JPH04142007A - magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To increase the Kerr rotation angle against readout light having a short wavelength and improve the S/N at the time of reproducing information by forming a recording layer by alternately piling up thin films of an alloy of rare earth metals and transition metals and thin films of an element having an absorption end at in a wavelength region of 100-1000nm. CONSTITUTION:This magnetic recording layer is formed by alternately piling up two or more first thin film layers 21-2n having a composition expressed by RxT1-x and two or more second thin film layers 31-3n having a composition expressed by NyM1-y to satisfy Expressions I and II (where, the R, T, M, and N respectively represents one or more elements selected out of Gd, Tb, Dy, Ho, and Nd, Fe, Co, and Ni, Ze, Nb, In, Sn, Sb, Ta, and W, and one or more elements other than the elements represented by the R, T, and M having an absorption end in a wavelength range of 100-1,000nm when the elements are formed to a thin film). Therefore, a large Kerr rotation angle can be obtained against light having a short wave-length and information reproduction can be performed at a high S/N.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical recording medium used in a magneto-optical recording/reproducing device constituting a large capacity memory, electronic file system, etc.

[Prior Art] Magneto-optical recording media can record information at high density, and
In recent years, there has been active development as a rewritable medium. Examples of such media include, for example, JP-A-58-7
As described in No. 3746, those equipped with a magnetic recording layer made of a rare earth-transition metal amorphous alloy thin film are often used.

The magneto-optical recording medium irradiates a light beam whose intensity is modulated according to information without applying a magnetic field in a fixed direction, or irradiates a magnetic field whose intensity is modulated according to information without continuously irradiating a light beam. Information is recorded as a change in the magnetization direction by a method such as applying an electric current. Further, the information recorded in this manner is reproduced by irradiating the medium with a linearly polarized light beam focused into a spot, and receiving the reflected light by a photodetector through an analyzer. This is because the polarization direction of the reflected light rotates in opposite directions depending on the magnetization direction of the magnetic recording layer due to the magneto-optic Kerr effect, and by passing it through an analyzer, this rotation is converted into a change in light intensity. This is because it can be detected. Therefore, the larger the rotation angle (Kerr rotation angle) due to the Kerr effect that the magnetic recording layer has, the higher the S/N ratio can be to reproduce information.

The recording density of the medium is limited by the spot diameter of the light beam. This is because if the magnetic domain (recorded bits) representing information formed in the recording layer becomes extremely smaller than the beam spot, consecutive recorded bits cannot be identified and read out using this beam spot. Therefore, in order to achieve higher recording density, it is necessary to make the spot diameter of the light beam smaller and smaller.

On the other hand, the spot diameter of the light beam is determined by the effective F number of the objective lens that focuses the beam onto the medium and the wavelength of the light beam, and the shorter the wavelength, the smaller the spot diameter can be. For this reason, the oscillation wavelength is currently 80
Semiconductor lasers are used as light sources with a wavelength of about 0 nm, but light sources that emit light beams with even shorter wavelengths are being actively developed.

[Problems to be Solved by the Invention] However, when a light beam with a shorter wavelength is used as described above, the Kerr rotation angle is There was a problem in that it became smaller. For example, traditional media has 40
The Kerr rotation angle for light in the wavelength range of 0 to 600 nm is
The Kerr rotation angle is 30 to 50% smaller than the Kerr rotation angle for light having a wavelength of 800 nm.

In contrast, Bulletin of the Japan Institute of Metals, Vol. 28, No. 9, No. 717
~722 pages (1989) describes transition metal thin films and C
A phenomenon has been described in which the Kerr rotation angle increases in a periodic structure film in which thin films made of metals such as u, Ag, and Au are alternately laminated.

By further improving the periodic structure film described above, the present invention exhibits a large Kerr rotation angle even for light in a short wavelength range, and S
An object of the present invention is to provide a magneto-optical recording medium capable of reproducing information with a high /N ratio.

Means for Solving Problem C] The above object of the present invention is to provide a magneto-optical recording medium having a magnetic recording layer having an axis of easy magnetization perpendicular to the film surface, in which R is replaced by Gd, Tb, Dy, Ho, One or more elements selected from Nd, T one or more elements selected from Fe, Co, and Ni, M Zr, Nb, In, Sn, Sb, Ta, and W.
one or more elements selected from N, 100 nm −
The magnetic recording layer is a first thin film having a composition represented by RxT, -, where one or more elements other than R, T and M have an absorption edge in the thin film in a wavelength range of 1000 nm. layer and a second thin film layer having a composition represented by N y M , -y are alternately laminated to form two or more layers, respectively, and under the following conditions: 0.15≦X≦03 03≦Y≦ This is achieved by satisfying 1.

[Example] FIG. 1 is a schematic cross-sectional view showing an example of the magneto-optical recording medium of the present invention. In the figure, 1 indicates a transparent substrate made of glass, plastic, or the like. On this substrate 1 is a first thin film layer 2. ．． 22. ...2I, and second thin film layer 3+, 3
i, . . . 3° are alternately stacked.

The first thin film layer has RxT+ −
It is made of a material having a composition represented by x. Here, X is set in the range of 0.15≦X≦0.3.

The second thin film layer has M as Zr, Nb, In, Sn, Sb,
One or more elements selected from Ta, W, N 100
It is made of a material having a composition represented by NvMl-r when one or more elements other than R, T and M have an absorption edge in a thin film in the wavelength range of -1000 nm. Here, Y is set in the range of 0.3≦Y≦1. Elements used as N include, for example, Al, Zn, Au, Ag, Bi, Cr, Mo, and Si.
, Ge, Cu, etc. Table 1 shows the light absorption edges (wavelengths at which changes in reflectance and transmittance occur) of these elements.

Table 1 Each of the first thin film layers is preferably formed to have a thickness of 5 to 50 layers, more preferably 5 to 20 layers. On the other hand, each of the second thin film layers is preferably formed to have a thickness of 1 to 50 layers. However, the thickness of the first thin film layer is 2
In the case of 0 Å or less, the second thin film layer needs to be 1 to 20 thick to maintain magnetic coupling between these first thin film layers.

First thin film layer2. ．． 2. ,...,2. , and the second thin film layers 31.3□, . . . , 3, the total thickness of the magnetic recording layer is preferably 100 to 1000. However, if a reflective layer made of a metal film or the like is provided on the opposite side of the recording layer from the substrate 1, the total film thickness of the recording layer will be 10
Preferably, the number is 0 to 300 people.

The periodic structure (superlattice structure) of the thin film layer as in the present invention is
For example, it can be created using a magnetron sputtering device. Magnetron sputtering equipment is
It has a configuration as shown in FIG. In FIG. 2, a rotating base 11 is provided within the vacuum chamber IO.

A substrate 12 of a recording medium is held on the lower surface of this base 11. At positions facing the base 11, a plurality of sputter sources 13, 14 are provided at equal intervals around the rotation axis of the base. 15 is a mask that restricts the radiation range of the thin film material from the sputtering source. Further, 16 indicates a shutter for controlling radiation from the spuck source, and 17 and 18 indicate magnets.

In the above configuration, without rotating the base 11, the material of the first thin film layer and the material of the second thin film layer are respectively emitted from the sputter source 13.14 and deposited alternately on the substrate 12. .

At this time, the residual gas pressure in the vacuum chamber 10 is 1,0XIO-
'Pa or less, the Ar gas pressure during sputtering is 1 to 5
It is assumed that X10-'Pa. Further, the sputtering source is on the negative electrode side. The target placed in the sputter source is
A variety of single element targets, alloy targets, or combinations thereof can be used to achieve the desired composition of the thin film layer.

More specific examples of the present invention are shown below.

Example 1 Example 2 Using a sputtering apparatus as shown in the second figure, the first
A magneto-optical recording medium as shown in the figure was fabricated. As the substrate 1, a polycarbonate disk plate in which preformat signals and guide grooves were carved in advance was used. The sputter source 13 includes Tbo, asFeo, and Tbo for forming the first thin film layer.
6GO0,18 was used, and Ag forming the second thin film layer was used as the sputtering source 14.

The thickness of the first thin film layer is 5 people each, and the thickness of the second thin film layer is 4 people each, and these thin film layers are arranged so that the total thickness of the recording layer is about 6 people.
00 people were stacked alternately. The easy axis of magnetization of the formed recording layer was perpendicular to the film surface. Furthermore, a protective layer made of 513N4 was formed on this recording layer to a thickness of 400 mm.

Using the same equipment as in Example 1, a sputtering source 1314 was sputtered at the same time on the same substrate as in Example 1.
, zsFeo, 5coo, +a]s A single film of Ag4 was formed. The thickness of this film was 600 people.

Furthermore, the sputtering speed during film formation was 5 persons/sec for the sputtering source 13 and 4 persons/sec for the sputtering source 14. A protective layer of 5131N4 was formed over this membrane to a thickness of 400 nm.

In the same apparatus as in Example 1, using only the sputter source 13, a 600-thick monolayer Tk)o, aJeo, 5cOo, +s film was deposited on the same substrate as in Example 1. Formed. A protective layer made of Si3N4 was then formed on top of this film to a thickness of 400 mm.

The wavelength dependence of the Kerr rotation angle in Example 1, Comparative Example 1, and Comparative Example 2 was measured through the substrate. This result is the third
As shown in the figure. In Figure 3, the horizontal axis is the wavelength of the readout light;
The vertical axis indicates the Kerr rotation angle at that wavelength.

The following can be seen from Figure 3. Example 1 is Comparative Example 2
Compared to the above, an increase in the Kerr rotation angle is observed in the wavelength range around 400 to 600 nm. This is an Ag film (second thin film layer) whose absorption edge wavelength is around 550 nm.
This is thought to be due to the effect of On the other hand, Comparative Example 1 has a lower Kerr rotation angle than both Example 1 and Comparative Example 2. This is thought to be because Ag dispersed in TbFeCo dilutes the magnetism of this film.

Examples 2-1 to 2-11 Magneto-optical recording with a periodic structure film in the same manner as in Example 1 by varying the materials of the first thin film layer and the second thin film layer as shown in Table 2. A medium was prepared. The easy magnetization axes of the formed recording layers were all perpendicular to the film surface.

Comparative Examples 3-1 and 3-2 In the same manner as Comparative Example 2, Dyo, 2□F
Comparative Example 3-1 was prepared by forming a single layer film of eo, ascOo, +aCro, 02, and further forming a protective layer. Similarly, Gdo, +zTbo, tJeo, gc
Comparative Example 3-2 having a single layer film of Oo, +a was produced.

Ar in Examples 1 to 2-11 and Comparative Examples 1 to 3-2 above
Table 2 shows the respective figures of merit for the gas laser (wavelength: 488 nm) and the He-Ne laser (wavelength: 633 nm). Here, the figure of merit indicates the magnitude of the magneto-optic effect at that wavelength, and in Table 2, the figure of merit of each side is expressed as a ratio with the figure of merit of Comparative Example 2 as 1.

Figures of merit were measured using a device such as Section 4. In FIG. 4, the laser beam emitted from the gas laser 21 is
The sample 23 is irradiated through the polarizer 22. The light reflected by the sample 23 passes through an analyzer 24 and is detected by a power meter 25. The measurement was performed in the following process. First, sample 23 was magnetized in one direction using an electromagnet (not shown). Next, while the sample 23 was irradiated with laser light, the transmission axes of the polarizer 22 and the analyzer 24 were adjusted to bring it into an extinction state. Next, sample 23
were magnetized in opposite directions by an electromagnet, and the amount of light incident on the power meter 25 was measured without changing the transmission axis directions of the polarizer 22 and analyzer 24. This measured value is approximately proportional to the reflectance of the sample and the Kerr rotation angle, and is an index indicating the performance of the magneto-optical recording medium. For example, Comparative Example 2 with reference value
The measured light amount is 600uW at a wavelength of 488 nm,
It was 480uW at a wavelength of 633nm.

In Table 2, Examples 2-1 to 2-4 and Comparative Example 3-1,
Comparing Example 2-5 and Comparative Example 3-2, it can be seen that by using a periodic structure film such as that of the present invention, the magneto-optic effect for short wavelength light is increased.

In the present invention, the element represented by N in the second thin film layer is replaced with an element having an absorption edge in the thin film in a wavelength range shorter than 500 nm (for example, A1, Zn, Mo, Si, Ge, etc.).
When alloyed with an element (for example, Au, Ag, Bi, Cr, Cu, etc.) that has an absorption edge in a thin film in a wavelength range longer than 500 nm, it is possible to obtain a medium that exhibits a large Kerr rotation angle at a desired wavelength. I can do it. This is because the absorption edge of the second thin film layer can be adjusted to a desired value by changing the composition of the alloy. An example of this will be explained below.

Examples 3-1 to 3-4 Magneto-optical recording media were produced in the same manner as in Example 1. At this time, one of the sputtering sources is Gd0°5Dyo1. which forms the first thin film layer. -Feo, 55co
Zn and Au forming the second thin film layer were used as the other sputtering source. The composition ratio of Zn and Au was varied for each example as shown in Table 3.

The thickness of the first thin film layer was 15 people each, and the thickness of the second thin film layer was 4 people each, and these thin film layers were stacked alternately so that the total thickness of the recording layer was about 600 people. did. The easy magnetization axes of the formed recording layers were all perpendicular to the film surface. Furthermore, a protective layer made of Si3N4 was formed on this recording layer to a thickness of 400 mm.

The absorption edge wavelength of each example varied as shown in Table 3.

Table 3 Comparative Example 4 In the same apparatus as Examples 3-1 to 3-4, a 600-nm thick monolayer of Gdo , oaDyo, +
5Feo, e5coo, and ts films were formed. A protective layer made of SiJ+ was then formed on this film to a thickness of 400 mm.

The wavelength dependence of the Kerr rotation angle in Examples 3-1 to 3-4 and Comparative Example 4 was measured through the substrate. The results are shown in FIG. In FIG. 5, the horizontal axis shows the wavelength of the readout light, and the vertical axis shows the Kerr rotation angle at that wavelength.

As can be seen from FIG. 5, by using the periodic structure of the present invention, the Kerr rotation angle at short wavelengths can be increased compared to a conventional medium using a single-layer magnetic film. Furthermore, in the configuration of the present invention, by making the second thin film layer an alloy and changing its composition, the wavelength dependence of the Kerr rotation angle can be adjusted to a desired value.

In the present invention, the second thin film layer is made of an element (for example, Mo) that improves corrosion resistance and heat resistance among the elements represented by N.
), it is possible to realize a magneto-optical recording medium with even better information storage stability. An example of this will be explained below.

As mentioned above, in the present invention, the composition of the second thin film layer is represented by N, M, -Y, and the element represented by M improves the corrosion resistance and heat resistance of the medium. It is something that makes you An example of this will be explained below.

115A Using a sputtering apparatus as shown in the second figure, the first
We created a magneto-optical recording medium similar to the above. As the substrate 1, a polycarbonate disk plate in which preformat signals and guide grooves were carved in advance was used. The sputtering source 13 is Tbo2Feo, tc, which forms the first thin film layer.
o. 1, and MoCu, which forms the second thin film layer, was used as the sputtering source 14.

The thickness of the first thin film layer is 10 people each, and the thickness of the second thin film layer is 4 people each, and these thin film layers are stacked alternately so that the total thickness of the recording layer is about 1000 people. did. The easy axis of the formed recording layer was perpendicular to the film surface. Furthermore,
A protective layer made of Si3N was formed on this recording layer to a thickness of 600 mm.

A recording medium having a magnetic recording layer with a periodic structure was produced in the same manner as in Example 4, except that Cu was used as the sputtering source 14.

The thickness of the first thin film layer is 50 people each, and the thickness of the second thin film layer is 8 people each, and these thin film layers are stacked alternately so that the total thickness of the recording layer is about 1000 people. did. A protective layer of 5IJ4 was formed over this membrane to a thickness of 600 mm.

Using the same equipment as in Example 4, sputtering sources 13 and 14 were used to simultaneously sputter and deposit tTb on the same substrate as in Example 4.
A single film of MoCu was formed. The thickness of this film was 1000 people. In addition, the sputtering speed during film formation was 12 for sputtering #i13.
5 people/sec, and the sputtering source 14 was set to 2 people/see.

A protective layer of Si3N was formed on this film to a thickness of 600 nm.

In the same apparatus as in Example 4, a single layer of Tbo, Jeo, 7COO, III with a thickness of 1000 layers was formed on the same substrate as in Example 4 using only the sputter source 13. A protective layer made of Si3N4 was then formed on top of this film to a thickness of 600 mm.

The wavelength dependence of the Kerr rotation angle of Example 4, Example 5, Comparative Example 5, and Comparative Example 6 was measured through the substrate. The results are shown in FIG. In FIG. 5, the horizontal axis shows the wavelength of the readout light, and the vertical axis shows the Kerr rotation angle at that wavelength.

The following can be seen from FIG. In Examples 4 and 5, when compared with Comparative Example 6, the Kerr rotation angle is increased over the wavelength range of 400 to 7 (In nm).
This is thought to be due to the effect of Cu, whose absorption edge wavelength is around 550 nm. On the other hand, in Comparative Example 5, the Cu element is mixed in the TbFeCo layer, and unlike Examples 4 and 5, the Kerr rotation angle does not increase, and exhibits characteristics similar to Comparative Example 6.

Next, the coercive force and saturation magnetization of the sample were measured. After leaving these samples in an oven heated to 1°C for 50 hours, the coercive force and saturation magnetization were measured again. The results of this measurement are shown in Table 4. In Table 4,
The unit of coercive force is KOe, and the unit of saturation magnetization is emu/cc.
It is.

Table 4 Table 4 shows that using an alloy containing O as the material for the second thin film layer has the effect of improving the corrosion resistance and heat resistance of the medium.

In the present invention, other elements than the element represented by N may be added to the second thin film layer. For example, when the composition of the second thin film layer is N and M, Zr, Nb, In, Sn, Sb, Ta, and W can be used as the element represented by M. These elements improve corrosion resistance and heat resistance. An example of this will be explained below.

Examples 6-1 to 6-12 Various magneto-optical materials as shown in Table 5 were prepared using the same method and configuration as in Example 4, except that the materials and film thicknesses of the first and second thin film layers were changed. A recording medium was produced. The easy axis of magnetization of the formed recording layer was perpendicular to the film surface.

Comparative Examples 7-1 and 7-2 Magneto-optical recording media were produced using the same method and configuration as Comparative Example 6, except that the material of the magnetic film was different.

After measuring the coercive force and figure of merit of the samples of Examples 6-1 to 6-12 and Comparative Examples 6 to 7-2, these samples were placed in an oven heated to 100'C for 50 minutes.
After leaving it for a while, the coercive force and figure of merit were measured again. The results are shown in Table 5. Here, the measurement of figure of merit is
The same method as described in Example 1 was used.

Furthermore, the performance index was expressed as a ratio with the performance index of Comparative Example 6 as 1.

Table 5 shows that adding the element represented by M to the second thin film layer has the effect of further improving the corrosion resistance and heat resistance of the medium.

\J The present invention can be applied in various ways in addition to the embodiments described above. For example, as mentioned above, a reflective layer may be provided on the opposite side of the recording layer from the substrate, or a Si3N layer may be provided between the recording layer and the substrate.
A protective layer made of a dielectric material such as , etc. may be provided. Further, the above R1T is applied to the first thin film layer and/or the second thin film layer.
, N and M may be added. However, in this case, the additive element should be added at a concentration of 30 atmi to the overall composition so as not to impair the properties of the thin film layer.
It is preferable that it be less than c%.

[Effects of the Invention] As explained above, the present invention provides a recording layer of a magneto-optical recording medium including a thin film made of a rare earth-transition metal alloy,
Since it is formed by alternately stacking thin films made of elements having an absorption edge at a wavelength of 1000 nm, it increases the Kerr rotation angle for short wavelength readout light and has the effect of improving the S/N ratio in information reproduction. Obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing an embodiment of the magneto-optical recording medium of the present invention, FIG. 2 is a schematic diagram of a fence showing an apparatus for producing the medium of the present invention, and FIG. 3 is an embodiment of the present invention. FIG. 4 is a schematic diagram showing an apparatus for measuring the figure of merit of a magneto-optical recording medium, and FIGS. 5 and 6 show other embodiments of the present invention, respectively. FIG. 3 is a diagram showing the wavelength dependence of the Kerr rotation angle in FIG. l... Transparent substrate 2, . 22. ...l 2n... first thin film layer 31,
3 □,..., 3o... Second thin film layer Fig. 2 Fig. 3 Wavelength (nm) Fig. 5 1 To Example 3-1 1 μ-← Example 3-2 Fish 4 (Xl Nuphant) ■Illusion 1X1 Warp Shingen Wavelength (nm) Figure 6 Implementation 11'14

Claims (3)

[Claims] (1) In a magneto-optical recording medium equipped with a magnetic recording layer having an axis of easy magnetization perpendicular to the film surface, R is one or more elements selected from Gd, Tb, Dy, Ho, and Nd, and T is Fe. , Co, and Ni, and M is Zr, Nb, In, Sn, Sb, and Ta.
, one or more elements selected from W, and N in a thickness of 100 nm to
A first thin film layer in which the magnetic recording layer has a composition represented by R_xT_1_-_x, where one or more elements other than R, T and M have an absorption edge in the thin film in a wavelength range of 1000 nm. and a second thin film layer having a composition represented by N_YM_1_-_Y, respectively.
1. A magneto-optical recording medium comprising a plurality of laminated layers and satisfying the following conditions: 0.15≦X≦0.3 and 0.3≦Y≦1. (2) the N is Al, Zn, Au, Ag, Bi, Cr,
The magneto-optical recording medium according to claim 1, comprising one or more elements selected from Mo, Si, Ge, and Cu. (3) The magneto-optical recording according to claim 1, wherein the N comprises an element having an absorption edge in the thin film in a wavelength range shorter than 500 nm and an element having an absorption edge in the thin film in a wavelength range longer than 500 nm. Medium.