JPS63181143A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To permit data recording of >=3 values in the same photoirradiation position by laminating magneto-optical recording layers having the recording sensitivity characteristics sufficiently different from each other on a substrate and changing the number of the layers recorded according to the degree of the heating quantity by the laser irradiation. CONSTITUTION:The magneto-optical recording media 1-n having the different magnetic characteristics are continuously laminated on the substrate (a) to form one recording medium. The term 'magnetic characteristics' refer to Curie temp., saturation magnetization and coercive force. This medium is formed by laminating n-layers in order of the media having the higher Curie temp. (lower recording sensitivity). The recording medium exhibits various bit forming states when a laser power 6 is changed at the time of recording. The respective layers of the magneto-optical recording layers form the recording bits successively in order of the higher recording sensitivity when the laser light (b) is projected thereto in such a manner. The magnetical interactions between the respective magnetic layers prevent disturbance of the bit formation by each of the respective recording layers. The recording capacity is thereby increased without increasing the diameter of the disk.

Description

[Detailed description of the invention] Technical field> The uninvented technology has magnetic anisotropy in the direction perpendicular to the film surface, and information recording (by magnetization reversal in the perpendicular direction) and reproduction (by magnetization reversal in the perpendicular direction) and reproduction (by magnetization reversal in the perpendicular direction) by laser beam irradiation. The present invention relates to a magneto-optical recording medium obtained by laminating magneto-optical recording #N#'.

<Prior art> In recent years, magneto-optical recording media, which have magnetic anisotropy in the direction perpendicular to the film surface and record and reproduce information by irradiation with laser light, are capable of being erased and re-recorded by the user, and have grooves with a diameter of 1 μm. Since high-density recording is possible with spot recording of a certain degree, it is being put into practical use as a recording medium for digital audio discs, document files, still image discs, etc.

In addition, expectations for use in high-definition color moving image recording are increasing, and further increases in recording capacity are desired.

However, in magneto-optical recording media, the minimum recording bit length is determined by the wavelength of the light source, and when a near-infrared semiconductor laser is used as the light source, a 1 μm groove is the limit, and improvements in recording density have reached a plateau.

Therefore, research has begun to move from the current two-dimensional recording on flat disks to three-dimensional recording, and increasing capacity by increasing the number of recording layers is being considered. For example, a GdTbFe medium with the same composition is stacked in two layers with a dielectric S:02 layer interposed therebetween to form a recording layer, and the missing bits written in each layer are each irradiated with two lights of different wavelengths.
By reading them out independently and combining them, a reproduced signal is created. (here 5i02
The layer is used to prevent magnetic coupling between the two recording media and to control the reproduction signal output, and its thickness is 1.
~2 μm, which is extremely thick compared to the recording medium film thickness. ) This method doubles the recording density compared to a single layer.

However, the above structure has the disadvantage that two recording/reproducing optical heads are required, which complicates the system.

<Purpose of the Invention> The present invention consists of continuously stacking magneto-optical recording media with different magnetic properties on a substrate to form a single recording medium, and by controlling the recording laser power, 8 or more values can be recorded at the same optical spot position. The purpose of this is to perform multivalue recording.

Note that when comparing the recording capacities of the conventional 1.0 binary recording method and the 3-value or higher recording method using the general definition of capacity, the n value for m bits is found.

<Embodiment> FIG. 1 shows the structure of an embodiment of a magneto-optical recording medium for multilevel recording according to the present invention.

+i[, a is a disk substrate, and 1-n are magneto-optical recording layers having different magnetic properties. As shown in the figure, the recording medium has a laminated structure of n layers of magneto-optical recording layers. The magnetic properties referred to here are Curie temperature Tc, saturation magnetization Ms, and coercive force He.

The magneto-optical recording medium shown in the figure is made by laminating n layers of media in the order of higher Curie temperatures (lower recording sensitivity 1.n) than the substrate, and by changing the laser power during recording, The recording medium shows a bit formation state as shown in FIG.

In FIG. 2, a is a disk substrate, b is a laser beam, C is a direction of magnetization, d is a recorded bit, and 1=n is a magneto-optical recording layer having different magnetic properties. As shown in the figure, when the magneto-optical recording layer is irradiated with a laser beam, recording bits are formed in each layer in the order of recording sensitivity. Note that magnetic interaction between each recording layer hinders bit formation in each recording layer (for example, when a bit is formed in the nth layer,
Because of this magnetic interaction, bits are formed in the (n-1)th layer regardless of the recording laser power. ) It is desirable that the magnetic properties of each layer satisfy the following two conditions.

■ Tc (k-1) > Tc (kl> Tc (k+
1) ■ Ms (k-1)t(ks), Ms(kl
The magnitude of t[k) ·Ms(k+x)j(k+t) has a specific relationship (experimental data when n=2 is shown in the example).

(2≦≦n-1) Here, Tc(k 1 ) −Tc(kl−Tc(k
+1) are the Curie temperature of the recording layer of 1(-1st, 2nd, l(+1st) counting the substrate side force, respectively. Also, Ms(k -1)t(ks), Msikl t (k
l-MsCk+t)t(k+x) are the products of the saturation magnetization MB and the film thickness t of the 11th, 2nd, and +1st recording layers, respectively, counting the substrate side force. It can be seen from the above that by controlling the recording power, n+1 types of bit formation states can be obtained. Reproduction is then performed by reading out the state of these bit formations as differences in the magnitude of the Kerr rotation angle or Faraday rotation angle using a laser beam. By identifying the signal outputs obtained in this way, it is possible to record up to (n+1) values. In addition, in order to be able to detect the magnetization state of the n-th medium when reading the recording signal using reflected laser light, the magnetic state of the n-th medium must be detected by The total thickness of the media up to the (n-1)th layer must be kept to about 500λ or less.

FIG. 3 shows the structure of a magneto-optical recording medium for ternary recording. In the figure, a is a glass disk substrate, e and f are SiO films that are transparent insulating films, 1 is an amorphous GdTbFeCo film that is a magneto-optical recording layer made of a rare earth-transition metal alloy, and 2 is the same <
It is a TbFe film. As shown in the figure, the recording layer is GdTbF
It has a laminated structure of an eCo layer and a TbFe layer. Here, the first Sin/me is used as a Kerr rotation angle enhancement layer, and the fourth SiO layer f is used as a protective film b. GdTbFeC.

The Curie temperatures of the TbFe layer and TbFe layer are each 300°C or higher11
0 to 140°C, and the recording sensitivity is higher for TbFe media than for GdTbFe media at low A power when irradiated with laser light.
Bits are formed in the TbFe layer 2 before CoJ-1. Therefore, this recording medium takes on three types of states shown in Figure 4 (al, (bl, and d) depending on the magnitude of the laser power. In the figure, a is the disk substrate, b is the laser beam, and C is the magnetization state. direction, d is bit, l is GdTbF
The eCo layer 2 is a ThF4 layer. The C3iO layer was omitted. ) In the same figure, the states [al, [bl, and fcl] are before recording, bit formation only in the TbFe layer, and Gd
Both the TbFeCo layer 1 and the TbFe layer 2 represent the state of bit formation. Hereinafter, these states will be referred to as ta) state, (b) state, and (C) state.

What must be noted here is that GdTbFeC
Even if the o layer l and the TdFe layer 2 satisfy the above-mentioned size relationship of one tCurie point, the bl state cannot be formed (at room temperature ).

FIG. 5 shows the first layer 1 of the recording layer (Qdx7b Zoo-x) 14.9 to 21.5 (
Fe70Coao)85.1~78.5(at
om%), the second recording layer 2 is T b xs, o-',
22. o Fe 84.0-7s, 9 (atom %
The results of a recording/reproduction experiment using a double-layered disc (2) are shown below.

The product of the saturation magnetization Ms and the film thickness t of each of the two layers constituting the recording layer is plotted on the vertical and horizontal axes, and it is confirmed that the fbl state cannot be obtained depending on the combination.

In the figure, O mark indicates (a), fbl due to recording power control.
, [cl can take on each state, and the X mark is (
It can only take the states al and fcl. This is it υ
It is considered that state [b] cannot be formed in the shaded area.

The saturation magnetization Ms and film thickness t of the recording medium shown in FIG. 3 are as shown in Table 1, which is located at point A in FIG.

At A in Table 1 and Figure 5, the first layer l of the recording layer is (GdxTbl
oo-)Ot4. c+~21.5 (Fe7oCOao
) so, x~78.5... (X=70~100), and the second recording layer 2 has T b 16.0~22. OF
e84. In a two-layer disc with a temperature of O~78.0, the MS-t of the first recording layer is 2.5 x 10-
' is larger than 222 cm and the Ms-t of the second recording layer C is 6 x 10-' -! -E! ! −
! ! It is shown that ternary recording is possible if both conditions of -.cm and C greater than m are satisfied.

FIG. 6 shows the spectrum obtained under the conditions of a recording frequency of IMHz, a disk recording radius of 55 mm, and a disk rotation speed of 180 Or, p, and m. The same figure (al is (b
0-term spectrum under l state, same figure (bl is ♀ spectrum under cl state. (bt state ate 47.0
57.2 dB was obtained in the dB and fcl states, each of which is large enough for digital recording.

-i Figure 7 shows the reproduced waveform output (
amplitude). fa) state is at level 0, and (al
, ibl, and fcl can be sufficiently distinguished electrically. About that time, I changed these to -1, 0, 1.
By processing it as a value signal, three-value recording becomes possible.

Furthermore, Fig. 8 shows the power required to obtain the fal state, (b) state, and (C) state in eight cases of auxiliary magnetic field (magnetic field that assists bit formation) HB = 0.800.500 0e. Shown against. In the figure, the vertical axis is the connection value, and the horizontal axis is the recording laser power. Regardless of the magnitude of the auxiliary magnetic field, the recording power value to obtain each state is wide, but the threshold power width between each state is narrow, making it easy to control the recording power.・Ru. However, if the auxiliary magnetic field is small, ibl, (cl) will be low in each prone state (particularly significantly low in HB-00e), so it is better that the auxiliary magnetic field is large enough to prevent the recording bit from becoming too large.

Next, in the same disk structure, the first recording layer (GdT
When the film thickness t of bFeCo medium) is changed, Tbl
Table 2 shows the percentage obtained from the state and (C) state. The measurement conditions are the same as above.

%2 By reducing the surface film thickness, the value obtained from the J(t)l state can be increased. This is the second recording layer (T
It is considered that the attenuation amount of the signal due to the bFe medium) 25 is reduced. Above (b), (from the value of the reproduced signal that can be applied to the CL state, the magnitude of the reproduced waveform output, and the controllability of the recording power, the disk has sufficient characteristics for 8-level recording, and the recording capacity is thereby increased. Approximately 58 compared to conventional binary recording
- will increase. Incidentally, according to the configuration according to the invention, both recording and reproduction can be performed using only a single optical head, as in the case of a conventional single-layer recording medium.

<Effects of the Invention> As described above, according to the present invention, the recording capacity can be increased without increasing the disk diameter.

- The information transfer rate can be increased.

- Recording and playback can be done with a single optical head.

Etc., the performance of magneto-optical disks can be greatly improved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the structure of an embodiment of the magneto-optical recording medium according to the present invention, FIG. 2 is an explanatory diagram showing the state of bit formation, and FIG. 8 is the structure of the magneto-optical recording medium for a-value recording. Explanatory diagram, Figure 4 is an explanatory diagram showing the state of bit formation, Figure %5 is an explanatory diagram showing the experimental results of recording conditions, Figure 6 is a waveform diagram of the connection ratio spectrum, and Figure 7 is a waveform diagram of the output signal. , Fig. 8 is a measurement graph diagram based on changes in the auxiliary magnetic field. In the figure 1.2.・4・:・n: Record layer agent Patent attorney Takeshi Sugiyama (1 other person) b-11
/I'') shi1, meeting/l'7-miss θ
l#z rO~σ 8a Doshito expansion proudly, Toπo~纂 4 mouth rbF# REF/QOd8m ArrlodB
MKRΔ1351HzREF 10. OdBm
Arrlo dB MKRΔ1901
tHz1 Town 6 Figure tb no $7 (21 Procedural amendment 20 Name of the invention Magneto-optical recording medium 3, Relationship to the person making the amendment case Patent applicant address 8545 22-22 Nagaike-cho, Abeno-ku, Osaka City Name (504) ) Sharp Corporation Representative Haruo Tsuji 4, Agent voluntarily 6, Subject of amendment 6, 62-' Near, Contents of amendment (1) Page 5, line 4 to line 19, 1 of the specification
-It is the product of... It is necessary to set the product (MS-t) of the saturation magnetization MS and the film thickness t of each layer to meet a specific condition to avoid the problem of ``.'' The conditions when n = 2 will be described later. It is also desirable that the Curie temperature TC has the following relationship: TC(+)>TC(2)>・>TC(n-2)>To
(n-1)>T((n) or To(1)<T((2
)<-<T. (n-2) <"r(,(n-'I
)<Tc(n) Here, Tc(k) represents the Curie temperature of the recording layer counting from the substrate side. (however,
Correct as 1≦≦n)J. (2) "Configuration" in the second line of page 6 of the specification is amended to read "configuration of the embodiment."

Claims (1)

[Claims] 1. By stacking magneto-optical recording layers with sufficiently different recording sensitivity characteristics on a substrate and changing the number of recorded layers depending on the degree of heating by laser irradiation, three or more values can be recorded at the same light irradiation position. A magneto-optical recording medium characterized by being capable of recording data.