JPH0660452A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain large Kerr rotation angle in a short wavelength region and to increase perpendicular anisotropy by alternately depositing rare earth- transition metal amorphous alloy layers essentially containing light rare earth elements and alloy layers containing heavy rare earth elements to form a magnetic layer. CONSTITUTION:A magnetic layer 3 comprising multilayered film is formed on a substrate. The magnetic layer 3 consists of alternately deposited rare earth transition metal amorphous alloy layers 6, 7 as the rare earth elements. The alloy layers 6 essentially contain light rare earth elements, and the layers 7 contain heavy rare earth elements. A UV-curing resin is applied on the magnetic layer 3 of the substrate 1 for protective coating to obtain the recording medium. The obtd. medium has large perpendicular anisotropy and the alloy films 6, 7, like light rare earth-transition metal alloy films, show no decrease in Kerr rotation angle in a short wavelength region so that the medium is suitable for high-density recording with short wavelength laser light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium for recording, reproducing and erasing information by using laser light.

[0002]

2. Description of the Related Art Conventionally, information is recorded by forming a magnetic domain magnetized in the direction perpendicular to the film surface of a magnetic thin film by heat from a laser beam and an external magnetic field. The magneto-optical recording method for reproducing information by utilizing the effect has been put into practical use as a highly reliable high-density information recording method in which recording and erasing can be repeated. Many kinds of magnetic alloys have been proposed as a magnetic film used for recording in this magneto-optical recording medium, but mainly transition metals such as Fe and Co and heavy rare earth metals such as Tb, Dy and Gd are mainly used. The amorphous alloy thin film described above has a Curie temperature within a range suitable for recording by a semiconductor laser, does not cause grain boundary noise during reproduction because it is amorphous, and can be easily perpendicularly magnetized by a method such as sputtering. Is most often used for the reason that it can form a magnetic field and can obtain a relatively large magnetic-optical Kerr effect.

At present, higher recording density is being studied for magneto-optical disks. As one method,
Shortening the wavelength of semiconductor lasers used for recording and reproduction is under study. That is, when the wavelength of the recording light source is shortened, the objective lens can focus the beam to a smaller beam spot diameter, and more information can be recorded per unit area. For this purpose, it is necessary to develop a short-wavelength semiconductor laser, but at the same time, it is also necessary to develop a magneto-optical recording film compatible with the short-wavelength semiconductor laser. The commonly used heavy rare earth-transition metal amorphous alloy thin film has a sufficient Kerr effect for laser light in the near-infrared wavelength region, but the Kerr effect decreases as the wavelength decreases. However, there is a problem that a sufficient reproduction signal cannot be obtained. On the other hand, it is known that the light rare earth-transition metal amorphous alloy can obtain a sufficiently large Kerr effect even in the wavelength region where the Kerr effect is reduced in the heavy rare earth-transition metal amorphous alloy thin film, as described above. However, since the easy axis of magnetization is in the film plane and perpendicular magnetic anisotropy cannot be obtained, it is not suitable for magneto-optical recording as it is.

[0004]

As one of the methods for forming this light rare earth-transition metal amorphous alloy thin film as a perpendicular magnetization film, a method of adding heavy rare earth such as Dy or Tb is known. However, in order to use this as a perpendicular magnetization film, heavy rare earths more than the content of light rare earths are required, and as a result, the Kerr effect in the short wavelength region is reduced.

As another method for obtaining a perpendicular magnetization film while maintaining the high Kerr effect in the short wavelength region possessed by the above light rare earth-transition metal amorphous alloy thin film, for example, Japanese Patent Application Laid-Open No. 3-1.
As described in JP-A-08144, a light rare earth-transition metal amorphous alloy thin film is formed by stacking a heavy rare earth-transition metal amorphous alloy thin film having vertical anisotropy and utilizing magnetic exchange interaction. A method of using a perpendicular magnetization film has been proposed. However, in the case of this method, if the thickness of the heavy rare earth-transition metal layer is not sufficiently thick, the perpendicular magnetic anisotropy of the light rare earth-transition metal layer is not sufficient and the coercive force in the vertical direction is small, so that the light rare earth -When high density recording is performed on the transition metal layer with a short wavelength laser, fine magnetic domains having a good shape cannot be obtained, and as a result, a high CN ratio cannot be obtained. Conversely, in order to obtain a large vertical anisotropy, the light rare earth-transition metal layer must be thin and the heavy rare earth-transition metal layer must be thick,
As a result, the Kerr rotation angle decreases as the wavelength becomes shorter.

An object of the present invention is to provide a magneto-optical recording medium having a magnetic layer which exhibits a large Kerr rotation angle on the short wavelength side and a large vertical anisotropy.

[0007]

In order to solve the above-mentioned problems, the present invention forms a magnetic layer composed of a multilayer film on a substrate, and the magnetic layer mainly contains a light rare earth element as a rare earth element. A magneto-optical recording medium, wherein the first rare earth-transition metal amorphous alloy layer and the second rare earth-transition metal amorphous alloy layer mainly containing heavy rare earth are alternately laminated. I will provide a.

According to the magneto-optical recording medium of the present invention, each light rare earth-transition metal alloy layer is subjected to exchange interaction from the adjacent heavy rare earth-transition metal alloy layer, so that a perpendicular magnetic field sufficient for magneto-optical recording is obtained. A magnetic material film having a directionality can be obtained. In addition, if the first alloy layer and the second alloy layer have the same thickness, the ratio of the light rare earth element to the heavy rare earth element can be increased, so that a large Kerr effect can be obtained at a short wavelength. it can.

As described above, in order to achieve the object of the present invention of simultaneously satisfying both the large vertical anisotropy and the large Kerr effect at short wavelength, the total thickness of the first alloy layer and the It is preferable that the total thickness of the two alloy layers is about the same. Specifically, assuming that the total thickness of the first magnetic layer is T ₁ and the total thickness of the second magnetic layer is T ₂ , the ratio of these thicknesses (T ₁ / T ₂ ). Is preferably 0.8 or more and 1.2 or less.

On the other hand, in order for the magnetic layer of the present invention to have an easy axis of magnetization in the above thickness in the direction perpendicular to the film surface, the first rare earth-transition metal amorphous layers alternately laminated. The thickness of each of the alloy layer and the second rare earth-transition metal amorphous alloy layer is preferably in the range of 1 nm to 5 nm. If this range is exceeded, the direction of the easy axis of magnetization of the first alloy layer will not be perpendicular to the film surface due to exchange interaction with the second alloy layer, and the coercive force of the entire magnetic film will be small. . On the other hand, if the thickness is smaller than this range, the vertical anisotropy of the second rare earth-transition metal amorphous alloy layer is small, and similarly the magnetic film as a whole cannot have sufficient vertical anisotropy.

In the present invention, the first rare earth-transition metal amorphous alloy layer contains at least one element selected from the group consisting of Fe and Co as a transition metal element and Nd and Pr as a light rare earth element. It is characterized by containing at least one element selected from the county. In addition, Gd, for the purpose of controlling magnetic properties such as perpendicular anisotropy and Curie temperature,
Heavy rare earth elements such as Dy and Tb may be added, but from the viewpoint of the Kerr effect at a short wavelength, it is preferable that the composition ratio of the light rare earth elements is not exceeded.

On the other hand, the second rare earth-transition metal amorphous alloy layer, like the first rare earth-transition metal amorphous alloy layer, is one selected from the group consisting of at least Fe and Co as transition metal elements. The element is characterized by containing at least one element selected from the group consisting of Dy and Tb as a heavy rare earth element.

In order to improve the oxidation resistance of the magnetic layer, the first and second rare earth-transition metal amorphous alloy layers described above are added.
A metal such as Ti, Cr, Zi, Pt, Nb or Ta may be added in an amount of 10% or less in terms of atomic number.

In the present invention, a magnetic layer is formed by alternately stacking a first rare earth-transition metal amorphous alloy layer and a second rare earth-transition metal amorphous alloy layer on a substrate. Although it may be used as a magneto-optical recording medium by just doing, for the purpose of amplifying the Kerr rotation angle and further obtaining good recording / reproducing characteristics, or for preventing deterioration of recording / reproducing characteristics due to oxidation of the magnetic layer, A structure in which a dielectric layer is provided on one side or both sides of the magnetic layer, and further, the recording sensitivity is adjusted,
A structure may be used in which a heat conductive layer that also serves as a reflective layer is provided in order to improve the durability against repeated recording and erasing. in this case,
It is preferable that the thickness of the entire magnetic film formed of the laminated first magnetic layer and the second magnetic layer be 40 nm or less, and that the light be transmitted. This is because the laser light used for recording and reproduction reaches all the layers in the thickness direction of the magnetic layer composed of the alternately laminated film, and as a result, the effect of the present invention can be sufficiently obtained, and the reflectivity and car A magneto-optical recording medium having a large rotation angle can be obtained. Examples of the dielectric layer described above are oxides and nitrides of Si, Al and the like, and examples of transparent thin films having a relatively large refractive index, a reflective layer, and a heat conduction layer are Al and Al alloys, An example of the metal film is Cu or the like, which has a large reflectance and a relatively large thermal conductivity.

[0015]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples.

(Embodiment 1) FIG. 1 is a cross-sectional view showing an example of a magneto-optical recording medium according to this embodiment. As shown in this drawing, the recording medium of this embodiment is formed on a transparent substrate. , A first dielectric layer, a magnetic layer, a second dielectric layer, and a reflective layer are sequentially laminated in the thickness direction. Here, the magnetic layer is the first
Of the rare earth-transition metal alloy layer and the second rare earth-transition metal alloy layer.

The magneto-optical recording medium of this embodiment has a diameter of 86 mm and a thickness of 1.
It was produced by successively forming each layer on a 2 mm polycarbonate substrate by a magnetron sputtering method without breaking the vacuum. In the sputtering chamber of the sputtering apparatus used here, there were cathodes to which four targets were attached, and the substrate was attached to a substrate holder that revolves around its axis while passing over each target.

As a film forming method, first, the first dielectric layer was formed. Here, using a Si target,
A SiN film having a thickness of 100 nm and a refractive index of 2.0 was formed by an RF sputtering method using Ar mixed with N ₂ as a sputtering gas.

Subsequently, a magnetic layer was formed on the first dielectric layer previously formed as follows. here,
NdCo and Tb mounted on separate DC cathodes that are partitioned so that the respective discharge plasmas do not mix
Voltages were applied to the FeCo alloy targets from different DC power supplies. During the film formation, the discharge current of each target, the revolution speed of the substrate holder, and the number of times were adjusted, and a total of 5 layers of Nd ₅₀ Co ₅₀ film and Tb ₂₁ Fe ₇₀ Co ₉ film each having a thickness of 3 nm were measured. A 30 nm magnetic layer was formed.

Then, using a Si target again as the second dielectric layer, a 20 nm S-doped layer is formed in the same manner as the first dielectric layer.
The iN film was laminated.

Finally, a 50 nm Al ₉₈ Ti ₂ film was formed by DC sputtering using an AlTi alloy target as the reflective layer.

A recording medium was prepared by coating the surface of the substrate on which the magnetic layer was formed as described above, on which the magnetic layer was formed, with a protective coating of an ultraviolet curable resin. The reflectance at a wavelength of 830 nm of this recording medium was 21%, and the Kerr rotation angle was 0.9 deg.

FIG. 2 shows the Kerr hysteresis loop of only the above magnetic layer. A light source with a wavelength of 830 nm was used for the measurement of this Kerr hysteresis loop. From the results shown in FIG. 2, it can be understood that the magnetic layer of this example can provide a perpendicular magnetization film having a large coercive force, good squareness, and a large Kerr rotation angle.

FIG. 3 shows the results of measuring the wavelength dependence of the Kerr rotation angle for the same sample. From FIG. 3, it can be understood that the magnetic layer of this example maintains a large Kerr rotation angle even when the wavelength of incident light is shortened, and is suitable for magneto-optical recording by light of short wavelength.

Next, recording and reproducing experiments were conducted using the above recording medium. When a 488.0 nm argon laser was used as the laser beam and a magnetic domain of 0.5 μm was recorded, a C / N of 47 dB was obtained. From this result, it can be understood that the recording medium of this example is suitable as a high density recording medium using a short wavelength laser.

Comparative Example 1 A Tb ₂₁ Fe ₇₀ Co ₉ film used for the magnetic layer of Example 1 was formed on a substrate. The wavelength dependence of the Kerr rotation angle of this thin film is shown in FIG.

From FIG. 3, in the thin film of this comparative example, the Kerr rotation angle decreases as the wavelength of the incident light becomes shorter. Therefore, when recording is performed with the short wavelength laser light as described above, It can be understood that such a high C / N cannot be expected.

(Embodiment 2) In the same manner as in Embodiment 1,
A magnetic film was formed on the substrate by an alternating laminated film of Nd ₅₀ Co ₅₀ layers and Tb ₂₁ Fe ₇₀ Co ₉ layers. At this time, the total thickness of the magnetic layer was kept constant at 30 nm, and the thicknesses of the Nd ₅₀ Co ₅₀ layers and the Tb ₂₁ Fe ₇₀ Co ₉ layers were changed. The relationship between the film thickness of each layer and the coercive force in this case is shown in FIG.

From these results, the thickness of each layer is 1 nm or more, 5
A high coercive force is obtained in the range of nm or less, and it can be understood from the magnetic torque measurement that the perpendicular anisotropy is obtained in this range.

(Embodiment 3) P having a thickness of 3 nm is formed on a substrate.
R ₅₀ Co ₅₀ and Dy ₂₃ Fe ₆₅ Co ₁₂ were alternately laminated and the Kerr hysteresis loop was measured. As a result, a Kerr hysteresis loop with good squareness was obtained, the coercive force was 5 kOe, and the Kerr rotation angle was 0.38 deg. Further, when the wavelength dependence of the Kerr rotation angle was measured, a high θ _K was obtained even at a short wavelength as in Example 1. Further, as a result of torque measurement, it can be understood that this disk has vertical anisotropy, and like the disk of Example 1, it is suitable for high density recording by a short wavelength laser beam.

(Embodiment 4) In the same manner as in Embodiment 1,
A magnetic film was formed on the substrate by an alternating laminated film of Nd ₅₀ Co ₅₀ layers and Tb ₂₁ Fe ₇₀ Co ₉ layers. At this time, the total thickness of the magnetic film is 30 nm and the number of layers of the alternately laminated film is constant, and then the first magnetic layer Nd ₅₀ Co ₅₀ and the second magnetic layer Tb ₂₁ Fe are formed. By changing the thickness of each of the ₇₀ Co ₉ layers, the ratio (T ₁ / T ₂ ) of the total thickness T ₁ of the first magnetic body layer and the total thickness T ₂ of the second magnetic body layer is calculated. Changed. Changes in coercive force and Kerr rotation angle at a wavelength of 500 nm with respect to T ₁ / T ₂ are shown in FIG.

From the results shown in FIG. 5, T ₁ / T ₂ is 0.8
It can be understood that a high coercive force and a Kerr rotation angle can be satisfied at the same time in the range from 1 to 1.2.

[0033]

According to the magneto-optical recording medium of the present invention, the magnetic layer has vertical anisotropy like the conventional heavy rare earth-transition metal amorphous alloy film, and the light rare earth-transition metal alloy film. In the same way as in the short wavelength region, the Kerr rotation angle does not decrease,
It is suitable for high density recording with short wavelength laser light.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a layer structure of a magnetic layer according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 First dielectric layer 3 Magnetic layer 4 Second dielectric layer 5 Reflective layer 6 First rare earth-transition metal amorphous alloy layer 7 Second rare earth-transition metal amorphous alloy layer

FIG. 2 is a chart showing a Kerr hysteresis loop of the magnetic film of the present invention in Example 1.

FIG. 3 is a table showing wavelength dependence of Kerr rotation angles of magnetic films in Example 1 and Comparative Example 1.

FIG. 4 is a table showing a change in coercive force with respect to each film thickness of rare earth-transition metal alloy layers that are alternately laminated in the magnetic film of Example 3.

FIG. 5 is a chart showing the relationship between the ratio of the total sum of the second magnetic layer to the total sum of the first magnetic layer, the coercive force, and the Kerr rotation angle at a wavelength of 500 nm in the magnetic film of Example 5. Is.

Claims (4)

[Claims] 1. A magnetic material layer formed of a multilayer film is formed on a substrate, and the magnetic material layer and a first rare earth-transition metal amorphous alloy layer mainly containing light rare earth as a rare earth element. A magneto-optical recording medium, characterized in that second rare earth-transition metal amorphous alloy layers mainly containing rare earth are alternately laminated. 2. The thickness of each of the first rare earth-transition metal amorphous alloy layer and the second rare earth-transition metal amorphous alloy layer is 1.
The magneto-optical recording medium according to claim 1, wherein the magneto-optical recording medium has a thickness of not less than 5 nm and not more than 5 nm. Wherein the sum T ₁ of the thickness of the first magnetic layer, a second sum T ₂ Togashiki Equation 1] of the thickness of the magnetic layer 0.8 ≦ T ₁ / T ₂ ≦ 2. The magneto-optical recording medium according to claim 1, which has a relationship represented by 1.2. 4. The light rare earth element contained in the first magnetic layer is at least one element selected from the group consisting of Nd and Pr, and the heavy rare earth element contained in the second magnetic layer is Tb. And Dy, and the transition metal element contained in the first and second magnetic layers is at least one element selected from the group consisting of Fe and Co. The magneto-optical recording medium according to claim 1.