JPS6184004A - Photo-magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide high-density recording and extended, stable life-time characteristics by selecting suitable value for X, Y, and Z in the photo-magnetic recording medium whose full composition is expressed by Tbx(Fe100-Y)100-X-ZCrz. CONSTITUTION:A photo-magnetic recording material is constructed with non- crystalline thin alloy film which possesses the magnetizable axis in vertical direction with respect to the film surface. In this photo-magnetic recording material, the full composition should be constructed so that the atomic ratio therein for Tb is 15-40atomic%, the atomic ratio for Cr is 2-10atomic%, and the rest is a two-element composition of Fe or Fe and Co. However, when the rest is a two-element composition of more than the value shown above, the atomic-ratio for Co in this composition should be below 50atomic%. With such composition, the titled photo-magnetic recording medium provides a high- density recording when used as a so-called beam addressable file memory device and can realise stable working characteristics for an extended period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a magneto-optical recording medium used in magneto-optical memories, magneto-optical recording display elements and the like.

"Prior art" Circular acid has an axis of easy magnetization perpendicular to the film surface and is used as a magneto-optical memory or magneto-optical recording/display element. Information is recorded by creating reversed magnetic domains of arbitrary shapes, and magnetic Kerr effect, etc. Thin-film magneto-optical recording media are used that read recorded information using the magneto-optic effect.

In general, in a ferromagnetic thin film whose axis of easy magnetization is perpendicular to the film surface, by irradiating it with a light beam such as a laser, it is possible to uniformly magnetize it to the S pole or N pole within the film surface. A small reversal magnetic domain with magnetization polarity and opposite magnetic poles can be created in the irradiated area. The presence or absence of this reversed magnetic domain is "1".

By recording information in correspondence with "0", such a ferromagnetic thin film can be used as a high-density magnetic recording medium. Information recorded in this manner can be read using the magneto-optic effect.

Among such ferromagnetic thin films, a thin film that has a small coercive force at room temperature and whose Curie temperature or magnetic compensation temperature is relatively close to room temperature is one that has a Curie temperature or magnetic compensation temperature relatively close to room temperature. It is used as a beam addressable file because information can be recorded by creating an inverted magnetic domain at an arbitrary position using a light beam.

Conventional ferromagnetic thin films that have an axis of easy magnetization perpendicular to the film surface, are capable of high-density magnetic recording, and can be used as beam-addressable files include polycrystalline metal thin films such as MnB1, and Gd-Tb-Fe.

Multi-component amorphous metal thin films such as Dy-Fe, Tb-Fe, Tb-Fe-Co, etc. or compound single crystal thin films typified by GIG are used. Each of these ferromagnetic thin films that can be used as a beam-addressable file has advantages and disadvantages as described below.

That is, a polycrystalline metal thin film typified by MnB1 is excellent as a magnetic recording medium in that writing is performed using the Curie temperature and has a large coercive force of several koe.

However, since the key temperature is high, for example, Tc=360° C. in MnB1, it has the disadvantage that a large amount of energy is required for writing.

Furthermore, since it is a polycrystalline substance, it is necessary to create a thin film with a composition that satisfies stoichiometric conditions, which has the disadvantage that its production is technically difficult.

Furthermore, compound single crystal thin films such as GIG have a high Curie temperature and require a large amount of energy to write, and their manufacturing costs are significantly higher than other films due to material or manufacturing technology. There is a difficulty in doing so.

A rare earth-transition metal amorphous thin film has been proposed as a solution to the various problems in the characteristics of these polycrystalline metal thin films or compound single crystal thin films as magneto-optical recording media.

The composition of this rare earth-transition metal amorphous thin film is Tb-Fe, Dy-Fe, Gd-Tb-Fe.
, Tb-Fe-C.

Amorphous thin films with multicomponent compositions have been proposed.

These proposed rare earth-transition metal amorphous thin films are
Since the Curie temperature is as low as 60° C. to 200° C., it is possible to write using the Curie temperature, and it has a large coercive force of several koe over a wide composition range under room temperature conditions.

Furthermore, when used as a recording medium, it is not necessary to create an amorphous thin film under particularly high-precision manufacturing conditions in terms of composition, and the manufacturing technology is relatively easy, resulting in a good manufacturing yield.

"Problems to be Solved by the Invention" - As described above, rare earth-transition metal amorphous thin films have a large coercive force over a wide composition range, can be written using the Curie temperature, and It has the advantage that the manufacturing technology is relatively easy and the manufacturing yield is good.

However, due to their characteristics, these rare earth-transition metal amorphous thin films all have the disadvantage that their surfaces are easily corroded, and if they are left in the atmosphere for a long time, their surface layers are corroded and their compositions tend to change. There is.

FIG. 3 shows measured data showing the results of a corrosion resistance test conducted by the inventors on this type of rare earth-transition metal amorphous thin film that has been proposed in the past.

In this case, the composition of the specimen is TbO, 25FeO, 7
5, a rare earth-transition metal amorphous thin film prepared by sputtering to a thickness of approximately 1000× on a soda silicate glass substrate with a diameter of 50 mm was used. Immerse in N NaCt solution. N
Remove the aCA g from the solution and apply 5
A laser beam of mW is irradiated, the power of the reflected laser beam from the subject is measured, and the power ratio of the reflected laser beam to the incident laser beam is measured as the reflectance.

The horizontal axis of FIG. 3 is the immersion time of the specimen in the NaC6 solution, and the vertical axis is the reflectance obtained as described above.
It serves as a guide to the corrosion resistance of the test object.

As is clear from Figure 3, for example, when the immersion time is 60 minutes, the reflectance decreases from the reflectance range of 50 without immersion to 30%, and when the immersion time is 120 minutes, the reflectance decreases to approximately 1.
This clearly shows that the corrosion rate of the test object is extremely severe.

The problem to be solved by this invention is how to maintain the conventional advantages of this type of rare earth-transition metal amorphous thin film, while improving the essential drawback of being easily corroded, to achieve high performance. The question is whether to obtain a corrosion-resistant amorphous thin film.

"Structure of the Invention" The magneto-optical recording medium of the present invention is an amorphous alloy thin film having an axis of easy magnetization perpendicular to the film surface. , Cr atomic ratio is 2~
It accounts for 10 atoms, and the rest is Fe! It is composed of a binary composition of iFe and Co. When the remainder is composed of a binary composition of Fe and Co, the atomic ratio of Co in the binary composition is 50 atomic proportions or less.

"Example" Hereinafter, the magneto-optical recording medium of the present invention will be described in detail based on the example and according to the manufacturing method using the drawings.

The inventors conducted extensive research and examination based on the conventionally proposed Tb-Fe binary amorphous thin film body and Tb-Fe-Co ternary amorphous thin film body, and found that these binary or discovered that by adding Cr to a ternary amorphous thin film, the corrosion resistance of the amorphous thin film could be significantly increased.

In this invention, as the substrate used for forming the thin film, for example, soda glass, quartz, silicon, garnet substrates, etc. can be used.

In the example, a quartz substrate or a synthetic resin substrate with a thickness of 0.3 rrm, for example, is used, and a target having a composition close to that of the film is used on this substrate, for example, by sputtering. A thin film magneto-optical recording medium is created. The atmosphere used is one in which alcohol gas is used as an inert gas, and the atmospheric pressure is maintained at 3 to 8 Pa.

In order to create a thin film with sufficient magnetic anisotropy to have magnetization in a direction perpendicular to the film surface, it is necessary to cool the substrate with water to lower the substrate temperature. In such an atmosphere, a magneto-optical recording medium in the form of a thin film having a film thickness of about 1000× is formed on the substrate with a power supply of 50 W.

When formed under such atmospheric conditions, collisions of ionized atoms are reduced and a thin film can be formed without increasing the substrate temperature.

In the magneto-optical recording medium of this invention, Tb, Fe.

The atomic ratio of Co and Cr is expressed as X110 in atomic ratio.
0-Y, Y, and Z, and the total composition of the magneto-optical recording medium is generally Tb)c(Fe1oo-y"y)1oo-x
-zCrz is displayed. In this compositional formula, when Y=O, the remainder other than Tb and Cr is a monolithic composition containing Co. In such a general compositional formula, the conditions required for the composition in this invention are 0 when the atomic ratio of each element is expressed in atomic ratios.
．． 15≦X≦0.40.0≦Y≦0.50, and 0.0
2≦Z≦0.10.

Generally, in a rare earth-iron amorphous film, the magnetic moment due to the rare earth element determined by the composition ratio of the rare earth element and the magnetic moment due to the iron element determined by the composition ratio of the iron element cancel each other out, resulting in the overall The saturation magnetization Ms of is determined. Therefore, by setting the ratio of rare earth elements and iron elements in the total composition, the saturation magnetization Ms that satisfies the perpendicular magnetization condition of Ku )2πMs can be obtained, with the magnetic anisotropy constant being Ku. If the magnetization conditions are satisfied, a magnetic thin film having an axis of easy magnetization in a direction perpendicular to the film surface can be obtained.

The total composition is TbX(Fe100-Y”Y)100-X-Z
Tb in the magneto-optical recording medium of this invention denoted by ``Z''
When the atomic ratio X of the elements in X is set to X < 0.15, the moment due to the iron element increases, and
When set to 4, the magnetic moment due to the rare earth element becomes large.

In either of these cases, the saturation magnetization Ms of the entire composition of the magneto-optical recording medium becomes large, and Ku) 2
It becomes impossible to satisfy the perpendicular magnetization condition of πMs2. Therefore, in this invention, the atomic ratio XK of the rare earth element is required to be 0.15≦X≦0.4+f.

On the other hand, if the atomic ratio 2 of Cr is set to Z≦0.02, the effect of adding Cr, which will be described later, cannot be observed;
If the setting is set to 1, a magneto-optical recording medium with excellent corrosion resistance can be obtained, but it is difficult to obtain one that satisfies the perpendicular magnetization condition.
A coercive force of several koe may not be obtained in some cases. In this case, even if the perpendicular magnetization condition is satisfied, the Kerr rotation angle is small9
If it is too long, the desired characteristics cannot be obtained. Therefore, 0.02≦Z≦0.10 is required for Cr's atomic ratio of 2.In general, when writing using the key temperature, if the key temperature is too high. A large laser beam is required, making it impossible to use a semiconductor laser.For this reason, the Curie temperature of the magneto-optical recording medium must be kept below 200°C.

In the magneto-optical recording medium of this invention, Tb, Cr.

If the remainder is a binary composition of Fe and Co, if the amount of Co added exceeds 50 atomic parts, the Curie temperature will increase to 20
When the temperature exceeds 0° C., the magneto-optical recording medium becomes extremely difficult to write to. Therefore, when the remainder has a binary composition of Fe and Co, the atomic ratio Y of Co in the remainder must satisfy the condition of 0≦Y≦0.50.

"Effects of the Invention" Actual data showing the effect of corrosion resistance in a corrosion test conducted by the inventors on the magneto-optical recording medium of the present invention are shown in FIGS. 1 and 2. In FIGS. 1 and 2, the horizontal axis shows the immersion time of the subject in the lN NaCl 1m solution, and the vertical axis shows the reflectance of the laser beam, which has already been defined and explained.

That is, after a subject is immersed in an IN NaC4 solution at room temperature for the immersion time shown on each horizontal axis, the subject is removed from the NaCl solution and a 5 mW laser beam is applied to the subject. Irradiate light.

At the same time, the power of the reflected laser light from the object is measured, and the reflectance is calculated from the ratio of the power of the irradiated laser light and the power of the reflected laser light, and this reflectance is recorded on the vertical axis in Figures 1 and 2. be done. In FIGS. 1 and 2, the degree of corrosion resistance of the test object can be determined based on the obtained reflectance.

In Figure 1, the total composition is T5o, zs(F”cas C0o,
+s) When the magneto-optical recording medium of the present invention represented by a, 7+Cra, o4 is used as an object to be tested, the object is approximately 100 mm on a nodal silicate glass substrate with a diameter of 5
A thin film formed by sputtering to a thickness of 0 was used.

As is clear from the results shown in Figure 1, l NNaC4
Even after being immersed in the NaCA solution for 120 minutes, the reflectance decreased from a reflectance of 47 degrees before being immersed in the solution to 38 degrees, which is lower than the reflectance obtained with the conventionally proposed amorphous thin films described above. It is clear that the corrosion resistance is significantly increased compared to the results shown in FIG.

Figure 2 shows that the total composition is TbO, 25FeO, 6
This is the case when the magneto-optical recording medium of the present invention represented by 8CrO,07 is used as the test object, and the test object shape is the first one.
This is the same as the case shown in the figure.

Even in this case, the reflectance decreases from 47 cycles before being immersed in the INNaC2 solution to only 32 cycles even after being immersed in the NaCA solution for 120 minutes. It is confirmed that its corrosion resistance is significantly increased.

As shown in FIGS. 1 and 2, the corrosion resistance of the magneto-optical recording medium of the present invention is greatly increased compared to the conventional one, because the surface of the medium has chromium, which has excellent corrosion resistance. This is thought to be due to the formation of an oxide layer.

Figure 4 shows that the total composition is TbO, 25 (FeO, 95”[1
05) This is the Kerr hysteresis loop obtained by measuring the magneto-optical recording medium of the present invention expressed as 0.71CrO.04.

In the figure, the horizontal axis is the magnetic field H, and the vertical axis is the Kerr rotation angle θ, which in this case is 0.34°. Also, the Kerr hysteresis loop has an angular shape and is almost saturated when the magnetic field is returned to zero. It is clear that the material exhibits excellent optical reproduction characteristics.

The Kerr hysteresis loop shown in FIG. 5 is the same measurement result for an amorphous thin film whose total composition is Tbo25Feo75, which has been proposed in the past and which has particularly excellent Kerr hysteresis loop characteristics.

Comparing FIG. 4 with FIG. 5, it is clear that the magneto-optical recording medium of the present invention has extremely excellent properties in terms of Kerr rotation angle and coercive force.

The magneto-optical recording medium of the present invention can be used not only as a single-layer thin film, but also as a Tb-Fe recording medium, which has already been proposed.
, Dy-Fe, Gd4'b-Fe, Tb-
It is also possible to use a two-layer structure covering the surface of an Fe--Co amorphous thin film.

As explained in detail above, 1.According to the present invention, the film has an axis of easy magnetization in the direction perpendicular to the film surface, has a small holding force at room temperature, and has a temperature close to room temperature. It is possible to provide a magneto-optical recording medium that can be easily manufactured under strict conditions and has extremely poor corrosion resistance.
゛The magneto-optical recording medium of the present invention is so-called beam addressable, in which information is written on a light beam nail type magnet using a dot, a hot pen, an electron beam, etc., and the written information is read out using the Kerr effect. When used as a file memory device, it is possible to perform high-density storage and realize long-stable life characteristics with stable operating characteristics over a long period of time.

[Brief explanation of drawings]

1 and 2 are characteristic curves showing the corrosion resistance of an embodiment of the magneto-optical recording medium of the present invention, FIG. 3 is a characteristic curve showing the corrosion resistance of a conventionally proposed magneto-optical recording medium, and FIG.
The figure shows a Kerr hysteresis loop according to an embodiment of the present invention, and FIG. 5 shows a characteristic curve showing the corrosion resistance of a conventionally proposed magneto-optical recording medium. Ku: magnetic anisotropy constant, MS: saturation magnetization, X: atomic ratio of Tb, Y: atomic ratio of Co, Z: atomic ratio of Cr.

Claims (1)

[Claims] Consisting of an amorphous alloy thin film having an axis of easy magnetization in the direction perpendicular to the film surface, the atomic ratio of Tb in the total composition is 15 to 40 at%,
The atomic ratio of Cr is 2 to 10 atomic%, the balance is Fe or F
If the remainder is this binary composition, the atomic ratio of Co in the binary composition is 50.
A magneto-optical recording medium characterized by having a composition of atomic percent or less.