JP3218735B2 - Magneto-optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable magneto-optical recording medium, and more particularly to a magneto-optical recording medium for reading a recording signal while changing a magnetization state of a reproducing layer.

[0002]

2. Description of the Related Art A magneto-optical recording medium is a rewritable optical recording medium, and has excellent repeated erasing / writing durability and erasing ratio as compared with a phase change type optical recording medium and the like, and is a portable large-capacity recording medium. Attention has been paid.

The magneto-optical recording medium employs a recording / reproducing method in which recording bits are formed by local heating by laser light irradiation, and the recording bits are read out by the Kerr effect. The interval between recording bits can be made much smaller than the laser spot diameter by adjusting the laser light irradiation power, the intensity of the recording magnetic field, etc., but the reading is performed at the laser wavelength at the time of reproduction. And the aperture ratio of the lens.

[0004] An attempt to improve the readout beyond the recording density determined by such restrictions during reproduction is disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 3-93058, and the magnetization of the reproduction layer is initialized by an initialization magnet before reproduction. A technique for improving reproduction resolution by reproducing the data while transferring the recording bits of the recording holding layer to the reproduction layer after aligning the orientations of the recording layers is described.

This method utilizes the temperature rise caused by the irradiation of the reproducing light, and reproduces the beam while transferring the recording bits of the recording holding layer to the reproducing layer only at the high temperature area in the beam spot. The recording magnetic domain is prevented from appearing in the other areas in FIG. 1 to reduce intersymbol interference during reproduction and to enable reproduction of a signal having a period equal to or less than the diffraction limit of light.

[0006] The technique disclosed in Japanese Patent Application Laid-Open No. 3-93058 is a floating type MSR (Magnetically).
induced Super Resolution
n) or RAD (Rear Aperture D)
(Election).
No. 55946 and Japanese Journal of Applied Physics (Japanese Journal of Applied Physics)
al of Applied Physics) Se
ries 6, Proc. Int. Symp. o
n Optical Memory, 1991, pp. 146-64.
203-210 proposes a reproducing system having at least a three-layer structure including a reproducing layer (first magnetic layer), an intermediate layer (second magnetic layer), and a recording layer (third magnetic layer). This method is
This is called double mask RAD, and after the magnetization direction of the reproducing layer is aligned by an initialization magnet before reproducing, the reproducing exceeding the Curie temperature of the intermediate layer or the reproducing auxiliary layer provided between the reproducing layer and the intermediate layer is performed. As a result, the region where the magnetization is directed to the third magnetic layer is divided into a region where the magnetization is directed to the direction of the initialization magnetic field (mask 1) and a region where the magnetization is read and directed to the direction of the bias magnetic field (mask 2). , And the signals from the mask 1 and the mask 2 are DC components that do not change over time.
By detecting a signal only from a region where the magnetization is directed to the direction of the third magnetic layer, a signal having a period equal to or less than the diffraction limit of light can be reproduced. Since the area where the magnetization is directed to the third magnetic layer is smaller in the double mask RAD than in the RAD, the resolution is further improved.

[0007]

Problems to be Solved by the Invention
In the embodiments of Japanese Patent Laid-Open Publication No.
All layers are composed of a film containing a rare earth transition metal as a main component. The four-layer structure is the most typical structure and the reproducing layer is GdF
eCo, TbFeCoAl for the auxiliary reproduction layer, and Gd for the intermediate layer
FeCo, the recording layer is TbFeCo.

When laminating magnetic films having complicated compositions,
It is desirable to sputter each layer using an alloy target, because the apparatus is simpler and desirable. However, in the case of rare earth transition metal based materials, the composition of the rare earth transition metal alloy target does not match the film composition, It is difficult or necessary to take special measures to make the target. The problem to be solved by the present invention is to reduce the number of rare-earth transition metal films among laminated films usable for RAD or double mask RAD.

[0009]

According to the present invention, as shown in FIG. 1, a first magnetic film, a second magnetic film, and a third magnetic film magnetically coupled to each other on a transparent substrate. And the Curie temperatures of the first, second, and third magnetic films are set to Tc, respectively.
1, Tc2, Tc3, Tc3, Tc1> Tc
2> room temperature, the first magnetic film and the third magnetic film are perpendicular magnetization films, and the second magnetic film is made of at least one element of Fe, Co, Ni, and Al, Si, Ge, Ti, V , Cr,
Mn, Zr, Nb, Mo, Hf, Ta, W, Cu, P
It is an in-plane magnetized film composed of at least one element of d, Ag, Pt, and Au, and is a magneto-optical recording medium capable of reproducing while deforming the magnetic domain of the first magnetic layer.

The first magnetic film has a large coercive force at room temperature,
Any perpendicular magnetization film having a small coercive force at Tc2 may be used. For example, GdFeCo, GdTbFeCo, Gd
dDyFeCo and the like. Further, a two-layer structure of a reproduction layer and a reproduction auxiliary layer, for example, a two-layer structure of GdFeCo / TbFe may be used. In the two-layer structure, the change in coercive force can be controlled by the Curie temperature of the auxiliary reproduction layer, so that the variation in coercive force of the first magnetic film due to the variation in composition can be reduced.

The third magnetic film is made of TbFeCo, DyFeC
Any material such as o and NdDyFeCo may be used as long as it has a sufficiently large coercive force from room temperature to Tc2.

The second magnetic film controls an effective magnetic field due to exchange coupling of the third magnetic film to the first magnetic film, and initializes the first magnetic film by an external magnetic field Hini for initialization. The temperature Tp at which transfer is started in a state where the state is stabilized and Hr (an external magnetic field for performing reproduction) is applied.
From the temperature T at which the first magnetic layer starts to turn uniformly in the direction of Hr
In the range of r, it also has a function of switching the transfer of the magnetization state from the third magnetic film to the first magnetic film.

As the second magnetic film having such a function, an in-plane magnetic film satisfying Tc3, Tc1>Tc2> room temperature, and at least one element of Fe, Co and Ni and Al and S
i, Ge, Ti, V, Cr, Mn, Zr, Nb, Mo,
A thin film composed of at least one element of Hf, Ta, W, Cu, Pd, Ag, Pt, and Au is preferable. Al, S
i, Ge, Ti, V, Cr, Mn, Zr, Nb, Mo,
Hf, Ta, W, Cu, Pd, Ag, Pt, and Au are included for controlling the Curie temperature and the saturation magnetization. Since such a composition does not contain a rare earth metal, it has a feature that when forming a film by a sputtering method, the composition of the target and the thin film is good, and the film is easy to handle because it has excellent corrosion resistance.

FIG. 2 shows an example of a reproducing method for a magneto-optical recording medium according to the present invention. While rotating the magneto-optical recording medium, an external magnetic field H for initialization is provided at a position away from the head.
ini is applied to align the magnetization of the first magnetic film in a certain direction. Thereafter, while applying an external magnetic field Hr for reproduction in a direction opposite to the direction of Hini, the laser beam is irradiated with a power such that the magnetic layer is formed in a temperature range of Tp or more, so that the laser beam is irradiated. The recorded state of the third magnetic film is transferred to and reproduced from the first magnetic film. Since the magnetization of the first magnetic film is aligned in a fixed direction (first mask) in the laser spot other than the transferred area (first mask), the signal of only the transferred area is detected and the code Interference can be reduced, and a signal having a period less than the diffraction limit of light can be reproduced. Further, where the temperature of the first magnetic film is in the region equal to or higher than Tr, the direction of the first magnetic film is oriented in the direction of Hr (second mask 2).
This prevents the area where the recording state of the third magnetic film is transferred onto the magnetic film from becoming too wide and causing intersymbol interference. Thus, information on the magneto-optical recording medium is reproduced while the magnetic domains of the first magnetic layer are deformed.

Note that an external magnetic field Hin for initialization is provided.
i (room temperature) is Hc1 for the coercive force of the first magnetic film, Hc3 for the coercive force of the third magnetic film, and the third coercive force with respect to the first magnetic film via the second magnetic film. Hc1 + Hw1 where Hw1 is the effective magnetic field due to exchange coupling from the first magnetic film and Hw3 is the effective magnetic field due to exchange coupling from the first magnetic film to the third magnetic film via the second magnetic film. <Hini <Hc3-Hw3.

An external magnetic field Hr for performing reproduction is T
In the temperature range of p to Tr, the relationship Hc1−Hw1 <Hr <Hc1 + Hw1 is satisfied, and Hc3 is sufficiently larger than Hr.

The structure of the magneto-optical recording medium of the present invention comprises a first magnetic film magnetically coupled to the above-mentioned transparent substrate,
There is no particular limitation so long as it is composed of the second magnetic film and the third magnetic film. A dielectric film is sandwiched between the transparent substrate and the magnetic film, and a protective film and a reflective film are laminated on the magnetic film. May be. The transparent substrate is not particularly limited to glass, polycarbonate, amorphous polyolefin and the like as long as the transparent substrate is sufficiently transparent in the wavelength region of the laser to be used and satisfies the characteristics of a medium substrate such as mechanical characteristics.

The thickness of the magnetic film of the magneto-optical recording medium of the present invention is such that the first magnetic film is a film in which most of the laser light is absorbed by the first magnetic film, and is 150 to 800 Å. The second magnetic film is preferably made of Tc2
The thickness which can cut off the exchange coupling force between the first magnetic film and the third magnetic film is preferably 20 Å or more and 300 Å or less, and the third magnetic film is a film which is enough to hold the recording. The thickness is preferably 200 to 1000 Å.

[0019]

【Example】

Example 1 A magneto-optical medium as shown in FIG. 3 was produced. A dielectric layer 2 (thickness: 800 Å) made of silicon nitride and a first magnetic film 3 (thickness: 300 Å) made of GdDyFeCo are formed on a polycarbonate substrate 1.
Hc1: 2 kOe (room temperature), Hc1: 0.2 kOe (1
50 ° C.), Tc1: 330 ° C.), (Fe ₉₂ Co ₈ ) ₅₇ S
second magnetic film made of i ₄₃ 4 (thickness: 80 Å, Tc2: 150 ℃), third composed of TbFeCo
Magnetic film 5 (thickness: 500 angstroms, Hc3:
> 12 kOe, Tc3: 260 ° C.), and a silicon nitride layer 6 (film thickness: 800 Å) was formed as a protective layer.

Next, this magneto-optical medium is set in a recording / reproducing apparatus, and a 780-n initializing magnetic field (Hini) generating section of 3 kOe is passed at a linear velocity of 7.3 m / sec.
The laser beam having a wavelength of m is 9% at a duty of 33%.
Recording was performed with a laser power of 8 mW while modulating at MHz. The bias magnetic field at the time of recording was 300 Oe and was applied in the direction opposite to the initialization magnetic field (Hini).

When the bias magnetic field (Hr) is set to 300 Oe and the laser power is increased to reproduce at 2.0 mW, C / N
Was 42 dB, and 46 dB when reproduced at 3 mW.

Further, the second magnetic film 4 is made of Ni ₉₅ Cr ₅ , Co ₁₂ Pt ₈₈ and Fe ₅₇ A so that Tc is around 150 ° C.
almost the same effect can be replaced with, such as l ₄₃ was obtained.

COMPARATIVE EXAMPLE 1 A magneto-optical recording medium obtained in the same manner as in Example 1 except that the second magnetic film 4 made of (Fe ₉₂ Co ₈ ) ₅₇ Si ₄₃ was used was changed to 2.0 mW. Upon reproduction, the value of C / N was 23 dB.

Comparative Example 2 In Example 1, the second magnetic film was made of (Fe ₉₂ Co ₈ ) ₇₂ S
When i ₂₈ (Tc2: 500 ° C.), the C / N value was 33 dB when reproduced at 2.0 mW, and 35 dB when reproduced at 3.0 mW, and a good C / N was not obtained.
This is probably because the transfer from the third magnetic film to the first magnetic film was not performed well.

Example 2 A dielectric layer (thickness: 800 angstroms) made of silicon nitride and a first magnetic film made of GdFeCo (thickness: 300 angstroms, H) were formed on a polycarbonate substrate.
c1: 0.3 kOe (room temperature), Hc1: 0.1 kOe
(150 ° C.), Tc1: 330 ° C.), TbFeCoSi
Reproduction assisting layer (film thickness: 100 Å,
Hcs: 4.0 kOe (room temperature), Tcs: 140 ° C.),
A second magnetic film 4 (film thickness: 80 angstroms, Tc2: 190 ° C.) of (Fe ₉₂ Co ₈ ) ₅₉ Si ₄₁ , Tb
Third magnetic film 5 made of FeCo (thickness: 500 Å, Hc3:> 12 kOe, Tc3: 260
° C) and a silicon nitride layer 6 (film thickness: 80
0 angstroms).

Recording is performed under the same conditions as in Example 1, and when the bias magnetic field is set to 300 Oe and the laser power is increased to reproduce at 2.0 mW, the C / N value is 43 dB, and when the reproduction is performed at 3 mW, 47 dB. It became.

[0027]

According to the magneto-optical recording medium of the present invention, the reproduction resolution of the magneto-optical recording medium can be improved. Second
Since a material containing no rare earth is used for the magnetic layer, the composition of the target and the thin film when forming a film by the sputtering method is good, and the corrosion resistance is also excellent.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of the structure of a magneto-optical recording medium according to the present invention.

FIG. 2 is a diagram showing a reproducing method of the magneto-optical recording medium of the present invention.

FIG. 3 is a sectional view showing an example of the structure of the magneto-optical recording medium of the present invention.

Claims (1)

(57) [Claims] And 1. A first magnetic film magnetically coupled to each other on a transparent substrate, a second magnetic layer, and a third magnetic film, while rotating the magneto-optical recording medium, from the head Away
The external magnetic field Hini for initialization
In addition, the magnetization of the first magnetic film is aligned in a certain direction.
After that, while applying an external magnetic field Hr for performing reproduction,
With a power such that the magnetic layer is formed in a temperature range above Tp
By irradiating the first magnetic film with the third beam,
Magneto-optical recording medium that reproduces the recorded state of the magnetic film
A body, the first magnetic layer and the third magnetic film is a perpendicular magnetization film, the second magnetic film is Fe, Co,
At least one element of Ni and Al, Si, Ge, Ti,
V, Cr, Mn, Zr, Nb, Mo, Hf, Ta, W,
An in-plane magnetized film composed of at least one element of Cu, Pd, Ag, Pt, and Au ;
The Curie temperature of the magnetic film is set to Tc1, Tc2, Tc, respectively.
3, when Tc3, Tc1>Tc2> room temperature,
The coercive force of the first magnetic film is Hc1, and the third magnetic film is
The coercive force of Hc3 and the second magnetic film with respect to the first magnetic film.
Through the exchange coupling from the third magnetic film through the magnetic film of
The effective magnetic field is Hw1 and the third magnetic film is
Exchange coupling from the first magnetic film through the second magnetic film
Assuming that the effective magnetic field is Hw3, Hc1 + Hw1 <H
ini <Hc3−Hw3, and a predetermined
In the temperature range Tp to Tr (Tp <Tr), Hc1−Hw1
<Hr <Hc1 + Hw1
Magneto-optical recording medium .