JP3089659B2 - Magneto-optical recording medium and recording method thereof - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium that performs recording and erasing using a temperature rise by a laser beam and performs reproduction using a magneto-optical effect.

2. Description of the Related Art In a magneto-optical recording medium, the temperature of a recording film is locally raised to a temperature higher than a compensation temperature or around a Curie temperature by laser light irradiation, and the recording film in a portion irradiated with the laser light is magnetized in the direction of an external magnetic field. Then, recording and erasing are performed (thermomagnetic recording). Reproduction is performed by irradiating a laser beam of lower intensity than the laser beam intensity at the time of recording / erasing, and detecting the situation where the polarization plane of reflected light or transmitted light rotates according to the recording state (magnetization direction) of the recording film. Do.

Conventionally, a method for performing an overwrite operation includes (a) irradiating a laser beam to locally raise the temperature of a recording film while applying a heat to an external magnetic field whose direction is modulated according to a recording signal. Magnetic recording method or (b)
First magnetic films exchange-coupled to each other as shown in FIG.
A composite recording film (here, the Curie temperature of the first magnetic film is lower than the Curie temperature of the second magnetic film) composed of a composite magnetic film 71 and a second magnetic film 72, and two external magnetic field applying devices 73, which provide mutually opposite magnetic fields. 74 and a method of performing thermomagnetic recording using a laser beam 75 intensity-modulated according to a recording signal (for example, Proceedings of the 34th Joint Lecture Meeting on Applied Physics 28p-2L-3, 1987), and (c) A laser whose pulse width is modulated in accordance with a recording signal using a rare earth-transition metal ferrimagnetic film having an appropriate composition (composition in which domain wall energy plays a major role in the stability of magnetic domains at room temperature or higher) as a recording film. Method of forming and erasing recording domains by irradiating light and controlling the change in domain wall energy in the irradiated area (eg, 13th Annual Meeting of the Japan Society of Applied Magnetics 23aC-1, 1989)
Etc.

However, in the first method of the related art, if the distance between the external magnetic field applying device and the recording film is set to several mm or more, it becomes difficult to apply a sufficient AC magnetic field at a frequency in the megahertz region. It cannot be applied to a magneto-optical recording medium having a double-sided configuration. Further, the second method requires two external magnetic field applying devices, and one of them needs to generate a strong magnetic field of 3 KOe or more, and thus has a disadvantage that the size of the device is increased. Further, the third method has a problem that it is difficult to achieve both the stability of the recorded magnetic domain and the erasability during the erasing operation.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides an overwritable magneto-optical recording medium which can be double-sided, does not require an external magnetic field applying device, and has excellent stability and erasability, and a recording method thereof.

Means for Solving the Problems In order to solve the above-mentioned problems, in the magneto-optical recording medium of the present invention, the recording film is formed by three perpendicular magnetic layers of a first magnetic film, a second magnetic film, and a third magnetic film from the light incident side. The first magnetic film and the second magnetic film are both ferrimagnetic, while the third magnetic film is ferromagnetic, and the Curie temperature T _C1 of the first magnetic film is made of a magnetic film.
<The Curie temperature T _C2 of the second magnetic film><The Curie temperature T _C3 of the third magnetic film is satisfied, and the compensation temperature of the second magnetic film is between room temperature and the Curie temperature T _C2 and near T _C1. While the third magnetic film has a composition in which the magnitudes of the two sublattice magnetizations are equal in the vicinity of T _C1 , each magnetic film is exchange-coupled to each other based on the respective sublattice magnetizations. ,
The exchange coupling force between the first magnetic film and the second magnetic film near room temperature is set to be weaker than the exchange coupling force between the second magnetic film and the third magnetic film and the coercive force of the first magnetic film, and near room temperature. The exchange coupling force between the second magnetic film and the third magnetic film is set to be stronger than the coercive force of the second magnetic film. Further, the recording method does not require an external magnetic field, and performs only the modulation of the irradiation laser beam to set the temperature reached by the recording film at two levels, high and low, thereby performing overwriting.

The present invention provides a first magnetic film for recording and reproducing information, a second magnetic film for controlling recording on the first magnetic film, and controlling a magnetization state of the second magnetic film. With the above-described configuration using the recording film composed of the third magnetic film, the Curie temperature of the first magnetic film differs depending on whether the temperature reached by the recording film in the laser beam irradiation area is high or low.
In addition to the operation of reversing the direction of the sublattice magnetization in the second magnetic film near T _C1 by the exchange coupling force from the third magnetic film, the direction of the sublattice magnetization of the second magnetic film is changed in the subsequent cooling process by the exchange coupling force. Thus, an operation of transferring to the first magnetic film can be performed to realize overwriting. Hereinafter, a specific description will be given.

First, the arrangement of the sublattice magnetization of the rare earth-transition metal based magnetic film will be described. When the rare earth metal is a light rare earth metal (having a 4f electron number of 6 or less), the transition metal and the sublattice magnetization of the rare earth metal are arranged in parallel to exhibit ferromagnetism, while the heavy rare earth metal (4f electron number Is 7 or more), the sublattice magnetizations of the transition metal and the rare earth metal are arranged antiparallel to exhibit ferrimagnetism. When the light rare earth metal is added to the heavy rare earth-transition metal based magnetic film, the light rare earth metal and the heavy rare earth metal have their sublattice magnetization arranged antiparallel to the sublattice magnetization of the transition metal. From the above, when the heavy rare earth-transition metal based magnetic film (including the case where the light rare earth metal is contained) and the light rare earth-transition metal based magnetic film are laminated, the secondary of the rare earth metal and the transition metal in each magnetic film is obtained. The magnitude relationship between the lattice magnetizations determines whether the sub-lattice magnetizations of the rare earth metals (also for transition metals) in the two magnetic films are arranged parallel or antiparallel to each other via exchange coupling force. become.

Next, the behavior of the sublattice magnetization in each film when the two magnetic films are exchange-coupled will be described. Assuming that the directions of the same type of sublattice magnetization of the first magnetic film and the second magnetic film are opposite, an exchange coupling force acts to align the directions.
The transfer magnetic field He ₁₂ acting from the first magnetic film to the second magnetic film based on the exchange coupling force is expressed as σ _w12 / (2M ₂ t ₂ ) −Hc ₂ and acts from the second magnetic film to the first magnetic film. Transfer magnetic field He
₂₁ is expressed as σ _w12 / (2M ₁ t ₁ ) −Hc ₁ . Here, σ _w12 is the domain wall energy per unit area of the interface between the two magnetic films, and M ₁ and M ₂ are the first
The saturation magnetizations t ₁ and t ₂ of the magnetic film and the second magnetic film are the thicknesses of the first magnetic film and the second magnetic film, respectively, and Hc ₁ and Hc ₂ are the coercive forces of the first magnetic film and the second magnetic film, respectively. is there. Therefore, if σ _w12 / (2M ₂ t ₂ ) <Hc ₂ and σ _w12 / (2M ₁ t ₁ )> Hc ₁ , the sublattice magnetization in the first magnetic film is of the same type in the second magnetic film. Inversion is performed so as to be aligned with the direction of the sublattice magnetization.

Further, the overall operation will be described. FIG. 2 schematically shows an overwriting operation of the magneto-optical recording medium of the present invention having a recording film composed of three magnetic films.
Here, solid and dashed arrows in the first magnetic film, the second magnetic film, and the third magnetic film indicate the sublattice magnetizations of the transition metal and the rare earth metal, respectively, and the length indicates the magnitude of the magnetization. The direction indicates the direction of magnetization. The hatched portion indicates the existence of the domain wall.

Since the exchange coupling force between the first magnetic film and the second magnetic film near room temperature is set to be weaker than the exchange coupling force between the second magnetic film and the third magnetic film, the coercive force of each film near room temperature is σ. _{w12 / (2M 1 t 1)} <Hc 1 ... (1) and _{σw 12 / (2M 2 t 2} ) <H c2 ... (2) cutlet _{σ w23 / (2M 2 t 2} )> Hc 2 ± σ w12 / ( 2M ₂ t ₂ ) (3) and σ _w23 / (2M ₃ t ₃ ) <Hc ₃ (4) If the relationship of (4) is satisfied, the arrangement of each sublattice magnetization is changed to the initial state (A) or (F). It can be set as follows. Here, σ _w12 and σ _w23 are domain wall energies per unit area of the interface between the first magnetic film and the second magnetic film and the interface between the second magnetic film and the third magnetic film, respectively, and M _1, M ₂ and M ₃ are the first magnetic layer and the second magnetic layer and the third saturation magnetization of the magnetic film, t ₁ and t ₂ and t ₃ the first magnetic layer and the second magnetic layer and the thickness of the third magnetic layer each respectively, Hc ₁ and Hc ₂ and Hc ₃ are the coercive forces of the first magnetic film, the second magnetic film, and the third magnetic film, respectively. Further, a second rare-earth-transition metal ferrimagnetic film is used.
FIGS. 3 and 4 are schematic diagrams showing the temperature dependence of the sublattice magnetization and the coercive force of the magnetic film and the third magnetic film, which is a rare earth-transition metal ferromagnetic film, respectively. In both the second magnetic film and the third magnetic film, the sub-lattice magnetization of the rare earth metal is dominant near room temperature, while the sub-lattice magnetization of the transition metal is dominant at high temperatures. The coercive force is maximized at the compensation temperature at which the two sublattice magnetizations are substantially equal in the case of the second magnetic film, which is a ferrimagnetic film, whereas the third magnetic film, which is a ferromagnetic film, is obtained. In the case of, it decreases monotonously with temperature.

First, when the temperature reached by the recording film is raised to a high level by modulation of the irradiation laser light (that is, the laser power is increased or the pulse width is increased), the average temperature of the second magnetic film in the laser light irradiation region is The temperature exceeds the Curie temperature T _C1 of the first magnetic film and reaches around the Curie temperature T _C2 of the second magnetic film (C). Since the cooling _{σ w23 / (2M 2 t 2} ) in the process> may satisfy the relationship of Hc _2, T _C2 sublattice dominant sublattice magnetization transition metal of the second magnetic film and the third in the magnetic film before and after Because of the magnetization, the sublattice magnetization of the transition metal of the second magnetic film in this region is reversed so as to be aligned with the direction of the sublattice magnetization of the transition metal of the third magnetic film (D). When the cooling proceeds further and the average temperature of the first magnetic film and the second magnetic film in the laser beam irradiation area becomes near T _C1 , the magnetization of the first magnetic film also occurs, but the compensation temperature of the second magnetic film is increased. Is set near T _C1 , HC ₂ takes a large value, σ _w12 / (2M ₁ t ₁ )> Hc ₁ and σ _w12 / (2M ₂ t ₂ ) <Hc ₂ ± σ _w23 / (2M ₂ t ₂ ), the respective sub-lattice magnetizations of the first magnetic film in this region are reversed so as to be aligned with the same type of sub-lattice magnetization of the second magnetic film. (E). After cooling to room temperature,
From the relations of the expressions (1) to (4), the direction of the sublattice magnetization of the first magnetic film is fixed as it is, while the direction of the second lattice around the room temperature is fixed.
Since the predominant sublattice magnetization in the magnetic film and the third magnetic film is the sublattice magnetization of the rare earth metal, the sublattice magnetization of the rare earth metal of the second magnetic film is the sublattice magnetization of the rare earth metal of the third magnetic film. (F).

Further, even if the laser beam is irradiated from the state of (F) and heated again to a high level, the state is returned from the state of (C) to the state of (F) by following the same process as that described above.

Next, when the temperature reached by the recording film is lowered to a low level by the modulation of the irradiation laser light in the state (F) (that is,
In order to reduce the laser power or shorten the pulse width), the average temperature of the first magnetic film and the second magnetic film in the laser light irradiation region is around T _C1 . Since the compensation temperature of the second magnetic film is set in the vicinity of T _C1 , the coercive force Hc ₂ of the second magnetic film increases in the course of this temperature increase, resulting in σ _w12 / (2M ₂ t ₂ ) <Hc ₂ ± σ _w23 / (2M ₂ t ₂ ) and σ _w23 / (2M ₂ t ₂ ) <Hc ₂ ± σ _w12 / (2M ₂ t ₂ ), and the direction of the sublattice magnetization of the second magnetic film is around room temperature. (G). In the cooling process, the _relationship of σ _w12 / (2M ₁ t ₁ )> Hc ₁ and σ _w12 / (2M ₂ t ₂ ) <Hc ₂ ± σ _w23 / (2M ₂ t ₂ ) can be satisfied. As a result of reversing each sublattice magnetization of one magnetic film so as to be aligned with the same type of sublattice magnetization of the second magnetic film, the recording magnetic domain existing in the first magnetic film in the state (F) is erased. (H).
Then, it is cooled to room temperature and returns to the initial state (A).

Further, even if the laser light is irradiated again from the state of (A) and heated to a low level again, the state of (G) returns to the state of (A) by following the same process as the above-described process.

By repeating the above-described four steps, an overwrite operation can be performed, and two external magnetic field applying devices which are disadvantages of the conventional overwrite method using two exchange-coupled magnetic films as recording films are required. The problem that there is can be solved.

Embodiment A magneto-optical recording medium according to an embodiment of the present invention and a recording method thereof will be described below with reference to the drawings.

FIG. 1 shows the configuration of a magneto-optical recording medium according to one embodiment of the present invention. In FIG. 1, 11 is a substrate made of a polycarbonate resin, 12 and 16 are protective films made of a ZnS film, and 13 has a large coercive force near room temperature.
A first magnetic film 14 made of a TbFe film, and a second magnetic film 14 made of a GdTbFe film having a compensation temperature near the Curie temperature T _C1 of the first magnetic film.
Magnetic film, 15 is a third magnetic film comprising a SmFeCo film size of the transition metal sublattice magnetization and the rare earth metal sublattice magnetization is composition comprising the same in the vicinity of T _C1, the first magnetic layer 13 and the second magnetic The recording film is composed of the film 14 and the third magnetic film 15. Here, each film on the substrate 11 is formed by a sputtering method,
The thicknesses of the protective films 12 and 16 are 80 nm, the thickness of the first magnetic film 13 is 60 nm,
The second magnetic film 14 and the third magnetic film 15 are set to 70 nm. The Curie temperature T _C1 of the first magnetic film 13 is set to 120 ° C., the Curie temperature T _C2 of the second magnetic film 14 is set to 200 ° C., and the Curie temperature T _C3 of the third magnetic film 15 is set to 250 ° C.

After magnetizing the magneto-optical recording medium configured as described above to the state (A) in FIG. 2, it was moved at a linear velocity of 6 m / sec.
As shown in FIG. 5, an intensity-modulated laser beam is irradiated. In the part irradiated with 9 mW laser light (a), the temperature reached by the recording film is at a high level, and a recording magnetic domain is formed. In the part irradiated with 5 mW laser light (b), the temperature reached by the recording film Becomes low level and the recording magnetic domain is erased, thereby achieving a stable overwrite operation.

As described above, according to the present invention, the stability and the simple configuration are improved.
Overwriting with excellent erasability becomes possible.

In the magneto-optical recording medium of this embodiment, the substrate 11 is made of polycarbonate, the protective films 12 and 16 are made of a ZnS film,
A TbFe film as the magnetic film 13, a GdTbFe film as the second magnetic film 14,
Although the SmFeCo film was used as the third magnetic film 15, the substrate 11 was made of another plastic or glass, and the protective films 12 and 16 were made of an oxide film such as TaO ₂ or another chalcogenide film such as ZnSe or SiN. For a nitride film, a film of a mixture thereof, and three magnetic films exchange-coupled to each other,
The first magnetic film 13 is a perpendicular magnetization film of another rare earth-transition metal based ferrimagnetic film or another ferrimagnetic material having a large coercive force near room temperature, and the second magnetic film 14 is a Curie temperature T _C1 of the first magnetic film. Other rare earths with compensation temperature near
A transition metal ferrimagnetic film or a perpendicular magnetization film of another ferrimagnetic material having a Curie temperature T _C2 higher than T _C1 , and a third magnetic film 15 having two types of sublattice magnetization near T _C1 . Perpendicular to other rare earth-transition metal ferromagnetic films (composed of light rare earth metals such as Sm, Nd, Pr, etc., alone or in combination) or other ferromagnetic materials having the same composition A magnetic film having a Curie temperature T _C3 higher than T _C2 may be used.

Further, in order to improve the perpendicularity and the stability of the magnetization direction of the third magnetic film at a high temperature and to make the overwriting operation of the magneto-optical recording medium of the present invention more stable,
It is effective to newly provide a fourth magnetic film exchange-coupled with the third magnetic film as shown in the figure. The fourth magnetic film needs to have a larger coercive force at room temperature or higher than the third magnetic film and have a Curie temperature T _C4 equal to or higher than T _C3 , so that a transition metal ferromagnetic film such as CoCr or the like can be used. Rare earth-transition metal based ferrimagnetic film or T in which transition metal sublattice magnetization is dominant in the temperature range from around room temperature to _TC3
Third and perpendicular magnetization film of predominant sublattice magnetization of the same type of other ferromagnetic material or ferrimagnetic material which is a dominant sublattice magnetization in a temperature range from about room temperature to T _C3 of the magnetic film is suitable in the vicinity _C3 I have.

Further, in the recording method of the present embodiment, modulation of only intensity is used as a modulation method of the irradiation laser light, but only at the time of high level and at the time of low level using only pulse width modulation or a combination of pulse width modulation and intensity modulation. May be provided.

As described above, according to the present invention, the first magnetic film for recording and reproducing information, the second magnetic film for controlling recording on the first magnetic film, and the second magnetic film By irradiating an intensity-modulated or pulse-width-modulated laser beam to a magneto-optical recording medium using a recording film composed of a third magnetic film for controlling the magnetization state, When the reached temperature is high level and low level,
The operation of reversing the direction of the sublattice magnetization in the second magnetic film near the Curie temperature T _C1 of the first magnetic film by the exchange coupling force from the third magnetic film, and in the subsequent cooling process, the sublattice of the second magnetic film By performing an operation of transferring the direction of magnetization to the first magnetic film by the exchange coupling force, overwriting with excellent stability and erasability can be realized with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a structural view of a magneto-optical recording medium according to one embodiment of the present invention, FIG. 2 is a schematic diagram of an overwrite operation of the magneto-optical recording medium of the present invention, and FIG. FIG. 4 is a schematic diagram of the temperature dependence of sublattice magnetization and coercive force of a rare earth-transition metal based ferrimagnetic film as a second magnetic film of a magnetic recording medium. FIG. 4 is a diagram of a magneto-optical recording medium according to an embodiment of the present invention. FIG. 5 is a schematic view showing the temperature dependence of the sublattice magnetization and coercive force of a rare earth-transition metal ferromagnetic film which is a three-magnetic film. FIG. 5 is a view showing a driving state of irradiation laser light in one embodiment of the present invention. FIG. 6 is a configuration diagram of a magneto-optical recording medium according to another embodiment of the present invention, and FIG. 7 is a configuration diagram of one conventional overwriting method. 11 ... substrate, 12 ... protective film, 13 ... first magnetic film, 14 ...
Second magnetic film, 15 Third magnetic film, 16 Protective film 61 Substrate, 62 Protective film, 63 First magnetic film, 64 Second magnetic film, 65 Third Magnetic film, 66: fourth magnetic film, 67: protective film.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-205835 (JP, A) JP-A-2-24801 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 11/105 506 G11B 11/105 586

Claims (7)

(57) [Claims] The recording film is composed of a first magnetic film, a second magnetic film, and a third magnetic film in order from the light incident side. The Curie temperature of the first magnetic film T _C1 <second magnetic film Curie temperature of membrane T _C2
<Satisfies the relationship of the Curie temperature T _C3 of the third magnetic film,
The magnetic film and the second magnetic film both have a ferrimagnetic film, whereas the third magnetic film is a ferromagnetic film, and the second magnetic film is between room temperature and the Curie temperature T _C2 and is compensated near T _C1. While there is a magnetic film having a composition having a temperature, the third magnetic film has T _C1
A magnetic film having a composition in which the magnitudes of the two sublattice magnetizations become equal in the vicinity of each other, and the respective magnetic films are exchange-coupled to each other based on the respective sublattice magnetizations.
The exchange coupling force between the magnetic film and the second magnetic film is higher than the third magnetic film and the third magnetic film.
The exchange coupling force with the magnetic film and the coercive force of the first magnetic film are set to be weaker, and the exchange coupling force between the second magnetic film and the third magnetic film near room temperature is stronger than the coercive force of the second magnetic film. A magneto-optical recording medium characterized by being set. 2. The method according to claim 1, wherein the first magnetic film and the second magnetic film are a rare earth-transition metal ferrimagnetic film, and the third magnetic film is a rare earth-transition metal ferromagnetic film. Magneto-optical recording medium. 3. The rare earth-transition metal ferrimagnetic film contains only rare rare earth metals such as Tb, Gd, and Dy as rare earth metals or both heavy rare earth metals and light rare earth metals such as Sm, Nd, and Pr. 3. The magneto-optical recording medium according to claim 2, wherein the metal-based ferromagnetic film contains only a light rare earth metal as the rare earth metal. 4. The recording film is composed of four perpendicular magnetic films of a first magnetic film, a second magnetic film, a third magnetic film, and a fourth magnetic film from the light incident side, and has a Curie temperature T of the first magnetic film. _C1 <Curie temperature T _C2 of second magnetic film <Curie temperature T _C3 of third magnetic film ≦ Curie temperature T _C4 of fourth magnetic film
While the second magnetic film is a ferrimagnetic film,
The magnetic film is a ferromagnetic film, and the second magnetic film is room temperature and T _C2
Be a third magnetic film magnetic film having a composition magnitudes of the two sub-lattice magnetization is equal around T _C1 whereas there is a magnetic film having a composition having a compensation temperature in the vicinity of T _C1 be between the fourth magnetic layer is an ferromagnetic film or ferrimagnetic film predominant in the temperature range from the third magnetic film predominant sublattice magnetization of the same type of sublattice magnetization near room temperature in the vicinity of T _C3 to T _C3 The respective magnetic films are exchange-coupled to each other based on their respective sublattice magnetizations, and the exchange coupling force between the first magnetic film and the second magnetic film near room temperature indicates the exchange coupling between the second magnetic film and the third magnetic film. And the exchange coupling force between the second magnetic film and the third magnetic film near room temperature is set to be stronger than the coercive force of the second magnetic film. Characteristic magneto-optical recording medium. 5. The first magnetic film and the second magnetic film are rare earth-transition metal ferrimagnetic films, the third magnetic film is a rare earth-transition metal ferromagnetic film, and the fourth magnetic film is a transition of CoCr. Metal-based ferromagnetic films or rare earths in which transition metal sublattice magnetization is dominant in the temperature range from room temperature to _TC3-
5. The magneto-optical recording medium according to claim 4, wherein the magneto-optical recording medium is a transition metal ferrimagnetic film. 6. The rare earth-transition metal ferrimagnetic film contains only rare rare earth metals such as Tb, Gd and Dy or both heavy rare earth metals and light rare earth metals such as Sm, Nd and Pr as rare earth metals. 6. The magneto-optical recording medium according to claim 5, wherein the metal ferromagnetic film contains only a light rare earth metal as the rare earth metal. 7. The temperature reached by a recording film is set to two levels, high and low, by modulating only the irradiation laser light without using an external magnetic field on the magneto-optical recording medium according to claim 1 or 4. Recording method for a magneto-optical recording medium, characterized in that overwriting is performed.