JPS6394449A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a medium having an excellent reproduction characteristic of a large signal quantity by laminating a transition metal layer having <=50Angstrom thickness and perpendicularly magnetized film consisting of a rare earth element and transition metal on a substrate and reading signals by the photoirradiation from the transition metal layer side. CONSTITUTION:The transition metal layer 2 consisting of Fe, Co, etc., is deposited by sputtering on one face of the transparent substrate 3 consisting of glass, etc., while the thickness thereof is adjusted to <=50Angstrom . The perpendicularly magnetized film 1 consisting of the rare earth element such as Gd, Tb, Dy or Ho and the transition metal layer of Fe, Co or the like is laminated by sputter vapor deposition thereon. The magneto-optical recording medium is constituted in the above-mentioned manner and is subjected to recording and reproduction by projecting laser light to the medium from the rear surface side of the substrate 3. The Kerr rotating angle or Faraday rotating angle of the plane of polarization is increased if the medium is constituted in the above-mentioned manner. In addition, the signal quantity increases, because the transition metal layer is the good perpendicularly magnetized film.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a magneto-optical recording medium that records and reproduces information using a laser beam or the like by utilizing the magneto-optic effect. This invention relates to the improvement of a magneto-optical recording medium having an optical recording layer made of a metal-based amorphous alloy.

[Summary of the invention]

The present invention provides a magneto-optical recording medium having a perpendicularly magnetized film made of a rare earth element and a transition metal as an optical recording layer. The purpose of this invention is to increase the Kerr rotation angle without reducing the ratio, and to realize a magneto-optical recording medium with excellent reproduction characteristics.

[Conventional technology]

In recent years, a rewritable high-degree recording method uses the magneto-optic effect to record with a half-door laser beam.

Magneto-optical recording methods for reproduction are attracting attention.

In this magneto-optical recording method, the recording materials used for the recording layer include rare earth elements such as Tb and Gd, and F.
Amorphous alloy films mainly composed of transition metals such as e, Co, etc. have been developed, and among them, TbFeCo, TbFe.

It has been reported that materials such as GdFe and GdTbFe provide fairly good characteristics in terms of sensitivity and readout characteristics.

By the way, in this magneto-optical recording method, signals are recorded using the magneto-optical effect (so-called Kerr effect, Faraday effect) in a rare earth element-transition metal amorphous alloy film, which is a perpendicularly magnetized film. The reality is that the Kerr rotation angle (Faraday rotation angle) of an element-transition metal amorphous alloy film is extremely small.

Therefore, in order to put such magneto-optical recording media into practical use, in many cases, for example, a transparent dielectric layer is used to utilize multiple reflections to increase the above-mentioned rotation angle.

However, such a method using multiple reflections inevitably causes a decrease in reflectance, and there is a limit in terms of signal amount improvement.

Therefore, as a method of increasing the Kerr rotation angle without lowering the reflectance, we have developed a method to increase the Kerr rotation angle without lowering the reflectance.
It has been considered to provide a film with a very large Kerr rotation angle such as nB1 and make the magnetic film have a two-layer structure, but MnB
The presence of grain boundaries in one film, MnB1! I! has problems such as the fact that it is difficult to form a perpendicularly magnetized film.

Or, for example, in Japanese Patent Application Laid-open No. 61-51637,
A film thickness of 100 to 500 mm is provided between the magneto-optical recording medium layer and the reflective film.
An attempt has been made to provide a Co layer to increase the apparent Kerr rotation angle and improve the reproduction characteristics. however,
According to the inventor's experiments, when the thickness of the Co layer is set to this value, it does not become a perpendicularly magnetized film, and furthermore, since there is no Co layer on the readout side, the Kerr rotation angle cannot be increased. We came to the conclusion that it makes little contribution to

[Problem that the invention seeks to solve]

As mentioned above, attempts to increase the Kerr rotation angle by making the magnetic film have a two-layer structure have not yielded much success because it is difficult to make a film with a large Kerr rotation angle into a perpendicularly magnetized film. It is.

Therefore, the present invention has been proposed in view of the conventional situation, and has a structure that exhibits excellent perpendicular magnetization characteristics, has a large Kerr rotation angle, and does not cause a decrease in reflectance. An object of the present invention is to provide a magneto-optical recording medium having excellent reproduction characteristics.

[Means for solving the problems] In order to achieve the above-mentioned object, the present invention provides 50
A transition gold I layer having a thickness of Å or less and a perpendicular magnetization film made of a rare earth element and a transition metal are laminated so that a signal can be read out by light irradiation from the transition metal layer side. be.

In rare earth element-transition metal alloy films, transition metal atoms are said to cause the Kerr effect.

Therefore, by increasing the areal density of transition metal atoms on the surface of the perpendicularly magnetized film, in other words, by superimposing Fe on the perpendicularly magnetized film,
By forming a transition metal layer mainly composed of Co alone or an alloy containing Co, the rotation angle of the plane of polarization is increased.

However, when the thickness of the transition metal layer is thin, the axis of easy magnetization of the transition metal layer is oriented in the perpendicular direction according to the perpendicular magnetization film, but gradually it becomes ll! As the l thickness increases, the surface side no longer exhibits vertical anisotropy. 1A to 1E schematically show the direction of magnetization in each layer when a transition metal layer (2) is deposited on a perpendicularly magnetized film (1), and the solid line arrows in the figures show the direction of magnetization in each layer. indicates the direction of magnetization due to the transition metal, and the dashed arrow indicates the direction of magnetization due to the rare earth element.As shown in Figure 1B, when the transition metal layer (2) is thin, the transition metal layer (2) ) becomes a good perpendicular magnetization film, but as the thickness of the transition metal layer (2) gradually increases from Figure 1C to Figure 1E, the direction of magnetization on the surface side shifts to the side, and finally becomes magnetized in the in-plane direction.

This means that if the transition metal layer (2) is too thick, the Kerr rotation angle will decrease.

Therefore, in the present invention, the thickness of the transition metal Fi (2) deposited on the perpendicularly magnetized film (1) is set to 50 Å or less. Transition money! If the film thickness of 11(2) exceeds 50 layers, the Kerr rotation angle may actually decrease, and the Kerr rotation angle may become smaller than that of a single-layer rare earth element-transition metal alloy film. Further, although the effect can be obtained even if the thickness of the transition metal 13 (2) is very small, it is actually preferable to set it to 5 Å or more.

On the other hand, the perpendicular magnetization film (1) contains the same transition metal as the transition metal layer (2) and rare earth elements (Gd, Tb, oy,
(Ho, etc.) or an alloy containing them, and the proportion of transition metals is usually 90 to 60 at%,
The proportion of rare earth elements is set in a range of about 10 to 40 atomic %. The film thickness of this perpendicular magnetization film (1) is 100
~1000 people.

As shown in FIG.
is formed on the signal read side of the perpendicular magnetization film (1). ) may be provided only on the perpendicular magnetization film (
It may be provided on both sides of 1). When the transition metal layer (2) is formed only on one side, the transparent substrate (
3) on the transition metal layer (2) side, and this transparent substrate (3)
A laser beam is irradiated from the side to read the signal.

When the transition metal layer (2) is provided on both sides of the perpendicularly magnetized film (1), as shown in FIG. Membrane (5
), the Faraday effect also contributes, and layers for increasing the plane of polarization are provided on both sides of the perpendicularly magnetized film (1), resulting in an extremely large effect.

In any case, it can be said that the present invention is advantageous in terms of productivity since almost no changes in the process for forming the transition metal layer (2) are required.

That is, for example, when performing binary simultaneous sputtering on a perpendicularly magnetized film using a transition metal target and a rare earth element target, if sputtering using only the transition metal target is performed before or after the simultaneous sputtering using both targets, the transition metal layer ( 2) is formed on one or both sides of the perpendicularly magnetized film (1). This method is simple and easy to process,
A laminated structure of transition gold rXJI (2) and perpendicularly magnetized film (1) is continuously produced.

Alternatively, when a rare earth element-transition metal alloy target is used, a transition metal target may be prepared separately from this alloy target, and sputtering may be performed using the transition metal target before or after film formation using the alloy target.

[Effect]

When a transition metal layer with a thickness of 50 Å or less is provided on a rare earth element-transition metal based perpendicular magnetization film, this transition metal layer becomes a good perpendicular magnetization film.

By forming this transition metal layer, the areal density of transition metal atoms on the surface of the perpendicularly magnetized film increases, and it is said that it is the transition metal atoms that cause the Kerr effect in the rare earth element-transition metal based perpendicularly magnetized film. As a result, the rotation angles (Kerr rotation angle and Faraday rotation angle) of the plane of polarization increase.

〔Example〕

The present invention will be explained below using specific experimental examples.

First, in this experimental example, a perpendicular magnetization film and a transition metal layer were formed using a sputtering apparatus as shown in FIG.

In this sputtering apparatus, a bell jar (not shown) is used.
Inside is a base (11) that rotates around the axis X-X゛.
A base body (12) made of a glass plate, a resin plate, etc. constituting the intended magneto-optical recording medium is placed, for example, on the lower surface of this base (11). And this base (12
) at equal intervals around the axis x-x', that is, 1
Two sputter sources (13) maintaining an angular spacing of 80°
, (14) is placed. Furthermore, between these sputtering sources (13), (14) and the substrate (12), there is a mask (15) for controlling the sputtering position of the metal sputtered from the sputtering source (13) and the sputter a<X4>, respectively. is provided. In addition, a sputter source (13
) has a target (16) made of a plate of a rare earth element (e.g. Tb), while the spafter source (14) has a target (17) made of a plate of transition gold II (e.g. Fe, Co, etc.). have.

For example, as shown in FIG. 7, the mask (15) has approximately fan-shaped (so-called ginkgo leaf-shaped) windows (1) in the portions facing the target (16) and the target (17), respectively.
8), (19) are drilled, and the base (11) is
(16), (IT)
The substrate (12
) An alloy film of the metal constituting the target (16) and the metal constituting the target (17) is formed on the target (16).

In this example, a Tb target is used as the rare earth element target (16), and a transition metal target (17) is used.
As a Fe-Co alloy target (Fe: 95 atomic%
.

Co: 5 atomic %) was used.

First, sputtering was performed using only a Fe-Co alloy target to knock out Fe and Co, and the substrate (1
2) A transition metal layer was formed thereon.

Next, two-light time sputtering was performed using both target films (16) and (17) to obtain Tb. Fet＊Coa
(However, the numerical values represent atomic %.) A rare earth element-transition metal-based perpendicular magnetization film having the following composition was deposited and formed.

Next, sputtering was performed again using only the Fe--Co alloy target to form a transition metal layer on the perpendicularly magnetized film.

Through the above steps, a magneto-optical recording medium having a configuration similar to that shown in FIG. 3 was manufactured.

Here, the thickness ay of the rare earth element-transition metal perpendicularly magnetized film and the thickness dx of the transition metal layer were varied, and the Kerr rotation angle (θk) was measured for each of the obtained magneto-optical recording media. Note that in the measurement, a semiconductor laser with a wavelength of 780 rv was used. The results are shown in FIG.

In this figure, the thickness dy of the rare earth element-transition metal perpendicular magnetization film was changed to dy=300, 500, and 800, and the thickness dx of the transition metal layer was changed from 0 to 150. It shows the change in the Kerr rotation angle (θk) when
- 30 people, the triangle mark "Δ" means dx - 60 people, the inverted triangle mark "" means dX - 100 people, the diamond mark "◇" means d
x-150 people each. Further, the horizontal axis represents the total film thickness (dY+2dx), which is the sum of the film thickness of the rare earth element-transition metal based perpendicular magnetization film and the film thickness of the transition metal layer.

It can be seen from FIG. 8 that the Kerr rotation angle θk uniformly increases when the transition metal layer is formed with a thickness of 50 Å or less, regardless of the thickness dy of the perpendicularly magnetized film. In particular, the change in the Kerr rotation angle θ as the film thickness increases when the transition metal layer thickness dx = 0 people (curve A in the figure), and the change when the transition metal layer thickness dx = 30 people. There is a difference of approximately 0.0% between the change in Kerr rotation angle θ (curve IB in the figure) due to the increase in film thickness.
A clear difference of 0.05° was observed, demonstrating that the formation of the transition metal layer was effective in increasing the Kerr rotation angle.

〔Effect of the invention〕

As is clear from the above description, in the present invention,
Since transition gold vsN with a film thickness of 50 Å or less is provided at least on the signal readout side of the perpendicularly magnetized film made of a rare earth element and a transition metal, the rotation angle of the polarization plane (Kerr rotation angle or Faraday rotation angle) can be increased. can, in addition,
Because the transition metal layer is a perpendicularly magnetized film with good perpendicular magnetization, and unlike those that use multiple reflection, there is almost no decrease in reflectance, magneto-optical recording media with large signal amounts and excellent reproduction characteristics are used. It is possible to achieve this.

Further, the configuration of the magneto-optical recording medium of the present invention can be used in combination with, for example, a multiple reflection structure, and it is also possible to further increase the Kerr rotation angle.

Furthermore, in producing the magneto-optical recording medium of the present invention,
There is almost no need to change the process, and it is highly practical in terms of productivity and capital investment.

[Brief explanation of the drawing]

FIGS. 1A to 1E are schematic diagrams showing how the magnetization state changes as the thickness of the transition metal layer increases. FIG. 2 is an enlarged cross-sectional view of a main part showing an example of a stacked state of a perpendicular magnetization film and a transition metal layer, and FIG. 3 is an enlarged cross-sectional view of a main part showing another example of a stacked state of a perpendicular magnetization film and a transition metal layer. It is a diagram. FIG. 4 is an enlarged cross-sectional view of a main part showing an example of the configuration of a magneto-optical recording medium to which the present invention is applied, and FIG. 5 is an enlarged cross-sectional view of a main part showing another example of the structure of a magneto-optical recording medium to which the invention is applied. It is a diagram. FIG. 6 is a schematic configuration diagram showing an example of a sputtering apparatus used in manufacturing the magneto-optical recording medium of the present invention, and FIG.
The figure is a plan view of a main part of a mask provided in a sputtering apparatus. FIG. 8 is a characteristic diagram showing how the Kerr rotation angle θ changes with the change in the thickness of the transition metal layer when the thickness dy of the perpendicularly magnetized film is changed. 1... Perpendicular magnetization film 2... Transition metal layer 3... Transparent substrate

Claims (1)

[Claims] A transition metal layer having a thickness of 50 Å or less and a perpendicular magnetization film made of a rare earth element and a transition metal are laminated on a substrate so that signals can be read out by light irradiation from the transition metal layer side. Magneto-optical recording medium.