JPS6190348A - Photomagnetic recording medium - Google Patents

Abstract

PURPOSE:To decrease modulation noise and to increase a C/N value by specifying the Curie temp. and compensation temp. of an amorphous rare earth-ferrous photomagnetic recording medium having the axis of easy magnetization in the direction perpendicular to the film plane. CONSTITUTION:The amorphous ally film is manufactured by a sputtering method using a composite target disposed with a rare earth element and transition metallic element such as iron element so as to attain a prescribed compsn. in area ratio on a Co disk. The Curie temp. of the photomagnetic recording medium is specified to <=250 deg.C and the compensation temp. thereof <=0 deg.C. The following film characteristics are exhibited when, for example, the amorphous vertically magnetizable film consisting of Tb20Fe70.5Co9.5 compsn. is formed as the recording film: Curie temp. Tc=190-230 deg.C, compensation temp. Tcomp<=-50 deg.C, coercive force Hc=1-3kOe, satd. magnetization Ms=120-195 emu/cc, Kerr rotating angle thetaK(lambda=633nm)=0.31-0.35 deg.. The modulation noise is substantially eliminated and the high C/N value is obtd. even if the Kerr rotating angle is not apparently increased by multiple reflections in the interfer ence structure.

Description

[Detailed description of the invention] [Field of application of the invention] The present invention uses laser light to record and reproduce information.

The present invention relates to magneto-optical recording for erasing, and particularly relates to a magneto-optical recording medium with high sensitivity and a large magneto-optic effect suitable for improving the signal-to-noise ratio C/N during reproduction.

[Background of the invention]

Recently, rare earth-iron group amorphous films have been attracting attention as recording materials for magneto-optical recording, which is a rewritable optical recording system, and can obtain a relatively large Kerr rotation angle. Among these amorphous films, Tb-Fe-G provides a particularly large Kerr rotation angle Ok.

Research and development of amorphous films is becoming more active. For example, Japanese Patent Laid-Open No. 58-73746 is a typical example. However, including these alloy-based amorphous films.

Conventional amorphous films have the following problems.

(1) Although the Kerr rotation angle when magnetization is saturated is large, the Kerr rotation angle at residual magnetization is small, so a sufficient reproduction signal cannot be obtained.

(2) Although the Kerr rotation angle due to residual magnetization is relatively large, the Curie temperature is too high, so the recording sensitivity is poor, and therefore a sufficient reproduction signal cannot be obtained.

(3) Although the Kerr rotation angle for residual magnetization is relatively large and the Curie temperature is relatively low, during recording, there is a portion that cannot be written in the center of the recording domain, resulting in large modulation noise (as a result, sufficient Signal to noise ratio during playback C
/I can't get N.

[Purpose of the invention]

An object of the present invention is to provide an amorphous magneto-optical recording material which has a sufficiently large magneto-optic effect, can obtain a high reproduction C/N ratio (or S,/N ratio), and is suitable for practical use.

[Summary of the invention]

When an amorphous perpendicularly magnetized film is actually used as a magneto-optical recording material, the following requirements were considered to be required.

(1) The Curie temperature (Tc) is approximately 250 °C due to limitations on the power of semiconductor laser light, recording sensitivity, and film life.
The following is desirable.

(2) It is also desirable that the coercive force (He) is about 1 koe or more in view of the thermal stability of recorded information. However, the present inventors have discovered that not only the above requirements but also the compensation temperature (Tcomp), in addition to the Curie temperature, has a great effect on recording sensitivity, reproduction noise, etc. due to the balance with Tc.

The magneto-optical recording medium of the present invention has the following configuration. That is.

In a rare earth-iron magneto-optical recording medium that has an axis of easy magnetization in a direction perpendicular to the film surface and is substantially amorphous, the Curie temperature of the amorphous rare earth-iron magneto-optical medium is 250.
℃ or less, the compensation temperature is 0℃ or less.

A binary system of the rare earth metal-iron group magneto-optical recording medium.

Examples of ternary or quaternary materials include Tb-Fe-C
o, Tb-Fe, Tb Gd-Fe, Tb
-Sm-Go etc. are fried.

In addition, in order for recorded information to exist stably, the Curie temperature is generally 100°C or higher (more preferably 15°C).
0℃ or higher).

However, even if the Tc of the above-mentioned magneto-optical recording medium is 250 degrees Celsius or lower, if 'I' comp is near room temperature, a recording domain with a uniform shape will not be formed during recording, resulting in high modulation noise, and during reproduction. It was found that the C/N of This greatly depends on the magnitude of saturation magnetization during recording and its temperature change.

In order to obtain low modulation noise and high C/N, the compensation temperature of the recording film is preferably 0° C. or lower, more preferably -50° C. or lower. In general, for rare earth-iron group energy recording media, the composition range that satisfies these temperature ranges is:
It was found that this is limited to compositions that are richer in iron group elements than the compensation composition. As a typical example, Fig. 1 shows Tb-F
e-C.

Amorphous perpendicular magnetization film (TbxFel.-〇-A-Co,)
The Tbfi degree dependence of the Curie temperature Tc and the compensation temperature T comp on each Co concentration is shown. The arrow in the figure indicates the Tb concentration of the compensation composition. In the figure, curve 1 is Tc at y=30.4, curve 2 is Tc at y=17.5, curve 3 is Tc at y=l l, curve 4 is Tc at y=10.3, and curve 5 is Tc at y=17.5.
Tc of 5, 6 T camp of y=30.4, 7 Tcomp of y=17.5, 8 T co of y:11
mp, 9 is Tcomp of y=10.3, 10 is y
=5 T comp is shown in each case. The figure shows that as the amount of Co increases, Tc increases, and the Tb concentration, where Tc and Tcomp match, shifts to the high concentration side.

Now, in the above composition where Tcomp is lower than room temperature, the composition is low Tb.
It can be seen that the composition is on the 'a degree side (that is, the composition is richer in iron group elements than the compensation composition).

Therefore, from the results shown in FIG. 1, the optimal composition of the Tb Fe Co amorphous perpendicularly magnetized film is 18 to 21.5 atomic % of Tb and 8 to tOE of Co, which are richer in iron group elements than the compensation composition.
It is necessary that the composition be within an extremely narrow composition range of % carbon and the balance consisting of iron element. Here, the Kerr rotation angle θ□ is 0.3° (λ”
In order to obtain a high value of 633 nm or higher, the lower limit of the Co content is 877X%. Of course, it is possible to further optimize the properties by adding small amounts of impurity elements such as other rare earth elements and transition metal elements to these ternary systems.

[Embodiments of the invention]

The present invention will be explained below using examples.

The amorphous alloy film of the present invention was placed on a Go disk with a diameter of 8 inches.
It was produced by the well-known Magne-1-ron sputtering method using a composite target in which a rare earth element of X1cnf and a transition metal element such as an iron element were arranged so as to have a predetermined composition by area calculation. In addition, as a disk for recording/playback evaluation, a tracking groove was formed on a 5"φ glass disk using UV tll resin, and a Tb-Fe-Co film (film thickness of about 1000 mm) was formed on top of it.
, 5in2 film (film thickness: about 700 layers) were used.

As an example of the present invention, Tb20 Fe70.5 is a representative example of a composition richer in iron group elements than the compensation composition.
Co9.5. Tb21 Fe70.5 G.

8.5. Tb21.5 Fe71.5. An amorphous perpendicular magnetization film having a composition such as Co7 was used as a recording film. The properties of those films are shown below. Curie temperature Tc = 190-230'C
, Compensation temperature T comp≦-50℃9 Coercive force Hc =
1-3 koe, saturation magnetization M s = 120-195
emu/cc, Kerr rotation angle θk (λ=633nm)=0
．． 31-0.35° Using these films, the above-mentioned 5"φ multilayer film disk was fabricated. In the evaluation of recording/reproducing characteristics, the laser light power during recording was 9 mW, and the read laser light power was 2.5 mW. 5
mW, the modulation noise during reproduction became zero when the external magnetic field during recording was 2000 e or more. External magnetic field 3000e
The reproduction output to noise ratio C/N when recorded under
f = 30kHz, track pitch 1.6μm).

In the above-described embodiments, similar effects can be achieved in rare earth-iron group magneto-optical materials.

As is clear from the above examples, the amorphous perpendicularly magnetized film of the present invention has almost no modulation noise, has an interference structure, and has high Cl without increasing the apparent Kerr rotation angle due to multiple reflections.
It was found that the N value was obtained. Of course, these films and ZnS, AQN, Si, N4. BN,
In the case of an interference multilayer film disk in which an interference film such as Si○ is combined, an even higher C/N of 56 dB or more can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the dependence of the Curie temperature Tc and the compensation temperature Tcomp of the Tb-Fe-Co amorphous perpendicularly magnetized film on the CO concentration and y, the Tb concentration, and X. Kuzu 1 area

Claims (1)

[Claims] 1. A substantially amorphous rare earth-iron magneto-optical recording medium having an axis of easy magnetization in a direction perpendicular to the film surface, the Curie temperature of the magneto-optical recording medium being A magneto-optical recording medium characterized in that the compensation temperature is 250°C or less and the compensation temperature is 0°C or less. 2. The magneto-optical recording medium has an atomic ratio of terbium 18~
21.5% cobalt, 8-10% cobalt, and the balance substantially iron, and is substantially amorphous and richer in iron group elements than the compensating composition, which is substantially amorphous. Magneto-optical recording medium.