JPH03235236A - Structure of magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording medium having high reliability, enough Kerr rotation angle for short wavelength and perpendicular magnetic anisotropy by providing a light-reflecting layer on a necessary side of a film comprising repeated layers of specified two elements and inorg. compd. CONSTITUTION:Platinum-group metal films 2 having perpendicular magnetic anisotropy and iron-group metal films 3 are alternately deposited on a transparent substrate 1, further, an inorg. compd. 4 is deposited, these layers are repeated, and then a reflecting layer 5 is provided on the opposite side to the reflection side of light. Thereby, the obtd. magneto-optical recording medium has high reliability suitable for super-high density recording with enough Kerr rotation angle for short wavelength and perpendicular magnetic anisotropy.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to optical recording using laser light, and in particular to a magneto-optical recording medium that is effective for ultra-high density recording and effective for stabilizing recorded magnetic domains. Regarding the structure of

[Conventional technology]

With the recent development of an advanced information society, the need for high-density, large-capacity file memory is increasing. Optical recording is attracting attention as one type of memory that can meet this demand.

Recently, read-only compact discs, laser discs, write-once optical discs that can be recorded only once, and rewritable magneto-optical discs have been put into practical use. Subsequently, efforts are being made to improve the performance of these disks. One of these is increasing storage capacity, and the most promising method is to shorten the wavelength of the laser light used. In that case, what matters is the recording material and the structure of the disc. In particular, when high-density recording is performed, the signal output during reproduction is small and errors may occur.

This is because the Kerr effect obtained decreases as the wavelength of the light used becomes shorter due to the characteristics of the recording material.

In order to solve this problem, various studies have been made on the materials constituting the recording film, as seen in US Pat. No. 4,695,514.

[Problem to be solved by the invention]

In the above-mentioned conventional technology, an element active against water and oxygen, such as Gd or Nd, is used for the recording film material, and the recording film may corrode, which poses a problem in terms of ensuring reliability. Furthermore, it has been difficult to obtain a sufficient figure of merit for ultra-high density recording due to the balance between the Kerr rotation angle and reflectance exhibited by these materials.

In particular, a recording method using short wavelength light is considered to be effective for ultra-high density recording. In this case, in addition to the well-known Nd-Ge-Fe system materials, materials in which platinum group elements (NM) such as pt and Pd and iron group elements (TM) such as Go and Fe are alternately laminated are used. be. Further, for the purpose of increasing the wavelength characteristics of the Kerr rotation angle and the rotation angle, an optically transparent dielectric layer (IC) typified by SiNx or SiO was formed between the NM layer and the TM layer. In that case, for example, NM/TM/IC/NM/TM/IC/
...and stacking layers repeatedly, NM/TM/NM/TM/
. . . The perpendicular magnetic anisotropy may be reduced compared to when stacked with . . . , and the stability of recorded information may become a problem.

The present invention provides a high-performance magneto-optical device that has a sufficiently large [err rotation angle and perpendicular magnetic anisotropy energy even for short-wavelength light] and has a structure suitable for ultra-high density optical recording with high reliability. The goal is to provide recording media.

[Means to solve the problem]

One of the problems when recording, reproducing, or erasing is performed using short wavelength light is that when short wavelength light is used, the magneto-optical effect (for example, Kerr rotation The problem is that the angle) decreases, making it impossible to obtain a large reproduction output. To solve this problem, platinum group elements (NM) represented by PT and Pd and iron group elements (TM) represented by Fe and CO are used as recording materials in a thickness of several to several tens of layers per layer. We have found that it is effective to use a recording film with a multilayer structure in which layers are alternately laminated. In order to improve this magneto-optic effect and wavelength characteristics, in addition to repeating the TM/NM process described above, a thin layer of optically transparent inorganic compounds (IC) such as SiNx, SiO, and Al2N is used. TM with added layers/
It was effective to have a multilayer structure of repeating NM/IC/TM/NM/IC.... However, in this case, the perpendicular magnetic anisotropy energy was about the lower limit value (I x 10', 7/m) that can stably exist as a perpendicularly magnetized film. In order to solve this problem, the laminated structure is TM/N
It has been found that it is effective to have a structure in which M/TM/IC or NM/TM/NM/IC is a repeating unit. This increases the perpendicular magnetic anisotropy energy to 6
A remarkable increase of 10s to I x 10'J/m' was observed. This value is the same as that of the currently widely used TbFeCo system, and exists stably as a perpendicularly magnetized film. This means that the recorded data is stable and
This means that recording and playback can be performed well.

Among the materials used, TMs include Fe and Co.

One element selected from Ni or an alloy of two or more types is used. Moreover, as NM, Pt, Pd.

One or more alloys of platinum group elements represented by Rh are used. Further, as the inorganic compound (IC), at least one compound selected from silicon nitride, aluminum nitride, and silicon oxide is used. And what is the method for forming multilayer films?

A vacuum evaporation method, a sputtering method, etc. are used. The simultaneous multi-element film formation method is effective in terms of characteristics and mass productivity. Also in film formation.

For the NM layer and TM layer, it is good to have a few to several dozen people, and for the IC layer, it is good to have about 100 people. This is particularly effective because the wavelength characteristics of the magneto-optic effect can be freely selected by controlling the thickness of the IC layer. Furthermore, by controlling the internal stress of the recording film, the perpendicular magnetic anisotropy energy can be arbitrarily selected.

On the other hand, as a recording method, magneto-optical recording using both an externally applied magnetic field and a laser beam, or only one of them may be used. That is, it may be carried out using the magnetic and magneto-optical properties of the magneto-optical recording film, or it may be carried out using only the magnetic properties. However, in order to perform high-density recording, it is more advantageous to use optical properties to determine the recording position of information.

[Effect]

Ultra-high-density information recording films are required to exhibit large magneto-optical properties for short-wavelength light and to exist stably as perpendicularly magnetized films.

When using an alternately laminated film of platinum group elements and iron group elements, N
The perpendicular magnetic anisotropy energy is increased by increasing the number of contact interfaces between M and TM and by increasing the internal stress of each layer.

Therefore, as in the present invention, this film is made of a platinum group element (N
M), an iron group element (TM) and an inorganic compound (IC),
For example, NM/TM/NM/IC/NM/TM/NM/・
..., or TM/NM/TM/IC/TM/NM/T
By repeating M/..., the perpendicular magnetic anisotropy energy can be increased. This is because the contact interface between NM and TM was increased compared to the case of NM/TM/IC/NM/TM/....

〔Example〕

Hereinafter, the present invention will be explained in detail using Examples 1 and 2.

[Example 1] FIG. 1 shows a cross-sectional structure of a recording medium manufactured in an example of the present invention. The medium was produced by a four-element simultaneous sputtering method using a magnetron sputtering device. On a plastic or glass substrate 1 having guide grooves, Co is used as the first and third layers of iron group element films 2, PT is used as the second layer of platinum group element films 3, and PT is used as the fourth layer. 5iNx (refractive index 2.0) was used as the inorganic compound film 4.

The sputtering conditions were a gas pressure of 5 mTorr and a discharge gas of A.
r, targets used were Co, Pt, Si, and N.

During sputtering, the substrate was rotated at 12 Orpm. The film thickness of each layer was controlled by the input RF power, and the film thickness was 15 for Go, 8 for PT, and 80 for SiNx, and 10 sets of Co/Pt/Co/SiNx were stacked. . Finally, AQ as the reflective film 5,
, Ta film was formed by sputtering method. AQTa alloy is used as the target, Ar gas is used as the discharge gas, and the discharge gas pressure is IX 10 '''' Torr.

FIG. 2 shows the Kerr rotation angle rotation angle wave 1 (λ) dependence of the recording medium thus formed. From this, λ=
It shows the maximum value at 500-600 nm, θm=1.1°,
The reflectance was R=15%. By selecting the film thickness of the inorganic compound 4, the wavelength at which the above-mentioned θk becomes maximum can be set to an arbitrary value.

Therefore, depending on the wavelength of the laser light used, the maximum 0
1 can be formed.

When the perpendicular magnetic anisotropy energy of this film was determined, it was found to be 8
It was X10'J/rn'. This is because Co
/ Pt / S i N / Co / Pt
2 of the recording film formed by repeating /S i N...
It is about 4 times larger than X10'J/rn'. This increases the stability of the perpendicularly magnetized film, making it possible to stably retain recorded information and improving the reliability of the disk.

Information was recorded on this disk by a light modulation recording method using a laser beam (λ=530 nm) and an electromagnet. The conditions at that time were a rotational speed of 3600 rpm, a laser power of 7 to 9 mW, and a pulse width of 60 to 80 ns, and the power and pulse width were changed depending on the disk position. 5.
When recording was performed on the innermost circumference (r=30 m) of a 25-inch disc at a recording cycle of 1.5 T, the C/N was 55 dB.

In addition, high-density recording can also be performed using a magnetic field modulation recording method using a magnetic head as a recording method. On this occasion,
The so-called feather-shaped tail of the recorded magnetic domain becomes shorter, causing interference between bits.<<, edge controllability is good, and it is suitable for bit edge recording. According to the recording medium of the present invention, it can be used as a perpendicular magnetic recording film by a magnetic head. The magnetic force must be 1 kOe or less. For this purpose, it is necessary to control the gas pressure during sputtering and the film thickness of PT and CO.

Furthermore, instead of CO in the iron group element film 2, Fe, Nj, or an alloy of iron group elements such as Fe-Co may be used.

Furthermore, Pt-Co, Pt-Fe, P
d-Go, Pd-Fe or Pt-Fe-Co.

An alloy such as Pd-Fe-Co may be used as the iron group element film 2. In this case, - the thinner the layer thickness, the greater the perpendicular magnetic anisotropy energy of the recording medium, 2X10
'J/rn' was obtained.

Furthermore, similar effects can be obtained by using aluminum nitride or silicon oxide in place of silicon nitride as the inorganic compound film 4. An important point in this case is control of the refractive index of the film. That is, in order to change the wavelength at which the maximum value of θ is obtained, the refractive index may be controlled in addition to the thickness of the inorganic compound film 4.

Furthermore, it goes without saying that it is desirable to reduce the light absorption rate as much as possible.

[Example 2] FIG. 3 shows a schematic cross-sectional structure of an optical recording medium manufactured in this example. The recording medium was produced by a four-element simultaneous sputtering method using a magnetron sputtering device. The procedure is as follows.

On a glass or plastic substrate 1 having a guide groove, Pd is used as the first and third platinum group element films 3.
Fe B, co 46 as iron group element 2 in the second layer
Silicon oxide was used as the alloy and as the fourth layer of inorganic compound film 4. The film thickness of each layer is 10 for Pd film and 10 for Fe film.
There were 15 people for Co film and 100 people for silicon oxide. Then, 12 sets of these four layers were laminated.

The sputtering conditions at this time were Pd alone and F as the target.
e Co alloy and SiO sintered body were used, Ar was used as the discharge gas, and the discharge gas pressure was set to 5 m Torr.

Finally, a 1° AΩ, Ti film was formed as a reflective film 5 by sputtering. Other sputtering conditions are as follows: Example 1
The conditions were the same as those for forming the reflective film.

During the above sputtering, the substrate was rotated at 12 Orpm.

FIG. 4 shows Kerr of the recording medium thus formed.
Rotation angle shows rotation angle wavelength dependence. In this figure, λ;48
It can be seen that θk is maximum between 0 and 520 nm.

At that time, θ was 1.2'', and the reflectance was 21%. Here, the wavelength at which θ is maximum is the inorganic compound film 4.
As in Example 1, it can be freely selected by selecting the film thickness and refractive index of . The perpendicular magnetic anisotropy energy of the recording film of this example obtained in this way is 7X1
0'J/rn', and FeCo/Pd/SiO/Fe
C.

/ P d / S i O/... was increased about 6 times compared to 1×10'J/m' of the film formed repeatedly.

This increased the stability of recorded information, making it possible to obtain a highly reliable recording medium.

Information was recorded on this disk by a magnetic field modulation recording method using a laser beam of λ=480 nm and a floating magnetic head. The conditions at that time were a disc rotation speed of 3600 r.
pm, laser power 7-9mW, recording frequency 20-2
It is 5MHz. The laser power and recording frequency were changed depending on the disk position. As a result, when recording was performed at the innermost circumferential position of a 5.25-inch magneto-optical disk at a laser power of near mW and a recording frequency of 20 MHz, a C/N of 54 dB was obtained. At that time, the recording magnetic domain size was 0.25 μm, and the recording period was 1.5T.

In addition, recording/reproduction characteristics similar to those of magnetic field modulation recording were also obtained in a so-called optical modulation recording method in which laser light was switched instead of switching the magnetic field.

Further, it is also possible to perform magnetic recording in which the laser beam is used only for positioning information, and recording and erasing is performed by a magnetic head. In this case, the important point is the coercive field force of the recording film, and its value must be large enough to allow the magnetic head to switch the magnetization direction.

In addition, although FeCo alloy was used as the iron group element film 2 in this example, Co-Ni
, a similar effect can be obtained by using an alloy of Fe-Nj.

When an alloy is used, there is a region along the Slater-Pauling curve in which the Kerr rotation angle increases. Furthermore, Pd-
Fe, Pt-Fe, Pt-Go, Pd-Go, Pt-N
i.

Pd-Ni, Pt-Fe-Go, Pd-Fe-Go, etc.
The perpendicular magnetic anisotropy energy can be increased by using an alloy of at least one of the platinum group elements and the iron group elements, and in particular by making these layers thick on the order of a few tens of people. can. Besides this, Ker
A similar effect can be obtained by changing the refractive index and thickness of the inorganic compound layer as a method of increasing the r rotation angle.

Furthermore, by changing the thermal conductivity of this material, it is possible to change the thermal conductivity of the entire recording film, making it possible to increase the controllability of the shape and position of the resulting recording magnetic domain. Thereby, bit edge recording can be performed and the recording density can be further increased.

〔Effect of the invention〕

According to the present invention, the perpendicular magnetic anisotropy energy can be increased by selecting the layer structure and film thickness of the recording film, which has the effect of increasing the stability of storage of recorded information. In addition, the effect obtained is NM/TM/NM/I
C or TM/NM/TM/IC is the minimum unit, and an IC layer may be sandwiched after several layers of NM and TM are alternately laminated. Furthermore, by selecting the material for the inorganic compound layer (IC), the thermal conductivity of the entire recording medium can be controlled, which improves not only the recording density on the disk but also the controllability of the recorded magnetic domain (for example, edge portion, shape and position). etc.) has the effect of increasing This effect is the same even if the thermal conductivity of the reflective film material is controlled. As a result, in addition to increasing the recording density simply by making the magnetic domains smaller, it is possible to further improve the recording density by introducing bit edge recording.

[Brief explanation of drawings]

1 and 3 are schematic cross-sectional views showing the structure of a magneto-optical recording medium according to an embodiment of the present invention, and FIGS. 2 and 4 are recording films of a magneto-optical recording medium according to an embodiment of the present invention. Ker of
FIG. 3 is a characteristic diagram showing the optical wavelength dependence of the r rotation angle. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Iron group element film, 3... Platinum group element film, 4... Inorganic compound film, 5... Reflective film. Part (2) Takuman Hina Nagairi (7th bay)

Claims (1)

[Claims] 1. A platinum group element (N
M), an iron group element (TM), and an inorganic compound material (IC) are alternately laminated to form a multilayer structure, and the film has perpendicular magnetic anisotropy. A structure of a magneto-optical recording medium characterized by forming a layer that reflects light on the opposite side. 2. A recording film having a multilayer structure in which a platinum group element (NM), an iron group element (TM), and an inorganic compound material (IC) are laminated according to claim 1, the constituent unit of which is TM/NM. /TM/IC,NM/
A structure of a magneto-optical recording medium characterized by having one set of TM/NM/IC, having at least two sets of this combination, and having a film thickness that allows light to pass through. 3. The light-reflecting layer described in claim 1 contains at least one element selected from Al, Au, Ag, Cu, Pt, Pd, and Rh, or is mainly composed of these elements. Elements listed in this section other than the mother element or T
1. A structure of a magneto-optical recording medium characterized by using an alloy to which at least one element selected from i, Ta, Cr, Al, Nb, Mo, and W is added. 4. A structure of a magneto-optical recording medium characterized in that at least one element selected from among Pt, Pd, and Rh is used as the platinum group element according to claims 1 and 2. 5. At least one iron group element selected from Fe, Co, and Ni as described in claims 1 and 2.
A structure of a magneto-optical recording medium characterized by using different types of elements. 6. A structure of a magneto-optical recording medium characterized in that silicon nitride, aluminum nitride, or silicon oxide is used as the inorganic compound material according to claims 1 and 2.