JP2589451B2 - Magneto-optical recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overwritable magneto-optical recording / reproducing apparatus using a Curie point writing type magneto-optical recording medium which can be read out by utilizing the magnetic Kerr effect.

[0002]

2. Description of the Related Art A magneto-optical disk is known as an erasable optical disk memory. Magneto-optical disks have higher density recording than magnetic recording media using conventional magnetic heads.
While there is an advantage that recording and reproduction can be performed in a non-contact manner, there is a disadvantage in that the recorded portion must be erased once (it must be magnetized in one direction) before recording. In order to compensate for this drawback, a method of separately providing a recording / reproducing head and an erasing head, or a method of recording while irradiating a continuous laser beam and modulating a magnetic field to be applied simultaneously are proposed.

[0003]

However, these methods have disadvantages such as an increase in the size of the apparatus, an increase in cost, and the inability to perform high-speed modulation.

[0004] It is possible to eliminate the above-mentioned disadvantages of the known art, and to simply add a magnetic field generating means having a simple structure to the conventional apparatus configuration.
The present applicant has filed a Japanese Patent Application No. 61-158787 on Jul. 8, 1986, which discloses a magneto-optical recording method that enables overwriting (overwriting) in the same manner as a magnetic recording medium.
The application will be a priority application in Japan on February 2, 2008).

However, since this method is a completely new recording method, many research problems still remain. That is, it is a measure for preventing deterioration of the quality of the reproduced signal in the long-term reproduction.

Therefore, the present inventor further studied and found that
Several results have been obtained.

The present invention has been completed in this way,
It is an object of the present invention to provide a magneto-optical recording / reproducing apparatus which is capable of not only overwriting, but also reproducing a recorded signal well over a long period of time.

[0008]

Magneto-optical recording and reproducing apparatus of the present invention According to an aspect of the first magnetic layer of an alloy of a transition element a rare earth element having a lower and Curie point T _L higher and the coercive force H _H and the first Curie point T _H higher than that of one magnetic layer
And a perpendicular magnetic film having a two-layer exchange-coupled perpendicular magnetic film composed of a second magnetic layer made of an alloy of a rare earth element and a transition element having a low coercive force _HL on the substrate. When the saturation magnetization of the second magnetic layer is M _s , the thickness is h, and the domain wall energy between the first and second magnetic layers is σ _w ,

[0009]

(Equation 2) Magneto-optical recording medium meets the sufficiently coercive force H _H in to magnetize the second magnetic layer of a coercive force H _L in one direction
Initialization magnetic field means for applying a magnetic field B having a magnitude that does not reverse the direction of magnetization of the first magnetic layer, and bias magnetic field applying means for applying a bias magnetic field different from the magnetic field B to the magneto-optical recording medium If the bias magnetic field the magneto-optical recording medium in a state of being applied to the vicinity of the high Curie point T _H and laser power of only the lower Curie point the magneto-optical recording medium to the vicinity of T _L is heating is heating Recording / reproducing means for selectively irradiating only the laser power according to the information and recording the information on the magneto-optical recording medium and reproducing the recorded information by using a magneto-optical effect; A rotating means for rotating a medium, wherein the coercive force H _H of the first magnetic layer and the magnetic field B are set such that the internal temperature of the device is 30 ° C.
At a temperature of not less than 60 ° C. and H _H ≧ 1.5 kOe and 0.2
× H _H −0.3> B (kOe).

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

FIGS. 1A and 1B are schematic sectional views showing one embodiment of a magneto-optical recording medium used in the present invention. The magneto-optical recording medium of FIG. 1A includes a first magnetic layer 2 made of an alloy of a rare earth element and a transition element, and a first magnetic layer 2 made of an alloy of a rare earth element and a transition element on a light transmitting substrate 1 provided with a pregroove. The second magnetic layer 3 made of an alloy is laminated.
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 higher Curie point T _H and a low coercive force H _L. Here, “high” and “low” indicate a relative relationship when the two magnetic layers are compared (coercive force is compared at room temperature). Usually, however, the T _L of the first magnetic layer 2 70 to 180 ° C., H _H is, 3~10kOe, T _H of the second magnetic layer 3 is 100 to 400 ° C., H _L is the order of 0.5~2KOe It should be within the range.

As each magnetic layer made of an alloy of a rare earth element and a transition element, a layer exhibiting perpendicular magnetic anisotropy and exhibiting a magneto-optical effect can be used, but an amorphous magnetic alloy is preferable.
For example, TbFe, GdTbFe, TbDyFe, TbD
yFeCo, TbFeCo, GdTbCo and the like.

In the magneto-optical recording medium used in the present invention, the first magnetic layer 2 is mainly involved in reproduction. That is, the first
The magneto-optical effect exhibited by the magnetic layer 2 is mainly used for reproduction,
The second magnetic layer 3 plays an important role in recording. On the other hand, in the exchange coupling two-layer film in the conventional magneto-optical recording medium, on the contrary, a magnetic layer having a low Curie point and a high coercive force is mainly involved in recording, and a magnetic layer having a high Curie point and a low coercive force. The layers were mainly involved in regeneration. In such a conventional exchange-coupled two-layer film, the saturation magnetization M _{s of} the magnetic layer mainly involved in reproduction is
, The film thickness h, and the domain wall energy σ _w between the two layers,
It was desirable to have the following relationship.

[0014]

(Equation 3) However, in the exchange-coupled two-layer film of the recording medium used in the present invention, the following relationship is required between the saturation magnetization M _s and the film thickness h of the second magnetic layer 3 and the domain wall energy σ _w between the two magnetic layers. It is.

[0015]

(Equation 4) This is to stabilize the magnetization state (shown in FIG. 2 (f)) of the bit finally completed by recording (the detailed reason will be described later).

Therefore, the film thickness, coercive force, saturation magnetization, domain wall energy, etc. of each layer may be appropriately set so that the two magnetic layers 2 and 3 (perpendicular magnetization films) satisfy the above relational expression. . The magnetic layers 2 and 3 are preferably exchange-coupled in consideration of the magnitude of the effective bias magnetic field due to the exchange force during recording or the stability of binary recording bits.

In FIG. 1B, reference numerals 4 and 5 denote protective films for improving the durability of the two magnetic layers or for improving the magneto-optical effect. Reference numeral 6 denotes an adhesive layer for bonding the bonding substrate 7. Also for the bonding substrate 7,
By laminating 2 to 5 layers and bonding them, recording and reproduction can be performed on both sides.

Hereinafter, the recording process will be described with reference to FIGS. 2 and 3. Before recording, the stable magnetization directions of the magnetic layers 2 and 3 may be parallel (same direction) or antiparallel (opposite direction). good. FIG. 2 illustrates a case where the stable directions of magnetization are parallel. FIG. 3 is a diagram showing a conceptual configuration of a magneto-optical recording / reproducing apparatus according to the present invention.

Reference numeral 35 in FIG. 3 denotes a magneto-optical disk having the above-described configuration. For example, it is assumed that a part of the magnetization state of the magnetic layer is initially as shown in FIG. The magneto-optical disk 35 is a spindle motor (not shown)
And passes through the initialization magnetic field generation unit 34. At this time, if the magnitude of the magnetic field of the initializing magnetic field generator 34 is set within a predetermined range between the coercive forces of the magnetic layers 2 and 3 (the direction of the magnetic field is upward in this embodiment), FIG. As shown in (2), the second magnetic layer 3 is magnetized in a uniform direction, while the magnetization of the first magnetic layer 2 remains at the beginning.

Next, the magneto-optical disk 35 is rotated for recording / recording.
When passing through the reproducing head 31, the recording signal generator 32
Irradiates a laser beam having two types (first type and second type) of laser power on the disk surface in accordance with the signals from the disk. The first type of laser power is sufficient to raise the temperature of the disk to near the Curie point of the first magnetic layer 2, and the second type of laser power is to increase the temperature of the disk to near the Curie point of the second magnetic layer 3. This is a warm bawa. That is, the two magnetic layers 2, 3 in FIG. 4 showing the慨略the relationship between the coercivity and the temperature, the first type of laser power around T _L, the second type of laser power of the disk to the vicinity of T _H Can raise the temperature.

The temperature of the first magnetic layer 2 rises to near the Curie point by the first type of laser power, but the second magnetic layer 3 has a coercive force at which the bits are stably present at this temperature. By properly setting the bias magnetic field at the time of recording, a bit as shown in FIG. 2C is formed from any of FIG. 2B (first type preliminary recording).

Here, to properly set the bias magnetic field has the following meaning. That is, in the first type of preliminary recording, a force (exchange force) in which the magnetization of the first magnetic layer 2 is arranged in a direction (here, the same direction) that is stable with respect to the direction of the magnetization of the second magnetic layer 3 is received. Therefore, a bias magnetic field is not originally required. However, the bias magnetic field is set in a direction that assists the magnetization reversal of the second magnetic layer 3 (that is, a direction that prevents the first type of preliminary recording) in preliminary recording using the second type of laser power described later. It is preferable for convenience that the magnitude and direction of the bias magnetic field be set to the same state in the preliminary recording using either the first type or the second type of laser power. From this viewpoint, it is preferable to set the bias magnetic field to the minimum necessary for preliminary recording of the second type of laser power according to the following principle.
A setting in consideration of this is an appropriate setting described above.

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

When the temperature is raised to near the Curie point of the second magnetic layer 3 by the second type of laser power (second type of preliminary recording), the bias magnetic field set as described above causes the second magnetic layer 3 to be heated. The direction of magnetization is reversed. Subsequently, the magnetization of the first magnetic layer 2 is also arranged in a stable direction (here, in the same direction) with respect to the second magnetic layer 3. That is, a bit as shown in FIG. 2 (d) is formed from any of FIG. 2 (b). As described above, each portion of the magneto-optical disk is preliminarily recorded in the state shown in FIG. 2 (c) or (d) by the bias magnetic field and the first and second types of laser power changed according to the signal. Will be.

Next, when the magneto-optical disk 35 is rotated, the bits (c) and (d) of the preliminary recording are initialized.
4 again, the recording bit (c) changes to the state shown in FIG. 2E without any change (final recording state) according to the magnitude of the magnetic field of the initialization magnetic field generation unit 34. . On the other hand, the recording bit (d) shows that the magnetization reversal occurs in the second magnetic layer 3,
The state shown in FIG. 2F is obtained (another final recording state).

In order for the state of the recording bit in the state (f) to exist stably, the magnitude of the saturation magnetization of the second magnetic layer 3 is M _s , the thickness is h, and the domain wall between the magnetic layers 2 and 3 is required. Energy to σ _w
Then, as described above, the following relationship may suffice.

[0027]

(Equation 5) Here σ _w / 2M _s h indicates the strength of the exchange force acting on the second magnetic layer 3. The words σ _w / 2M _s h in the size of the magnetization direction of the second magnetic layer 3 in a magnetic field, a stable direction F with respect to the first magnetization direction of the magnetic layer 2 (in this case the same direction) try Mukeyo I do. Therefore, in order that the second magnetic layer 3 does not reverse its magnetization against this magnetic field, the coercive force of the second magnetic layer 3 is set to H _L and H _L >
It may be a σ _w / 2M _s h.

The recording bit states (e) and (f) are controlled by the power of the laser at the time of recording and do not depend on the state before recording, so that overwriting (overwriting) is possible. The recording bits (e) and (f) can be reproduced by irradiating a reproduction laser beam and processing the reproduction light by the recording signal reproducer 33.

FIG. 2 shows an example in which the magnetization state is stable when the magnetization directions of the first magnetic layer 2 and the second magnetic layer 3 are the same (parallel). The same can be considered for a magnetic layer that is more stable. FIG. 5 shows the magnetization state in the recording process in this case in correspondence with FIG.

Next, a case where reproduction is performed for a long period of time on a magneto-optical recording medium having the recording bits (e) and (f) formed by the above recording process will be examined.

The reproduction of the recording bits (e) and (f) differs from the conventional reproduction method in that the recording bit and the reproduction are always affected by the magnetic field from the initializing magnetic field generator 34 during recording and reproduction.
During reproduction, there is a laser irradiation of about 1/3 to 1/10 of the energy at the time of recording. Considering the temperature rise during recording and reproduction, the temperature of the magneto-optical disk passing through the initialization magnetic field generating unit 34 becomes , Up to about 70 ° C.

[0032] Then, according to experiments of the present inventors, the recording and reproducing when the device was subjected to only play sets a medium without recording the, from the coercive force H _H smaller than the initializing magnetic field generator 34 During the long time reproduction (about 10 ¹⁰ times reproduction) by the magnetic field B, the first magnetic layer 2
Reversal of magnetization occurs.

Therefore, as a result of further study to prevent this reversal, the values of the coercive force H _H and the magnitude of the magnetic field B of the first magnetic layer were set within the range of the conventional H _H > B. It is clear that it is more preferable to set the value in the range of 0.2 × H _H −0.3> B (kOe), and more preferably in the range of satisfying this condition and satisfying H _H > 5 kOe. .

[0034]

【Example】

Example 1 In a sputtering apparatus provided with a ternary target source, a polycarbonate disk-shaped substrate on which pregrooves and preformat signals were engraved was set at a distance of 10 cm from the target and rotated. .

In argon, the sputtering rate is 100 ° / min from the first target, and the sputtering pressure is 5 × 10 ⁻³ Torr.
And ZnS was provided as a protective layer to a thickness of 1000 °. Next, in argon, a sputtering rate of 1
TbFe at 00 ° / min, sputtering pressure 5 × 10 ^-3 Torr
The alloy is sputtered to a thickness of 300 °, T _L = about 140 ° C,
A first magnetic layer of Tb ₁₈ Fe ₈₂ of H _H = about 10 kOe was formed. Next, in argon at a sputtering pressure of 5 × 10 ⁻³ Torr, T
sputtered bFeCo alloy, thickness 500 Å, T _H = about 250 ° C., to form a second magnetic layer of H _L = about 1kOe Tb ₂₃ Fe ₆₀ Co _17. Next, a sputtering rate of 100 ° / min and a sputtering pressure of 5 × were applied from the first target in argon.
At a pressure of 10 ⁻³ Torr, ZnS was provided as a protective layer to a thickness of 3000 °. Next, the substrate on which the film formation was completed was bonded to a polycarbonate bonding substrate using a hot melt adhesive to prepare a sample of a magneto-optical disk.

Example 2 The same film as in Example 1 except that the material composition of the first magnetic layer 2 and the coercive force H _H and the Curie temperature _TL were changed in the same manner as described above. With the same thickness and the same configuration, a sample of a magneto-optical disk was prepared.

After recording the samples prepared in Examples 1 and 2 under the same conditions, the same track was reproduced 10 ¹⁰ times while changing the magnitude B of the magnetic field of the initializing magnetic field generating section 34. The change of the noise component in the signal was examined.

Next, the internal temperature of the recording / reproducing apparatus is set to 30 ° C.
The temperature was set in the order of 45 ° C. and 60 ° C., and at each temperature, the value of the magnetic field at which the noise component of the reproduced signal increased was checked. Table 1 shows the results.

[0039]

[Table 1] Table 1 shows that the smaller the coercive force H _H of the first magnetic layer and the higher the internal temperature of the recording / reproducing apparatus, the smaller the value of the magnetic field B at which the noise component in the reproduced signal increases. I have. This shows that this relationship does not change depending on the material composition of the first magnetic layer. FIG. 6 shows the relationship between the H _H value of each sample and the B value at which noise increases based on the above experimental results.

As shown in the figure, when the temperature inside the machine is up to 60 ° C.,
It can be seen that at least 0.2 × H _H −0.3> B in the relationship between H _H and B in order to prevent noise from increasing in the reproduced signal. Also, H _H is at least 1.5k
If it is not Oe or more, even if B is a small value, an increase in noise occurs.

Incidentally, since the actual internal temperature of the recording / reproducing apparatus does not exceed 60 ° C., generally, if the above conditions are satisfied, no increase in noise will occur even if the reproduction is performed for a long time.

In addition to satisfying the above conditions, it is more preferable to set the value of H _H to 5 kOe or more for the following two reasons.

(1) The minimum required value of B is a value obtained by adding the coercive force H _L of the second magnetic layer and the magnetic field due to the exchange force acting on the second magnetic layer. Practically, it is considered to be about 1 to 2 kOe.
The magnetic field B generated by the initializing magnetic field generating unit B is set to 1～2KOe, the generation of noise by performing continuous playback until internal temperature 60 ° C. is slight, the value of H _H Figures 6 5k
Oe or more.

(2) FIG. 6 shows the respective in-machine temperatures.
The magnitude of the magnetic field B set in the initialization magnetic field generation unit;
H required for no noise at the set B value
_HAre shown. For example, at an internal temperature of 60 ° C., H_H<
In the range of 5 kOe, H_H= 5 (B + 0.3)
You. That is, the initialization magnetic field generation unit B is increased by a certain amount ΔB.
If you set_HIs increased by 5 × ΔB
Indicates what must be done. However, H_HIs 5k
In the range above Oe, a magnetic field is generated at an in-machine temperature of 30 to 60 ° C.
When the value of the raw portion B is increased by a certain amount, the value does not increase correspondingly.
H that must be _HThe value is within the range of 5 kOe or less.
It turns out that it is smaller than this.

[0045]

As described [Effect Invention above in detail, as a magneto-optical recording medium, a first magnetic layer comprising an alloy of a transition element a rare earth element having a lower Curie point T _L and a high coercive force H _H, relative A magnetic layer having a two-layer structure composed of an alloy of a rare earth element and a transition element having a high Curie point _TH and a low coercive force _HL ;
By setting the coercive force H _H of the magnetic layer and the magnetic field B from the initializing magnetic field generating section to satisfy a predetermined relationship, it is possible to perform overwrite recording by recording with binary laser power. That is, even when the data is reproduced continuously over a long period of time, a good reproduced signal can be obtained.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams each showing a configuration of an example of a magneto-optical recording medium used in the present invention.

FIG. 2 is a diagram illustrating the direction of magnetization of each of magnetic layers 2 and 3 during execution of a recording method performed by the magneto-optical recording / reproducing apparatus of the present invention.

FIG. 3 is a diagram showing a conceptual configuration of a magneto-optical recording / reproducing apparatus according to the present invention.

FIG. 4 is a schematic diagram showing a relationship between coercive force and temperature in each of the magnetic layers 2 and 3;

FIG. 5 is a view for explaining another form of the magnetization direction of each of the magnetic layers 2 and 3 shown in FIG.

FIG. 6 is a characteristic diagram showing a relationship between a coercive force H _H of a first magnetic layer and a value of a magnetic field B at which noise increases.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 translucent substrate 2 first magnetic layer 3 second magnetic layer 4, 5 protective film 6 adhesive layer 7 bonding substrate 31 recording / reproducing head 32 recording signal generator 33 recording signal reproducer 34 initialization magnetic field generator 35 Magneto-optical disk

Claims (1)

(57) [Claims] 1. A first magnetic layer made of an alloy of a rare earth element and a transition element having a low Curie point T _L and a high coercive force H _H , and a Curie point T relatively higher than the first magnetic layer. A perpendicular magnetic film having a two-layer exchange-coupled perpendicular magnetization film composed of a second magnetic layer made of an alloy of a rare earth element and a transition element having _H and a low coercive force _HL on a substrate;
The saturation magnetization of the second magnetic layer is M _s , the film thickness is h,
And the domain wall energy between the second magnetic layers as σ _w , Magneto-optical recording medium meets the sufficiently coercive force H _H in to magnetize the second magnetic layer of a coercive force H _L in one direction
Initialization magnetic field means for applying a magnetic field B having a magnitude that does not reverse the direction of magnetization of the first magnetic layer, and bias magnetic field applying means for applying a bias magnetic field different from the magnetic field B to the magneto-optical recording medium If the bias magnetic field the magneto-optical recording medium in a state of being applied to the vicinity of the high Curie point T _H and laser power of only the lower Curie point the magneto-optical recording medium to the vicinity of T _L is heating is heating Recording / reproducing means for selectively irradiating only the laser power according to the information and recording the information on the magneto-optical recording medium and reproducing the recorded information by using a magneto-optical effect; and in a magneto-optical recording and reproducing apparatus and a rotating means for rotating the medium, coercivity H _H of the first magnetic layer, the magnetic field B is below 60 ° C. internal temperature is 30 ° C. over the device Stomach, _H H ≧ 1.
A magneto-optical recording / reproducing apparatus which satisfies 5 kOe and 0.2 × H _H −0.3> B (kOe).