JPH05325283A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To enhance sensitivity to a magnetic field while keeping stability of recording and to adapt the recording medium to high-speed recording and regeneration by limiting the constituents of each layer for composing a recording layer, and giving a gradient to the constituent of a second magnetic layer. CONSTITUTION:The magneto-optical recording medium is formed by successively laminating on a transparent substrate 1 a dielectric layer 2, a magnetic layer 3 made of Tbx1(Fey1CO1-y1)1-x1, a magnetic layer 4 made of Tbx2(Fey2CO1-y2)1-x2, (0.14<x1<0.2, x1<x2<0.4, and y1>0.05, y2<0.2), and a dielectric layer 5, and a reflective layer 6. The value of x2 in the layer 4 is given a increasing gradient in the thickness direction, and the thickness of each of the layers 3 and 4 is 50-300Angstrom , and the sum of them is 150-600Angstrom .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable magneto-optical recording medium, which is suitable for magnetic field modulation overwriting, and has both high magnetic field sensitivity and recording stability. Is.

[0002]

2. Description of the Related Art A magneto-optical recording medium is a rewritable recording medium and is excellent in repeated erasing / writing durability and erasing ratio as compared with a phase change type optical recording medium and is a portable large-capacity recording medium. Attention has been paid.

In the case of recording on a magneto-optical recording medium, conventionally, after erasing by applying a constant value of an erasing magnetic field while irradiating continuous light of a laser, the laser power is followed by a recording pattern. A method of recording by applying a constant recording magnetic field while modulating was used. This method has a drawback that it takes time because it is recorded after erasing.

In order to solve this problem, in recent years, while irradiating laser continuous light, the magnetic field is modulated according to the recording pattern to perform erasing and recording at the same time, that is, superimposing on the previous recording. Magnetic field modulation over to write (overwrite)
A method called a burn method has been developed. or,
Further, it has been attempted to increase the number of rotations of the medium in order to shorten the recording time, but in this case, the recording frequency also needs to be increased at the same time. In the magnetic field modulation overwrite method, the current of the magnetic head is changed. It is necessary to improve the switching speed. At this time, the smaller the peak current is, the easier it is to improve the switching speed. Therefore, there is a demand for a magneto-optical recording medium capable of overwriting with a smaller recording modulation magnetic field.

In order to improve the magnetic field sensitivity of the magneto-optical recording medium, the magnetic film is made of GdFeCo and TbF in the medium of the reflection type structure.
A medium made of a laminated film of eCo (15th Annual Scientific Lectures of Japan (1991) p430-440) and TbFeCo
A medium having an in-plane film such as PtCo as a laminated film has been reported (Summary of Abstracts of the Lecture, p. 306), both of which use a laminated film for a magnetic layer.

A medium having a laminated film of in-plane films such as TbFeCo and PtCo can be reproduced with a sufficient C / N even if recording is performed with a modulation magnetic field of about 100 Oe.
When modulated below e, the C / N is not sufficient and the over
The light causes an unerased portion of the previous signal. In this medium,
The magnetization of an in-plane film such as PtCo having a Curie temperature close to that of TbFeCo is reduced at the recording temperature of TbFeCo, so that the demagnetizing field is lowered and the spin tends to be directed in the direction of the external magnetic field. Recording was performed on TbFeCo near the compensating composition having a large coercive force by utilizing the function of strengthening the magnetic field. However, the exchange coupling between the in-plane film and TbFeCo is Tb.
It was about 1/10 of that of FeCos, and was not necessarily sufficiently strong at the temperature at the time of recording, and the carrier level could not be sufficiently increased in the modulation magnetic field of 50 Oe or less.

In addition, the composition of TbFeCo is changed to some extent FeC.
o Magnetic field sensitivity is improved to some extent when moved to the rich side,
The influence of the demagnetizing field of the TbFeCo film is increased, and the erase magnetic field is less likely to decrease. If it is moved to the FeCo rich side extremely, the coercive force is lowered, and there is a problem in recording stability.

The magneto-optical medium using the composition gradient of the magnetic film is
For example, as disclosed in Japanese Patent Application Laid-Open No. 54-121719, there is a technique in which the composition ratio of GdCo is changed in the film thickness direction to stabilize the recording bit. The disclosure of this publication does not particularly disclose the effect of the TbFeCo film.

As a composition gradient magneto-optical medium limited to TbFeCo, for example, there is one having a composition gradient monotonically in the thickness direction (see Japanese Patent Laid-Open No. 63-228945), but a separate magnetic layer is used. If provided, it is not disclosed.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to obtain a medium suitable for high speed recording / reproducing by further increasing the magnetic field sensitivity while maintaining the recording stability of the magneto-optical recording medium.

[0011]

As a result of various investigations, the present inventors have found that when an external magnetic field is applied to FeCo-rich TbFeCo for recording, recording noise due to the influence of the demagnetizing field of the recording film in a low magnetic field. Since it is necessary to reduce the influence of the demagnetizing field immediately below the recording temperature as much as possible in order to reduce the magnetic field, the composition of the magnetic layer is provided with a gradient so that the magnetization of the entire film is close to zero immediately below the recording temperature, and then the large TbFeCo particles By transferring to FeCo-rich TbFeCo with an effective magnetic field by exchange coupling and recording, the high magnetic field sensitivity and the stability of recording retention can be achieved at the same time.

That is, according to the present invention, in a magneto-optical recording medium in which a dielectric layer, a magnetic recording layer, a dielectric layer and a reflective film layer are laminated in this order on a transparent substrate, the magnetic recording layer is Tb _x1.
A first magnetic layer made of (Fe _y1 Co _1-y1 ) _1-x1 and a second magnetic layer made of Tb _x2 (Fe _y2 Co _{1- y2} ) _1-x2 (provided that 0.14 <x1 <0. Two
0, x1 <x2 <0.40, 0.05 <y1, y2 <
0.2), and the composition of the second magnetic layer is based on the value of x2,
The present invention relates to a magneto-optical recording medium comprising a magnetic recording layer having an increasing gradient in the thickness direction.

FIG. 1 shows an example of the laminate of the present invention. A transparent substrate 1 is made of a transparent material such as glass or polycarbonate. 2 and 5 are dielectric layers (protective layers) which are generally made of, for example, silicon nitride. Reference numerals 3 and 4 are magnetic recording layers that characterize the present invention and are composed of first and second magnetic layers. The order of stacking these magnetic layers may be from the substrate side in this order, or vice versa. Reference numeral 6 is a reflective film, and a normal Al film is used.

The magnetic recording layer constituting the present invention is TbFeC.
o is the main component, but in the sense of improving durability, Cr,
Several percent of components such as Ti and Ta may be added. The present invention is characterized in that the constituent components of each layer constituting the magnetic recording layer are limited and the composition of the second magnetic layer has a gradient.

That is, the first magnetic layer is Tb _x1 (Fe _y1 C
o _1-y1 ) _1-x1 , the second magnetic layer is Tb _x2 (Fe
_{y2Co1 -y2} ) _1-x2 . Here, it is essential that x1, 2, y1, 2 satisfy the following conditions. That is, 0.14 <x1 <0.2, x1 <x2
<0.4, 0.05 <y1, y2 <0.2, and the value of x2 in the second magnetic layer is a value having an increasing gradient in the thickness direction. If it is out of the above range, it is not preferable for improving the recording stability and the magnetic field sensitivity of the medium.

In the above magneto-optical recording medium, the thickness of the magnetic recording layer is 50 to 300 A for both the first and second magnetic layers, and the total thickness of these layers is preferably 150 to 600 A in order to enable high magnetic field sensitivity. It is a range. The thicknesses of the protective layer and the reflective film are not particularly limited, but are usually 50 to 1000, respectively.
It is A.

The method for laminating the medium of the present invention may be an ordinary sputtering method. The magnetic recording layer may be laminated with Tb after the first magnetic layer is formed at a constant sputtering current and voltage and then at intervals. Alloy target or FeC
The second magnetic layer is formed by gradually changing the sputtering current and the voltage of the o alloy target so that the composition has a gradient. The degree of the composition gradient provided to the second magnetic layer is not particularly limited, and it is sufficient that the composition changes continuously or discontinuously, and the gradient may be changed linearly or curvilinearly or in a stepwise manner. It is something that was kept.

By forming the magnetic layer as described above, a magnetic layer of TM-rich composition having relatively good recording magnetic field sensitivity can be obtained.
Since the composition gradient is applied so that the effective magnetic field immediately below the recording temperature is in the opposite direction to that of the recording magnetic layer, the effective magnetic field near the recording temperature is almost cancelled. Erase noise is reduced. Also, the recorded magnetic domain is transferred to the second magnetic layer during the cooling process.

[0019]

The magneto-optical recording medium of the present invention has a normal Tb.
It is a medium suitable for high-speed recording / reproducing, which can increase the magnetic field sensitivity while maintaining the recording stability more than the FeCo single layer film.

[0020]

【Example】

Example As shown in FIG. 1, Si was formed on a polycarbonate substrate 1.
Dielectric layer 2 (thickness 900A) made of Nx, Tb
_0.16 (Fe _0.92 Co _0.08 ) _0.84 (Tc
1 = 220 ° C.), the first magnetic layer 3 having a film thickness of 100 A, Tb
_{x (Fe 0.92 Co 0.08) 1} -x, the x 0.16
To 0.36 and change the film thickness to approximately 150A
The second magnetic layer 4 is sequentially sputtered by using targets having respective compositions to be laminated, and the dielectric layer 5 (thickness 300 A) made of SiNx and the Al reflection film 6 (thickness 50).
0A) was laminated.

A laser beam of 780 nm was applied to this medium for 8 m.
While continuously irradiating with a power of W, while rotating at a linear velocity of 8 m / sec, the magnetic field from the floating magnetic head was 50
While modulating at 4.9 MHz with a duty of 100%, the value of the modulation magnetic field was changed to 100 and 50 Oe and recorded.
Reproduce by irradiating with a laser beam of 1.5 mW C
/ N was measured. The results are shown in the table.

Comparative Example The magnetic layer was made of Tb _0.16 (Fe _0.92 Co _0.08 ).
_A film was formed and tested in the same manner as in Example 1 except that the film thickness was set to 250 A at _0.84 (Tc1 = 220 ° C.). The results are shown in the table.

Table 4.9 MHz C / N (dB) recording magnetic field 100 Oe 500 Oe Example 44 39 Comparative example 42 36

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of the structure of a magneto-optical recording medium of the present invention.

[Explanation of symbols]

 1: Substrate 2: Protective film 3: First magnetic layer 4: Second magnetic layer 5: Protective film 6: Reflective film

Claims (2)

[Claims] 1. In a magneto-optical recording medium in which a dielectric layer, a magnetic recording layer, a dielectric layer and a reflective film layer are laminated in this order on a transparent substrate, the magnetic recording layer is Tb _x1 (Fe _y1 Co
_1-y1 ) _1-x1 first magnetic layer, Tb _x2 (F
e _y2 Co _1-y2 ) _1-x2 and a second magnetic layer (provided that 0.14 <x1 <0.2, x1 <x2 <
0.4, 0.05 <y1, y2 <0.2), and the composition of the second magnetic layer is composed of a magnetic recording layer having an increasing gradient in the thickness direction based on the value of x2. A characteristic magneto-optical recording medium. 2. The magneto-optical recording medium according to claim 1, wherein the first and second magnetic layers have a thickness of 50 to 300 A.