JPH08124228A - Magnetooptic recording medium - Google Patents

Abstract

PURPOSE: To form a stabilized recording spot by applying a steady field to a recording layer at a second auxiliary recording layer and reducing the magnetization through the temperature variation of the recording spot at a first auxiliary recording layer. CONSTITUTION: At a first auxiliary recording layer 6a, internal magnetization is varied through temperature variation caused by irradiation with laser beam and the effective field being applied to a recording layer 4 is regulated. Curie point of the film is set lower than the highest temperature caused by irradiation with beam but slightly higher than that of the recording layer 4. Consequently, the domain disappears at the highest temperature and returns earlier than the domain is recovered to the recording layer 4. Consequently, when the domain returns to the recording layer 4, magnetostatic force of the auxiliary layer 6a has effect on the recording layer 4. A second auxiliary recording layer 6b is magnetically exchange coupled with the auxiliary layer 6a which is thereby magnetized constantly in a predetermined direction thus increasing the coercive force. Furthermore, the domain does not disappear at the highest temperature at the time of recording and the exchange coupling force higher than a predetermined level is transmitted thus transmitting magnetostatic force to the recording layer 4. Consequently, a stabilized recording mark is formed thus realizing high density recording.

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, a so-called magneto-optical disc, and to an optical disc which can be used in a recording method such as optical modulation recording or magnetic field modulation recording known as a recording method.

[0002]

2. Description of the Related Art In the field of magneto-optical disks, a super-resolution reproducing method for recording at an information density exceeding a spatial frequency determined by the wavelength and the numerical aperture of a light spot has been developed in response to the recent demand for high-density recording. Has been done. This method improves the reproduction characteristics, and the recording method is the same as before, and the margin for recording information recorded in a minute area (called a minute mark) is small.

Conventional recording methods include an optical modulation recording method and a magnetic field modulation recording method. In the optical modulation recording method, information is recorded by adjusting the laser power and the intensity of light. In the magnetic field modulation recording method, the laser power for irradiation is kept constant and the intensity of the applied magnetic field is adjusted to record information.

The magnetic field modulation recording method related to the present invention will be described below. FIG. 16 shows the state of magnetization during recording in the magnetic field modulation recording method. As shown in FIG. 16, in the optical disc 40, when the light spot LB is irradiated, the coercive force of the writing layer 48 becomes weak. By applying the external magnetic field H _b , the internal magnetization of the write layer 48 can be easily reversed. The magnetic field modulation recording system applies this principle, irradiates a light spot to such an extent that the coercive force of the layer to be recorded is sufficiently weakened, and changes the direction of the applied external magnetic field _Hb to "0" or "1" of information. By reversing accordingly, the direction of magnetization of the recording layer is controlled and information is recorded. For this reason, the recording external magnetic field H _b in the magnetic field modulation recording method is adjusted to a strength that allows reversal.

FIG. 17 shows an example of recording marks in which information is recorded by the magnetic field modulation recording method. Each closed curve T ₁ through T ₄ denotes the isotherm (and _{T 1> T 2> T 3} > T 4.). It is assumed that the recording material in FIG. 17 has magnetic domains reversed at a predetermined temperature (for example, T ₂ ) or higher.

As shown in FIG. 17, when a magnetic field indicating information "1" is applied at time t ₁ , the magnetic domain from the isotherm T ₂ to the high temperature portion is inverted, and information "1" is recorded. Then, as the optical disk rotates, the information pits extend in the linear velocity direction in the recording pits with the width of the isotherm T ₂ . Time t ₂
At, the magnetic field is inverted when a magnetic field indicating information "0" is applied. Then, isotherm at the position of time t ₂ T ₂
The magnetic domains of the magnetic material are inverted from the above temperature distribution region. Therefore, the recording pit in the magnetic field modulation recording system has a so-called arrow blade shape.

[0007]

In the magneto-optical disk medium, however, there is a problem in each of the information recording methods in an attempt to increase the stability of the recording spot area and the recording density.

In the optical modulation recording method, the size of the information recording portion (that is, the high temperature portion 36 in FIG. 16) on the optical disk can always be stabilized due to the influence of laser power fluctuation and focus servo stability. Have difficulty. Further, if the thermal interference of the optical disk is essentially large, the boundary of the temperature rising point becomes ambiguous and the information recording itself becomes impossible.

In the magnetic field modulation recording method, the track density could not be increased due to the spread of heat in the radial direction of the optical disk. In addition, since the recording marks also have an arrow-blade shape with respect to the tangential direction of the track as shown in FIG.
If the tails of the two overlap, the information cannot be reproduced with good separation.

Therefore, an object of the present invention is to provide a magneto-optical recording medium capable of forming stable recording spots and suitable for high density recording.

[0011]

In order to achieve the above object, the invention according to claim 1 has a high coercive force in the vicinity of a reproducing temperature for reproducing information and is higher than the reproducing temperature. A recording layer for reaching a Curie temperature near the recording temperature for recording and a magnetic exchange coupling force between the first recording auxiliary layer and the recording layer interposed between the recording layer and the first recording auxiliary layer are provided. A blocking layer for blocking; a first recording auxiliary layer having a Curie temperature higher than the recording temperature and lower than the maximum temperature attainable by writing light by transmitting a static magnetic force to the recording layer through the blocking layer;
Second recording having a Curie temperature higher than the maximum temperature and having a coercive force capable of constantly applying an initializing magnetic field to the recording layer between the room temperature and the maximum temperature. And an auxiliary layer.

According to a second aspect of the present invention, the recording temperature is higher than the reproducing temperature and reaches the Curie temperature near the recording temperature for information recording, and the recording layer is provided so as to be capable of magnetic exchange coupling with the recording layer. And a recording auxiliary layer having a high Curie temperature which can be reached by writing light.

According to the third aspect of the present invention, the recording for information recording has a coercive force exceeding the strength of the magnetic field from the magnetic field generating layer near the reproducing temperature for reproducing information and is higher than the reproducing temperature. A recording layer which reaches a Curie temperature near the temperature, a blocking layer which is interposed between the recording layer and the recording auxiliary layer and blocks a magnetic exchange coupling force between the first recording layer and the recording auxiliary layer, and a rare earth A ferrimagnetic material having a compensation point of a metal-transition metal alloy, which is magnetostatically coupled to a recording layer through a blocking layer, the magnetization spins of the rare earth metal and the transition metal are reversed above the compensation temperature, and the temperature is higher than the compensation temperature. And a magnetic field generating layer having a coercive force of a certain value or less.

[0014]

According to the invention of claim 1, the second recording auxiliary layer applies a steady magnetic field to the recording layer, and the first recording auxiliary layer reduces the magnetization in response to the temperature change of the recording spot. Therefore, the direction of the magnetization of the recording layer that appears when the temperature decreases from the recording temperature follows the direction of the effective magnetic field when the magnetic domain returns.
Therefore, in the central portion of the recording spot where the effective magnetic field follows the direction of the external magnetic field, the magnetization direction of the recording layer is oriented in the direction of the external magnetic field, and the effective magnetic field is around the recording spot where the magnetization directions of the first and second recording auxiliary layers are oriented. In the portion, the magnetization direction of the recording layer faces the direction of the initializing magnetic field of the recording auxiliary layer.

According to the second aspect of the invention, the recording auxiliary layer is provided so as to be capable of magnetic exchange coupling with the recording layer,
Before the magnetic domain of the recording layer is recovered due to the temperature rise, its own magnetic domain is recovered. Writing is normally performed in the center of the light spot where the Curie temperature of both layers reaches the Curie temperature. Then, only the recording layer loses the magnetization in the slightly lower temperature portion in the peripheral portion. Since the exchange coupling force is stronger than the external magnetic field during cooling, the recording layer is oriented in the direction of the magnetization of the recording auxiliary layer in the low temperature portion.

According to the third aspect of the invention, the magnetic field generating layer is a ferrimagnetic material having a compensation point, and the spin defining the overall magnetization changes at the compensation point. Therefore, the direction of overall magnetization of the magnetic field generation layer is also reversed. However, when a predetermined external magnetic field is applied in the direction opposite to the reversed direction of the overall magnetic field, when the coercive force of the magnetic field generation layer decreases and the strength of this external magnetic field exceeds this coercive force, the magnetic field is generated. The direction of the overall magnetization of the layer is reversed at once. Since the magnetic field applied to the recording layer is a combination of the static magnetic force generated by the magnetic field generating layer and the external magnetic field, the magnetic field received by the recording layer is sharply emphasized at a predetermined temperature. Therefore, a recording spot is well generated at a temperature at which the strength of the magnetic field received by the recording layer is increased,
Since the effective magnetic field is directed in the opposite direction in the middle temperature portion around the recording spot, the recording mark is clearly recorded.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments of the present invention will be described with reference to the drawings. (I) First Example In the first example of the present invention, recording is performed in the central portion of the recording spot and erasing is performed in the peripheral portion of the recording spot.
The present invention relates to an optical disc capable of realizing super-resolution recording.

FIG. 1 shows the layer structure of an optical disc according to the first embodiment of the present invention. As shown in FIG. 1, the optical disc 1 according to the first embodiment has a substrate 2 which is the main body of the optical disc 1 in order from the light beam irradiation side, a dielectric protective film 3 for protecting the magneto-optical layer, and information. Recording layer 4 for recording, and recording layer 4
To the recording auxiliary layer 6a, the non-magnetic layer 5 for blocking the exchange coupling force, the recording auxiliary layer 6a for transmitting a static magnetic force to the recording layer 4 through the blocking layer 5, and the magnetic recording layer 6a for magnetic recording. Recording auxiliary layer 6b for transmitting the selective exchange coupling force, a dielectric protective film 7 for protecting the magneto-optical layer, and a resin protective film 8 formed by a 2P (photo polymer) overcoat or the like for coating an optical disk. And are laminated.
The layer that substantially carries out magneto-optical recording is an interaction of the recording layer 4, the non-magnetic layer 5, the recording auxiliary layer 6a, and the recording auxiliary layer 6b, and these are collectively referred to as a magneto-optical layer. Description of Each Layer Next, the function, composition, and film thickness of each layer will be described.

The dielectric protective films 3 and 7 serve to protect the magneto-optical layer. The property of this film is that it should be transparent and have a dense composition that does not allow moisture and the like to pass through.
Compositions having this property include SiN _x , AlN, T
a ₂ O ₅ or the like can be used. The film thickness is such that it can resist aging and oxidation (for example, 20
A thickness of about [nm] or more is necessary, and a thickness (eg, 100 [n]
m])) or less.

The recording layer 4 has a function of holding recorded information.
You. The property of this film is that the magnetic material has perpendicular magnetization.
And can be reached by irradiating the laser beam during recording
Maximum temperature (hereinafter T_MAnd ) From Curie point (below
T_C1And ) Is low and the magnetic domains disappear once at the maximum temperature.
Need to be made. The recording layer 4 functions as a reproducing layer during reproduction
It is also necessary to provide high spatial frequency reproduction.
Has the properties of a so-called super-resolution reproducing film
Good. The composition of the recording layer 4 is used for the conventional recording layer.
TbFeCo alloy (for example, Tb_{twenty three}(Fe₉₀Co
_Ten)₇₇[At%] (70 [nm])) can be used. Also,
Multi-layer film for super-resolution reproduction instead of TbFeCo alloy
(For example, FAD type super-resolution reproducing film: Gd_{twenty three}(Fe₈₀
Co₂₀)₇₇[At%] (30 [nm]) / Tb_{twenty two}Fe₇₈(At
%] (10 [nm]) / Tb_{twenty three}(Fe ₉₀Co_Ten) (At%)
(40 [nm]) and the like can be used. Also, PtCo
Oxide magnetism such as gold, Pt / Co laminated film, garnet
Membranes can also be used.

The numerical values in the composition formula represent the atomic quantity ratio of the two alloys and are called atomic percentages. For example, in the notation A _n B _m [at%], n + m = 100, and this formula shows that this material is composed of n% A atoms and m% B atoms in the total number of atoms. means.

The thickness of the recording layer 4 needs to be equal to or larger than the minimum Kerr rotation angle and not larger than the thickness at which it becomes difficult to form fine marks due to thermal interference ( For example, a range of 10 [nm] to 100 [nm]).

The nonmagnetic layer 5 includes the recording layer 4 and the recording auxiliary layer 6a.
It has a function of blocking the magnetic exchange coupling force generated between and. The nonmagnetic layer 5 must be a nonmagnetic material that is not magnetized. The composition of the film having this property is a dielectric such as SiNx, ZnS, SiO, or AlN,
A non-magnetic metal such as Al can be used. The film thickness range is
A thickness that is sufficient to block the exchange coupling force between the recording layer 4 and the recording auxiliary layer 6a (for example, 0.5 nm or more) and is not too far away to transmit the static magnetic force between the two layers. (For example, 50 [nm] or less). 5 nm in terms of characteristics
.About.20 [nm] is a preferable film thickness range for satisfying the above condition.

The recording auxiliary layer 6a has a function of adjusting the effective magnetic field applied to the recording layer 4 because the internal magnetization changes with the temperature change accompanying the irradiation of the laser beam. As a property of the recording auxiliary layer 6a, the Curie temperature (hereinafter referred to as T _C2 ) is lower than the maximum temperature rise of the laser beam irradiation and slightly higher than the Curie temperature T _C1 of the recording layer 4. Must have With this property, the magnetic domain returns to the recording auxiliary layer 6a earlier than the magnetic domain disappears at the maximum temperature and the magnetic domain recovers in the recording layer 4. Therefore, when the magnetic domain returns to the recording layer 4, the static magnetic force of the recording auxiliary layer 6a affects the recording layer 4. In addition, it is necessary to have a sufficient coercive force in a medium temperature state due to temperature rise, that is, in a temperature due to temperature propagation that leaks from an adjacent track (hereinafter referred to as a leak temperature T _F ).

As the film having these properties, a material having no compensation point and a material having a compensation point (compensation point material) are considered. FIG. 2A shows a characteristic diagram (first characteristic) in the case of a material having no compensation point, and FIG. 2B shows a characteristic diagram (second characteristic) in the case of a material having a compensation point. .

As shown in FIG. 2A, the material having the first characteristic has large magnetization at the leakage temperature T _F , and is kept at the writing temperature T _W at which information is recorded on the recording layer 4. The magnetic force is weak, and at the maximum temperature T _M , the Curie temperature becomes higher than T _C1 and the magnetic domains disappear.

Further, as shown in FIG. 2B, the compensation point material having the second characteristic has a compensation temperature T at which the magnetization becomes zero.
Temperature at which _COMP reads information during playback (playback temperature)
Is preferred. Therefore, the composition of the material is adjusted so that the compensation temperature T _COMP and the reproduction temperature T _P coincide with each other.
The arrangement state of temperatures equal to or higher than the compensation temperature T _COMP is the same as that in the first characteristic diagram. That is, the coercive force is high at the leakage temperature T _F , and the coercive force is small at the writing temperature T _W , and the maximum temperature T
_The Curie point T _C1 must be below _M.

As a material exhibiting the above-mentioned characteristics, a general rare earth metal (RE) -transition metal (TM) magnetic material having a magnetization strength of 150 [emu / cm ³ ] or more is required. There is. In particular, the strength of magnetization is 400 to 600.
[Emu / cm ³ ] (room temperature) is preferable. As a magnetic material having such a property, a TbFeCo alloy can be given, and its composition formula is Tb _x (FeCo) _(100-x) (x = 13 to 20 or 26 to 35 [at%]). The first characteristic and the second characteristic are selected depending on the composition ratio of terbium (Tb) and the composition of iron (Fe) or cobalt (Co).

In addition to the above compositions, rare earth metal (RE) -transition metal (TM) based materials such as GdTbFeCo alloy and TbCo alloy can be considered as compositions exhibiting these characteristics.
Further, a medium exhibiting perpendicular magnetization such as PtCo alloy, Pt / Co laminated film, oxide system such as garnet, or CoCr alloy can also be used.

As the film thickness of the recording auxiliary layer 6a, the total amount of magnetization is thicker than the required amount (for example, about 30 nm), and a minute recording mark cannot be formed due to thermal interference. (For example, about 300 [nm]). In particular, it is preferably in the range of 50 [nm] to 150 [nm] in order to provide stable magnetization and obtain good recording marks.

The recording auxiliary layer 6b is magnetically exchange-coupled with the recording auxiliary layer 6a, and functions to always magnetize the recording auxiliary layer 6a in a constant magnetization direction (direction of initial magnetic field). Therefore, the recording auxiliary layer 6b is required to have a large coercive force. That is, it is preferable that the magnetization intensity at room temperature is 150 [emu / cm ³ ] or less and the coercive force is 1 [kOё] or more. Further, the magnetic domain does not disappear at the maximum temperature T _M during recording (that is, Curie temperature (hereinafter referred to as T _C3 )> T _M ), and the exchange coupling force of a certain level or more is always transmitted to the recording auxiliary layer 6a. However, it is necessary to transfer the static magnetic force to the recording layer 4. Further, it is necessary that the direction of magnetization is stable without being reversed from room temperature T _R to the maximum temperature T _M. An actual Curie temperature of 250 ° C. or higher is necessary, and 350 ° C. or higher is sufficient. In the manufacturing process, the recording auxiliary layer 6b is magnetized in a constant direction (initial magnetic field direction) by applying a strong magnetic field after film formation.

As the composition of the film having the above-mentioned properties, a rare earth metal (RE) -transition metal (TM) based ferrimagnetic material having general perpendicular magnetization can be used. For example, (Gd ₆₀ Tb ₄₀ ) ₂₃ (Fe ₆₀ Co ₄₀ ) ₇₇ [at%] shows preferable characteristics.

The thickness of the recording auxiliary layer 6b is preferably as thin as possible in order to avoid thermal interference, but it is necessary that the recording auxiliary layer 6b has a sufficient exchange coupling force to prevent magnetization reversal of the recording auxiliary layer 6a. . Therefore, it is preferable (for example, about 30 [nm] or more) to have a thickness (for example, about 100 [nm] or less) at which the influence of thermal interference is not too strong. Explanation of Recording Principle Next, the principle of recording on the optical disc of the first embodiment will be explained. The optical disc 1 of this embodiment can be used for both the optical modulation recording method and the magnetic field modulation recording method. In the disc 1, the recording auxiliary layers 6a and 6b are aligned in a certain direction by a strong magnetic field during film formation. For example, in FIG. 4, the magnetizations of both layers are oriented downward in the figure. The direction of this magnetization is set to the initialized state and the state of recorded information “0”.

FIG. 3 shows a state of heat distribution generated when the optical disk is irradiated with a light beam. FIG. 3 (A) shows the state of heat distribution in the magneto-optical layer immediately after the irradiation of the light beam.
(B) shows a state in which heat due to light beam irradiation is conducted and the heat reaches the lower layer of the magneto-optical layer. In FIG. 3, T ₁
Each closed curve from ~ T ₃ represents an isotherm. The relationship between the temperatures is T ₁ > T ₂ > T ₃ .

As shown in FIGS. 3A and 3B, the heat distribution generated by the temperature rise accompanying the irradiation of the light beam propagates from the irradiation side of the light beam to the lower layer side over time. In the recording of the present embodiment, the magnetization characteristics of each layer accompanying the movement of the temperature distribution occur according to the change of the temperature distribution.

In the case of optical modulation recording The principle of optical modulation recording on the optical disc 1 of this embodiment will be described with reference to FIGS. 4 to 7.

In the case of light modulation recording, the recording external magnetic field is required to have a constant value. The recording auxiliary layers 6a and 6b of the optical disc 1 are aligned in the direction of the initializing magnetic field. At room temperature, the magnetization state of each layer is as shown in FIG. Further, the strength of the magnetic field applied to the recording layer 4 is shown in FIG. In FIG. 5, the upward magnetic field in FIG. 4 is a positive magnetic field, and the downward magnetic field is a negative magnetic field. FIG. 5 (A) shows the respective states of the magnetic field of the recording auxiliary layer and the external magnetic field, and FIG. As shown in FIG. 5A, an external magnetic field _Hex applied by a magnet or the like of the recording device and a static magnetic force applied from the recording auxiliary layer 6a are applied to the recording layer 4. Therefore, the effective magnetic field applied to the recording layer 4 is a synthetic magnetic field as shown in FIG.

FIG. 6 shows the state of the combined magnetic field received by the recording layer 4 when compared with the state of the magnetization of each layer in FIG. 4 in accordance with the description method of the combined magnetic field in FIG. At room temperature, the magnetic field applied to the recording layer 4 is directed in the direction opposite to the strong external magnetic field H _ex and the static magnetic force exerted by the recording auxiliary layer 6a. Therefore, the combined magnetic field is at the level of the combined magnetic field H ₀ that cancels the magnetic fields, as shown in FIG. 6 (C).

Now, when the light spot is irradiated, the temperature of the irradiation surface of the optical disk rises, and due to the temperature distribution as shown in FIG. 3, heat propagates from the recording layer 4 side to the recording auxiliary layers 6a and 6b side.

When the temperature is raised as shown in FIG. 4B, the temperature of the recording layer 4 reaches the Curie temperature T _C1 of the recording layer 4, and the magnetic domains of the recording layer 4 start to disappear. At this time, since the Curie temperature of the recording auxiliary layer 6a is higher than that of the recording layer 4 and sufficient heat is not transferred, the magnetization does not change.

At the writing temperature in FIG. 4C, the temperature of the recording layer 4 reaches the maximum temperature, and the magnetic domains in a wide range disappear. Since the temperature of the recording auxiliary layer 6a rises and exceeds the Curie temperature T _C2 of the recording auxiliary layer 6a, the magnetic domains start to disappear. After this,
The temperature rise of the recording layer 4 tends to decrease. When the magnetic domain of the recording auxiliary layer 6a disappears, the static magnetic force applied to the recording layer 4 up to that point is greatly reduced, and the recording layer 4 is greatly affected by the external magnetic field H _ex . The state of the combined magnetic field at this time is as shown in FIG.

When the high temperature (writing temperature) state is changed to the temperature lowering state, the recording layer 4 and the recording auxiliary layer 6a are magnetized.
The magnetization direction of the recording auxiliary layer 6a is determined by the direction of the magnetization.
The exchange coupling force of b follows the magnetization direction of the recording auxiliary layer 6b. Since the Curie temperature T _C2 of the recording auxiliary layer 6a is set to a temperature slightly higher than the Curie temperature T _C1 of the recording layer 4, the magnetic domain of the recording auxiliary layer 6a returns a little earlier.

FIG. 7 shows the relationship between the temperature of the recording layer 4 and the coercive force.
The figure is shown. In FIG. 7, the coercive force of the recording layer 4 is at room temperature.
T_RFrom the Curie temperature T _C1Will be zero. this
The recording layer 4 has a constant external magnetic field (reversing magnetic field H_WTosu
You. ) Is applied, the write temperature T_WAbove the coercive force
Force is reversal magnetic field H_WBecomes less than the level of_Wof
Due to the influence, the direction of internal magnetization can be reversed.
Therefore, the writing temperature T_WHigher temperature and coercivity curve
On the higher magnetic field side, that is, in the shaded area, the recording layer 4
Can be written to. Effective on the recording layer 4
When considering the magnetic field, the high temperature part at the center of the recording mark is shown in FIG.
Enter the shaded area and the surrounding area should not enter this area.
Yes.

When magnetized, if the combined magnetic field applied to the recording layer 4 is not less than the reversal magnetic field H _W , the magnetic domains are reversed. At the central portion of the recording mark, as shown in FIG. _6A , a strong combined magnetic field exceeding this reversal magnetic field H _W is applied to the recording layer 4, so that the magnetic domain of the recording layer 4 is reversed and information is recorded. It
On the contrary, in the peripheral portion of the recording mark, as shown in FIG. 6B, the combined magnetic field exerted on the recording layer 4 becomes weak and only a magnetic field equal to or less than the reversal magnetic field H _W is applied. The magnetic domain faces the direction of the static magnetic force from the recording auxiliary layer 6a (initializing magnetic field). This indicates that the magnetic field is switched depending on the strength of the temperature distribution. In the optical modulation recording method, the intensity of the light of the light spot causes the intensity of the temperature distribution to change. Due to the strength of this temperature distribution, a high magnetic field portion at a high temperature portion and a low magnetic field portion at a low temperature portion are generated.

Therefore, as compared with the conventional optical modulation recording system in which only the temperature is changed and recording is performed, in the present embodiment, the magnetic field strength can be changed while using the same modulation of the optical spot, so that a minute spot Can be formed.

In the case of magnetic field modulation recording The principle of magnetic field modulation recording in the present invention will be described with reference to FIGS. 8 and 9. As a condition of the magnetic field modulation recording, the laser power of the laser light to be irradiated is constant.

FIG. 8 shows the magnetization of each layer by magnetic field modulation recording. As shown in FIG. 8, the change in the magnetization due to the magnetic field modulation shows almost the same change as that in the optical modulation recording. FIG.
(A) is a room temperature state, and the recording auxiliary layers 6a and 6b are constantly magnetized in the direction of the initializing magnetic field (downward direction in the drawing). When the optical beam is applied to the optical disc 1, the light is absorbed by the recording layer 4 and converted into heat. When the temperature of the recording layer 4 rises, the magnetic domain disappears when the Curie temperature T _C1 is exceeded (FIG. 8B). Further, since the Curie temperature T _C2 of the recording auxiliary layer 6a is also close to the Curie temperature T _C1 of the recording layer 4, disappearance of magnetic domains starts. Since both Curie temperatures are slightly lower in the recording layer 4, the area where the magnetic domains disappear is larger in the recording layer 4 than in the recording auxiliary layer 6a.

As shown in FIG. 8C, the direction of magnetization of the recording layer 4 is determined when the temperature is lowered. However, since heat propagates to the lower layer, the recording auxiliary layer 6a is in a higher temperature state. Therefore, as shown in FIG. 8C, the periphery of the maximum temperature of the recording mark is reversed according to the orientation of the recording auxiliary layer 6b. Further, since the magnetic field canceling the external magnetic field _Hex disappears due to the disappearance of the magnetic domain of the recording auxiliary layer 6a, the central portion of the recording mark is reversed according to the direction of the external magnetic field _Hex .

FIG. 9 shows the state of the composite magnetic field exerted on the recording layer 4. As shown in FIG. 9, writing of magnetization in the recording layer 4 is performed in a sharp magnetic field distribution as shown in FIG. 9B. In the state of FIG. 9C in which the recording auxiliary layer 6a is in the temperature rising process, since the recording layer 4 is already in the temperature decreasing process, the middle temperature portion around the recording mark is magnetized due to the influence of the exchange coupling force of the recording auxiliary layer 6b. The direction of the initializing magnetic field is fixed. Therefore, arbitrary information ('1' or '0') can be recorded by adjusting the direction of the external magnetic field at the center of the recording mark.

As described above, according to the optical disc of the first embodiment, the recording state and the recording mark at the central portion (high temperature portion) of the recording mark are recorded regardless of whether the optical modulation recording or the magnetic field modulation recording is used. As a result of erasing in the peripheral portion (medium temperature portion), super resolution recording can be realized. Therefore, it is possible to write a mark smaller than the heat distribution originally possessed by the light spot or a mark having a shorter mark length.

In the first embodiment, since the non-magnetic material (non-magnetic layer 5) is used to block the exchange coupling force,
Magnetostatic magnetic coupling was performed between the recording layer and the recording auxiliary layer, but the layer structure is such that the exchange coupling force between the recording layer and the recording auxiliary layer is used to transfer the magnetization to the recording layer. May be configured. In this case, in the layer structure of FIG. 1, the non-magnetic layer 5 is omitted and the recording layer 4 and the recording auxiliary layer 6a are in direct contact with each other. When the non-magnetic layer does not exist, the recording layer and the recording auxiliary layer are connected by a magnetic exchange coupling force. When the magnetic domain of the recording auxiliary layer exists at the time of temperature decrease, the magnetization direction of the recording layer in which the magnetic domain disappears or the coercive force is weak aligns with the direction of the recording auxiliary layer due to the strong exchange coupling force. When the magnetic domain of the recording auxiliary layer disappears,
As described in the above embodiment, the directions of the external magnetic fields are aligned. (Ii) Second Embodiment In the second embodiment of the present invention, a single generation layer is provided in place of the two recording auxiliary layers of the first embodiment, and switching in the magnetic field direction exerted on the recording layer is reliably performed. Is.

FIG. 10 shows the layer structure of the optical disc according to the second embodiment of the present invention. As shown in FIG. 10, the optical disc 11 of the second embodiment includes a substrate 12, a dielectric protective film 13 for protecting the magneto-optical layer, a recording layer 14 for recording information,
A blocking layer 15 for blocking the magnetic exchange coupling force between the recording layer 14 and the magnetic field generating layer 16, a magnetic field generating layer 16 for changing the magnetic field exerted on the recording layer 14, and a dielectric for protecting the magneto-optical layer. A protective film 17, a resin protective film 18 formed by a 2P overcoat or the like for protecting the entire optical disc 11,
It is configured by stacking.

In the magneto-optical layer of the optical disk 11, the substrate 12, the dielectric protective films 13 and 17, the recording layer 14 and the blocking layer 1
For each layer of No. 5, a material having the same composition as in the first embodiment is used. Since the properties, composition, and film thickness of the film have been described in the first embodiment,
Description is omitted. Description of Each Layer The magnetic field generating layer 16 newly used in this embodiment is the recording layer 14
It acts to switch the strength and direction of the magnetic field on the. The film must be a compensation point material having a compensation point at a temperature higher than room temperature T _R and a temperature lower than the recording temperature T _W. In addition, the direction of the generated magnetic field needs to be reversed at the compensation point.

FIG. 11 shows a characteristic diagram that the ferrimagnetic material used for the magnetic field generating layer 16 should have. FIG. 11A is a relationship diagram between temperature and coercive force and magnetization strength, and FIG. 11B is a relationship diagram between temperature and the direction of the generated magnetic field. The large arrow in the lower part of FIG. 11A indicates the direction and magnitude of the entire magnetization of the compensation point material, and the solid arrow inside the arrow of the overall magnetization indicates the direction and magnitude of the magnetization of the rare earth metal (RE). The dashed arrow indicates the direction and magnitude of magnetization of the transition metal (TM). The direction of the arrow indicates the direction of magnetization, and the length of the arrow indicates the magnitude of magnetization.

A predetermined external magnetic field H _ex (upward in FIG. 11) is applied to the entire film. In the compensation point material, the strength of magnetization decreases as the temperature of the material rises above room temperature, and the compensation temperature T
_The magnetization becomes zero at _COMP (for example, T _COMP = 180 ° C.). At this stage, since the main spin of the compensation point material is carried by the rare earth metal (RE), the direction of the overall magnetization is in the direction of the rare earth metal (RE). Rare earth metal (RE)
The partial magnetization of the transition metal (T
The partial magnetization of M) also decreases with increasing temperature. But,
Since the rare earth metal (RE) has a larger reduction rate, the magnitude of the overall magnetization becomes smaller as the temperature rises as shown in FIG. 11B, and the magnitudes of the partial magnetizations of both metals are balanced at the compensation point. As a result, the magnitude of the total magnetization becomes zero.

When the compensation point material exceeds the compensation temperature T _COMP ,
The main magnetization spin inside the compensation point material is a rare earth metal (R
E) replaces the transition metal (TM). Therefore, the direction of overall magnetization is reversed from the direction of magnetization from room temperature to the compensation point,
The orientation of the transition metal (TM) is the same as the orientation of overall magnetization. An external magnetic field is applied to the film, but the coercive force of the compensation point material is extremely large in a predetermined range above the compensation point (the range of'a 'in FIG. 11B), and the compensation point material itself has an external magnetic field. It is not affected by H _ex . However, when the coercive force of the compensation point material decreases and falls below the strength of the external magnetic field H _ex , the overall magnetization of the compensation point material follows the direction of the external magnetic field H _ex . Therefore, _assuming that the temperature at which the coercive force exceeds the external magnetic field H _ex is T _x (for example, T _x = 230 ° C.), the direction of the overall magnetization sharply reverses at the temperature T _x .

As described above, in the compensation point material of the magnetic field generating layer of this embodiment, the magnetic field generated by the magnetic field generating layer itself is slightly higher than that of the compensation point, even though a constant external magnetic field is applied. It has a discontinuity at which the direction of the magnetic field reverses at high temperature (T _x ).

As a composition of the material having such properties, a rare earth metal (RE) -transition metal (TM) based ferrimagnetic material (amorphous alloy film) is considered. It should be a compensation point material and have a compensation point between 100 and 300 ° C. The applied external magnetic field is usually 0.5 [kO].
Since e] or less, a material having a relatively low coercive force is required. As a metal film having such a property, for example, G
A dFeCo-based ferrimagnetic material is desirable, and its composition ratio is Gd: 24 to 30 [at%] Co: 5 to 30 [at%]. However, the composition of the magnetic field generation film depends on the recording temperature of the recording layer, and the compensation temperature is determined by the recording temperature. The composition of the layer is undefined. Therefore, FIG. 10 shows an example of a combination of compositions of the recording layer and the magnetic field generation layer.

Regarding the film thickness, it is thick enough to transmit a sufficient static magnetic force to the recording layer (for example, 30 [nm]), and is a thickness that does not prevent recording of minute recording marks due to thermal interference. (For example, 100 [nm]) or less. Description of Recording Principle Next, the recording operation on the optical disk 11 having the magnetic field generating layer will be described.

In the case of optical modulation recording FIG. 12 shows the direction of the magnetic field generated by the magnetic field generating film 16 during optical modulation recording. In FIG. 12, the external magnetic field H _ex is applied from the other side of the drawing to the front side.

With the irradiation of the light beam, the heat distribution spreads on the surface of the optical disk 11. As the temperature rises, FIG.
The magnetization of the magnetic field generation layer 16 changes according to the characteristics of (B). In T ₁₀ of FIG. 12, the magnetic field generation layer 16 has a compensation temperature T _COMP.
Is the isotherm when it reaches. Therefore, inside the recording mark higher than this temperature, the magnetic field generation layer 16 is formed as shown in FIG.
Since it falls within the range'a 'shown in (B), the direction of the magnetic field is reversed. The isotherm T ₁₁ is the reversal temperature T _x of the magnetic field shown in FIG. Therefore, the inside of the isotherm T ₁₁ is shown in FIG.
Since it enters the range'b 'shown in (B), the direction of the magnetic field again follows the direction of the external magnetic field H _ex .

In the area surrounded by the isotherms T ₁₀ and T ₁₁ , the magnetic field of the magnetic field generating layer 16 works so as to cancel the direction of the external magnetic field H _ex , so the magnetic field applied to the recording layer 14 is weak. On the other hand, inside the isotherm T _11, the direction of the magnetic field of the magnetic field generation layer 16 acts in the same direction as the external magnetic field H _ex , so that the magnetic field applied to the recording layer 14 further emphasizes the strength of the external magnetic field H _ex. Becomes

Therefore, even if the area where the coercive force of the recording layer 14 is weakened or the area where the magnetic domain disappears is widened due to heat propagating to the surroundings due to the light spot, only a small area surrounded by the isotherm T ₁₁ has a strong magnetic field. Is held, a minute recording mark is formed.

In the case of magnetic field modulation recording, basically the same thing as in the case of optical modulation recording occurs. That is, the magnetic field applied to the recording layer is changed by the applied light beam to raise the temperature of the magnetic field generation layer to a temperature equal to or higher than the compensation temperature, and the applied external magnetic field is changed. ) If you move back and forth between the range'a 'and'b',
Minute recording marks are formed on the recording layer.

As described above, according to the second embodiment, in the optical modulation recording and the magnetic field modulation recording, even if the temperature in a wide range rises due to the heat distribution, the switching of the magnetic field of the magnetic field generating layer causes a minute recording mark. Can be formed. In particular, in magnetic field modulation recording, switching of a magnetic field is usually not as fast as in the case of optical modulation. On the other hand, in this embodiment, switching of the magnetic field occurs at the magnetization reversal speed of the magnetic field generation layer. Therefore, the present embodiment assists the high-speed response at the time of magnetic field modulation and enables high-speed writing.

FIG. 13 shows how the crosstalk changes with and without the magnetic field generating layer of the second embodiment. As can be seen from FIG. 13, due to the function of the magnetic field generating layer, the crosstalk is remarkably reduced particularly at the time of high density recording with a narrow track pitch. (Iii) Third Example A third example of the present invention shows another composition example of the optical disk having the magnetic field generating layer described in the second example.

FIG. 14 shows the layer structure of the optical disc 21 of the third embodiment. As shown in FIG. 14, the optical disc 21 is
The substrate 22, the dielectric protection film 23, the super-resolution reproduction layer 24 for performing super-resolution reproduction at the time of reproduction, the recording layer 25, and the exchange coupling force between the recording layer 25 and the magnetic field generation layer 27 are blocked. Blocking layer 26, magnetic field generating layer 27 of the present invention, and dielectric protective film 2
8, a heat dissipation layer 29, and a resin protective film 30 formed by a 2P overcoat or the like are laminated.

In this embodiment, a super-resolution reproducing film 24 for performing super-resolution reproduction is provided adjacent to the recording layer 25, and
The difference is that a heat dissipation layer 29 that dissipates heat associated with laser beam irradiation is provided.

As the super-resolution reproducing layer 24, a normal super-resolution reproducing film may be provided. A single-layer GdFeCo layer or the laminated film for super-resolution reproduction shown in the first embodiment can be used. However, it is desirable that the film thickness is such that the heat conduction during recording is not hindered.

The heat dissipation layer 29 is necessary for efficiently propagating the heat generated by the irradiated laser beam at a high speed when a large number of layers are laminated as in this embodiment. for that reason,
The required properties of the film are that it has a high thermal conductivity. The composition of such a film is generally A
An l-based alloy is used. As a typical alloy, AlTi
(Ti: 1 to 5 [wt%]) is often used as a heat dissipation material.

The operation of the third embodiment is exactly the same as the operation principle of the second embodiment. Since the super-resolution reproducing layer 24 is related only during reproduction, it does not affect the recording layer 25 during recording. In the optical disc 21, since the heat dissipation layer 29 is provided, heat generated in each magnetic layer does not spread in the magnetic layer, and flows toward the heat dissipation layer 29 perpendicularly to the film surface. In the heat dissipation layer 29, the inflowing heat is diffused in the horizontal direction. Therefore, the upper magnetic layer is rapidly cooled during recording,
The "blurring" of recording marks is reduced.

FIG. 15 shows the relationship between the mark length and the change in the C / N characteristics depending on the presence or absence of the magnetic field generating film. FIG. 15 was measured under the following conditions. Recording wavelength λ = 680 [nm] Numerical aperture NA = 0.55 Recording method = optical modulation recording As can be seen from FIG. 15, C / N is improved during high density recording with a short mark length.

As described above, also in the third embodiment, the presence of the magnetic field generating layer enables recording of minute recording marks on the optical disc, which can contribute to increasing the density of the optical disc.
Further, in this embodiment, the heat dissipation layer is used to rapidly cool the magnetic layer during recording, and as a result, minute recording marks can be formed.

[0074]

According to the first aspect of the present invention, the function of the second auxiliary recording layer for applying a constant magnetic field to the recording layer and the effect of the first effective magnetic field on the recording layer are changed. Due to the function of the recording auxiliary layer, stable recording marks can be formed in the magneto-optical disk medium and high density recording becomes possible.

According to the second aspect of the present invention, the recording layer and the first recording auxiliary layer are coupled by the exchange coupling force, and the stationary magnetic field of the second recording auxiliary layer is adjusted and exerted on the recording layer. Therefore, stable recording marks can be formed on the magneto-optical disk medium, and high-density recording becomes possible.

According to the third aspect of the present invention, by using the ferrimagnetic material having the compensation points in the magnetic field generation layer, recording is performed at the point where the external magnetic field applied and the coercive force of the magnetic field generation layer are balanced. The direction of the magnetic field applied to the layers is suddenly reversed. Therefore, the recording mark is emphasized (enhancement).
Is performed, and high density recording becomes possible.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a layer structure of an optical disc according to a first embodiment of the present invention.

FIG. 2 is a characteristic diagram of the optical disc of the first embodiment,
(A) is a first characteristic diagram, (B) is a second characteristic diagram.

FIG. 3 is a state of heat distribution when an optical disc is irradiated with a light beam, (A) is a light beam irradiation, and (B) is a heat transfer.

4A and 4B are explanatory diagrams showing a state of magnetization of each layer by optical modulation recording, in which (A) is room temperature, (B) is temperature increase, (C) is write temperature, and (D) is temperature decrease. Is.

FIG. 5 is an explanatory diagram of a magnetic field exerted on a recording layer,
(A) is each magnetic field, (B) is a synthetic magnetic field.

FIG. 6 is a distribution diagram of the magnetic field strength exerted on the recording layer in the optical modulation recording, (A) shows a high temperature (writing temperature),
(B) is at medium temperature, and (C) is at room temperature.

FIG. 7 is a diagram showing the relationship between the temperature of the recording layer and the coercive force.

8A and 8B are explanatory views showing a state of magnetization of each layer by magnetic field modulation recording, (A) at room temperature, (B) at a temperature rise, and (C).
Shows the start of cooling and (D) shows the end of cooling.

FIG. 9 is a distribution diagram of magnetic field strength exerted on a recording layer in magnetic field modulation recording, in which (A) shows room temperature, (B) shows temperature increase, (C) shows temperature decrease start, and (D) shows temperature decrease end. This is how it looks.

FIG. 10 is a diagram illustrating a layer structure of an optical disc according to a second embodiment of the present invention.

11A and 11B are views for explaining the characteristics of the optical disc of the second embodiment, where FIG. 11A is a relationship diagram between temperature and coercive force and magnetization intensity, and FIG. 11B is a relationship diagram between temperature and the direction of the generated magnetic field. is there.

FIG. 12 is a diagram illustrating a state of magnetization generated by a magnetic field generation layer.

FIG. 13 is a relationship diagram between the presence or absence of a magnetic field generation layer and crosstalk.

FIG. 14 is a diagram for explaining the layer structure of the optical disc in the third embodiment of the present invention.

FIG. 15 is a relationship diagram between a mark length and C / N.

FIG. 16 shows a state of magnetization during recording in magnetic field modulation recording.

FIG. 17 is an explanatory diagram of a state of recording pits in magnetic field modulation.

[Explanation of symbols]

1, 11, 21, 34, 40 ... Optical disc 2, 12, 22 ... Substrate 3, 13, 23 ... Dielectric protective film 4, 14, 25, 46 ... Recording layer 5, 15, 26 ... Nonmagnetic layer (blocking layer) ) 6a ... Recording auxiliary layer 6b ... Recording auxiliary layer 7, 17, 28 ... Dielectric protective film 8, 18, 30 ... Resin protective film 16, 27 ... Magnetic field generating layer 24 ... Super-resolution reproducing layer 29 ... Heat dissipation layer 32, 42 ... lens 36 ... high temperature section 44 ... recording mark 48 ... Shokomiso 50 ... initialization magnet 52 ... external magnetic field magnet LB ... light spot _{T 1 ~T 4, T 10,} T 11 ... isotherms T _C0 through T _C3 ... Curie temperature T _R ... room temperature T _W ... write temperature T _F ... leak temperature T _M ... maximum temperature H _C1, T _C2 ... coercivity

Claims (3)

[Claims] 1. A recording layer having a high coercive force in the vicinity of a reproducing temperature for reproducing information, which is higher than the reproducing temperature and reaches a Curie temperature in the vicinity of the recording temperature for recording information, the recording layer and the first recording layer. A blocking layer interposed between the recording auxiliary layer and the recording auxiliary layer for blocking magnetic exchange coupling between the first recording auxiliary layer and the recording layer; and a static magnetic force applied to the recording layer via the blocking layer. And a first recording auxiliary layer having a Curie temperature higher than the recording temperature and lower than the maximum temperature that can be reached by writing light, and the first recording auxiliary layer is magnetically exchange-coupled with the first recording auxiliary layer. A second recording auxiliary layer having a Curie temperature higher than the maximum temperature and having a coercive force capable of constantly applying an initializing magnetic field to the recording layer between room temperature and the maximum temperature; Magnetic recording medium. 2. A recording layer, which is higher than the reproducing temperature and reaches a Curie temperature near the recording temperature for information recording, and which is provided so as to be capable of magnetic exchange coupling with the recording layer by the recording temperature and writing light. A magneto-optical recording medium comprising: a recording auxiliary layer having a Curie temperature higher than the maximum attainable temperature. 3. A coercive force exceeding the intensity of magnetization from the magnetic field generating layer near the reproducing temperature for information reproduction, and a Curie temperature near the recording temperature for information recording which is higher than the reproducing temperature. A recording layer, a blocking layer interposed between the recording layer and the recording auxiliary layer and blocking a magnetic exchange coupling force between the first recording layer and the recording auxiliary layer, and a rare earth metal-transition metal A ferrimagnetic material having a compensation point of an alloy, which is magnetostatically coupled to the recording layer through the blocking layer, and the magnetization spins of the rare earth metal and the transition metal are inverted at a temperature equal to or higher than the compensation temperature and the temperature is higher than the compensation temperature A magneto-optical recording medium, comprising: the magnetic field generating layer having a coercive force of a predetermined value or less;