JPH0373446A - Medium for magneto-optical memory - Google Patents

Abstract

PURPOSE:To improve an exchange bond together with recording characteristics and corrosion resistance by forming both of a 1st magnetic layer and a 2nd magnetic layer of the thin films of amorphous alloys consisting of rare earth- transition metals and incorporating Cr into the 1st magnetic layer and Co into the 2nd magnetic layer. CONSTITUTION:The 1st magnetic layer having a high coercive force at room temp. and a low Curie temp. and the 2nd magnetic layer having the coercive force lower than the coercive force of the 1st magnetic layer and a high Curie temp. are provided. Both of the 1st magnetic layer and the 2nd magnetic layer are the thin films of the amorphous alloys consisting of the rare earth-transition metals. The 1st magnetic layer contains the Cr and the 2nd magnetic layer contains the Co. Namely, the reading out sensitivity and durability of the reading out layer (the 2nd magnetic layer) are improved by adding the Co thereto. The increase of the Curie temp. is suppressed and the durability is improved without degrading the recording sensitivity by adding the Cr to the recording layer (the 1st magnetic layer). The exchange bond is improved together with recording characteristics and the corrosion resistance in this way.

Description

[Detailed description of the invention] [Industrial Application Field J The present invention relates to a magneto-optical memory medium.

[Prior art] Magneto-optical memory using rare earth-iron group amorphous alloy thin film is
Its read characteristics are not sufficient, and various proposals have been made for ways to improve it. One of them is an exchange-coupled two-layer film consisting of a film with good recording properties and a film with good read-out properties (for example, Japanese Patent Application Laid-Open No. 57-78652). In the conventional exchange-coupled 2N film, the recording layer has Tb- Fe, Dy
-Fe, Gd-Fe in readout layer %Gd-Fe-C
O etc. are used for teita.

[Problem that the invention seeks to solve]

In a magneto-optical memory, information is recorded using the thermal effect of laser light, so the lower the Curie temperature of the magnetic film, the higher the recording sensitivity. In an exchange-coupled two-layer magnetic film, what determines the recording sensitivity is the Curie temperature of the recording layer.
Lowering the Curie temperature of the recording layer increases recording sensitivity.

However, considering the stability of recorded information and the internal temperature of the magneto-optical memory drive device (>50°C), the Curie temperature of the recording layer is preferably about 100°C. Considering this point, Tb-Fa, which was conventionally used as a recording layer,
has a slightly high Curie temperature of about 130°C, and Dy-Fe has a slightly low Curie temperature of about 70°C, which cannot be said to be the optimum Curie temperature for practical use.

Furthermore, for practical use of magneto-optical memories, the corrosion resistance of the magnetic film is a very important issue. It is known that the corrosion resistance of a rare earth-iron group amorphous alloy thin film is improved as the amount of Co contained as an iron group element increases. In the exchange-coupled two-layer magnetic film, the readout layer contains Gd-Fe-C.
By increasing the concentration of Co, it is possible to improve not only the readout characteristics but also the corrosion resistance. However, Tb--Fe or Dy--Fe is used in the recording layer 5, and when CO is added to this, the Curie temperature increases considerably even in a small amount, resulting in poor recording sensitivity.

The present invention has been made to improve the above-mentioned conventional drawbacks, and its purpose is to provide a magneto-optical memory medium that has improved recording characteristics, corrosion resistance, and exchange coupling.

[Means for Solving the Problems] The present invention provides a first magnetic layer having a high coercive force and a low Curie temperature at room temperature, and a second magnetic layer having a lower coercive force and a higher Curie temperature than the first magnetic layer. In the exchange-coupled magneto-optical memory medium, the first magnetic layer and the second magnetic layer are both amorphous alloy thin films made of rare earth-transition metal, and the first magnetic layer is made of Cr. and the second magnetic layer contains Go.

According to the present invention, in a magneto-optical memory medium having an exchange-coupled double-layer film consisting of a layer with good recording properties and a layer with good read properties, the read properties are good without reducing the recording sensitivity of the layer with good recording properties. Durability can be improved without degrading the readout characteristics of the layer, and for this purpose, in the present invention, Co is added to the readout layer (second magnetic N) to increase the amount of Co and improve readout sensitivity and durability. In addition, Cr is added to the recording layer (first magnetic layer) to increase the amount of Cr to suppress the rise in Curie temperature and improve durability without lowering recording sensitivity.

In one embodiment of the present invention, a magnetic film has an exchange-coupled three-layer structure in which a recording layer having a high coercive force and a low Curie temperature at room temperature is sandwiched between a reading layer having a low coercive force and a high Curie temperature. Examples include a magneto-optical memory medium in which the recording layer is made of Tb-Fe-Cr and the reading layer is made of Gd-Fe-Co.

Differences between the conventional example and the magneto-optical memory medium of the present invention will be explained in detail below.

First, we will discuss the difference in the Curie points of the recording layers of both media. The recording layer of conventional media includes Tb-Fe, Dy
-Fe etc. were used, but as mentioned above, Tb-
Fe has a slightly high Curie temperature of approximately 130℃<, Dy
-Fe is a little low at about 70℃, so (Tb-Fe)
+-, M-[0≦Z≦0.1 (Cr) When various magnetic films represented by 1 were prepared, their Curie temperature T
Between c and M atomic ratio 2, there is approximately Tc = 130-500z ('C) (
The relationship M=Cr) was obtained. Therefore, if Z=0.06 in Cr, the Curie temperature is about 10 degrees Celsius, which is lower than that of Tb-Fe, and that of Dy-Fe.
A magnetic film with superior temperature stability can be obtained. Based on this knowledge, a magnetic film containing zero Tb, Fe, and Cr was used as the recording layer of the magneto-optical memory medium of the present invention.

The optimum value of the Curie temperature varies depending on the power of the laser used, the configuration of the optical system, the configuration of the medium, the rotation speed of the disk, the diameter of the disk, etc., for example 90.110℃.
The Curie point of the recording layer of the magneto-optical memory medium of the present invention may differ from the conventional It is also possible to set the value to be similar to the Curie point shown by the recording layer of the medium. However, in general, if the recording sensitivity of the medium is high, the power of the laser used will be small, the optical system will be simple and therefore inexpensive, and recording will be stable even when the recording power fluctuates due to external disturbances. This increases reliability. Therefore, it is desirable to set the Curie point to a low value so that the recording sensitivity is as high as possible, but from the viewpoint of stability against temperature, a higher Curie temperature is better, so the Curie point to be set is preferably 120 to 90°C.

Next, the difference in corrosion resistance between the conventional example and the RM of the magneto-optical memory medium of the present invention will be described. In the corrosion process of a magnetic film made of a rare earth-iron amorphous alloy thin film, free oxygen present in the film mainly combines with the rare earth element and is oxidized, and oxygen and moisture pass through the interface between the magnetic film and the protective film. It is thought that it diffuses into the film and becomes oxidized. Regarding the former, it can be considerably improved by reducing the oxygen concentration in the target in sputtering or the evaporation source in vapor deposition, the residual gas pressure in the vacuum device, and the impurities in Ar gas. On the other hand, although the latter can be considerably suppressed by a dense protective film that does not contain oxygen, it is desirable to improve the corrosion resistance of the magnetic film itself. In particular, when using plastic for the substrate, the substrate has a certain degree of water absorption.
It is particularly desirable to improve the corrosion resistance of not only the protective film but also the magnetic film.

In the case of an exchange-coupled bilayer membrane, Gd--Fe--Co can be used in the readout layer since it may have a high Curie point, and the corrosion resistance can be improved by increasing the concentration of CO. However, the recording layer of conventional media contains Tb-Fe and D.
y-Fe is used, and when Co is added to it, the Curie temperature increases considerably even in a small amount, which has the disadvantage of deteriorating recording sensitivity.

In the present invention, by adding C to the recording layer, an increase in Curie temperature is suppressed and corrosion resistance is improved without lowering recording sensitivity.

In addition, in exchange-coupled bilayer films, the magnitude of exchange coupling between magnetic films greatly influences the characteristics of the medium, but the magnitude of exchange coupling varies considerably depending on the difference in the vacuum pressure reached during fabrication. This is due to the influence of residual gas adsorbed at the interface between the manufacture of one magnetic film and the manufacture of the next magnetic film, and this influence can be significantly improved by improving corrosion resistance.

Therefore, improved corrosion resistance! ! The magneto-optical memory medium of the present invention using a layer is effective not only in improving the aging of the medium but also in improving exchange coupling.

The magneto-optical memory medium of the present invention is characterized in that the magnetic film is configured as described above.In addition to the magnetic film, it also has a reflective layer for effectively utilizing light, and a protective layer that protects the magnetic film. Various auxiliary layers may be optionally provided as desired, such as a protective layer for enhancing the performance.

[Example 1 Example 1 Using a normal sputtering method, a conventional example and a method of the present invention were prepared.
A disk-shaped magneto-optical memory medium with a diameter of 30 mm was prepared,
An experiment was conducted on recording sensitivity. In the conventional example, the magnetic film is Gd
-Fe-Co (Gd: Fe: Co= f8
: 62 : 20 film thickness 500 layers);
The two-layer film with the recording layer of Tb-Fe (Tb:Fe=22+78, film thickness 500A) and the magnetic film of the present invention are made of Gd-Fe-Go (Gd:Fe:
Co = 18: 62: 20, film thickness 300), (TtrFe) + -xcrx (z
= 0.06, film thickness: 400 mm). Polycarbonate was used for the substrate.

At a rotational speed of IBOOrpm, recording on the conventional medium required a laser power of 4.9 mW and a bias magnetic field of 2000 s, but the present invention requires a laser power of 4.0 mW.
Recording was possible with W and a bias magnetic field of 2000 seconds, and the recording characteristics were improved.

In addition, in a corrosion resistance test using a specified NaCl aqueous solution, in the conventional example, considerable pinholes were visually observed after immersion for 15 minutes, but in the case of the present invention, no pinholes were visually observed. I couldn't see it.

The measurement of exchange coupling contains a considerable amount of error, so it was not possible to obtain an accurate value, but the value of the present invention is approximately 1
．． There was a tendency to improve by a factor of three.

Example 2 In the following examples including this example, examples will be explained using a two-layer film of the #i layer and the readout layer.

130 nmφ disk-shaped magneto-optical recording media of the conventional example and the present invention were prepared using a conventional magnetron sputtering method, and experiments were conducted on recording sensitivity, readout characteristics, and durability. Ar gas pressure was approximately 0.15 Pa. As a protective film, SiN was provided on both sides of the 70OA recording medium. The readout layer in the conventional example is Gd, *2 (Fe, 70C0,3
0), ta, film thickness 200A, recording layer Tb, x*
(Fe, e, Co,.) 11, film thickness 600A, readout layer in the present invention is Tb, +5 (Fe, toC
O, so), aa, film thickness 20mm, recording layer (Tb,
ax (Fe, asco, Is), tag, *
3Cr, O? , the film thickness was 600 people. Polycarbonate was used for the substrate. The Curie temperature of the recording layer was about 170° C. in both the conventional example and the present invention.

At a rotation speed of 1500 rpm, a radius of 35 m+n, and a bias magnetic field of 2000 e, a laser power of 4.9 mW is required for recording on the conventional medium, whereas recording can be performed on the medium of the present invention with a laser power of 4.7 mW. Yes, the recording characteristics did not change. Further, the read CN ratio at 3.08 MHz was 49 dB for the conventional medium, and 48 dB for the medium of the present invention, and the read characteristics were also unchanged.

In addition, in a durability test using a 1N NaCl aqueous solution, in the conventional example, considerable pinholes were visually observed after immersion for 15 minutes, but in the case of the present invention, pinholes were visually observed. was not seen.

Example 3 The recording layer in the conventional example was DV, 21 (Fe,
szc.

1J79, film thickness 600A, and the recording layer in the present invention was (Dy, H(Fe, 7SCO, xs), t
o), esCr, at, film thickness 600A, readout layer is Oy, Is (Fe, toco, so), a
The experiment was conducted under the same conditions as in Example 2 except that the film thickness was 200A. The Curie temperature of the recording layer was about 170° C. in both the conventional example and the present invention.

At a rotation speed of 150 rpm and a radius of 35 mm, a laser power of 4.8 mW is required to record on the conventional medium under a bias magnetic field of 2000 e, whereas the medium of the present invention can record with a laser power of 4.9 mW. The characteristics did not change. In addition, 3.08MHz readout C
The N ratio was also 48 dB for the conventional medium, and 48 dB for the medium of the present invention, and the read characteristics were also unchanged.

In addition, in a durability test using a 1N NaCl aqueous solution, in the conventional example, considerable pinholes were visually observed after immersion for 15 minutes, but in the case of the present invention, pinholes were visually observed. was not seen.

Example 4 As the recording layer in the conventional example (Tb, B.Cy, a
. ), 22 (J'a, ayco, Is), 78
% film thickness of 600A, and the recording layer in the present invention ((
Tb, 5oDyio), 22 (Fe, moco
, to>, ya), esCr, a7, film thickness 60
0A, the readout layer is (Tb, s.

DV, 40), +a (Fa, toco, so
The experiment was conducted under the same conditions as in Example 2, except that the film thickness was 200A. The Curie temperature of the recording layer was about 170° C. in both the conventional example and the present invention.

At a rotational speed of 1500 rpm, 4 radius of 35 m+n, and a bias magnetic field of 2000 e, a laser power of 4.8 mW is required for recording on the conventional medium, and the recording medium of the present invention can be recorded with a laser power of 4.9 mW. The characteristics did not change. Further, the read CN ratio at 3.08 MHz was 47 dB for the conventional medium and 48 dB for the medium of the present invention, and the read characteristics were also unchanged.

In addition, in a durability test using a 1N NaCl aqueous solution, in the conventional example, considerable pinholes were visually observed after immersion for 15 minutes, but in the case of the present invention, pinholes were visually observed. was not seen.

Example 5 Using a conventional magnetron sputtering method, disk-shaped magneto-optical recording media of the conventional example and the present invention (1 mm diameter) were prepared, and experiments were conducted on recording sensitivity, read characteristics, and durability. Ar gas pressure was The pressure was approximately 0.+5 Pa. A protective film and SiN were provided on both sides of the 70OA recording medium.

The readout layer in the conventional example is Gd, zz (Fe,
? 0CO1o1.711. Film thickness 300A, recording layer Tb,
zx (Fe, 92Co, .11) 111, film thickness 5
00A, and the readout layer in the present invention is (Gd, oT
b, no), go [Fe, to Co, so
), no.

The film thickness is 300A, and the recording layer is (Th, 22 (Fe, 6
sCo, 1ll), ya)esCr,. 7. Film thickness 5
It was set to 00A. Polycarbonate was used for the substrate. The Curie temperature of the recording layer is approximately 1 in both the conventional example and the present invention.
The temperature was 70°C.

At a rotation speed of 1500 rpm, a radius of 35 mm, and a bias magnetic field of 2000 e, a laser power of 4.7 mW is required to record on the conventional medium, whereas the medium of the present invention can record with a laser power of 4.9 mW. The characteristics did not change. In addition, 3.08MHz readout C
The N ratio was also 49 dB for the conventional medium and 50 dB for the medium of the present invention, and the read characteristics were also unchanged.

In addition, in a durability test using a 1N NaCl aqueous solution, in the conventional example, considerable pinholes were visually observed after immersion for 15 minutes, but in the case of the present invention, pinholes were visually observed. was not seen.

Furthermore, the maximum playback power without deteriorating recorded information is 60
In a magnetic field of 0 os, approximately 1.4
mW, which was low, but that of the present invention was high, about 1.9 mW.

Example 6 As a recording layer in a conventional example, ay, z+ (Fe,
azc.

1&)-19, with a film thickness of 500A, and in the present invention, as a recording layer (Dy, 11 (Fe, tsco, ss
), 79), e*cr, 07, film thickness 500A, readout layer (Cd, S.Dy, a.), 3
゜(Fe, yaCo, so), so % ffl thickness 30
The experiment was conducted under the same conditions as in Example 5 except that the current was 0A.

The Curie temperature of the recording layer was about 170° C. in both the conventional example and the present invention.

At a rotation speed of 1500 rpm and a radius of 35 mII+,
Under a bias magnetic field of 2000e, a laser power of 4.6 d was required for recording on the conventional medium, and the medium of the present invention could record with a laser power of 4.6 mW, with no change in recording characteristics. Further, the read CN ratio of 3.08 M) Iz was 48 d[3 in the conventional medium, and 49 dB in the medium of the present invention, and the read characteristics were also unchanged.

In addition, in a durability test using a specified NaCl aqueous solution, in the conventional example, considerable pinholes were visually observed after 15 minutes of immersion, but in the case of the present invention, pinholes were visually observed. was not seen.

Furthermore, the maximum playback power without deteriorating recorded information is 60
In a magnetic field of 0 0 s, the conventional media has a magnetic field of about 1.3
mW, which was low, but that of the present invention was high, about 1.9 mW.

Example 7 As the recording layer in the conventional example (Tb, .Dy, s.

), 22(Fe, atco, +s), ta, film thickness 500A, and the recording layer in the present invention was ((Tb
, aoDV, sol, +*(Fe, 5oco,
2o), a+), esCr, ot, film thickness 500
A, and as a readout layer (Gd, 54Tb, 5s
Dy, ss), zx (Fe, tocO, so),
The experiment was conducted under the same conditions as in Example 5 except that ta and film thickness were 300A. The Curie temperature of the recording layer was about 170° C. in both the conventional example and the present invention.

At a rotation speed of 1500 rpm, a radius of 351 fiI11, and a bias magnetic field of 2000 s, a laser power of 4.9 mW is required to record on the conventional medium, whereas the medium of the present invention can record with a laser power of 5.1 mW. The characteristics did not change. Further, the read CN ratio at 3.08 MHz was 49 dB for the conventional medium, and 59 dB for the medium of the present invention, and the read characteristics were also unchanged.

In addition, in a durability test using a 1N NaCl aqueous solution, in the conventional example, many pinholes were visually observed after 15 minutes of immersion, but in the case of the present invention, no pinholes were observed visually. was not seen.

Furthermore, the maximum playback power without deteriorating recorded information is 60
In a magnetic field of 00s, the conventional media has a magnetic field of about 1.4+
++W, which was low, but that of the present invention was high, about 2.0 mW.

〔Effect of the invention〕

As described above, the present invention provides a magneto-optical memory medium with improved recording characteristics, corrosion resistance, and exchange coupling.

Claims (1)

[Claims] 1. Exchange coupling having a first magnetic layer having a high coercive force and a low Curie temperature at room temperature and a second magnetic layer having a lower coercive force and a higher Curie temperature than the first magnetic layer. In the magneto-optical memory medium, both the first magnetic layer and the second magnetic layer are amorphous alloy thin films made of rare earth-transition metal, the first magnetic layer contains Cr, and the first magnetic layer contains Cr. A magneto-optical memory medium, characterized in that the bimagnetic layer contains Co.