JPH0620314A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain the medium having recording/reproducing property, especially high C/N over a range of the intensity from low to high external magnetic field intensity by laminating the magnetic films having different magnetic property adjacently to each other. CONSTITUTION:In the magneto-optical recording medium having at least two kinds of magnetic film on a substrate, the composition of at least one of magnetic film is expressed by Tbx(Fe100-y-zCoyTiz)100-x, and the magnetic film 2 which has different magnetic properties from the magnetic film 1 is laminated adjacently to the magnetic film 1. Here, (x) is 10-25 atom%, (y) is 25-75 atom% and (z) is 15-50 atom%. The composition of the magnetic film 1 described subsequently is essential to obtain the effects, Tb is 10-25 atom%, the ratio of Co and Ti except Tb is 25-75 atom% and 15-50 atom% respectively. Further, the film has high Curie point and low coercive force, and it is pref. >=180 deg.C Curie point, <=500oe coercive force at room temp. and <=5X10<5>/m<3> perpendicular magnetic anisotropy at room temp.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium. More specifically, it relates to a magneto-optical recording medium having improved recording / reproducing characteristics.

[0002]

2. Description of the Related Art Among rewritable types capable of writing and erasing among optical recording media, there are phase change type, photochromic type, magneto-optical type and the like which have been conventionally known. Among these rewritable types, the magneto-optical type is characterized by being excellent in writing speed and repetition resistance. A rare earth-transition metal alloy film that is relatively easy to prepare and has a large coercive force is often used for a magneto-optical recording medium.

The magneto-optical recording method is a method of heating a recording film by light irradiation and applying an external magnetic field to determine the magnetization direction. The external magnetic field is usually installed not in the recording medium but in the device. However, it is desired that the external magnetic field is as small as possible for downsizing, low power consumption and cost reduction of the device. However, the strength of the external magnetic field has a great influence on the recording / reproducing characteristics of the medium. In general, when the strength of the external magnetic field is low, the carrier level decreases, the noise level rises, and the C / N (carrier-to-noise ratio) deteriorates.

[0004]

The following studies have heretofore been made in order to improve the problems of lowering the carrier level and increasing the noise level in the region where the external magnetic field is weak. One of them is the examination of the composition of the recording film.

The rare earth-transition metal amorphous alloy is generally composed of a compensating composition that qualitatively balances the magnetizations of the rare earth metal and the transition metal at room temperature, and a composition (RErich) in which the magnetization of the rare earth metal is dominant with the compensating composition as a boundary. There are three types of transition metal dominant compositions (TMrich).
Conventionally, the characteristics of a magnetic film have been improved by adjusting such a composition (IEEE T.
RANSACTIONS ON MAGNETICS,
Vol. MAG-22, No. 5, p931,198
6). Also, by using the exchange coupling multilayer film, high C / N at low magnetic field
There is also a proposal to obtain (Japanese Patent Laid-Open No. 1-130).
345).

[0006]

According to the present invention, coercive force, perpendicular magnetic anisotropy, and domain wall energy are improved by adding magnetic films having different magnetic properties, such as Ti and Co, to TbFe.
By directly laminating a magnetic film having a small Curie point and a magnetic film having a high Curie point and a film having a large Coercive force and a low Curie point, respectively, a high C / N ratio can be obtained from a region where the recording / reproducing characteristics are low, to a region where the external magnetic field strength is high. Is used as the medium. In this recording medium, a high C / N can be obtained from a region having a low magnetic field intensity to a region having a high magnetic field intensity. Therefore, while irradiating light, the magnetic field is modulated according to the signal to perform the overwriting. A suitable medium can also be supplied.

A feature of the magneto-optical recording medium of the present invention is that a plurality of perpendicularly magnetized films having different characteristics are provided close to each other. More specifically, for example, TbFeCoTi having a high Curie point, a low coercive force, and a low perpendicular magnetic anisotropy, in which a relatively large amount of Co and Ti are added, and a film having a low Curie point and a high coercive force as compared with this film are continuously formed. That is, it is characterized in that they are laminated directly opposite each other.

A film having a low Curie point and a large coercive force may be a film capable of sufficiently retaining recorded information by itself,
It is not necessary that a high C / N can be obtained from a low magnetic field to a high magnetic field. Since a film having a high Curie point and a small coercive force has a small coercive force, the recording property is inferior and recording retention is not sufficient by itself. That is, since the coercive force is small, the information to be recorded is not retained in the cooling process, and even if recording is possible, the information retention is poor.

The present inventors have found that a high C / N from a low magnetic field to a high magnetic field can be obtained by directly laminating two kinds of films having different magnetic properties, for example, as described above. That is, the present invention provides at least 2 on the substrate.
A magneto-optical recording medium having a seed of the magnetic film, at least one composition of the magnetic film is formula Tbx following these magnetic films _{(Fe 100-y-z Co} y Ti z) 100-x x: 10-25 Atomic% y: 25-75 atomic% z: 15-50 atomic% (1), and a magnetic film (2) having different magnetic properties from this is directly opposed to the magnetic film (1). The present invention relates to the constructed magneto-optical recording medium.

One of the magnetic films (1) having different magnetic characteristics is
In order to obtain the effect of the present invention, it is essential that Tb is 10 to 25 atomic%, Co and Ti are 25 to 75 atomic% and 15 to 50 atomic% in a ratio excluding Tb, respectively. A film having a high point and a low coercive force, preferably having a Curie point of 180 ° C. or higher and a coercive force of 500 O at room temperature.
e or less, and the perpendicular magnetic anisotropy at room temperature is 5 × 10 ⁵ J /
m ³ or less. The other magnetic film (2) having different magnetic properties is, for example, a film having a low Curie point and a high coercive force, and preferably has a coercive force of 3 kOe or more at room temperature in the Curie point range of 150 to 250 ° C. For a film with a low Curie point and a high coercive force, the coercive force is 4
It is further preferable that the perpendicular magnetic anisotropy is 7 × 10 ⁵ J / m ³ or more at kOe or more. Further, when the above-mentioned two kinds of films are laminated, it is preferable that the difference in Curie point is 30 ° C. or more. If it deviates from the above range, it is not preferable in order to obtain the further effects of the present invention.

A film having a low Curie point and a large coercive force has a T
bFeCo, DyFeCo, TbGdFeCo, TbD
yFeCo, TbDyGdFeCo, DyGdFeCo
It is possible to use materials such as the above, and there is no problem even if additives and impurities are included within a range satisfying the above characteristics. A film having a high Curie point and a low coercive force is formed in the above composition range, but there is no problem even if an additive or an impurity is included in the range satisfying the above characteristics.

In the present invention, TbFeCoTi was used as one of the magnetic films (1) having different magnetic characteristics, but Dy, TbDy, TbGd, DyGd, TbDy was used as the rare earth metal.
Gd can be used. When using a plurality of films (1), instead of Ti, a non-magnetic metal such as Cr, Ta,
It is also possible to use W, Mo, Nb, Al, Pt alone or a film in which a plurality of these metals including Ti are combined.

The thickness of the magnetic film (1) of the present invention is preferably 2 nm or more and 20 nm or less in order to obtain the effect of lamination. If the thickness exceeds 20 nm, this film is originally inferior in recording holding action, so that the recording characteristics are deteriorated even when laminated and the storage stability of information is also deteriorated. Further, the film thickness of the magnetic layer having a low Curie point and a large coercive force is preferably 120 nm or less from the viewpoint of recording sensitivity.

The method of forming the magnetic film of the present invention is preferably the sputtering method because of its high controllability and high productivity, but the film forming conditions are not limited to the above.
Other conditions are also possible, and vapor deposition methods are also possible.

By stacking the above-mentioned two types of magnetic films, the medium of the present invention is recorded in a film having a low perpendicular magnetic anisotropy at a Curie point of a layer having a low Curie point or higher, and the state is low in the Curie point. Information is retained by being transferred to the film.
A film with low perpendicular magnetic anisotropy has a sufficiently small coercive force in the high temperature region and a small domain wall energy, but since it has magnetization, it reacts to the external magnetic field at the time of recording and has no inversion domain even in a low magnetic field. Sufficiently large magnetic domains are formed and transferred to a layer with a low Curie point in the cooling process to fix the information. It is considered that such a mechanism can obtain a high C / N from a low magnetic field to a high magnetic field.

The characteristic that a sufficient C / N can be ensured from a low magnetic field to a high magnetic field becomes more remarkable in the magnetic field modulation recording system in which an external magnetic field is modulated and recorded. In the magnetic field modulation method, light is normally applied to DC to invert and modulate the polarity of the magnetic field, so that a state where recording is always performed with a weak magnetic field occurs. In this inverted modulation state, inversion is insufficient and the magnetic domain is small, and
The noise increases due to the formation of the inverted magnetic domains. However, according to the present invention, noise rise is suppressed. Further, even with a small reversal magnetic field strength, a noise-free medium having a large signal strength can be obtained.

Many proposals have been made to add Ti to the magneto-optical recording film (see JP-A-61-40012 and JP-A-61-6807). However, these disclosed techniques are mainly aimed at improving the durability against corrosion by adding Cr to the single magnetic layer. Therefore, the magnetic film to which Cr is added is different from the present invention in that it is necessary to satisfy the basic characteristics as a magneto-optical recording medium.

It has been proposed to use a magneto-optical recording film containing Ti as a medium composed of a two-layer magnetic film of a reading layer and a recording layer (see Japanese Patent Laid-Open No. 2-141950). However, this disclosed technique is aimed mainly at improving the durability against corrosion by adding Ti, and the magnetic layer containing Ti must satisfy the basic characteristics as a recording layer of a magneto-optical recording medium. The present invention is different from the present invention in this respect.

[0019]

EXAMPLES SiN was formed on a glass substrate as a protective film with a thickness of 100 nm by a sputtering device, and then a Tb target and a Co / Ti chip or a FeCo target on which only a Co chip was mounted was subjected to binary sputtering. A magnetic film having a thickness of 30 nm was formed, and then SiN having a thickness of 30 nm was formed as a protective film.

Table 1 shows the composition, Curie point, perpendicular magnetic anisotropy at room temperature, and coercive force of this product analyzed by X-ray fluorescence.

Table 1 Sample composition Curie point Perpendicular magnetic anisotropy Coercive force 1 x: 12 230 230 1.4 1.4 y: 35 z: 16 2 x: 18 240 1.1 1.1 y: 41 z: 20 3 x: 20 310 0.7 0.1 y: 52 z: 35 4 x: 23 290 0.6 0.1 y: 61 z: 43 5 x: 14 180 0.4 0.1 y: 32 z: 50 6 x: 18 180 7.6 5.4 y: 8 z: 0 7 x: 22 220 220 8.2 10.8 y: 10 z: 0 8 x: 26 150 150 6.9 13.0 y: 4 z : 0 9 x: 22 240 5.8 6.9 y: 15 z: 0 unit composition Tb _x (Fe _100-yz Co _y Ti _z ) _100-x x, y, z atomic% Curie point ° C perpendicular magnetic field Anisotropy 10 ⁵ J / m ³ Coercive force kOe 1.6 μm Diameter 3 with guide grooves SiN was formed to a thickness of 100 nm on a glass substrate that was installed at the same time as a 0.5-inch polycarbonate substrate, and then the first
A magnetic film was formed to have a thickness of 10 nm, a second magnetic film was formed to have a thickness of 20 nm, SiN was formed to have a thickness of 30 nm, and Al was formed to have a thickness of 50 nm. The magnetic film was manufactured by the combinations shown in Table 2.

Table 2 Sample First magnetic film Second magnetic film 10 Same composition as sample 1 Same composition as sample 6 11 Same composition as sample 2 Same composition as sample 6 12 Same composition as sample 3 Same composition as sample 7 13 Sample 4 Same composition as Sample 9 Same composition as Sample 14 Same composition as Sample 5 Same composition as Sample 8 The recording / reproducing characteristics of these samples as recording media were examined. The measuring device is a magnetic field modulation over equipped with an optical head with a wavelength of 780 nm and an NA of 0.53, and a floating magnetic head.
A light type magneto-optical disk measuring device was used. The measurement conditions are as follows: measurement radius 30 mm, disk rotation speed 2400 rpm,
Recording / reproducing frequency 5.0MHz (Magnetic field reversal duty 10
0 ns) applied magnetic field during recording ± 50, 100, 300
The recording power as Oe was 9 mW (continuous light) to determine the C / N ratio.

Table 3 shows the measurement results of each sample. Table 3 Sample magnetic field strength ± 50 ± 100 ± 300 10 41.6 45.2 46.8 11 42.2 46.4 46.7 12 44.9 45.8 47.1 13 44.8 46.1 47. 2 14 44.6 45.9 46.9 Unit C / N ratio dB

[0024]

Comparative Example A sample having a single magnetic film as shown in Table 4 was prepared in the same manner as in the example.

Table 4 Sample composition Curie point Perpendicular magnetic anisotropy Coercive force 15 x: 20 220 4.6 2.9 y: 10 z: 9 16 x: 20 240 7.7 9.2 y: 19 z: 7 Unit composition Tbx (Fe100-y-zCoyTiz) 100-xx, y, z atom% Curie point ° C Perpendicular magnetic anisotropy 10 ⁵ J / m ³ coercive force kOe In the same manner as in the example, a polycarbonate substrate was used. A sample having two layers as shown in Table 5 was prepared on a glass substrate.

Table 5 Sample 1st magnetic film 2nd magnetic film 17 Same composition as sample 15 Same composition as sample 6 18 Same composition as sample 16 Same composition as sample 8 19 Same composition as sample 2 Same composition as sample 9 20 Sample 6 Same composition as Sample 6 Same composition as Sample 6 The samples in Table 5 were evaluated in the same manner as in Example. The results are shown in Table 6.

Table 6 Sample magnetic field strength ± 50 ± 100 ± 300 17 34.2 38.5 43.1 18 21.3 34.5 35.9 19 33.4 35.7 43.1 20 37.9 41. 946.1 These samples have a low C / N especially when the magnetic field is low. Sample 20 is a TbFeCo single layer sample, and a high C / N is obtained at 300 Oe, but the C / N is low when the magnetic field is low.

Examples (Samples 10 to 14) and Comparative Example (17)
-20), the curl of the sample of the glass substrate was measured from room temperature to the Curie point using a curl effect measuring device (wavelength 780 nm). As a result, the samples of the examples all have the results shown in FIG. In the figure, (1) is the coercive force, (2)
Indicates the saturated curl rotation angle, and (3) indicates the residual curl rotation angle.
In the figure, (2, 3) indicates that the saturated curve rotation angle and the residual curve rotation angle match. That is, up to the point (Tc1) where the Curie point is low, the residual curl rotation angle and the saturated curl rotation angle are the same, exhibiting a good squareness ratio, and the coercive force also has a relatively large value. Beyond the low Curie point (Tc1), the difference between the residual curl rotation angle and the saturated curl rotation angle becomes large, and the squareness ratio and the coercive force sharply decrease.

The results of Comparative Samples 17 and 18 are shown in FIG. In the figure, (4) shows the coercive force, and (5) shows the saturated curl rotation angle and the residual curl rotation angle, both of which are in agreement.
These samples show a relatively large coercive force even if they exceed the low Curie point (Tc1), and the residual car rotation angle and the saturated car rotation angle are the same and have a good squareness ratio. Since these samples have a large coercive force up to a high temperature, it is considered that sufficient recording cannot be performed especially when the magnetic field strength is low. Comparative example sample 1
In No. 9, there was no difference in the Curie points of the two types of magnetic films, and no sharp decrease in coercive force and squareness was observed as in the samples of the examples. Moreover, the same results as those of the comparative sample 19 were obtained for the comparative sample 20.

From these results, the coercive force is low above the low Curie point, and since the magnetization is sufficiently retained, it is easy to reverse the external magnetic field and a large C / N can be obtained even in the low magnetic field. The fact that the coercive force is small and the magnetization is relatively large is considered to be due to the low perpendicular magnetic anisotropy, which leads to a small squareness ratio. It is considered that at a low Curie point or below, a good squareness ratio is maintained by the exchange coupling force. It can be seen that a Curie point difference of 30 ° C. or more is required to satisfy such characteristics.

[0031]

With the structure of the magneto-optical recording medium of the present invention, a sufficient C / N can be secured from a low magnetic field to a high magnetic field.

Further, by defining the composition, Curie point, coercive force, and perpendicular magnetic anisotropy of a plurality of continuous magnetic films,
A large margin for the external magnetic field at the time of recording of the recording / reproducing characteristics can be secured.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of temperature characteristics of a curl of a magneto-optical recording medium of the present invention.

FIG. 2 is a diagram showing an example of temperature characteristics of a curl of a magneto-optical recording medium of a comparative example.

Claims (4)

[Claims] 1. A magneto-optical recording medium having at least two types of magnetic films on a substrate, wherein the composition of at least one of these magnetic films is represented by the following formula (1): A magneto-optical recording medium in which a magnetic film (2) having a magnetic characteristic different from that of the magnetic film is directly opposed to the magnetic film (1). _{Tbx (Fe 100-y-z} Co y Ti z) 100-x x: 10-25 atomic% y: 25-75 atomic% z: 15-50 atomic% 2. The magneto-optical recording medium according to claim 1, wherein the coercive force of at least one magnetic film containing Ti is 500 Oe or less at room temperature. 3. The magneto-optical recording medium according to claim 1, wherein the Curie point of at least one magnetic film containing Ti is 180 ° C. or higher. 4. The magneto-optical recording medium according to claim 1, wherein the magnetic films having different magnetic properties are magnetic films having a Curie point difference of 30 ° C. or more.