JP2595638B2 - Magneto-optical recording medium and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is used for magneto-optical recording. In particular, it relates to a magnetic film of a magneto-optical recording medium and a method of manufacturing the same.

〔Overview〕

The present invention provides a magneto-optical recording medium in which a magnetic film whose magneto-optical characteristics change according to the state of magnetization is provided on a substrate, by using a ternary alloy thin film of manganese Mn, antimony Sb, and bismuth Bi as the magnetic film. An object of the present invention is to provide a magneto-optical recording medium which is structurally and chemically stable and has excellent characteristics.

The present invention further provides a method for manufacturing the magneto-optical recording medium.

[Conventional technology]

In recent years, studies on a magneto-optical recording medium for performing high-density recording and reproduction with a semiconductor laser beam have been actively conducted. The most basic type of this type of recording medium is one in which a magnetic film having excellent magneto-optical properties is provided on a transparent substrate such as glass or plastic by sputtering, vacuum deposition, or another method. As the magnetic film, a film whose easy axis of magnetization is oriented in a direction perpendicular to the film surface is used.

In order to record information on such a magneto-optical recording medium, magneto-optical characteristics (in this case, coercive force) corresponding to a temperature change near the Curie temperature (or compensation temperature) of the magnetic film.
The laser beam modulated with the information signal is irradiated to the magnetic film which has been magnetized in advance by using the rapid change of the magnetic signal to heat the magnetic film, and the direction of the magnetization is reversed by applying the opposite magnetic field. Also,
To reproduce the recorded information, the information signal is optically converted by a polarized laser beam by utilizing the difference in the magneto-optical effect between the recorded portion and the non-recorded portion in the recorded magnetic film due to the reversal of the magnetization. To be detected.

In order to perform such recording and reproduction, it is considered that the magnetic film needs a Curie temperature of about 100 to 300 ° C. and a coercive force of about 300 to 5000 Oe.

Conventionally, as a magnetic film for these magneto-optical recording media, an amorphous alloy of gadolinium Gd, dysprosium Dy, terbium Tb and other rare earth elements and iron Fe, cobalt Co, nickel Ni and other transition metals, manganese-bismuth Mn
Bi, manganese copper bismuth MnCuBi, platinum manganese / tin Pt
MnSn and other manganese-based alloy thin films or cobalt ferrite and other oxide-based thin films are known.

In particular, an amorphous alloy thin film of a rare earth and a transition metal has a polar magnetic Kerr effect, and can easily form a perpendicular magnetization film.Furthermore, by changing the composition, the Curie temperature and coercive force can be continuously changed. it can. For this reason, a Curie temperature and a coercive force suitable for recording and reproduction by a semiconductor laser are obtained, and the material is most suitable for practical use.

Among manganese-based alloy thin films, manganese-bismuth
Since MnBi has a large Kerr rotation angle and is c-axis oriented with respect to the film surface, it is known that this material having an easy axis of magnetization along the c-axis easily becomes a perpendicular magnetization film.

Since the cobalt ferrite thin film is an oxide, there is no problem of oxidation and other corrosion, and the Kerr rotation angle is large.

[Problems to be solved by the invention]

However, the amorphous alloy thin film of a rare earth and a transition metal has a disadvantage that the Kerr rotation angle is small and the signal intensity during reproduction is small. In order to solve this drawback, an apparent Kerr rotation angle is increased by using a multilayer thin film structure and utilizing light reflection and interference. However, although the Kerr rotation angle increases, the light reflectance decreases, and the signal intensity cannot be fundamentally increased. Further, there is a drawback that it is expensive because of containing rare earth elements.

In addition, since manganese-bismuth MnBi undergoes a phase transition at around 350 ° C., there is a problem that the structure becomes unstable at the time of writing by irradiation with laser light. Furthermore, it has the disadvantage of being chemically unstable with respect to humidity and the like. In order to solve this drawback, a thin film to which copper Cu is added has been developed.
However, this material requires the use of stress due to the difference in thermal expansion between the substrate and the substrate in order to form a perpendicular magnetization film, and thus has the disadvantage that the substrate is limited and orientation is difficult.

PtMnSn, which has recently attracted attention due to its large Kerr rotation angle, cannot form a perpendicular magnetization film and is not suitable for magneto-optical recording. In addition, there is a disadvantage in that the use of platinum Pt, which is a noble metal, is expensive.

In the case of a cobalt ferrite thin film, in order to form a perpendicular magnetization film, it is necessary to epitaxially grow on a magnesium oxide MgO or other single crystal substrate, or to use stress due to a difference in thermal expansion with the substrate. For this reason, there is a disadvantage that the substrate is limited or difficult to orient.

An object of the present invention is to solve the above problems and to provide a magneto-optical recording medium using a chemically stable magnetic film having a large Kerr rotation angle.

Another object of the present invention is to provide a method for manufacturing such a magneto-optical recording medium.

[Means for solving the problem]

The magneto-optical recording medium of the present invention has a magnetic film of manganese.
A ternary alloy thin film composed of Mn, antimony Sb and bismuth Bi and having a composition represented by Mn _X Sb _1-XY Bi _Y 0.4 <X <0.7, 0.01 <Y <0.15 is used. I do.

In order to obtain such a magnetic film, a vacuum vapor deposition method, a sputtering method, an ion plating method, or another physical vapor deposition method is used. For example, when formed by a vacuum deposition method, manganese Mn, antimony Sb
And bismuth Bi is deposited. At this time, the composition ratio can be changed by the difference in the deposition rate. As the substrate, glass, PMMA, PC or other transparent plastic can be used. The thickness of the magnetic film is preferably about 100 to several μm.

In addition, to obtain a perpendicular magnetization film, a thin film of antimony Sb and bismuth Bi is formed on a substrate, a thin film of manganese Mn is further formed on the surface of the thin film, and the obtained thin film is heat-treated to form an axis of easy magnetization. Is desirably formed in a direction perpendicular to the film surface.

In order to form a thin film of antimony Sb and bismuth Bi, antimony Sb and bismuth Bi are vapor-phase grown simultaneously or sequentially. In the case of simultaneous growth, it is desirable to use an alloy of antimony Sb and bismuth Bi as a base material. Further, it is desirable to keep the substrate temperature at a relatively low temperature of 100 ° C. or less during vapor phase growth.

In this case, a heat-resistant transparent substrate as the substrate, for example,
Use quartz or other glass materials, GGG, sapphire or other single crystals and other heat-resistant inorganic materials. The composition of the film can be set by changing the composition ratio of the antimony-bismuth alloy used as the base material for vapor phase growth, and by changing the thickness of the antimony-bismuth alloy and the thickness of manganese.

To form a sufficiently uniform alloy of manganese, antimony and bismuth, a heat treatment at 300 to 600 ° C. is performed after the formation of the thin film. Further, when magnetization is applied during the heat treatment, a perpendicular magnetization film can be easily obtained. Silicon oxide Si for heat treatment
It is desirable to provide O _X , aluminum nitride AlN, and other protective films. This protective film prevents evaporation of antimony and bismuth during the heat treatment, and can increase the chemical stability after formation.

[Action]

Manganese-antimony MnSb, which has the same nickel-arsenic NiAs-type crystal structure as manganese-bismuth, is not as large as the Kerr rotation angle of manganese-bismuth, but has a relatively low Curie temperature of 310 ° C and is similar to manganese-bismuth. Less structural instability due to phase transition and chemically stable to humidity. However, it is difficult to induce perpendicular magnetic anisotropy because the axis of easy magnetization is in the c-plane. Therefore, the present inventors have conducted various studies by adding a bismuth element to a manganese-antimony alloy. (1) In the composition formula of Mn _X Sb _1-XY Bi _Y , 0.4 <X <0.7, 0.01 < In the range of Y <0.15, the Kerr rotation angle is equal to or larger than that of manganese / antimony (0.3 °) and the axis of easy magnetization is oriented in the c-axis direction. (2) Important in recording / reproducing by laser light With respect to the appropriate coercive force and Curie temperature, it was found that the coercive force was 300 Oe or more and the Curie temperature was 100 to 300 ° C when 0.5 <X <0.7 and 0.01 <Y <0.15.

Furthermore, in these compositions, a perpendicular magnetization film can be easily obtained by simultaneously or sequentially depositing antimony and bismuth on a substrate, then depositing manganese, and then performing heat treatment to form a ternary alloy. I discovered that.

〔Example〕

(Example 1) High-purity manganese Mn, antimony Sb and bismuth Bi
Put each metal into separate crucibles for evaporation
By simultaneously heating these crucibles in a vacuum of ^-6 Torr, a thin film having a thickness of about 1000 mm was formed on a glass substrate. At this time, for a manganese deposition rate of about 1 mm / sec,
Antimony and bismuth deposition rates of 0.5 to
The thickness was changed from 3.7 ° / sec to 0.04 to 1.1 ° / sec, thereby forming thin films of various compositions.

The Kerr rotation angle of the obtained thin film was measured by a Kerr rotation angle measurement device using a He-Ne laser (wavelength: 633 nm). One example of the measured values is shown in FIG. In FIG. 1, circles indicate compositions (mol%), numerical values indicate Kerr rotation angles, and broken lines indicate 0.4 <X <0.7, 0.0 in the composition formula of Mn _X Sb _1-XY Bi _Y.
The range of 1 <Y <0.15 is shown. As comparative examples, measured values outside this range are also shown. For the components of the thin film, use EDX by analytical electron microscope.
Was analyzed by the method.

(Example 2) A high-purity antimony-bismuth alloy and metallic manganese were put in separate evaporation crucibles, and these crucibles were heated in a vacuum of 1 × 10 ⁻⁶ Torr in order, and first placed on a glass substrate. An antimony-bismuth alloy was deposited, followed by manganese. For antimony-bismuth alloy, the deposition rate is 2-5Å / sec, and the film thickness is about 500-1500Å.
And Regarding manganese, the deposition rate is set to 1-2Å / sec, and the total film thickness with the antimony-bismuth alloy film is about 20 mm.
Deposition was performed so as to be 00 °. Here, thin films having various compositions were formed by changing the base material composition of the antimony-bismuth alloy and changing the ratio of the antimony-bismuth alloy film to the manganese film. Next, the obtained sample was heat-treated at 500 ° C. for 5 hours in a vacuum of 1 × 10 ⁻⁶ Torr to uniform the thin film.

FIG. 2 shows the measured value of the Kerr rotation angle of the obtained sample,
The measured values of the coercive force are shown in FIG. In these figures,
Circles indicate composition (mol%), numerical values indicate Kerr rotation angle or coercive force, and dashed lines indicate 0.5 <X <0.0 in the composition formula of Mn _X Sb _1-XY Bi _Y.
7, 0.01 <Y <0.15. As comparative examples, measured values outside this range are also shown.

When the magnetization characteristics of the obtained thin films were examined with a VSM and a torque meter, these thin films were perpendicular magnetization films. Furthermore, X-ray analysis confirmed that the thin film was oriented along the c-axis.

FIG. 4 shows the in-plane and perpendicular magnetization curves of the Mn _0.62 Sb _0.36 Bi _0.02 thin film, and FIG. 5 shows the X-ray break pattern of the same thin film. This composition was analyzed by an EDX method using an analytical electron microscope.

〔The invention's effect〕

As described above, the magneto-optical recording medium of the present invention is based on manganese / antimony which has been conventionally used, and is obtained by adding bismuth to the manganese / antimony. Due to the composition ratio of the magnetic film, the desired Kerr rotation angle, coercive force, Curie temperature, and the easy axis of magnetization in the c-axis direction required for the perpendicular magnetic film as a magneto-optical material capable of high-density recording with a semiconductor laser beam are obtained. can get. In particular, since the Kerr rotation angle is large, magneto-optical reading is facilitated, and the signal-to-noise ratio of magneto-optical storage can be increased. In addition, the magnetic film is structurally and chemically stable. Therefore, there is an effect that a magneto-optical recording medium having excellent recording and reproducing characteristics and being structurally and chemically stable can be realized.

Further, according to the method of the present invention, the axis of easy magnetization of the above-described magnetic film can be easily oriented to the c-axis, and there is an effect that an excellent perpendicular magnetic film can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing the composition dependence of the Kerr rotation angle θ _K of a manganese-antimony-bismuth thin film obtained in Example 1. FIG. 2 is a diagram showing the composition dependence of the Kerr rotation angle θ _K of the manganese-antimony-bismuth thin film obtained in Example 2. FIG. 3 is a diagram showing the composition dependence of the coercive force H _C of a manganese-antimony-bismuth thin film. FIG. 4 is a diagram showing a magnetization curve of a Mn _0.62 Sb _0.36 Bi _0.02 thin film. FIG. 5 is a view showing an X-ray diffraction pattern.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mikiya Ono 2270 Yokoze, Yokoze-cho, Yokoze-cho, Chichibu-gun, Saitama Prefecture Inside the Ceramics Research Laboratory Mitsubishi Mining Cement Co., Ltd. (72) Yoshihiro Kikuchi 1-35-9, Sakuragaoka, Sendai City, Miyagi Prefecture (72) Inventor Norio Wakiyama 2-27-16 Komatsushima, Sendai City, Miyagi Prefecture

Claims (5)

(57) [Claims] 1. A magneto-optical recording medium comprising: a substrate; and a magnetic film formed on the substrate and whose magneto-optical characteristics change depending on a state of magnetization, wherein the magnetic film comprises manganese Mn, antimony Sb and bismuth. A magneto-optical recording medium comprising Bi, wherein the composition is represented by Mn _X Sb _1-XY Bi _Y 0.4 <X <0.7, 0.01 <Y <0.15. 2. A first step of forming a thin film of antimony Sb and bismuth Bi on a substrate, a second step of further forming a thin film of manganese Mn on the surface of the thin film, and heat treating the obtained thin film. A step of forming an easy axis of magnetization in a direction perpendicular to the film surface by the method. 3. The method of manufacturing a magneto-optical recording medium according to claim 2, wherein the first step includes a step of simultaneously growing vapor phase of antimony Sb and bismuth Bi. 4. The method according to claim 3, wherein the first step uses an alloy of antimony Sb and bismuth Bi as a base material for vapor phase growth. 5. The method of manufacturing a magneto-optical recording medium according to claim 2, wherein the first step includes a step of sequentially growing vapor phase of antimony Sb and bismuth Bi.