JPH09282726A - Magneto-optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-sensitivity magneto-optical recording medium which is expanded in an erasing power region (PL margin) by compressing an insufficiently erased power region. SOLUTION: Exchange bond films are so constituted as to have a two-layered structure composed of a memory layer consisting of a first perpendicularly magnetized film which exhibits ferrimagnetism an exhibits relatively high coercive force and low Curie temp. at room temp. and a writing layer consisting of a second perpendicularly magnetized film which exhibits relatively low coercive force and high Curie temp. at room temp. The recording medium of this case is so constituted that the compensation temp. of the memory layer of such exchange bond films is made approximately the same as the temp. (erasing temp.) at which the information of the writing layer is transferred to the memory layer by heating of the medium irradiated with the laser beam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overwritable magneto-optical recording medium using a magneto-optical recording medium which can be recorded thermomagnetically and can be read out by utilizing the Kerr effect.

[0002]

2. Description of the Related Art A magneto-optical recording medium is known as one of large-capacity erasable optical recording media. The magneto-optical recording medium is
Compared with a magnetic recording medium using a conventional magnetic head, it has advantages such as high density recording medium, portability, and excellent durability due to a non-contact recording / reproducing system. On the other hand, it has a drawback that the recorded portion must be erased once before recording (it must be magnetized in one direction), and the data transfer rate becomes slow.

In order to compensate for this drawback, a method of separately providing a recording / reproducing head and an erasing head, or a method of irradiating a continuous laser beam and simultaneously applying while modulating a magnetic field for recording is proposed. . However, these methods have a drawback that the device becomes large in size and the cost increases, or that data cannot be transferred at a high rotation speed.

Therefore, as proposed in JP-A-62-175948, JP-A-63-52354, JP-A-63-153752 and the like, the first one showing a high coercive force and a low Curie temperature at a relatively room temperature. An exchange coupling film having at least a two-layer structure of a memory layer made of a perpendicular magnetization film and a writing layer made of a second perpendicular magnetization film showing a low coercive force and a high Curie temperature at room temperature is used. Kaisho 63-268103, WO90 / 024
No. 00, JP-A-3-219449, etc., a memory layer formed of a first perpendicular magnetization film capable of storing information bits, and a Curie temperature higher than that of the memory layer. A write layer made of a second perpendicularly magnetizable film in which bits can be written, a switch layer made of a third magnetic film having a Curie temperature lower than the Curie temperature of the memory layer and higher than room temperature, and the write layer Using a magneto-optical recording medium in which at least four magnetic layers made of a rare earth-transition metal magnetic thin film and an initialization layer made of a fourth perpendicularly magnetized film having a high Curie temperature are exchange-coupled to each other and sequentially laminated Then, a method of performing overwriting by changing the power of the laser beam (light modulation overwrite method) is disclosed.

The basic process of the optical modulation overwrite method using the above magneto-optical recording medium will be described. In the exchange coupling film having a two-layer structure of a memory layer and a writing layer, the information bit (magnetic domain) recorded in the writing layer is transferred to the memory layer during the temperature rising / falling process by laser irradiation. The laser modulates with two kinds of laser power capable of forming respective temperature states of a high temperature level for recording on the writing layer and a low temperature level for transferring to the memory layer according to the information to be recorded.

After the laser irradiation, the medium temperature returns to room temperature, and a required initialization magnetic field is applied to initialize the writing layer. The information bits transferred to the memory layer are
Since this layer has a large coercive force at room temperature, it is retained without being erased by the initializing magnetic field. As a result, regardless of the state of the memory layer before recording, the information newly recorded in the write layer is always recorded and held in the memory layer, and overwrite is established.

This method requires a means for applying a required initializing magnetic field, and therefore has a drawback that the recording apparatus becomes large and complicated. The way to solve this problem is
A switch layer having a Curie temperature lower than the Curie temperature of the memory layer and higher than room temperature, and an initialization layer having a Curie temperature higher than the write layer are added on the write layer of the exchange-coupling laminated film. Use medium. The initialization layer is preliminarily initialized. After the laser irradiation, if the medium temperature returns to room temperature and the temperature becomes equal to or lower than the Curie temperature of the switch layer, the exchange coupling force acts between the writing layer and the initialization layer to initialize the writing layer. Other than this, the overwrite is established in the same manner as the above-mentioned process.

[0008]

The above-mentioned optical modulation overwrite method modulates the laser light intensity between two levels of high and low levels (P _H , P _L ) higher than the reproduction power, so that the medium is kept above ambient temperature. Is also heated to two high and low temperature levels, and two different magnetization states are formed in accordance with each temperature level, and information is overwritten. Therefore,
As shown in Fig. 2, when a predetermined margin is allocated to the three power levels of recording, erasing, and reproducing, the laser output required for recording is the principle compared to the normal recording method in which recording and erasing are performed at the same temperature level. Will grow large. In order to solve this problem, it is important to form the medium so as to lower P _H after compressing the power region where erasure / recording is insufficient as shown as regions A and B in FIG. 2 as much as possible. Is.

Further, a power area where erasure / recording is insufficient (see FIG.
The middle regions A and B) will be described in detail with reference to FIG. FIG.
Temperature distribution that occurs when the medium is irradiated with laser light
Is shown. P_Rmax(P _Wth ) Laser power
The temperature distribution at that time is represented by the dotted line. Such a shape
This temperature distribution occurs because the laser light intensity distribution is
This is due to the fact that it exhibits a Usus distribution. This laser power
ー P_Rmax(P_Wth ) On the recording medium for the first time
Leaving temperature T_E (Recording temperature T_W ) Appears and the part
Start erasing (recording) in the area. Also, P
_Lmin(P_Wopt) Temperature when irradiated with laser power
The distribution is shown by the solid line. At this time, just the recording mark
The entire width can be heated to the erase temperature (recording temperature).
Information can be completely erased (recorded). P
_Rmax(P_Wth ) To P_Lmin(P_Wopt) Power range up to
Remains as an area where erasure (recording) is insufficient.

In the magneto-optical recording medium of the optical modulation overwrite system, it is necessary to allocate a predetermined margin to three power levels of recording, erasing and reproduction, and in principle, the optical modulation overwrite in which the recording laser power becomes large. In the system, the existence of a power region in which erasing (recording) is insufficient as described above has been an obstacle to further increasing the sensitivity of recording light.

The present invention solves the above problems and provides a high-sensitivity magneto-optical recording medium in which the power region where erasure is insufficient is compressed and the erase power region (P _L margin) is expanded. The purpose is.

[0012]

It is important to optimize the shape of the temperature distribution generated by laser light irradiation in order to reduce the power region where erasure / recording is insufficient when manufacturing a high-sensitivity magneto-optical recording medium. become. It has been known that the shape of this temperature distribution is influenced by the thermal structure of the recording medium, and the temperature distribution has been optimized by studying the thermal structure.

However, it has been experimentally confirmed that even in a medium having the same thermal structure (same temperature distribution), the power region in which erasing / recording is insufficient changes as the magnetic characteristics of the recording magnetic film change. This is considered to be due to the non-uniformity of the magnetic characteristics caused by the composition unevenness, the film thickness unevenness, etc. depending on the location on the disk.

The present invention has been made to solve the above problems, and the above objects can be achieved by the present invention described below. That is, the present invention shows a ferrimagnetism, a memory layer formed of a first perpendicular magnetization film having a high coercive force and a low Curie temperature at room temperature, and a low coercive force and a high Curie temperature at room temperature. In an exchange coupling film having at least a two-layer structure of a writing layer made of a second perpendicular magnetization film, the compensation temperature of the memory layer is a temperature at which information of the writing layer is transferred to the memory layer by heating the medium by laser irradiation (erasing). The present invention discloses a magneto-optical recording medium, which is characterized in that the temperature is approximately the same.

Further, according to the present invention, it is possible to write the information bit by exhibiting the ferrimagnetism and having the memory layer formed of the first perpendicular magnetization film capable of storing the information bit and the Curie temperature higher than that of the memory layer. A write layer made of a second perpendicular magnetization film, a switch layer made of a third magnetic film having a Curie temperature lower than the Curie temperature of the memory layer and higher than room temperature, and a Curie temperature higher than the write layer. In the exchange coupling film having at least a four-layer structure with the initialization layer made of the fourth perpendicular magnetization film, the compensation temperature of the memory layer is transferred to the memory layer by heating the medium by laser irradiation. The present invention also discloses a magneto-optical recording medium characterized in that the temperature is substantially the same as the erasing temperature.

Then, the compensation temperature (T
_comp. ) is in the range of 30 to 180 ° C., and the composition of the memory layer has a composition formula T
b _x Fe _{100 -xy} Co _y , and 20 ≦ x ≦ 26
(At%) and 2 ≦ y ≦ 12 (at%).

[0017]

DETAILED DESCRIPTION OF THE INVENTION The details of the present invention will be described below. First, the principle of erasing in the light modulation overwrite method will be described with reference to the drawings. Regarding recording on an optical modulation overwrite type magneto-optical recording medium having a two-layer structure, when the memory layer and the writing layer are made of ferromagnetism,
The magnetizations of the memory layer and the writing layer face in opposite directions,
The state in which the interface domain wall exists between both layers is the recording state, and the state in which the magnetizations of the two layers are parallel and the interface domain wall does not exist is the erase state. In particular, when the two layers are rare earth transition metals, the transition metal (or rare earth) sublattice magnetizations of both layers are directed in opposite directions to each other, and an interface domain wall exists between the two layers as a recording state. (Or rare earth) A state in which the sublattice magnetization is parallel and the interface domain wall does not exist is defined as an erased state. In the following description, “magnetization” means “transition metal (or rare earth) sublattice magnetization” when the memory layer and the writing layer are rare earth transition metals.

FIG. 4 is a schematic diagram illustrating the interface domain wall.
That is, the interface domain wall is a magnetization transition region that gradually changes from the magnetization direction of the memory layer to the magnetization direction of the write layer.
In this interface domain wall, there exists interface domain wall energy that acts in a direction in which the magnetizations of the two layers are aligned in parallel. On the other hand, coercive force energy that acts in a direction to maintain the respective magnetization directions also acts on the memory layer and the writing layer. The coercive force energies of the memory layer and the writing layer exceed the interfacial domain wall energy between the two layers, and the state when the interfacial domain wall is formed is the recorded state, which means that information is recorded.

FIG. 5 shows the temperature characteristics of the coercive force energy (E) of the memory layer and the interfacial domain wall energy (σ _W ) when the medium is heated by laser light irradiation from such a recorded state. At room temperature (T _R ), the coercive force energy of the memory layer is larger than the interface wall energy and the recording state is maintained. From this state, the coercive force energy monotonously decreases as the medium temperature rises due to laser light irradiation. At the erasing temperature (T _E ) or higher, the coercive force energy of the memory layer becomes smaller than the interfacial domain wall energy, and the magnetization of the memory layer cannot maintain the direction of the recording magnetization and is reversed.
The magnetization directions of the two layers are aligned in parallel. Then, in that state, it is cooled down to room temperature and becomes an erased state, and the erase is completed. Therefore, in the erasing process in the optical modulation overwrite type magneto-optical recording medium, it is particularly important to understand the relationship between the coercive force energy of the memory layer and the interfacial domain wall energy existing between the memory layer and the write layer.

With the above in mind, the correlation between the insufficiently erased power region and the magnetic characteristics will be described with reference to FIG. Here, it is assumed that the coercive force energy of the memory layer and the interfacial domain wall energy between the memory layer and the write layer have nonuniform characteristics. At this time, variation ΔT _E also occurs in the temperature at which the temperature characteristics of both energies intersect, that is, the erasing temperature T _E. In such a case, as shown in FIG. 6, the power P _Rmax for starting to erase the recording mark is lower than that in the ideal case, and conversely, the power P _Lmin for completely erasing the recording mark is Shows a high value,
The power range from P _Rmax to P _Lmin is expanded compared to the ideal case. In other words, the smaller the erase temperature variation ΔT _E , the smaller the power region where erasure is insufficient.

As shown in FIG. 7, as one method for reducing the variation in erase temperature, when the interfacial domain wall energy between the memory layer and the write layer is the same, the coercive force energy of the memory layer near the erase temperature is reduced. The variation ΔT _{E of the} erasing temperature can be reduced as the temperature characteristic changes more rapidly.

On the other hand, the compensation temperature of the memory layer, which is ferrimagnetic, is made substantially the same as the temperature (erasing temperature) at which the information of the writing layer is transferred to the memory layer by heating the medium by laser irradiation. When selected, the apparent magnetization and diamagnetic field energy of the memory layer, which has a compensation temperature near the erase temperature, disappears. At this time, the coercive force energy Ec of the memory layer showing a square hysteresis loop is
Since it is represented by the following general formula, Ec = MsHc-NMs ² (where Ms is the saturation magnetization of the memory layer, Hc is the coercive force, and N is the demagnetizing factor), the memory layer selected as described above The temperature characteristic of the coercive force energy changes sharply in comparison with the other because the demagnetizing field energy is small in the vicinity of the erasing temperature (see FIG. 10). Therefore, by selecting and forming the memory layer such that the compensation temperature of the memory layer is substantially the same as the temperature (erasing temperature) at which the information of the writing layer is transferred to the memory layer by heating the medium by laser irradiation. , It is possible to reduce the variation of the erasing temperature and to compress the power region where the erasure is insufficient compared with the conventional magneto-optical recording medium, and accordingly,
It is possible to extend the P _L margin and reduce the recording power.

The basic structure of a magneto-optical recording medium used in the present invention is such that at least a first magnetic layer (memory layer) and a second magnetic layer (writing layer) are formed on a transparent substrate as shown in FIG.
Are sequentially laminated. The memory layer is a ferrimagnetic material having a compensation temperature above room temperature and exhibits a high coercive force and a relatively low Curie temperature at room temperature, and the write layer exhibits a relatively low coercive force and a high Curie temperature at room temperature. . The expressions “high” and “low” here indicate a relative relationship when the two magnetic layers are compared.
Specifically, the coercive force of the memory layer, which is the first magnetic layer, is 7 kO.
e or higher, compensation temperature is 60 to 180 ° C, Curie temperature is 1
20-200 degreeC is preferable. The coercive force of the writing layer, which is the second magnetic layer, is 2 to 5 kOe, and the Curie temperature is 16.
0-280 degreeC is preferable.

As the material of each magnetic layer, a material exhibiting perpendicular magnetic anisotropy and exhibiting a relatively large magneto-optical effect can be used, but for the memory layer, Tb-Fe, Tb-Dy-.
Fe, Dy-Fe, Tb-Fe-Co, Tb-Dy-F
e-Co, Dy-Fe-Co, Gd-Tb-Fe, Gd
-Dy-Fe, etc., and the writing layer is Tb-Fe, Tb
-Dy-Fe, Dy-Fe, Tb-Fe-Co, Tb-
Dy-Fe-Co, Dy-Fe-Co, Gd-Tb-F
e, Gd-Tb-Dy-Fe, Gd-Dy-Fe, Gd
-Tb-Fe-Co, Gd-Tb-Dy-Fe-Co,
An amorphous magnetic alloy of a rare earth element such as Gd-Dy-Fe-Co and an iron group element is preferable.

Further, a magnetic layer having good reproduction characteristics (reproduction layer) is laminated on the information reading side of the memory layer, or a suitable magnetic layer for controlling the magnitude of exchange coupling between the memory layer and the writing layer. Alternatively, a non-magnetic layer (adjustment layer) may be sandwiched.

Further, it is located between the magnetic layer (initialization layer) having a Curie temperature higher than that of the writing layer and playing the role of the initializing magnet (initialization layer), and lower than the memory layer. A magnetic layer (switch layer) having a Curie temperature and magnetically coupling the writing layer and the initialization layer at room temperature may be laminated in the order of the switching layer and the initialization layer after the writing layer is laminated. Specifically, the Curie temperature of the adjustment layer is preferably 170 to 250 ° C., the Curie temperature of the switch layer is preferably 100 to 150 ° C., and the initialization layer is preferably 300 ° C. or higher.

It is to be noted that between the translucent substrate and the magnetic layer or on the side of the magnetic layer opposite to the substrate, suitable for improving durability, or for improving recording / erasing sensitivity and magneto-optical effect. A dielectric layer or a reflective layer may be provided. As the material of the dielectric layer, SiN, SiO, SiC, SiAlO
N, ZnS or the like is used.

[0028]

The present invention will be described in detail below with reference to the examples, but the present invention is not limited thereto.

[First Embodiment] A first embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 8, a first dielectric layer is formed on a translucent disc-shaped substrate made of polycarbonate with pregrooves and preformatted signals,
The magnetic layer, the second dielectric layer, and the reflective layer were formed in this order by a sputtering method. The magnetic layer has a three-layer structure, and the memory layer, the adjustment layer, and the writing layer were laminated in this order on the first dielectric layer.

The first dielectric layer is made of Ar,
A SiN film having a film thickness of 90 nm was formed by sputtering using Si as a target in an N ₂ mixed gas atmosphere.
Then, a magnetic layer having a three-layer structure was formed on the first dielectric film.

As the first magnetic layer, three targets of Tb, Fe, and Co were used, and the sputtering Ar gas pressure was 0.5.
In an atmosphere of ₉ Pa, the film composition Tb _25.5 Fe _65.5 Co ₉ ,
A memory layer having a film thickness of 25 nm was formed. The compensation temperature of the memory layer is 150 ° C and the Curie temperature is 165 ° C.

As the second magnetic layer, Gd, Fe, Fe
Film composition Gd ₃₂ Fe ₅₈ Co was used in an atmosphere of sputtered Ar gas pressure of 0.21 Pa using three Co ₃₀ targets.
_10, to form an adjusting layer having a thickness of 20 nm.

As the third magnetic layer, Tb, Fe, Co
Sputtered Ar gas pressure of 0.
A writing layer having a film composition of Td ₁₆ Fe ₇₂ Co ₁₂ and a film thickness of 40 nm was formed in an atmosphere of 22 Pa. The Curie temperature of the writing layer is 260 ° C. Further, as a second dielectric layer, a SiN film having a film thickness of 10 nm was formed on the film by a sputtering method using Si as a target in a mixed gas atmosphere of Ar and N ₂ . Finally, as the reflective layer, a film having a thickness of 40 nm was formed on the film by a sputtering method using an Al target in an Ar gas atmosphere.

The magneto-optical recording medium produced as described above was set in a magneto-optical recording / reproducing apparatus, and the power region where erasure was insufficient was measured. The measurement was carried out by rotating at a linear velocity of 9.04 m / s and collecting a wavelength of 780 n at a spot diameter of about 1 μm.
m laser beam. First, while irradiating continuous light with a laser power of 10 mW,
The recording medium was erased by passing the magneto-optical recording medium through the magnetic field generating portion of 500 Oe. After that, while applying a bias magnetic field of 350 Oe, a 33% duty ratio, 5.
Recording was performed with a laser beam having a peak power of 12 mW modulated at a frequency of 8 MHz. Irradiating continuous light while applying a bias magnetic field 350 Oe in the recording direction to this recording portion,
The minimum power of P _Lmin to erase the recorded data completely, P _Rmax / P the maximum reproduction power playable without destroying the data when irradiated with continuous light in the recording unit as P _{Rm ax
By obtaining} the ratio of _Lmin , it was used as an index of the power region in which the medium was not sufficiently erased. In the above medium, as shown in Table 1, P _Rmax / P _Lmin = 0.62.

Comparative Example 1 As the first magnetic layer, Tb,
Sputtering Ar using three targets of Fe and Co
Film composition Tb _17.5 Fe in an atmosphere with a gas pressure of 0.59 Pa
A memory layer having a thickness of _76.5 Co ₆ and a film thickness of 25 nm was formed. The Curie temperature of the memory layer is 165 ° C. Other than that, the magneto-optical recording medium has the same configuration as that of the first embodiment.
Under the same conditions as above, the power region where erasure was insufficient was measured.
As shown in Table 1, P _Rmax / P _Lmin = 0.51.

[0036]

[Table 1] From the results shown in Table 1, the value of P _Rmax / P _Lmin of Example 1 of the present invention was closer to 1 than that of Comparative Example 1, and the power region in which erasure was insufficient was compressed, showing good characteristics. I understand that. FIG. 10 shows the temperature characteristics of the coercive force energy of the memory layers of Example 1 of the present invention and Comparative Example 1.
It can be seen that in Example 1, the change in coercive force energy of the memory layer of Comparative Example 1 with respect to temperature is more rapid on the high temperature side. Further, the temperature characteristics of the interfacial domain wall energy generated between the memory layer and the write layer in Example 1 of the present invention and Comparative Example 1 are as shown in FIG. Regarding the temperature characteristics of the interfacial domain wall energy, no difference was observed between Example 1 and Comparative Example 1. From the above results of the coercive force energy, the temperature characteristics of the interfacial domain wall energy, and the dynamic characteristics of P _Rmax / P _Lmin , the coercive force of a medium having a memory layer whose compensation temperature is higher than room temperature and near the erase temperature is higher. The change in energy with temperature becomes sharp near the erasing temperature, and P _Rmax
It can be seen that the value of / P _Lmin approaches 1 and the area of insufficient erasure is reduced.

[Second Embodiment] Next, a second embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 9, a first dielectric layer is formed on a translucent disk-shaped substrate made of polycarbonate with pregrooves and preformatted signals,
The magnetic layer, the second dielectric layer, and the reflective layer were formed in this order by a sputtering method. The magnetic layer has a five-layer structure, and a memory layer, an adjustment layer, a writing layer, a switch layer, and an initialization layer were laminated in this order on the first dielectric layer.

The first dielectric layer is made of Ar,
A SiN film having a film thickness of 90 nm was formed by sputtering using Si as a target in an N ₂ mixed gas atmosphere.
Then, a magnetic layer having a five-layer structure was formed on the first dielectric film.

As the first magnetic layer, three targets of Tb, Fe, and Co were used, and the sputtering Ar gas pressure was 0.5.
In an atmosphere of ₉ Pa, the film composition Tb _25.5 Fe _65.5 Co ₉ ,
A memory layer having a film thickness of 25 nm was formed. The compensation temperature of the memory layer is 150 ° C and the Curie temperature is 165 ° C.

As the second magnetic layer, Gd, Fe, Fe
Film composition Gd ₃₂ Fe ₅₈ Co was used in an atmosphere of sputtered Ar gas pressure of 0.21 Pa using three Co ₃₀ targets.
_10, to form an adjusting layer having a thickness of 20 nm.

As the third magnetic layer, Tb, Fe, Co
Sputtered Ar gas pressure of 0.
A writing layer having a film composition of Td ₁₆ Fe ₇₂ Co ₁₂ and a film thickness of 15 nm was formed in an atmosphere of 22 Pa. The Curie temperature of the writing layer is 260 ° C.

As the fourth magnetic layer, two targets of Tb and Fe were used, and the sputtering Ar gas pressure was 0.22 Pa.
In the atmosphere, a switch layer having a film composition of Tb ₂₅ Fe ₇₅ and a film thickness of 10 nm was formed. The Curie temperature of the switch layer is 13
0 ° C.

As the fifth magnetic layer, three targets of Tb, Fe, and Co were used, and the sputtering Ar gas pressure was 0.2.
In an atmosphere of 2 Pa, an initialization layer having a film composition of Tb ₂₄ Fe ₁₅ Co ₆₁ and a film pressure of 30 nm was formed. The Curie temperature of the initialization layer is 300 ° C. or higher. Due to the fourth and fifth magnetic layers, no initialization magnetic field device is required for recording.

Further, as a second dielectric layer, A is formed on the film.
A SiN film having a film thickness of 10 nm was formed by a sputtering method using Si as a target in an r, N ₂ mixed gas atmosphere. Finally, as a reflective layer, an Al target is used on the film in an Ar gas atmosphere by a sputtering method,
It was manufactured with a film thickness of 40 nm. The power region where erasure was insufficient was measured under the same conditions as in Example 1. As a result, as shown in Table 2, P _Rmax / P _Lmin = 0.61.

[Comparative Example 2] As the first magnetic layer, Tb,
Sputtering Ar using three targets of Fe and Co
Film composition Tb _17.5 Fe in an atmosphere with a gas pressure of 0.59 Pa
A memory layer having a thickness of _76.5 Co ₆ and a film thickness of 25 nm was formed. The Curie temperature of the memory layer is 165 ° C. Other than that, the magneto-optical recording medium having the same structure as in Example 2 was used. Under the same conditions as in Example 1, the power region where erasure was insufficient was measured. As shown in Table 2, P _Rmax / P _Lmin = 0.52.

[0046]

[Table 2] From the results shown in Table 2, Example 2 of the present invention has a value of P _Rmax / P _Lmin close to 1 as compared with Comparative Example 2, and the power region in which erasure is insufficient is compressed, showing good characteristics. I understand that. FIG. 10 shows temperature characteristics of coercive force energy of the memory layers of Example 2 of the present invention and Comparative Example 2. It can be seen that in Example 2, the change in coercive force energy of the memory layer of Comparative Example 2 with respect to temperature is more rapid on the high temperature side. Further, the temperature characteristics of the interfacial domain wall energy generated between the memory layer and the write layer in Example 2 of the present invention and Comparative Example 2 are as shown in FIG.

Regarding the temperature characteristics of the interfacial domain wall energy, no difference was observed between Example 2 and Comparative Example 2.
From the above results of the coercive force energy, the temperature characteristics of the interfacial domain wall energy, and the dynamic characteristics of P _Rmax / P _Lmin , the coercive force of a medium having a memory layer whose compensation temperature is higher than room temperature and near the erase temperature is higher. It can be seen that the change of energy with respect to temperature becomes sharp near the erasing temperature, the value of P _Rmax / P _Lmin approaches 1, and the insufficient erasing area is reduced.

[0048]

As described above in detail, in the magneto-optical recording medium capable of optical modulation overwriting by the exchange coupling film, the compensation temperature of the memory layer is the information of the writing layer due to the heating of the medium by the laser irradiation. By selecting and configuring the memory layer so that the temperature is almost the same as the temperature transferred to the memory (erasing temperature), the variation in the erasing temperature is reduced, the power region where erasure is insufficient is compressed, and the P _L margin is reduced. It becomes possible to expand and reduce the recording power P _H.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the basic configuration of a magneto-optical recording medium according to the present invention.

FIG. 2 is a schematic explanatory view showing general photosensitivity characteristics of a light modulation overwrite type magneto-optical recording medium.

FIG. 3 is a schematic explanatory diagram of an area where recording and erasing are insufficient.

FIG. 4 is a schematic explanatory view showing an interface domain wall.

FIG. 5 is an explanatory diagram of an erasing principle in an optical modulation overwrite type magneto-optical recording medium.

FIG. 6 is a schematic explanatory view showing a correlation between an insufficiently erased region and magnetic characteristics.

FIG. 7 is a schematic explanatory diagram showing a correlation between variations in erase temperature and magnetic characteristics.

FIG. 8 is a structural explanatory view showing a magneto-optical recording medium used in Example 1 and Comparative Example 1.

9 is a structural explanatory view showing a magneto-optical recording medium used in Example 2 and Comparative Example 2. FIG.

FIG. 10 is a graph showing the temperature characteristics of coercive force energy of memory layers in Examples and Comparative Examples.

FIG. 11 is a graph showing temperature characteristics of interfacial domain wall energy between the memory layer and the write layer in the example and the comparative example.

Claims (4)

[Claims] 1. A memory layer composed of a first perpendicularly magnetized film which exhibits ferrimagnetism and has a high coercive force and a low Curie temperature at room temperature, and a low coercive force and a high Curie temperature at room temperature. In an exchange coupling film having at least a two-layer structure of a writing layer made of a second perpendicular magnetization film, the compensation temperature of the memory layer is a temperature at which information of the writing layer is transferred to the memory layer by heating the medium by laser irradiation (erasing). The magneto-optical recording medium is characterized in that the temperature is substantially the same as the temperature. 2. A memory layer which exhibits ferrimagnetism and is composed of a first perpendicular magnetization film capable of storing information bits, and a second memory layer having a Curie temperature higher than that of the memory layer and capable of writing information bits. A write layer made of a perpendicularly magnetized film, and a switch layer made of a third magnetic film having a Curie temperature lower than the Curie temperature of the memory layer and higher than room temperature,
In an exchange coupling film having at least a four-layer structure with an initialization layer composed of a fourth perpendicularly magnetized film having a Curie temperature higher than that of the writing layer, the writing layer is obtained by heating the medium by compensation of the memory layer with laser irradiation. A magnetic-optical recording medium, characterized in that the temperature is substantially the same as the temperature (erasing temperature) at which the information is transferred to the memory layer. 3. The compensation temperature (T _comp. ) Of the memory layer
Is in the range of 30 to 180 ° C. 3. The magneto-optical recording medium according to claim 1, wherein 4. The composition of the memory layer has a composition formula Tb _x F.
e _100-xy Co _y , and 20 ≦ x ≦ 26 (at
%), 2 ≦ y ≦ 12 (at%), The magneto-optical recording medium according to claim 1 or 2, characterized in that