JPH0782671B2 - Magneto-optical recording medium - Google Patents

Description

The present invention relates to a magneto-optical recording medium, for example, a rewritable recording medium by heating by irradiation with laser light or the like.

[Outline of Invention]

The present invention, in the magneto-optical recording medium, in addition to the heavy rare earth metals Tb, Gd, Dy, transition metals Fe, Co, Ni that have been conventionally used, light rare earth metals Sm, Pr, Nd, Ce and further Cr, Ti, By adding Al and Cu, the magneto-optical characteristics are improved, the alloy target for sputtering can be easily manufactured, and the magneto-optical characteristics can be stabilized for a long period of time.

[Conventional technology]

A conventional magneto-optical recording medium is composed of, for example, an amorphous alloy thin film composed of one or more kinds of heavy rare earth metals Tb, Gd, Dy and one or more kinds of Fe or Co as in JP-A-57-94948. Become.

The condition for obtaining the perpendicularly magnetized film is written as Ku><2πM ² _S ▼, as is known. However, Ku is magnetic anisotropy energy (erg / cc) and Ms is saturation magnetization (emu / cc). The heavy rare earth metal-iron-based alloy and the heavy rare earth metal-cobalt-based alloy produced by sputtering are amorphous and, like their crystalline materials, become a ferrimagnetic material. Therefore, a thin film made of a composition having a small residual magnetization and a large coercive force has been used as a magneto-optical recording medium.

[Problems to be solved by the invention]

However, Tb, Gd, Dy used as a magneto-optical recording medium has a drawback that it is easy to form transition metals and intermetallic compounds in the vicinity of the compensating composition as known, and they are easily cracked only by melting and casting them. Special technology is required to fabricate. Therefore, a composite target is used to form a thin film by sputtering.

The composite target method makes it difficult to control the composition of thin films.

In order to obtain a thin film having a uniform composition, complicated procedures such as the placement of pellets are necessary. It has the drawback.

In particular, the above-mentioned item is a serious defect that must be overcome in order to improve the C / N of the magneto-optical recording medium because the non-uniformity of the thin film composition causes noise during reproduction.

Furthermore, rare earths are generally very susceptible to oxidation, and when used as a magneto-optical recording medium, stability of characteristics over a long period of time becomes a problem.

Therefore, the present invention solves such problems,
Its purpose is to facilitate the production of the alloy target required for producing a film with a uniform composition, improve the stability of the magneto-optical characteristics over a long period of time, and make it cheaper and have higher performance than conventional ones. It is to provide a magneto-optical recording medium.

[Means for solving problems]

The magneto-optical recording medium of the present invention is a combination of a light rare earth metal (hereinafter referred to as LR) Sm, Nd, Pr and Ce and a heavy rare earth metal (hereinafter referred to as HR) Tb, Dy, TbGd or DyTb. One selected from among the combinations of transition metals FeCo or FeCoNi and other elements Cr, Ti, Al, Cu
The composition formula is {(LR) _1-x (HR) _x }.
When expressed as _y (FeCo, FeCoNi) _1-yz (Cr, Ti, Al, Cu) _z , it is characterized in that 0.2 <x ≤ 0.8 0.1 ≤ y ≤ 0.5 0 <z ≤ 0.1. When the composition formula is (LR _1-x HR _x ) _y TM _1-yz (Cr, Ti, Al, Cu) _z , in the present invention, x, y, and z are 0.1 ≦ x ≦ 0.8, 0.2 ≦ y ≦ 0.5,0
<Z ≦ 0.1. x is more preferably 0.4 ≦ x ≦ 0.
8. Most preferably, 0.5 ≦ x ≦ 0.7. The upper limit of x is stipulated because the casting target cannot be easily prepared above this, and the strength of the recording film is affected, and the lower limit of x is stipulated below this. This is because the perpendicular magnetic anisotropy cannot be obtained and it cannot be used as a recording film of a magneto-optical recording medium. Further, y is more preferably 0.25 y0.4, and most preferably 0.3 y0.4. Further, z is more preferably 0.02z0.1, and most preferably 0.03z0.08.

〔Example〕

The effects of the present invention will be described with reference to examples. All the thin films shown in this example were formed by sputtering. When the composition formula is expressed as {(LR) _1-x (HR) _x } _y (TM) _1-yz (Cr, Ti, Al, Cu) _z , the thin film of x0.8 has low frequency melting. After melting and casting in a furnace, an alloy having a diameter of 4 inches and a thickness of 4 mm was used as a target.

The sputtering conditions are an initial vacuum degree of 1 × 10 ⁻⁶ Torr or less, an argon pressure of 5 m Torr, and a substrate bias of 0V.

Figure 1 shows (Nd _0.4 Dy _0.6 ) _0.35 (Fe _0.7 Co _0.3 ) _0.65-z (C
The composition dependence of the Kerr rotation angle of r, Ti, Al, Cu) ^z (hereinafter referred to as θk) is shown. In Fig. 2, the Kerr rotation angle is slightly lowered by adding Cr, Ti, and Al. However, the improvement of the weathering tendency due to the addition of these elements only compensates for such a disadvantage.

Fig. 2 shows (Nd _0.4 Tb _0.4 Gd _0.2 ) _0.35 (Fe _0.7 Ni _0.1 Co _0.2 )
The time dependence of the light transmittance change of _0.60 (Cr, Ti, Al, Cu) _0.05 is shown. The sample has no protective film. Since the increase of the transmittance means the decrease of the reflectance, the increase of the transmittance is very disadvantageous at the time of reading. Cr, Ti, Al, and Cu are in the order of large addition effect on the improvement of weather resistance.

Fig. 3 shows (LR _0.4 Tb _0.6 ) _0.35 (Fe _0.7 Co _0.3 ) _0.60 Cr _0.05
7 shows the time dependence of the change in the light transmittance of. It shows the same trend as the example above.

Next, FIG. 4 and Table 1 show data on the critical point (range of X) of the composition of light rare earths. FIG. 4 is a plot of the effective perpendicular magnetic anisotropy for the samples having the respective compositions shown in Table 1, in which the negative value changes to the positive value between Samples 2 and 3. That is, since the magneto-optical recording medium uses the perpendicular magnetization film as a recording film,
From the figure, the upper limit of the composition of light rare earths is about 0.9.

[Effects of the Invention] As described above, according to the present invention, it is possible to obtain the same characteristics as those of the magneto-optical recording medium that has been conventionally used with a composition that allows easy production of an alloy target. In addition, since Tb, which is scarce in terms of resources, can be replaced with abundant Nd, it has an effect of being able to escape from the depletion of materials expected in the future.

Further, the magneto-optical recording medium has an effect that essential magneto-optical characteristics are stable for a long period of time.

[Brief description of drawings]

Fig. 1 (Nd _0.4 Dy _0.6 ) _0.35 (Fe _0.7 Co _0.3 ) _0.65-z (Cr, T
i, Al, Cu) z dependence view of Kerr rotation angle of ^z. Fig. 2 (Nd _0.4 Tb _0.4 Gd _0.2 ) _0.35 (Fe _0.7 Co _0.2 Ni _0.1 )
Relationship between the transmittance of _0.60 (Cr, Ti, Al, Cu) _0.05 and the time of exposure to the atmosphere. Fig. 3 Relation between transmittance of (LR _0.4 Tb _0.6 ) _0.35 (Fe _0.7 Co _0.3 ) _0.60 Cr _0.05 and time of exposure to the atmosphere. FIG. 4 is a diagram showing the relationship between each composition sample and effective perpendicular magnetic anisotropy.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Shimokawa 3-5 Yamato, Suwa, Nagano Prefecture 3-5 Suwa Seikosha Co., Ltd. (72) Mamoru Sugimoto 3-3.5 Yamato, Suwa, Nagano Prefecture No. Stock Company Suwa Seikosha Co., Ltd. (72) Inventor Satoshi Nehashi 3-5 Yamato, Suwa City, Nagano Prefecture Stock Company Suwa Seikosha Co., Ltd. (56) Reference JP-A-59-103314 Kai 59-68854 (JP, A) JP 61-222104 (JP, A) JP 61-34744 (JP, A) JP 61-22608 (JP, A)

Claims (1)

[Claims] 1. Light rare earth metal (hereinafter referred to as LR) Sm, Nd, P
One of r and Ce and heavy rare earth metal (hereinafter referred to as HR) T
1 selected from the combination of b, Dy, TbGd or DyTb, 1 selected from the combination of transition metals FeCo or FeCoNi and other elements Cr, Ti, Al, Cu The composition formula is {(LR) _1-x (HR) _x } _y (FeCo, FeCoN
i) _1-yz (Cr, Ti, Al, Cu) _z , where expressed as 0.2 <x≤0.8 0.1≤y≤0.5 0 <z≤0.1.