JPH0770095B2 - Magneto-optical recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical recording medium in which high-sensitivity recording / reproduction is easy and deterioration with time is small.

<Technical Background of the Invention> In information recording in which information is written or read by light, a recording medium used is usually one in which a magneto-optical recording material layer is provided as a recording layer on the upper surface of a support.

Information is written, read, and erased by the magneto-optical recording medium having such a configuration as follows. That is, as shown in FIGS. 4 (A), (B), and (C), a weak magnetic field H is applied to the recording layer 1 in a direction perpendicular to the film surface of the recording layer 1 so as to magnetize the recording layer 1 in a perpendicular direction, and a portion 2 to be recorded. When the laser beam 3 is irradiated on the surface and heated to near the Curie point (or the compensation point), the coercive force H _c decreases and the magnetic field H reverses the spontaneous magnetization M _s .

The magnetization region 2 thus reversed retains its magnetization reversal state even after the laser irradiation is stopped, so that it is possible to record information.

Then, the information recorded in this way, when the recording portion is directly irradiated with polarized light, depending on the magnetization direction of the recording portion,
The vibrating surface of the reflected light or the transmitted light rotates in different directions due to the magnetic Kerr effect or the Faraday effect. Therefore, by inserting an analyzer, a signal corresponding to the magnetization can be read.

Furthermore, when the recorded information is erased, by applying a magnetic field in a direction opposite to the magnetic field H at the time of writing the information and applying heat, the magnetization of the heated portion can be returned to the original direction. , The recording medium can be used repeatedly.

The table below shows the main material names of magneto-optical recording materials and their characteristics.
Listed in 1.

However, in Table-1, θ _k and θ _f are Kerr rotation angle and Faraday rotation angle, respectively; LPE is film formation by liquid layer epitaxial method; IC is iron garnet.

The crystal structures of the films formed by the above-mentioned magneto-optical recording materials can be classified into polycrystalline films, single crystal films, and amorphous (hereinafter referred to as "amorphous") films.

A) Polycrystalline film: Many crystalline film materials have been investigated and studied from the latter half of the 1960s to the first half of the 1970s, but they have not been put to practical use yet.

That is, MnBi has a phase transition point at 360 ° C and is chemically unstable. EuO has a Curie point below room temperature and cannot obtain perpendicular magnetization.

PtCo has a disadvantage that the Curie point is too high and the erasing magnetic field must be increased.

MuBiCu, which has been developed in recent years, is considered to be a promising material because it has no phase transition and an appropriate Curie point, but it has not yet been put to practical use.

B) Single crystal film: As a single crystal film material capable of magneto-optical recording, a magnetic garnet is mainly known, but it is chemically unstable. On the other hand, there is an advantage that the magneto-optical effect is large. However, the laser power required for recording is large, and the liquid phase epitaxial growth method (LPE
Method, it is not possible to make a large area.

Recently, garnet and ferrite films have been developed as polycrystalline films formed by vapor deposition or sputtering, or as solid-phase epitaxial films formed by heat treatment thereof, but they have not reached the stage of practical use.

C) Amorphous film: Gd, Tb, Dy are known as amorphous film materials.
It is an alloy of rare earth elements such as Fe and Co, and transition elements such as Fe and Co, and all exhibit ferrimagnetism. Among these alloy materials, there are a compensation point recording material and a Curie point recording material.

Compensation point recording materials include GdCo and GdFe, but they have problems such as coercive force being too small and lacking in stability, and it is difficult to obtain a large-area element with uniform characteristics.

Recently, studies have been conducted to increase the coercive force H _c by adding Tb to GdCo, and investigations into materials with large coercive force such as TbFeCo.

Of the amorphous film materials, the TbFe film was first examined as a Curie point recording material. This film has high recording sensitivity and large coercive force.

Of the various magneto-optical recording material films described above, an amorphous film is considered to be capable of writing, reproducing and erasing with a semiconductor laser, and is useful as a large capacity memory material. Although the polycrystalline film has not been put to practical use sufficiently, it is considered that a useful magneto-optical recording material film can be produced depending on the type of material and the processing method.

<Problems to be Solved by the Invention> However, in the above-described magneto-optical recording material film, the constituent elements of the amorphous film are a rare earth element and a transition metal element, and these elements are originally easily oxidized and prevent deterioration over time. It was difficult and the biggest problem in practical use.
In order to improve such deterioration over time, a method of adding a third element has been proposed. For example, it has been attempted to add precious metal elements such as Al, Cr, Ti or Pt.

However, when the additive amount of these additive elements is increased, the original reflectance, Kerr rotation angle, etc. are deteriorated. For example, the report by Mr. Tanaka et al., “Long-life of magneto-optical disk due to additional element”, which was published on page 209 of “9th Japan Society for Applied Magnetics Academic Lectures” at 9th Japan Applied Magnetics Society sponsored by Japan Society for Applied Magnetics. , And the report by Matsushima et al., “Durability of GdTbFeCo Quaternary Magneto-Optical Recording Medium” on page 210 of the same document, when the addition amounts of Ti and Cr are increased, Kerr rotation angle deterioration and Pt Even with the addition, the deterioration of the Kerr rotation angle was not very satisfactory.

Also, in the case of a magneto-optical recording material film of a polycrystalline film such as MnBi or MnBiCu, the magneto-optical characteristics tend to deteriorate.

The present invention is intended to provide a magneto-optical recording medium having a recording layer which is less deteriorated with time.

Further, the present invention is intended to provide a magneto-optical recording medium which is easy to record and reproduce with high sensitivity as well as having little deterioration with time.

<Means for Solving the Problems> In order to solve the above problems, the magneto-optical recording medium of the present invention is an optical recording medium in which the recording layer is composed of an amorphous film or a polycrystalline film of a magneto-optical recording material to which In is added. A magnetic recording medium, in which In added to the magneto-optical recording material is given a concentration distribution such that one or both of the surface and the bottom surface of the recording layer is higher than the inside, so that deterioration over time is particularly caused. Can be efficiently reduced.

Further, the magneto-optical recording medium of the present invention is particularly excellent in its effect when the recording layer is composed of an amorphous film obtained by adding In to an alloy material composed of a rare earth element and a transition metal element.

Furthermore, in the magneto-optical recording medium of the present invention, the recording layer is MnB.
It may be composed of a polycrystalline film such as i, MnBiCu.

<Operation> As described above, since the magneto-optical recording layer is composed of the magneto-optical recording material with In added, moisture, oxygen, etc. enter the inside of the magneto-optical recording layer from the surface and oxidize the material to improve the magnetic characteristics. It does not deteriorate. Further, according to the experimental results, the Kerr rotation angle or the Faraday rotation angle of the magneto-optical recording layer is hardly deteriorated.

<Example> Next, the present invention will be specifically described based on Examples and Comparative Examples.

(Examples 1 to 5) (A) Manufacturing method: FIG. 1 shows a schematic configuration of a high frequency sputtering apparatus 11 used for forming a film on a magneto-optical recording medium of an example.

The high frequency sputtering apparatus 11 of FIG. 1 comprises a target side electrode 5, a substrate side electrode 7, a high frequency power source 8 and a sputtering gas supply source 9 provided in a vacuum chamber 4. Further, the target-side electrode 5 and the substrate-side electrode 7 are cooled by cooling water supplied from the outside of the vacuum chamber 4, and the purity of 99.99% which is a constituent element of the magneto-optical recording medium to be formed on the target-side electrode 5 , Size 100mmφFe6-1, purity 99.99%,
10mm square Tb pellets 6-2 and 5mm square or smaller In
Pieces 6-3 are placed to form a composite target. Further, a glass plate as the substrate 10 is arranged on the substrate side electrode 7.

However, since In has a low melting point, it is likely to be sputtered first.
Therefore, attention must be paid to the control of In. For example, it is necessary to install the In piece at a site in the electrode where the electric field density is low, or to make the In piece small so that the influence thereof is small. Specifically, in order to increase the In concentration of the substrate 10, the In piece 6-3
Should be placed on the target, and if it is desired to increase the In concentration on the surface side, the In piece should be placed at the site where the electrolytic strength is low. Further, it is easy to give the In concentration distribution by a method such as sputtering In from another target not shown.

When forming a magneto-optical recording medium using this device 11,
Operate an exhaust system (not shown) to move the vacuum chamber 4 to 8 × 10 ^-7 Torr.
After exhausting to the following, Ar gas was introduced into the vacuum chamber 4 from the gas supply source 9 as the sputtering gas, the sputtering gas pressure in the chamber was set to 4 × 10 ⁻² to 8 × 10 ⁻² Torr, and high frequency discharge was performed.
500-800 TbFe amorphous film with In added on substrate 10
It was deposited to a thickness of Å. The film thickness was measured by a step meter (not shown), the film composition was controlled by the numbers of Tb and In pellets, and analyzed by an X-ray photoelectron spectrometer.

No.1, No.2, ..., No.
Name it 5. However, the film composition of No. 1, No. 2, No. 3, and No. 5 is
The composition Y (at.%) Of In is given a concentration distribution of 0.7 to 1.4; 2; 3 to 6; 50, and has a composition of (TbFe) _{1 -Y} In _Y. No. 4 has a composition of TbFeCo (25-60-15 atm.% Each).
It is produced using an alloy target made of.

(Comparative Example 1) Sample No. 6 was prepared in the same manner as in Example 1 except that the In pellet was not placed on the target-side electrode 5.

(Comparative example 2) The In amount on the surface or the surface layer was 0.7 to
The sample having a concentration distribution of 0.9 was designated as No. 7.

(Example 6) Except for using polycarbonate (PC) as the substrate 10,
Sample No. 8 was prepared using the same composite target and method as Sample No. 3.

(Example 7) Sample No. 9 was prepared by the same composite target and method as Sample No. 3 except that polymethyl methacrylate (PMMA) was used as the substrate.

(B) Characteristic test: Next, Table 2 shows the measurement results of the Kerr rotation angle and the deterioration rate of the magnetization change rate with time of the above-mentioned samples No. 1 to No. 9.

The reflectance of each sample in Table-2 was scanned in the wavelength range of 850-600 nm using a Hitachi H-340L type UV / visible spectrophotometer (Table 2 shows the rate of change of the value at 830 nm). . The magnetic characteristics were measured with a vibrating magnetometer (Princeton model 155 model, USA) at a maximum magnetic field of 10 kOe. The samples with <> in Table 2 are arranged at points crossing the y (magnetization) axis corresponding to the residual magnetization Ir.

In addition, the Kerr rotation angle of the sample was
Measured according to the polarization plane modulation method according to the report by Mr. Abe, "Kerr effect of CoCr film and its application to magneto-optical memory," published in "27th Study Group Sample" No.27-9, pp.41-48. The value of θ _k (relative value) was obtained from the Kerr hysteresis after the film, and shown as a relative value based on θ _k of Sample No. 6 (Comparative Example).
As can be seen, the initial characteristic of θ _k is y = 0.7−20
(At.%) Is rather large as compared with the comparative example of y = 0. However, when y = 50 (at.%), 0.95 (membrane surface), 0.9
(Glass surface), which is slightly lower, indicating that the In concentration has an appropriate concentration range (at least 0.7 at.% And less than 50 at.%).

In addition, the element concentration in the depth direction of the sample after film formation was examined using an Auger spectrometer. The results are shown in Table 2 for In concentration ratio. The characteristic is that the average concentration of In element as an impurity inside the film is 50 to 80
Comparative Example N shows that the In concentration in the surface layer between Å is 1.02 to 10
Different from o.7.

The element concentration was normalized to 100% in total by paying attention to the three elements of Tb, Fe and In elements excluding contamination.

Next, the deterioration characteristics over time are shown as the results of measurement by placing the sample in a constant temperature bath at 70 ° C and 85%.

As for the characteristics, the sample was taken out temporarily from the constant temperature, and the reflectance and magnetization (magnetization when H = 10 kOe) or residual magnetization Ir (I-H
The value at the point where the curve crosses the y-axis) is shown in Table 2. In the table, the change (relative value) from the initial characteristic value of each sample is described. The exposure time is shown by integrating the time of placing in the constant temperature bath under the above conditions excluding the measurement time.

The following can be seen from Table-2.

(1) In Comparative Example No. 6, the reflectance and the magnetization start to decrease significantly from the initial stage (2 hours), but the sample of the example containing In
In the case of No. 1 to No. 5, no change in reflectance (1-ΔR / R) was observed and the decrease in magnetization I / Io was small.

(2) In the case of the sample No. 6 of the comparative example, the film was completely deteriorated by leaving it for 20 hours and the surface of the film was transparent and the magnetism was lost, but the samples No. 1 to No. In the case of 5, the reflectance change and the decrease in magnetism are small even if left for 120 hours.

For reference, sample No. 2 of this example and sample No. 6 of comparative example are
After holding for 120 hours and 2 hours in a constant temperature bath at 70 ° C and relative humidity of 85%, the surface of each sample obtained was irradiated with visible light and the reflected light was observed with an optical microscope. Shown in Figures and FIG. However, FIG. 2 is a copy of the above-mentioned micrograph of sample No. 2, and FIG. 3 is a micrograph. In the figure, the sample surface shows a metallic luster in the facing part,
The irradiation light is strongly reflected and appears white in the photograph, and the black portion is oxidized and made transparent because it is left in the atmosphere. Therefore, it is observed as a black density on the photograph depending on the degree of progress of oxidation.

In other words, in the case of sample No. 2, pin holes as shown by black dots are observed on the surface when kept in a constant temperature bath at 70 ° C and relative humidity of 85% for 120 hours, which is the initial state of heating under the above conditions. There is almost no change compared with the above, indicating that the surface is not oxidized at all. On the contrary, in the case of the sample No. 6 of the comparative example, it was shown that the surface blackening drastically increased and was oxidized only after being kept in a thermostat at 70 ° C. and a relative humidity of 85% for 2 hours. There is.

(3) Although not shown in the table, the Kerr hysteresis of the film after exposure to 70 ° C and 85% environment for 120 hours was measured.
Kerr hysteresis was obtained from both the substrate surface and the film surface for the No. 2 and No. 3 samples. Especially in No. 2, the Kerr rotation angle (relative value) from the substrate surface was the same as the value before the test and did not deteriorate.

(4) Sample No. 4 is TbFeCo composed of two elements FeCo as TM
Although it is based on three elements, the effect of In was seen to be exactly the same as in the TbFe binary system.

(5) When a large amount of In is added (Sample No. 5), square car loops are not shown, but magnetism is present. In this case as well, the reflectance and the magnetization stability over time are high.

(6) Since Comparative Example No. 7 was formed by the same method as that of Example No. 3, the average deterioration characteristics over time are good as in No. 3. However, fine pinholes occurred. This is because the surface or surface layer has a low In concentration.

(7) In the curl loop immediately after film formation, the value of θ _k is the same as or greater than that of No. 6, and θ due to the inclusion of the In element.
_There is no decrease in _k .

As described above, it is clear that the rare earth-transition metal element amorphous film containing In according to the present invention exhibits extremely stable characteristics even under the environment of 70 ° C. and 85% and has few pinholes. The amount of added In is 50 at% or less, preferably less than 20 at%.

In this example, as the magneto-optical recording material, TbFe, TbFeCo was used, but instead of Tb as a rare earth element, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Dy, Ho, Er, Tu, Yb, Lu, Sc, Y
May be used alone or in combination, and F may be used as the transition metal.
Similar effects can be obtained by using Fe, Co, Ni alone or in combination instead of e, FeCo, or by using an amorphous film containing In.

Further, the same effect can be obtained by the addition of the In element even in MnBi, MuBiCu, and PtCo, which are magneto-optical recording media having a crystalline and crystalline structure, without being an amorphous film in which In is added to the rare earth element-transition metal element.

Further, in the present embodiment, the film formed by the high frequency sputtering method is described, but the same effect can be obtained by using another film forming means such as another vapor deposition method or ion beam sputtering. The same effect can be expected by using an element having an equivalent electronegativity other than the In element, for example, an element such as Zn, Ga, Cd, Ge, Sn, Pb or Sn.

In control can be easily realized with a sputtering or vapor deposition apparatus having multiple targets. Moreover,
The concentration and gradient of In can be expanded within a range that does not interfere with the original magnetic and optical characteristics, and the fact that the surface or surface layer does not limit the effect of the present invention.

<Effects of the Invention> As is clear from the above description, the magneto-optical recording medium of the present invention contains, firstly, the In element, and further, as a second factor, the concentration of the film surface or the surface layer is the film. Since it is as high as 1.03 to 10 times the average internal density, it is an extremely stable magneto-optical recording medium with little deterioration over time. Further, there is an advantage that the decrease in the Kerr rotation angle θ _k , which has been pointed out in the past, is small, but rather increased.

Further, the magneto-optical recording medium of the present invention is a rewritable magneto-optical disc which is extremely highly reliable as a rewritable magneto-optical disc by providing a base layer, a protective layer such as an overcoat, or combining it with an air sandwich structure. It is clear that

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a high frequency sputtering apparatus used for film formation of the magneto-optical recording medium of the example, and FIG. 2 is a sample of the example left for 120 hours in a constant temperature bath at a temperature of 70 ° C. and a relative temperature of 85%. A micrograph showing the condition of the sample surface after that, and FIG. 3 shows the condition of the sample surface after leaving Sample No. 6 of the comparative example in a constant temperature bath at a temperature of 70 ° C. and a relative humidity of 85% for 2 hours. Micrograph, 4th
(A) (B) (C) is an explanatory view of the principle of the method of writing information on the magneto-optical recording medium. In the figure, 1 ... Recording layer, 2 ... Area to be recorded, 3
... magnetic field, 4 vacuum chamber, 5 target electrode, 7
…… Substrate side electrode, 8 …… High frequency power supply, 9 …… Sputter gas supply source, 10 …… Substrate, 11 (whole code) …… High frequency sputtering device.

Claims (3)

[Claims] 1. A magneto-optical recording medium in which the recording layer is composed of an amorphous film or a polycrystalline film of a magneto-optical recording material containing In, wherein In added to the magneto-optical recording material is A magneto-optical recording medium characterized by giving a concentration distribution such that the surface or bottom surface or both sides are higher than the inside. 2. The magneto-optical recording medium according to claim 1, wherein the magneto-optical recording material to which In is added is an alloy material of a rare earth element and a transition metal element. 3. The magneto-optical recording material to which In is added is MnBi, M
The magneto-optical recording medium according to claim 1, wherein the magneto-optical recording medium is one of nBiCu and PtCo.