JPS609855A - Magnetic alloy - Google Patents

Abstract

PURPOSE:To provide a magnetic alloy which has low magnetorestriction and is suitable for a magnetic recording medium having an excellent noise characteristic by specifying the compsn. of a Dy-Fe-Co alloy contg. Gd, Tb, Ho. Er, etc. CONSTITUTION:A magnetic alloy consists of 0.2<= a <=0.7, 0.02<= b <=0.8, 1.0<= z <=4.0 in (Fe1-aCoa)ZDy1-bRb (where R; >= combination of >=1 kind among Gd, Tb, Ho and Er) has low magnetorestriction and has excellent uniaxial magnetic anisotropy and coercive force characteristic. Magnetic recording to a high density is made possible by forming said alloy in the form of a thin film. The alloy is preferably amorphous as the grain boundary is liable to be a cause for nonuniform properties and leads to a decreased noise characteristic if the alloy is polycrystalline. The above-mentioned alloy of the amorphous thin film is obtainable by melting and cooling the alloy having the prescribed comps. in a vacuum or inert gaseous or reducing gaseous atmosphere to form an ingot., cutting the resulting ingot to a suitable size to make a target and sputtering the alloy on a glass base plate by using such target.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a magnetic alloy, and particularly to a Dy-Fe-Co based low magnetostriction magnetic alloy suitable for use in magnetic recording media with excellent noise characteristics.

[Technical background of the invention and its problems] In general, magnetic recording media in which the axis of easy magnetization of the magnetic layer is aligned perpendicular to the substrate surface are suitable for high-density recording because self-demagnetization is small. Among these, the thin film magnetic recording medium in which the Curie point is slightly higher than room temperature is particularly expected to be used as a high-density magneto-optical recording medium.

A magneto-optical recording medium is a recording medium that records information by irradiating the medium with light (laser) and thermomagnetically reversing the direction of magnetization, and by measuring the Kerr rotation angle of the light. It is a recording medium from which information can be extracted.

At present, magnetic thin films that are well known as such magneto-optical recording media include polycrystalline metal thin films represented by MnB1, G I G (Gaclol inium I
There are compound single-crystal thin films typified by (Ron Garnet), and amorphous metal thin films such as ...-Fe and Dy-Fe.

By the way, polycrystalline metal thin films such as MnB1 have too high a Curie point (in MnBi, the Curie point Tc
= 360°C), it requires a large amount of energy to write, and since it is polycrystalline, it must be made into a thin film with a chemical composition, making it technically difficult to manufacture. are doing.

Since the manufacturing cost of single crystal thin films of compounds such as GIG is too high, it is difficult to put them into practical use. Dimensions, Gd -
An amorphous metal thin film such as Fe has a small coercive force (300 to 5000e) at room temperature, and has the disadvantage that recorded information is unstable.

However, amorphous metal thin films such as Dy-Fe and MnB
i + G I Unlike G, it is amorphous, so it can be made into a thin film on any substrate, and the Curie point can be controlled arbitrarily to some extent by adding some impurities. and also DY
Due to the one-ion anisotropy of, compared to the above Gd-Fe,
It has the advantage of having a significantly large coercive force (c number KOe). For this reason, magnetic alloys such as Dy-Fe are attracting attention as magnetic recording media, especially magneto-optical recording media. There was a problem that magnetic recording media were difficult to obtain. In other words, when manufacturing a magnetic recording medium from a Dy-Fe alloy material, if internal stress σ is generated in the medium for some reason, σ caused by the reverse effect of magnetostriction
Due to the magnetic anisotropy energies Kd=, λ, and σ in the directions, physical properties such as anisotropy become microscopically nonuniform, resulting in a decrease in the S/N ratio. For example, when producing a Dy-Fe magnetic alloy thin film using the bias sputtering method, the stress within the film varies depending on the gas pressure in the Pelger and the bias voltage during sputtering, resulting in microscopically non-uniform physical properties of the film. As a result, there has been a problem in that the noise characteristics of the resulting magnetic recording medium are significantly degraded.

[Objective of the Invention] An object of the present invention is to provide a magnetic alloy with low magnetostriction and excellent coercive force characteristics, and to improve the noise characteristics of magnetic recording media. .

[Summary of the Invention] In order to achieve the above object, the present inventors have conducted extensive research on the composition and structure of Dy-Fe alloys, and have found that the effect of replacing CO with Fe on the magnetostriction properties is significant. When we discovered this and tried to analyze the phenomenon in more detail, we found that (Fel −
When the composition is a Co a ) z Dy 1-b Rb, the magnetostrictive property [for example (Fe 1-a Co a ) z Dy
1-b In Rb crystal, λ11. (Cubic crystal (1
11) The magnetostriction properties in the direction of the crystal axis are significantly different,
In the case of a≧02, we have discovered a new fact that shows a low magnetostriction property in which the magnetostriction property under a strong magnetic field exceeding IKOe is one order of magnitude smaller than that in a (0,2), and we have completed the present invention.

That is, the magnetic alloy of the present invention has (Fe 1-a Co
a) zDyl-bRb (where R: Gd, Th, Ho
, Er) 0.2
≦a≦0.7.0.02≦b≦0.8.1.0≦2≦4
．． It is characterized by being 0.

In the present invention, a (substitution amount of Co) is 0.2 or more 07
If the value is less than 0.2, the decrease in λ5 will not be noticeable, and the following is particularly preferable in the case of a recording medium having a high coercive force (IKOe or more), where the applied magnetic field is large, and the object of the present invention is sufficiently achieved. If it is not achieved and still exceeds 0.7, the Curi point will be significantly reduced, and the amorphous crystallization temperature will also be significantly lowered to below the Curi point, which will not satisfy the purpose of the present invention.

Setting b (substitution amount of H) to 0.02 or more and 0.8 or less improves recording medium characteristics (coercive force, operating temperature, Kerr rotation angle) while maintaining low magnetostriction characteristics. is 0.
If it is less than 02, the effect is not recognized.

Moreover, if it exceeds 0.8, it becomes difficult to achieve both low magnetostriction characteristics and recording medium characteristics, and therefore the object of the invention is not achieved.

2z (transition metal/rare earth element molar ratio) is 1.0≦2≦4
．． 4. Even if it is set to 0, if it is less than 1.0, the coercive force decreases.
Even if it exceeds 0, the coercive force will decrease and the object of the present invention will not be achieved.

In the magnetic alloy of the present invention, DY is an essential component for increasing perpendicular magnetic anisotropy and coercive force through the effect of Dy alone or in combination with R.

The magnetic alloy of the present invention is usually provided as a thin film or powder. More preferably, it takes the form of a thin film. This is because higher density magnetic recording is possible in thin films.

The alloy structure may be polycrystalline or amorphous, but it is preferably amorphous because polycrystalline grain boundaries are the main cause of non-uniform physical properties and tend to crease, reducing noise characteristics.

Next, the present invention (7) (Fe s -a Co a )
A method for preparing a z Dy 1-b Rb-based magnetic alloy and a method for producing an amorphous thin film thereof will be exemplified.

The present invention tD (Fe 1-a Co a ) z Dy
The 1-b Rb-based magnetic alloy is obtained as an ingot by melting an alloy material having the above composition at a temperature above the melting point in vacuum, an inert gas or reducing gas atmosphere by a well-known method, and then cooling the melted material.

This ingot is cut into appropriate dimensions to obtain a sputtering target (cathode), which is then used to deposit Dy-Fe-C on a glass substrate, for example.

By sputtering the alloy, an amorphous thin film magnetic alloy is obtained.

The amorphous thin film magnetic alloy obtained in this way has magnetic anisotropy in the direction perpendicular to the film surface (C-axis), and as this direction is the axis of easy magnetization, the temperature is 50°C to 200°. There is one key point between C, and the absolute value of the saturation magnetostriction constant is 1.
Since it is less than ×10 −5 , it is suitable for magnetic recording media with excellent noise characteristics, and particularly for magneto-optical recording media.

[Embodiments of the invention] Hereinafter, the magnetic alloy of the present invention will be explained in detail with reference to Examples.

Example 1゜(Fe, 5Co, 5)3,35 Dyo, 6Tbo,
An alloy material consisting of 2HO0,2 was melted in a vacuum induction melting furnace and cooled to obtain an alloy ingot. Next, this alloy ingot was cut into appropriate dimensions to produce a sputtering target (cathode).

Using the above target, argon gas pressure 6×10”
A magnetic alloy of the present invention consisting of an amorphous thin film with a thickness of 1000 mm was obtained on a glass substrate by bias sputtering at Torr and a substrate bias voltage of -50 V.

This magnetic alloy has perpendicular magnetic anisotropy, has a saturation magnetic flux density of 4 πMs 600 Gauss, and a coercive force of 5.0.
KOe, Kiley single point 120°C and saturation magnetostriction value (
λ5〈1×10J.

Table 1 shows the specifications of the rewritable disk when it is used as a magneto-optical recording medium.

Comparative Example 1゜Except that the alloy composition is Fe 3.8 Dy,
An amorphous alloy film was produced in the same manner as in Example 1. The obtained amorphous magnetic thin film with perpendicular magnetic anisotropy has a film thickness of 1000A.
, saturation magnetic flux density 750 Gauss, coercive force 1.2K
Oe, key point 65°C1 saturation magnetostriction value λ, )20
It was X10. Table 1 shows the specifications of a rewritable disk using this magnetic thin film as a recording medium.

From Example 1 and Comparative Example 1, CO was added (Fe
1-a Co a ) z Dy 1-b It is clear that the Rb-based low magnetostriction amorphous magnetic thin film exhibits an excellent S/N ratio compared to the DY-Fe-based magnetic thin film, which has a large magnetostriction value.

In addition, the Kerr rotation angle was also improved by the addition of CO, and the synergistic effect of the two brought about a significant improvement in the SA ratio.

Table 1 Examples 2 to 6 and Comparative Examples 2 to 5 Using nine types of alloy materials of Examples 2 to 6 and Comparative Examples 2 to 5 having the compositions (atomic atoms) shown in Table 2, Example 1 and Comparative Examples 2 to 5 were used. A magnetic alloy consisting of an amorphous alloy film was obtained in a similar manner.

The film thicknesses, saturation magnetic flux densities, Kiley points, and saturation magnetostriction constants of these magnetic alloys are shown in Table 2 together with their compositions.

As is clear from Table 2, the magnetic alloy of the present invention (Example 2
-6) have significantly smaller absolute values of saturation magnetostriction constants than the magnetic alloys of Comparative Examples 2-5.

Blank space below [Effects of the Invention] As is clear from the above explanation, the magnetic alloy of the present invention exhibits magnetic anisotropy due to the internal stress applied during processing, since the absolute value of the saturation magnetostriction constant is less than I Since the properties are not subject to microscopic fluctuations and the uniformity of physical properties is maintained, the resulting magnetic recording medium has excellent noise characteristics. )
deterioration of the characteristics of the medium due to thermal disturbances at times is prevented;
■Additionally, the addition of COa increases the Kel rotation angle of the magneto-optical recording medium, and the noise characteristics are significantly improved due to the synergistic effect of item 2.■7. Since it is an alloy, it has excellent uniaxial magnetic anisotropy and coercive force characteristics, ■A single point of key is 50~2
Since the temperature is between 00°C and magneto-optical writing does not require much energy, its industrial value is extremely high.

Agent: Patent attorney: Nori Chika, Yu (1 other person)

Claims (3)

[Claims] (1) (Fe 1-a Co a )z Dy 1-
b Rb (where R: one or a combination of two or more of Gd, Tb, Ho, Er) 0.2 ≦a≦0,7 0.02≦b≦0.8 1.0≦2≦ 40. A magnetic alloy characterized in that: (2) Claim 1 in which the shape of the magnetic alloy is a thin film.
Magnetic alloys described in section. (3) The magnetic alloy according to claim 1, wherein the magnetic alloy is amorphous.