JPH0535492B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] 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. [Prior Art] Magneto-optical disks are known as erasable optical disk memories. Magneto-optical disks have advantages over conventional magnetic recording media using 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. It had the disadvantage that it had to be magnetized in one direction. To compensate for this drawback, methods have been proposed, such as providing a recording/reproducing head and an erasing head separately, or recording while simultaneously irradiating a continuous laser beam and modulating the applied magnetic field. [Problems to be Solved by the Invention] However, these methods have drawbacks such as the need for large-scale equipment, high costs, and the inability to perform high-speed modulation. We have developed a magneto-optical recording method that eliminates the drawbacks of the above-mentioned known techniques and enables overwriting similar to that of magnetic recording media by simply adding a magnetic field generating means of 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 the basic application with domestic priority dated 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 searching for a simpler manufacturing method for the recording medium used for this recording. As a result of further research, the present inventors obtained several results. The present invention has been completed in this manner, and its purpose is to provide a simpler method for manufacturing a magneto-optical recording medium that can be used in an overwritable recording method. [Means for Solving the Problems] The present invention, which can achieve the above-mentioned objects, comprises: a first magnetic layer having a low Kyrie point T _L and a high coercive force H _H ; and a relatively high Kyrie point compared to this magnetic layer. The second with T _H and low coercive force H _L
It is composed of magnetic layers, each of which has a two-layer exchange-coupled perpendicular magnetization film on a substrate, the main component of which is an amorphous alloy of rare earth elements and transition metals, and a second magnetic layer. The saturation magnetization of is Ms, the film thickness is h,
If the domain wall energy between two magnetic layers is σw, then _after forming the _first magnetic layer, , A manufacturing method characterized in that any one of the following steps (A) to (C) is performed before forming the second magnetic layer. (A) Step _of allowing _the first magnetic layer to react _with the residual gas by leaving it for _{5 minutes} or more _{. (} B) Step of reacting the first magnetic layer with the residual gas. Partial pressure at least 2x
Step of leaving in an atmosphere of 10 ^-6 Torr or more (C) Under an atmosphere of H ₂ O, O ₂ , H ₂ , N ₂ , H ₂ S, CS ₂ , CH ₄ or an inert gas. Process of plasma treatment. Hereinafter, the present invention will be explained in detail with reference to the drawings. FIGS. 1a and 1b are schematic sectional views each showing an embodiment of a magneto-optical recording medium manufactured according to the present invention. The magneto-optical recording medium shown in FIG. 1a has a first magnetic layer 2 and a second magnetic layer 3 laminated on a transparent substrate 1 provided with pregrooves. The first magnetic layer 2 has a low Curie point T _L and a high coercive force H _H
The second magnetic layer 3 has a high Curie point T _H and a low coercive force H _L. Here "high", "low"
represents the relative relationship when comparing both magnetic layers (coercive force is compared at room temperature). However, normally the T _L of the first magnetic layer 2 is 70 to 180°C, and the H _H is 3 to 180°C.
10KOe, T _H of the second magnetic layer 3 is 150 to 400℃, H _L is
It is preferable to set it within the range of about 0.5 to 2 KOe. Materials that exhibit perpendicular magnetic anisotropy and magneto-optical effects can be used as the material for each magnetic layer.
GdCo, GdFe, TbFe, DyFe, GdTbFe,
Amorphous magnetic alloys of rare earth elements and transition metal elements such as TbDyFe, GdTbFeCo, TbFeCo, and GdTbCo are preferred. 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 bilayer film in the conventional magneto-optical recording method, conversely, the magnetic layer with a low Kyrie 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 h, and the domain wall energy σw between the two layers. It was. H _H ＞σw/2Msh＞H _L However, in the exchange-coupled double-layer film of the recording medium used in the present invention, the difference between the saturation magnetization Ms and film thickness h of the second magnetic layer 3 and the domain wall energy σw between the two magnetic layers is To,
The following relationship is required. H _H > H _L > σw/2Msh This is to ensure that the magnetization state of the bit (shown in Figure 2 f) that is finally completed by recording can exist stably (the detailed reason will be explained later). do). Therefore, the film thickness, coercive force, magnitude of saturation magnetization, domain wall energy, etc. of each layer may be appropriately set so that both magnetic layers 2 and 3 (perpendicularly magnetized films) satisfy the above relational expression. A concrete and practical method is to increase the saturation magnetization Ms of the second magnetic layer, increase the film thickness h, or decrease the domain wall energy σw. However, increasing the film thickness h has the disadvantage that sensitivity decreases in the recording method described in detail later. Also, as the saturation magnetization Ms increases, the value of H _L also decreases, so if the value of H _L is made smaller than 1KOe, it is actually empirically shown that H _L
<σw/2Msh is likely to occur. Therefore, the best method at present is to reduce the domain wall energy σw, but for example, if a nonmagnetic layer is provided between the first magnetic layer 2 and the third magnetic layer, σw decreases dramatically even at a thickness of Therefore, when manufacturing magneto-optical recording media, it is difficult to control the setting of a small σw with good reproducibility. Therefore, in order to set a small σw with good reproducibility and perform good overwriting recording, in the manufacturing method of the present invention, which was completed as a result of further research, as described above, after forming the first magnetic layer, Before forming the second magnetic layer, one of the following steps is performed to treat the magneto-optical recording medium that is in the process of being manufactured. (A) A step of leaving it in a residual gas or inert gas atmosphere of 7×10 ^-7 Torr for 5 minutes or more. (B) A step that reacts with the constituent elements of the first magnetic layer or the second magnetic layer or chemically affects the elements. Step (C) of leaving in an atmosphere with a partial pressure of at least 2×10 ^-6 Torr or more of a substance that has the property of adsorbing to Step of exposing to a plasma atmosphere using an adsorbing substance or an inert gas As a film forming method for the first magnetic layer and the second magnetic layer, a sputtering method, vapor deposition such as electron beam heating, etc. can be used. The above residual gases include H ₂ O, O ₂ , H ₂ , N ₂ , and compounds consisting of low molecular weight C, H, N, and O. Examples of the inert gas include Ar, He, Ne
etc. Furthermore, examples of gases that react with or chemically adsorb to constituent elements of the first magnetic layer and the second magnetic layer include H ₂ O, O ₂ , H ₂ , N ₂ , H ₂ S, CS ₂ ,
Examples include _CH4 . In a typical media manufacturing process, after the first magnetic layer is formed, the second magnetic layer is formed quickly (for example, within one minute) in a high vacuum and cleaning atmosphere. By adding the steps according to methods (A) to (C) above, the exchange force and coercive force of the recording magnetic layer can be improved.
Storage stability, etc. will vary. Therefore, the processing conditions,
Recording characteristics with good reproducibility can be obtained by precisely controlling the processing time and other factors. The specific effects of methods (A) to (C) will be demonstrated in Examples. Note that, in consideration of the magnitude of the effective bias magnetic field during recording, the stability of binary recorded bits, etc., it is desirable that both magnetic layers 2 and 3 be exchange-coupled. Although it is possible to provide a nonmagnetic layer between the magnetic layers 2 and 3 in order to obtain a stable magnetostatic coupling film, it is difficult to set σw with good reproducibility as described above. In FIG. 1b, 4 and 5 are protective films 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. If layers 2 to 5 are laminated on the bonding substrate 7 and bonded together, recording and reproduction can be performed on the front and back 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. 2a. The magneto-optical disk 35 is rotated by a spindle motor and passes through the magnetic field generating section 34 . At this time, if the magnitude of the magnetic field of the magnetic field generating section 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), the magnetic field will appear as shown in FIG. The two magnetic layers 3 are magnetized in a uniform direction, while the magnetization of the first magnetic layer 2 remains as it was. Next, when the magneto-optical disk 35 rotates and passes the recording/reproducing head 31, the recording signal generator 3
According to the signal from 2, 2 types (1st type and 2nd type)
The disk surface is irradiated with a laser beam with a laser power value of (seed). 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, in FIG. 4, which schematically shows the relationship between the coercive force and temperature of both magnetic layers 2 and 3, the first type laser power is
The temperature of the disk can be raised to around T _L and the second type laser power around T _H. The first magnetic layer 2 is
The temperature rises to near the Curie point, but the second magnetic layer 3
has a coercive force that allows bits to exist stably at this temperature, so by setting the bias magnetic field appropriately during recording, bits like those in Figure 2 c can be obtained from any of Figure 2 b. Formed (preliminary record of type 1). 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 originally required. However, 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, a direction that hinders the first type of preliminary recording). And this bias magnetic field is the first
For convenience, it is preferable to set the magnitude and direction to be the same in preliminary recording of both the seed and second type laser powers. 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. The second magnetic layer 3 is
When the temperature is raised to near the Curie point (second type of preliminary recording), the direction of magnetization of the second magnetic layer 3 is reversed by the bias magnetic field set as described above. 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. 2d is formed in any of the bits shown in FIG. 2b. In this way, each location on the magneto-optical disk is preliminarily recorded in the state shown in FIG. Become. Next, the magneto-optical disk 35 is rotated, and the bits (c) and (d) of the preliminary recording move the magnetic field generating section 34 to the magnetic field generating section 3.
4, the magnitude of the magnetic field of the magnetic field generating section 34 is set between the magnetization reaction magnetic fields of the magnetic layers 2 and 3 as described above, so the recorded bit (c) remains unchanged ( e) (final recording state). On the other hand, the recording bit (d) undergoes magnetization reversal in the second magnetic layer 3 and becomes the state shown in (f) (another final recording state). In order for the state of the recorded bit in (f) to exist stably, the magnitude of the saturation magnetization of the second magnetic layer 3 must be Ms, the film thickness must be h, and the domain wall energy between the magnetic layers 2 and 3 must be σw.
Then, as mentioned above, the following relationship is sufficient. σw/2Msh<H _L <H _H Here, σw/2Msh indicates the strength of the exchange force acting on the second magnetic layer. That is, a magnetic field having a magnitude of σw/2Msh 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 for the second magnetic layer 3 to resist this magnetic field and not reverse its magnetization, it is necessary to
Assuming that the coercive force of the magnetic layer 3 is H _L , it is sufficient if H _L >σw/2Msh. The states (e) and (f) of the recorded bits are controlled by the laser power during recording and do not depend on the state before recording, so overwriting is possible. Recorded bits (e) and (f) can be reproduced by irradiating a reproduction laser beam and processing the reproduction light by a recording signal regenerator 33. In the explanation of FIG. 2, the first magnetic layer 2 and the second magnetic layer 3 are
We showed an example of stability when the direction of magnetization is the same, but
The same can be said of a magnetic layer that is stable when the direction of magnetization is antiparallel. 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 pregroove and preformat signals engraved thereon was set in a sputtering device equipped with a three-dimensional target source, with a distance of 10 cm between the targets, and rotated. I let it happen. After the inside of the sputtering device was evacuated to 1×10 ^-7 Torr or less, the first target was sputtered at a sputtering speed of 100 Å/min and a sputtering pressure of 5×10 ^-3 Torr in argon.
SiO was provided as a protective layer with a thickness of 1000 Å. Next, in argon, TbFe was sputtered from a second target at a sputtering speed of 100 Å/min and a sputtering pressure of 5×10 ^-3 Torr.
Sputter the alloy to a film thickness of 300 Å, T _L = approximately 140°C,
A first magnetic layer of Tb ₁₈ Fe ₈₂ with H _H =about 10 KOe was formed. Even after the spatsuta is finished, the spatsuta chamber continues to be filled with argon.
The water was kept flowing for 30 minutes at ×10 ^-3 Torr. Next, TbFeCo alloy was sputtered in argon at a sputtering pressure of 5×10 ^-3 Torr to give a film thickness of 400 Å and T _H =
A second magnetic layer of Tb ₂₃ Fe ₇₀ Co ₇ was formed at 200° C. and H _L =about 1 KOe. Next, in argon, the first target was sputtered at a sputtering speed of 100 Å/min and a sputtering pressure of 5×10 ^-3 Torr.
SiO was provided as a protective layer with a thickness of 2000 Å. Next, the above substrate on which the film had been formed was bonded to a polycarbonate bonding substrate using a hot melt adhesive to create a magneto-optical disk. This magneto-optical disk was set in a recording/reproducing device, and the magnetic field generator of 2.5 KOe was set at a linear velocity of approximately 8 m/sec.
Recording was performed using a binary laser power of 4 mW and 8 mW while modulating a laser beam with a wavelength of 830 mm focused at approximately 1 μm at 2 MHz with a duty of 50%. Bias magnetic field is 100
It was Oe. After that, a 1.5 mW laser beam was irradiated to perform reproduction, and a binary signal could be reproduced. Next, an experiment similar to that described above was conducted on a magneto-optical disk that had been completely recorded. As a result, previously recorded signal components were not detected, confirming that overwriting is possible. Example 2 and Comparative Example The method was the same as Example 1, but the conditions (atmosphere, degree of vacuum, etc.) after forming the first magnetic layer until starting the sputtering of the second magnetic layer were as shown in Table 1. Instead, each sample of magneto-optical disk was produced. (Those marked with * are examples, others are comparative examples) Of these, in 2-30 to 2-33, a disk-shaped electrode with a diameter of 20 cm was installed at a distance of about 5 cm from the polycarbonate substrate, and various types of electrodes shown in Table 1 were installed. The gas sputtering chamber is 3x
The plasma was introduced to a vacuum level of ^-3 Torr and a discharge power of 50W was applied to perform plasma treatment. Of these, in 2-5 to 2-14, the main valve of the exhaust system was adjusted to close in order to change the residual gas atmosphere. By applying an external magnetic field to each sample and measuring the magnetic field that occurs when the magnetization of each magnetic layer is reversed,
The stability of the recorded bit (f) without an external magnetic field was investigated and evaluated. Those that can exist stably are marked with a circle, and those that cannot exist are marked with an x in Table 1. Further, as in Example 1, recording and reproducing experiments were conducted for each sample. Items that can be recorded well are marked with a circle, and items that are not recorded are marked with an x. The results are summarized in Table 1. From the results of Example 1, Example 2, and Comparative Example, the above
It is clear that by manufacturing a magneto-optical recording medium by employing the methods (A) to (C), an overwritable recording method can be performed satisfactorily.

【table】

〔Effect of the invention〕

As explained in detail above, the low Kyrie point
A magneto-optical medium having a two-layered magnetic layer consisting of a first magnetic layer having a relatively high coercive force _H and T _L and a second magnetic layer having a relatively high Kyrie point T _H and a low coercive force H _L By using a device manufactured using any of the methods (A) to (C) above, and during recording, a magnetic field generating section is provided at a position separate from the recording head, and recording is performed with binary laser power. , it became possible to perform good overwriting.

[Brief explanation of the drawing]

FIGS. 1a and 1b are diagrams each showing an example configuration of a magneto-optical medium used in the present invention, and FIG. 2 is a diagram showing the magnetization directions of magnetic layers 2 and 3 during implementation of the recording method of the present invention. , FIG. 3 is a conceptual diagram of the recording/reproducing apparatus, and FIG. 4 is a schematic diagram showing the relationship between coercive force and temperature of both magnetic layers 2 and 3. FIG. 5 is a diagram showing the magnetization state of the magnetic layer in another embodiment of the present invention. 1: Transparent substrate with pregroove, 2, 3: Magnetic layer, 4, 5: Protective layer, 6: Adhesive layer, 7: Bonding substrate, 31: Recording/reproducing head, 32:
Recording signal generator, 33: Recording signal regenerator, 34:
Magnetic field generation section, 35: magneto-optical disk.

Claims (1)

[Claims] 1. A first magnetic layer having a low Kyrie point T _L and a high coercive force H _H ; and a first magnetic layer having a relatively high Kyrie point T _H and a low coercive force H _L compared to this magnetic layer. It is composed of two magnetic layers, each of which has a two-layer exchange-coupled perpendicular magnetization film on the substrate, the main component of which is an amorphous alloy of rare earth elements and transition metals. The saturation magnetization of the layer is Ms, the film thickness is h,
If the domain wall energy between two magnetic layers is σw, then _after forming the _first magnetic layer, , A manufacturing method characterized in that any one of the following steps (A) to (C) is performed before forming the second magnetic layer. (A) Step _of allowing _the first magnetic layer to react _with the residual gas by leaving it for _{5 minutes} or more _{. (} B) Step of reacting the first magnetic layer with the residual gas. Partial pressure at least 2x
Step of leaving in an atmosphere of 10 ^-6 Torr or more (C) Under an atmosphere of H ₂ O, O ₂ , H ₂ , N ₂ , H ₂ S, CS ₂ , CH ₄ or an inert gas. Process of plasma treatment.