JPS61194640A - Optical disk device - Google Patents

Abstract

PURPOSE:To obtain an information recording and reproducing device capable of easily re-writing information with the use of a high density recording medium by giving at least two types of crystal structures in the solid state and using a recording medium employing metal or alloy holding the crystal structure inherent to one temperature area in the other one. CONSTITUTION:The recording medium has at least two types of crystal structures in the solid state, holds the crystal structure inherent to one temperature area in the other one, and/or composed of the metal or alloy causing different volume changes in the crystal state. Assuming that a semiconductor laser 12 used for recording and reproducing and semiconductor lasers for erasure are symbol numbers 12, 13 and 14, respectively, a parallel light beam (i) is direction-changed by 90 deg. by means of an optical synthesizer, and an approximately circular optical spot is formed in the center of the recording line of a disk through almost the center of an object lens 5. On the other hand, parallel light beams (j) and (k) advance in the same direction of the optical synthesizer 33, and take such a path that the optical spot can be formed at a position deviated by a fine distance DELTAl with respect to the recording line of the disk.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a new information recording/reproducing device, and particularly to information recording, erasing, and reproducing information by changing the crystal structure of a recording medium using light or thermal energy. The present invention relates to a recording/reproducing device.

[Background of the invention]

In recent years, as information recording becomes more dense and digital, various information recording and reproducing methods are being developed. Especially for recording information using laser light energy.

The optical disc used for erasure and playback is made of industrial rare metal 48.
0,1983 (Optical Disks and Materials), it is possible to achieve higher recording density than magnetic disks.
This is a promising method for recording information in the future. Among these, laser playback devices have been put into practical use as compact discs (CDs).

-10,000, Recordable systems can be broadly divided into two types: write-once type and rewritable type. The former can only be written once and cannot be erased. The latter is a method that allows repeated recording and erasing. In the write-once type recording method, a laser beam is used to destroy or shape the medium in the recorded area to create unevenness, and for reproduction, a change in the amount of light reflected due to the interference of the laser beam at the uneven area is used for reproduction. For this recording medium, it is generally known that Te or its alloy is used to form irregularities by melting and sublimating Te. Magneto-optical materials are the mainstream for rewritable recording media. This method uses optical energy to invert and record the local magnetic anisotropy of the medium near the Curie point or the compensation point temperature, and the polarization plane of the polarized incident light at that part is caused by the magnetic Faraday effect and magnetic Kerr effect. Play with the amount of rotation. This method is considered to be the most promising rewritable method, and active research and development is underway with the aim of putting it into practical use in the next few years. However, there is currently no material with a large amount of rotation of the plane of polarization, and even with various measures such as multilayer film formation, there is a big problem that output levels such as S/N and C/N are low. As another rewritable system, for example, Japanese Patent Publication No. 47-26897 utilizes a change in reflectance due to a reversible phase change between amorphous and crystalline recording media. Furthermore, write-once types that utilize a unidirectional phase change between crystalline and amorphous are also known.

However, this method has a major problem in that the source of crystallization of the amorphous phase is low, and the instability of the phase at room temperature affects the reliability of the disk.

[Purpose of the invention]

An object of the present invention is to provide an information recording/reproducing device that uses a high-density recording medium and can be easily rewritten.

[Summary of the invention]

The present invention uses a recording medium using a metal or an alloy that has at least two types of crystal structures in a solid state and maintains the crystal structure in one temperature range in the other temperature range, and in particular, By providing an optical system that applies erasing spots from both sides of the recording line, it is possible to eliminate the influence of changes in reflectance before and after recording as described later, and the recording medium has at least two types of crystal structures in a solid state. The information recording and reproducing device is characterized in that it is made of a metal or an alloy that maintains a crystalline structure in one temperature range in another temperature range and/or causes different volume changes in the crystalline state.

Note that any alloy that causes a change in unevenness can be used even if no crystal change occurs.

(Alloy Composition) The crystal mass transition alloy of the present invention has different crystal structures at high and low temperatures, and the rapidly cooled crystal structure is formed by rapid cooling from a high temperature.

Furthermore, the phase formed by this rapid cooling changes into a crystalline structure at a low temperature by heating at a predetermined temperature. In this way, such a change in crystal structure occurs when the cooling rate is 10"07 seconds or more or 10"07 seconds or more to obtain a crystal structure different from the crystal structure at a low temperature. Preferably.

The crystal mass transition alloy of the present invention is preferably made of an alloy of at least one element of group lb of the periodic table and at least one element selected from group b, llb, b, and yb. .

Examples of alloys include cu-Az gold alloy, Cu-Zn alloy, c
u-At-zn alloy, Cu-At-Ni alloy #Cu
-At-Mn alloy, Cu-A/, -Fe-Cr alloy, C
u-Ge alloy, Cu-At-Ge alloy, Cu-In alloy, Cu-At-In alloy.

Cu-Qe alloy, (::u-A1-Ge alloy, Cu
-8L1 alloy, Cu-'l'e alloy, Cu-4'i alloy.

CLI-At-8n alloy, Cu-7,n alloy, (:
: u-8i alloy, Cu-3b alloy, Cu-Be alloy.

Cu-Be alloy, Cu-Mn alloy, Cu-PD gold alloy (
::upt gold alloy Ag-Zr1 alloy, Ag-At alloy, Ag-Cd alloy, Ag-In alloy.

Ag-Ga alloy, Ag-At-AU gold alloy Ag-AL-
Cu alloy, Ag-A4-Au-Cu alloy.

Ag-At-Cd alloy, Ag-Pt alloy, Ag-8 alloy, Ag-8n alloyt Ag T' Gold alloy Ag-T
i alloy, Ag-Zr alloy, Ag-As alloy.

Ag-AIJ alloy, Ag-Be alloy, Ag-Mg alloy,
Ag-Li alloy, Ag-Mn alloy, At-pe gold alloy, At-Mg alloy, At-Mn alloy.

At-Pd alloy, At-Te alloy, ht-T; alloy,
A1-7. n alloy, Al-Zr alloy, Nj-sb gold alloy Ni-8n alloy, Ni-8n alloy.

N i -Q n alloy, Mrl-Ge alloy,]]'Jj
-Gl! Alloy, N1-M1 alloy Ni-8 alloy, Ni-4
'i alloy, Fe-As alloy #AS S alloy, As -
Zn alloy, 'e-Be alloy, gold alloy-Ni alloy.

F'e-Cr alloy, i;'e-p alloy, Mn-Pd
alloy.

Mn-pt gold alloy Mn-5b alloy, Mrt-87 alloy,
Au-Ca alloy, Au-At, alloy, Au-In alloy,
AU-Ga alloy, Au-Cd alloy.

Au-Cu alloy, Au-Fe alloy, Au-Mn alloy,
Au-Zn alloy, Ba-Ca alloy, Bi-pb
Gold alloy Bi-T/, alloy, Ti-Ni alloy.

N1-V alloy, Nt-Zn alloy, cd-Li alloy.

Cd-Mg alloy, cd-pb gold alloy (::d-i9
b alloy, 5b-In alloy, 3b-In-3e alloy.

M g -Ce alloy, Co-Cr alloy, Co-Ga alloy, co-Mn alloy, Go-3b alloy, Co-V alloy, I
n-Mg alloy, In-Mn alloy, In-Ni alloy, Jn
-8n alloy, In-Tt alloy.

L r-Zn alloy, Mn-7,n alloy, Pb-Tt alloy, pb-s alloy, pb-8b alloy, pd-2n alloy, f3n-8b alloy, Tt-8b alloy, 5b-Zn alloy, Ti- 5n alloy, 'rz-sn alloy.

7rr-8n alloy, 7. r-Th alloy, 'pi-2
There are n alloys, Tt-zr gold alloys, etc.

As examples of alloys, the following are preferred in terms of weight composition.

AgK30-40%Zn, 6-10%At, 40-60
%Cd, 20-30% In alone, 10-20% in Cu
At, 20-30% Ga, 20-40% In,
20~301Ge, 15~35@3n, lo
~60%Zn, 5-10%sr, 4-15%Be, 3
0-45% sb alone, 15-25% I on Au
n, 10-15% Ga, 5-25% Zn, 20
~55% Cd, 2.5~5% At alone, 55~55% At in Ni
Alloy with 60% At and 40-50% Ti added, I
n-25~35%Tt alloy, 55% or less P in Fe
tt-added alloy, Mn-5~50% Cu alloy I
5e15-25%-In30-40%-8b alloy, and the following elements other than the second component can be added as a third component to these alloys.

Ia, I[a, IVa, Va, ■a, V
Ia, *.

1b-4b, the total of one or more rare earth elements is 1
It is 5% by weight or less.

Specifically, li is used for group Ia, and Mg is used for group lea.

Ca and Va groups are Ti, zr, Hf, and Va groups are V.

Nb, Ta, ■a group is Cr, MO, W, ■a group is Mn%
■The groups are Co, Rh, Ir, pe, R, u.

Qs, Ni, Pd, Pt, lb group is Cu, Ag.

Au, ib group is Zn, Cd, llb group is H, At.

Ga, In, ■b group is C, Si, Qe, 3n.

P b%V b group HaP, 13 b, B i,
Rare earth element RhaY.

L at Cep S my G dy T bt
D'/pL u is preferred. In particular, 0.1 to 5% by weight is preferred.

It is also possible to use an alloy that forms irregularities by melting and sublimating an alloy mainly consisting of 'f'e and Se.

(Manufacturing method) In order to obtain reflectance variability, the crystal mass transition alloy of the present invention must be able to form a supercooled phase by heating and rapidly cooling the material. For high-speed information production and storage, K is preferably a non-bulk material with a small heat capacity and a high rapid heating and cooling effect. That is, it is desirable to be a non-bulk material having a volume that allows substantially only a desired area portion to change over the entire depth into a crystal structure different from the reference crystal structure by energy input to a desired minute area. Therefore, in order to fabricate high-density information in a desired small area, a non-bulk foil with a small heat capacity is required.

Films, thin wires, powders, etc. are desirable. As recording density,
For producing information in a minute area such as 20 megabits/- or more, the film thickness is preferably 0.01 to 0.2 μm. In general, intermetallic compounds are difficult to undergo heavy processing. Therefore, it is effective to directly rapidly cool and solidify the material from the gas phase or liquid phase to form it into a predetermined shape as a method for producing foil, film, thin wire, or powder. These methods include PVD method (vapor deposition, sputtering method, etc.), CVD method, molten metal quenching method in which molten metal is poured onto the circumferential surface of a metal roll and rapidly solidified, consisting of a member with high thermal conductivity that rotates the molten metal at high speed. .

There are electroplating methods, chemical plating methods, etc. When using a film or powder material, it is effective to form it directly on the substrate or to apply it and adhere it to the substrate. When applying, a binder that does not cause any reaction even when the powder is heated is preferred. Furthermore, in order to prevent oxidation of the material due to heating, it is also effective to coat the surface of the material, the film formed on the substrate, or the surface of the coating layer.

The foil or thin wire is preferably formed by a molten metal quenching method, and preferably has a thickness or diameter of 0.1 rxm or less.

In particular, in order to produce foil or thin wire with a crystal grain size of 0.1 μm or less, a thickness or diameter of 0.05 m or less is preferable.

The powder is preferably formed by an atomization method in which molten metal is sprayed together with a gaseous or liquid refrigerant and then poured into water to be rapidly cooled. The particle size is preferably 0.1 wm or less, and ultrafine powder with a particle size of 1 μm or less is particularly preferable.

The film can be formed by vapor deposition, sputtering, CVD electroplating, chemical plating, etc., as described above.

In particular, sputtering is preferable to form a film with a thickness of 0.1 μm or less. Sputtering allows easy control of the target alloy composition.

(Structure) The crystal mass transition alloy of the present invention has different crystal structures at high and low temperatures, and must have a composition of a supercooled phase in which the crystal structure at high temperature is maintained at low temperature by rapid cooling from high temperature. . Although the intermetallic compound has an irregular lattice crystal structure at high temperatures, the supercooled phase is preferably an intermetallic compound having a cs-ct type or DOs type regular lattice, for example. As the alloy of the present invention is capable of greatly changing optical properties, it is preferable that the alloy mainly forms this intermetallic compound, and a composition in which the entire alloy forms an intermetallic compound is particularly preferable. This intermetallic compound is called an electronic compound,
In particular, alloy compositions near 3/2 electron compounds (average outer shell electron concentration e/a of 3/2) are good.

Further, the crystal mass transition alloy of the present invention preferably has an alloy composition having in-phase transformation, for example, eutectoid transformation or enveloping transformation, and the alloy can be obtained with a large difference in spectral reflectance by quenching from high temperature and non-quenching. .

The alloy of the present invention preferably has ultrafine crystal grains, and particularly preferably has a crystal grain size of 0.1 μm or less.

That is, the crystal grains are preferably smaller than the wavelength of visible light, but may be smaller than the wavelength of semiconductor laser light.

(Characteristics) The recording material of the present invention can form at least two types of spectral reflectance in the visible light region at the same temperature.

That is, it is necessary that the spectral reflectance of a material having a crystal structure (structure) formed by rapid cooling from a high temperature is different from that of a material having a crystal structure (structure) formed by non-quenching.

Further, the difference in spectral reflectance obtained by quenching and non-quenching is preferably 5% or more, particularly preferably 10% or more. If the difference in spectral reflectance is large, it will be easy to visually distinguish colors, and this will have a significant effect in various uses described later.

As a light source for spectrally reflecting, electromagnetic waves other than visible light can be used, and infrared rays, ultraviolet rays, etc. can also be used.

Other properties of the crystal mass transition alloy of the present invention include electrical resistivity, optical refractive index, optical polarization rate, and optical transmittance, which can be changed reversibly in the same way as spectral reflectance, and various information can be obtained. It can be used to record and reproduce recorded information.

Since the spectral reflectance is related to the surface roughness of the alloy, it is preferable that at least the intended portion has a mirror surface so as to have 10% or more in the visible light region as described above.

(Applications) The crystal mass transition alloy of the present invention can be used to improve physical or electrical properties such as spectral reflectance of electromagnetic waves, electrical resistivity, refractive index, polarization index, transmittance, etc. due to partial or total change in crystal structure by heating and quenching. It can be used as an information recording element by changing the characteristics and utilizing the changes in these characteristics.

As a means of recording information, electrical energy in the form of voltage and current, electromagnetic waves (visible light, radiant heat, infrared, ultraviolet,
Light from photographic flash lamps, electron beams, proton beams, laser beams such as argon lasers, semiconductor lasers, high-voltage spark discharges, etc.) can be used, and in particular, the change in spectral reflectance caused by the irradiation can be used to record optical discs. It is preferable to use it as a recording medium. Optical discs include digital audio discs (DAD or compact discs), video discs, memory discs, floppy discs, microfiche, etc., and can be used for these. By using the alloy of the present invention in the recording medium of an optical disk, a reproduction-only disk and an additional recording medium can be obtained.

It can be used in any rewritable disk device, and is particularly effective in rewritable disk devices.

The recording method may be either a method of applying energy intermittently in pulses or a method of applying energy continuously. In the former case, it can be recorded as a digital signal.

[Embodiments of the invention]

The present inventors conducted various experiments on the crystal mass transition alloy of the present invention, and determined how the light reflectance changes before and after recording, with the intention of using it in an optical disk device. I looked into it. Specifically, we created a crystal mass transition alloy and investigated its properties.

Figure 6 shows a typical example of KF:. In this figure, (a) shows the state before recording, and (b) shows the state after recording. Optical disc devices take advantage of this characteristic, and use a light beam with a wavelength of 780 (nm), for example, to determine the amount of reflection when the light hits a recorded area and the amount of reflection when the light hits an unrecorded area. The presence or absence of information is determined according to the difference in the amount of reflection. As is clear from this figure, when recording, the reflectance increases as shown in C, and when erasing, the reflectance decreases as shown in d. Further, when ssO (nm) is selected, the reflectance is small like C' when recording, and becomes large like d' when erasing.

The wavelength side longer than the reference wavelength where the reflectance is the same before and after recording is called the long wavelength side, and the wavelength side shorter than the reference wavelength is called the short wavelength side.

By the way, in order for this crystal mass transition alloy to record or erase information, it must be heated to a temperature as shown in FIG. When recording, it is necessary to heat the recording medium to a temperature of 02 or above and cool it quickly.When erasing, a sufficient amount of It is necessary for the recording medium to receive the energy.

It is necessary to satisfy this relationship for recording and erasing.Ninth, if a wavelength of 550 (rum) is used, the third
It will look like the figure. As explained in Figure 6, as soon as recording is performed, the reflectance decreases and the absorption rate increases (
Since crystal mass transition alloys are metals, their transmittance is negligible. ), the temperature will rise rapidly if a certain amount of optical power is applied. Optical discs have a thin multilayer structure for heat absorption, light interference, and other purposes, and in order to prevent deformation, it is best not to heat them more than necessary. Therefore, it is necessary to control the optical power so as to heat up to θ' which is slightly higher than θ1.

On the other hand, during erasing, the reflectance increases (absorptivity decreases) as erasing is completed, so the temperature rise reaches a ceiling under a constant optical power. This in itself is a desirable direction and does not pose a problem.

By the way, the wavelength of semiconductor lasers, which are currently the most advanced in terms of size and cost reduction, is around 800 nm, and if this wavelength is used, there is a fear that erasing may not be possible as shown in FIG. In other words, when the temperature of the recording medium reaches θ2 and erasing is completed, the reflectance decreases (the absorption rate increases) as shown in Figure 6, so it is rapidly heated and the minimum temperature for recording is θ2.
This is a problem where the data exceeds the limit and is rewritten.

This phenomenon can be solved by reducing the optical power PzI for erasing and lengthening the time 11 until the temperature θ1 is reached, thereby increasing Δt, but high-speed erasing cannot be achieved.

It was confirmed that the volume of the recording medium changes as a result of recording and erasing, and that a concave or convex portion is formed on the base surface by recording, and the base surface returns to its original flat surface by erasing.

Hereinafter, one embodiment of the configuration of the optical disc device of the present invention will be described with reference to FIG.

In FIG. 5, the diverging light emitted from the semiconductor lasers 12, 13.degree. 14 becomes parallel light 'z Jp k by the collimating lens 22.degree. 23.24. Here, 12 semiconductor lasers are used for recording and reproduction, and 1 semiconductor laser is used for erasing.
3.14, the parallel light i is changed in direction by 90 degrees by the light combiner, and then passes through the polarizing beam splitter 31, the λ/4 plate 4,
A substantially circular light spot is formed at the center of the recording line of the disk by passing through the mirror 39 and substantially the center of the objective lens 5.

On the other hand, parallel lights j and k travel in the same direction through photosynthesis 33,
From 32 onwards, the process proceeds in the same manner as i, but takes an optical path such that a light spot is formed at a position shifted by a minute distance Δt with respect to the recording line of the disc, as shown in FIG. Here, an example is shown in which parallel light i is used for recording and reproduction and j and k are used for erasing, but these may be replaced. More specifically, a shaping prism is provided for recording and reproducing to make the ellipse of the light spot of the semiconductor laser substantially circular. The purpose and effect of this will be described later with reference to FIG.

The light reflected by the disk 1 passes through an objective lens, a mirror 39,
After passing through the λ/4 plate 4 and having its direction changed by the polarizing beam splitter 31, the coupling lens 6 and the cylindrical lens 62
and reaches the photodetector 7. Depending on the image formation state of this photodetector, υ controls the distance between the objective lens and the disk, that is, controls the focus lens and the track direction of the disk.
That is, a tracking servo signal is obtained. Various types of these methods are well known and will not be described here. This detection system is provided with a filter 42 for blocking the erase light reflected by j to prevent disturbance from entering the photodetector.

Next, the effect of shifting the erase spot by Δt from the center of the track will be explained using FIG.

As shown in FIG. 1, since the erasing light spot is deviated from the recorded nine signals, most of the erasing spots hit areas with low reflectance. Therefore, absorption of optical energy is high, and an equivalent temperature rise curve can be obtained with a power E2 that is lower than the optical power E1 described above. When the temperature reaches θl and the recorded area is erased, the reflectance decreases, but since the erase spot is applied to an area with originally low reflectance, the absorption of light energy remains almost unchanged, as shown in Figure 7. Stable erasure is possible with a temperature rise curve like this.

FIG. 8 shows another embodiment of the invention.

In the figure, 8 is a diffraction grating, and the rest of the structure is the same as in FIG. 5. This diffraction grating 8 is provided after the light from the laser diode 14 is made into parallel light by the collimating lens 24, and has a grating constant that emphasizes only the ±1st-order light. When this diffraction grating is rotated, the light spot formed on the disk becomes two light spots across the recording line, and the width of the light spot can be changed depending on the rotation angle. With such a configuration, it is natural that the above-mentioned effects can be achieved. This method of applying optical power from both sides of the recording line is particularly effective for recording media made of metals or alloys, which have high thermal conductivity, as described above.

The following experiment was conducted using this device.

An optical disk was manufactured by forming an Ag-40% by weight Zn alloy film on a glass substrate by sputtering. In order to prevent the alloy film from being oxidized by heating during recording and erasing, and to prevent it from peeling off from the substrate, 8!0 is applied to the surface of the alloy film.
A protective film (thickness: 30 nm) of No. 2 was formed by vapor deposition.

A DC-magnetron type was used for vapor deposition of the alloy film on the glass plate, and Sigh! An RF type sputtering method was applied to the formation of each. Sputtering power is 140-200W.

The substrate temperature was set to 200C. Inside the container 10-
' After evacuation to about Torr, Ar gas is
A thin film was prepared by introducing mTorr. The film thickness is S
The film thickness is about 30 nm, and the alloy film thickness is 0.05 to 10μ.
The thickness of the grain was varied within the range of m.

Using the optical disk thus manufactured, recording and erasing were performed, and these operations were repeated. The Ar gas laser was continuously oscillated. The sample was placed on a manual movement stage, the sample was moved, and the 200 mW laser beam was focused and scanned on the film surface of the sample. The area irradiated with the laser light turned pink. The alloy film, together with the substrate, has been heat-treated in advance to become silvery white. Next, the focus of the laser beam was slightly shifted from the film surface, the output density of the laser was lowered, and the laser beam was scanned in a direction K (vertical direction in the figure) intersecting the pink part. As a result, the original pink color was erased and the color changed to silvery white. It was confirmed that concave or convex portions were formed on the base surface at the same time as these color changes, which could be recorded, and that it returned to its original flat surface when erased.9.

From the above results, it was confirmed that recording and erasing can be performed using the alloy in a thin film state. It has been confirmed that this writing and erasing can be repeated any number of times.

〔Effect of the invention〕

According to the present invention, a highly stable recording medium can be used, and a highly reliable apparatus can be obtained.

[Brief explanation of drawings]

Figure 1 is a diagram for explaining the basic principle of erasing in the optical disk device of the present invention, Figure 2 is the principle of erasing records on the recording medium used in the present invention, and Figure 3 is a diagram for explaining the principle of erasing records on the short wavelength side. FIG. 4 is a temperature characteristic diagram for erasing on the long wavelength side, FIG. 5 is an example of the configuration of the optical disk device of the present invention, and FIG. 6 is the wavelength λ of the alloy used in the present invention. FIG. 7 is a temperature characteristic diagram showing the effects of the present invention, and FIG. 8 is another example. 1... Disk, 12, 13.14... Laser diode, 22, 23.24... Collimating lens, 3
1... Polarizing beam splitter, 32.33... Light combiner, 4... λ/4 plate, 5... Objective lens. 1 -eye 躬 2 躬 躬 時間 時間 時間 千 千 千 千 千 ５ ５ ５ ５ ５ ５ ５ ５ ま ま ま ま ま ま ま

Claims (1)

[Claims] 1. In an optical disc device that erases information recorded along a recording line of a recording medium on which information is recorded by irradiating a light beam and heating it, an information erasing light beam is provided on both sides of the recording line. The recording medium has at least two types of crystal structures in a solid state, the crystal structure in one temperature range is maintained in the other temperature range, and/or the recording medium has different volumes in the crystal state. An optical disc device characterized by being made of a metal or alloy that undergoes change. 2. The optical disc device for recording according to claim 1, wherein the recording medium is made of a metal or an alloy whose crystal structure at high temperatures in a solid state is maintained by supercooling from high temperatures. 3. The recording medium is a metal or alloy in a crystalline state that undergoes phase transformation, and has phases with different crystal structures in at least two temperature ranges in a solid state, and the recording medium has phases with different crystal structures in at least two temperature ranges in a solid state, and the recording medium has different crystal structures due to the transformation between the phases. By forming recesses or protrusions to change the state of light reflection with the base surface, signals, characters, figures, and symbols as information can be memorized in an identifiable manner, or the recesses or protrusions can be erased to their original state. The optical disc device according to claim 1, comprising heating means and means for reproducing the information. 4. The recording medium contains elements from groups I, b to VII, of the periodic table.
Claims 1 to 3 consist of a metal or alloy whose main component is a transition metal element of Group B or Group VIII metal element.
The optical disc device according to any one of paragraphs.