JP2869449B2 - Magneto-optical recording method and magneto-optical recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magneto-optical recording method capable of overwriting (overwriting) and a magneto-optical recording medium used for the method.

[Problems to be solved by conventional technology and invention]

The magneto-optical recording medium has a large recording capacity because information is recorded and reproduced by using a laser beam similarly to a conventional optical recording medium, and can be rewritten. Further, recording and reproduction can be performed without contact between the head and the medium, and the recording medium is not affected by dust, so that the stability is excellent. For this reason, magneto-optical recording media are being actively studied at present, and document information files,
It is expected to be used for video / still image files, memory for computers, etc. or to replace floppy disks and hard disks, and some of them have reached the stage of commercialization.

As a magnetic film used for the recording layer of such a magneto-optical recording medium, a transition metal (Fe, Co) and a rare earth metal (Gd, Dy, Tb,
Nd) and TbFe, TbFeCo, GdTbFeCo, NdDyFe
Various amorphous (amorphous) magnetic alloy films such as Co have been proposed. Since this magnetic alloy film is amorphous, there is no medium noise due to grain boundaries, and there is an advantage that a perpendicular magnetization film can be easily produced by a sputtering method or a vapor deposition method.

Fast recent recording, in order to correspond to densification, Curie temperature T _c, the coercive force H _c, is necessary thermomagnetic properties such as Kerr rotation angle theta _k is even better, Therefore, new Various magneto-optical recording materials have been developed and magneto-optical recording films have been improved. Among them, a magneto-optical recording medium having a so-called function-separated double-layer film structure has been proposed in which the magneto-optical recording film has a two-layer structure, and each of the films has a recording and reproducing function (Japanese Patent Application Laid-Open No. Sho 56). -153546, 57-78652, 60-177455, 63-1
No. 53752).

In a conventional magneto-optical recording medium having a two-layer film structure, recording and erasing are performed by utilizing an exchange coupling effect in which spins of both magnetic layers try to be parallel to each other. However,
When recording and erasing are performed in this manner, if recording and reproduction are repeated many times, a change in composition or oxidative deterioration occurs at the interface between the two magnetic layers, which affects the exchange coupling action between the two magnetic layers. Become like As a result, records,
The erasing conditions such as the optimum laser power and the magnitude of the bias magnetic field at the time of recording and erasing were changed, and there was a problem in long-term stability.

As a magneto-optical recording method, an optical modulation method is generally employed in which an information signal is modulated by a laser beam, and the direction of application of a bias magnetic field is changed in accordance with recording and erasing to perform recording and erasing. In this method, overwriting cannot be performed unlike a hard disk. Therefore, when new information is to be recorded when information has already been recorded, it is necessary to perform erasure first and then perform new recording. Therefore, there is a disadvantage that the access time is delayed by the erasing wait time.

In order to solve the above disadvantages, the present applicant has disclosed in
In Japanese Patent Laid-Open Publication No. 2 (1994), a magnetic field modulation method for continuously irradiating a magneto-optical recording medium with laser light and modulating an information signal with a magnetic field from a magnetic head was proposed. According to this method, overwriting can be performed similarly to a hard disk.

On the other hand, from the viewpoints of high-speed information processing, substitution of a hard disk, and the like, it has been demanded that magneto-optical recording media can perform high-speed and high-density recording equal to or higher than a hard disk.

However, performing overwritable recording by the magnetic field modulation method under such a high speed condition has the following inconveniences.

It is necessary to perform the magnetic field reversal of the magnetic head at a high speed of 15 MHz or more, but this is practically difficult.

In order to obtain a magnetic field of 200 to 3000 e required for magnetization reversal, the magnetic head must be levitated to a height that almost contacts the magneto-optical recording medium. In the same way as in the case of a hard disk, problems such as wear and damage occur, and the reliability of non-contact recording, which is an advantage of the magneto-optical recording method, is impaired.

When performing recording at high frequency, the shape of the recording bit becomes a crescent shape with a long tail due to the heat conduction and thermomagnetic recording characteristics of the magneto-optical recording medium, which causes noise and causes C / N
Lower.

Therefore, unlike the above methods, a method of performing overwriteable recording by changing the light intensity of a single laser beam is described in the 34th Annual Meeting of the Japan Society of Applied Physics (Spring 1987), p.721, 28P-
ZL-3 has been proposed in JP-A-62-175948. The magneto-optical recording method described in the document uses a magneto-optical recording medium provided with a ferrimagnetic exchange-coupling two-layer film composed of a memory layer and an auxiliary layer, and a light intensity modulation method using an auxiliary magnet for initialization. is there. Hereinafter, the overwriting process by this method will be described with reference to FIGS. 30 and 31.

The magneto-optical recording medium used in this method is composed of a memory layer 31 and an auxiliary layer 32 as shown in FIG. 30 (a). _c is large, is used Curie temperature T _c is less material (e.g. TbFeCo), the auxiliary layer 32 has a small coercive force H _c was dominant magnetic moments of the rare-earth metals at room temperature, the Curie temperature T _c higher material (e.g. TbDyFeCo) is used. During Figure 30 (a), a ₁ is recorded portion, a ₂ denotes an erase unit. The thermomagnetic properties of each amorphous magnetic alloy film used for the memory layer 31 and the auxiliary layer 32 are as shown in FIG. In FIG. 31, Hex is a bias magnetic field, and T ₁ and T ₃ are erasing and recording operating temperatures, respectively.

First, as shown in FIG. 30 (a), a medium recorded and erased by laser beam intensity modulation is applied to a medium using an initialization auxiliary magnet.
An initialization magnetic field Hin of ~ 7KOe is applied. Then since the memory layer 31 of the recording unit a ₁ is the coercive force is large at room temperature, as shown in FIG. 31, only the auxiliary layer 32 of the recording unit a ₁ is inverted as Figure 30 (b). In this state, when the bias magnetic field Hex is applied upward and laser irradiation (low power) is performed to raise the temperature (T ₁ ), the coercive force H _c of the memory layer 31 of the recording unit a ₁ rapidly decreases,
Magnetization reversal in the memory layer 31 of the recording unit a ₁ occurs, the recording unit a ₁ as Figure 30 when lowering the temperature in this state (d) are erased. Laser irradiation (high power) from the state of Fig. 30 (d)
Was carried out, when the heated auxiliary layer 32 to the temperature T ₂ higher than the compensation temperature Tcomp, since the magnetization of the memory layer 31 is lost, the coercive force H _c of the auxiliary layer 32 is smaller than the bias field Hex, Figure 30 ( As shown in e), the magnetization of the auxiliary layer 32 is changed by the bias magnetic field Hex.
When it is cooled to room temperature from this state,
Recording is performed as shown in FIG.

However, in the above method, 6K
It is necessary to initialize by applying a magnetic field as large as Oe to make the direction of magnetization uniform.Therefore, a permanent magnet or electromagnet must be provided for initialization, making it difficult to reduce the size of the magneto-optical head. The exchange coupling effect acting between two types of magnetic films having different thermomagnetic properties and the magnetic properties of each magnetic layer are complicatedly changed by temperature, so that the recording and erasing processes are also complicated, and characteristics with good reproducibility are obtained. Is difficult, and the heat due to the repeated laser beam irradiation of reproduction and erasure promotes oxidation, and the movement of metal atoms at the interface between the two magnetic layers deteriorates the recording and erasure characteristics, which is considered to be difficult to put to practical use. ing.

The present invention solves the above-mentioned drawbacks of the prior art, achieves an overwriteable magneto-optical recording that can be initialized, has a short access time, and can cope with high-speed recording, and repeatedly performs recording and reproduction. It is another object of the present invention to realize magneto-optical recording having excellent long-term stability in which recording and reproduction conditions do not change.

[Means and Actions for Solving the Problems]

To achieve the above object, according to the present invention, a magneto-optical recording medium having a recording layer formed by laminating first and second magnetic layers having different temperature characteristics of coercive force is used. By changing the beam intensity, applying a bias magnetic field in the same direction during recording and erasing at the same time, and changing the magnitude of the bias magnetic field during recording and erasing, or applying a bias magnetic field to only one of recording and erasing A magneto-optical recording method for performing overwritable recording, wherein the magneto-optical recording medium includes a recording layer between the first magnetic layer and the second magnetic layer where no exchange coupling force acts. A magneto-optical recording method using a magneto-optical recording medium is provided.

Further, according to the present invention, the first and second magnetic layers each composed of a perpendicular magnetization film having different temperature characteristics of coercive force are laminated.
A magneto-optical recording medium for use in the above method is provided, which comprises a recording layer having a layer structure and having no exchange coupling force acting between both magnetic layers.

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

Magneto-optical recording medium used in the present invention, as shown in FIGS. 1 and 2, were laminated essentially coercive force H first magnetic layer 1 and the second magnetic layer 2 in which the temperature characteristics different _c A recording layer having a two-layer structure and having only a magnetostatic force acting without an exchange coupling force acting between the two magnetic layers 1 and 2 is provided. Both magnetic layers 1,
Focusing on the temperature characteristic of the coercive force _Hc of No. 2, the magneto-optical recording medium used in the present invention has three types (hereinafter referred to as type A and type A) as shown in FIG. 3, FIG. 4 and FIG. Type B and Type C). In order to form a recording layer in which no exchange coupling force acts between the two magnetic layers 1 and 2, an appropriate material and an appropriate thickness between the two magnetic layers 1 and 2 are required as shown in FIG. The layer 3 may be provided. Also, depending on the combination of materials used for the two magnetic layers 1 and 2, there is no center layer 3, that is, with a recording layer configuration as shown in FIG.
The exchange coupling force can be prevented from acting between the two magnetic layers 1 and 2.

The magneto-optical recording medium used in the present invention and the principle of recording and erasing in the magneto-optical recording method using the same will be described in detail below for each type.

The type A magneto-optical recording medium is composed of a first magnetic layer 1 made of a ferromagnetic material or a ferrimagnetic material in which a transition metal (TM) has a superior magnetic moment at room temperature and a ferrimagnetic material in which a rare earth metal (RE) is superior at a room temperature. The second magnetic layer 2.
Temperature characteristics of the coercive force H _c of the magnetic layers 1 and 2 is as shown in Figure 3. This type A magneto-optical recording medium has seven types as shown in FIGS. 6 to 19, depending on the magnetization directions of the first magnetic layer 1 and the second magnetic layer 2 in the initialized state (erased state). Can be divided into Sixth
FIG. 7 (FIG. 7), FIG. 8 (FIG. 9), FIG. 10 and FIG. 11 show cases where the magnetizations of the first magnetic layer 1 and the second magnetic layer 2 in the initialized state are in the same direction. Fig. 12 (Fig. 13),
Fig. 14 (Fig. 15), Fig. 16 (Fig. 17) and Fig. 18 (Fig. 19
FIG. 3 shows a case where the magnetization directions of the magnetic layers 1 and 2 in the initialized state are opposite to each other.

First, recording when using a medium of the type shown in FIG. 6 (FIG. 7), that is, a type in which the magnetization directions of the first magnetic layer 1 and the second magnetic layer 2 in the initialized state are the same as each other, The operation principle of erasing will be described. In FIG. 6 (FIG. 7), (a) shows the magnetization state after recording (the recording bit is in the middle), and (c) shows the magnetization state after erasing.

Figure 6 small bias magnetic field downward in the figure together with the recording as shown in (a) are irradiated with a laser beam of high power P _H to the bit (middle of bits) that are performed Hb [L]
The application of a temperature of the medium is increased to T _H corresponding to P _H,
In the first magnetic layer 1 that temperature T _H is the Curie temperature Tc ₁
Since the magnetization becomes larger, the magnetization disappears, and the magnetization of the remaining transition metal (TM) in the second magnetic layer 2 is changed by the bias magnetic field.
It is inverted by Hb [L] (FIG. 6 (b)). Here the second
The coercive force of the magnetic layer 2 is almost zero, and the magnetic field from the surroundings
Since Hf acts, magnetization reversal can be performed when the bias magnetic field Hb [L] is zero or a small value. And when the medium temperature drops, the second
Since magnetization of the rare earth metal (upward in the figure) occurs in the magnetic layer 2 and the magnetostatic force Hs is larger than the bias magnetic field Hb [L],
The magnetization reversal occurs in the first magnetic layer 1 so as to be aligned with the magnetization, and an erasing state as shown in FIG. 6C is obtained.

Next, when irradiated with a laser beam of low power P _L to the bits of the erase state of FIG. 6 (c) (the middle of the bit), the medium temperature is raised to T _L corresponding to P _L. At this time, the coercive force Hc ₁ (T _L ) of the first magnetic layer 1 becomes smaller than the bias magnetic field Hb [H], and the magnetization of the first magnetic layer 1 is reversed. On the other hand, since the coercive force Hc ₂ (T _L ) of the second magnetic layer 2 is larger than the bias magnetic field Hb [H], the magnetization of the second magnetic layer 2 does not reverse. This is the state shown in FIG. When the temperature drops to room temperature in this state, the coercive force Hc _{2 of} the second magnetic layer 2 decreases, and the sum Hb [H] + of the bias magnetic field Hb [H] and the magnetostatic force Hs from the first magnetic layer.
Hs becomes larger than the coercive force Hc ₂ (T _R ) at room temperature of the second magnetic layer 2, that is, Hb [H] + Hs> Hc ₂ (T _R ), and becomes equal to the magnetization of the first magnetic layer 1. The magnetization of the two magnetic layers 2 is reversed,
The recording state is as shown in FIG. 6 (e) (same as FIG. 6 (a)), indicating that overwriting has been performed. In the case of the present case, it erases with a laser power of high power P _H,
It is adapted to perform recording with a laser beam of low power P _L. That is, the laser beam for recording and erasing is set to P
w, a _{P E (≡P H)> Pw} (≡P L) the relationship when the P _E, and the direction of the bias magnetic field Hb during recording, both the second magnetic layer 2 when erasing initialization state The direction is opposite to the direction of magnetization. The application of the bias magnetic field Hb may be performed as follows.

During laser beam irradiation of lower power P _L in of the laser beam at the time of erasing the recording are rendered the laser beam irradiation greater bias magnetic field Hb from the time of higher power P _H, when the laser beam irradiation of a high power P _H Applies a small bias magnetic field Hb, but in this case, it is not always necessary to apply the bias magnetic field Hb. A large (small or zero) bias magnetic field Hb is always applied by an electromagnet or a permanent magnet when driving a magneto-optical device, and is used when irradiating a high power P _H laser beam or using a low power.
P _L of the laser beam irradiation either only one small synchronously or zero when (large) to impart a bias magnetic field Hb.

FIG. 7 is an explanatory diagram of the recording and erasing operations when erasing is performed using a medium of the same type as in FIG. 6 using a laser beam having a low power P _L and recording is performed using a laser beam having a high power P _H. In this case, the direction of the bias magnetic field Hb is the same as the direction of the magnetization in the initialized state of the second magnetic layer 2 both during recording and erasing.

Figure 7 drawing upward large bias magnetic field Hb irradiates a laser beam of low power P _L bit (middle of bits) of recording as shown in (a) is being performed [H]
Is applied. Then, the medium temperature rises to T _L corresponding to P _L , and the coercive force in the first magnetic layer 1 as shown in FIG.
Hc ₁ (T _L ) becomes smaller than the bias magnetic field Hb [H], and the magnetization is reversed (FIG. 7B). When the temperature of the medium drops, the magnetization of the second magnetic layer 2 is reversed so as to be aligned with the magnetization of the first magnetic layer 1, and an erase state as shown in FIG.

Next, the bits of the erase state of FIG. 7 (c) irradiating a laser beam (middle bit) to a high power P _H, the bias magnetic field Hb [L] is smaller than when laser beam irradiation at the same time lower power P _L Granting, medium temperature is raised to T _H corresponding to P _H. Then, the first magnetic layer 1 has its Curie temperature Tc
Since the temperature rises to ₁ or more, the magnetization disappears, while the second magnetic layer 2
, The magnetization (downward in the figure) of the remaining transition metal (TM) is reversed to the direction of the bias magnetic field Hb [L] (upward in the figure) (FIG. 7 (d)). When the medium is cooled, the second magnetic layer 2 has a rare earth metal (RE) magnetization (downward in the figure).
Is generated, and magnetization reversal occurs in the first magnetic layer 1 so as to be aligned with the magnetization due to the magnetostatic force, and a recording state as shown in FIG. 7 (e) (same as FIG. 7 (a)) is obtained. Has been done.

FIG. 8 (FIG. 9) shows, similarly to FIG. 6 (FIG. 7), the erasing and recording of a medium in which the magnetizations of the first magnetic layer 1 and the second magnetic layer 2 in the initialized state are in the same direction as each other. It is a figure showing a principle. In the Figure 8 case, during recording, by applying a bias magnetic field Hb of magnetization in the same direction in the initial state of the erasing both the second magnetic layer 2, it erases with a laser beam of low power P _L, high performing recording by a laser beam of power P _H.
On the other hand, FIG. 9 shows a case where erasing is performed using a laser beam having a high power P _H and recording is performed using a laser beam having a low power P _{L. In} this case, the bias magnetic field Hb is applied to the second magnetic field both during recording and erasing. It is applied in the direction opposite to the direction of the magnetization in the initialized state of the layer 2.

10 and 11, similarly to FIG. 6, the magnetizations of the first magnetic layer 1 and the second magnetic layer 2 in the initialized state are in the same direction as each other. In these cases, erasing is performed using a laser beam having a low power P _L and recording is performed using a laser having a high power P _H , and the direction of the bias magnetic field Hb is opposite to the direction of the magnetization in the initialized state of the second magnetic layer 2. I do. In these cases, the first magnetic layer 1 becomes a recording / reproducing layer.

Fig. 12 (Fig. 13), Fig. 14 (Fig. 15), Fig. 16 (Fig. 17
FIG. 18 and FIG. 18 (FIG. 19) show a type A medium in which the magnetization directions of the first magnetic layer 1 and the second magnetic layer 2 in the initialized state are opposite to each other. FIG. Bias magnetic field when using these media
The magnitude of Hb is Hc ₁ (T _L ) <H _b <Hc ₂ (T _L ) as in FIG.

In FIG. 12 (FIG. 13) and FIG. 14 (FIG. 15), when the first magnetic layer 1 is used as a recording and reproducing layer, (c) shows an erased state, and (a) shows a recorded state. Fig. 16 (Fig. 17
In FIG. 18 and FIG. 18 (FIG. 19), when the first magnetic layer 1 is used as a recording / reproducing layer, (a) shows an erased state, and (c)
Indicates a recording state. Therefore, in these media, erasing is performed with a laser beam of low power P _L and high power P _H
When recording is performed with the laser beam of Pw (≡P _H )> P _E
In the case of (≡P _L ), overwriting can be achieved by setting the direction of the bias magnetic field Hb to the direction opposite to the magnetization direction of the initialized state of the second magnetic layer 2. On the other hand, when erasing the laser beam with the high power P _H and performing recording with the laser beam with the low power P _L , that is, when Pw (LP _L )> P _E (≡P _H ), the direction of the bias magnetic field Hb Is set in the same direction as the magnetization direction of the initialized state of the second magnetic layer 2, overwriting can be achieved.

Among the type A media described above, the media shown in FIGS. 6 (FIG. 7) and FIG. 8 (FIG. 9) have the first magnetic layer 1 and the second magnetic layer 1.
Any of the magnetic layers 2 may be used as the recording and reproducing layers. In the medium of FIGS. 10 and 11, the first magnetic layer 1 is recorded,
Used as a reproduction layer. For other media, the first magnetic layer 1
Is a recording / reproducing layer, and the recording / erasing state is switched between when the second magnetic layer 2 is a recording / reproducing layer.

Examples of the magnetic material used for the first magnetic layer 1 of the type A medium include TbFe, TbDyFe, GdDyFe, GdTbFe, GdTbDyFe, D
yFeCo, TbFeCo, TbDyFeCo, GdDyFeCo, GdTbFeCo, GdDyFeCo, T
bHoFeCo, TbErFeCo, NdDyFeCo or the like having a compensation temperature lower than room temperature and a Curie temperature of 70 ° C. or more and 200 ° C. or less are used.

Examples of the magnetic material used for the second magnetic layer 2 include GdTbFe, GdDyFe, GdTbDyFe, TbFeCo, DyFeCo, GdFeCo, and Tb.
DyFeCo, GdDyFeCo, GdTbFeCo, GdTbDyFeCo and the like are used as amorphous magnetic materials whose compensation temperature is higher than room temperature and whose Curie temperature is 160 ° C. or more and 300 ° C. or less.

In the type B magneto-optical recording medium, both the first magnetic layer 1 and the second magnetic layer 2 are made of a ferrimagnetic material in which rare earth metal (RE) is superior at room temperature. These magnetic layers 1 and 2 are as shown in FIG. It has temperature characteristics of coercive force Hc. Media of this type are of the type shown in FIG. 20 (FIG. 21) and FIG. 22 (FIG. 23) depending on the direction of magnetization in the initialized state of the first magnetic layer 1 and the second magnetic layer 2. Divided. The medium shown in FIG. 20 (FIG. 21) is a case where the magnetization directions in the initialized state of the first magnetic layer 1 and the second magnetic layer 2 are the same, and the medium shown in FIG. 22 (FIG. 23). Is a case where the magnetization directions of the first magnetic layer 1 and the second magnetic layer 2 in the initialized state are opposite to each other.

When applying a bias magnetic field Hb [H] larger downward in FIG irradiates the laser beam of FIG. 20 lower bits of the recording is being performed as shown in (middle bit) (a) power P _L, the medium temperature Rises to T _L corresponding to P _L, and the coercive force Hc ₁ (T _L ) of the first magnetic layer 1 becomes equal to the bias magnetic field Hb [H].
The magnetization becomes smaller and the magnetization is reversed in the direction of the bias magnetic field Hb [H]. When the medium temperature decreases, the sum of the magnetostatic force Hs and the bias magnetic field Hb [H] increases the coercive force of the second magnetic layer 2 at room temperature.
It becomes larger than Hc ₂ (T _R ), the magnetization of the second magnetic layer 2 is reversed so as to be aligned with the magnetization of the first magnetic layer 1, and an erasing state as shown in FIG.

Next, FIG bit smaller bias magnetic field than during laser beam irradiation of a low power P _L irradiates the laser beam of high power P _H (bit middle) Hb [L] in the erased state FIG. 20 (c) When applied to a medium downward, the medium temperature is T _H rises corresponding to P _H. At this time, since the temperature of the first magnetic layer 1 rises to the Curie point Tc ₁ or more, the magnetization disappears, and the magnetization of the remaining transition metal (TM) in the second magnetic layer 2 is changed by the bias magnetic field Hb [L]. And the magnetization becomes upward in the figure (FIG. 20 (d)). When the medium is cooled from this state, the rare-earth metal (RE) magnetization (downward in the figure) is generated in the second magnetic layer 2. Then, the magnetization of the first magnetic layer 1 is reversed in the direction of the bias magnetic field Hb [L]. That is, the recording state is as shown in FIG. 20 (e) (the same as FIG. 20 (a)), and the overwriting has been performed.

Above, it erases with a laser beam of low power P _L,
Is a case of recording with a laser beam of high power P _H, on the contrary, erases the laser beam or high power P _H, the in the case of performing recording with a laser beam of low power P _L When the bias magnetic field Hb is applied in the same direction as the magnetization direction of the initialized state of the second magnetic layer 2 as shown in FIG. 21, overwriting can be similarly achieved.

Figure 22 in the case shown in (FIG. 23), erases with a laser beam of low power P _L, in the case of recording laser beam of high power P _H, the second magnetic layer 2 in the initial state By applying the bias magnetic field Hb in the direction opposite to the direction of the magnetization, overwriting is achieved. On the other hand, high power P _H
Erases a laser beam, in the case of recording laser beam of low power P _L, by applying a bias magnetic field Hb of magnetization in the same direction of the second initialization state of the magnetic layer 2, over Light is achieved.

In the medium shown in FIG. 20 (FIG. 21) of the type B medium described above, either the first magnetic layer 1 or the second magnetic layer 2 may be used as a recording / reproducing layer. Fig. 22 (Fig. 23)
In the medium shown in (1), recording and reproduction are performed between the case where the first magnetic layer 1 is a recording and reproduction layer and the case where the second magnetic layer 2 is a recording and reproduction layer.
The state of erasure changes.

The magnetic material used for the first magnetic layer 1 of the type B medium is an amorphous magnetic material exemplified as the material used for the first magnetic layer 1 of the type A medium, and has a compensation temperature higher than room temperature. Is used.

The magnetic material used for the second magnetic layer 2 includes:
The same material as that used for the second magnetic layer 2 of the type A medium is used.

The type C magneto-optical recording medium has a first magnetic layer 1 made of a ferromagnetic material or a ferrimagnetic material in which the transition metal (TM) has a superior magnetic moment at room temperature and a ferrimagnetic material in which the transition metal (TM) has a superior magnetic moment at room temperature. Magnetic materials other than magnetic materials, for example, γ
-Fe ₂ O ₃ , Fe ₃ O ₄ , Co _x Fe _3-x O ₄ , Be (CoTi) _x Fe _12-x O ₁₉ , Ba
_{(Al) x Fe 12-x} O 19, Sr (Ga) x Fe 12-x O 19, Co-Cr, composed second magnetic layer 2 made of Co-Ni-P or the like. These magnetic layers 1
The temperature characteristic of the coercive force Hc of No. 2 is as shown in FIG. The erasing and recording processes of this type of medium are as shown in FIGS. 24 and 25.

In this type of medium, magnetization reversal is not performed by laser beam irradiation during recording and erasing in one of the two magnetic layers 1 and 2, here, the second magnetic layer 2, and the magnetization is always in the same direction. In the other first magnetic layer 1, magnetization reversal is performed by laser beam irradiation during recording and erasing, and recording and erasing are performed.

That is, FIG. 24 in the drawing upward large bias magnetic field Hb irradiates a laser beam of low power P _L bit (middle of bits) of recording as shown in (a) is being performed
[H] is applied. Here, the value between the bias field Hb [H] of magnitude the temperature T _L second magnetic layer 2 coercivity in Hc ₂ (T _L) and the first magnetic layer 1 coercivity Hc ₁ (T _L) And That is, Hc ₂ (T _L ) <Hb [H] <Hc ₁ (T _L ). At this time,
The temperature of the medium rises to T _L corresponding to P _L , and the second magnetic layer 2 has a high Curie temperature Tc _{2 and a} sufficiently large coercive force Hc _2, so that no reversal of magnetization occurs, but the coercive force of the first magnetic layer 1 hc ₁ magnetization of the transition metal remaining to become smaller (TM) is drawing upward inverted by the bias magnetic field Hb [H] (Figure 24 (b)). Then, when the medium is cooled, an erasing state as shown in FIG.

Next, when a laser beam having a high power P _H of the 24th (c) erased bit (middle bit) is irradiated and a small bias magnetic field Hb [L] is applied upward in the drawing,
Medium temperature was increased to T _H corresponding to P _H, a state where the first magnetic layer 1 magnetized is lost, whereas the magnetization of the second magnetic layer 2 remains sufficiently large and the same direction (Figure 24 ( d)). When the medium is cooled from this state, the sum of the stray magnetic field Hf from the periphery of the bit to be recorded and the magnetostatic force Hs from the second magnetic layer 2 becomes larger than the magnitude of the bias magnetic field Hb [L], and the first magnetic The magnetization of the layer 1 is reversed, and FIG.
The recording state is as shown in FIG. 24 (a), indicating that overwriting has been performed. In this case, the direction of the bias magnetic field Hb [L] is opposite to the direction of the magnetization of the second magnetic layer 2 in the initialized state.

FIG. 25 shows a case where the magnetizations of the first magnetic layer 1 and the second magnetic layer 2 in the initialized state are both upward, and the bias magnetic field Hb in the opposite direction to the magnetization of each layer in the initialized state is applied. Overwriting can be performed as in the case of FIG.

Although the case where the magneto-optical recording method of the present invention is performed by using a single laser beam has been described above, the method of the present invention can be applied to a so-called two-beam method using two beams, a leading beam and a trailing beam. Can be.

Next, a specific configuration of the magneto-optical recording medium used in the present invention will be described.

26 to 29 are sectional views showing examples of the layer structure of the magneto-optical recording medium used in the present invention. The configuration example shown in FIG. 26 is such that an underlayer 12, a first magnetic layer 13 (1), an intermediate layer 14
(3) The second magnetic layer 15 (2), the protective layer 16, and the organic protective layer (cover layer) or the bonding layer 17 are sequentially laminated.
In the configuration example shown in FIG. 27, a reflection layer 18 is provided between the protective layer 16 and the organic protective layer or the bonding layer 17 in the configuration shown in FIG. The configuration example of FIG. 28 is different from the configuration of FIG.
16 is not provided. In the configuration example of FIG. 29, the intermediate layer 14 (3) is not provided in the configuration of FIG.

As the substrate 11, plastics such as polycarbonate, amorphous polyolefin resin, epoxy resin, methyl methacrylate resin, phenol resin, or soda glass, aluminosilicate glass, Vycor glass,
Glass such as Pyrex glass can be used. substrate
A guide track for guiding a laser beam spot (optical head) at the time of recording, erasing, and reproducing may be formed on the 11 or a pre-groove for reading format information. These guide tracks and microgrooves of the pregroove can be formed by, for example, injection, 2P method, or can be formed directly on glass by a photoresist method. Also, the laser light incident surface of the substrate 11 is
In order to prevent H ₂ O and O ₂ from entering, it may be covered with a dielectric layer, a hydrophobic, gas-resistant layer (for example, a fluororesin layer) or the like.

The underlayer 12 prevents the magnetic properties of the recording layers (the first magnetic layer 13 (1) and the second magnetic layer 15 (2)) from deteriorating due to H ₂ O and O ₂ entering from outside the substrate. It plays the role of enhancing the magneto-optical effect (Kerr rotation angle θ _k and Faraday effect θ _F ) by multiple reflection of light. For this reason,
For the underlayer 12, a material having a refractive index of 1.9 or more and a film thickness of 500 to 2000 °, preferably 600 to 1000 ° is used. In addition, from the viewpoint of heat loss due to heat conduction, the thermal conductivity of the underlayer 12 is 50
It is preferable that the value is lower than K / W · m. As such materials, specifically, Si _x N _y , Si _x O _y , Al _x N _y , Zr _x N _y , Cr
_{x N y, Al 2 O 3} , TiO 2, Zn x S y, Zn x O y, Mg x O y, Al 2 O 3, Al x O
yN _z , Zr _x Al _y Si _z N _w , Zr _x Al _y Si _z , Zr _x Si _y O _z , Zr _x Si _y N _z , S
i _x N _y O _z , Zr _x Al _y N _z , Zr _x Al _y O _z N _w , Al _x Si _y N _z , Zr _x Al _y Si _z N
_w O _V , Al _x Si _y N _z O _w , In ₂ O ₃ , ZrO ₂ , Ta ₂ O ₅ , Cr ₂ O _3, etc., and at least one of these is used. As a film forming method, a sputtering method, an evaporation method, an ion plating method, a CVD method, or the like is used.

The first magnetic layer 13 (1) and the second magnetic layer 15 which are recording layers
(2) includes at least one of transition metals (Fe, Co) and rare earth metals (Gd, Tb, Dy, Ho, Er, Nb, Yb, Sm, Ce, Rb,
An amorphous magnetic alloy film comprising at least one of Pr) is particularly preferably used. In order to prevent the deterioration and corrosion of the magnetic properties of the amorphous magnetic alloy film, T
Metals such as i, Cr, Pt, Sm, Sn, Ni, and In may be added. Also, in addition to the amorphous magnetic alloy film as a recording material, Co-C,
Magnetic alloy film such as Co-Ni-P, R ₃ [M _x Fe _sx O ₁₂ ] (where R
Are Y, Bi, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er,
At least one of Yb, Lu, Tm, and Nb, and M is Ga,
At least one kind of Al, Ge, Si, etc., but M may not be included. ), Me (M _x Fe
_12-x O ₁₂ ) (where Me is at least one or more of Ba, Pb, Sr, La and the like, and M is Co, Ti, Ga, Al, Cr, Cu, Ni,
Sn, Ge, Mg, Mn, In, Re, Rb, Rh, Zr, Pt, Au, Sb, Ta
And the like. ) Barium-based ferrite film M _x Fe _3-x O ₄ (where M is Co, Al, N
It is at least one or more of i, Zn, Mn, Mg and the like. ) Spinel ferrite film Co _x O _y film, MnBi-based (MnB
i, MnSb, MnCuBi, a Heusler alloy (MnAlSb) film or the like is used. First magnetic layer 13 (1) and second magnetic layer 15 (2)
The film thickness varies depending on the layer configuration, but is generally 10
0 to 2000 °, preferably 200 to 1000 ° is suitable. On the other hand, in the case of a medium without a reflective layer as shown in FIG.
The thickness of 13 (1) and 15 (2) is preferably 350 to 1000 °.
In the case of a medium having a reflective layer 18 as shown in FIG. 27 to FIG.
(1) and 15 (2) need to be transmitted. For example, when an alloy is used for both magnetic layers 13 (1) and 15 (2), 350
A film thickness of less than Å, preferably 100 to 250 Å is suitable. As a film forming method, a sputtering method, an evaporation method, and an ion plating method are used. As a medium configuration, the first magnetic layer 13 (1) and the second magnetic layer 15 (2) may be interchanged in the recording layer.

When the first magnetic layer 13 (1) and the second magnetic layer 15 (2) have an exchange coupling function, for example, when both of the magnetic layers use an amorphous magnetic material, an intermediate layer which does not cause the exchange coupling function 14 (3) intervention is required. Middle layer 14
As the constituent material of (3), for example, a dielectric material used for the underlayer 12, or Ni-Zn ferrite, Mn-Zn ferrite, Co-Zr-Nb ferrite, Fe-Al-Si ferrite, Mg-Zn
Soft magnetic materials such as ferrite are used, and carbides, nitrides, metal oxides, and metals (Pt, Au, Cr, Ni, Al, Cu, etc.)
Etc. may be used. The thickness of the intermediate layer 14 (3) is 100 to 1000
Å is appropriate. If the thickness of the intermediate layer 14 (3) is less than 50 °, the exchange coupling force acts and the intended purpose cannot be achieved. If the thickness exceeds 3000 °, the laser power required for recording and erasing is reduced. Too big. As a film forming method, a method similar to that for the underlayer 12 can be used.

The protective layer 16 serves to prevent the magnetic film from deteriorating due to intrusion of H ₂ O and O ₂ . For this reason, the same dielectric material, metal, or the like as used for the underlayer 12 is used for the protective layer 16. The film thickness is 50
The film thickness is suitably 0 to 2000 °, preferably 600 to 1000 °, and the same film forming method as that for the underlayer 12 can be used. In addition, as shown in FIG. 25 and FIG.
When the reflective layer 18 is provided on the surface 16, the protective layer 16 has a role as a heat insulating layer, so that the heat conductivity is relatively small.
_{x N y, Si x O y} , Zr x O y, Al 2 O 3, Ta 2 at least one or more O ₅ and the like are preferably used. The film thickness in this case is 300-100
0Å is appropriate.

The reflective layer 18 further enhances the magneto-optical effect, prevents heat diffusion in the protective layer 16, and also functions as a heat absorbing layer. The heat generated in the magnetic layers 13 (1) and 15 (2) by the laser beam irradiation during recording is conducted to the protective layer 16 having a low thermal conductivity, and the heat of the protective layer 16 is conducted to the reflective layer 18. In addition, heat diffusion in the protective layer 16 is prevented.
As a result, the trailing edge of the recording bit is short and the bit shape is sharp and more faithful to the laser spot diameter.
Materials used for the reflective layer 18 include Al, Pt, Sn, Au, and R.
h, Cu, Ag, Ni, Zr, Fe, Zn, In, Cr and the like or alloys thereof are preferable. As shown in FIG. 28, the reflective layer 18 is
When provided in contact with (2), it is particularly desirable to use Ni, Cr, Pt, Zr, Fe, Te, Se, Nd, In, Sd, and alloys containing these, which have relatively low thermal conductivity. As a film forming method, a method such as a sputtering method or a vapor deposition method is used, and the film is formed to have a thickness of 200 to 1000 °. The reflective layer 18 may not be provided in some cases. However, when a glass plate is used as the substrate 11, the heat generated in the magnetic layers 13 (1) and 15 (2) is
It is desirable to provide the reflective layer 18 because the protective layer 14 is effectively absorbed by the protective layer 14 in the horizontal direction.

The organic protective layer or bonding layer 17 is provided for the purpose of preventing damage to the medium or for bonding a medium having the same structure to form a double-sided recording type medium. The layer 17 is made of, for example, a hot melt resin or an ultraviolet curable resin, and is formed into a thickness of 1 to 100 μm by a spinner coating method, a hot roller coating method, or the like.

Although the layer configuration of the magneto-optical recording medium of the present invention has been described with reference to some examples, it is needless to say that the present invention is not limited to these, and various modifications and changes can be made.

For example, the surface may be coated with a thin layer of a polymer containing an antistatic agent in order to prevent dust and dirt from adhering to the surface of the medium. When the magneto-optical recording medium is a single-sided disk of a single-sided recording type, an organic protective layer is used to prevent warpage.
Film film (thickness 50-500μm) for preventing warpage on 17,
For example, polycarbonate, methyl methacrylate, amorphous polyolefin, or the like having the same coefficient of linear expansion and expansion and contraction due to absorption as the material of the substrate may be used.

Furthermore, when a double-sided recording type magneto-optical recording medium is used, it is more preferable to join the ends of the medium with a dielectric material or a plastic material in order to prevent deterioration of the recording layer.

〔Example〕

Examples of the present invention will be described below, but the present invention is not limited to these examples.

Example 1 A Si _x N _y film was formed as a base layer on a polycarbonate substrate having an outer diameter of 130 mm, an inner diameter of 15 mm, and a thickness of 1.2 mm (with a guide track having a groove width of 0.6 μm, a groove depth of 0.06 μm, and a groove pitch of 1.67 μm). Formed to a thickness of 800 mm,
As the magnetic layer _{(Tb 0 · 3 Dy 0 ·} 7) 22 (Fe 0 · 9 Co 0 · 1) 76 film 100Å
Under the same conditions as the underlayer as an intermediate layer.
Si _x N _y film was formed to a thickness of 400 Å, the second as a magnetic layer _{(Gd 0 · 8 Dy 0 ·} 2) 28 (Fe 0 · 9 Co 0 · 1) 72 film thickness of 150Å thereon And a Si _x O _y film is formed thereon as a protective layer to a thickness of 600 、, and then as a reflective layer, an Al film is formed to a thickness of 400 で under the same conditions as the first magnetic layer. Finally, an ultraviolet curable resin (trade name: EH214 manufactured by Yokohama Rubber Co., Ltd.) was spin-coated to a thickness of 10 μm to produce a magneto-optical disk. The conditions for forming each layer at this time are as follows.

Recording layer (first magnetic layer, second magnetic layer, and reflective layer): R
F magnetron sputtering method, back pressure 1 × 10 ^-6 Torr or less, Ar gas pressure 3 mmTorr, RF power 200 W, film formation time 4 minutes 50
Seconds Underlayer, intermediate layer and protective layer: RF magnetron sputtering, back pressure 1 × 10 ^-6 Torr or less, total of Ar gas pressure and N ₂ gas pressure 10 mmTorr, RF power 300 W, film formation time 25 minutes 22 seconds Examples 2 to 17 The materials shown in Tables 1 and 2 were used as a substrate, an underlayer, a recording layer, a protective layer, a reflective layer, and an organic protective layer.
A magneto-optical disk was produced in the same manner as described above.

Table 3 shows the thermomagnetic characteristics of each magnetic material and the type of medium used for the magnetic layer of each magneto-optical disk manufactured as described above.

Next, recording, erasing, and reproducing (overwriting) experiments were performed using each of the above magneto-optical disks. For recording and erasing, the intensity of a single laser beam is shown for recording and erasing.
4, the magneto-optical disks of Examples 1 to 6 and 8 to 17 were subjected to a linear velocity of 10 m / sec, a duty of 50%, and a recording frequency of 5 MHz. Recording and erasing were performed under the conditions of a linear velocity of 4 m / sec, a duty of 50%, and a recording frequency of 1.5 MHz. The bias magnetic field was applied in the same direction during recording and erasing. Table 4 shows the experimental results.

As a result of the above experiment, overwriting that does not require reversal of the bias magnetic field was achieved only by changing the power of the laser beam during recording and erasing.

〔The invention's effect〕

As described above in detail, according to the present invention, it is possible to perform overwriting (overwriting) recording without changing the direction of the bias magnetic field between recording and erasing by changing the intensity of the laser beam. Magneto-optical recording at a linear velocity can be realized. In addition, since the initialization as in the conventional method of performing overwritable recording by changing the light intensity of a single laser beam is unnecessary, it is not necessary to provide an auxiliary magnet for initialization, so that the magneto-optical head can be downsized. Can be.

Further, when a single laser beam is used, there is an advantage that high access can be achieved in addition to the above advantages.

In addition, in a medium having a recording layer provided with an intermediate layer between the first magnetic layer and the second magnetic layer, the characteristics of the interface between the two magnetic layers are not deteriorated, the long-term stability is improved, and a highly reliable magneto-optical There are advantages that records can provide.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are cross-sectional views each showing the structure of a recording layer of a magneto-optical recording medium according to the present invention, and FIGS. FIGS. 6 to 19 are graphs showing the temperature characteristics of the coercive force of each magnetic layer constituting the recording layer of the magneto-optical recording media of type A, type B and type C. FIGS. 20 to 23 are explanatory diagrams of the principle of recording and erasing of a type B magneto-optical recording medium, and FIGS. 24 and 25 are recording and erasing of a type C magneto-optical recording medium. Illustration of the principle of the 26th
29 are cross-sectional views showing examples of the layer structure of the magneto-optical recording medium of the present invention, FIG. 30 is an explanatory diagram of a conventional method for performing overwriting by changing the light intensity of a single laser beam, and FIG.
The graph is a graph showing the temperature characteristics of the coercive force of the magneto-optical recording medium used in the method of FIG. 1,13 ... first magnetic layer, 2,15 ... second magnetic layer 3,14 ... intermediate layer, 11 ... substrate 12 ... underlayer, 16 ... protective layer 17 ... organic protective layer or bonding layer 18 ... reflective layer

Claims (3)

(57) [Claims] The present invention relates to a magneto-optical recording medium having a recording layer formed by laminating first and second magnetic layers having different coercive force temperature characteristics. By applying a bias magnetic field in the same direction at the time of erasing and erasing, and by changing the magnitude of the bias magnetic field at the time of recording and erasing, or by applying a bias magnetic field to only one of recording and erasing, overwriting is possible. A magneto-optical recording method for performing recording, wherein the magneto-optical recording medium is provided with a recording layer in which no exchange coupling force acts between a first magnetic layer and a second magnetic layer. Characteristic magneto-optical recording method. 2. A recording layer having a two-layer structure in which first and second magnetic layers each composed of a perpendicular magnetization film having different temperature characteristics of coercive force are laminated, and no exchange coupling force acts between both magnetic layers. A magneto-optical recording medium used in the magneto-optical recording method according to claim 1, wherein: 3. The method according to claim 2, wherein an intermediate layer having a thickness of 100 to 1000.degree. Is provided between the first magnetic layer and the second magnetic layer so that no exchange coupling force acts between the two magnetic layers. Magneto-optical recording medium.