JPH0522302B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] 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). 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 while 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 and high cost, or the inability to perform high-speed modulation. The present invention was made in order to eliminate the drawbacks of the above-mentioned conventional example, and by using a new magneto-optical recording medium, a magnetic field generating means of a simple structure is added to the conventional device configuration. It is an object of the present invention to provide a magneto-optical recording method that enables overwriting in the same way as with magnetic recording media by simply performing the following steps. [Means for Solving the Problems] The above objects can be achieved by the following present invention. That is, a first magnetic layer having a Kyrie point T ₁ and a coercive force H ₁ , a second magnetic layer having a Kyrie point T ₂ and a coercive force H ₂ , and a third magnetic layer having a Kyrie point T ₃ and a coercive force H ₃ . A magneto-optical recording medium comprising a perpendicularly magnetized film having a three-layer structure on at least a substrate, the magnetic layer comprising: (A) each magnetic layer being an alloy of rare earth and transition metal; (B) H ₁ ＞H ₃ ＞H ₂ T ₃ ＞T ₁ ＞T ₂ , (C) The first magnetic layer and the third magnetic layer appear through the second magnetic layer.
If the apparent domain wall energy of the magnetic layer is σw ₁₃ and the film thicknesses of the first and third magnetic layers are h ₁ and h ₃ in this order, then σw ₁₃ /2Ms ₁ h ₁ <H ₁ and σw ₁₃ /2Ms ₃ The present invention describes a magneto-optical recording medium that satisfies h ₃ <H ₃ 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 showing one embodiment of a magneto-optical recording medium used in the present invention. The magneto-optical recording medium shown in FIG. 1a has a first magnetic layer 1, a second magnetic layer 2, and a third magnetic layer 3 laminated on a transparent substrate B provided with a pregroove. It is something that Let T _{1 be the Kyrie point of the first magnetic layer 1, H 1 be} its coercive force, T ₃ be the Kyrie point of the third magnetic layer 3, and H ₃ be its coercive force, then H ₁ > H ₃ T ₃ > T ₁ satisfy. (The coercive force is at room temperature.) However, usually the T ₁ of the first magnetic layer 1 is 70 to 200.
℃, H ₁ is 2 to 10 KOe, T ₃ of the third magnetic layer 3 is 100
~400℃, _H3 should be set within the range of about 0.1~4KOe. Curie point T ₂ of the second magnetic layer, coercive force
Details of H ₂ will be explained later. The first magnetic layer 1 and the third magnetic layer of the magneto-optical recording medium of the present invention
It is relatively weakly coupled to the magnetic layer 3 via the second magnetic layer. In the magneto-optical recording medium of the present invention, the apparent domain wall energy between the first magnetic layer 1 and the third magnetic layer 3 appearing through the second magnetic layer is σw ₁₃ , and the film thickness of the first magnetic layer 1 is h ₁ , the thickness of the third magnetic layer 3 is h ₃ , and the saturation magnetization of these layers is Ms ₁ and Ms ₃ in order of magnitude, then 2
The two magnetic layers 1 and 3 are coupled so as to satisfy the following equation. σw ₁₃ /2Ms ₁ h ₁ <H ₁ σw ₁₃ /2Ms ₃ h ₃ <H _3The reason why such a bond is necessary will be discussed in detail later, but to put it simply, it is This is to stabilize the magnetization of the bit (the state shown in FIG. 2f). Therefore, the film thickness, coercive force, magnitude of saturation magnetization, domain wall energy, etc. of the two magnetic layers 1 and 3 may be set so as to satisfy the above relational expression. The materials for each magnetic layer include GdCo, GdFe, which exhibits perpendicular magnetic anisotropy and magneto-optic effect.
TbFe，DyFe，GdTbFe，TbDyFe，GdFeCo，
Amorphous magnetic alloys of rare earth elements and transition metal elements such as TbFeCo, GdTbCo, and GdTbFeCo can be used. In FIG. 1b, which is another example of the magneto-optical recording medium of the present invention, 4 and 5 indicate protection for improving the durability of the three magnetic layers 1, 2, and 3 or for improving the magneto-optical effect. It is a membrane. 6 is an adhesive layer for bonding the bonding substrate 7 together. If layers 1 to 5 are also laminated on the bonding substrate 7 and bonded together, recording and reproduction can be performed on the front and back 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 third 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, if the magnitude of the magnetic field of the magnetic field generator 34 is set to a value between the coercive forces of the first magnetic layer 1 and the third magnetic layer 3 (the direction of the magnetic field is upward in this embodiment), as shown in FIG. As shown in , the third magnetic layer 3 is magnetized in a uniform direction,
On the other hand, the magnetization of the first magnetic layer 1 remains unchanged. Next, when the magneto-optical disk 35 rotates and passes the recording/reproducing head 31, a laser beam having two types (first type and second type) of laser power values is emitted by a signal from the recording signal generator 32. Accordingly, the disk surface is irradiated with either power. 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 third 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 1 and 3, the first type laser power is near T ₁ (at a temperature close to T ₁ , the magnetization of the first magnetic layer is The direction of the 3rd
The second type of laser power is around T ₃ (temperature close to T ₃ , which is the temperature at which the direction of magnetization of the third magnetic layer can be uniformly reversed). ) can increase the temperature of the disk. The temperature of the first magnetic layer 1 and the third magnetic layer 3 is raised to near the Curie point of the first magnetic layer 1 by the first type of laser power, but the bits stably exist in the third magnetic layer 3 at this temperature. By setting the bias magnetic field appropriately, the magnetization state shown in Fig. 2c can be changed from either of the magnetization states shown in Fig. 2b.
Recording bits such as the following are formed (first type of preliminary recording). Here, setting the bias magnetic field appropriately means:
The meaning is as follows. In the first type of preliminary recording, the direction is stable with respect to the direction of magnetization of the third magnetic layer 3 (in the same direction here).
Since the magnetization of the first magnetic layer 1 receives a force (exchange force) that aligns it, a bias magnetic field is not originally required. However, the bias magnetic field is set in a direction that assists magnetization reversal of the third magnetic layer 3 in preliminary recording using the second type of laser power, which will be described later. For convenience, it is preferable to set the bias magnetic field 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 according to the principle shown below, and this point was taken into consideration in the previous section. This means setting it appropriately. On the other hand, when the temperature of the disk is raised to near the Curie point of the third magnetic layer 3 using the second type of laser power (second type of preliminary recording), the direction of magnetization of the third magnetic layer 3 is changed by the above bias magnetic field. Invert. 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 third magnetic layer 3.
That is, pre-recorded bits as shown in FIG. 2d are formed from either of the magnetization states 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 recording bits c and d pass through the magnetic field generating section 34 again, the magnetic field generating section 34 is set between the first magnetic layer 1 and the third magnetic layer 3 as described above. Therefore, the recorded bit c remains in the state e without any change. On the other hand, the third magnetic layer 3 undergoes magnetization reversal in the recording bit d, resulting in a state of f. In order for the state of the recording bit f to exist stably, it is necessary that σw ₁₃ /2Ms ₁ h ₁ <H ₁ σw ₁₃ /2Ms ₃ h ₃ <H ₃ as described above. Here, σw ₁₃ /2Ms ₁ h ₁ indicates the strength of the exchange force acting on the first magnetic layer. In other words, an attempt is made to orient the magnetization direction of the _first magnetic layer in a stable direction (in this case, in the same _direction ) as the magnetization direction of the third magnetic layer using a magnetic field with a magnitude of _σw 13 /2Ms 1 h 1. do. Therefore, in order to prevent the magnetization of the first magnetic layer from reversing against this magnetic field, it is sufficient that the coercive force H ₁ of the first magnetic layer is greater than this exchange force. In other words, σw ₁₃ /2Ms ₁ h ₁ <H ₁ is sufficient. Similarly, an exchange force acting on the third magnetic layer that aligns the magnetization of the first magnetic layer in a stable direction with a magnitude of σw ₁₃ /2Ms ₃ h ₃ from the interfacial domain wall causes the recording bit of f to be aligned in a stable direction. In order for it to be stable, σw ₁₃ /
It is sufficient if 2Ms ₃ h ₃ <H ₃ . In order to satisfy this condition (the coercive force is larger than the exchange force acting on both the first and third magnetic layers), the exchange force acting on the first and third magnetic layers must be reduced. In order to achieve this, the film thickness and saturation magnetization of both layers may be adjusted as described above, but since the recording sensitivity or coercive force has an appropriate value, it cannot be set arbitrarily. Therefore, in the present invention, by providing the second magnetic layer with a very small thickness of, for example, 10 to 150 Å, the exchange interaction acting at the interface between the first magnetic layer 1 and the third magnetic layer 3 is suppressed, and the second magnetic layer is
This made it possible to reduce the apparent size of σw ₁₃ that appears through the magnetic layer. Regarding the coercive force of the second magnetic layer, it is desirable that the magnetization of the second magnetic layer is uniformly arranged in the same direction as shown in FIG. 2b during the first type of preliminary recording. Therefore, when the disk rotates and passes through the magnetic field generation section 34, it is desirable that the magnetization of the second magnetic layer be aligned in a direction that is stable with respect to the magnetic field, similar to the magnetization of the third magnetic layer. . Further, since it is desirable that the second magnetic layer is always aligned in a stable direction with respect to the direction of magnetization of either the first magnetic layer or the third magnetic layer, it is preferable that the coercive force H ₂ is small. Therefore, the relationship between coercive forces may be H ₁ > H ₃ > H ₂ . The material used for the second magnetic layer is the same rare earth element-transition metal alloy as the first and second magnetic layers, but it is necessary that the Curie temperature is lower than that of the first magnetic layer. This is due to the following reasons. The magnitude of the exchange force (the force that aligns the magnetic moments of each atom in a certain direction) acting on the interface between the first magnetic layer and the third magnetic layer depends on the type and number of atoms coordinated at each interface, and on each the exchange constant between atoms (indicating the magnitude of the interaction), and
It is determined by the Curie temperature of each layer. For example, the Kyrie temperature is involved.
This is because at temperatures above the Curie temperature, the alignment of magnetic moments disappears due to thermal motion, so exchange forces no longer work. Therefore, when the Curie temperature of the second magnetic layer provided between the first and third magnetic layers is low (close to room temperature), it is difficult for the magnetic moments to align due to thermal motion even at room temperature, so the first magnetic layer The exchange force acting between the third magnetic layers can be reduced. In fact, in a configuration in which a second magnetic layer whose Curie temperature is below room temperature is sandwiched between the first and third magnetic layers, the exchange force from both the first and third magnetic layers causes the second magnetic layer to become magnetic even at room temperature. We also confirmed through experiments that an array of moments occurs. In the recording method of the present invention, 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. Recording bits e and f
can be reproduced by irradiating a reproduction laser beam and processing the reproduction light by the recording signal regenerator 33. In the explanation of FIG. 2, the first magnetic layer 1 and the second magnetic layer 2 are
Although an example has been shown in which the magnetic layer is stable when the directions of magnetization of the magnetic layer and the third magnetic layer 3 are parallel, the same can be considered for a magnetic layer that is stable when the directions of magnetization are 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.
A TbFeCo alloy was sputtered to form a first magnetic layer of Tb ₁₇ Fe ₈₀ Co ₃ with a film thickness of 300 Å and a Kyrie point T ₁ =about 160°C. The H ₁ of this first magnetic layer itself is approximately 12KOe
, and the sublattice magnetization was larger in transition metals. The above operation was carried out several times, and DyFe alloy was sputtered from the fourth target onto each of the resulting targets under an argon pressure of 2×10 ^-3 Torr, and the Curie point T ₂ was approximately 60°C.
A second magnetic layer of Dy ₁₇ Fe ₈₃ with H ₂ 500 (Oe) was provided.
The film thickness was varied in steps of 10 Å from zero (no second magnetic layer was provided at this time) to 70 Å. The sublattice magnetization of the second magnetic layer itself was larger in the transition metal element. Next, each was sputtered from a third target in argon at a sputtering speed of 50 Å/min and a sputtering pressure of 2.
Sputter TbFeCoCu alloy at ×10 ^-3 Torr,
A third magnetic layer of Tb ₂₃ Fe ₅₁ Co ₁₁ Cu ₁₅ was formed with a film thickness of 250 Å and T ₃ =approximately 190°C. This third magnetic layer itself
H ₃ was 1.1KOe, and the sublattice magnetization was larger for rare earth elements. Next, Si ₃ N ₄ was sputtered from the first target under the same conditions as before to form a protective layer of 1200 Å.
₄ layers of Si ₃ N with a thickness of . 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 magneto-optical disk samples. The stability of bits (particularly in the f state) 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 third magnetic layer starts to be reversed by a smaller external magnetic field, we were able to measure the exchange force acting on the third magnetic layer σw ₁₃ /2Ms ₂ h ₂
It is. Next, the sample of the magneto-optical disk was set in the recording/reproducing device, and the 2KOe magnetic field generator was set at a linear velocity of approximately
830mm light focused to approximately 1μ while passing at 9m/sec
laser beam with a wavelength of 50% duty.
Recording was performed with binary laser powers of 4 mW and 8 mW while modulating at 2 MHz. The bias magnetic field at the recording head was 120 Oe. After that, a 1mW laser beam was irradiated to reproduce the signal, and a binary signal could be reproduced.
This experiment was carried out on samples after the entire surface had been recorded to check whether previously recorded signal components were detected, that is, 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 bits that were insufficiently recorded were the bits for which the first type of bits were performed, and can be correlated with the measured value of the exchange force acting on the third magnetic layer in Table 1. That is, sample 1
-1 and 1-2 are values in which the magnitude of the exchange force is not smaller than the coercive force _H3 of the third magnetic layer, and this is because the recording bit of f does not exist stably. This is thought to be because, in sample 1-8, the exchange force acting on both the second magnetic layer and the first magnetic layer was too small to allow complete type 1 recording, making it impossible to reverse the magnetization of the first magnetic layer. . 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 second magnetic layer 2 were changed. The material used for the second magnetic layer has a Kyrie temperature of 80
Dy ₁₂ Tb ₆ Fe ₈₂ whose Kyrie temperature is 30 °C, DyFeCr whose Kyrie temperature is 5 °C Dy ₁₇ Fe ₇₈
Cr ₅ was used, and the film thickness was varied. The same evaluation as in Example 1 was performed for each of the prepared samples. The results are shown in Table 2.

【table】

[Table] From the results in Tables 1 and 2, it is clear that by providing a second magnetic layer with a temperature lower than the Curie temperature of the first magnetic layer with an appropriate thickness between the first and third magnetic layers, the third magnetic layer It is clear that the exchange forces acting on the layers can be reduced. For example, if the second magnetic layer is used with a Curie temperature of room temperature or below room temperature, the thickness of the second magnetic layer will increase.
Recording bits become stable at a thickness of about 50 to 150 Å, so the recording layer thickness (the sum of the first, second, and third magnetic layer thicknesses) can be set to a small value, which improves recording sensitivity. It never declines. Comparative Example 1 A fourth target was used, and the same configuration and materials as Examples 1 and 2 were used, except that the following materials were provided at the positions of the second magnetic layer with varying thicknesses. A sample of a magnetic disk was produced. The material used is Si, which is a nonmagnetic layer, and has a Curie temperature of 170°C, which is higher than T ₁ of the first magnetic layer, and a coercive force of 500 (Oe), which is lower than that of the third magnetic layer.
Two types of Tb ₁₅ Fe ₈₂ Co ₃ were used with varying film thicknesses. For each of the prepared samples, Example 1
A similar evaluation was conducted. The results are shown in Table 3.

〔Effect of the invention〕

As explained in detail above, as a magneto-optical medium,
a first magnetic layer having a Kyrie point T ₁ and a coercive force H ₁ ;
a second magnetic layer having a Kyrie point T ₂ and a coercive force H ₂ ;
It has three magnetic layers consisting of a third magnetic layer having a Kyrie point T ₃ and a coercive force H ₃ . In addition, by using a medium that satisfies other predetermined requirements, providing a magnetic field generating means at a location separate from the recording head during recording, and recording with binary laser power, good overwriting has become possible. .

[Brief explanation of the drawing]

FIGS. 1a and 1b are diagrams each showing the structure of an 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 3 during implementation of the recording method of the present invention. Figure 3 is a conceptual diagram of the recording/reproducing device;
The figure is a schematic diagram showing the relationship between coercive force and temperature of the first magnetic layer 1 and the third magnetic layer 3. B...Transparent substrate with pregroove, 1, 2,
3... Magnetic layer, 4, 5... Protective layer, 6... Adhesive layer, 7... Bonding substrate, 31... Recording/reproducing head, 32... Recording signal generator, 35...
Magneto-optical disk.

Claims (1)

[Claims] 1. A first magnetic layer having a Kyrie point T ₁ and a coercive force H ₁ , a second magnetic layer having a Kyrie point T ₂ and a coercive force H ₂ , and a Kyrie point T ₃ and a coercive force H _3. the third with
1. A magneto-optical recording medium comprising a perpendicularly magnetized film having a three-layer structure including a magnetic layer on at least a substrate, the magneto-optical recording medium satisfying the following conditions. (A) Each magnetic layer is an alloy of a rare earth element and a transition metal, (B) H ₁ > H ₃ > H ₂ T ₃ > T ₁ > T ₂ , (C) the magnetic layer appears through the second magnetic layer. 1 magnetic layer and 3rd magnetic layer
If the apparent domain wall energy of the magnetic layer is σw ₁₃ and the film thicknesses of the first and third magnetic layers are h ₁ and h ₃ in this order, then σw ₁₃ /2Ms ₁ h ₁ <H ₁ and σw ₁₃ /2Ms ₃ h ₃ <H ₃ 2 The magneto-optical recording medium according to claim 1, wherein the Curie temperature of the second magnetic layer is below room temperature and the thickness of the second magnetic layer is 10 to 150 Å. 3. A first magnetic layer having a Kyrie point T ₁ and a coercive force H ₁ , a second magnetic layer having a Kyrie point T ₂ and a coercive force H ₂ , and a third magnetic layer having a Kyrie point T ₃ and a coercive force H ₃ .
A magneto-optical recording medium having a perpendicularly magnetized film with a three-layer structure consisting of a magnetic layer on at least a substrate, which satisfies the following conditions (A) to (B): (A) Each magnetic layer is made of a rare earth metal. (B) H ₁ > H ₃ > H ₂ T ₃ > T ₁ > T ₂ , (C) The first magnetic layer appearing through the second magnetic layer and the third
If the apparent domain wall energy of the magnetic layer is σw ₁₃ and the film thicknesses of the first and third magnetic layers are h ₁ and h ₃ in this order, then σw ₁₃ /2Ms ₁ h ₁ <H ₁ and σw ₁₃ /2Ms ₃ h A recording method characterized by recording the following binary values using a magneto-optical recording medium that satisfies ₃ < H ₃ . (a) At a location different from the recording head on the medium, change the direction of magnetization of the first magnetic layer with coercive force H ₁ in a direction sufficient to magnetize the third magnetic layer with coercive force H ₃ in one direction. Magnetic field B of a magnitude that does not cause reversal
(b) Next, by applying a bias magnetic field using the recording head and at the same time irradiating the medium with enough laser power to raise the temperature of the first magnetic layer to near the Curie point _T1 , the third magnetic layer is heated. The first type of preliminary recording involves aligning the magnetization directions of the first and second magnetic layers in a stable direction with respect to the third magnetic layer without changing the magnetization direction of the third magnetic layer, or the first type of preliminary recording involves applying a bias magnetic field and simultaneously recording the third By irradiating the medium with enough laser power to heat up the medium to near the Curie point T ₃ of the magnetic layer, the direction of magnetization of the third magnetic layer is reversed, and at the same time both the first and second magnetic layers are heated to the third magnetic layer. A second type of preliminary recording, in which the magnetic layer is magnetized in a stable direction, is carried out in response to the signal; (c) Next, the medium is moved and the preliminary recorded bits are exposed to the magnetic field B. By passing
Regarding the bits formed by the first type of preliminary recording, the magnetization directions of the first magnetic layer, the second magnetic layer, and the third magnetic layer are not changed as they are, and the bits formed by the second type of preliminary recording are For binary recording, the direction of magnetization of the second and third magnetic layers is reversed in the same direction as the magnetic field B, and the direction of magnetization of the first magnetic layer is left unchanged.