JP2002025136A - Magneto-optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magneto-optical recording medium which achieves the transfer of magnetic domain walls in the desired track width by the control of magnetic characteristics, is excellent in mass productivity and enables high density recording and reproduction. SOLUTION: In the magneto-optical recording medium comprising a first magnetic layer 3 which functions as a magnetic domain wall transferring layer, a third magnetic layer 5 which functions as a recording layer and a second magnetic layer 4 which controls exchange interaction between the first and second magnetic layers, the first magnetic layer 3 comprises heavy rare earth- iron family metal amorphous thin films stacked in such a way that the Curie temperatures of the films rise stepwise from the second magnetic layer 4 side by a certain temperature difference ΔTc as a unit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium for recording and reproducing information by irradiating light such as a laser beam.

[0002]

2. Description of the Related Art In a magneto-optical recording system, a ferrimagnetic thin film is locally heated to a Curie temperature Tc or a vicinity of a compensation point by laser light irradiation, and the coercive force of this portion is reduced, and an external magnetic field is applied. The basic principle is to reverse the direction of the magnetization to the direction of the recording magnetic field applied from. In the magneto-optical recording / reproducing, in which a portion where the magnetization is inverted, that is, the information bit forms a magnetic domain and reads it out by a magnetic force-effect, in order to improve the recording density, the recording bit length is shortened, that is, the information domain is miniaturized. It is necessary to aim at. However, the reproduction resolution of a signal is almost determined by the wavelength λ of the light source of the reproduction optical system and the numerical aperture NA of the objective lens, and the reproduction limit is a spatial frequency of 2 NA / λ. Therefore, it is conceivable to shorten the wavelength λ of the light source in order to increase the recording density, or to reduce the spot light diameter of the reproducing apparatus by using a high NA lens. However, the wavelength of a laser that is currently at a practical level is only about λ = 640 nm. Also, when a high NA lens is used, the depth of focus becomes shallower, and the distance between the lens and the disc requires accuracy, and the manufacturing accuracy of the optical disc becomes severe. Therefore, the NA of the lens cannot be so high, and the NA of the lens that can be practically used is at most 0.6. That is, there is a limit in improving the recording density by the wavelength λ of the light source and the numerical aperture NA of the objective lens.

In order to solve the problem of the recording density defined from the conditions at the time of reproduction, Japanese Patent Laid-Open Publication No.
There is a recording medium and a signal reproducing method disclosed in Japanese Patent Application Laid-Open No. -290496 (hereinafter, referred to as "first related art"). This reproducing method is a method in which a recording magnetic domain of a recording layer (third magnetic layer) of a magneto-optical recording medium is transferred at room temperature to a domain wall moving layer which is a first magnetic layer by an exchange coupling force via a second magnetic layer. is there. That is, domain walls are moved in the laser spot by utilizing the temperature gradient in the laser spot due to laser beam irradiation during reproduction, and a small mark (magnetic domain) can be largely enlarged and reproduced. Thus, the reproduction of the minute magnetic domains that cannot be reproduced with the normal reproduction resolution described above is performed, thereby achieving a dramatic improvement in the recording density.

On the other hand, a method disclosed in Japanese Patent Application No. 11-056237 has been proposed as a magnetically dividing method having mass productivity (hereinafter referred to as "second conventional technique"). This aims to provide a mass-producing magnetic separation method by a combination of a substrate shape and a film formation method. That is, the purpose of the present invention is to control or suppress the deposition of the magnetic film on the groove wall surface between the tracks on which recording and reproduction are performed, and to realize a discontinuous state of the recording medium in the direction perpendicular to the tracks. If the discontinuous state of the medium is continuous in the track direction, the recording magnetic domain can exist in the first magnetic layer as a magnetic domain divided by two front and rear domain walls in the track direction.

[0005]

However, in order to realize magnetic domain expansion reproduction by domain wall motion in the first prior art, the magnetic domain recorded in the recording layer is provided in the domain wall motion layer (first magnetic layer). It must be transferred as a magnetic domain separated by two front and rear magnetic domains. For that purpose, it is necessary to magnetically separate the tracks on both sides of the track used for recording by annealing or the like. That is, it is necessary that the recording magnetic domain exists as one recording magnetic domain in a region surrounded by the tracks on both sides that are magnetically different from the track to be recorded and the front and rear magnetic domain walls. The annealing process
This can be realized by tracing a track with a certain laser power or more. However, this annealing significantly impairs the mass productivity of the recording medium. Further, in the first prior art, the jitter of the reproduced signal is deteriorated because the movement start position of the domain wall deviates from the edge of the beam spot. This tendency increases as the mark length (magnetic domain length) becomes shorter. Therefore, in order to enable higher-density recording and reproduction, it is necessary to minimize the deviation of the domain wall movement start position.

On the other hand, realization of the control or suppression of the deposition of the magnetized film according to the second prior art, which is equivalent to realizing the above-mentioned annealing process by another method, is performed when a condition of a specific film forming method and a substrate shape is satisfied. It is extremely difficult, except for Consider a case where there is no magnetic separation, that is, a case where a domain wall exists at the boundary of the track. If the amount of decrease in the domain wall energy when the domain wall moves due to the temperature gradient in the track direction is larger than the increase in the domain wall energy that increases due to the increase in the area of the domain wall existing at the track boundary due to the domain wall movement, recording is performed. The domain wall in front of the mark (magnetic domain) moves. Therefore, if a certain condition is satisfied, that is, if the width of the recording mark is wider than a certain width, the above condition is satisfied, and even if a domain wall exists at a track boundary, magnetic domain expansion reproduction by domain wall movement is possible. become. However, in the magnetic properties of a normal domain wall displacement layer (first magnetic layer),
The threshold value becomes a fairly wide mark width (magnetic domain width), which is contrary to the direction of higher density for increasing the track density.

In view of the above problems, the present invention realizes domain wall displacement at a desired track width by controlling the magnetic characteristics of the domain wall displacement layer (first magnetic layer), and is excellent in mass productivity and high-density recording. It is an object of the present invention to provide a magneto-optical recording medium that enables reproduction.

Another object of the present invention is to increase the domain wall driving force by increasing the number of domain wall moving layers (first magnetic layers), thereby improving the quality of reproduced signals, and increasing the density of magneto-optical recording media. Is provided.

[0009]

In order to achieve the above object, a first feature of the present invention is to provide a first magnetic layer functioning as a domain wall displacement layer, a third magnetic layer functioning as a recording layer, and a third magnetic layer functioning as a recording layer. The present invention relates to a magneto-optical recording medium comprising a second magnetic layer for controlling exchange interaction between first and third magnetic layers. That is, the first feature of the present invention is that the first magnetic layer has a Curie temperature Tc1 (z) that is different from the second magnetic layer side by a constant temperature difference ΔTc.
In the thickness z direction in steps (in steps)
It is composed of a plurality of heavy rare earth / iron group amorphous thin films stacked so as to ascend. The “first magnetic layer” is a domain wall displacement layer in which a domain wall moves due to a temperature gradient created by laser beam irradiation. The “third magnetic layer” is a recording layer having a coercive force sufficient for a recording mark (magnetic domain) to exist stably at room temperature. The recording of this recording layer is performed by heat generated by laser beam irradiation and an external magnetic field, and has an easy axis of magnetization in a direction perpendicular to the film surface.

According to the first feature of the present invention, the distribution of the Curie temperature Tc1 (z) in the thickness direction z is controlled by forming the domain wall displacement layer (first magnetic layer) into multiple layers, and the domain wall displacement is controlled. A structure is obtained in which the hindering force is reduced more rapidly. As a result, domain wall movement can be made steeper (sharp), and high-density recording becomes possible. Also, the jitter of the reproduced signal can be reduced.

In the first aspect of the present invention, the plurality of heavy rare earth / iron group amorphous thin films constituting the first magnetic layer are:
It is preferable to be formed of three to five laminated films having different compositions. In addition, the above "constant temperature difference"
Is preferably ΔTc = 10 ° C. to 50 ° C. The plurality of “heavy rare earth / iron group amorphous thin films” constituting the first magnetic layer are respectively gadolinium / iron (Gd-F
e) or gadolinium / iron / cobalt (Gd-Fe-C
Preferably, it is constituted by a ferrimagnetic perpendicular magnetization film based on o).

According to the first feature of the present invention, in order for the Curie temperature Tc1 (z) to increase stepwise from the second magnetic layer side in units of a constant temperature difference ΔTc, the respective Curie temperatures Tc1 (z) are required. (Z) may be controlled by the addition amount of the nonmagnetic element. For example, a non-magnetic element such as aluminum (Al) or chromium (Cr)
m%, the Curie temperature Tc1 (z) is increased to 8 to 9 ° C.
It is possible to lower.

The second magnetic layer is made of terbium-iron (T
It is preferable to use a perpendicular magnetic film to which cobalt (Co) or dysprosium (Dy) is added or substituted based on (b-Fe). Further, the Curie temperature Tc2 of the second magnetic layer is preferably adjusted by adding a non-magnetic element. Further, the second magnetic layer is made of terbium iron (Tb-Fe) or dysprosium iron (Dy).
-Fe) is preferably a ferrimagnetic perpendicular magnetization film composed of a base and having a composition whose compensation temperature is close to room temperature. For example, terbium (Tb)
22atm%, dysprosium (Dy) 24-25atm%
With such a composition, the compensation temperature becomes near room temperature.

In the first aspect of the present invention, the third magnetic layer is made of terbium-iron-cobalt (Tb-Fe-Co) or dysprosium-iron-cobalt (Dy-Fe-Co).
It is preferable to use a ferrimagnetic perpendicular magnetization film based on. Further, the third magnetic layer is a ferrimagnetic perpendicular magnetization film based on a Tb-Fe-Co or Dy-Fe-Co film, and its Curie temperature Tc3 is preferably adjusted by adding a nonmagnetic element. .

A second feature of the present invention is that the first magnetic layer functioning as a domain wall displacement layer, the third magnetic layer functioning as a recording layer, and the exchange interaction between the first and third magnetic layers are controlled. And a second magnetic layer. That is, the second feature of the present invention is that the first magnetic layer is made of a rare earth (R)
It is composed of a heavy rare earth (HRE) / transition metal (TM) group amorphous thin film having a small exchange energy between E) and the transition metal (TM). The “first magnetic layer”
The domain wall moves due to the temperature gradient created by the laser beam irradiation, and the “third magnetic layer” has a coercive force sufficient to allow a recording mark (magnetic domain) to exist stably at room temperature. It has an easy axis of magnetization in a direction perpendicular to the film surface on which recording is performed by heat due to irradiation and an external magnetic field.

According to a second feature of the present invention, the rare earth (R
By lowering the exchange energy between E) and the transition metal (TM), the sublattice magnetization of the rare earth (RE) supported by the sublattice magnetization of the transition metal (TM) is weakened, and the rare earth (RE) The lattice magnetization decreases rapidly with temperature. As a result, the temperature change of the saturation magnetization Ms can be made sharp. Then, a sharp anisotropic temperature change can be obtained in a temperature region of 350 ° K or more where domain wall movement starts,
It can cause a sharp change in Bloch domain wall energy. The sharp decrease in Bloch domain wall energy increases the domain wall driving force, and thus greatly improves the reproduction characteristics of domain domain expansion reproduction by domain wall movement whether or not a domain wall exists at a track boundary. That is, domain wall movement can be made steeper (sharp), and high-density recording becomes possible. Also, the jitter of the reproduced signal can be reduced.

In a second aspect of the present invention, the first magnetic layer is formed of gadolinium / iron / cobalt / bismuth (Gd-F
e-Co-Bi), gadolinium-iron-cobalt-tin (Gd-Fe-Co-Sn) and gadolinium-cobalt-nickel (Gd-Co-Ni). Further, terbium (T
It is preferable that the film be a film in which a super heavy rare earth element having a mass number larger than that of b) is added or gadolinium (Gd) is substituted by the super heavy rare earth element. Here, the “super heavy rare earth element” is, for example, holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Y
b), lutetium (Lu).

Alternatively, in the second aspect of the present invention, the first magnetic layer is formed of gadolinium-iron-cobalt (Gd-Fe).
It is preferable that the film be based on (-Co) and have a fourth element added or substituted with a fourth element to reduce other rare earth spins. Further, the first magnetic layer is a film based on gadolinium-iron-cobalt (Gd-Fe-Co), in which a fourth element is added or replaced with a fourth element in order to reduce the transition metal spin. Preferably, there is. Further, the first magnetic layer is made of gadolinium / iron /
It is preferable that the film be a film based on cobalt (Gd-Fe-Co) to which a fourth element is added or replaced by a fourth element in order to reduce the exchange integral between the rare earth and the transition metal.

On the other hand, in the second aspect of the present invention, the Curie temperature Tc1 (z) of the first magnetic layer may be adjusted by adding a nonmagnetic element other than bismuth (Bi) or tin (Sn). preferable.

Further, in the second aspect of the present invention, it is preferable that the second magnetic layer is constituted by a perpendicular magnetization film based on terbium-iron (Tb-Fe) to which Co or Dy is added or substituted. . The Curie temperature Tc2 of the second magnetic layer can be adjusted by adding a non-magnetic element. Further, the second magnetic layer is made of terbium.
Iron (Tb-Fe) or dysprosium-iron (Dy-F
In the case of a ferrimagnetic perpendicular magnetization film configured based on e), the composition preferably has a compensation temperature near room temperature.

Further, according to the second feature of the present invention, the third magnetic layer is preferably made of terbium-iron-cobalt (Tb-Fe-C).
o) or dysprosium-iron-cobalt (Dy-Fe-
It is preferable to use a ferrimagnetic perpendicular magnetization film based on Co). In this case, the Curie temperature Tc of the third magnetic layer
3 can be adjusted by adding a non-magnetic element.

[0022]

Next, first and second embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic,
It should be noted that the relationship between the thickness and the plane dimension, the ratio of the thickness of each layer, and the like are different from actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. In addition, it goes without saying that parts having different dimensional relationships and ratios are included between the drawings.

(First Embodiment) As shown in FIG. 1, a magneto-optical recording medium according to a first embodiment of the present invention is provided on a light-transmitting substrate 1 such as a glass plate or polycarbonate (see FIG. 1). Note that 1 is shown upside down, that is, in this case, a transparent first dielectric material serving as a protective film or a multi-interference film is formed on the lower surface of the light-transmitting substrate 1 in FIG. A first magnetic layer 3, a second magnetic layer 4, and a third magnetic layer 5 are sequentially laminated via the layer 2, and a second dielectric layer (the lower surface in FIG. 1) is formed on the third magnetic layer 5 (the lower surface in FIG. 1). Alternatively, a protective film made of a nonmagnetic metal film 6 is formed. Further, if necessary, a protective layer 7 made of a UV curable resin or the like may be formed thereon (the lower surface in FIG. 1). The three-layer magnetic film including the first magnetic layer 3, the second magnetic layer 4, and the third magnetic layer 5 may be sequentially stacked in vacuum, for example, by continuous sputtering or the like.
Irradiation with laser light or the like is performed from the light transmitting substrate 1 side.

The first magnetic layer 3 of the magneto-optical recording medium according to the first embodiment of the present invention has, at room temperature, a film having an easy magnetization direction in the vertical direction (perpendicular to the film surface), so-called perpendicular magnetization. It is an amorphous thin film made of heavy rare earth and iron group metal to be a film. The first magnetic layer 3 is composed of three to five laminated films having different compositions. The Curie temperature Tc1 (z) of each layer constituting the first magnetic layer 3 is:
A constant temperature difference ΔTc = from the second magnetic layer 4 side in the thickness z direction.
It is composed of a film that rises stepwise at 10 ° C. to 50 ° C., for example, about 10 ° C. at a time. Further, in order to facilitate domain wall movement, the first magnetic layer 3 is preferably a film having a small magnetic anisotropy.

FIG. 2 is a schematic sectional view of the first magnetic layer 3 having a three-layer structure as an example of a detailed structure of the first magnetic layer 3 of the magneto-optical recording medium according to the first embodiment of the present invention. Is shown.
As shown in FIG. 2, gadolinium-iron (Gd _0.2 Fe
_0.8 ) on the second magnetic layer 4 made of gadolinium.
A first layer 43 made of iron (Gd _0.22 Fe _0.78 );
Gadolinium, iron, cobalt (Gd _0.24 Fe
_A second layer 42 of _0.75 Co _0.01 , gadolinium-iron-cobalt (Gd _0.26 Fe _0.72 Co _{0
. 02} ) are laminated. The first layer 43, the second layer 42 and the third layer 41 have the same thickness 10
nm. When cobalt (Co) is added so as to increase by 1 atm%, the Curie temperature Tc1 (z) of each of the first layer 43, the second layer 42 and the third layer 41 becomes ΔTc =
It is possible to increase by 6-7 ° C. Furthermore, the first layer 4
3. In the second layer 42 and the third layer 41, the Curie temperature Tc1 of each of the first layer 43, the second layer 42, and the third layer 41 is increased by increasing the composition of gadolinium (Gd) by 2%. (Z) is increased by ΔTc = 10 ° C. at a time.

The second magnetic layer 4 and the third magnetic layer 5 are films having an easy axis of magnetization in the vertical direction (perpendicular to the film surface), so-called perpendicular magnetization films, and are amorphous thin films made of heavy rare earth elements and iron group metals. It is. The Curie temperatures Tc1, Tc2, and Tc3 of the first magnetic layer 3, the second magnetic layer 4, and the third magnetic layer 5 are set to Tc3 in consideration of the temperature state at the time of recording and reproduction by the laser light.
>Tc1> Tc2 (1) is desirable.
Here, the Curie temperature Tc1 of the first magnetic layer 3 is Tc3
For the Curie temperature Tc1 of the uppermost layer of the multilayer structure
(Z _max ). On the other hand, the Curie temperature Tc1 of the first magnetic layer 3 is defined by the Curie temperature Tc1 (z _min ) of the lowermost layer of the multilayer structure with respect to Tc2. The first magnetic layer 3 serving as a domain wall displacement layer needs to be a film having a small anisotropy and a low coercive force in order to easily cause domain wall displacement. It is desirable to use a film-based material. On the other hand, the third magnetic layer 5 serving as a memory layer for holding recorded information
Needs to be a film having a coercive force sufficient for a recording mark (magnetic domain) to exist stably at room temperature and having a Curie temperature Tc3 suitable for recording. for that reason,
The third magnetic layer 5 is made of a Tb—Fe—Co film or Dy—Fe—
It is desirable to use a material based on a Co film.
It is desirable that the above-mentioned Curie temperatures Tc1, Tc2, and Tc3 be adjusted by adding a nonmagnetic element that does not significantly change these magnetic properties.

FIG. 3B shows a beam intensity profile of the laser beam when the laser beam moves at a certain constant linear velocity relative to the disk, that is, at the time of reproduction. It can be seen that the beam intensity of the laser light has a Gaussian distribution. FIG. 3A shows the temperature distribution in the track direction when the center position of the laser beam is set to zero and the coordinate axis is set in the track direction. Actually, it shows the temperature distribution when the disk rotates at a certain linear velocity. Here, the position coordinates assume that the traveling direction of the laser beam is positive. The maximum temperature reaching point is located slightly behind the center of the laser beam. It can be seen that the domain wall movement for magnetic domain expansion reproduction is a so-called “front process” that occurs on the positive side of the horizontal axis, that is, in front of the traveling beam.

Then, the domain wall driving force in this front process will be considered. FIG. 4 is a plot of the change in the domain wall energy of the magnetic domain caused by the temperature gradient, that is, the domain wall driving force ∂σ _B / ∂x, and the force obstructing the change, 2MsHc + σ _w / h, with respect to the position x where the front process occurs. .

The domain wall movement starts when ∂σ _B / ∂x> 2MsHc + σ _w / h (2). Here, σ _B is the domain wall energy of the magnetic domain of the recording mark, that is, Bloch domain wall energy, x is the position coordinate in the track direction, M
s is the saturation magnetization of the moving layer, Hc is the domain wall coercive force of the moving layer, σ
_w is the interface domain wall energy due to exchange coupling between the moving layer and the recording layer, and h is the thickness of the moving layer.

FIG. 4 shows the force that hinders the movement of the domain wall when the domain wall displacement layer (first magnetic layer) 4 is a single layer, and when the layer has a three-layer or five-layer laminated structure. The domain wall displacement layer (first magnetic layer) is set such that the Curie temperature Tc1 (z) of each layer increases from the second magnetic layer 4 side by ΔTc = 10 ° C. to 50 ° C., for example, about 10 ° C. at a time. The temperature characteristic of the saturation magnetization shows a characteristic that the temperature-dependent curve moves in parallel with the increase in the Curie temperature Tc1 (z) without changing the rate of change. In order to satisfy this characteristic, it is necessary to control the distribution of the Curie temperature Tc1 (z) in the thickness z direction by adding a nonmagnetic element that does not affect the magnetic characteristics. For domain wall motion,
(2) may be considered the threshold F _th domain wall movement starting given by the difference between the left and right sides of the equation. Compared to the threshold value _Fth , the result of FIG. 4 shows that the domain wall displacement layer (first magnetic layer) 4
It can be seen that the multi-layering of three or five layers is effective for improving the reproduction signal characteristics. It can be seen that the force that hinders the domain wall movement is reduced more rapidly with the three or five layers. In other words, the domain wall displacement layer (first magnetic layer) 4 has a multi-layer structure, so that the domain wall displacement can be steeper (sharp). As a result, the jitter of the reproduced signal is reduced.

(Second Embodiment) A magneto-optical recording medium according to a second embodiment of the present invention has a basic structure similar to that of the first embodiment. That is, similarly to FIG. 1, on a light-transmitting substrate 1 such as a glass plate or polycarbonate (the lower surface in FIG. 1) via a transparent first dielectric layer 2 serving as a protective layer or a multiple interference film. One magnetic layer 3, second magnetic layer 4, and third magnetic layer 5 are sequentially laminated to form a three-layer magnetic film. Further, a protective film made of a second dielectric layer (or a non-magnetic metal film) 6 is formed on the third magnetic layer 5 (the lower surface in FIG. 1), and the lower surface of FIG. A protective layer 7 is formed. However, the first embodiment is characterized in that the first magnetic layer is composed of a heavy rare earth (HRE) / transition metal (TM) group amorphous thin film having a small exchange energy between the rare earth (RE) and the transition metal (TM). It is different from the form. The first magnetic layer 3 is an amorphous thin film that becomes a film having a direction of easy magnetization in a vertical direction (direction perpendicular to the film surface) at room temperature, that is, a so-called perpendicular magnetization film. In particular,
The transition metal (TM) is a 3d transition metal, and more specifically, an iron group metal is preferable.

That is, the first magnetic layer 3 of the magneto-optical recording medium according to the second embodiment of the present invention is an amorphous thin film made of a heavy rare earth / iron group metal and exchanged with a heavy rare earth / iron group metal. It is composed of a film with low energy. The first magnetic layer 3 is desirably a film having small magnetic anisotropy in order to facilitate domain wall movement. Each of the second magnetic layer 4 and the third magnetic layer 5 is a film having an easy axis of magnetization in a vertical direction (a direction perpendicular to the film surface), that is, a so-called perpendicular magnetization film, and is an amorphous thin film made of a heavy rare earth / iron group metal. The Curie temperatures Tc1, Tc of the first magnetic layer 3, the second magnetic layer 4, and the third magnetic layer 5 are considered in consideration of the temperature state during recording and reproduction by the laser beam.
2, Tc3 desirably satisfies the above equation (1).

The first magnetic layer 3 serving as a domain wall displacement layer needs to be a film having small anisotropy and coercive force in order that domain wall displacement can easily occur. Therefore, the first magnetic layer 3 is based on a Gd—Fe film. Gd-Fe-Co-Bi or Gd-Fe-Co
It is desirable to use a material such as -Sn. On the other hand, the third magnetic layer 5 serving as a memory layer for holding recorded information
Needs to be a film having a coercive force sufficient for a recording mark (magnetic domain) to exist stably at room temperature and having a Curie temperature Tc3 suitable for recording.
It is desirable to use a material based on -Fe-Co or Dy-Fe-Co films. It is desirable that the above-mentioned Curie temperatures Tc1, Tc2, and Tc3 be adjusted by adding a nonmagnetic element that does not significantly change these magnetic properties.

FIG. 5 shows a Gd—Fe film, Gd—Fe—Co
5 shows temperature characteristics of saturation magnetization Ms of a Bi film. The white circles indicate the measured values of the saturation magnetization Ms of the Gd-Fe film, and the black triangles indicate the measured values of the saturation magnetization Ms of the Gd-Fe-Co-Bi film. The solid lines indicate the calculated values of the saturation magnetization Ms of the Gd—Fe film and the Gd—Fe—Co—Bi film based on the molecular field theory, respectively. Gd-Fe film and Gd-F
In any of the e-Co films, by adjusting the composition of Gd,
It is possible to make the temperature change of the saturation magnetization Ms steeper. From FIG. 5, it can be seen that the saturation magnetization Ms of the Gd—Fe—Co—Bi film decreases more steeply with the temperature rise than that of the Gd—Fe film. That is, Gd-F in FIG.
Looking at the temperature change of the saturation magnetization Ms of the e film, the temperature change of the saturation magnetization Ms of the Gd—Fe film is represented by Gd—Fe—Co—Bi.
It can be seen that it is impossible to change the saturation magnetization Ms of the film more rapidly than the temperature change.

FIG. 6 shows a Gd—Fe film, Gd—Fe—Co
-True anisotropy Ku and effective anisotropy Ku-2πM of Bi film
shows the temperature change of s ^2. Since the temperature change of the demagnetizing field energy 2πMs ² can be made sharper as the temperature change of the saturation magnetization Ms in FIG. 5 is sharper, the effective difference in the Gd—Fe—Co—Bi film is larger than that in the Gd—Fe film. It can be seen that the anisotropic temperature change is sharp. Controlling this anisotropic temperature change improves the problems of the first and second prior arts described above.

These good results can be explained by the effect of the addition of Bi, ie, the reduction of the exchange integral between the rare earth (RE) and the transition metal (TM). Due to the decrease of the exchange integral, the exchange energy between the rare earth (RE) and the transition metal (TM) decreases, and the magnetization sharply decreases.

Generally speaking, the magnitude of the exchange energy between the rare earth (RE) and the transition metal (TM) is such that S _RE is the spin of the rare earth (RE), S _Fe is the spin of iron (Fe),
The S _Co as a spin cobalt (Co), is expressed as _{J RE-Fe · S RE ·} S Fe + J RE-Co · S RE · S Co ····· (3). Here, J _RE-Fe is an exchange integral between rare earth (RE) and Fe, and J _RE-Co is an exchange integral between rare earth (RE) and Co. Rare earth (RE) and transition metal (T
When the exchange energy during (M) decreases, the transition metal (T
Rare earth (R) supported by the sublattice magnetization of (M)
The sub-lattice magnetization of E) becomes weak, and the rare-earth (RE) sub-lattice magnetization decreases rapidly with temperature. As a result, it is considered that the temperature change of the saturation magnetization Ms becomes steep. Gd-F
The addition of Bi or Sn to the e-film is based on J in equation (3).
_This corresponds to lowering _RE-Fe . Therefore, the same result as when the above-described Gd-Fe-Co-Bi film is used also occurs when the Gd-Fe-Co-Sn film is used.

The problem of the first and second prior arts can be solved by lowering the exchange energy between the rare earth (RE) and the transition metal (TM).
It can be seen from the equation that the exchange energy can be reduced by reducing the spin of Fe. The Fe spin can be reduced by adding Ni or replacing Fe with Co.

FIG. 7 shows the result of verifying this effect.
The graph of FIG. 7 is normalized on both the vertical and horizontal axes in order to directly compare the temperature changes of three types of films having different Curie temperatures Tc1 and different absolute values of the saturation magnetization Ms. Further, a black triangle indicates an actually measured value of the saturation magnetization Ms of the Gd-Co-Ni film, and a white circle indicates Gd-Fe-Co-B.
The measured value of the saturation magnetization Ms of the i-film, the white square mark is Gd
-It is an actually measured value of the saturation magnetization Ms of the Fe film. The solid line shows the calculated value. FIG. 7A is a graph comparing the temperature change of the saturation magnetization Ms. In order to show that the difference in temperature change of the saturation magnetization Ms shown in FIG. 7A is caused by the above-described difference in temperature change of the sublattice magnetization, FIG.
(B) and (c) show comparison graphs of the temperature change of the rare earth (RE) sublattice magnetization and the temperature change of the transition metal (TM) sublattice magnetization, respectively. It can be seen that the temperature change of the saturation magnetization Ms of the three types of films causes a difference in the reduction ratio with respect to the temperature rise due to the difference in the change of the rare earth (RE) sublattice magnetization of each film. To solve the problems mentioned above,
Since it is desirable to have a sharp decrease in the saturation magnetization Ms, Gd−
It can be said that using a Co—Ni film as the first magnetic layer 3 is effective for solving the problem.

The spin of the rare earth (RE) decreases as the atomic number increases. Therefore, from the relationship of the formula (3), replacing Gd of the Gd—Fe—Co film with a heavy rare earth having a larger atomic number can reduce the exchange integral between the rare earth (RE) and the transition metal (TM), It is considered that the magnitude of the exchange energy between the rare earth (RE) and the transition metal (TM) is reduced as in the case of the decrease in the spin of Fe. Therefore, the temperature change of the saturation magnetization Ms caused by replacing Gd of the Gd-Fe-Co film with another heavy rare earth is described by Hund (Hu).
The parameters were calculated according to the molecular field logic and compared with the parameters according to the law of nd). FIG. 8 shows the result. Tb-Fe-C
It can be seen that the saturation magnetization Ms of the o film, the Dy-Fe-Co film, and the Ho-Fe-Co film decreases more rapidly with temperature rise than that of the Gd-Fe-Co film. However, since the Tb-Fe-Co film and the Dy-Fe-Co film are films having large magnetic anisotropy, their use is not preferable. From these results, the addition and substitution of heavy rare earth elements to the above-described first magnetic layer 3, ie, Ho, Er, Tm, Yb, Lu
It can be seen that addition or substitution of a super-heavy rare earth element such as is effective in solving the above-mentioned problems.

Also in the magneto-optical recording medium according to the second embodiment of the present invention, as shown in FIG. 3 described in the first embodiment, the temperature distribution in the track direction by laser beam irradiation and the laser beam Beam intensity profile is adopted. That is, as shown in FIG. 3B, the beam intensity profile of the laser beam intensity has a Gaussian distribution.
When the disk rotates at a certain linear velocity, if a coordinate axis is set in the track direction, a temperature distribution as shown in FIG. 3A is obtained. Here, the position coordinates assume that the traveling direction of the laser beam is positive. As shown in FIG. 3A, the highest temperature reaching point is located slightly behind the center of the laser beam.

As shown in FIG. 3, domain wall movement for magnetic domain expansion reproduction is a so-called front process that occurs on the positive side of the horizontal axis, that is, in front of the traveling beam. In the magneto-optical recording medium according to the second embodiment of the present invention, the domain wall driving force in this front process will be considered. FIG. 9 shows a change in domain wall energy of a magnetic domain caused by a temperature gradient, that is, a domain wall driving force ∂σ _B / ∂x in a Gd—Fe—Co film, similar to FIG.
It is a plot of 2MsHc + σ _w / h, which is a force that prevents this. When the expression (2) described in the first embodiment of the present invention is already satisfied, the domain wall movement starts.

Next, let us consider a case where there is no magnetic division described above, that is, a case where a domain wall exists at the boundary between tracks. Due to the temperature gradient in the x direction, when the domain wall moves by dx, the domain wall energy σ _B decreases by dσ _B. Reduction of the domain wall energy because the area of the domain wall is a hw when the track width is w becomes hwdσ _B. On the other hand, the domain wall of the track boundary is increased energy because the area is increased, the increase in the magnetic wall energy, a 2hσ _B dx.

If hwdσ _B > 2hσ _B dx (4) holds, domain wall movement will occur. Therefore, the condition for the domain wall movement to occur even if a domain wall exists at the boundary of the track is ∂σ _B / ∂x> 2σ _B / w (5).

Using the track width w of the magneto-optical recording medium using the Gd—Fe—Co film as a parameter, the magnitude relationship between the terms on the right and left sides of the equation (5) is plotted in FIG.
It is. FIG. 10 compares the magnitude relationship between the right side and the left side of Expression (5) at the temperature at which the domain wall movement starts in FIG. In FIG. 10, a curve indicating the right side of the equation (5) and a curve indicating the left side intersect with a track width w = 0.9 μm.
That is, in the case of the Gd—Fe—Co film, the track width is set to be equal to 0.1.
It can be seen that when the thickness is 9 μm or more, the domain wall movement occurs at the same temperature even if the domain wall exists at the track boundary.

Further, in the case of the Gd-Fe-Co film, the magnitude relation between the left side and the right side of the equation (5) when the track width is set to 0.7 μm and 0.9 μm is plotted with respect to the position coordinates in the track direction. FIG. 11 shows the result. It can be seen that when the track width is 0.7 μm, the domain wall movement start position is larger than in the case of FIG. 9 and is shifted toward the beam center.
The deviation of the domain wall movement start position deteriorates the jitter of the reproduction signal. In the case of the Gd-Fe-Co film, the reproduction signal quality deteriorates, which hinders the high density.

In order to solve this problem, in the second embodiment, the magnetic properties of the domain wall displacement layer (first magnetic layer) 4 were adjusted using a Gd—Fe—Co—Bi film. Here, as an example, Bi is added at 10 atm% to the Gd—Fe—Co film. And this Gd-Fe-
While comparing the Co-Bi film and the Gd-Fe-Co film,
FIG. 12 shows the temperature change of the perpendicular magnetic anisotropy of the domain wall motion layer (first magnetic layer) 4. That is, Gd shown in FIG.
The dotted line indicates the temperature change of the perpendicular magnetic anisotropy of the domain wall displacement layer (first magnetic layer) 4 made of the -Fe-Co film. On the other hand, Gd-
The solid line shows the temperature change of the perpendicular magnetic anisotropy of the domain wall displacement layer (first magnetic layer) 4 in which the exchange energy between the rare earth (RE) and the transition metal (TM) is reduced by using the Fe—Co—Bi film. ing. In the figure, a and b are true anisotropic Ku, and c
And d are the effective anisotropy Ku-2πMs ² . It can be seen that the temperature change of the anisotropy of the Gd-Fe-Co-Bi film shown by the solid line changes more rapidly than the temperature change of the anisotropy of the Gd-Fe-Co film shown by the dotted line.

The abrupt anisotropic temperature change in the temperature range of 350 ° K or higher at which the domain wall movement starts causes the abrupt change in the Bloch domain wall energy shown in FIG. The dotted line a in FIG. 13 corresponds to the Gd—Fe—Co film in FIG. 12, and the solid line b corresponds to the Gd—Fe—Co—Bi film in FIG. The sharp decrease in Bloch domain wall energy is
Since the left side of equation (5), that is, the domain wall driving force, is increased, the reproduction characteristic of domain expansion reproduction by domain wall movement is greatly improved whether or not a domain wall exists at the track boundary.

FIG. 14 is a diagram showing the domain wall driving force corresponding to FIG. 9 and the force obstructing it. That is, Gd-Fe-Co
FIG. 7 is a diagram in which the domain wall driving force of the domain wall motion layer (first magnetic layer) 4 using a Bi film and the force that hinders the domain wall driving force are plotted with respect to position. As shown in FIG. 14, Gd—Fe—Co—Bi
It can be seen that by using the film, the position at which the domain wall movement starts is closer to the edge side of the beam spot, and the force 2MsHc + σ _w / h for preventing the domain wall movement is sharply reduced. For this reason, by using the Gd-Fe-Co-Bi film, high-density recording / reproduction with reduced jitter of the reproduction signal becomes possible.

In FIG. 15, Gd-Fe-Co-B
It can be seen that the use of the i film allows domain wall movement to start earlier even when the track width is 0.7 μm. Therefore, even when the magnetic separation by a method other than the annealing treatment is incomplete, the domain wall movement is smoothly realized, and higher-density recording by improving the track density can be realized.

As described above, not only Bi but also G
Even when Sn is added to the d-Fe-Co film, the characteristics of the domain wall motion layer (first magnetic layer) 4 are improved. That is, Gd-
The same effect as in the case of using the Fe—Co—Bi film is obtained by Gd
-Fe-Co-Sn film can also be used. Furthermore, Ni
The Fe spin may be reduced by adding Fe or replacing Fe with Co. Therefore, a Gd-Co-Ni film may be used.

[0052]

As described above, according to the present invention, it is possible to provide a high-performance magneto-optical recording medium capable of high-density recording with reduced jitter of a reproduction signal and improved reproduction signal quality. .

According to the present invention, it is possible to provide a high-performance magneto-optical recording medium capable of easily improving mass productivity and capable of high-density recording by increasing track density.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view schematically showing the structure of a magneto-optical recording medium according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional view showing an example of a detailed structure of a first magnetic layer of the magneto-optical recording medium according to the first embodiment of the present invention.

FIG. 3A is a diagram showing a temperature distribution in a track direction by laser beam irradiation, and FIG. 3B is a diagram showing a profile of a beam intensity of a laser beam used.

FIG. 4 is a diagram plotting a domain wall driving force generated by a temperature gradient and a force obstructing the domain wall driving force with respect to a position in the magneto-optical recording medium according to the first embodiment of the present invention.

FIG. 5 compares the temperature characteristics of the saturation magnetization of a Gd—Fe film and a Gd—Fe—Co—Bi film as a material of a first magnetic layer used for a magneto-optical recording medium according to a second embodiment of the present invention. FIG.

FIG. 6 is a diagram showing temperature changes of true anisotropy and effective anisotropy of a Gd—Fe film and a Gd—Fe—Co—Bi film.

FIG. 7 (a) is a graph comparing the temperature change of the saturation magnetization of each of the three types of films, and FIG. 7 (b) is a graph of the rare earth (RE) sublattice magnetization of each of the three types of films. FIG. 7C is a graph showing a comparison of temperature change of transition metal (TM) sublattice magnetization of each of the three types of films.

FIG. 8 is a diagram comparing the results of calculating the temperature change of the saturation magnetization Ms by molecular field logic when Gd of the Gd—Fe—Co film is replaced with another heavy rare earth.

FIG. 9 is a diagram plotting a domain wall driving force generated by a temperature gradient and a force obstructing the domain wall driving force with respect to a position when a Gd—Fe—Co film is used as the first magnetic layer.

FIG. 10 shows a temperature (432.2 ° K) at which domain wall movement starts when a Gd—Fe—Co film is used for the first magnetic layer.
FIG. 9 is a diagram showing the magnitude relationship between terms on the right side and the left side of the expression (5) described in the specification in FIG.

FIG. 11 shows the relationship between the magnitude of the left side and the right side of equation (5) when the track width is 0.7 μm and 0.9 μm when a Gd—Fe—Co film is used for the first magnetic layer, and the position coordinates in the track direction. FIG.

FIG. 12 shows a magneto-optical recording medium according to a second embodiment of the present invention, in which a Gd—Fe—Co—Bi film is used as a domain wall motion layer (first magnetic layer). FIG. 4 is a diagram showing a change in temperature of perpendicular magnetic anisotropy in comparison with the case of a Gd—Fe—Co film.

FIG. 13 shows the temperature of the Bloch domain wall energy when the Gd—Fe—Co—Bi film is used for the domain wall moving layer (first magnetic layer) in the magneto-optical recording medium according to the second embodiment of the present invention. It is a figure which shows a change compared with the case of a Gd-Fe-Co film.

FIG. 14 shows a domain wall generated by a temperature gradient when a Gd—Fe—Co—Bi film is used as a domain wall displacement layer (first magnetic layer) in the magneto-optical recording medium according to the second embodiment of the present invention. It is the figure which plotted the driving force and the force which obstructs it with respect to a position.

FIG. 15 shows a magneto-optical recording medium according to a second embodiment of the present invention, in which a Gd—Fe—Co—Bi film is used as a domain wall displacement layer (first magnetic layer) and has a track width of 0.1 mm. 7μ
FIG. 9 is a diagram illustrating the magnitude relationship between the left side and the right side of Expression (5) for m and 0.9 μm with respect to position coordinates in the track direction.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 substrate 2 first dielectric layer 3 first magnetic layer 4 second magnetic layer 5 third magnetic layer 6 second dielectric layer 7 protective layer 41 first layer 42 second layer 43 third layer

Claims (8)

[Claims] A first magnetic layer functioning as a domain wall displacement layer, a third magnetic layer functioning as a recording layer, and a second magnetic layer controlling exchange interaction between the first and third magnetic layers. In the magneto-optical recording medium comprising: the first magnetic layer, a plurality of heavy rare earth / iron group stacked in such a manner that each Curie temperature gradually increases from the second magnetic layer side in units of a constant temperature difference. A magneto-optical recording medium characterized by being composed of an amorphous thin film. 2. The method according to claim 1, wherein the plurality of heavy rare earth / iron group amorphous thin films constituting the first magnetic layer are formed of three to five laminated films having different compositions. A magneto-optical recording medium according to claim 1. 3. The magneto-optical recording medium according to claim 1, wherein the constant temperature difference is 10 ° C. to 50 ° C. 4. The plurality of heavy rare earth / iron group amorphous thin films constituting the first magnetic layer are gadolinium / iron (Gd-Fe) or gadolinium / iron / cobalt (Gd
The magneto-optical recording medium according to any one of claims 1 to 3, wherein the magneto-optical recording medium is constituted by a ferrimagnetic perpendicular magnetization film based on -Fe-Co). 5. The method according to claim 1, wherein the Curie temperature of at least one of the plurality of heavy rare earth / iron group amorphous thin films constituting the first magnetic layer is controlled by adding a nonmagnetic element. Item 5. A magneto-optical recording medium according to any one of items 1 to 4. 6. A first magnetic layer functioning as a domain wall displacement layer, a third magnetic layer functioning as a recording layer, and a second magnetic layer controlling exchange interaction between the first and third magnetic layers. 2. The magneto-optical recording medium according to claim 1, wherein the first magnetic layer comprises a heavy rare earth / transition metal group amorphous thin film having a small exchange energy between the rare earth and the transition metal. 7. The method according to claim 1, wherein the first magnetic layer comprises gadolinium / iron /
Cobalt bismuth (Gd-Fe-Co-Bi), gadolinium-iron-cobalt-tin (Gd-Fe-Co-S)
n) and gadolinium-cobalt-nickel (Gd-C
o-Ni).
A magneto-optical recording medium according to claim 1. 8. The method according to claim 1, wherein the first magnetic layer further comprises terbium (T
b) a composition in which a super heavy rare earth element having a mass number larger than that of b) is added, or a composition in which at least a part of gadolinium (Gd) of the first magnetic layer is substituted with the super heavy rare earth element. Claim 6 or 7
A magneto-optical recording medium according to claim 1.