JPS6376134A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a magneto-optical recording medium which excels in all of recording and erasing characteristics as well as reproducing characteristics by forming said medium composed of elements selected respectively from light rare earth metals, heavy rare earth metals, transition metals and a group consisting of Cr, Ti, and Al. CONSTITUTION:The compsn. is so formulated as to consist of >=1 kinds among the light rare earth metals Sm, Nd, Pr, and Ce, >=1 kinds among the heavy rare earth metals Tb, Dy and Gd, >=1 kinds among the transition metals Fe, Co and Ni and >=1 kinds among Cr, Ti and Al. The compsn. is expressed by the formula I in the ranges of 0.1<=x<=0.4, 0.1<=y<=0.5, and 0.01<=z<=0.1, and the residual magnetic flux density given by this composition is taken as <=1,200 Gauss in the direction perpendicular to the substrate plane. In the formula I, LR denotes >=1 kinds among the light rare earth metals; HR denotes >=1 kinds among the heavy rare earth metal; TM denotes >=1 kinds among the transition metals; and A denotes >=1 kinds among Ti, Al and Cr. A magneto- optical recording medium having excellent recording and erasing characteristics and reproducing characteristics is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical recording medium that can be recorded, reproduced, and erased by, for example, irradiation with a laser beam or the like.

[Conventional technology]

In conventional magneto-optical recording media, for example, heavy rare earth iTb as in JP-A-57-94948,
Amorphous alloys formed of one or more of Dy, Gd and one or more of Fe4 or Co have been used.

Recording is performed by applying an external magnetic field to form reversed magnetic domains while heating the recording layer with the original laser spot.The laser beam spot is linearly polarized with a lower power than during recording, and the Kerr effect or 7 Alladay effect is generated. A recording medium used in the so-called magneto-optical recording method, in which reproduction is performed using the magnetic field, must satisfy at least the following properties.

1. The Curie temperature is low enough to allow recording and erasing with a semiconductor laser, and the Curie temperature is sufficiently high compared to the normal usage environment temperature.

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

5. Since regeneration utilizes the Kerr effect and Faraday effect, the Kerr rotation angle and Faraday rotation angle caused by the above effects must be large.

4. Must be a perpendicular magnetization film.

Therefore, amorphous alloys of heavy rare earth metals and transitional metals as described above have been used as recording layers.

[Problems to be Solved by the Invention] However, the present rare earth-transition metal amorphous alloy used as a magneto-optical recording medium has the following drawbacks.

1. Heavy rare earth metals and alpha-transfer metals tend to form intermetallic compounds near the compensation composition where apparent magnetization disappears at room temperature. Since these metal r■ compounds are easily cracked ψ, special techniques are required to produce alloy targets.

In a region where there is more transition metal than the Z compensation composition, by increasing CO in the transition metal, the Kerr rotation angle and Faraday rotation angle can be significantly increased while increasing the Curie temperature. However, o.

It is known that when the Kerr rotation angle and Faraday rotation angle are increased by substitution, the magnetic field HW required for saturation recording also increases, and the range of compositions in which Hw can be reduced (about 100 Oersteds) becomes extremely narrow.

On the other hand, in the region where the IIi cherry metal is less than the compensation composition, the improvement in the magneto-optical effect as described above is slight, but the range where the minimum magnetic field HW required for saturation recording can be about 100 oersteds is in the region where the transition metal is large. Because it is wider than the one on the market, its playback characteristics are inferior, but its recording and erasing characteristics are superior.

In other words, in rare earth-transition metal amorphous alloys that are normally used as magneto-optical recording media, it is difficult to produce one with good recording and erasing characteristics in regions where the transition metal is more than the compensation composition, and in regions where there is less transition metal. However, it has been difficult to produce a material with good reproduction characteristics.

In the ye magnetic recording system, the bias magnetic field applied during recording and erasing usually does not exceed 500 to 600 oersteds. Therefore, it is essential for a magneto-optical recording medium to have the property of being able to perform saturation recording with a magnetic field of approximately several hundred oersteds.

Therefore, the present invention is intended to solve the shortcomings caused by the narrow composition range having favorable characteristics in conventional magneto-optical recording media, and its purpose is to:
The object of the present invention is to provide a magneto-optical recording medium with excellent recording/erasing characteristics and reproduction characteristics, which has been difficult to manufacture in the past.

[Means for solving problems]

The magneto-optical recording medium of the present invention is a recording medium formed on a substrate and capable of recording, erasing, and reproducing information using light. FIT Tb e Dy *One or more of Ga, transition metal Fe, I:! o.

One or more of N1 and one of Cr, Ti, Aλ
The recording medium is characterized in that the residual magnetic flux density in the direction perpendicular to the film surface at 25° C. is 1200 Gauss or less.

[Example 1] The effects of the present invention will be described with reference to Examples.

The magnetic recording media shown in Example 1, Examples 2, and 5.4 were all melted and cast in a low frequency melting furnace, and then molded to a diameter of 8 inches and a thickness of 4 tpaa, which was used as a sputtering target.

Table 1 shows the correspondence between the alloy target composition and sample number used to actually produce the recording layer, and Table 2 shows the correspondence between the recording layer composition and sample number. As described above, a magneto-optical recording medium obtained by sputtering from an alloy target tends to contain less rare earth metal than the alloy target. However, the extent of such compositional changes depends on the type of sputtering gas.

It also changes depending on the type, pressure, power input to the target, and distance between the target and the board. The conditions for producing the recording layer shown in Table 2 were as follows: ultimate vacuum level I x 10-' Torr or less, sputtering gas was Ar, Ar gas pressure was 1 mTorr, D(1
! Using the sputtering method, the power input to the target is approximately 40
It was 0W. ``Furthermore, the distance between the target substrate used to be 10 cW1 between the center of the substrate and the center of the target.

Note that the oxygen concentration of the alloy target produced in Example 1 is 0.05% or less by weight, which is much lower than that of the sintered body. The target with a low oxygen concentration was able to be created because the # contained in rare earth metals and transition metals was left behind in the slag left in the furnace after the target was cast. be. In other words, this is one of the advantages obtained by alloying the target, and this effect is one reason why the magneto-optical recording medium of the present invention exhibits favorable characteristics as shown in Example 2.5 below. It becomes.

It is usually very difficult to produce alloy targets by casting, which are used to produce heavy rare earth/transition metal amorphous alloy thin films used as magneto-optical recording media by sputtering. However, according to the present invention, heavy rare earth metals, yθ
, Co, Ni, as well as light rare earth metals and Cr, Ti, A
Since it contains ll, targets can be produced by casting. 1
The method of producing thin films made of multiple elements by sputtering using individual targets has been successfully used in the mass production of recording media for fixed disk magnetic storage devices, and has high industrial value. .

[Example 2] In a magneto-optical recording medium, the magnitude of the bias magnetic field on the recording layer is usually several hundred oersteds.

Therefore, it is desirable that the bias magnetic field required for saturation recording be as small as possible (approximately 100 oersteds). Figure 1 shows the relationship between the minimum magnetic field Hw required for saturation recording of the magneto-optical recording medium of the present invention and magnetization at 25°C. shows. Table 5 is the first
It is a correspondence table between the composition of the recording medium shown in the figure and the residual magnetic flux density at 25°C.

Table 3 However, in FIG. 1 and Table 3, those whose residual magnetic flux density exceeds 1200 Gauss are outside the scope of the claims of the present invention, but are listed for comparison. From Figure 1 25
There is a strong correlation between the magnitude of the residual magnetic flux density at °C and the recording magnetic field Hw, and the smaller the residual magnetic flux density, the higher the recording magnetic field Hw.
It is found that w also becomes smaller.

The above recording medium had a structure as shown in FIG. 2, and was manufactured by sputtering from a melted/cast target.

[Example 5] Used in Example 2 (Ndo, z 5Dy0.7+1)
0.2 s (yeLsooo, 4 sT1α05)
0.77 was used to create a magneto-optical recording medium having the structure shown in FIG. 2, and FIG. 3 shows its reproduction characteristics in terms of recording power and C/N ratio. Conventionally used Tb0.2
2 (7eQ, 80COQ, 2G) (L7Jl) is similarly evaluated as shown in FIG.

The recording medium of the present invention is not inferior to conventional media in terms of reproduction characteristics, and is actually superior in that it can perform low-power recording. In producing the magneto-optical recording medium, as shown in FIG. 4, the substrate was made of polycarbonate, and the protective layer was made of a mixture of aluminum nitride and silicon nitride. The evaluation was performed by magnetizing (erasing) in advance in the opposite direction to the recording direction using a thermomagnetic recording method, and then reproducing the recorded material.

Table 4 shows the evaluation results of magneto-optical recording media in which the light rare earth metal was changed using the same method.

Table 4 Regarding the reproduction characteristics, Sm and Nd are almost at the same level, followed by Pr and Oe. The above samples were also produced by sputtering from melted and cast targets.

〔Effect of the invention〕

As described above, according to the present invention, the target can be manufactured by melting and casting, making it easy to create the recording layer by sputtering. A magneto-optical recording medium with excellent erasing and reproducing characteristics can be produced.

[Brief explanation of the drawing]

Figure 1 (NdQJ5Dy0.75)! (78α500
(L45T10.05) A diagram showing the relationship between the minimum magnetic field required for saturation recording of 1-H and the residual magnetic flux density. Fig. 2 (NdoJsDyo, ys) azs(
? eo, 5sOoo, *5Ti0.05)Q, A diagram showing the relationship between recording power and O/N ratio of 77. Fig. 3 Conventional TM, 22(?811L90000.
1G) A diagram showing the relationship between the recording power of 0.78 and the 07N ratio. FIG. 4 A diagram showing the configuration of a magneto-optical recording medium used for evaluating recording/reproducing characteristics. 1... Polycarbonate 2... Aluminum nitride and silicon nitride 3.
...Magneto-optical recording medium of the present invention or Tb1FeO
O4...Aluminum nitride and silicon nitride5
・・・・・・Aluminium and above Applicant Seiko Epson Co., Ltd. Agent Patent Attorney Mogami 7 (1 person) 1F-ゝノ0 50C) +000
15001 (Gara Mata) Noboru 1 Figure 1 Power (mW) Figure 2 Figure 1 Power (mW) Figure 3 - 1

Claims (1)

[Claims] (1) Formed on a substrate, information can be recorded, erased, and
As playable recording media, light rare earth metals Sm, Nd,
One or more of Pr, Ce, heavy rare earth metals Tb, Dy
, one or more of Gd, one or more of transition metals Fe, Co, and Ni, and one or more of Cr, Ti, and Al, and has a compositional formula of (LR_xHR_1_-_x)_yTM_1_-_y_
-_zA_z, in the range of 0.1≦x≦0.4 0.1≦y≦0.5 0.01≦z≦0.1 in the direction perpendicular to the base surface A magneto-optical recording medium having a residual magnetic flux density of 1200 Gauss or less. (However, LR is one or more of the above light rare earth metals,
BR is one or more of the heavy rare earth metals listed above, TM is one or more of the transition metals listed above, and A is Ti, Al,
Represents one or more elements of Cr. )