JPH07141708A - Magneto-optical thin film and magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain magneto-optic characteristics of a thin film formed at room temp. suitable for use in a short wavelength region by constituting the thin film of a ternary alloy having the axis of easy magnetization in the perpendicular direction to the film plane. CONSTITUTION:The magneto-optical thin film consists of a ternary alloy of cobalt Co, platinum Pt, and ruthenium Ru having a compsn. of CoaPtbRuc. In this formula, a, b, c represent atomic % of each element and satisfy 35<=a<=55, 25<=b<=40, 10<=c and a+b+c=100. The film has the axis of easy magnetization in the perpendicular direction to the film plane and the film thickness is <=50nm. When this thin film is to be used for the recording layer of a magneto-optical recording medium, the recording layer is preferably formed to such film thickness that light can enough transmit in order to increase signals for reproducing by using the optical interference effect of a multilayer structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical thin film which is useful for a recording layer of a magneto-optical recording medium and which utilizes the magneto-optical effect.

[0002]

2. Description of the Related Art Various researches and developments have been made on optical recording media as high-density, large-capacity information recording media. In particular, a magneto-optical recording medium capable of repeatedly recording and erasing information has a wide application field, and various magneto-optical recording media have been announced.
By the way, in the conventional magneto-optical recording system, the wavelength of 830
Laser light of nm is usually used. However, in the system that will realize higher density recording in the future, 400 to 550 nm, which is shorter than the wavelength of laser light currently used,
It is considered to use short wavelength laser light.

By the way, in such a magneto-optical recording medium, a magneto-optical thin film having a magneto-optical effect is used as a recording layer. In the magneto-optical recording medium currently on the market, a normal recording layer has a magnetic easy axis in the direction perpendicular to the film surface and has a squareness ratio of 1 which is a ratio of saturation magnetization to residual magnetization.
A rare-earth transition metal amorphous alloy such as a TbFeCo film is used.

However, such a recording film cannot obtain effective magneto-optical characteristics in the short wavelength region. On the other hand, as a magneto-optical thin film having a magneto-optical property in the short wavelength region and a perpendicular magnetic anisotropy and a squareness ratio of 1, Co / Pt having a structure in which platinum (Pt) layers and cobalt (Co) layers are alternately laminated. Multilayer films have been actively studied so far for practical use. However, this Co / Pt multilayer film has a drawback that it requires complicated film formation because it has a multilayer film structure. This is inconvenient when considering productivity and the like. In addition, a CoPt alloy film is widely known as a magneto-optical thin film having excellent magneto-optical characteristics in the short wavelength region (for example, KHJ
Buschow et al., J. Magn. Magn. Mat., 38,1 (198
3)).

[0005]

[Problems to be Solved by the Invention] However, this Co
In order to obtain a magneto-optical thin film with perpendicular magnetic anisotropy in Pt alloy, it was necessary to form the film at a substrate temperature of 200 ° C by the electron beam evaporation method (C.-J. Linet al., Appl. Phys. Lett., 6
1,1600 (1992)). This is inconvenient in view of productivity, and it has been impossible to form a film on a plastic substrate such as polycarbonate currently used in a magneto-optical recording medium. Further, the Co / Pt multilayer film that can be formed at room temperature has a drawback that it requires complicated film formation because it has a multilayer film structure. This is also inconvenient when considering productivity and the like.

An object of the present invention is to provide a magneto-optical characteristic which does not require a complicated film forming method such as an artificial lattice structure, can be formed at room temperature, and is suitable for use in a shorter wavelength region than at present. Furthermore, it is to obtain a magneto-optical thin film having a practically sufficient squareness ratio and perpendicular magnetic anisotropy. Further, it is to obtain a magneto-optical recording medium having such characteristics in the magneto-optical recording film constituting the recording layer.

[0007]

The magneto-optical thin film according to the present invention is made of cobalt (Co), platinum (Pt), ruthenium (Ru).
Is _a ternary alloy consisting of Co _a Pt _b R
u _c , 35 ≦ a ≦ 55, 25 ≦ b ≦ 40, 10 ≦ c, a + b + c = 10
0 (however, a, b and c are composition ratios by atomic%),
Further, it is characterized in that it has an axis of easy magnetization in a direction perpendicular to the film surface and that the film thickness is 50 nm or less.

In the present invention, in order to enable high density recording as a magneto-optical recording film, a perpendicularly magnetized film having an easy axis of magnetization perpendicular to the recording layer forming surface, that is, effective perpendicular magnetic anisotropy energy. Must be positive (the vertical direction must be a positive sign). For that, the film thickness is 50 nm
In the following cases, the composition is Co _a Pt _b Ru _c , 35 ≦ a
It is necessary that ≦ 55, 25 ≦ b ≦ 40, 10 ≦ c, and a + b + c = 100.

In particular, when the magneto-optical thin film of the present invention is used as a recording layer of a magneto-optical recording medium, the recording layer is formed in order to increase the signal at the time of reproduction by utilizing the optical interference effect of the multilayer structure. A film thickness that allows sufficient light transmission is desirable. Also, when heating with a laser beam during recording, it is desirable that the heat capacity of the entire recording layer be small, that is, that the film thickness be thin. For these reasons, the thickness of the magneto-optical recording thin film is
50 nm or less is desirable.

Here, in order to obtain a perpendicularly magnetized film in the above CoPtRu alloy composition, sputtering, vacuum deposition, molecular beam epitaxy (MBE) method or the like can be used. The evaporation source used at this time may be a CoPtRu alloy evaporation source or an independent evaporation source for each element.
However, the method is not limited to these. For example, when creating an alloy thin film by sputtering,
A CoPtRu alloy target may be used, or a so-called composite target in which Pt and Ru chips are mounted on a Co target may be used. It is also possible to improve the characteristics by heating during film formation or heat treatment after film formation.

Further, the magneto-optical thin film according to the present invention can be used not only as a recording layer of a magneto-optical recording medium by utilizing the above characteristics but also as a material of a magneto-optical element such as an optical isolator.

When it is used as a recording layer of a magneto-optical recording medium, it is laminated on a glass or plastic substrate such as polycarbonate. It is also possible to improve performance by forming a multilayer structure including a dielectric film and a metal film. The structure of this multi-layer structure, the film thickness of each layer, the physical properties, etc. are determined by optical or thermal optimum design in order to improve the recording / reproducing characteristics. The dielectric film and the metal film also have a function as a corrosion-resistant protective film for the recording film. Further, an organic protective film may be laminated on the recording layer or a multilayer structure including the recording layer for corrosion resistance.

The substrate, the underlayer and the dielectric film used in the magneto-optical thin film of the present invention are not particularly limited.

Further, the magneto-optical thin film according to the present invention may be further improved in characteristics by the effect of additive elements, the effect of the underlying layer and the like. However, it is desirable that the amount of the additional element is 5 atomic% or less. At this time, as additive elements, Al, Si,
Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Ga, Ge, Zr, Rh, A
Examples thereof include g, In, Sn, Sb, Hf, Ir, Au, Pb, Pd, Bi and the like.

Alternatively, it is possible to improve the efficiency as a so-called artificial lattice structure magneto-optical recording medium by alternately laminating another metal thin film or dielectric thin film and the CoPtRu alloy thin film.

[0016]

Examples and Comparative Examples Co target (diameter:
100 mm) and a Pt and Ru chip thereon were appropriately placed according to the film composition to be produced. Furthermore, a Si substrate was placed on a water-cooled base facing the composite target.

Then, in an Ar gas atmosphere with a gas pressure of 1.3 Pa (= 10 mTorr), DC sputtering with an input power of 100 W was performed, and the film thickness was formed on the AlSiN amorphous dielectric film with a film thickness of 20 nm laminated on the Si substrate. A CoPtRu alloy thin film of 20 to 26 nm was formed. The obtained CoPtRu alloy thin film is a polycrystalline thin film by X-ray diffraction analysis.

FIG. 1 shows the composition of CoPtRu alloy thin film samples prepared as examples of the present invention and comparative examples. In the figure, the bottom is the composition ratio of Pt (atomic%, the left end is 100 atomic%, the right end is 0%).
%), The left hypotenuse is the composition ratio of Co (atomic%, the upper end is 100 atomic%, the lower end is 0 atomic%), and the right hypotenuse is the composition ratio of Ru (atomic%, the lower end is 100 atomic%, the upper end is 0 atomic%). ) Indicates the scale axis. Further, in the figure, the mark ◯ indicates the compositions of Examples 1 and 2, the mark X indicates the compositions of Comparative Examples 1 to 8, and the mark □ indicates the compositions of Comparative Examples 9 to 12.

The composition of the obtained CoPtRu alloy thin film is
It was confirmed by Auger electronic analysis. Further, various magnetic properties were measured and evaluated by a circular polarization modulation method Kerr spectrum measuring device, a vibrating sample magnetometer (VSM) and a magnetic torque meter.

Table 1 shows the composition ratio of each sample and the measurement results.
However, in Table 1, the composition ratio is atomic%. Also, in the table, Keff (× 10 ⁶ erg / cc) is the effective magnetic anisotropy energy (the positive sign indicates the direction perpendicular to the film surface of the magnetic thin film. However, here, the value measured by the magnetic torque meter is the sample. (The value is divided by the volume of the magnetic film inside, demagnetizing field energy is not corrected), Hc (kOe) is the perpendicular coercive force, and θk
(Deg) indicates the absolute value of the saturated Kerr rotation angle at the measurement wavelength of 400 nm.

In Comparative Examples 1 to 8, the effective magnetic anisotropy energy was negative, but in Examples 1 and 2 shown in Table 1, the effective magnetic anisotropy energy was positive. In Comparative Examples 9 to 12 having a film thickness of 50 nm or more, the effective magnetic anisotropy energy was negative.

[0022]

[Table 1]

[0023]

As described above, the present invention does not require a complicated film forming method such as substrate heating or an artificial lattice structure at the time of film forming, and has a shorter wavelength region than that at present in a state where the film is formed at room temperature. It is possible to obtain a magneto-optical thin film having a magneto-optical characteristic suitable for use and having practically sufficient perpendicular magnetic anisotropy. Further, it is possible to obtain a magneto-optical recording medium having the characteristics of the magneto-optical recording film constituting the recording layer.

[Brief description of drawings]

FIG. 1 is a composition of Examples and Comparative Examples and a composition range of the present invention.

Claims (2)

[Claims] 1. A ternary alloy of cobalt (Co), platinum (Pt) and ruthenium (Ru), the composition of which is Co _a
Pt _b Ru _c , 35 ≤ a ≤ 55, 25 ≤ b ≤ 40, 10 ≤ c, a + b +
c = 100 (where a, b, and c are the composition ratios in atomic%), the easy axis of magnetization is in the direction perpendicular to the film surface, and the film thickness is 50 nm or less. Thin film. 2. A magneto-optical recording medium comprising the magneto-optical thin film according to claim 1 in a recording layer.