Magneto-optical recording medium

An auxiliary magnetic layer for generating a reproduction magnetic field which can be positive or negative in accordance with the front and rear edges of a reproduction waveform is provided on the opposite side of the magnetic layer to the substrate for recording and reproducing data. Consequently, a magnetic field which has an advantageous polarity to each of the front and rear edges of the reproduction waveform functions and both edges can have steep inclinations, which enhances the quality of the reproduction signal.

BACKGROUND OF THE INVENTION
 The present invention relates to a magneto-optic recording medium and more
 specifically to a magneto-optic recording medium which can perform
 Magnetically Induced Super Resolution (MSR) reproduction.
 Magneto-optic disks are known as a high-density recording medium and are
 expected to have a higher-density recording capacity in response to an
 increase in the amount of data. Higher density can be realized by
 shortening the intervals of the recording signals (marks), but the
 recording and the reproduction are restricted by the size (spot diameter)
 of the light beam on the medium. In order to reproduce a small mark whose
 period is equal to or smaller than the spot diameter, the spot diameter
 can be reduced. However, this reduction is restricted by the wavelength
 .lambda. of the light source and the numerical aperture NA of the object
 lens. Consequently, it has been difficult to reproduce a recording mark
 which is more minute than the resolution of the optical system.
 Recently, magnetically induced super resolution (MSR) media which can bring
 about the same effects as reducing the spot diameter by making a
 multi-layered recording medium and utilizing the temperature distribution
 of a medium formed in a beam spot have been suggested (Japanese Patent
 Application Laid-Open Nos. 1-143041 (1989), 3-93058 (1991), 4-271039
 (1992), and others).
 The MSR medium suggested in Japanese Patent Application Laid-Open No.
 1-143041 (1989) can reproduce a mark smaller than the spot diameter
 without providing an initializing magnet, by applying a magnetic field of
 about several hundred Oe on reproducing. However, the detection area is
 too large to reduce the truck pitch, so that it is disadvantage to a
 densification in the direction of a disk radius. The MSR medium suggested
 in Japanese Patent Application Laid-Open No. 3-93058 (1991) requires an
 additional initializing magnet of about 3.4 to 4 kOe, and has a problem
 that the detection area is enlarged in accordance with an increase in the
 power of the reproduction beam, although it has a smaller detection area
 than Japanese Patent Application Laid-Open No. 1-143041 (1989). The
 provision of a magnet of several kOe makes it difficult to reduce the size
 of the recording/reproducing device. The MSR medium suggested in Japanese
 Patent Application Laid-Open No. 4-271039 (1992) has a small detection
 area regardless of the power of the reproduction beam, and can reproduce a
 mark recorded with a high resolution in the direction of the disk radius.
 However, there is a problem that an initializing magnet of several kOe is
 needed in addition to a reproduction magnetic field of several hundred Oe.
 In order to solve these problems, the applicant of the present application
 has suggested a magnet-optic medium in Japanese Patent Application
 Laid-Open No. 7-244877 (1995) which can realize MSR reproduction by a RAD
 double mask method, by applying a reproduction magnetic field as low as
 several hundred Oe, without using an initializing magnet. FIG. 1 shows the
 magnetized condition of the reproduction of the MSR medium which has been
 disclosed by the applicant of the present application, and a film
 structure. As shown in FIG. 1, a magneto-optic disk 3 comprises a
 reproduction layer 33, a control layer 34, and a recording layer 35
 accumulated in this order on a substrate (not shown). The reproduction
 layer 33 is a transition metal magnetization dominant film and has an easy
 axis of magnetization in the perpendicular direction, that is, the
 direction in which the layers are deposited. The control layer 34 is a
 rare-earth magnetization dominant film and has an easy axis of
 magnetization in the in-plane direction at room temperature (10.degree. C.
 to 35.degree. C.). The easy axis of magnetization changes from the
 in-plane direction to the perpendicular direction when the temperature
 reaches a predetermined temperature higher than the room temperature. The
 recording layer 35 is a transition metal magnetization dominant film and
 has an easy axis of magnetization in the perpendicular direction.
 The magneto-optic disk 3 having such a structure is provided with a mark
 which is recorded in the downward direction, and when this mark is
 reproduced, a reproduction laser beam is irradiated while a reproduction
 magnetic field is being applied. The magnet-optic disk 3 generates a
 temperature distribution in the laser spot S, and the magnetization
 direction of the recording layer 35 is masked in a high temperature area
 (front mask) and a low temperature area (rear mask), and the mark is read
 from an intermediate temperature area (opening). FIG. 1 shows the case
 where the reproduction magnetic field is applied in the upward direction,
 that is, the direction for erasing data. Such a film structure and a
 reproducing principle of the MSR medium are detailed in Japanese Patent
 Application Laid-Open No. 7-244877 (1995) and Japanese Patent Application
 No. 8-276672 (1996), so that their description will be omitted.
 According to the MSR medium which forms a mask in the beam spot S, the beam
 spot S has a slightly different mask formation area depending on the
 direction in which the magnetic field is applied in order to reproduce.
 Such a difference in the mask formation area makes the edges before and
 after the waveform of the reproduction signal (reproduction waveform) have
 different inclination from each other. FIGS. 2A and 2B show the waveforms
 of the reproduction signals which are obtained by applying magnetic fields
 in the erasing direction and in the recording direction on the
 magneto-optic disk 3 obtained by the applicant of the present application.
 As shown in FIG. 2A, when reproduction is performed by applying the
 magnetic field on the MSR medium in the erasing direction, the inclination
 of the front edge of the reproduction waveform is less steep than that of
 the rear edge, so that the front edge has a larger jitter than that of the
 rear edge against the same strength of noise power. Consequently, the
 quality of the reproduction signal is affected by the jitter of the front
 edge. On the other hand, as shown in FIG. 2B, when reproduction is
 performed by applying the magnetic field on the MSR medium in the
 recording direction, the inclination of the rear edge of the reproduction
 waveform is less steep than that of the front edge, so that the quality of
 the reproduction signal is affected by the jitter of the rear edge. In
 either case, the reproduction waveform has nonlinearity, and the edge on
 the side where the magnetization direction of the reproduction layer
 accords with the erasing direction is more steep. Since the jitter
 increases on the side where the edge is less steep, it is difficult to
 perform correct detection of reproduction data.
 In order to solve this problem, the applicant of the present invention has
 disclosed a method of detecting the timing of an edge of a reproduction
 waveform based on the obtained reproduction signal and then reversing
 (modulating) the reproduction magnetic field after the detection of the
 edge. According to this reproduction method, when the front edge and the
 rear edge of the recording mark are outputted, the magnetic field in the
 direction of the steeper edge can be applied, so that both edges of the
 reproduction waveform can be closer to be symmetrical. However, this
 method has a problem that the strength of the magnetic field is
 insufficient when the modulation frequency of the reproduction magnetic
 field is high. FIG. 3 is a graph showing the relationship between the
 frequency of the applied magnetic field and the intensity of the magnetic
 field according to the reproduction method disclosed by the applicant of
 the present invention. The ordinate axis indicates the intensity of the
 magnetic field and the abscissa axis indicates time. As shown in this
 graph, when the modulation frequency of the reproduction magnetic field is
 higher, the intensity of the magnetic field is low. There has been a
 problem that when the intensity of the magnetic field is low, it is hard
 to detect the reproduction signal correctly. Furthermore, it is necessary
 for a device for executing this reproduction method to provide an
 additional driving circuit for modulating the reproduction magnetic field.
 BRIEF SUMMARY OF THE INVENTION
 The present invention has been achieved in order to solve the
 aforementioned problems, and has an object of providing a magneto-optic
 medium which can obtain a high-quality reproduction signal, by making the
 inclinations of the edges before and after the reproduction waveform more
 steep and closer to be symmetrical, by providing an auxiliary magnetic
 layer which generate reproduction magnetic fields each having positive or
 negative polarity according to the edges before or after the reproduction
 waveform, without providing an additional circuit for the modulation of
 the magnetic field, and without making the intensity of the magnetic field
 insufficient.
 The magneto-optic recording medium of the present invention is
 characterized by comprising: a magnetic layer for recording and
 reproducing data; and a magnetic field generation layer for generating two
 magnetic fields having reverse polarities, the magnetic field generation
 layer being formed by a magnetic film and situated on one surface of said
 magnetic layer.
 Consequently, magnetic fields each having a reverse polarity from the other
 are generated, and the magnetic layers can be provided with a reproduction
 magnetic field having an advantageous polarity according to the front and
 rear edges of the reproduction waveform. As a result, there is no need of
 providing an additional circuit for reversing the polarity of the external
 magnetic field, which makes it possible to obtain a reproduction waveform
 which has front and rear edges whose inclinations are both steep.
 Furthermore, the magneto-optic recording medium of the present invention is
 characterized by comprising: first, second, and third magnetic layers for
 recording and reproducing data for generating a temperature distribution
 in the magneto-optic recording medium due to the irradiation of a light
 beam which relatively moves with the first, second, and third magnetic
 layers and for reading data from an area determined by the temperature
 distribution in the magneto-optic recording medium; and a magnetic field
 generation layer for generating simultaneously two magnetic fields having
 reverse polarities, the magnetic field generation layer being formed by a
 magnetic film and situated on the opposite side of the third magnetic
 layer to the second magnetic layer.
 Furthermore, the magneto-optic recording medium of the present invention is
 characterized by comprising: first, second, and third magnetic layers for
 recording and reproducing data for being made from a
 rare-earth/transition-metal alloy, the first and third magnetic layers
 having characteristics of easy magnetization in the direction of layer
 deposition and the second magnetic layer being rare-earth magnetization
 dominant and having characteristics of easy magnetization in the in-plane
 direction at room temperature; and a magnetic field generation layer for
 generating simultaneously two magnetic fields having the reverse
 polarities, the magnetic field generation layer being formed by a magnetic
 film and situated on the opposite side of the third magnetic layer to the
 second magnetic layer.
 Consequently, the magnetization direction of the third magnetic layer is
 transcribed into the first magnetic layer and read out in the intermediate
 temperature area of the temperature distribution which is generated inside
 the beam spot as the result of the irradiation of the light beam.
 Consequently, magnetic fields, which have respective polarities and are
 generated by the magnetic field generation layer, are given to the low
 temperature area and the high temperature area between which the
 intermediate temperature area exists. As a result, reproduction magnetic
 fields having opposite polarities from each other can be given to each of
 the front and rear edges of a reproduction waveform.
 Furthermore, the magneto-optic recording medium of the present invention is
 characterized by further comprising a non-magnetic layer between the
 magnetic layer and the magnetic field generation layer, and the magnetic
 field generation layer including a plurality of magnetic layers which have
 magnetically exchange coupled force at room temperature.
 Thus, the non-magnetic layer disposed between the magnetic layer and the
 magnetic layer generation layer functions to eliminate the exchange
 coupled force between the magnetic field generation layers and the
 magnetic layers. Consequently, the magnetization directions of the
 plurality of magnetic layers in the magnetic field generation layers can
 be made to point to the same predetermined direction, regardless of the
 magnetization directions of the magnetic layers.
 Furthermore, the magneto-optic recording medium of the present invention is
 characterized in that the magnetic field generation layer includes fourth,
 fifth, and sixth magnetic layers from the side closer to the third
 magnetic layer, and in that the coercive forces Hc1 to Hc6 of the first to
 sixth magnetic layers, respectively, and the Curie temperatures Tc1 to Tc6
 of the first to sixth magnetic layers, respectively, satisfy following
 relations: Hc6&gt;Hc3&gt;Hc5&gt;Hc1, Hc4&gt;Hc2, and Tc6&gt;Tc4&gt;Tc1&gt;Tc3&gt;Tc2&gt;Tc5.
 Thus, the magnetic characteristics of the first, second, and third magnetic
 layers for recording and reproducing data and the fourth, fifth, and sixth
 magnetic layers for generating magnetic fields are specified.
 Consequently, when an external magnetic field is applied while a light
 beam is being irradiated to reproduce data, the magnetic direction of the
 fourth magnetic field is determined so as to generate two magnetic fields
 having the reverse polarities from each other, and also mask areas which
 prevent the magnetization direction of the third magnetic layer from being
 transcribed into the first magnetic layer are formed front and rear the
 read-out area which is determined by the temperature distribution inside
 the medium, and these mask areas are given the reverse polarities from
 each other.
 Furthermore, the magneto-optic recording medium of the present invention is
 characterized in that the fourth magnetic layer is formed by a transition
 metal magnetization dominant rare-earth/transition-metal alloy film.
 Furthermore, the magneto-optic recording medium of the present invention is
 characterized in that the fourth magnetic layer is formed by a rare-earth
 metal magnetization dominant rare-earth/transition-metal alloy film.
 Consequently, when the fourth magnetic layer is transition metal
 magnetization dominant, it is possible to make the fourth and sixth
 magnetic layers have the same magnetization directions due to the exchange
 coupled force at the high temperature area. On the other hand, when the
 fourth magnetic layer is rare-earth magnetization dominant, it is possible
 to make the fourth and sixth magnetic layers have the opposite
 magnetization directions from each other due to the exchange coupled force
 at the high temperature area. When the magnetization directions of the
 fourth and the sixth magnetic layers are the same as that of the external
 magnetic field which is applied when data are reproduced, it is
 advantageous to the generation of a magnetostatic field, and the intensity
 of the external magnetic field can be reduced.
 The above and further objects and features of the invention will more fully
 be apparent from the following detailed description with accompanying
 drawings.

DETAILED DESCRIPTION OF THE INVENTION
 The present invention will be detailed based on the drawings which show the
 embodiments.
 FIRST EMBODIMENT
 FIG. 4 shows the film structure of the magneto-optic disk of the present
 invention. As shown in FIG. 4, the magneto-optic disk 1 comprises a SiN
 foundation layer 12, a reproduction layer 13 a control layer 14, a
 recording layer 15, a SiN intermediate layer 16, a first auxiliary layer
 17, a second auxiliary layer 18, a third auxiliary layer 19, and a SiN
 protection layer 20 which are accumulated in this order on a polycarbonate
 substrate 11. The first, second, and third auxiliary layers 17, 18, and
 19, which are disposed on the opposite side of the recording layer 15 to
 the substrate with the SiN intermediate layer 16 therebetween, are the
 above-mentioned magnetic field generation layers for generating
 magnetostatic fields. Each of these layers which compose the magneto-optic
 disk 1 is formed by a DC spatter process in a vacuum chamber having a
 vacuum degree of 5.times.10.sup.-5 Pa or below. Each SiN layer is formed
 under the conditions of a gas pressure of 0.3 Pa and a making power of 0.8
 kW. The reproduction layer 13, the control layer 14, the recording layer
 15, the first auxiliary layer 17, the second auxiliary layer 18, and the
 third auxiliary layer 19, which are magnetic layers, are formed under the
 conditions of a gas pressure of 0.5 Pa and a making power of 1.0 kW. The
 film composition, the film thickness, and the magnetic characteristics of
 each layer are shown in TABLE 1.
 The control layer 14 is a rare-earth metal magnetization dominant
 (hereinafter RE-rich) in-plane magnetic film which does not have a
 compensation point until a Curie temperature, and the other magnetic
 layers are transition metal magnetization dominant (hereinafter TM-rich)
 perpendicular magnetic films. The relationship between the Curie
 temperature Tc and the coercive force Hc of each magnetic layer is as
 follows:
 Tc6&gt;TC4&gt;Tc1&gt;Tc3&gt;Tc2&gt;Tc5
 Hc6&gt;HC3&gt;Hc5&gt;Hc1, Hc4&gt;Hc2
 Here, Tc1 and Hc1 indicate the Curie temperature and the coercive force of
 the reproduction layer 13, and the numbers following each Tc and each Hc
 correspond to the orders (2, 3, 4, 5, and 6) of the magnetic layers on the
 side of closer to the substrate.
 The following is a description of the magnetized conditions during the
 erasure, recording, and reproduction of the magneto-optic disk 1 when a
 laser beam is emitted while an external magnetic field is being applied on
 the magneto-optical disk 1 having such a structure. First of all, a laser
 beam is emitted by using a power for erasure which makes the temperature
 in the irradiation area higher than the Curie temperature Tc6 of the third
 auxiliary layer, so as to apply an external magnetic field in the S
 direction (upward) for the initial erasure. FIG. 5 shows the magnetized
 conditions of the magneto-optic disk 1 in this step. In FIG. 5, the spin
 directions of the transition metal magnetization are indicated by arrows,
 and the directions of the actual magnetization are indicated by whitened
 arrows. As shown in FIG. 5, the magnetizing directions of the recording
 layer 15 are all upward, and the magnetizing directions of the first,
 second, and third auxiliary layers 17, 18, and 19 are all upward. This
 initial erasure step is performed only once when the disk is shipped, and
 not needed after shipment.
 A laser beam is emitted by using a power for erasure which makes the
 temperature in the irradiation area higher than the Curie temperature Tc3
 of the recording layer 15 and lower than the Curie temperature Tc6 of the
 third auxiliary layer 19, so as to apply an external magnetic field in the
 N direction (downward) for the erasure to the recording layer 15. FIG. 6
 shows the magnetized conditions of the magneto-optic disk 1 at this step.
 As shown in FIG. 6, the magnetized conditions of the reproduction layer
 13, the control layer 14, and the recording layer 15 change to the reverse
 direction. Since the SiN intermediate layer 16 is disposed between the
 recording layer 15 and the auxiliary layer 17, an exchange coupled force
 never exists between the recording layer 15 and the auxiliary layer 17.
 The erasure step in the N direction is performed every time data in the
 magneto-optic disk are rewritten.
 When data are recorded in the magneto-optic disk 1, a laser beam is emitted
 by using a power for recording which makes the temperature in the
 irradiation area higher than the Curie temperature Tc3 of the recording
 layer 15 and lower than the Curie temperature Tc6 of the third auxiliary
 layer 19, and by applying a recording magnetic field which is larger than
 the coercive force Hc3 of the recording layer 15 and smaller than the
 coercive force Hc6 of the third auxiliary layer, so as to perform the
 recording of data with the light modulation system. FIG. 7 shows the
 magnetized conditions of the magneto-optic disk 1 at this step. As shown
 in FIG. 7, the recording layer 15 has magnetizing directions according to
 the data and the third auxiliary layer 19 has the magnetizing directions
 which have been unchanged since the erasure step. This is because the
 recording is performed by using a power for recording which is lower than
 the Curie temperature Tc6 and a recording magnetic field which is smaller
 than the coercive force Hc6.
 Thus, in order to reproduce recorded data, the laser beam is emitted by
 using a low power for reproduction, and a reproduction magnetic field Hr
 of 100 Oe is applied in the erasure direction, that is, the N direction
 (downwards). FIG. 8 shows the magnetized conditions of the magneto-optic
 disk 1 in this step. In the magneto-optic disk 1, a temperature
 distribution occurs within the laser spot S as mentioned above, and a low
 temperature area, an intermediate temperature area, and a high temperature
 area are formed. In the low and intermediate temperature areas, the
 magnetizing directions of the first auxiliary layer 17 keep their initial
 conditions. This is due to the exchange coupled force between the first
 auxiliary layer 17 and the third auxiliary layer 19 via the second
 auxiliary layer 18, and the exchange coupled force is far greater than
 that of the reproduction magnetic field Hr. The temperature of the high
 temperature area becomes equal to or higher than the Curie temperature
 Tc5, so that the second auxiliary layer 18 blocks the exchange coupled
 force between the first auxiliary layer 17 and the third auxiliary layer
 19. As a result, the magnetizing directions of the first auxiliary layer
 17 become the directions of the reproduction magnetic field Hr (N
 direction).
 Thus, the magnetizing directions of the first auxiliary layer 17 are in the
 S direction at the low area and intermediate temperature area and in the N
 direction at the high temperature area. Consequently, a magnetostatic
 field Hs1 occurs at the low temperature area, and satisfies Hs1&gt;Hr. When
 the exchange coupled force which acts between the control layer 14 and the
 recording layer 15 at the low temperature area is made Hex (23), the
 following relationship is satisfied:
EQU Hs1&gt;Hex(23)+Hc(12) (1)
 Here, Hc (12) indicates the coercive force related to the reproduction
 layer 13 and the control layer 14. Therefore, at the low temperature area,
 the magnetizing directions of the control layer 14 all become the S
 direction due to the magnetostatic field Hs1 of the S direction, so that
 the magnetization of the reproduction layer 13 which has coupled-exchange
 with the control layer 14 always point to the N direction.
 At the intermediate temperature area, too, a magnetostatic field occurs in
 the S direction, satisfying Hs1&gt;Hr. However, the size difference in the
 formula (1) is the opposite of the low temperature area, becoming
 Hs1&lt;Hex (23)+Hc (12).
 As a result, the exchange coupled force becomes stronger, and the
 magnetizing directions of the recording layer 15 are transcribed into the
 reproduction layer 13.
 On the other hand, at the high temperature area, the magnetizing directions
 of the first auxiliary layer 17 point to the N direction, and the
 magnetostatic field Hs2 occurs in the N direction. Since the magnetostatic
 field Hs2 has a smaller magnetization value than at the low temperature
 area, it satisfies
 Hs1&gt;Hs2.
 In addition,
 Hr=Hs2, or Hr&gt;Hs2
 is satisfied; however, Hs2 has the same direction as the reproduction
 magnetic field Hr, so that a magnetic field (Hr+Hs2) in the N direction is
 given to the high temperature area and the magnetization of the
 reproduction layer 13 always points to the N direction.
 Thus, when the reproduction magnetic field in the N direction is applied to
 reproduce data in the magneto-optic disk 1, an S-direction magnetostatic
 field Hsl occurs at the low temperature area and an N-direction
 magnetostatic field Hs2 occurs at the high temperature area. Consequently,
 the magnetizing directions of the reproduction layer 13 corresponding to
 the front edge and the rear edge both point to the N direction, which is
 the erasure direction, so that both edges are given a magnetic field in
 the direction for reducing the jitter. As a result, the quality of the
 reproduction signal is improved.
 Of the auxiliary magnetic layers, the first auxiliary layer 17 is a main
 magnetic layer for generating a reproduction magnetic field, so that the
 layer is made of a magnetic film having so high a Curie temperature as not
 to lose its magnetization at a high temperature.
 The following is a description of the size of the magnetostatic field which
 is generated by an auxiliary magnetic layer at the low temperature area.
 In order to estimate the size of the magnetostatic field, an N-direction
 reproduction magnetic field is given to the magneto-optic disk 1 while a
 laser beam is being eradicated by a power for reproduction of 1 mW or
 below, so as to examine the changes in the levels of the reproduction
 signal under the same conditions as the low temperature area. FIG. 9 shows
 the magnetization conditions of the magneto-optic disk 1 when the initial
 erasure is applied to the third auxiliary layer 19 in the N direction.
 FIG. 10 shows the magnetization conditions of the magneto-optic disk 1
 when the initial erasure is applied to the third auxiliary layer 19 in the
 S direction. In either case, data in the recording layer 15 are erased in
 the N direction. When the initial erasure is performed in the N direction
 (refer to FIG. 9), an N-direction magnetostatic field is generated, and as
 a whole, (Hr+Hs) magnetic field is applied. On the other hand, when the
 initial erasure is performed in the S direction (refer to FIG. 10), an
 S-direction magnetostatic field is generated, and as a whole, (Hr-Hs)
 magnetic field is applied. Here, Hr indicates the intensity of the
 reproduction magnetic field, and Hs indicates the intensity of the
 magnetostatic field generated by the first auxiliary layer 17.
 FIG. 11 is a graph showing the changes in the levels of the reproduction
 signals of both cases, where the ordinate axis indicates the reproduction
 signal level and the abscissa axis indicates the intensity of the magnetic
 field in the N direction. When the initial erasure is performed in the S
 direction, the reproduction signal level is reversed at about 800 Oe, and
 when the initial erasure is performed in the N direction, the reproduction
 signal level is reversed at about 200 Oe. Consequently, the intensity of
 the magnetostatic field Hs corresponds to a half of the difference between
 (Hr+Hs) and (Hr-Hs), and in the case shown in FIG. 11, a magnetostatic
 field Hs of about 300 Oe occurs.
 In order to confirm the occurrence of a magnetic field at the high
 temperature area in the direction opposite to that at the low temperature
 area, a power for reproduction is increased while a magnetic field of 100
 Oe is being applied in the S direction under the conditions that data on
 the third auxiliary layer 19 are initially erased in the S direction, and
 the level of the reproduction signal is measured. FIG. 12 is a graph
 showing the changes of the levels of the reproduction signal, and the
 ordinate axis indicates the reproduction signal level and the abscissa
 axis indicates a power for reproduction. As is known from the graph, the
 reproduction signal level decreases until the power for reproduction
 reaches 3 mW, and then begins to increase after 3 mW. This indicates that
 the magnetizing directions of the reproduction layer 13 change from the N
 direction to the S direction at the point where the power for reproduction
 is 3 mW. In conventional MSR media, such a change can never be observed
 with a laser beam of 3 mW when a magnetic field of 100 Oe is applied. This
 indicates that a magnetostatic field is generated at the high temperature
 area by the first, second, and third auxiliary layers 17, 18, 19.
 A 1.44 .mu.m mark was recorded on the magneto-optic disk 1 having the
 above-mentioned structure, and a reproduction magnetic field was applied
 in the erasure direction (N direction) at 100 Oe. A reproduction signal
 was obtained at a linear velocity of 6 m/s and a reproduction waveform was
 confirmed. Both the front edge and the rear edge had steep inclinations.
 FIG. 13 shows the reproduction waveform. Thus, in the magneto-optic disk
 of the present embodiment, the inclinations of both the edges of the
 reproduction waveform are close to be symmetrical, which means that a
 highly qualified reproduction signal can be obtained. In addition, since a
 magnetic field for reproduction is generated, it becomes possible to
 reduce the intensity of a magnetic field to be applied from outside.
 SECOND EMBODIMENT
 As a second embodiment of the present invention, a magneto-optic disk 2
 which uses a RE-rich rare-earth transition metal alloy film (GdFeCo film)
 as the first auxiliary layer 27 will be described. The Curie temperature
 Tc4 of the first auxiliary layer 27 is about 340.degree. C., and its
 compensation temperature is 200.degree. C. Since the film structure and
 the film forming process are the same as those in the first embodiment,
 their description will be omitted.
 The following is a description of the magnetized conditions during the
 erasure, recording, and reproduction of the magneto-optic disk 2 when a
 laser beam is emitted while an external magnetic field is being applied.
 First of all, a laser beam is emitted by using a power for erasure which
 makes the temperature in the irradiation area higher than the Curie
 temperature Tc6 of the third auxiliary layer, so as to apply an external
 magnetic field in the N direction (downward) for the initial erasure. FIG.
 14 shows the magnetized conditions of the magneto-optic disk 2 in this
 step. As shown in FIG. 14, the magnetizing directions of the recording
 layer 15 are all downward, the magnetizing directions of the first
 auxiliary layer 17 are all upward, and the magnetizing directions of the
 second and third auxiliary layers 18 and 19 are all downward. This initial
 erasure is performed only once when the disk is shipped.
 A laser beam is emitted by using a power for erasure which makes the
 temperature higher than the Curie temperature Tc3 of the recording layer
 15 and lower than the Curie temperature Tc6 of the third auxiliary layer
 19, so as to apply an external magnetic field in the N direction
 (downward) for the erasure of the recording layer 15. This erasure is
 performed every time data in the magneto-optic disk 2 are rewritten.
 When data are recorded in the magneto-optic disk 2, a laser beam is emitted
 by using a power for recording which makes the temperature in the
 irradiation area higher than the Curie temperature Tc3 of the recording
 layer 15 and lower than the Curie temperature Tc6 of the third auxiliary
 layer 19, and by applying an external magnetic field which is larger than
 the coercive force Hc3 of the recording layer 15 and smaller than the
 coercive force Hc6 of the third auxiliary layer 19, so as to perform the
 recording of data with the light modulation system. FIG. 15 shows the
 magnetized conditions of the magneto-optic disk 2 in this moment. As shown
 in FIG. 15, the recording layer 15 has magnetizing directions according to
 the data, and the third auxiliary layer 19 has the magnetizing directions
 which have been unchanged since the erasure step. This is because the
 recording is performed by using a power for recording which is lower than
 the Curie temperature Tc6 and a magnetic field which is smaller than the
 coercive force Hc3.
 Thus, in order to reproduce recorded data, the laser beam is emitted by
 using a low power for reproduction, and a reproduction magnetic field Hr
 of 100 Oe is applied in the erasure direction, that is, the N direction
 (downwards). FIG. 16 shows the magnetized conditions of the magneto-optic
 disk 1 in this step. In the magneto-optic disk 2, a temperature
 distribution occurs within the laser spot S as mentioned above, and a low
 temperature area, an intermediate temperature area, and a high temperature
 area are formed. In the low and intermediate temperature areas, the
 magnetizing directions of the first auxiliary layer 27 keep their initial
 conditions. This is due to the exchange coupled force between the first
 auxiliary layer 27 and the third auxiliary layer 19 via the second
 auxiliary layer 18, and the exchange coupled force is far greater than
 that of the reproduction magnetic field Hr. The temperature of the high
 temperature area becomes equal to or higher than the Curie temperature
 Tc5, so that the second auxiliary layer 18 blocks the exchange coupled
 force between the first auxiliary layer 27 and the third auxiliary layer
 19. As a result, the magnetizing directions of the first auxiliary layer
 27 become the directions of the reproduction magnetic field Hr (N
 direction). Of the auxiliary magnetic layers, the first auxiliary layer 27
 is a main magnetic layer for generating a reproduction magnetic field, so
 that the layer is made of a magnetic film having so high a Curie
 temperature as not to lose its magnetization at a high temperature.
 In the same manner as in the first embodiment, such a magnetization of the
 first auxiliary layer 27 makes an S-direction magnetostatic field Hsl
 occur at the low temperature area and an N-direction magnetostatic field
 Hs2 occur at the high temperature area. Consequently, the magnetizing
 directions of the reproduction layer 13 corresponding to the front edge
 and the rear edge both point to the N direction, which is the erasure
 direction, so that both edges are given a magnetic field in the direction
 for reducing the jitter. A 1.44 .mu.m mark was recorded on the
 magneto-optic disk 2 having the above-mentioned structure, and a
 reproduction magnetic field was applied in the erasure direction (N
 direction) at 100 Oe. A reproduction signal was obtained at a linear
 velocity of 6 m/s and a reproduction waveform was confirmed. Both the
 front edge and the rear edge had steep inclinations. FIG. 17 shows the
 reproduction waveform. Thus, in the magneto-optic disk of the present
 embodiment, the inclinations of both the edges of the reproduction
 waveform are steep and close to be symmetrical, which means that a highly
 qualified reproduction signal can be obtained.
 In addition, according to the magneto-optic disk 2, the magnetization
 direction of the first auxiliary layer 27 is the same as that of the third
 auxiliary layer 19 at the high temperature area, and less affected by the
 magnetostatic field from the third auxiliary layer 19 as compared with the
 first embodiment which indicates the opposite direction, so that it is
 advantageous to the generation of the magnetostatic field Hs2.
 Consequently, the intensity of the external magnetic field can be further
 reduced than in the first embodiment.
 In the above-mentioned embodiments, the SiN intermediate layer 16 is
 disposed between the recording layer 15 and the first auxiliary layer 17.
 However, the intermediate layer is not restricted to SiN and can be a
 nitride film such as SiN, AlN, and TiN, an oxidized film such as
 SiO.sub.2, TiO.sub.2, and Y.sub.2 O.sub.3, or a non-magnetic film such as
 Al and Cu.
 As explained hereinbefore, according to the present invention, magnetic
 field generation layers which generate simultaneously two magnetic fields
 having reverse polarities to each other are provided so as to give each
 magnetic field to the area before and after the transcription area of the
 recorded mark. Consequently, it becomes possible to give a magnetic field
 having an advantageous polarity to each of the front and rear edges of the
 reproduction waveform, so that the inclinations of the front and rear
 edges become steep and closer to being symmetrical. As a result, the
 present invention has excellent effects including the enhancement of the
 quality of the reproduction signal.
 As this invention may be embodied in several forms without departing from
 the spirit of essential characteristics thereof, the present embodiments
 are therefore illustrative and not restrictive, since the scope of the
 invention is defined by the appended claims rather than by the description
 preceding them, and all changes that fall within metes and bounds of the
 claims, or equivalence of such metes and bounds thereof are therefore
 intended to be embraced by the claims.
 TABLE 1
 Film
 thick- Curie Coercive
 Composi- ness temperature force
 Deposited layer tion (nm) Dominant (.degree. C.) (0e)
 SiN foundation SiN 70 -- -- --
 layer
 Reproduction GdFeCo 35 TM-rich 300 300
 layer
 Control layer GdFe 35 RE-rich 170 &lt;10
 Recording TbFeCo 40 TM-rich 270 12000
 layer
 SiN inter- SiN 5 -- -- --
 mediate layer
 First auxiliary GdFeCo 30 TM-rich 350 200
 layer
 Second TbFe 10 TM-rich 150 5000
 auxiliary
 layer
 Third auxiliary TbFeCo 20 TM-rich 380 15000
 layer
 SiN protection SiN 60 -- -- --
 layer