, "initialization (ini) for" A direction "
tialized) ”media is high level P _HLaser bee
When the medium is irradiated, the temperature of the medium rises and the M layer becomes coercive.
Power Hc₁Becomes zero, and the coercive force Hc of the W layer₂Is very small
Or it will be extremely zero. So very small
Coercive force Hc₂The magnetization of the W layer with
Face a predetermined direction (for example, "reverse A direction"). If W layer
When the temperature rises a little, the magnetization of the W layer becomes zero
Even in that case, the irradiation of the laser beam is stopped and the medium
Curie point Tc₂Slightly lower
Then, magnetization appears in the W layer. At this time, similarly, the recording magnetic field H
The magnetization of the W layer is lost in a predetermined direction (for example, “inverse A
Direction "). Furthermore, the temperature of the medium cools and the Curie point T
c₁When it goes down a little, magnetization appears in the M layer. At this time,
The force of the W layer extends to the M layer via the exchange coupling force. for that reason,
The magnetization appearing in the M layer is a predetermined direction dominated by the W layer.
(For example, "reverse A direction"). From this state to room temperature
However, the orientation is maintained. However, when returning to room temperature
If there is a compensation temperature in the M layer or W layer, there
When it exceeds, the direction of the magnetization is reversed. This process
The so-called high temperature process or high temperature cycle.

The above low temperature process and high temperature process are M
It occurs regardless of the direction of magnetization of the layer and the W layer. anyway,
Before the laser beam irradiation, the W layer is “initialized (initializ
e) ”, so that overwriting is possible. In the basic invention, the laser beam is pulse-modulated according to the information to be recorded. However, this is itself a conventional magneto-optical recording. However, the means for pulse-modulating the beam intensity according to the binary information to be recorded is a known means, for example, THEBELLSYSTEMTECHNIC.
ALJOURNAL, Vol. 62 (1983), 1923-1936. Therefore, given the required high and low levels of beam intensity, they are readily available with some modifications to conventional modulation means. For those skilled in the art, such a modification is such that given high and low levels of beam intensity,
It will be easy.

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

The recording medium used in the basic invention has a multilayer structure including an M layer and a W layer. The M layer is a magnetic layer having a high coercive force and a low magnetization reversal temperature at room temperature. The W layer is a magnetic layer having a lower coercive force and a higher magnetization reversal temperature at room temperature than the M layer. Both the M layer and the W layer may themselves be composed of a multilayer film. In some cases, an intermediate layer (for example, an exchange coupling force σ _W adjusting layer: hereinafter, this layer is abbreviated as I layer) may be present between the M layer and the W layer. For the I layer, refer to JP-A-64-50257 and JP-A-1-273248.

Further, regarding the overwritable magneto-optical recording, in addition, Japanese Patent Application Laid-Open No. 4-123339 and Japanese Patent Application Laid-Open No. 4-13
Since many materials such as No. 4741 have been issued, here,
Omit further explanation. The disc having a four-layer structure disclosed in Japanese Patent Laid-Open No. 4-123339 has, in addition to the M layer and the W layer,
An "Initializing layer" (hereinafter abbreviated as Ini layer) and a switching layer (Swithing layer: hereinafter) for turning on / off exchange coupling between the Ini layer and the W layer
Abbreviated as S layer).

In order to increase the C / N value, a read-out layer (hereinafter, R) having a Curie point and a high Kerr effect on the M layer (that is, on the laser beam incident side) is higher than that on the M layer.
A stack of abbreviated layers is also proposed. For example,
See JP-A-63-64651 and JP-A-63-48637. The proposed R layer is also composed mainly of GdFeCo.

[0020]

Even in an overwritable magneto-optical recording medium, a high C / N value is required for high density recording. However, if the mark length is recorded in the ISO standard recording area at a pitch of 1.3 to 1.4 μm on a φ130 mm size disc, the high-density recording equivalent to 1 gigabyte or more per side will result in a C / N value in the conventional medium. There was a problem that was not high enough.

[0021]

DISCLOSURE OF THE INVENTION As a result of earnest studies for solving this problem, the inventors of the present invention have found that in the magneto-optical recording medium having four or more magnetic layers, the GdFeCo Rd layer It was found that a high C / N value can be obtained when the ratio of is in the range of 23.0 to 25.5 in atomic%, and the present invention has been completed. In this case, the Fe ratio is 50.5 to 6 in atomic%.
The range of 0.0 is more preferable.

Therefore, according to the present invention, overwriting by light modulation has at least four magnetic layers of "reading layer (R layer), memory layer (M layer), intermediate layer (I layer) and recording layer (W layer)". A possible magneto-optical recording medium, wherein the read layer is GdFeCo, and the ratio of Gd is 23.0 to 25.5 (atomic%).

[0023]

In the magneto-optical recording medium according to the present invention, for example, a guide groove for tracking is formed on a glass substrate with an ultraviolet curable resin, and a first protective layer, an R layer, an M layer, an I layer is formed on the guide groove.
The W layer and the second protective layer are laminated by sputtering. The substrate does not have to have a guide groove for tracking, and a molded resin substrate may be used.

The first and second protective layers are made of silicon nitride (S
i ₃ N ₄ ), Al ₂ O ₃ , SiO ₂ or the like. The R layer is formed of GdFeCo and has a thickness of generally 10 to 70 nm, preferably 20 to 40 nm. The M layer, the I layer, and the W layer are made of a magnetic substance of an amorphous RE-TM alloy such as GdFe, GdCo, GdFeCo, TbFe, TbCo, and TbFeCo.
The layer has a thickness of 10 to 50 nm, preferably 15 to 35 nm, the I layer has a thickness of 5 to 30 nm, preferably 10 to 20 nm, and the W layer has a thickness of 20.
.About.90 nm, preferably 40 to 70 nm is suitable.

Between the M layer and the W layer, there may be an Ini layer or an S layer made of an amorphous RE-TM alloy similar to these. A protective substrate may be adhered on the second protective layer, and the two protective layers formed on the substrate up to the second protective layer may be adhered to the inner side of the second protective layer. Good.

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

[0027]

Example 1 First, a sputtering apparatus was prepared. This device has three vacuum tanks as shown in FIG. 2, of which the left and right two tanks are sputtering tanks 11 each having four sputtering targets 12, and the remaining central tank is a load / unload tank. It is 13. Using this device, a magneto-optical recording medium having the structure shown in FIG. 1 was manufactured by the following procedure.

First, the pitch is set in the loading / unloading tank 13.
A glass substrate having a resin layer having a tracking guide groove of 1.4 μm and a depth of 70 nm was engraved and set to a vacuum state of 5 × 10 ⁻⁵ Pa or less. Then, Ar gas and N ₂ gas were introduced into the sputtering tank, and reactive sputtering of Si and N ₂ was performed by the first target Si under the conditions of a sputtering rate of 10 nm / min and an Ar pressure of 0.2 Pa. A silicon nitride (hereinafter abbreviated as SiN) layer as the first protective layer was formed to a thickness of 70 nm.

Next, GdFeCo was used as a second target under the conditions of a sputtering rate of 20 nm / min and an Ar pressure of 0.3 Pa.
An R layer of _24.7 Fe _51.8 Co _23.5 was formed to a thickness of 30 nm. next,
Simultaneous sputtering is performed with the third target Tb and the fourth target FeCo under the conditions of a sputtering rate of 20 nm / min and an Ar pressure of 0.4 Pa, and an M layer of Tb ₂₁ Fe ₇₅ Co ₄ is 25 nm thick.
Formed.

Next, the fourth target GdFeCo, sputtering rate 20 nm / min, under the conditions of Ar pressure of 0.3 Pa, Gd ₃₅ F
An I layer of e ₅₂ Co ₁₃ was formed to a thickness of 15 nm. Next, using the fifth target Dy and the sixth target FeCo, co-sputtering was performed under the conditions of a sputtering rate of 20 nm / min and an Ar pressure of 0.2 Pa to form a Dy _28.5 (Fe ₅₀ Co ₅₀ ) _71.5 W layer with a thickness of 50 nm
Formed.

Finally, by the first target, the Si
The SiN layer, which is the second protective layer, has a thickness of 30
After the formation, the medium having the structure shown in FIG. 1 is completed.

[0032]

Examples 2 to 5 Media were manufactured under the same conditions as in Example 1 except that the composition of the R layer was changed to that shown in Table 1 by replacing the second target with one having a different composition ratio. .

[0033]

[Comparative Examples 1 to 6] A medium was manufactured under the same conditions as in Example 5 except that the composition of the R layer was changed to that shown in Table 2 by replacing the second target with one having a different composition ratio. . [Measurement of C / N value]
The recording magnetic field Hb of Oe and the initial auxiliary magnetic field Hini of 3000 Oe were set in the magneto-optical recording / reproducing apparatus. While rotating the medium at a linear velocity of 11.3 m / s, the medium was irradiated with a laser beam having a wavelength of 830 nm condensed to a diameter of about 1 μm. According laser beam binary information, frequency 3MHz as the first standard information, at a duty ratio of 50% 8.0 mW and (P _H) 4.0 mW
Pulse modulation was performed between (P _L ). Then, 1.0mW of P _R
When the first standard information was reproduced with, it was reproduced sufficiently.

Next, the second standard information is recorded (overwriting) under the same conditions as above except that the frequency is changed to 4 MHz.
And reproduces the recorded signal at P _R of 1.0 mW, was measured C / N value. The results are shown in Tables 1 and 2. From these results, it is understood that a high C / N value can be obtained by setting the ratio of Gd in the R layer of GdFeCo to be 23.0 to 25.5 in atomic%.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

According to the present invention, a high C / N value can be obtained even in high density recording, and it can sufficiently withstand high density recording expected in the future.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view of a medium manufactured in an example of the present invention.

FIG. 2 is a schematic view of a sputtering apparatus used for manufacturing a medium in an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Glass substrate 2 ... Resin layer 3 ... 1st protective layer (SiN layer) 4 ... R layer (GdFeCo layer) 5 ... M layer (TbFeCo layer) 6 ... I Layer (GdFeCo layer) 7 ... W layer (DyFeCo layer) 8 ... Second protective layer (SiN layer) 11 ... Sputtering tank 12 ... Sputtering target 13 ... Load / unload tank

Claims (1)

[Claims] 1. An overwritable magneto-optical recording medium by optical modulation having at least four magnetic layers of a read layer, a memory layer, an intermediate layer and a recording layer, wherein the read layer is GdFeCo, of which Gd Is 23.0 to 25.5 (atomic%).