JPS6148148A - Thermooptical magnetic recording medium - Google Patents

Abstract

PURPOSE:To form a vertical magnetization film with recording and reproducing characteristics by the method with a small thermal load to a base by adopting a specific ferrimagnetic amorphous alloy film as a reproducing layer and a magnetic film with a low Curie temperature and a large coercive force as a recording layer. CONSTITUTION:Since a ferrimagnetic amorphous alloy film of Tbx(Co1-yMy) having a large magnetooptic effect, that is, large rotary angle and Farady rotating angle and large reflected luminous amount is used as the reproduction layer, the reproducing characteristic is excellent. Further, the recording layer made of a magnetic film low in the Curie temperature is used in combination with the ferrimagnetic amorphous alloy film of the reproducing layer with respect to the recording characteristic, the magnetization inversion of the reproducing layer is caused near the Curie temperature of the recording layer. Thus, the characteristic with higher sensitivity than that of a TbCo film single layer and the same degree as the single layer film of the TbFe film only is attained.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention records information using heat based on irradiation with at least a light beam such as a laser beam, and records information recorded by irradiation with a light beam. It relates to a photothermal magnetic recording medium for reproducing a magnetic layer, especially a magnetic layer consisting of a recording layer and a reproducing layer.
The present invention relates to a photothermal magnetic recording medium having a layered structure.

(Technical background of the invention and its problems) Recording media on which information is recorded and reproduced by irradiation with light beams (mainly laser beams), so-called optical disks, are categorized based on their functions as read-only types.

DRAW (Dtrect Read After
Write: There are three types: one-time writeable/non-erasable) type and rewritable type. Of these, read-only type and DRA
The W type has already been put into practical use. In a DRAW type optical disk, a groove (hereinafter referred to as a pregroup) for guiding an optical head is usually provided on the disk base to facilitate accurate tracking and high-speed random access. In addition, in both the read-only type and the DRAW type, in order to prevent reproduction errors due to adhesion of dust, the light beam enters from the opposite side to the side where the recording layer is formed, that is, from the back side of the substrate. It has become so.

Although it has not yet been put into practical use, it is desirable to provide a pre-group as described above even in the rewritable optical disk memory to which the present invention is directed, and the light beam is also incident from the back side of the base. method is advantageous.

In order to make the light beam enter from the back side of the base, the base naturally has to at least react to this light beam.
In other words, it must be transparent in the wavelength range of the light beam used. Specific examples of substrate materials that meet this requirement include glass-based materials and resin-based materials such as PMMA (polymethyl methacrylate), PC (polycarbonate), and epoxy. On the other hand, methods for forming pre-groups on substrates made of such materials include, for glass-based materials, two methods: coating a flat glass disk with resin, exposing and developing it, and another method using a glass disk locally. For transparent resin materials, there is a method of creating a substrate with pre-groups by injection molding or casting using a mold with a surface shape that corresponds to the pre-groups. Can be mentioned.

If we compare the suitability of the two types of substrate materials mentioned above, taking into account the formation of pre-groups, we find that resin-based materials are advantageous in terms of mass production and cost.
Resin-based materials are also more reliable than glass-based materials in terms of safety when rotating at high speed during playback.

In fact, most read-only and DRAW optical disk memories use polymethyl methacrylate or polycarbonate as the base material.

Also in a rewritable optical disk memory in which a recording layer that can be recorded, reproduced, and erased is formed on a substrate, it is desirable to use a resin-based material as the substrate material for the same reason. However, resin-based materials have drawbacks such as gas permeability, high water absorption, and poor heat resistance.

Therefore, the recording layer formed on the substrate is required to have corrosion resistance, and a manufacturing process that imposes a heat load on the substrate during disk formation cannot be used.

Several specific construction methods have been proposed for rewritable optical disc memory, but the one with the most stable memory effect is a magnetic film that has an axis of easy magnetization perpendicular to the substrate surface as the recording layer. This is a photothermal magnetic recording medium in which a perpendicular magnetization film (hereinafter referred to as a perpendicular magnetization film) is formed. As is already well known, the principle of photothermal magnetic recording media using perpendicularly magnetized films is that a light beam modulated by the information signal to be recorded is irradiated onto the recording layer to locally heat it to around one Curie temperature. Alternatively, information is recorded in the form of magnetization reversal of the perpendicularly magnetized film by applying an external magnetic field in addition to the above heating. On the other hand, to reproduce recorded information, a perpendicularly magnetized film is irradiated with a linearly polarized light beam, and the polarization plane of the reflected light is rotated (as much as possible) based on the magnetization reversal of the perpendicularly magnetized film, and the polarization plane of the transmitted light is This is done by detecting the rotation of (Faraday rotation).

Here, the materials for the perpendicular magnetization film include Mn3i polycrystalline material, Eu-chalcogenide material, and so on. i-type garnet-based single crystal materials, and rare earth-transition metal amorphous alloy materials (hereinafter abbreviated as RE-TM-based materials; fii earth elements are abbreviated as RE, and i!!transfer metals are abbreviated as TM). ).

Among these, Mn-B1-based materials tend to undergo phase changes and have narrow recording margins.

EU-chalcogenide materials have the disadvantage of large grain boundary noise; EU-chalcogenide materials have the disadvantage of not being able to retain recorded bits at room temperature; magnetic garnet-based single crystal materials are difficult to manufacture and are not effective; has the disadvantage that it is impossible to form a film at the current technological level.

On the other hand, RE-TM materials generally have a C of the reproduced signal.
Although it has drawbacks such as low effectiveness and poor corrosion resistance, it can be formed on large-area substrates by mass-producible methods such as evaporation and sputtering, and it is It is considered the most promising because it has the advantage that its properties can be controlled over a wide range by combining 9 composition ratios of RE and TM, and research and development are currently being actively carried out in various places with the aim of putting it into practical use. RE-TM
Gd and Tb are used as RE in the system materials.

Dy is typical, and l''e and co are typical for TM, and the characteristics vary greatly depending on their combination and composition ratio.

The following can generally be said about RE-TM materials. First, regarding recording characteristics, that is, whether magnetization reversal can easily occur due to the coercive force of the irradiated part decreasing to several hundred Oel or less when irradiated with a low-power light beam from a semiconductor laser, etc., RE Especially when TM is Fe, Dy.

Since the Curie temperature is lower in this order, Tb and Gd are preferred in this order. Regarding reproduction characteristics, that is, whether the rotation angle θK of the reflected light during irradiation with the linearly polarized light beam for reproduction is as large as possible and the amount of reflected light is large, for RE, Gd, Tb, and DV are adjusted to θ in the order of It is good because the value of is large, and TM is good because the light reflectance of the film is large in the order of CO and l"e. Stability of minute recording bits (larger coercive force at holding temperature) difference)
Regarding RE, Tb, Dy, and Gd are good in that order. Furthermore, from the perspective of corrosion resistance of recording media,
It is much more advantageous for the TM to be CO than for Fe, and conversely, from the viewpoint of uniformly producing a perpendicularly magnetized film with uniform characteristics over a large area, it is more advantageous for the TM to be CO than for Fe.
is more difficult than if it were.

As described above, it is difficult to satisfy all the performance requirements for a photothermal magnetic recording medium with a single layer RE-7M film. As an effective means to solve this problem, two layers of R
It has been proposed to stack E-TMII. RE-
Regarding the improvement of photothermal magnetic recording and magneto-optical reproducing characteristics by double-layering TMII, see, for example, references (1) [Magneto-optical Memory Comprehensive Technology Collection] published by Science Forum, Section 3 Amorphous Materials ■ Amorphous Multilayer Film 9 Reference (2) )
J, Appl, Phys, 55 (6),
15 March1984, JP-A-56-153
This method is disclosed in Japanese Patent Application Laid-open No. 546, Japanese Patent Application Laid-open No. 78652/1983, and the like.

In these known examples, GdFe1li and GdC011, which have a large effect as much as possible, are formed in the direction of incidence of the light beam, and TbFe11, which has a large coercive force at room temperature, is laminated thereon.
, a structure in which a DyFe film is formed has been specifically described, and it has been reported that recording characteristics, reproduction characteristics, and stability of recorded bits are improved compared to a structure with a single layer.

However, it is difficult to apply such a two-layer RE-7M film to a photothermal magnetic recording medium with a practical configuration, that is, a medium having a structure in which a substrate is preferably made of a resin material, and a reproducing layer and a recording layer are laminated on this substrate. In this case, for example, if the reproducing layer is a GdFe film, the oxidation of the GdFe film progresses due to oxygen in the air that permeates from the substrate side, causing a problem in terms of service life. In order to avoid these problems with the GdFe film, it is possible to interpose a transparent protective layer between the substrate and the GdFe film, but it is possible to Depending on the film method, it is difficult to form a pinhole-free transparent protective layer over a large area at the current technological level;
It has no effect on the progression of a. In addition, GdC in the reproduction layer
When using an O film, it is extremely advantageous in terms of lifespan, but on the other hand, a GdCo film becomes a perpendicularly magnetized film without using the bias sputtering method for film formation, so the resin substrate is exposed to heat during film formation. The problem is that it cannot withstand the load. Furthermore, the RE-Co film, which has excellent corrosion resistance, has the problem that when recording and reproducing are repeated over a long period of time, the perpendicular magnetic anisotropy decreases due to thermal relaxation, making it impossible to record information.

In this way, in a photothermal magnetic recording medium using two layers of RE-TMIIm, both the reproducing layer and the recording layer are subject to heat load on the substrate surface during film formation using non-bias or low-bias sputtering or vapor deposition. It is required that a perpendicularly magnetized film can be easily formed using a small film formation method, and that the reproducing layer on the side where the light beam is incident has excellent corrosion resistance, but known configurations do not meet these requirements. It was difficult to meet the requirements.

(Objective of the Invention) The object of the present invention is to provide a perpendicularly magnetized film with good recording and reproducing characteristics, to form a perpendicularly magnetized film using a method that places little heat load on the substrate, and to have excellent corrosion resistance and thermal stability. The object of the present invention is to provide an excellent long-life photothermal magnetic recording medium.

[Summary of the invention]

The present invention is constructed by laminating a recording layer and a reproducing layer having an axis of easy magnetization in a direction perpendicular to the surface of the substrate on a substrate, and records information by at least heat based on irradiation of a light beam. In a photothermal magnetic recording medium that reproduces information by irradiation with Tb)((CO+ −
y My )t-x (However, M is B, Affi, C
, Si, Ge, P, Ti, Zr.

Hf, V, Nb, Ta, Cr, Mo, W (7) is an element consisting of at least 1 PIl, and X is 0.1≦x≦Of
, 4 numbers, 1. to, Q1≦y≦Q, 3(7) number), and the recording layer is a magnetic film having a lower Curie temperature and a larger coercive force than the reproducing layer. Features.

Here, the component M added to the reproducing layer increases the crystallization temperature of the reproducing layer to improve thermal stability. In this case, if y is less than 0.01, no improvement in thermal stability will be observed, and if y exceeds 0.3, the magneto-optic effect will deteriorate, so it is necessary to keep it within the above range. especially,
A composition in which the magnetic compensation temperature is below room temperature has a large magneto-optical effect, and the thermal stability is significantly improved. The composition is Tb
An appropriate atomic ratio of /Tb+Go is 0.22 or less. Furthermore, if X is less than 0.1 or exceeds 0.4, the reproduction layer will be in a state where it does not have an axis of easy magnetization in the direction perpendicular to the film surface, so it was set in the above range.

On the other hand, the magnetic film constituting the recording layer, which has a lower Curie temperature and higher coercive force than the reproduction layer, has a coercive force of 1 to 2 at room temperature.
kOe or more, and the Curi temperature is 50°C or more and 250°C or less (more preferably 100°C
above, and below 200°C). An example of a magnetic film that satisfies these conditions is a TbFe film.

TbFeC0 film, TbGdFe111. A TbDyFe film, a TbGdFeCo film, etc. can be used.

In addition, for the reproduction layer, Curie humidity (writing temperature)
is 100℃ or higher and 200℃ or lower, and the coercive force is 0.5k.
Oe or less is preferable.

In addition, the present invention uses a transparent resin material such as polymethylmethacrylate-1-, polycarbonate, or epoxy, which facilitates the formation of pre-groups and does not pose any safety problems during high-speed rotation. This is particularly effective when

In addition, in the present invention, as a transparent protective layer that enhances the magneto-optic effect between the substrate and the magnetic film,
For example, 3iQ, SiO2゜TiO2, SnO2, Bi2
Oxide film such as O3, or S ii N4, Af
It is also possible to insert a nitride film such as fiN.

Furthermore, the thickness of the reproduction layer in the present invention is 100 to 50 mm.
Appropriately, the number of participants is approximately 0, and the thickness of the recording layer is approximately 100 or more. These reproduction layers and recording layers have a clear boundary.
It does not necessarily have to be divided into layers, and the composition may change continuously from the reproducing layer to the recording layer.

〔Effect of the invention〕

According to the present invention, the reproduction layer has a magneto-optical effect, that is, a large rotation angle and a Faraday rotation angle, and the reflected light m
Since a ferrimagnetic amorphous alloy film with a large Tbx (COI-, M,) is used, the reproduction characteristics are good. In addition, regarding the recording characteristics, by using the ferrimagnetic amorphous alloy film of the reproducing layer in combination with a recording layer made of a magnetic film with a lower Curie temperature than that of the ferrimagnetic amorphous alloy film, the magnetization reversal of the reproducing layer is caused by the recording layer. Since this occurs near the Curie temperature of , it is possible to obtain higher sensitivity than, for example, in the case of a single layer of TbFe1l, and as good characteristics as in the case of using a single layer of only TbFe11.

Furthermore, in the present invention, both the reproduction layer and the recording layer have Gd
Not bias sputtering like Co11l,
Polymethyl methacrylate, polycarbonate, and epoxy materials can be fabricated using film-forming methods that place a small heat load on the substrate, such as non-bias sputtering and vapor deposition, making it easy to create pre-groups that are normally required for this type of recording media. Resin-based substrates such as the following can be used. In addition, since such a resin base has good gas permeability, corrosion of the magnetic film is a problem, but according to the present invention, for example, a material transparent to the light beam is used as the resin base, and the reproduction layer and The reproduction layer of the recording layer is formed on the substrate side, and a light beam is irradiated from the back side of the substrate to record.

During reproduction, the ferrimagnetic amorphous alloy film of the reproduction layer has good corrosion resistance, so there is no risk of corrosion of the recording layer through the substrate, and the high crystallization temperature makes it stable over a long period of time. Recording and playback will become possible, and the lifespan will be extended.

[Embodiments of the invention]

The first factor is a recording cross-sectional view of a photothermal magnetic recording medium according to an embodiment of the present invention. In FIG. 1, a substrate 11 is, for example, a polymethyl methacrylate substrate, on which a 5iiN+ film, for example, is formed as a first protective layer 12, and a reproducing layer 13, for example, TbCoT igI, is formed on this substrate 11.
is formed.

The recording layer 14 is formed on the reproducing layer 13 by using, for example, TbF.
A film 2.1 is formed on the recording layer 14.
As the protective layers 15 and 16 of No. 3, for example, a 5isN+ film and a polymer layer are sequentially formed.

FIG. 2 is a schematic diagram of the sputtering apparatus used for forming each layer in this example. In FIG. 2, a chamber 20 as shown in FIG.

A composite target 22 in which a predetermined number of T1 thin plate chips are layered to have a predetermined composition is arranged.

Then, the degree of vacuum inside the chamber 20 is adjusted to lXl by the gas introduction pulp 23 and the exhaust pulp 24 connected to the chamber 20.
After reducing the pressure to 0-'Torr or less, high-purity Ar gas is introduced into the chamber 20 to a pressure of 3X10-'Torr, and RF power of about 300W is applied from the high-frequency power source 25 to perform sputtering, and sputtering is performed on the substrate 21. Approximately 500 CoTbT igI26 films were deposited.

The state of the CoTbTi film 26 formed in this way 2
When examined by 6-ray diffraction, it was found to be amorphous. Moreover, as a result of analyzing the composition of this film, T bss (COO, 95
Ti. 1. os) was 84. Furthermore, when we measured the magnetic Kerr hysteresis loop using a polarizer in a magnetic field, it was confirmed that this film has an axis of easy magnetization perpendicular to the film surface, and the maximum rotation angle is 0.25" (wavelength λ -633 nm) J-large, and the coercive force was 1 kOe at 25 °C and 0.4 kOe at 150 °C.In addition, when the crystallization temperature was measured by the four-terminal method, it was 470 °C, indicating good thermal stability. This was confirmed.

Similar experiments were conducted on examples and comparative examples in which the composition of T b z (COI-y M y ,) l-X- was different from the above, and the crystallization temperature was measured. The result is the first
Shown in the table.

Based on the embodiment of the present invention <Tbx(Cot-, M,)1. −
It is clear from the above table that the crystallization temperature of the X film is much higher than that of 'rbcogt which does not contain M, which supports the embryonic properties of the present invention. Similar effects were obtained with other M's.

Next, a process for manufacturing a photothermal magnetic recording medium based on an embodiment of the present invention shown in FIG. 1 using the sputtering apparatus shown in FIG. 2 will be described.

First, a polymethyl methacrylate substrate with a thickness of 1.5IIa and a diameter of 305m+ having a groove for an optical head guide was fabricated by injection molding as the base 11, and after its surface was Freon-cleaned, it was placed in the chamber 20 of FIG. It was set as shown in 21. Inside the chamber 20 are Tb, )'-e as targets 22.

C0Ti and Si3N+ targets are placed. In this state, first, the gas introduction valve 23 and the exhaust valve 2
4 to control the degree of vacuum in the chamber 20 to lXl.
After reducing the pressure to 0-'Torr or less, flow high-purity Ar gas into the chamber 20! 10105c, chamber 20
The gas pressure in the chamber 20 is adjusted to 5x10-3 Torr by adjusting the opening of the gate valve between the
was held at Next, while rotating the substrate 21, 500 W of RF power was applied to the 3i3N+ target and sputtering was performed for 20 minutes to form a first protective layer 1 on the substrate 21.
A 3i3N+gl with a thickness of about 1000 people as 2 was formed. Next, a Tb target and a CoTi
A direct current voltage was simultaneously applied to the alloy target so as to obtain a predetermined composition, and sputtering was performed for 2 minutes to form a TbCoTi film with a thickness of about 500 layers as the reproducing layer 13'. On top of this reproducing layer 13, a recording layer 14 is formed using a similar method to form a TbFe1 layer with a thickness of about 500 layers. , and furthermore, as a second protective layer 15, a Si3N layer with a thickness of about 1000 layers is formed.
+A film was formed. Furthermore, in order to prevent these multilayer films from coming into contact with the atmosphere, a polymer layer (sealing layer) 16 was applied by a spin code method.

The photothermal magnetic recording medium produced as described above was
It was set in an optical recording and reproducing system equipped with a 30nn+ semiconductor laser, a focusing and tracking servo system, and a signal detection system, and was rotated at 1800 rpm.
After forming a recording bit by irradiating a pulsed laser beam of 20Q n5eC width, 8 mW, and a diameter of 1 μm with a period of oonsec and applying an auxiliary magnetic field for recording of 300 [Oe], a continuous laser beam of 3 mW and a diameter of 1 μm was applied. When the recording bit signal (information signal) was reproduced by detecting the rotation angle as much as possible of the reflected light (@front light), the C/N of the reproduced signal was 1q of 55 dB.

Further, when the shape of the recording bit was observed using a polarizing microscope, a circular magnetic domain with a diameter of about 1 μm was observed with good contrast. Furthermore, after recording, the medium was left in a constant temperature and humidity layer, and the C/N ratio of the reproduced signal after one month and three months was measured, and the results were 54 dB and 55 dB, respectively, which were significantly different from the initial value within the measurement error. was not recognized.

The present invention is not limited to the embodiments described above; for example, in the embodiments, the recording layer is TbFe1! were exemplified, but TbFeCo and TbGdFe.

A similar effect can be obtained even when a film such as TbDyFe or TbGdFeCo is used, and in short, any magnetic material that has a lower Curie temperature than the reproducing layer and a high coercive force is sufficient. Further, in the embodiments, a resin material is used as the base material, but glass, ceramics, etc. may also be used. Furthermore, in the embodiment, the substrate is transparent and the light beam is incident from the back side of the substrate, but the present invention can also be applied to a photothermal magnetic recording medium in which the substrate is opaque and the light beam is incident from the side opposite to the substrate. Can be applied. In addition, various modifications can be made to the present invention without departing from the scope thereof.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of a photothermal magnetic recording medium according to an embodiment of the present invention, and FIG. 2 is a sectional view showing an example of a sputtering apparatus used for forming each layer of the photothermal magnetic recording medium. 11... Base, 12, 15.16... Protective layer, 13
...Reproducing layer, 14...Recording layer.

Claims (4)

[Claims] (1) Consisting of a recording layer and a reproducing layer that have an axis of easy magnetization in a direction perpendicular to the surface of the substrate, which are laminated on a substrate. In a photothermal magnetic recording medium that reproduces information by irradiation, the reproducing layer has Tb_x(CO_1_-_
yM_y)_1_-_x (However, M is B, Al, C, S
i, Ge, P, Ti, Zr, Hf, V, Nb, Ta, C
An element consisting of at least one of r, Mo, and W, and
is a number with 0.1≦x≦0.4, and y is 0.01≦y≦0.3
A photothermal magnetic recording medium, characterized in that the recording layer is a magnetic film having a lower Curie temperature and a larger coercive force than the reproducing layer. (2) The photothermal magnetic recording medium according to claim 1, wherein the magnetic compensation temperature of the photothermal magnetic recording medium is below room temperature. (3) The base is transparent to the light beam, and the reproduction layer and the recording layer are laminated on the base in the order of the reproduction layer and the recording layer.
The photothermal magnetic recording medium described in . (4) The photothermal magnetic recording medium according to claim 1 or 2, wherein the substrate is made of a resin material.