JPH0249240A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To improve sensitivity without deteriorating reproduction CN ratio by specifying the compsn. of a thin magnetic film having the axis of easy magnetization in the direction perpendicular to the film plane. CONSTITUTION:The compsn. of the thin magnetic film having the axis of easy magnetization in the direction perpendicular to the film plane is composed to have the general formula >>Rx(Fe1-uCou)1-x]1-yCuy, where R is >=1 kinds of heavy rare earth elements the atomic weight of which is Gd or above; x is 0.23<=x<=0.36, Y is 0.1<=y<=0.3; U is zero<=u<=100, and 0.06<=u(1-x)(1-y)<=0.12. The (x) of the thin magnetic film material is specified to 0.23<=x<=0.36, by which the reproduction CN ratio is sufficiently increased. The recording sensitivity is improved without deteriorating the reproducing CN by confining y to 0.1<=y<=0.3. The CN is deteriorated if u(1-x)(1-y) is below 0.06 and the recording density is deteriorated if this value exceeds 0.12.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention records information photothermomagnetically using laser light,
The present invention relates to a magneto-optical recording medium in which recorded magnetic information is read using the magneto-optic effect.

[Conventional technology]

In recent years, the practical application of rewritable magneto-optical memory has been viewed as promising. The magneto-optical recording medium used in this magneto-optical memory is made of glass with a perpendicularly magnetized thin film having an axis of easy magnetization perpendicular to the disk surface.

It is formed on a substrate such as a resin. Information is recorded by thermomagnetic writing using Raded light on the magnetic thin film, and the recorded information is reproduced by changing the direction of magnetization using the magneto-optical toleration (err) effect. This is done by detecting. As a magnetic thin film material for such recording media, Tb -Fe -Co-
A Cu-based material is known from JP-A-60-231306.

[Problem to be solved by the invention]

However, the Kerr rotation angle θ of the magnetic thin film currently used as a perpendicularly magnetized thin film is 0.3 to 0.4°, and the degree of modulation of the reproducing light by the recording bit is as small as about 1%, making it difficult to read during reproduction. The problem is that the CN ratio is not sufficient.

Therefore, there is a method to improve the CN ratio by placing a dielectric film such as 513N4.3iQ between the magnetic thin film and the substrate and taking advantage of the apparent increase in the Kerr rotation angle when the reflectance of the recording medium is lowered. Proposed 1° On the other hand, information is recorded on a magneto-optical recording medium using a semiconductor laser, but when the disk rotation speed is increased to increase the information transfer speed, the information is recorded at a single point on the recording medium. The irradiation time of the laser beam is shortened, and semiconductor lasers have disadvantages in that the temperature of the recording medium does not rise to the recording operating point, that is, the Curie temperature, and the data transfer rate is slow.

In view of the above-mentioned problems, it is an object of the present invention to provide a magneto-optical recording medium that has improved recording sensitivity and can be sufficiently recorded with a semiconductor laser even at high speed rotation without deteriorating the reproduction CN ratio during information recording and reproduction. It's about doing.

[Failure to solve the problem]

In order to solve the second problem, the composition of the magnetic thin film with the axis of easy magnetization perpendicular to the film surface is (Rx (FeucOu)
l-X) +-yCu, R is Gd
one or more heavy rare earth elements having an atomic weight of
is 0.23≦x≦0.36, y is 0.1≦y≦0.3,
U is 0≦u≦100, and u(1,-x)(1-y)
are in the range of 0.06≦u(1-x)(1-y)≦0.12, respectively.

Alternatively, RFe has an easy axis of magnetization perpendicular to the film surface.
It consists of a plurality of magnetic layers including a first magnetic thin film of Co and a second magnetic thin film of RFeCoCu, and R is one or more heavy rare earth elements having an atomic weight of Gd or more.

[Effect]

The composition is [:RX(Fe1-1.C0u)+-X:l 1
-x of a known magnetic thin film material with the general formula of yCuy is 0
．． By setting 23≦x≦0.36, the reproduction CN ratio becomes sufficiently large, and by setting y to 0.1≦y≦0.3, the recording sensitivity can be improved without deteriorating the reproduction CN ratio. . Also, the ratio of Fe and Co can be changed in any way, but if u(1-x)(1-y) is 0.06
When it is less than 0.12, the CN ratio deteriorates, and when it exceeds 0.12, the effect of adding Cu disappears and recording sensitivity deteriorates.

Furthermore, RFeC has a higher Curie temperature Tc and a relatively smaller coercive force Hc than the magnetic thin film material.

By adding a magnetic thin film, the recording magnetic domain recorded on the magnetic thin film with low laser power becomes RF due to exchange coupling force.
Since it is transferred to the eCo magnetic thin film, the reproduction CN ratio can be further improved without deteriorating the recording sensitivity.

〔Example〕

FIG. 2 is a cross-sectional view of the configuration of a magneto-optical recording medium produced according to the present invention. In one embodiment, a SiO dielectric layer 2 is laminated on a transparent substrate 1 made of polycarbonate (PC) with a diameter of 5.25 inches. On top of that is Tb-Fe-C.

A metal amorphous magnetic thin film 3 made of a Cu alloy is formed and further covered with a protective layer 4 made of a dielectric film. The material for the substrate 1 is not limited to PC, but also glass, resin, etc. can be used.

As a magneto-optical recording medium according to an embodiment of the present invention, first, an argon gas pressure of 06 Pa is applied onto a sufficiently degassed PC board 1.
After forming the dielectric layer 2 to a thickness of 90 nm by RF magnetron sputtering with a sputtering power of 300 W, sputtering was performed using a composite target in which copper pieces with dimensions of 1 mm x 1 mm x 40 mm were embedded in a Tb2sFegsC06 alloy target. 4. Argon gas pressure without breaking the vacuum of the device. OPa
, I:Tbo, s + 3(
Feo162COO, +3s) o, s,,]o-t
Tb-Fe- with a composition of 3scuo, 284
A magnetic thin film 3 made of a Co-Cu alloy was formed to a thickness of 70 nm. Further, a dielectric layer 2 is added thereon as a protective layer 4.
The same film was formed to a thickness of 1001 m using the RF magnetron sputtering method under the same conditions. Optimum recording laser power Pl'1 of the magneto-optical recording medium produced in this way
When I measured the CN ratio during opt and signal reproduction,
PWOPt is a sufficiently low value of 6.0mW, and the reproduction CN
The ratio was also 49.4 dB, which is much higher than the 45 dB required for digital recording. Similarly, Tb23Fess
By changing the number of Cu pieces embedded in the Cos alloy target, (Tbo, ag(Feo, e2scOo
, +72) 0. ass ] o, 5saCuo
In the magneto-optical recording medium provided with the magnetic thin film 3 having a composition of -362, the p w op t improved to 3.5 mW, but the reproduction CN ratio decreased by about 12 dB to 36.5 dB.

With this method, magnetic thin films with different Cu contents and C
Tb, , Fe, , [:0. A magneto-optical recording medium with a magnetic thin film having a composition of
Figure 1 shows the results of measuring L and regenerated CN ratio.
PL is shown by line 11, and CN ratio is shown by line 12. This figure shows that when the amount of Cu exceeds 10.0 atomic %, PWopt begins to decrease and sensitivity improves.
If it exceeds 0 atomic %, the reproduction CN ratio will deteriorate to 45d8 or less. In particular, when the Cu content is in the range of 18.0 to 28.0 at%, the reproduction CN ratio is 48 to 50 dB, and the Pwopt is 6.0.
Approximately uniform and good characteristics of ~7.0 mW were achieved.

Next, using the configuration shown in Figure 2 and changing the composition of the target under the same spuckling conditions as described above [Tb++, 2G
(Feo, 6cOo, + 4)O,so) o-t
A magnetic thin film having a composition of 264 was formed. PWOPL of magneto-optical recording medium having this magnetic thin film
is 5.5 mW, which is Q, 5 ml+ lower than that of the example shown in Fig. 1 with the same Cu content, but the regenerated CN
The ratio was 43.0 dB, which was degraded by 6.4 dB. Similarly, T
b The third result is the measurement results obtained by forming magnetic thin films with different compositions.
In the figure, P W and Op t are expressed by line 31, and CN ratio is expressed by line 3.
2. From this figure, [Tbx(FeCo)
l -
When it becomes 5 dB or more and X becomes 0.36 or more, the reproduction CN ratio deteriorates again to 45 dB or less. Especially 0.25≦x≦
When in the range of 0.32, reproduction CN ratio 48-50dB
, P wop t of 640 to 6.5 mW, and the best recording and reproducing characteristics were obtained.

Furthermore, (Tt++ (Fed-, Cou) l-X ]+
-yCu, x = 0.3 of the magnetic thin film alloy with the composition
1. Figure 4 shows the measurement results when U is changed when Y = 0.26, and Pw. 1, by line 41, CN
The ratio is shown by line 42 for u(1-x)(1-y). From this figure, u(1-x)(1-y) is 0.06
If it is less than 0.06, the CN ratio deteriorates due to a decrease in the Kerr rotation angle θ8, and at 0.06, the CN ratio is 45 dB. Also, u(1-
When x>(1-y) is 0.12, PWOPt is 9.0mW, and beyond that, the effect of adding Cu disappears and pWo
pt further increases, and recording sensitivity deteriorates. Therefore, u
It is necessary to keep (1-x)(1-y) within the range of 0.06 to 0.12.

Note that the above results are the same when other rare earth elements such as Gd and ay are used instead of Tb0, or in recording media in which a magnetic thin film is formed by replacing part of Tb with one of these rare earth elements. obtained.

Next, FIG. 5 is a cross-sectional view of the configuration of a magneto-optical recording medium according to another embodiment of the present invention, and in this embodiment, polycarbonate (
A transparent substrate 1 with a diameter of 5.25 inches made of PC) is coated with SlO
A dielectric layer 2 is laminated, and a first metal amorphous magnetic thin film 5 made of a Tb-Fe-Co alloy having a high temperature and a low coercive force is formed thereon. A second metal amorphous magnetic thin film 3 made of a Tb-Fe-Co-Cu alloy having high temperature and high coercive force is formed, and is further covered with a protective layer 4 made of a dielectric film. The material for the substrate 1 is not limited to PC, but resins such as acrylic and epoxy, glass, etc. can also be used.

As for the magneto-optical recording medium of the other three embodiments of the present invention, first, the argon gas pressure is set to 0.
RF condition of 6Pa, sputtering power 300W
Dielectric layer 2 is 9Q formed by magnetron sputtering method.
After forming the film to a thickness of 2.0 nm, using a TbFeCo alloy target, the argon gas pressure was increased to 2.0 nm without breaking the vacuum of the sputtering apparatus. OPa, sputtering power 3
T by DC magnetron sputtering method under 00W condition.
A first magnetic thin film 5 having a composition of tlo, 1sFeQ, 73co0.12 was formed to a thickness of 50 nm. Next, under the same conditions, using a composite target in which copper pieces were embedded in a TbFeC0 alloy target, Tbo, 20pe0
．． 4? A second magnetic thin film 3 having a composition of COO, osCuo, and zs was formed to a thickness of 50 nm. Furthermore, the same film as the dielectric layer 2 is applied as a protective layer 4 on top of the protective layer 4 under the same conditions.
A film with a thickness of 1100 nm was formed by F magnetron sputtering. Optimum recording laser power pwopt (medium rotation speed 18
0Orpm, recording signal frequency 1.88 & lHz, d
Uty 50%.

Hex = 4000e, r = 30 > and when the CN ratio during signal reproduction was measured, PWOP was affected.4.
The value was 5 mW, which was sufficiently low, and the reproduction CN ratio was 56.3 dB, which was much higher than the 45 dB required for digital recording. By changing the composition of the TbFeCo alloy target in the same way, Tbo, +5Feo, oCOo
-12,Tt)o, +4Feo, 64CO1),
12+Tbo, 5oFeo, 5scOo, +2
A medium having a first magnetic thin film 5 having a composition of 1 was prepared. Each optimum recording laser power Pw. , t and CN ratio were measured, pwOPL was 4.5 mW
, 4. Button W, 4.5mL CN ratio is 57.1dB,
56.8dB and 55.4dB were obtained.

Next, the following three media were prepared for comparison.

(Comparative Example 1) First magnetic thin film 5 in the above example. Instead of the second magnetic thin film 30, a magnetic thin film having a composition of TbzoFet2C08 was used alone, and the film thickness was 70 nm, and a medium having the same structure as above was fabricated.

Reproduction CN ratio, optimum recording laser power P w a p t
When measured, the CN ratio was 54.8dB, Pw
Opt was obtained at 6°OmW.

(Comparative Example 2) First magnetic thin film 5 in the above example. Instead of the second magnetic thin film 3, a magnetic thin film having a composition of Tb2aFes*CO@Cu+o was used alone, and the film thickness was 70 nm, and a medium with the other configurations the same was fabricated.

A CN ratio of 51.9 dB and a PWopt of 5.5 m- were obtained.

(Comparative Example 3) First magnetic thin film 5 in the above example. Instead of the second magnetic thin film 30, a magnetic thin film having a composition of TtlzoFea7CJICu2s was used alone, and the film thickness was 70 nm, and the other configurations were the same.

The CN ratio is 51. gdB, Pwopt is 4.5+nW
was gotten.

In Comparative Example 1, a high CN ratio of 54.8 dB is obtained, but the optimum recording laser power is as large as 6.0+nW. Here, by incorporating Cu into TbFeCo as in Comparative Example 2゜3, the optimum recording laser power was increased to 4.5 mW.
It can be seen that it can be reduced to However, since the CN ratio is about 52 dB, which is 2 to 3 dB lower than that of TbFeCo, it is desirable to further improve the CN ratio while keeping the optimum recording laser power low.

In FIG. 6, the conditions of the second magnetic thin film 30 having a composition of Tt12oFe<tcOscUzs are fixed, and the Co content of the first magnetic thin film 5 having a TbFeCo composition is constant at 12 atomic %1,
This figure shows the relationship between the reproduction CN ratio and the optimum recording laser power when the Tb content I is changed, and Pwopt is expressed as line 6.
1, the CN ratio is indicated by a line 62. From this, it can be seen that the optimum recording laser power is 4.5 mW, which is the same as the recording characteristics of the second magnetic thin film 3, regardless of the Tb content, and C
Regarding the N ratio, a CN ratio of about 55 dB or more was obtained when the Tb content was in the range of 15 at % to 30 at %. It can be seen that by forming the second magnetic thin film 5.3 into a laminated structure, a magneto-optical recording medium with a low optimum recording laser power and a high C/N ratio can be obtained.

This is because the recorded magnetic domain recorded with low laser power on the second magnetic thin film 3 made of TbFeCoCu with a low Tc is transferred to the first magnetic thin film made of TbFeCo by exchange coupling force, and the Tc of the first magnetic thin film 5 is This is because the reproduction CN ratio is improved because both the recording sensitivity and the reproduction CN ratio are high, and therefore the recording sensitivity and the reproduction CN ratio of the medium with this configuration are improved.

Further, FIG. 7 shows that the Tb content of the first magnetic thin film 5 is 19
Regenerated CN when the atomic % is constant and the CO content is changed
The line 72 shows the CN ratio. It can be seen from this that the regenerated CN ratio begins to become saturated when the Co content exceeds 12 at % and reaches saturation at about 20 at %.

The above results show that when other heavy rare earth elements such as Gd and Dy are used instead of Tb0, or in recording media in which a part of Tb is replaced with these heavy rare earth elements to form a magnetic thin film. was similarly obtained.

〔Effect of the invention〕

According to the present invention, when R-Fe-Co-Cu (where R is one or more heavy rare earth elements) is used as the material of the perpendicular magnetization film of the recording thin film layer of a magneto-optical recording medium, the composition is changed to C.
Rx(Fe+-uCo) l-X] +-yCuy
With the general formula, 0.23≦x≦OJ6, 0.1≦
y≦0.3. O≦u≦100.0.06≦u(1-
x)(1-y)≦0.12, the reproduction CN ratio during signal reproduction is 45, which is necessary for digital recording.
It was possible to obtain a magneto-optical recording medium with sufficiently high recording sensitivity of dB or more and excellent recording sensitivity.

Furthermore, by adding an RFeCo magnetic thin film having a higher Curie temperature and a smaller coercive force than the magnetic thin film material, it was possible to further improve the reproduction CN ratio without deteriorating the recording sensitivity.

[Brief explanation of the drawing]

Figure 1 shows the recording and reproducing characteristics of a magneto-optical recording medium with a magnetic thin film of Tb-Fe-Co-Cu alloy and Cu.
Fig. 2 is a cross-sectional view of the configuration of a magneto-optical recording medium in which the present invention is implemented, Fig. 3 is a diagram showing the relationship between Tb-Fe-Co and Tb-Fe-Co.
- Figure 4 is a diagram showing the relationship between the recording and reproducing characteristics of a recording medium having a magnetic thin film of Cu alloy and the Tb content.
x (Pe+-ucot+) l-X ]+-ycuy
FIG. 5 is a diagram showing the relationship between the recording and reproducing characteristics of a recording medium having a magnetic thin film of an alloy coated with a magnetic thin film and the value of u(1-x)(15'). A cross-sectional view of the configuration of the magnetic recording medium, FIG. 6 is a diagram showing the relationship between recording and reproducing characteristics and Tb content in a magneto-optical recording medium having a first magnetic thin film of Tb-Fe-Co alloy, and FIG. 7 is the same diagram. FIG. 3 is a relationship diagram between regeneration characteristics and CO content. 1 Transparent substrate, 2 Dielectric layer, 3, 5 Magnetic thin Tb content X110.736 (atomic %) Figure 3 0υ content (atomic %)

Claims (1)

[Claims] 1) The composition of the magnetic thin film having an axis of easy magnetization perpendicular to the film surface is [Rx(Fe_1_−_uCo_u)_1_−_x
]_1_-_xCu_y, R is one or more heavy rare earth elements with an atomic weight of Gd or more, and x is 0
．． 23≦x≦0.36, y is 0.1≦y≦0.3, u is 0≦u≦100, and u(1-x)(1-y) is 0.0
A magneto-optical recording medium characterized in that the values are in the range of 6≦u(1-x)(1-y)≦0.12. 2) Consisting of a plurality of magnetic layers including a first magnetic thin film of RFeCo and a second magnetic thin film of RFeCoCu having an axis of easy magnetization perpendicular to the film surface, R is a heavy rare earth element having an atomic weight of Gd or more. A magneto-optical recording medium characterized by being one or more of the following.