JP2526906B2 - Magneto-optical recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magneto-optical recording medium, and more particularly to a magneto-optical recording medium having a rare earth-transition metal magnetic film.

[Outline of Invention]

According to the present invention, in a magneto-optical recording medium having a rare earth-transition metal magnetic film, a first rare earth-transition metal magnetic film having a dominant transition metal sublattice magnetic moment and a rare earth sublattice magnetic moment exchange-coupled to the first rare earth-transition metal magnetic film are provided. By stacking a dominant second rare earth-transition metal magnetic film and forming at least the second rare earth-transition metal magnetic film into a superlattice structure in which rare earth metal and transition metal are alternately stacked, C /
The N ratio and the frequency characteristic are improved.

[Conventional technology]

Rare earth-transition metal magnetic film (that is, perpendicular magnetization film) that constitutes a rewritable magneto-optical disk or other magneto-optical recording medium
Is usually composed of a magnetic film having a single composition (that is, a single layer film). In this rare earth-transition metal magnetic film, the perpendicular magnetization M _S is obtained in the film thickness direction, that is, in the vertical direction, by the combination of the sublattice magnetic moment M _RE of the rare earth metal and the sublattice magnetic moment M _TM of the transition metal. It is a thing.

This rare earth-transition metal based magnetic film has advantages and disadvantages depending on the types of rare earth and transition metal, but the magneto-optical disk characteristics of amorphous rare earth-transition metal materials (recording / erasing characteristics, C /
Reproduction characteristics such as N ratio and frequency characteristics further depend on the composition. For example, in the case of a single-layer film of a rare earth-transition metal-based magnetic film (hereinafter referred to as a transition metal abundant film) having a composition having a large transition metal composition with respect to the compensating composition, and thus a composition having a dominant transition metal sublattice magnetic moment M _TM , , The higher the transition metal composition, the more magnetized
M _S is large and the demagnetizing field is large accordingly. When the temperature rises, these become larger and become larger than the perpendicular anisotropy magnetic field, so that the magnetization is easily reversed and the recording sensitivity becomes high. That is, recording can be performed with low laser power. Also, a high _K / N with a large Kerr rotation angle θ _K can be obtained. However, regarding the erasing characteristics, the recording bit is magnetostatically stable and the erasing becomes difficult because the surrounding magnetization is large. That is, a large laser power is required, and the erasing sensitivity becomes low. Further, since the magnetization M _S is large, unless the perpendicular anisotropy magnetic field is large, the perpendicular anisotropy is poor and stable recording bits cannot be obtained. Therefore, the frequency characteristic is deteriorated.

Next, in the case of a single layer film of a rare earth-transition metal based magnetic film (hereinafter, referred to as a rare earth metal large amount film) having a composition with a large rare earth metal composition relative to the compensation composition, and thus a composition with a rare earth metal sublattice magnetic moment M _RE predominant. , The Kerr rotation angle θ _K is smaller than that of the transition metal large amount film, and thus the C / N ratio is poor. Also, the recording sensitivity is low and high laser power is required. On the other hand, since the magnetization M _S is small, erasing is easy and frequency characteristics are good.

On the other hand, recently, as a rare earth-transition metal based magnetic film, a two-layer film has been proposed which is formed by laminating a transition metal abundant film and a rare earth metal abundant film so as to exchange-couple with each other. In the case of this two-layer rare earth-transition metal magnetic film, a high C / N ratio can be obtained because a transition metal large amount film having a large Kerr rotation angle θ _K is used as a layer for reading by the Kerr effect. Since a large amount of transition metal film with good recording sensitivity is heated, writing can be performed with low laser power and high recording sensitivity. Since the rare earth metal abundant film and the transition metal abundant film are exchange-coupled with each other, the total magnetization M _S is small, so that the erasing power can be made small and the erasing sensitivity is high. Furthermore, the frequency characteristic is good because the vertical anisotropy of the transition metal large amount film is secured by the exchange coupling.

[Problems to be solved by the invention]

By the way, it is desired to further increase the C / N ratio and extend the frequency characteristics. Therefore, in the two-layer film, in order to increase the C / N ratio, it is necessary to increase the Kerr rotation angle θ _K, and it is conceivable that the transition metal abundant film has a composition with a larger transition metal composition. However, when the transition metal composition is increased, the magnetization M _S is increased and the magnetization of the transition metal multi-layer film tends to collapse, that is, the perpendicular anisotropy is deteriorated, resulting in a low C / N ratio and poor frequency characteristics. .

In view of the above points, the present invention provides a magneto-optical recording medium having high recording sensitivity and erasing sensitivity, and further improved C / N ratio and frequency characteristics.

[Means for solving problems]

The present invention relates to a first rare earth-transition metal magnetic film (2) in which a transition metal sublattice magnetic moment M _TM is predominant on a substrate (1), and the first rare earth-transition metal magnetic film (2).
A second rare earth-transition metal magnetic film (6) having a predominant rare earth sublattice magnetic moment M _RE exchange-coupled with is laminated, and at least the second rare earth-transition metal magnetic film (6) is formed on the rare earth metal (22 ) And a transition metal (21) are alternately laminated in a superlattice structure to form a magneto-optical recording medium (8) having a perpendicular magnetization film (7).

That is, in this case, only the second magnetic film (6) may have a superlattice structure, or both the first and second magnetic films (2) and (6) may have a superlattice structure.

The first magnetic film (2) and the second magnetic film (6) are made of Tb, G
Each magnetic film (2) and (6) is composed of one or more elements of a rare earth metal such as d, Dy, Ho ... and a transition metal such as Fe, Co, Ni. Other elements may be added in small amounts, for example, trace amounts of Cr, Ti, Pt, Al, etc. may be added to improve corrosion resistance.

The first magnetic film (2) is formed of a composition having a transition metal composition higher than the composition having a compensation temperature at room temperature, that is, a transition metal content film, and a similar compensation composition for the second magnetic film (6). It is formed of a composition having a higher rare earth metal composition, that is, a rare earth metal large amount film. Thereby, the magnetic film (2)
Since (1) and (6) are ferrimagnetic, the transition metal sublattice magnetic moment M _TM predominantly acts on the first magnetic film (2) which is a transition metal large amount film at room temperature to generate the magnetization M _S1 . In the second magnetic film (6) which is a rare earth metal large amount film, the rare earth metal sublattice magnetic moment M _RE acts predominantly to generate the magnetization M _S2 opposite to the magnetization M _S1 . At this time, regarding the magnetization distribution, the magnetizations of the magnetic films (2) and (6) are made as small as possible (total), that is, they cancel each other.
And the second magnetic films (2) and (6) are required to be arranged in parallel so that the same sub-lattice magnetic moments M _TM and M _RE are aligned. This can be achieved when the effective magnetic field due to the exchange coupling between the magnetic films (2) and (6) is larger than the static magnetic force of the films (2) and (6).

The period λ (total thickness of the rare earth metal layer and the transition metal layer) of the superlattice structure of the second magnetic film (6) is 5Å to 30Å. If the period λ is smaller than 5Å, the superlattice structure is not formed and the entire film becomes a homogeneous film. If the period λ is larger than 30Å, it becomes polycrystalline and does not become amorphous, so that it cannot be used. The rare earth-transition metal composition of the first and second magnetic films (2) and (6) is such that the rare earth metal is in the range of 10 to 40 at%. When the rare earth metal content is less than 10 at% or more than 40 at%, it becomes polycrystalline and has no perpendicular magnetic film property.

[Action]

Since the second magnetic film (6), which is a rare earth metal large amount film, is formed in a superlattice structure in a microscopic view, the vertical anisotropy of the second magnetic film is increased, and thus the second magnetic film ( The perpendicular anisotropy of the first magnetic film (2), which is a transition metal multi-layer film exchange-coupled to 6), is improved, and as a result, the C / N ratio and frequency characteristics are further improved compared to the above-mentioned two-layer film. To do.

In addition, since it is a two-layer film in which the first magnetic film (2) which is a transition metal abundant film and the second magnetic film (6) which is a rare earth metal abundant film are exchange-coupled macroscopically, as described above. Recording sensitivity and erasing sensitivity are high.

〔Example〕

FIG. 7 shows a schematic configuration of an example of a magnetron sputtering apparatus for forming a rare earth-transition metal magnetic film. This is the axis 0-0 'in the bell jar (not shown).
A base (10) that rotates around the center is provided, and a base (1) that constitutes the magneto-optical recording medium is arranged on the base (10). 180 ° centering on axis 0-0 'facing this base (1)
Two sputter sources (11) and (1
2) is placed. These sputter sources (11) and (12)
A mask (13) for controlling the sputter position of the metal sputtered by the sputter sources (11) and (12) is disposed between the base (10) and the substrate (1). In this example, the sputter source (11) is the transition metal target (14)
And the sputter source (12) comprises a rare earth metal target (15). (16) and (13) show magnets, respectively. For example, as shown in FIG. 8, the mask (13) spreads outward at a portion facing the targets (14) and (15) outward in a straight line x direction passing through the centers of the targets (14) and (15). Y-shaped windows (18) and (1
9) is drilled. In this device, the transition metal target (14) has a DC power source, and the rare earth metal target (1
A high-frequency power source is connected to 5) so that two-way simultaneous sputtering is performed while rotating the substrate (1) together with the base (10). In this case, the DC voltage and DC power are controlled respectively. A rare earth-transition metal based magnetic film having a desired composition is formed by controlling the sputtering rate of.

Comparative Example 1 Using the sputtering apparatus of FIG. 7 (using a Fe ₉₀ Co ₁₀ alloy target as the transition metal target (14) and using a Tb target as the rare earth metal target (15)), rotate the base (10) at 60 rpm. While rotating at a number, on the polycarbonate substrate (1), Tb ₁₈ (Fe ₉₀ Co) with a thickness of 300 Å
₁₀ ) A transition metal abundant film (2) consisting of ₈₂ films is formed, and subsequently, a thickness of 300 is formed on the transition metal abundant film (2) at a rotation speed of 60 rpm.
A rare-earth-metal-rich film (3) made of Å Tb ₂₅ (Fe ₉₀ Co ₁₀ ) ₇₅ film is formed to form a perpendicular magnetization film (4). ) Is created. The transition metal abundant film (2) and the rare earth metal abundant film (3) produced under these conditions were both small angle X-ray diffraction results,
It was not a periodic structure.

And, for this magneto-optical disk (5), 1800rp
C / N ratio and frequency characteristics were measured by rotating at m, recording with 4.0 mW laser light, and reading with 1.5 mW laser light. The result is shown in the curve (I) of FIG. The laser light was applied from the substrate (1) side.

Example 1 The same sputtering apparatus as in Comparative Example 1 was used, and the base (1
0) rotating at 60 rpm, a transition metal abundant film (2) consisting of a 300 Å Tb ₁₈ (Fe ₉₀ Co ₁₀ ) ₈₂ film with a thickness of 300 Å is formed on the polycarbonate substrate (1), and subsequently, the base The rotation speed of (10) was set to 20 rpm, and a rare earth metal bulk film (6) of Tb ₂₅ (Fe ₉₀ Co ₁₀ ) ₇₅ with a thickness of 300 Å was formed on the transition metal bulk film (2) to form a perpendicular magnetization film (7). ) Forming the first
A magneto-optical recording medium shown in the figure, that is, a magneto-optical disk (8) is prepared. As a result of small-angle x-ray diffraction, the rare-earth metal multi-layer film (6) formed under these conditions has a superlattice structure with alternating FeCo layers (21) and Tb layers (22) with a period λ of 6Å. It was confirmed. Then, this magneto-optical disk (8) was evaluated in the same manner as in Comparative Example 1. The result is shown in the curve (II) of FIG.

Comparative Example 2 Using the sputtering apparatus of FIG. 7 (using a Co target as the transition metal target (14) and a Tb target as the rare earth metal target (15)), rotate the base (10) at a rotation speed of 60 rpm. On the other hand, a transition metal abundance film (31) made of a Tb ₁₉ Co ₂₁ film having a thickness of 300 Å is formed on the polycarbonate substrate (1), and then the rotation speed is 60 rpm at a speed of 60 rpm on the transition metal abundance film (31). 300Å Tb ₂₂ Co ²¹
A magneto-optical disk (34) shown in FIG. 4 is formed by forming a rare earth metal large amount film (32) made of a film to form a perpendicular magnetization film (33).
Create Transition metal abundant film prepared under these conditions (31)
Neither the or the rare earth metal multi-layer film (32) was a periodic structure as a result of small-angle x-ray diffraction.

Then, Comparative Example 1 was applied to this magneto-optical disk (34).
The same evaluation as was done. The result is shown in Fig. 6 (II
I).

Example 2 The same sputtering apparatus as in Comparative Example 2 was used, and the base (1
0) rotating at 60 rpm while forming a transition metal abundant film (31) made of Tb ₁₉ Co ₂₁ film having a thickness of 300 Å on the polycarbonate substrate (1), and then continuously rotating the base (10). At a rate of 20 rpm and a thickness of 300 Å on the transition metal mass film (31).
A magneto-optical disk (37) is prepared by forming a rare earth metal large amount film (35) made of a Tb ₂₂ Co ²¹ film and forming a perpendicular magnetization film (36). As a result of small-angle x-ray diffraction, it was confirmed that the rare earth metal multi-layer film (36) formed under these conditions had a superlattice structure in which Co layers (38) and Tb layers (39) were alternately laminated. .

Then, this magneto-optical disk (37) was evaluated in the same manner as in Comparative Example 1. The results are shown in the curve (I
V).

As is clear from FIGS. 5 and 6, the magneto-optical disks (8) and (37) of the present invention in which a transition metal multi-layer film and a rare earth metal multi-layer film are laminated and the rare earth metal multi-layer film has a superlattice structure. In some cases, a magneto-optical disk of a comparative example (5) having a two-layer film of a simple transition metal multi-layer film and a rare earth metal multi-layer film.
Compared with (34) and (34), a high C / N ratio is obtained and the frequency characteristic is improved.

In the above example, only the rare earth metal large amount film has the superlattice structure, but both the transition metal large amount film and the rare earth metal large amount film may have the superlattice structure.

〔The invention's effect〕

According to the magneto-optical recording medium of the present invention, the first rare earth-transition metal based magnetic film in which the transition metal sublattice magnetic moments predominantly exchange-coupled with each other and the second rare earth-transition in which the rare earth sublattice magnetic moment predominates are used. By having a perpendicular magnetization film laminated with a metal-based magnetic film, the recording sensitivity and the erasing sensitivity are improved, and at the same time, at least the second rare earth-transition metal-based magnetic film has a superlattice structure so that C /
The N ratio and the frequency characteristic can be further improved.

[Brief description of drawings]

1 is a sectional view showing an example of a magneto-optical recording medium according to the present invention, FIG. 2 is a sectional view showing an example of a magneto-optical recording medium for comparison, and FIG. 3 is another example of the magneto-optical recording medium according to the present invention. FIG. 4 is a cross-sectional view showing another example of a magneto-optical recording medium for comparison, and FIG. 5 is a C / N ratio of the magneto-optical recording medium of FIGS. 1 and 2. Graph showing frequency characteristics, No. 6
FIG. 7 is a graph showing the C / N ratio and frequency characteristics of the magneto-optical recording medium of FIGS. 3 and 4, FIG. 7 is a block diagram showing an example of a sputtering apparatus, and FIG. It is a top view of a part. (1) is a substrate, (2) is a first rare earth-transition metal magnetic film, and (6) is a second rare earth-transition metal magnetic film having a superlattice structure.

Claims (1)

(57) [Claims] 1. A first rare earth-transition metal magnetic film having a dominant transition metal sublattice magnetic moment on a substrate, and a rare earth sublattice magnetic moment exchange-coupled to the first rare earth-transition metal magnetic film. A dominant second rare earth-transition metal magnetic film is laminated, and the second rare earth-transition metal magnetic film is formed by alternately laminating a rare earth metal and a transition metal in a superlattice structure. Medium.