JPH0619861B2 - Magneto-optical recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magneto-optical recording medium capable of recording, reproducing and erasing information by using a laser beam.

"Prior Art" For example, a thin film made of an amorphous magnetic material of a rare earth transition metal typified by TbFe, TbFeCo or the like can have magnetic anisotropy in a direction perpendicular to the film surface. Therefore, the recording density of the magneto-optical recording medium in which the amorphous magnetic thin film of this kind of rare earth transition metal is formed on the transparent substrate can be greatly improved.

On the other hand, when an amorphous magnetic thin film is used as a magneto-optical recording medium, the rewritable magneto-optical recording medium can be constructed because the magnetic substance itself is a rewritable recording medium, and the amorphous magnetic thin film is used. Therefore, there is also an advantage that a magneto-optical recording medium that does not generate noise due to grain boundaries can be constructed. For this reason, it has been conventionally desired to use this kind of amorphous magnetic thin film of a rare earth transition metal as a rewritable high-density magneto-optical recording medium, for example, for a video desk.

However, this type of rare-earth transition metal amorphous magnetic thin film has a drawback that its reproduction SN ratio is small. In order to improve the reproduction SN ratio in the magneto-optical recording medium,
It is necessary that the rotation angle of the polarization plane due to the magnetic Kerr effect is large and the squareness of the Kerr hysteresis loop is as close to 1 as possible. That is, it is desired that the residual Kerr rotation angle at the zero magnetic field is as close as possible to the Kerr rotation angle at the saturation value.

For the amorphous magnetic thin film of rare earth transition metal of this kind, the influence of the composition of the magnetic thin film and the sputtering condition at the time of thin film formation on the reproduction SN ratio has been studied, and various conditions have been discussed. Has been.

The inventors of the present invention have also studied the reproduction S of an amorphous magnetic thin film of a rare earth transition metal in terms of its composition and spattering.
Research and actual measurement based on this research were carried out in an attempt to improve the N ratio, but satisfactory results with sufficient reproducibility were not obtained.

As a result of research by the inventors, in a magneto-optical recording medium in which an amorphous magnetic thin film of a rare earth transition metal is formed on a transparent substrate, one of the important factors that determines the squareness of the Kerr hysteresis loop is a thin film. It has been confirmed that there is an in-plane magnetic layer in which the magnetization direction distributed and formed in the interface between the film surface portion, the thin film and the transparent substrate is parallel to the film surface.

However, it has not been clearly understood in the past how the presence of the in-plane magnetization layer quantitatively affects the squareness of the Kerr hysteresis loop.

[Problems to be Solved by the Invention] According to the present invention, in a magneto-optical recording medium in which an amorphous magnetic thin film of a rare earth transition metal is formed on a transparent substrate, a surface portion of the thin film and an interface portion between the thin film and the transparent substrate. Clarifies the quantitative relationship to the reproduction SN ratio of the in-plane magnetized layer existing in
We propose a quantitative constitutional condition between the amorphous magnetic thin film of rare earth transition metal and the in-plane magnetized layer formed on the transparent substrate for improving the reproduction SN ratio.

According to the present invention constituted on the basis of the quantitative relationship between the thus obtained amorphous magnetic thin film of rare earth transition metal and the in-plane magnetized layer, the rotation angle of the polarization plane due to the magnetic Kerr effect is A magneto-optical recording medium having a large size and excellent Kerr hysteresis loop squareness can be obtained.

[Constitution of the Invention] In the present invention, an amorphous magnetic thin film of a rare earth transition metal is formed on a transparent substrate, and the amorphous magnetic thin film has a thickness of 8
It is set to 00 to 1000Å. Further, in the present invention, the thickness of the in-plane magnetized layer portion whose magnetization direction is parallel to the film surface, which is formed on the surface of the amorphous magnetic thin film and the interface between the amorphous magnetic thin film and the transparent substrate, is 40Å as a whole. It is set in the range of 80 to 80Å.

By setting the film thickness and the film surface portion of the amorphous magnetic thin film and the thickness of the in-plane magnetized layer formed at the boundary portion between the amorphous magnetic thin film and the substrate within the above ranges, respectively, the present invention Increases the Kerr rotation angle and improves the squareness of the Kerr hysteresis loop.

[Examples] Hereinafter, a magneto-optical recording medium of the present invention will be described in detail based on Examples with reference to the drawings and manufacturing methods thereof.

An amorphous magnetic thin film of a rare earth transition metal is formed on a transparent substrate, and the amorphous magnetic thin film has a thickness of 800 to 1000.
Selected as Å.

As the transparent substrate, soda silicate glass is used as an example in the embodiment, and TbFe is used as the rare earth transition metal on the transparent substrate in the first embodiment.
An amorphous magnetic thin film of Fe is formed on a transparent substrate of soda silicate glass by a high frequency sputtering method. The target used in the sputtering method in this case is a composite target in which a Tb chip is placed on an Fe substrate. The atmosphere for forming the amorphous magnetic thin film is an inert gas atmosphere of argon gas, and the pressure of the argon gas is 3 to
It is held at 8 Pa.

Under such a production atmosphere, the surface temperature of the substrate is kept at about 300 ° K to 600 ° K0 in the spatula, and the power supply is 50%.
W-100 W, and a thin film of TbFe is first formed on the transparent substrate by the high frequency sputtering method to a thickness of 2000Å.
To be formed.

Thus, a thin film of TbFe having a thickness of 2 is formed on the transparent substrate.
The film thickness of the Tb-Fe thin film is reduced by the reverse sputtering method from the state of being formed so that the film thickness becomes 000 Å.
Amorphous magnetic thin films of Å, 890 Å and 700 Å are formed. To measure the film thickness in this case, an edge having a width of about 1 mm was prepared, and the film thickness was measured using a needle contact type film thickness meter.

Thus obtained Tb- having each film thickness
When the Kerr hysteresis loop is actually measured for the Fe amorphous magnetic thin film, the results shown in FIGS. 1A to 1E are obtained. FIGS. 1 (A) to (E) show Tb, respectively.
-Fe amorphous magnetic thin film has a thickness of 1680Å, 135
It is a Kerr hysteresis loop obtained in the case of 0Å, 1160Å, 890Å and 700Å.

At a film thickness of 1680Å, the squareness of the Kerr hysteresis loop cannot be said to be good, but due to reverse sputtering, Tb
As the thickness of the —Fe amorphous magnetic thin film is reduced, the in-plane magnetized portion existing on the film surface, whose magnetization direction is parallel to the film surface, is reduced, and as shown in FIG. ) And (D), the squareness of the Kerr hysteresis loop is improved as shown in the figure.

However, if the thickness of the Tb-Fe amorphous magnetic thin film is further reduced to 700 Å as shown in Fig. 1 (E),
Deterioration of squareness is left again. This is due to the influence of the in-plane magnetic layer portion whose magnetization direction existing at the interface with the transparent substrate is parallel to the film surface.

A relatively large number of in-plane magnetized layers that deteriorate the squareness are formed on the surface of the Tb-Fe amorphous magnetic thin film and the interface between the amorphous magnetic thin film and the substrate. It is considered that this is because oxidation occurs at the interface between the crystalline magnetic thin film and the substrate.

It is confirmed that the degree of this oxidation depends on the ratio of the rare earth element to the transition element in the measurement result of the inventors because the rare earth element is oxidized prior to the transition metal in the amorphous magnetic substance of the rare earth transition metal. Has been done. In the embodiment shown in FIG. 1, the degree of oxidation depends on the proportion of Tb in TbFe, which is the proportion of Tb in TbFe in this case.
It is about 30 atomic%.

FIG. 1 (A) to (E) shows the film thickness and the Kerr rotation angle of the amorphous magnetic thin film measured by the inventors for the Tb-Fe amorphous magnetic thin film having the film thickness. The relationship is the curve C _{1 in} FIG.
Through C ₄ . The composition of the amorphous magnetic thin film used for the measurement in FIG. 3 is Tb ₁₅ Fe ₈₅ . Here, C _{1 and} C ₂ are cases where an in-plane magnetized layer having a film thickness of approximately 400Å was formed on the surface of the amorphous magnetic thin film from the beginning, and C ₃ and C ₄ were prepared. Initially, this is the case where such an in-plane magnetization layer is not formed. Also, C ₁ and C ₄ are initially set to approximately 1200 Å, and the film thickness is reduced from this state. C ₂ and C ₃ are set to approximately the same as the amorphous magnetic thin film. The film thickness is reduced to 2000 Å, and the film thickness is reduced from this state and the measurement is performed. That is, C
_{In 1} and C ₂ , the Kerr rotation angle θ with respect to each film thickness t was gradually removed when the in-plane magnetized layer having a film thickness of 400 Å originally formed on the surface of the Tb-Fe amorphous magnetic thin film was gradually removed. _k is being measured.

In FIG. 3, curves C ₃ and C ₄ are Tb-F in which a thin film is formed uniformly without positively forming an in-plane magnetization layer portion on the surface.
e is a curve showing the relationship between the film thickness and the Kerr rotation angle obtained for each film thickness while the film thickness is similarly reduced for the amorphous magnetic thin film.

As is clear from the actual measurement results of FIG. 3, the film thickness is obtained both when the in-plane magnetized layer portion is positively formed on the surface and when the in-plane magnetized layer portion is not actively formed on the surface. Has a maximum value in the Kerr rotation angle in the range of 1000Å to 700Å. The existence of the maximum value with respect to the Kerr rotation angle is considered to be due to the enhancement effect due to the interference caused by the decrease in the reflectance in this film thickness portion.

FIG. 4 shows the relationship between the reflectance R and the film thickness t of the Tb-Fe amorphous magnetic thin film actually measured by the inventors, which corresponds to C ₂ in FIG. Its composition is Tb ₁₅ Feb ₈₅ . Apparently, the minimum value of the reflectance R is recognized at the position where the film thickness exceeds 1000Å.

When measuring the reflectance in this case, the Tb
A laser beam of 5 mw is irradiated as an incident laser beam on the Fe amorphous magnetic thin film, the power of the reflected laser beam reflected and emitted from the subject is measured, and the power of the reflected laser beam with respect to the incident laser beam is measured. The ratio is measured and the reflectance is calculated from these power ratios.

According to actual measurements by the inventors, in the initial state shown in FIG. 1 (A), the total thickness of the in-plane magnetized layers formed on the boundary surface between the thin film surface and the substrate was about 160Å. First
In the states of FIGS. (B) and (C), the total thickness of the in-plane magnetized layers formed on the boundary surface between the thin film surface and the substrate is 80Å ~
It was about 50Å.

As a result of actual measurement of amorphous magnetic thin films of various rare earth transition metals, the total thickness of the in-plane magnetic layers formed on the boundary surface between the thin film surface and the substrate is the thickness of the amorphous magnetic thin film. It was confirmed that the squareness of the Kerr hysteresis loop was deteriorated when it was 10% or more.

Even if the substrate is washed to reduce oxidation at the interface with the substrate as much as possible, oxidation occurs at this boundary portion and an in-plane magnetization layer is formed. Further, on the surface of the amorphous magnetic thin film, the in-plane magnetic layer is formed by oxidation without positively forming the in-plane magnetic layer. Therefore, these in-plane magnetized layers cannot be removed at all, and even if the in-plane magnetized layers are most reduced according to the measurement by the inventors, the total amount of the in-plane magnetized layers is 20%.
It was confirmed that an in-plane magnetized layer having a thickness of about Å was formed.

On the other hand, as a result of actual measurement by the inventors, it has been confirmed that the recording retention of the perpendicular magnetization is stabilized if the in-plane magnetization layer is slightly present. This is considered to be because the recording of the perpendicular magnetization is stably held by the loop of the magnetic field. According to the measurement by the inventors, when the thickness of the amorphous magnetic thin film is 800 Å to 1000 Å and the thickness of the entire in-plane magnetized layer is 40 Å to 80 Å, the rotation angle of the polarization plane due to the magnetic Kerr effect is large and It was confirmed that an amorphous magnetic thin film of a rare earth transition metal having excellent squareness of the Kerr hysteresis loop was obtained.

FIGS. 2A to 2E show a second embodiment of the present invention. In this second embodiment, T is used as a rare earth transition metal.
Using bFeCo, this amorphous magnetic thin film of TbFeCo is formed on a transparent substrate of soda silicate glass by a high frequency sputtering method.

Since the conditions for forming the amorphous magnetic thin film of rare earth transition metal in the second embodiment are the same as those in the first embodiment described above, duplicate description thereof will be omitted. In addition, FIG.
In (A) to (E), the film thickness of the TbFeCo amorphous magnetic thin film is 1600Å, 1300Å, 1040Å, 950, respectively.
It is a Kerr hysteresis loop obtained in the case of Å and 710Å, respectively.

In the second embodiment, the same characteristics as in the first embodiment are recognized. When the film thickness of 1600Å is not good, the squareness of the Kerr hysteresis loop is not good, but when the film thickness is reduced by the reverse sputtering, The in-plane magnetization layer existing in the film surface portion whose magnetization direction is parallel to the film surface is reduced, and as shown in FIG. 2 (B).
As shown in (C) and (D) respectively, the squareness of the Kerr hysteresis loop is improved.

However, if the thickness of the TbFeCo amorphous magnetic thin film is further reduced, the squareness deteriorates again as is apparent from FIG. 2 (E) corresponding to the thickness 710Å. This is because, as in the case of the first embodiment, the effect of the in-plane magnetic layer portion in which the magnetization direction existing at the interface between the amorphous magnetic thin film and the transparent substrate is parallel to the surface appears.

Oxidation that tends to occur at the film surface and at the interface between the amorphous magnetic thin film and the transparent substrate causes the presence of in-plane magnetized layers in these parts, and the degree of this oxidation depends on the ratio of the rare earth element to the transition element. What has been done has been confirmed by the inventors as in the case of the first embodiment.

It has also been confirmed that the squareness of the Kerr hysteresis loop deteriorates when the thickness of the entire in-plane magnetized layer exceeds 10% of the thickness of the amorphous magnetic thin film, as in the first embodiment.

Further, as a result of the actual measurement by the inventors, the second implementation is carried out regardless of the relationship between the film thickness of the amorphous magnetic thin film and the Kerr rotation angle and the relationship between the film thickness of the amorphous magnetic thin film and the reflectance. It has been confirmed that the example has the same tendency as the first example.

[Effects of the Invention] As confirmed in each example, according to the present invention, the film thickness of the amorphous magnetic thin film of rare earth transition metal formed on the transparent substrate is set to 800Å to 1000Å, A magneto-optical recording medium having desired characteristics can be obtained by forming a thin film so that the thickness of the in-plane magnetized layer portion formed at the interface with the transparent substrate does not exceed 40Å to 80Å.

That is, in this case, the reproduction Kerr rotation angle becomes large, and the Kerr hysteresis loop also has excellent squareness, so that a magneto-optical recording medium having excellent operation characteristics and an improved reproduction SN ratio can be obtained.

[Brief description of drawings]

FIGS. 1A to 1E show the first part of the magneto-optical recording medium of the present invention.
Showing the Kerr hysteresis loop curve corresponding to each film thickness of the amorphous magnetic thin film of rare earth transition metal in the embodiment of FIG. 2, and FIGS. 2 (A) to 2 (E) show the magneto-optical recording medium of the present invention. FIG. 3 is a diagram showing Kerr hysteresis loop curved images corresponding to respective film thicknesses of the amorphous magnetic thin film of rare earth transition metal in Example 2, and FIG. 3 is a graph showing non-existence of rare earth transition metal of the same composition as in Example 1. FIG. 4 is a graph showing the relationship between the film thickness and the Kerr rotation angle for the amorphous magnetic thin film, and FIG. 4 shows the relationship between the film thickness and the reflectance for the amorphous magnetic thin film of the rare earth transition metal having the same composition as in the first embodiment. It is a figure which shows a relationship. t: film thickness, θ _k : Kerr rotation angle, R: reflectance.

Claims (1)

[Claims] 1. A rare earth transition metal amorphous magnetic thin film is formed on a transparent substrate, and a magnetization direction is provided on a surface of the amorphous magnetic thin film and an interface between the amorphous magnetic thin film and the transparent substrate. In the magneto-optical recording medium in which an in-plane magnetized layer parallel to the film surface is formed, the film thickness of the amorphous magnetic thin film is 800Å
To 1000 Å, and the thickness of the entire in-plane magnetized layer is set to 40 Å to 80 Å.