JPH0782672B2 - Magnetic thin film recording medium - Google Patents

Description

The present invention relates to a magnetic thin film recording medium used for optical (thermo) magnetic recording, thermomagnetic transfer, magnetic display elements and the like.

[Prior art]

In a magnetic thin film recording medium having an easy axis of magnetization in the direction perpendicular to the film surface, for example, by irradiating a light beam such as a laser and applying a bias magnetic field to the irradiation area, the irradiation area is uniformly magnetized. Information can be recorded by creating an inverted magnetic domain in the direction opposite to the magnetization direction of the region and associating the presence or absence of this inverted magnetic domain with “1” or “0”. Then, the information thus recorded can be read by utilizing the magneto-optical effect. Therefore, this kind of magnetic thin film recording medium is under development as a magneto-optical disk which can satisfy various requirements such as high density, large capacity and high speed access.

As a ferromagnetic thin film recording medium having an easy axis of magnetization in a direction perpendicular to the film surface and capable of high-density magnetic recording and usable as a beam addressable file, there is conventionally known one as shown in FIG. There was something like the one shown.

In FIG. 4, reference numeral 1 denotes a transparent substrate, which is formed of a flat glass substrate or a resin substrate in which a groove is formed so that tracking can be easily performed when the disc is rotated or in which a groove is not formed. Reference numeral 2 denotes a magneto-optical recording layer provided on the substrate 1, which is a polycrystalline metal thin film typified by MnBi or a compound single crystal thin film such as magnetic garnet or Gd-Co, Gd-Fe, Tb-F.
e. Dy-Fe, Gd-Tb-Fe, Tb-Co-Fe and other rare earth-transition metal amorphous thin films.

Further, in order to write on such a ferromagnetic thin film recording medium, the recording / reproducing / erasing apparatus as shown in FIG. 5 is actually used. LD is a laser diode, L is a collimator lens, P is a polarizer, and OL is an objective (condensing lens), which constitute a polarized laser irradiation optical system for the recording medium RM. BMC is a bias magnetic field applying coil, which constitutes a recording / erasing system together with the polarized laser irradiation optical system. M ₁ , M ₂ are half mirrors, A ₁ ,
A ₂ is an analyzer, PD ₁ and PD ₂ are photo diodes, and DAMP is a differential amplifier. These are magneto-optical effects (rotation directions of polarization planes of reflected light and transmitted light depending on the magnetization direction of the recording medium RM). However, different effects are used) to construct a playback system.

At the time of writing, the recording medium magnetized in one direction as shown in FIG. 6A is irradiated with the laser beam 4 as shown in FIG. 6B, and at the same time, the bias magnetic field Hex is applied by the bias magnetic field applying coil 5. And then in the state
When the laser beam 4 is turned off as shown in FIG. 6C, a reversed magnetic domain (bit having a diameter of 1 to 2 μm) is formed in the irradiated region.

[Problems to be solved by the invention]

However, the recording medium having only the magneto-optical recording layer 2 provided on the substrate 1 as described above has the following drawbacks.

That is, although the one using the polycrystalline thin film as the magneto-optical recording layer 2 has a large coercive force of several KOe at room temperature,
It is thermally unstable due to the phase transformation, and the Curie temperature is high (for example, the Curie temperature Tc is 360 ° C for MnBi), the laser power required for writing is several tens.
There were drawbacks such as increase in mW and noise of light scattering due to grain boundaries that cannot be ignored.

Also, in the case of using a compound single crystal thin film, this is also recorded using the Curie temperature, but the Curie temperature is high (for example, in the case of magnetic garnet, the Curie temperature is approximately
280-300 ° C. Therefore, there is a drawback that a large energy is required for writing and it is difficult to increase the area because it is a single crystal thin film.

In addition, among those using rare earth metal-transition metal amorphous thin films, when recording is performed by using magnetic compensation temperature of Gd-Co, Gd-Fe, etc., the magnetic compensation temperature greatly depends on the composition of the thin film. Therefore, it is difficult to form a film having uniform characteristics, and there is a problem that recorded information is unstable because the coercive force is small.

Further, among those using a rare earth metal-transition metal amorphous thin film, those recorded using the Curie temperature of Tb-Fe, Dy-Fe, Gd-Tb-Fe, Tb-Co-Fe, etc. Curie temperature is typically 10
It has a relatively low value of 0 to 250 ° C and a relatively large coercive force of 2 to 3 KOe or more, but the required bias magnetic field is about 500 Oe, so recording, reproduction and erasing can be performed stably. In addition, in order to suppress heat generation of the bias magnetic field applying coil, the size and weight of the bias magnetic field applying device become large, which has been a major obstacle to downsizing and weight saving of the recording / reproducing / erasing device.

In view of the above problems, the present invention requires less energy required for writing, and can lower the bias magnetic field used during writing and erasing, and as a result, the recording / reproducing / erasing apparatus can be made smaller and lighter. It is an object to provide a magnetic thin film recording medium.

[Means and Actions for Solving Problems]

A magnetic thin film recording medium according to the present invention is provided with a first layer made of a crystalline or amorphous alloy thin film having an easy axis of magnetization in a direction perpendicular to the film surface on a substrate, and is laminated on the first layer. A second layer having an antiferromagnetic-ferromagnetic phase transition temperature lower than the Curie temperature of the first layer is provided, and an inversion domain is formed in the first layer by utilizing the magnetic phase transition of the second layer. Thus, the leakage magnetic field and the magnetic interaction due to the spontaneous magnetization of the second layer act in addition to the bias magnetic field when forming the inverted magnetic domain.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the illustrated embodiment.

FIG. 1 is a cross-sectional view of a magnetic thin film recording medium according to the present invention, in which a transparent substrate 11 is provided with a groove or grooves so that tracking can be easily performed when the disk is rotated. Not made of flat glass substrate or resin substrate. Reference numeral 12 denotes a magneto-optical recording layer (first layer) made of a crystalline or amorphous alloy thin film having an easy axis of magnetization in a direction perpendicular to the film surface provided on the substrate 1, and is, for example, R-Co- Fe
And other rare earth metal-transition metal amorphous films. However, R is one or more metals of Gd, Tb, Dy and Ho. Reference numeral 13 denotes an auxiliary layer (second layer) having an antiferromagnetic-ferromagnetic phase transition temperature (50 to 150 ° C.) lower than the Curie temperature of the magneto-optical recording layer 12 provided on the magneto-optical recording layer 12. And is made of an alloy film such as Fe—Rh—Co. Then, the magneto-optical recording layer 12 and the auxiliary layer 13 are
It is formed by a sputtering method or a vacuum deposition method, and the film thickness thereof is set to 200 to 5000Å, preferably about 1000Å.

The composition of the magneto-optical recording layer 12 is R _x Co _y Fe _1-xy ,
For each atomic ratio x, y, 0.15 ≦ x ≦ 0.35,0.01
It is necessary to satisfy the condition ≦ y ≦ 0.30. That is, if the condition of 0.15 ≦ x ≦ 0.35 is not satisfied, the coercive force appropriate for the recording medium is lost. If y <0.01 is not satisfied with the condition of 0.01 ≦ y ≦ 0.30, the effect of adding Co does not appear.
The car rotation angle θ _k becomes small. If y> 0.30, the coercive force becomes too large, and the Curie temperature becomes too high, so that the energy required for writing becomes large and it becomes unsuitable for recording.

The composition of the auxiliary layer 13 is Fe _a Rh _b Co _1-ab , and the atomic ratios a and b are 0.45 ≦ a ≦ 0.55 and 0.45 ≦ b ≦ 0.5.
It is necessary to satisfy the condition of 0. That is, 0.45
If the conditions ≦ a ≦ 0.55, 0.45 ≦ b ≦ 0.50 are not satisfied,
The present invention does not hold because the alloy film does not have a CsCl structure that causes antiferromagnetic / ferromagnetic phase transition. On the other hand, a film having a composition such as Fe _0.49 Rh _0.49 Co _0.02 that satisfies this condition, as shown in FIG.
Then, a phase transition from antiferromagnetism to ferromagnetism occurs. This phenomenon is reversible, and when the temperature drops below about 65 ° C., the phase transition occurs and the ferromagnetism returns to antiferromagnetism.

Next, a process of forming a reversed magnetic domain when writing is performed on the magnetic thin film recording medium of the present invention will be described with reference to FIG.

First, at room temperature, that is, T <Tp (phase transition temperature of the auxiliary layer) <Tc (Curie temperature of the recording layer), the recording layer 12 is unidirectional in the direction perpendicular to the film surface as shown in FIG. 3 (a). It is magnetized, the auxiliary layer 13 exhibits antiferromagnetism, and does not form spontaneous magnetization. Next, as shown in FIG.
When the bias magnetic field Hex is applied by the bias magnetic field applying coil 15 at the same time, the laser light 1 of the recording layer 12 is irradiated.
The magnetization of the portion indicated by 4 decreases, and disappears when the temperature exceeds the Curie temperature, that is, T <Tc. When the temperature of the auxiliary layer 13 exposed to the laser light is equal to or higher than the phase transition temperature, that is, T> Tp, the phase transitions from antiferromagnetism to ferromagnetism, and the spontaneous magnetization aligns with the bias magnetic field Hex. Next, when the laser beam 14 is turned off, the temperature decreases, but at the phase transition temperature or higher, that is, T> Tp, the auxiliary layer 13 exhibits ferromagnetism, so as shown in FIG. When the layer 12 is cooled to a Curie temperature or lower, that is, Tc>T> Tp, a reversal magnetic domain is formed by a bias magnetic field Hex and a leakage magnetic field and magnetic interaction due to spontaneous magnetization of the auxiliary layer 13. Finally, as shown in FIG. 3D, when the temperature drops to room temperature, that is, Tc>Tp> T, the magnetization of the auxiliary layer 13 returns from ferromagnetic to antiferromagnetic, and the recording layer 12 has an inversion domain. It remains formed.

Thus, although the writing is completed, in the magnetic thin film recording medium of the present invention, the leakage magnetic field and the magnetic interaction due to the spontaneous magnetization of the auxiliary layer 13 act in addition to the bias magnetic field at the time of forming the reversed magnetic domain in the recording layer 12, The bias magnetic field applied from the outside can be small. Further, for the same reason, formation of the reversed magnetic domain, that is, writing is facilitated. In addition, as described above, the recording layer 12
Since the Curie temperature and the magnetic phase inversion temperature of the auxiliary layer 13 are low, the energy required for writing can be small. Therefore, from the above results, downsizing the recording / playback / erasing device,
This has an important practical advantage that the weight can be reduced.

Next, the following table shows the comparison results between the experimental example and the comparative example.

If the bias magnetic field Hex is within the range shown in the above table, there is almost no change in the C / N ratio, which is a measure of the signal quality of the magneto-optical disk.

From the above table, it is clear that the magnetic thin film recording medium of the present invention can reduce the required bias magnetic field as compared with the conventional example.

〔The invention's effect〕

As described above, the magnetic thin film recording medium of the present invention has an important practical advantage that the recording / reproducing / erasing apparatus can be made compact and lightweight.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of an embodiment of a magnetic thin film recording medium according to the present invention, FIG. 2 is a view showing magnetization change characteristics according to temperature of an auxiliary layer of the above embodiment, and FIG. FIG. 4 is a diagram showing a reversed magnetic domain formation process when writing is performed in the above embodiment, FIG. 4 is a sectional view of a conventional example, and FIG.
FIG. 6 is a configuration diagram of the erasing device, and FIG. 6 is a diagram showing a process of forming an inverted magnetic domain when writing is performed in the conventional example. 11 ... Transparent substrate, 12 ... Magneto-optical recording layer (first layer), 13 ...
… Auxiliary layer (second layer), 14 …… Laser light, 15 …… Bias magnetic field application coil.

Claims (1)

[Claims] 1. A first layer comprising a crystalline or amorphous alloy thin film having an easy axis of magnetization in a direction perpendicular to a film surface is provided on a substrate, and the first layer is laminated on the first layer. A magnetic thin film recording medium comprising a second layer having an antiferromagnetic-ferromagnetic phase transition temperature lower than the Curie temperature.