JPH077534B2 - Magneto-optical recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magneto-optical recording medium that records / reproduces information by light such as laser light.

<Prior Art> In a magneto-optical recording medium, a recording film is heated to a temperature near the Curie point by irradiation with light such as a laser beam, and a demagnetizing field in the recording film or an external magnetic field in addition to Record and erase. And the reproduction of information is
The recording film is irradiated with light such as laser light and the rotation of the plane of polarization of the reflected light or transmitted light is read.

The recording film of such a magneto-optical recording medium needs to be made of a material exhibiting the Kerr effect or the Faraday effect, and preferably has a large rotation angle, a low Curie point, and a high coercive force. .

Amorphous thin films of rare earth-transition metal alloys are often used for recording films of such magneto-optical recording media because of their low Curie point and high coercive force.

However, an amorphous thin film of a rare earth-transition metal alloy has low oxidation resistance and has a problem in reliability over a long period of time.

For this reason, Bi-substituted garnet, which is an oxide having excellent oxidation resistance, has been receiving attention.

However, Bi-substituted garnet has a low coercive force, for example, an amorphous thin film of a rare earth-transition metal alloy has a coercive force of several kOe or more, while a glass substrate uses 1k.
Only coercive force less than Oe can be obtained. Therefore, there is a limit to the improvement of recording density.

Further, the oscillation wavelength of the semiconductor laser used for recording on the magneto-optical recording medium is about 600 to 900 nm, but the Bi-substituted garnet has a low light absorption property, and in particular, the light absorption property in the wavelength range of 500 nm or more is low. Since it is low, it requires high power during recording.

In order to solve these problems of the Bi-substituted garnet, Japanese Patent Laid-Open No. 239448/1987 discloses a magneto-optical device that increases the optical absorption by precipitating a metal element having a light-absorbing ability at the crystal grain boundaries of the magnetic garnet. Proposing a disc. And, as a metal element having a light absorbing ability, ruthenium, rhodium,
Palladium, osmium, iridium and platinum are listed.

<Problems to be Solved by the Invention> However, when these metal elements described in JP-A-62-239448 are added, the Faraday rotation angle does not change, but the coercive force decreases, and recording There is a problem in terms of density. Further, in this case, there is a disadvantage that the heat treatment temperature and the heat treatment time required for garnet crystallization increase.

The present invention has been made under these circumstances, and an object thereof is to provide a magneto-optical recording medium having a recording film having high coercive force and high recording sensitivity.

<Means for Solving the Problems> Such an object is achieved by the present invention of the following (1) and (2).

(1) A magneto-optical recording medium having a recording film on a substrate, the recording film containing Bi-substituted garnet represented by the following formula and Ag and / or Au.

[Formula] BixRa _- xFeyMb _- yO ₁₂ (In the above formula, R is 1 of a rare earth element containing Y.)
Represents one or more kinds, and M represents one or more kinds of elements capable of substituting Fe.

Further, x <a, y <b, 1 ≦ x ≦ 3, 3 ≦ y ≦ 5, 2 ≦ a ≦ 4, and 4 ≦ b ≦ 6. (2) The magneto-optical recording medium according to (1), wherein the content of Ag and / or Au in the recording film is 0.1 to 15 at%.

<Operation> In the magneto-optical recording medium of the present invention, the Bi-substituted garnet contained in the recording film is heated to near the Curie point by a laser beam or the like, and the magnetic field is inverted by applying a magnetic field from the outside if necessary. To record information. Further, the recording film is irradiated with light such as laser light to reproduce the recorded information by the Faraday effect of Bi-substituted garnet.

In the present invention, the recording film contains Ag and / or Au in addition to Bi-substituted garnet.

Therefore, the recording film of the magneto-optical recording medium of the present invention has a high coercive force. This is due to Ag and / or contained in the recording film.
It is considered that Au exists in the crystal grain boundaries or in the crystal grains and suppresses the movement of the domain wall.

Further, since Ag and / or Au has a high light absorption ability, the temperature rise efficiency of the recording film due to the light irradiation is high, and the recording sensitivity is improved.

Furthermore, the addition of Ag and / or Au does not decrease the Faraday rotation angle, and does not affect the heat treatment temperature and heat treatment time for garnet crystallization. .

<Specific Configuration> The specific configuration of the present invention will be described in detail below.

The recording film of the magneto-optical recording medium of the present invention contains the Bi-substituted garnet represented by the above formula.

In the above formula, R represents at least one rare earth element including Y.

Preferred elements for R are Y, Sm, Eu, Gd, Tb, Dy, H
O, Er, Tm, Yb, Lu, etc., and among these, particularly preferable elements are Y, Gd, Dy, and Ho because the saturation anisotropy constant shows a negative value because the vertical anisotropy becomes larger. , Er, Yb, Lu
Is.

M represents at least one element that can replace Fe. As such an element, Al, Ga, Ti, Co, Ge, Sn, Zn, Mn or the like is preferably used, and particularly preferable elements are Ga,
It is Al.

If x, y, a and b in the above formula deviate from the above ranges, different phases will be precipitated during heat treatment, resulting in poor film uniformity.

The composition of Bi-substituted garnet in the recording film can be measured by EPMA, ICP, fluorescent X-ray analysis and the like.

The Bi-substituted garnet having such a composition usually exists in a polycrystal state in the recording film, and its crystal grain size is 0.02 to 0.08.
It is about μm.

The recording film of the magneto-optical recording medium of the present invention contains Ag and / or Au in addition to such Bi-substituted garnet. Ag
And / or Au is contained in order to enhance the light absorption ability and improve the recording sensitivity.

The reason why Ag and / or Au is selected in the present invention is as follows.

Does not react with garnet constituent elements to precipitate a heterogeneous phase.

No solid solution in garnet.

For these reasons, it is considered that the inclusion of these metals does not deteriorate the characteristics of garnet.

Ag and / or Au is 0.1 to 15 at in the recording film.
%, Particularly 0.5 to 15 at% is preferable. If the content is less than the above range, the effect of the present invention is insufficient, and if it exceeds the above range, the light absorption is too large and the read sensitivity is lowered.

The upper limit of the Ag content is preferably 15.0 at%, more preferably 12.0 at% and even more preferably 7.0 at%. Also, the upper limit of the content of Au is preferably 12.0 at%,
It is more preferably 8.0 at% and even more preferably 5.0 at%.

The contents of Ag and Au in the recording film are EPMA, ICP, fluorescent X
It can be measured by line analysis or the like.

Further, in the recording film, Ag and Au do not form a solid solution with Bi-substituted garnet and do not precipitate a hetero phase with a garnet constituent element. This can be confirmed by X-ray diffraction, transmission electron diffraction or the like.

By containing Ag and Au, the absorption coefficient increases to about 2 to 25 times in the wavelength range of 500 nm or more, especially in the wavelength range of 600 to 900 nm which is the oscillation wavelength of the semiconductor laser, and the Faraday rotation angle decreases. do not do.

In the present invention, the thickness of the recording film is preferably about 50 to 500 nm in order to increase the writing sensitivity.

The recording film as described above is preferably formed by a vapor phase film forming method such as a sputtering method.

When the sputtering method is used, the target is Bi
It is preferable to use Bi-substituted garnet having almost the same composition as the substituted garnet. In order to contain Ag and / or Au, the pellet of Ag and / or Au is placed on the target of this Bi-substituted garnet and sputtering is performed. It is preferable to carry out. In addition to this, Ag and / or Au can be contained by simultaneously sputtering the Bi-substituted garnet and the Ag and / or Au targets.

As the sputtering conditions, an atmosphere of an inert gas such as Ar or an inert gas containing oxygen is preferable, and the operating pressure is 4 to
About 20 mTorr is preferable.

The sputtering method may be any of various methods, and the input power and the like are arbitrary.

The substrate temperature is room temperature to 500 ° C, and the film formation rate is 0.01
It is preferably about 0.1 μm / min.

The obtained sputtered film is preferably subjected to heat treatment to promote crystallization. The heat treatment may be performed in air or in an oxygen atmosphere, and may be performed at 550 to 650 ° C. for about 1 to 5 hours.

There is no particular limitation on the material of the substrate on which the recording film is formed, but it is preferable to heat at the time of forming the recording film, and the sputtered film obtained is usually in an amorphous state and can be crystallized by heat treatment. It is preferable to use glass because it is preferable and transparent for detecting the magneto-optical effect.

The glass used preferably has a thermal expansion coefficient close to that of garnet, and for example, high silicate glass or the like is preferable.

The thickness of the substrate is usually about 0.5 to 3 mm, and the outer shape may be a disk shape or other suitable one according to the purpose.

Further, since the garnet film has a light-transmitting property and the rotation of the polarization plane due to the Faraday effect is used for the reproduction of recording, it is preferable to provide a reflective film of Al, Cr or the like on the recording film.

Further, an intermediate layer made of various dielectric materials such as SiO ₂ and having an enhancing effect may be provided between the recording film and the reflective film.

The magneto-optical recording medium thus configured is normally irradiated with recording and reproducing light from the substrate side.

<Example> Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention.

[Example 1] A 5 mm square Ag pellet was placed on the surface of a sintered body having a composition represented by atomic ratio of Bi _2.22 Dy _0.96 Fe _3.86 Ga _0.96 O ₁₂ to obtain a target.

Using this target, a 500 nm-thick film was formed by sputtering on a glass (Corning # 0317) substrate with a diameter of 50 mm and a thickness of 1 mm, and the film was heat-treated to crystallize and contain Ag. A sample having a Bi-substituted garnet recording film was obtained.

Also, by changing the number of Ag pellets to form recording films with different Ag contents, various samples were prepared (Sample No. 2 ~
4). For comparison, a sample formed without depositing Ag pellets was prepared (Sample No. 1).

Furthermore, using Au pellets, various samples containing Au were prepared in the same manner as described above (Sample Nos. 6 and 7).
We also prepared a sample using a target on which both Ag pellets and Au pellets were placed (Sample N
o.8, 9). Then, a sample was prepared without placing any Ag or Au pellets (Sample No. 5). Further, for comparison, Pt-containing samples were prepared using Pt pellets (Sample Nos. 10 to 12). However, in these cases, the composition of the sintered body on which the pellets were placed was Bi _1.95 Dy _1.39 Fe _3.76 Ga _0.90 O ₁₂ .

In addition, when preparing these samples, the sputtering conditions were:
Ar pressure was 15 mTorr, substrate temperature was 300 ° C., and RF power was 180 W. The heat treatment was performed in air at 600 ° C. for 3 hours. However, since the Pt-containing sample was not crystallized by this heat treatment, it was crystallized by heat treatment at 650 ° C. for 5 hours.

The composition of each obtained sample was measured by EPMA. The results are shown in Table 1. The compositions shown in Table 1 are Bi, Dy, Fe,
Atomic ratio of Ga and O and atomic% of Ag, Au and Pt in recording film
Is.

For these samples, coercive force (Hc), λ = 630 nm
The Faraday rotation angle (θ _F ), the squareness ratio (θr / θs) of the Faraday loop, and the absorption coefficient (α) at λ = 630 nm and λ = 830 nm were measured. The results are shown in Table 1.

In addition, each of these measurements was performed as follows.

Hc ... A garnet film formed on a glass substrate was cut into 8 mm x 8 mm, and a vibrating sample magnetometer (VSM manufactured by Toei Industry Co., Ltd.)
-3 type). The applied magnetic field was 5 kOe.

θ _F ... Measured with a magnetic field of 5 kOe applied by a Faraday effect measuring device manufactured by Mizojiri Optical Co., Ltd.

α ... The light absorptivity was measured with a spectrophotometer UV-365 manufactured by Shimadzu Corporation, and calculated from it.

The results are shown in Table 1.

From the results shown in Table 1, it can be seen that the sample of the present invention has extremely high coercive force as compared with the comparative sample containing neither Ag nor Au. Further, the sample of the present invention has a higher absorption coefficient than the comparative sample containing neither Ag nor Au, and is improved by 8 times or more at λ = 630 nm and 20 times or more at λ = 830 nm.

Moreover, the Faraday rotation angle and the squareness ratio of the Faraday loop are not reduced.

Further, it is found that the coercive force and the Faraday loop squareness are good with respect to the comparative sample containing Pt.

[Example 2] X-ray diffraction was performed on the recording films of Sample Nos. 2, 3, and 4. The X-ray diffraction chart of these samples is shown in FIG.

Further, X-ray diffraction was performed on Sample Nos. 5, 6, and 7. The X-ray diffraction chart of these samples is shown in FIG.

As shown in FIG. 1, in the sample of the present invention, Bi ₂ D
A peak corresponding to the garnet crystal of YFe ₄ Ga ₁ O ₁₂ was observed, and further, an Ag (111) peak was present, indicating that Ag was crystallized in the recording film.

Further, from the results shown in FIG. 2, it can be seen that Au is crystallized and similarly exists.

[Example 3] A thickness of 100 n was formed on the recording film of each sample prepared in the above example.
An Al film of m was formed by sputtering to prepare a magneto-optical recording medium sample having a reflective film.

When recording was performed on these samples using a laser beam of λ = 830 nm, the sample of the present invention containing Ag and / or Au exhibited a power required for recording as compared with a comparative sample containing no these. It was about 30 to 50%.

<Effects of the Invention> According to the present invention, a magneto-optical recording medium having a recording film having high coercive force and high recording sensitivity is realized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 and FIG. 2 are X-ray diffraction charts of a recording film of a magneto-optical recording medium.

Claims (2)

[Claims] 1. A magneto-optical recording medium having a recording film on a substrate, the recording film containing Bi-substituted garnet represented by the following formula and Ag and / or Au. [Formula] BixRa _- xFeyMb _- yO ₁₂ (In the above formula, R is 1 of a rare earth element containing Y.)
Represents one or more kinds, and M represents one or more kinds of elements capable of substituting Fe. Further, x <a, y <b, 1 ≦ x ≦ 3, 3 ≦ y ≦ 5, 2 ≦ a ≦ 4, and 4 ≦ b ≦ 6. ) 2. The magneto-optical recording medium according to claim 1, wherein the content of Ag and / or Au in the recording film is 0.1 to 15 at%.