JPH0676380A - Magnetic field modulation type garnet magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain an overwritable magneto-optical recording medium using a garnet which is capable of reducing the magnetic field necessary for the write-in without adversely affecting the bit form. CONSTITUTION:A recording film 1, an auxiliary film 2 and a reflection film 3 are formed in that order on a transparent substrate 4. The recording film 1 and the auxiliary film 2 are magnetically bonded with each other in the interface 1A by the exchange interaction. Each of the recording film 1 and the auxiliary film 2 comprises the garnet film represented by the formulas BixR3-xMyFe5-yO12 and R3MyFe5-yO12 respectively (wherein 0<x<3, 0<y<2; R is yttrium or at least one metal selected from the rare earth elements; M is an element which can be substituted by iron (Fe) element).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overwritable magneto-optical recording medium, and more particularly to a magnetic field modulation type overwritable magneto-optical recording medium using garnet as a magneto-optical recording film.

[0002]

2. Description of the Related Art A bismuth-substituted garnet film formed by a sputtering method has a very large Faraday rotation angle with respect to light of wavelengths of green and blue, and has a large coercive force. It has advantageous characteristics as a high-density magneto-optical recording medium using a laser.

In a recording method using a magneto-optical disk, overwriting is indispensable for increasing the transfer rate. Current,
The overwrite system of a magneto-optical disk using a rare earth-transition metal amorphous alloy that is mainly used is roughly classified into two types, a light modulation system and a magnetic field modulation system.

In the optical modulation method, recording and erasing are performed by irradiating a magneto-optical recording medium in which two or more layers of rare earth-transition metal amorphous alloys exchange-coupled with each other are laminated with laser beams of different binary powers. .

In the magnetic field modulation method, overwriting is performed by switching the magnetic field on the medium surface by the magnetic head while irradiating the laser beam with a constant power. When the garnet film is used as the recording film, overwriting is practically limited to the magnetic field modulation method. The reason for this is that in the optical modulation method, it is necessary to stack two or more magnetic films, but since the garnet film is transparent, the information of two layers is read at the same time, so it is practical to apply this method. Have difficulty.

[0006]

A major problem of the magnetic field modulation system is that high-speed magnetic field modulation is difficult. In other words, in order to improve the writing speed, the frequency of the current applied to the coil of the magnetic head must be increased. However, when the frequency is increased, the impedance of the coil of the magnetic head used for writing increases, so It becomes difficult to generate the required magnetic field.

For example, the upper limit of the frequency at which a magnetic field of 300 Oe or more can be generated on the surface of a magneto-optical recording medium is about 10 MHz.
Therefore, it is required that the medium for high-speed magnetic field modulation recording can be written with a small magnetic field. In addition, writing with a small magnetic field has the effect of reducing the power consumption of the magnetic head, which is very important in constructing an optical disk device.

However, writing with a small magnetic field and stable formation of small bits (magnetic domains) in a magneto-optical recording medium are mutually contradictory concepts. In order to write with a small magnetic field, the coercive force must be made small, but this generally leads to a small magnetic anisotropy, and the bit shape becomes poor.

An object of the present invention is to provide a magneto-optical recording medium using a garnet capable of reducing the magnetic field required for writing without impairing the bit shape.

[0010]

A magnetic field modulation type gar according to the present invention
The net magneto-optical recording medium, as defined in claim 1, is transparent.
A recording film, an auxiliary film and a reflective film are sequentially provided on the substrate, and
At the interface between the recording film and the auxiliary film, exchange interaction is caused.
Magnetically coupled, the recording film is Bi_xR_3-xM_yFe _5-y, Supplement
The auxiliary film is R₃M_yFe_5-yO₁₂(However, 0 <x <3, 0 <y <
2, R is selected from yttrium or rare earth elements
At least one element, M replaced with iron (Fe) element
It is a garnet film displayed with
And

According to a second aspect of the present invention, the recording film and the auxiliary film according to the first aspect have substantially equal Curie temperatures, and the auxiliary film is an in-plane magnetized film. Further, as described in claim 3, a heat-resistant substrate is used as the substrate described above,
The recording film and the auxiliary film are formed by a sputtering method.

[0012]

[Operation] An attempt to reduce the writing magnetic field by the magnetic field modulation recording method has been made with a rare earth-transition metal amorphous alloy film. For example, "15th Annual Meeting of the Applied Magnetics Society of Japan,"
31pB-1, Shimazaki, et al. ”, And the contents are summarized as follows.

The structure of the magneto-optical recording medium is as shown in FIG. 2, and terbium-iron-cobalt (TbFeCo) of the perpendicular magnetization film is used.
An in-plane magnetized film made of a platinum-cobalt (PtCo) alloy film is laminated as an auxiliary film 2 on the recording film 1 of the rare earth-transition metal film. In FIG. 2, 6 is a protective film made of a silicon nitride film, and 4 is a substrate.

The spin magnetic moments of the two layers of the recording film 1 and the magnetic film of the auxiliary film 2 are exchange-coupled with each other at the boundary surface 1A. The Curie temperatures of the recording film 1 and the auxiliary film 2 are set to be approximately the same.

The magneto-optical recording medium having this structure has the characteristics that it has a better response to an external magnetic field than a single-layer recording film of a TbFeCo film, and that micro magnetic domains are less likely to occur in the recording bit.

The reason for this is qualitatively considered as follows. When the Curie temperature of the auxiliary film 2 of the in-plane magnetized film made of the PtCo alloy film is similar to that of the recording film 1 made of the TbFeCo film, the magnetic moment of the auxiliary film 2 of the PtCo alloy film is increased by the temperature rise during laser light irradiation. Rotate in the direction of the external magnetic field. Since the recording film 1 of the TbFeCo film and the auxiliary film 2 of the PtCo alloy film described above are exchange-coupled to each other, the magnetic moment of the transition metal of the recording film 1 of the TbFeCo film is also easily oriented in the direction of the external magnetic field.

This acts on the magnetization 5 of the recording film 1 of the TbFeCo film as a bias magnetic field applied in the external magnetic field direction. If the bias magnetic field is small, micro-domains are likely to occur in the bit due to the effect of the demagnetizing field. In this case, however, since a strong bias magnetic field is effectively applied, micro-domains are less likely to occur in the bit. .

In the above structure, the two-layer recording film 1 and the auxiliary film 2 are provided.
Both of the magnetic films are limited to media made of metal films, and the exchange coupling also utilizes the effect between the metal films. In the present invention, this principle is applied to a garnet magneto-optical recording medium, and its configuration is shown in FIG.

In FIG. 1, the recording film 1 is a bismuth-substituted garnet film exhibiting perpendicular magnetization, on which an auxiliary film 2 made of garnet containing no bismuth and having in-plane magnetization is laminated, and a metal film is further formed thereon. The reflective film 3 of FIG.

Here, the boundary surface between the recording film 1 and the auxiliary film 2
At 1A, they are magnetically coupled by exchange interaction. Further, the Curie temperatures of the recording film 1 and the auxiliary film 2 are made approximately the same by adjusting the composition of each film. With this configuration, since the auxiliary film 2 is an in-plane magnetized film, the magnetization direction becomes horizontal during reproduction when the temperature drops, so that noise does not occur,
It has no effect on the playback signal.

[0021]

Embodiments of the present invention will be described in detail below with reference to the drawings. As shown in FIG. 1, a substrate 4 of GGG (gadolinium gallium garnet, Gd ₃ Ga ₅ O ₁₂ ) 4 having a thickness of 0.5 mm, a diameter of 3 inches, and a groove depth of 300 Å. The thickness is 0.12μm and the composition is Bi ₂ DyGa by RF high frequency magnetron sputtering.
A bismuth-substituted garnet film of _0.8 Fe _4.2 O ₁₂ is formed as the recording film 1.

Then, a garnet film having a composition of Y ₃ Ga _0.8 Fe _4.2 O ₁₂ and a thickness of 0.1 μm and containing no bismuth is continuously formed thereon as the auxiliary film 2 by the high frequency bipolar magnetron sputtering method.

The procedure for forming the garnet film is such that the recording film 1 and the auxiliary film 2 are formed subsequently, and in each case, the substrate temperature was kept at 550 ° C. and the film was crystallized during the film formation.
This film forming method is a method proposed by the present applicant in Japanese Patent Laid-Open No. 2-239448, and the composition of Bi ₂ DyGa _0.8 Fe is used for forming the recording film 1.
_{A 4.2} O ₁₂ ceramic target was used, and for forming the auxiliary film 2, a ceramic target having a composition of Y ₃ Ga _0.8 Fe _4.2 O ₁₂ was used.

Table 1 shows the magnetic characteristics when the recording film or the garnet film of the recording film is independently formed on the GGG substrate.

[0025]

[Table 1]

When the recording film and the auxiliary film are sequentially formed,
Since these garnet films grow epitaxially,
They are magnetically exchange-coupled to each other at the interface between the recording film and the auxiliary film. Furthermore, by vacuum deposition on these garnet films,
An aluminum film having a thickness of 0.07 μm was formed as the reflection film 3 to obtain a magneto-optical disk.

Then, using this magneto-optical disk, a wavelength of 51
Magnetic field modulation recording was performed using a 4 nm argon laser.
A floating magnetic head was used to generate the modulating magnetic field. When recording / reproducing was performed on such a magneto-optical disk under the conditions shown in Table 2, the C / N value was 50 dB.

[0028]

[Table 2]

When this magneto-optical disk is used for overwriting with a 7 MHz signal, no unerased residue occurs,
It was completely overwritten. For comparison with the present embodiment, a bismuth-substituted garnet film (Bi ₂ DyGa _0.8 Fe _4.2 O ₁₂ ) was formed as a recording film 1 on a GGG substrate 4 in a single layer as shown in FIG. Aluminum reflective film 3 on top
When magnetic field modulation recording is carried out using a magneto-optical disk having a film formed thereon, the modulation magnetic field intensity needs to be 300 Oe, which is three times that of the present embodiment, and the C / N value is 48 dB. The value was smaller than the example.

[0030]

As described above, according to the magneto-optical disk of the present invention, the modulation magnetic field strength is compared with that of a single layer film.
It can be reduced to about 1/3. Therefore, the load on the magnetic head is reduced, the recording frequency can be improved, and the transfer speed can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a magneto-optical recording medium of the present invention.

FIG. 2 is a sectional view of a conventional magneto-optical recording medium.

FIG. 3 is a sectional view of a conventional magneto-optical recording medium.

[Explanation of symbols]

 1 Recording film 1A Boundary surface 2 Auxiliary film 3 Reflective film 4 Substrate

Claims (3)

[Claims] 1. A recording film (1) and an auxiliary film on a transparent substrate (4)
(2) and a reflective film (3) are sequentially provided, and the recording film (1) and the auxiliary film (2) are magnetically coupled at the boundary surface (1A) by exchange interaction, and the recording film (1) 1) _{Bi x R 3-x M y} Fe 5-y O
_12, wherein the auxiliary layer (2) is _{R 3 M y Fe 5-y} O 12 ( where, 0 <x
<3, 0 <y <2, R is yttrium or at least one element selected from rare earth elements, and M is a garnet film represented by an element that can replace the iron (Fe) element. A magnetic field modulation type garnet magneto-optical recording medium. 2. The recording film (1) and auxiliary film (2) according to claim 1.
Have a substantially equal Curie temperature and the auxiliary film (2) is an in-plane magnetized film. 3. A magnetic field modulation type garnet magneto-optical device, characterized in that a heat resistant substrate is used as the substrate (4) according to claim 1, and a recording film (1) and an auxiliary film (2) are formed by a sputtering method. recoding media.