JPH0731830B2 - Magneto-optical recording medium - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium capable of high density recording, and more particularly to a magneto-optical recording medium in which a magnetic material is filled in fine pores of an anodized film of an aluminum or aluminum alloy substrate. It is about.

2. Description of the Related Art In recent years, a magneto-optical recording method utilizing the magnetic Kerr effect has been developed. In this magneto-optical recording method, a signal such as a laser beam is locally irradiated onto the surface of the magnetic material at the time of recording and the portion is heated to a temperature higher than the Curie temperature of the magnetic material to write a signal. The magnetic recording is read by irradiating the surface of the magnetic material with a light flux having a specific polarization angle such as a laser beam and detecting the rotation angle (polarization angle) of the deflection surface of the reflected light due to the magnetic Kerr effect.

As a recording medium used in such a magneto-optical recording system, particularly one capable of high density recording has already been disclosed.
A magneto-optical recording medium described in Japanese Patent Publication No.-72663 has been proposed. The recording medium of this proposal has a porous anodic oxide film 2 formed on the surface of a substrate 1 made of aluminum or an aluminum alloy as shown in FIG.
The magnetic material 4 such as pure iron is filled in each of the micropores 3 by electrolytic deposition. Although the recording medium having such a structure was originally developed as a perpendicular magnetic recording medium capable of high-density magnetic recording, it is apparent from the above proposal that the recording medium is also suitable for use in a magneto-optical recording system. Has been done. That is, when the recording medium having such a structure is used in the magneto-optical recording method, the magnetic material 4 in each fine hole 3 is magnetized in the direction perpendicular to the film surface in advance. Since the magnetic material 4 filled in the holes 3 has anisotropy in the direction perpendicular to the film surface, it is sufficiently magnetized in the vertical direction, and in this case, the light radiated to the end surface of the magnetic material 4 magnetized in the vertical direction is irradiated. Since the polarization angle of the reflected light due to the magnetic Kerr effect becomes large, it is said that the signal reading becomes easy.

Problems to be Solved by the Invention As described above, the magneto-optical recording medium itself in which the micropores of the porous anodic oxide film are filled with a magnetic material has already been proposed. When this was actually applied, the following problems were found.

That is, in this type of magneto-optical recording medium, when writing a signal, the magnetic material filled in the fine holes must be irradiated with laser light to be heated to a temperature above the Curie temperature (Tc) of the magnetic material. However, the Curie temperature of Co (cobalt) described as an example in the above proposal is extremely high at 1120 ° C, and the Curie temperature of Fe (iron) is also high.
Although it is considerably high at 770 ° C, the power is insufficient for a simple and inexpensive semiconductor laser that is expected to be used as a general-purpose writing light source, and it is difficult to raise it to a temperature higher than the above Curie temperature. Therefore, there is a problem that a special and expensive laser light source must be used. Further, when the anodic oxide film is heated to a high temperature of about 400 ° C. or higher, cracks are generated, which causes a problem that it cannot be put to practical use as a magneto-optical recording medium. Ni (nickel)
Has a Curie temperature of 358 ° C, which is quite low in the case of Ni, but the polarization angle (hereinafter referred to as Kerr rotation angle) θk due to the magnetic Kerr effect with respect to the irradiation light is only 0.17 °, and that of Fe is θk = 1.1. , Or θk = 0.9 ° in the case of Co, it is extremely small, and therefore it is difficult to use Ni alone.

The present invention has been made in view of the above circumstances, and it is possible to write a signal even with a low-power laser light source such as a semiconductor laser, and cracks do not occur in the anodized film due to high temperature heating. As described above, the Curie temperature (Tc) of the magnetic material filled in the micropores of the porous anodic oxide film is lowered, specifically, the Curie temperature is lowered to 400 ° C or lower, preferably 200 ° C or lower. Another object of the present invention is to provide a magneto-optical recording medium. Here, the saturation magnetic flux density Bs of the magnetic material in the micropores is
It is not preferable for the magneto-optical recording medium to lower the B.sub.2, and therefore it is necessary to lower the Curie temperature without lowering Bs.

Means for Solving the Problems The present inventors have found that the saturation magnetic flux density in a magneto-optical recording medium of the type in which a magnetic material is filled in the fine pores of a porous anodic oxide coating of aluminum or aluminum alloy as described above.
As a result of various studies on a method of lowering the Curie temperature Tc without lowering Bs, basically, to reduce the volume (dimension) of the magnetic material in the micropores, the pore diameter of the micropores should be reduced. In particular, it has been found that the thickness of 18 nm or less is effective for lowering the Curie temperature. Secondly, as a magnetic material to be filled in the micropores, Fe is a main component and one or two selected from Ni, Cr, Mn, Cu, Be, As, Re, Ru, and Os. It was also found that the use of an alloy containing the above is also effective in lowering the Curie temperature.

Therefore, the present invention is basically a magneto-optical method in which a porous anodic oxide film is formed on the surface of a substrate made of aluminum or an aluminum alloy, and the magnetic material is filled in the fine pores of the porous anodic oxide film. In the recording medium, the diameter of the fine holes is 18 to 6 nm.

Further, the magneto-optical recording medium of the present invention, Ni (nickel), Cr (chromium), as a magnetic material filled in the fine pores,
50 atoms of one or more selected from Mn (manganese), Cu (copper), Be (beryllium), As (arsenic), Re (rhenium), Ru (ruthenium), Os (osmium) % Or less, with the balance being substantially Fe (iron).

Function In the magneto-optical recording medium of the present invention, the pore diameter (pore diameter) of the porous anodic oxide film on the surface of the substrate made of aluminum or aluminum alloy is set to 18 to 6 nm. The pore diameter of a normal porous anodic oxide film is about 100 to 200 nm, and even if it is small, it is about several tens of nm at most, so in the case of this invention, it is significantly smaller than the pore diameter of a general porous anodic oxide film. To do. By reducing the pore diameter in this way, the size of the magnetic material filled in the fine pores is significantly reduced. That is, the same effect as when the magnetic material is remarkably pulverized is brought about, whereby the magnetic material becomes in a state close to superparamagnetism (super para), so that it exhibits paramagnetic behavior, the coercive force Hc decreases, and the Curie temperature decreases. Tc decreases. Such a decrease in Curie temperature means a decrease in temperature to be reached by laser light irradiation during signal writing, and therefore, a low output laser light source such as a general-purpose semiconductor laser is used as a laser light source for writing. Can be used. In addition, since the heating temperature by the laser at the time of writing becomes low, there is no possibility of cracks in the anodized film.

For example, the present inventors have used Fe, Ni as the magnetic material to fill the micropores of the porous anodic oxide film, and the pore diameter (pore diameter) and Curie temperature Tc when variously changing the pore diameter of the micropores.
When the relationship with the coercive force Hc was investigated, the results shown in FIGS. 1 and 2 were obtained. As is clear from FIG. 1, especially Fe
In the case of, the Curie temperature Tc decreases to about 400 ° C by setting the pore diameter to 18 nm or less. Here
Ni also has a lower Curie temperature Tc when the pore diameter is 18 nm or less, and the Curie temperature is lower than that of Fe as a whole. However, Ni has a small Kerr rotation angle θk, as described above,
It is not preferred to use alone. If the pore diameter is less than 6 nm, the Curie temperature may be excessively lowered and the recording may be lost even at room temperature. Therefore, the lower limit of the pore diameter was set to 6 nm.

Further, in the magneto-optical recording medium of the present invention, in addition to the pore diameter of 18 nm or less, 6 nm or more as described above, as a magnetic material to fill the micropores, Fe as a main component and Ni,
1 selected from Cr, Mn, Cu, Be, As, Re, Ru, Os
The Curie temperature Tc can be further reduced by using one kind or an alloy containing two or more kinds. That is,
The additive elements below Ni are metallic elements that are weaker in magnetism or non-magnetic than Fe, but by adding these to Fe, which is a ferromagnetic material, and diluting them, the Curie temperature is much higher than in the case of Fe alone. Can be reduced to.

Such a phenomenon is explained as follows. That is, the Curie temperature means a limit temperature at which an electron spin that determines the magnetism of a magnetic metal can be held, but if other non-magnetic metal elements or outer-shell electrons of a weakly magnetic metal element are mixed,
If the critical temperature for having a spin decreases and the mixing ratio of the non-magnetic metal element or the metal element with weak magnetism increases,
The limit temperature at which the spin that brings about magnetism can be maintained is further lowered.

As mentioned above, Fe is the main constituent, and other diluents
When using a magnetic material to which an element such as Ni is added, the compounding ratio of Fe and other diluent elements is 50% or more of Fe in atomic%,
It is appropriate that the total content of other diluent elements such as Ni is 50% or less. That is, when the proportion of the diluent element is high, the Curie temperature Tc is usually further lowered, but the Kerr rotation angle θk is also small. The Kerr rotation angle θk that can be practically used as a magneto-optical recording medium is at least 0.2 ° or more, preferably 0.3 ° or more, but it becomes difficult to secure a sufficient Kerr rotation angle if Fe is less than 50 atom%. , Fe was 50 atomic% or more, and other diluent elements were 50 atomic% or less.

It should be noted that any one of the diluent elements such as Ni may be added alone, or two or more kinds may be added in combination. It is desirable to use Cr and other Mn, Cu, Be, As, R
It is desirable to add e, Ru, and Os together with Ni and / or Cr. Further, when any one or more of Mn, Cu, Be, As, Re, Ru, and Os is added here, although all of them are effective in lowering the Curie temperature,
Since it also has a large effect on the decrease of the Kerr rotation angle θk and the decrease of the saturation magnetic flux density Bs, it is desirable that the total amount of these is 10 atomic% or less.

The lower limit is not specified because the effect of lowering the Curie temperature can be obtained by adding even a small amount of the diluent element such as Ni added to Fe.
It is preferable to add at least atomic%.

In addition, as described above, the pore size of the fine pores of the porous anodizing film can be set to 18 nm to 6 nm by appropriately adjusting the voltage during the anodizing process. That is, it is generally known that the lower the voltage during the anodizing treatment, the smaller the pore diameter of the fine pores. In the case of the present invention, the pore diameter of 6 to 6 can be obtained by reducing the anodizing treatment voltage.
It is possible to form an anodized film with 18 nm micropores. The specific anodizing treatment voltage for making the pore diameter 18 nm or less is slightly different depending on the components of the treatment liquid (electrolyte), but according to the experiments conducted by the present inventors, the following Examples 4 to 7 were performed. As shown, the anodizing voltage is DC 10
It has been found that when the content is V or less, an anodic oxide film having fine pores with a diameter of 18 nm or less is formed.

Example [Example 1] The surface of a rolled plate made of a 4% Mg-Al alloy was melted by using Al having a purity of 99.99%, and the surface of the rolled plate was used as an Al substrate. The surface of the Al substrate was 3% oxalic acid. Anodizing treatment was performed at various electrolytic voltages using an aqueous solution as an electrolytic solution to form anodized films with various different pore sizes.

Then, iron sulphate 10g /
l, nickel sulfate 40g / l, boric acid 30g / l, glycerin 2g / l
Performed electrolytic deposition treatment by alternating current electrolysis in an electrolyte solution containing Fe50 atomic% -Ni50 atomic% in the fine pores of the anodic oxide film.
The alloy (Fe ₅₀ Ni ₅₀ alloy) having the composition of was filled. In addition, for anodized films with various pore diameters similar to the above, iron sulfate 10 g /
l, nickel sulfate 40g / l, manganese sulfate 5g / l, boric acid 30g /
AC electrolytic deposition treatment was performed with an electrolytic solution containing l and glycerin 2 g / l, and Fe50 atom%-
An alloy (Fe ₅₀ Ni ₄₅ Mn ₅ alloy) having a composition of Ni ₄₅ atom% -Mn 5 atom% was filled.

The results of examining the relationship between the pore diameter (Dp) and the Curie temperature (Tc) when filling the anodic oxide coatings with various pore diameters filled with Fe ₅₀ Ni ₅₀ and Fe ₅₀ Ni ₄₅ Mn ₅ alloys as described above Is shown in FIG. Note that FIG. 3 also shows the results of filling Fe alone (the same as in FIG. 1) for comparison.

As is clear from FIG. 3, the Curie temperature is significantly lower in both the case of using the Fe ₅₀ Ni ₅₀ alloy and the case of using the Fe ₅₀ Ni ₄₅ Mn ₅ alloy, as compared with the case of using Fe alone. Moreover, it can be seen that the Curie temperature is remarkably lowered when the pore diameter is 18 nm or less. And in particular, when the Fe ₅₀ Ni ₄₅ Mn ₅ alloy is used, the Curie temperature is lower than when the Fe ₅₀ Ni ₅₀ alloy is used. Note that the residual magnetic flux density Bs is based on the Fe ₅₀ Ni ₅₀ alloy.
0.32T, 0.31T for Fe ₅₀ Ni ₄₅ Mn ₅ alloy, and Kerr rotation angle θk is 0.46 ° for the former and 0.45 ° for the latter, both of which are practically applicable as a magneto-optical recording medium.

[Example 2] An anodic oxide coating having various pore diameters was formed in the same manner as in Example 1, and Fe70 atom%-was formed in the fine pores of the anodic oxide coating.
Cr30 atomic% of the alloy (Fe ₇₀ Cr ₃₀ alloy), Fe70 atomic% -Cr25
Electrodeposition that deposits an alloy of atomic% -Cu5 atomic% (Fe ₇₀ Cr ₂₅ Cu ₅ alloy) and an alloy of Fe ₇₀ atomic% -Cr ₂₅ atomic% -Os 5 atomic% (Fe ₇₀ Cr ₂₅ Os ₅ alloy) by AC electrolysis. Processed. The electrolytic solution used for electrolytic deposition is
For Fe ₇₀ Cr ₃₀ alloy, FeSO ₄ 10g / l, CrSO ₄ 20g / l, boric acid
It contains 30 g / l and glycerin 2 g / l.
_{For 70} Cr ₂₅ Cu ₅ alloy, FeSO ₄ 10 g / l, CrSO ₄ 15 g / l, CuSO ₄
1g / l, boric acid 30g / l, glycerin 2g / l, FeSO ₄ 10g / l, CrSO ₄ 15g / l, H ₂ OSO ₄ 1g / l, boric acid for Fe ₇₀ Cr ₂₅ Os ₅ alloy
It is 30 g / l and glycerin 2 g / l.

The results of examining the relationship between the pore diameter (Dp) and the Curie temperature (Tc) in these cases are shown in FIG. In addition, Table 1 shows the results of examining the saturation magnetic flux density Bs and the Kerr rotation angle in each case.

As is clear from FIG. 4, it can be seen that the same effect as in the case of Fe—Ni system shown in FIG. 3 can be obtained in the case of Fe—Cr system.
Further, from Table 1, the saturation magnetic flux density Bs and the Kerr rotation angle θk
It is clear that the above is practically applicable as a magneto-optical recording medium.

Example 3 Used in Example 1 in forming anodized films with various pore diameters in the same manner as in Example 1 and performing electrolytic deposition treatment on the fine pores of the anodized film. The concentration of nickel sulfate in the electrolytic solution for depositing the Fe-Ni alloy was changed variously to deposit the Fe-Ni alloy with various component ratios. Further, the concentration of chromium sulfate in the electrolytic solution for depositing the Fe-Cr alloy used in Example 2 was changed variously to deposit the Fe-Cr alloy with various component ratios. FIG. 5 shows the results of investigating the relationship between the pore diameter (Dp) and the Curie temperature (Tc) of the anodic oxide coatings having various pore diameters filled with each Fe-Ni alloy and each Fe-Cr alloy. Table 2 shows the results of examining the saturation magnetic flux density Bs and the Kerr rotation angle θk of each alloy filled in the anodized film having a porosity of 20% (pore diameter: about 15 nm).

As is clear from FIG. 5, the Curie temperature (Tc) is lower in both Fe—Ni alloy and Fe—Cr alloy than in the case of Fe alone. However, as is clear from Table 2, when the Fe content is less than 50 atomic% (x> 50 atomic%), Bs and θk are small and it is not suitable as a magneto-optical recording medium.

Example 4 An Al substrate similar to that used in Example 1 was subjected to anodization treatment using a 3% aqueous solution of oxalic acid at a direct current of 10 V and a bath temperature of 20 ° C. to form an anodized film having a pore diameter of 18 nm. Was generated.

Next, iron sulfate 10 g /, nickel sulfate 40 g /, manganese sulfate 5 g /, boric acid 30 g /, AC electrolytic deposition treatment was performed with an electrolytic solution containing glycerin 2 g /, and Fe50 atom% -in the fine pores of the anodic oxide film. A magnetic material made of an alloy (Fe ₅₀ Ni ₄₅ Mn ₅ alloy) having a composition of Ni ₄₅ atomic% -Mn 5 atomic% was filled. When the Curie temperature of the magnetic material filled in the fine holes in this way was examined, it was found to be 220 ° C.

[Example 5] For an Al substrate similar to that used in Example 1, a 3% oxalic acid aqueous solution was used, as in Example 4, using a DC voltage of 5 V and a bath temperature.
Anodizing treatment was performed at 20 ° C to form an anodized film with a pore diameter of 15 nm.

Next, iron sulfate 10 g /, chromium sulfate 15 g /, copper sulfate 1 g /
AC electrolytic deposition treatment was performed with an electrolytic solution containing boric acid, 30 g /, and glycerin, 2 g /, and the magnetic material of Fe ₇₀ Cr ₂₅ Cu ₅ alloy was filled in the micropores of the anodic oxide film. When the Curie temperature of the magnetic material filled in the fine holes in this way was examined, it was found to be 230 ° C.

Example 6 For an Al substrate similar to that used in Example 1, 80 ml /
Using an aqueous solution of H ₂ SO ₄ having a concentration of 10 V and anodizing treatment at a bath temperature of 20 ° C., an anodic oxide film having a pore diameter of 15 nm was formed.

Next, iron sulfate 10 g /, chromium sulfate 20 g /, boric acid 30 g /
AC electrolytic deposition treatment was performed with an electrolytic solution containing 2 g / of glycerin, and Fe ₇₀ Cr ₃₀ was formed in the fine pores of the anodic oxide film.
A magnetic material made of an alloy was filled. When the Curie temperature of the magnetic material filled in the fine holes in this way was examined, it was found to be 35
It was found to be 0 ° C.

[Example 7] An Al substrate similar to that used in Example 1 was subjected to anodizing treatment using the same 80 ml / concentration H ₂ SO ₄ aqueous solution as in Example 6 at a DC voltage of 5 V and a bath temperature of 20 ° C. Then, an anodic oxide film having a pore diameter of 8 nm was formed.

Next, an AC electrolytic deposition treatment was carried out with an electrolytic solution having the same components as those used in Example 6 to fill the micropores of the anodized film with a magnetic material made of Fe ₇₀ Cr ₃₀ alloy. When the Curie temperature of the magnetic material filled in the fine holes in this way was examined, it was found to be 190 ° C.

[Comparative Example] For an Al substrate similar to that used in Example 1, the same 800 ml / concentration H ₂ SO ₄ aqueous solution as in Example 6 was used and a direct current of 15 V,
Anodizing treatment was performed at a bath temperature of 20 ° C to form an anodized film with a pore diameter of 21 nm.

Next, iron sulfate 10g /, nickel sulfate 40g /, boric acid 30
AC electrolytic deposition treatment was performed with an electrolytic solution containing g / and glycerin 2 g /, and Fe ₅₀ Ni was formed in the fine pores of the anodic oxide film.
_A magnetic material made of ₅₀ alloy was filled. When the Curie temperature of the magnetic material filled in the fine holes in this way was examined,
It was found to be 410 ° C.

As shown in Examples 4 to 7 above, when the anodizing voltage is DC of 10 V or less, it is possible to form an anodized film having fine pores having a pore diameter of 18 nm or less. The Curie temperature of the body fell below 400 ° C.

On the other hand, in the comparative example (voltage 15V) in which the anodizing voltage exceeded DC 10V, large pores of 21nm with pore diameter exceeding 18nm were formed. In this case, the Curie temperature was 400 ° C.
I have crossed over. In this case, when writing a signal, it must be heated to a high temperature exceeding 400 ° C., which may cause cracks in the anodized film.

EFFECTS OF THE INVENTION The magneto-optical recording medium of the present invention is such that by setting the pore diameter (pore diameter) of the micropores of the porous anodic oxide film filled with the magnetic material to 18 nm or less, the Curie temperature of the magnetic material in the micropores is reduced. Therefore, it becomes possible to write a signal using a low-power laser light source such as a general-purpose semiconductor laser, and it is possible to prevent cracks from occurring in the anodized film due to heating during writing. became. Then, as the magnetic material to be filled in the micropores, an alloy containing Fe as a main component and diluting it with one or more of Ni, Cr, Mn, Cu, Be, As, Re, Ru and Os is used. As a result, the Curie temperature can be further lowered and the use of the low power laser light source can be further facilitated.

[Brief description of drawings]

Fig. 1 is a graph showing the relationship between the pore diameter (Dp) and the Curie temperature (Tc) of the anodized film when Fe and Ni are used as magnetic materials. Fig. 2 uses Fe and Ni as magnetic materials. Fig. 3 is a graph showing the relationship between the pore diameter (Dp) of the anodic oxide film and the coercive force (Hc) when it is present. Fig. 3 is the pore diameter (Dp) of the anodic oxide film in Example 1.
Is a graph showing the relationship between Curie temperature (Tc) and Fig. 4 is the pore diameter (Dp) of the anodized film in Example 2.
Is a graph showing the relationship between the Curie temperature (Tc) and Fig. 5 is the pore diameter (Dp) of the anodized film in Example 3.
And a Curie temperature (Tc). FIG. 6 is a longitudinal sectional view schematically showing an example of a magneto-optical recording medium of the prior art. 1 ... Substrate, 2 ... Porous anodized film, 3 ... Micropores, 4 ... Magnetic material.

Claims (2)

[Claims] 1. A magneto-optical recording medium in which a porous anodic oxide film is formed on the surface of a substrate made of aluminum or an aluminum alloy, and a magnetic material is filled in each micropore of the porous anodic oxide film. A magneto-optical recording medium in which the diameter of the fine pores of the porous anodized film is in the range of 6 to 18 nm. 2. The magneto-optical recording medium according to claim 1, wherein the magnetic material is Ni, Cr, Mn, Cu, Be,
A magneto-optical recording medium comprising an alloy containing one or more selected from As, Re, Ru and Os in a total amount of 50 atomic% or less, and the balance being substantially Fe.