JPS63195845A - Magneto-optical recording medium and magneto-optical recording method - Google Patents

Abstract

PURPOSE:To provide a magneto-optical recording medium which has perpendicularly magnetized films of three-layered structure and is utilized for a recording method permitting overwriting by forming the above-mentioned recording medium in such a manner as to satisfy the prescribed conditions. CONSTITUTION:A magnetic layer 1 has a high Curie point TH1 and low coercive force HL1, a magnetic layer 2 has a low Curie point TL2 and high coercive force HH2, and a magnetic layer 3 has a high Curie point TH3 and low coercive force HL3. The conditions expressed by the equation I are satisfied. In the equation, sigmaw12, sigmaw13 are respectively the magnetic wall energies of the magnetic layers 1, 2, and 2, 3, h1-h3 are respectively the film thicknesses of the magnetic layers 1-3, MS1-MS3 are respectively the magnitudes of the saturation magnetization of the magnetic layers 1-3. All the magnetic layers 1-3 are required to consist of an amorphous alloy of a rare earth element and transition metal element. The magnetic layers 1, 2 are required to consist of the compsn. contg. the transition metal element at the ratio higher than in the compensation compsn. or the magnetic layers 1, 2 are required to consist of the compsn. contg. the rare earth element at the ratio higher than in the compensation compsn. and the magnetic layer 3 is required to consist of the compsn. cotg. the transition metal element at the ratio higher than in the compensation compsn. The purpose is attained by satisfying the above-mentioned conditions.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a Curie point writing type magneto-optical recording medium that can be read using the magnetic Kerr effect, and an overwritable optical recording medium using the same. Related to magnetic recording methods.

[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. It had the disadvantage that it cannot be magnetized in one direction (it must be magnetized in one direction). 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 disadvantages such as a large-scale apparatus, high cost, or inability to perform high-speed modulation.

The present invention provides a magneto-optical recording method that eliminates the drawbacks of the known techniques mentioned above and enables overwriting similar to that of magnetic recording media by simply adding a magnetic field generating means with a simple structure to a conventional device configuration. The applicant proposed this in Japanese Patent Application No. 91202 on September 17, 1986.

However, since this method is a completely new recording method,
Many research questions remain regarding this method. In other words, we are searching for a recording medium that is more suitable for this type of 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 suitable for this overwritable recording method.

[Means for solving problems]

The present invention, which can achieve the above objects, comprises a first magnetic layer having a high Curie point (THI) and a low coercive force (HLI), and a relatively low Curie point (TL2) and high coercive force compared to the first magnetic layer. A three-layer structure consisting of a second magnetic layer having a magnetic force (HN3) and a third magnetic layer having a relatively higher Curie point (TI43) and a lower coercive force (HL3) than the second magnetic layer. A magneto-optical recording medium comprising a perpendicularly magnetized film on at least a substrate, wherein the three magnetic layers meet the following conditions (a) to (c): (a) a first magnetic layer and a second magnetic layer; The domain wall energy is (f
fW+2, the domain wall energy of the second magnetic layer and the third magnetic layer is σw23, and the film thicknesses of the first magnetic layer, second magnetic layer, and third magnetic layer are h+, h2. h3. and the magnitude of the saturation magnetization of these layers is Ms+, MS21M!, in order. ! 3, -< HL3 2Ms, h3 (b) Each magnetic layer is made of an amorphous alloy of a rare earth element and a transition metal element (c) The 1.2nd magnetic layer has a transition metal element rather than a compensation composition. The third magnetic layer has a composition richer in rare earth elements than the compensation composition, or the first and second magnetic layers have a composition richer in rare earth elements than the compensation composition and the third magnetic layer has a composition richer in rare earth elements than the compensation composition. This is a recording method characterized by recording the following binary values using a magneto-optical recording medium whose layer satisfies the requirement that the composition is richer in transition metal elements than the compensation composition. .

(a) With respect to the medium, at a location different from the recording head,
Applying a magnetic field B having a magnitude sufficient to magnetize the third magnetic layer having a coercive force HL3 in one direction and not reversing the direction of magnetization of the second magnetic layer having a coercive force HH2, (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 medium to near the low Curie point (TL2),
The first type of preliminary recording, in which the direction of magnetization of the first and second magnetic layers is aligned in a stable direction with respect to the third magnetic layer without changing the direction of magnetization of the third magnetic layer, or the bias magnetic field is applied. By irradiating the medium with enough laser power to raise the temperature of the medium to near the high Curie point (T□3), the direction of magnetization of the third magnetic layer is reversed and the first and second magnetic layers are simultaneously applied. A second type of preliminary recording is performed in response to a signal, in which both the magnetic layer and the third magnetic layer are magnetized in a stable direction, and (C) the medium is then moved to perform preliminary recording. By passing the magnetic field B through the bit formed by the first type of preliminary recording, the first magnetic layer,
For bits formed by the second type of preliminary recording without changing the direction of magnetization in both the second and third magnetic layers,
Binary recording, in which the direction of magnetization of the third magnetic layer is reversed in the same direction as the magnetic field B, and the directions of magnetization of the first and second magnetic layers remain unchanged.

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

FIGS. 1(a) and 1(b) are schematic cross-sectional views each showing an example of a magneto-optical recording medium used in the present invention. Figure 1 (a
) is a magneto-optical recording medium in which a first magnetic layer 1, a second magnetic layer 2, and a third magnetic layer 3 are laminated on a transparent substrate B provided with a pre-group. be. First magnetic layer 1
has a high Curie point (T1) and a low coercive force (HLI), the second magnetic layer 2 has a low Curie point (TL2) and a high coercive force (HN3), and the third magnetic layer 3 has a high Curie point (TL2) and a high coercive force (HLI). point (TH3) and low coercive force (HL3). Here, "high" and "low" refer to the relative relationship when comparing the first and third magnetic layers and the second magnetic layer (coercive force is compared at room temperature).

However, normally the T of the first magnetic layer 1. 1 is 150-400
°C, HLI is 0.1~IKOe, T of second magnetic layer 2
L2 is 70-200℃, HN3 is 2-10KOe, 3rd
TBG of magnetic layer 3 is 100 to 250°C, HL3 is 0.5
It is preferable to set it within a range of about 4 KOe.

The materials of each magnetic layer include GdCo, GdFe, TbFe, which exhibit perpendicular magnetic anisotropy and magneto-optic effect.
DyFe, GdTbFe, TbDyFe, GdF
Amorphous magnetic alloys of rare earth elements and transition metal elements such as eCa, TbFeCo, and GdTbCo can be used.

Adjacent magnetic layers of the magneto-optical recording medium of the present invention are coupled by exchange force, the first magnetic layer 1 and the second magnetic layer 2 are strongly coupled relative to each other, and the second magnetic layer 2 and the second magnetic layer 2 are coupled strongly relative to each other. The three magnetic layers 3 are mutually weakly coupled.

In the magneto-optical recording medium of the present invention, the domain wall energy of the first magnetic layer 1 and the second magnetic layer 2 is σw+2, and the domain wall energy of the second magnetic layer 2 and the third magnetic layer 2 is σw+2.
The domain wall energy of the magnetic layer 3 is σw23, and the first magnetic layer 1. Second magnetic layer2. The film thickness of the third magnetic layer 3 is h+, h
2. h3, and the magnitude of the saturation magnetization of these layers is M in order.
When SI +MS2 +'S3, the above three magnetic layers are coupled so as to satisfy the following formula.

This is to ensure that the magnetization state of the bit finally formed by recording (the state shown in FIG. 2(f)) can exist stably (the detailed reason will be described later).

The thickness, coercive force, magnitude of saturation magnetization, domain wall energy, etc. of each layer should be set so as to satisfy the above relational expression. This leads to strong exchange coupling between the two magnetic layers and weak exchange coupling between the second magnetic layer and the third magnetic layer.

As a result of research taking this point into consideration, as shown in the examples,
In order to achieve strong coupling between magnetic layers, it is effective to make both of them rich in rare earth elements or to make both compositions rich in transition metals.Also, in order to make weak coupling between magnetic layers, it is effective to make one of the compositions rich in rare earth elements or to make both compositions rich in transition metals. It has become clear that it is effective to make the compensation composition rich in rare earth elements and the other composition rich in transition metals.

In FIG. 1(b), which is another example of the magneto-optical recording medium of the present invention, a protective film is provided to improve the durability of the three magnetic layers 1, 2.3 or to improve the magneto-optical effect. 4.5 is provided.

Note that 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 with reference to FIGS. 2 to 4. Before recording, the direction of magnetization of the magnetic layer 1.2 is parallel and stable, and the magnetic layer 1.2 and the magnetic layer 1.2 are in a stable state. It is antiparallel to the magnetization direction of No. 3 and is in a stable state.

35 in FIG. 3 is a magneto-optical disk having the configuration described above. For example, assume 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, the magnetic field generating section 3
When the magnitude of the magnetic field 4 is set to a value between the coercive forces of the second magnetic layer 2 and the third magnetic layer 3 (the direction of the magnetic field is upward in this example), as shown in FIG. 2(b), The third magnetic layer 3 is magnetized in a uniform direction, while the magnetization of the second magnetic layer 2 remains the same. Furthermore, the magnetization of the first magnetic layer 1, which is strongly coupled to the second magnetic layer, remains as it was.

Next, the magneto-optical disk 35 rotates and the recording/reproducing head 3
1, a laser beam having two types of laser power values (first type and second type) is irradiated onto the disk surface with one of the powers according to the signal from the recording signal generator 32. do. The first type of laser power is enough to raise the temperature of the disk to around the Curie point of the second 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 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 2.3, the first type laser power is around TL2, and the second type laser power is around TH.
The temperature of the disk can be raised to around 3.

The temperature of the second magnetic layer 2 and the third magnetic layer 3 is raised to near the Curie point of the second magnetic layer 2 by the first type of laser power, but bits stably exist in the third magnetic layer 3 at this temperature. By setting the bias magnetic field appropriately, a bit as shown in Fig. 2(C) can be formed from either magnetization state shown in Fig. 2(b). (1st
Preliminary records of species). Note that the first magnetic layer 1 and the second magnetic layer 2
Due to exchange coupling with the magnet, the magnetized state shown in the figure is created.

Here, setting the bias magnetic field appropriately means the following.

In the first type of preliminary recording, the magnetization of the second magnetic layer 2 is subjected to a force (exchange force) that aligns it in a stable direction (here, in the opposite direction) to the direction of the magnetization of the third magnetic layer 3. does not require a bias magnetic field. However, the bias magnetic field is set in a direction that assists the magnetization reversal of the third magnetic layer 3 (a direction that hinders the first type of preliminary recording) in the second type of preliminary recording with laser power, which will be described later. And this bias magnetic field is
It is preferable to set the magnitude and direction to be the same in both the first type and the second type of laser power preliminary recording.

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 settings that take this into consideration are the appropriate settings as mentioned above. The installation is fixed.

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, the direction of magnetization of the third magnetic layer 3 is reversed by the bias magnetic field set as described above. Next, the second magnetic layer 2 and the first magnetic layer 1
The magnetization is also arranged in a stable direction (here, in the opposite direction) with respect to the third magnetic layer 3. That is, bits as shown in FIG. 2(d) are formed from either of the magnetization states shown in FIG. 2(b) (second type of preliminary recording).

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 magnetic field of the magnetic field generating section 349 is transferred to the second magnetic layer 2 as described above.
and the coercive force of the third magnetic layer 3, the recording bit (C) remains in the state (e) without any change (final recording state). On the other hand, in the recording bit (d), the third magnetic layer 3 undergoes magnetization reversal and becomes the state (f) (
Another final recording state).

In order for the state of the recording bit (f) to exist stably, it is necessary that the state described above be met. This is due to the following reasons.

σ111 + '2 / 2 M S 1 h + indicates the strength of the exchange force acting on the first magnetic layer □. That is, σ−, 2
A magnetic field with a magnitude of /2Ms,h changes the direction of magnetization of the first magnetic layer in a direction that is stable with respect to the direction of magnetization of the second magnetic layer (
In this case, try to point them in the same direction). Therefore, in order for the □ magnetization of the first magnetic layer to always be oriented in a stable direction (in this case, in the same direction) as the direction of the second magnetic layer, it is necessary to
It is sufficient that the coercive force HLI of the magnetic layer is smaller than this exchange force. In other words, it is sufficient if σw12/2M5ih+>HLl.

Further, σw23/2M53h3 indicates the strength of the exchange force acting on the third magnetic layer. In other words, σw23 / 2M53F1
A magnetic field of magnitude 3 attempts to direct the magnetization direction of the third magnetic layer in a direction that is stable with respect to the magnetization direction of the second magnetic layer (in this case, in the same direction). Therefore, in order for the magnetization of the third magnetic layer not to be reversed in response to this magnetic field (for the recorded bits in Fig. 2(f) to exist stably), the coercive force of the third magnetic layer should be set to HL3, a W23 / 2M53h3kuHL3
In the recording method of the present invention, the recording bit states (e) and (f
) is controlled by the laser power during recording and does not depend on the state before recording, so overwriting is possible.
is possible. Recording bits (e) and (f) are irradiated with a laser beam for reproduction, and the reproduction light is transmitted to a recording signal regenerator 33.
It can be played back by processing it. The magnitude and degree of modulation of the reproduced signal mainly depend on the magneto-optical effect of the first magnetic layer.

In addition to this, in the medium having three magnetic layers used in the recording method of the present invention, the first f/j where the reproduction light is irradiated
Since a material with a high Curie temperature (that is, a material with a large magneto-optical effect) can be used for the i-type layer 1, the present invention enables recording with a large reproduced signal (with a large degree of modulation).

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

Sputtering speed 1 from the first target in argon
A protective layer of ZnS was formed at a thickness of 800 mm/min and a sputtering pressure of sx to -3 Torr.

Next, in argon, sputtering was performed from the second target at a sputtering rate of 100 people/min and a sputtering pressure of 5 x 10 = Tor.
GdFeCo alloy was sputtered at r, film thickness was 400mm, T
A first magnetic layer of Gd2oFe66Go24 was formed at a temperature of about 350°C. The HLI of this first magnetic layer itself is approximately 50.
00e or less, and the sublattice magnetization was larger in the transition metal.

Next, under the same conditions, TbFe alloy was sputtered from the third target to a film thickness of 200A and T L2 = approximately 140.
A second magnetic layer of Tb, 8Fe82 of C was formed. The HH2 of this second magnetic layer itself was approximately 100,000e or more, and the sublattice magnetization was larger in the transition metal.

Next, under the same conditions, GdTbFeG was prepared from the fourth target.
Sputter o alloy, film thickness 300, T, 3 = approx. 210
Gd13Tb13Fe69. A third magnetic layer of C, GO4,5 was formed. The HL3 of the third magnetic layer itself was about 500 to 15,000e, and the sublattice magnetization was larger in the rare earth metal.

Next, under the same conditions, ZnS was sputtered from the first target to form a ZnS layer with a thickness of 2000 nm as a protective layer.

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 2KOe magnetic field generator was
While passing at a linear velocity of about 7 m/sec, a laser beam with a wavelength of 830 mm focused to about 1 μ was modulated at 2 MHz with a duty of 50%, and recording was performed with binary laser powers of 4 mW and 8 mW. . The bias magnetic field was 1500e. Thereafter, a 1[11 W laser beam was irradiated to perform reproduction, and a binary signal could be reproduced.

Next, an experiment similar to the one 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 overriding is possible.

Example 2 and Comparative Example The magneto-optical disk of Example 1, the protective layer, the magnetic layer, and the coercive force were not changed, but 3.
Regarding the combination of two magnetic layers, by changing the ratio of transition metal elements and rare earth elements in each magnetic layer,
Samples of magneto-optical disks were fabricated as shown in Table 1 instead.

While applying an external magnetic field to each sample, examine the applied magnetic field when the magnetization of each magnetic layer is reversed.Record bit (e)
, '(f) was investigated.

Next, a recording experiment was conducted in the same manner as in Example 1, and 4 mW
The state of binary recording of 8 mW and 8 mW was evaluated. The results are shown in Table 1.

Regarding the stability of the recorded bits, if states (e) and (f) can exist stably in the absence of an external magnetic field, Table 1
If not, it is indicated by ○, otherwise, it is indicated by ×.

For evaluation of the recording condition, when recording with binary values of 4 mW and 8 mW, if the playback signal cannot be confirmed, mark it with an X, if it can be confirmed but it is not good, mark it with a △ mark, and if the playback signal is good with a C/N of about 40 dB or more. Those obtained are indicated with a circle.

As is clear from the results in Table 1, in order to obtain stable recording bits and perform good recording, the compositions of both the first and second magnetic layers must be richer in transition metals than the compensation composition (sublattice magnetization is transition metal is larger), or both are rich in rare earth elements (submultiple lattice magnetization is larger in rare earth elements)
It can be seen that the composition of the third magnetic layer is limited to those in which the element having a large sublattice magnetization is opposite to that of the first magnetic layer (Example 1.2).

〔Effect of the invention〕

As explained in detail above, a magneto-optical recording medium having a perpendicular magnetization film with a three-layer structure that satisfies predetermined requirements is used, and during recording, a magnetic field generating section is provided at a separate position from the recording head, and recording is performed using a binary laser power. By doing so, it became possible to perform good overwriting.

Furthermore, the magnetic layer of the recording medium used in the recording method of the present invention, which is mainly used for reproduction, can be selected from materials with a large magneto-optical effect, so that as a result, the bits recorded by the present invention have a large reproduction signal. There are advantages. .

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are diagrams each showing the structure of an example of a magneto-optical medium used in the present invention, and FIG. FIG. 3 is a conceptual diagram of the recording/reproducing device, and FIG. 4 is a schematic diagram showing the relationship between the coercive force and temperature of the second magnetic layer 2 and the third magnetic layer 3. . Transparent substrate with B nibli groove, 1.2, 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) High Curie point (T_H_1) and low coercive force (H_
a first magnetic layer having a relatively low Curie point (T_L_2) and a high coercive force (H_H_2) compared to the first magnetic layer; A magneto-optical recording medium comprising, at least on a substrate, a perpendicularly magnetized film having a three-layer structure consisting of a third magnetic layer having a relatively high Curie point (T_H_3) and a low coercive force (H_L_3), The three magnetic layers meet the following conditions (
A magneto-optical recording medium characterized by satisfying (a) to (c). (a) The domain wall energy of the first magnetic layer and the second magnetic layer is σw
_1_2, the domain wall energy of the second magnetic layer and the third magnetic layer is σw_2_3, the film thicknesses of the first magnetic layer, the second magnetic layer, and the third magnetic layer are h_1, h_2, h_3 in order, and the saturation of these layers is The magnitude of magnetization is sequentially Ms_1, M_s_2,
If M_s_3, σw_1_2/(2M_s_1h_1)>H_L_1σ
w_2_3/(2M_s_3h_3)<H_L_3 (b) Each magnetic layer is made of an amorphous alloy of a rare earth element and a transition metal element (c) The first and second magnetic layers have a composition richer in transition metal elements than the compensation composition and the third magnetic layer has a composition richer in rare earth elements than the compensation composition, or the first and second magnetic layers have a composition richer in rare earth elements than the compensation composition, and the third magnetic layer has a composition richer in rare earth elements than the compensation composition. 2) High Curie point (T_H_1) and low coercive force (H_
a first magnetic layer having a relatively low Curie point (T_L_2) and a high coercive force (H_H_2) compared to the first magnetic layer; A magneto-optical recording medium comprising, at least on a substrate, a perpendicularly magnetized film having a three-layer structure consisting of a third magnetic layer having a relatively high Curie point (T_H_3) and a low coercive force (H_L_3), The three magnetic layers meet the following conditions (
A) ~ (C), that is, (A) The domain wall energy of the first magnetic layer and the second magnetic layer is σw
_1_2, the domain wall energy of the second magnetic layer and the third magnetic layer is σw_2_3, the film thicknesses of the first magnetic layer, the second magnetic layer, and the third magnetic layer are h_1, h_2, h_3 in order, and the saturation of these layers is The magnitude of magnetization is M_s_1, M_s_2
, M_s_3, σw_1_2/(2M_s_1h_1)>H_L_1σ
w_2_3/(2M_s_3h_3)<H_L_3 (b) Each magnetic layer is made of an amorphous alloy of a rare earth element and a transition metal element (c) The first and second magnetic layers have a composition richer in transition metal elements than the compensation composition and the third magnetic layer has a composition richer in rare earth elements than the compensation composition, or the first and second magnetic layers have a composition richer in rare earth elements than the compensation composition, and the third magnetic layer has a composition richer in rare earth elements than the compensation composition. A recording method characterized by recording the following binary values using a magneto-optical recording medium that satisfies the following conditions: the composition is richer in transition metal elements than the composition. (a) With respect to the medium, at a location different from the recording head,
Applying a magnetic field B of a magnitude sufficient to magnetize the third magnetic layer with coercive force H_L_3 in one direction but not reversing the direction of magnetization of the second magnetic layer with coercive force H_H_2, (b) Next, The recording head applies a bias magnetic field and at the same time irradiates the medium with laser power sufficient to raise the temperature of the medium to near the low Curie point (T_L_2), thereby increasing the temperature of the first magnetic layer without changing the direction of magnetization of the third magnetic layer. and the first type of preliminary recording in which the direction of magnetization of the second magnetic layer is aligned in a stable direction with respect to the third magnetic layer, or the medium is heated to near the high Curie point (T_H_3) at the same time as a bias magnetic field is applied. By irradiating with a laser power of (c) Next, by moving the medium and passing the prerecorded bits through the magnetic field B, the first type of preliminary recording is performed. For the bits formed, the direction of magnetization of the first, second, and third magnetic layers remains unchanged, and for the bits formed by the second type of preliminary recording,
Binary recording in which the direction of magnetization of the third magnetic layer is reversed in the same direction as the magnetic field B, and the directions of magnetization of the first and second magnetic layers are left unchanged.