JPH06150415A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To increase CNR and to lessen the generation of noises under a low magnetic field by setting the magnitude of the saturation magnetization in the direction parallel with the main plane of a recording film consisting of a rare earth-transition metal amorphous alloy at a 20 to 100emu/cm<3> range. CONSTITUTION:A dielectric substance film 3 consisting of SiN, a recording film 4 consisting of TbFeCo, a dielectric substance 5 and a reflection film 6 consisting of AlTi are laminated on a polycarbonate substrate 2. After the formation of the film 4, gaseous oxygen is introduced and the time of the surface oxidation of the film 4 is changed in a 30 to 120 second range, by which the film 4 having the magnitude of the saturation magnetization different in the direction parallel with the main plane of the film is obtd. The relation between the magnitude of the saturation magnetization and Ho at which the CNR begins to appear and the noise level at the point of the time of 0 magnetic field is measured. Consequently, the Ho is small and the noise level is low with the magneto-optical disk having the magnitude of the saturation magnetization in the 20 to 100emu/cm<3> range. As a result, the recording and erasing of information are possible even in a small external magnetic field. In addition, the magneto-optical recording medium having the high CNR is obtd.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a magneto-optical recording medium.

[0002]

2. Description of the Related Art Among optical recording elements, a magneto-optical recording medium capable of additionally recording and erasing information is in the stage of practical use. As a recording film of this magneto-optical recording medium, a thin film of a rare earth-transition metal amorphous alloy is most often used because its comprehensive characteristics are suitable. The rare earth-transition metal amorphous alloy is a perpendicular magnetization film whose saturation magnetization is oriented in the direction perpendicular to the film surface, and information is recorded by utilizing this magnetization direction.

The Curie point recording method is one of the recording methods for a magneto-optical recording medium. In this method, first, an external magnetic field is applied to the recording medium by an electromagnet or the like, and under the action of the magnetic field, the laser light focused by the lens is irradiated to the recording film, thereby locally ) Is increased until it reaches the Curie temperature or higher. At the portion reaching the Curie point temperature, the coercive force becomes 0, and the information is recorded or erased by being magnetized in the same direction as the external magnetic field.

[0004]

However, in the case of an overwrite type magneto-optical disk having a general single-layer rare earth-transition metal amorphous alloy recording film, in order to record or erase information, 200 to 400 is used. An extremely large external magnetic field of about Oersted (Oe) was required. Therefore, a large-sized magnetic field generator for generating a magnetic field must be provided, and it takes a long time to form the magnetic field, which is an obstacle to speeding up the process, which is smaller. Development of a recording film capable of recording and erasing information by an external magnetic field is awaited.

The characteristics of the disk required to reduce the external magnetic field required for the overwrite operation of the magnetic field modulation method will be described with reference to FIGS. 4 and 5. FIG. 4 shows the relationship between the intensity of the external magnetic field and the CNR when the disk is initialized by aligning the directions of magnetization in advance and then an external magnetic field is applied and a laser pulse is applied to write information on the recording film. 5 is a graph, and FIG. 5 is a cross-sectional view showing the state of the perpendicular magnetization film of the disk at the time of writing. In the magnetic field modulation type overwrite, as shown in FIG.
Between the s level and the Ho level at which CNR begins to appear,
Since the external magnetic field is switched, both the Hs and Ho levels must be reduced in order to reduce the external magnetic field.

Further, as shown in FIG. 5, at a recording portion (high temperature portion) which has been heated to a high temperature by being irradiated with a laser beam, in addition to the external magnetic field Hex formed by the magnetic field generator, a portion around the high temperature portion is generated. The demagnetizing field Hd that depends on the magnitude of the magnetization of the portion below the Curie point temperature acts. It is this demagnetizing field Hd that greatly affects the magnitude of the Ho level, and if the demagnetizing field Hd is large, it is necessary to form a large Ho level external magnetic field that cancels it. Demagnetizing field Hd
Is dependent on the magnitude of the magnetization of the perpendicularly magnetized film. Therefore, in the case of a disc having a single recording film, the Ho level can be reduced by selecting a compensating composition having a small magnetization to construct the disc. Practically, it is extremely difficult to stably produce a film having such a composition. Therefore, conventionally, by applying the input power at the time of film formation of the dielectric layer and the recording layer, adjusting the sputtering gas pressure, reverse sputtering of the dielectric layer, etc.
A method of reducing the Ho level is adopted regardless of the compensation composition.

However, the disk manufactured by the above method has a problem that the noise level increases under a low magnetic field as the Ho level decreases. In the process of switching the magnetic field in the magnetic field modulation, the external magnetic field always becomes 0 at a certain time point, but noise at the time point when this magnetic field is 0 must be reduced and CNR should be increased.

The present invention has been made to solve the above problems, and by reducing noise under a low magnetic field, CNR can be enhanced, and information can be recorded or erased with a small external magnetic field. It is an object to provide a magneto-optical recording medium.

[0009]

In order to achieve the above object, the magneto-optical recording medium of the present invention has a main surface of a recording film in a recording film made of a rare earth-transition metal amorphous alloy laminated on a substrate. The saturation magnetization in the parallel direction is 2
It is characterized by being in the range of 0 to 100 emu / cm ² .

[0010]

According to the above construction, the demagnetizing field at the recording portion is reduced, and the noise in the low magnetic field is reduced. As a result, information can be recorded / erased even with a small external magnetic field, and a magneto-optical recording medium having a high CNR can be obtained.

[0011]

EXAMPLE An example of the magneto-optical recording medium of the present invention will be described below. FIG. 1 shows the structure of a magneto-optical disk according to this embodiment. In the figure, a magneto-optical disk 1 is constituted by laminating a dielectric film 3, a recording film 4 made of a rare earth-amorphous alloy, a dielectric film 5, and a reflective film 6 in this order on a light-transmissive substrate 2. . The substrate 2 may be formed by arbitrarily selecting materials such as plastics such as polycarbonate and epoxy resin, glass, ceramics, and metals. The dielectric films 3 and 5 include SiN, AlSiN, AlSiON,
SiO, ZnS, etc. can be used. Reflective layer 6
Is Ti, Cr, In, Al, Au, Ag, Pt, etc.
It is possible to use a material to which one or more kinds of Cu have been added.

A SiN film 3 is formed on a polycarbonate substrate 2.
(Film thickness: 1100Å), TbFeCo recording film 4 (film thickness:
200Å), SiN film 5 (film thickness: 350Å) and Al
In manufacturing a magneto-optical disk having a structure of FIG. 1 in which a Ti film 6 (film thickness: 500Å) is laminated, TbF
After forming the eCo film, oxygen gas (vacuum degree: 0.02 Pa)
And the surface oxidation time of the TbFeCo film is set to 30 to 1
The magneto-optical disk having different saturation magnetization in the direction parallel to the main surface of the TbFeCo film was manufactured by changing the range within 20 seconds. FIG. 2 shows the result of measurement of the relationship between the magnitude of saturation magnetization in such a magneto-optical disk, Ho (indicated by a solid line in the figure) at which CNR begins to appear, and the noise level (indicated by a broken line in the figure) at the time when the magnetic field is 0. The measurement conditions are a linear velocity of 7.54 m / s and a recording frequency of 4.93 MH.
z, duty 25%, power of laser light used for recording 7 mW. Also, using a vibrating sample magnetometer,
Saturation magnetization was determined by applying a maximum magnetic field of 15 kOe. From FIG. 2, the magnitude of the saturation magnetization is 20 to 10
It can be seen that in the magneto-optical disk in the range of 0 emu / cm ³ , the above Ho is small and the noise level is low.

Next, the magnitude of the saturation magnetization produced by the above method is 5 emu / cm ³ (magneto-optical disk A shown by the solid line in the figure) and 50 emu / cm ³ (magneto-optical disk shown by the broken line in the figure). FIG. 3 shows the results of measuring the relationship between the external magnetic field and the CNR for three types of magneto-optical disks, B) and 120 emu / cm ³ (magneto-optical disk C shown by the one-dot chain line in the figure). The measurement conditions are a linear velocity of 1.4 m / s, a writing power of 4.5 mW, a reading power of 0.7 mW, a recording frequency of 720 kHz and a duty of 50%. Figure 3
Therefore, the magnitude of the saturation magnetization is 20 to 100 emu / c.
It can be seen that the magneto-optical disk A in the range of m ³ has an excellent CNR in a low magnetic field as compared with the magneto-optical disks B and C not in this range.

For a magneto-optical recording medium in which a recording film of a rare earth-transition metal amorphous alloy has a saturation magnetization within the above range, 0.01 to 0.03 Pa of oxygen gas is added to 60 to 360.
In addition to the oxidation treatment of the recording film by introducing the second, a recording film formed by laminating a rare earth-transition metal amorphous alloy layer and a Fe layer, a Co layer or a Ni layer having a film thickness of 10 Å or less or these alloy layers It is obtained by using.

[0015]

As described above, according to the present invention, noise generation under a low magnetic field can be reduced and CNR can be enhanced. As a result, information can be recorded / erased with a small external magnetic field, and the magnetic field generating portion of the recording apparatus using this medium can be downsized and the power consumption can be reduced.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of a magneto-optical disk according to an embodiment of the present invention.

FIG. 2 is a diagram showing the results of measurement of the relationship between the magnitude of saturation magnetization in the direction parallel to the main surface of the recording film, Ho at which CNR begins to appear, and the noise level at the time of zero magnetic field.

FIG. 3 is a diagram showing a result of measuring a relationship between an external magnetic field and CNR with respect to magneto-optical disks having different saturation magnetizations.

FIG. 4 is a graph showing the relationship between the magnitude of an external magnetic field and CNR.

FIG. 5 is a cross-sectional view showing a state of a perpendicular magnetization film at the time of writing.

[Explanation of symbols]

 1 Magneto-optical disk 2 Substrate 3 Dielectric film 4 Recording film 5 Dielectric film 6 Reflective film

Claims (1)

[Claims] 1. A recording film made of a rare earth-transition metal amorphous alloy laminated on a substrate has a saturation magnetization of 20 to 100 emu in a direction parallel to the main surface of the recording film.
A magneto-optical recording medium characterized by being in the range of / cm ² .