JPS63239636A - Magneto-optical recording medium and magneto-optical recording method - Google Patents

Abstract

PURPOSE:To permit over writing like with a magnetic recording medium by providing perpendicularly magnetized films having specific three-layered structure on a substrate and forming the same so as to satisfy prescribed conditions. CONSTITUTION:This medium has at least the perpendicularly magnetized films having the three-layered structure consisting of a 1st magnetic layer 1 having a Curie point T1 and coercive force H1, the 2nd magnetic layer 2 having a Curie point T2 and coercive force H2 and the 3rd magnetic layer having a Curie point T3 and coercive force H3 on the substrate B. The respective magnetic layers are made of the alloy of rare earths and transition metals and have H1>H3>H2 T3>T1>T2. These layers satisfy the conditions expressed by equation I when the apparent magnetic wall energies of the 1st magnetic layer and the 3rd magnetic layer appearing through the 2nd magnetic layer are designated as deltaw13, and the film thicknesses of the 1st magnetic layer and the 3rd magnetic layer are successively designated as h1, h3. A magnetic field generating means is provided on the position separate from a recording head and recording is executed by binary laser power at the time of recording. The good over writing is thereby enabled.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a novel Curie point writing type magneto-optical recording medium that can be read using the magnetic Kerr effect, and an overwritable optical recording medium using the same. Related to magnetic recording methods.

[Conventional technology]

A magneto-optical disk is known as an erasable optical disk memory. Magneto-optical disks have advantages over magnetic recording media using conventional magnetic heads, such as high-density recording and non-contact recording and playback, but on the other hand, the recorded area must be erased before recording. It had the disadvantage that it cannot be magnetized in one direction (it must be magnetized in one direction). To compensate for this drawback, proposals have been made such as a method in which a recording/reproducing head and an erasing head are provided separately, or a method in which recording is performed while irradiating a continuous laser beam while simultaneously modulating the applied magnetic field.

[Problem that the invention seeks to solve]

However, these methods have disadvantages such as a large-scale apparatus, high cost, or inability to perform high-speed modulation.

The present invention was made in order to eliminate the drawbacks of the conventional example mentioned above, and by using a new magneto-optical recording medium, a magnetic field generating means of a simple structure is added to the conventional device configuration. Just like magnetic recording media, overwriting (
The purpose of the present invention is to provide a magneto-optical recording method that enables overriding.

(Means for solving the problem) The above object can be achieved by the present invention as follows.
Three layers consisting of a first magnetic layer having a Curie point T1 and a coercive force H1, a second magnetic layer having a Curie point T2 and a coercive force H2, and a third magnetic layer having a Curie point T3 and a coercive force H3. A magneto-optical recording medium having a perpendicular-uniform structure on at least a substrate, wherein (A) each magnetic layer is an alloy of rare earth and transition metal; (B) H+ > H3 > H2 T 3> T + > 72, (C) the first Mi layer and the third v appearing through the second magnetic layer
Assuming that the apparent domain wall energy of the magnetic layer is σ"13, and the film thicknesses of the first magnetic layer and the third magnetic layer are 1, h3, and H3 in that order, then a magneto-optical recording medium that satisfies the following is used. This is a recording method whose representative aspects will be shown later.

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

FIGS. 1(a) and 1(b) are schematic cross-sectional views each showing an embodiment of a magneto-optical recording medium used in the present invention. Figure 1 (
The magneto-optical recording medium of a) has a first magnetic layer 1, a second magnetic layer 2, and a third magnetic layer 3 laminated on a transparent substrate B provided with a pre-group. It is. The Curie point of the first magnetic layer 1 is T1, h3, its coercive force is Hl, the third
If the Curie point of the magnetic layer 3 is 3rd and its coercive force is H3, then H,>H3 3rd>T is satisfied.

(The coercive force is at room temperature.) However, normally the T of the first magnetic layer 1 is 70 to 200°C,
H6 is 2 to 10 KOe, and the third of the third magnetic layer 3 is 100
~400° C., and H3 is preferably set within a range of about 0.1 to 4 KOe. Curie point T2 of second magnetic layer, coercive force H
The details of 2 will be explained later.

The first &fi layer 1 and the third magnetic layer 3 of the magneto-optical recording medium of the present invention are relatively weakly coupled via the second magnetic layer.

In the magneto-optical recording medium of the present invention, the apparent domain wall energy between the first magnetic layer 1 and the third magnetic layer 3 appearing through the 26i-th layer is σWI3, and the film thickness of the first magnetic layer 1 is hl+3. Assuming that the film thickness of the magnetic layer 3 is H3, and the order of the saturation magnetization of these layers is "gI+MS3," the two magnetic layers 1.3 are coupled so as to satisfy the following equation.

−＜　　H.

2Ms, h.

□<H3 Ms3h3 The reason why such a combination is necessary will be discussed in detail later, but in Kanto terms, it stabilizes the magnetization of the bit (the state shown in Figure 2 ()) that is finally formed during recording. Therefore, the film thickness, coercive force, magnitude of saturation magnetization, domain wall energy, etc. of the two magnetic layers 1.3 may be set so as to satisfy the above relational expression.

The materials of each magnetic layer include GdCo, GdFe, TbFe, which exhibit perpendicular magnetic anisotropy and magneto-optic effect.
DyFe, GdTbFe, TbDyFe, Gd
FeCo, TbFeCo, GdTM:o.

An amorphous magnetic alloy of a rare earth element and a transition metal element such as GdTbFeGo can be used.

In FIG. 1(b) which is another example of the magneto-optical recording medium of the present invention, 4 and 5 are for improving the durability of the three magnetic layers 1 and 2.3 or for improving the magneto-optical effect. It is a protective film.

6 is an adhesive layer for bonding the bonding substrate 7 together. If layers 1 to 5 are laminated on the bonding substrate 7 as well, and these are bonded 1-, recording and reproduction can be performed on the front and back sides.

The recording process of the present invention will be described below using FIGS. 2 to 4.

35 in FIG. 3 is a magneto-optical disk having the configuration described above. For example, the magnetization state of a certain part of this magnetic layer is initially as shown in FIG. 2(a). That is, the second
In the figure, a case will be described in which the magnetization is stable when the magnetization directions of the first and third magnetic layers are parallel (same direction) before recording.

The magneto-optical disk 35 is rotated by a spindle motor and passes through the magnetic field generator 34 . At this time, the magnetic field generating section 3
When the magnitude of the magnetic field 4 is set to a value between the coercive forces of the first magnetic layer 1 and the third magnetic layer 3 (the direction of the magnetic field is upward in this example), as shown in FIG. 2(b), The third magnetic layer 3 is magnetized in a uniform direction, while the magnetization of the first magnetic layer 1 remains the same.

Next, the magneto-optical disk 35 rotates and the recording/reproducing head 3
1, a laser beam having two types (first type and second type) of laser power values is transmitted to a recording signal generator 3.
According to the signal from 2, the disk surface is irradiated with either power. The first type of laser power is enough to raise the temperature of the disk to around the Curie point of the first magnetic layer 1, and the second type of laser power is enough to raise the temperature of the disk to around the Curie point of the third Wl magnetic layer 3. It is a power that can be heated. That is, both magnetic layers 1. In Figure 4, which shows an outline of the relationship between the coercive force and temperature of -3, the first type of laser power is near T1 (at a temperature close to TI, the magnetization direction of the first magnetic layer is uniformly changed to the third (temperature that allows alignment in a stable direction with respect to the orientation of the magnetic layer), and the second type of laser power is T
The temperature of the disk can be raised to around 3 (a temperature close to T3, at which the direction of magnetization of the third Idi layer can be uniformly reversed).

The temperature of the first magnetic layer 1 and the third magnetic layer 3 is raised to near the Curie point of the first ifi layer 1 by the first type of laser power, but bits stably exist in the third magnetic layer 3 at this temperature. By setting the bias magnetic field appropriately, recording bits as shown in Fig. 2(C) can be formed from either magnetization state shown in Fig. 2(b). (Type 1 preliminary record).

Here, setting the bias magnetic field appropriately means the following.

In the first type of preliminary recording, the magnetization of the first magnetic layer 1 is subjected to a force (exchange force) that aligns it in a stable direction (here, in the same direction) as the direction of magnetization of the third magnetic layer 3. does not require a bias magnetic field. However, in the preliminary recording of the second type of laser power, which will be described later, the bias magnetic field is applied to the third magnetic layer 3.
The direction is set to assist in magnetization reversal. For convenience, it is preferable that the bias magnetic field is set to have the same magnitude and direction in preliminary recording with either the first type or the second type of laser power. From this point of view, it is preferable to set the bias magnetic field to the minimum size necessary for preliminary recording of the second type of laser power according to the principle shown below, and this point was taken into consideration in the previous section. This means setting it appropriately.

On the other hand, with the second type of laser power, the third Wl property layer 3
When the temperature of the disk is raised to near the Curie point (second type of preliminary recording), the direction of magnetization of the third if-sensitive layer 3 is reversed by the bias magnetic field. Subsequently, the magnetization of the first Wt magnetic layer 1 is also aligned in a stable direction (here, in the same direction) with respect to the third magnetic layer 3.

In other words, from either magnetization state in FIG. 2(b), FIG.
d) Preliminary recording bits are formed.

In this way, the bias magnetic field and the first
Depending on the laser power of the seed and the second type, each location on the magneto-optical disk is preliminarily recorded in the state shown in FIG. 2(C) or FIG. 2(d).

Next, rotate the magneto-optical disk 35 to record bits (C).
, (d) passes through the magnetic field generating section 34 again, the magnetic field generating section 34 is divided into the first magnetic layer 1 and the third!, as described above. f!
Since the recording bit (C) is set between the sexual layers 3 and 3, no change occurs and the recording bit (C) remains in the state (e). On the other hand, the recorded bit (d) is caused by magnetization reversal in the third magnetic layer 3 (Cf)
becomes the state of

In order for the state of the recorded bits (') to exist stably, as described above, σW13 − < H.

2Ms+h+ σW11 <H3 Ms3h3 It is necessary that the

Here, σ19+3/2Ms, h indicates the strength of the exchange force acting on the first magnetic layer. In other words, σWI372M5lh
The direction of magnetization of the first Wl layer is changed by a magnetic field of magnitude l, and the direction of magnetization of the first Wl layer is
An attempt is made to orient it in a direction that is stable (in this case, in the same direction) as the direction of magnetization of the magnetic layer. Therefore, in order to prevent the magnetization of the first rdi layer from reversing against this magnetic field, the first Wt
It is sufficient that the coercive force H of the magnetic layer is larger than this exchange force.

In other words, it is sufficient if σW+3/2Ms+t+, <H+.

Similarly, in the third magnetic layer, σW13.
/ 2M53t+3, an exchange force acts to align the magnetization of the 16th tA layer in a stable direction, so (
In order for the recording bit of f) to be stable, σW13/2M53
It is sufficient if hs<Ha.

In order to satisfy this condition (the coercive force is larger than the exchange force acting on both the first and third magnetic layers), that is, the first and third ff! In order to reduce the exchange force acting on the magnetic layer, the film thickness and saturation magnetization of both layers can be adjusted as described above, but since there is an appropriate value for the recording sensitivity or coercive force, you can adjust it arbitrarily. cannot be set. Therefore,
In the present invention, by providing the second Mi layer with a very small thickness of, for example, 10 to 150 layers, the exchange interaction acting at the interface between the first magnetic layer 1 and the third magnetic layer 3 is suppressed, and the second magnetic layer This made it possible to reduce the apparent size of 0w13 appearing through the layers.

Regarding the coercive force of the second magnetic layer, during the first type of preliminary recording, in FIG. 2(b), the magnetization of the second magnetic layer is uniform.
It is desirable that they be arranged in the same direction.

Therefore, when the disk rotates and passes through the magnetic field generating section 34, it is desirable that the magnetization of the second &Ii magnetic layer be arranged in a stable direction with respect to the magnetic field, similar to the magnetization of the third magnetic layer. .

Further, since it is desirable that the second magnetic layer is always aligned in a stable direction with respect to the direction of magnetization of either the first magnetic layer or the third magnetic layer, it is preferable that the coercive force H2 is small.

Therefore, the relationship of coercive force may be set as Hr > 83 > 82.

The material used for the second iH layer is different from the first and second magnetic layers.
Although it is an alloy of the same rare earth element and transition metal element, it is necessary that the Curie temperature is lower than that of the first magnetic layer. This is due to the following reasons.

The magnitude of the exchange force (the force that aligns the magnetic moments of each atom in a certain direction) acting on the interface between the first filtration layer and the third magnetic layer depends on the type and number of atoms coordinated at each interface. It is determined by the exchange constant between each atom (indicating the magnitude of interaction) and the Curie temperature of each layer.

The Curie temperature is involved because, for example, above the Curie temperature, the alignment of magnetic moments disappears due to thermal motion, and therefore the exchange force ceases to work. Therefore,
When the Curie temperature of the second magnetic layer provided between the first and third magnetic layers is low (close to room temperature), it is difficult for magnetic moments to align due to thermal motion even at room temperature.
The exchange force acting between the magnetic layer and the third magnetic layer can be reduced. In reality, in a configuration in which a second magnetic layer whose Curie temperature is below room temperature is sandwiched between the first and third magnetic layers, the exchange force from both the first and third magnetic layers causes the second magnetic layer to become magnetic even at room temperature. We also confirmed through experiments that an array of moments occurs.

In the recording method of the present invention, the recording bit states (e) and (f
) is controlled by the laser power during recording and does not depend on the state before recording, so it is possible to override
is possible. Recording bits (e) and ([) are irradiated with a laser beam for reproduction, and the reproduction light is transmitted to a recording signal regenerator 33.
It can be played back by processing it.

In the explanation of FIG. 2, an example is shown where the magnetization direction of the 111Ii magnetic layer 1, the second magnetic layer 2, and the third ifi magnetic layer 3 are parallel to each other. The same can be said of a magnetic layer that is stable when .

[Example] Example 1 A polycarbonate disc-shaped substrate with pregroup and preformat signals engraved thereon was placed in a sputtering apparatus equipped with four target sources at a distance of 11 mm from the target.
They were set at 10 cm intervals and rotated.

Sputtering speed 7 from the first target in argon
A protective layer of Sf and N4 was formed to a thickness of 650 mm at a sputtering pressure of 8 x 10-3 Torr.

Next, in argon, sputtering was performed from the second target at a sputtering rate of 50 people/min and a sputtering pressure of 2 x 10' Torr.
TbFe1l:.

Sputtered alloy, film thickness 300mm, Curie point T.

= Tb at about 160°C, , Fe8. A first magnetic layer of Go was formed. The H of this first magnetic layer itself is approximately 12 KOe.
However, the sublattice magnetization was larger in transition metals.

The above operation was carried out several times, and DyFe alloy was sputtered from the fourth target onto each of the resulting targets at an argon pressure of 2 x 10' Torr, and the Curie point T2 was about 60°C, H2
A second magnetic layer of 500 (Oe) Dy+7Fea3 was provided.

The film thickness is zero (no second magnetic layer is provided at this time)
The number of participants was changed from 10 to 70 in increments of 10. The sublattice magnetization of the second IF layer itself was larger in the transition metal element.

Then, each from a third target in argon,
Sputtering speed 50 people/min, sputtering pressure 2X10'
A TbFeGoCu alloy was sputtered at Torr, the film thickness was 250 mm, T3=approximately 190°C, Tb2. Fe5. Go1
, h3, and Cu 1, h3. The H3 of the third magnetic layer itself was 1.1 Oe, and the sublattice magnetization was larger for the rare earth element.

Next, Si3N4 was sputtered from the first target under the same conditions as before to provide a Si3N4 layer with a thickness of 1200 mm as a protective layer.

Next, each of the substrates on which the film had been formed was bonded to a polycarbonate bonding substrate using a hot melt adhesive to produce a plurality of magneto-optical disk samples.

For each sample created, the bit stability (especially (
) was investigated by applying an external magnetic field and measuring the magnetic field at which the magnetization of the magnetic layer was reversed using a VSM (vibrating sample magnetometer).

In this example, since the magnetization of the third magnetic layer starts to be reversed by a smaller external magnetic field, what was able to be measured was the exchange force σw acting on the third magnetic layer and the three layers 2M52h2.

Next, the sample of the magneto-optical disk was set in the recording/reproducing device, and the magnetic field generator of 2 KOe was set at a linear velocity of about 9 m/sec.
83oIII11 which was focused to about 1μ while passing through
2M1 laser beam with a wavelength of 50% duty
Recording was performed using binary laser powers of 4 mW and 8 mW while modulating the laser beam with lz. The bias magnetic field at the recording head was 1200e.

Thereafter, a 1 mW laser beam was irradiated to perform reproduction, and a binary signal could be reproduced. This experiment was performed on the sample after the entire surface was recorded, and it was checked whether the previously recorded signal component was not detected (in other words, whether it was possible to override it).The above results are summarized in Table 1. show.

In Table 1, in determining whether or not to override, those that are capable of recording binary signals are marked with a circle, those that are not are marked with an x, and those that are incomplete are marked with a Δ. The reason why the recording was insufficient can be correlated with the measured value of the exchange force acting on the third magnetic layer in Table 1 in the bit where the first type bit was performed. That is,
Samples 1-1 and 1-2 have the third largest exchange force! f
This is because the recording bit of (f) does not exist stably because the value is not small compared to the coercive force H3 of the I-type layer.

In sample 1-8, the exchange force acting on both the second ifi layer and the first magnetic layer was so small that type 1 recording could not be performed completely.
This is thought to be because the magnetization of the first magnetic layer cannot be reversed.

Example 2 A magneto-optical disk sample was prepared using the same configuration and materials as in Example 1, except that a fourth target was used and the material and film thickness of the second magnetic layer 2 were changed.

The material of the second magnetic layer used was DV+2TbsFea2. having a Curie temperature of 80°C. DyFeCr whose Curie temperature is 30°C DV+Je7 whose Curie temperature is 5°C
aCrs was used, and the film thickness was varied.

The same evaluation as in Example 1 was performed for each of the prepared samples. The results are shown in Table 2.

Table 2 From the results in Table 1.2, it is clear that by providing a second magnetic layer with a temperature lower than the Curie temperature of the first magnetic layer with an appropriate thickness between the first magnetic layer and the third Mi layer, the third magnetic layer can be It is clear that the exchange forces acting on the layers can be reduced.

Curie temperature, for example, at room temperature or a second temperature below room temperature.
When a magnetic layer is used, the thickness of the second magnetic layer is 5O-150A.
Since the recording bits become stable with a thickness of about do not have.

Comparative Example 1 Example 1 except that the fourth target was used and the following materials were provided at the positions of the second magnetic layer with varying film thicknesses.
A magneto-optical disk sample was fabricated using the same configuration and materials as in Example 2.

The materials used are Si, which is a nonmagnetic layer, and the Curie temperature is the first.
The temperature is 170°C, which is higher than T1 of the magnetic layer, and the coercive force is 3rd.
Tb1 which is 500·(Oe) smaller than the &Ii layer
Two types of 3Fea2CO3 were used and the film thickness was varied.

The same evaluation as in Example 1 was performed for each of the prepared samples. The results are shown in Table 3.

Table 3 From the results in Table 3, the material for the layer provided between the first magnetic layer and the third magnetic layer is Si for the non-magnetic layer, or Tb, 5Fe for the magnetic layer with a Curie temperature of 18 or higher and a coercive force of H3 or lower. ,2
Both Co3 have the effect of reducing the exchange force acting on the third magnetic layer.

However, with Si, which is a non-magnetic material, the appropriate film thickness to enable override is 20 to 40, and it is not necessarily easy to provide it with good reproducibility.
With Co3, overriding is possible even with a film thickness of 150 Å or more, but the sum of the film thicknesses of the first, second, and third Mi layers also increases, which tends to reduce the recording sensitivity of the magneto-optical recording disk.

Furthermore, when the second magnetic layer is not provided as in the present invention,
It is desirable that the third magnetic layer has a thickness of 600 to 10QQ8; if the thickness is small, recording bits tend to become unstable.

〔Effect of the invention〕

As explained in detail above, the magneto-optical medium includes a first magnetic layer having a Curie point T and a coercive force H0, a second magnetic layer having a Curie point T2 and a coercive force H2, and a Curie point T3 and a coercive force H3. and a third magnetic layer having three magnetic layers. In addition, when recording using a medium that meets other predetermined requirements, good overwriting is possible by providing a magnetic field generating means in a position separate from the recording head and recording with binary laser power. became.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) each show the structure of an example of a magneto-optical medium used in the present invention, and FIG. 2 shows the magnetization of the magnetic layer 1.3 during the recording method of the present invention. FIG. 3 is a conceptual diagram of the recording/reproducing apparatus, and FIG. 4 is a schematic diagram showing the relationship between the coercive force and temperature of the first magnetic layer 1 and the third magnetic layer 3. B Transparent substrate with nibli groove, 1.2, 3: Magnetic layer 4.5: Protective layer, 6: Adhesive layer, 7: Substrate for bonding. 31: recording/reproducing head, 32: recording signal generator, 35: magneto-optical disk,

Claims (1)

[Claims] 1) A first magnetic layer having a Curie point T_1 and a coercive force H_1, a second magnetic layer having a Curie point T_2 and a coercive force H_2, and a third magnetic layer having a Curie point T_3 and a coercive force H_3.
1. A magneto-optical recording medium comprising a perpendicularly magnetized film having a three-layer structure including a magnetic layer on at least a substrate, the medium satisfying the following conditions. (A) Each magnetic layer is an alloy of a rare earth element and a transition metal, (B) H_1>H_3>H_2 T_3>T_1>T_2, (C) The first magnetic layer and the third magnetic layer appear through the second magnetic layer. The apparent domain wall energy of the magnetic layer is σw_1_3, and the film thicknesses of the first magnetic layer and third magnetic layer are h in that order.
_1, h_3, σw_1_3/2Ms_1h_1<H_1 and σw_1
_3/2Ms_3h_3<H_3 2) The Curie temperature of the second magnetic layer is below room temperature, and the second
2. The magneto-optical recording medium according to claim 1, wherein the magnetic layer has a thickness of 10 to 150 Å. 3) A first magnetic layer having a Curie point T_1 and a coercive force H_1, a second magnetic layer having a Curie point T_2 and a coercive force H_2, and a third magnetic layer having a Curie point T_3 and a coercive force H_3.
A magneto-optical recording medium having a perpendicularly magnetized film with a three-layer structure consisting of a magnetic layer on at least a substrate, which satisfies the following conditions (
A) to (B), that is, (A) each magnetic layer is an alloy of rare earth and transition metal, (B) H_1>H_3>H_2 T_3>T_1>T_2, (C) via the second magnetic layer The apparent domain wall energy of the first and third magnetic layers that appear is σw_1_3, and the film thicknesses of the first and third magnetic layers are h in that order.
_1, h_3, σw_1_3/2Ms_1h_1<H_1 and σw_1
A recording method characterized by performing the following binary recording using a magneto-optical recording medium that satisfies _3/2Ms_3h_3<H_3. (a) With respect to the medium, at a location different from the recording head,
Applying a magnetic field B of a magnitude sufficient to magnetize the third magnetic layer with coercive force H_3 in one direction but not reversing the direction of magnetization of the first magnetic layer with coercive force H_1, (b) Next, The recording head applies a bias magnetic field and at the same time irradiates laser power sufficient to raise the temperature of the medium to near the Curie point T_1 of the first magnetic layer. The first type of preliminary recording, in which the direction of magnetization of the magnetic layer and the second magnetic layer is aligned in a stable direction with respect to the third magnetic layer, or the medium is recorded until the third magnetic layer reaches near the Curie point T_3 at the same time as applying a bias magnetic field. By irradiating the laser with enough power to raise the temperature, the direction of magnetization of the third magnetic layer is reversed, and at the same time both the first and second magnetic layers are magnetized in a stable direction relative to the third magnetic layer. (c) Next, by moving the medium and passing the prerecorded bits through the magnetic field B, a first type of preliminary recording is performed. For the bits formed by the second type of preliminary recording, the magnetization directions of the first, second, and third magnetic layers are not changed, and for the bits formed by the second type of preliminary recording,
Binary recording in which the magnetization directions of the second and third magnetic layers are reversed in the same direction as the magnetic field B, and the magnetization direction of the first magnetic layer is left unchanged.