JPH01178151A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To decrease noises at the time of recording by forming a magnetic recording layer of a magnetic layer having relatively small coercive force and high Curie temp. and a magnetic layer having relatively large coercive force and low Curie temp. adjacently thereto and providing a reflecting layer on the side of the recording layer opposite to a light incident layer. CONSTITUTION:The magnetic layer 2 having the relatively small coercive force and the high Curie temp. and the magnetic layer 3 having the relatively large coercive force and the low Curie temp. are laminated on a light transparent substrate 1 and an reflecting layer 4 is further laminated thereon. Amorphous magnetic alloys which exhibit perpendicular magnetic anisotropy and magneto- optical effect, i.e., amorphous magnetic alloys of rare earth elements and transition metal elements such as GdCo, GdFe, TbFe and DyFe are usable for the material of the respective magnetic layers 2, 3. The apparent coercive force is thereby increased and the noises at the time of recording are decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a Curie point writing type magneto-optical recording medium.

(Prior Art) Magneto-optical disks are known as erasable optical memories. Recorded signals are reproduced using magneto-optical effects, but they have the disadvantage that a large degree of signal modulation cannot be obtained compared to optical discs that use changes in reflectance.

Therefore, JP-A-55-87332, JP-A-54-84
As disclosed in No. 702, a new reflective layer is provided on the opposite side of the thin magnetic recording layer to which the incident light transmits, and the Kerr effect and the reflected light from the reflective layer are reduced. Efforts have been made to obtain a large reproduction signal by using the Faraday effect.

Furthermore, since magneto-optical disks use inverted magnetic domains as recording bits, compared to optical disks, if they are left in an environment with high temperatures and a magnetic field, errors may increase in the reproduced signal or the recorded signal may be erased. There is a fear that it will get lost. Therefore, the coercive force of the magnetic recording layer is usually 5 to 15 kOe.
It is set to a relatively large value.

[Problem that the invention seeks to solve]

However, when a magnetic recording layer with a large coercive force is used, there is a problem in that noise increases significantly during recording, especially when the film thickness is set to 400 Å or less.

The object of the present invention is to provide a magneto-optical recording medium using a thin film magnetic layer, which has a reflective layer on the opposite side to the incident light and can obtain a large reproduction signal, with a film thickness of 400 Å or less, and a large apparent coercive force. It is an object of the present invention to provide a magneto-optical recording medium in which there is less fear that information will be erased and noise during recording is also low.

(Means for Solving the Problems) The present invention, which can achieve the above object, has a film thickness of 4 mm on a transparent substrate.
In a magneto-optical recording medium provided with a magnetic recording layer made of an alloy of a rare earth element and a transition metal with a thickness of 00 Å or less, the magnetic recording layer comprises a magnetic layer having a relatively small coercive force and a high Curie temperature, and a magnetic layer having a relatively small coercive force and a high Curie temperature. A magneto-optical recording medium comprising an adjacent magnetic layer having a relatively large coercive force and a low Curie temperature, and a reflective layer is provided on the side opposite to the light incident side of the magnetic recording layer. be.

Hereinafter, the present invention will be described in detail with reference to the drawings. first,
The structure, materials, etc. of the magneto-optical recording medium of the present invention will be mentioned.

FIGS. 1(a) and 1(b) are each a schematic cross-sectional view showing an example of the magneto-optical recording medium. In the magneto-optical recording medium shown in FIG. 1(a), a magnetic layer 2 with a relatively low coercive force and a high Curie temperature is formed on a transparent substrate 1 provided with pre-groups, and a magnetic layer 2 with a relatively low coercive force and a high Curie temperature. The magnetic layer 3 has a high Curie temperature and a low Curie temperature. Furthermore, a reflective layer 3 is laminated thereon.

Usually, the coercive force of the magnetic layer 2 is in the range of 1 to 4 Oe, the Curie temperature is in the range of 100 to 250°C, and the coercive force of the magnetic layer 3 is in the range of 5 to 4 Oe.
15 KOe, and the Curie temperature is preferably selected from a range of about 100 to 250°C. Further, the difference in Curie temperature of the inner magnetic layers is preferably within a range of about 10 to 50°C.

The material of each magnetic layer includes an amorphous magnetic alloy that exhibits perpendicular magnetic anisotropy and magneto-optic effect, namely GdCo, G
dFe, TbFe, DyFe, GdTbFe,
TbDyFe, GdTbFe (:o, GdTb(
An amorphous magnetic alloy of a rare earth element and a transition metal element such as :o can be used.

Note that the magnetic layer 2 and the magnetic layer 3 may be stacked such that either one is closer to the substrate.

Materials for the reflective layer 4 include A], Ag, Cu, Ti
, PT, or other metal materials can be used.

In FIG. 1(b), 5.6.7 is a protective film for improving the durability of the magnetic layer 2 or for improving the magneto-optical effect. SiO, Sin, , TiO2, Si
A dense film made of oxide, nitride, sulfide, etc. such as 3N4, AN%ZnS, etc. is used.

8 is an adhesive layer for bonding the bonding substrate 9 together.

Note that if layers 2 to 7 are laminated on the bonding substrate 9 and these are adhered, recording and reproduction can be performed on the front and back sides.

Next, the reason why recording noise is reduced according to the present invention will be explained. For this purpose, first, FIG. 2(a) shows a plurality of samples in which a single magnetic layer 3 is provided on a substrate 1 instead of the configuration of the present invention (that is, a polycarbonate substrate with a protective film on it). As, 700 5t3N layers, magnetic layer 3 as Tb
x (Fe9z(:oa) + oo-x for 400 people,
500 layers of Si3N4 as a protective layer, 500 layers of A1 as a reflective layer 4, and 700 layers of Si3 as a protective layer.
The results of measuring the noise level during recording of a magneto-optical disk provided with an N+ layer, in which the composition of the magnetic layer is varied in various ways by changing X, are shown.

The horizontal axis shows the composition ratio X (atomic %) of Tb atoms, and the vertical axis shows the noise level during recording of each disk and the coercive force value (koe) of the magnetic layer 3. Here, Tb is about 20 atomic %
When , the compensation composition is established. As described above, as the composition approaches the composition where the coercive force value is maximum (compensation composition), the noise during recording increases.

On the other hand, as shown in Figure 2 (C),! TbF in fi layer
Regarding magneto-optical disks manufactured in the same manner except that the thickness of the eCo layer was changed to 800 nm, the noise level during recording did not depend on the composition ratio of Tb atoms and remained constant at a low level (more than 800 Å). If so, it is almost the same for other film thicknesses).

The reason for this difference is the magnitude of saturation magnetization of the magnetic layer (
For example, when the thickness of the magnetic layer is small, the composition is non-uniform near the interface, and the demagnetizing field that assists magnetization reversal during recording is small. It is thought that this may be influenced by the following.

On the other hand, in FIG. 2(b), a magnetic layer 2 and a magnetic layer 3 are formed on the substrate.
A sample according to the present invention, which was provided with a thin film magnetic layer of Si3N4 layer, magnetic layer 2: TbFe(:o layer: 200A, magnetic layer 3: TbFeCo layer: 200A, protective layer: 5
00 Si3N4 layer, 500 A1 as reflective layer 4
The results of measuring the noise level during recording on a magneto-optical disk (with 700 Si and N4 layers provided as a protective layer) are shown below.

Here, the magnetic layer 2 had an atomic composition ratio of TI)+5Fl17acO7. The sublattice magnetization is dominated by transition metals, the coercive force in a single magnetic layer is ~IKOe, and the Curie temperature is 20
It was 0°C. In FIG. 2(b), the horizontal axis represents the magnetic layer 3Tb.
x (Fes□(:oa) too-X indicates the composition ratio X (atomic %) of Tb atoms, and the vertical axis indicates the noise level during recording of each disk and the value of the coercive force (KOe) of the magnetic layer 3. show.

The magnetic layer 3 TbFeCo had an atomic ratio of Fe to Go of 9228, and the Curie temperature of each composition was about 180°C.

In FIG. 2(b), unlike in FIG. 2(a), no increase in noise during recording was observed even when the composition approached the maximum coercive force value (compensation composition of the magnetic layer 3).

The reason for this is thought to be as follows.

That is, since a single-layer recording film having the composition of magnetic layer 2 (Tb+5Fe76Co7) does not show any increase in noise during recording, a stacked layer of magnetic layer 2 and magnetic layer 3 of Tb+5Fe76CO7 has a structure in which the magnetic layer is This is thought to be because the magnetic layer 3 always reverses its magnetization in a direction that is stable for the magnetization of the inner magnetic layer (with the aid of an exchange force).

In general, in order to increase the coercive force, the magnitude of saturation magnetization is set small, and if a layer with a composition that increases the saturation magnetization is laminated in contact with a magnetic layer, the following points will be improved. .

(1) Magnetization reversal during recording occurs from laminated layers with compositions that increase the saturation magnetization, forming recorded bits with high contrast with unrecorded areas.

(2) The demagnetizing field that assists magnetization reversal during recording (due to the magnetization of a layer with a small coercive force) increases, and recorded bits with high contrast with unrecorded areas are formed.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 First, a protective film Si3N4 film was applied by sputtering to a polycarbonate disk-shaped substrate in which pregroup and preformat signals were engraved, and a magnetic layer TJ was applied.
5 FeyaCOy (coercive force I KOe, Curie temperature is 200°C) for 200 people, magnetic layer TbFeCo for 20 people
0 people, protective layer Si3N4 300 people, reflective layer A! 50
0 person, and then a protective layer of Si3N4 was formed by 700 people in this order. Note that the magnetic layer is TbFeC.

Six types of laminates were formed by varying the composition of the laminates.

The composition and coercive force of each of the six types of TbFeCo magnetic layers are shown in Table 1 below.

Table 1 Next, each of the above-mentioned substrates on which film formation had been completed was bonded to a polycarbonate bonding substrate using a hot melt adhesive to create a magneto-optical disk.

Each of these magneto-optical disks was set in a recording/reproducing device, and a laser beam with a wavelength of 830 nl focused on approximately one scale was used at a linear velocity of 8 m/sec, an erase bias magnetic field of 4000e, and a laser power of 61IIw. After erasing, write bias (reverse polarity during erasing) 2000
e, recordings were performed with a laser power of 4.5 mW modulated at a frequency of 2 MHz. Recorded signal playback is 1.0m
This was carried out using a continuous beam of W. The results are shown in Table 2 below.

Table 2 Comparative Example 1 A magneto-optical disk was manufactured using the same configuration, materials, and conditions as in Example 1, except that the magnetic layer TbFeCo was changed as shown in Table 3 (however, the magnetic layer TbFeCo was a single layer). ).

For each of these samples, recording and reproduction evaluation was performed in the same manner as in Example 1. The results are also shown in Table 3.

The results of Example 1 and Comparative Example show that in a magneto-optical disk in which a magnetic layer with a small coercive force of about IKOe and a magnetic layer with a large coercive force are laminated, the apparent coercive force (when laminated) is large and the recording noise is small. It was found that a large reproduction C/N value could be obtained.

Magneto-optical disks are sometimes left in an environment at high temperatures and in the presence of a magnetic field, such as during continuous reproduction of the same track, so it is desirable that the disk has a coercive force of 8 KOe or more at room temperature, for example.

When the samples of Example 1 and Comparative Example were reproduced by repeating the same track 1 million times while applying a bias magnetic field of 2000e at the recording head, the reason why the reproduced signal did not deteriorate was because the coercive force was 7. Examples 1-3.1-4.1-5 and comparative examples with XOe or more! -3,! -4,
There were only 1-5, 1-7, and 1-8.

Further, from the results of Comparative Examples 1-8, it was confirmed that even if a single magnetic layer with a large coercive force is used, recording noise does not become large if the thickness is about 800 mm.

In addition, the value of the apparent coercive force when stacked in Table 2 is
Comparing with the coercive force values shown in Table 1, if the compositions of both magnetic layers are rich in FeGo elements with respect to the compensation composition, the apparent coercive forces in Table 2 will be the values shown in Table 1. On the other hand, the composition of both magnetic layers changes to become smaller, and the composition of both magnetic layers is rich in Tb element with respect to the compensation composition, and the other is Tb,
When the Go element is enriched, the apparent coercive force shown in Table 2 changes to become larger than the value shown in Table 1.

In other words, by using a compensation composition in which one magnetic layer is rich in rare earth elements and the other magnetic layer is rich in transition metals, the apparent coercive force becomes large and the recording bits are Improved stability.

Example 2 A magneto-optical device was created using the same configuration, materials, and conditions as in Example 1, except that the composition of the magnetic layer with a large coercive force and the magnetic layer with a small coercive force and the order in which the films were formed on the substrate were changed. The properties of the magnetic layer of each sample are shown in Table 4.

The thickness of each magnetic layer was 200.

In the composition section shown in Table 4, the TM side shows a composition rich in transition metal elements compared to the compensation composition, and the RE
The side indicates that the composition is rich in rare earth elements compared to the compensation composition.

When the same recording and reproducing experiment as in Example 1 was conducted,
For all samples in the example, low recording noise (
-56~-57dBm) and good C/N (54~55dBm)
B) was shown.

Next, we set the internal temperature of the recording/reproducing device to 60°C and repeatedly reproduced the recorded signal 100 times, and found that the magnetic layer with a large coercive force has a composition rich in rare earth elements relative to the compensation temperature. Only the sample (Example 2-1.2-2) in which the compensation temperature was between room temperature and the Curie temperature showed no signal deterioration. This is because when the temperature of the magnetic layer rises during playback, the coercive force changes even further for those with a compensation temperature between room temperature and the Curie temperature, making the recorded bits more stable. Conceivable.

[Effects of the Invention] As explained in detail above, a film with a thickness of 40 mm is formed on a transparent substrate.
In a magneto-optical recording medium provided with a magnetic recording layer of an alloy of a rare earth element and a transition metal with a thickness of 0 Å or less, the magnetic recording layer is composed of a magnetic layer having a relatively small coercive force and a high Curie temperature; By using an adjacent magnetic layer with a relatively large coercive force and a low Curie temperature, and by providing a reflective layer on the side opposite to the light incident side of the magnetic recording layer, a large apparent coercive force with high stability of recording bits can be achieved. It has now become possible to achieve both high CAN value characteristics with low recording noise.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) each show the structure of an example of the magneto-optical medium of the present invention, and FIG. 2(a) shows the composition of the TbFeCo11i layer with a thickness of 400 mm and the created optical A diagram showing the relationship with recording noise of a magnetic medium, FIG. 2(b) shows the TbFeC laminated on the Tbl5Fe76Coy layer of the present invention
o A diagram showing the relationship between the composition of the magnetic layer and the recording noise of the prepared magneto-optical medium. Figure 2 (C) is a TbF film with a thickness of 800 mm.
FIG. 3 is a diagram showing the relationship between the composition of an eCo magnetic layer and the recording noise of the produced magneto-optical medium. 1: Transparent substrate with nibli groove, 2.3: Magnetic layer, 4: Reflective layer, 5.6, 7: Protective film, 8: Adhesive layer, 9: Bonding substrate. Patent applicant Canon Co., Ltd.

Claims (1)

[Claims] 1) A magneto-optical recording medium in which a magnetic recording layer of an alloy of a rare earth element and a transition metal is provided on a transparent substrate and has a film thickness of 400 Å or less, wherein the magnetic recording layer is It consists of a magnetic layer with a relatively small coercive force and a high Curie temperature, and an adjacent magnetic layer with a relatively large coercive force and a low Curie temperature, and a reflective layer on the side opposite to the light incident side of the magnetic recording layer. A magneto-optical recording medium characterized by being provided with a layer. 2) A magnetic layer with a relatively small coercive force and a high Curie temperature has a composition in which the sublattice magnetization is dominated by transition metals, and a magnetic layer with a relatively large coercive force and a low Curie temperature has a composition in which the sublattice magnetization is dominated by rare earth elements. 2. The magneto-optical recording medium according to claim 1, which has a composition of: