JP2505602B2 - Magneto-optical record carrier and method of manufacturing magneto-optical record carrier - Google Patents

Description

The present invention relates to a magneto-optical record carrier having an optical modulation overwrite function capable of directly writing new information on old information, and production for producing this magneto-optical record carrier. It is about the method.

The magneto-optical record carrier is composed of a ferrimagnetic transition metal (TM) -rare earth metal (RE) alloy magnetic thin film except in special cases. First, the properties of this TM-RE alloy magnetic thin film of ferry magnetism will be briefly described. The TM-RE alloy magnetic thin film has magnetization derived from TM spin (TM sublattice magnetization) and magnetization derived from RE spin (RE sublattice magnetization). The TM sublattice magnetizations are coupled so as to be parallel to each other, and the RE sublattice magnetizations are also coupled to be parallel to each other. On the other hand, the TM sublattice magnetization and the RE sublattice magnetization are coupled antiparallel to each other. Therefore, in one TM-RE alloy magnetic thin film, the TM sublattice magnetization oriented in one direction and the RE antiparallel to it
Sublattice magnetization coexists. The magnitude of the magnetization of the entire layer is given by the difference between the TM sublattice magnetization and the RE sublattice magnetization, and its direction is TM
When the sublattice magnetization is greater than the RE sublattice magnetization, it is in the same direction as the TM sublattice magnetization and the layer is said to be "TM rich". On the other hand, when the RE sublattice magnetization is larger, the magnetization direction of the entire layer is the same as the RE sublattice magnetization, and the layer is called "RE rich". Especially when the TM sub-lattice magnetization and the RE sub-lattice magnetization have the same magnitude, that is, when the magnitude of the magnetization of the entire layer becomes zero, the composition of that layer is called the “compensation composition. The RE sublattice magnetization also decreases with temperature, but the degree of decrease is greater in the RE sublattice magnetization, so the layer as a whole transitions from RE rich to TM rich with temperature.
The temperature at which the composition changes to rich, that is, the temperature at which the composition becomes the compensation, is called the compensation temperature. When the layers are stacked in layers, a force called exchange coupling force acts between the layers. This force acts to make adjacent TM sublattice magnetizations parallel. Furthermore, during reproduction, the rotation of the polarization angle of the reflected light is used due to the magneto-optical Kerr effect, but this rotation direction is determined by the TM sublattice magnetization direction, not the magnetization direction of the entire layer. Therefore, the binary information depends on whether the TM sublattice magnetization of the read layer is from top to bottom. However, in the following, for the sake of explanation, the recording that occurs with strong power will be described as 2
The value information is "1", and the recording generated with weak power is the value information "0".

[Conventional technology]

 Next, a specific conventional technique will be described.

FIGS. 90 (a), (b) and (c) are conventional examples shown in, for example, a publication (Proceedings of the 34th Joint Lecture on Applied Physics, Spring 1987, 28P-ZL-3). FIG. 3 is a perspective view showing a configuration of a main part of an optical recording / reproducing apparatus, a cross-sectional view of a main part showing an optical recording / reproducing state of a record carrier, and a characteristic diagram showing a laser power change for recording in a region of the record carrier. In the figure, (1) is a magneto-optical record carrier, (2) is a substrate made of glass or plastic, (3) is a first magnetic layer, (4) is a second magnetic layer, and the record carrier (1) is It is composed of a substrate (2), a first magnetic layer (3) and a second magnetic layer (4), and an exchange coupling force acts between the first magnetic layer (3) and the second magnetic layer (4). This exchange coupling force is due to both magnetic layers (5),
It works to make the TM sublattice magnetization directions of (4) equal. (5) is an objective lens that irradiates the information carrier (1) with a laser beam, (6) is a focused spot converged by the objective lens (5), and (7) is the first magnetic layer (3)
In the information recorded in FIG. 90, the TM sublattice magnetization direction of the first magnetic layer (3) is shown in FIG. 90 (b), and the upward portion is indicated as "0" in the binarized data. There is. The arrow in each magnetic layer indicates the direction of TM sublattice magnetization. (9) is an initializing magnet for generating a magnetic field of about 5000e for initial magnetization of the TM sublattice of the second magnetic layer (4), (8) is an information lens (1) sandwiched between the objective lens (5) ) Is a bias magnet which is provided at a position facing the magnetic field of 200 to 6000e. Further, in FIG. 90 (c), R ₁ is the laser power for recording the information 1, R ₀ is the laser power for recording the information 0, the vertical axis represents the laser power, and the horizontal axis represents the area. In FIG. 90 (a), the left side shows the new data (DM) and the right side shows the old data (DO) with respect to the alternate long and short dash line.

Next, the operation will be described. The record carrier (1) is rotationally driven in the direction of arrow a in FIGS. 90 (a) and 90 (b) by a holding drive mechanism (not shown). The first magnetic layer (3) has the same properties as the recording layer of an information carrier using a general magneto-optical disk which sounds, for example, from Tb ₂₁ Fe ₇₉ , and also acts as a recording layer and a reading layer here.
The second magnetic layer (4) is called an auxiliary layer made of, for example, Gd ₂₄ Tb ₃ Fe ₇₃ , and is provided to exhibit overwrite performance, that is, performance of overwriting old data with new data in real time. . Here, the first magnetic layer (3)
The characteristics of the second magnetic layer (4) and the Curie temperature are Tc ₁ and Tc ₂ , and the coercive force near room temperature is H, respectively.
c ₁ , Hc ₂ , and the exchange coupling forces at room temperature are Hw ₁ and Hw ₂ respectively.
Then, the following relation holds.

Tc ₁ <Tc ₂ Hc ₁ −Hw ₁ > Hc ₂ + Hw ₂ Here, first, a case of reproducing information recorded in the recording layer, that is, the first magnetic layer (3) will be described. As shown in FIG. 90 (b), the first magnetic layer (3) is magnetized upward or downward in the film thickness direction in the direction corresponding to the binary code, that is, "0" or "1". . At the time of reproduction, the focused spot (6) is irradiated onto the first magnetic layer (3), and the magnetization direction of the first magnetic layer (3) at the irradiation portion of the focused spot (6) is well known than before. The information is detected from the information carrier (1) by exchanging optical information by the light power-effect. At this time, the laser intensity applied to the record carrier (1) is the intensity corresponding to the intensity A shown in the characteristic diagram in FIG. 91 showing the temperature change of the magnetic film in the spot due to the laser beam power. The maximum rising temperatures of the first magnetic layer (3) and the second magnetic layer (4) in the irradiated portion of the light spot (6) are the same as those of the first magnetic layer (3) and the second magnetic layer (4).
The Curie temperatures Tc ₁ and Tc ₂ of the magnetic layer (4) are not reached.
Therefore, the irradiation of the focused spot does not erase the magnetization direction, that is, the recorded information.

Next, the overwrite operation will be described. The initialization magnet (9) in FIG. 90 generates a magnetic field of Hini in the direction of directing the TM sublattice magnetization of the second layer in the direction of arrow b (upward) shown in the figure. This magnetic field Hini has a relationship of Hc ₁ −Hw ₁ >Hini> Hc ₂ + Hw ₂ with respect to the coercive force and exchange coupling force of the first magnetic layer (3) and the second magnetic layer (4). There is. As a result, as shown in FIG. 90 (b), when the information carrier (1) rotates in the direction of arrow a, the TM sublattice magnetization direction of the second magnetic layer (4) passing through the initialization magnet (9) part. Are all magnetized upward regardless of the TM sublattice magnetization direction of the first magnetic layer (3). At this time, the TM sublattice magnetization direction of the first magnetic layer (3) is not affected near room temperature by the magnetic field of the initializing magnet or the exchange coupling force acting from the second magnetic layer (4), and remains as it is. Hold the state of.

When information "0" is recorded, that is, in the first magnetic layer (3)
The laser beam intensity when the TM sublattice magnetization direction is upward corresponds to the intensity B in FIG. At this time, the temperature inside the focused spot (6) rises and exceeds the Curie temperature Tc ₁ of the first magnetic layer (3), but does not reach the Curie temperature Tc ₂ of the second magnetic layer (4). . As a result, the magnetization of the first magnetic layer (3) disappears, but the second magnetic layer (4) disappears.
The TM sub-lattice magnetization direction of remains in the upward direction magnetized by the initialization magnet (8). Then, when the disk rotates and the focused spot (6) is not irradiated and the temperature of the first magnetic layer (3) falls below its Curie temperature Tc ₁ , the TM sublattice of the second magnetic layer (4) is reached. The magnetization direction is transferred to the first magnetic layer (3) by the exchange coupling force, and the first magnetic layer (3)
The TM sublattice magnetization direction of is the upward direction, that is, the direction corresponding to the information “0”.

When recording information "1", that is, in the first magnetic layer (3)
The laser beam intensity when the TM sublattice magnetization direction is downward corresponds to the intensity C in FIG. At this time, the temperature inside the focused spot (6) rises and exceeds not only the Curie temperature Tc _{1 of} the first magnetic layer (3) but also the Curie temperature Tc _{2 of} the second magnetic layer (4). As a result, both the first magnetic layer (3) and the second magnetic layer (4) have a focused spot (6).
The magnetization inside disappears. Then, the disk rotates and the focused spot (6) is not irradiated, and the second magnetic layer (4)
At the stage where the temperature of drops below its Curie temperature Tc ₂ ,
The weak magnetic field applied by the bias magnet (8) so as to direct the TM sublattice magnetization of the second magnetic layer in the direction of arrow C (downward) in FIG. 90 causes the TM sublattice of the second magnetic layer (4). The magnetization direction is downward. Furthermore, at the stage where the temperature of the first magnetic layer (3) falls below its Curie temperature Tc ₁ , the TM sublattice magnetization direction of the second magnetic layer (4) becomes the first due to the exchange coupling force.
After being transferred to the magnetic layer (3), the magnetization direction of the first magnetic layer (3) is downward, that is, the direction corresponding to the information "1".

By the above operation, at the time of overwriting, the intensity of the laser beam is modulated into the intensity B and the intensity C in FIG. 91 according to the binary code “0” and “1” of the information, and the old data is obtained. Overwriting is possible in real time on top. Since the conventional magneto-optical record carrier is configured as described above, it is necessary to use an initialization magnet having a large magnetic field, which complicates the entire structure of the optical disk recording / reproducing apparatus and increases the size of the apparatus. There was such a problem.

Further, FIGS. 92 and 93 are cross-sectional views of a magneto-optical record carrier and a description of a magnetization process relating to a method of performing overwriting only by the intensity of a laser described in JP-A-63-268103. It is a figure. In the figure,
(100) is the first magnetic layer, (200) is the second magnetic layer, (300)
Is a third magnetic layer, (400) is a fourth magnetic layer, (500) is a light transmissive substrate, (600) is a dielectric film, (700) is a protective film, (90)
0) is an interface magnetic wall, (101) is a magneto-optical record carrier, and Hex is an arrow indicating the bias magnetic field application direction.

This conventional record carrier has four magnetic layers for the purpose of improving the above-mentioned problem of the overwrite method using two magnetic layers (requiring a large initializing magnetic field). The first magnetic layer (100) and the second magnetic layer (200) are almost the same as the first magnetic layer (3) and the second magnetic layer (4) of the overwrite type by the two magnetic layers described above. It has a structure and functions. The fourth magnetic layer (400) is the second magnetic layer (200)
On top of which there is a corresponding third magnetic layer (300) of the resetting magnet (9) of FIG. 90. As can be seen from FIG. 93, the third magnetic layer has its TM
The sub-lattice magnetization does not reverse. The Curie temperature of each layer is selected as follows.

Tc ₁ <Tc ₂ Tc ₄ <Tc ₂ , Tc ₃ Tc ₄ <Tc _{1 In} this example, the Curie temperature as shown in the following table,
Materials etc. are selected.

Next, the operation will be described. Since the reproducing operation is completely the same as the reproducing operation of the overwrite method using the two magnetic layers described above, the description thereof is omitted, and the overwrite recording operation will be described with reference to FIG.

The arrow shown in each layer in FIG. 93 indicates the direction of the TM sublattice magnetization of each layer. At room temperature (T _R ), the magnetization state of each magnetic layer is in state A or state C. When the record carrier (101) is irradiated with the laser power of power B shown in FIG. 91, the average temperature of the record carrier (101) rises to T1. At this time, the magnetization of the first magnetic layer (100) disappears (state E). Then, in the process of lowering the temperature, the TM sublattice magnetization of the first magnetic layer (100) is aligned with the TM sublattice magnetization direction of the second magnetic layer (200) by the exchange coupling force and becomes upward. When the temperature drops to room temperature, the state A is entered and "0" is recorded.

When the record carrier (101) is irradiated with the laser power of the power C shown in FIG. 91, the average temperature of the record carrier (101) rises to T2. At this time, the magnetization of the first magnetic layer (100) disappears, and the TM sublattice magnetization direction of the second magnetic layer (200) is inverted downward by the bias magnetic field Hex (state F). At this time, the exchange force from the third magnetic layer (300) is the second.
It works to make the TM sublattice magnetization of the magnetic layer upward,
(Because the record carrier temperature exceeds the Curie temperature Tc ₃ )
This exchange force is extremely weakened by the presence of the fourth magnetic layer (400) that does not function as a magnetic substance, and as a result, the TM sublattice magnetization of the second magnetic layer (200) can be made downward even with a small bias magnetic field Hex. . When the temperature falls below T1, the first
The TM sublattice magnetization of the magnetic layer (100) is aligned in the TM sublattice magnetization direction of the second magnetic layer (200) due to the exchange coupling force, and faces downward (state G). When the temperature further lowers, the fourth magnetic layer (400) regains its function as a magnetic body, so that the exchange coupling force from the third magnetic layer acts on the second magnetic layer (200) and the second magnetic layer (200). The TM sublattice magnetization direction of is
State C is reached. In this way, "1" is recorded.

The inventor of the present invention first developed a magneto-optical record carrier having three overwritable magnetic layers which does not require an initializing magnet, and based on this, a magneto-optical record carrier having four magnetic layers of the present invention was used as a base. The invention of the record carrier was reached. Therefore, in order to facilitate understanding of the present invention, a three-layer magneto-optical record carrier will be described as a pre-stage of the present invention.

This three-layer magneto-optical record carrier was provided with a third magnetic layer corresponding to the initialization magnet (9) in FIG. 90,
Since the Curie temperature of the third magnetic layer is set higher than the Curie temperatures of the first magnetic layer and the second magnetic layer, the magnetization direction of the third magnetic layer does not reverse during the recording operation, and therefore, the Curie temperature of many times It is characterized by high reliability against repeated recording.

FIG. 94 illustrates a three-layer film structure and overwrite recording as an overwritable magneto-optical recording medium that does not require an initializing magnet.

In FIG. 94, the components with the same symbols as in FIG.
It is similar to Figure 90. (24) is the first magnetic layer, (25) is the second magnetic layer
The magnetic layer, (26) is the third magnetic layer. First magnetic layer (2
4), the second magnetic layer (25), and the third magnetic layer (26) are all transition metal-rare earth alloys, and all layers are TM rich. The first magnetic layer (24) and the second magnetic layer (25) are connected by an exchange coupling force, and this exchange coupling force works so as to make the TM sublattice magnetization directions of both layers equal. The second magnetic layer (25) and the third magnetic layer (26) are also bound together by the exchange coupling force.

The magnetization of the third magnetic layer (26) has been initialized beforehand by an electromagnet or the like so as to face upward in the figure.

The first magnetic layer (24) is a recording layer for holding sublattice magnetization (here, TM sublattice magnetization) representing information "0" and "1". The second magnetic layer (25) and the third magnetic layer (26) are provided to exert overwrite performance. Especially the second
The magnetic layer (25) is called an auxiliary layer, and this second magnetic layer (25)
The sublattice magnetization direction of is transferred to the first magnetic layer (24) (that is, the sublattice magnetization direction of the first magnetic layer (24) is aligned with the sublattice magnetization direction of the second magnetic layer). Thus, the first magnetic layer (24) can be oriented in a desired magnetization direction. The third magnetic layer (26) is an initialization layer. This third
By utilizing the fact that the sub-lattice magnetization direction of the magnetic layer (26) is transferred to the second magnetic layer (25), the second magnetic layer (2
It is possible to align the sublattice magnetization direction of 6) in a fixed direction.

Next, specific characteristics of the first magnetic layer (24), the second magnetic layer (25), and the third magnetic layer (26) will be described.

When the Curie temperatures of the respective layers are Tc ₁ , Tc ₂ and Tc ₃ , respectively, Tc ₁ <Tc ₂ <Tc ₃ . Since the Curie temperature Tc ₃ of the third magnetic layer is higher than the Curie temperatures of the other magnetic layers, the magnetization direction is stable and does not reverse during the recording operation. Since all three layers are TM rich here, it is necessary to satisfy the following conditions at room temperature.

At room temperature, the coercive force of the first magnetic layer and the third magnetic layer is larger than the exchange force received from the adjacent layers,
The magnetization does not reverse. This can be expressed by the following formula.

Hc ₁ −Hw ₁ (2)> 0… (1) Hc ₃ −Hb−Hw ₃ (2)> 0… (3) There is a temperature that satisfies the following conditions from room temperature to Tc ₁ , and this temperature In the third
The exchange coupling force exerted on the second magnetic layer by the magnetic layer becomes larger, and the magnetization direction of the second magnetic layer is aligned with the magnetization direction of the third magnetic layer and initialized.

Hc ₂ + Hw ₂ (1) −Hw ₂ (3) <0 (2) where Hc _i (j): coercive force of i-th magnetic layer Hw _i (j): exchange acting between j-th layer and i-th layer Shift amount of reversal magnetic field of the i-th layer due to coupling force Hb: magnetic field applied at the time of recording by the bias magnet (18) In this magneto-optical recording medium of three-layer film, the third magnetic layer is the second magnetic layer.
Since the exchange coupling force Hw ₂ (3) exerted on the magnetic layer is very large, the magnetic field of the bias magnet is erased by raising the temperature of the second magnetic layer to the Curie temperature or more during overwriting to erase the magnetization.
There is a problem that a large magnetic field Hb is required to overcome Hw ₂ (3) when magnetization is given in the direction of newly recorded information by Hb.

In order to solve this problem, the exchange coupling force from the third magnetic layer to the second magnetic layer is made to reach from room temperature to a certain temperature, but when the temperature is raised above a certain temperature, the exchange coupling force is weakened. The coupling force control layer may be provided between the second magnetic layer and the third magnetic layer. The four-layer magnetic film magneto-optical recording medium of the present invention is based on such an idea.

[Problems to be solved by the invention]

As described above, the magneto-optical record carrier having the three magnetic layers requires the initializing magnet having a large magnetic field, but needs the large bias magnet to record information in the second magnetic layer. there were.

According to the method disclosed in Japanese Patent Laid-Open No. 63-268103, an initializing magnet having a large magnetic field is unnecessary, and the device can be downsized. However, when using this conventional magneto-optical record carrier,
It is impossible to realize an overwrite method with sufficient reliability for repeated recording. With this method, overwrite recording may be successful the first few times,
Overwriting becomes partially impossible during repeated recording on the carrier. This is because the Curie temperature Tc ₃ of the third magnetic layer (300) is low, and the TM sublattice magnetization of the third magnetic layer (300) is partially reversed due to the temperature increase during recording. When recording is further repeated, the area where overwriting is impossible gradually increases, and eventually the entire carrier is covered. Generally, when it is used as an external storage device of a computer, repetitive recording of 1,000,000 times or more is required, but it is completely impossible to satisfy this requirement with the conventional overwrite method.

The present invention has been made to solve the above problems, and provides a magneto-optical record carrier that can be easily overwritten without the need for an initializing magnet and has sufficient reliability for repetitive recording. The purpose is.
A further object is to obtain a method for manufacturing such a magneto-optical record carrier.

[Means for solving the problem]

According to a first aspect of the present invention, a first magnetic layer having perpendicular magnetic anisotropy, a second magnetic layer provided on the first magnetic layer and coupled to the first magnetic layer by exchange force, and a second magnetic layer are provided. A third magnetic layer provided and coupled to the second magnetic layer by exchange force, and a fourth magnetic layer provided on the third magnetic layer and coupled to the third magnetic layer by exchange force, Tc ₄ > Tc ₂ > Tc ₂ , Tc ₄ > Tc ₂ > Tc ₃ , Tc ₄ > 300 ° C. However, Tc ₁ : Curie temperature of the first magnetic layer Tc ₂ : Curie temperature of the second magnetic layer Tc ₃ : Curie of the third magnetic layer Temperature Tc ₄ : The Curie temperature of the fourth magnetic layer is satisfied, Hc ₁ > Hw ₁ (2) and Hc ₄ > Hw ₄ (3) are satisfied at room temperature, and the lower of room temperature Tc ₁ and Tc ₃ Up to the temperature, Hc ₂ <Hw ₂ (3) −Hw ₂ (1) where Hc ₁ : Coercive force of the first magnetic layer Hc ₂ : Coercive force of the second magnetic layer Hc ₄ : The fourth magnetic layer coercivity Hw _i (j) A magneto-optical record carrier, wherein the temperature that satisfies the shift amount of the switching field of the i-magnetic layer by exchange coupling force acting on the j-th magnetic layer and the i-magnetic interlayer is present.

The invention of claim 2 is the same as that of claim 1, except that Tc ₁ and T
Hc ₃ <Hw ₃ (4) -Hw during the lower temperature of c _{3
2 A} magneto-optical record carrier having a temperature satisfying (2). However, Hc ₃ is the coercive force of the third magnetic layer.

A third aspect of the present invention is the magneto-optical record carrier according to the first aspect, which is provided with an interface control layer for controlling the exchange force at the interface between the magnetic layers.

[Action]

The fourth magnetic layer of the magneto-optical record carrier of the present invention corresponds to the initializing magnet of FIG. 90, and the magnetization direction of the second magnetic layer after overwriting is changed by the exchange force. By aligning with the same direction as the above, the magnetization direction of the second magnetic layer is initialized, and functions to prepare for the next overwrite recording.

Further, since the Curie temperature Tc ₄ of the fourth magnetic layer is higher than the Curie temperatures of the other magnetic layers and higher than 300 ° C., the magnetization direction does not reverse during the temperature rising process of overwrite recording. Therefore, as compared with the prior art shown in FIGS. 92 and 93, the reliability when overwrite recording is repeated many times is significantly improved.

The first magnetic layer is a recording layer for holding sub-lattice magnetization (TM sub-lattice magnetization in the embodiment) representing information "0" and "1". The second magnetic layer and the fourth magnetic layer are provided for overwriting recording. The second magnetic layer is called an auxiliary layer, and the fact that the sublattice magnetization direction of the second magnetic layer is transferred to the first magnetic layer is used to direct the magnetization direction of the first magnetic layer to a desired direction. Record information “0” or “1”. The information "1" or "0" means that the second magnetic layer is magnetized in a desired direction by an external magnetic field after the second magnetic layer is heated to the Curie temperature or higher to eliminate the magnetization, and thus the second magnetic layer is formed. Given. At this time, since the strong exchange coupling force from the fourth magnetic layer (corresponding to the third magnetic layer of the three-layer magneto-optical record carrier) is weakened by the third magnetic layer, the information to be recorded in the second magnetic layer. The external magnetic field magnetized in the direction of is small.
The information provided to the second magnetic layer is then transferred to the first magnetic layer as described above. To prepare for the next overwrite recording, the information temporarily recorded in the second magnetic layer is erased. This is called initialization of the second magnetic layer, and when the temperature is lower than a certain temperature, the third magnetic layer loses its ability to weaken the exchange coupling force of the fourth magnetic layer. Are realized by being aligned in the same direction as the magnetization direction of the fourth magnetic layer. The fourth magnetic layer is an initializing layer that functions like an initializing magnet, and its Curie temperature is higher than the Curie temperatures of other magnetic layers and has a coercive force up to 300 ° C, so even if recording is repeated many times. The sublattice magnetization direction is never reversed.

Since the four-layer magneto-optical record carrier of the present invention is based on the three-layer magneto-optical record carrier, the relations similar to the basic relational expressions (1) to (3) of the three-layer magneto-optical record carrier are the same. The magneto-optical record carrier of the present invention is also valid.

〔Example〕

Example 1. A highly reliable overwritable magneto-optical record carrier that does not require an initialization magnet will be described in detail below. First
(A), (b) and (c) are perspective views of the essential parts of a magneto-optical recording apparatus equipped with the magneto-optical recording carrier of the present invention, a partial sectional view showing the optical recording / reproducing state of the present invention, and FIG. 6 is a characteristic diagram showing a change in beam power of a recording laser, for example, on the magneto-optical record carrier of one embodiment of the present invention. In the figure, (30) is a magneto-optical record carrier of one embodiment of the present invention, and (2)
0) is a laser beam for irradiating the magneto-optical record carrier (30) to record / reproduce information, and (18) is a magneto-optical record carrier by converging the laser beam (20) by the objective lens (5). A magnetic field generator in which a magnetic field applied in the vicinity of a light spot (16) formed on (30) is in a constant direction. FIG. 2 is a sectional view of the essential parts of a magneto-optical record carrier according to an embodiment of the present invention.

(27), (28) and (29) are a second magnetic layer, a third magnetic layer and a fourth magnetic layer, respectively. The record carrier (30) is formed on a glass substrate by a sputtering method or the like. For example, the first magnetic layer: Dy ₂₃ Fe ₆₈ Co ₉ 500 Å [compensation composition (room temperature)] the second magnetic layer: Tb ₂₅ Fe ₆₀ Co ₁₅ 700 Å [RE rich ] Third magnetic layer: Tb ₁₆ Fe ₈₄ 200Å [TM rich] Fourth magnetic layer: Tb ₃₀ Co ₇₀ 700Å [RE rich] Ferrimagnetic material, and adjacent magnetic layers are coupled by exchange force. The fourth magnetic layer (29) has a high Curie temperature and has a coercive force of 700 e or more from room temperature to about 300 ° C., and the fourth magnetic layer (29) operates in response to temperature rise due to irradiation of the laser beam (20). Does not cause magnetization reversal in the range.
The second magnetic layer has a compensation temperature at room temperature or higher. The external magnet (18) generates a magnetic field of 200 to 400e. The TM sublattice magnetization of the fourth magnetic layer (29) is first once uniformly, for example, downward by exposing the recording medium (30) to a magnetic field higher than the magnetization reversal magnetic field of the fourth magnetic layer (29). Keep it magnetized. At this time, the magnetic field generated by the external magnet (18) is generated upward.
The arrow in each magnetic layer indicates the direction of TM sublattice magnetization. When the magnetization direction (7) of the first magnetic layer (24) is upward, it indicates information "1", and when it is downward, it indicates information "0".

The temperature characteristics of each layer and the magnetic characteristics of each layer are as follows.

Tc ₄ > Tc ₂ > Tc ₁ > Tc ₃ (room temperature) (4) where Tc ₁ : Curie temperature of the first magnetic layer Tc ₂ : Curie temperature of the second magnetic layer Tc ₃ : Curie temperature of the third magnetic layer Tc ₄ : Curie temperature of the fourth magnetic layer.

The Curie temperature Tc ₄ of the fourth magnetic layer is higher than the Curie temperatures of the other magnetic layers and has a coercive force up to 300 ° C. Therefore, the magnetization does not reverse due to the temperature rise during overwrite recording.

Hc ₁ > Hw ₂ (2) + Hb (room temperature) (5) where Hc ₁ : Coercive force of the first magnetic layer Hw ₁ (2): Exchange force exerted by the second magnetic layer on the first magnetic layer Hb: External It is the magnetic force of a magnet.

This equation is the same as the equation (1) of the three-layer film under the condition of stabilizing the sub-lattice magnetization direction of the first magnetic layer at room temperature.

The coercive force Hc ₁ of the first magnetic layer is the exchange force H from the second magnetic layer.
Since it is stronger than w ₁ (2) and the external magnetic field Hb, the magnetization direction of the first magnetic layer is stable and does not reverse at room temperature.

Hw ₁ (2) −Hb> Hc ₁ (reference temperature: a certain temperature from room temperature to Tc ₁ ) This expression is the transfer condition of the sublattice magnetization direction from the second magnetic layer to the first magnetic layer at the reference temperature. .

When the first magnetic layer is heated to a Curie temperature Tc ₁ or higher by light irradiation and then cooled, the magnetization reappears in the first magnetic layer, but the direction thereof is larger than the coercive force Hc ₁ of the first magnetic layer. Since the exchange coupling force Hw ₁ (2) from the second magnetic layer is larger, it is aligned with the magnetization direction of the second magnetic layer. As a result, the information temporarily recorded on the second magnetic layer from the outside during the overwrite recording operation is transferred to the first magnetic layer.

Hc ₂ > Hw ₂ (1) -Hw ₂ (3) -Hb (room temperature) (7) However, Hc ₂ : Coercive force of the second magnetic layer Hw ₂ (1): The first magnetic layer is the second magnetic layer Exchange coupling force Hw ₂ (3): the third magnetic layer and the fourth magnetic layer are second
Sum of Exchange Coupling Force on Magnetic Layer This equation is a condition for stabilizing the sublattice magnetization of the second magnetic layer at room temperature.

Since the coercive force of the second magnetic layer is larger than the exchange coupling force from the adjacent layer, the magnetization direction of the second magnetic layer is stable and does not reverse at room temperature.

Hw ₂ (3) -Hw ₂ (1) -Hb> Hc ₂ (from room temperature to Tc ₁ and Tc ₃
(8) This formula is an initialization condition in the sublattice direction of the second magnetic layer at the initialization temperature, and is similar to the formula (2) of the three-layer film. .

The information given to the second magnetic layer as information to be overwritten from the outside is erased and initialized in preparation for the next overwriting after being transferred to the first magnetic layer. Since the exchange coupling force Hw ₂ (3) −Hw ₂ (1) from the adjacent layer is larger than the coercive force Hc _{2 of} the second magnetic layer, the magnetization direction of the second magnetic layer is It is aligned with the magnetization direction of a certain fourth magnetic layer.

Hw ₃ (4) -Hw ₃ (2) -Hb> Hc ₃ (from room temperature to Tc ₁ and Tc ₃
There temperature) to lower of However, Hw ₃ (4): exchange coupling force fourth magnetic layer on the third magnetic layer Hw ₃ (2): the first magnetic layer and the second magnetic layer 3 magnetic Sum of exchange coupling forces exerted on the layer Hc ₃ : Coercive force of the third magnetic layer This equation is an initialization condition for the sublattice magnetization direction of the third layer at the initialization temperature.

At the initialization temperature, the coercive force Hc ₃ of the third magnetic layer is larger than the exchange coupling force Hw ₃ (4) −Hw ₃ (2) from the adjacent layer. 4 Aligned with the magnetization direction of the magnetic layer.

Hc ₄ > Hw ₄ (3) (All operating temperature range) (10) where Hc _{4 is} the coercive force of the fourth magnetic layer Hw ₄ (3) is the first magnetic layer, the second magnetic layer and the third magnetic layer Exchange coupling force exerted by the layer on the fourth magnetic layer This equation is the same as the equation (3) for the three-layer film under the stabilizing condition of the sublattice magnetization direction of the fourth magnetic layer in the entire operating temperature region. The coercive force Hc ₄ of the fourth magnetic layer is larger than the sum Hw ₄ (3) of the exchange coupling forces of the first to third magnetic layers received from the adjacent third magnetic layer. The direction is stable and does not reverse.

In these conditional expressions, the term relating to the external magnetic field Hb is smaller than the other terms and may be neglected, but is shown for accuracy. Further, the sign of the term regarding the external magnetic field Hb changes depending on whether each layer is TM-rich or RE-rich at each temperature. Therefore, in another embodiment described below, the reference numeral is different from the above case, but this point is not the essence of the invention.

FIG. 2A shows an initial state in which information "0" is recorded. FIG. 2B shows an initial state in which information "1" is recorded.

Overwrite recording is possible by binary-modulating the laser intensity described above. The recording made by the stronger laser intensity R ₁ is called “HIGH recording”, while the recording made by the weaker laser intensity R ₀ is “LOW”.
Record ”.

The direction and magnitude of the sublattice magnetization of TM is represented by a dotted line vector, that of RE sublattice magnetization is represented by an experimental vector ↑, and the direction and magnitude of magnetization of the entire alloy is represented by a double solid line vector. At this time, the vector is represented as the sum of the vector and the vector ↑.

Next, the operation will be described. However, since the magnetization direction of the TM sublattice is related to the recording of information, the magnetization direction of each magnetic layer should be focused only on the TM sublattice.

[LOW recording] The laser output was increased from the time of reproduction and the part inside the condensing spot (6) exceeded the reference temperature and the second magnetic layer (27)
TM sub-lattice magnetization reversal temperature (the coercive force becomes smaller than the external magnetic field due to temperature rise and the magnetization is reversed in the external magnetic field direction) When it does not reach, the sub-lattice of TM and RE of the second magnetic layer (27) The magnetization direction does not change and the relationship of the formula (6) is established at the reference temperature, the TM sublattice magnetization direction of the second magnetic layer (27) is transferred to the first magnetic layer (24), and the first magnetic layer (24 The magnetization direction of the TM sublattice of) is downward as shown in FIG. At the reference temperature, the first magnetic layer is TM rich. At this time, the third magnetic layer (28) and the fourth magnetic layer (29) have no particular contribution to the operation, and even if the TM sublattice magnetization of the third magnetic layer (28) disappears, the third magnetic layer (28) and the fourth magnetic layer (29) become It is magnetized again in a fixed direction by the exchange force with the TM sublattice magnetization (29) of the four magnetic layers. After this, the focused spot is removed, so cool down to around room temperature and
The magnetic layer (24) returns to the compensation composition.

[HIGH recording] When the magnetization reversal temperature of the second magnetic layer (27) is exceeded and the magnetization reversal temperature of the fourth magnetic layer (29) is not reached, the first,
The magnetization of the third magnetic layer disappears, but the TM sublattice magnetization direction of the fourth magnetic layer (29) does not change due to the relationship of the expression (10). Since the compensation temperature of the second magnetic layer is exceeded, the second magnetic layer is TM
It becomes rich (Fig. 3). At the magnetization reversal temperature of the second magnetic layer (27), the magnetization direction of the second magnetic layer (27) becomes upward due to the magnetic field generated by the external magnet (18) without receiving the exchange force of the first and third magnetic layers (see FIG. 3). ), Further, the magnetization direction of the second magnetic layer (27) is transferred to the first magnetic layer (24) by the relation of the expression (6), and the magnetization direction of the first magnetic layer becomes upward (FIG. 3). First magnetic layer (24) and second magnetic layer (27), second magnetic layer (27) and third magnetic layer (28), third magnetic layer (28) and fourth
By increasing the exchange force with the magnetic layer (29) in this order, the third magnetic layer (28) at this time is below the Curie temperature and the third magnetic layer (28) has a relationship of the formula (9). The TM sublattice magnetization of is aligned with that of the TM sublattice of the fourth magnetic layer (29),
(Fig. 3) When the temperature further decreases and the exchange force increases, the TM sublattice magnetization of the second magnetic layer (27) is changed by the equation (8) to the TM sublattice of the third magnetic layer (28) by the exchange force. The magnetization returns to the initial state in alignment with the TM sublattice magnetization of the fourth magnetic layer (29). (FIG. 3) Light modulation direct overwrite is possible by modulating only the laser light intensity by the above operation. In a magneto-optical recording medium in which an enhanced dielectric layer is provided on a grooved substrate at 1.6 μm intervals and the magnetic layer is provided, a linear velocity of 11 m / sec, a pit length of 0.76 μm, and an applied magnetic field of 2000
e, the peak power of 18 mW and the bottom power of 7 mW are optically modulated to obtain C / ratio of 45 dB and erase ratio of 40 dB or more.

Example 2 The recording medium of Table 2 was formed on the glass substrate by sputtering the magnetic layer in the same manner as in the above example. By optimizing the recording conditions for any of the recording media, almost perfect light modulation direct overwrite is possible.

Further, FIGS. 4 to 84 show patterns for all cases in which the composition of the alloy of transition metal and rare earth metal is different in each layer. The definition of each symbol in these figures is as follows.

TM: transition metal rich transition metal-rare earth metal alloy having no compensation temperature between room temperature and Curie temperature RE: rare earth metal rich transition metal having compensation temperature between room temperature and Curie temperature-rare earth metal alloy re: Rare earth metal rich transition metal-rare earth metal alloy without compensation temperature between room temperature and Curie temperature t: film thickness [Å] Ms: saturation magnetic moment [emu.cc ^-1 ] Hc: coercive force [e] Tc : Curie temperature [° C] Sw (≡ σw): Interface domain wall energy [erg.cm ^-2 ] Hw _i : Sum of exchange forces received by the i layer Hw _i (j): Exchange force exerted by the j layer on the i layer (≡ σwij / 2 | Msi | t
i)) where i and j are from the substrate side. ↑: TM sublattice magnetization direction: Magnetization of the sum of TM sublattice magnetization and RE sublattice magnetization Tstor: All temperatures in the storage temperature range. (Ex.-10 ° C ~ 6
0 ° C) Tread: All temperatures that the medium reaches from the minimum operating temperature during playback.

_TL : a temperature at which the magnetization of the first magnetic layer is higher than the temperature during reproduction and is Tc ₁ or less and the transfer occurs depending on the magnetization direction of the width 2 magnetic layer.

Tini: A temperature range that is higher than room temperature and lower than the lower one of Tc ₁ and Tc ₃ , and is a certain temperature at which the initialization operation occurs and the magnetization of the second magnetic layer or the third magnetic layer is reversed.

Tall: All temperatures within operating temperature. (0 ° C-) Tuse: Operating temperature of the driving device. (0 ° C to 50 ° C) Also, in each figure, (a1) is the state where information "0" is recorded (a2).
Indicates a state in which information "1" is recorded. In (a2) Indicates a domain wall.

The Curie temperature Tc ₄ of the fourth magnetic layer is higher than 300 ° C. in any pattern.

In the present invention, it is important to properly control the exchange force between the magnetic layers. Therefore, an interface control layer may be interposed between the magnetic layers.

In a four-layer magnetic layer medium, the first magnetic layer Dy ₂₃ Fe ₆₈ Co ₉ 500Å interface control layer SiNx 10 Å second magnetic layer Gd ₁₃ Dy ₁₂ Fe ₆₀ Co ₁₅ 1200 Å third magnetic layer Tb ₁₆ Fe on a glass substrate by sputtering. ₈₄ 200Å 4th magnetic layer Tb ₃₀ Co ₇₀ 700Å ferrimagnetic material and dielectric were formed. Also at this time, the adjacent magnetic layers including those via the interface control layer are coupled to each other by the exchange force. In this medium, a linear velocity of 11 m / sec, a bias magnetic field of 200 e, a laser power of a peak power of 18 mW,
The bottom power was light-modulated to 7 mW and the C / N ratio was 45 dB, which showed good overwrite characteristics.

As the interface control layer, the following ones including the above may be used.

1. Usually, the pressure is set to 5 times or more the pressure of the sputtering gas used for forming the magnetic layer.

2. Use a dielectric such as nitride (SiN, AlN, etc.) or oxide (SiOx, etc.).

3. Normally, the magnetic layer is formed by a neutral sputtering method using only Ar. At this time, a reactive gas (oxygen, nitrogen) is mixed in and the reactive layer is formed.

4. When using a rare earth (RE) -transition metal (TM) alloy film,
Increase the RE composition to 30 at% or more. In this case, the sputtering gas pressure may be a normal value.

5. Use non-magnetic metal (Al, Cu, etc.).

6. Use a magnetic film whose easy axis is in the in-plane direction.

The interface control layer can be formed by the above method, but the method shown here may be used as long as the exchange coupling force can be controlled.

As described above, in the four-layer medium of the present invention, an interface control layer that does not contribute to the essential operation may be interposed, and any of the magnetic layers may be at the interface.

The magneto-optical record carrier that can be overwritten without the initializing magnet has been described above. Next, a method for manufacturing such a record carrier will be described by taking a four-layer film as an example. As shown in FIG. 85, a SiNx film was formed as a dielectric film (34) on a polycarbonate substrate (2) having a diameter of 130 mmφ by a sputtering apparatus, and then the first layer (35) and the second layer ( 36), 3rd layer (37), 4th layer (3
8) is formed, and finally a protective film (39) is formed.

In this case, the magnetic domains of the fourth layer (38), which is an initialization layer after the sputtering film formation, are random.

Therefore, it is necessary to align with the magnetization direction of the fourth layer (38) in one direction. First, as the first method, FIG. 86 (a),
The method shown in (b) can be considered. In the figure, (41) is an initial magnetic field applying means, and (42) is an adhesive layer.

First, before bonding, the coercive force of the fourth layer (38) at room temperature
A magnetic field He of Hc ₄ is applied to align the magnetization direction of the fourth layer (38). Then, after that, an adhesive layer is formed with an epoxy adhesive, a hot melt agent, or the like, and they are bonded together.

As a second method, the coercive force Hc ₄ (A) and Hc ₄ (B) of each of the fourth layers to be bonded to each other are | He (A) |> to Hc ₄ (B) (A and B are two film-forming substrates to be bonded). | Hc ₄ (A) ｜> | He (B)
|> | Hc ₄ (B) | (He (A) and He (B) are the magnetic fields applied by the initial magnetic field applying means).

And after bonding such two substrates,
As shown in Figure (a), first, the Hc
A magnetic field He (A) exceeding ₄ (A) is applied by the magnetic field applying means (43) to align the magnetization of the A-plane initialization layer. Next, as shown in FIG. 87 (b), a magnetic field He (B) in the opposite direction to He (A) that exceeds Hc ₄ (B) and does not exceed Hc ₄ (A) is applied, and B
Align the magnetization of the surface initialization layer. This method can be similarly initialized even if the disc is turned over halfway as shown in FIGS. 88 (a) and 88 (b). Also, FIG. 89 shows the laminated disk initialized in FIG. 88 (a). In this way, the bonded disk, in which the fourth layer of the substrates (40A) and (40B) is initialized in one direction, detects the A-side and B-side on the device side, changes the direction of the bias magnetic field, and performs signal processing. The final reproduction signal processing may be performed after the circuit determines that the direction of the recorded bit has changed.

〔The invention's effect〕

The magneto-optical record carrier of the present invention is constructed by laminating four magnetic layers, and since the fourth magnetic layer functions as an initializing magnet, overwriting is possible without the need for an initializing magnet. Play.

The Curie temperature of the fourth magnetic layer is higher than the Curie temperature of the first magnetic layer to the third magnetic layer, and the Curie temperature of the fourth magnetic layer is from room temperature.
Since it has a coercive force up to 300 ° C, the magnetization direction is not reversed even when overwriting is repeated many times, and the reliability of many times recording is significantly improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 (a) is a perspective view showing the configuration of the main part of a magneto-optical recording device equipped with the magneto-optical recording carrier of the present invention, and FIG. FIG. 3C is a partial sectional view showing a characteristic diagram showing a laser beam power change for recording in the region of the magneto-optical record carrier, FIG. 2 is a concrete constitutional diagram of the four-layered magneto-optical record carrier of the present invention, and FIG. FIG. 4 is a state diagram of each layer in the recording state of the four-layer film magneto-optical record carrier of the present invention, and FIGS. 4 to 84 show conditions when the composition of each layer of the four-layer film magneto-optical record carrier of the present invention is different. FIG. 85 is an explanatory diagram showing the specific structure of the four-layered magneto-optical recording medium carrier of the present invention before initialization, and FIG. 86 (a) is an explanatory diagram showing a method for initialization.
(B) is a block diagram when the initialized products are pasted together,
Fig. 87 is a block diagram showing another method for initialization, Fig. 88 is an explanatory diagram showing another method for initialization, and Fig. 89 is shown in Fig. 89.
Specific configuration diagram of the magneto-optical disk carrier initialized in FIG. 88,
FIG. 90 (a) is a perspective view showing the structure of the main part of a conventional optical recording / reproducing apparatus, and FIG. 90 (b) is a cross-sectional view of the main part showing the optical recording / reproducing state of a magneto-optical record carrier. FIG. 92 is a characteristic diagram showing a change in recording laser power, FIG. 92 is a sectional view of a conventional magneto-optical record carrier, and FIG. 93 is a magnetization state of each layer in the recording state of the magneto-optical record carrier of FIG. FIG. 94 is a diagram showing a three-layer magneto-optical record carrier in the preceding stage of the present invention.

Explanation of symbols 2 ... Substrate, 18 ... External magnetic field, 24 ... First magnetic layer, 27 ...
... second magnetic layer, 28 ... third magnetic layer, 29 ... fourth magnetic layer,
30 ... Recording medium

Continuation of front page (31) Priority claim number Japanese Patent Application No. 1-175591 (32) Priority Day 1 (1989) July 10 (33) Country of priority claim Japan (JP) (72) Inventor Yoshiyuki Nakagi 8-1, Tsukaguchi Honcho, Amagasaki City, Hyogo Mitsubishi Electric Corporation, Industrial Systems Laboratory (72) Inventor Takashi Tokunaga 8-1-1, Tsukaguchi Honmachi, Amagasaki City, Hyogo Prefecture Mitsubishi Electric Corporation Industrial Systems Laboratory (( 56) References JP-A 1-224958 (JP, A)

Claims (3)

(57) [Claims] 1. A first magnetic layer having perpendicular magnetic anisotropy, a second magnetic layer provided on the first magnetic layer and coupled to the first magnetic layer by exchange force, and provided on the second magnetic layer. A third magnetic layer coupled to the second magnetic layer by exchange force, and a fourth magnetic layer provided on the third magnetic layer and coupled to the third magnetic layer by exchange force, Tc ₄ > Tc ₂ > Tc ₁ , Tc ₄ > Tc ₂ > Tc ₃ , Tc ₄ > 300 ° C. However, Tc ₁ : Curie temperature of the first magnetic layer Tc ₂ : Curie temperature of the second magnetic layer Tc ₃ : Curie temperature of the third magnetic layer Tc ₄ : The Curie temperature of the fourth magnetic layer is satisfied, and Hc ₁ > Hw ₁ (2) and Hc ₄ > Hw ₄ (3) are satisfied at room temperature, and from room temperature to the lower temperature of Tc ₁ and Tc _3. Hc ₂ <Hw ₂ (3) −Hw ₂ (1) where Hc ₁ : Coercive force of the first magnetic layer Hc ₂ : Coercive force of the second magnetic layer Hc ₄ : Coercive force of the fourth magnetic layer Hw _i (j): j-th Sexual layer and the magneto-optical recording carrier, characterized in that the temperature that satisfies the shift amount of the switching field of the i-magnetic layer by exchange coupling force acting on the i-th magnetic layer is present. 2. From room temperature to the lower temperature of Tc ₁ and Tc ₃ , Hc ₃ <Hw ₃ (4) −Hw ₃ (2) where Hc ₃ is the temperature at which the coercive force of the third magnetic layer is satisfied. The magneto-optical record carrier according to claim 1, characterized in that 3. The magneto-optical record carrier according to claim 1, further comprising an interface control layer for controlling the exchange force at the interface between the magnetic layers.