JPH02123543A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording film having high coercive force and high recording sensitivity by incorporating specific Bi-substituted garnet and Ag and/or Au into the recording film formed on a substrate. CONSTITUTION:The specific Bi-substd. garnet expressed by the formula and Ag and/or Au is incorporated into the recording film formed on the substrate. In the formula, R represents one or more kinds of rare earth elements including Y, M represents one or more kinds of elements which can be substituted for Fe. x, y, (a) and (b) satisfy x<a, y<b, 1<=x<=3, 3<=y<=5, 2<=a<=4, and 4<=b<=6. Thereby, the obtained magneto-optical recording medium has high coercive force and high recording sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a magneto-optical recording medium in which information is recorded and reproduced using light such as a laser beam.

<Prior art> Magneto-optical recording media heat a recording film to a temperature near the Chierly point by irradiating light such as a laser beam, and then record information by applying a demagnetizing field within the recording film or an external magnetic field in addition to the demagnetizing field. Record and erase. Information is reproduced by irradiating the recording film with light such as a laser beam and reading the rotation of the polarization plane of the reflected or transmitted light.

The recording film of such a magneto-optical recording medium must be made of a material that exhibits the Kerr effect or Faraday effect, and preferably has a large rotation angle, a low Curie point (and a high coercive force). desirable.

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

However, amorphous thin films of rare earth-transition metal alloys have low oxidation resistance (and have problems with long-term reliability).

For this reason, Bi-substituted garnet, which is a fluoride with excellent oxidation resistance, is attracting attention.

However, Bi-substituted garnet has a low coercive force; for example, while an amorphous thin film of a rare earth-transition metal alloy has a coercive force of several koe or more, when a glass substrate is used, only a coercive force of 1 koe or less can be obtained. . Therefore, there is a limit to the improvement in recording density.

Furthermore, the oscillation wavelength of the semiconductor laser used for recording on magneto-optical recording media is approximately 600 to 900 nm, but Bi
Substituted garnet has low light absorption (especially at 500 nm)
Since light absorption in the above wavelength range is low, high power is required during recording.

In order to solve these problems of Bi-substituted garnet, JP-A No. 62-239448 discloses a magneto-optical method in which a metal element with light-absorbing ability is precipitated at the grain boundaries of magnetic garnet to increase light absorption. I'm suggesting a disc.

The authors list ruthenium, rhodium, palladium, osmium, iridium, and platinum as metal elements with light absorption ability.

<Problems to be Solved by the Invention> However, when these metal elements listed in JP-A No. 62-239448 are added, the Faraday rotation angle does not change, but the coercive force decreases, making it difficult to record. There is a problem with density. Further, in this case, there is also the disadvantage that the heat treatment temperature and heat treatment time required for garnet crystallization increase.

The present invention was made under these circumstances, and an object of the present invention is to provide a magneto-optical recording medium having a recording film with high coercive force and high recording sensitivity.

Means for Solving the Problems> These objects are achieved by the present invention described in (1) and (2) below.

(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] B I X Rh-x Fe y Mb-
y O (However, in the above formula, R represents one or more rare earth elements including Y, and M represents one of the elements that can be substituted for Fe.
Represents more than one species.

Also, X<a.

y<b.

1≦x≦3.

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

<Function> The magneto-optical recording medium of the present invention has BL contained in the recording film.
The substituted garnet is heated to near the Curie point using a laser beam or the like, and if necessary, a magnetic field is applied from the outside to reverse the magnetic field and record information. Further, the recording film is irradiated with light such as a laser beam, and the recorded information is reproduced by the Faraday effect of Bi-substituted garnet.

In the present invention, in addition to Bi-substituted garnet, A
g and/or Au.

Therefore, the recording film of the magneto-optical recording medium of the present invention has a high coercive force. This is considered to be because Ag and/or Au contained in the recording film exists at the grain boundaries or within the grains and suppresses the movement of the Mi walls.

In addition, since Ag and/or Au have high light absorption ability,
The temperature increase efficiency of the recording film due to light irradiation is high, and the recording sensitivity is improved.

Further, the addition of Ag and/or Au does not cause a decrease in the Faraday rotation angle, nor does it affect the heat treatment temperature and heat treatment time for garnet crystallization. .

Specific composition> Hereinafter, the specific configuration of the present invention will be explained in detail.

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

In the above formula, R represents one or more rare earth elements including Y.

Preferred elements as R are Y, Sm, Eu, Gd%Tb
, Dy, Ho, Er, Tm, Yb, Lu, etc. Among these, particularly preferable elements are Y, Gd, because the perpendicular anisotropy becomes larger when the saturation magnetostriction constant shows a negative value.
, Dy, Ho, Er, Yb, and Lu.

M represents one or more elements that can be substituted for Fe. Such elements include Al1, Ga, Ti, Co%G
It is preferable to use e1Sn, Zn%Mn, etc., and particularly preferable elements are Ga and Al1.

If x, y, a, and b in the above formula are out of the above range, different phases will precipitate during heat treatment, resulting in poor film uniformity.

The composition of Bi-substituted garnet in the recording film is EPMA, I
It can be measured by CP, fluorescent X-ray analysis, etc.

Bi-substituted garnet with such a composition usually exists in a polycrystalline state in the recording film, and its crystal grain size is 0.02
~O,OS μm.

The recording film of the magneto-optical recording medium of the present invention contains Ag and/or Au in addition to the i-substituted garnet. Ag and/or Au are contained in order to increase light absorption ability and improve recording sensitivity.

In the present invention, the reason why Ag and/or Au is selected is as follows.

■It does not react with garnet constituent elements and precipitate foreign phases.

■There is no solid solution in garnet.

For the above reasons, it is considered that even if these metals are contained, the properties of garnet will not deteriorate.

In the recording film, Ag and/or Au is 0.1
It is preferably contained in an amount of 15 at% to 15 at%, particularly 5 to 15 at% O. If the content is less than the above range, the effect of the present invention will be insufficient, and if it exceeds the above range, light absorption will be too large and read sensitivity will decrease.

Note that the upper limit of the Ag content is preferably 15, Oat
%, more preferably 12. oat%, more preferably 7. Oat%. In addition, the upper limit of the Au content is
Preferably 12. Oat%, more preferably 8. Oat
%, more preferably 5. Oat%.

The content of Ag and Au in the recording film is
P can be measured by fluorescent X-ray analysis or the like.

Further, in the recording film, Ag and Au do not form a solid solution in the Bi-substituted garnet, and do not precipitate a phase different from the garnet constituent elements. This can be confirmed by X-ray diffraction, transmission electron beam diffraction, etc.

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

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

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

When using the sputtering method, the target is the above B.
It is preferable to use a Bi-substituted garnet having almost the same composition as the i-substituted garnet, and in order to contain Ag and/or Au, a pellet of Ag and/or Au is placed on the target of the Bi-substituted garnet and sputtered. It is preferable to do this. In addition, Ag and/or Au can be contained by simultaneously sputtering two targets of Bi-substituted garnet and Ag and/or Au.

In addition, as 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.
~20 mTorr is preferable.

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

The substrate temperature is room temperature to 500°C, and the film formation rate is 0.
．． The rate is preferably about 01 to 0.1 μm/min.

The obtained sputtered film is preferably subjected to heat treatment to promote crystallization. The heat treatment may be performed either in air or in an oxygen atmosphere, and is heated at 550 to 650°C for 1
All you have to do is wait ~5 hours.

There are no particular restrictions on the material of the substrate on which the recording film is formed, but it is preferable to heat the recording film during formation, and the resulting sputtered film is usually in an amorphous state and cannot be crystallized by heat treatment. It is preferred to use glass, both because of its preference and because it is preferably transparent for detecting magneto-optic effects.

The glass used is preferably one having a thermal expansion coefficient similar to that of garnet, such as high silicate glass.

The thickness of the substrate is usually about 0.5 to 3 mm, and the external shape may be a disk shape or any other suitable shape depending on the purpose.

Furthermore, since the garnet film has optical transparency and the rotation of the plane of polarization due to the Faraday effect is utilized for recording and reproduction, it is preferable to provide a reflective film of AA, Cr, etc. on the recording film.

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

A magneto-optical recording medium constructed in this manner is normally irradiated with recording and reproducing light from the substrate side.

<Example> Hereinafter, the present invention will be explained in further detail by giving specific examples of the present invention.

[Example 1] The composition expressed in atomic ratio is B ia, 22D yo, *aF e 3. as
5mm on the surface of the sintered body with G ao, eao +2
A corner Ag pellet was placed and used as a target.

Using this target, a film with a thickness of 500 nm was formed by sputtering on 4 glass (Corning #0317) substrates with a diameter of 50 mm and a thickness of 1 mm, and was heat-treated to crystallize it to contain Ag. A sample having a recording film of Bi-substituted garnet was obtained.

In addition, recording films with different Ag contents were formed by changing the number of Ag pellets, and various samples were prepared (sample N
o, 2-4). For comparison, a sample in which the film was formed without placing Ag pellets was also prepared (sample N
o, 1).

Furthermore, using Au pellets, various samples containing Au were prepared in the same manner as above (sample N006
．． 7). In addition, a sample using a target on which both Ag pellets and Au pellets were mounted was also produced (sample No. 8.9). And Ag and A
A sample was prepared without placing any pellets of u (sample No. 5). Additionally, for comparison, pt
A sample containing pt was prepared using the pellet (
Sample no.

10-12), However, in these cases, the composition of the sintered body on which the pellet is placed is B i +, esD 3/ +, seF e
g, f a G a o, eo.

And so.

In addition, when preparing these samples, the sputtering conditions were as follows:
The Ar pressure was 15 mTorr, the substrate temperature was 300° C., and the RF power was 180 W. In addition, heat treatment was performed in air for 600 min.
℃ for 3 hours. However, for pt-containing samples,
Since this heat treatment did not result in crystallization, a heat treatment was performed at 650° C. for 5 hours to crystallize.

The composition of each sample obtained was measured by EPMA.

The results are shown in Table 1. Note that the composition shown in Table 1 is Bi
, Dy, Fe, Ga and 0 atomic ratios and A in the recording film
g, Au, and Pt in atomic percent.

For these samples, the coercive force (Hc), λ=63
The Faraday loop (θF) at 0 nm, the squareness ratio of the Faraday loop (θ, /θ,), and the absorption coefficient (α) at n=630 nm and λ=830 nm were measured.

The results are shown in Table 1.

Note that these measurements were each performed as follows.

Hc... Garnet film formed on a glass substrate is 8
It was cut out into a size of a+m×8 ohm and measured with a vibrating sample magnetometer (VSM-3 model) manufactured by Toei Kogyo ■. Note that the applied magnetic field was 5 koe.

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

α・・・Spectrophotometer U V-3 manufactured by Shimadzu Corporation
The light absorption rate was measured at 65 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 an extremely high coercive force compared to the comparative sample containing neither Ag nor Au. In addition, the sample of the present invention has a higher absorption coefficient than a comparative sample containing neither Ag nor Au (improved by more than 8 times at λ=630 nm and more than 20 times at λ=830 nm).

Moreover, no decrease in the Faraday rotation angle or the squareness ratio of the Faraday loop is observed.

It is also seen that the coercive force and Faraday loop squareness are better than the comparative sample containing pt.

[Example 2] X-ray diffraction was performed on the recording film of sample No. 2.3.4. The X-ray diffraction charts of these samples are shown in FIG.

In addition, X-ray diffraction was performed on sample No. 5.6.7. The X11 diffraction charts of these samples are shown in FIG.

As shown in FIG. 1, in the sample of the present invention, B
A peak corresponding to the garnet crystal of it DyFe4Ga+ O+* was observed, and an Ag (111) peak was also present, indicating that Ag was crystallized and present in the recording film.

Moreover, from the results shown in FIG. 2, it can be seen that Au is present in the same manner as crystallized.

[Example 3] A film with a thickness of 11
A 00n AJ2 film was formed by sputtering to produce a magneto-optical recording medium sample having a reflective film.

When these samples were recorded using a laser beam of λ = 830 nm, Ag and/or A
The sample of the present invention containing u has a power required for recording of 30 to 50
It was about %.

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

4,

[Brief explanation of the drawing]

1 and 2 are X-ray diffraction charts of a recording film of a magneto-optical recording medium. 9 degree

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] Bi_xR_a_-_xFe_yM_b_-_
yO_1_2 (However, in the above formula, R represents one or more rare earth elements including Y, and M represents one or more elements that can be substituted for Fe. Also, x<a, y<b, 1≦x≦ 3, 3≦y≦5, 2≦a≦4, 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%.