JPH038154A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain good recording and reproducing characteristics and erasing ratio in low magnetic field by providing a reflecting layer consisting of Al on a recording layer consisting of an alloy of a rare earth and transition metal and specifying the coercive force of the recording layer at room temp. CONSTITUTION:An interference layer, the recording layer consisting of the alloy of the rare earth and transition metal and the reflecting layer consisting of an aluminum alloy are provided on a transparent substrate. The recording layer has the coercive force larger than 15 kilo oersted at room temp. and is low in saturation magnetization. Such coercive force and saturation magnetization are obtd. by adjusting the compsn. of the rare earth and transition metal, the film thicknesses and film forming conditions, etc., of the layers, etc. The magneto-optical recording medium having high signal intensity and low noises in the magnetic field modulation recording at a relatively low magnetic field is obtd. by adopting such layer constitution provided with the reflecting layer on the recording layer.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a magneto-optical recording medium used for optical recording.

(Prior art and its challenges) / Among rewritable optical recording media, magneto-optical recording media are approaching the stage of practical use.

However, in the conventional magneto-optical recording method, a new signal is added to the recorded part. When recording, it is necessary to erase the previous signal by knowing the direction of magnetization of the recording layer in advance, and dyne overwriting, which is generally performed with magnetic duplexes, is impossible. . This becomes an obstacle to improving the data transfer rate in optical recording media. As one recording method to solve this problem, magnetic field modulation recording using a magneto-optical recording medium is seen as promising. In this method, the temperature of the recording layer is locally raised by irradiation with laser light to a temperature higher than that which can be reversed by an external magnetic field.
Since a new signal is recorded thereon by modulating the external magnetic field in accordance with the recording signal, direct override in which erasing and recording are performed at the same time is possible. Another feature of this method is that a good erasing ratio can be obtained because the temperature of the recording layer can be sufficiently raised.

In such a magnetic field modulation recording method, it is necessary to reduce the inductance of the electromagnetic coil in order to increase the modulation frequency of the magnetic field, but this requires miniaturizing the electromagnetic coil and increasing the efficiency of magnetic field generation. becomes. However, in reality, there is a limit to the frequency that can be modulated due to the inductance of the electromagnetic coil, and there is also a problem in that the magnetic field generated by the electromagnetic coil becomes low on the high frequency side of the modulation frequency.

In addition, when attempting to actually perform magnetic field modulation recording by rotating the magneto-optical disk, the force of the surface runout of the magneto-optical disk,
There is also the problem that the distance between the electromagnetic coil and the recording layer fluctuates, making it impossible to supply a sufficient magnetic field depending on the location, making it difficult to record data stably and without errors.

In order to deal with these problems, it has been desired to develop a magneto-optical recording medium that can perform stable magnetic field modulation recording even in low magnetic fields.

(Means for Solving the Problems) As a result of intensive studies to solve the above problems, the inventors of the present invention have used a specific layer configuration and further improved the physical properties of the recording layer such that the coercive force at room temperature is Ørsted (KOe)
We have found a medium that enables direct override by magnetic field modulation recording with a recording magnetic field of p, /, rθ Oersted (Oe) or higher by having a composition that has a larger composition, and that also provides good recording/reproducing characteristics and erasing ratio. Ta.

The gist of the present invention is to provide a magneto-optical recording medium in which an interference layer, a recording layer made of an alloy of a rare earth metal and a transition metal, and a reflective layer made of an aluminum alloy are sequentially provided on a transparent substrate.
The present invention resides in a magneto-optical recording medium for magnetic field modulation recording, characterized in that the coercive force of the recording layer is greater than /jKOe at room temperature.

[Structure of the invention]

The magneto-optical recording medium of the present invention has a layer structure of a substrate, an interference layer, a recording layer, and a reflective layer.

By combining such a layer structure with the use of physical properties of the recording layer that are different from those of conventional ones, the magneto-optical recording medium of the present invention has a unique effect in the magnetic field modulation recording method. It becomes.

First, substrates used in the present invention include plastics such as acrylic resins and polycarbonate resins, glass, metals such as aluminum, and substrates in which grooved resin is formed on glass.

The thickness of the substrate is generally about /-2tttx.

As the interference layer, metal oxides, metal nitrides, inorganic carbides, etc. are used. Al2O is the gold layer oxide! ,
Metal oxides of Ta2O, Sin, and Sin□. In addition to these, other elements such as Ti*Zr, Mo, Y, etc. may be present alone in the form of oxides or in the form of Al. It may be combined with Ta to form an oxide. These metal oxides are dense and prevent moisture and oxygen from entering from the outside, have high corrosion resistance, and have low reactivity with the magneto-optical recording layer.Also, when using a resin substrate as a substrate, it is difficult to interact with the resin. Excellent adhesion.

Specific examples of metal nitrides include Si, Al, and Ge nitrides (eg, 5iNbN, 5iTaN, etc.). Among them, a titanide containing Si'lx gives good results.

Metal nitride is dense and prevents moisture and oxygen from entering from the outside, has high corrosion resistance, and has low reactivity with the magneto-optical recording layer.

On the other hand, examples of the inorganic carbide include SiC.

In particular, tantalum oxide (Taxes) is preferably used because it has low internal stress and is less prone to cracking.

The optimum thickness of this interference layer varies depending on the refractive index, but
Usually about 6ooi to gooi is appropriate.

The magneto-optical recording layer is made of an alloy of rare earth and transition metal, such as TbFeCo, GdTbFe, GdTbFe.
C0°GdDyFeCo, NdDyFeCo, etc. are used. In the present invention, the coercive force of the recording layer at room temperature is /! A recording layer larger than KOe and with low saturation magnetization is required. A self-recording layer having a coercive force at room temperature greater than /T (Oe) can be obtained by adjusting the rare earth-transition metal composition, film thickness, and film forming conditions, such as Ar pressure.

For example, in the case of T b Fe Co , Tb heat T
bFeC.

2/~2 atomic% of the total amount, CO to 3 of the total amount of FeCo
A recording layer containing up to 3θ atom % is preferable. More preferably, in the present invention, a recording layer is used in which the direction of the magnetic moment of the unit volume equivalent υ of the recording layer is the same as the direction of the magnetic moment of the transition metal in the recording layer. , in the case of T b Fe Co, Tb+Y
A recording layer containing 27 to 23 atomic % of TbFeCo based on the total amount is preferable.

The thickness of the recording layer is 200 to 600A, and more preferably 23O
~G00 is preferred.

Such characteristics? The recording layer should be configured as a reflective recording medium with a reflective layer provided on the recording layer. The reason for this is not completely clear, but by using a recording layer with low saturation magnetization and making the recording layer thinner, stray magnetic fields to the recording area can be reduced. It is believed that this is the main factor that has made it possible to perform magnetic field modulation recording that provides good recording and reproducing characteristics even with a weak external magnetic field.The saturation magnetization is / o Oemu/cc or less, preferably θemu/cc or less. The one is good.

In the present invention, a reflective layer and a protective layer are provided on the magneto-optical recording layer. The reflective layer may be made of any material as long as it has a high reflectance, but Au, Ag, and Pt are expensive (Cu is susceptible to corrosion, so a thin film of Al or Al alloy is desirable. In particular, Al 1cTa and Ti.

Zr, V, Pt, Mo, Cr, Pd etc./
The alloy containing 5 at% or less brings about good characteristics in terms of C/N ratio and sensitivity. The thickness of the reflective layer is 250~! ;OO
A is preferred. A protective layer may be provided on the reflective layer. As the protective layer, T' and its oxides are preferably used.

The purpose of this protective layer is to prevent oxidation of the reflective layer. It is sufficient to provide the protective layer with a thickness of about 0-j00A.

Physical vapor deposition (PVD) such as sputtering, chemical vapor deposition (CVD) such as plasma CVD, etc. are applied to create the interference layer, recording layer, and reflective layer.

To create a film by PVD, a target with a predetermined composition is used. It is common practice to deposit each layer on a substrate by electron beam evaporation or sputtering.

Furthermore, a method using ion blating is also considered.

Does film stress occur if the film deposition rate is too fast? If it is too slow, it will affect productivity, so usually θ, /A/sec ~/
It is assumed to be about 00 A/sec.

(Example) The present invention will be explained in more detail with reference to Example t below, but the present invention is not limited to the following Example unless the gist of the invention is exceeded.

Examples/Comparative Examples 1 to 3 A polycarbonate substrate was introduced into a magnetron sputtering apparatus and evacuated to a level below IO'Pa.
J Osccm, 02 Beg'l sccm introduced,
The pressure was adjusted by θ and jPaK. In this state, soow's 7
(RF sputtering with a 7 inch 2 Ta target at a deposition rate of 11 A/sec, refractive index co, /
'47's oxidized mental interference layer! OA was formed.

After evacuating the chamber once, Ar'ftJθsecm
, Tb and FegoCo were introduced to a pressure of 0.3 Pa.
,(.

targets were simultaneously sputtered.

When changing the composition, the power input to the Tb target and FEG at the time of spacing. By changing the power input to the co1G target, Tb and TbFeC.

The proportion of the total amount was changed. The thickness of the recording layer is /Io
It was created to be oA.

Next, a Ta chip was placed on the Al meta-get,
A reflective layer of Ta3 was formed. The discs produced are shown in Table/. Disc/Vi3. (Example 112) Disc 16/, λ, 5 are those of Comparative Examples 1 to 3. This disk was incorporated into a conventional magneto-optical dual playback device with an electromagnetic coil for magnetic field modulation, and the recording/reproducing characteristics and override characteristics due to magnetic field modulation were measured under the following conditions.

(Conditions) ■ Recording and playback characteristics CLV '1. Om/s f=/MHz, duty! ro% recording magnetic field/! 00e, θ00e Reproduction power /, 0HIW ■ Override characteristic CLV s, 6m/s Pre-recorded signal' /MHz, duty! ;
0% new override signal /, ! ; M
Hz 5duty kθ Recording magnetic field: 000e Reproduction power /, OmW Figures 1 and 2 show the recording and reproduction characteristics when the recording magnetic field is ±1s00e (Figure 1) and -〇〇〇e (Figure 2), respectively. The measurement results are shown below. As is clear from FIGS. 1 and 2, the Tb i dependence of the carrier level tends to decrease as the amount of Tb increases.

However, the noise level when performing magnetic field modulation recording in a weak recording magnetic field such as the above conditions largely depends on the n content, and the lowest value can be achieved by using a recording layer with a Tb content of Col atomic % to 24 atomic %. take. Above the recording magnetic field on disk 3/! 00e.

C/N rl, s dB, st at ±2000e
l and sdB were obtained.

FIG. 3 shows the laser power dependence of the erasure ratio as an example of the override characteristics of the disk 30.

The cancellation ratio is defined by the following equation.

Elimination ratio=Ko toIg (P//P2)PlNio-
Signal amplitude P2 of 1, θMHz left after pearlite = newly overridden / ,! rME-
1z under the condition of θθOs on the recording magnetic field with a signal amplitude of 1! ; Recording power of more than mW! A very good cancellation ratio of less than θdB was obtained.

Comparative Examples q to g For comparison with Examples, discs with a sand inch structure sandwiched between recording 1 hot tantalum oxide dielectric layers without a reflective layer (disc 6...lo) y2 (hereinafter That is, under the same conditions as in Example 1, the interference layer,
Recording layer! Created.

In this case, the recording layer was created to have a film thickness of toooi. Next, in place of the reflective layer, oxidized mental t1 was added again.
7!08 was created under the same conditions as when creating the interference layer. Table 2 shows the discs produced. The recording and reproducing characteristics of this disc t1 were examined under the same conditions as in Example 1. Measurement results 9th
As shown in the figure. In the sandwich structure, the amount of Tb is 23-2S
The noise takes the lowest value in atomic %. The highest C/N$♂d8 was obtained for the disk with the sand inch structure in the disk countermeasure, but the C/N was considerably lower than that of disks 3 and d8 of the present invention.

Comparative Example For comparison with Example//, a sandwich-structured disc (Disc//) without a reflective layer was produced. That is, the interference layer/recording layer was created under the same conditions as in Example 1. In this case, the recording layer was formed to have a film thickness of 1I00. Next, replace the reflective layer with tantalum oxide again under the same conditions as when creating the interference layer? jOA was created. The manufactured disks are shown in Table λ. The recording and reproducing characteristics of this disc were examined under the same conditions as in Example 1. The measurement results are shown in Figure 2.

In the sandwich structure, by making the recording layer thinner, the dependence on the magnetic field was improved and it became possible to reduce noise, but due to the decrease in signal strength, C/N = 4ta, s dB L could not be obtained.

Tb/ (Tb + Fe Co) (atZ) (Effects of the Invention) According to the present invention, /! ;0-2! A magneto-optical recording medium suitable for magnetic field modulation recording which has good and stable characteristics due to the low magnetic field of 00e can be obtained.

[Brief explanation of drawings]

Figures 1, 2, and j show recording and reproducing characteristics (carrier level, noise level) according to the embodiment of the present invention and comparative example.
This shows the composition dependence of FIG. 3 shows the overwriting percentage according to Example π of the present invention.

Claims (2)

[Claims] (1) In a magneto-optical recording medium in which an interference layer, a recording layer made of an alloy of a rare earth metal and a transition metal, and a reflective layer made of Al or an Al alloy are sequentially provided on a transparent substrate, the recording layer has a coercive force of 15 KOe at room temperature. A magneto-optical recording medium for magnetic field modulation recording, which is characterized by being larger. (2) The magneto-optical recording medium according to claim 1, characterized in that the direction of the magnetic moment per unit volume of the recording layer is the same as the direction of the magnetic moment of the transition metal in the recording layer. A magneto-optical recording medium for magnetic field modulation recording.