JPH0772946B2 - Magneto-optical recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to magneto-optical recording in which information is recorded, reproduced and erased by using a laser beam, and particularly, the recording sensitivity is high and the ratio of signal and noise at the time of reproduction. The present invention relates to a magneto-optical recording medium having a large magneto-optical effect, which is suitable for improving C / N.

BACKGROUND OF THE INVENTION Recently, as a recording material for magneto-optical recording, which is a rewritable optical recording system, a rare earth-iron group amorphous film, which can obtain a relatively large curve rotation angle, has attracted attention. Among these amorphous films, research and development of a Tb-Fe-Co amorphous film, in which a large value of the Kerr rotation angle θ _k can be obtained, is particularly active.
For example, Japanese Patent Laid-Open No. 58-73746 is a typical example. However, conventional amorphous films including these alloy-based amorphous films have the following problems.

(1) The curl rotation angle is large when the magnetization is saturated, but the Kerr rotation angle in the residual magnetization is small, so that a reproduction signal cannot be obtained sufficiently.

(2) The Kerr rotation angle due to remanent magnetization is relatively large, but the Curie temperature is too high and the recording sensitivity is poor. Therefore, a sufficient reproduced signal cannot be obtained.

(3) The Kerr rotation angle due to remanent magnetization is relatively large, and the Curie temperature is relatively low, but at the time of recording, an unwritable portion occurs at the center of the recording domain, which causes large modulation noise, resulting in sufficient reproduction. Signal-to-noise ratio C /
N cannot be taken.

[Object of the Invention]

The object of the present invention is to achieve a sufficiently high magneto-optical effect and high reproduction.
An object is to provide an amorphous magneto-optical recording material that can obtain a C / N ratio (or S / N ratio) and is suitable for practical use.

[Outline of Invention]

When the amorphous perpendicularly magnetized film was actually used as a magneto-optical recording material, it was considered that the following was required.

(1) It is desirable that the Curie temperature (Tc) is about 250 ° C. or lower in terms of the power limit of semiconductor laser light, recording sensitivity and film life.

(2) Also, the holding power (Hc) is preferably about 1 kOe or more from the viewpoint of thermal stability of recorded information. However, the present inventors have found that not only the above requirements but also the compensation temperature (Tcomp) in addition to the Curie temperature have a great influence on the recording sensitivity, reproduction noise, etc. in the balance with Tc.

The magneto-optical recording medium of the present invention has the following constitution. That is, in a rare earth-iron group magneto-optical recording medium that has an easy axis of magnetization in the direction perpendicular to the film surface and is substantially amorphous, the compensation temperature is equal to or higher than the Curie temperature, or the compensation temperature is higher than the Curie temperature. It is also characterized by being low and the difference being within 100 ° C.

Binary system, ternary system of the rare earth-iron group magneto-optical recording medium,
Alternatively, examples of quaternary materials include Tb-Fe-Co, Tb-Fe, Tb-
Gd-Fe, Tb-Sm-Fe, Tb-Co, Tb-Dy-Fe, Tb-Dy-Fe-C
o, Tb-Gd-Fe-Co, Tb-Sm-Fe-Co, Tb-Er-Fe-Co, Dy
-Sm-Fe-Co etc. are fried.

In addition, the Curie temperature is generally set to 100 ° C. or higher (more preferably 150 ° C. or higher) so that recorded information can be stably present.

However, even if Tc is 250 ° C. or lower, if Tcomp is near room temperature, a recording domain with a uniform shape is not formed during recording,
Therefore, it was found that high modulation noise occurs and C / N at the time of reproduction decreases. This largely depends on the magnitude of saturation magnetization during recording and its temperature change.

If Tcomp is room temperature or higher, Tcomp is Tc or higher, or Tc
Even if it is lower, it is desirable that the difference from Tc is within the vicinity of Tc within 100 ° C, and more preferably within the range of Tc-Tcomp_60 ° C. In general, it has been found that in the rare earth-iron group optical gas recording medium, the composition range satisfying these temperature ranges is limited to the composition side rich in the rare earth element rather than the compensation composition.
As a typical example, FIG. 1 shows the Curie temperature Tc and the compensation temperature Tco of a Tb-Fe-Co amorphous perpendicular magnetization film (Tb _x Fe _100-xy Co _y ).
The dependence of Tb concentration on each Co concentration of mp is shown. The arrow in the figure indicates the Tb concentration of the compensation composition. In the figure, the curve of 1 is y =
30.4 Tc, 2 is y = 17.5 Tc, 3 is y = 11 Tc, 4 is y = 10.3
Of Tc, 5 is Tc of y = 5, 6 is Tcomp of y = 30.4, and 7 is y = 17.5.
, Tcomp of 8 is y = 11, 9 is Tcomp of y = 10.3, and 10 is y
= 5 for each Tcomp. From the figure, it can be seen that as the amount of Co increases, Tc rises, and the Tb concentration at which Tc and Tcomp match shifts to the high concentration side. Well, above Tcomp
It can be seen that the composition near or above Tc is a composition on the high Tb concentration side (that is, a composition richer in Tb element than the compensation composition). Therefore, from the results of FIG. 1, the optimum composition of the Tb-Fe-Co amorphous perpendicular magnetization film is 24 to 30 atomic% of Tb which is richer in Tb element than the compensating composition, 7 to 14 atomic% of cobalt, and the balance is iron. A narrow composition range consisting of elements. Where the car rotation angle θ
_In order to obtain a high value of _k of 0.3 ° (λ = 633 nm) or more, the lower limit of Co content is 8 atom%. Needless to say, it is possible to further improve the characteristics by adding a small amount of another impurity element such as a rare earth element or a transition metal element to the ternary system.

Example of Invention

 The present invention is described above with reference to the embodiments.

The amorphous alloy film of the present invention is 1 × on a Co disk having a diameter of 8 inches.
It was produced by a well-known magnetron sputtering method using a plurality of targets in which 1 cm ² of rare earth elements and transition metal elements such as iron elements were arranged so as to have a predetermined composition in area. Also, as a recording / playback evaluation disk, a tracking groove was formed with UV resin on a 5 ″ φ glass disk, and Tb was formed on it.
-Fe-Co film (film thickness approx. 1000Å), SiO ₂ film (film thickness approx. 700Å)
Was used in this order.

As one example of the present invention, as a representative example of a composition richer in Tb element than the compensating composition, Tb26 Fe62 Co12, Tb28 Fe59 Co1
An amorphous perpendicular magnetization film having a composition such as 3, Tb28.5 Fe60.5, Co11 was used as the recording film. The film characteristics thereof are shown below. Curie temperature Tc = 180 to 230 ℃, compensation temperature Tcomp ≧ 180 ℃, holding power Hc ＝
1 to 8 kOe, saturation magnetization Ms = 100 to 190 emu / cc, Kerr rotation angle θ _k
(Λ = 633 nm) = 0.3 to 0.35 ° In the same manner, a 5 ″ φ multilayer film disk was manufactured using these films. Even in this case, when the recording laser light power was 5 mW to 9 mW, the external magnetic field at the time of recording was 200 Oe. With the above, the modulation noise becomes zero.
Was 51 to 54 dB.

Although Tb-Fe-Co is shown as a representative example of the rare earth-iron group magneto-optical recording medium in the above-described embodiments, the same effect can be obtained in the rare earth-iron group magneto-optical recording medium described above.

As is clear from the above examples, the amorphous perpendicular magnetization film of the present invention has almost no modulation noise and has a high C / N ratio even if the Kerr rotation angle is not apparently increased due to multiple reflection in the interference structure.
It turns out that a value is obtained. An interference multilayer film disk that combines these films and an interference film of ZnS, AlN, Si ₃ N ₄ , BN, SiO, etc., which has a relatively high refractive index, has an even higher C / value of 56 dB or more.
N is obtained.

[Brief description of drawings]

Figure 1 shows the Curie temperature Tc of the Tb-Fe-Co amorphous perpendicular magnetization film.
FIG. 3 is a diagram showing the dependence of each compensation temperature Tcomp on Co concentration, Tb concentration on y, and x dependency.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Sugita 1-280, Higashi Koigakubo, Kokubunji, Tokyo (56) References JP-A 58-159252 (JP, A) JP-A 59 -159510 (JP, A)

Claims (1)

[Claims] 1. A recording medium having a rare earth-iron group amorphous film, which waits for an easy axis of magnetization in a direction perpendicular to the film surface, wherein the recording medium has an atomic ratio of terbium of 24 to 30% and cobalt of 7.
〜14%, the balance is richer in rare earth elements than the compensation composition consisting essentially of iron, and is substantially amorphous, and the Curie temperature is 250 ° C or lower and the compensation temperature is 50 ° C or higher. Magneto-optical recording medium.