JPH0395742A - Magneto-optical recording system - Google Patents

Abstract

PURPOSE:To attain the magneto-optical recording at a high recording density and high CN by forming artificial grid films alternately laminated with Co layers, Pt layers and/or Pd layers as a recording layer and combining the layer with a light source which radiates the light of <=600nm wavelength. CONSTITUTION:The magneto-optical recording medium consisting of the artificial grid films alternately laminated with the Co layers, the Pt layers A, B and/or the Pd layers C as the recording layer is used. The artificial grid films exhibit excellent magneto-optical characteristics even at 780 to 850nm which is the wavelength region of a semiconductor laser used generally as the light source. Against that the magneto-optical characteristics of E-TM films D, E, such as Tb-Fe-Co, are extremely degraded at <=600nm, the tendency to the maintenance of nearly the specified magneto-optical characteristics or a slight increase therein is recognized for the artificial grid films A to C and the reproduction at the higher CN than with the RE-TM films is possible. Thus, the high-grade and high-density recording and reproducing utilizing the light of the short wavelength are possible.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical 6B recording system that records and reproduces information using a laser beam or the like using magneto-optic effect.
In particular, it relates to shortening recording/reproducing wavelengths.

[Summary of the Invention] The present invention provides recording and recording using light with a wavelength of 600 nm or less on a magneto-optical recording medium whose recording layer is an artificial lattice film in which CoN, PtN and/or Pd layers are alternately laminated. By performing reproduction, it is possible to increase the recording density, increase the speed, and improve the CN ratio in magneto-optical recording.

[Conventional technology]

In recent years, magneto-optical recording, which records information by writing magnetic domains on a magnetic thin film using thermodynamics such as semiconductor laser light, has been developed as a high-density recording method that can be used to record data easily. The method is attracting attention.

The recording material used in this magneto-optical recording method is C
d, Tb. A typical example is a non-quality alloy film (hereinafter referred to as RE-TM film) which is a combination of rare earth elements such as Dy and transition elements such as Fe and Co. The RE-TM membrane is
■Because it is ferrimagnetic, its magnetization is small even in the temperature range considerably lower than the Curie point. In addition, since the perpendicular anisotropy energy is large, it is easy to form a perpendicularly magnetized film required for high-density recording; ■ Medium noise is small due to low quality; ■ Force-per-rotation angle θK is relatively large; ■ Curie point is low ( 150～
It has a number of advantages, such as being able to achieve recording/erasing power of 200'C) and recording/erasing power using a commercially available semiconductor laser (20 to 40 mW). In particular, Tb containing Tb as a rare earth element
FeCo films, GdTbFe films, etc. have large perpendicular magnetic anisotropy, and there are many research reports.

Incidentally, in order to increase the recording capacity of a magneto-optical recording medium without increasing the volume of the medium in response to the demands of a highly information-oriented society, it is essential to improve the recording density. The recording density is
The smaller the beam diameter on the medium surface when the light from the light source (mainly laser light) is condensed by a lens, the higher the diameter. Means for reducing the beam diameter include increasing the numerical aperture of the lens and shortening the wavelength of light from the light source. However, a lens with a large numerical aperture has low aberrations. Considering that it is extremely difficult to produce light weight and at low cost, shortening the wavelength of light is a method that is more likely to be realized quickly.

Against this background, light sources that can emit light at shorter wavelengths are being used instead of light sources that emit light in the near-infrared region, such as conventional lit-V group compound semiconductor lasers typified by GaAsAE-based compounds. Development is underway.

For example, a blue LED (light emitting diode) using II-Vl group compounds represented by Zn-Se compounds. Furthermore, the development of laser elements is progressing. or,
There is also active development of second harmonic generation elements that can obtain light in the blue to near-ultraviolet region by using, for example, a conventional semiconductor laser as an excitation source by halving the wavelength of laser light at once.

[Problems to be Solved by the Invention] By the way, if the wavelength of light for recording and reproduction is shortened, it goes without saying that optical recording media are required to have good characteristics in the wavelength band.

However, in the conventional RE-TM film, as the wavelength of light becomes shorter, the Kerr rotation angle θ and the reflectance R decrease monotonically.
There was a problem that a practically sufficient recording/reproducing speed and CN ratio could not be achieved.

Therefore, an object of the present invention is to provide a magneto-optical recording system that can utilize excellent magneto-optical properties in a short wavelength range.

(Means for Solving the Problems) As a result of intensive studies to achieve the above-mentioned object, the present inventors have developed an artificial lattice in which CO layers, PT layers, and/or Pd layers are alternately laminated. The inventors have discovered that a magneto-optical recording medium having a film as a recording layer exhibits extremely excellent magneto-optical properties in a short wavelength region of 600 nm or less, leading to the completion of the present invention.

That is, the magneto-optical recording system according to the present invention uses Co
A magneto-optical recording medium whose recording layer is an artificial lattice film in which layers, PL layers and/or Pd layers are alternately laminated, is characterized in that recording and reproduction are performed using light with a wavelength of 600 nm or less. It is something to do.

First, the magneto-optical recording medium used in the magneto-optical recording system of the present invention has, as a recording layer, an artificial lattice film in which CO layers, PL layers, and/or Pd layers are alternately laminated. Specifically, the above-mentioned superlattice film includes a Co-PL superlattice film in which CO layers and PL layers are alternately laminated, a CO-Pd-based superlattice film in which CO layers and Pd layers are alternately laminated, and a Co layer, Co-Pt with a PL layer and a Pd layer (however, the latter two may be Pt-Pd alloy layers) laminated in any order.
- Any Pd-based superlattice film.

In either case, the total thickness of the superlattice film is desirably 50 to 400 mm from the viewpoint of achieving practically necessary and sufficient magneto-optical properties.

Furthermore, in the Co-PL superlattice film, the thickness of the CO layer is 2 to 8 layers, and the thickness of the PL layer is 3 to 40 layers.
In the Pd-based superlattice film, the thickness of the CO layer is 1 to 9,
It is desirable to select the layer thickness of the Pd layer from 2 to 40 layers. These layer thickness ranges are set from the viewpoint of optimizing the magneto-optical properties, and in any case, satisfactory properties cannot be obtained outside the above range.

Ideally, each of the superlattice films described above should have a so-called superlattice structure, in which the interfaces of each metal layer are flat and do not mix with each other. It may also have a group precept modulation structure in which the group precept changes while maintaining a constant period as a whole. For example, looking at the range of the layer thickness of the metal layer mentioned above, the metal bond radius of each metal (C o = 1.25 people. Pd = 1.38 people P
t = 1.39), the lower limit may be less than one atom, but this is also a result of consideration of the set or modulation structure.

The superlattice film is most commonly produced by sputtering. The source of energy during sputtering is Co-
When producing a binary artificial lattice film such as PL system or Co-Pd system, it is necessary to prepare each metal component independently. In addition, when creating a ternary artificial lattice film such as Co-Pt-Pd system, in addition to preparing an independent source for each predetermined metal, especially for Pd and pt, Possible methods include using a combination of these as an alloy evaporation source, or using a compound stalk source in which the chip of the smaller number of precepts is placed on the target node of the larger precept.

In addition to the above-mentioned subanotaling, methods for forming the artificial lattice film include vacuum welding and molecular beam epitaxy (MBE).
) etc. can be applied.

Furthermore, before coating the artificial lattice film on the substrate,
If necessary, a metal base film may be formed, thereby controlling the film quality of the artificial lattice film and increasing the force rotation angle θ. In this case, it is particularly preferable that the metal base film has a face-centered cubic structure and has a lattice constant similar to that of a metal layer whose lattice constant is fI of the artificial lattice film.

In the present invention, recording/reproduction on a magneto-optical recording medium having the above-mentioned artificial lattice film as a recording layer is performed at a wavelength of 600.
This is done using light of nm or less. As a means of obtaining such light, it is possible to use a semiconductor having a suitable band gap energy to suppress the laser element, or to combine a conventionally used semiconductor laser element and a second harmonic generation element. .

(Function) In the magneto-optical recording system of the present invention, the recording layer is a Co layer and a P layer.
A magneto-optical recording medium consisting of an artificial lattice film in which t-layers and/or PdN are alternately laminated is used. The artificial lattice film exhibits excellent magneto-optical properties even in the wavelength range of 780 to 850 nm, which is the wavelength range of semiconductor lasers commonly used as conventional light sources. However, below 600 nm, RE
While the magneto-optical properties of the -TM film are markedly degraded, the above-mentioned superlattice film tends to remain almost constant or to increase slightly, making it possible to reproduce with a higher CN ratio than with the RE-TM film. Therefore, high-quality, high-density recording and reproduction using short wavelength light becomes possible.

[Example] Hereinafter, preferred examples of the present invention will be described based on experimental results.

First, in each manufacturing example below, sample disks A to
Sample disk E was manufactured.

Production Example 1 In this production example, a Co-PL superlattice film was formed on a glass substrate by dual simultaneous magnetron subsotering.
This is an example of manufacturing a sample disk.

First, a Co target with a diameter of 100 mm and a Pt target were placed in the chamber of the magnetron sputtering device.
A glass substrate was placed in a position facing these target nodes. Next, increase the vacuum level of the Hachinoku Ground to 5X.
10-' Torr, argon gas pressure 5 XIO-'
Torr, while cooling the glass substrate with water, for Co, DC sputtering (input power: o.2 ~ IA,
300 V), for Pt, DC sputtering (input power: 120.2 to IA, 300 V), or high frequency sputtering (input power: 200 V).
~500 W), a Co layer with a thickness of 5 layers and a Pt layer with a thickness of 8 layers were alternately laminated to form a Co-PL superlattice film with a total thickness of 150 layers, and sample disk 8 was obtained. .

Production Example 2 Sample disk B was produced in the same manner as Production Example 1, except that the total thickness of the Co--Pt superlattice film was 320 pieces.

-: 200 to 500 W), and a Co layer with a thickness of 5 and a Pd layer with a thickness of 8 were alternately laminated for a total cost of ¥15.
A sample disk C was formed by forming a Co-Pd-based superlattice film containing 0.

Production Example 3 In this production example, a Co-Pd-based superlattice film was formed on a glass substrate by dual simultaneous magnetron sputtering.
This is an example of manufacturing a sample disk.

First, a Co target with a diameter of 100 mm and a PT target were placed in the chamber of a magnetron/subanotaring device.
And a glass substrate was installed at a position facing these targets. Then increase the background vacuum level to 5
10-' Torr, argon gas pressure 5 XIO-'
Torr, and while cooling the glass substrate with water, Co was subjected to direct current spanotaring (input power: 0.2 to IA,
300 V), and for Pd, DC sputtering (
Input power = 0.2~I A. ．． 300■), or high-frequency subanotaring (input power production example 4) In this production example, TbFeC was placed on a glass substrate for comparison.
This is an example in which a sample disk was manufactured by forming an o-based amorphous alloy by simultaneous binary supersokling.

In other words, 100
A Tb target and a FeCo alloy target with a diameter of mm were placed, and a glass substrate was placed at a position facing these targets. Next, increase the Hank Ground vacuum level to 5 x 1.
0-'Torr, argon gas pressure 3XIO-3To
rr, and while cooling the glass substrate with water, a TbzzFeb7cOx film with a film thickness of 2,000 ml was formed to form a sample disk D.

Production Example 5 In the wood production example, T was placed on a glass substrate for further comparison.
This is an example in which a sample disk was manufactured by forming a bFe-based non-quality alloy film by simultaneous dual sputtering.

In other words, there are 100
A Tb target and a Fe target with a diameter of mm were placed, and a glass substrate was placed at a position facing these targets. Then apply Hank ground vacuum to 5 x 10-'
Torr, argon gas pressure 3 XIO-' Torr
Then, the glass substrate was water-cooled and a Tb film with a film thickness of 2000 was applied.
The zaFeqb film was coated to form a sample disk.

Sample disk A produced in each of the above production examples
~ Immediately after coating the recording layer on sample disk E, light of various wavelengths in the near-ultraviolet to near-infrared regions was irradiated from the recording layer side, and the force rotation angle θ and reflectance R were measured. Based on these values, a performance index R1''·θ was calculated. This performance index is proportional to the SN ratio and serves as a guideline for determining the quality of the CN ratio. The results are shown in FIG. In the figure, the vertical axis represents the figure of merit Rl/l・θ, and the horizontal axis represents the wavelength (nm) of the recording/reproducing light.
Curve E corresponds to the characteristics of sample disc A to sample disc E, respectively.

From this figure, first, sample disk A (recording layer: Co-
Pt superlattice film) and sample disk B C recording layer: Go-P L superlattice II! ) It is clear that a high figure of merit is exhibited over the entire Hifi II constant wavelength band. In particular, in the blue wavelength region (400 to 450 nm), a figure of merit equivalent to or higher than the value in the near-infrared region was obtained. In addition, in sample disk C (recording layer: Co-Pd superlattice film), from the near-infrared region to the red region, sample disk D (recording layer: Tb2zFeb7CO), which will be described later,
Although it is slightly inferior to zllff), the figure of merit is rather improved on the lower wavelength side, indicating that it is suitable for short wavelength recording.

On the other hand, the recording layer of sample disc D and sample disc EC for comparison was TbzaFeq (film),
In both cases, the figure of merit decreased almost monotonically as the wavelength became shorter. The figure of merit at 400 nm for these disks is about half that at 800 nm, and an additional 4
It was about 1/3 of the value of sample disk A and sample disk B at 00 nm.

From the above results, it is clear that sample disks A to C can constitute an extremely good magneto-optical recording system when combined with a suitable peripheral optical system that uses fII recording and reproducing light of 600 nm or less. .

[Effects of the Invention] As is clear from the above description, the magneto-optical recording system according to the present invention has a Co layer, a Pt layer and/or a Pd layer.
A magneto-optical recording medium whose recording layer is an artificial lattice film in which layers are alternately laminated is used, and a light source that emits light with a wavelength of 600 nm or less and peripheral optics that exhibit suitable performance in this wavelength range are used. It is something that can be observed by combining systems.
It enables magneto-optical recording with high recording density and high C/N ratio.

[Brief explanation of drawings]

Figure 1 shows a Co-PL superlattice film. FIG. 2 is a characteristic diagram showing the wavelength dependence of the figure of merit of a magneto-optical recording medium having a Co--Pd superlattice film, a TbFeCo-based non-quality alloy film, and a TbFe-based amorphous alloy film as recording layers, respectively.

Claims (1)

[Claims] For magneto-optical recording media whose recording layer is an artificial lattice film in which Co layers and Pt layers and/or Pd layers are alternately laminated,
A magneto-optical recording system characterized in that recording and reproduction are performed using light with a wavelength of 600 nm or less.