JPS6371961A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To enable improvement in oxidation resistance, increase in the rotating angle at the time of reproduction and increase in area by disposing respective fine magnetic particles into a dispersion medium in such a manner that the direction of the magnetization thereof face perpendicularly the film surface of the dispersion medium. CONSTITUTION:This recording medium consists of plural pieces of the fine magnetic particles having magnetic anisotropy and the film-like dispersion medium. The respective fine magnetic particles are so disposed in the dispersion medium that the direction of the magnetization of the fine magnetic particles faces perpendicularly the film surface of the dispersion medium. For example, the fine magnetic particles 12 consisting of cobalt ferrite CoFe2O4 which has the magnetization 11 of the crystal magnetic anisotropy and has 1,000Angstrom average grain size are dispersed randomly at 4% volume ratio into the dispersion medium 13 consisting of a liquid polyimide type photosetting resin and the external magnetic fields 14 are impressed thereto perpendicularly to the film surface of the dispersion medium 13 to uniform the direction of the magnetization 11 of the fine magnetic particles 12, then in this stage UV light 15 is projected thereto. The magneto-optical recording medium 17 which consists of the photoset film-like dispersion medium 16 and the fine magnetic particles 12 magnetized perpendicularly to the film surface of the medium 16 and has 30cm diameter and 5,000Angstrom film thickness is thereby obtd.

Description

[Detailed description of the invention] FObjective of the invention (Industrial application field) The present invention relates to an erasable magneto-optical recording medium.

(Prior Art) Optical recording media are capable of large-capacity recording and are being put into practical use and developed as compact discs, video discs, external memories for computers, and the like. Among optical recording media, resetting type optical recording media are called erasable optical recording media because they can be recorded, reproduced, and erased. A magneto-optical recording medium is one type of optical recording medium, is composed of a perpendicularly magnetized film, and utilizes the magneto-optic effect during reproduction. The recording principle of such a magneto-optical recording medium will be explained below with reference to FIGS. 2(a) to 2(C), and the reproduction principle will be explained with reference to FIG. 3, respectively.

First, prepare a magneto-optical recording medium 1 in which the direction of magnetization 2 is aligned as shown in FIG. When heat is applied by irradiating light (mainly laser light) 4 while applying heat, the coercive force decreases, and the magnetization 2 is reversed and directed in the direction of the external LA field 3. As a result, recording points 5 are formed on the magneto-optical recording medium 1 as shown in FIG. To play,
As shown in FIG. 3, when the linearly polarized light 6 is irradiated onto the magneto-optical recording medium 1, the reflected light has a polarization plane of θ due to the magneto-optic effect.
It rotates only. θ is proportional to the strength of magnetization of the magnetic material, and when the direction of magnetization is reversed, it rotates in the opposite direction. Therefore, since the reflected light from the recording point 5 of the magneto-optical recording medium 1 and the reflected light from areas other than the recording point 5 differ only in 2θ, they are detected through an analyzer. The above-mentioned magneto-optical effect is called the Kerr effect, and θ is called the Kerr rotation angle. When a similar phenomenon is observed with transmitted light, it is called the Faraday effect, and the rotation angle θf at that time is called the Faraday rotation angle.

By the way, although it has already been mentioned that the magneto-optical recording medium is composed of a perpendicularly magnetized film, an amorphous alloy of a rare earth-transition metal has been conventionally used as the material thereof. The rare earths mainly include Tb, Qd, DV, i! ! Fe-FCOl is mainly used as the transfer metal.

However, the conventional magneto-optical recording medium mentioned above has problems in that it is easily oxidized and the rotation angle θ and θf are small. Further, since conventional magneto-optical recording media are usually manufactured by sputtering, there are problems in that it is difficult to increase the area and control the composition.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned conventional problems, and has excellent oxidation resistance, a large rotation angle during regeneration, and a large surface area. The purpose is to provide a magneto-optical recording medium that is possible and compositionally stable.

[Configuration of the Invention (Means and Actions for Solving Problems) Does the present invention have magnetic anisotropy? It consists of a dispersion medium in the form of a film of several magnetic fine particles, and each magnetic fine particle is arranged in the dispersion medium so that the direction of magnetization of the magnetic fine particles is perpendicular to the surface of the film of the dispersion medium. This is a magneto-optical recording medium characterized by the following.

The magnetic anisotropy possessed by the magnetic fine particles includes shape magnetic anisotropy and crystal magnetic anisotropy. Such magnetic fine particles include various single metals, alloys, and inorganic compounds, and are not particularly limited. However, it is necessary that the magnetic anisotropy, coercive force, and magneto-optical effect be large, and that the oxidation resistance be excellent. Also, the higher the recordable temperature, the better the temperature characteristics of the magneto-optical effect, which is desirable, but if the recordable temperature of 78 degrees is too high, a large amount of energy will be required during recording, so it is practically recommended to set it at around 200 degrees Celsius. It is preferable to have one. Further, the size of the magnetic fine particles is desirably 4000 or less in average particle size from the viewpoint of reproduction efficiency and the like.

For this reason, it is desirable to use cobalt ferrite or cobalt ferrite in which iron is partially substituted with other elements (for example, manganese, chromium, aluminum, etc.) as magnetic fine particles.

Examples of the dispersion medium include various ceramics, glasses, and polymers, and are not particularly limited.

However, the dispersibility of the magnetic fine particles must be good during the production of the magneto-optical recording medium, the dispersed magnetic fine particles must not move much during use, the dispersion medium must not be degraded by laser light, and the optical transparency must be good. is required. For this reason, it is desirable to use a resin such as a polyimide photocurable resin as the dispersion medium.

(Function) Since the magneto-optical recording medium of the present invention is composed of magnetic fine particles and a film-like dispersion medium, it has high optical transparency and can be reproduced using the Faraday effect. Further, the magnetism required for the magnetic fine particles may be shape magnetic anisotropy in addition to crystal magnetic anisotropy, so there are few restrictions on material selection, and many magnetic fine particles can be applied. As a result, magnetic fine particles with excellent oxidation resistance can be used, and a longer life can be achieved. Furthermore, a magneto-optical recording medium with large θ and θf can be realized by appropriately selecting appropriate magnetic particles from a wide range of magnetic particles. Furthermore, since the magneto-optical recording medium of the present invention can be manufactured by coating means, it is easy to make the composition homogeneous and to increase the size, and the mass productivity is also good.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to FIGS. 1(a) to (C).

First, as shown in FIG. 1(a), one set of magnetic fine particles made of cobalt ferrite Co Fe 204 with an average particle diameter of 1000 and having magnetization 11 of magnetocrystalline anisotropy is dispersed in a liquid polyimide-based photocurable resin. It was randomly dispersed in fi13 at a volume ratio of 4%.

Subsequently, as shown in FIG. 4B, an external magnetic field 14 was applied perpendicularly to the film surface of the dispersion medium 13, and ultraviolet light 15 was irradiated while changing the direction of the magnetization 11 of the magnetic fine particles 12. As a result, the film-like dispersion medium 1 is photocured as shown in FIG.
A magneto-optical recording medium 17 having a diameter of 30α and a film thickness of 5,000 was obtained, which consisted of a magnetic particle 12 magnetized perpendicularly to the film surface of the dispersion medium 16.

The Faraday rotation angle θf of the obtained magneto-optical recording medium was examined using a currently commonly used semiconductor laser with a wavelength of 800 nm, and was found to be approximately 1.0 degrees. This value is different from the conventional Tb that performs regeneration using the Kerr effect.
The Kerr rotation angle θk of the magneto-optical recording medium made of Fe alloy is 0.
．． It is large compared to 3 degrees. Furthermore, the optical recording medium of this example has a light transmittance of 2 at a wavelength of 800 r+m.
5%, and has a good figure of merit, so CZ during playback
The N ratio showed a large value of 60 CIB. Furthermore, since the magnetic fine particles 12 were oxides and were protected by the dispersion medium 16, their oxidation resistance was also extremely excellent.

In the above embodiment, a polyimide photocurable resin was used as the dispersion medium, but a translucent ceramic may be used instead of the resin.

[Effects of the Invention] As detailed above, the present invention has remarkable effects such as excellent oxidation resistance, a large rotation angle during regeneration, the possibility of increasing the area, and excellent profilability. It is possible to provide a magneto-optical recording medium having the following properties.

[Brief explanation of the drawing]

FIGS. 1(a) to (C) are schematic diagrams showing a method for manufacturing a magneto-optical recording medium in an embodiment of the present invention, and FIGS. 2(a) to (C)
) is a schematic diagram showing the recording principle of a magneto-optical recording medium, and FIG. 3 is a schematic diagram showing the reproduction principle of a magneto-optical recording medium. 1.17... Magneto-optical recording medium, 2.11... Magnetization,
3.14...External magnetic field, 4...Light, 5...Recording point, 6...Direct $2 polarized light, 12...Magnetic fine particles, 13.
... Dispersion medium, 15 ... Ultraviolet light, 16 ... Film-like dispersion medium. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2

Claims (1)

[Claims] Consisting of a plurality of magnetic fine particles having magnetic anisotropy and a film-like dispersion medium, each magnetic fine particle is placed in the dispersion medium so that the direction of magnetization of the magnetic fine particles is perpendicular to the film surface of the dispersion medium. A magneto-optical recording medium characterized by being arranged as follows.