JPH10199058A - Magneto-optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a recording medium with read durability, wide low recording margin, and a good bias magnetic field characteristic, and consequently, to obtain an excellent overwriting characteristic. SOLUTION: This magneto-optical recording medium has a recording layer 2, which has a low Curie temp. TC1 and high coercive force and has perpendicular magnetic anisotropy, a recording auxiliary layer 5, which has perpendicular magnetic anisotropy, the Curie tap. TC2 higher than the Curie temp. of the recording layer 2 and the coercive force lower than the coercive force of the recording layer, and an intermediate layer, which is disposed between the recording layer 2 and the recording auxiliary layer 5 and adjusts the exchange bonding forces of both layers. The intermediate layer consists of at least two layers of the first intermediate layer 3 on the recording layer side and the second intermediate layer 4 on the recording auxiliary layer side. The first intermediate layer 3 is a perpendicularly magnetized film having the Curie temp. TC11 higher than TC1 and the second intermediate layer 4 is an intra-surface magnetized film having the Curie temp. TC12 of 100 deg.C<=TC12 <=TC2 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is capable of overwriting binary information by thermomagnetic recording such as a light intensity modulation method.
The present invention relates to a magneto-optical recording medium that performs reproduction by a magneto-optical effect such as the Kerr effect.

[0002]

2. Description of the Related Art As an example of a conventional overwritable magneto-optical recording medium (hereinafter abbreviated as a medium), a first magnetic layer having a low Curie temperature and a high coercive force and a relatively high Curie A two-layer perpendicular magnetization film composed of a second magnetic layer having a low temperature and a low coercive force; and an intermediate layer provided between the two magnetic layers. Since the coercive force of the second magnetic layer is large and the material forming the intermediate layer is made of an inorganic non-magnetic substance or a magnetic material having a composition such that the magnetization component is larger than the perpendicular one at room temperature, A proposal has been made in which the exchange interaction acting between the first and second magnetic layers is suppressed to an appropriate magnitude and the recording bit is made to exist stably (see JP-A-63-239637). Hereinafter, this is referred to as Conventional Example A.

In Conventional Example A, the intermediate layer has a Curie temperature of room temperature or higher and a Curie temperature of the recording layer or lower, and has an in-plane magnetized film of Dy ₁₅ Fe ₈₅ (Curie temperature of 60 ° C.),
Tb ₇ Dy ₆ Fe ₈₃ Cr ₄ (Curie temperature 50 ° C.)
Good overwrite characteristics, 20-50mm thick
It is said that the film thickness range is wider than the above and other materials.

Further, a first magnetic layer having a low Curie temperature and a high coercive force and exhibiting perpendicular magnetic anisotropy, and a first magnetic layer having a relatively high Curie temperature and a low coercive force having a perpendicular magnetic anisotropy A second magnetic layer provided between the two magnetic layers and exhibiting in-plane magnetic anisotropy at room temperature and exhibiting perpendicular magnetic anisotropy at elevated temperature.
By comprising the magnetic layer (intermediate layer),
It is known that the exchange force acting between the first and third magnetic layers is adjusted so that a greater exchange force acts at a higher temperature when recording is performed than at room temperature (Japanese Patent Laid-Open No. 63-316343).
No.). Hereinafter, this is referred to as Conventional Example B.

[0005]

However, with respect to the above-mentioned conventional example A, the present inventor has proposed that the Dy ₁₅ Fe ₈₅ , Tb ₇
As a result of conducting detailed research on materials such as Dy ₆ Fe ₈₃ Cr ₄ , overwrite characteristics, in particular, stability against low power recording (hereinafter, referred to as low recording) and reproduction (read) (hereinafter, referred to as read durability). In terms of the above, there was not found any one satisfying both characteristics. This is presumably because it is difficult to obtain a clear and steep threshold value for the temperature between the medium temperature that has risen during reproduction and the medium temperature that has risen during low recording. In other words, it is recognized that the above materials have a Curie temperature that is too low, and thus lead durability tends to deteriorate. Further, the above-mentioned materials have a very narrow suitable composition range, and thus cannot be said to be suitable for mass production.

In the case of the above-mentioned conventional example B, if an attempt is made to provide the intermediate layer with characteristics of in-plane magnetic anisotropy at room temperature and perpendicular magnetic anisotropy at elevated temperature, the Curie temperature of most materials is reduced. As a result, there is a problem in recording magnetic field sensitivity characteristics and the like. That is, the temperature range in which the recording layer and the recording auxiliary layer are exchange-coupled becomes too wide, and it is difficult to reverse the magnetization direction of only the recording auxiliary layer by the recording magnetic field in a state where these exchange couplings are cut off at a high temperature.

This is based on the following reasons. Conventionally, materials having the property of in-plane magnetic anisotropy at room temperature and perpendicular magnetic anisotropy at elevated temperatures have been known as materials exhibiting spin rearrangement due to temperature, particularly electron spin rearrangement. For example, Conventional Example B describes that DyCo ₅ changes its easy axis of magnetization in the temperature range of 50 to 100 ° C. from the in-plane direction of the substrate surface to the vertical direction. Conventionally, the saturation magnetization of the magnetic thin film is represented by M _S , and the uniaxial anisotropy in the direction perpendicular to the film surface is represented by H
When _K, to the magnetic thin film with perpendicular magnetization direction in the film plane, it is necessary that H _K ≧ 4πM _S. Therefore, in order to satisfy the above condition, the Curie temperature of the intermediate layer should be set near the recording temperature of the recording auxiliary layer (approximately 200
℃ or more). That is, since there is a reduction in the sudden M _S near the Curie temperature can be an H _K ≧ 4πM _S at room temperature H _K <4πM _S is a thing recording temperature range.

However, the TbG shown in the prior art B
The dFe film has a Curie temperature as low as about 150 ° C., and in the case of an actual high C / N medium, the Curie temperature of the recording layer is generally around 200 ° C., so that the TbGdFe film cannot be used practically. Therefore, a GdFeCo film is often used. However, since this film does not contain Tb, the magnetic anisotropy is small, and the reproducibility of forming a perpendicular magnetization film immediately before the Curie temperature is extremely unstable. In addition, the magnetic anisotropy and the Curie temperature fluctuate due to the fluctuation of the internal stress of the intermediate layer, the recording layer and the recording auxiliary layer due to the fluctuation of the film forming conditions, or the fluctuation of the composition of these magnetic layers.
In the case of a dFeCo film, it is difficult to express these characteristics uniformly and with good reproducibility.

Further, since the exchange coupling force due to the perpendicular magnetization generated in the GdFeCo film is too small, it is difficult to reverse the magnetization direction of the recording layer by the exchange coupling force.
Therefore, raw recording is impossible, or even if possible, the reproduction sensitivity is insufficient. In order to avoid this, it is possible to make the composition richer in rare earth elements (hereinafter, referred to as RE) and set the compensation temperature around 200 ° C. to increase the exchange coupling force due to the perpendicular magnetization around the compensation temperature. However, since the Curie temperature is as high as 350 ° C. or more, the magnetization of the intermediate layer sufficiently remains near the Curie temperature of the recording auxiliary layer.
As a result, the recording auxiliary layer and the intermediate layer are exchange-coupled, and it is necessary to increase an effective bias magnetic field for reversing the magnetization direction of the recording auxiliary layer. The magnetic field characteristics will be significantly degraded.

Accordingly, the present invention has been completed in view of the above circumstances, and an object thereof is to have read durability and good low recording characteristics, and as a result, to have excellent overwrite characteristics. It is in.

[0011]

The magneto-optical recording medium of the present invention comprises: a recording layer having perpendicular magnetic anisotropy and a Curie temperature of T _C1 ;
A perpendicular magnetic anisotropic recording auxiliary layer having a higher Curie temperature T _C2 and a lower coercive force than the recording layer; and an intermediate layer provided between the recording layer and the recording auxiliary layer for adjusting the exchange coupling force of both layers. Wherein the intermediate layer comprises at least two layers, a first intermediate layer on the recording layer side and a second intermediate layer on the recording auxiliary layer side, wherein the first intermediate layer is A perpendicular magnetization film having a Curie temperature T _CI1 higher than T _C1 ,
The intermediate layer has a Curie temperature T _CI2 of 100 ° C. ≦ T _CI2 ≦ T _C2
Characterized in that it is an in-plane magnetic film.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a basic structure of a magnetic layer according to the present invention.
Is shown in the sectional view. In FIG. 1, reference numeral 1 denotes a disc-shaped substrate on which a pregroove is formed, made of a material such as plastic such as polycarbonate or glass, and 2 denotes recording and reproduction of binary information (0, 1) depending on whether the perpendicular magnetization is upward or downward. 3 is a first intermediate layer of the perpendicular magnetization film (exchange coupling force adjusting layer: Interface Wall Energy Controlling Layer).
Hereafter, the first int layer is abbreviated), 4 is the second intermediate layer of the in-plane magnetized film (hereinafter, abbreviated as the second int layer), 5 is the magnetization direction reversed by a bias magnetic field (recording magnetic field) at a high temperature. Enabled recording auxiliary layer (Writing Layer,
And a control layer (Switching) 6 which has a low Curie temperature and interrupts exchange coupling between the magnetic layers above and below it at a high temperature.
An initialization layer (Initializing Layer, hereinafter abbreviated as I layer) which has the highest Curie temperature and initializes the magnetization directions of the S layer 6 and the W layer 5 when the temperature is lowered. It is. The magnetic layers other than the first int layer 3 are perpendicular magnetization films. Further, the first int layer 3 and the second int
The intermediate layer composed of the t layer 4 is hereinafter referred to as an int layer.

Each of the above magnetic layers is basically made of Cr, Fe, C
Transition metal elements such as o, Ni, and Cu
lement, hereinafter abbreviated as TM), Nd, Sm, Gd,
It is made of an amorphous alloy with RE, such as Tb, Dy, and Ho. In the above-described layer structure, Si ₃ N is provided between the substrate 1 and the M layer 2.
_{4. A} protective layer made of amorphous SiN or the like and a Kerr rotation angle enhance layer may be laminated, or the above-mentioned protective layer may be further laminated on the I layer 7.

The int layer of the present invention has at least a first in
It is composed of a t-layer 3 and a second int layer 4, and another magnetic layer, a non-magnetic layer, a protective layer, and the like may be laminated thereon or inserted as an intermediate film. For example, the first int layer 3 and the second
A magnetic layer that has in-plane magnetic anisotropy at room temperature and perpendicular magnetic anisotropy at elevated temperature may be provided between the int layers 4 as an intermediate film.

FIG. 2 is a magnetization phase diagram for explaining a basic mechanism of direct overwriting (hereinafter, referred to as overwriting) by a light intensity modulation method (Journal of the Japan Society of Applied Magnetics Vol. 14, p165-170, NO.2, 1990). In the figure, the net magnetization direction of each magnetic layer is represented by a combined vector of the TM sublattice magnetization and the RE sublattice magnetization, and the reading (reproduction) of information by the Kerr effect involves the TM sublattice magnetization. The magnetic composition is such that the M layer 2 is TM rich (composition in which TM sublattice magnetization is dominant), the W layer 5 is RE rich (composition in which RE sublattice magnetization is dominant), the S layer 6 is TM rich, and the I layer 7 is RE
Rich, the W layer 5 and the I layer 7 have a compensation temperature above the _room temperature T _room . Curie temperature of M layer 2 is T _c1 , W layer 2
Curie temperature is T _c2, compensation temperature is T _comp2 , S layer 6
If the Curie temperature of the I layer 7 is T _c3 , the Curie temperature of the I layer 7 is T _c4, and the compensation temperature is T _comp4 , T _room <T _c3 <T
_comp2 <a _{T c1 <T comp4 <T c2} <T c4. If the maximum temperature during low recording by the low-temperature process is T _L and the maximum temperature during high recording by the high-temperature process is T _H , then T T
In _L ≒ T _c1 is a T _H ≒ T _c2.

FIG. 3 is a graph showing the relationship between the coercive force H _C of the M layer 2, the W layer 5, the S layer 6, and the I layer 7 and the temperature. At room temperature, the coercive force of the I layer 7 is the largest, followed by the M layer 2, the W layer 5, and the S layer 6. The S layer 6 has the lowest coercive force and Curie temperature, and its magnetization disappears at about 140 ° C. W layer 5
The I layer 7 has a divergent coercive force near the compensation temperature. When the M layer 2 and the W layer 5 are compared, the M layer 2 has a low Curie temperature T _C1 and a high coercive force, and the W layer 5 has a relatively high Curie temperature T _C2 and a low coercive force.

In FIG. 2, the state before overwriting is a state of T _room , in which the TM sublattice magnetization of the M layer 2 is directed downward (first state from the top left, and the binary information "
1 ”), or the TM sublattice magnetization of the M layer 2 is upward (first state from the left in the bottom row, temporarily
0 "). In the low-temperature process, a low-level beam of a laser beam pulse-modulated into two levels of high and low is irradiated, so that the temperature is raised starting from one of the two states. When returning to T _room , "1"
The state is unified. At this time, when starting from the “0” state, the W sublayer 5 has the TM sublattice magnetization and R before and after T _comp2.
Since the magnitude relation of the E sublattice magnetization is inverted and the net magnetization direction changes downward at a temperature _higher than T _comp2 , the magnetization direction of the M layer 2 is inverted by the exchange coupling force to change to the “1” state. .

In the high-temperature process, the laser beam is irradiated with a high-level beam, so that the temperature is raised starting from one of the two states, and is unified to the "0" state when returning to T _room. . In this case, starting from any state, the magnetization of the M layer 2 and the S layer 6 disappears, and the magnetization of the W layer 5 also disappears or is in a very small state (1 from the bottom right).
Or the second state). At this time, the net magnetization direction of the W layer 5 is reversed by the bias magnetic field, and the magnetization direction of the M layer 2 is made uniform by the exchange coupling force near T _c1.
As the temperature decreases, the magnitude relationship between the TM sub-lattice magnetization and the RE sub-lattice magnetization of the W layer 5 is _inverted near T _comp2 , and the W layer 5 is _initialized at T _room by the exchange coupling force of the I layer 7 through the S layer 6. In the “0” state after the high-temperature process, since the directions of the TM sub-lattice magnetization and the RE sub-lattice magnetization of the M layer 2 and the W layer 5 are different, an interface domain wall is generated at the interface.

In order for the recording bit state (“0” or “1”) of the M layer 2 to be stable, the magnetization of the M layer 2 is M _SM , the thickness is h _M , and the magnetization of the W layer 5 is M _SW , the thickness is h _W, and the domain wall energies of the M layer 2 and the W layer 5 are represented by σ _W.
H _CM > σ _W / (2M _SM h _M ), H _CW > σ _W / (2M _SW h
_W ) should be satisfied. However, H _CM in coercivity of the M layer 2, H _CW is the coercivity of W layer 5, the sigma _W
/ (2M _SM h _M ) and σ _w / (2M _SW h _W )
And the exchange coupling force acting on each of the W layer 5. An int layer is provided to suppress the exchange coupling force and maintain the stability of the recording bit.

In the low-temperature process, the M layer 2
Of when the coercive force is reduced, in order to reverse the magnetization direction of the recording bit of the M layer 2 by the exchange coupling force, H _CM <
σ _W / (2M _SM h _M ). It is important that the following three temperatures exist independently in terms of good overwrite recording and read durability.

(A) Temperature near the Curie temperature of the M layer 2 at which a magnetic transfer operation from the W layer 5 to the M layer 2 occurs (low recording temperature).

(B) A temperature near the Curie temperature of the W layer 5 at which a writing operation to the W layer 5 by a bias magnetic field occurs (high recording temperature).

(C) The temperature below the Curie temperature of the S layer 6 and at which the initialization operation of the W layer 5 occurs (initialization temperature).

In particular, regarding the low recording temperature of (a),
A bias magnetic field in the opposite direction (upward in FIG. 2) to the magnetization reversal direction (downward in FIG. 2) of the M layer 2 is applied. Although no bias magnetic field is applied during reproduction, the low recording start temperature (low power minimum) Value) and the medium temperature at the maximum reproduction power at the time of reproduction in a state where the recording bit is stably maintained, although the difference is subtle, though it is actually an important temperature.

FIG. 4 illustrates the change in C / N with respect to the laser power of the M layer 2. Curves a and b show characteristics during reproduction, and curve c shows characteristics during high recording. Generally, when only the magnitude of the exchange coupling force is adjusted by providing one int layer, when the exchange coupling force is reduced, there is read durability, that is, the maximum power at the time of reading is increased, but the low recording margin is narrow. The low recording sensitivity decreases (characteristics represented by curves b and c). On the other hand, when the exchange coupling force is increased, the row recording margin is expanded and the row recording sensitivity is improved, but the read durability is deteriorated (characteristics represented by curves a and c).

In order to solve such a problem, int
It has been proposed to apply a layer having a magnetic transition temperature such as in-plane magnetic anisotropy at room temperature and perpendicular magnetic anisotropy at high temperature. FIG. 5 shows the M layer 2 in that case.
5 shows the change in C / N with respect to the laser power of the present invention. C / N shows a steep change with respect to the laser power, so that it has read durability and a sufficient low recording margin can be secured.

The present invention has the same characteristics as FIG.
The characteristic will be specifically described with reference to FIG. In the figure, a curve d is a characteristic at the time of reproduction, and a curve e is a characteristic at the time of high recording. It is assumed that overwrite recording and reproduction are performed at a rotation speed of the medium of 3600 rpm. First, a bit for overwrite recording is irradiated with a laser for reproduction, and its power is gradually increased to measure C / N during reproduction. . At the time of reading (curve d), reproduction is performed with a linearly polarized laser without a bias magnetic field. However, in an actual system, read durability up to 2 mW is required. C / N over 2mW
Starts decreasing because the magnetization direction of the recorded bit has been reversed or the magnetization has started to decrease, which means that the row recording has started. For low recording and high recording, low power P _L = 4 mW and high power P _H = 10 m
W, duty is performed by a laser pulse pulse-modulated to 50%, and at the time of high recording (curve e), a bias magnetic field of 300 Oe is applied. The power width between the curve d and the curve e is a low recording margin in which the low recording can be performed, and it is desirable that this is wider.

Thus, the magneto-optical recording medium of the present invention is excellent in read durability, has a wide low recording margin and good bias magnetic field characteristics (the ability to follow the bias magnetic field of the W layer 5). This has the operational effect of obtaining a suitable overwrite characteristic.

It should be noted that the present invention is not limited to the above embodiment, and various changes may be made without departing from the scope of the present invention.

[0030]

Embodiments of the present invention will be described below. As shown in FIG. 1, on a disk-shaped substrate 1 made of polycarbonate, a first int is provided between the M layer 2, the W layer 5, the S layer 6, the I layer 7 and the M layer 2 and the W layer 5. A magneto-optical disk having the layer 3 and the second int layer 4 was prepared. Substrate 1 and M layer 2
In between, as a protective layer, yttrium sialon (YSiA) made of amorphous Y, SiN and Al ₂ O ₃ is used.
1ON) layer, and an Al alloy (AlTi) layer was provided as the uppermost layer on the I layer 7. Table 1 shows various characteristics of the basic four layers, and Table 2 shows an example of the int layer. In Table 2, NO.
1-1 to 6-2, 8-1, 8-2 are Comparative Examples, 7-1, 7
Reference numerals -2, 7-3, and 9 are examples of the present invention. 1-1 to 9
In each sample, the thickness of the Al alloy layer was adjusted for each sample so that the C / N after high recording had substantially the same sensitivity.

[0031]

[Table 1]

[0032]

[Table 2]

In Table 2, a comprehensive judgment was made that good read durability was obtained, that is, a record bit was stable up to 2 mW and a low recording margin was 2.5 mW or more. Those of 1-1 to 5-2, 8-1, and 8-2 are defective (x), 7-1, 7-2, 7-3, and 9 of the present invention.
Was a good product. In the case of 6-1 and 6-2, the bias magnetic field required for overwriting is as large as 1 kOe, which makes it difficult to reduce the size of the device. did. This is because, in the case of an int layer having perpendicular magnetization in the same direction as the W layer 5, an effective perpendicular magnetization opposite to the bias magnetic field exists at the time of high recording, so that a very large bias magnetic field is required. Because.

[0034] Figure 6, by measuring the C / N with respect to the bias magnetic field H _B of the M layer 2 when a int layer of 6-1,7-1, showed a bias magnetic field dependence of the W layer 5 Things. In the figure, the curve g is 6-1. For the above-mentioned reason, the bias magnetic field starts rising at 500 Oe or more, and a large bias magnetic field of 1 kOe or more is required for saturation. On the other hand, the curve f is the case of 7-1, is saturated at about 300 Oe, and has a suitable bias magnetic field characteristic (bias magnetic field follow-up property or bias magnetic field dependence).

Of the two int layers of the present invention, NO. 9 As in, first 1int layer 3 is higher than the Curie temperature T _CI1 is T _C1, the case of those changes to the vertical magnetization from in-plane magnetization as the temperature is raised, the magnetic interaction of the 1int layer, that is, the exchange coupling force To be able to cut off substantially above T _C1 ,
The thickness of the int layer 4 is adjusted. The preferred range is 2
0-80 °, and less than 20 °, the first int layer 3 during reproduction
Is insufficient, the bias magnetic field characteristics are degraded. If the angle exceeds 80 °, the exchange coupling force of the W layer 5 at the time of low recording is interrupted, and the low recording becomes insufficient.

[0036]

Magneto-optical recording medium of the present invention exhibits, int layer consists of at least two layers of the second 2int layer of the 1int layer and the W layer side of the M layer side, the first 1int layer Curie temperature T _CI1
Is a perpendicular magnetization film higher than T _C1 , and the second int layer is an in-plane magnetization film having a Curie temperature T _CI2 of 100 ° C. ≦ T _CI2 ≦ T _C2 , so that it has excellent read durability and a wide low recording margin. And the preferred bias magnetic field characteristics, and as a result, an excellent effect that good overwrite characteristics can be obtained.

The magneto-optical recording medium of the present invention may be any medium that can be overwritten by thermomagnetic recording, and is applicable to magneto-optical disks, magneto-optical cards, magneto-optical tapes, and the like.

[Brief description of the drawings]

FIG. 1 is a sectional view of a basic configuration of a magnetic layer of a magneto-optical recording medium according to the present invention.

FIG. 2 is a magnetization state diagram for explaining a basic mechanism of overwriting.

FIG. 3 is a graph showing a relationship between coercive force H _C and temperature of each magnetic layer of FIG. 2;

FIG. 4 is a graph showing a change in C / N with respect to a laser power of a conventional M layer.

FIG. 5 is a graph showing a change in C / N with respect to a laser power of an M layer when an intermediate layer having a magnetic transition temperature is applied.

FIG. 6 is a graph illustrating bias magnetic field dependence of a medium having an int layer according to the present invention.

[Explanation of symbols]

 1: substrate 2: M layer 3: first int layer 4: second int layer 5: W layer 6: S layer 7: I layer

Claims (1)

[Claims] 1. A recording layer having a perpendicular magnetic anisotropy and a Curie temperature of T _C1 , a perpendicular magnetic anisotropic recording auxiliary layer having a higher Curie temperature T _C2 and a lower coercive force than the recording layer, and A magneto-optical recording medium comprising a layer and a recording auxiliary layer, and an intermediate layer for adjusting the exchange coupling force between the two layers,
The intermediate layer includes at least two layers of a first intermediate layer on a recording layer side and a second intermediate layer on a recording auxiliary layer side, and the first intermediate layer is a perpendicular magnetization film having a Curie temperature T _CI1 higher than T _C1 ,
The second intermediate layer has a Curie temperature T _CI2 of 100 ° C. ≦ T
_A magneto-optical recording medium comprising an in-plane magnetization film _{satisfying CI2} ≦ T _C2 .