JPS63224054A - Production of magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To enable satisfactory overwriting by forming a magnetic layer having a specified two-layered structure, incorporating a nonmagnetic element into the second magnetic layer so as to reduce exchange force applied to the second magnetic layer and using the resulting magneto-optical recording medium. CONSTITUTION:A perpendicularly magnetizable film having a two-layered struc ture subjected to exchange coupling is formed on a substrate 1 to obtain a magneto-optical recording medium. The film consists of a first magnetic layer 2 having a low Curie point TL and high coercive force HH and a second mag netic layer 3 having a higher Curie point TH and lower coercive force HL than the layer 2 and satisfies inequality I (where Ms is the saturation magnetization of the layer 3, (h) is the thickness of the layer 3 and sigmaw is the domain wall energy between the layers 2, 3). Each of the layers 2, 3 contains an amorphous alloy of a rare earth element and transition metal as the principal component. The layer 3 is formed by simultaneously vapor-depositing a rare earth element- transition metal material and a nonmagnetic element material from separately positioned evaporating sources. When the recording medium is used, satisfactory overwriting is enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a Curie point writing type magneto-optical recording medium that can be read using the magnetic Kerr effect.

[Conventional technology]

A magneto-optical disk is known as an erasable optical disk memory. Magneto-optical disks have advantages over magnetic recording media using conventional magnetic heads, such as high-density recording and non-contact recording and playback, but on the other hand, the recorded area must be erased before recording. The disadvantage of having to magnetize in one direction has been eliminated. In order to compensate for this drawback, proposals have been made such as a method in which a recording/reproducing head and an erasing head are provided separately, or a method in which recording is performed while irradiating a continuous laser beam and simultaneously modulating the applied magnetic field.

[Problem that the invention seeks to solve]

However, these methods have drawbacks such as requiring large-scale equipment, high costs, and inability to perform high-speed modulation.

This book describes a magneto-optical recording method that eliminates the drawbacks of the above-mentioned known techniques and makes it possible to perform overwriting similar to that of magnetic recording media by simply adding a magnetic field generating means with a simple structure to the conventional device configuration. The applicant proposed this in Japanese Patent Application No. 158787-1987 on July 8, 1985 (this application became a basic application with domestic priority (Japanese Patent Application No. 20384) filed on February 2, 1988). .

However, since this method is a completely new recording method, there are still many research issues related to this method. In other words, we are researching methods for producing magneto-optical recording media that are more suitable for use in this recording.

As a result of further research, the present inventors obtained several results.

The present invention has been completed in this way, and its purpose is not only to provide an overwritable recording method, but also to provide a method for manufacturing a magneto-optical recording medium suitable for the overwritable recording method. .

[Means for solving problems]

The present invention, which can achieve the above objects, provides a first i magnetic layer having a low Curie point (TL) and high coercive force (HH), and a relatively high Curie point (Tt1) and low coercive force compared to this magnetic layer. It consists of a second magnetic layer having magnetic force (HL), and each layer has an exchange-coupled perpendicular magnetization film on the substrate with a two-layer structure mainly composed of an amorphous alloy of rare earth elements and transition metals. A method for producing a magneto-optical recording medium which satisfies H''>HL>2ySh, where the saturation magnetization of the second magnetic layer is Ms, the film thickness is h, and the domain wall energy between the two magnetic layers is σ. The second magnetic layer is made of ■a rare earth element-transition metal material (an alloy of a rare earth element and a transition metal, or a material simply using a combination of a rare earth element and a transition metal) and ■a nonmagnetic element material. This is a method of manufacturing a magneto-optical recording medium in which a film is formed by simultaneously scattering evaporation onto a substrate from evaporation sources provided at separate locations.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIGS. 1(a) and 1(b) are schematic sectional views each showing an example of a magneto-optical recording medium manufactured according to the present invention.

The magneto-optical recording medium shown in FIG. 1(a) has a first magnetic layer 2 and a second magnetic layer 3 laminated on a transparent substrate 1 provided with a pre-group. The first magnetic layer 2 has a low Curie point (TL') and a high coercive force (HH), and the second magnetic layer 3 has a high Curie point ("rn) and a low coercive force (HL). Here, "High" and "low" represent a relative relationship when comparing the inner magnetic layers (coercive force is compared at room temperature). However, normally, the TL of the first magnetic layer 2 is 70 to 180°C, the H, is Oe to 3 to IO, the TH of the second magnetic layer 3 is 100 to 400°C, and the HL is 0.5 to IO.
It is preferable to set it within the range of about 2 to Oe.

The main component of each magnetic layer exhibits perpendicular magnetic anisotropy and exhibits a magneto-optic effect. Amorphous magnetic alloys of rare earth elements and transition metal elements are available. For example, GdC:o, G
dFe, TbFe, DyFe, GdTbFe,
TbDyFe.

GdTbFeCo, TbFeGo, GdTb(:o
etc.

By the way, in the recording method using the magneto-optical recording medium according to the present invention, the first magnetic layer 2 is mainly involved in reproduction. That is, the magneto-optic effect exhibited by the first magnetic layer 2 is mainly used for reproduction, and the second magnetic layer 3 plays an important role in recording.

On the other hand, in the exchange-coupled double-layer film in the conventional magneto-optical recording method, conversely, the magnetic layer with a low Curie point and high coercive force is mainly involved in recording; The magnetic layer was mainly involved in reproduction.

In such a conventional exchange-coupled two-layer film, it is desirable that the following relationship exists between the saturation magnetization Ms of the magnetic layer mainly involved in reproduction, the film thickness, and the domain wall energy σw between the two layers. Ta.

HH>-> HL Msh However, in the exchange-coupled two-layer film of the recording medium used in the present invention, between the saturation magnetization Ms and film thickness of the second magnetic layer 3 and the m-magnetic energy σw between the two magnetic layers, The following relationship is required.

HH>HL, >□Msh This is to ensure that the magnetization state of the bit finally completed by recording (shown in FIG. 2(f)) remains stable (detailed reasons will be described later).

Therefore, when forming the bimagnetic layer 2.3 (perpendicular magnetization film), the film thickness, coercive force, magnitude of saturation magnetization, domain wall energy, etc. of each layer should be appropriately set so as to satisfy the above relational expression. However, as a concrete and realistic method, the second method is
The choice is to increase the saturation magnetization Ms of the magnetic layer, increase the film thickness, or decrease the domain wall energy σw. However, increasing the film gh has the disadvantage that the sensitivity of the magneto-optical recording medium decreases. In addition, as the saturation magnetization Ms increases, the value of Ht also decreases, so empirically, when the value of HL becomes 1, which is smaller than Oe, HL, <0w7
It's easy to get 2M5h).

Therefore, the best method at present is to reduce the Mi wall energy a. For example, if an intermediate layer made of a non-magnetic element is provided between the first magnetic layer 2 and the second magnetic layer 3, the exchange interaction through the intermediate layer will be drastically reduced even if the thickness is only a few tens of layers, so the apparent The upper σ stomach becomes smaller.

However, even if an attempt is made to actually produce a magneto-optical medium having an appropriate size of aW with good reproducibility, there is a drawback that reproducibility is not possible due to the large dependence on the thickness of the intermediate layer.

Therefore, we proceeded with our research and mixed a non-magnetic element into the second magnetic layer, and found that a substance that reduces exchange interaction was dispersed within the layer, and it was found that the substance that reduces the exchange interaction was dispersed within the layer, and the , although the magnitude of the exchange force acting on the second magnetic layer can be reduced in the same way as when the above-mentioned intermediate layer is provided, unlike the intermediate layer, the exchange force acting on the second magnetic layer cannot be reproduced. It became clear that the settings could be easily configured.

Therefore, the second magnetic layer of the illustrated magneto-optical recording medium contains a non-magnetic element, and when mixed into the second magnetic layer, the non-magnetic element does not easily affect Mg in that layer. (hard to reduce MS and hard to lower Curie temperature) are used. A preferred example thereof is Cu.

Examples include Ag, Ti, Mn, B, Pt, Si, and Ge. The amount added is preferably about 2% to 70% in terms of atomic weight.

It is preferable to suppress the decrease in the Curie temperature to within about 30° C., but if possible, it is better not to decrease the Curie temperature.

Here, it is thought that the decrease in Curie temperature occurs mainly because the added nonmagnetic element is alloyed with the rare earth element or transition metal of the second magnetic layer. In order to prevent this, further studies were conducted and it was found that when forming the second magnetic layer, an evaporation source for rare earth elements and transition metal elements and an evaporation source for non-magnetic layer elements should be provided separately. Regular sputtering, ion beam evaporation or sputtering, and electron beam evaporation are performed while rotating the substrate.

It has become clear that forming a film using a film forming method such as cluster beam evaporation is effective. That is, as mentioned above, this is the greatest feature of the present invention, and as a result, even if a large amount of non-magnetic layer elements are added, the Curie temperature does not decrease much, and the adverse effects caused by the decrease in MS, that is, the first and second It has become possible to reduce the apparent aW without adversely affecting the recording sensitivity and recording state of the magnetic layer. The reason for this is thought to be that, when viewed microscopically, a laminated structure of the rare earth transition metal and the nonmagnetic layer element is formed.

Note that, in consideration of the magnitude of the effective bias magnetic field during recording or the stability of binary recorded bits, it is desirable that both magnetic layers 2.3 are exchange-coupled.

In the magneto-optical recording medium of FIG. 1(b) manufactured using the present invention, 4.5 is a protective film for improving the durability of both magnetic layers or for improving the magneto-optical effect.

6 is an adhesive layer for bonding the bonding substrate 7 together. By laminating 2 to 5 layers on the bonding substrate 7 and gluing them together, recording and reproduction can be performed on both sides.

The recording process will be described below with reference to FIGS. 2 to 4. Before recording, the stable magnetization directions of both magnetic layers 2 and 3 may be parallel (same direction) or antiparallel (opposite directions). In FIG. 2, a case will be explained in which the stable directions of magnetization are parallel.

35 in FIG. 3 is a magneto-optical disk having the configuration described above. For example, suppose that the magnetization state of a certain part of this magnetic layer is initially as shown in FIG. 2(a). The magneto-optical disk 35 is rotated by a 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 both magnetic layers 2 and 3 (the direction of the magnetic field is upward in this embodiment), as shown in FIG.
As shown in b), the second magnetic layer 3 is magnetized in a uniform direction,
On the other hand, the magnetization of the first magnetic layer 2 remains unchanged.

Next, the magneto-optical disk 35 rotates and the recording/reproducing head 3
1, laser beams having two types of laser power values (first type and second type) are irradiated onto the disk surface in accordance with a signal from the recording signal generator 32. The first type of laser power is enough to raise the temperature of the disk to around the Curie point of the first magnetic layer 2, and the second type of laser power is enough to raise the temperature of the disk to around the Curie point of the second magnetic layer 3. It is a power that can be heated. That is, both magnetic layers 2.
In FIG. 4, which shows an outline of the relationship between coercive force and temperature in No. 3, the first type of laser power can raise the temperature of the disk to around TL, and the second type of laser power can raise the temperature of the disk to around T.

The temperature of the first magnetic layer 2 is raised to near the Curie point by the first type of laser power, but the second magnetic layer 3 has a coercive force that allows bits to stably exist at this temperature, so the bias magnetic field during recording is By setting properly, Figure 2 (
A bit as shown in FIG. 2(c) is formed from any of the bits (b) (first type preliminary recording).

Here, setting the bias magnetic field appropriately means the following. That is, in the first type of preliminary recording, the magnetization of the first magnetic layer 2 receives a force (exchange force) that aligns it in a stable direction (here, in the same direction) as the direction of magnetization of the second magnetic layer 3. Therefore, a bias magnetic field is not necessary in the first place. but,
The bias magnetic field is set in a direction that assists magnetization reversal of the second magnetic layer 3 in preliminary recording using the second type of laser power (described later) (that is, in a direction that hinders the first type of preliminary recording). For convenience, it is preferable that the bias magnetic field is set to have the same magnitude and direction in preliminary recording with either the first type or the second type of laser power.

From this point of view, it is preferable to set the bias magnetic field to the minimum size necessary for preliminary recording of the second type of laser power based on the principle shown below, and settings that take this into account are the appropriate setting as mentioned above. It is a setting.

Next, the second type of preliminary recording will be explained.

When the temperature of the second magnetic layer 3 is raised to near the Curie point using the second type of laser power (second type of preliminary recording), the direction of magnetization of the second magnetic layer 3 is changed by the bias magnetic field set as described above. is reversed. Subsequently, the magnetization of the first magnetic layer 2 is also aligned in a stable direction (here, in the same direction) with respect to the second magnetic layer 3.

That is, a bit as shown in FIG. 2(d) is formed from any of the bits shown in FIG. 2(b).

In this way, the bias magnetic field and the first
Depending on the laser power of the seed and the second type, each location on the magneto-optical disk is preliminarily recorded in the state shown in FIG. 2(C) or FIG. 2(d).

Next, when the magneto-optical disk 35 is rotated and the preliminary recorded bits (C) and (d) pass through the magnetic field generating section 34 again, the magnitude of the magnetic field of the magnetic field generating section 34 changes between the magnetic layers 2 and 3 as described above. Therefore, the recording bit (C) remains in the state (e) without any change (fi
final recording state). On the other hand, in the recording bit (d), the second magnetic layer 3 undergoes magnetization reversal and becomes the state (f) (another final recording state).

In order for the state of the recorded bit (f) to exist stably, the magnitude of the saturation magnetization of the second magnetic layer 3 must be Ms, the film thickness must be changed, and the domain wall energy between the Then, as mentioned above, the following relationship is sufficient.

Here, 0w72M5h indicates the strength of the exchange force acting on the second magnetic layer. That is, a magnetic field with a magnitude of 0w/2M5h attempts to direct the magnetization direction of the second magnetic layer 3 in a direction that is stable with respect to the magnetization direction of the first magnetic layer 2 (in this case, the same direction). Therefore, in order to prevent the magnetization of the second magnetic layer 3 from being reversed against this magnetic field, it is sufficient that the coercive force of the second magnetic layer 3 is HL>0w72M5h.

The states (e) and (f) of the recorded bits are controlled by the power of the laser during recording and do not depend on the state before recording, so overwriting is possible. Recording bits (e) and (f) are generated by irradiating a laser beam for reproduction and processing the reproduction light by a recording signal regenerator 33.
Can be played.

In the explanation of FIG. 2, an example was shown in which the first magnetic layer 2 and the second Mi layer 3 are stable when their magnetization directions are the same, but the same idea can be applied to magnetic layers that are stable when their magnetization directions are opposite. It will be done. FIG. 5 shows the magnetization state during the recording process in this case, corresponding to FIG. 2.

〔Example〕

Example 1 A polycarbonate disc-shaped substrate with pregroup and preformat signals engraved thereon is placed in a sputtering apparatus equipped with three target sources at a distance of 1 from the target.
They were set at 0 cm intervals and rotated at 15 rpm.

After evacuating the inside of the sputtering apparatus to below I×10 Torr, the sputtering speed was set to 10 from the first target in argon.
0 people/win, sputtering pressure sx to -: (Torr) ZnS was formed as a protective layer to a thickness of 1000 people. Next, in argon, sputtering speed io was increased from the second target.
TbFe alloy was sputtered at a sputtering pressure of 5X 10-' Torr with a film thickness of 300 A, TI,
= approx. 140°C, HH = approx. 10 KOe Tb+aFeaz
A first magnetic layer was formed in which the sublattice magnetization of the Fe element was dominant.

Next, in argon, sputtering pressure 5x IQ-:I To
TbFeCo alloy from the third target at rr,
Cu was simultaneously sputtered from the target at a sputtering speed of 100 sputtering/min, a film thickness of 500 sputtering, T, 4 = approximately 2
00°C, HL = approx. 1 Oe TI) + a, 4Fesa
A second magnetic layer in which the sublattice magnetization of the Tb element of CO6,s CLI2o is dominant was formed.

Next, in argon, the first target is sputtered at a sputtering rate of 1
00 people/min, sputtering pressure 5 x 10” 3 Torr
Then, ZnS was formed as a protective layer to a thickness of 2000 mm.

Next, the above substrates on which the film had been formed were bonded to a polycarbonate bonding substrate using a hot melt adhesive to create a sample of a magneto-optical disk.

Set this sample on the recording/playback device and set Oe to 2.5.
A laser beam with a wavelength of 830 mm condensed to approximately 1 μm is passed through the magnetic field generating part at a linear velocity of approximately 8 m/sec, and is modulated at 2 MHz with a duty of 50%. Recording was performed using laser power. The bias magnetic field was 1000e. After that 1.
After irradiation with a 5*W laser beam for reproduction, a binary signal could be reproduced.

Next, an experiment similar to the above was conducted on the magneto-optical disk after the entire surface had been recorded. As a result, previously recorded signal components were not detected, confirming that overriding is possible.

Example 2 and Comparative Example The same method as Example 1 was used except that the type and amount of the non-magnetic element added to the second magnetic layer and the number of rotations of the substrate during film formation were changed. Therefore, magneto-optical disk samples as shown in Table 1 were prepared using the same materials, film thickness, and coercive force as in Example 1, except that the second magnetic layer was formed using one target.

For each sample including Example 1, the recording bit (f
), while applying an external magnetic field, the magnitude of the magnetic field at which reversal of the magnetization of the first and second magnetic layers occurs was investigated. Next, record bits without applying an external magnetic field (
The stability of f) was investigated. Those that are stable are marked with an O, and those that are not are marked with an X in Table 1.

Next, for each sample shown in Table 1, samples were prepared in which only the thickness of the second magnetic layer was changed, and the recording bit (f
) The thickness of the second magnetic layer when it starts to become unstable was investigated. The results are also shown in Table 1.

From the results in Table 1, for the sample in which the evaporation source (sputter source) of the second magnetic layer is divided into magnetic material and non-magnetic material,
It can be seen that in all cases, the Curie temperature decreases little and the stability of the bit (f) is good.

In sample 2-4.2-8.2-12, the stability of bit (f) is marked x because the coercive force of the second magnetic layer has decreased. In particular, the effect of separating the evaporation sources is that Cr, A
This is remarkable for materials such as n, which have a large effect of lowering the Curie temperature when added to transition metals.

〔Effect of the invention〕

As explained in detail above, the low Curie point ("rt,
＞ and a first magnetic layer having a high coercive force (I(H));
Relatively high Curie point (T, ) and low coercive force ()II
, ), and a second magnetic layer is formed by adding a non-magnetic element to the second magnetic layer.
Using a magneto-optical recording medium adjusted to reduce the exchange force acting on the magnetic layer, a magnetic field generating section is installed at a separate position from the recording head during recording, and recording is performed using binary laser power, thereby achieving good overwriting. ) is now possible.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) each show an example of the structure of the magneto-optical medium used in the present invention, and FIG. 2 shows the magnetization of the magnetic layer 2.3 during the recording method of the present invention. Diagram showing orientation, 3rd
The figure is a conceptual diagram of the recording/reproducing apparatus, and FIG. 4 is a schematic diagram showing the relationship between the coercive force of the inner magnetic layers 2 and 3 and temperature. FIG. 5 is a diagram showing the magnetization state of the magnetic layer in another embodiment of the present invention. 1 Transparent substrate with nibli groove, 2.3: Magnetic layer 4.5: Protective layer, 6: Adhesive layer, 7: Bonding substrate, 31: Recording/reproducing head, 32: Recording signal generator, 33 : Recorded signal regenerator 34 : Magnetic field generator 35 : Magneto-optical disk,

Claims (1)

[Claims] 1) Low Curie point (T_L) and high coercive force (H_H)
and a second magnetic layer having a relatively high Curie point (T_H) and low coercive force (H_L) compared to this magnetic layer, each of which contains a rare earth element and a transition metal. It consists of a two-layer exchange-coupled perpendicular magnetization film mainly composed of an amorphous alloy of
A method for producing a magneto-optical recording medium that satisfies H_H>H_L>(σw/2Msh), where the saturation magnetization of the second magnetic layer is Ms, the film thickness is h, and the domain wall energy between the two magnetic layers is σw. , the second magnetic layer is formed by simultaneously depositing a rare earth element-transition metal material and a nonmagnetic element material onto the substrate from separate evaporation sources provided at separate positions. Method of manufacturing magnetic media.