JPH10340492A - Magneto-optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magneto-optical recording medium with which the embodiment of super-high resolution recording and reproducing of improved reproduction characteristics is possible. SOLUTION: This magneto-optical recording medium has a first magnetic layer 3 which is a (reading out layer) magnetic layer formed on a transparent substrate 1 and consists mainly of a rear earth metal-3d transition metal alloy that has an easy direction of magnetization in an intra-surface direction at room temp., is changed, on rising of its temp. up to a prescribed temp. above room temp., in the easy direction of magnetization to a perpendicular direction and is small in the exchange energy between the rear earth metal and the 3d transition metal and a second magnetic layer 4 which is formed on this, first magnetic layer 3, is a magnetic layer for magneto-optical recording of information and consists of a rear earth metal-3d transition metal alloy having the easy direction of magnetization in the perpendicular direction at room temp. or above.

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 laser light.

[0002]

2. Description of the Related Art In a magneto-optical recording system, the temperature of a ferrimagnetic thin film is locally increased to a point near a Curie point or a compensation point, and the coercive force of this portion is reduced to increase the temperature in the direction of an externally applied recording magnetic field. The basic principle is to reverse the direction of magnetization. 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 the magnetic domain is read out by the magnetic Kerr effect, in order to improve the recording density, the recording bit length is shortened, that is, the information domain is reduced. It is necessary to reduce the size.

However, the reproduction resolution of the signal is almost the same as the wavelength λ of the light source of the reproduction optical system and the numerical aperture N of the objective lens.
The spatial frequency 2NA / λ is the reproduction limit.
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 which is currently at a practical level is only about 680 nm, and when a high NA lens is used, the depth of focus becomes shallow, and the distance between the lens and the disk is required to be high. Becomes severe.

Therefore, the NA of the lens cannot be so high, and the practically usable lens NA is at most 0.6. That is, the wavelength λ of the light source and the numerical aperture NA of the objective lens
There is a limit to the improvement of the recording density due to this.

[0005] To solve the problem of increasing the recording density specified from the conditions at the time of reproduction, there is the following recording medium and signal reproduction method (for example, Japanese Patent Laid-Open No. 6-150418). ). This reproducing method utilizes an exchange interaction between a reading layer (first magnetic layer) and a recording layer (second magnetic layer) caused by a temperature rise caused by irradiating a recording medium with laser light. Information is reproduced by transferring information domains recorded on the recording layer to the readout layer.

The configuration of the above-mentioned recording medium is as follows. That is, it is formed on a light-transmissive substrate and exhibits an in-plane magnetization state in which in-plane magnetic anisotropy is superior at room temperature, and shifts to a perpendicular magnetization state in which perpendicular magnetic anisotropy is superior with increasing temperature. It has a readout layer and a recording layer formed on the readout layer to record information magneto-optically, and the readout layer is a magneto-optical recording medium made of a rare earth transition metal alloy.

Recording of information using this magneto-optical recording medium is performed as follows. That is, while applying a constant magnetic field for magnetizing the readout layer, the recording layer is irradiated with a laser beam switched between a relatively low first laser power and a relatively high second laser power according to a recording signal. Recording is performed by reversing the direction of magnetization.

[0008] The information recorded on the magneto-optical recording medium is reproduced in the following manner. That is, by irradiating a laser beam having a laser power even lower than the first laser power, the irradiation area corresponding to the laser spot diameter of the readout layer is shifted to the perpendicular magnetization state, and the perpendicular magnetization state of the readout layer is changed. The sub-lattice magnetization of the changed region is aligned in a direction stable with respect to the sub-lattice magnetization of the recording layer, and information is reproduced from the region of the readout layer in the perpendicular magnetization state.

[0009]

However, the materials constituting the readout layer in the above-mentioned magneto-optical recording medium have a wide temperature range of the magnetization transition from the in-plane magnetization state to the perpendicular magnetization state. However, it was not sufficient to reproduce information recorded in an area (information magnetic domain) much smaller than the laser spot diameter of the readout layer with a good S / N (C / N). Accordingly, the present invention provides a method of forming a readout layer (first magnetic layer) as a material of a magnetization transition that transitions from an in-plane magnetization state to a perpendicular magnetization state due to a small exchange energy between a rare earth metal and a 3d transition metal. By using an alloy with a narrow temperature range,
Super-resolution reproduction that can reproduce high-density recorded information recorded in an area (information domain) much smaller than the laser spot diameter of the readout layer with better S / N (C / N) than conventional ones It is an object of the present invention to provide a possible high-performance magneto-optical recording medium.

[0010]

In order to solve the above-mentioned problems, the present invention provides a magneto-optical recording medium having the following constitutions (1) to (10).

(1) As shown in FIG. 1, a (readout layer) magnetic layer formed on a transparent substrate 1
0K), the direction of easy magnetization is in the in-plane direction (x direction in the figure), and when the temperature is raised to a predetermined temperature higher than room temperature, the direction of easy magnetization changes in the vertical direction (y direction in the figure), and the rare earth metal A first magnetic layer 3 mainly composed of a rare earth metal-3d transition metal alloy having a small exchange energy between -3d transition metals, and a magnetic layer formed on the first magnetic layer 3 for magneto-optically recording information. A second magnetic layer 4 made of a rare earth metal-3d transition metal alloy having an easy magnetization direction in the vertical direction at room temperature or higher
A magneto-optical recording medium A comprising:

(2) The first magnetic layer 3 is made of GdFeC
The magneto-optical recording medium A according to the above (1), which is oBi.

(3) The first magnetic layer 3 is made of GdFeC
The magneto-optical recording medium A according to the above (1), which is oSn.

(4) The first magnetic layer 3 is made of GdCoN
i. The magneto-optical recording medium A according to the above (1), wherein i is i.

(5) The first magnetic layer 3 is made of GdFeC
oBi includes rare earth elements Tb, Dy, Ho, Er, Tm,
At least one of Yb and Lu is added;
Alternatively, the magneto-optical recording medium according to the above (1), wherein Gd constituting GdFeCoBi is an alloy in which Gd is substituted by any one of rare earth elements Tb, Dy, Ho, Er, Tm, Yb, and Lu. A.

(6) The first magnetic layer 3 is made of GdFeC
oSn includes rare earth elements Tb, Dy, Ho, Er, Tm,
At least one of Yb and Lu is added;
Or (d) a rare earth metal-3d transition metal obtained by substituting Gd constituting GdFeCoBi with any one of the rare earth elements Tb, Dy, Ho, Er, Tm, Yb, and Lu. Magneto-optical recording medium A.

(7) The first magnetic layer 3 is made of GdCoN
i is the rare earth element Tb, Dy, Ho, Er, Tm, Y
An alloy in which at least one of b and Lu is added or Gd constituting GdFeCoBi is substituted with any one of rare earth elements Tb, Dy, Ho, Er, Tm, Yb and Lu. The magneto-optical recording medium A according to the above (1), wherein:

(8) The first magnetic layer 3 is made of GdFeC
an alloy in which a fourth element for reducing rare earth spin is added to o or an alloy in which any element of GdFeCo is replaced with another element for reducing rare earth spin. The magneto-optical recording medium A according to the above (1).

(9) The first magnetic layer 3 is made of GdFeC
an alloy in which a fourth element for reducing transition metal spin is added to o, or an alloy in which one of GdFeCo is replaced by another element for decreasing transition metal spin. The magneto-optical recording medium A according to the above (1).

(10) The first magnetic layer 3 is made of GdFe
An alloy in which Co is added with a fourth element for reducing the exchange integral between the rare earth and the transition metal, or one of the elements of GdFeCo is added to another element for decreasing the exchange integral between the rare earth and the transition metal. The magneto-optical recording medium A according to the above (1), which is an alloy substituted with an element.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The magneto-optical recording medium of the present invention will be described below in detail with reference to FIGS. FIG. 1 is a diagram showing the structure of a magneto-optical recording medium according to the present invention, FIG. 2 is a graph comparing the temperature characteristics of the magnetization of a substance to be the first magnetic layer, and FIGS.
FIG. 4 is a graph comparing the true magnetic anisotropy and the temperature dependence of the demagnetizing field energy of the material used as the first magnetic layer,
FIG. 5 is a graph comparing the temperature dependence of the true magnetic anisotropy and the effective magnetic anisotropy of the first magnetic layer constituting the magneto-optical recording medium. FIG.
FIG. 7 is a graph showing the temperature dependence of the residual Kerr rotation angle in a magneto-optical recording medium in which o is the second magnetic layer.
FIG. 8 is a graph showing the temperature dependence of the residual Kerr rotation angle in a magneto-optical recording medium having oBi as the first magnetic layer and DyFeCo as the second magnetic layer. FIG. 8 shows GdFe as the first magnetic layer and DyFe as the second magnetic layer.
The temperature dependence of the magneto-optical effect in a magneto-optical recording medium having Co as the second magnetic layer, and the temperature dependence of the magneto-optical effect in the magneto-optical recording medium having GdFeCoBi as the first magnetic layer and DyFeCo as the second magnetic layer. FIG. 9 is a graph in which the residual Kerr rotation angle is normalized by the saturation Kerr rotation angle, FIG. 9 is a graph in which the temperature characteristics of the magnetization of the material used as the first magnetic layer are compared, FIG. The magnetization transition angle at the last atomic plane of the read surface of the first magnetic layer is set to 0 in the direction perpendicular to the film plane.
FIG. 11 is a graph showing a calculation result based on molecular field theory plotted with the degree and the in-plane direction being 90 degrees, and FIG. 11 is a graph comparing the temperature characteristics of the magnetization of the material used as the first magnetic layer with the calculation based on molecular field theory. . The magneto-optical recording medium of the present invention,
(1) Example 1 to (4) Example 4 will be described in this order.

(1) Embodiment 1 As shown in FIG. 1, a magneto-optical recording medium A of the present invention has a dielectric layer 2 on a light-transmitting substrate 1 (the lower surface in FIG. 1).
The first magnetic layer 3, the second magnetic layer 4, and the dielectric layer 5 are sequentially laminated. The protective layer 6 is provided on the dielectric layer 5 (the lower surface in the figure) as needed. The arrows in the figure indicate the directions of the laser beams irradiated on the magneto-optical recording medium A during recording and reproduction (these laser beams are emitted from the light transmitting substrate 1 side).

The light transmissive substrate 1 is made of a glass plate, polycarbonate or the like. The above-mentioned dielectric layer 2 is formed of a transparent dielectric film which becomes a protective film or a multiple interference film.
The first and second magnetic layers 3 and 4 form a two-layer magnetic thin film sequentially laminated in vacuum, for example, by continuous sputtering or the like. The dielectric layer 5 is made of a non-magnetic metal film or a dielectric film. The above-mentioned protective layer 6 is formed on the dielectric layer 5 (the lower surface thereof in the figure) as necessary, using a UV (ultraviolet) curable resin or the like.

The first magnetic layer 3 is formed at room temperature (300
K) functions as an in-plane magnetization film having an easy magnetization direction in the in-plane direction (x direction in the figure), and when heated to a predetermined temperature above room temperature, the easy magnetization direction in the vertical direction (y direction in the figure). Mainly rare earth metal-3d that functions as a perpendicular magnetization film having
It is made of a transition metal alloy. In the first magnetic layer 3, the exchange energy between the rare earth metal and the 3d transition metal is small. The first magnetic layer 3 has a reversibility of returning to the original state of functioning as an in-plane magnetic film when the temperature is lowered after the first magnetic layer 3 functions as a perpendicular magnetic film.

The above-mentioned second magnetic thin film 4 is a rare earth metal-3d transition metal which functions as a perpendicular magnetization film having an easy magnetization direction in the vertical direction (from the room temperature to the Curie temperature) at all times (from the room temperature to the Curie temperature). Made of alloy. Then, information is recorded on the second magnetic thin film 4.

The first magnetic layer 3 is made of, for example, GdFe
It is composed of CoBi (gadolinium-iron-cobalt-bismuth alloy). On the other hand, the aforementioned second magnetic layer 4
Is composed of, for example, DyFeCo (dysprosium-iron-cobalt alloy).

When GdFe, GdFeCo, and GdFeCoBi are considered as the materials constituting the first magnetic layer 3, the magnetization temperature characteristics are as shown in FIG. In the figure, Temperature (K) is an absolute temperature, Magnetization (emu / c
m ³ ) indicates the magnitude of magnetization.

As shown in the figure, GdFe, GdFeC
The temperature characteristics of the respective magnetizations of o and GdFeCoBi are such that the magnitude of the magnetization gradually decreases as the temperature rises. The order of decreasing degree is GdFeCoB
i, GdFe, and GdFeCo in this order. Gd
By adjusting the composition of Gd in Fe and GdFeCo, it is possible to change the temperature characteristics shown in the figure, but it is not possible to make the temperature characteristics as steep as GdFeCoBi.

[0029] As materials constituting the first magnetic layer 3 mentioned above, GdFe, when considering each GdFeCoBi, its true magnetic anisotropy K _u and demagnetizing energy 2π
The temperature dependence of M _s ² is as shown in FIGS. In both figures, 2πM _s ² is the demagnetizing energy magnitude, K _u refers respectively to the magnitude of the true magnetic anisotropy. Each unit is 10 ⁵ erg / cm ³ .

Incidentally, the temperature characteristic of the magnetization of GdFeCoBi is, as apparent from FIG.
The temperature change of the magnetization is the steepest as compared with the temperature characteristics of each magnetization of e and GdFeCo. On the other hand, GdFeCoBi
The temperature dependence of the demagnetizing field energy 2πM _s ² of
As is apparent from FIG. 4, the change with respect to the temperature rise is much steeper than the temperature dependence of the demagnetizing field energy 2πM _s ² of GdFe. From these facts, it can be said that the steeper the temperature characteristic of the magnetization, the steeper the temperature change of the demagnetizing field energy. An example of such a material is GdFeCoBi.

Now, the above-mentioned GdFe and GdFeCo
The case where Bi is used as the first magnetic layer 3 of the magneto-optical recording medium A will be described. Specifically, there are two cases where the first magnetic layer 3 constituting the magneto-optical recording medium A shown in FIG. 1 is composed of GdFe and GdFeCoBi. In this case, the other components (light-transmitting substrate 1, dielectric layers 2 and 5, second magnetic layer 4, and protective layer 6) are the same.

[0032] Thus, GdFe, two magneto-optical recording medium A constituted respectively first magnetic layer 3 at GdFeCoBi, true magnetic anisotropy of the first magnetic layer 3 K _u and effective magnetic anisotropy K _u The temperature dependence of −2πM _s ² is as shown in FIG. In the figure, K _u -2πM _s ² (10
⁵ erg / cm ³ ) refers to the effective magnetic anisotropy. As shown in the figure, GdFe, each true magnetic anisotropy K _u of GdFeCoBi is approximately the same are varied in value, 3, demagnetizing energy temperature dependence of 2πM _s ² respectively shown in FIG. 4 well it reflects the sex, effective magnetic anisotropy K _u -2πM _s ² of GdFeCoBi, compared with the effective magnetic anisotropy K _u -2πM _s ² of GdFe, rapidly increases with temperature rise I have.

The true magnetic anisotropy K _u and the temperature dependence of the effective magnetic anisotropy K _u -2πM _s ² such GdFeCoBi is valid to improve the above-mentioned problems occurring in the prior art That's it. That is, in the above-described conventional magneto-optical recording medium, the material constituting the readout layer (first magnetic layer) has a wide temperature range of magnetization transition from the in-plane magnetization state to the perpendicular magnetization state. It is possible to solve the problem of the conventional technology that information recorded in an area (information domain) smaller than the laser spot diameter is insufficient to reproduce information with good S / N (C / N). . Specifically, as a material constituting the readout layer (first magnetic layer), a magnetization transition from an in-plane magnetization state to a perpendicular magnetization state due to a small exchange energy between the rare earth metal and the 3d transition metal is made. By using an alloy whose temperature range is narrow, a region (information domain) smaller than the laser spot diameter of the readout layer
The high-density recording information recorded on the
It is possible to provide a high-performance magneto-optical recording medium capable of realizing super-resolution reproduction capable of reproducing with good N (C / N).

[0034] In FIG. 5 mentioned above, the effective magnetic anisotropy K _u
The temperature at which the sign of −2πM _s ² changes from negative to positive (ie, G
dFeCoBi, GdFe of effective magnetic anisotropy K _u -2
The temperature at which πM _s ² becomes “0” is GdFe
It is about 440K in both CoBi and GdFe. Here, the sign of the effective magnetic anisotropy K _u -2πM _s ² is the negative state is that in-plane magnetization state, whereas it is a positive state is that the perpendicular magnetization state. This temperature is the temperature at which super-resolution reproduction is realized.

Therefore, how steeply the magnetization transition occurs near this temperature (about 440 K) is extremely important in improving the above-mentioned problem of the prior art, and determines the effect of improving the super-resolution detection. is there. FIGS. 6 and 7 show comparisons of magnetization transitions near about 440K.

FIGS. 6 and 7 show GdFe and GdF, respectively.
5 is a graph showing the temperature dependence of the residual Kerr rotation angle in a magneto-optical recording medium A having eCoBi as the first magnetic layer 3 and DyFeCo as the second magnetic layer 4. In both figures, Remane
nt Kerr rotation θ _kr (deg.)
_{Indicates the} residual Kerr rotation angle θ _kr (degree).

Specifically, the first magnetic layer 3 constituting the magneto-optical recording medium A shown in FIG. 1 is made of GdFe, GdFeCoB.
i. The other configurations (light-transmitting substrate 1, dielectric layers 2 and 5, second magnetic layer 4 made of DyFeCo, and protective layer 6) are the same.
Here, the thickness of the first magnetic layer 3 made of GdFe, GdFeCoBi is 50 nm, and the thickness of the second magnetic layer 4 is 30 nm.
nm.

As shown in FIG. 6, the temperature dependence of the residual Kerr rotation angle in the magneto-optical recording medium A in which the first magnetic layer 3 is made of GdFe indicates that the magneto-optical effect for reading, that is, the Kerr rotation angle is Temperature range (300K to 440K)
And is slowly rising to 440K. On the other hand, the temperature dependence of the residual Kerr rotation angle in the magneto-optical recording medium A in which the first magnetic layer 3 is made of GdFeCoBi is, as shown in FIG. 7, compared with the temperature dependence of GdFe shown in FIG. And the car rotation angle is narrower (37
(0K to 440K), it is rapidly rising to 440K. 6 and 7 show an improvement in the super-resolution detection effect from the conventional technology.

FIG. 8 is a diagram shown to make it easier to understand the difference in the temperature dependence of the residual Kerr rotation angle shown in FIGS. 6 and 7, respectively. In the figure, θ _kr / θ _k is GdFe, GdF
The values obtained by normalizing the residual Kerr rotation angle in the magneto-optical recording medium A in which the first magnetic layer 3 is made of eCoBi by the saturation Kerr rotation angle and comparing the reading characteristics, that is, the temperature dependence of the magneto-optical effect, are shown.

As shown in FIG. 3, the first magnetic layer 3 made of GdFeCoBi is made of GdFe.
The magneto-optical effect shows a sharper rise than that of the structure of (1). The fact that the value of θ _kr / θ _k shows a steep rise is equivalent to the fact that the magnetization transition occurs rapidly around about 440K. Therefore, Gd
The effectiveness of forming the first magnetic layer 3 with FeCoBi can be well understood.

This good result is due to the effect of Bi of GdFeCoBi constituting the first magnetic layer 3 of the magneto-optical recording medium A,
That is, it can be explained by the fact that the exchange integral between the rare earth (RE) and the transition metal (TM) is reduced. Due to the reduction of the exchange integral, the exchange energy decreases, and as a result, GdFeC
That is, the magnetization of oBi sharply decreases with the temperature rise.

Generally speaking, the magnitude of the exchange energy between RE and TM in a RE—Fe—Co alloy is expressed by the following equation (1). J _RE-Fe・ S _RE・ S _Fe + J _RE-Co・ S _RE・ S _Co (1) where J _RE-Fe : exchange integral between RE and Fe J _RE-Co : between RE and Co Exchange integral S _RE : RE spin S _Fe : Fe spin S _Co : Co spin

When the exchange energy between the RE and the TM decreases, the sublattice magnetization of the RE supported by the sublattice magnetization of the TM weakens, and the RE sublattice magnetization rapidly decreases with temperature. As a result, it is considered that the temperature change of the saturation magnetization becomes steep. Addition of Bi or Sn to GdFe is equivalent to lowering J _RE-Fe in the formula (1). Therefore, the same result as the case where the first magnetic layer 3 is formed of GdFeCoBi is obtained by GdFeCoSi.
This also occurs when the first magnetic layer 3 is composed of n.

(2) Embodiment 2 The problem described above is solved by the reduction of the exchange energy between the rare earth (RE) and the transition metal (TM) in the first magnetic layer 3 of the magneto-optical recording medium A of the present invention. However, it can be seen from the above equation (1) that the exchange energy can be reduced by reducing the spin of Fe in the first magnetic layer 3. Fe spin reduction can be achieved by adding Ni or Co. FIG. 9 shows the result of verifying this effect, and shows the temperature characteristics of the magnetization of three types of films of GdCoNi, GdFe having a Gd-rich composition, and GdFe having a Fe-rich composition. It can be seen that the magnetization of the GdCoNi film sharply decreases as the temperature rises. Therefore, it can be said that the above problem can be solved by using the GdCoNi film as the first magnetic layer 3.

(3) Embodiment 3 FIG. 10 shows (1) Embodiment 1 and (2) Embodiment 2 described above.
Is a calculation result based on the molecular field theory for verifying. The abscissa plots the temperature, and the ordinate plots the magnetization transition angle on the read surface of the first magnetic layer 3 with the direction perpendicular to the film surface as 0 degree. GdFeCoBi in which the exchange integral between the rare earth (RE) and the transition metal (TM) in the first magnetic layer 3 of the magneto-optical recording medium A of the present invention has decreased, and Gd in which the spin of Fe has decreased.
In CoNi, the magnetization transition of the first magnetic layer 3 changes from the in-plane direction (90 degrees) to the vertical direction (0 degrees) in the conventional GdFeC.
It can be seen that the transition is sharper than in the case of o. In this calculation, the calculation is performed by matching the temperatures at which the magnetization directions are completely perpendicular so that the difference between the magnetization transition characteristics of the three types of first magnetic layers 3 becomes clear. GdFeC
The results for oSn are similar to those for GdFeCoBi.

(4) Example 4 The spin of rare earth (RE) decreases as the atomic number increases. Therefore, from the relationship of the above equation (1), replacing Gd of GdFeCo with a heavy rare earth element having a larger atomic number can reduce the RE-TM exchange integral and the Fe spin, similarly to the decrease of the RE-TM exchange integral. It is considered that the magnitude of the exchange energy between TMs is reduced. Therefore, the temperature change of Ms caused by substituting Gd of GdFeCo with another heavy rare earth element was calculated by molecular field theory using parameters based on Hund's law and compared. FIG. 11 shows the result.

As shown in FIG. 11, TbFeCo, Dy
It can be seen that the saturation magnetization Ms of FeCo and HoFeCo decreases more rapidly with temperature rise than that of GdFeCo. From these results, the addition or substitution of heavy rare earths to the above-mentioned first magnetic layer 3, that is, Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb
It can be seen that the addition or substitution of an element such as (ytterbium) or Lu (lutetium) is effective in solving the above problem.

[0048]

As described above, according to the present invention, in particular, a rare earth metal is used as a material constituting the readout layer (first magnetic layer).
By using an alloy in which the exchange energy between the 3d transition metals is small and the temperature range of the magnetization transition from the in-plane magnetization state to the perpendicular magnetization state is narrow,
High-density recording information recorded in an area (information domain) smaller than the laser spot diameter of the readout layer can be reproduced, and crosstalk during reproduction can be eliminated. To achieve high-density recording and reproduction, and to achieve higher reproduction S /
It is possible to provide a magneto-optical recording medium as a super-resolution medium capable of improving N (C / N).

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of a magneto-optical recording medium of the present invention.

FIG. 2 is a graph comparing the temperature characteristics of the magnetization of a substance to be a first magnetic layer.

FIG. 3 is a graph comparing the temperature dependence of the true magnetic anisotropy and the demagnetizing field energy of the material used as the first magnetic layer.

FIG. 4 is a graph comparing the temperature dependence of the true magnetic anisotropy and the demagnetizing field energy of the material used as the first magnetic layer.

FIG. 5 is a graph comparing temperature dependency of true magnetic anisotropy and effective magnetic anisotropy in a first magnetic layer constituting a magneto-optical recording medium.

FIG. 6 is a graph showing temperature dependence of a residual Kerr rotation angle in a magneto-optical recording medium in which GdFe is a first magnetic layer and DyFeCo is a second magnetic layer.

FIG. 7 shows a first magnetic layer made of GdFeCoBi and DyFeCo.
7 is a graph showing the temperature dependence of a residual Kerr rotation angle in a magneto-optical recording medium having a second magnetic layer.

FIG. 8 shows the temperature dependence of the magneto-optical effect in a magneto-optical recording medium having GdFe as the first magnetic layer and DyFeCo as the second magnetic layer, and GdFeCoBi as the first magnetic layer and DyFeC as the first magnetic layer.
5 is a graph comparing the temperature dependence of the magneto-optical effect in a magneto-optical recording medium in which o is the second magnetic layer, with the residual Kerr rotation angle normalized by the saturation Kerr rotation angle.

FIG. 9 is a graph comparing the temperature characteristics of the magnetization of the material used as the first magnetic layer.

FIG. 10 is a graph in which the horizontal axis represents temperature, and the vertical axis represents the magnetization transition angle at the final atomic plane of the readout surface of the first magnetic layer as 0 relative to the direction perpendicular to the film plane.
9 is a graph showing calculation results based on molecular field theory plotted with degrees and an in-plane direction set to 90 degrees.

FIG. 11 is a graph comparing temperature characteristics of magnetization of a material used as a first magnetic layer, calculated by molecular field theory.

[Explanation of symbols]

 Reference Signs List 1 transparent substrate 3 first magnetic layer (reading layer) 4 second magnetic layer (recording layer) A magneto-optical recording medium

Claims (10)

[Claims] 1. A magnetic layer formed on a transparent substrate, having an easy direction of magnetization in an in-plane direction at room temperature, and changing the easy direction of magnetization to a vertical direction when the temperature is raised to a predetermined temperature higher than room temperature.
A first magnetic layer mainly composed of a rare earth metal-3d transition metal alloy having a small exchange energy between the rare earth metal and the 3d transition metal; and a magnetic layer formed on the first magnetic layer and magneto-optically recording information. And a second magnetic layer made of a rare earth metal-3d transition metal alloy having a direction of easy magnetization in a perpendicular direction at room temperature or higher. 2. The magneto-optical recording medium according to claim 1, wherein said first magnetic layer is made of GdFeCoBi. 3. The magneto-optical recording medium according to claim 1, wherein said first magnetic layer is GdFeCoSn. 4. The magneto-optical recording medium according to claim 1, wherein said first magnetic layer is made of GdCoNi. 5. The method according to claim 1, wherein the first magnetic layer is made of GdFeCoBi.
Rare earth elements Tb, Dy, Ho, Er, Tm, Yb, Lu
At least one of the above, or
Gd constituting GdFeCoBi is converted to a rare earth element Tb,
2. The magneto-optical recording medium according to claim 1, wherein the alloy is an alloy substituted with any one of Dy, Ho, Er, Tm, Yb, and Lu. 6. The method according to claim 1, wherein the first magnetic layer is made of GdFeCoSn.
Rare earth elements Tb, Dy, Ho, Er, Tm, Yb, Lu
At least one of the above, or
Gd constituting GdFeCoBi is converted to a rare earth element Tb,
2. The magneto-optical recording medium according to claim 1, wherein the alloy is an alloy substituted with any one of Dy, Ho, Er, Tm, Yb, and Lu. 7. The first magnetic layer according to claim 1, wherein at least one of the rare earth elements Tb, Dy, Ho, Er, Tm, Yb and Lu is added to GdCoNi.
Gd constituting FeCoBi is converted to a rare earth element Tb, D
2. The magneto-optical recording medium according to claim 1, wherein the alloy is an alloy substituted with any one of y, Ho, Er, Tm, Yb, and Lu. 8. The alloy according to claim 1, wherein the first magnetic layer is formed by adding a fourth element for reducing rare earth spin to GdFeCo;
Alternatively, to reduce rare earth spin, GdFeC
2. The magneto-optical recording medium according to claim 1, wherein the alloy is an alloy in which one of the elements o is replaced with another element. 9. The alloy according to claim 1, wherein the first magnetic layer is made of an alloy obtained by adding a fourth element for reducing transition metal spin to GdFeCo or GdFeCo for decreasing transition metal spin.
2. The magneto-optical recording medium according to claim 1, wherein the alloy is one in which one of FeCo is replaced by another element. 10. The alloy according to claim 1, wherein the first magnetic layer is an alloy of GdFeCo to which a fourth element for reducing the exchange integral between the rare earth and the transition metal is added, or an alloy for decreasing the exchange integral between the rare earth and the transition metal. 2. The magneto-optical recording medium according to claim 1, wherein said alloy is an alloy in which one of GdFeCo is replaced by another element.