JPH0684214A - Production of magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To provide the process for production of the magneto-optical recording medium with which overwriting can be executed in the same manner as for a magnetic recording medium simply by adding a magnetic field generating means of a simple construction to the conventional device constitution. CONSTITUTION:The Curie temps. of a first magnetic layer 1, a second magnetic layer 2 and a third magnetic layer 3 are respectively designated as TH1, TL2, TH3, the coercive forces thereof respectively as HL1, HH2, HL3, the film thicknesses as h1, h2, h3, and the saturation magnetizations as MS1, MS2, MS3, the magnetic wall energy between the first and second magnetic layers 1 and 2 is designated as sigmaW12 and the magnetic wall energy between the second and third magnetic layers 2 and 3 as sigmaW23. At this time, TH1>TL2, TL2<TH3, HL1<HH2, HH2>HL3 hold at this time and (sigmaW12/2MS1h1)>HL1, (sigmaW23/2MS3h3)< HL3 hold at this time. The exchange bonding force between the second and third magnetic layers 2 and 3 is adjusted by adjusting the time before the third magnetic layer is formed after the formation of the first and second magnetic layers 1, 2 on the substrate B in this method for production of the magneto- optical recording medium.

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 a novel Curie point write type magneto-optical recording medium capable of reading by utilizing the magnetic Kerr effect.

[0002]

2. Description of the Related Art A magneto-optical disk is known as an erasable optical disk memory. Magneto-optical discs have higher density recording than magnetic recording media using conventional magnetic heads.
On the other hand, there is an advantage that recording and reproduction can be performed in a non-contact manner, but on the other hand, there is a problem that the recorded portion must be erased once before recording (it must be magnetized in one direction). In order to compensate for this problem, a method of separately providing a recording / reproducing head and an erasing head, or a method of irradiating a continuous laser beam and recording while modulating a magnetic field applied at the same time has been proposed. .

[0003]

However, these methods have problems that the device becomes large and the cost is high, or high-speed modulation cannot be performed.

The present invention has been made in order to eliminate the above-mentioned problems of the conventional example, and only by adding a magnetic field generating means of a simple structure to the conventional apparatus configuration, overwriting (as in the case of a magnetic recording medium). It is an object of the present invention to provide a method of manufacturing a magneto-optical recording medium capable of overwriting.

[0005]

The above object can be achieved by the present invention described below. That is, a first magnetic layer having a high Curie point T _H1 and a low coercive force H _L1 and a second magnetic layer having a Curie point T _L2 and a high coercive force H _H2 relatively lower than the first magnetic layer. , At least on the substrate, a three-layered perpendicular magnetization film composed of a third magnetic layer having a Curie point T _H3 and a low coercive force H _L3 relatively higher than that of the second magnetic layer, (σ _W12 / 2M _S1 h ₁ )> H _L1 , (σ _W23 / 2M _S3 h ₃ ) <
H _L3 {the domain wall energies of the first magnetic layer and the second magnetic layer are σ _W12 ,
The domain wall energies of the second magnetic layer and the third magnetic layer are σ _W23, and the film thicknesses of the first magnetic layer, the second magnetic layer, and the third magnetic layer are h ₁ , h ₂ , and h ₃ in this order. The magnitude of the saturation magnetization is sequentially set to M _S1 , M _S2 , and M _S3 . A method for manufacturing a magneto-optical recording medium satisfying the above conditions, wherein the time until the third magnetic layer is formed after the first magnetic layer and the second magnetic layer are formed on the substrate is adjusted. Is used to adjust the exchange coupling force between the second magnetic layer and the third magnetic layer.

The present invention will be described in detail below with reference to the drawings.

FIGS. 1A and 1B are schematic sectional views showing an embodiment of a magneto-optical recording medium manufactured by the method of the present invention. The magneto-optical recording medium of FIG. 1 (a) has a first magnetic layer 1, a second magnetic layer 2 and a third magnetic layer 3 laminated on a transparent substrate B having a pre-groove. Is. The first magnetic layer 1 has a high Curie point (T _H1 ) and a low coercive force (H _L1 ), and the second magnetic layer 2 has a low Curie point (T _L2 ) and a high coercive force.
(H _H2 ), and the third magnetic layer 3 has a high Curie point (T _H3 ).
And a low coercive force ( _HL3 ). Here, “high” and “low” represent relative relationships when the first and third magnetic layers and the second magnetic layer are compared (coercive force at room temperature).

Further, in this magneto-optical recording medium, the domain wall energy of the first magnetic layer 1 and the second magnetic layer 2 is σ _W12 , and the domain wall energy of the second magnetic layer 2 and the third magnetic layer 3 is σ _W23 .
The film thicknesses of the first magnetic layer 1, the second magnetic layer 2, and the third magnetic layer 3 are sequentially set to h ₁ , h ₂ , and h _3, and the magnitudes of the saturation magnetizations of these layers are sequentially set to M _S1 , M _S2 , and M. _{If S3} , the above three magnetic layers are coupled so as to satisfy the following equation.

[0009]

[Equation 1] The reason why this expression should be satisfied will be described later.

The relationship between the Curie point and the coercive force between the first magnetic layer 1 and the third magnetic layer 3 is not particularly limited, but T _H1 ≧ T _H3 and H _L1 ≦ H _L3 are preferable.

However, normally, T _H1 of the first magnetic layer 1 is 15
0 to 400 ° C., H _L1 is 0.1 to ₁ KOe, second magnetic layer 2
T _L2 is 70 to 200 ° C., H _H2 is ₂ to 10 KOe, and the third
The magnetic layer 3 has T _H3 of 100 to 250 ° C. and H _L3 of 0.5 to 4
It is preferable to set it within the range of about KOe.

In the magneto-optical recording medium manufactured by the method of the present invention, the adjacent magnetic layers are coupled by exchange force, and the first magnetic layer 1 and the second magnetic layer 2 are relatively strongly coupled, The second magnetic layer 2 and the third magnetic layer 3 are relatively weakly coupled.

The three magnetic layers 1, 2 and 3 allow the magnetization states of the finally recorded two kinds of bits (states shown in FIG. 2 (f)) to exist stably, that is, the above relational expressions. The film thickness of each layer, the coercive force, the magnitude of the saturation magnetization, the domain wall energy, etc. may be set so as to satisfy the above.

As a material for each magnetic layer, a material exhibiting perpendicular magnetic anisotropy and exhibiting a magneto-optical effect can be used.
Co, GdFe, TbFe, DyFe, GdTbFe,
TbDyFe, GdFeCo, TbFeCo, GdTb
An amorphous magnetic alloy of a rare earth element such as Co and a transition metal element is preferable.

In FIG. 1 (b) which is another example of the magneto-optical recording medium according to the manufacturing method of the present invention, numerals 4 and 5 are for improving the durability of the three magnetic layers 1, 2 and 3, or are magneto-optical. It is a protective film for improving the effect.

Reference numeral 6 is an adhesive layer for bonding the bonding substrate 7. The bonding substrate 7 also has 2 to 6
By stacking the layers up to and adhering them, recording and playback can be performed on the front and back.

The process of recording on the magneto-optical recording medium by the manufacturing method of the present invention will be described below with reference to FIGS. Before recording, the magnetization directions of the magnetic layers 1 and 2 may be parallel and stable, or may be antiparallel and stable.

Reference numeral 35 in FIG. 3 is a magneto-optical disk having the above-described structure. For example, assume that a part of the magnetization state of the magnetic layer is initially as shown in FIG. That is, in FIG. 2, before recording, the first and second magnetic layers 1 and 2 are recorded.
A case will be described in which it is stable when the magnetization directions of the third magnetic layer 3 and the third magnetic layer 3 are parallel. The magneto-optical disk 35 is rotated by the spindle motor and passes through the magnetic field generator 34. At this time, if the magnitude of the magnetic field of the magnetic field generator 34 is set to a value between the coercive forces of the second magnetic layer 2 and the third magnetic layer 3 (the direction of the magnetic field is upward in this embodiment), FIG. ), The third magnetic layer 3 is magnetized in a uniform direction, while
The magnetization of the magnetic layer 2 remains unchanged. In addition, the magnetization of the first magnetic layer 1 that is strongly coupled to the second magnetic layer remains unchanged.

Next, the magneto-optical disk 35 rotates to record / record.
When passing through the reproducing head 31, there are two types (first type and second type).
A laser beam having a laser power value of (seed) is applied to the disk surface with either power according to a signal from the recording signal generator 32. The laser power of the first type is power enough to raise the temperature of the disk to near the Curie point of the second magnetic layer 2, and the laser power of the second type raises the disk to the vicinity of the Curie point of the third magnetic layer 3. Power that can be warmed. That is, in FIG. 4 which shows the outline of the relationship between the coercive force of both magnetic layers 2 and 3 and the temperature, the laser power of the first type is close to T _{L2 and} the laser power of the second type is close to T _H3. Can rise.

The second magnetic layer 2 and the third magnetic layer 3 are heated up to near the Curie point of the second magnetic layer 2 by the laser power of the first kind, but the third magnetic layer 3 has a bit at this temperature. Since it has a stable coercive force, by properly setting the bias magnetic field, the recording bit as shown in FIG. 2 (c) can be obtained from both magnetization states shown in FIG. 2 (b). Formed (first type of preliminary recording). The first magnetic layer 1 is also in the magnetized state as shown by the exchange coupling with the second magnetic layer 2.

The proper setting of the bias magnetic field has the following meaning.

In the first type of preliminary recording, a force (exchange force) in which the magnetization of the second magnetic layer 2 is arranged in a stable direction (here, in the same direction) with respect to the magnetization direction of the third magnetic layer 3 is applied. Therefore, the bias magnetic field is not necessary originally. However, the bias magnetic field is set in such a direction as to assist the reversal of the magnetization of the third magnetic layer 3 in the prerecording with the second type laser power described later. Further, it is preferable that the bias magnetic field is set to have the same size and direction in the preliminary recording with the laser power of both the first type and the second type. From this point of view, it is preferable to set the bias magnetic field to the minimum level necessary for the preliminary recording of the second type laser power according to the principle described below.

On the other hand, when the temperature of the disk is raised to near the Curie point of the third magnetic layer 3 by the second type laser power (second type preliminary recording), the magnetization of the third magnetic layer 3 is caused by the above bias magnetic field. The direction of is reversed. Subsequently, the magnetizations of the second magnetic layer 2 and the first magnetic layer 1 are also arranged in the stable direction (here, in the same direction) with respect to the third magnetic layer 3. That is, FIG.
A recording bit as shown in FIG. 2D is formed from either of the magnetization states of (b).

As described above, each portion of the magneto-optical disk is recorded in the state shown in FIG. 2 (c) or (d) by the bias magnetic field and the first and second type laser powers which change according to the signal. Will be.

Next, when the magneto-optical disk 35 is rotated and the recording bits (c) and (d) again pass through the magnetic field generating section 34, the magnetic field generating section 34 causes the second magnetic layer 2 and the third magnetic layer 2 to return to each other as described above. Since it is set between layers 3, the recording bit (c) is in the state (e) without any change. On the other hand, recording bit (d)
Becomes the state of (f) because the third magnetic layer 3 causes magnetization reversal.

In order for the state of the recording bit of (f) to exist stably, as described above,

[0027]

[Equation 2] It is necessary to be. This is for the following reasons.

Σ _W12 / 2M _S1 h ₁ represents the strength of the exchange force acting on the first magnetic layer 1. In other words, the direction of magnetization of the first magnetic layer 1 is oriented in a stable direction (in this case, the same direction) with respect to the direction of magnetization of the second magnetic layer 2 with a magnetic field of σ _W12 / 2M _S1 h _1. Try to. Therefore, since the magnetization of the first magnetic layer 1 is always oriented in a stable direction (in this case, the same direction) with respect to the direction of the second magnetic layer 2, the coercive force H _L1 of the first magnetic layer 1 is , If it is smaller than this exchange power. So σ _W12
/ 2M _S1 h ₁ > H _L1 .

Σ _W23 / 2M _S3 h ₃ represents the strength of the exchange force acting on the third magnetic layer 3. That is, the direction of magnetization of the third magnetic layer 3 is directed to a stable direction (in this case, the same direction) with respect to the direction of magnetization of the second magnetic layer 2 with a magnetic field of σ _{W2 3} / 2M _S3 h _3. Try to. Therefore, the coercive force of the third magnetic layer 3 is set to H in order that the magnetization of the third magnetic layer 3 is not reversed with respect to this magnetic field (in order for the recording bit of FIG. 2 (f) to exist stably).
_L3 may be σ _W23 / 2M _S3 h ₃ <H _L3 .

As described above, in the magneto-optical recording medium to be manufactured by the method of the present invention, the second magnetic layer 2 and the third magnetic layer 3 are used.
It is necessary that the and are exchange-coupled so that an effective bias magnetic field due to the exchange force works during recording. However, when the exchange coupling force is large to some extent or more, the above formula is not satisfied, that is, the bit in the recording state of (f) cannot exist stably. For this reason, it is desirable to set the coercive force of the third magnetic layer 3 to a relatively large value within a range smaller than the magnetic field in the magnetic field generation unit so as to satisfy the above expression. Furthermore, it is necessary to optimize the magnitude of exchange coupling between the second magnetic layer 2 and the third magnetic layer 3.

In the present invention, since the exchange force σ _W23 / 2M _S3 h ₃ between the second magnetic layer and the third magnetic layer is adjusted, the time from the formation of the second magnetic layer to the formation of the third magnetic layer is changed. Let
Generally, the exchange force σ _W23 / 2M _S3 h ₃ is reduced by prolonging the time from the formation of the second magnetic layer to the formation of the third magnetic layer. Therefore, the time is set to an appropriate value. As a result, the magnitude of the exchange force can be optimized.

In the above-described recording method for the magneto-optical recording medium according to the manufacturing method of the present invention, the states (e) and (f) of the recording bits are recorded.
Is controlled by the power of the laser at the time of recording and does not depend on the state before recording, so that overwriting is possible. The recording bits (e) and (f) can be reproduced by irradiating a reproduction laser beam and processing the reproduction light in the recording signal regenerator 33. The magnitude of the reproduction signal (modulation degree) mainly depends on the magneto-optical effect of the first magnetic layer 1.
This and the fact that a material having a high Curie temperature (that is, a material having a large magneto-optical effect) can be used for the first magnetic layer 1 of the magneto-optical recording medium according to the manufacturing method of the present invention, on which the reproducing light is incident, can be used. With the magneto-optical recording medium manufactured by the method (1), recording with a large reproduced signal (large degree of modulation) becomes possible.

In the description of FIG. 2, an example is shown in which the magnetization directions of the first magnetic layer 1, the second magnetic layer 2 and the third magnetic layer 3 are stable, but these magnetization directions are opposite. The same applies to a magnetic layer that is stable when parallel. Figure 5 (A), (B)
The magnetization states in the recording process in these cases are shown in correspondence with FIG.

[0034]

EXAMPLE A polycarbonate disc-shaped substrate with pregrooves and preformatted signals set in a sputtering device equipped with a quaternary target source at a distance of 10 cm from the target and rotated. It was

In argon, the sputtering rate was 100 Å / min and the sputtering pressure was 5 × 10 ^-3 T from the first target.
ZnS was provided at a thickness of 800 Å as a protective layer by orr.

Next, in argon, the sputtering rate from the second target was 100 Å / min, and the sputtering pressure was 5 × 10 ^-3.
GdFeCo alloy is sputtered with Torr and the film thickness is 400
Å, T _H1 = about 350 ° C. The first magnetic layer of GdFeCo was formed. The H _L1 of the first magnetic layer itself was about 500 Oe or less, and the sublattice magnetization was larger in the transition metal.

Next, under the same conditions, a TbFe alloy was sputtered from a third target to a film thickness of 400 Å and T _L2 = 1.
A second magnetic layer of TbFe at 40 ° C. was formed. The H _H2 of the second magnetic layer itself was about 5000 Oe or more, and the sublattice magnetization was larger in the transition metal.

Next, under the same conditions, G from the fourth target
sputtered dTbFeCo alloy, thickness of 300Å, T _H3
= A third magnetic layer of GdTbFeCo was formed at about 260 ° C. H _L3 of the third magnetic layer itself is about 500 to 1500
Oe, and the sublattice magnetization was larger in the rare earth metal.

Next, under the same conditions, Zn was evaporated from the first target.
Sputtered S to form a protective layer with a thickness of 2000Å Zn
An S layer was provided.

Next, the substrate on which the above-mentioned film formation was completed was bonded to a polycarbonate bonding substrate using a hot melt adhesive to form a magneto-optical disk. This magneto-optical disk was set in a recording / reproducing device, and while passing through a 2KOe magnetic field generating section at a linear velocity of about 7 m / sec, a laser beam with a wavelength of 830 nm focused on about 1 μm was 50% duty at 2 MHz. 4m while modulating
Recording was performed with a binary laser power of W and 8 mW. The bias magnetic field was 150 Oe. 1m after that
When it was reproduced by irradiating a W laser beam,
I was able to reproduce a binary signal.

Next, the same experiment as described above was conducted on the magneto-optical disk after the entire surface was recorded. As a result, it was confirmed that the previously recorded signal component was not detected and overwriting was possible.

After the formation of the second magnetic layer, the time until the formation of the third magnetic layer was changed to 30 seconds, 30 minutes and 3 hours. The values of σ _W23 / 2M _S3 h ₃ were 1.0 KOe, respectively. 0.
As the time was increased to 7 KOe and 0.4 KOe, the value could be decreased, and the value of the exchange force σ _W23 / 2M _S3 h ₃ could be optimized.

[0043]

As described in detail above, according to the manufacturing method of the present invention, a high Curie point (T _H1 ) and a low coercive force (H
_A first magnetic layer having _L1 ), a second magnetic layer having a Curie point (T _L2 ) relatively low and a high coercive force (H _H2 ) relatively to the first magnetic layer, and a second magnetic layer The magnetic layer has a three-layer structure including a third magnetic layer having a relatively high Curie point ( _TH3 ) and a low coercive force ( _HL3 ) as compared with the second magnetic layer and the third magnetic layer. It is possible to obtain a magneto-optical recording medium in which the exchange force between them is suitably controlled. When this magneto-optical recording medium is used, a magnetic field generating means is provided at a position different from the recording head at the time of recording and recording is performed with a binary laser power, thereby enabling overwriting.

The magnetic layer mainly used for reproduction of the magneto-optical recording medium manufactured by the method of the present invention can be selected from materials having a large magneto-optical effect, and as a result, the optical layer produced by the manufacturing method of the present invention can be used. The bit recorded on the magnetic recording medium has an advantage that a reproduction signal is large.

[Brief description of drawings]

1A and 1B are diagrams showing an example of a structure of a magneto-optical recording medium manufactured by the method of the present invention.

FIG. 2 is a diagram showing directions of magnetization of magnetic layers 1, 2, and 3 during recording on a magneto-optical recording medium by a manufacturing method of the present invention.

FIG. 3 is a conceptual diagram of a recording / reproducing device.

FIG. 4 is a schematic diagram showing the relationship between coercive force and temperature of the second magnetic layer 2 and the third magnetic layer 3.

5A and 5B are diagrams showing a magnetization state of a magnetic layer in another example of the present invention.

[Explanation of symbols]

 B Transparent substrate with pre-groove 1, 2, 3 Magnetic layer 4, 5 Protective layer 6 Adhesive layer 7 Laminating substrate 31 Recording / reproducing head 32 Recording signal generator 35 Magneto-optical disk

Claims (1)

[Claims] 1. A first magnetic layer having a high Curie point T _H1 and a low coercive force H _L1, and a second magnetic layer having a relatively low Curie point T _L2 and a high coercive force H _H2 as compared with the first magnetic layer. At least a three-layered perpendicular magnetization film including a magnetic layer and a third magnetic layer having a Curie point T _H3 and a low coercive force H _L3 relatively higher than that of the second magnetic layer is provided on at least a substrate, (Σ _W12 / 2M _S1 h ₁ )> H _L1 , (σ _W23 / 2M _S3 h ₃ ) <
H _L3 {the domain wall energies of the first magnetic layer and the second magnetic layer are σ _W12 ,
The domain wall energies of the second magnetic layer and the third magnetic layer are σ _W23, and the film thicknesses of the first magnetic layer, the second magnetic layer, and the third magnetic layer are h ₁ , h ₂ , and h ₃ in this order. The magnitude of the saturation magnetization is sequentially set to M _S1 , M _S2 , and M _S3 . A method for manufacturing a magneto-optical recording medium satisfying the above conditions, wherein the time until the third magnetic layer is formed after the first magnetic layer and the second magnetic layer are formed on the substrate is adjusted. A method for manufacturing a magneto-optical recording medium is characterized in that the exchange coupling force between the second magnetic layer and the third magnetic layer is adjusted by.