JPS6398855A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To realize a magneto-optical disk which uses a Faraday effect for reproduction and has improved detection sensitivity by using specific magnetic garnet implanted with metal elements between lattices or grain boundaries as a recording medium. CONSTITUTION:The Bi-substd. magnetic garnet which is implanted with the metal elements between the lattices or the grain boundaries and is expressed by the general formula BixR3-xMyFe5-yO12 (R is Y or a combination f >=1 kinds or more among rare earth element, M is a combination of >=1 kinds or more which can be substd. with Fe, and 1<X<3.0<Y<2) is formed as the magnetic layer on a glass substrate, by which the magneto-optical recording medium is formed. The magneto-optical disk which is improved in the detection sensitivity is realized by using the stable bismuth-subtd. garnet which is a transparent magnetic material and has a large Faraday rotating angle thetaF as the recording medium and making detection by using the Faraday effect.

Description

[Detailed Description of the Invention] [Summary] As a method for realizing a magneto-optical disk with improved sensitivity, a general formula Bi in which metal elements are injected into interstitial spaces or grain boundaries is used.
x 1h-x F'lv Fe5-v 012 (here, R is a combination of one or more types of Y or rare earth elements, M is a combination of one or more types that can be replaced with Fe, and 1 <X < A recording medium for a magneto-optical disk with a new configuration using Bi-substituted magnetic garnet represented by 3.0<Y<2).

[Industrial application field]

The present invention relates to a magneto-optical recording medium having a new structure with improved photosensitivity.

A magneto-optical disk is a memory that uses laser light to record high-density information. Like an optical disk, it has a large storage capacity, can record and read without contact, and is unaffected by dust. It has certain characteristics.

Here, an optical disk is a read-only memory that uses a low-melting point metal as a recording medium and records and reproduces information depending on the presence or absence of holes (bits).
y), whereas magneto-optical disks are developed mainly for rewritable memory (EraserbIe).
It is currently being developed as ``Memory''.

[Conventional technology]

Magneto-optical disks are made by forming a film of an amorphous rare earth-transition metal alloy on a disk-shaped transparent substrate made of plastic or glass by vacuum evaporation or sputtering to create a recording layer consisting of a perpendicularly magnetized film. A disk substrate is manufactured by providing a protective film thereon.

Here, polymethyl methacrylate (
A transparent plastic substrate such as PMMA (abbreviation: PMMA), polycarbonate (abbreviation: PC), or a glass substrate is used.

The recording layer is made of a perpendicularly magnetized film showing ferrimagnetism made of a rare earth-transition metal, as described above, and is made of a terbium-transition metal.
It is composed of iron/cobalt (Tb Fe Co), gadolinium/terbium/iron (Gd Tb Fe), etc., and is formed using a vacuum evaporation method, a sputtering method, or the like.

The fragrant protective film is made of silicon oxide (Sin) or silicon nitride (Si3S).
It is formed using thin films of inorganic materials and metals such as 4).

To record information on a magneto-optical disk with such a structure, a laser beam focused by a lens is irradiated from the side of the transparent disk substrate while a vertical magnetic field is applied, and the temperature of the irradiated part of the perpendicularly magnetized film is adjusted. This is done by utilizing the fact that J2 rises to reach the Curie temperature, and the magnetization is reversed in the direction of the magnetic field.

Furthermore, information is erased by applying a magnetic field in the opposite direction to the direction of magnetization at the recorded position, heating the recording position by irradiating it with laser light, and reversing the magnetization in the same direction.

A magneto-optical disk has such a structure, and uses a thin film of a ferrimagnetic alloy made of a rare earth-transition metal such as TbFeCo as a recording medium, and uses the Kerr effect (Kerr effect).
effect).

Here, the Kerr effect refers to a phenomenon in which the plane of polarization rotates when linearly polarized light is reflected by a magnetic material, and it refers to the difference in the orientation direction of the perpendicular cW magnetized film that constitutes the recording layer of a magneto-optical disk (information recording state and erasing state). This is done by taking advantage of the fact that the direction of rotation of the plane of polarization differs due to the difference between be.

That is, the figure of merit is expressed as 2θ,・R1″, where θ is the Kerr rotation angle, and R is the reflectance. However, in the case of conventional recording media made of rare earth-transition metals such as Tb Fe Co, θ3 is about 0.3° and R is 0.4 to 0.5, and the figure of merit is as small as about 0.4 even under the best conditions.

Therefore, it is necessary to improve detection sensitivity.

[Problem that the invention seeks to solve]

As mentioned above, conventional magneto-optical disks are constructed using a thin film of a ferrimagnetic alloy made of rare earth-transition metals as a recording medium, and information is detected using the Kerr effect. The problem is low sensitivity.

[Failure to solve the problem]

The above purpose is to use a general BiXR3- in which metal elements are injected into interstitial spaces or grain boundaries as a recording medium for magneto-optical disks.
X Mv Fe5-v 012 (here, R is one or more combinations of Y or rare earth elements, M
can be solved by using as a magneto-optical recording medium a Bi-substituted magnetic garnet having 1 <

[Effect]

The present invention uses the Faraday effect instead of using the Kerr effect as a reproduction method for magneto-optical disks.
By using ct), detection sensitivity is significantly improved.

Here, the Faraday effect refers to a phenomenon in which the plane of polarization rotates when linearly polarized light is incident on a transparent magnetic material or a transparent material placed in a magnetic field. When used as a recording medium for
The figure of merit is similarly 2θ, ・R1/2. However, R is the effective reflectance of the substrate viewed from the substrate side when a reflective film is attached, θF is expressed as the Faraday rotation angle, and θ is 8 °/μm (wavelength 514nm)
.

0.5°//11m (wavelength 800nm), which is an order of magnitude larger than the Kerr rotation angle, and unlike the case of natural optical rotation,
Since the rotation angle is the same even if the traveling direction of the light is reversed, there is an advantage that the rotation angle is doubled when linearly polarized light is reflected in a transparent magnetic material.

The present invention uses magnetic garnet, which is a transparent magnetic material, as a recording medium and performs detection using the Faraday effect.

However, when recording and erasing information on a magneto-optical disk, when the recording layer is irradiated with laser light, the temperature of the irradiated area rises, as described in 1. The magnetic recording medium constituting the blue layer is heated:
The recording medium must be made of a material whose temperature increases rapidly when irradiated with laser light because the coercive force decreases as the i+ IJ temperature approaches and the magnetization is reversed in the direction of the external magnetic field. be.

However, ordinary magnetic garnet has low light absorption, and as it is, a large amount of power is required to record information.

The present invention is characterized in that bismuth (Bi)-substituted garnet has a large Faraday rotation angle θ and is an extremely stable substance, and in a film formed by sputtering, a large amount of Bi can be substituted, and it has a large coercive force. We focused on

However, a garnet film formed using a sputtering method has a large amount of light absorption in the ultraviolet region, but gradually decreases in the visible light region, and very little in the near-infrared region.

On the other hand, semiconductor lasers are suitable for use as irradiation light sources for optical disks in terms of miniaturization and high efficiency, but the oscillation wavelength of semiconductor lasers is near-infrared around 0.8 μm, so the recording medium for magneto-optical disks is Therefore, it is necessary to increase optical absorption in this wavelength region.

Here, light absorption in the visible to near-infrared range of magnetic garnet is mainly caused by iron ions (Fe”) at the a- and d-sites.
) is known to occur due to

Here, the a site refers to the center position of an octahedron made of oxygen ions (0-), and the d site refers to the center position of a tetrahedron made of 0-.

Now, as a way to increase the optical absorption of magnetic garnet in the visible to near-infrared region, metal elements have a large optical absorption in this region, so when forming a magnetic thin film using the sputtering method, we can co-sputter a metal. However, in this case, the metal element enters the a-site or d-site by replacing Fe++-, and in this case, like Fe''+゛, it has a large absorption in the visible to near-infrared region. will no longer be shown.

Therefore, in the present invention, absorption in this wavelength range is increased by introducing a metal element into interstitial spaces or grain boundaries.

In order to introduce the metal element into interstitial spaces or grain boundaries in this way, ions such as argon (Ar) may be used for implantation, or ζ may be introduced by thermal diffusion.

The inventors focused on the fact that Bi-substituted magnetic garnet has a large θ1, and the general formula Bix R3-X MY Fe5-y
0+2 (here, R is one or more combinations of Y or rare earth elements, M is one or more combinations that can be replaced with Fe, and 1<X<3.0<Y<2
It has been found that when a metal element is introduced into the interstitial spaces or grain boundaries of Bi-substituted magnetic garnet represented by ) using an ion beam, light absorption increases from the visible to the near-infrared region.

〔Example〕

A Ga-substituted YIG (yttrium iron garnet) film was formed to a thickness of 0.5 μm on a glass substrate (manufactured by HOYA, NA-40) by high-frequency sputtering.

The garnet used for sputtering was BizY Ga Fe,
It is 0.2.

Since the as-sputtered film is amorphous, it is crystallized by heat treatment at 650°C in the air, and then a reflective film of Cr (Cr) is applied to a thickness of 0.1 μm on top of this. It sputtered.

Next, this Cr film is irradiated with an Ar ion beam to
Elements were implanted into the YIG film.

The irradiation conditions are an accelerating voltage of 100 KV, an ion current of 0°1 mA, and the amount of Ar implanted in this case is 6×10” ions/cm 2 .

Next, the substrate was heat-treated at 500° C. for 30 minutes in a nitrogen (N2) stream in order to remove the particles from the YIG film and to recover the crystal disorder caused by ion implantation.

When we measured the reflectance of a magneto-optical disk with a new configuration in which magnetic garnet is used as a recording layer on a glass substrate and Cr is used as a reflective film by irradiating a semiconductor laser with a wavelength of 0.83 μm from the substrate side, we found that Cr The reflectance of the magneto-optical disk without Cr injection was 35%, while the reflectance of the Cr-injected disk was 20%, proving that the optical absorption of magnetic garnet had increased.

Next, we investigated the recording sensitivity by irradiating a laser beam with a spot diameter of 1 μm and a power of 101, and found that the recordable pulse width was 0.5 μm on a magneto-optical disk without Cr injection.
s, whereas the Cr-injected one had a diameter of 0.15μ.
The results showed that it was possible to record with an energy of 1 no 3 or less.

〔Effect of the invention〕

As described above, by carrying out the present invention, it becomes possible to put into practical use a magneto-optical disk with a new configuration that uses the Faraday effect and has improved detection sensitivity.

Claims (1)

[Claims] A recording layer formed on a transparent substrate is irradiated with linearly polarized light through the transparent substrate, and the difference in the direction of the rotation angle of the reflected light depending on the presence or absence of magnetization reversal of a vertically aligned magnetic film is utilized. In a magneto-optical disk on which information is recorded and reproduced, the general formula Bi_XR_3_-_X is used as a recording medium of the magneto-optical disk, in which a metal element is injected into the interstitial space or at the grain boundary.
M_YFe_5_-_YO_1_2 (here, R is a combination of one or more types of Y or rare earth elements, M is a combination of one or more types that can be replaced with Fe, 1<X<3, 0<Y<2) A magneto-optical recording medium characterized by using a Bi-substituted magnetic garnet having the following properties.