KR930002168B1 - Magneto-optic memory medium - Google Patents

Abstract

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Description

Magneto-optical memory media

1 is a partial cross-sectional view of an embodiment of this invention.

2 shows the relationship between the component ratio and larger rotation angle of a GdNdFe film when using a long wavelength light source.

3 shows the relationship between the component ratio and larger rotation angle of a GdNdFe film when using a short wavelength light source.

FIG. 4 is a diagram showing wavelength dependence of a larger rotation angle of an Nd GdNdFe film and a GdTbFe film.

5 shows the relationship between the component ratio and the coercive force of a GdNdFe film.

6 to 8 show the temperature dependence of coercive force and larger rotation at different GdNdFe in composition ratio.

9 shows the relationship between the component ratio of Gd and the magnetic saturation of a GdNdFe film.

10 shows the relationship between the component ratio and the coercive force of a GdNdFe film.

11 shows the relationship between the component ratio and the coercive force of a GdTbFe film.

12 to 15 show the temperature dependence of the coercive force of different GdTbFe films at different component ratios.

FIG. 16 shows the relationship between the rare earth element and the coercive component ratio and the rare earth element ratio and the Curie temperature when the component ratio of Gd is equal to that of the GdTbFe film.

FIG. 17 shows the relationship between the component ratio of rare earth elements and the coercive force of a GdTbFe film.

FIG. 18 shows the relationship between the rare earth element component ratio and the Curie temperature of the GdTbFe film. FIG.

* Explanation of symbols for main parts of the drawings

2: first nitride film 3: readout film

4: recording film 5: second nitride film.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optic memory medium, and more particularly to a magneto-optical memory medium having an exchange coupled ferrimagnetic double layer structure in which recording films and reading films are laminated.

Because amorphous rare earth transition metal alloys have properties suitable for magneto-optical recording (as disclosed in Japanese Laid-Open Patent Publication Nos. 60-11746 / 1985 and 57-12428 / 1982 and US Patent Nos. 4390600, 4414650, 4489139). Thin films of rare earth-transition metal alloys (hereinafter abbreviated as RE-TM films) have been used as memory media in magneto-optical disk devices.

RE-TM films disclosed in this application are known to exhibit sufficient recording strength and recording density.

However, these RE-TM films are worse at S / N ratios when using read-only or read-only materials than optical recording.

The readability of the magneto-optical memory medium is highly dependent on the magneto-optical effect, in particular Kerr rotation angle and Faraday rotation angle. In order to improve the magneto-light effect of RE-TM film, efforts have been made to add elements such as Bi and Sn to date.

In addition, in order to improve the readability of magneto-optical memory media, an exchange-coupled quasi-magnetic double layer structure, that is, a recording film made of a material suitable for holding recorded information and a read film made of a material exhibiting a stronger magneto light effect are known. . ("Exchange-bonded quasi-magnetic bilayer film", Japanese Journal of Applied Physics vol 20, no.11 Nov. 2089-2095)

The recording film in such a double layer structure requires an appropriate Curie temperature and high coercive force for recording.

On the other hand, recording films require the above-mentioned magneto-light effect.

As an example, such an exchange bonding group magnetic bilayer structure is disclosed in Japanese Laid Open Patent Application No. 63-18544.

In this case, TbFeM (M is Cr or Al) is used for the recording film and GdFeCo is used for the reading film.

In general, the stronger the magneto-optical effect, i.e. the greater the angle of rotation or Faraday, the better the readability.

The magneto-optical effect is generally dependent on the wavelength of the application laser beam.

However, in the above-described conventional exchange coupling quasi-magnetism dual layer structure, the magneto-optical effect is large, which reduces the rotation angle or Faraday rotation angle, which is reduced in relation to the application laser beam in the short wavelength region, resulting in poor S / N.

There is also a limitation in improving the recording medium in the recording density using the laser beam in the short wavelength region.

Therefore, the wavelength of the laser beam used in recording / reproducing is limited.

This allows limited material to be used for the recording medium and inappropriate media for general purposes.

In short, a conventional magneto-optical memory medium having an exchange coupled quasi-magnetic double layer structure has disadvantageous disadvantages in that the reproducibility is poor with respect to the short wavelength laser beam and the improvement of the recording capability using the short wavelength laser beam is limited.

It is therefore an object of the present invention to provide a magneto-optical memo medium comprising a stack of a recording film made of an amorphous rare earth transition metal alloy having a high coercivity and a read film made of an amorphous rare earth transition metal alloy having a high magneto-optical effect.

The recording film made of amorphous alloy is represented by the following formula.

(Gd _P Tb _1-P ) _q Fe _1-q

q

0.35, 0

p×q

0.25, 0

(1-p)×q

0.25를 만족시킨다.)Where p and q are 0.1

q

0.35, 0

p × q

0.25, 0

(1-p) × q

Satisfies 0.25)

The read film made of amorphous alloy is represented by the following formula.

Gd _x Nd _y Fe _1-xy

x

0.3, 0

y

0.25를 만족시킨다.)(Where x, y is 0.1

x

0.3, 0

y

Satisfies 0.25)

By the above configuration of the present invention, information is recorded on the GdTbFe recording film, while the recorded information is reproduced by the GdNdFe reading film.

Here, when the laser beam is applied from the GdNdFe film side, the quantum mechanical exchange coupling action between the GdTbFe recording film and the GdNdFe read film causes the exchange coupling magnetic field to be applied from the former to the latter.

This makes the coercive force of the GdNdFe readout film stronger, so that the recording information can be kept stable.

Therefore, the recording capability and the reproduction capability can be greatly improved, especially with respect to a short wavelength laser beam (typically 600 nm or less).

The magneto-optical memory medium of the present invention is composed of a specific recording film or a specific reading film laminated on a suitable substrate.

The read film and the recording film are usually appropriately laminated in this order on a transparent substrate via a first dielectric film made of SiN, AlN, ZnS, SiO ₂ , SiAlON, AlNGe, or the like.

The recording film is also covered with the second dielectric film.

In the present invention, the recording film is made of amorphous GdTbFe alloy of special composition and the read film is made of amorphous GdNdFe alloy of special composition.

The amorphous alloy film may be formed by sputtering or deposition, for example, by using an alloy of a special composition as a target or by sputtering using a target as a composition or by multi-source covapor deposition. Can be.

The thickness of each of the recording and reading films is preferably 500 nm or less and preferably 10 to 100 nm in a battery in which the range and exchange sensitivity occur where possible.

An embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 1, the magneto-optical memory medium according to the present invention includes a substrate 1, a first nitride film 2, a GdNdFe read film 3, a GdTbFe recording film 4 and a second nitride film 5 It consists of and it lies in order from the laser beam application side.

For example, a transparent substrate made of polycarbonate or glass may be used for the substrate 1.

The substrate 1 allows the laser beam to irradiate the GdNaFe reading film 3 and the GdTbFe recording film 4 and to support the first nitride 2 with respect to the films, that is, the second nitride 5.

In the nitride film 2, such a dielectric film, for example, 80 to 100 nm thick SiN or AlN is used to increase the rotation angle by increasing the magneto-optical effect.

Thus, the result shows greater readability.

The characteristics of the recording and reading films will be described below.

The properties are evaluated in relation to the GdNdFe film and the GdTbFe film, which are respectively films having a thickness of 50 to 150 nm formed on the glass substrate, which differ in the component ratios.

As shown in FIG. 2, when a GdNdFe having a component ratio of Gd denoted by x or less is used for a GdNdFe readout film (hereinafter referred to as a "reading film"), the rotation angle θ _K is a long wavelength laser beam having a wavelength of 780 nm. About 0.4 °.

The larger angle of rotation of 0.4 ° is relatively large and therefore this film is suitable for the reading film but FIG. 2 shows the case where the component ratio of Nd denoted by y is 0.1 and 0.04, respectively.

Also, when using a short wavelength laser beam having a wavelength of 400 nm, FIG. 3 is clearly large, showing a slight decrease in the rotation angle.

3 shows the case where the component ratios of Nd denoted by y are 0.1 and 0.04, respectively.

Moreover, the larger rotation angle θ _K of GdNdFe is essentially constant depending on the wavelength of the entire wavelength region of the visible light source (FIG. 4).

The larger rotation angle of GdTbFe tends to decrease as a decrease in wavelength in the short wavelength region as shown in FIG.

On the other hand, the temperature dependence of the larger rotation angle of the read film does not change with the change in the component ratio of the film.

As described above, GdNdFe can be effectively used so that the diameter of the beam can be reduced when used in the readout film.

Therefore, the memory medium is remarkably improved in writing density.

For example, the recording density is four times higher when the wavelength of the laser beam used is reduced in half using the Second Harnonic Generator (S.H.G.).

The coercive force of the read film becomes less than about 1 KOe even when the component ratio of GdNdFe is changed as shown in FIG. 5 illustrating the case where the component ratio of Nd represented by y is 0.1 and 0.04, respectively.

As shown in Figs. 6 to 8, the temperature dependence of the coercive force of the read film changes as the component ratio changes.

In FIG. 7 (Gd0.206 Nd0.048 Fe0.746) and 8 (Gd0.21 Nd0.044 Fe0.746), the compensation temperature is developed within the temperature range demonstrated for the Curie temperature.

On the other hand, in FIG. 6 (Gd 0.191 Nd 0.038 Fe 0.771), the coercive force is generally small since the compensation temperature is not found within the demonstrated temperature range.

However, in the present invention, since the read film 3 is exchange coupling with the GdTbFe recording film 4 described below, the read film 3 can be sufficiently used as the read film even if its coercive force is small due to quantum mechanical exchange defect action. have.

The exchange coupling action may increase the absolute value Hc of the superficial coercive force of the reading film 3.

The raised absolute value Hc represented by the equation

Where σw is the domain wall energy density (erg / cm 2) at the interface of the bilayer film; Ms represents self saturation (emu / cm 3); h denotes the thickness of the read film 3.

For example, if the coercive force Hc is calculated by substituting Ms = 30 emu / cm 3 into the equation (1), which is determined not to exceed 100 emu / cm 3 based on σ w = 1 (erg / cm 2), h = 500 mW, Hc is about 6.7 KOe.

This value is strong enough to hold a small alert write bit.

Therefore, in FIG. 10 where the value indicates the coercive force, the component ratio of the reading film 3 is limited within the range that satisfies the following inequality (1) (2) at the same time based on the condition that vertical magnetic anisotropy can be obtained. do.

Here x is the component ratio of Gd and y represents the component ratio of Nd in Gd _x Nd _y Fe _1-xy .

As apparent from FIG. 10, a GdTbFe-based film 4 (hereinafter referred to as "recording film") having a high coercive force of 5 KOe or more can be relatively easily produced.

The temperature dependence of the coercive force of the recording film 4 changes with its composition ratio.

As shown in Figs. 12 to 15, the recording film 4 exhibits high coercive force in either case.

It is therefore suitable for recording films.

12 shows temperature dependence of the coercive force when the component ratio of the recording film is (Gd0.5 Tb0.5) 0.145 Fe0.855.

FIG. 13 shows the temperature dependence of the coercive force when the component ratio of the recording film is (Gd0.5 Tb0.5) 0.169 Fe0.831. FIG. 14 shows that the recording film component ratio is (Gd0.5 Tb0.5) 0.182 Fe0.818. The coercive force is expressed in the case of and FIG. 15 shows the coercive force when the component ratio of the recording film is (Gd0.5 Tb0.5) 0.235 Fe0.765.

As shown in FIG. 16, the Curie temperature of the recording film is in a temperature range higher than about 150 캜 to 170 캜.

Therefore, the recording sensitivity can be improved.

Also, as shown in FIG. 16, the larger rotation angle of the recording film is substantially constant in a considerably longer wavelength region.

That is, about 0.4 °.

Note that the wavelength of the light source is 780 nm.

However, in the short wavelength region, the larger rotation angle is significantly reduced as shown in FIG.

The component ratio of the recording film 4 is 1 KOe or more in view of the stability required for the information recording bits having a small coercive force; The Curie temperature range is limited to a range that satisfies the following inequalities (4) to (6) under the condition of 100 ° C to 200 ° C in view of recording sensitivity.

0.1은 보자력이 0.1KOe 보다 더 작은 경우이다.In Fig. 17, the value represents the coercive force, and> 10 is the coercive force greater than 10 KOe.

0.1 is when the coercive force is smaller than 0.1 KOe.

In FIG. 18, the value represents the Curie temperature.

(Gd _p Tb _1-p ) _{q In} Fe _1-q , p is a component ratio of Gd and q is a component ratio of (GdTb).

In addition, the second nitride film 5 provided to protect the reading film 3 and the recording film 4 is made of the same material as that of the first nitride film 2.

It should be understood that a metal film such as Al can be used in place of the second nitride film 5.

When the laser beam projected from a semiconductor laser or a HeNe laser is collected by an optical system (not shown here) and becomes a dot on the medium, the beam point is due to the configuration of the above embodiment of the magneto-optical memory medium, and therefore the beam point is reduced by the substrate 1 and the first nitrogen. The reading film 3 and the recording film 4 are reached through the cargo film 2.

On the other hand, the temperature of the beam point portion of the read film 3 increases. The magnetization of the read film 3 does not appear when the temperature exceeds its Curie temperature.

When no magnetization occurs, the exchange-bonding action of the bilayer film does not appear.

At this time, if a deflection magnetic field (not shown) or the like is used for recording the recording film 4, an iron core of an inverse magnetic region is generated which is opposite to that in the vicinity of the magnetic spin direction.

This magnetic region then expands to become a small bit and to a cylindrical magnetic region.

When the application of the laser beam is stopped the temperature of that part is reduced.

When the temperature decreases immediately below the Curie temperature of the read film, the small bits formed in the recording film are transferred to the read film 3 by an exchange coupling action.

When linearly classified laser beams are applied to the substrate 1 in regeneration (reading), the polarization plane of the reflected light rotates in the direction of the orientation of the magnetic spin with the aid of the magneto-optical effect.

At this time, a change in the amount of reflected light is detected by using a photo detector connected to the analyzer.

Therefore, the recorded information can be reproduced.

According to the present invention, the magneto-optical memory medium is not limited to the above configuration.

Various supplemental films, such as protective gloves, may be provided according to certain requirements.

By way of example, a reflective film can be added on the side of the second nitride 5 opposite the laser beam application side.

In this case, both the reading film 3 and the recording film 4 constituting the double layer film are thinned enough to pass the laser beam there through. Reflective films are effective for effectively utilizing the light rays used.

As described above, the magneto-optical memory medium according to the present invention has a specific component ratio of GdNaFe read film formed on the laser-use side of the GdTbFe recording film and the GdTbFe recording film of a specific component ratio. It is composed of an excellent GdTbFe recording film and a GdNdFe reading film having a high curie temperature, a low coercive force, and a high reproducibility since the magneto-optical effect is large in the short wavelength region.

This structure increases memory sensitivity and readability by increasing the quantum mechanical exchange coupling action.

In addition, the read film can use GdNdFe to greatly reduce the wavelength dependence of the magneto-optical effect.

Therefore, it is possible to use a laser beam having a short wavelength because the diameter of the laser beam is minimized in order to improve the recording density and at the same time improve the S / N ratio in the short wavelength region.

Moreover, this arrangement makes use of a wide range of selectivity, such as a light source, allowing the laser beam to be used, ignoring its wavelength.

Claims (6)

Lamination of a recording film of a rare earth transition metal alloy with high coercivity and a reading film of an amorphous rare earth transition metal alloy with magneto-optical effect; Formula (Gd _p Tb _1-p ) _q Fe _1-q , where p and q are 0.1

q

0.35, 0

p × q

0.25 and 0

(1-p) × q

The recording film of an amorphous alloy represented by a formula satisfying 0.25; A magneto-optical memory medium comprising the read film of an amorphous alloy represented by the formula Gd _x Nd _y Fe _1-xy , wherein x and y satisfy 0.1 <x <0.3 and 0 <y <0.25. The magneto-optical memory medium according to claim 1, wherein each of the recording film and the reading film has a thickness of 500 nm or less. The magneto-optical memory medium according to claim 1, wherein each of the recording film and the reading film has a thickness of 10 to 100 nm. The magneto-optical memory medium according to claim 1, wherein the read film is laminated on the transparent substrate via the dielectric film and the recording film is laminated on the read film. The magneto-optical memory medium according to claim 4, wherein the recording film is covered with another dielectric film. The magneto-optical memory medium according to claim 1, which is used for recording and / or reproduction information using a short wavelength laser beam.

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