JPH0535499B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Industrial Application] The present invention relates to a novel magneto-optical recording medium of the Curie point writing type that can be read using the magnetic Kerr effect, and a magneto-optical recording method that allows overwriting using the same. [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 has the disadvantage that it cannot be magnetized in one direction (it must be magnetized in one direction). In order to compensate for this drawback, methods have been proposed 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. [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 present applicant filed Japanese Patent Application No. 61-158787 on July 8, 1988 [this application is the basis of Japanese Patent Application No. 62-20384, which was filed on February 2, 1988 and claimed domestic priority]. Proposed. 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 magneto-optical recording medium that is 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 magneto-optical recording medium that is more suitable for the overwritable recording method. [Means for Solving the Problems] The present invention capable of achieving the above-mentioned objects comprises: a first magnetic layer having a low Kyrie point _T1 and a high coercive force _H1 ; and a relatively high Kyrie point compared to this magnetic layer. The second with T ₂ and low coercive force H ₂
A magneto-optical recording medium comprising, on a substrate, two exchange-coupled perpendicular magnetization films composed of magnetic layers and an intermediate layer provided between the two magnetic layers, the following: Conditions (A) and (B), that is, (A) saturation magnetization of the first magnetic layer is Ms ₁ , film thickness is h ₁ , saturation magnetization of the second magnetic layer is Ms ₂ , film thickness is h ₂ , intermediate If the apparent domain wall energy between two magnetic layers appearing through the layer is σw ₁₂ , then σw ₁₂ /2Ms ₁ h ₁ <H ₁ , σw ₁₂ /2Ms ₂ h ₂ <H ₂ (B) Material forming the intermediate layer is an inorganic non-magnetic material, or is made of a magnetic material with a composition such that in a single intermediate layer with respect to the substrate surface at room temperature, the in-plane magnetization component is larger than the magnetization component perpendicular to the substrate surface. These are a magneto-optical recording medium and a recording method using the same, representative embodiments of which will be shown later. Hereinafter, the present invention will be explained in detail with reference to the drawings. FIGS. 1a and 1b are schematic cross-sectional views each showing an embodiment of the magneto-optical recording medium of the present invention. The magneto-optical recording medium shown in FIG. 1a has a first magnetic layer 1, an intermediate layer 3, a second magnetic layer 2, and a magnetic layer 3 laminated on a transparent substrate B provided with a pregroove. It is something.
The first magnetic layer 1 has a low Curie point T ₁ and a high coercive force
H ₁ and the second magnetic layer 2 has a high Curie point T ₂
and has a low coercive force _H2 . Here, "high" and "low" represent a relative relationship when comparing both magnetic layers (coercive force is compared at room temperature). however,
Usually, T ₁ of the first magnetic layer 1 is 70 to 200°C, H ₁ is 2
~10KOe, _T2 of second magnetic layer 2 is 100~400℃, _H2
is preferably within the range of about 0.1 to 4 KOe. The main component of each magnetic layer can be one that exhibits perpendicular magnetic anisotropy and exhibits a magneto-optic effect.
Amorphous magnetic alloys of rare earth elements and transition metal elements are available. Examples include GdCo, GdFe, TbFe,
DyFe, GdTbFe, TbDyFe, GdTbFeCo,
Examples include TbFeCo, GdTbCo, and the like. The first magnetic layer 1 and the second magnetic layer of the magneto-optical recording medium of the present invention
Exchange coupling with the magnetic layer 2 is relatively weak via the intermediate layer 3. Then, the saturation magnetization of the first magnetic layer 1
MS ₁ , its film thickness h ₁ , and saturation magnetization of the second magnetic layer 2
The following relationship is required between MS ₂ , its film thickness h ₂ , and the apparent domain wall energy σw ₁₂ between the two magnetic layers. σw ₁₂ /2Ms ₁ h ₁ <H ₁ σw ₁₂ /2Ms ₂ h ₂ <H ₂ This means that the magnetization state of the bit (shown in Figure 2 f) that is finally completed by recording exists stably. (The detailed reason will be explained later). Therefore, in order for the two magnetic layers 1 and 2 (perpendicular magnetization films) to satisfy the above relational expression, the film thickness, coercive force, magnitude of saturation magnetization, domain wall energy, etc. of each magnetic layer should be set. Bye. However, since this may not always be appropriate, the intermediate layer 3 is provided. (The detailed reason for providing the intermediate layer 3 will be described later). The intermediate layer 3 is made of a non-magnetic material (for example, Si ₃ , N ₄ , SiC,
ZnS, Si, Cr, etc.) or magnetic materials whose magnetization component is larger in the plane than perpendicular to the substrate surface at room temperature (e.g. Fe ₉₀ Dy ₁₀ , Fe ₆₀ Gd ₂₀ Tb ₂₀ , etc.)
or materials whose main easy magnetization direction is directed toward the substrate surface of the magneto-optical recording medium (e.g., Fe, Co, Ni,
It is desirable to use Fe ₉₅ Tb ₅ , etc.). In FIG. 1b, 4, 5 are two magnetic layers 1,
This is a protective film for improving the durability of the intermediate layer 2 and the intermediate layer 3 or for improving the magneto-optical effect. 6 is an adhesive layer for bonding the bonding substrate 7 together. By laminating layers 1 to 5 on the bonding substrate 7 and gluing them together, recording and reproduction can be performed on both sides. The recording process of the present invention will be described below using FIGS. 2 to 4. 35 in FIG. 3 is a magneto-optical disk having the configuration described above. For example, the magnetization state of a certain part of this magnetic layer is initially as shown in FIG. 2a. That is, in FIG. 2, a case will be described in which stability is achieved when the magnetization directions of the first and second magnetic layers are parallel (same direction) before recording. The magneto-optical disk 35 is rotated by a spindle motor and passes through the magnetic field generating section 34 . At this time, the magnitude of the magnetic field of the magnetic field generating section 34 is adjusted to
When the coercive force is set to a value between and 2 (the direction of the magnetic field is upward in this example), the second magnetic layer 2 is magnetized in a uniform direction as shown in FIG.
The magnetization of the magnetic layer 1 remains as it was at the beginning. 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)
A laser beam with a laser power value of either of these powers is irradiated onto the disk surface. 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 1, 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 2. It is a power that can be heated. That is, both magnetic layers 1 and 2
In FIG. 4, which schematically shows the relationship between coercive force and temperature, the first type of laser power can raise the temperature of the disk to around _T1 , and the second type of laser power can raise the temperature of the disk to around _T2 . The first magnetic layer 1 is
The temperature rises to near the Curie point, but the second magnetic layer 2
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 the first type). 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 1 is subjected to 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 2. Therefore, a bias magnetic field is not originally required. However, the bias magnetic field is set in a direction that assists in reversing the magnetization of the second magnetic layer 2 (that is, in a direction that hinders the first type of preliminary recording) in preliminary recording using the second type of laser power, which will be described later. 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. On the other hand, when the second type of laser power is used to raise the temperature of the second magnetic layer 2 to near the Curie point (second type of preliminary recording), the bias magnetic field set as described above magnetizes the second magnetic layer 2. The direction of is reversed. Subsequently, the magnetization of the first magnetic layer 1 is also aligned in a stable direction (here, in the same direction) with respect to the second magnetic layer 2. That is, a bit as shown in FIG. 2d is formed from 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, 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 1 and 2 as described above. Since the coercive force is set between the two, the recorded bit (c) remains in the state of (e) without any change (final recorded state). On the other hand, the recording bit
In (d), the second magnetic layer 2 causes a magnetization reaction and becomes the state in (f) (another final recording state). In order for the recorded bit state (f) to exist stably, the following relationship is required as described above. σw ₁₂ /2Ms ₁ h ₁ <H ₁ σw ₁₂ /2Ms ₂ h ₂ <H ₂ where σw ₁₂ /2Ms ₁ h ₁ indicates the strength of the exchange force acting on the first magnetic layer 1. In other words, a magnetic field with a magnitude of σw ₁₂ /2Ms ₁ h ₁ changes the direction of magnetization of the first magnetic layer 1 and the direction of magnetization of the second magnetic layer 1.
The magnetization is attempted to be directed in a stable direction (in this case, in the same direction) with respect to the direction of magnetization of the magnetic layer 2. Therefore, in order to prevent the magnetization of the first magnetic layer 1 from being reversed against this magnetic field, it is sufficient that σw ₁₂ /2Ms ₁ h ₁ <H ₁ where the coercive force of the first magnetic layer 1 is H ₁ . Similarly, an exchange force acts on the second magnetic layer 2 that aligns the magnetization of the first magnetic layer 1 in a stable direction with a magnitude of σw ₁₂ /2Ms ₁ h ₁ from the interface domain wall, so (f) In order for the recorded bits to be stable, σw ₁₂ /
It is sufficient if 2Ms ₂ h ₂ <H ₂ . As described above, in order to satisfy the above conditions (that is, to reduce the exchange force), it is sufficient to adjust the film thickness and saturation magnetization of both magnetic layers, but such adjustment may not be appropriate. This is because recording sensitivity, coercive force, etc. have appropriate values and cannot be set arbitrarily. As a result of researching countermeasures, it was discovered that creating an intermediate layer would be effective. By providing the intermediate layer with a thickness of 10 to 50 Å, it is possible to suppress the exchange interaction acting at the interface between the first magnetic layer and the second magnetic layer, and to reduce the apparent size of σw ₁₂ . In other words,
It becomes very easy to meet the above requirements and, after all, is suitable for good overwriting. 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 1 and the second magnetic layer 2 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. [Examples] Example 1 A polycarbonate disk-shaped substrate with pregroove and preformat signals engraved thereon was set in a sputtering device equipped with a four-dimensional target source at a distance of 10 cm from the target. Rotated. In argon, from the first target at a sputtering speed of 70 Å/min and a sputtering pressure of 8×10 ^-3 Torr.
A protective layer of Si ₃ N ₄ was provided to a thickness of 650 Å. Next, in argon, a second target was sputtered at a sputtering speed of 50 Å/min and a sputtering pressure of 2×10 ^-3 Torr.
Sputter TbFeCo alloy, film thickness 200 Å, T ₁ = approx.
A first magnetic layer of Tb ₁₇ Fe ₈₀ Co ₃ was formed at 160°C.
The H ₁ of the first magnetic layer itself was about 12 KOe, and the sublattice magnetization was larger in the transition metal. The above operations were performed on each set of substrates, and Si ₃ N ₄ was added to each of the resulting substrates from the first target.
was sputtered under the same conditions as before to form an intermediate layer. The film thickness was varied in steps of 10 Å from zero (no Si ₃ N ₄ was provided at this time) to 70 Å. Next, TbFeCoTi alloy was sputtered onto each of them from a third target in argon at a sputtering speed of 50 Å/min and a sputtering pressure of 2×10 ^-3 Torr.
A second magnetic layer of Tb ₂₃ Fe ₅₁ Co ₁₁ Ti ₁₅ was formed with a film thickness of 400 Å and T ₂ =approximately 190°C. This second magnetic layer itself
H ₂ was 1.1KOe, and the sublattice magnetization was larger for rare earth elements. Next, each layer was sputtered from the first target under the same conditions as before to provide a 1200 Å thick Si ₃ N ₄ layer as a protective layer. Next, each of the substrates on which the film had been formed was bonded to a polycarbonate bonding substrate using a hot melt adhesive to produce a plurality of samples of magneto-optical disks. The stability of bits (particularly in state (f)) was investigated for each of the prepared samples. This was done by applying an external magnetic field and measuring the magnetic field at which the magnetization of the magnetic layer was reversed using a vibrating sample magnetometer (VSM). In this example, since the magnetization of the second magnetic layer starts to be reversed by a smaller external magnetic field, we were able to measure the exchange force acting on the second magnetic layer σw ₁₂ /2Ms ₂ h ₂
It is. Next, set each sample in the recording/playback device,
A binary laser beam of 4 mW and 8 mW is transmitted through the magnetic field generating part of 2KOe at a linear velocity of about 9 m/sec, while modulating a laser beam with a wavelength of 830 nm focused to about 1 μ at 2 MHz with a duty of 50%. Recorded with power. The bias magnetic field at the recording head was 120 Oe. After that, when I irradiated a laser beam of 1mW and performed reproduction, 2
I was able to play the value signal. This experiment was conducted for each sample after the entire surface had been recorded, to check that no signal component recorded before the present example was detected, that is, to check whether overwriting was possible. The above results are summarized in Table 1.

[Table] In Table 1, when determining whether overwriting is possible, mark ○ for those that can record binary signals, and mark × for those that cannot.
I marked the incomplete ones with a △ mark. The results of evaluating the recording state can be made to correspond to the measured values of the exchange force acting on the second magnetic layer in Table 1. That is,
In samples 1-1 and 1-2, the magnitude of the exchange force is not smaller than the coercive force _H2 of the second magnetic layer.
This is because the recording bit in (f) is not stable. In Samples 1-6 to 1-8, the exchange force acting on both the second magnetic layer and the first magnetic layer is too small to allow complete type 1 recording, and the magnetization of the first magnetic layer cannot be reversed. It is thought that this is because of this. Example 2 A magneto-optical disk sample was prepared using the same configuration and materials as in Example 1, except that a fourth target was used and the material and film thickness of the intermediate layer 3 were changed in the same manner as in Example 1. Created. The materials used for the intermediate layer 3 are as follows. Dielectric materials include SiC and ZnS; metal and semimetal materials include Si and Cr; magnetic materials with large in-plane magnetic anisotropy and a higher Curie temperature than the recording magnetic layer include Fe, Co, Ni, and Currie. Materials with large in-plane magnetic anisotropy whose temperature is between room temperature and the Curie temperature of the recording magnetic layer include Dy ₁₅ Fe ₈₅ .
Tb ₇ Dy ₆ Fe ₈₃ Cr ₄ . Each material was sputtered from a fourth target to provide different film thicknesses. The same evaluation as in Example 1 was performed for each of the prepared samples. The results are shown in Table 2.

〔Effect of the invention〕

As explained in detail above, as a magneto-optical recording medium, the first magnetic layer has a low Curie point _T1 and a high coercive force _H1 , and a relatively high Curie point _T2.
and a second magnetic layer having a low coercive force _H2 , and an intermediate layer, and which also satisfies other predetermined requirements, and a magnetic field generating section is provided at a location separate from the recording head during recording. By recording with binary laser power, good overwriting became possible.

[Brief explanation of the drawing]

FIGS. 1a and 1b are diagrams each showing a configuration example of a magneto-optical medium used in the present invention, and FIG. 2 is a diagram showing the magnetization directions of magnetic layers 1 and 2 during implementation of the recording method of the present invention. , FIG. 3 is a conceptual diagram of the recording/reproducing device, FIG. 4 is a schematic diagram showing the relationship between the coercive force and temperature of both magnetic layers 1 and 2, and FIG. 5 is a diagram of the intermediate layer of each sample in the example. FIG. 3 is a diagram showing the relationship between the thickness and the exchange force of the first and second magnetic layers. B: Transparent substrate with pregroove, 1, 2: Magnetic layer, 3: Intermediate 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 generator, 35: Magneto-optical disk.

Claims (1)

[Claims] 1. A first magnetic layer having a low Kyrie point T ₁ and a high coercive force H ₁ and a second magnetic layer having a relatively high Kyrie point T ₂ and a low coercive force H ₂ compared to this magnetic layer. A magneto-optical recording medium comprising, on a substrate, an exchange-coupled two-layer perpendicular magnetization film composed of two magnetic layers and an intermediate layer provided between the two magnetic layers, A magneto-optical recording medium characterized by satisfying the following conditions (A) and (B). (A) The saturation magnetization of the first magnetic layer is Ms ₁ , the film thickness is h ₁ , the saturation magnetization of the second magnetic layer is Ms ₂ , the film thickness is h ₂ , and the apparent difference between the two magnetic layers appearing through the intermediate layer When the domain wall energy is σw ₁₂ , σw ₁₂ /2Ms ₁ h ₁ <H ₁ , σw ₁₂ /2Ms ₂ h ₂ <H ₂ (B) The material forming the intermediate layer is an inorganic non-magnetic material, or the substrate at room temperature Consists of a magnetic material whose composition is such that in a single intermediate layer, the in-plane magnetization component is larger than the magnetization component perpendicular to the plane. 2. The light according to claim 1, wherein the intermediate layer is mainly made of a transition metal or a rare earth-transition metal alloy, and its Curie temperature is higher than room temperature and lower than the Curie point _T1 of the first magnetic layer. magnetic recording medium. 3. The magneto-optical recording medium according to claim 1, wherein the intermediate layer has a thickness of 10 to 50 Å. 4 Consisting of a first magnetic layer having a low Kyrie point T ₁ and a high coercive force H ₁ and a second magnetic layer having a relatively high Kyrie point T ₂ and a low coercive force H ₂ compared to this magnetic layer. A magneto-optical recording medium comprising, on a substrate, two exchange-coupled perpendicularly magnetized films and an intermediate layer provided between the two magnetic layers, which comprises the following (A): The conditions of (B) are as follows: (A) The saturation magnetization of the first magnetic layer is Ms ₁ , the film thickness is h ₁ , the saturation magnetization of the second magnetic layer is Ms ₂ , the film thickness is h ₂ , through the intermediate layer If the apparent domain wall energy between the two magnetic layers is σw ₁₂ , then σw ₁₂ /2Ms ₁ h ₁ <H ₁ , σw ₁₂ /2Ms ₂ h ₂ <H ₂ (B) If the material forming the intermediate layer is an inorganic non- A magneto-optical recording medium that satisfies the requirement that it is made of a magnetic material or a magnetic material whose composition is such that in a single intermediate layer at room temperature, the in-plane magnetization component is larger than the perpendicular magnetization component with respect to the substrate surface. A recording method characterized by recording the following binary values using . (a) With respect to the medium, at a location different from the recording head, change the direction of magnetization of the first magnetic layer with coercive force H ₁ enough to magnetize the second magnetic layer with coercive force H ₂ in one direction. Magnetic field B of a magnitude that does not cause reversal
(b) Next, the recording head applies a bias magnetic field and at the same time irradiates laser power sufficient to raise the temperature of the medium to near the low Curie point _T1 , thereby changing the direction of magnetization of the second magnetic layer. Either the first type of preliminary recording, in which the direction of magnetization of the first magnetic layer is aligned in a stable direction with respect to the second magnetic layer without changing the magnetic field, or the medium is raised to near the high Curie point T ₂ while applying a bias magnetic field. A second type of preliminary recording that reverses the direction of magnetization of the second magnetic layer by irradiating it with enough laser power to heat the layer, and simultaneously magnetizes the first magnetic layer in a stable direction relative to the second magnetic layer. (c) then moving the medium to cause the prerecorded bits to pass through the magnetic field B;
For the bits formed by the first type of preliminary recording, the direction of magnetization of both the first magnetic layer and the second magnetic layer remains unchanged, and for the bits formed by the second type of preliminary recording, the direction of magnetization is unchanged in the second magnetic layer. Binary recording in which the direction of magnetization of the first magnetic layer is reversed in the same direction as the magnetic field B, and the direction of magnetization of the first magnetic layer is left unchanged.