JPS627611B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magneto-optical recording medium used in a magneto-optical recording device, and in particular, a magnetic medium formed on a flexible plastic substrate and a magnetic thin film formed on a transparent substrate are stacked together. The present invention relates to an improvement in a medium in which the former is used as an information storage medium and the latter is used as a readout medium.

As described above, a device that writes and records information on a magnetic material using light and reproduces information by reading the information is generally called a magneto-optical recording device.

On the other hand, in ordinary magnetic recording devices, the medium for storing information is often a flexible plastic substrate coated with magnetic powder. Today, the manufacturing method for such magnetic powder-coated media has been established, and it is easy to obtain media with uniform characteristics over a wide area. Some of these media have magnetic properties that change with a relatively small temperature rise, and this property can be used to record information thermomagnetically using laser light or the like. However, in such a medium, it is practically impossible to directly read written information using the Faraday effect or magnetic Kerr effect of the medium. The reason for this is that the light incident for reading is scattered because the surfaces of these media are not of sufficiently good quality in an optical sense. Therefore, it is known to place a magnetic thin film that is optically smooth and has a large Faraday effect or magnetic Kerr effect in close proximity to such an information storage medium. In this case, a magnetic field generated from the storage medium forms a magnetization pattern in the magnetic thin film that corresponds to information held by the storage medium. This transfer of the magnetization information of the storage medium onto the magnetic thin film is called transfer. By utilizing the Faraday effect or magnetic Kerr effect of this magnetic thin film, it becomes possible to optically read information from the magnetization pattern.

There are roughly two methods for arranging an information storage medium and a magnetic thin film in close proximity. The first method is to place the two in close proximity with a thin layer of gas such as air interposed between them to enable relative movement between the two.
In this method, the two are brought into close contact with each other by an appropriate method. An example of the first method conventionally considered is shown in FIG. Here, 1 is a flexible plastic substrate, and 2 is a magnetic layer coated on the substrate 1 as a magnetic medium for information storage. Reference numeral 3 denotes a magnetic thin film disposed close to the magnetic layer 2 via a gas layer 4, and this magnetic thin film 3 is disposed on a transparent substrate 5. Information is recorded on the moving magnetic layer 2 using the magnetic head 6. The information is transferred to the magnetic thin film 3, and the transferred information is optically read out using the converging lens 7 and the laser beam 8.

However, this method has the following drawbacks.

(1) The track width recorded on the medium 2 is determined by the track width of the magnetic head 6.
It is not easy to reduce the thickness to less than μm. Therefore, the recording density is limited to about 2×10 ⁶ bits/cm ² .

(2) Since the magnetic head 6 and the medium 2 move relative to each other in or near contact, there is a risk that wear and the like will occur on both of them, reducing the reliability of the recording system.

As an example of the second method, as shown in FIG.
2, a magnetic thin film, for example a metal thin film 13 made of iron or the like, is closely placed on the magnetic layer 12, and a transparent substrate 15 is placed on the thin film 13. A magnetic head 16 and a converging lens 17 are disposed facing each other between the upper and lower surfaces of the recording medium having the above configuration, and the laser beam 18
is focused onto the thin film 13 by the lens 17 to locally heat the thin film 13. As a result, thin film 1
The temperature of the information storage medium 12 in contact with the information storage medium 3 increases, and recording is performed by the magnetic field from the magnetic head 16. The information recorded on the magnetic layer 12 is transferred to the thin film 13, and optical reading is performed using converging lenses 17' and 17'' and a laser beam.However, in this second method, the thin film 13 is made of a metal with high reflectivity. Because it is a thin film, less than 40% of the convergent light contributes to heating, which has the disadvantage of greatly reducing optical efficiency during recording.

An object of the present invention is to eliminate the above-mentioned drawbacks of conventional magneto-optical recording, and to provide a magneto-optical recording medium appropriately configured to perform high-density recording with high light utilization efficiency and high reliability. It is about providing.

The present invention has a transparent substrate, a transparent magnetic thin film is arranged on the transparent substrate, and a first
A dielectric film that transmits light of a specific wavelength and reflects light of a second specific wavelength is arranged, and via the dielectric film,
By arranging magnetic media for information storage in close proximity or in close contact with each other,
Information is magnetically written onto the information storage medium while light of the first specific wavelength is incident from the transparent substrate side, and the information transferred to the transparent magnetic thin film is transferred from the transparent substrate side to the second specific wavelength. The device is characterized in that it can be read by inputting light of the same wavelength.

The present invention will be described below with reference to the drawings.

FIG. 3 shows an example of the structure of the magneto-optical recording medium of the present invention, where 21 is a flexible plastic substrate, for example, a substrate made of polyethylene terephthalate, etc., and on this substrate 21 there is formed a magnetic material as a magnetic medium for information storage. The layer 22 is, for example, a magnetic powder-coated recording medium and has a relatively low Curie temperature (200°C).
A magnetic layer 22 in the form of a magnetic tape or sheet of chromium dioxide (CrO ₂ ), for example, is coated and formed. 23 is an optically transparent magnetic thin film deposited on a transparent substrate 24, for example (YEuYb) ₃ (FeGa) ₅ O ₁₂
It is a rare earth iron-based garnet LPE membrane. The board 24 is
It can be formed from Gd ₃ Ga ₅ O ₁₂ (gadolinium gallium garnet single crystal). Substrate 2 of magnetic thin film 23
A dielectric multilayer film 25, for example, a dielectric multilayer film 25 formed by alternately depositing dielectric materials such as SiO ₂ and TiO ₂ at appropriate thicknesses, is disposed on the surface opposite to 4. As shown in FIG. 4, this dielectric multilayer film 25 is configured to have a high transmittance T for light with a wavelength of λ ₁ and a high reflectance R for light with a wavelength of λ ₂ . It is assumed that there is The magnetic thin film 23 is placed close to the information storage medium 22 with the multilayer film 25 interposed therebetween. In the example shown in FIG. 3, a thin gas layer 26 such as air is interposed between the multilayer film 25 and the magnetic layer 22, and the magnetic thin film 23 is placed close to the magnetic layer 22. Alternatively, as shown in FIG. 5, the multilayer film 25 and the magnetic layer 22 can be brought into close contact with each other.

In order to write information using light on the magneto-optical recording medium of the present invention configured as described above, the magnetic head 27 applies a magnetic field of about 100 Oe or less whose strength and direction are constant or vary. A laser beam 29 with a wavelength λ ₁ focused by a converging lens 28 is irradiated onto the surface of the magnetic layer 22 . Here, the magnetic thin film 23
Since the multilayer film 25 is transparent (transmittance 90%) to light of wavelength λ ₁ , the irradiated light is efficiently used to heat the magnetic layer 2. The light utilization efficiency in the transparent magnetic thin film 23 of this example is improved by 5 to 6 times compared to the conventional metal thin films 3 and 13.
On the other hand, the information recorded in the magnetic layer 22 in this way is transferred to the magnetic thin film 23. This magnetic thin film 2
The magnetization pattern formed in 3 can be read out using the Faraday effect with a laser beam 29 having a wavelength of λ ₂ . At this time, the multilayer film 25 acts as a reflective mirror with a high reflectance for the readout light 29.

Next, FIG. 6 shows a first example in which the magneto-optical recording medium of the present invention is applied to a magneto-optical recording device. Here, a medium having a close contact structure as shown in FIG. 5 is used. For example, a writing laser beam 31 with a wavelength λ ₁ =633 nm and an output light obtained by passing a read laser beam 32 with a wavelength λ ₂ =514 nm through a polarizer 33 are mixed by a dichroic mirror 34, and then half The light passes through the mirror 35 and is focused onto the chromium dioxide magnetic layer 22 by the converging lens 28. The magnetization pattern formed in the magnetic layer 22 by writing by the magnetic head 26 while being irradiated with the laser beam 31 is a magnetic garnet film 23 with a thickness of about 2 μm.
transcribed into. Of the irradiated lights 31 and 32, the laser beam 32 is linearly polarized by the polarizer 33, and is reflected by the multilayer film 25, but undergoes Faraday rotation in the process of passing back and forth through the thin film 23. occurs. This light is reflected again by the half mirror 35 and enters a polarization detection system consisting of an analyzer 36 and a photodetector 37. Here, the magnetization pattern transferred onto the thin film 23 is converted into an electric signal, and the signal processing system 3
Guided by 8.

FIG. 7 shows an example of a magneto-optical recording apparatus using the magneto-optical recording medium of the present invention constructed as shown in FIG. Here, the same parts as in FIG. 6 are given the same reference numerals. In this example, the integrally formed substrate 21 and magnetic layer 22 have a disk shape, and the disk-shaped information storage medium 22, for example, the chromium dioxide magnetic sheet 22, is rotated by a motor 39 at, for example, 1800 rpm. Writing to the magnetic layer 22 is performed by converging light with a wavelength λ ₁ onto the magnetic layer 22, as in the above example, and reading is performed using light with a wavelength λ ₂ . Here, both the distance between the multilayer film 25 and the magnetic layer 22 and the film thickness of the multilayer film 25 can be about 1 μm, and the sum of both is smaller than the depth of focus (≧3 μm) of the converging lens 28. Since the multilayer film 25 and the magnetic layer 22 are separated, there is no difference in resolution between writing and reading.

As is clear from the above, according to the present invention, a magnetic powder-coated recording medium with a relatively low Curie temperature (200°C or less), such as a chromium dioxide tape or sheet, can be used as a magneto-optical recording medium. Therefore, it is possible to construct a magnetic recording device that has the general features of optical memory, such as high density, high speed access, and high reliability. Furthermore, in magneto-optical reading, the signal-to-noise ratio (SN ratio) generally increases with the intensity of the reading light. Therefore, in conventional magneto-optical recording media, writing is performed using the same light.
If the intensity of the read light is increased to increase the signal-to-noise ratio, the temperature of the medium will rise, and if the temperature rises too much, the written information will disappear. According to the present invention, since writing and reading are performed using light of different wavelengths, the above-mentioned problem is solved, and reading can be performed using strong light, so that reading can be performed with a high signal-to-noise ratio. be able to. As described above, according to the present invention, writing and reading can be performed with high light utilization efficiency, and a magnetic powder coated recording medium can be used as a storage medium. is possible, and the readout signal-to-noise ratio is also large. Therefore, the present invention is extremely effective when applied to fields that require the recording and processing of large amounts of high-quality images, such as recording devices at broadcasting stations.

In the embodiment of the invention shown in FIG. 5, the magnetic layer 22 serves as a storage medium during writing and reading.
and the magnetic thin film 23 are in close contact with each other and are treated as one body. However, if the magnetic layer 22 can be replaced with another one, the same magnetic thin film 23
Information can be written to and read from a large number of storage media. At present, the magnetic thin film 23 that can be obtained, for example, a magnetic garnet film, has a diameter of about 7 cm, and with an area of 10 μm ² per bit, it has a recording capacity of 3 × 10 ⁸ bits per storage medium. However, by preparing a large number of storage media, a recording system with a large recording capacity can be constructed.

In the embodiment of the present invention shown in FIG. 3, the transfer readout medium comprising a magnetic thin film 23 and a multilayer film 25 disposed on a transparent substrate 24 has an extremely small area, for example, 1/1000 or less, compared to the storage medium 22. Can be done. While it is easy to obtain a magnetic layer 22 with a diameter of about 50 cm, for example, magneto-optical recording with a single magnetic thin film such as manganese bismuth (MnBi) with uniform characteristics and a diameter of about 30 cm is possible. Producing media is not easy. Therefore, as described above, being able to reduce the area of the transfer readout medium is a great advantage in cases where it is not easy to produce a uniform, large-area magnetic thin film for transfer.

[Brief explanation of the drawing]

Figures 1 and 2 are block diagrams of two examples of conventional magneto-optical recording media, Figure 3 is a block diagram of an example of the magneto-optical recording medium of the present invention, and Figure 4 is the optical wavelength of the dielectric multilayer film. FIG. 5 is a cross-sectional view showing another example of the magneto-optical recording medium of the present invention, and FIGS. 6 and 7 are diagrams showing the relationship between the magneto-optical recording medium of the present invention and the magneto-optical recording medium of the present invention. FIG. 2 is a configuration diagram showing two examples of magneto-optical recording devices. 21...Plastic substrate, 22...Magnetic layer, 23...Magnetic thin film, 24...Transparent substrate, 25
... Dielectric multilayer film, 26 ... Gas layer, 27 ... Magnetic head, 28 ... Converging lens, 29 ... Laser light, 31 ... Laser light for writing, 32 ... Laser light for reading, 33 ... Polarizer, 34... Dichroic mirror, 35... Half mirror, 36
... Analyzer, 37 ... Photodetector, 38 ... Signal processing system, 39 ... Sheet rotation motor.

Claims (1)

[Claims] 1 A transparent substrate is provided, a transparent magnetic thin film is disposed on the transparent substrate, and a dielectric film is disposed on the transparent magnetic thin film that transmits light of a first specific wavelength and reflects light of a second specific wavelength. A magnetic medium for information storage is arranged close to or in close contact with each other via the dielectric film, and information is magnetically written on the medium with the first specific wavelength being incident from the transparent substrate side. A magneto-optical recording medium, characterized in that the information transferred to the transparent magnetic thin film can be read by making light of the second specific wavelength incident from the transparent substrate side.