Information recording method, apparatus and information reproducing method and apparatus for domain wall mobile type magneto-optical medium

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an information recording method, apparatus and reproducing method and apparatus which scans with heating means recording tracks configured by perpendicular magnetic anisotropy substance and stores information signals by applying a magnetic field to a heating region of the recording tracks.

[0003] 2. Related Background Art

[0004] Various methods to reproduce information signals recorded in magnetic recording media are conventionally known. In particular, a domain wall mobile reproducing method which the present applicant proposed in Japanese Patent Application Laid-Open No. 6-290496 is characterized by having recoding tracks of magnetooptical medium in which information signals are formed by a magnetic domain wall, operating driving power to this magnetic wall to move rapidly, and detecting that movement so as to reproduce information signals, and is to enable the information signals described with extremely high storing density with high resolution capability. A method of recording information signals into magneto-optical medium and reproducing method of information signals by magnetic wall mobile reproducing method will be described as follows.

[0005]
FIGS. 10A and 10B are partially enlarged view showing a configuration of a magneto-optical medium 1, and FIG. 10A is a longitudinal section while FIG. 10B is a plan view. Here, the magneto-optical medium 1 is configured by a substrate 2 in which is configured by transparent resin material such as polycarbonate, etc. and is shaped as a belt so that a groove G and a land L are alternately formed in parallel, a magnetic layer 3 formed on the substrate 2 and configured by perpendicular magnetic anisotropy substance, and a protection coat 4 configured by ultraviolet hardened resin. The magnetic layer 3 formed on the land L configures a belt-shape recording track RT on which information signals are recorded. The magnetic layer 3 is to be configured by laminating three layers made of perpendicular magnetic anisotropy substance, rare earth such as, for example, Tb, Gd and Dy, and transition metal such as Fe and Co, etc., that is, a displacement layer 3a, a switching layer 3b, and a memory layer 3c. Here, the displacement layer 3a is a perpendicular magnetic anisotropy film having magnetic domain wall coercivity which is smaller than memory layer 3c and large magnetic wall movement, the switching layer 3b is a perpendicular magnetic anisotropy substance film having curie temperature lower than the domain wall displacement layer 3a and the memory layer 3c, and the memory layer 3c is a perpendicular magnetic anisotropy film.

[0006] In addition, with a method such as radiating highly powered laser beams locally for heating, etc., magnetic feature of the magnetic layer 3 on a bottom surface and a side surface of a groove G has been made lower (for example, deteriorated on perpendicular magnetic anisotropy). This causes to be weakened magnetic combination between the recording track RT and a region in which the magnetic feature on its both side surfaces is lowered.

[0007] Next, a method to implement thermal magnetic recording information signals to the above described magnetic recording media 1 with a storing apparatus will be described. The recording apparatus comprises driving means for an optical head, a magnetic head and magneto-optical medium 1. FIGS. 8A and 8B are partially enlarged view of the magneto-optical medium 1, showing a recording method of information signals, and FIG. 8A is a cross-sectional view while FIG. 8B is a plan view looked at from the direction of a lower surface. At the time when information signals are recorded, the optical head implements radiation by concentrating a highly powered recording light beam 7 being heating means to a recording track RT through a substrate 2. At the same time, the driving means drives the magneto-optical medium 1, and thereby the recording light beam 7 scans the recording track RT toward the direction indicated by an arrow A. Temperature of a magnetic layer 3 increases with radiation of the recording light beam 7, and in the periphery of the radiation region of the recording light beam 7 a thermal distribution shown by an isothermal line in the drawing is formed. Here, a reference numeral 8 denotes an isothermal line of a temperature Tc approximately equal to the curie temperature of the magnetic storing layer 3c.

[0008] Radiation of the light beam for storing 7 by way of an optical head concurs with the magnetic head's application of a perpendicular magnetic field the direction of which varies upward and downward to the radiation region of the recording light beam 7 corresponding with information signals. The memory layer 3c loses magnetization when it passes the front portion of the isothermal line 8 resulting in its temperature being not less than the curie temperature Tc and gives rise to magnetization in the same direction as the magnetic field applied at that time when it passes the back portion of the isothermal line 8 resulting in its temperature being not more than Tc. Moreover, as it moves remotely from the back portion of the isothermal line 8, the temperature drops while coercivity increases so that the above described magnetization is fixed. Thus, magnetization regions having magnetization in the upward direction and in the downward direction corresponding with the direction of the applied magnetic field are arranged alternately to be formed on the storing track RT as shown by an arrow in the upward and downward direction in FIG. 8A, and in the boundary portion between the magnetization region and the preceding and following magnetization region, magnetic domain walls W1, W2, W3, W4, W5 and W6 are formed. These magnetic walls, which are formed along the back portion of the isothermal line 8, will be shaped as an arc which bends convexly in the direction opposite from the scanning direction (an arrow A) of the light beam for storing. In addition, the displacement layer 3a, the switching layer 3b, and the memory layer 3c are mutually brought into exchange coupling so that magnetization and the magnetic domain walls W1, W2, W3, W4, W5 and W6 are transfer-formed onto the displacement layer 3a and the switching layer 3b as well.

[0009] The thermal magnetic storing method as described above is referred to as a magnetic field modulation storing method, and can form magnetic walls at an interval shorter than concentration diameter of the light beam for storing, and therefore is suitable to store information signals at high density. Next, a method to reproduce information signals from the above described magneto-optical medium 1 with a reproducing apparatus will be described. The reproducing apparatus comprises driving means for an optical head and magneto-optical medium 1. FIGS. 9A and 9B are partially enlarged view of the magneto-optical medium 1 showing a reproducing method of information signals by way of displacement layer system, and FIG. 9A is a cross-sectional view while FIG. 9B is a plan view looked at from the direction of a lower surface. At the time when information signals are reproduced, the optical head implements radiation by concentrating a low powered light beam for reproducing 9 to a recording track RT through a substrate 2. At the same time, the driving means drives the magneto-optical medium 1, and thereby the light beam for reproducing 9 scans the recording track RT toward the direction indicated by an arrow A. Temperature of a magnetic layer 3 increases with radiation of the light beam for reproducing 9, and in the periphery of the radiation region of the light beam for reproducing 9 a thermal distribution shown by an isothermal line in the drawing is formed. Here, a reference numeral 30 denotes an isothermal line of a temperature Ts approximately equal to the curie temperature of the switching layer 3b, and a reference character Xp denotes a peak position of temperature. As described later, in the displacement layer 3a of the recording track RT, the magnetic domain wall is movable only in a region of temperature not less than Ts, that is, a region surrounded by the isothermal line 30, and in the other region movement of a magnetic domain wall is impossible.

[0010] Here, in a position sufficiently remote from the radiation region of the light beam for reproducing 9, temperature of the magnetic layer 3 is low and in this position, the displacement layer 3a, the switching layer 3b, and the magneto-optical layer 3c have mutually undergone exchange coupling, and magnetization as well as the magnetic domain wall formed in the magnetic storing layer 3c have been transfer-formed in the switching layer 3b and the displacement layer 3a as well. In addition, since the temperature distribution is approximately unanimous, a driving power to move the magnetic domain wall transcribed into the displacement layer 3a does not act and therefore the magnetic domain wall remain fixed. However, in the location closer to the radiation region of the light beam for reproducing 9, the temperature of the magnetic layer 3 increases, and subject to passing the forefront portion of the isothermal line 30, the temperature of the switching layer 3b reaches not less than Ts to cancel magnetization. Thus, since exchange coupling among the displacement layer 3a, the switching layer 3b, and the magnetic memory layer 3c is cut in the region with temperature surrounded by the isothermal line 30 higher than Ts and magnetic coupling between the displacement layer 3a and the region of the both side surfaces of the recording track RT is weakened, the magnetic domain wall will become movable without being restricted. Moreover, since the surrounding temperature is inclined, the driving power will act on the magnetic domain wall in the direction of higher temperature, that is, of lower energy. Thus, the magnetic domain wall (W1 in FIGS. 9A and 9B) which has past through the forefront portion of the isothermal line 30 moves rapidly toward a position Xp whose temperature reaches the peak as shown in the arrow B in the displacement layer 3a. Incidentally, in the drawing, the magnetic domain wall W1 prior to movement is indicated by a broken line. Accompanied by movements of this magnetic domain wall, a magnetization region Mex having magnetization in one direction (the downward direction in the drawn example) is extended and formed. Incidentally, the magnetic memory layer 3c is configured by a material having small degree of displacement of domain wall mobility, and therefore the magnetic domain wall does not move in the magnetic memory layer 3c.

[0011] Thus, the magnetic domain walls W1, W2, . . . and, W6 move toward the position Xp every time when they pass the forefront portion of the isothermal line 30 subsequently, and each time the magnetization region Mex which has magnetization upward and downward and extended is formed alternately. A polarization direction of the reflecting light of the reproducing light beam 9 from this magnetization region Mex is rotated corresponding with direction of magnetization of the magnetization region Mex due to magneto-optics effect (Kerr effect). Rotation of such polarization surface is detected with an optical head. Since this detected signals include changes in signals corresponding with movement of the magnetic domain wall, with the magnetic domain wall as information signal domain being formed at a position corresponding with the information signals to be stored, information signals can be reproduced from timing of changes in signals.

[0012] Problems in recording and reproduction of information signals by way of combination of the above described conventional magnetic field modulation storing system and magnetic domain wall mobile reproducing system will be described as follows.

[0013] As described with reference to FIGS. 9A and 9B, according to the magnetic domain wall mobile reproducing system, when the magnetic domain wall passes the forefront portion of the isothermal line 30, it will be no longer restrained by exchange coupling, and moreover temperature inclination cause driving power to act to start movement. Incidentally, as shown in FIG. 8B, according to the magnetic field modulation recording system, the magnetic domain wall is formed along the back portion of the isothermal line 8, and thus its shape will be an bent arc that is shaped convex in the direction opposite from the scanning direction (the arrow A) of the recording light beam 7. That is, since the scanning direction of the recording light beam and the scanning direction of the reproducing light beam are normally the same, the bending direction of the formed magnetic domain wall is opposite from the bending direction of the forefront portion of the isothermal line 30 at the time of reproduction as shown in FIG. 9B. Accordingly, as understood with FIG. 9B, at the time of information reproduction, the magnetic domain wall passes the forefront portion of the isothermal line 30 gradually from the central portion thereof and at last the both end portions will pass. Thus the entire magnetic domain wall will not become movable at a time, and the driving power will not act evenly on the entire portion, start time of the magnetic domain wall movement is apt to vary. As a result thereof, jitter of detected signals increases, making exact reproduction of information signals impossible.

[0014] In addition, in the case where forming interval of the magnetic domain wall has been made short, before the both ends of the magnetic domain wall have not yet passed the forefront portion of the isothermal line 30, the central portion of the subsequent magnetic wall moving layer passes the forefront portion of the isothermal line 30. As a result thereof, detection by separating signal changes corresponding with movement of continuous magnetic domain walls became impossible and detection resolution capability dropped.

SUMMARY OF THE INVENTION

[0015] Objectives of the present invention is to provide an information recording method as well as apparatus forming a recording magnetic domain having magnetic domain walls movable evenly and all together and to provide a method as well as apparatus to reproduce the above described recording magnetic domain.

[0016] The above described objectives are attained by the following configurations.

[0017] According to an aspect of the present invention, there is provided an information recording method to a domain wall mobile type magneto-optical medium, wherein a light beam scans on the medium for heating and at the same time a magnetic field modulated corresponding to the information is applied to a heated point, and a recording magnetic domain having an arc-shaped magnetic domain wall bending convex in a forward direction of an operation of the light beam is formed so that the information is recorded.

[0018] According to another aspect of the present invention, there is provided an information recording apparatus comprising an optical head to radiate the light beam for executing the information recording method, a magnetic head to generate a magnetic field modulated corresponding to information, and means for causing the optical head, the magnetic head and the medium to relatively move.

[0019] According to still another aspect of the present invention, there is provided a method of reproducing a recording magnetic domain formed on a medium by the information recording method by scanning a light beam in a direction along a magnetic domain wall which is bent in a convex state.

[0020] According to further aspect of the present invention, there is provided an information reproducing apparatus comprising an optical head to radiate a light beam and means for causing the optical head and a medium to relatively move in order to execute the reproducing method.

[0021] Similar reference characters are used in the figures to denote similar parts for the sake of clarity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]
FIGS. 1A and 1B are drawings showing a recording method of the present invention;

[0023]
FIGS. 2A and 2B are drawings showing a method of reproducing information signals with the magnetic domain wall mobile reproducing system from a magnetic recording medium in which the information signals are recorded with the recording method of the present invention;

[0024]
FIGS. 3A and 3B are drawings showing another recording method of the present invention;

[0025]
FIGS. 4A and 4B are drawings showing a method to reproduce information signals with the super-resolution reproducing system from the magnetic recording medium in which the information signals are recorded with the recording method of the present invention;

[0026]
FIGS. 5A and 5B are drawings showing an example of configuration of the magnetic recording medium to be used for the recording method of the present invention;

[0027]
FIGS. 6A and 6B are drawings showing another example of configuration of the magnetic recording medium to be used for the recording method of the present invention;

[0028]
FIGS. 7A and 7B are drawings showing another example of configuration of the magnetic recording medium to be used for the recording method of the present invention;

[0029]
FIGS. 8A and 8B are drawings showing a conventional recording method of information signals;

[0030]
FIGS. 9A and 9B are drawings showing a method to reproduce information signals with the magnetic domain wall mobile reproducing system from the magnetic recording medium in which the information signals are recorded with a conventional recording method;

[0031]
FIGS. 10A and 10B are drawings showing a configuration of a conventional magnetic recording medium;

[0032]
FIG. 11 is a partially enlarged view of the configuration in FIG. 7A to be used in a recording method of the present invention; and

[0033]
FIG. 12 is a block diagram showing a configuration of a recording apparatus of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0034] A method of recording information signals to a magnetic recording medium with a thermo-magnetic recording method according to the present invention will be described as follows.

[0035]
FIGS. 5A and 5B are partially enlarged views showing an example of a configuration of a magnetic recording medium to be used in a recording method of the present invention, and FIG. 5A is a longitudinal section while FIG. 5B is a plan view. Here, a magnetooptical medium 1 is configured by a transparent resin material such as polycarbonate, and is formed by injection forming, etc.

[0036] In a substrate 2, grooves G and lands L, which are belt-shaped and have the same width, exist in parallel alternately, and on the substrate 2, magnetic layers 3 configured by perpendicular magnetic anisotropy substance and a protection coat 4 configured by ultraviolet hardened resin.

[0037] The magnetic layer 3 formed on the grooves G and the lands L both configure a belt-shape recording tracks RT on which information signals are recorded. The magnetic layer 3 is to be configured by laminating three layers made of perpendicular magnetic anisotropy substance, rare earth such as, for example, Tb, Gd and Dy, and transition metal such as Fe and Co, that is, a displacement layers 3a, switching layers 3b, and memory layers 3c.

[0038] Here, the displacement layers 3a are perpendicular magnetic anisotropy films having smaller magnetic domain wall coercivity and larger degree of displacement of domain wall than memory layers 3c, the switching layers 3b are perpendicular magnetic anisotropy substance films having Curie temperature lower than the displacement layers 3a and the memory layers 3c, and the memory layers 3c are perpendicular magnetic anisotropy films.

[0039] These three magnetic layers are formed into film by an anisotropy sputtering method so that the magnetic layers are not formed into film on side walls of the grooves G, but are formed only on the bottom surfaces of the grooves G and the upper surfaces of the lands L.

[0040] Thus, side walls of the grooves G in which no magnetic layers exist separate spaciously as well as magnetically the recording tracks RT from their both adjacent recording tracks RT.

[0041] Moreover, configuring material for the substrate 2 coating the both side faces of the recording tracks RT and the protection coat 4 has their thermal conductivity smaller than that of substance configuring the magnetic layers 3.

[0042] As described above, thermal conductivity of the protection coat 4 as well as the substrate 2 is desirably not less than 5 percent of thermal conductivity of the perpendicular magnetic anisotropy substance. Moreover, the percentage not more than three percent would be still further preferable. Thus, no members having thermal conductivity not less than thermal conductivity of the substance configuring the magnetic layers 3 are brought into connection with the both side faces of the recording tracks RT, but the both side faces of the recording tracks RT have been configured only by members having thermal conductivity less than thermal conductivity of the substance configuring the magnetic layers 3 so that the recording tracks RT are structured to restrain heat being spilt out from the both side faces of the recording tracks RT rather than from its extending direction.

[0043] Incidentally, as the protection coat 4, ultraviolet hardened resin, and adhesive sheet, etc. are used.

[0044]
FIGS. 6A and 6B are partially enlarged views showing another configuration of a magneto-optical medium to be used in a recording method of the present invention, and FIG. 6A is a longitudinal section while FIG. 6B is a plan view.

[0045] Here, a magneto-optical medium 1 is configured by a substrate 2 made of a transparent resin material such as polycarbonate, magnetic layers 3 that are formed on the substrate 2 and are made of perpendicular magnetic anisotropy substance and a protection coat 4 made of ultraviolet hardened resin. The magnetic layers 3 are belt-shaped in parallel, and respectively configure recording tracks RT. The magnetic layer 3 is to be configured by laminating three layers made of perpendicular magnetic anisotropy substance as in the above described example, that is, displacement layers 3a, switching layers 3b, and memory layers 3c. Here the adjacent recording tracks RT are formed by bringing predetermined positions in the magnetic layers formed into film all over the substrate into dry etching for removal. Thus, recording tracks RT are spaciously and magnetically separated from the regions on the faces of the both sides thereof.

[0046] Moreover, configuring material for the protection coat 4 coating the both side faces of the recording tracks RT has their thermal conductivity smaller than that of substance configuring the magnetic layers, that is, perpendicular magnetic anisotropy substance configuring the magnetic layers 3. Thus, no members having thermal conductivity not less than thermal conductivity of the substance configuring the magnetic layers 3 are brought into connection with the both side faces of the recording tracks RT, but the both side faces of the recording tracks RT have been configured only by members having thermal conductivity less than thermal conductivity of the magnetic layers 3 so that the recording tracks RT are structured to restrain heat being spilt out from the both side faces of the recording tracks RT rather than from its extending direction.

[0047] In the present embodiment, since the both side faces of the recording tracks RT are coated only by the protection coat 4, thermal conductivity of the substrate 2 is not necessarily required to be made small.

[0048] In addition, FIGS. 7A and 7B are partially enlarged views showing another configuration of a magneto-optical medium to be used in a recording method of the present invention, and FIG. 7A is a longitudinal section while FIG. 7B is a plan view.

[0049] Here, for a magneto-optical medium 1 a transparent resin material such as polycarbonate, is used as a material, and grooves G and lands L, which are belt-shaped and have the same width, are formed in parallel alternately.

[0050] On the substrate 2, the magnetic layers 3 exist to become recording tracks. Front surfaces of the magnetic layers 3 are covered by thermal conduction layer 5 made of Al, Au, and Ag which have thermal conductivity larger than that of the magnetic layers 3 or an alloy containing them, etc. so as to hasten heat proliferation on the surfaces of the recording tracks.

[0051] The rear surfaces as well as the both side surfaces of this magnetic layers 3 are covered by dielectric layer 6 made of non-polarized inorganic materials such as SiN, Si3N4, SiO2, and ZnS. This dielectric layer 6 coats intervals between recording tracks. Moreover, the entire surfaces of the dielectric layer 6 are coated with the protection coat 4.

[0052] In the present example, the recording tracks RT are formed both of the lands L and the grooves G. As in the above described example, the magnetic layers 3 are configured by three layers made of perpendicular magnetic anisotropy substance. Here, the three magnetic layers, which are formed into film by an anisotropy sputtering method, are not formed into on side walls of the grooves G, but are formed only on the bottom surfaces of the grooves G and the upper surfaces of the lands L. Thereby, the recording tracks RT are separated spaciously as well as magnetically from the adjacent recording tracks.

[0053] In addition, the dielectric layers 6 are formed around the recording tracks RT in order to prevent the magnetic layers 3 configuring the recording tracks RT from undergoing corrosion, and are formed into film by isotropy sputtering method before and after forming of the magnetic layers 3 so that the entire surfaces (both side faces, front surfaces and rear surfaces) of the recording tracks RT are coated. Configuring material of the dielectric layer 6 preferably has thermal conductivity smaller than that for substance configuring the magnetic layers, but in order to prioritize performance to protect the magnetic layers 3 and the optical features, it is not necessarily required to be so small as that of the protection coat 4 or the substrate 2. In its place, bays (thickness given rise to by the dielectric layer 6 covering the recording tracks RT in the both side faces of the recording tracks RT) Wd of the dielectric layer are preferably made sufficiently small compared with the width Wt of the recording tracks RT. Desirable value of this thickness Wd is as described above not more than 0.25 being Wd/Wt. In addition, in order to sufficiently protect the magnetic layers 3, arrangement to give Wd≧10 nm is desirable.

[0054] Next, magneto-optical apparatus to thermo-magnetic record information signals into the magneto-optical medium 1 having been shown in FIGS. 5A and 5B, FIGS. 6A and 6B, or FIGS. 7A and 7B will be described.

[0055] A schematic configuration of the recording apparatus is shown in FIG. 12. Here, a reference numeral 1 denotes a magneto-optical medium (for example, a magneto-optical disk) in which information signals are recorded and which is mounted onto a spindle motor 31 being its driving means. A magnetic head 32 is disposed on the upper surface side of the magneto-optical medium 1, and in addition, an optical head 33 to radiate recording light beams or reproducing light beams into the magneto-optical medium is disposed in the manner of being opposite against the magnetic head 32.

[0056] The magnetic head 32 is configured by a core 40 made of a soft magnetic material and a magnetic field generating coil 41 which is caused to wind the periphery of the core 40. A magnetic head driving circuit 34 is brought into connection with the magnetic field generating coil 41 of the magnetic head 32 and a record signal generating circuit 35 to implement processing, such as coding, on information signals inputted from an input terminal T1 for transmitting into the magnetic head driving circuit 34 and a CPU (Central Processing Unit) 36 controlling the magnetic head driving circuit 34. The magnetic head driving circuit 34 provides the magnetic field generation coil 41 of the magnetic head 32 with electric currents that can switch the direction and intensity corresponding with information signals so that the magnetic head 32 generates magnetic field that can be switched in terms of direction and intensity corresponding with information signals and perpendicularly applies it to the magneto-optical medium 1.

[0057] The optical head 33 is configured by a not shown laser beam source, optical sensor, and optical system, etc. A laser driving circuit 37 is brought into connection with the laser beam source and an amplifying circuit 38 and an information signal reproducing circuit 39 are with the optical sensor so as to configure a reproduction signal processing system.

[0058]
FIGS. 1A and 1B are partially enlarged view of the magneto-optical medium 1, showing a recording method of information signals, and FIG. 1A is a cross-sectional view while FIG. 1B is a plan view looked at from the direction of a lower surface. At the time when information signals are recorded, the optical head 33 implements radiation by concentrating a highly powered recording light beam 7 to recording tracks RT through a substrate 2. At the same time, a spindle motor 31 drives the magneto-optical medium 1, and thereby the recording light beam 7 scans the recording tracks RT toward the direction indicated by an arrow A. Temperature of magnetic layers 3 increases with radiation of the recording light beam 7, and in the periphery of the radiation region of the recording light beam 7 a thermal distribution shown by an isothermal line in the drawing is formed. Here, a reference numeral 8 denotes an isothermal line of a temperature Tc approximately equal to the curie temperature of the memory layer 3c.

[0059] Here, in the trailing direction of the radiation region of the recording light beam 7 in particular, that is, in the region where the recording light beam 7 has already past, conductive proliferation of heat accumulated mainly while the recording light beam 7 radiates will become a main cause to determine temperature distribution. In the present invention, the recording tracks RT is structured to restrain heat release from the both side surfaces thereof, and therefore in the trailing direction of the recording light beam 7, heat quantity being piled up gets larger in the position closer to the both side surfaces rather than in the center of the recording tracks RT. As a result thereof, the trailing portion of the isothermal line 8 will get shaped as shown in FIGS. 1A and 1B approximately linear in the direction perpendicular to the direction of scanning (arrowed by A) of the recording light beam 7 or as an arc which is bent convex forward in the direction of scanning (arrowed by A) of the recording light beam 7.

[0060] On the other hand, in a conventional art, since magnetic layers with weakened magnetism remain in the gaps between the recording tracks, heat supplied by the concentrated light beam is released also from the both side surfaces of the recording tracks RT, and thus the isothermal line 8 will be shaped approximately oval by extending in the trailing direction of the recording light beam 7 (FIG. 8B).

[0061] Thus, the optical head radiates the recording light beam 7 and at the same time, the magnetic head 32 applies onto the radiation region of the recording light beam 7 a perpendicular magnetic field that varies its direction up and down corresponding with information signals. The memory layer 3c loses magnetization when it passes the front portion of the isothermal line 8 resulting in its temperature being not less than the curie temperature Tc and gives rise to magnetization in the same direction as the magnetic field applied at that time when it passes the back portion of the isothermal line 8 resulting in its temperature being not more than Tc. Moreover, as it moves remotely from the back portion of the isothermal line 8, the temperature drops while coercivity increases so that the above described magnetization is fixed. Thus, magnetization regions having magnetization in the upward direction and in the downward direction corresponding with the direction of the applied magnetic field are arranged alternately to be formed on the recording track RT as shown by an arrow in the upward and downward direction in FIG. 1A, and in the boundary portion between the magnetization region and the preceding and following magnetization region, magnetic domain walls W1, W2, W3, W4, W5 and W6 are formed. These magnetic walls, which are formed along the back portion of the isothermal line 8, will be shaped approximately linear in the direction perpendicular to the direction of scanning (arrowed by A) of the recording light beam 7 or as an arc which is bent convex in the same direction as the direction of scanning. In addition, the displacement layer 3a, the switching layer 3b, and the memory layer 3c are mutually brought into exchange coupling so that magnetization and the magnetic domain walls W1, W2, W3, W4, W5 and W6 are transfer-formed onto the displacement layer 3a and the switching layer 3b as well.

[0062] Next, a method to reproduce information signals from the magneto-optical medium 1 in which information signals are recorded with a reproducing apparatus by magnetic domain wall displacement reproducing system will be described. The reproducing apparatus is as shown in FIG. 12. In FIG. 12, the detection signals detected with the optical head is amplified by the amplifying circuit 38 and moreover an information signal reproducing circuit 39 reproduces information signals from the amplified detection signals for outputting from the output terminal T2.

[0063]
FIGS. 2A and 2B are partially enlarged view of the magneto-optical medium 1 showing a reproducing method of information signals by way of magnetic domain wall displacement reproducing system, and FIG. 2A is a cross-sectional view while FIG. 2B is a plan view looked at from the direction of a lower surface. At the time when information signals are reproduced, the optical head 33 implements radiation by concentrating a low powered light beam for reproducing 9 to a recording track RT through a substrate 2. At the same time, the spindle motor 31 drives the magneto-optical medium 1, and thereby the light beam for reproducing 9 scans the recording track RT toward the direction indicated by an arrow A. Temperature of a magnetic layer 3 increases with radiation of the light beam for reproducing 9, and in the periphery of the radiation region of the light beam for reproducing 9 a thermal distribution shown by an isothermal line in the drawing is formed. Here, a reference numeral 10 denotes an isothermal line of a temperature Ts approximately equal to the curie temperature of the switching layer 3b, and a reference character Xp denotes a peak position of temperature. As described later, in the displacement layer 3a of the recording track RT, the magnetic domain wall is movable only in a region of temperature not less than Ts, that is, a region surrounded by the isothermal line 10, and in the other region movement of a magnetic domain wall is impossible.

[0064] Here, in the forefront portion of the radiation region of the reproducing light beam 9, since lapse of time is still short from starting of temperature increase, influence of heat conductive proliferation to temperature distribution is small, and mainly energy distribution of the reproducing light beam 9 will become a main cause to influence the temperature distribution. Accordingly, even if the recording tracks RT are structured so that heat release from their both side surfaces are restrained, the isothermal line 10 will get shaped as shown in the drawing as an arc which is bent convex in the same direction of scanning (arrowed by A) of the reproducing light beam 9. That is, the direction of bending in the forefront portion of the isothermal line 10 is the same as in the conventional art shown by the reference numeral 30 in FIG. 9B. Incidentally, in the example shown in FIG. 2B, in the trailing portion of the radiation region of the reproducing light beam 9, that is, the region which comes after the reproducing light beam has already passed the radiation region, as at the time of recording, mainly conductive proliferation on heat that has been accumulated while the reproducing light beam was being radiated influences temperature distribution, and therefore the isothermal line will get shaped as an arc which is bent convex in the same direction (that is, in the opposite direction of the prior art) as the scanning direction (arrowed by A) of the reproducing beam of the back portion of the isothermal line 10, but this little influences reproducing performance.

[0065] Here, in a position sufficiently remote from the radiation region of the reproducing light beam 9, temperature of the magnetic layer 3 is low and in this position, the displacement layer 3a, the switching layer 3b, and the memory layer 3c have mutually undergone exchange coupling, and magnetization as well as the magnetic domain wall formed in the memory layer 3c have been transfer-formed in the switching layer 3b and the displacement layer 3a as well. In addition, since the temperature distribution is approximately unanimous, a driving power to move the magnetic domain wall transcribed into the displacement layer 3a does not act and therefore the magnetic domain wall remain fixed. However, in the location closer to the radiation region of the reproducing light beam 9, the temperature of the magnetic layer 3 increases, and subject to passing the forefront portion of the isothermal line 10, the temperature of the switching layer 3b reaches not less than Ts to cancel magnetization. Thus, since exchange coupling among the displacement layer 3a, the switching layer 3b, and the memory layer 3c is cut in the region with temperature surrounded by the isothermal line 10 higher than Ts and the displacement layer 3a and the region of the both side surfaces of the recording track RT are not brought into magnetic coupling between, the magnetic domain wall will become movable without being restricted in the displacement layer 3a. Moreover, since the surrounding temperature is inclined, the driving power will act on the magnetic domain wall in the direction of higher temperature, that is, of lower energy. Thus, the magnetic domain wall (W1 in FIG. 2A and 2B) which has past through the forefront portion of the isothermal line 10 moves rapidly toward a position Xp whose temperature reaches the peak as shown in the arrow B in the displacement layer 3a. Incidentally, in the drawing, the magnetic domain wall W1 prior to movement is indicated by a broken line. Accompanied by movements of this magnetic domain wall, a magnetization region Mex having magnetization in one direction (the downward direction in the drawn example) is extended and formed. Incidentally, the memory layer 3c is configured by a material having small degree of displacement of domain wall domain wall mobility, and therefore the magnetic domain wall does not move in the memory layer 3c.

[0066] Thus, the magnetic domain walls W1, W2, . . . and, W6 move toward the position Xp every time when they pass the forefront portion of the isothermal line 10 subsequently, and each time the magnetization region Mex which has magnetization upward and downward and extended is formed alternately. A polarization direction of the reflecting light of the reproduction light beam 9 from this magnetization region Mex is rotated corresponding with direction of magnetization of the magnetization region Mex due to magneto-optics effect (Kerr effect). Rotation of such polarization direction is detected with an optical head. Since this detected signals include changes in signals corresponding with movement of the magnetic domain wall, with the magnetic domain wall as information signal domain being formed at a position corresponding with the information signals to be stored, information signals can be reproduced from timing of changes in signals.

[0067] Here, since the directions of the recording light beam and the direction of the reproduction light beam scanning the recording tracks are normally the same, as shown in FIGS. 1A and 1B and FIGS. 2A and 2B, the shape of formed magnetic domain wall is at least not convex toward the opposite direction of the scanning direction (arrowed by A) of the recording light beam 7, but will be linear, or coincide with the direction of the bending in the forefront portion of the isothermal line 10 formed by the reproducing light beam 9. Thus the entire magnetic domain wall passes the forefront portion of the isothermal line 10 formed by the reproducing light beam 9 approximately at a time, and the driving power acts approximately evenly on the entire portion, variation at the point of time when the magnetic domain wall starts moving. As a result thereof, jitter of detected signals decreases, making more exact reproduction of information signals possible.

[0068] In addition, even in the case where forming interval of the magnetic domain wall has been made short, before the entire magnetic domain wall has not yet past the forefront portion of the isothermal line 10, a portion of the subsequent magnetic wall will never passes the forefront portion of the isothermal line 10. As a result thereof, detection resolution capability will be improved.

[0069] (Practical Embodiment 1)

[0070] Magneto-optical medium with the most simple configuration corresponding with FIG. 5A and 5B was produced.

[0071] As a substrate for magneto-optical medium, a disk made of polycarbonate with thickness of 1.2 mm was used. Incidentally, thermal conductivity K2 of the substrate material is 0.2 J·m−1·s−1·K−1.

[0072] At first, by injection forming method, lands L and grooves G are formed in this disk. Width of the lands L (excluding the inclined face portions) is 0.6 μm, and width of the grooves G (excluding the inclined face portions) is 0.6 μm. In addition, depth of the grooves G is 0.18 μm. Moreover, the side wall inclined portion of the groove G has width of 0.11 μm when it is looked at from above the disk.

[0073] Next, in the doughnut-shaped region in which the land L and the groove G are formed in this disk a magnetic layer 3 is formed. The magnetic layer 3 comprises a displacement layer 3a having perpendicular magnetic anisotropy, a switching layer 3b, and a memory layer 3c, is never released to the atmosphere, and is formed into film by sputtering filming of continuous anisotropy. There magnetic layers are not formed on the side walls of the grooves G, but formed only on the upper surface of the lands L and the bottom surfaces of the grooves G, and form recording tracks RT respectively.

[0074] Composition of the displacement layer 3a is GdFeCo, and film thickness is 30 nm. Composition of the switching layer 3b is TbFe, and film thickness is 10 nm. Composition of the memory layer 3c is TbFeCo, and film thickness is 80 nm.

[0075] The thermal conductivity K1 as this entire magnetic layer 3 subject to assessment by another experiment is 12 J·m−1·s−1·K−1 and fulfils K2/K1<0.05.

[0076] Lastly, a protection coat 4 for protecting the magnetic layer against mechanical impact as well as corrosion is filmed to coat at least side surfaces of the recording tracks. As the protection coat, an ultraviolet hardened resin of acrylic system is used. Its thermal conductivity K2 is approximately equal to that of the substrate and is 0.2 J·m−1·s−1·K−1.

[0077] When reproduction characteristic test of this magneto-optical medium was implemented, jitter decreased by approximately 15 percent from a comparative example to be described later, enabling memory density to be improved in exchange.

[0078] (Practical Embodiment 2)

[0079] The present practical embodiment is to correspond with FIGS. 6A and 6B. As shown in FIGS. 6A and 6B, a magneto-optical medium substrate 2 of the present practical embodiment is featured by its front surface being flat.

[0080] Next, a magnetic film 3 as in the practical embodiment 1 was formed into doughnut-shaped film by isotropy sputtering onto the sites where recording tracks of this substrate are formed.

[0081] Subsequently, the magnetic films 3 between the recording tracks RT were removed by means of photolithography method and dry etching, and the recording tracks RT were produced into belts At this time, width Wt of the recording track is 0.6 μm, and width of the gap between the recording tracks is 0.25 μm.

[0082] Lastly, as in the present practical embodiment 1, a protection coat 4 was applied to the front surface of the magneto-optical medium to obtain the magnetooptical medium of the present invention.

[0083] When reproduction characteristic test of this magneto-optical medium was implemented, jitter improvement effect equivalent to that in the practical embodiment 1 could be confirmed.

[0084] (Practical Embodiment 3)

[0085] The present practical embodiment is to correspond with FIGS. 7A and 7B.

[0086] As a substrate 2 of a magneto-optical medium, the same one as in the practical embodiment 1 was used, and by injection forming method, lands L and grooves G were formed.

[0087] At this time, width of the lands L (excluding the inclined face portions) is 0.6 μm, and width of the grooves G (excluding the inclined face portions) is 0.6 μm. In addition, depth of the grooves G is 0.18 μm. Moreover, the side wall inclined portion of the groove G has width of 0.11 μm when it is looked at from above the disk.

[0088] Subsequently, a dielectric layer of SiN was formed into film with thickness of 80 nm all over the substrate 2 inclusive of the side walls of the grooves by isotropy sputtering method.

[0089] Subsequently, the magnetic layers 3 were formed into film with the configuration similar to that in the practical embodiment 1 onto the upper surface of the lands L and the bottom surfaces of the grooves G by anisotropy sputtering method.

[0090] Subsequently, also all over the entire predetermined region in which gaps between the recording tracks and the recording tracks are formed, an AlTi film 5 to become thermal conductive film on the recording tracks in the later steps was formed into film with thickness of 40 nm by anisotropy sputtering method. Incidentally, the thermal conductivity of the thermal conductive film is 80 J·m−1·s−1·K−1 and is 6.7 times of the magnetic film. Lastly, a dielectric film of SiN with thickness of 40 nm was formed all over the substrate again by isotropy sputtering method so that the upper surfaces and side surfaces of the recording tracks RT configured by the magnetic layers 3 were all protected. Incidentally, thermal conductivity K3 of the dielectric layer is 1.5 J·m−1·s−1·K−1 and a value smaller than that of the magnetic layer.

[0091] Lastly as in the practical embodiment 1, a protection coat 4 was applied to obtain a magneto-optical medium of the present practical embodiment.

[0092] The magneto-optical medium of the present practical embodiment has recording track width Wt of 0.6 μm, and the bay Wd of the dielectric layer of 0.08 μm, fulfilling the condition of Wd/Wt<0.25.

[0093] When reproduction characteristic test of this magneto-optical medium was implemented, compared with a comparative example to be described later, it was confirmed that jitter decreased by approximately 17 percent, enabling memory density to be improved in exchange. Moreover, the magneto-optical medium was left under an environment of temperature 50° C. and moisture of 80 percent for 1000-hour, giving rise to no change in this feature, and was confirmed to have sufficient endurance.

COMPARATIVE EXAMPLE 1

[0094] A magneto-optical medium of a conventional method shown in FIGS. 10A and 10B was produced.

[0095] As a substrate of a magneto-optical medium, the same one as in the practical embodiment 1 was used At first, by injection forming method, lands L and grooves G were formed in this disk. Width of the lands L (excluding the inclined face portions) is 0.6 μm, and width of the grooves G (excluding the inclined face portions) is 0.2 μm. In addition, a balance between the heights of the lands L and of the grooves G is 0.08 μm. Moreover, the side portion between a land L and a groove G has width of 0.15 μm when it is looked at from above the disk.

[0096] Next as in the practical embodiment 1, in the doughnut-shaped region in which the land L and the groove G are formed in this disk a magnetic layer 3 is formed.

[0097] After film-formation of the magnetic layer 3 was over, along the grooves G, a light beam for thermal processing having energy higher than intensity of the rewritable reproducing concentrated light beam was brought into scanning. Since this will change composition and structure of the magnetic layer 3 in the grooves G, magnetism of the magnetic layer 3 in the grooves G decreases to enable the recording tracks to be magnetically separated.

[0098] Lastly, a protection coat 4 as that in the practical embodiment 1 was filmed so as to coat side surfaces of the recording tracks.

[0099] (Practical Embodiment 4)

[0100] The above described practical embodiment was described by taking as an example the case where with thermal magnetic recording method being the present invention, the magneto-optical medium in which information signals have been recorded is reproduced by the magnetic domain wall mobile reproduction system, but application of the present invention will not be limited hereto. As follows, an example of a case where with thermal magnetic recording method being the present invention, the magneto-optical medium in which information signals have been recorded is reproduced by a super resolution reproduction system will be described. Incidentally, details on the perpendicular magnetic anisotropy substance configuring the magnetic layer 3 and the reproducing principle, which are described for example in Japanese Patent Application Laid-Open No. 7-334877 which is an application of the present applicant, will be limited to schematic description here, and the description will be focused onto an effect obtainable by combination of the thermal magnetic recording system being the present invention.

[0101] Also in the present practical embodiment, the configuration of the magneto-optical medium 1 being a magnetic memory medium is the same as in FIGS. 5A and 5B, a magneto-optical medium 1 is configured by a substrate 2 made of a transparent resin material such as polycarbonate, etc. in which belt shaped grooves G and lands L with approximately same width are formed alternately in parallel, magnetic layers 3 that are formed on the substrate 2 and are made of perpendicular magnetic anisotropy substance and a protection coat 4 made of ultraviolet hardened resin. The magnetic layers 3 formed on the bottom surface of the grooves G and the magnetic layers 3 formed on the lands L both configure belt-shaped recording tracks RT in which information signals are recorded. The magnetic layers 3 are not formed on the side walls of the grooves G.

[0102] In addition, as having been shown in FIG. 6A, a magneto-optical medium 1 is configured by a substrate 2 made of a transparent resin material such as polycarbonate, etc., magnetic layers 3 that are formed on the substrate 2 and are made of perpendicular magnetic anisotropy substance and a protection coat 4 made of ultraviolet hardened resin. The magnetic layers 3 are belt-shaped in parallel, and respectively configure recording tracks RT in which information signals are recorded. The adjacent recording track RT is formed at an interval.

[0103] Or as having been shown in FIG. 7A, a magnetooptical medium 1 is configured by a substrate 2 made of a transparent resin material such as polycarbonate, etc. in which belt shaped grooves G and lands L with approximately same width are formed alternately in parallel, magnetic layers 3 that are formed on the substrate 2 and are made of perpendicular magnetic anisotropy substance, thermal conductive layers 5 which are formed on the magnetic layer 3 and are made of Al, Au and Ag or an alloy containing them, etc., dielectric layers 6 made of non-polarized inorganic materials such as SiN, Si3N4, SiO2, and ZnS, etc., and a protection coat 4 made of ultraviolet hardened resin. The magnetic layers 3 formed on the bottom surface of the grooves G and the magnetic layers 3 formed on the lands L both configure belt-shaped recording tracks RT in which information signals are recorded. The magnetic layers 3 are not formed on the side walls of the grooves G. In addition, the thermal conductive layers 5 are formed only on the magnetic layers 3 configuring the recording tracks RT, and at least are not formed on the both side surfaces of the recording tracks RT. The dielectric layers 6 are formed in the periphery of the recording tracks RT and the both side surfaces of the recording tracks RT are covered by tightly contacted dielectric layers 6.

[0104] Thus, also in the present practical embodiment, as in the first practical embodiment, the recording tracks RT and both of their adjacent recording tracks RT are not connected with the magnetic layers 3. Due to this, the recording tracks RT are not brought into magnetic connection with the regions of their both side surfaces.

[0105] In addition, a member having its thermal conductivity not less than the thermal conductivity of substance configuring the magnetic layer 3 is not brought into connection with the both side surfaces of the recording tracks RT, and the both side surfaces of the recording tracks RT are configured by a material having its thermal conductivity less than the thermal conductivity of substance configuring the magnetic layer 3. Thus, the recording tracks RT are configured to restrain heat release from the both side surfaces of the recording tracks RT rather than from their extended direction.

[0106] Incidentally, in the present practical embodiment, the magnetic layer 3 is to be configured by laminating three layers made of perpendicular magnetic anisotropy substance, rare earth such as, for example, Tb, Gd and Dy, and transition metal such as Fe and Co, etc., that is, a reproducing layer 3d, an intermediate layer 3e, and a memory layer 3f. Here, the reproducing layers 3d as well as the intermediate layers 3e are inter-surface magnetic films under room temperature, and will be perpendicular magnetic anisotropy film under high temperature. In addition, the curie temperature of the intermediate layers 3e is higher than room temperature and lower than the other two layers. In addition, the memory layers 3f are perpendicular magnetic anisotropy films.

[0107] Next, the method to record information signals into the magneto-optical medium 1 shown in FIGS. 5A and 5B, FIGS. 6A and 6B and FIGS. 7A and 7B with a recording apparatus will be described. The recording apparatus comprises driving means for an optical head, a magnetic head and magneto-optical medium 1. FIGS. 3A and 3B are partially enlarged views of the magnetooptical medium 1, showing a recording method of information signals, and FIG. 3A is a cross-sectional view while FIG. 3B is a plan view looked at from the direction of a lower surface. At the time when information signals are recorded, the optical head implements radiation by concentrating a highly powered recording light beam 7 for being heating means to a recording track RT through a substrate 2. At the same time, the driving means drives the magneto-optical medium 1, and thereby the recording light beam 7 scans the recording track RT toward the direction indicated by an arrow A. Temperature of a magnetic layer 3 increases with radiation of the recording light beam 7, and in the periphery of the radiation region of the recording light beam 7 a thermal distribution shown by an isothermal line in the drawing is formed. Here, a reference numeral 8 denotes an isothermal line of a temperature Tc approximately equal to the curie temperature of the memory layer 3c.

[0108] Here, in the trailing direction of the radiation region of the recording light beam 7 in particular, that is, in the region where the recording light beam 7 has already passed the radiation region, conductive proliferation of heat accumulated while the recording light beam 7 passes the radiation region mainly influences temperature distribution. In the present invention, the recording tracks RT is structured to restrain heat release from the both side surfaces thereof, and therefore in the trailing direction of the recording light beam 7, heat quantity being piled up gets larger in the position closer to the both peripheries rather than in the center of the recording tracks RT. As a result thereof, the trailing portion of the isothermal line 8 will get shaped as shown in FIG. 3B as an arc which is bent convex in the same direction as the direction of scanning (arrowed by A) of the recording light beam 7. On the other hand, in a conventional art, since heat is conducted and proliferates also to the both side surfaces of the recording tracks RT, as show in FIG. 8B, the isothermal line 8 will be shaped approximately oval by extending in the trailing direction of the recording light beam 7. That is, in the present invention, the direction of bending of the isothermal line formed in the trailing direction of the radiation region of the recording light beam will be opposite against the prior art.

[0109] Thus, radiation of the recording light beam 7 by way of an optical head concurs with the magnetic head's application of a perpendicular magnetic field the direction of which varies upward and downward to the radiation region of the recording light beam 7 corresponding to information signals. The memory layer 3f loses magnetization when it passes the front portion of the isothermal line 8 resulting in its temperature being not less than the curie temperature Tc and gives rise to magnetization in the same direction as the magnetic field applied at that time when it passes the back portion of the isothermal line 8 resulting in its temperature being not more than Tc. Moreover, as it moves remotely from the back portion of the isothermal line 8, the temperature drops while coercivity increases so that the above described magnetization is fixed. Thus, magnetization regions having magnetization in the upward direction and in the downward direction corresponding to the direction of the applied magnetic field are arranged alternately to be formed on the recording track RT as shown by an arrow in the upward and downward direction in FIG. 1A, and in the boundary portion between the magnetization region and the preceding and following magnetization region, magnetic domain walls W1, W2, W3, W4, W5 and W6 as marks of information signal are formed. These magnetic domain walls, which are formed along the back portion of the isothermal line 8, will be shaped as an arc which bends convexly in the same direction as the scanning direction (an arrow A) of the recording light beam. In addition, in the temperature around the room temperature, the reproducing layer 3d, the intermediate layer 3e, and the memory layer 3f are not brought into exchange coupling each other, and since the memory layer 3f only is the perpendicular magnetic anisotropy film, the formed magnetic domain walls W1, W2, W3, W4, W5 and W6 are held only in the memory layer 3f.

[0110] Next, a method to reproduce information signals from the magneto-optical medium 1 in which information signals are recorded with a reproducing apparatus by super resolution reproducing system will be described. The reproducing apparatus comprises driving means for an optical head, and magneto-optical medium 1. FIGS. 4A and 4B are partially enlarged view of the magnetooptical medium 1, showing a reproducing method of information signals according to the super resolution reproducing system, and FIG. 4A is a cross-sectional view while FIG. 4B is a plan view looked at from the direction of a lower surface. At the time when information signals are reproduced, the optical head implements radiation by concentrating a low powered reproducing light beam 9 to a recording track RT through a substrate 2. At the same time, the driving means drives the magneto-optical medium 1, and thereby the reproducing light beam 9 scans the recording track RT toward the direction indicated by an arrow A. Temperature of a magnetic layer 3 increases by the radiation of the reproducing light beam 9, and in the periphery of the radiation region of the reproducing light beam 9 a thermal distribution shown by an isothermal line in the drawing is formed. Here, a reference numeral 11 denotes an isothermal line of the temperature Tex when the intermediate layers 3e as well as the reproducing layers 3d are transformed from inter-surface magnetic films to perpendicular magnetic anisotropy films, and a reference numeral 12 denotes an isothermal line of the temperature Tci approximately equal to the curie temperature of the intermediate layer 3e. With the temperature being not more than Tex, the intermediate layer 3e as well as the reproducing layer 3d are both inter-surface magnetic films, and are not brought into exchange coupling with the memory layer 3f. Within the temperature range where the temperature is higher than Tex and lower than Tci, the intermediate layer 3e as well as the reproducing layer 3d will become perpendicular magnetic anisotropy films, and are mutually brought into exchange coupling with the memory layer 3f. Moreover, since the intermediate layer 3e loses magnetization with the temperature not less than Tci, the reproducing layer 3d is not brought into exchange coupling. That is, only in the region (aperture Ap) between the isothermal line 11 corresponding to the temperature Tex and the isothermal line 12 corresponding to the temperature Tci, the reproducing layer 3d, the intermediate layer 3e, and the memory layer 3f are brought into exchange coupling, and magnetization as well as the magnetic domain wall of the memory layer 3f are transcribed onto the reproducing layer 3d.

[0111] Here, in the forefront portion of the radiation region of the reproducing light beam 9, since lapse of time is still short from starting of temperature increase, influence of heat conductive proliferation to temperature distribution is small, and mainly energy distribution of the reproducing light beam 9 will influence the temperature distribution. Accordingly, even if the recording tracks RT are structured so that heat release from their both side surfaces are restrained, the isothermal lines 11 and 12 will get shaped as shown in FIG. 4B as an arc which is bent convex in the same direction of scanning (arrowed by A) of the reproducing light beam 9. That is, the direction of bending in the forefront portions of the isothermal line 11 and 12 is the same as in the prior art shown by the reference numeral 30 in FIG. 9B. Incidentally, in the example shown in FIGS. 4A and 4B, in the trailing portion of the radiation region of the reproducing light beam 9, that is, the region which comes after the reproducing light beam has already passed the radiation region, as at the time of recording, mainly conductive proliferation on heat that has been accumulated mainly while the reproducing light beam was passing the region of the radiation of the reproducing light beam influences temperature distribution, and therefore the back portions of the isothermal lines 11 and 12 will get shaped as an arc which is bent convex in the same direction (that is, in the opposite direction of the prior art) as the scanning direction (arrowed by A) of the reproducing light beam, but this little influences reproducing performance.

[0112] Here, in a position sufficiently remote from the radiation region of the reproducing light beam 9, temperature of the magnetic layer 3 is low and in this position, the reproducing layer 3d, the intermediate layer 3e, and the memory layer 3f are not brought into exchange coupling each other, and therefore the magnetic domain wall formed in the memory layer 3f does not undergo h-transcription into the reproducing layer 3d. However, in the location closer to the radiation region of the reproducing light beam 9, the temperature of the magnetic layer 3 increases, and subject to passing the forefront portion of the isothermal line 11 to enter the interior of the aperture Ap, the reproducing layer 3d, the intermediate layer 3e, and the memory layer 3f are mutually brought into exchange coupling, and thus the magnetic domain wall of the memory layer 3f (W1 in FIGS. 4A and 4B) together with the subsequent magnetization region Md is transcribed into the reproducing layer 3d. Moreover, passing through the forefront portion of the isothermal line 12 to get out of the aperture Ap, the intermediate layer 3e loses magnetization so that the exchange coupling among the reproducing layer 3d, the intermediate layer 3e, and the memory layer 3f are cut out, and therefore magnetization as well as magnetic domain wall formed in the memory layer 3f are not transcribed into 3d.

[0113] Thus, every time the magnetic domain walls W1, W2, W3, W4, W5 and W6 formed in the memory layer 3f pass through the isothermal line 11 to enter the interior of the aperture Ap sequentially, the magnetic domain wall and the subsequent magnetization region Md having magnetization upward and downward are alternately transcribed onto the reproducing layer 3d. A polarization direction of the reflecting light of the reproducing light beam from the magnetization region Md rotates corresponding to direction of magnetization of the magnetization region Md due to magneto-optics effect (Kerr effect). Rotation of such polarization direction is detected with an optical head. With the magnetic domain wall as information signal domain being formed at a position corresponding to the information signals to be stored, information signals can be reproduced from timing of changes in signals.

[0114] Here, since the direction in which the recording light beam 7 as well as the reproducing light beam scan the recording tracks RT are normally the same, as shown in FIG. 3B and FIG. 4B, the formed magnetic domain wall is shaped as an arc which is bending convex in the same direction as the scanning direction (arrowed by A) of the recording light beam 7, and in the same direction as the bending direction of the forefront portion of the isothermal lines 11 as well as 12 formed by the reproducing light beam 9. Thus, the magnetic domain wall in its entirety enters the interior of the aperture Ap formed by the reproducing light beam 9 approximately at the same time to be transcribed together with the subsequent magnetization region Md into the reproducing layer 3d. Accordingly, changes in detection signals corresponding therewith are steep compared with the case where the magnetic domain wall is directed oppositely from the bending of the isothermal line, and as a result thereof jitter of the detection signals decreases and more exact reproduction of the information signals can be feasible. In addition, even in the case where forming interval of the magnetic domain walls is made short, unless a magnetic domain wall has entered the aperture Ap completely, no portion of the subsequent magnetic domain wall will enter the aperture Ap. As a result thereof, detection resolution capability is improved.

Information recording method, apparatus and information reproducing method and apparatus for domain wall mobile type magneto-optical medium

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CPC

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