Magneto-optical recording medium and reproduction method therefor

A magneto-optical recording medium comprises, on a substrate, a dielectric layer, a GdFeCo reproducing layer, a non-magnetic layer, and a TbFeCo recording layer. Upon reproduction, a DC magnetic field Hex is applied in the recording direction, and a reproducing light beam is radiated while being modulated to have a low power and a high power in synchronization with a reproducing clock. The reproducing layer is a magnetic film which changes from in-plane magnetization into perpendicular magnetization at a critical temperature Tcr, which has a compensation temperature Tcomp between room temperature and a Curie temperature Tc, and which satisfies Troom<Tcr<Tcomp<Tco<Tc in relation to a Curie temperature Tco of the recording layer.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a magneto-optical recording medium and a 
reproducing method thereon. In particular, the present invention relates 
to a magneto-optical recording medium and a reproducing method thereon 
which are suitable for high density recording and which make it possible 
to perform reproduction by magnifying a minute recording magnetic domain 
which is extremely smaller than a reproducing light spot. 
2. Description of Related Art 
The magneto-optical recording medium is a highly reliable recording medium 
having a large storage capacity on which information is rewritable. 
Therefore, the magneto-optical recording medium begins to be practically 
used as a computer memory and the like. However, a technique for 
performing recording and reproduction at a higher density is demanded in 
view of the increase in amount of information and the advance of the 
apparatus to acquire a compact size. In order to record information on the 
magneto-optical recording medium, a recording system based on the magnetic 
field modulation is used, in which a magnetic field having a polarity 
corresponding to a recording signal is applied to a portion at which the 
temperature is raised, while irradiating the magneto-optical recording 
medium with a laser beam. This system makes it possible to perform 
overwrite recording, in which high density recording has been achieved. 
For example, recording has been achieved with a shortest mark length of 
0.15 .mu.m. A recording system based on the optical modulation has been 
also practically used, in which recording is performed by radiating a 
power-modulated light beam corresponding to a recording signal while 
applying a constant magnetic field. 
When it is intended to reproduce information from a recording mark having 
been recorded at a high density, a problem arises concerning the optical 
reproducing resolving power which is determined by a spot diameter of a 
reproducing light beam. For example, it is impossible to perform 
reproduction while distinguishing a minute mark having a magnetic domain 
length of 0.15 .mu.m by using a reproducing light beam having a spot 
diameter of 1 .mu.m. In order to eliminate the restriction for the 
reproducing resolving power resulting from the optical spot diameter of 
the reproducing light beam as described above, one approach has been 
suggested concerning the magnetically induced super resolution technique 
(MSR) as described, for example, in Journal of Magnetic Society of Japan, 
Vol. 17, Supplement No. S1, p. 201 (1993). This technique utilizes the 
occurrence of the temperature distribution over a magnetic film included 
in a reproducing light beam spot when a magneto-optical recording medium 
is irradiated with a reproducing light beam. A magnetic mask is generated 
in the spot so that the effective spot diameter, which contributes to 
signal reproduction, is reduced. The use of this technique makes it 
possible to improve the reproducing resolving power without reducing the 
actual spot diameter of the reproducing light beam. However, in the case 
of this technique, since the effective spot diameter is decreased by means 
of the magnetic mask, the amount of light which contributes to the 
reproduction output is decreased, and the reproduction C/N is lowered to 
that extent. As a result, it is difficult to obtain sufficient C/N. 
Japanese Laid-Open Patent Publication No. 1-143041 discloses a method for 
performing reproduction on a magneto-optical recording medium comprising a 
first magnetic film, a second magnetic film, and a third magnetic film 
which are magnetically coupled to one another at room temperature. 
Assuming that the first, second, and third magnetic films have Curie 
temperatures of T.sub.C1, T.sub.C.sub.2, and T.sub.C3 respectively, there 
are given T.sub.C2 &gt;room temperature and T.sub.C2 &lt;T.sub.C1, T.sub.C3. The 
coercive force H.sub.C1 of the first magnetic film is sufficiently small 
in the vicinity of the Curie temperature T.sub.C2 of the second magnetic 
film. The coercive force H.sub.C3 of the third magnetic film is 
sufficiently larger than a required magnetic field in a temperature range 
from room temperature to a required temperature T.sub.PB which is higher 
than T.sub.C2. The magneto-optical recording medium is used to perform 
reproduction while magnifying the recording magnetic domain in the first 
magnetic film. This method utilizes the increase in temperature of the 
medium when the reproducing light beam is radiated so that the magnetic 
coupling between the first and third magnetic films is intercepted. In 
this state, the magnetic domain in the first magnetic film is magnified by 
using the externally applied magnetic field and the diamagnetic field 
acting on the recording magnetic domain. It is noted that this technique 
uses the second magnetic film in which the Curie temperature is set to be 
lower than the temperature of the readout portion during reproduction. 
However, the present invention does not use any magnetic film having such 
a magnetic characteristic. 
Japanese Laid-Open Patent Publication No. 8-7350 discloses a 
magneto-optical recording medium comprising a reproducing layer and a 
recording layer on a substrate, on which reproduction can be performed 
while magnifying a magnetic domain in the recording layer during the 
reproduction. When the magneto-optical recording medium is subjected to 
reproduction, an alternating magnetic field is used as a reproducing 
magnetic field to alternately apply a magnetic field in a direction to 
magnify the magnetic domain and a magnetic field in the opposite 
direction. Thus, the magnetic domain is magnified and reduced for each of 
the magnetic domains. 
The present inventors have disclosed, in International Publication WO 
97/22969, a method for performing reproduction on a magneto-optical 
recording medium, in which a reproducing light beam is radiated onto the 
magneto-optical recording medium having a magneto-optical recording film 
which is a perpendicularly magnetizable film at a temperature not less 
than room temperature to detect the magnitude of the magneto-optical 
effect so that a recorded signal is reproduced. 
The magneto-optical recording medium to be used is a magneto-optical 
recording medium comprising, on the magneto-optical recording film, an 
auxiliary magnetic film which causes transition from an in-plane 
magnetizable film to a perpendicularly magnetizable film when the 
temperature exceeds a critical temperature, with a non-magnetic film 
interposed therebetween. The magneto-optical recording film and the 
auxiliary magnetic film satisfy a relationship of room 
temperature&lt;T.sub.CR &lt;T.sub.CO, T.sub.C provided that the magneto-optical 
recording film and the auxiliary magnetic film have Curie temperatures of 
T.sub.CO and T.sub.C respectively, and the critical temperature of the 
auxiliary magnetic film is T.sub.CR. The recording signal is reproduced by 
irradiating the magneto-optical recording medium with the reproducing 
light beam which is power-modulated at the same cycle as that of a 
reproducing clock or at a cycle created by the multiplication of an 
integer and the reproduction clock. In this reproducing method having the 
foregoing feature, the reproducing light beam is modulated to have 
reproducing light powers of Pr.sub.1 and Pr.sub.2 at the same cycle as 
that of the reproducing clock or at the cycle created by the 
multiplication of an integer and the reproducing clock. This patent 
document discloses that one of the reproducing light powers of Pr.sub.1 
and Pr.sub.2 is a power to cause magnification of the magnetic domain in 
the auxiliary magnetic film. The principle of the reproducing method will 
be explained by using a schematic diagram concerning the reproducing 
method shown in FIG. 19. In this reproducing method, as conceptually shown 
in FIGS. 6A and 6B, a magneto-optical recording medium is used, which has 
a structure comprising, on a recording layer 10, an auxiliary magnetic 
layer 8 with a non-magnetic layer 9 intervening therebetween. At first, a 
predetermined recording pattern as shown in FIG. 19(a) is recorded on the 
second type magneto-optical recording medium as the magneto-optical 
recording medium by using, for example, the optical modulation recording 
system. In FIG. 19(a), the recording mark is recorded at a shortest mark 
pitch DP, and the recording mark length DL is set to give DL=DP/2. Upon 
reproduction, a pulse laser beam, which is modulated to have two kinds of 
reproducing powers Pr2, Pr1, is used as the reproducing laser beam to be 
radiated so that the cycle which synchronized with the recording mark 
position is DP, and the light emission width of the high power Pr2 is DL 
as shown in FIG. 19(b). The light beam having the low reproducing power 
Pr1 is always radiated in an erasing state (onto portions at which no 
recording mark exists), and the light beam having the high reproducing 
power Pr2 is radiated in a recording state (onto portions at which the 
recording mark exists) and in the erasing state. 
FIG. 19(c) illustrate a reproduced signal waveform obtained by radiating 
the reproducing pulse laser as shown in FIG. 19(b). On the other hand, 
FIG. 19(d) illustrates a reproduced signal waveform obtained when the same 
track is subjected to reproduction by using a continuous light beam having 
a constant reproducing light power. Pr2 and Pr1 are selected as follows. 
That is, Pr2 is a recording power to cause the magnification of the 
magnetic domain in the auxiliary magnetic film 8 as described later on. 
Pr1 is a power to extinguish the magnified magnetic domain. When the 
reproducing power is selected as described above, the amplitude H.sub.p1, 
which is provided between the recording state and the erasing state 
observed during the reproduction with the pulse light beam, is allowed to 
satisfy H.sub.p1 &gt;H.sub.dc with respect to the amplitude H.sub.dc obtained 
upon the reproduction with the constant laser beam. Further, the 
magnetization information, which is recorded in each of the magnetic 
domains of the magneto-optical recording film, can be independently 
magnified and reproduced without being affected by adjacent magnetic 
domains. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a reproducing method which 
is achieved by further improving the reproducing method disclosed in 
International Publication WO 97/22969. 
The present invention has been made in order to solve the problems involved 
in the conventional technique, by means of a method different from the 
methods described in Japanese Laid-Open Patent Publication Nos. 1-143041 
and 8-7350, an object of which is to provide a magneto-optical recording 
medium and a method for reproducing signals thereon, wherein a reproduced 
signal is obtained with sufficient C/N even when a minute magnetic domain 
is subjected to recording. 
Another object of the present invention is to provide a magneto-optical 
recording medium and a reproducing method thereon which make it possible 
to reliably erase a magnified magnetic domain immediately after 
reproduction of a recording magnetic domain even when the magnetic domain 
is magnified during reproduction. 
According to a first aspect of the present invention, there is provided a 
method for performing reproduction on a magneto-optical recording medium 
for reproducing a recorded signal by irradiating the magneto-optical 
recording medium with a reproducing light beam to detect magnitude of an 
magneto-optical effect, the reproducing method comprising the steps of: 
using, as the magneto-optical recording medium, a magneto-optical recording 
medium comprising a magneto-optical recording film having perpendicular 
magnetization, an auxiliary magnetic film which transfers from an in-plane 
magnetizable film to a perpendicularly magnetizable film when a 
temperature exceeds a critical temperature Tcr and a non-magnetic film 
intervened between the magneto-optical recording film and the auxiliary 
magnetic film, the magneto-optical recording medium having a magnetic 
characteristic to satisfy a relationship of room 
temperature&lt;Tcr&lt;Tcomp&lt;Tco&lt;Tc concerning a Curie temperature Tco of the 
magneto-optical recording film and a Curie temperature Tc and a 
compensation temperature Tcomp of the auxiliary magnetic film; and 
executing reproduction of the recorded signal through the steps of 
irradiating the magneto-optical recording medium with the reproducing 
light beam which is power-modulated to have at least two light powers of 
Pr.sub.1 and Pr.sub.2 at the same cycle as that of a reproducing clock or 
at a cycle created by the multiplication of an integer and the reproducing 
clock while applying a DC magnetic field so that a recording magnetic 
domain in the magneto-optical recording film is transferred to the 
auxiliary magnetic film, the transferred magnetic domain is magnified, and 
the magnified magnetic domain is reduced or extinguished, wherein: 
the magneto-optical recording medium is specified, under a condition in 
which an external magnetic field Hex is applied to the magneto-optical 
recording medium, such that a temperature curve A of a transfer magnetic 
field which is generated by the external magnetic field Hex and the 
magneto-optical recording film, and a temperature curve B of a coercive 
force of the auxiliary magnetic film in a perpendicular direction 
intersect at a point between room temperature and the compensation 
temperature Tcomp of the auxiliary magnetic film, and the temperature 
curve A and the temperature curve B intersect at a point between the 
compensation temperature Tcomp of the auxiliary magnetic film and the 
Curie temperature Tco of the magneto-optical recording film. 
It is preferable in the reproducing method of the present invention that 
the light power Pr.sub.1 of the reproducing light beam is a power to heat 
the auxiliary magnetic film to a temperature from Tcr to Tcomp so that the 
recording magnetic domain in the magneto-optical recording film is 
transferred to the auxiliary magnetic film and the magnetic domain is 
magnified, and the light power Pr.sub.2 of the reproducing light beam is a 
power to heat the auxiliary magnetic film to a temperature from Tcomp to 
Tco so that the magnified magnetic domain is reduced or extinguished. 
The transfer magnetic field may be represented by a sum of the external 
magnetic field Hex and a static magnetic field Ht from the magneto-optical 
recording film, and the coercive force of the auxiliary magnetic film in 
the perpendicular direction may be represented by a sum of a coercive 
force Hr in the perpendicular direction of the magnetic domain subjected 
to the transfer and an exchange coupling force Hw exerted on the magnetic 
domain subjected to the transfer by adjoining magnetic domains. 
The method for transferring the recording magnetic domain inscribed on the 
recording layer to the reproducing layer so that the transfer signal on 
the reproducing layer is magnified and read in order to obtain a high 
quality reproduced signal is called "magnetic amplification-mediated 
magneto-optical system (MAMMOS)", which has been confirmed by the present 
applicant by using the external magnetic field modulation reproducing 
method (WO 98-02878). In the external magnetic field modulation 
reproducing method, the magnification and the reduction are executed for 
the magnetic domain transferred to the reproducing layer by using an 
alternating magnetic field during reproduction. In the present invention, 
experiments have been carried out from various viewpoints for the 
magneto-optical system based on the magnetic amplification to advance 
detailed analysis and investigation. As a result, the present inventors 
have succeeded in development of the method which makes it possible to 
reliably realize the magnification and the reduction of the transferred 
magnetic domain by making modulation to give two or more kinds of 
reproducing light powers by using the direct current magnetic field. 
Explanation will be made for the principle of the reproducing method on the 
magneto-optical recording medium according to the first aspect of the 
present invention. The reproducing method is based on the use of the 
magneto-optical recording medium comprising the magneto-optical recording 
film having the perpendicular magnetization, and the auxiliary magnetic 
film which causes transition from the in-plane magnetizable film to the 
perpendicularly magnetizable film when the temperature exceeds the 
critical temperature Tcr, with the non-magnetic film interposed 
therebetween. FIG. 9 shows an illustrative structure of the 
magneto-optical recording medium of this type. A magneto-optical disk 90 
shown in FIG. 9 comprises, in a stacked form on a substrate 1, a 
dielectric film 3, an auxiliary magnetic film 8, a non-magnetic film 3, a 
magneto-optical recording film 10, and a protective film 7. The auxiliary 
magnetic film 8 has a compensation temperature Tcomp between a critical 
temperature Tcr and its Curie temperature Tc. The magneto-optical 
recording medium 90 satisfies the relationship of room 
temperature&lt;Tcr&lt;Tcomp&lt;Tco&lt;Tc concerning the Curie temperature Tco of the 
magneto-optical recording film 10, the critical temperature Tcr, the Curie 
temperature Tc, and the compensation temperature Tcomp of the auxiliary 
magnetic film 8. 
Reproduction is performed in accordance with the reproducing method of the 
present invention by radiating the light power-modulated reproducing light 
beam while applying the external DC magnetic field to the magneto-optical 
recording medium 90 having the magnetic characteristic as described above. 
FIG. 11 shows magnetic characteristics of the magneto-optical recording 
film 10 and the auxiliary magnetic film 8 of the magneto-optical disk 90 
in a state in which the constant DC magnetic field Hex is applied to the 
magneto-optical recording medium 90 in the recording direction. The 
magnetic temperature curve A shown in FIG. 11 denotes a 
temperature-dependent change in transfer magnetic field (static magnetic 
field) generated by the magnetization of the recording layer from the 
magneto-optical recording film 10 (hereinafter simply referred to as 
"recording layer") to the auxiliary magnetic film 8 (hereinafter simply 
referred to as "reproducing layer"). The transfer magnetic field of the 
curve A represents the magnitude of the magnetic field obtained by adding 
an amount of offset of the external magnetic field Hex. Therefore, the 
magnetic filed having the magnitude of (Hex-Ht) and the magnetic field 
having the magnitude of (Hex+Ht) exist as the entire transfer magnetic 
field depending on the direction of the magnetic domain of the recording 
layer, with a boundary of the Curie temperature Tco of the recording 
layer. The two magnetic fields constitute the curve A. In FIG. 9, the 
downward direction is the recording direction. Hex is applied in the 
downward direction. In this case, the external magnetic field Hex is 
adjusted to be small as compared with the magnitude of the static magnetic 
field Ht in the initializing direction generated from the magnetization of 
the recording layer at room temperature. Therefore, the entire transfer 
magnetic field includes those directed in the upward direction (negative) 
and in the downward direction (positive) depending on the magnetization 
direction of the recording magnetic domain in the recording layer as 
illustrated by the curve A. 
The magnetic temperature curve B denotes the temperature-dependent change 
of the coercive force in the perpendicular direction of the reproducing 
layer in a state of having the perpendicular magnetization. The coercive 
force is represented by Hr+Hw as including the pure coercive force Hr of 
the magnetic domain in the reproducing layer in the perpendicular 
direction and the magnetic field Hw corresponding to a virtual magnetic 
field regarded to be applied by generation of the magnetic wall of the 
reproducing layer (in other words, the exchange coupling magnetic field in 
the in-plane direction of the reproducing layer). That is, Hr+Hw 
represents the magnetic field necessary to perform inversion of the 
magnetization in the direction perpendicular to the film surface of the 
reproducing layer. As shown in FIG. 11, the magnetization in the direction 
perpendicular to the film surface of the reproducing layer appears at a 
temperature which is not less than the critical temperature Tcr (T0 in 
FIG. 11) at which the reproducing layer behaves as a perpendicularly 
magnetizable film. The coercive force is maximal at the compensation 
temperature Tcomp because the magnetization of the reproducing layer is 
zero. 
The temperature curves A and B shown in FIG. 11 are divided into those 
belonging to three areas (a) to (c) as shown in FIG. 11. The three areas 
(a) to (c) correspond to the three steps of i) magnetic domain transfer 
from the recording layer to the reproducing layer, ii) magnification of 
the transferred magnetic domain in the reproducing layer, and iii) 
extinguishment of the magnified magnetic domain, in the reproducing method 
of the present invention as shown in FIG. 12A respectively. Accordingly, 
explanation will be made with reference to FIG. 12 for the magnetic 
characteristics required for the recording layer and the reproducing layer 
in the areas (a) to (c) shown in FIG. 11. Arrows in the recording layer 
and the reproducing layer shown in FIG. 12A denote the direction of the 
magnetic moment of the rare earth metal included in each of the magnetic 
domains. 
The area (a) is a temperature area in which the magnetic domain is 
transferred from the recording layer to the reproducing layer in the 
reproducing method of the present invention, which belongs to a 
temperature range of T0 to T1 in FIG. 12A. T0 means the critical 
temperature Tcr, and T1 is a temperature at which the magnetic temperature 
curve A on the side of Hex-Ht initially intersects the magnetic 
temperature curve B. The temperature range T0 to T1 can be achieved by 
adjusting the light power of the reproducing light beam to be a relatively 
low power as described later on. In order to actually perform the magnetic 
transfer as shown in FIG. 12A (1) in this temperature area, it is 
necessary that the magnitude of the transfer magnetic field in this 
temperature area exceeds the coercive force of the reproducing layer in 
the perpendicular direction. That is, when the magnetization recorded on 
the recording layer is in the direction .dwnarw. (recording direction), it 
is necessary that the transfer magnetic field represented by Hex+Ht is 
larger than Hr+Hw or -(Hr+Hw) (requirement for magnetic domain transfer). 
When the magnetization recorded on the recording layer is in the direction 
.uparw. (erasing direction), it is necessary that the negative transfer 
magnetic field represented by Hex-Ht is smaller than the coercive force 
Hr+Hw or -(Hr+Hw) of the reproducing layer in the perpendicular direction 
(requirement for magnetic domain transfer). 
On the other hand, when the magnetic temperature curves A and B are 
compared with each other in the area (a) shown in FIG. 11, it is 
appreciated that the relationships of the following expressions (a1) to 
(a3) hold. 
EQU Hr&lt;Hex+Ht-Hw (a1) 
EQU -Hr&gt;Hex-Ht+Hw (a2) 
EQU Hr&gt;Hex-Ht-Hw (a3) 
Therefore, the area (a) satisfies the magnetic domain transfer requirement 
described above, and the recording magnetic domain in the recording layer 
can be transferred to the reproducing layer regardless of the direction of 
magnetization thereof. FIG. 12A (1) shows a case in which the 
magnetization in the direction .dwnarw.; recorded in a magnetic domain 210 
in the recording layer is transferred to an area of the reproducing layer 
at a temperature which exceeds the temperature T0 within the reproducing 
light spot so that a transferred magnetic domain 201a is formed. 
Subsequently, in the area (b) shown in FIG. 11, the magnetic domain 
magnification is performed for the magnetic domain 201b transferred to the 
reproducing layer as shown in FIG. 12A (2) and (3). This temperature area 
resides in a range indicated by T1 to T2 in FIG. 11. The temperature T2 is 
a temperature at which the magnetic temperature curve A on the side of 
Hex-Ht intersects the magnetic temperature curve B on the high temperature 
side. The magneto-optical disk having the magnetic characteristic shown in 
FIG. 11 is adjusted such that T2 is approximately coincident with the 
compensation temperature Tcomp of the reproducing layer (the temperature 
exists between the compensation temperature Tcomp and the Curie 
temperature Tco of the recording layer, and the temperature is a 
temperature extremely close to the compensation temperature Tcomp) in 
relation to the external magnetic field Hex. In this temperature area, as 
shown in FIG. 12A (2), magnetic domains 203, 203', which are subjected to 
magnetic transfer from magnetic domains 212, 212' in the recording layer 
in the upward direction, exist on both sides of the magnetic domain 201b 
transferred to the reproducing layer, as a result of being heated to T0 to 
T1 within the reproducing light spot. In order to allow the magnetic 
domain 201b transferred to the reproducing layer to start magnification in 
the in-plane direction, it is necessary that the directions of the 
magnetic domains 203, 203' disposed on the both sides are directed to the 
recording direction (direction .dwnarw.) in the same manner as the 
magnetic domain 201b. The magnetic domains 203, 203' receives the transfer 
magnetic field (Hex-Ht) (totally in the direction .uparw.) obtained by 
adding, to the external magnetic field Hex, the static magnetic field Ht 
in the upward direction from magnetic domains 212 in the recording layer 
existing just thereover. On the other hand, the magnetic domains 203, 203' 
have the coercive force in the perpendicular direction including the 
exchange coupling magnetic field Hw (in the downward direction) exerted by 
the magnetic domain 201b and the coercive force Hr to invert the 
magnetization of the magnetic domains 203, 203' themselves. Therefore, 
when the coercive force in the perpendicular direction (Hr+Hw) is made 
larger than the transfer magnetic field (Hex-Ht) of the magnetic domains 
203, 203', the magnetic domains 203, 203' are inverted (requirement for 
magnetic domain inversion). 
It is appreciated that the following relational expressions hold in the 
area (b) according to the relative magnitude between the magnetic 
temperature curves A and B. 
EQU Hr&lt;Hex+Ht-Hw (b1) 
EQU -Hr&lt;Hex-Ht+Hw (b2) 
EQU Hr&gt;Hex-Ht-Hw (b3) 
The foregoing expression (b2) is the condition of magnetic domain inversion 
itself under which the coercive force (Hr+Hw) in the perpendicular 
direction is larger than the transfer magnetic field Hex-Ht (in the upward 
direction) of the magnetic domains 203, 203'. Therefore, the magnetic 
domain magnification occurs in the area (b) for the magnetic domain 201b 
in the reproducing layer as shown in FIG. 12A (3). According to the 
relationship of (b2), it is demonstrated that no magnetic domain in the 
downward direction appears in the reproducing layer when there is no 
magnetic domain in the recording direction in the reproducing layer, in 
the temperature area (b). In FIG. 12A (3), the both sides of the magnified 
magnetic domain 201b are the temperature area of T0 to T1. Therefore, the 
magnetic domains 203, 203' in the direction .uparw., which are subjected 
to the magnetic domain transfer from the magnetic domains 212, 212' in the 
recording layer, exist therein. 
Subsequently, in the area (c), the transferred and magnified magnetic 
domain is inverted (extinguished), and a magnetic domain 201c in the 
erasing direction is formed as shown in FIG. 12A (4). This temperature 
area exists in a range from T2 which slightly exceeds the compensation 
temperature of the reproducing layer, to the Curie temperature Tco of the 
recording layer. The magnified and reproduced magnetic domain can be 
extinguished or reduced by applying the reproducing magnetic field in the 
erasing direction, i.e., by using the alternating magnetic field as the 
reproducing magnetic field. However, in the reproducing method of the 
present invention, the DC magnetic field is used to extinguish the 
magnified magnetic domain by power-modulating the reproducing light beam 
to have the power higher than the reproducing light power used to perform 
the magnetic transfer and the magnification. The reproducing light power 
may be modulated to be further small in order to extinguish the magnified 
magnetic domain, as described in the first embodiment of the reproducing 
method on the magneto-optical recording medium according to the present 
invention as described later on. 
Explanation will be made with reference to FIGS. 13A and 13B for the 
principle to invert (extinguish) the magnified magnetic domain in the area 
(c). FIGS. 13A and 13B illustrate the temperature-dependent change of the 
direction and the magnitude of sub-lattice magnetization of the rare earth 
metal and the transition metal of the magnetic domain 210 in the recording 
layer composed of the rare earth-transition metal (TbFeCo alloy) and the 
magnetic domain 201b in the reproducing layer composed of the rare 
earth-transition metal (GdFeCo alloy) subjected to the magnetic domain 
transfer therefrom shown in FIG. 12A (2). As shown in FIG. 13A, when the 
temperature of the reproducing layer is less than the compensation 
temperature Tcomp, then the magnetization of the rare earth metal in the 
reproducing layer is dominant, and it is parallel to the magnetization 
direction of the recording layer of the transfer source (the magnetization 
of the transition metal is dominant). Subsequently, when the temperature 
of the reproducing layer exceeds the compensation temperature Tcomp by 
radiating the high power laser in accordance with the reproducing method 
of the present invention, the magnetic moment of the transition metal in 
the reproducing layer is dominant. It is appreciated that the following 
expressions (c1) and (c2) hold according to the relative magnitude of the 
magnetic temperature curves A and B of the reproducing layer and the 
recording layer in the area (c) shown in FIG. 11. 
EQU Hr&lt;Hex+Ht-Hw (c1) 
EQU Hr&lt;Hex-Ht-Hw (c2) 
That is, the coercive force Hr of the magnetic domain 201b is smaller than 
the entire magnetic field (Hex+Ht-Hw or Hex-Ht-Hw) in the recording 
direction acting on the magnetic domain 201b. As a result, when the 
temperature of the reproducing layer is not less than the compensation 
temperature Tcomp (exactly, when it is not less than T2), the dominant 
magnetic moment of the transition metal is inverted to be directed in the 
recording direction as shown in FIG. 13B. Therefore, the magnetic moment 
of the rare earth metal in the downward direction of the magnified 
magnetic domain 201b shown in FIG. 12A (3) is inverted in the area which 
is heated to the temperature not less than the temperature of the area 
(c), i.e., not less than the compensation temperature Tcomp. Thus, the 
inverted magnetic domain 201c is generated (FIG. 12A (4)). The magnetic 
domains 201d, 201d', which are disposed on the both sides of the inverted 
magnetic domain 201c, have their temperatures ranging from T1 to T2. 
Therefore, the magnetic domains 201d, 201d' have the same magnetization 
direction as that of the magnified magnetic domain 201b. 
In the reproducing method according to the present invention, the three 
temperature areas (a) to (c) can be achieved by modulating the reproducing 
light power to have at least the two power levels Pr.sub.1 and Pr.sub.2 as 
shown in FIG. 12B. That is, the light power Pr.sub.1 of the reproducing 
light beam may be the power for heating the auxiliary magnetic layer to 
the temperature of Tcr to Tcomp and making it possible to transfer the 
recording magnetic domain in the magneto-optical recording film to the 
reproducing layer and magnify the magnetic domain. The light power 
Pr.sub.2 of the reproducing light beam may be the power for heating the 
auxiliary magnetic layer to the temperature of Tcomp to Tco and reducing 
or extinguishing the magnified magnetic domain as described above. The 
Pr.sub.1 /Pr.sub.2 power-modulated reproducing light beam is used as the 
reproducing light beam in synchronization with the reproducing clock. 
Thus, the recording magnetic domain in the recording layer can be 
subjected to reproduction through the steps of i) transfer to the 
reproducing layer, ii) magnification of the transferred magnetic domain, 
and iii) extinguishment of the magnified magnetic domain. 
According to a second aspect of the present invention, there is provided a 
magneto-optical recording medium having at least a magneto-optical 
recording film on a substrate, the magneto-optical recording medium 
comprising the magneto-optical recording film having perpendicular 
magnetization, an auxiliary magnetic film which transfers from an in-plane 
magnetizable film to a perpendicularly magnetizable film when a 
temperature exceeds a critical temperature Tcr with a non-magnetic film 
intervened between the magneto-optical recording film and the auxiliary 
magnetic film, wherein a relationship of room temperature&lt;Tcr&lt;Tcomp&lt;Tco&lt;Tc 
holds concerning a Curie temperature Tco of the magneto-optical recording 
film and a Curie temperature Tc and a compensation temperature Tcomp of 
the auxiliary magnetic film, and wherein under a condition in which an 
external magnetic field Hex is applied to the magneto-optical recording 
medium, a temperature curve A of a transfer magnetic field which is 
generated by the external magnetic field Hex and the magneto-optical 
recording film, and a temperature curve B of a coercive force of the 
auxiliary magnetic film in a perpendicular direction intersect at a point 
between room temperature and the compensation temperature Tcomp of the 
auxiliary magnetic film, and the temperature curve A and the temperature 
curve B intersect at a point between the compensation temperature Tcomp of 
the auxiliary magnetic film and the Curie temperature Tco of the 
magneto-optical recording film. 
The magneto-optical recording medium according to the second aspect of the 
present invention is a magneto-optical recording medium which is 
preferably used for the reproducing method according to the first aspect 
of the present invention. Even in the case of a minute magnetic domain 
which is smaller than the light spot, the magnetic An domain can be 
subjected to reproduction independently from other magnetic domains to 
give an amplified reproduced signal, by performing reproduction on the 
magneto-optical recording medium by using the reproducing method according 
to the first aspect of the present invention. It is preferable that the 
temperature T.sub.2, at which the temperature curve A and the temperature 
curve B intersect, satisfies Tcomp.ltoreq.T.sub.2 .ltoreq.Tco. 
According to a third aspect of the present invention, there is provided a 
magneto-optical recording medium having at least a magneto-optical 
recording film on a substrate, the magneto-optical recording medium 
comprising: 
a first auxiliary magnetic film which causes transition from a 
perpendicularly magnetizable film to an in-plane magnetizable film when a 
temperature exceeds a critical temperature Tcr.sub.11 ; and 
a second auxiliary magnetic film which causes transition from an in-plane 
magnetizable film to a perpendicularly magnetizable film when the 
temperature exceeds a critical temperature Tcr.sub.12. 
Explanation will be made with reference to FIG. 14 for an example of the 
structure of the magneto-optical recording medium according to the third 
aspect of the present invention. As shown in FIG. 14, the magneto-optical 
recording medium 100 successively comprises, on a magneto-optical 
recording film 10, a first auxiliary magnetic film 28, a non-magnetic film 
29, and a second auxiliary magnetic film 24. The magneto-optical recording 
film 10 is a perpendicularly magnetizable film. The first auxiliary 
magnetic film 28 is a magnetic film which causes transition from a 
perpendicularly magnetizable film to an in-plane magnetizable film when 
the temperature exceeds the critical temperature Tcr.sub.11. The second 
auxiliary magnetic film 24 is a magnetic film which causes transition from 
an in-plane magnetizable film to a perpendicularly magnetizable film when 
the temperature exceeds the critical temperature Tcr.sub.12. It is assumed 
herein that materials and compositions of the magnetic films are adjusted 
so that the critical temperature Tcr.sub.11 of the first auxiliary 
magnetic film is higher than the critical temperature Tcr.sub.12 of the 
second auxiliary magnetic film. The second auxiliary magnetic film 24 
functions as a reproducing layer. 
Explanation will be made with reference to FIGS. 16A to 16C for the 
principle of reproduction on the magneto-optical recording medium 
according to the third aspect. FIG. 16A conceptually illustrates main 
components of the magneto-optical recording medium shown in FIG. 14. It is 
assumed that the magnetization in the upward direction is recorded in a 
magnetic domain 22 of the magneto-optical recording film 10. The 
magneto-optical recording film 10 and the first auxiliary magnetic layer 
28 make exchange coupling to one another. The same magnetization as that 
of the magnetic domain 22 is transferred to a magnetic domain 28a of the 
first auxiliary magnetic layer 28 disposed just under the magnetic domain 
22. When the magneto-optical recording medium is irradiated with a 
reproducing light means, and the temperature begins to rise, then the 
transition occurs from the in-plane magnetization to the perpendicular 
magnetization in an area of the second auxiliary magnetic film 24 in which 
its temperature exceeds the critical temperature Tcr.sub.12. The area 
subjected to the transition corresponds to magnetic domains 24a, 24b shown 
fin FIG. 16B. During the transition, the magnetic domain 24a is aligned in 
the same magnetization direction as that of the magnetic domain 22 as 
shown in FIG. 16B by the aid of the magnetostatic coupling force exerted 
by the magnetic domain 22 of the recording layer 10 disposed just 
thereover and the magnetic domain 28a of the first auxiliary magnetic film 
28. FIG. 16B illustrates the temperature-rising process of the 
magneto-optical recording medium effected by the reproducing light beam, 
and it represents a magnetization state in which the temperature T of the 
magneto-optical recording medium does not arrive at a maximum arrival 
temperature yet and the temperature is within a range of Tcr.sub.12 
&lt;T&lt;Tcr.sub.11. In this state, the recording layer 10, the first auxiliary 
magnetic layer 28, and the second auxiliary magnetic layer 24 are 
magnetically coupled (magnetostatically coupled) to one another, and any 
of them exhibits the perpendicular magnetization. Minute magnetic domains 
24b, which have the magnetization in the downward direction by the aid of 
the magnetostatic coupling force exerted by the both magnetic domains 
adjacent to the magnetic domain 22 and the magnetic domains in the 
downward direction in the first auxiliary magnetic film 28 disposed just 
thereunder, are present on both adjoining sides of the magnetic domain 
24a. 
When the temperature of the medium is further raised to arrive at the 
heating maximum temperature, if the temperature of the high temperature 
area of the first auxiliary magnetic layer 28 exceeds the critical 
temperature Tcr.sub.11, then the coercive force of the first auxiliary 
magnetic layer 28 is lowered, and thus the first auxiliary magnetic layer 
28 in the high temperature area causes transition from the perpendicular 
magnetization to the in-plane magnetization. As a result, a magnetic 
domain 28a' is formed as shown in FIG. 16C. 
FIG. 17 shows a relationship between the temperature distribution and the 
magnetization state of the medium shown in FIG. 16C. In the case of this 
magneto-optical recording medium, there is given Tcr.sub.12 &lt;Tcr.sub.11 as 
described above. Accordingly, as shown in FIG. 17, the area, in which the 
temperature exceeds Tcr.sub.12 in the temperature distribution of the 
medium, is wider than the area in which the temperature exceeds 
Tcr.sub.11. The transition occurs from the in-plane magnetization to the 
perpendicular magnetization in the area in which the temperature exceeds 
Tcr.sub.12 in the second auxiliary magnetic layer 24. The transition 
occurs from the perpendicular magnetization to the in-plane magnetization 
in the area in which the temperature exceeds Tcr.sub.11 in the first 
auxiliary magnetic layer 24. Therefore, the magnetic domain 24a' having 
the perpendicular magnetization in the second auxiliary magnetic layer 24 
is larger than the magnetic domain 28a' having the in-plane magnetization 
in the first auxiliary magnetic layer 24. The reproducing light power and 
Tcr.sub.12 are adjusted so that the area, in which the temperature exceeds 
Tcr.sub.12 in the second auxiliary magnetic layer 24 upon irradiation with 
the reproducing light beam, is larger than the magnetic domain in the 
recording layer 10. 
On the other hand, the magnetic domain 28a' in the first auxiliary magnetic 
layer 28 has the in-plane magnetization. Therefore, the magnetic influence 
can be intercepted, which would be otherwise exerted from the 
magneto-optical recording film 10 to the second auxiliary magnetic film 
24, due to, for example, the leakage magnetic field and the static 
magnetic field caused by the magnetization in the direction .dwnarw.; 
existing on both adjoining sides of the magnetic domain 22. Accordingly, 
it is possible to facilitate the magnification of the magnetic domain 
24a'. The magnification of the magnetic domain increases the reproduced 
signal. It is considered that C/N is improved owing to the function of the 
first auxiliary magnetic film 24 to cause magnetic interception. In order 
to more effectively use the magnetically intercepting function of the 
first auxiliary magnetic film 28, it is preferable that the critical 
temperature Tc.sub.11 of the first auxiliary magnetic film 28 and the 
reproducing light power are selected so that the area, in which the 
temperature exceeds Tcr.sub.11 in the first auxiliary magnetic layer 28 
during reproduction, is larger than the recording magnetic domain 11. In 
order to obtain a sufficiently large reproduced signal by the aid of the 
magnetic domain magnification in the second auxiliary magnetic layer 24, 
it is preferable that the critical temperature Tc.sub.12 of the second 
auxiliary magnetic film 24 and the reproducing light power are selected so 
that the area, in which the temperature exceeds Tcr.sub.12 in the second 
auxiliary magnetic layer 24 during reproduction, is larger than the 
recording magnetic domain 11. In order to simultaneously satisfy the 
facilitating effect for magnifying the magnetic domain and the 
magnetically intercepting function of the first auxiliary magnetic film 
28, it is desirable to appropriately control the relationship 
(.DELTA.T=Tcr.sub.11 -Tcr.sub.12) between the critical temperature 
Tcr.sub.11 of the first auxiliary magnetic film 28 and the critical 
temperature Tcr.sub.12 of the second auxiliary magnetic film 24. 
The effect of the magnification of the magnetic domain of the second 
auxiliary magnetic film 24, i.e., the reproduced signal intensity is 
maximized when the transferred magnetic domain in the second auxiliary 
magnetic film 24 is magnified to be not less than the reproducing light 
spot diameter. In this state, an extremely large reproduction output, 
which is determined by only the performance index of the second auxiliary 
magnetic film 24 and the reproducing light beam, is obtained regardless of 
the size and the shape of the magnetic domain recorded in the 
magneto-optical recording film 10. After the reproduction, i.e., after the 
unit for radiating the reproducing light beam is moved, the readout 
portion is cooled to be not more than Tcr.sub.12, and the second auxiliary 
magnetic film is in the in-plane magnetization state to return to the 
state shown in FIG. 16A. The coercive force of the magneto-optical 
recording film 10 is sufficiently large even at the temperature during the 
reproducing operation as described above. Therefore, the information 
recorded as magnetization is completely retained. 
It is desirable for the magneto-optical recording medium according to the 
third aspect of the present invention that a relationship of room 
temperature&lt;Tcr.sub.12 &lt;Tcr.sub.11 &lt;Tco, Tc.sub.1, Tc.sub.2 holds 
concerning a Curie temperature Tco of the magneto-optical recording film, 
a Curie temperature Tc, and the critical temperature Tcr.sub.11 of the 
first auxiliary magnetic film, and a Curie temperature Tc.sub.2 and the 
critical temperature Tcr.sub.12 of the second auxiliary magnetic film.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments and Examples of the magneto-optical recording medium and the 
reproducing method thereon according to the present invention will be 
explained with reference to the drawings. However, the present invention 
is not limited thereto. 
First Embodiment 
This embodiment is illustrative of specified embodiments of the medium 
belonging to the magneto-optical recording medium of the present invention 
and the reproducing method for performing reproduction by using the medium 
while changing the reproducing laser beam in a pulse form. A medium having 
a structure shown in FIG. 1 is used as the magneto-optical recording 
medium. 
[Production of magneto-optical recording medium] 
A glass substrate was used as a transparent substrate 1 of the 
magneto-optical recording medium 70 shown in FIG. 1. A transparent resin 
film 2, onto which a preformat pattern is transferred, is formed on one 
surface of the glass substrate. A dielectric film 3 is composed of SiN, 
and it is formed to have a film thickness for causing multiple 
interference with the reproducing laser beam so that the apparent Kerr 
rotation angle is increased. An auxiliary magnetic film 8 is composed of a 
ferri-magnetic amorphous alloy GdFeCo comprising rare earth and transition 
metals. The auxiliary magnetic film 8 exhibits the in-plane magnetic 
anisotropy at a temperature from room temperature to a certain critical 
temperature T.sub.CR not less than room temperature, and it exhibits the 
perpendicular magnetic anisotropy at a temperature not less than T.sub.CR. 
A non-magnetic film 9 is composed of SiN, and it is inserted to 
magnetostatically couple the auxiliary magnetic film 8 and a 
magneto-optical recording film 10. The magneto-optical recording film 10 
is composed of a ferri-magnetic amorphous alloy TbFeCo comprising rare 
earth and transition metals, and it has the perpendicular magnetic 
anisotropy at a temperature from room temperature to the Curie 
temperature. A protective film 7 is composed of SiN, and it is provided to 
protect the thin films stacked between the substrate 1 and the protective 
film 7, from chemical harmful influences such as corrosion. 
The dielectric film 3, the auxiliary magnetic film 8, the non-magnetic film 
9, the magneto-optical recording film 10, and the protective film 7 were 
formed as films to have the following film thicknesses by means of 
continuous sputtering by using a magnetron sputtering apparatus 
respectively. The dielectric film 3 had a thickness of 60 nm, the 
auxiliary magnetic film 8 had a thickness of 60 nm, the non-magnetic film 
9 had a thickness of 20 nm, the magneto-optical recording film 10 had a 
thickness of 50 nm, and the protective film 7 had a thickness of 60 nm. 
The composition of TbFeCo for constructing the magneto-optical recording 
film 10 is Tb.sub.21 Fe.sub.66 Co.sub.13 as represented by an atomic % 
ratio to exhibit a characteristic such that the magnetization component of 
the transition metal is more dominant than the magnetization component of 
the rare earth at a temperature from room temperature to the Curie 
temperature T.sub.CO =270.degree. C. On the other hand, the composition of 
GdFeCo for constructing the auxiliary magnetic film 8 is Gd.sub.28 
Fe.sub.53 Co.sub.19 as represented by an atomic % ratio to exhibit, as a 
single layer film, a temperature-dependent characteristic of the Kerr 
rotation angle as shown in FIG. 2. 
With reference to FIG. 2, the horizontal axis denotes the temperature, and 
the vertical axis denotes the ratio .theta.KR/.theta.KS of the remaining 
Kerr rotation angle .theta.KR to the saturated Kerr rotation angle 
.theta.KS of the GdFeCo auxiliary magnetic film 8 determined from the 
hysteresis of the Kerr rotation angle with respect to the temperature. 
According to this graph, the critical temperature T.sub.CR, at which the 
auxiliary magnetic film 8 is converted from the in-plane magnetizable film 
into the perpendicularly magnetizable film, is about 200.degree. C. The 
auxiliary magnetic film 8 has a Curie temperature Tc of not less than 
300.degree. C., and it has a compensation temperature T.sub.comp between 
room temperature T.sub.room and the Curie temperature, in which T.sub.comp 
is about 230.degree. C. The following relationship is given concerning the 
critical temperature T.sub.CR, the compensation temperature T.sub.comp, 
and the Curie temperature Tc of the auxiliary magnetic film 8, and the 
Curie temperature T.sub.CO of the magneto-optical recording film 10. 
T.sub.room &lt;T.sub.CR &lt;T.sub.comp &lt;T.sub.CO &lt;Tc. By satisfying this 
condition, it is extremely easy to perform reproduction by using the 
power-modulated pulse light beam as described later on. 
The reproducing method as explained in the description of the principle of 
the present invention with reference to FIG. 19 is executed by using the 
magneto-optical recording medium 70 having the structure as described 
above. 
[Preparatory experiment for determining intensity of reproducing laser 
pulse] 
In the reproducing method of the present invention, the recording magnetic 
domain is magnified to perform reproduction by using the pulse light beam 
obtained by power-modulating the laser power to have the high power Pr2 
and the low power Pr1. Accordingly, a preparatory experiment is firstly 
performed to determine the optimum laser powers of Pr2 and Pr1 for 
reproducing data recorded on the magneto-optical recording medium 70. In 
this preparatory experiment, a magneto-optical drive comprising an optical 
system having a laser beam wavelength of 680 nm and a numerical aperture 
of 0.55 is used to radiate recording and reproducing laser beams onto the 
side of the substrate 1 (side of the auxiliary magnetic film 8). A 
continuous light beam is used as the reproducing laser beam as described 
later on. The reproducing laser beam is changed to have various powers to 
observe respective reproduced signal waveforms. 
A laser beam having a recording power of 4.5 mW was modulated with a cycle 
of 640 ns and a pulse width of 213 ns at a linear velocity of 5.0 m/s for 
a track disposed at a radius of 40 mm of the previously initialized 
magneto-optical recording medium 70 to perform optical modulation 
recording while applying a recording magnetic field of 500 Oe. 
Accordingly, recording marks each having a length of about 1.6 .mu.m were 
continuously recorded at a pitch of 3.2 .mu.m on the track. 
Subsequently, the track recorded with the recording marks was subjected to 
reproduction with continuous light beams having various reproducing powers 
Pr. In order to determine the optimum modulation condition for the 
reproducing power, the value of the power Pr of the continuous light beam 
was changed to be at five levels, i.e., Pr=1.0 mW, 1.5 mW, 1.9 mW, 2.0 mW, 
and 2.1 mW to determine reproduced signals respectively. No magnetic field 
was actively applied to the magneto-optical recording medium 70 during the 
reproduction. However, a leakage magnetic field (about 80 Oe), which 
leaked from the actuator of the optical head, was generated in the 
recording direction. 
FIGS. 3A to 3E show reproduced signal waveforms obtained when the recording 
track of the magneto-optical recording medium 70 was subjected to 
reproduction with the respective reproducing powers Pr as described above. 
In this experiment, the reproduced signal waveform itself was subjected to 
triggering to observe the waveform by using an oscilloscope. FIG. 3A shows 
a reproduced signal waveform obtained for the reproducing light power 
Pr=1.0 mW, from which it is understood that the reproduced signal arises 
corresponding to the pattern of the recording mark. On the graph, the base 
line indicates an erased state, and the rising peak signal indicates a 
recording state. The amplitude between the recording state and the erased 
state was 50 mV. When the reproducing light power was increased to Pr=1.5 
mW, the signal amplitude was increased to about 200 mV as shown in FIG. 
3B. According to the waveform shown in FIG. 3B, it is understood that the 
adjoining peak signals are continuous on the side of the recording state 
in a part of the area of the waveform. 
FIG. 3C shows a reproduced signal waveform for the reproducing power of 
Pr=1.9 mW, indicating that the peak signals are completely continuous on 
the side of the recording state (at an upper portion in the drawing). This 
result demonstrates that the magnetic domain is magnified in the auxiliary 
magnetic film as described later on, and the magnified magnetic domain 
undergoes movement on the track in accordance with the scanning for the 
track with the reproducing light spot. When the reproducing light power is 
further increased to Pr=2.0 mW, the peak signals having been continuous 
begin to be discontinuous as shown in FIG. 3D. In this case, the amplitude 
H.sub.plo between the connected portion of the peak signal and the base 
line was about 350 mV. When the reproducing light power was further 
increased up to Pr=2.1 mW, the peak signal is completely dis continuous as 
shown in FIG. 3E, giving a waveform corresponding to the recording mark 
pattern. In FIG. 3E, the amplitude between the recording state and the 
erased state was 200 mV. 
The magnetization states of the auxiliary magnetic film 8 and the 
magneto-optical recording film 10 stacked with the non-magnetic film 9 
intervening therebetween, which are given when the reproduced signal 
waveforms shown in FIGS. 3A to 3E are obtained, will be explained with 
reference to conceptual drawings shown in FIGS. 4 to 6. FIG. 4 shows a 
situation in which the signal waveform shown in FIG. 3A is obtained 
(reproducing light power Pr=1.0 mW), illustrating the relationship between 
the reproducing light spot 80 and the directions of magnetization of the 
auxiliary magnetic film 8 and the magneto-optical recording film 10 
irradiated with the reproducing light spot 80. At first, the auxiliary 
magnetic film 8, which is irradiated with the reproducing light spot 80 as 
shown in FIG. 4A, exhibits perpendicular magnetization in an area in which 
its temperature is raised to be not less than the critical temperature 
T.sub.CR. The magnetization of the magneto-optical recording film 10 is 
transferred to an area 83a of the auxiliary magnetic film 83a by the aid 
of the magnetostatic coupling. As shown in FIG. 4B, when the reproducing 
light spot 80 is disposed just under a magnetic domain (recording magnetic 
domain) 82 in which the magnetization is directed in the recording 
direction, the magnetization of the recording magnetic domain 82 is 
transferred to the auxiliary magnetic film 8 by the aid of the 
magnetostatic coupling. In this case, the reproducing light power Pr is 
1.0 mW which is low. Therefore, only the central portion of the auxiliary 
magnetic film 8 within the light spot 80, i.e., only the area 83b has the 
temperature which exceeds the critical temperature T.sub.CR. The 
transferred area 83b of the auxiliary magnetic film 8 is not magnified to 
be larger than the width of the recording magnetic domain 82. Accordingly, 
as shown in FIG. 3A, the reproduced signal intensity is small. When the 
reproducing light spot 80 passes over the recording magnetic domain 82, a 
transferred area 83c has the same direction of magnetization as that of 
the magnetic domain in the magneto-optical recording film 10 located just 
thereover, as a result of transfer from the magnetic domain in the 
magneto-optical recording film 10 located just thereover. 
FIG. 5 shows a situation in which the signal waveform shown in FIG. 3C is 
obtained (reproducing light power Pr=1.9 mW), illustrating the 
relationship between the reproducing light spot 80 and the directions of 
magnetization of the auxiliary magnetic film 8 and the magneto-optical 
recording film 10 irradiated with the reproducing light spot 80. In this 
case, the reproducing light power is 1.9 mw which is relatively large. 
Therefore, as shown in FIG. 5A, an entire area 85a within the spot in the 
auxiliary magnetic film 8 irradiated with the reproducing light spot 80 
has a temperature raised to be not less than the critical temperature 
T.sub.CR, giving perpendicular magnetization. The magnetic domain in the 
magneto-optical recording film 10 is transferred to the area 85b by the 
aid of the magnetostatic coupling effected by the magneto-optical 
recording film 10. When the reproducing light spot 80 is subjected to 
scanning to locate the reproducing light spot 80 just under the recording 
magnetic domain 82 as shown in FIG. 5B, the magnetization of the recording 
magnetic domain 82 is transferred. In this case, the area 85b of the 
auxiliary magnetic film 8, which is heated to a temperature not less than 
the critical temperature T.sub.CR, has its width larger than the recording 
magnetic domain 82. Accordingly, the recording magnetic domain 82 is 
transferred while being magnified in the auxiliary magnetic film 8. The 
large signal waveform is obtained owing to the magnification of the 
magnetic domain. After the reproducing light spot 80 passes over the 
recording magnetic domain 82, the area 85c maintains the same 
magnetization state as that of the area 85b. Therefore, the waveform, in 
which the reproduced signal peaks are continuous as shown in FIG. 3C, is 
obtained. 
In the case of the situation shown in FIG. 5, the area 85c maintains the 
same magnetization state as that of the area 85b after the reproducing 
light spot 80 passes over the recording magnetic domain 82. A phenomenon 
arises, in which the light spot draws the recording magnetic domain which 
is transferred to the auxiliary magnetic layer to be subjected to the 
magnetic domain transfer and the magnetic domain magnification. The reason 
for this phenomenon is considered to be as follows. The temperature of the 
auxiliary magnetic layer 8 is raised to be not less than the critical 
temperature by being irradiated with the reproducing laser beam, and the 
auxiliary magnetic layer 8 is converted into the perpendicularly 
magnetizable film having the coercive force Hc in the perpendicular 
direction. During the reproduction, the auxiliary magnetic film 8 is 
applied with the external magnetic field Hex (in the recording direction, 
i.e., in the downward direction in this embodiment) which is caused by the 
leakage magnetic field, for example, from the actuator of the optical 
head, and the static magnetic field Hs which is generated from the 
magnetization of the magneto-optical recording film 10 at a temperature 
not less than the critical temperature of the auxiliary magnetic film 8. 
The applied magnitude is Hex+Hs (when the magnetization of the recording 
magnetic domain is in the downward direction) or Hex-Hs (when the 
magnetization of the recording magnetic domain is in the upward direction) 
depending on the direction of the magnetization of the magneto-optical 
recording film 10. If the absolute value of Hc is larger than the absolute 
value of (Hex+Hs) or the absolute value of (Hex-Hs) concerning the 
magnitude of the combined magnetic field of the external magnetic field 
Hex and the static magnetic field Hs and the coercive force Hc of the 
auxiliary magnetic film 8, the magnetization formed in the auxiliary 
magnetic film 8 is maintained as it is. As shown in FIG. 5C, the magnetic 
domain, which is once transferred to the auxiliary magnetic film, does not 
cause reinversion even when the reproducing spot proceeds to the area in 
which no recording magnetic domain exits in the magneto-optical recording 
film 10. Hc is the coercive force in the perpendicular direction, obtained 
when the auxiliary magnetic film 8 is in the perpendicular magnetization 
state. In the case of the situation shown in FIG. 4, Hc of the auxiliary 
magnetic film is lower than that in FIG. 5, because the temperature of the 
auxiliary magnetic layer subjected to transfer by the low reproducing 
power is relatively low. Accordingly, the magnetic domain transferred to 
the auxiliary magnetic film 8 causes reinversion when the reproducing spot 
proceeds to the area in which no recording magnetic domain exists in the 
magneto-optical recording film 10 (FIG. 4C). 
FIG. 6 shows a situation in which the signal waveform shown in FIG. 3E is 
obtained (reproducing light power Pr=2.1 mW), illustrating the 
relationship between the reproducing light spot 80 and the directions of 
magnetization of the auxiliary magnetic film 8 and the magneto-optical 
recording film 10 irradiated with the reproducing light spot 80. In this 
case, the reproducing light power is 2.1 mW which is relatively large. 
Therefore, a front portion area 87a within the spot in the auxiliary 
magnetic film 8 irradiated with the reproducing light spot 80 has a 
temperature raised to be not less than the critical temperature TCR, 
giving perpendicular magnetization, and it is subjected to magnetic domain 
transfer of the magnetic recording layer 10 located just thereunder. 
However, the central portion and the back portion within the spot are 
heated intensely as compared with the front portion to exceed the 
compensation temperature Tcomp of the auxiliary magnetic film 8. 
Therefore, it is considered that a state is given, in which the 
magnetization is inverted (detailed reason for inversion of magnetization 
will be described later on in the specified embodiment of the second 
reproducing method). Accordingly, as shown in FIG. 6A, only the area 87a, 
which is disposed at the front portion of the auxiliary magnetic film 
within the reproducing light spot 80, has the magnetization in the upward 
direction, and the central portion and the back end portion have the 
magnetization in the downward direction. 
Subsequently, when the track is subjected to scanning with the reproducing 
light beam so that the spot 80 is located just under the recording 
magnetic domain 82, the magnetization of the recording magnetic domain 82 
is transferred to only the area 87b having the relatively low temperature 
disposed at the front portion of the auxiliary magnetic film 8. Therefore, 
no magnetic domain magnification occurs. It is impossible to obtain the 
signal as shown in FIG. 3C having the large reproduced signal intensity. 
When the reproducing light spot 80 passes over the recording magnetic 
domain 82, the transfer area 87c includes the magnetization having the 
same direction as that of the magnetic domain in the magneto-optical 
recording film 10 disposed just thereover and the inverted magnetic domain 
thereof in a mixed manner by the aid of the magnetostatic coupling 
effected by the magneto-optical recording film 10. 
In the case of the situation shown in FIG. 5 (FIG. 3C), the reproduced 
signal intensity is increased, because the magnetic domain magnification 
occurs in the auxiliary magnetic film 8 as described above. The magnetic 
domain 85b, which is magnified from the recording magnetic domain 82, is 
moved together with the reproducing light spot 80 while being magnified. 
However, in the situation shown in FIG. 5C, when the center of the 
reproducing light spot 80 is located just under a magnetic domain 84 
adjacent to the recording magnetic domain 82, it is necessary to avoid the 
phenomenon in which the magnified magnetic domain is drawn by the light 
spot, in order to reproduce the magnetization of the magnetic domain 84 by 
the aid of the auxiliary magnetic layer 8. That is, it is necessary to 
erase the magnified magnetic domain 85c of the recording magnetic domain 
82 and transfer the magnetization of the magnetic domain 84 to the 
auxiliary magnetic layer 8 followed by magnification. 
On the other hand, as shown in FIG. 4 (corresponding to FIG. 3A) and FIG. 6 
(corresponding to FIG. 3E) respectively, when the reproducing power Pr is 
relatively small (reproducing light power Pr=1.0 mW), and when the 
reproducing power Pr is relatively large (reproducing light power Pr=2.1 
mW), the magnetic domain 83b (87b) transferred from the recording magnetic 
domain 82 is extinguished after the reproducing light spot 80 passes over 
the recording magnetic domain 82. That is, the phenomenon, in which the 
magnified magnetic domain is drawn, does not take plate. Therefore, if the 
reproducing light beam to be used is a pulse light beam which is 
power-modulated at a reproducing clock cycle or at a cycle created by the 
multiplication of an integer and the reproduction clock between the 
reproducing light power Pr=1.9 mW at which the magnetic domain 
magnification occurs and the reproducing light power Pr=2.1 mW (or 1.0 mW) 
at which the magnetic domain magnification does not occur, the magnetic 
domain can be magnified, and then the magnified magnetic domain can be 
extinguished when the center of the reproducing light spot is moved from 
the recording magnetic domain in the magneto-optical recording film onto 
the adjacent recording magnetic domain. 
According to the result of the preparatory experiment described above, if 
the reproducing laser beam is applied as the pulse light beam which is 
intensity-modulated between Pr=1.9 mW as shown in FIG. 3C and Pr=2.1 mW as 
shown in FIG. 3E, the reproduced signal is detected as a difference 
between the reproduced signal intensities obtained as shown in FIG. 3C and 
FIG. 3E. The difference is considered to correspond to H.sub.plo =350 mV 
shown in FIG. 3D, suggesting that the reproduction can be performed with 
an amplitude which is larger than the amplitudes obtained in FIGS. 3A and 
3E. Therefore, in the following experiment in reproduction based on the 
use of the reproducing light pulse, the high power Pr2 is set to be 
Pr2=2.1 mW, and the low power Pr1 is set to be Pr1=1.9 mW. 
[First reproducing method on magneto-optical recording medium with 
power-modulated pulse light beam] 
After the magneto-optical recording medium 70 produced in this embodiment 
was initialized, a laser beam having a recording power of 6.3 mW was 
modulated with a cycle of 320 ns and a pulse width of 53.3 ns to perform 
optical modulation recording with a recording magnetic field of 500 Oe, at 
a linear velocity of 5.0 m/s for a track disposed at a radius of 40 mm. 
This corresponds to a condition in which recording marks of about 1.6 
.mu.m were continuously recorded at a pitch of 3.2 .mu.m. 
The recording track of the magneto-optical recording medium 70 thus 
subjected to the recording is irradiated with the power-modulated pulse 
laser having the reproducing light laser powers of Pr2=2.1 mW and Pr1=1.9 
mW as determined by the preparatory experiment so that reproduction is 
performed. As shown in FIG. 7, the reproducing laser pulse was adjusted to 
give Pr2=2.1 mW in a pulse width of 10 ns starting from the front end of 
the recording mark, and Pr1=1.9 mW in a pulse width of 150 ns following 
thereafter. No magnetic field was actively applied during the 
reproduction. However, a leakage magnetic field (about 80 Oe) was 
generated in the recording direction from the actuator of the optical 
head. 
An obtained reproduced signal waveform is shown in FIG. 8. The obtained 
reproduced signal had an amplitude of about 220 mV corresponding to the 
recording marks. When the mark pattern recorded under the same condition 
was subjected to reproduction with continuous light beams having constant 
reproducing powers of Pr=1.0 mW and Pr=2.1 mW, the amplitudes were 100 mV 
and 170 mV respectively. According to these results, it is understood that 
the reproduction with the reproducing light beam which is power-modulated 
to have the pulse form makes it possible to magnify and transfer the 
recording magnetic domain in a form of being synchronized with the 
reproducing clock and extinguish the magnified magnetic domain immediately 
thereafter, and the reproduction can be performed with higher C/N when the 
magnetic domain is magnified. 
In this embodiment, the respective pulse laser intensities, i.e., the high 
power Pr2=2.1 mW and the low power Pr1=1.9 mW were selected. The low power 
pulse was used to generate the magnified magnetic domain, and the high 
power pulse was used to extinguish the magnified magnetic domain. However, 
the high power pulse may be Pr2=1.9 mW to generate the magnified magnetic 
domain, and the low power pulse may be Pr1=1.0 mW to extinguish the 
magnified magnetic domain. The illustrative case shown in FIG. 19 used to 
explain the principle is representative of the latter case. The pulse 
width ratio between the high power pulse and the low power pulse, i.e., 
the duty is not limited to those shown in FIGS. 19 and 7. The duty may be 
appropriately changed in order to obtain an enhanced reproduced signal. 
The magneto-optical recording medium produced in the first embodiment may 
comprise a heat control layer having an appropriate heat conductivity 
disposed on the protective film of the magneto-optical recording medium, 
in order to give a desired shape for the temperature profile of the medium 
obtained when the reproducing light beam is radiated, or in order to 
decrease the linear velocity dependency of the temperature profile. 
Further, in order to obtain a better reproducing CN ratio, it is also 
allowable to add, between the dielectric film 3 and the auxiliary magnetic 
film 8, a reproducing magnetic film which is a perpendicularly 
magnetizable film at a temperature not less than room temperature in which 
the Kerr rotation angle .theta.k is not less than .theta.k of the 
auxiliary magnetic film at the maximum arrival temperature of the medium 
when the reproducing light beam is radiated. 
Second Embodiment 
[Second reproducing method on magneto-optical recording medium with 
power-modulated pulse light beam] 
In the foregoing embodiment of the reproducing method, the leakage magnetic 
field generated from the magnetic head during reproduction is applied to 
the magneto-optical recording medium. In this embodiment, reproduction is 
performed while actively applying a DC magnetic field in the same 
direction as the magnetization direction of the recording magnetic domain. 
Reproduction was performed in this embodiment by modulating the laser beam 
intensity as well in order to realize magnification and extinguishment of 
the transferred magnetic domain. 
At first, explanation will be made for a magneto-optical disk used in this 
embodiment. As shown in FIG. 9, the magneto-optical disk 90 comprises, on 
a polycarbonate substrate 1 in a stacked manner, a dielectric layer 3 
composed of SiN, a reproducing layer (auxiliary magnetic film) 8 composed 
of a GdFeCo alloy, a non-magnetic layer 9 composed of SiN, a recording 
layer (magneto-optical recording film) 10 composed of a TbFeCo alloy, and 
a protective layer 7 composed of SiN. The TbFeCo recording layer 10 and 
the GdFeCo reproducing layer 8 are coupled magnetostatically with the 
non-magnetic layer 9 interposed therebetween. The GdFeCo reproducing layer 
8 is a magnetic film which is an in-plane magnetizable film at room 
temperature and which is changed into a perpendicularly magnetizable film 
when the temperature exceeds a critical temperature Tcr. The GdFeCo 
reproducing layer 8 used in this embodiment has a critical temperature Tcr 
of 175.degree. C. and a Curie temperature Tc of 340.degree. C. The GdFeCo 
reproducing layer 8 has a compensation temperature Tcomp=240.degree. C. 
between the critical temperature Tcr and the Curie temperature Tc. The 
TbFeCo recording layer 10 has its Curie temperature Tco of 270.degree. C. 
and its compensation temperature Tcomp' of not more than room temperature. 
That is, there is given the relationship of Troom&lt;Tcr&lt;Tcomp&lt;Tco&lt;Tc. The 
relationship concerning the temperatures has been explained with reference 
to FIG. 11. 
When the reproduction is performed for the recording signal recorded in the 
recording layer 10 of the magneto-optical recording medium 90 as described 
above, the reproducing power is modulated to have the two powers in 
synchronization with the reproducing clock or the integral multiple 
thereof (recording clock or a cycle created by the multiplication of an 
integer and the reproducing clock), as explained concerning the principle 
of the reproducing method of the present invention. The reduction and the 
extinguishment of the magnified magnetic domain may occur at any one of 
the low power and the high power as described above. However, in this 
embodiment, the reproducing light beam to transfer and magnify the 
magnetic domain was modulated to have the low power, and the reproducing 
light beam to reduce or extinguish the magnified magnetic domain was 
modulated to have the high power. The power levels are applied when the 
recording track is subjected to scanning while irradiating the 
magneto-optical disk with the reproducing light beam. 
An optical head having a wavelength of 680 nm and a numerical aperture of 
the lens of 0.55 was used as a light source for performing recording and 
reproduction. Recording was performed on the magneto-optical disk 90 shown 
in FIG. 9 by using the light pulse intensity modulation method. Recording 
was performed under a condition of a linear velocity of 5 m/s, a recording 
cycle of 320 ns, a recording laser power of 7.5 mW, a pulse width of 53.3 
ns, and a recording magnetic field of 500 Oe. Recording magnetic domains 
of 0.8 .mu.m were subjected to recording at intervals of 0.8 .mu.m 
corresponding to data including, for example, 1 and 0. The magnetic 
domains subjected to recording are shown in FIG. 10(a) together with the 
recording signal. 
The recording magnetic domains were subjected to reproduction under the 
following reproducing condition. The linear velocity was 5.0 m/s. The 
reproducing laser power was modulated to have two power levels of 1.5 mW 
as the low power Pr1 to magnify the magnetic domain, and 3.5 mW as the 
high power Pr2 to reduce (or extinguish) the magnetic domain. A timing 
signal for the reproducing light power is shown in FIG. 10(b). The 
modulation cycle for the reproducing power was 160 ns. Radiation was 
performed for 150 ns at the low power Pr1, and radiation was performed for 
10 ns at the high power Pr2. A constant direct current magnetic field was 
used as the reproducing magnetic field, which was applied at about 80 Oe 
in the recording direction. This magnetic field may be substituted with 
the leakage magnetic field from the objective lens actuator as in the 
first reproducing method (first embodiment). 
FIG. 10(c) shows an obtained reproduced signal waveform. It is understood 
from this reproduced signal waveform that the signal is enhanced only at 
portions at which the recording magnetic domain exists, and the signal is 
not enhanced at portions at which the recording magnetic domain does not 
exist. This fact means that the recording magnetic domain is transferred 
and magnified in the reproducing layer only when the reproducing light 
beam makes scanning for the portion of the track at which the recording 
magnetic domain exists. The reproduced signal was obtained in accordance 
with the magnetically induced super resolution mode. That is, the 
reproduced signal was amplified to have the magnitude which was about 1.5 
times the reproduced signal obtained by reproduction without magnifying 
the magnetic domain subjected to the magnetic domain transfer. The 
amplifying effect on the reproduced signal was remarkably effective for 
further minute recording magnetic domains. Even when minute magnetic 
domains of not more than 0.4 .mu.m were subjected to recording, it was 
possible to obtain a reproduced signal output of 80% (ratio to the 
saturated amplitude) with respect to the saturated amplitude (difference 
between the reproduced signal obtained when all magnetization in the 
reproducing layer was in the downward direction and the reproduced signal 
obtained when all magnetization in the reproducing layer was in the upward 
direction). 
The reproducing condition in this embodiment may be explained as follows in 
relation to FIG. 11 used to explain the principle. That is, the 
reproducing layer is heated by the low power Pr1 of the power-modulated 
reproducing light beam to be in the temperature areas (areas (a) and (b)) 
shown in FIG. 11 in which the magnetic domain transfer and the magnetic 
domain magnification are caused, i.e., up to Tcr=175.degree. C. to 
Tcomp=240.degree. C. The recording layer is heated by the high power Pr2 
to be in the temperature area (area (c)) shown in FIG. 11 in which the 
magnetic domain extinguishment is caused, i.e., from a temperature 
exceeding Tcomp (240.degree. C.) to Tco=270.degree. C. The direct current 
magnetic field of about 80 Oe applied in the recording direction allows 
the magnetic temperature curves A and B to be disposed so that the 
relationship as shown in FIG. 11 is given. That is, the relationship 
between the magnetic temperature characteristic of the magneto-optical 
disk used in this embodiment and the applied direct current magnetic field 
satisfies the following requirements (3) and (4). The requirements 
necessary for the reproducing method described in this embodiment will be 
enumerated below. The magnetic characteristics of the reproducing layer 
and the recording layer of the magneto-optical recording medium used in 
this embodiment satisfy the following requirements (1) and (2) as 
described above. 
(1) The reproducing layer, which is magnetized in the film surface 
direction at least at room temperature, has the compensation temperature 
Tcomp between the Curie temperature Tco and the critical temperature Tcr 
to cause magnetization in the perpendicular direction. 
(2) The Curie temperature Tco of the recording layer exists between the 
compensation temperature Tcomp of the reproducing layer and the Curie 
temperature Tco of the reproducing layer. 
(3) The magnetic temperature curve A and the magnetic temperature curve B 
intersect at a point (T1) between room temperature and the compensation 
temperature Tcomp of the reproducing layer under the condition in which 
the external magnetic field Hex is applied in the recording direction. 
(4) The magnetic temperature curve A and the magnetic temperature curve B 
intersect at a point (T2) between the compensation temperature Tcomp of 
the reproducing layer and the Curie temperature Tco of the recording 
layer. 
In this embodiment, the foregoing requirements (1) to (4) are satisfied by 
constructing the magneto-optical disk with the specified materials shown 
in FIG. 9, and applying the DC magnetic field=80 Oe in the recording 
direction. However, arbitrary combinations may be used provided that the 
magneto-optical recording medium comprising the materials and the stacked 
structure and the magnitude of the external magnetic field applied during 
the reproduction are capable of satisfying the requirements (1) to (4). 
The direction of the DC magnetic field applied during the reproduction is 
not limited to the recording direction, which may be the erasing 
direction. 
In the reproducing method of the present invention, the process of (a) 
magnetic domain transfer, (b) magnetic domain magnification, and (c) 
extinguishment of transferred magnetic domain is executed by modulating 
the reproducing light power intensity under the DC magnetic field. The 
period of time, in which the process is carried out, depends not only on 
the magnetic characteristics of the recording layer and the reproducing 
layer but also on the temperature rising velocity and the heat transfer 
velocity between the respective layers concerning, for example, the 
recording layer, the reproducing layer, the non-magnetic layer, the 
dielectric layer, and the protective layer, as well as other stackable 
magnetic layers, non-magnetic layers, and substrates. The velocities can 
be controlled by appropriately changing, for example, the stacked 
structure, the thickness, and the thermal conduction characteristics of 
the materials for constructing the layers. Accordingly, it is possible to 
respond to a desired reproducing access velocity. 
It is preferable that the dielectric layer and the non-magnetic layer, 
which adjoin the reproducing layer (auxiliary magnetic layer), have 
appropriate degrees of thermal insulation properties. However, the degree 
of the thermal insulation property can be appropriately adjusted in 
relation to the thermal characteristics obtained by combining the access 
velocities upon recording and reproduction, the magnitude of the linear 
velocities upon recording and reproduction on the recording medium, and 
the thermal conduction characteristics of the reproducing layer and the 
recording layer. 
The foregoing embodiment is illustrative of the structure in which the 
reproducing layer (auxiliary magnetic layer) of the magneto-optical 
recording medium is interposed by the dielectric layer and the 
non-magnetic layer. However, a magnetic member having magnetic anisotropy 
in the in-plane direction may be stacked in contact with the reproducing 
layer (auxiliary magnetic layer). It is desirable that the magnetic 
anisotropy in the in-plane direction is dominant in the magnetic member up 
to its Curie temperature, and the Curie temperature is approximately equal 
to the Curie temperature of the reproducing layer. When such a magnetic 
member is stacked in contact with the reproducing layer, it is possible to 
suppress occurrence of the Bloch line in the transferred magnetic domain 
during the reproduction, and it is possible to reduce the noise during the 
reproduction owing to its suppressing action. Those usable as materials 
for such a magnetic member include, for example, Pt--Co alloys such as 
Pt--Co alloys containing 25 atomic % of Co and GdFeCo alloys. Such a 
magnetic member may be stacked to make contact with any one of the upper 
and lower sides of the reproducing layer. 
In the first and second embodiments, recording is performed by using the 
optical modulation system in which light intensity is modulated in 
conformity with the recording signal while applying the DC magnetic field. 
However, it is allowable to use any one of the magnetic field modulation 
recording system, the optical modulation recording system, and the optical 
magnetic field modulation system based on the use of the ordinary DC light 
beam. 
Third Embodiment 
[Third reproducing method on magneto-optical recording medium with 
power-modulated pulse light beam] 
Reproduction is performed in this embodiment while actively applying a DC 
magnetic field in the same direction as the magnetization direction of the 
recording magnetic domain in the same manner as in the second embodiment. 
Reproduction was performed in this embodiment by modulating the laser beam 
intensity as well in order to realize magnification and extinguishment of 
the transferred magnetic domain. 
At first, explanation will be made for a magneto-optical disk used in this 
embodiment. As shown in FIG. 14, the magneto-optical disk 100 comprises, 
in a stacked manner on a surface of a polycarbonate substrate 1 formed 
with a preformat pattern 2, a dielectric layer 3 composed of SiN, a 
reproducing layer (second auxiliary magnetic film) 24 composed of a GdFeCo 
alloy, a non-magnetic layer 29 composed of SiN, a magnetic layer (first 
auxiliary magnetic film) 28 composed of a GdFeCo alloy, a recording layer 
(magneto-optical recording film) 10 composed of a TbFeCo alloy, and a 
protective layer 7 composed of SiN. The TbFeCo recording layer 10 and the 
GdFeCo reproducing layer 24 are magnetostatically coupled to one another 
through the non-magnetic layer 9 and the magnetic layer (first auxiliary 
magnetic film) 28 composed of the GdFeCo alloy. 
The reproducing layer (second auxiliary magnetic layer) 24 composed of the 
GdFeCo alloy is a magnetic film which exhibits in-plane magnetization at 
room temperature and which causes transition to a perpendicularly 
magnetizable film at a temperature exceeding a critical temperature 
Tcr.sub.12 higher than room temperature. In this embodiment, Gd.sub.28 
Fe.sub.56 Co.sub.16 is used as the reproducing layer 24, which behaves as 
an in-plane magnetizable film at room temperature and which is changed 
into a perpendicularly magnetizable film at a temperature exceeding the 
critical temperature Tcr.sub.12 =175.degree. C. The Curie temperature 
Tc.sub.2 of the reproducing layer 24 is 340.degree. C. 
The magnetic layer (first auxiliary magnetic layer) 28 composed of the 
GdFeCo alloy is a magnetic film which exhibits perpendicular magnetization 
at room temperature and which causes transition to an in-plane 
magnetizable film at a temperature above a critical temperature Tcr.sub.11 
higher than room temperature. In this embodiment, Gd.sub.21 Fe.sub.64 
Co.sub.15 is used as the magnetic layer 28 composed of the GdFeCo alloy, 
which behaves as a perpendicularly magnetizable film at room temperature 
and which is changed into an in-plane magnetizable film at a temperature 
exceeding the critical temperature Tcr.sub.11 =200.degree. C. The Curie 
temperature Tc.sub.1 of the magnetic layer 28 was 350.degree. C. 
The recording layer 10 is based on the use of the TbFeCo alloy having its 
Curie temperature Tco of 270.degree. C. and its compensation temperature 
of not more than room temperature. That is, the relationship of room 
temperature&lt;Tcr.sub.12 &lt;Tcr.sub.11 &lt;Tc, Tc.sub.1, Tc.sub.2 holds 
concerning the Curie Temperature Tco of the recording layer 10, the Curie 
temperature Tc.sub.2 and the critical temperature Tcr.sub.12 of the 
reproducing layer 24, and the Curie temperature Tc.sub.1 and the critical 
temperature Tcr.sub.11 of the magnetic layer 28 (first auxiliary magnetic 
film). The temperature relationship is shown in FIG. 15. In the same 
manner as FIG. 11, FIG. 15 shows the magnetic characteristics of the 
recording layer 10, the reproducing layer 24, and the magnetic layer 28 
(first auxiliary magnetic film) of the magneto-optical recording medium 
100 in a state in which a constant DC magnetic field Hex is applied in the 
recording direction to the magneto-optical recording medium 100. As shown 
in FIG. 15, temperature ranges for the reproducing layer 24 and the 
magnetic layer 28 (first auxiliary magnetic film) to exhibit the 
perpendicular magnetization overlap in a relatively narrow temperature 
range (arrow in FIG. 15). In this temperature range, the recording layer 
10, the magnetic layer 28, and the reproducing layer 24 can be 
magnetically coupled. 
The principle of reproduction on the magneto-optical disk 100 shown in FIG. 
14 is the same as that explained with reference to FIG. 16. That is, the 
reproducing layer 24 of the magneto-optical disk 100 is irradiated with 
the reproducing light beam, and the temperature of the reproducing layer 
24 is raised. The area, in which the temperature exceeds the critical 
temperature Tcr.sub.12, causes transition from the in-plane magnetization 
to the perpendicular magnetization, simultaneously with which the 
magnetization in the recording layer 10 is transferred to the reproducing 
layer 24 by the aid of the magnetostatic coupling force. The reproducing 
light power and Tcr.sub.12 are adjusted so that the area in which the 
temperature exceeds the critical temperature Tcr.sub.12 is larger than the 
magnetic domain in which the magnetization information of the recording 
layer 10 is recorded. Therefore, the portion of the reproducing layer 24 
having the perpendicular magnetization is magnified to be larger than the 
magnetic domain in the recording layer 10 as the transfer source (see FIG. 
16C). On the other hand, the perpendicular magnetization in the magnetic 
layer 28 undergoes transition to the in-plane magnetization in the area in 
which the temperature exceeds the critical temperature Tcr.sub.11 existing 
inside the area in which the temperature exceeds the critical temperature 
Tcr.sub.12 in accordance with the temperature distribution of the 
magneto-optical disk 100. The in-plane magnetization area in the magnetic 
layer 28 intercepts the leakage magnetic field directed from the recording 
layer 10 to the reproducing layer 24, especially in the non-recording 
direction. Accordingly, the magnification in the reproducing layer 24 is 
facilitated, simultaneously with which C/N of the reproduced signal 
obtained from the recording layer 24 is improved. In the present 
invention, it is required to satisfy Tcr.sub.12 &lt;Tcr.sub.11. However, it 
is preferable that the difference in temperature .DELTA.T between 
Tcr.sub.12 and Tcr.sub.11 is selected so that C/N of the reproduced signal 
is optimized, and the reproduced signal intensity brought about by the 
magnetic domain magnification is maximized. 
When the recording signal recorded on the recording layer 10 of the 
magneto-optical disk 100 is reproduced, the reproducing power is modulated 
to have the two powers in synchronization with the reproducing clock or 
the integral multiple thereof (recording clock or a cycle created by the 
multiplication of an integer and the reproducing clock), as explained in 
the principle of the reproducing method of the present invention. The 
reduction and the extinguishment of the magnified magnetic domain may be 
caused by using any one of the low power and the high power as described 
above. However, in this embodiment, the reproducing light beam to transfer 
and magnify the magnetic domain was modulated to have the low power, and 
the reproducing light beam to reduce or extinguish the magnified magnetic 
domain was modulated to have the high power. The power levels are applied 
during the period in which the recording track is subjected to scanning by 
irradiating the magneto-optical disk with the reproducing light beam. 
A heat diffusion layer may be formed between the nonmagnetic layer 29 and 
the first auxiliary magnetic layer 28, concerning the structure of the 
magneto-optical disk 100 shown in FIG. 14. The heat diffusion layer serves 
to facilitate the magnification of the magnetic domain by diffusing, in 
the in-plane direction of the film, the heat accumulated between the 
non-magnetic layer 26 and the first auxiliary magnetic layer 28. Those 
usable as the heat diffusion layer include materials having high thermal 
conduction, such as Al, AlTi, AlCr, Ag, Au, and Cu. 
According to the reproducing method on the magneto-optical recording medium 
of the present invention, it is possible to perform the magnetically 
induced super resolution-based reproduction in which the amount of light 
to contribute to the reproduction output in accordance with the magnetic 
mask is hardly decreased, or the amount of light is not decreased, as 
compared with the ordinary magnetically induced super resolution type 
magneto-optical recording medium provided with the mask function. The use 
of the magneto-optical recording medium and the reproducing method thereon 
according to the present invention makes it possible to perform 
reproduction independently with a recording mark which is extremely minute 
as compared with the spot diameter of the reproducing light beam. 
Therefore, it is possible to remarkably improve the recording density of 
the magneto-optical recording medium. Further, the use of the magnetic 
domain magnification-based reproduction makes it possible to amplify the 
reproduced signal and greatly improve C/N of the reproduced signal. 
The reproducing method of the present invention makes it possible to 
reliably execute the process of transferring the magnetic domain, 
magnifying the transferred magnetic domain, and extinguishing the 
magnified magnetic domain by optically modulating the reproducing light 
power. Therefore, this method is extremely useful to practically use the 
method for magnifying and reproducing the magnetic domain. The magnetic 
field applied during the reproduction is appropriately the DC magnetic 
field, and it is unnecessary to use the alternating magnetic field. 
Therefore, the reproducing operation can be performed by using the cheap 
reproducing apparatus having the simple structure. 
The magneto-optical recording medium of the present invention is 
constructed such that the relationship of room 
temperature&lt;Tcr&lt;Tcomp&lt;Tco&lt;Tc holds concerning the Curie temperature Tco of 
the magneto-optical recording film and the Curie temperature Tc and the 
compensation temperature Tcomp of the auxiliary magnetic film, and under 
the condition in which the external magnetic field Hex is applied to the 
magneto-optical recording medium, the temperature curve A of the transfer 
magnetic field which is generated by the external magnetic field Hex and 
the magneto-optical recording film, and the temperature curve B of the 
coercive force of the auxiliary magnetic film in the perpendicular 
direction intersect at the point between room temperature and the 
compensation temperature Tcomp of the auxiliary magnetic film, and the 
temperature curve A and the temperature curve B intersect at the point 
between the compensation temperature Tcomp of the auxiliary magnetic film 
and the Curie temperature Tco of the magneto-optical recording film. 
Accordingly, when the reproduction is performed under the DC external 
magnetic field by using the power-modulated reproducing light beam, it is 
possible to reliably execute the process of i) transferring the magnetic 
domain from the magneto-optical recording film to the auxiliary magnetic 
film, ii) magnifying the transferred magnetic domain, and iii) 
extinguishing the magnified magnetic domain. Therefore, the use of the 
magneto-optical recording medium makes it possible to perform recording of 
the recording signal with the minute magnetic domain which is smaller than 
the reproducing light spot, and then detect the minute magnetic domain 
while distinguishing it from other magnetic domains with the amplified 
reproduced signal. Accordingly, the magneto-optical recording medium of 
the present invention is extremely useful as the high density 
magneto-optical recording medium. 
The magneto-optical recording medium of the present invention 
simultaneously comprises the first auxiliary magnetic layer which causes 
transition from the perpendicularly magnetizable film to the in-plane 
magnetizable film in the area in which the temperature exceeds the 
critical temperature Tcr.sub.11, and the second auxiliary magnetic layer 
which causes transition from the in-plane magnetization to the 
perpendicular magnetization at the temperature exceeding the critical 
temperature Tcr.sub.12. Accordingly, the leakage magnetic field from the 
recording layer to the second auxiliary magnetic layer is intercepted by 
the first auxiliary magnetic layer, while the magnetization information in 
the recording layer 10 can be reproduced with magnification in the second 
auxiliary magnetic layer. Therefore, the intensity of the signal 
reproduced from the second auxiliary magnetic layer is increased, and C/N 
of the reproduced signal is improved. 
The optical recording medium and the reproducing method thereon according 
to the present invention are applicable to the magneto-optical recording 
media and the reproducing methods thereon disclosed in International 
Publications WO 97/22969 and WO 98-02878. The disclosure of the 
International Publications is incorporated herein by reference.