JP2543677B2 - Magneto-optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is directed to recording / recording by irradiation with laser light or the like.
The present invention relates to an erasable / reproducible magneto-optical recording medium.

[Conventional technology]

In a conventional magneto-optical recording medium, as a recording medium, for example, as disclosed in JP-A-57-94948, an amorphous material formed of one or more kinds of heavy rare earth metals Tb, Dy, Gd and one or more kinds of Fe or Co Quality alloys have been used.

While heating the recording layer with laser light spots, an external magnetic field is applied to form inverted magnetic domains for recording, and the laser light spots of linearly polarized light with lower power than during recording are incident to produce the Kerr effect or Faraday effect. A recording medium used for so-called magneto-optical recording, which is reproduced by utilizing it, must satisfy at least the following properties.

1. The Curie temperature is low enough to record and erase with a semiconductor laser, and the Curie temperature is sufficiently higher than the normal operating environment temperature.

2. The recording medium should be amorphous in order to avoid grain boundary noise that occurs when the recording medium is polycrystalline and manufacturing difficulties that occur when the recording medium is single crystal. In this case, the crystallization temperature needs to be sufficiently higher than the Curie temperature.

3. Since the car effect and the Faraday effect are used for reproduction, the car rotation angle and the Faraday rotation angle are large.

4. Must be a perpendicular magnetic film.

Therefore, the heavy rare earth metal-transition metal amorphous alloy as described above has been used as the recording layer.

[Problems to be solved by the invention]

However, heavy rare earths used as magneto-optical recording media
The transition metal amorphous alloy has the following drawbacks.

1. Heavy rare earth metals and transition metals tend to form intermetallic compounds near the compensating composition where the apparent magnetization disappears at room temperature.
Since these intermetallic compounds are easily cracked, a special technique is required to produce an alloy target.

2. In the region where the amount of transition metal is larger than that of the compensating composition, the Kerr rotation angle and the Faraday turning point angle can be increased by increasing Co in the transition metal. However, replacing Fe with Co raises the Curie temperature, which increases the thermal energy required for recording and erasing.

3. Rare earth-transition metal amorphous alloys are easily oxidized.

Therefore, the present invention solves such a problem, and its purpose is to enable the production of an alloy target that facilitates the production of a film having a uniform composition, improve the recording / erasing characteristics, and An object of the present invention is to provide a magneto-optical recording medium which improves the stability of magneto-optical characteristics over a period of time and is cheaper and has higher performance than conventional ones.

[Means for solving problems]

The magneto-optical recording medium of the present invention comprises a light rare earth metal (LR) selected from at least one selected from Nd, Sm, Pr and Ce, and a heavy rare earth metal (HR) selected from at least one selected from Tb, Dy and Gd. In a magneto-optical recording medium containing a ferromagnetic transition metal (TM) consisting of Fe, Co and Fe, or Fe and Co and Ni, in addition to the ternary metal, a non-magnetic layer consisting of Cr, Al and Ti. It is characterized in that a kinetics forming metal (A) is added.

Further, the ratio of LR to HR is 0.25 to 0.75, and the ratio of Fe to Co or Fe to Ni of the TM is 0.55 to 0.
45, and the ratio of (LR + HR) to TM to A was 0.23 to 0.72 to 0.005.
It is characterized by being.

〔Example〕

Examples of the present invention will be described below. The recording medium of the present invention was manufactured by melting and casting in a low-frequency melting furnace, and then forming a target having a diameter of 8 inches and a thickness of 4 mm as a sputtering target.

[Example 1] Table 1 shows a correspondence table of alloy target compositions and sample numbers of Examples of the present invention, and Table 2 shows a correspondence table of recording layer compositions and sample numbers. Sample number 1 is an example of the present invention, and sample numbers 2 to 4 are comparative examples.

As can be seen from Tables 1 and 2, in the magneto-optical recording medium obtained by sputtering from the alloy target, there is a tendency that the rare earth metal is less than that contained in the alloy target. However, the degree of such composition change also changes depending on the type of the spatula gas, the pressure, the power applied to the target, the target, and the distance between the substrates. The recording layer shown in Table 2 was prepared under the conditions that the ultimate vacuum was 1 × 10 ⁻⁶ Torr or less, the sputtering gas was Ar, the Ar gas pressure was 1 m Torr, the DC sputtering method was used, and the input power to the target was about 400 W. It was
Further, the distance between target substrates was 10 cm in the distance between the center of the substrate and the center of the target.

The oxygen concentration of the alloy target produced in Example 1 is 0.05% or less by weight, which is far smaller than that of the sintered body.

[Comparison experiment]

Fig. 1 shows that (Nd _0.25 Dy _0.75 ) 0.28 on a glass substrate.
(Fe0.55Co0.45) 0.72-z (Cr, Ti, Al) z about 2000Å formed and Al about 1000Å formed as a protective layer on it, Kerr rotation angle when light enters from the substrate side And z
Shows the relationship. The wavelength of incident light is 7800Å.

In Ti and Al, if z is smaller than 0.05, the Kerr rotation angle does not decrease, but in Cr, it decreases.

[Embodiment 2] FIG. 2 shows that the sample Nos. 1, 2, and 3 shown in Table 2 of Embodiment 1 were each formed on a glass substrate to a thickness of about 500 Å, and Tb0.2
About 0 (Fe0.90Co0.10) 0.80 formed about 500Å, the relationship between the time of keeping at 60 ℃ and 90% RH and the standardized Faraday rotation angle is shown. No protective film is attached. Apparently, the corrosion resistance is improved by adding Cr, Ti and Al. These elements are effective when added at an atomic ratio of about 5%. As shown in the comparative experiment, with this amount of addition, the Kerr rotation angle was not significantly reduced. Therefore, by adding these elements in an atomic ratio of about 5%, it was possible to improve the corrosion resistance without deteriorating the magneto-optical characteristics.

[Example 3] In order to investigate the recording / reproducing characteristics of the magneto-optical recording media of Material Nos. 1, 2, and 3 shown in Table 2, about 500 Å each was formed on a grooved polycarbonate substrate, and aluminum nitride was formed thereon. About 1000Å is formed, aluminum nitride is formed on it about 1000Å, and aluminum is further formed on it about 50Å
0 Å formed. FIG. 3 shows the structure of a magneto-optical recording medium used for recording / reproducing characteristic evaluation. The reproduction signal was obtained from the reflected light of the magneto-optical recording medium, and recording / reproduction was performed under the following conditions.

Groove recording, reproduction power 1 mW, recording magnetic field 600 Oe, linear velocity 4.
7m, recording frequency 1MHz, bandwidth 30KHz.

FIG. 4 shows the relationship between the recording laser power and the C / N ratio and the second harmonic suppression ratio during reproduction of the magneto-optical recording medium of the present invention. Tb0.20 (Fe0.90Co0.1) with a thickness of about 500Å
0) FIG. 5 is a view similar to FIG. 4 when changed to 0.80.

Table 3 shows the magneto-optical recording medium of the present invention and the Tb0.20 (Fe0.90).
This is a summary of the results of the recording / reproducing characteristic evaluation of the magneto-optical recording medium using the information recording medium using Co0.10) 0.80. Sample numbers 1 to 3 correspond to Tables 1 and 2. Sample No. 4 shows the above Tb0.20 (Fe0.90Co0.10) 0.80.

The optimum recording power in Table 3 is defined as the recording power at which the second harmonic suppression ratio is the smallest, and the C / N ratio is the value when the data recorded with the optimum recording power is reproduced. The optimum recording power corresponds roughly to the statically measured Kyuriy temperature Tc.
The recording power is large when the Tc is large.

As described above, in the magneto-optical recording medium of the present invention, a high C / N ratio can be obtained without unnecessarily increasing the recording power.

〔The invention's effect〕

As described above, according to the magneto-optical recording medium of the present invention, it is easy to form an alloy that is not easily broken, and thus an alloy target having a large area can be formed. A large-area alloy target has an effect of being suitable for mass production because the composition and film thickness can be made uniform.

Further, the Kerr rotation angle and the Faraday rotation angle can be increased by increasing the Co concentration in the transition metal, but in the magneto-optical recording medium of the present invention, the Curie temperature does not become so high that the optimum recording / erasing power does not become too large. It also has the effect of

Further, since it also contains passivation forming metals Ti, Cr, and Al, it also has an effect that corrosion resistance can be improved.

[Brief description of drawings]

Fig. 1 (Nd _0.25 Dy _0.75 ) _0.30 (Fe _0.55 Co _0.45 )
_{0.70-z (Cr, Ti,} Al) z magneto-optical recording medium shown in FIG. FIG. 2 the present invention showing the relationship between the Kerr rotation angle and z of and Tb0.20
Fig. 3 shows the relationship between the Faraday rotation angle standardized by the initial value and the time when (Fe0.90Co0.10) 0.80 was kept at 60 ° C, 90% RH. Fig. 3 The magneto-optical recording medium used for recording / reproducing characteristics evaluation FIG. 1 shows the structure 1 ... Polycarbonate 2 ... Aluminum nitride 3 ... Magneto-optical recording medium of the present invention or TbFeCo 4 ... Aluminum nitride 5 ... Aluminum FIG. 4 (Nd0.25Dy0.75) 0.23 (Fe0 of the present invention .55Co0.4
5) A graph showing the relationship between the recording power of 0.72 (Cr0.2Al0.4Ti0.4) 0.05 and the C / N ratio. Fig. 5 Recording power and C / N of Tb0.20 (Fe0.80Co0.10) 0.80 of the conventional example. Diagram showing the relationship with N ratio

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Nebashi 3-3-5 Yamato, Suwa-shi Seiko Epson Corporation (72) Inventor Akira Aoyama 3-3-5 Yamato, Suwa-shi Seiko Epson Corporation ( 72) Inventor Mamoru Sugimoto 3-3-5 Yamato, Suwa-shi, Seiko Epson Corporation (56) References JP 61-22608 (JP, A)

Claims (2)

(57) [Claims] 1. A light rare earth metal (LR) selected from at least one selected from Nd, Sm, Pr and Ce, a heavy rare earth metal (HR) selected from at least one selected from Tb, Dy and Gd, and Fe and Co. Or a ferromagnetic transition metal (TM) composed of Fe, Co and Ni, and a passivation forming metal (Cr), Al and Ti (in addition to the ternary metal). A magneto-optical recording medium containing A). 2. The ratio of LR to HR is 0.25 to 0.75, and the ratio of Fe to Co or Fe to Ni of the TM is 0.55 to 0.45.
The magneto-optical recording medium according to claim 1, wherein the ratio of (LR + HR) to TM to A is 0.23: 0.72: 0.005.