JPS6289254A - Photomagnetic recording medium - Google Patents

Abstract

PURPOSE:To lower a Curie temp. without decreasing a performance index, to improve recording and reproducing sensitivity and to remarkably improve corrosion resistance by substituting part of Tb with Dy and adding Cr thereto to form a thin binary or ternary amorphous film. CONSTITUTION:This recording medium consists of the thin amorphous alloy film having the axis of easy magnetization in the direction perpendicular to the film plane. The atomic ratio of the binary compsn. material consisting of Tb and Dy in the entire compsn. occupies 15-40atom% and the atomic ratio of Cr occupies 2-10atom%. The balance is constituted Fe or the binary compsn. material consisting of Fe and Co. The atomic ratio of Dy in the binary compsn. material consisting of Tb and Dy is made <=50atom% and the atomic ratio of Co is made <=50atom% in the case of the binary compsn. material of Fe and Co as the balance. The Curie temp. lowers and the Kerr rotating angle decreases accordingly if the content of Dy in the binary compsn. material consisting of Tb and Dy exceeds 50atom%. On the other hand, the effect of adding Cr is not admitted if the atomic ratio Z of Cr is set at Z<0.02. Conversely, the medium which satisfied vertical magnetization conditions is hardly obtd. if said ratio is set at Z>0.10.

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'' Magneto-optical memory and magneto-optical recording display elements have an axis of easy magnetization perpendicular to the film surface, and circular acids record information by creating reversed magnetic domains of arbitrary shapes, and the magnetic Kerr effect Thin-film magneto-optical recording media are used to 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. Such a ferromagnetic thin film can be used as a high-density magnetic recording medium by recording information based on the presence or absence of this inverted magnetic domain corresponding to 1j, roJ. It is possible to read out using the magneto-optic effect.

Among these ferromagnetic thin films, thin films that have a large coercive force at room temperature and whose Curie temperature or magnetic compensation temperature is relatively close to room temperature are those that have a Curie temperature or magnetic compensation temperature that is relatively close to room temperature. It is used as a beam-addressable file because information can be recorded by creating inverted magnetic domains at arbitrary positions using a light beam. ``Conventionally, polycrystalline metals such as MnBi have been used as 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. Thin film or Gd-Tb-? e, Dy-F
Multi-component amorphous metal thin films such as 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 Curie 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, T
b-Fe-C.

Amorphous thin films with multicomponent compositions have been proposed. These proposed rare earth-transition metal amorphous thin films have a low Curie temperature of 60°C to 200°C, so they can be written using the Curie temperature and have a wide composition range under room temperature conditions. It has a large coercive force of several KOe. Furthermore, when used as a recording medium, there is no need to create an amorphous thin film under particularly high-precision manufacturing conditions in terms of composition, and the manufacturing technology is relatively easy, making it easier to produce small droplets.

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

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 specimen has composition 75'Tb025"e075
A rare earth metal expressed as $- and (TbO80DyO20)025Fe075, created by sputtering on a soda silicate glass substrate with a diameter of 50 to a film thickness of approximately
A transition metal amorphous thin film is used, and the metal amorphous thin film is immersed in an I N NaC2 solution at room temperature. The specimens were immersed in NaCl solution for various immersion times.
The specimen is removed from the L solution, irradiated with a 5 mW laser beam, the power of the reflected laser beam from the specimen 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 50% without immersion to 30%, and when the immersion time is 120 minutes, the reflectance decreases to approximately 1.
011, clearly indicating that the corrosion of the test object is severe.

The problem to be solved by this invention is how to maintain the conventional advantages of this type of rare ±1-transition metal amorphous thin film and improve the essential drawback of being easily corroded. The question is whether to obtain an amorphous thin film with high corrosion resistance.

"Structure of the Invention" The magneto-optical recording medium of the present invention is composed of an amorphous alloy thin film having an axis of easy magnetization in the direction perpendicular to the film surface, and has a total composition of Tt).
The atomic ratio of the binary composition of
It is composed of a binary composition of e or F'e and Co. The atomic ratio of Dy in the binary composition of Tb and Dy is 50
When the remainder is composed of a binary composition of Fe and Co, the atomic ratio of Co in the binary composition is 5.
It is less than 0 atoms.

"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 with reference to the drawings.

The inventors conducted extensive research and examination based on the conventionally proposed Tb-Fe binary amorphous thin film body and Tb-Fe-C〇 ternary amorphous thin film body. Alternatively, by substituting a part of Tb with Dy for a ternary amorphous thin film body, the figure of merit can be changed to θK (R: reflectance, θ:
We have found that it is possible to significantly increase the corrosion resistance of amorphous thin film materials by lowering the Curie temperature and improving recording and reproducing sensitivity without reducing the force (rotation angle) and, at the same time, adding Cr. It was.

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

In the example, a quartz substrate or a synthetic resin substrate with a thickness of 0.3 mm is used, and a thin film-like magneto-optical film is formed on this substrate by sputtering, for example, using a target with a composition close to that of the film. Create a recording medium. The created atmosphere was an atmosphere using argon gas as an inert gas.
The atmospheric pressure is maintained at 3-8 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.

Under such an atmosphere, a film thickness of 1 was applied to the substrate with a power supply of 50 W.
A thin film-like magneto-optical recording medium having a thickness of approximately 000λ is prepared.

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.

DyXFa, co and Or each expressed as x in atomic ratio
ly, z, and w, and the total composition of the magneto-optical recording medium is generally (TbI-y Dyv) x (Fet-
yooy) I-x-zCrz. In this compositional formula, when Y=Q, the remainder other than Tb, Dy and Or is a monolithic composition containing no Co. In such a general compositional formula, the conditions required for the composition in this invention are 0.15≦X≦0.40.0≦Y when the amount of each element is expressed as an atomic ratio.
≦0.50.0.02 ≦Z≦0.10 and o<w
≦o, s.

It is.

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, it is possible to obtain the saturation magnetization Ms that satisfies the perpendicular magnetization condition of Ku)2πMl/, where the magnetic anisotropy constant is Ku. If the perpendicular magnetization condition is 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 (TbI -v Dyw) x (F'e,
-, Coy ) t-X-ZCrZ When the atomic ratio X of the binary composition of Tb and Dy in the magneto-optical recording medium of the present invention is set to X < 0.15, the moment due to the iron element becomes large, and when X>0.4 is set, the magnetic moment due to the rare earth element becomes large.

In any of these cases, the saturation magnetization Ms of the entire composition of the magneto-optical recording medium becomes large, and Ku)2πM
It becomes impossible to satisfy the perpendicular magnetization condition of Bt. Therefore, in this invention, the atomic ratio X of rare earth elements is 0.
．． The condition of 15≦X≦0.40 is required.

When Dy exceeds 50 atoms in the binary composition of Tb and Dy, the Curie temperature decreases and the Kerr rotation angle decreases accordingly.

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, and conversely, z>o,
If it is set to io, a magneto-optical recording medium with excellent corrosion resistance can be obtained, but a medium that satisfies the perpendicular magnetization condition may not be obtained, and a coercive force of several KOe may not be obtained. In this case, even if the perpendicular magnetization condition can be satisfied, the Kerr rotation angle becomes too small and predetermined characteristics cannot be obtained.

Therefore, for an atomic ratio of 2 of Cr, 0.02≦2≦0.10
is required.

Generally, when writing is performed using the Curie temperature, if the Curie temperature is too high, a large laser power is required, making it impossible to use a semiconductor laser. Therefore, the Curie temperature of the magneto-optical recording medium is 2
It is necessary to keep the temperature below 00°C.

In the magneto-optical recording medium of this invention, Tb1Dy10r
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 200
℃, 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 O≦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 IN Na0A solution, and the vertical axis shows the reflectance of the laser beam, which has already been defined and explained.

That is, after the specimen was immersed in the INNaCt solution at room temperature for the immersion time shown on each horizontal axis, the specimen was taken out of the Na CL bath solution and a 5 mW laser beam was applied to the specimen. irradiate. 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 reflected laser light to the power of the irradiated 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 (Tb0.80 Dy0.20)
0.25 (Fe (L85000.15) (L71 C
When the magneto-optical recording medium of the present invention, which is expressed as r0.04, is used as the test object, the test object is a thin film formed by sputtering to a thickness of about 100 oz on a soda silicate glass substrate with a diameter of 50 cm. did.

As is clear from the results shown in Figure vJ1, I N Na
120% from the state of reflectance of 47% before immersion in Ct solution
Even after being immersed in NaC2 solution for a minute, the reflectance was only reduced to 38%, and compared to the results shown in Figure 3 obtained with the conventionally proposed amorphous thin film described above, the corrosion resistance was lower. It is clear that there has been a significant increase in

Figure 2 shows that the total composition is (TbQ, 70 DyQ
, 30) Q, 25Feα68Cr (107) This is a case where the magneto-optical recording medium of the present invention, denoted by 107, is used as a test object, and the test object shape is the same as that in FIG.

Even in this case, the reflectance decreases from 47% before being immersed in the I N Na06 solution to only 32% even after being immersed in the NaC4 solution for 120 minutes. It is confirmed that the 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 oxidized layer.

Figure 4 shows that the total composition is (Tb[180Dy0.20)α2
5 (Foo, 95CocL05) 0.71 Or
The Kerr hysteresis is loose when measured for the magneto-optical recording medium of the present invention, which is expressed as 0.04. In the figure, the horizontal axis is the magnetic field, and the vertical axis is the Kerr rotation angle θ, which in this case is 20 or 0.32 degrees, and the Kerr hysteresis loop has an angular shape, which returns the magnetic field to zero. It is clear that the sample exhibits a nearly saturated value at the point and has excellent optical reproduction characteristics.

The Kerr hysteresis 7 sloop shown in FIG. 5 is the same measurement result for an amorphous thin film whose total composition is Tbα25''[L75, which has been proposed in the past and which has particularly excellent Kerr hysteresis loop characteristics.

As is clear from comparing FIG. 4 with FIG. 5, it is clear that the magneto-optical recording medium of the present invention has extremely excellent characteristics 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-F
e, Dy-Fe, Ga-Tb-Fe, Tb-Fe
It is also possible to use it as a two-layer structure covering the surface of a -C0-based amorphous thin film.

As explained in detail above, the present invention has an axis of easy magnetization perpendicular to the film surface, a large coercive force at room temperature, and a Curie temperature close to room temperature, and the manufacturing conditions are not severe. It is possible to provide a magneto-optical recording medium that is easy to manufacture and has extremely excellent corrosion resistance.

The magneto-optical recording medium of the present invention writes information using a light beam nail-type magnetic head, a thermal pen, an electron beam, etc., and reads the written information using the Kerr effect, making it a so-called beam-addressable file memory device. It is possible to achieve high-density storage and 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.
This figure shows a Kerr hysteresis loop according to an embodiment of the present invention, and FIG. 5 is a diagram showing Kerr hysteresis loop 1 of a conventionally proposed magneto-optical recording medium. Ku: magnetic anisotropy constant, Me: saturation magnetization, X: Tb
atomic ratio of and Dy, Y: atomic ratio of Co, Z: C!
Atomic ratio of r, W:Dy atomic ratio. Patent applicant: Sumitomo Metal Mining Co., Ltd. Figure 1: Immersion time (current) Figure 2: Immersion time (public) Figure 3: Immersion time (minutes)

Claims (1)

[Claims] Consisting of an amorphous alloy thin film with an axis of easy magnetization perpendicular to the film surface, the atomic ratio of the binary composition of Tb and Dy in the total composition is 15 to 40 at%, and the atomic ratio of Cr is 2 to 10 atoms. %, the remainder consists of Fe or a binary composition of Fe and Co, the atomic ratio of Dy in the binary composition of Tb and Dy is 50 at % or less, and the remainder is a binary composition. A magneto-optical recording medium having a composition such that the atomic ratio of Co in the binary composition is 50 atomic % or less.