JPH07320314A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To carry out optical modulation over write stably regardless of fluctuation in the temperature rise caused through a high level irradiation with laser light by suppressing the bonding of an intermediate layer and an auxiliary recording layer due to exchange force surely. CONSTITUTION:An intermediate layer (second magnetic layer) 4 having lower Curie point than a recording layer and exhibiting in-plane magnetization on the room temperature side but vertical magnetization in such a temperature region that an auxiliary recording layer has lower coercive force than a recording layer, is provided between the recording layer (first magnetic layer) 3 and the auxiliary recording layer (third magnetic layer) 5. Optical modulation overwrite can be carried out through irradiation with a laser light subjected to intensity modulation while applying a recording field after conventional initialization.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium such as a magneto-optical disk, a magneto-optical tape, a magneto-optical card and the like.

[0002]

2. Description of the Related Art In a magneto-optical disk in which a perpendicularly magnetized film made of a magnetic material is provided on a substrate as an information recording layer, information is recorded / reproduced by the following method. When recording,
First, after a strong external magnetic field aligns the magnetization direction of the recording layer in one direction (upward or downward) and initializes it,
The area to be recorded is irradiated with laser light to raise the temperature of the irradiated portion to a temperature near the Curie point of the recording layer or above, or above the compensation point. As a result, the coercive force at that portion is set to zero or almost zero, and then the direction of magnetization is reversed by applying an external magnetic field (bias magnetic field) in the direction opposite to that at the time of initialization. When the irradiation of the laser beam is stopped, the temperature of the recording layer returns to room temperature, so that the reversed magnetization is fixed.
In this way, information is thermomagnetically recorded.

During reproduction, a linearly polarized laser beam is applied to the disk, and the planes of polarization of the reflected light and the transmitted light rotate according to the direction of magnetization of the recording layer (magnetic Kerr effect, magnetic Faraday effect). ) Is used to read out optical information.

On the other hand, a magneto-optical disk on which information is recorded by the above-mentioned magneto-optical recording method is also attracting attention as a rewritable large-capacity storage element. In this case,
As a magneto-optical disk capable of rewriting information by modulating the light intensity while applying a recording magnetic field after performing initialization with a relatively small initializing magnetic field, a so-called optical modulation overwritable magneto-optical disk, A recording layer composed of an exchange-coupling bilayer film has been conventionally proposed.

Further, in Japanese Patent Publication No. 5-22303, in order to make the initializing magnetic field smaller and improve the stability of the recording bit, as shown in FIG.
There is disclosed a magneto-optical disk configured by providing three magnetic layers 11, 12, and 13. The first magnetic layer 11 as a recording layer and the third magnetic layer 13 as a recording auxiliary layer each exhibit perpendicular magnetization from room temperature to each Curie point, while serving as an intermediate layer provided between both layers 11 and 13. The second magnetic layer 12 has a characteristic that it exhibits in-plane magnetization at room temperature and exhibits perpendicular magnetization as the temperature rises. Further, as shown in FIG. 8, the third magnetic layer 13 is smaller coercive force H _L in the room temperature than the coercive force H _H of the first magnetic layer 11, the Curie point T _H is the first magnetic layer 11 Curie point T
Those higher than _L are selected. Although not shown, the Curie point T _{M of} the second magnetic layer 12 is
Curie points T _H and T _{L of} the first and third magnetic layers 11 and 13
Those between are selected.

The procedure of overwriting in the magneto-optical disk having the above construction will be briefly described. As shown in FIG. 7, first, at room temperature, the first and third magnetic layers 11 and 13 are first formed.
An initialization magnetic field H _init having a magnitude between the coercive forces H _H and H _L at each room temperature is applied. As a result, the first magnetic layer 11 is maintained in the same magnetization direction as before, and only the magnetization of the third magnetic layer 13 is aligned in one direction along the initialization magnetic field H _init . In the figure, the arrows in the magnetic layers 11 to 13 indicate the directions of transition metal sublattice magnetization in the magnetic layers 11 to 13.

At this time, since the second magnetic layer 12 exhibits in-plane magnetization at room temperature, the magnetic coupling force (exchange force) between the first magnetic layer 11 and the third magnetic layer 13 is hindered, whereby the initialization is performed. By making the magnitude of the magnetic field H _{in it} smaller, it is possible to align only the magnetization direction of the third magnetic layer 13 in one direction as described above.

Next, smaller than the initializing magnetic field H _init ,
At the same time, while applying the recording magnetic field H _{w in the} opposite direction, the laser light intensity-modulated to the high level I and the low level II is irradiated according to the information to be recorded.

When the laser beam of high level I is irradiated, the irradiated portion is at the Curie point T of the first and second magnetic layers 11 and 12.
_The temperature exceeds _L · T _M and rises to a temperature near the Curie point T _H of the third magnetic layer 13. Thereby, the third magnetic layer 13
Magnetization is reversed along the recording magnetic field H _w , and in the process of cooling to room temperature, the second magnetic layer 12 showing perpendicular magnetization.
Then, the magnetization direction of the third magnetic layer 13 is transferred by the exchange force acting on the interface, and further transferred to the first magnetic layer 11.

On the other hand, when the low-level II laser beam is irradiated, the irradiated portion is heated only to a temperature near the Curie point T _L of the first magnetic layer 11, and at this time, the third magnetic layer 13 is
Since the coercive force is larger than the recording magnetic field H _w , the magnetization direction is not inverted, and the magnetization direction is maintained at the initialization. Then, in the process of cooling to room temperature, similar to the above,
Due to the exchange force acting on the interface, the magnetization direction of the third magnetic layer 13 is transferred to the first magnetic layer 11 via the second magnetic layer 12.

With this procedure, new recording information corresponding to the intensity-modulated laser light is written in the first magnetic layer 11. It should be noted that the reproduction of the recorded information is at the low level described above.
It is performed by irradiating a laser beam whose intensity is set to a level smaller than II.

[0012]

However, in the above-described magneto-optical disk, the Curie point T _M of the second magnetic layer 12 showing in-plane magnetization to perpendicular magnetization as the temperature rises, and the first
Since the Curie points T _H and T _{L of} the third magnetic layers 11 and 13 have a relation of T _L <T _M <T _H , T _M should be close to T _H. If configured,
There is a problem that smooth light modulation overwrite cannot be performed.

That is, in order to improve the reproduction signal characteristics by increasing the Kerr rotation angle and the like when the linearly polarized laser light is irradiated during reproduction, the Curie point T _L of the first magnetic layer 11 is set so as to improve the reproduction signal characteristics. It is effective to select the higher one. At this time, the second that satisfies the above relationship
When the magnetic layer 12 is selected, its Curie point T _M becomes closer to the Curie point T _H of the third magnetic layer 13. In fact, in the magneto-optical disk described in the above publication, for example, the Curie point T _H = 180 ° C. of the third magnetic layer 13 and the Curie point T _M = 170 ° C. of the second magnetic layer 12 are exemplified ( Japanese Patent Publication No. 5-22303, column 9, line 42 to column 10, line 12).

In such a structure in which T _H and T _M are close to each other, for example, when the laser beam of the high level I is irradiated in an attempt to raise the temperature to the vicinity of T _H , the ambient temperature changes, for example. Due to the variation in the temperature rise according to the above, it is necessary to reverse the magnetization of the third magnetic layer 13 along the recording magnetic field H _w in the temperature state below the Curie point T _M of the second magnetic layer 12. Become. At this time, since the second magnetic layer 12 exhibits perpendicular magnetization, the exchange force from the second magnetic layer 12 acts on the third magnetic layer 13, and therefore only the coercive force in the third magnetic layer 13 is expected. With the set recording magnetic field H _w , the magnetization direction of the third magnetic layer 13 may not be reliably inverted. As a result, as described above, the light modulation overwrite is not smoothly performed.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to be able to perform light modulation overwrite more smoothly and to improve reproduction signal characteristics. It is to provide a possible magneto-optical recording medium.

[0016]

In order to achieve the above object, the magneto-optical recording medium of the present invention has a recording layer exhibiting perpendicular magnetization from room temperature to the Curie point and a perpendicular magnetization from room temperature to the Curie point. The coercive force at room temperature is smaller than that of the recording layer, and between the recording auxiliary layer having a higher Curie point than that of the recording layer, in-plane magnetization is exhibited at the room temperature side, and the recording layer is better than the recording auxiliary layer. It is characterized in that an intermediate layer having a characteristic of exhibiting perpendicular magnetization in a temperature region having a small coercive force and having a Curie point lower than that of the recording layer is provided.

[0017]

In the magneto-optical recording medium having the above structure, the optical modulation overwrite can be performed by the same procedure as the conventional one. That is, first, at room temperature, an initialization magnetic field having a magnitude between the coercive forces of the recording layer and the recording auxiliary layer is applied, and only the magnetization direction of the recording auxiliary layer is aligned with the direction of the initialization magnetic field. At this time, since the intermediate layer exhibiting in-plane magnetization at the room temperature side is provided therebetween, the coupling due to the exchange force between the recording layer and the recording auxiliary layer is prevented, and the above initialization is performed with a smaller initialization magnetic field. Can be made.

Next, while applying a recording magnetic field, the intensity-modulated laser beam is irradiated. When the irradiation portion is irradiated with high-level laser light and the temperature of the irradiated portion exceeds the Curie point of the recording layer to a temperature near the recording auxiliary layer, the magnetization direction of the recording auxiliary layer is reversed along the direction of the recording magnetic field. After that, since the intermediate layer exhibits perpendicular magnetization in a temperature region where the coercive force of the recording layer is smaller than that of the recording auxiliary layer in the process of lowering the temperature to room temperature, the recording auxiliary layer passes through this intermediate layer in this temperature region. Is transferred to the recording layer by the exchange force acting on the interface.

On the other hand, when the irradiation portion is heated to a temperature near the Curie point of the recording layer by being irradiated with a low level laser beam, the magnetization direction of the recording auxiliary layer is maintained in the direction at the initialization. Since the coercive force of the recording layer is lowered, the magnetization direction of the recording auxiliary layer is also transferred to the recording layer via the intermediate layer in the process of lowering the temperature in this case as well. In this way, new information is written in the recording layer according to the intensity-modulated laser light.

Further, in the above, since the Curie point is lower than that of the recording layer, even when the temperature rise during high-level laser beam irradiation varies, the coupling between the intermediate layer and the recording auxiliary layer due to the exchange force occurs. This makes it possible to stably perform the light modulation overwrite.

Moreover, in this case, since the Curie point of the intermediate layer is not set between the recording layer and the recording auxiliary layer as in the conventional case, the Curie point of the recording layer is higher than that of the conventional case. It is possible to increase the Kerr rotation angle at the time of laser light irradiation at the time of reproduction and the like, thereby improving the reproduction signal characteristic.

[0022]

【Example】

[Embodiment 1] The following description will explain a specific embodiment of the present invention with reference to FIGS.

As shown in FIG. 2, a magneto-optical disk as a magneto-optical recording medium in this embodiment has a transparent substrate 1 as shown in FIG.
A dielectric layer 2, a first magnetic layer 3 as a recording layer, and
The second magnetic layer 4 as an intermediate layer, the third magnetic layer 5 as a recording auxiliary layer, the protective layer 6, and the overcoat layer 7 are sequentially laminated.

The substrate 1 has, for example, an outer diameter of 86 mm and an inner diameter of 15
mm, and a 1.2 mm-thick disk-shaped glass plate. One surface of the substrate 1 (the lower surface in the figure) is not shown in the figure, but is uneven for guiding a light beam. Of the guide track is formed by the reactive ion etching method. The track pitch is 1.6 μm, the width of the groove (recess) is 0.8 μm, and the width of the land (convex) is 0.8 μm. A film thickness of 8 is formed on the guide track forming surface of the substrate 1.
The transparent dielectric layer 2 made of 0 nm AlN is formed by reactive sputtering.

The first magnetic layer 3 on the dielectric layer 2 is composed of DyFeCo which is a rare earth metal-transition metal alloy.
Co-sputtering of e and Co targets gives a film thickness of 5
It is formed with 0 nm. Its composition is Dy _0.21 (Fe _0.81 Co
_0.19 ) _0.79 , which is rich in transition metals and, as shown in FIG. 1, has a Curie point T lower than that of the third magnetic layer 5 described later.
_C1 (= 180 ° C) and high coercive force at room temperature H _C1 (= 120
0 kA / m), and has the characteristic of exhibiting perpendicular magnetization from room temperature to T _C1 .

The second magnetic layer 4 provided on the first magnetic layer 3 is also a rare earth metal-transition metal alloy Dy.
It is made of FeCo and has a film thickness of 50 nm formed by simultaneous sputtering of Dy, Fe, and Co targets. Its composition is Dy _0.29 (Fe _0.80 Co _0.20 ) _0.71 and it is rich in rare earth metals, and the Curie point T _C2 is the Curie point T of the first magnetic layer 3.
_It is lower than _C1 and 140 ℃. Further, the coercive force H _C2 at room temperature is almost zero (coercive force here means the substrate 1
Is the coercive force in the vertical direction. It exhibits in-plane magnetization at room temperature, and has perpendicular magnetization at about 100 ° C. as the temperature rises. In addition, in FIG. 1, the range of this in-plane magnetization is shown by a broken line. As shown by the solid line, the range of perpendicular magnetization is a temperature region where the coercive force of the first magnetic layer 1 is smaller than that of the third magnetic layer 5.

The third magnetic layer 5 on the second magnetic layer 4 is made of GdDyFeCo which is a rare earth metal-transition metal alloy, and Gd,
It is formed with a film thickness of 50 nm by simultaneous sputtering of Dy, Fe, and Co targets. Its composition is (Gd _0.40 Dy _0.60 ).
_0.27 (Fe _0.70 Co _0.30 ) _0.73 , which is rich in rare earth metals.
The Curie point T _C3 is higher than the Curie point T _C1 of the first magnetic layer 3 and is 250 ° C. The compensation temperature T _COMP3 is 2
The coercive force H _C3 at 00 ° C. at room temperature is 64 kA / m, which is smaller than the coercive force H _C1 of the first magnetic layer 3. This third magnetic layer has the property of exhibiting perpendicular magnetization from room temperature to T _C3 .

The protective layer 6 made of AlN is formed on the third magnetic layer 5 to have a film thickness of 80 nm. Further, the protective layer 6 is coated with an acrylate-based ultraviolet curable resin and cured by irradiation with ultraviolet rays to form the overcoat layer 7 to form a magneto-optical disk having a sectional structure shown in FIG.

The sputtering conditions for forming the first to third magnetic layers 3 to 5 are as follows: ultimate vacuum of 2.0 × 10 ^-4 Pa.
Hereafter, Ar gas pressure is 6.5 × 10 ⁻¹ Pa and discharge power is 300 W. Moreover, the sputtering conditions at the time of forming each of the dielectric layer 2 and the protective layer 6 are as follows: ultimate vacuum of 2.0 × 10 ⁻⁴ Pa or less, N ₂ gas pressure of 3.0 × 10 ⁻¹ Pa, and discharge power of 800 W. is there.

When information is recorded using the magneto-optical disk having the above-described structure, as shown in FIG. 3, first, for example, an upward initialization magnetic field H _init is applied as shown in the figure to perform initialization. After that, while applying a recording magnetic field H _w in the same direction as the initializing magnetic field H _init and sufficiently smaller than H _init , as shown in FIG. 4, laser light intensity-modulated into a high level I and a low level II is obtained. Information is recorded by irradiating with.

The change in the magnetization state of each of the magnetic layers 3 to 5 at the time of recording information will be described with reference to FIG. In the figure, the horizontal axis represents temperature. When the initialization magnetic field H _init is applied at room temperature, and when the recording magnetic field H _w is applied, the high-level I and low-level II laser beams are emitted. 9 shows changes in the magnetization states of the magnetic layers 3 to 5 when the temperature rises due to the increase in temperature. In addition, each magnetic layer 3-5
Are made of rare earth-transition metal alloys. In this case, the magnetization directions of the magnetic layers 3 to 5 can be indicated by either the total magnetization, the rare earth metal sublattice magnetization, or the transition metal sublattice magnetization. However, in the figure, each magnetic layer 3-5
The arrows indicate the directions of transition metal sublattice magnetization.

First, the above-mentioned initialization magnetic field H _init at room temperature.
Is applied, the magnetization directions of the magnetic layers 3 to 5 are S in the figure.
One of two stable states, 1 and S2. Here, the initializing magnetic field H _init is _equal to the first magnetic layer 3 and the third magnetic layer 5.
And coercive force H _C1 (= 1200 kA / m) ・ H at each room temperature
It is set to a value between _C3 (= 64 kA / m), for example, 80 kA / m. Therefore, by this initialization, the third
Only the magnetization of the magnetic layer 5 is aligned in one direction along the initialization magnetic field H _init . That is, when the initializing magnetic field H _init is applied upward as shown in the figure and the total magnetization in the third magnetic layer 5 is directed in the direction of the initializing magnetic field H _init , the third magnetic layer 5 is rich in rare earth metal. Therefore, the direction of the transition metal sublattice magnetization is aligned downward, which is opposite to the direction of the initializing magnetic field H _init .

At this time, the coercive force H _C1 of the first magnetic layer 3 is H
_It is sufficiently larger than _init , and since the second magnetic layer 4 exhibits in-plane magnetization at room temperature, the magnetization direction of the third magnetic layer 5 is the second direction.
It is not transferred to the first magnetic layer 3 through the magnetic layer 4, and the reversal of the magnetization of the first magnetic layer 3 does not occur. Therefore, the magnetization direction of the first magnetic layer 3 is maintained in the direction corresponding to the recording state up to that point, and depending on this direction, the state is either S1 or S2.

For such initialization, a permanent magnet is incorporated in the recording / reproducing apparatus, and the initialization magnetic field H is generated by this magnet.
_With the configuration in which _init is applied, it is always performed during rotational driving of the magneto-optical disk. Further, for example, an apparatus in which the initialization magnetic field _Hinit is applied by an electromagnet is configured to be performed only during recording.

After the initialization as described above, as described above, while applying the recording magnetic field H _w (for example, 16 kA / m), the high level I and the low level I are set according to the information to be newly recorded. The intensity-modulated laser light is emitted to level II.

The high-level I laser beam irradiates the area irradiated with the laser beam at each Curie point Tc _{1 of} the first and second magnetic layers 3 and 4.
・ Tc ₂ is exceeded, and further, the Curie point of the third magnetic layer 5 is T _c3
The laser power is set so as to raise the temperature to (= 250 ° C.) or higher. On the other hand, the laser beam of low level II is the irradiation area, beyond the Curie point Tc ₂ of the second magnetic layer 4, the Curie point of the first magnetic layer 3 Tc ₁
The laser power is set so as to raise the temperature to the vicinity of (= 180 ° C.).

Therefore, first, in the process of irradiating the laser beam of the high level I and raising the temperature of the irradiation area as described above, the above-mentioned states S1 and S2 go through S3 and S4 in the figure and the state of S5. Becomes That is, S3 is a magnetic coupling force from the third magnetic layer 5 to the first magnetic layer 4 via the second magnetic layer 4 because the second magnetic layer 4 once exhibits perpendicular magnetization during the temperature rising process. (Exchange force) acts, which causes the first
The state in which the magnetization direction of the magnetic layer 3 matches the direction of the third magnetic layer 5 is shown. Once the state of S3 is passed, the first
The magnetizations of the second magnetic layers 3 and 4 become zero as shown in S4 and S5 as the temperature rises until they exceed the Curie points Tc ₁ and Tc ₂ .

On the other hand, the magnetization of the third magnetic layer 5 rises to a temperature near the Curie point T _{c3 in} the state of S3 during the temperature rising process while maintaining the magnetization direction forcibly aligned by the initialization. The coercive force decreases at the stage of occurrence of the magnetic field, which causes the recording magnetic field H _w applied at this time to move in the direction along the recording magnetic field H _w as shown by the change state from S4 to S5. Invert.

It should be noted that as the temperature rises as described above, the third
The magnetic layer 5 exceeds its compensation temperature T _comp3 (= 200 ° C.) in the process of transition from S3 to S4. At this point, the magnitude relation of the sublattice magnetizations of the rare earth metal and the transition metal in the third magnetic layer 5 is reversed. Therefore, S4 and S5
In the state (3), the direction of the transition metal sublattice magnetization of the third magnetic layer 5 coincides with the direction of total magnetization, which is the reverse of the room temperature state. Therefore, as shown in the figure, by the recording magnetic field H _{w in the} same direction as the initialization magnetic field H _init ,
The direction of the transition metal sublattice magnetization of the third magnetic layer 5 is reversed as shown from S4 to S5.

When such a reversal occurs, the first
Since the second magnetic layers 3 and 4 each exceed the Curie point, the exchange forces from these magnetic layers 3 and 4 do not act on the third magnetic layer 5, and as a result, the inversion of the third magnetic layer 5 occurs. The recording magnetic field H _w to be generated can be made smaller.

As described above, after the magnetization direction of the third magnetic layer 5 is reversed along the recording magnetic field H _w, when the laser light irradiation section moves due to the rotation of the magneto-optical disk, the laser light irradiation section of the above-mentioned laser light irradiation section moves. The temperature drops to room temperature. During this cooling process, the second magnetic layer 4 becomes perpendicularly magnetized, and at this time, the magnetization direction is changed to the third magnetic layer by the exchange force acting on the interface with the third magnetic layer 5, as shown in S6. Aligned with the magnetization direction of 5. Furthermore, due to the exchange force acting on the interface between the first magnetic layer 3 and the second magnetic layer 4, the magnetization direction of the first magnetic layer 3 also changes.
It follows the magnetization direction of the second magnetic layer 4.

After that, when cooled to room temperature, the second magnetic layer 4 shifts to in-plane magnetization as shown in S7, and an exchange force acts between the first magnetic layer 3 and the third magnetic layer 5. Will not do.
In this state, even if the magneto-optical disk rotates and the initialization magnetic field H _init is applied at room temperature, the magnetization direction of the first magnetic layer 3 having a large coercive force does not change, and the third magnetic layer 5 having a small coercive force.
Only the magnetization direction of is reversed as described above, and the state S7 shifts to the state S2. Thus, the magnetization direction of the first magnetic layer 3 is opposite to the direction of the initializing magnetic field, which causes
This means that new recording information corresponding to the laser beam modulated to the high level I is written in the first magnetic layer 3.

Next, a description will be given of changes in the magnetization states of the magnetic layers 3 to 5 when the low-level II laser beam is applied while applying the recording magnetic field H _w after the above initialization.

At this time, the above laser light irradiation section is
Exceeds the Curie point Tc ₂ of the magnetic layer 4, the temperature is raised to a temperature near the Curie point T _c1 of the first magnetic layer 3. This temperature is the third
It is lower than the compensation temperature T _comp3 of the magnetic layer 5, and the coercive force of the third magnetic layer 5 in this temperature state is larger than the recording magnetic field H _W. Therefore, the direction of magnetization of the third magnetic layer 5 is H
Not reversed by _W. After that, in the process of cooling to room temperature, the second magnetic layer 4 starts to exhibit perpendicular magnetization, and at this time, as shown in S3, the magnetization direction of the first magnetic layer 3 is the same as the second direction. It is along the magnetization direction of the third magnetic layer 5 via the magnetic layer 4. That is, both the states S1 and S2 after the initialization become the state S3.

After that, when the temperature is further lowered to room temperature, the second
The magnetic layer 4 shifts to in-plane magnetization, the exchange force does not act between the first magnetic layer 3 and the third magnetic layer 5, and the state S3 shifts to the state S1. In this way, the magnetization direction of the first magnetic layer 3 becomes a direction along the initializing magnetic field, which causes the low level
New recording information according to the laser beam modulated to II is the first
This means that the magnetic layer 3 has been written.

The information recorded on the first magnetic layer 3 as described above is irradiated with laser light of level III, which is lower than that at the time of recording, as shown in FIG. Reproduced by detecting rotation.

The measurement results of such reproducing operation characteristics will be described below by further giving concrete numerical examples. First, an initializing magnetic field H _init = 80 kA / m, a recording magnetic field H _w = 16 kA / m, a high level I laser power (P _H ) = 8 mW, and a low level II laser power (P _L ).
= 4 mW, recording bit length = 0.78 μm and recording was performed. As a result, it was possible to perform light modulation overwriting without erasure. Then, when the reproduction laser power (P _R ) of level III was set to 1 mW and reproduction was performed, a signal-to-noise ratio (C / N) = 47 dB was obtained.

In the magneto-optical disk having the conventional exchange-coupling bilayer film in which the intermediate layer 4 is not provided as in this embodiment, it is necessary to set the initialization magnetic field H _init to 240 kA / m. . Therefore, in this case, a device for generating a larger initializing magnetic field is required, and it is impossible to sufficiently reduce the size and power consumption of the entire device.

In this conventional magneto-optical disk, the recording power H _w is set to 16 to 40 kA / m after setting the high level I laser power P _H at the time of recording to 10 mW or more.
In as it was necessary to hand, in the present embodiment, as described above, setting of P _H = 8 mW, recording magnetic field H _w 16
Light modulation overwrite was possible under the condition of -40 kA / m. That is, in this embodiment, when the high temperature state is brought about by the irradiation of the laser beam of the high level I, the first and second magnetic layers 3 and 4 each exceed the Curie point, so that the third magnetic field H _w causes the third The magnetization reversal of the magnetic layer 5 is
It occurs in a state where the exchange force from the second magnetic layers 3 and 4 does not act.

Therefore, as the recording magnetic field H _w , the first
Without considering the exchange force from the second magnetic layers 3 and 4, if the coercive force of the third magnetic layer 5 is higher than the coercive force in the high temperature state at the time of high-level I laser beam irradiation, the high-level I laser power is Even if it is set smaller, or the recording magnetic field H _w
It is possible to reliably cause the reversal of the magnetization in the third magnetic layer 5 as described above, even if the size of is smaller.

The first to third magnetic layers 3 to 5 in the above-described magneto-optical disk (hereinafter referred to as sample # 1).
The composition and the film thickness of are not limited to these, and can be variously configured. In the following, regarding 27 types of magneto-optical disks (hereinafter, referred to as samples # 2 to # 28) manufactured with different compositions, magnetic layers different from sample # 1 in Tables 1 to 4 are shown below. The composition and magnetic properties of Samples # 2 to # 28 are also shown in Table 4.
The measurement results of the reproducing operation characteristics in are shown. In addition, in Tables 1 to 4, the corresponding items are selected and reprinted from the above description of the sample # 1.

Samples # 2 to # 8 differ from sample # 1 only in the composition of the second magnetic layer 4, and the other structures are the same as sample # 1. The composition and magnetic properties of those second magnetic layers 4 are as shown in Table 1. The second magnetic layer 4 in each of the samples # 2 to # 8 is rich in rare earth metal as in the sample # 1, and the coercive force H _C2 at room temperature is almost zero.

[0053]

[Table 1]

Samples # 9 to # 13 differ from Sample # 1 only in the composition of the first magnetic layer 3, and the composition and magnetic characteristics of the first magnetic layer 3 are as shown in Table 2. . The first magnetic layer 3 of these samples # 9 to # 13
Shows perpendicular magnetization from room temperature to the Curie point T _C1 as in sample # 1, and samples # 9 and # 12 · # 13 are transition metal rich, sample # 10 and # 10 as in sample # 1. # 11 is a compensation composition.

[0055]

[Table 2]

Samples # 14 to # 27 are samples # 1
On the other hand, only the composition of the third magnetic layer 5 is different, and the composition and magnetic characteristics of those third magnetic layers 5 are as shown in Table 3. Like Sample # 1, the third magnetic layer 5 of Samples # 14 to # 27 is rich in rare earth metals and exhibits perpendicular magnetization from room temperature to the Curie point T _C3 .

[0057]

[Table 3]

Sample # 28 is the second sample in sample # 1.
While the thickness of the magnetic layer 4 is 50 nm, this is 30
The only difference is in nm.

[0059]

[Table 4]

As shown in Table 4, samples # 2 to # 28
In each case, under the recording conditions shown in the same table, optical modulation overwriting with no erasure remained, and a signal-to-noise ratio (C / N) = 47 dB was obtained.

In sample # 13, C / N = 48
dB was obtained. This is as shown in Table 2 above.
By increasing the Curie point of the magnetic layer 3, the recording / reproducing characteristics are improved as compared with, for example, Sample # 1.

On the other hand, the film thickness of the second magnetic layer 4 was changed to Sample # 1.
Sample # 28, which is thinner than the above sample, can perform optical modulation overwrite without erasure under the recording conditions shown in the table, and further, the duty of the recording pulse is 40%.
However, it was possible to record sufficiently. Considering that the duty of the recording pulse of the sample # 1 was 60%, it was possible to obtain a magneto-optical disk having a recording sensitivity higher than that of the sample # 1.

[Embodiment 2] Another embodiment of the present invention will be described below with reference to FIG. In addition,
For convenience of explanation, parts having the same functions as those shown in the drawings of the above-described embodiment are designated by the same reference numerals, and the description thereof will be omitted.

As shown in FIG. 6, a magneto-optical disk as a magneto-optical recording medium according to this embodiment has a dielectric layer 2 and a first layer.
This embodiment is different from the above embodiment in that a fourth magnetic layer 8 is further provided between the magnetic layer 3 and the magnetic layer 3.

The fourth magnetic layer 8 is composed of GdFeCo, which is a rare earth metal-transition metal alloy, and is formed to have a film thickness of 30 nm by simultaneous sputtering of Gd, Fe and Co targets. Its composition is Gd _0.25 (Fe _0.80 Co _0.20 ) _0.75 ,
It is rich in rare earth metals and has no Curie point (T _C4 ), which is higher than the Curie point T _C1 of the first magnetic layer 3,
It is 300 ° C. Further, the coercive force (H _C4 ) at room temperature is almost zero, and it has the characteristics of showing in-plane magnetization at room temperature and perpendicular magnetization at about 100 ° C.

Under the recording conditions shown in Table 5, the optical modulation overwrite without erasure could be performed on the magneto-optical disk having the fourth magnetic layer 8 (hereinafter referred to as sample # 29). For comparison, the same table also shows the recording conditions for Sample # 1.

[0067]

[Table 5]

C / N (Signal to Noise Ratio) for sample # 1
Is 47 dB, the C / N in this embodiment is 49
It was dB, and the signal quality was improved. This is T _C4 > T _C1
Since it was set to, it is thought that the car rotation angle became large.

When the recording bit length was shortened, the C / N ratio of sample # 1 dropped sharply.
C / N did not decrease so much. This is because the fourth magnetic layer 8 exhibits in-plane magnetization at room temperature, and exhibits perpendicular magnetization when irradiated with a laser beam having a level III reproducing laser power. This is because it could be played back without being affected by.

That is, when the fourth magnetic layer 8 is irradiated with the reproducing laser beam, the temperature distribution of the irradiated portion becomes almost Gaussian. At this time, the intensity of the laser beam was set so that the temperature rising temperature in the central region smaller than the spot diameter exceeded the temperature indicating the perpendicular magnetization in the fourth magnetic layer 8. At this time, the magnetization of only the region near the center of the fourth magnetic layer 8 shifts from in-plane magnetization to perpendicular magnetization. The direction of the magnetization of the fourth magnetic layer 8 follows the direction of the magnetization of the first magnetic layer 3 due to the exchange force between the two layers of the fourth magnetic layer 8 and the first magnetic layer 3 in the part where the perpendicular magnetization is transferred.

As a result, only the vicinity of the center of the laser light irradiation portion exhibits the polar Kerr effect, and information is reproduced based on the reflected light from the portion.

When the laser beam irradiator moves to reproduce the next recorded bit, the temperature of the previous reproducing portion decreases and the perpendicular magnetization changes to the in-plane magnetization, so that the polar Kerr effect is not exhibited. This means that the magnetization recorded in the first magnetic layer 3 is masked by the in-plane magnetization of the fourth magnetic layer 8 and cannot be read. This eliminates signal mixing from adjacent bits, which causes noise and reduces reproduction resolution. In this way, since reading can be performed in which only a region smaller than the spot diameter of the laser beam is involved in reproduction, it is possible to reproduce a recording bit smaller than before and improve the recording density.

As described above, in the magneto-optical disk of each of the above embodiments, while the recording magnetic field H _W is applied after the initialization, the high-level I and low-level II intensity-modulated laser light is irradiated. By doing so, it is possible to rewrite information by overwriting, that is, perform light modulation overwriting.

Moreover, in the above, the second magnetic layer 4 provided between the first magnetic layer 3 and the third magnetic layer 5 exhibits substantially in-plane magnetization at room temperature, and the first and third magnetic layers are formed. Since the Curie point is lower than that of the layers 3.5, the initialization magnetic field H _init can be reduced, and further, the power of the laser beam at the time of recording or the recording magnetic field H can be reduced. _W can be reduced. In addition, the third magnetic layer 5 and the first
Since the magnetic coupling between the second magnetic layers 3 and 4 is surely suppressed, it is possible to perform stable light modulation overwrite even if the temperature rise during irradiation of the high-level I laser beam varies. Has become.

Furthermore, in each of the above embodiments, the third magnetic layer 5 is used.
_{Has a} compensation temperature T _comp3 between room temperature and the Curie point T _c3 , the initialization magnetic field H _init and the recording magnetic field H _W can be set in the same direction. Therefore, for example, it is possible to provide the two magnetic field generating units in the vicinity of each other in the apparatus, or to set the initialization magnetic field H _init and the recording magnetic field H _W by a combination of the magnetic fields generated by the two magnetic field generating units. Therefore, it is possible to reduce the size of the device and save power.

The above embodiments are not intended to limit the present invention, and various modifications can be made within the scope of the present invention. For example, the materials and compositions of the first to fourth magnetic layers 3 to 5 and 8 can be other than those listed in the above embodiments. For example, as the material of the first to third magnetic layers 3 to 5, at least one selected from Gd, Tb, Dy, Ho and Nd
The same effect can be obtained by using an alloy composed of one kind of rare earth metal and at least one kind of transition metal selected from Fe and Co.

In addition to the above materials, Cr, V, N
At least 1 of b, Mn, Be, Ni, Ti, Pt, Rh, Cu
Addition of a kind of element improves the environment resistance of the first to third magnetic layers 3 to 5 themselves. That is, the deterioration of the characteristics due to the oxidation of the first and third magnetic layers 3 and 5 due to the invasion of water and oxygen is reduced, and the magneto-optical disk having excellent long-term reliability can be provided.

The Curie point T _C1 of the first magnetic layer 3 is 1
When the temperature is lower than 00 ° C., the C / N is lower than 45 dB which is the minimum required for digital recording / reproducing. If the Curie point T _C1 exceeds 250 ° C., the recording sensitivity will be poor. Therefore, the Curie point T _C1 of the first magnetic layer 3 is 100.
A temperature of ~ 250 ° C is suitable. Further, when the coercive force H _{C1 of} the first magnetic layer 3 at room temperature is less than 400 kA / m, there is a possibility that the initialization magnetic field H _init partially initializes the magnetic field. Therefore, the coercive force H _C1 of the first magnetic layer 3 at room temperature is 400 kA /
m or more is suitable.

On the other hand, when the temperature indicating the perpendicular magnetization of the second magnetic layer 4 is less than 80 ° C., the temperature is between room temperature and the temperature when the laser beam of the level III reproducing laser power P _R is irradiated. The transfer of magnetization from the third magnetic layer 5 to the second magnetic layer 4 and the transfer of magnetization from the second magnetic layer 4 to the first magnetic layer 3 may occur. In this case, not only the third magnetic layer 5 but also the first magnetic layer 3 is initialized by the initializing magnetic field H _init, so that the information recorded in the first magnetic layer 3 is not retained. Therefore, it is appropriate that the temperature at which the second magnetic layer 4 exhibits perpendicular magnetization is 80 ° C. or higher.

The Curie point T _C3 of the third magnetic layer 5 is 1
If the temperature is lower than 50 ° C., the difference between the low-level II laser power P _L and the reproduction laser power P _R becomes small, so that the optical modulation overwrite is not properly performed. On the other hand, Curie point T
_{If C3} exceeds 400 ° C, the recording sensitivity becomes poor. Therefore, the Curie point T _C3 of the third magnetic layer 5 is 150 to 40.
0 ° C is suitable.

Further, the coercive force H _{C3 of} the third magnetic layer 5 at room temperature is
Of more than 240 kA / m is not preferable because the initializing magnetic field H _init generator becomes large. Therefore, the coercive force H _C3 of the third magnetic layer 5 at room temperature is suitably 240 kA / m or less.

On the other hand, the film thickness of the first to third magnetic layers 3 to 5 is
It is determined in consideration of the materials and compositions of the first to third magnetic layers 3 to 5. The film thickness of the first magnetic layer 3 is 20 nm or more, more preferably 30 nm or more. If the thickness is too thick, the information in the third magnetic layer 5 will not be transferred.
It is preferably 0 nm or less. The thickness of the second magnetic layer 4 is 5n
m or more, more preferably 10 to 50 nm, and if it is too thick, information of the third magnetic layer 5 will not be transferred, so 100 nm or less is preferable. The thickness of the third magnetic layer 5 is 20 nm or more, more preferably 30 to 100 nm, and if it is too thick, the recording sensitivity deteriorates.
It is preferably 0 nm or less.

In each of the above embodiments, the substrate 1
Although a normal plate glass was used as the above, other than this, chemically strengthened glass, a so-called 2P layer-attached glass substrate having an ultraviolet curable resin layer formed on these glass substrates,
Polycarbonate (PC), polymethylmethacrylate (PMMA), amorphous polyolefin (AP
It is possible to use a substrate 1 made of O), polystyrene (PS), polychlorinated biphenyl (PVC), epoxy, or the like.

On the other hand, the film thickness of AlN as the transparent dielectric layer 2 is not limited to 80 nm in the above embodiments. The thickness of the transparent dielectric layer 2 increases the polar Kerr rotation angle from the first magnetic layer 3 or the fourth magnetic layer 8 by utilizing the light interference effect when reproducing the magneto-optical disk.
It is determined in consideration of so-called car effect enhancement. In order to maximize the C / N during reproduction, it is necessary to increase the polar Kerr rotation angle. Therefore, the film thickness of the transparent dielectric layer 2 is set so that the polar Kerr rotation angle is the largest. To be done.

This polar Kerr rotation angle changes depending on the wavelength of the reproducing light and the refractive index of the transparent dielectric layer 2. Since the refractive index of AlN in each of the above examples is 2.0, the wavelength of the reproduction light is 7
When the thickness is 80 nm, the AlN film thickness of the transparent dielectric layer 2 is 30 to
When it is about 120 nm, the effect of Kerr effect enhancement becomes large. In addition, preferably, the transparent dielectric layer 2
The film thickness of AlN is 70 to 100 nm, and in this range, the polar Kerr rotation angle becomes almost maximum.

When the wavelength of the reproduction light is 400 nm,
Half the film thickness of the transparent dielectric layer 2 (= 400/780)
You can do it. Further, when the refractive index of the transparent dielectric layer 2 is different from the above due to the difference in material or the manufacturing method, the value obtained by multiplying the refractive index and the film thickness (optical path length) becomes the same,
The thickness of the transparent dielectric layer 2 may be set.

The larger the refractive index of the transparent dielectric layer 2, the smaller the film thickness. Also, the greater the refractive index, the greater the enhancement effect of the polar Kerr rotation angle. AlN
Changes its refractive index by changing the ratio of Ar to N ₂ which is the sputtering gas during sputtering, the gas pressure, etc.
It is a material having a relatively large refractive index of about 1.8 to 2.1 and is suitable as a material for the transparent dielectric layer 2.

In addition to the Kerr effect enhancement described above, the transparent dielectric layer 2 is used together with the protective layer 6 in the first to the first layers.
Third magnetic layers 3-5 or first to fourth magnetic layers 3-5
It has a role of preventing the rare earth metal-transition metal alloy magnetic layer of 8 from being oxidized.

The magnetic film made of a rare earth metal-transition metal alloy is very easily oxidized, and particularly the rare earth metal is easily oxidized. For this reason, if the invasion of oxygen and moisture from the outside is not prevented as much as possible, the characteristics will be significantly deteriorated by oxidation.

Therefore, in each of the above embodiments, the first to third
Magnetic layers 3-5, or first to fourth magnetic layers 3-5.
Both sides of the are sandwiched by AlN. AlN
Is a nitride film that does not contain oxygen as its component, and is a material with extremely excellent moisture resistance. Furthermore, AlN can perform reactive DC (direct current) sputtering by introducing N ₂ gas or a mixed gas of Ar and N ₂ by using an Al target, and RF (high frequency) sputtering can be performed. Compared with this, it is also advantageous in that the film forming rate is high.

As a material for the transparent dielectric layer 2 other than AlN,
SiN, AlSiN, AlTaN, SiAlON, TiN, TiON, B
N, ZnS, TiO ₂ , BaTiO ₃ , SrTiO _{3 and the} like are suitable. Of these, especially SiN, AlSiN, AlTaN, TiN, BN, ZnS
Can provide a magneto-optical disk which does not contain oxygen as its component and has excellent moisture resistance.

On the other hand, the film thickness of AlN of the protective layer 6 was set to 80 nm in each of the above-mentioned embodiments, but it is not limited to this. The thickness range of the protective layer 6 is 1 to 200 nm.
Is preferred.

In each of the above embodiments, the total thickness of the first to third magnetic layers 3 to 5 or the first to fourth magnetic layers 3 to 5.8 is 100 nm or more. In this case, the light incident from the optical pickup hardly passes through the magnetic layer. Therefore, the thickness of the protective layer 6 is not particularly limited as long as it is necessary to prevent oxidation of the magnetic layer for a long period of time. If the material has a low antioxidation ability, the film thickness may be increased, and if it is high, the film thickness may be decreased.

The thermal conductivity of the protective layer 6 affects the recording sensitivity characteristics of the magneto-optical disk together with the transparent dielectric layer 2. The recording sensitivity characteristic means how much laser power is required for recording or erasing. Most of the light incident on the magneto-optical disk passes through the transparent dielectric layer 2 and is the absorption film of the first to third magnetic layers 3 to 5 or the first to fourth magnetic layers 3 to 5. It is absorbed by 8 and turns into heat. At this time, the heat of the first to third magnetic layers 3 to 5 or the first to fourth magnetic layers 3 to 5.8 is transferred to the transparent dielectric layer 2 and the protective layer 6 by heat conduction. Therefore, the thermal conductivity and heat capacity (specific heat) of the transparent dielectric layer 2 and the protective layer 6 affect the recording sensitivity.

This means that the recording sensitivity of the magneto-optical disk can be controlled to some extent by the film thickness of the protective layer 6, and for the purpose of, for example, increasing the recording sensitivity (recording and erasing can be performed with low laser power). For example, the thickness of the protective layer 6 may be reduced. Usually, in order to prolong the life of the laser, it is advantageous that the recording sensitivity is high to some extent, and the protective layer 6 is preferably thin.

AlN is also suitable in this sense and has excellent moisture resistance. Therefore, when it is used as the protective layer 6, the film thickness can be reduced and a magneto-optical disk having high recording sensitivity can be provided.

In each of the above embodiments, the protective layer 6 is made of the same AlN as the transparent dielectric layer 2 to provide a magneto-optical disk having excellent moisture resistance, and the protective layer 6 and the transparent dielectric layer 2 are made of the same material. By forming with, the productivity is also improved.

In addition to AlN, the protective layer 6 may be made of SiN, AlSiN, AlTaN, Si, which is used as the material of the transparent dielectric layer 2 in consideration of the above-mentioned objects and effects.
AlON, TiN, TiON, BN, ZnS, TiO ₂ , BaTiO ₃ , Sr
TiO ₃ is preferred. Among them, especially SiN, AlSiN, AlTa
N, TiN, BN, and ZnS do not contain oxygen as a component, and can provide a magneto-optical disk having excellent moisture resistance.

The magneto-optical disk exemplified in each of the above embodiments is generally called a single-sided type. When the transparent dielectric layer 2, the first to third magnetic layers 3 to 5 (or the first to fourth magnetic layers 3 to 5 · 8), and the thin film portion of the protective layer 6 are collectively referred to as a recording medium layer, The single-sided type magneto-optical disk has a structure of a substrate 1, a recording medium layer, and an overcoat layer 7. On the other hand, a magneto-optical disc in which two recording medium layers are formed on the substrate 1 and adhered by an adhesive layer so that the recording medium layers face each other is called a double-sided type.

In this case, the material of the adhesive layer is particularly preferably a polyurethane acrylate adhesive. This adhesive is a combination of three types of curing functions of ultraviolet rays, heat and anaerobic, and the curing of the portion of the recording medium layer where ultraviolet rays do not pass is cured by the heat and anaerobic curing functions. It is possible to provide a double-sided type magneto-optical disk which has an advantage that it has extremely high humidity resistance and is extremely excellent in long-term stability.

Since the single-sided type requires only half the thickness of the element as compared with the double-sided type, it is advantageous for a recording / reproducing apparatus that requires miniaturization, for example. Since the double-sided type is capable of double-sided reproduction, it is advantageous for a recording / reproducing apparatus that requires a large capacity, for example.

[0102]

As described above, the magneto-optical recording medium of the present invention comprises a recording layer exhibiting perpendicular magnetization from room temperature to the Curie point,
It exhibits perpendicular magnetization from room temperature to the Curie point, has a coercive force at room temperature smaller than that of the recording layer, and has an in-plane magnetization on the room temperature side between the auxiliary recording layer and the Curie point higher than that of the recording layer. The recording layer has a characteristic that it exhibits perpendicular magnetization in a temperature region where the coercive force is smaller than that of the recording auxiliary layer, and an intermediate layer having a Curie point lower than that of the recording layer is provided.

As a result, as in the conventional case, after initialization is performed, while applying the recording magnetic field, the recording layer is irradiated with the laser light intensity-modulated to the high level and the low level, whereby new information is recorded on the recording layer. Can write. At this time, since the Curie point of the intermediate layer is lower than the Curie points of the recording layer and the recording auxiliary layer, even if the temperature rise during high-level laser beam irradiation varies, the intermediate layer and the recording auxiliary layer should be exchanged. The binding due to force is reliably suppressed, which allows
It is possible to stably perform the light modulation overwrite.

Since it is not necessary to set the Curie point of the intermediate layer between the recording layer and the recording auxiliary layer, it is possible to configure the recording layer with a Curie point higher than that of the conventional one. As a result, the Kerr rotation angle at the time of laser light irradiation at the time of reproduction can be made larger, so that there is an effect that the reproduction signal characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a graph showing temperature dependence of coercive forces of first to third magnetic layers in a magneto-optical recording medium according to an example of the present invention.

FIG. 2 is a schematic sectional view showing a schematic configuration of the magneto-optical recording medium.

FIG. 3 is an explanatory diagram showing a recording process in the magneto-optical recording medium.

FIG. 4 is an explanatory diagram showing the intensity of laser light with which the magneto-optical recording medium is irradiated.

FIG. 5 is an explanatory diagram showing changes in a magnetization state during a recording operation on the magneto-optical recording medium.

FIG. 6 is a schematic sectional view showing a schematic configuration of a magneto-optical recording medium in another example of the present invention.

FIG. 7 is an explanatory diagram showing a configuration and a recording process of a conventional magneto-optical recording medium.

8 is a graph showing the temperature dependence of the coercive force of each magnetic layer in the magneto-optical recording medium of FIG.

[Explanation of symbols]

 1 Substrate 2 Dielectric Layer 3 First Magnetic Layer (Recording Layer) 4 Second Magnetic Layer (Intermediate Layer) 5 Third Magnetic Layer (Recording Auxiliary Layer) 6 Protective Layer 7 Overcoat Layer 8 Fourth Magnetic Layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Junji Hirokane 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (72) Inventor Akira Takahashi 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Osaka Incorporated (72) Inventor Kenji Ota 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Prefecture

Claims (1)

[Claims] 1. A recording layer exhibiting perpendicular magnetization from room temperature to the Curie point, a perpendicular magnetization from room temperature to the Curie point, a coercive force at room temperature smaller than that of the recording layer, and a Curie point higher than that of the recording layer. Between the recording auxiliary layer and the recording auxiliary layer, in-plane magnetization is exhibited at the room temperature side, and the recording layer has a characteristic that it exhibits perpendicular magnetization in a temperature region where the coercive force is smaller than that of the recording auxiliary layer, and is lower than the recording layer. A magneto-optical recording medium comprising an intermediate layer having a Curie point.