Magneto-optical recording medium whereon recording is carried out with an overwriting function

A magneto-optical recording medium is consisted of a recording layer, a readout layer and a writing layer. The readout layer is made of rare earth-transition metal alloys wherein an easy magnetization axis is parallel to the recording layer at room temperature, and the easy magnetization axis is perpendicular to the recording layer as the temperature of the readout layer is raised above a predetermined temperature by irradiating thereon with a light beam. The writing layer is made of rare earth-transition metal alloys having such coercive force that a magnetization direction thereof is switched by an external magnetic field at room temperature and Curie temperature that is above Curie temperature of the recording layer. With the above arrangement, an overwriting function can be achieved by adjusting a light intensity of the light beam so that the temperature falls within the range between the Curie temperature of the writing layer and the Curie temperature of the recording layer, or above the Curie temperature of the writing layer.

FIELD OF THE INVENTION 
The present invention relates to a recording medium to be adopted in 
magneto-optical recording devices, such as a magneto-optical disk, a 
magneto-optical tape, magneto-optical card, etc. 
BACKGROUND OF THE INVENTION 
There has been a limit in improving the recording density of a 
magneto-optical recording medium by being dependent on the size of a light 
spot of a light beam used for recording and reproducing on and from the 
recording medium. This is because a diameter of the light spot on the 
recording medium becomes a diameter of a recorded bit. However, recently, 
a magneto-optical recording medium has been proposed wherein recorded bits 
with a size smaller than the size of a light spot can be reproduced. 
Normally, the light beam for use in optical recording is converged to a 
diffraction limit by a converging lens. Therefore, the light intensity 
distribution shows a Gaussian distribution, and thus the temperature 
distribution due to the light beam on the recording medium also exhibits 
the Gaussian distribution. As a result, a spot having a temperature above 
a predetermined temperature becomes smaller in size than the size of the 
light spot. Consequently, a significant improvement in the recording 
density can be achieved if only the spot having a temperature above the 
predetermined temperature is used for reproduction. 
Referring to FIG. 16, the following description will discuss a 
magneto-optical disk wherein a recorded bit with a size smaller than the 
size of a light spot can be reproduced. 
The magneto-optical disk is mainly consisted of a substrate 21 having a 
readout layer 23 and a recording layer 24 formed on a surface thereof. The 
recording layer 24 has great coercive force at room temperature. On the 
other hand, the readout layer 23 has small coercive force at room 
temperature. When the temperature of an area of the readout layer 23 to be 
reproduced is raised by irradiating thereon with a reproduction-use light 
beam, the magnetization direction thereof becomes coincident with the 
magnetization direction of the recording layer 24 due to the effect of the 
recording layer 24. That is, the magnetization of the recording layer 24 
is copied to the readout layer 23 by exchange coupling force between the 
readout layer 23 and the recording layer 24. 
Recording on the described magneto-optical disk is executed by the ordinary 
thermomagnetic writing method. When the recorded bits are to be 
reproduced, it is necessary to initialize the magnetization direction of 
the readout layer 23 so as to make it coincident with the predetermined 
direction (upward in the figure) by applying an external magnetic field 
for initializing from a magnetic field generating device 26. Then, by 
projecting thereto a reproduction-use light beam 27, the temperature of 
the readout layer 23 is locally raised. As a result, the portion having a 
temperature rise of the readout layer 23 has small coercive force, and the 
magnetization direction of the recording layer 24 is copied to the readout 
layer 23 by the exchange coupling force. In this way, since only the 
information stored in the center area which has received the 
reproduction-use light beam 27 and undergone a temperature rise is 
reproduced, recorded bits with a size smaller than that of the light spot 
are permitted to be read out. 
However, when using the discussed magneto-optical disk, the following 
problem arises. During reproduction, a recorded bit that has been copied 
to the readout layer 23 from the recording layer 24 remains as it is even 
after the temperature of the spot has cooled off. This means that when a 
spot to be irradiated by the light beam 27 is shifted by a rotation of the 
magneto-optical disk so as to reproduce the next bit, the bit previously 
copied still exists within the light beam 27 and tends to be reproduced. 
This causes noise and has prevented improvement in recording density. 
Furthermore, the magneto-optical disk having the described configuration 
cannot be provided with the overwriting function through a light intensity 
modulation method. This presents another problem by requiring a long time 
for data writing. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a magneto-optical 
recording medium including recorded bits each of which having a diameter 
smaller than that of a light spot, whereon a recording operation can be 
carried out using an overwriting function through a light intensity 
modulation method. 
In order to achieve the above object, the magneto-optical recording medium 
in accordance with the present invention comprising a substrate through 
which a light beam is to be transmitted and a recording-reproduction layer 
whereon information is recorded magneto-optically is characterized by the 
following arrangements. 
The recording-reproduction layer includes a readout layer and a recording 
layer and a writing layer made of rare earth-transition metal alloys, each 
of which has its Curie temperature. A magnetic condition of the readout 
layer exhibits in-plane magnetization at room temperature. On the other 
hand, when the temperature of the readout layer is raised above a 
predetermined temperature by irradiating thereon with a light beam, a 
transition of the magnetic condition occurs from the in-plane 
magnetization to the perpendicular magnetization. (Here, the in-plane 
magnetization indicates a magnetic characteristic wherein an easy 
magnetization axis is parallel to the recording layer surface, and the 
perpendicular magnetization indicates a magnetic characteristic wherein 
the easy magnetization axis is perpendicular to the recording layer 
surface.) A recording layer is provided for storing information. A writing 
layer has such small coercive force that the magnetization direction 
thereof is switched by external recording magnetic filed at room 
temperature. In addition, the Curie temperature of the writing layer is 
above the Curie temperature of the recording layer. 
Here, the readout layer, the recording layer and the writing layer are 
laminated in this order. Further, it is arranged such that when the 
temperature of the recording-reproduction layer is raised to a temperature 
within the range between the Curie temperature of the recording layer and 
the Curie temperature of the writing layer by irradiating thereon with a 
light beam, a magnetization direction of the recording layer is arranged 
in the magnetization direction of the writing layer. Whereas, when the 
temperature of the recording-reproduction layer is raised above the Curie 
temperature of the writing layer, the magnetization direction of the 
recording layer is arranged in the magnetization direction of an external 
recording magnetic field. 
When recording operation is carried out on the magneto-optical disk having 
the above configuration using the overwriting function through the light 
intensity modulation method, the writing layer is initialized by applying 
thereto an initialization-use magnetic field prior to recording so that 
the magnetization direction thereof is arranged in one direction. Next, 
the temperature of the recording-reproduction layer is raised to a 
temperature within the range between the Curie temperature of the 
recording layer and the Curie temperature of the writing layer by 
adjusting a light intensity of the light beam. In this way, the 
magnetization direction of the writing layer, i.e., the initialized 
magnetization direction is copied to the recording layer by exchange 
coupling force between the recording layer and the writing layer. Or the 
temperature of the recording-reproduction layer is raised above the Curie 
temperature of the writing layer by adjusting the light intensity of the 
light beam. Consequently, the magnetization direction of the recording 
layer is arranged in the magnetization direction of an externally applied 
recording magnetic field. 
As described, by adjusting the light intensity of the light beam, a 
recording operation can be carried out on the magneto-optical recording 
medium using the overwriting function. Here, the magnetic condition of the 
readout layer exhibits in-plane magnetization and thus has no effect on 
the recording operation. 
On the other hand, when reproducing information, the magnetic condition of 
the readout layer exhibits the in-plane magnetization at room temperature 
and does not show the magneto-optical effect (polar Kerr effect) that is 
effective on a perpendicular incident light beam. Further, when the 
temperature of the central portion thereof is raised by irradiating 
thereon with a reproduction-use light beam, a transition of the magnetic 
condition occurs in the readout layer from the in-plane magnetization to 
the perpendicular magnetization. As a result, the magnetization direction 
of the readout layer is arranged in the magnetization direction of the 
recording layer. In this way, the readout layer shows the magneto-optical 
effect, thereby permitting to perform a reproducing operation. Further, 
when the reproduction-use light beam is shifted, the previously irradiated 
spot has cooled off. Thus, the magnetic condition of the readout layer 
again exhibits in-plane magnetization, thereby no longer showing the 
magneto-optical effect. 
According to the above arrangement, the reproducing operation is carried 
out only with respect to a central portion of a light spot having a 
temperature above a predetermined temperature. This means that the 
recording density is determined by a temperature distribution but by a 
diameter of the light spot. In this way, as long as a enough signal 
intensity required for reproduction is ensured, in principle, a 
significant increase can be obtained in the recording density. 
In addition, the magnetic condition of the readout layer exhibits the 
in-plane magnetization at room temperature, and thus has no effect on the 
recording operation. Moreover, the readout layer does not show the 
magneto-optical effect that is effective on the perpendicular incident 
light. This permits to reduce the occurrence of crosstalk from the 
adjacent track.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1 through 9, the following description will discuss one 
embodiment of the present invention. 
As shown in FIG. 1, a magneto-optical disk as a magneto-optical recording 
medium in accordance with the present embodiment is consisted of a 
substrate 1, a transparent dielectric film 2a, a readout layer 3, a 
recording layer 4, a writing layer 6, a transparent dielectric film 2b and 
an overcoat film 11 that are laminated in this order. Further, a 
recording-reproduction layer is consisted of the readout layer 3, the 
recording layer 4 and the writing layer 6. 
FIG. 4 shows the magnetic condition of rare earth-transition metal alloys 
used in the readout layer 3, where a range in which the magnetic condition 
of the alloys exhibits a perpendicular magnetization is extremely narrow. 
This is because the perpendicular magnetization only appears in the 
vicinity of a compensating composition (T.sub.comp) where the magnetic 
moments of the rare-earth metal and the transition metal balance one 
another (range A in the figure). Here, temperature dependence of the the 
magnetic moments of the rare-earth metal and the transition metal are 
respectively different from one another. That is, at high temperatures, 
the magnetic moment of the transition metal is set greater than that of 
the rare-earth metal. Therefore, it is arranged that the content of the 
rare-earth metal is set greater that in the compensating composition at 
room temperature (composition indicated by dot lines in the figure), and 
such an alloy then exhibits a in-plane magnetization at room temperature 
without showing the perpendicular magnetization. Whereas, when a 
temperature of the alloy is raised above the temperature T.sub.1, the 
magnetic moment of the transition metal becomes relatively greater until 
it balances the magnetic moment of the rare-earth metal, thereby 
permitting the alloy to show the perpendicular magnetization as a whole. 
Further, when a temperature rises above temperature T.sub.2, the balance 
is no longer kept, and thus the alloy exhibits the in-plane magnetization 
again. 
FIG. 3 shows temperature dependencies of respective coercive forces H.sub.c 
of the readout layer 3, the writing layer 6 and the recording layer 4. The 
recording layer 4 has greater coercive force at Curie temperature T.sub.R 
that is below Curie temperature T.sub.S of the writing layer 6 and at room 
temperature. Whereas, the magnetization direction of the recording layer 4 
becomes coincident with the magnetization direction of the writing layer 6 
at high temperature. On the other hand, the writing layer 6 has small 
coercive force at low temperature, and the magnetization direction thereof 
is uniformly arranged in one direction by applying thereto an 
initialization-use external magnetic field. 
In the present embodiment, Gd.sub.0.28 (Fe.sub.0.8 Co.sub.0.2).sub.0.72 is 
employed as the readout layer 3, whose Curie temperature is on the order 
of 300.degree. C.-400.degree. C. As described earlier, since the content 
of the rare-earth metal is set greater, it exhibits the in-plane 
magnetization at room temperature, and the compensating composition is 
marked in the vicinity of 100.degree. C. Here, T.sub.1, T.sub.C and 
T.sub.2 respectively represent 90.degree. C., 120.degree. C. and 
150.degree. C. On the other hand, Dy.sub.0.23 (Fe.sub.0.82 
Co.sub.0.18).sub.0.77 is employed as the recording layer 4 whose Curie 
temperature T.sub.R is set on the order of 150.degree. C.-250.degree. C. 
Further, Tb.sub.0.25 (Fe.sub.0.8 Co.sub.0.2).sub.0.75 is used for the 
writing layer 6, whose Curie temperature T.sub.S is 300.degree. C. 
The thickness of the transparent dielectric film 2a is set to be a value 
that is obtained by dividing one-forth of the wavelength of a 
reproduction-use light beam by the refractive index. For example, assuming 
that the wavelength of the reproduction-use light beam is 800 nm, the film 
thickness of the transparent dielectric film 2a is on the order of 80 
nm-100 nm. In addition, the transparent dielectric film 2b is a protective 
film made of a nitride, having a thickness of 50 nm. 
FIGS. 5 through 8 respectively show the relationships between the 
externally-applied magnetic field H.sub.ex and the Kerr rotation angle 
.theta..sub.K, that is, the magnetic characteristics within respective 
ranges: from room temperature to temperature T.sub.1 ; from temperature 
T.sub.1 to temperature T.sub.c ; from temperature T.sub.c to temperature 
T.sub.2 ; and from temperature T.sub.2 to the Curie temperature 
T.sub.curie. 
The graph shows an abruptly rising hysteresis characteristic, i.e., the 
perpendicular magnetization, within the range from temperature T.sub.1 to 
temperature T.sub.2 ; however, within the range from room temperature to 
temperature T.sub.1 as well as within the range from temperature T.sub.2 
to the Curie temperature T.sub.curie, no hysteresis characteristic is 
shown. 
The following description will discuss the recording operation on the 
magneto-optical disk having the described arrangement using the 
overwriting function through an optical modulation method referring to 
FIGS. 1 and 2. 
First, the initialization-use magnetic field is applied onto the 
magneto-optical disk by a magnetic field generation device 12. Here, since 
the writing layer 6 has small coercive force at room temperature, the 
magnetization direction of the writing layer 6 is arranged in the 
magnetization direction of the applied magnetic field (upward in the 
figure), thereby completing the initialization of the writing layer 6. 
Next, a light beam 7 is projected onto a portion to be recorded from the 
side of the substrate 1 through a converging lens 8. Whereas, a recording 
magnetic field 5 whose magnetization direction is opposite to the 
magnetization direction of the initialization-use magnetic field is 
applied to the portion. For example, as shown in FIG. 1, when the 
magnetization direction of the recorded portion of the recording layer 4 
is coincident with that of the initialization-use magnetic field (upward 
in the figure), the temperature of the irradiated spot is raised above the 
Curie temperature T.sub.s of the writing layer 6 by adjusting the light 
intensity of the light beam 7. Here, since the Curie temperature T.sub.R 
of the recording layer 4 is below the Curie temperature T.sub.s, both the 
recording layer 4 and the writing layer 6 have respective temperatures 
above the respective Curie temperatures. As a result, the respective 
magnetization directions become coincident with the magnetization 
direction of the recording magnetic field 5, thereby completing the 
recording operation. 
On the other hand, as shown in FIG. 2, when the magnetization direction of 
the recorded portion of the recording layer 4 is opposite to that of the 
initialization-use magnetic field (downward in the figure), and thus needs 
to be reversed so as to make it coincident with that of the 
initialization-use magnetic field, the temperature of the irradiated spot 
of the recording layer 4 is raised to a temperature within the range 
between the Curie temperature T.sub.R of the recording layer 4 and the 
Curie temperature T.sub.S of the writing layer 6 by adjusting the light 
intensity of the light beam 7. In this way, the magnetization direction of 
the writing layer 6 is copied to the recording layer 4 by exchange 
coupling force between the recording layer 4 and the writing layer 6. 
Consequently, the magnetization direction of the recording layer 4 is 
arranged in the magnetization direction of the initialization-use magnetic 
field. 
Additionally, in either one of the above cases, the temperature of the 
readout layer 3 is raised above temperature T.sub.2 by irradiating thereon 
with the light beam 7, thus the magnetic condition of the readout layer 3 
exhibits the in-plane magnetization. In other words, this does not affect 
the recording operation. 
When reproducing from the magneto-optical disk having the above-mentioned 
arrangement, as shown in FIG. 9, a reproduction-use light beam 9 is 
projected onto the readout layer 3 through the converging lens 8 from the 
side of the substrate 1. In this case, assuming that recordings have been 
made on the recording layer 4, for example, as shown in FIG. 9 (i.e., a 
magnetization direction is downward in the figure), a temperature rise 
occurs at a spot of the readout layer 3, located in the vicinity of the 
center of the reproduction-use light beam 9, to the vicinity of 
100.degree. C., i.e., between T.sub.1 and T.sub.2. Then, at the spot 
having a temperature rise, a transition of the magnetic condition occurs 
from the in-plane magnetization to the perpendicular magnetization. In 
this way, the magnetization direction of the recording layer 4 is copied 
to the readout layer 3 by exchange coupling force between the readout 
layer 3 and the recording layer 4, whereby the magnetization direction of 
the readout layer 3 is coincident with the magnetization direction of the 
recording layer 4. 
After the transition of the magnetic condition from the in-plane 
magnetization to the perpendicular magnetization has occurred in the spot 
of the readout layer 3 having the temperature rise, the Kerr effect is 
shown, whereby the information recorded on the recording layer 4 is 
reproduced according to the reflected light from the spot. 
On the other hand, in other areas on the readout layer 3 except the spot in 
the vicinity of the center of the reproduction-use light beam 9, the 
temperature is not raised above T.sub.1, and thus the in-plane 
magnetization is maintained. As a result, the Kerr effect is not shown 
with respect to the perpendicular incident light beam. 
When the reproduction-use light beam 9 is shifted so as to reproduce the 
next recorded bit, the temperature of the previous bit has cooled off and 
the transition of the magnetic condition of the readout layer 3 occurs 
from the perpendicular magnetization to the in-plane magnetization. 
Accordingly, the Kerr effect is not shown at the spot having the 
temperature drop. Consequently, the interference by signals from the 
adjoining bits, which causes noise, is eliminated. 
Since the Kerr effect is obtained only in the vicinity of the center of the 
reproduction-use light beam, as long as enough signal intensity is 
ensured, the application of this magneto-optical disk for information 
recording and reproduction makes it possible to reproduce a recorded bit 
with a size smaller than the diameter of the light spot, resulting in a 
significant increase in the recording density. 
Besides the above-mentioned Gd.sub.0.28 (Fe.sub.0.8 Co.sub.0.2).sub.0.72, 
for example, Gd.sub.0.25 Co.sub.0.75 may be preferably employed as a 
material for the readout layer 3. In this case, since Gd.sub.0.25 
Co.sub.0.75 has smaller coercive force than Gd.sub.0.28 (Fe.sub..8 
Co.sub.0.2).sub.0.72, in addition to the effect of the above embodiment, 
one of the disturbing factors to the externally-applied magnetic field at 
a temperature where the readout layer exhibits the perpendicular 
magnetization during recording can be minimized, thereby making smoother 
the shape of the recorded bit. 
Referring to FIGS. 10 through 13, the following description will discuss 
another embodiment of the present invention. For the sake of convenience, 
members having the same function as in the first embodiment will be 
designated by the same code and their description will be omitted. 
A magneto-optical recording medium of the present embodiment differs from 
that of the first embodiment in that only a recording layer 13 made of 
(Gd.sub.0.8 Tb.sub.0.2).sub.0.35 Fe.sub.0.65 is used instead of the 
readout layer 3 and the recording layer 4. Namely, as shown in FIG. 10, 
the magneto-optical recording disk is consisted of the substrate 1, the 
transparent dielectric film 2a, a recording layer 13, the writing layer 6, 
the transparent dielectric film 2b and the overcoat film 11 that are 
laminated in this order. 
FIG. 11 shows magnetic conditions of GdTbFe. As shown by dot lines in the 
figure, (Gd.sub.0.8 Tb.sub.0.2).sub.0.35 Fe.sub.0.65 used in the present 
embodiment does not fully exhibit in-plane magnetization at room 
temperature, and have some components of perpendicular magnetization and 
thus stores information. In addition, the Curie temperature of the 
recording layer 13 is below the Curie temperature of the writing layer 6. 
FIGS. 12 and 13 show the relationship between the externally applied 
magnetic field H.sub.ex to be applied on (Gd.sub.0.8 Tb.sub.0.2) .sub.0.35 
Fe.sub.0.65 and the Kerr rotation angle .theta..sub.K. 
When recording on the magneto-optical disk using the overwriting function, 
as shown in FIG. 10, the temperature of the irradiated spot is raised 
above Curie temperature of the writing layer 6, or within the range 
between the Curie temperature of the recording layer 13 and Curie 
temperature of the writing layer 6 by adjusting the light intensity of the 
light beam 7 as in the case of the first embodiment. As a result, the 
magnetic condition of the recording layer 13 exhibits a perpendicular 
magnetization that is arranged in a predetermined direction (upward or 
downward in the figure). Further, when the light beam 7 is shifted, and 
thus the temperature of the previously recorded bit has cooled off, the 
magnetic condition of the recording layer 13 exhibits in-plane 
magnetization while keeping components of perpendicular magnetization. 
On the other hand, when reproducing information, only the recorded bit on 
the recording layer 13 having a temperature rise above temperature T.sub.1 
shown in FIG. 11 exhibits the perpendicular magnetization. This means that 
the light reflected from the spot having the temperature rise shows the 
Kerr effect, thereby reproducing the information. 
As described, the employed magneto-optical disk has a double-layered 
magnetic layer composed of the recording layer 13 and the writing layer 6. 
This permits to simplify the manufacturing process thereof in comparison 
with the case of employing the magneto-optical disk of the first 
embodiment having a magnetic layer consisted of three layers. 
A still another embodiment of the present invention is described 
hereinbelow referring to FIG. 14. For the sake of convenience, members 
having the same function as in the first embodiment will be designated by 
the same code and their description will be omitted. 
A magneto-optical disk of the present embodiment is consisted of the 
substrate 1, the transparent dielectric film 2a, the readout layer 3, the 
recording layer 4, the writing layer 6, a switching layer 14, an 
initialization-use magnetic layer 15, the transparent dielectric film 2b 
and the overcoat film 11 that are laminated in this order. Namely, the 
magneto-optical disk of the present embodiment differs from that of the 
first embodiment in that the switching layer 14 and the initialization-use 
magnetic layer 15 are further laminated under the writing layer 6. 
The initialization-use magnetic layer 15 whose Curie temperature is above 
300.degree. C. has large coercive force at whole range of temperature, and 
the magnetization direction thereof is always fixed to one direction. For 
the switching layer 14, for example, TbFe may be used, and in this case 
Curie temperature thereof is 120.degree. C. Therefore, at room 
temperature, the magnetization direction of the initialization-use 
magnetic layer 15 is copied to the switching layer 14. Further, the 
magnetization direction of the switching layer 14 is copied to the writing 
layer 6. Consequently, the magnetization direction of the writing layer 6 
is arranged in the magnetization direction of the initialization-use 
magnetic layer 15. 
In the case of recording information, when the temperature of the switching 
layer 14 is raised above the Curie temperature thereof by irradiating 
thereon with the light beam 7, the magnetization direction of the 
initialization-use magnetic layer 15 is no longer copied. Thus, the 
writing layer 6 is not affected by the magnetization direction of the 
initialization-use magnetic layer 15. As a result, the temperature of the 
irradiated spot is raised to a predetermined temperature by adjusting the 
light intensity of the light beam 7 as in the case of the first 
embodiment, whereby the magnetization direction of the recording layer 4 
is arranged either in the magnetization direction of the recording 
magnetic field 5 or the writing layer 6, thereby recording information. In 
addition, the readout layer 3 exhibits the in-plane magnetization as in 
the case of the first embodiment, and thus has no effect on the recording 
operation. 
When the spot irradiated by the light beam 7 is shifted, and thus the 
temperature of the previously recorded bit has cooled off, the 
magnetization direction of the writing layer 6 is again arranged in the 
magnetization direction of the initialization-use magnetic layer 15 
through the switching layer 14. 
According to the above arrangement of the magneto-optical disk, the 
magnetization direction of the writing layer 6 can be arranged in the 
magnetization direction of the initialization-use magnetic field by the 
switching layer 14. This permits to reduce the number of the components of 
the recording-reproducing apparatus because the magnetic field generation 
device 12 of FIG. 1 for applying the initialization-use magnetic field is 
no longer required. 
A still another embodiment of the present invention is described 
hereinbelow, referring to FIG. 15. 
A magneto-optical disk employed in the present embodiment differs from that 
of the second embodiment in that the switching layer 14 and the 
initialization-use magnetic layer 15 of the third embodiment are further 
laminated under the writing layer 6. Namely, the magneto-optical recording 
disk is consisted of the substrate 1, the transparent dielectric film 2a, 
a recording layer 13, the writing layer 6, the switching layer 14, the 
initialization-use magnetic layer 15, the transparent dielectric film 2b 
and the overcoat film 11 that are laminated in this order. 
According to the arrangement of the present embodiment, the recording layer 
and the readout layer are integrated into a single layer. This simplifies 
the manufacturing processes of the disk compared with the disk having them 
separately. Moreover, since the switching layer 14 and the 
initialization-use magnetic layer 15 are provided, the magnetization 
direction of the writing layer 6 can be arranged in a magnetization 
direction of the initialization-use magnetic field. This permits to reduce 
the number of the components because the magnetic field generation device 
12 of FIG. 10 is no longer required. 
The invention being thus described, it will be obvious that the same may be 
varied in many ways. Such variations are not to be regarded as a departure 
from the spirit and scope of the invention, and all such modifications as 
would be obvious to one skilled in the art are intended to be included 
within the scope of the following claims.