JPS63122034A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To prevent oxidation of a recording film so as to improve the corrosion resistance of a disk and to extend the life thereof by adding 3-8atom% Ta to a magneto-optical disk recording medium essentially consisting of a rare earth-iron family element. CONSTITUTION:An SiO2 film having 1,000Angstrom film thickness is formed by sputtering or the like on a substrate 1 made of cleaned glass or heat resistant resin. The film is formed under the conditions of using a sintered SiO body as a target material and Ar as a discharge gas and 5mmTorr discharge gaseous pressure 1W/cm<2> RF power to be thrown and 10min sputtering time. The magneto-optical recording film 3 having the compsn. Tb26Fe62Co12 is then formed to 1,000Angstrom thickness by a sputtering method. A mosaic-shaped composite target formed by using an FeCo alloy for a target substrate and arraying uniformly chips of Tb and Ta thereon is used. Ta is added at 3-5atm% to the film by controlling the content of Ta by the number of the chips to be arrayed, by which the corrosion resistance is improved and the life of the disk is greatly extended without degrading the magnetic and magneto-optical characteristics thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to magneto-optical recording in which recording, reproduction and erasing are performed using a laser, and particularly to a recording medium suitable for extending the life of a disk.

[Conventional technology]

In recent years, magneto-optical recording that allows arbitrary reading and rewriting of high-density and large-capacity information has attracted attention. Currently, rare earth-iron group amorphous alloys are the focus of research as magneto-optical recording media, and among them, TbFeCo amorphous alloy is at the closest stage to practical application. However, these materials are active against oxygen and water in the atmosphere and produce hydroxides or oxides. This reaction progresses from the surface of the medium to the inside of the membrane over time. As a result, the magnetic and magneto-optical properties (eg, Kerr rotation angle, coercive force, saturation magnetization, etc.) of the recording medium have deteriorated. Therefore, in conventional magneto-optical disks, the methods of adding elements with an anti-corrosion effect to the magneto-optical recording material to provide high corrosion resistance, or forming a protective film on the surface of the magneto-optical recording film to shield the recording film from the atmosphere. Two methods have been considered to do this. Of these, if only the former method is used, the formation of a protective film can be omitted and the process can be simplified (a problem that the invention aims to solve). The example problem was as follows: That is, when additive elements are added to rare earth-iron group alloys to improve corrosion resistance, the corrosion resistance improves as the amount added increases, but the magneto-optical properties deteriorate.
It was necessary to find an additive element and an amount thereof that can improve the corrosion resistance of the magneto-optical recording film without deteriorating the magneto-optical properties.

An object of the present invention is to provide a magneto-optical disk having a long life and high reliability by improving corrosion resistance without deteriorating the magneto-optical properties of the magneto-optical recording film.

[Means for solving problems]

The above object is achieved by adding Ta to a magneto-optical recording material mainly composed of rare earth-iron group elements. , T
The reason why a is more advantageous than other elements is that the magneto-optical properties (Kerr rotation angle, coercive force, and quenching temperature) do not decrease significantly in the S range with 2 to 8 atm% Ta added, which provides sufficient corrosion resistance. .

[Effect]

Since Ta usually has an oxide passive film on its surface, the progress of corrosion is suppressed. When this element is added to a magneto-optical recording film mainly composed of rare earth-iron group elements that are active in the environment, Ta is relatively concentrated on the film surface and a passive film is formed.

Inert to moisture and oxygen in the air. This coating protects the magneto-optical recording film from the outside air.

〔Example〕

The present invention will be explained in detail using Examples 1 to 6 below.

[Example 13 A schematic diagram of the cross-sectional structure of the produced magneto-optical disk is shown in FIG. An SiO film 2 with a thickness of 1000 was formed on a substrate 1 made of cleaned glass or heat-resistant resin by sputtering or the like. The conditions at that time were as follows: a SiO sintered body was used as the target material, Ar was used as the discharge gas, the discharge gas pressure was 5 mTorr, the input RF power was IW/d, and the sputtering time was 10 minutes. Following this, Tbxe FeexCox with a film thickness of 1000 people
A magneto-optical recording film 3 having a composition x was formed by sputtering.

Now apply F a Co 179 to the target substrate. A mosaic-like composite target made of gold and having Tb and Ta chips evenly arranged thereon was used. The sputtering conditions were as follows: Ar was used as the discharge gas, and the discharge gas pressure was 5×10''2 (Torr).
), input RF power IW/cd, and sputtering time are 3 minutes. Also, before sputtering, 3x10''7 (To
rr) or below. Further, the amount of Ta added to improve corrosion resistance was controlled by the number of chips arranged.

The amount of Ta added and the magnetic and magneto-optical properties of the magneto-optical disk prepared in this way (Kerr rotation angle = θK.

Figure 3 shows the relationship between coercivity Hc and cue temperature Tc. First, Tbx8Fef1mCox, which does not contain Ta,
Theta of s was Q, 54', Ha was 8, Okoe, and Tc was 200°C. When Ta is added to this material, it gradually decreases to 0 as shown in curve 4.
Addition of 7 atm % or more causes a sharp decrease in θ.

As shown in curve 5, HC decreases in inverse proportion to the increase in the amount of Ta added. Further, as shown in curve 6, Ta gradually decreases as the amount of Ta added increases.In this way, as the amount of Ta increases, Ha and Ta decrease to θ. Here, we set these characteristics at a practical level (Hc
)2koa, Tc ”200℃, θ≧−0,3
@) In order to achieve the above, the amount of co is increased to θ, Tc is increased, and the ratio of rare earth elements to iron group elements is changed to increase HC. As a result, the decrease in properties due to the addition of Ta can be compensated for, so the decrease in properties is not a problem when designing practical materials.

Corrosion resistance tests were conducted on the magneto-optical disks prepared in this manner using the following three methods. That is, there are three tests: high temperature high humidity test, pitting corrosion test, and high temperature oxidation test. The high temperature and high humidity test was conducted to determine the saturation magnetization (
Ms) was measured over time. In addition, high temperature oxidation test
The produced disk was stored in dry air at a temperature of 200° C., and the change in saturation magnetization (Ms) over time was measured.

In the pitting corrosion test, the change in light transmittance of the film over time was measured when the sample was immersed in a 1N sodium chloride aqueous solution (IN-NaCQ) for a certain period of time at a liquid temperature of 25°C. The test results are summarized in Figure 1. First, curve 7 is the high temperature and high humidity test result.
It shows the Ta concentration dependence of the change in Ms after storage in %RH for 500 hours. As you can see from this graph, Ta
The rate of change in saturation magnetization in the T b Fe Co film not added was an initial increase of 43%. When Ta is added to this, the rate of change in saturation magnetization decreases dramatically as the amount added increases. When Ta was further added to 2.5 atm% or more, the increase was approximately 5%. Curve 8 shows the change in light transmittance of the film in the pitting corrosion test. It can be seen from this figure that there is a peak in the amount of change in the light transmittance of the film around about 2 atm%. When Ta is further added to this, the amount of change in light transmittance decreases rapidly. For this reason, adding 3% or more of Ta to T b Fe Co is effective in suppressing pitting corrosion. Curve 9 shows the results of the high temperature oxidation test. 200℃
When the sample was stored for 100 hours, the rate of change in saturation magnetization of the Ta-free TbFeCc film was as large as 200%. As Ta is added to this system, the rate of change in Ms gradually decreases until the amount added is 2 atm%.

Then, it suddenly decreased between 2 atm% and 3 atm%, and after that, the rate of change in Ms remained almost constant at about 10%.

Combining the above results, adding 3 to 8 atm % of Ta can improve corrosion resistance without deteriorating magnetic and magneto-optical properties, and greatly extend the life of the disk.

The C/N (carrier-to-noise ratio) of these magneto-optical disks (disks containing 4 atm% or more of Ta) is 55 dB.
Even if it is stored for 500 hours at 80°C and 95% RH, it shows almost no change over time. This shows that the addition of Ta is extremely useful for improving corrosion resistance.

[Example 2] The cross-sectional structure of the produced magneto-optical disk was the same as that of Example 1, as shown in FIG. The magneto-optical dig was created using an in-line magnetron sputtering device. An Al2N film 2 with a thickness of 1000 was created by sputtering on a cleaned glass or heat-resistant resin substrate 1.The conditions for creation were as follows: A sintered body of 1,000 N was targeted, and the discharge gas was
Using 0%N260%Ar standard mixed gas, discharge gas pressure 5
■ Torr, input RF power I W/cal, sputtering time was 10 minutes. Next, (Gdo, 5Tbo, t)o, zz(Feo, 7Coo
, s)o, 7a-xTax was formed to a thickness of 1000 mm. A 51111 square G was placed on a Fe-C0 alloy disk at 152°C as a target.
A mosaic-shaped target in which dTb alloy chips and Ta chips were uniformly arranged was used. Other conditions for forming the magneto-optical recording film were the same as in Example 1.

Figure 4 shows the relationship between the amount of Ta added and the magnetic and magneto-optical properties (θ, HO and Tc) of the magneto-optical disk prepared in this way.
, a) o, zz (Feo, gCoo, z) o, 7g θ
is 0.75”, Ha is 7, 8 Woe and 're is 1
The temperature was 90°C. When Ta is added to this, θ gradually decreases as shown in curve 10, and when 8 atm % or more is added, θ rapidly decreases. As shown in curve 11, the value of Ha decreased as the amount of Ta added increased, and reached 2.5 KOa when IQ atm% was added.

Furthermore, as shown by curve 12, as the amount of Ta added increases, Tc gradually decreases to 10 atm%.
The temperature decreased to 100°C with the addition of . However, these fluctuations in magneto-optical properties are caused by G d −T b −F e −G o
-Characteristics required when using the Ta system as a practical material (Ha-≧-2KOθ, Tc=200℃, θ2≧-0
, 3') or more, increase the amount of Go to θ,
Ha is increased by increasing Tc and changing the ratio of rare earth elements to iron group elements. This makes it possible to increase the respective characteristic values that have decreased due to the addition of Ta, so that the decrease in characteristics does not become a problem when designing practical materials.

The corrosion resistance test of the magneto-optical disk thus prepared was conducted in the same manner as in Example 1, and the results are shown in FIG. First, the Ta concentration dependence of the rate of change in saturation magnetization when stored at 80° C. and 95% RH for 500 hours increases by 47% in the case without Ta, as shown in curve 13. When Ta is added to this, the rate of change in saturation magnetization decreases rapidly as the amount of addition increases. Also, 2,
When 5 at+m% or more of Ta is added, the rate of change in saturation magnetization gradually decreases. It can be seen that when 10 atm % of Ta is added, the rate of change is 2%, which is significantly smaller than when no Ta is added. In addition, as shown in curve 14, the pitting corrosion test results show that as the amount of Ta added increases, the change in light transmittance of the film also increases, reaching a peak at 2 atm%. As the amount of addition increases, the amount of change in light transmittance decreases rapidly, and becomes almost constant when the amount of addition is 5 atm % or more. The amount of change in the light transmittance of the film when 10 atm % of Ta is added is 0.1%, which is significantly smaller than that when Ta is not included, and the amount of change in transmittance can be reduced.

The occurrence of pitting corrosion can be greatly suppressed. Furthermore, a high temperature oxidation test was conducted and the results are shown in curve 15.

When a sample is stored in the atmosphere at 200°C for 100 hours, Ta
The rate of change of the saturation magnetization of the G d T b Fe Co thin film that does not contain Mg is as large as 200%, and this is in addition to the
As the amount of addition increases to 2,5 atm%, the rate of change in Ms gradually decreases;
It decreases sharply between m% and 3 atm%, and thereafter Ms
The rate of change was approximately constant at approximately 10%.

To summarize the above results, when Ta is added in an amount of 3 to 8 atm %, the corrosion resistance can be improved without significantly deteriorating the magnetic and magneto-optical properties, and the life of the disk can be greatly extended.

The C/N (carrier-to-noise ratio) of these magneto-optical disks (disks containing 4 atm% or more of Ta) is 57 d.
Even when stored for 500 hours in BTe80''C-95%RH, there was almost no change over time.This shows that Ta is useful for extending the life of the disk.

[Example 3] The cross-sectional structure of the produced magneto-optical disk was the same as that of Example 1, as shown in FIG. The magneto-optical disk was produced using an in-line magnetron sputtering device. On a cleaned glass or heat-resistant resin substrate 1, a 5isN4 thin film 2 with a film thickness of 1000 was created by sputtering 6. The creation conditions were as follows: a 5iaNa sintered body was targeted, and the discharge gas was 40%Nx-60%Ar. [Using semi-mixed gas.

Discharge gas pressure 5 mTorr, input RF power I W/a1,
Sputtering time is 10 minutes. Continuing, (Gdo,
aDyo, z) o, xz (Feo,
A magneto-optical recording film 3 having a composition of 7COO, 11) 0, 7a-xTax was formed to a thickness of 1000 mm.

As a target, a mosaic-shaped target was used, in which GdDy alloy chips and Ta chips of 5nw++ square and lllll thickness were uniformly arranged on a 152 mφ F6-Go alloy disk. Other conditions for forming the recording film are the same as in Example 1.

FIG. 6 shows the relationship between the amount of Ta added and the magnetic/magneto-optical properties (θKF Ha and Tc) of the magneto-optical disk produced in this manner. First, it does not contain Ta (Gdo, ac
yo, z) o, 22 (F2O, 7COO,
s) was 0.78″', Hc was 7.8 KOe, and Tc was 185°C. When Ta was added to this system, θ
gradually decreases as shown in curve 16, and 8
Addition of more than atm % causes a sharp decrease in θ. Hc is
As shown in curve 17, the value decreases as the amount of Ta added increases, and with addition of 10 atm%, 2.5K
It became Oe.

In addition, as shown in curve 18, Tc gradually decreases as the Ta addition amount increases, and increases to 10 atm%.
The temperature decreased to 100°C with the addition of . but.

These fluctuations in magneto-optical properties are G d −D y −F
Characteristics required when using the a-G o -Ta system as a practical material (Ha>2.0KOa, Tc=200'
It is clear from Example 1 that in order to satisfy C, σK>0.3°), it is possible to increase CoM to θ and return Tc to the required value, and there is no problem in practice. .

A corrosion resistance test of the magneto-optical disk thus prepared was conducted in the same manner as in Example 1. The results are shown in FIG. First, as shown in curve 19, the Ta concentration dependence of the rate of change in saturation magnetization when stored at 80° C. and 95% RH for 500 hours shows a 48% increase in the case without Ta. When Ta is added to this, the rate of change in saturation magnetization decreases rapidly as the amount added increases.
It becomes almost constant above atm%. And 10atI
It can be seen that the addition of 11% resulted in an increase of 2%, which is a significantly smaller change than in the case of no addition. Further, as shown in curve 20, the results of the pitting corrosion test showed that the rate of change in light transmittance of the film without Ta was 1.5%.

As Ta is added to this, the light transmittance increases and reaches a maximum when 2 at+i% is added. As Ta was gradually added, the amount of change in light transmittance decreased rapidly, and became almost constant when Ta was added at a concentration of 4 atm% or more. The amount of change in light transmittance of the film when 10 atm % of Ta is added is 0.15%, which is significantly smaller than that in the case where Ta is not included, and the occurrence of pitting corrosion can be greatly suppressed. Furthermore, a high-temperature oxidation test was conducted, and curve 21 shows the results. When a sample is stored in the atmosphere at 200°C for 100 hours, the rate of change in saturation magnetization 2Ms of a GdDyFeCo-based film that does not contain Ta is as large as 295%, and when Ta is added to this, the change gradually decreases to 3 atm%. The rate decreases, and the rate of change suddenly decreases around 3 to 4 atm%, and becomes almost constant at about 10% above 7 atm%.

Summarizing the above results, when Ta was added in an amount of 3 to 8 ata+%, the corrosion resistance could be improved without significantly deteriorating the magnetic and magneto-optical properties, and the disk life could be greatly extended.

The C/N (carrier-to-noise ratio) of these magneto-optical disks (disks containing 4 atm% or more of Ta) is 80°C.
Even when stored for 500 hours in −95% RH, it showed almost no change over time at 53 dB. This shows that the addition of Ta is extremely useful for improving low eating properties.

[Example 4] The cross-sectional structure of the produced magneto-optical disk was the same as that of Example 1, and a schematic diagram thereof is shown in FIG. Approximately 1,000 ml of
A human SiO film 2 was created.

The conditions at that time are the same as in Example 1. Continuing,
Tbz+5Co7oTaa*Gdz as magneto-optical recording film
gTb7Co7oTas was formed by sputtering under the same conditions as in Example 1. Further, Ndzs FseoCozo Ta7 was created by electron beam evaporation (EB method). The conditions at that time were 4X1
After evacuation to 0 Torr, pre-evaporation was performed for about 10 minutes with the shutter closed, and then the above 8 films were deposited on a disk substrate with an optical effect film. The corrosion rate of rare earth elements is faster than that of iron group elements for magnetic disks such as N d Fe Co.

Therefore, when evaluated by saturation magnetization, a large decrease in saturation magnetization was observed for both wet corrosion and axons. However, by adding Ta to these alloys, it was possible to significantly reduce the change over time in saturation magnetization due to wet corrosion and axons. Also.

Pitting corrosion is evaluated by the change in light transmittance before and after immersion in IN NaCQaq for a certain period of time (100 minutes).
In the case of a recording film not containing a, the increase was significantly large, reaching 5 to 6%. When this is observed with an optical microscope, it is found that it is 10 to 100 μm.
A large number of holes with different diameters in the range of m are observed, and rare earth-iron group elements alone cannot be used as a recording film for magneto-optical disks.

Therefore, if Ta is added to this recording film, the occurrence of pitting corrosion can be significantly suppressed. As a result of microscopic observation, the number of pores observed was small, and the diameter was several μm, which resulted in a significant reduction in both density and size. In addition, the C/N (carrier-to-noise ratio) of a disk using a recording film containing Ta was 48 dB immediately after creation, but at 80°C-95
Even after 500 hours of storage at %RH, there was no significant change of 47 dB, indicating that the present invention can significantly extend the disk life. When a recording film not containing Ta was used, the recording film became transparent and C/N measurement was not possible. Thus, it can be seen that Ta is equally useful for improving the corrosion resistance of disks in all rare earth-iron alloys.

[Example 5] A schematic diagram of the cross-sectional structure of the produced magneto-optical disk is shown in FIG. Cleaned glass or resin substrate 22
On top, TbzsFesx-x was deposited by two-dimensional simultaneous sputtering method.
A co1oTa* film 23 was created. At that time, the Ta concentration was made to increase from the substrate surface toward the recording film surface. Ta plate (152mφX 1m
A sintered target (152 mφX 1,
5 na t ) was used. Prior to sputtering, the inside of the chamber was evacuated to a high vacuum of 4×10'' (Torr) or more. The sputtering conditions were as follows: Ar was used as the discharge gas, and for the RF specific output Ta target after bliss sputtering, the initial output was 0.3 W/1 ffl, and after 2 minutes, I W/1 ffl was used.
cd and held for 4 minutes to complete sputtering.

On the other hand, the sintered target starts at IW/d and 2
After 4 minutes, the RF specific output gradually decreases, and after 4 minutes, it is O
The output was controlled to be W/cd. In this way, 1200 magnetic films with modulated compositions were formed.

The characteristics of this disk are: Kerr rotation angle: θ = 0.3
5", Ha = 6 KOa, and C/N = 50 dB. A life test of the primary disk was conducted in the same manner as in Example 1. As a result, pitting corrosion and wet corrosion were detected.

Changes in optical transmittance, saturation magnetization, and C/N, which occur in the case of axons and axons, did not occur at all, indicating that the addition of Ta is extremely effective in inhibiting corrosion.

[Example 6] The cross-sectional structure of the produced magneto-optical disk was the same as that of Example 5, as shown in FIG. A T baa Fe esx-x C010T a-x film 23 was formed on the cleaned glass or heat-resistant resin substrate 22 by magnetron sputtering. The target then has the following shape: In other words, on a Fe plate of 152 aaφ, an outer diameter of 152
■Place a ring-shaped Ta plate with φ, inner diameter 132 mmφ, and 1 m thickness, and place a disc-shaped Ta plate with 30 nn + φ and 101 mm in thickness near the center, and place Ta, Tb, and C in between.
It is a composite target in which O is placed uniformly. Prior to sputtering, the interior of the chamber was 4 x 10"-' (T
It was evacuated to a high vacuum above (orr). The sputtering conditions used Ar as a discharge gas.

Input RF output 1. W/d, discharge gas pressure 5 (nmTorr
) After bliss sputtering for 30 minutes, main sputtering was performed for 4 minutes. In this way, 1200 magneto-optical recording films were formed.

The characteristics of this disk are: Kerr rotation angle 20 = 0.3
5@, Ha = 6 KOa, and C/N = 50 dB. Next, we conducted a disk life test and found that the corrosion resistance of the track portion of the disk was the same as in Example 1, but corrosion from the inner and outer circumferential portions of the disk to the information recording portion sometimes became a problem. There was, but
It can be seen that by significantly increasing the Ta concentration in the outer and inner peripheral parts, corrosion can be prevented from these parts.

〔Effect of the invention〕

According to the present invention, Ta is added to the rare earth-iron alloy thin film.
By adding 3 to 8 at. moreover,
This effect can be increased by concentrating Ta on the surface of the recording film. Further, by creating a Ta concentration gradient in the direction perpendicular to the disk surface, the effect of improving corrosion resistance can be greatly increased, and this is a result of further promoting the formation of a passive state. On the other hand, by creating a Ta concentration gradient in the direction parallel to the disk surface, corrosion from the outer circumferential portion or the inner circumferential portion can be significantly suppressed. This is because Ta has the same effect in this case as before.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the corrosion resistance test results in Example 1, and FIG. 2 is a schematic diagram of the cross-sectional structure of the disks of Examples 1 to 4. Figures 3 to 7 are diagrams showing the corrosion resistance test results in Examples 2 to 6, and Figure 8 is a schematic diagram of the cross-sectional structure of the disk in Examples 5 and 6. Dependency, 5...T a 'aa degree dependence of coercive force 6...78 m degree dependence of Curie temperature, 7-80°C-95%RH-500hr
T a of subsequent change in Ms: a degree dependence, 8-IN
Ta concentration dependence of light transmittance after storage in NaCjl hq for 100 minutes, 9...100 hours in 200℃ air
Ta concentration dependence of change in Ms after storage, 10... Ta concentration dependence on θ, 11... Ta concentration dependence of HC,
12... Ta concentration dependence of Tc, 13-80°C-95
%RH - Ta concentration dependence of change in Ms after 500 hours, 14...Ta concentration dependence of light transmittance after storage for 100 minutes in IN-NaCQ, 15...in 200'C atmosphere Ta concentration dependence of Ms after storage for 100 hours. 16...Ta concentration dependence on O, 17...T of Hc
a concentration dependence, 18... Tc T a degree dependence,
19- Ta concentration dependence of change in Ms after 500 hr at 80°C and 95% RH, 20- I N N a CQ a
T a degree dependence of light transmittance after 100 minutes immersion in Q, Ta concentration dependence of change in Ms after storage in air at 21-200°C for 100 hours, 22...Substrate, 23...Light magnetic recording film. yIc1 Figure 2 Figure 13 Figure 1 Kume force Y: J ((Mu outside) 6,,,Q,? ”/-) lao'csuj(Lee(-, +0okp@7 blasphemy)”””
Ms QLApi551jLK'fFt"Figure 6

Claims (1)

[Scope of Claims] 1. A magneto-optical disk recording medium mainly composed of rare earth-iron group elements having an axis of easy magnetization perpendicular to the substrate, containing at least 3 atomic percent and 8 atomic percent Ta. A magneto-optical recording medium characterized by containing the following additives: 2. In Ta(7) addition in magneto-optical recording media,
2. The magneto-optical recording medium according to claim 1, wherein the Ta concentration has a composition gradient in the film thickness direction. 3. In adding Ta to magneto-optical recording media, Ta
2. The magneto-optical recording medium according to claim 1, wherein the concentration has a composition gradient in a direction horizontal to the substrate surface.