JPH0757309A - Magneto-optical thin film and magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording film having an axis of easy magnetization perpendicular to the surface by using a compsn. represented by CoaPtbWc [where (a), (b) and (c) show the ratio (at.%) among the components] and regulating the ratio to a prescribed range. CONSTITUTION:A magnetic recording film is made of a Co-Pt-W ternary alloy having a compsn. represented by CoaPtbWc (where 30<=a<=75at.%, 1<=c<=20at.% and a+b+c=100at.%). This film has an axis of easy magnetization in a direction perpendicular to the surface. A Co target is set in the chamber of a DC sputtering device, a Pt chip or Pt and W chips are put on the Co target and an Si substrate is set on a table confronting the Co target. DC sputtering is carried out in gaseous Ar to form a thin film of CoPt and CoPtW alloys on an amorphous dielectric thin film of AlSiN laminated on the Si substrate. The objective magneto-optical thin film having magneto-optical characteristics fit for utilization in a shorter wavelength region, a practically satisfactory squareness ratio and perpendicular magnetic anisotropy is obtd. by formation at room temp. without adopting a complex method.

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 magneto-optical characteristics and perpendicular magnetic anisotropy in the short wavelength region and having 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)).

[0004]

[Problems to be Solved by the Invention] However, this Co
In order to obtain a magneto-optical thin film with perpendicular magnetic anisotropy in a Pt alloy, it was necessary to deposit the film at a substrate temperature of 200 ° C by the electron beam evaporation method (C.-J. Linet al., Appl. Phys. Lett.
61, 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 magneto-optical recording media. In addition, the Co / Pt multilayer film that can be formed at room temperature has a drawback that complicated film formation is required 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 magnetic recording film constituting the recording layer.

[0006]

The magnetic recording film of the present invention is a ternary alloy composed of cobalt (Co), platinum (Pt) and tungsten (W), and its composition is Co _a Pt.
_b W _c , 30 ≤ a ≤ 75, 1 ≤ c ≤ 20, a + b + c = 100
(Where a, b, and c are component ratios in terms of atomic%) and has an easy axis of magnetization in the direction perpendicular to the film surface.

In the present invention, as a recording film for high-density recording, a perpendicular magnetization film whose easy axis of magnetization is perpendicular to the surface on which the recording layer is formed, that is, the effective perpendicular magnetic anisotropy energy becomes positive (in the perpendicular direction, It must be a plus sign). Therefore, the composition is Co _a Pt _b W _c , 30 ≦ a ≦ 75, 1 ≦ c ≦ 20, a
It is necessary to set + b + c = 100.

Here, in order to obtain a perpendicular magnetization film in the above CoPtW 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 CoPtW alloy evaporation source or an independent evaporation source for each element. However, the method is not limited to these. For example, when forming an alloy thin film by sputtering, a CoPtW alloy target may be used, or a so-called composite target in which Pt and W 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 as a material for a magneto-optical element such as an optical isolator in addition to the recording layer of a magneto-optical recording medium by taking advantage of the above characteristics. When used as a recording layer of a magneto-optical recording medium, it is laminated on a plastic substrate such as glass or polycarbonate. Also, by forming a multilayer structure with a dielectric film and a metal film,
It is also possible to improve performance. 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, underlayer, and 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, 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, Ag, In, Sn, S
Examples thereof include b, 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 CoPtW alloy thin film.

[0013]

Examples and Comparative Examples Co target (diameter:
100 mm) and a Pt or Pt and W chip thereon were appropriately placed according to the composition of the film to be produced. Furthermore, a Si substrate was placed on the base facing the composite target. Then, DC sputtering with an input power of 100 W was performed in an Ar gas atmosphere with a gas pressure of 0.67 Pa or 1.3 Pa, and a film thickness of 7 to 7 was formed on the AlSiN amorphous dielectric film with a film thickness of 20 nm laminated on the Si substrate.
11 nm CoPt and CoPtW alloy thin films were formed. The obtained CoPtW alloy thin film is a polycrystalline thin film by X-ray diffraction analysis.

FIG. 1 shows the composition of CoPtW 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 (atom%, the upper end is 100 atom%, the lower end is 0 atom%), and the right hypotenuse is the composition ratio of W (atomic%, the lower end is 100 atom%, the upper end is 0 atom%). ) Indicates the scale axis. Further, in the figure, the mark ◯ indicates the compositions of Examples 1 to 8 and the mark X indicates the compositions of Comparative Examples 1 to 5.

The composition of the obtained CoPtW alloy thin film was determined by Auger electron analysis. Circular polarization modulation method Kerr spectrum measurement device, vibration sample magnetometer (V
SM) and a magnetic torque meter were used for evaluation.

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. Value is divided by the volume of the magnetic film of No., 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 5, the effective magnetic anisotropy energy was negative, but in Examples 1 to 8 shown in Table 1, the effective magnetic anisotropy energy was positive.

[0018]

[Table 1]

[0019]

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 a practically sufficient squareness ratio and perpendicular magnetic anisotropy. Furthermore, it is possible to obtain a magneto-optical recording medium having such characteristics of the magnetic 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 comprising cobalt (Co), platinum (Pt) and tungsten (W), the composition of which is Co.
_a Pt _b W _c , 30 ≤ a ≤ 75, 1 ≤ c ≤ 20, a + b + c = 10
0 (however, a, b and c are composition ratios by atomic%),
A magneto-optical thin film having an easy axis of magnetization in a direction perpendicular to the film surface. 2. A magneto-optical recording medium comprising the magneto-optical thin film according to claim 1 in a recording layer.