JP3079308B2 - Magneto-optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magneto-optical recording medium capable of overwriting (overwriting information) by a magnetic field modulation method.

[0002]

2. Description of the Related Art Magneto-optical recording media (hereinafter referred to as recording media)
Various methods of overwriting by a magnetic field modulation method have been studied. When overwriting is performed by a magnetic field modulation method, a laser beam having a constant light intensity is projected onto a recording medium, and a modulation magnetic field having a predetermined intensity is applied to the projection position, so that information already written on the recording medium can be read. Erase and new information can be written. Also,
The results of research conducted on magneto-optical recording using such a magnetic field modulation method are described in, for example, “The Institute of Electrical Engineers of Japan, Magnetics Research Group” published by the Institute of Electrical Engineers of Japan on November 24, 1987.
MAG-87-173-180 ".

On the other hand, a magneto-optical recording element suitable for a magnetic field modulation method using a low bias magnetic field and capable of overwriting (overwriting) is disclosed in JP-A-1-199342. In this magneto-optical recording element, the perpendicular magnetization film contains at least a Gd element as a rare earth metal component and an Fe element as a transition metal component, and has a predominant Fe sublattice magnetization, and the dielectric layer on the substrate is made of amorphous silicon nitride. Wherein the magnetization M _S of the perpendicular magnetization film of the magneto-optical recording element is 20 emu / cc ≦ M _S ≦
70 emu / cc and the product of the magnetization M _S and the coercive force H _C is 100 emu
It is set so that kOe / cc ≦ M _S · H _C ≦ 500 emu · kOe / cc.

[0004]

By the way, in order to write information on a recording medium at a high density, it is necessary to increase the modulation frequency of a magnetic head that applies a modulation magnetic field. In addition, it is necessary to increase the distance between the magnetic head and the recording medium in consideration of the warpage of the recording medium and the thickness variation.

However, when the modulation frequency is increased, the intensity of the magnetic field generated from the magnetic head decreases. In addition, since the recording medium rotates at a high speed, the intensity of the modulation magnetic field applied to the recording medium does not follow the intensity of the modulation magnetic field of the magnetic head, and the intensity of the modulation magnetic field applied to the recording medium decreases. There is also a problem that the intensity of the modulation magnetic field applied to the recording medium is reduced even when the distance between the magnetic head and the recording medium is increased.

Therefore, in order to record information on a recording medium in a sufficient recording state, the intensity of the modulation magnetic field of the magnetic head must be reduced to 20.
Must be 0 Oe or more. It is thought that this is because the floating magnetic field generated from the recording medium itself repels the modulation magnetic field given from the magnetic head.

On the other hand, in a magneto-optical recording element disclosed in Japanese Patent Application Laid-Open No. 1-199342, the perpendicular magnetization film contains at least a Gd element as a rare earth metal component and an Fe element as a transition metal component. , The magnetization M _S of the perpendicular magnetization film is 20
emu / cc ≦ M _S ≦ 70 emu / cc and the product of the magnetization M _S and the coercive force H _C is set so as to be within a range of 100 emu · kOe / cc ≦ M _S · H _C ≦ 500 emu · kOe / cc. Therefore, it is possible to provide a magneto-optical recording element that can be overwritten by a compensation temperature recording method suitable for a magnetic field modulation method, but a magneto-optical recording medium that can be overwritten with a small magnetization by a Curie point recording method suitable for a magnetic field modulation method. There is a problem that it cannot be provided.

In view of the above problem, the present invention provides a recording medium capable of recording information in a sufficient recording state on the recording medium by the Curie point recording method even when the intensity of the modulation magnetic field of the recording medium is 200 Oe or less. The purpose is to do.

[0009]

According to the magneto-optical recording medium of the present invention, a magnetic thin film having perpendicular magnetic anisotropy is formed on a substrate, and a protective film made of a dielectric is formed on the magnetic thin film. In a magneto-optical recording medium which is used in a magnetic field modulation type apparatus and is capable of overwriting, the magnetic thin film
b, Fe, a magnetic thin film whose main component is Co, the thickness Timyuemu, the saturation magnetization in the case of the M _s emu / cc t
× M _s <5 μm · emu / cc (where t = 0.04 μm and (1) Tb18.0 (Fe0.89 Co0.11) 82.0 (2) Tb19.5 (Fe0.89 Co0.11) 80.5 (3 ) Tb21.0 (Fe0.89 Co0.11) 79.0 ( 4) Tb22.5 (Fe0.89 Co0.11) was expressed in 77.5 (5) Tb24.0 (Fe0.89 Co0.11 ) 76.0 atomic ratio of ( Excluding five types of compositions ) . The strength of the stray field of the record medium is proportional to the multiplication value of the film thickness tμm magnetic thin film of the recording medium and its saturation magnetization M _s emu / cc. When the thickness of the magnetic thin film t × saturation magnetization M _s ≦ 5 μm · emu / cc is satisfied, when the information is recorded with the intensity of the modulation magnetic field of the recording medium set to 200 Oe, the carrier / noise ratio C / N is 45 dB or more. Jitter σ becomes 4 nsec or less. As a result, the intensity of the modulation magnetic field does not need to be increased to record information in a sufficient recording state.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings showing embodiments of the present invention. Figure 1 is the relationship between the jitter σ and carrier-to-noise ratio C / N, and FIG. 2 is a graph showing the relationship between the carrier-to-noise ratio C / N and the thickness t × saturation magnetization M _S. Before describing the embodiments of the present invention, the principle of the present invention will be described. In order to record information on a recording medium in a sufficient recording state, the inventor of the present application increases the intensity of the modulation magnetic field of the recording medium.
At 200 Oe or more, the existence of the influence of the stray magnetic field generated from the recording medium itself was confirmed by an experiment. Then, it was confirmed that the stray magnetic field of the recording medium was proportional to the product of the thickness t of the information recording film in the recording medium, that is, the magnetic thin film, and the saturation magnetization M _S thereof. Then, information was recorded using a recording medium, and the relationship between jitter σ indicating the time lag between the recording signal and the reproduction signal and the carrier-to-noise ratio C / N was obtained. The result shown in FIG. 1 was obtained. Was. In FIG. 1, the vertical axis represents the jitter σ.
The horizontal axis indicates the carrier-to-noise ratio C / N. As is apparent from FIG. 1, when the jitter σ is 3.5 nsec or more, the carrier-to-noise ratio C / N becomes 45 dB or less, and information cannot be recorded in a sufficient recording state. On the other hand, the intensity of the modulation magnetic field of the recording medium was set to 200 Oe, and the carrier-to-noise ratio C / N
When the relationship between the product of the film thickness t and the saturation magnetization M _S was determined, the results shown in FIG. 2 were obtained. In FIG. 2, the vertical axis represents the carrier-to-noise ratio C / N, and the horizontal axis represents the film thickness t and the saturation magnetization M _S.
Is shown as a multiplication value. As is clear from FIG. 2, the carrier-to-noise ratio C / N increases as the product of the film thickness t × the saturation magnetization M _S decreases, and the curve showing the relationship between them slightly curves downward. It is shown in the shape of a downward right arc. The product of the film thickness t and the saturation magnetization M _S is 5 μm · emu / cc.
Below this, the carrier-to-noise ratio C / N is maintained at 45 dB or more. On the other hand, at 5 μm · emu / cc or more, the carrier-to-noise ratio C / N drops to 45 dB or less, and information cannot be recorded in a sufficient recording state as described above. In other words, in order to record information on the recording medium in a sufficient recording state, it is understood that the product of the thickness t of the magnetic thin film of the recording medium and the saturation magnetization M _S should be 5 μm · emu / cc or less. . Now,
FIG. 3 is a schematic enlarged sectional view of the recording medium according to the present invention. On one surface of a substrate 1 made of a polycarbonate substrate or a 2P glass substrate, a dielectric film 2 made of a SiN film and having a thickness of 0.06 μm is formed.
It is composed of a FeCo film, has a thickness of 0.08 μm, and has a saturation magnetization M _S
A magnetic thin film 3 serving as an information recording film of 60 emu / cc is formed. The magnetic thin film 3 is made of a SiN film and has a thickness of
A protection film 4 of 0.08 μm is formed. Each of these thin films is formed by a sputtering method. As a result, the product of the film thickness tμm and the saturation magnetization M _S emu / cc becomes 4.8.
μm ・ emu / cc. Information is recorded on the thus-produced prototype recording medium at a recording signal frequency F = 7.4 MHz, a recording medium rotation speed N = 3600 rpm, a modulation magnetic field intensity of 200 Oe, and a carrier-to-noise ratio C / N and jitter are recorded. When σ was measured, the results shown in Table 1 were obtained. Thickness t of magnetic thin film 3
Is 0.08 μm, and the prototype recording medium S1 having a saturation magnetization M _S of 60 emu / cc has a carrier-to-noise ratio C / N of 46.0 dB and a jitter σ of 3.58 nsec.

[0011]

[Table 1]

In the prototype recording medium S2 in which the thickness t of the magnetic thin film is 0.10 μm and the saturation magnetization M _S is 50 emu / cc, the carrier-to-noise ratio C / N is 45.0 dB and the jitter σ is 3.80 nsec. Thickness t of magnetic thin film is 0.08μm, saturation magnetization is 30em
The carrier-to-noise ratio C / N is 4 for the prototype recording medium S3 with u / cc
8.0dB and jitter σ were obtained in 3.50nsec.

On the other hand, a conventional recording medium in which a magnetic thin film having the same composition as the prototype recording media S1, S2, S3 is formed and the product of the film thickness t and the saturation magnetization M _S is 5 μm · emu / cc or more. Medium SS1,
When SS2 was similarly measured, as shown in Table 1, the carrier-to-noise ratio C / N was 45 dB or less and the jitter σ was 5.0 nsec or more.

By setting the multiplication value of the thickness t of the magnetic thin film of the recording medium and the saturation magnetization M _S to 5 μm · emu / cc or less, even if the intensity of the modulation magnetic field of the recording medium is 200 Oe, Carrier-to-noise ratio C / N of 45.0dB and jitter σ
Can be obtained in 4 nsec or less, and it is possible to obtain a recording medium having a low error rate and capable of overwriting with a small modulated magnetic field intensity by rotating at a high speed.

FIG. 4 is a schematic enlarged sectional view of a recording medium showing another embodiment of the present invention. On one side of a substrate 1 made of a polycardate substrate or a 2P glass plate, SiN
A dielectric film 2 made of a film and having a thickness t of 0.06 μm is formed. On this dielectric film 2 is formed, for example, a TbFeCo film.
A magnetic thin film 3 having a thickness t of 0.03 μm and a saturation magnetization M _S of 100 emu / cc is formed. On the magnetic thin film 3, a reflective film 5 made of an AlNi film and having a thickness of 0.04 μm is formed. Further, a protective film 4 made of a SiN film and having a thickness t of 0.08 μm is formed on the reflective film 5. The magnetic thin film 3 may be a film of DyFeCo, GdTbFe, GdTbFeCo, BiYIG, or BiDy-Garnet.

With the recording medium thus configured, information was recorded on the recording medium in the same manner as the recording media S1, S2, and S3, and the carrier-to-noise ratio C / N and the jitter σ were measured. was gotten.

[0017]

[Table 2]

As apparent from Table 2, the magnetic thin film 3
The recording medium S1, S
2, Even when the thickness is set to 0.03 μm, which is approximately 1/3 of the thickness t of S3,
And the saturation magnetization M to a multiplication value of the _S below 5 [mu] m · emu / cc, the trial recording medium S4, was Uyo, S5, S6 in carrier-to-noise ratio C / N is 45dB or more and the jitter σ is 4.0nsec Obtained below. Then, the magnetic thin film 3 is formed with the same composition as the recording media S4, S4, and the carrier-to-noise ratio C is set in the conventional recording medium SS3 in which the multiplication value of the film thickness t and the saturation magnetization M _S is 6 μm · emu / cc. / N was 44.2 dB and jitter σ was 4.4 nsec. Thus, even when the magnetic thin film 3 is thin, the error rate is small by making the multiplication value of the film thickness t and the saturation magnetization M _S equal to or less than 5 μm · emu / cc. A possible recording medium can be obtained. FIG. 5 is a schematic enlarged sectional view of a recording medium showing still another embodiment of the present invention. A first dielectric film 2A made of a SiN film and having a thickness t of 0.06 μm is formed on one surface of the same substrate 1 as above, and a TbFeCo film such as a TbFeCo film is formed on the dielectric film 2A. A magnetic thin film 3 having a thickness t of 0.03 μm and a saturation magnetization M _S of 50 emu / cc is formed. On the magnetic thin film 3 is formed a second SiN film having a thickness t of 0.06 μm.
Dielectric film 2B is formed on the dielectric film 2B.
A reflection film 5 made of an AlNi film and having a thickness t of 0.04 μm is formed. Further, the reflective film 5 is made of a SiN film and has a thickness t of 0.08.
A μm protective film 4 is formed. Information was recorded on the recording medium thus configured in the same manner as described above, and the carrier-to-noise ratio C / N and jitter σ were measured. The results shown in Table 3 were obtained.

[0019]

[Table 3]

As apparent from Table 3, the magnetic thin film 3
Even in a recording medium that is as thin as 0.03 or 0.04 μm and has a dielectric film 2B interposed between the magnetic thin film 3 and the reflective film 5, the multiplication value of the thickness t of the magnetic thin film 3 and the saturation magnetization M _S To 5 μm
The prototype recording media S6, S7, and S8 having an emu / cc or less have a carrier-to-noise ratio C / N of 45 dB or more and a jitter σ of 4.0 n.
Obtained in seconds. On the other hand, in the conventional recording medium SS4 in which the product of the film thickness t and the saturation magnetization M _S is 6.4 μm · emu / cc, the carrier-to-noise ratio C / N is 45 dB or less and the jitter σ is 4 ns.
more than ec. As described above, even in the recording medium in which the dielectric film 2B is formed between the magnetic thin film 3 and the reflection film 5, a recording medium having a low error rate and capable of being rotated at high speed and overwritten with a small modulation magnetic field intensity is obtained. Can be. The recording medium in which the dielectric film 2B is formed between the magnetic thin film 3 and the reflection film 5 has a large Kerr rotation angle θk.

[0021]

Magneto-optical recording medium according to the present invention as described in detail above, according to the present invention, when by the intensity of the modulated magnetic field to 200 Oe was recorded information, the carrier-to-noise ratio C / N of the information 45dB or more,
Give no jitter σ below 4 nsec, therefore the error rate is small, an excellent effect capable of providing a magneto-optical recording medium capable of overwriting by Curie point recording method with a small modulated magnetic field intensity at a high speed.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between jitter and carrier to noise ratio.

FIG. 2 is a graph showing a relationship between a carrier-to-noise ratio and a product of a thickness of a magnetic thin film and a saturation magnetization.

FIG. 3 is a schematic enlarged sectional view showing an embodiment of the magneto-optical recording medium of the present invention.

FIG. 4 is a schematic enlarged cross-sectional view of a magneto-optical recording medium showing another embodiment of the present invention.

FIG. 5 is a schematic enlarged sectional view of a magneto-optical recording medium showing another embodiment of the present invention.

[Explanation of symbols]

1 substrate, 2, 2A, 2B dielectric film, 3 magnetic thin film, 4
Protective film, 5 reflective film.

Claims (1)

(57) [Claims] 1. A magnetic thin film having perpendicular magnetic anisotropy is formed on a substrate, and a protective film made of a dielectric is formed on the magnetic thin film. in magneto-optical recording medium with said magnetic thin film is Tb, Fe, a magnetic thin film whose main component is Co, Timyuemu its thickness, its saturation magnetization M _s emu / cc and the case t × M _s <5 μm · emu / cc (however , t = 0.04 μm and (1) Tb18.0 (Fe0.89 Co0.11) 82.0 (2) Tb19.5 (Fe0.89 Co0.11) 80.5 (3) Tb21. 0 (Fe0.89 Co0.11) 79.0 (4) Tb22.5 (Fe0.89 Co0.11) 77.5 (5) Five kinds of Tb24.0 (Fe0.89 Co0.11) 76.0 A magneto-optical recording medium characterized by comprising a magnetic thin film satisfying (excluding composition ) .