JPH0773526A - Production of magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To expand a range for setting the power of an L process and to stabilize the max. reproducing power by decreasing the initializing magnetic field of the W layer of the overwritable magneto-optical recording medium. CONSTITUTION:A heat treatment is executed at least after a memory layer (M layer) and a writing layer (W layer) are formed and thereafter, recording is executed in the case of production of the overwritable magneto-optical recording medium consisting of at least two layers; the M layer and the W layer having perpendicular magnetic anisotropy and making exchange bond on a substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an overwritable magneto-optical recording medium. Overwrite (o
Ver write) 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 term "overwrite" used in the present specification refers to overwriting by irradiating a laser beam while modulating the pulse according to the information to be recorded, without modulating the direction and intensity of the recording magnetic field Hb. Say that.

[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 layer (perpendicular magnetic layer or layers) consisting of one layer or multiple layers as a layer for recording. This magnetic film is made of, for example, amorphous GdFe or Gd.
It is composed of Co, GdFeCo, TbFe, TbCo, TbFeCo and the like. The perpendicular magnetic 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. Conversely, the space between the grooves is called a land. In reality, the land and groove are reversed on the front and back of the disc. Therefore, looking at the disk in the same way as the beam enters, the front side is called a groove and the back side is called a land. Since the perpendicularly magnetized film is formed over both the groove and the land, the groove portion may be the track or the land portion may be the track. There is no particular relationship between the width of the groove and the width of the land.

In order to form such a land and groove,
Generally, a 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 film is formed on such a substrate. As a result, the perpendicular magnetization film has lands and grooves. [Mark] In the present specification, “upward (upwar
d) "or" downward "
Orientation "and the other is defined as" reverse A orientation ".

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. Then, the mark (B
₁ ) to form. Information is represented by the presence or absence of the mark (B ₁ ), the position, the front end position, the rear end position of the mark, the mark length, and the like. In particular, a method in which the edge position of a mark represents information is called mark length recording. A mark has been called a pit or a bit in the past, but is recently called a mark.

By the way, in order to reuse the recorded medium, (1) initialize the medium again ^* initialize it with the device ^* , or
Or (2) it is necessary to add an erasing head similar to the recording head to the recording device, or (3) it is necessary to erase the recorded information in advance by using the recording device or the erasing device 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 technical 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. A patent application has been filed (JP-A-62-175948 = DE3,619,61)
8A1 = US patent pending Ser. No. 453,255). Hereinafter, this invention is referred to as a "basic invention". [Description of Basic Invention] In the basic invention, "a recording / reproducing layer basically composed 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 M layer) and a recording auxiliary layer consisting of a perpendicularly magnetizable magnetic thin film reference layer (in this specification, this recording auxiliary layer is a writing layer Writing layer or W).
Layer) and both layers are exchange-coupled (exchange-coupl
ed), and at the room temperature, the overwritable multilayer 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 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”.

The W layer has a lower coercive force H _C and a higher Curie point T _C 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 unique to overwritable media.

Then, the medium is irradiated with a 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 is already known, the laser beam may be turned on at a <very low level> even when recording is not performed, for example, to access a predetermined recording position on the medium. This <very low level> is also the same as or close to the reproduction level P _R.

For example, "initialize" for "A direction"
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 H _{c1 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 H _c2 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.
tal: hereinafter abbreviated as RE) -transition metal (transition meta
l: abbreviated as TM hereinafter). The exchange coupling force is composed of a force that aligns the RE magnetic moments of both layers and a force that aligns the TM magnetic moments of both layers. 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. Above the compensation temperature, the TM sublattice magnetization is stronger, and below the compensation temperature, the RE sublattice magnetization is stronger.

There are two types of marks before irradiation with the laser beam: a state in which an interface domain wall exists between the M layer and the W layer and a state in which no interface magnetic wall exists. The mark which does not exist corresponds to the mark to be formed.
The existing mark does not match the mark to be formed. In the latter case, 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 H _c1 is determined in a predetermined direction (eg, "A direction"). 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 magnetization of the M layer is zero (T _c1 or more), the irradiation of the laser beam is stopped, and the temperature of the medium naturally lowers to slightly lower than the Curie point T _c1.
Magnetization appears in the 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, if there is a compensation temperature in the M layer and the W layer during returning to room temperature, the magnetization direction of the layer is reversed when the temperature exceeds the compensation temperature. This process is called a cold cycle or cold process.

On the other hand, for example, "Initialization (ini
tialize) "is media receives the irradiation of the laser beam of high level P _H, the coercive force H _c1 of the M layer is improved temperature of the medium is zero, the coercive force H _c2 of W layer is very Therefore, the magnetization of the W layer, which has a very small coercive force H _c2 , loses the recording magnetic field Hb and faces a predetermined direction (for example, the “reverse A direction”). Even if the magnetization of the W layer is zero, the irradiation of the laser beam is stopped and the temperature of the medium is naturally lowered to the Curie point T _c2.
When it goes down a little, magnetization appears in the W layer, but at this time,
Similarly, when the recording magnetic field Hb is lost, the magnetization of the W layer is oriented in a predetermined direction (for example, "reverse A direction"). Further, when the temperature of the medium cools and falls slightly below the Curie point T _c1 , magnetization appears in the M layer. At this time, the force of the W layer reaches the M layer via the exchange coupling force. Therefore, the magnetization appearing in the M layer is oriented in a predetermined direction (for example, “reverse A direction”) dominated by the W layer.
From this state, the temperature returns to room temperature, but the predetermined orientation is maintained. However, if there is a compensation temperature in the M and W layers on the way back to room temperature,
When it exceeds that, the magnetization directions of the M layer and the W layer are reversed. This process is called a high temperature cycle or high temperature process.

The above low temperature cycle and high temperature cycle 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, the means for pulse-modulating the beam intensity according to the binary information to be recorded is a known means, for example, THE BELL SYSTEM T.
It is described in detail in ECHNICAL JOURNAL, 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 modification would be easy given the high and low levels of beam intensity.

One of the features of the basic invention is
There are high and low levels of beam intensity. That is, when the beam intensity is at a high level, the "A direction" magnetization of the W layer is reversed (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.

In the present specification, ○○○ [or △△△]
With the expression, when XX outside [] is read first, XX outside [] will be read also in the following XX [or ΔΔΔ ]. On the contrary, ○○○
If you select and read the △△△ one in [] without reading, you can also read △ ○ △ in [] without reading ○○○ even in the following ○○○ [or △△△ ] Should be read.

The medium used in the basic invention is roughly classified into a first embodiment and a second embodiment. In any of the embodiments, the recording medium 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, between the M layer and the W layer)
Exchange coupling force σ _W adjusting layer ... (Hereinafter, this layer is abbreviated as Int. Layer). For the Int. Layer, see JP-A-64-50257 and JP-A-1-273248.

Further, regarding overwritable magneto-optical recording, in addition to the above, JP-A-4-123339 and JP-A-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,
"Initializing layer" (hereinafter abbreviated as I layer), and exchange coupling between I layer and W layer is turned on.
It has a switching layer (Swithing layer: hereinafter, abbreviated as S layer) to be turned off.

In order to increase the C / N ratio, a read-out layer (Readout layer: below) having a higher Curie point and a higher Kerr effect than the M layer on the M layer (that is, on the laser beam incident side):
A laminate of R layers) is also proposed. For example, see JP-A-63-64651 and JP-A-63-48637. The proposed R layer is also composed of a RE-TM based alloy.

An exchange coupling force adjusting layer may be added between the M layer and the W layer for the purpose of reducing the initialization magnetic field of the W layer and increasing the sensitivity. The Kerr rotation angle can be further increased by adding the readout layer (R layer). Further, in order to form a pit having a large contrast with the peripheral portion in the recording layer, the composition of RE in the recording layer was set to about 27 to 29% in atomic percentage.

[0023]

However, when the conventional medium is used, the initialization magnetic field becomes large because the coercive force of the M layer is large even if the exchange coupling force adjusting layer of the M layer and the W layer is provided. . It was found that the power setting range for performing the L process was narrowed. The L process is a process of transferring the magnetization direction of the W layer to the M layer, and this L process is used for recording / reproducing on / from an overwritable magneto-optical recording medium.
It is necessary to set three laser beam intensities of a process (laser beam intensity at the time of erasing), an H process (laser beam intensity at the time of writing), and a laser beam intensity at the time of reproduction for irradiating the lowest intensity laser beam.
When the power margin of the L process is narrowed, there is a problem in that old recorded information remains unerased.

Further, when the change in the maximum reproduction power before and after the repeated recording becomes large, the reproduction power margin becomes small and the data retention becomes unstable. Particularly in an overwritable magneto-optical recording medium, an exchange coupling force acts between the M layer and the W layer, and this force acts in the direction of erasing data, so that the reproduction power margin is originally small. Therefore, the fluctuation of the maximum reproducing power margin of the overwritable magneto-optical recording medium having such a small reproducing power margin is a serious problem.

The present invention has been made in view of the problems peculiar to such an overwritable magneto-optical recording medium. The reduction of the initializing magnetic field of the W layer, the expansion of the power setting range capable of L process, And to stabilize the maximum reproducing power.

[0026]

In order to solve the above-mentioned problems, in the present invention, firstly, "a memory layer having perpendicular magnetic anisotropy, which is laminated on the substrate in any order of top and bottom, is provided. A method of manufacturing an overwritable magneto-optical recording medium comprising at least two layers of (M layer) and a writing layer (W layer) having perpendicular magnetic anisotropy exchange-coupled thereto, at least the M layer and the above A method for manufacturing a magneto-optical recording medium (claim 1) is provided, in which the substrate on which the W layer is formed is heat-treated and then recording is performed.

[0027]

The medium of the present invention is heat-treated after forming at least the M layer and the W layer in the manufacturing process of the conventional overwritable magneto-optical recording medium. The heat treatment has the effect of stabilizing the structure of the magnetic film. Therefore, if the temperature is too low or the time is too short, the structure cannot be sufficiently stabilized. Further, if the heating temperature is too high (for example, 100 ° C. or higher), the substrate (particularly the plastic substrate) may be adversely affected by warpage or the like. A heating time that is too long decreases productivity. The exact cause of the decrease in the coercive force of the M layer when heat-treated as in the present invention is unknown. However, as a result, the reversal magnetic field of the W layer is reduced, and surprisingly, the power for erasing the pits previously recorded on the medium is greatly reduced with almost no influence on the power at which the H process starts to occur. Proven by experiment. That is, the heat treatment expands the setting range of the L process power. Furthermore, it was confirmed that the stabilization of the medium structure by heat treatment reduces not only the change of the maximum reproducing power before and after the repeated recording but also the change of the optimum recording power.

[0028]

Example 1 (1) Manufacture of Overwritable Magneto-Optical Recording Medium A 2P (Photo Polimer) substrate in which an ultraviolet curable resin-curable resin is formed on a glass substrate having a diameter of 130 mm and a thickness of 1.17 mm is prepared. . Inner circumference (radius r = 29m on this resin layer
A large number of grooves are formed in a spiral shape from the position (m) to the outer circumference (position of radius r = 60 mm). The width of the groove is
0.5 μm, pitch 1.6 μm, depth 600 Å.

A 6-element RF sputtering apparatus is prepared, and a 2P substrate is set in the chamber of the apparatus. Then, the substrate is rotated. Once in the chamber 7 × 10
After evacuation to a vacuum degree of ^-7 Torr or less, 3 Torr of Ar gas is introduced. Then, sputtering is performed at a deposition rate of about 2Å / sec. First, a Si target (first target) is used, N ₂ gas is introduced into the chamber in addition to Ar gas, reactive sputtering is performed, and a film thickness of 70 is formed on the resin layer.
Form 0Å silicon nitride (first protective layer).

Then, the introduction of N ₂ gas is stopped, and sputtering is performed in a 0.4 Pa Ar gas using a GdFeCo alloy target (second target). As a result, an R layer having a film thickness of 300 Å is formed on the first protective layer. The composition of the R layer is Gd ₂₂
Fe _54.6 Co _23.4 perpendicularly magnetized film with Curie point T _CR
Is above 250 ° C. Next, while maintaining the vacuum state, Tb target (third target) with the same Ar gas pressure
And FeCo target (4th target) are used to perform two-way simultaneous sputtering. Thereby, the film thickness t is formed on the R layer.
₁ = 300Å M layer is formed. The M layer has an ultrathin layered periodic structure, and its average composition is Tb ₂₀ Fe ₇₆ Co ₄ , which exhibits perpendicular magnetization, and the Curie point T _C1 is about 180 ° C.

Then, while maintaining the vacuum state, 0.25 Pa
In Ar gas, the sputtering is performed using a GdFeCo alloy target (fifth target) having a different Gd / FeCo ratio from the second target. This gives a film thickness of 10 on the M layer.
An Int layer composed of 0 Å Gd ₃₅ Fe ₅₂ Co ₁₃ is formed. Furthermore,
While maintaining the vacuum state, sputtering is performed in a gas of 0.15 Pa using a DyFeCo alloy target (sixth target). As a result, a W layer having a film thickness t ₂ = 500Å is formed on the Int layer. The W layer is composed of a perpendicularly magnetized film having a composition of Dy ₂₈ Fe ₃₆ Co ₃₆ .

Finally, in the same manner as the first protective layer, a 700-Å-thick silicon nitride film (second protective layer) is formed on the W layer. The Dy composition of the W layer is set to 28% in atomic percentage.
Thus, an overwritable magneto-optical recording medium was obtained. A schematic view of this vertical section is shown in FIG. In this embodiment,
This overwritable magneto-optical recording medium was used. (2) Heat treatment of magneto-optical recording medium The heat treatment is performed in a commercially available constant temperature bath. The one used in this embodiment is one in which the temperature and the heating time can be set, and air can be circulated in the tank. With such a device,
The magneto-optical recording medium manufactured in (1) was heat-treated. The heating temperature is set in the range of 50 to 100 ° C, and the heating time is set to 5 to 48.
Set to time. (3) Recording linear velocity 11.3m / s (r = 45mm, 2400rpm), recording magnetic field Hb 35
Recording was performed at 0 O _e , 4 MHz, Duty 50%, and reproduction power 1.0 mW.

[0033]

Example 2 An overwritable magneto-optical recording medium similar to that in Example 1 was prepared, and heat treatment was performed in the same apparatus at a heating temperature of 80 ° C. and a heating time of 24 hours. Also, recording was performed in the same manner.

[0034]

Example 3 An overwritable magneto-optical recording medium similar to that in Example 1 was prepared, and heat treatment was performed in the same apparatus at a heating temperature of 60 ° C. and a heating time of 24 hours. Also, recording was performed in the same manner.

[0035]

Comparative Example 1 An overwritable magneto-optical recording medium similar to that of Example 1 was prepared, heat treatment was not performed, and recording was performed by the same method.

[0036]

Comparative Example 2 An overwritable magneto-optical recording medium similar to that of Example 1 was prepared, and heat treatment was performed in the same apparatus at a heating temperature of 80 ° C. and a heating time of 3 hours. Also, recording was performed in the same manner.

[0037]

[Evaluation test] Recording layer reversal magnetic field for each sample, power (PL _th ) capable of completely erasing prerecorded pits by DC process by DC irradiation, and before and after 1 million times repetitive recording (WC: Write Cycle) The maximum reproducing power (Pr _max ) was measured. The results are shown below.

[0038]

[Table 1]

As can be seen from the above, in the case of the embodiment, the _switching magnetic field and P _Lth of the W layer can be lowered. Again 10
Maximum playback power (P
It was found that r _max ) did not substantially change in the case of the example, and the recording layer did not deteriorate.

[0040]

As described above, by performing the heat treatment after the film formation, the initializing magnetic field of the W layer is reduced, the fluctuation of the maximum reproducing power before and after the repeated recording is suppressed, and a stable reproducing signal is obtained. You can There is also an effect that the power setting range of the L process is expanded.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a cross-sectional structure of an overwritable magneto-optical recording medium according to an embodiment of the present invention. that's all

Claims (2)

[Claims] 1. A memory layer (M) having perpendicular magnetic anisotropy, which is laminated on the substrate in any order of top and bottom.
Layer) and a writing layer (W layer) having a perpendicular magnetic anisotropy exchange-coupled to the layer, and at least the M layer and the W layer. A method for manufacturing a magneto-optical recording medium, characterized in that the substrate on which is formed is heat-treated and then recording is performed. 2. The heating temperature in the heat treatment is 50.degree.
The method according to claim 1, wherein the temperature is within the range of 00 ° C and the heating time is set to 5 to 48 hours.