JP2012221517A - Playback device and playback method of optical magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a playback device and the like for an optical magnetic recording medium capable of achieving higher recording density by controlling a temperature distribution in a laser spot to obtain a satisfactory playback signal.SOLUTION: In the playback device for an optical magnetic recording medium, a first magnetic layer on which a laser beam is made incident, a second magnetic layer on which information is recorded, a third magnetic layer whose Curie temperature is lower than those of the first magnetic layer and the second magnetic layer, and a fourth magnetic layer formed in a concave part of the third magnetic layer to have a magnetic anisotropy in an in-plane direction are formed on a substrate in which a convex part corresponding to a recording track and a concave part on both sides of the convex part are formed, and information recorded on the second magnetic layer is transferred to the first magnetic layer through the third magnetic layer. When a laser beam of a wavelength of 405 nm±5 nm conforming to a Blu-ray standard is applied from above the first magnetic layer, the laser beam satisfies a condition being Rrim>1 like (a) where a rim strength Rrim of the laser beam is defined as the rim strength in a track direction of an optical magnetic recording medium/the rim strength in a radial direction of the optical magnetic recording medium.

Description

  The present invention relates to a magneto-optical recording medium reproducing apparatus and reproducing method for reproducing information recorded on a magneto-optical recording medium by irradiating light.

  In a magneto-optical recording medium using a magnetic film, it is necessary to shorten the recording mark, that is, to reduce the information magnetic domain in order to improve the information recording density. However, the signal reproduction resolution is almost determined by the wavelength λ of the laser beam of the reproduction optical system and the numerical aperture NA of the objective lens, and the spatial frequency 2NA / λ is the reproduction limit.

  On the other hand, a technique described in Patent Document 1 below is known as a technique for further improving the recording density. In Patent Document 1, a first magnetic layer, a second magnetic layer, and a third magnetic layer are sequentially stacked, and the first magnetic layer is relatively magnetic domain resistant compared to the third magnetic layer. A magneto-optical recording medium is described in which the magnetic force is small and the domain wall mobility is large, and the second magnetic layer has a lower Curie temperature than the first magnetic layer and the third magnetic layer. In Patent Document 1, laser light is irradiated from the first magnetic layer side while moving relative to the magneto-optical recording medium, and the light beam spot moves on the medium with respect to the moving direction of the spot of the light beam. A magnetic distribution formed in the first magnetic layer is moved by forming a temperature distribution having a gradient and setting the temperature distribution to a temperature distribution having a temperature region higher than the Curie temperature of the second magnetic layer. In addition, it is described that the recorded information is reproduced by detecting the change in the polarization plane of the reflected light of the light beam.

  As other techniques for improving the recording density, those described in Patent Documents 2 and 3 below are known.

  Patent Document 2 describes a magneto-optical recording medium in which at least three or more magnetic layers for enlarging and reading a magnetic domain by domain wall movement are stacked on a substrate on which lands and grooves are formed. This magneto-optical recording medium has in-plane magnetic anisotropy only on both sides of the recording track between the first magnetic layer on which the laser beam is incident and the second magnetic layer positioned below the first magnetic layer. An in-plane magnetic anisotropic layer is formed.

  Patent Document 3 describes that the rim intensity Rim of the laser beam spot BLS is adjusted when reproducing information recorded on the magneto-optical recording medium.

Japanese Patent Application Laid-Open No. 6-290496 JP 2007-102829 A JP 2006-18943 A

  The techniques described in Patent Documents 1 to 3 described above make it possible to reproduce information recorded in a short width by moving a domain wall using a temperature distribution in a laser spot, that is, a temperature gradient. For this reason, if the wavelength of the laser beam is shortened to improve the recording density in the track direction and the laser spot size is reduced, the temperature gradient in the laser spot changes, so the medium structure of Patent Document 2 is optimal for domain wall motion reproduction. It becomes difficult to produce an exchange coupling membrane.

  In addition, the magneto-optical recording medium described in Patent Document 2 performs domain wall motion (magnetic domain expansion) reproduction not only in the track direction but also in the radial direction perpendicular to the track direction. In order to obtain it, it is important to control the temperature distribution in the laser spot.

  Accordingly, the present invention has been proposed in view of the above-described circumstances, and magneto-optical recording that can achieve a higher recording density by obtaining a good reproduction signal by controlling the temperature distribution in the laser spot. An object of the present invention is to provide a medium reproducing apparatus and method.

  A reproducing apparatus for a magneto-optical recording medium according to a first aspect of the present invention for solving the above problems includes a convex portion (101a) corresponding to a recording track on which information is recorded and concave portions (101b) on both sides of the convex portion (101a). A first magnetic layer (104) having magnetic anisotropy in at least a perpendicular direction where laser light is incident and a magnetic anisotropy in a perpendicular direction on which information is recorded on a substrate (101) formed with A second magnetic layer (108), a third magnetic layer (106, 107) having a Curie temperature lower than that of the first magnetic layer (104) and the second magnetic layer (108), and the third magnetic layer (106). , 107) and a fourth magnetic layer (105) having magnetic anisotropy in the in-plane direction. The third magnetic layer (106, 107) is formed on the first magnetic layer (104). Recorded in the second magnetic layer (108) A reproducing apparatus for a magneto-optical recording medium (100) to which information is transferred, having a light irradiation unit (40) for irradiating a laser beam having a wavelength of 405 nm ± 5 nm conforming to the Blu-ray standard from the first magnetic layer. When the rim intensity Rrim of the laser beam is defined as the rim intensity in the track direction of the magneto-optical recording medium (100) / the rim intensity in the radial direction of the magneto-optical recording medium (100), The laser beam irradiated from (40) satisfies the condition of Rrim> 1.

  The reproducing method of the magneto-optical recording medium according to the first invention for solving the above-mentioned problems is a convex portion (101a) corresponding to a recording track on which information is recorded, and a concave portion (101b) on both sides of the convex portion (101a). A first magnetic layer (104) having magnetic anisotropy in at least a perpendicular direction where laser light is incident and a magnetic anisotropy in a perpendicular direction on which information is recorded on a substrate (101) formed with A second magnetic layer (108), a third magnetic layer (106, 107) having a Curie temperature lower than that of the first magnetic layer (104) and the second magnetic layer (108), and the third magnetic layer (106). , 107) and a fourth magnetic layer (105) having magnetic anisotropy in the in-plane direction. The third magnetic layer (106, 107) is formed on the first magnetic layer (104). Recorded in the second magnetic layer (108) A reproducing apparatus for a magneto-optical recording medium (100) to which information is transferred, and the rim intensity of the laser beam when irradiated with a laser beam having a wavelength of 405 nm ± 5 nm conforming to the Blu-ray standard from the first magnetic layer When Rrim is defined as the rim intensity in the track direction of the magneto-optical recording medium (100) / the rim intensity in the radial direction of the magneto-optical recording medium (100), the laser beam to be irradiated satisfies the condition that Rrim> 1. It is characterized by satisfying.

  According to the present invention, when the rim intensity Rrim of the laser beam is defined as the rim intensity in the track direction of the magneto-optical recording medium / the rim intensity in the radial direction of the magneto-optical recording medium, the irradiated laser beam has Rrim> 1. As a result, the steep temperature distribution (temperature gradient) in the track direction within the narrowed laser spot can be moderated by adjusting the rim intensity of the laser spot and recorded at a higher density. The recorded information can be reproduced with a good reproduction signal, and the recording density can be further increased.

1 is a cross-sectional view showing a configuration of a magneto-optical recording medium reproduced by a magneto-optical recording medium recording / reproducing apparatus shown as an embodiment of the present invention. 1 is a perspective view showing a reproduction state of a magneto-optical recording medium reproduced by a magneto-optical recording medium recording / reproducing apparatus shown as an embodiment of the present invention. FIG. 1 is a block diagram showing a configuration of a magneto-optical recording medium recording / reproducing apparatus shown as an embodiment of the present invention. FIG. (A) is the magnetization state of the magneto-optical recording medium reproduced by the magneto-optical recording medium recording / reproducing apparatus shown as an embodiment of the present invention, (b) the temperature distribution of the magneto-optical recording medium, and (c) is the domain wall motion. It is the figure which showed the force to raise. It is the figure typically shown in order to demonstrate the front process in the moving direction front side of a laser beam spot. (A) is the magnetization state of the magneto-optical recording medium reproduced by the magneto-optical recording medium recording / reproducing apparatus shown as an embodiment of the present invention, (b) the temperature distribution of the magneto-optical recording medium, and (c) is the domain wall motion. It is the other figure which showed the force to raise. It is the figure typically shown in order to demonstrate the rear process in the moving direction front side of a laser beam spot. It is a figure which shows the temperature distribution of the magneto-optical recording medium of an Example, and the temperature distribution of the magneto-optical recording medium of a comparative example. (A) is the temperature distribution of the magneto-optical recording medium where Rrim> 1, (b) is the temperature distribution of the magneto-optical recording medium where Rrim = 1, and (c) is the temperature distribution of the magneto-optical recording medium where Rrim <1. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  The magneto-optical recording medium reproducing apparatus shown as an embodiment of the present invention reproduces information recorded on the magneto-optical recording medium 100 shown in FIGS. 1 and 2, for example.

  First, an outline of the magneto-optical recording medium 100 will be described. The magneto-optical recording medium 100 includes a cover layer 102, a first dielectric layer 103, a first magnetic layer 104, a second magnetic layer 105, a third magnetic layer 106, a fourth magnetic layer 107, a fifth layer on a substrate 101. A magnetic layer 108 and a second dielectric layer 109 are stacked.

  The substrate 101 is made of a glass board or polycarbonate. The substrate 101 has a convex portion 101a corresponding to a recording track on which substrate information is recorded, and concave guide grooves 101b on both sides of the convex portion 101a.

  The substrate 101 is formed in a disk shape with a thickness of 1.1 mm, an outer diameter of 120 mm, and a center hole diameter of 15 mm, for example. Further, the convex portion 101a corresponds to the recording track, protrudes with a slight height toward the incident side of the laser beam spot, and is formed in a spiral shape or a concentric shape with a predetermined track pitch P. Further, the guide grooves 101b are formed on both sides of the convex portion 101a, whereby the convex portions 101a and the guide grooves 101b are alternately formed on the substrate 101 in the radial direction.

  The pitch (track pitch) of the guide grooves 101b is set to about half (about 160 nm) with respect to 320 nm which is the track pitch of a so-called Blu-ray Disc. In addition, the track width W (see FIG. 2) of the recording track is set to about 50 nm to narrow the track. A second dielectric layer 109 serving as a protective film is formed on the substrate 101.

  On the second dielectric layer 109, a fifth magnetic layer 108, a fourth magnetic layer 107, and a third magnetic layer 106 are sequentially formed. The fifth magnetic layer 108, the fourth magnetic layer 107, and the third magnetic layer 106 are sequentially stacked in a vacuum by, for example, continuous sputtering, and formed as a three-layer magnetic film. Further, the second magnetic layer 105 is formed on the third magnetic layer 106 only on the guide groove 101b. The second magnetic layer 105 is formed by once forming a vacuum film on the entire surface and then removing only the magnetic film on the convex portion 101a by ion rimming in a vacuum. This ion trimming process can be performed continuously with the film forming process of the magnetic film, and only the magnetic film formed on the convex portion 101a can be removed without providing a mask by photolithography or the like. is there.

  A first magnetic layer 104 is formed on the third magnetic layer 106 and the second magnetic layer 105. The first magnetic layer 104 is formed in a vacuum, and a first dielectric layer 103 serving as a protective layer and an optical interference layer is formed on the first magnetic layer 104 in a vacuum. A cover layer 102 having a thickness of about 0.1 mm and having light transmittance is formed thereon. The film thicknesses of the first dielectric layer 103 and the second dielectric layer 109 are preferably about 20 to 60 nm.

  Next, each layer of the above-described magneto-optical recording medium 100 will be described.

  The second dielectric layer 109 is formed using a transparent dielectric material such as AlN having a high thermal conductivity of about 14.4 W / mK, for example. At this time, the second dielectric layer 109 is alternately formed in a convex shape and a concave shape following the convex portions 101 a and the concave guide grooves 101 b formed alternately on the substrate 101.

  The fifth magnetic layer 108 formed on the second dielectric layer 109 has a recording mark corresponding to an information signal in a vertical direction by an external magnetic field from a magnetic head (not shown) while irradiating a blue laser beam spot during recording. After recording in the form of magnetic domains (magnetization reversal regions) on the film surface having the easy axis of magnetization, it has a sufficient coercive force to stably maintain the magnetic domains recorded at room temperature. Further, the fifth magnetic layer 108 needs to be a film having a Curie temperature Tc suitable for recording an information signal. The fifth magnetic layer 108 functions as a recording layer (memory layer) for recording information.

  The fifth magnetic layer 108 is formed as a film having an easy magnetization direction in the vertical direction (direction perpendicular to the film surface), that is, an amorphous thin film made of heavy rare earth-iron group metal to be a so-called perpendicular magnetization film. For the fifth magnetic layer 108, for example, a material based on a Tb—Fe—Co film or a Dy—Fe—Co film is used. Further, the fifth magnetic layer 108 has a Curie temperature Tc adjusted by adding a nonmagnetic element such as Al or Cr or Co. The fifth magnetic layer 108 is also alternately formed in a convex shape and a concave shape following the convex portions 101a and the guide grooves 101b that are alternately formed on the substrate 101 with the second dielectric layer 109 interposed therebetween.

  At least the fourth magnetic layer 107 of the fourth magnetic layer 107 and the third magnetic layer 106 controls the exchange coupling force when the magnetic domain (record mark) is transferred from the fifth magnetic layer 108 to the first magnetic layer 104. It functions as an exchange coupling force control layer. The fourth magnetic layer 107 and the third magnetic layer 106 are so-called perpendicular magnetization films having an easy magnetization direction in the vertical direction (direction perpendicular to the film surface). The fourth magnetic layer 107 and the third magnetic layer 106 are formed as an amorphous thin film made of heavy rare earth-iron group metal, and rare earth metal dominates using a material based on a Tb-Fe film or a Dy-Fe film. (RE-rich). The fourth magnetic layer 107 and the third magnetic layer 106 are each adjusted to have a Curie temperature by adding a nonmagnetic element such as Al or Cr or Co. Of the fourth magnetic layer 107 and the third magnetic layer 106, the third magnetic layer 106 is formed into a very thin film. Thereby, the third magnetic layer 106 has a function of improving the domain wall moving performance from the front in the moving direction of the blue laser beam spot in the temperature region (about 430 K to about 490 K) where the domain wall can move. Thereby, it is possible to omit application of a reproducing magnetic field at the time of reproducing described later. The fourth magnetic layer 107 and the third magnetic layer 106 have a convex shape following the convex portions 101a and the guide grooves 101b alternately formed on the substrate 101 via the second dielectric layer 109 and the fifth magnetic layer 108. The films are alternately formed in a concave shape.

  The second magnetic layer 105 is the same as the magnetic layer formed by being magnetized in the longitudinal direction of a known magnetic tape. The second magnetic layer 105 is made of Fe, Co alone, an alloy of rare earth metal and Fe, or an alloy of rare earth metal and Co in a thin film.

  The first magnetic layer 104 is located on the incident side of the blue laser beam spot, and has a small magnetic anisotropy in order to facilitate the movement of the domain wall due to the temperature gradient characteristic created by the irradiation of the blue laser beam spot. And function as a domain wall motion layer.

  The first magnetic layer 104 is a so-called perpendicular magnetization film having a magnetization easy direction in the vertical direction (direction perpendicular to the film surface). The first magnetic layer 104 is formed as an amorphous thin film made of heavy rare earth-iron group metal, and a material based on a Gd—Fe film or a Gd—Fe—Co film is used. The first magnetic layer 104 has a Curie temperature adjusted by adding a nonmagnetic element such as Al or Cr, or Co.

  The first dielectric layer 103 has a thermal conductivity close to 28.8 W / mK of the Tb—Fe—Co metal film used for the fifth magnetic layer 108 serving as a recording layer, for example, about 14.4 W / mK. The film is formed using a transparent dielectric material such as AlN having a high thermal conductivity. On the first dielectric layer 103, a light-transmitting cover layer 102 having a thickness of about 0.1 mm is attached.

  The first magnetic layer 104, the third magnetic layer 106, the fourth magnetic layer 107, and the fifth magnetic layer 108 described above in consideration of the temperature rise state during reproduction by the blue laser beam spot, The Curie temperatures of the third magnetic layer 106, the fourth magnetic layer 107, and the fifth magnetic layer 108 are desirably set in the vicinity of about 480K, about 430K, about 420K, and about 590K.

  The thicknesses of the first magnetic layer 104, the third magnetic layer 106, the fourth magnetic layer 107, and the fifth magnetic layer 108 are preferably set to about 30 nm, about 5 nm, about 10 nm, and about 80 nm, respectively. .

  In the magneto-optical recording medium 100, an information signal is recorded using a blue laser beam BL having a wavelength of 405 nm ± 5 nm conforming to the so-called Blu-ray standard. At this time, an external magnetic field from a magnetic head (not shown) is applied to the magneto-optical recording medium 100 while irradiating the blue laser beam BL from the cover layer 102 side. Thereby, a recording mark corresponding to the information signal is recorded in the form of a magnetic domain on the fifth magnetic layer 108. The magnetic domain of the fifth magnetic layer 108 is exchange-coupled to the first magnetic layer 104 via the fourth magnetic layer 107 and the third magnetic layer 106 during reproduction. At the time of this reproduction, at least the magnetization of the fourth magnetic layer 107 disappears due to the temperature rise due to the irradiation with the blue laser beam BL, and the domain wall motion is changed to expand the magnetic domain exchange-coupled in the first magnetic layer 104. A reproduction signal is obtained by being generated in the layer 104.

  In particular, as shown in an enlarged view in FIG. 2, when the exchange coupling is established between the first magnetic layer 104 and the third magnetic layer 106 on the side where the blue laser beam spot BLS is incident, Since the second magnetic layer 105 having internal magnetic anisotropy exists, the mark expansion direction of the recording track T, which is the perpendicular magnetization range in the first magnetic layer 104, extends not only in the track direction but also in the radial direction. As a result, even if the recording track T has a narrow track width of about 50 nm and recorded, a good reproduction signal without jitter can be obtained.

  Note that two directions perpendicular to the optical axis of the blue semiconductor laser 42 are a radial direction (radial direction) of the magneto-optical recording medium 100 and a tangential direction (tangential direction) of the magneto-optical recording medium 100 substantially orthogonal to the radial direction. Track direction).

  More specifically, when the second magnetic layer 105 and the first magnetic layer 104 provided on both sides of the recording track T are exchange coupled, the first magnetic layer 104 has a magnetic spin as indicated by an arrow in FIG. The in-plane magnetization film faces in the in-plane direction. At the time of reproduction, the boundary on both sides of the recording track T of the reproduction mark transferred from the fifth magnetic layer 108 to the first magnetic layer 104 via the fourth magnetic layer 107 and the third magnetic layer 106 is in-plane magnetization. This is a so-called 90 ° domain wall that spins from 1 to perpendicular magnetization.

  Accordingly, the domain wall energy stored in the 90 ° domain wall is smaller than the energy stored in the 180 ° domain wall (region where the magnetic spin rotates 180 °) in the perpendicular magnetization film existing in the track direction. Accordingly, it becomes easy to move to a higher temperature side that is more energetically stable under a temperature gradient created by irradiation with a laser beam spot. As a result, even in the magneto-optical recording medium 100 with a narrowed track, the magnetic domain of the reproduction mark extends not only in the track direction but also in the radial direction during reproduction. For this reason, the domain wall motion detection operation can be realized smoothly. Therefore, even if recording is performed on a narrow track, a reproduced signal with a small amount of jitter can be obtained satisfactorily.

  Note that the recording area does not have to be present immediately under the second magnetic layer 105, and it is sufficient that the minimum width indicated by the track width W in FIG. 2 is maintained. Therefore, when recording information, even if the area immediately below the second magnetic layer 105 is cross-erased, there is no problem in maintaining and enlarging the recorded information.

  Next, a recording / reproducing apparatus for the magneto-optical recording medium 100 will be described with reference to FIG.

  In the recording / reproducing apparatus for the magneto-optical recording medium 100, a turntable 33 is fixed to a shaft of a spindle motor 32 that is rotationally driven by a spindle motor drive circuit 31. The magneto-optical recording medium 100 is mounted on the turntable 33. The magneto-optical recording medium 100 is rotated integrally with the turntable 33, for example, at a constant linear velocity (CLV) at 3.0 m / sec.

  A magnetic head 36 connected to a magnetic head drive circuit 35 via a switch 34 for switching between a magnetic field modulation recording signal and a reproducing magnetic field signal is provided on the upper surface side of the magneto-optical recording medium 100. It is movably provided in the radial direction (radial direction).

  An optical pickup 40 connected to the laser drive circuit 37 is disposed on the lower surface side of the magneto-optical recording medium 100. The optical pickup 40 is provided so as to be movable in the radial direction of the magneto-optical recording medium 100 while always facing the magnetic head 36 with the magneto-optical recording medium 100 interposed therebetween. The detection output from the optical pickup 40 is processed by the reproduction signal processing circuit 38.

  The optical pickup 40 includes a blue semiconductor laser 42, a collimator lens 43, a beam shaping element 44, a polarization beam splitter 45, a two-dimensional actuator 46, an objective lens 47, an analyzer 48, a detection lens 49, and light detection in a pickup housing 41. The container 50 is stored.

  The blue semiconductor laser 42 emits a blue laser beam BL having a wavelength of 405 ± 5 nm or less. The wavelength of the blue laser beam BL is based on the so-called Blu-ray standard, and the blue semiconductor laser 42 based on the Blu-ray standard is used for the recording / reproducing apparatus of the magneto-optical recording medium 100.

  The collimator lens 43 converts the blue laser beam BL emitted from the blue semiconductor laser 42 in the state of diverging light into parallel light.

  The beam shaping element 44 enlarges only the tangential direction of the magneto-optical recording medium 100 using a double-sided cylindrical lens or the like, and reduces the rim intensity of the blue laser beam spot BLS irradiated on the magneto-optical recording medium 100 from the objective lens 47 described below. adjust. As will be described in detail later, the beam shaping element 44 is designed so that Rrim> 1 when the rim intensity of the blue laser beam BL is rim intensity in the track direction / rim intensity in the radial direction = Rrim.

  The polarization beam splitter 45 forms a transflective dielectric multilayer film 45a having polarization so as to separate the blue laser beam BL that has passed through the beam shaping element 44 and the reflected light from the magneto-optical recording medium 100. Become.

  The objective lens 47 has a numerical aperture NA of 0.7 or more, and at least one surface is formed as an aspherical surface. The objective lens 47 narrows down the blue laser beam BL transmitted through the transflective dielectric multilayer film 45a of the polarization beam splitter 45 and irradiates the magneto-optical recording medium 100 with the blue laser beam spot BLS. For this reason, the objective lens 47 is subjected to focus control and tracking control by the two-dimensional actuator 46.

  In the analyzer 48, the detection lens 49, and the photodetector 50, the 90 ° direction of the reflected light from the magneto-optical recording medium 100 is converted by the transflective dielectric multilayer film 45 a of the polarization beam splitter 45 through the objective lens 47. Later, the reflected light is detected.

  When recording an information signal on the magneto-optical recording medium 100, the recording / reproducing apparatus of the magneto-optical recording medium 100 uses a magnetic field modulation recording signal obtained by modulating input data according to a predetermined disk format via a switch 34 and a magnetic head drive circuit 35. To the magnetic head 36. Then, the magneto-optical recording medium 100 is irradiated with a blue laser beam BL for recording from the blue semiconductor laser 42. Then, the magnetic head drive circuit 35 generates a recording magnetic field from the magnetic head 36 according to the magnetic field modulation recording signal while the temperature of the magneto-optical recording medium 100 is raised, and information is recorded on the magneto-optical recording medium 100.

  On the other hand, when reproducing the recorded information signal, the blue laser beam BL for reproduction with weak laser power from the blue semiconductor laser 42 in the optical pickup 40 is rotated by the laser driving circuit 37 with the magneto-optical recording medium 100 rotated. Is emitted. This reproduction blue laser beam BL is converted into parallel light by the collimator lens 43 and then expanded by the beam shaping element 44 only in the tangential direction (tangential direction, track direction) of the magneto-optical recording medium 100 to obtain a polarization beam splitter. 45 is passed and narrowed down by the objective lens 47. As a result, the reproduction blue laser beam spot BLS is irradiated onto the magneto-optical recording medium 100. Then, the return light reflected by the magneto-optical recording medium 100 is detected by the photodetector 50 through the objective lens 47, the polarization beam splitter 45, the analyzer 48, and the detection lens 49, and sent to the reproduction signal processing circuit 38. Play the information signal. A reproducing magnetic field may be generated from the magnetic head 36 by a reproducing magnetic field signal.

  Next, the principle of reproducing information from the magneto-optical recording medium 100 by the above-described recording / reproducing apparatus for the magneto-optical recording medium 100 will be described with reference to FIGS. 4 to 7, the fourth magnetic layer 107 and the third magnetic layer 106 are shown as a single layer that transfers the information of the fifth magnetic layer 108 to the first magnetic layer 104.

  4 and 6, (a) shows the magneto-optical recording medium 100, (b) shows the medium temperature distribution, and (c) shows the force that causes the domain wall motion. FIG. 5 is a diagram illustrating a front process on the front side in the moving direction of the blue laser beam spot BLS, and FIG. 7 is a diagram illustrating a rear process on the rear side in the moving direction of the blue laser beam spot BLS. The vertical arrows in the fifth magnetic layer 108, the fourth magnetic layer 107, the third magnetic layer 106, and the first magnetic layer 104 indicate atomic spins corresponding to “0” and “1” of the recording marks corresponding to the information signal. Represents the direction. A domain wall 110 is formed at the boundary between regions where spin directions are opposite to each other.

  As shown in FIG. 4B, when the magneto-optical recording medium 100 rotating at a constant speed is irradiated with the focused blue laser beam spot BLS and the magneto-optical recording medium 100 is heated, the blue laser beam spot BLS proceeds. Elliptical temperature distribution regions having different temperature gradients in the front and rear in the direction are formed in the magneto-optical recording medium 100. This temperature gradient is steeper at the front in the traveling direction of the blue laser beam spot BLS than at the rear in the traveling direction of the blue laser beam spot BLS.

  As shown in FIG. 4A, due to the temperature gradient ahead of the blue laser beam spot BLS in the traveling direction, the domain wall as shown by the arrow A in the figure for signal detection in front of the blue laser beam spot BLS in the traveling direction. 110 movement occurs in the first magnetic layer 104.

  In the figure, a region where no arrow exists in the fourth magnetic layer 107 and the third magnetic layer 106 (referred to as a region S) indicates a region heated to a temperature equal to or higher than the threshold temperature Ts. Here, since the threshold temperature Ts> Tc4 (the Curie temperature of the fourth magnetic layer 107 and the third magnetic layer 106), the magnetization disappears in the fourth magnetic layer 107. As a result, exchange coupling between the fifth magnetic layer 108 and the first magnetic layer 104 via the fourth magnetic layer 107 and the third magnetic layer 106 is cut off in the region S in the first magnetic layer 104.

The recording signal is formed and stored as a magnetization reversal region (magnetic domain) in the fifth magnetic layer 108. In FIG. 4, the hatched area of the downward arrow corresponds to the magnetization switching area (magnetic domain). In the region outside the region S in the fourth magnetic layer 107 and the third magnetic layer 106, transfer is performed from the fifth magnetic layer 108 to the first magnetic layer 104 by exchange coupling via the fourth magnetic layer 107 and the third magnetic layer 106. When the recorded mark (magnetic domain) enters the region S of the fourth magnetic layer 107 as the magneto-optical recording medium 100 rotates, the domain wall formed on one side of the recording mark is the region of the fourth magnetic layer 107. It moves to the peak temperature position in S (arrow A in FIG. 4). This process of domain wall movement is referred to herein as a front process. As shown in the following formula 1, the force F that is the origin of causing domain wall motion is
F = −∂σ / ∂χ (Formula 1)
It is expressed. Here, σ represents the domain wall energy, and χ represents the distance in the track direction in which the traveling direction of the blue laser beam spot BLS is positive.

  FIG. 5 shows how the movement of the domain wall 110 is detected. In the case of a specific mark length, movement of the domain wall 110 as shown by an arrow B in FIG. 6 can also occur due to a temperature gradient behind the blue laser beam spot BLS in the traveling direction. This process of domain wall motion is referred to as a rear process here.

  The mark length at which both the front process and the rear process can occur is considered to be 0.25 μm or more when a laser of about 650 nm is used. When information is reproduced without applying a reproduction auxiliary magnetic field, a reproduction signal of a mark of 0.25 μm or more is detected as a waveform superimposed with a certain delay time due to detection of domain wall motion by both processes. become. This superimposed signal detection waveform causes an inconvenient state in normal signal reproduction processing. Therefore, this problem can be solved by applying the reproduction assisting magnetic field Hr as shown in FIGS.

That is, the magnetic domain wall movement in the rear process is suppressed when the mark of any length is reproduced by the reproduction auxiliary magnetic field. As described above, the temperature gradient in the region S in the fourth magnetic layer 107 has a relationship of (temperature gradient used in the front process)> (temperature gradient used in the rear process), and thus this operation becomes possible. . FIGS. 5 and 7 are diagrams for explaining this. FIGS. 5 and 7 show the domain wall moving operation portions of FIGS. 4 and 6 in an enlarged manner, respectively. An arrow F1 in FIG. 5 is a domain wall driving force due to a temperature gradient, and is represented by the above-described Expression 1. A white arrow F2 in the figure is a domain wall driving force by Zeeman energy generated by the reproduction auxiliary magnetic field. On the other hand, an arrow F4 in FIG. 7 is a domain wall driving force due to a temperature gradient.
F = ∂σ / ∂χ (Formula 2)
It is expressed. Further, an arrow F3 in FIG. 7 is a domain wall driving force by Zeeman energy generated by the reproduction assist magnetic field.

Now, the temperature gradient difference (temperature gradient used in the front process)> (temperature gradient used in the rear process)
From the following equation 3,
F1> F2 and F3> F4 (Formula 3)
There is a strength of the reproducing auxiliary magnetic field that satisfies the above.

  Therefore, by selecting a reproduction assisting magnetic field strength that satisfies Equation 3, it is possible to suppress the domain wall movement of the rear process and cause only the domain wall movement of the front process.

  In the magneto-optical recording medium 100, the action of preventing the domain wall movement in the rear process described above can be realized by adding a third magnetic layer 106 between the first magnetic layer 104 and the fourth magnetic layer 107. . In the magneto-optical recording medium 100, the Curie temperature of the fourth magnetic layer 107 is lower than the Curie temperature of the third magnetic layer 106. Therefore, when the blue laser beam spot BLS is irradiated while moving, the fourth magnetic layer 107 first reaches the Curie temperature, and then the third magnetic layer 106 reaches the Curie temperature. Therefore, a step is generated between the region S in the fourth magnetic layer 107 and the region S in the third magnetic layer 106, and the timing at which the domain wall motion is generated by the rear process can be delayed. In other words, a time difference is created for storing the domain wall energy sufficient to generate the domain wall, and the rear domain wall of the recording mark enters the rear process area during the time difference, thereby detecting by the unnecessary rear process. Signal generation is suppressed.

  Therefore, in the magneto-optical recording medium 100, the reproducing magnetic field Hr is unnecessary. However, in order to suppress this rear process, the state of the temperature gradient that is the origin of domain wall motion is important. Therefore, when recording / reproduction is performed at an extremely high density using the blue laser beam BL having a wavelength of 405 nm ± 5 nm of the present embodiment, the temperature gradient curve becomes steeper. For this reason, the suppression of the domain wall movement in the rear process cannot be sufficiently achieved only by adding the third magnetic layer 106.

  Therefore, the recording / reproducing apparatus for the magneto-optical recording medium 100 of the present embodiment shows the temperature distribution (temperature gradient) in the blue laser beam spot BLS output from the blue semiconductor laser 42 and focused on the magneto-optical recording medium 100, The rim intensity of the blue laser beam spot BLS is adjusted. Thus, the temperature gradient generated in the magneto-optical recording medium 100 by laser irradiation is controlled, and unnecessary domain wall movement due to the rear process is prevented, so that a good reproduction signal can be obtained.

  FIG. 8 shows a temperature gradient in the track direction generated in the magneto-optical recording medium 100 of this embodiment and the comparative example. In FIG. 8, the position of the horizontal axis is a position coordinate with the blue laser beam spot BLS center being zero and the beam traveling direction being positive, and the beam is moving at a linear velocity of 3.0 m / s.

  In the comparative example, the temperature distribution (temperature gradient) in the spot focused by the short wavelength blue laser beam BL is not adjusted by the rim intensity of the blue laser beam spot BLS. On the other hand, the temperature distribution of the present embodiment adjusts the temperature distribution (temperature gradient) within the blue laser beam spot BLS focused by the short wavelength blue laser beam BL by the rim intensity of the blue laser beam spot BLS.

  The size of the effective blue laser beam spot BLS in which the operation of the magneto-optical recording medium 100 during reproduction as described above is performed is in a temperature region of about 150 ° C. or more. In this temperature region, the temperature distribution of the present embodiment. However, the curve becomes gentler than the temperature distribution in the comparative example. The temperature distribution of this embodiment is close to the temperature distribution in which the magneto-optical recording medium 100 is irradiated with, for example, a 650 nm laser. Accordingly, as described above, by adding the third magnetic layer 106 to the magneto-optical recording medium 100 in addition to the fourth magnetic layer 107, it is possible to suppress the rear process without the auxiliary reproduction magnetic field.

  FIG. 9 is an explanatory diagram for smoothing the temperature gradient in the track direction in the magneto-optical recording medium 100 when the blue laser beam spot BLS is irradiated in this way. FIG. 9 is a diagram schematically showing a temperature gradient in the blue laser beam spot BLS when the rim intensity of the blue laser beam spot BLS is changed.

  In FIG. 9, a thick line indicates an effective blue laser beam spot size that causes the above-described reproducing operation of the magneto-optical recording medium 100, and a thin line indicates an isothermal line in the magneto-optical recording medium 100. Of the isothermal lines, the region drawn on the innermost side corresponds to the region with the highest temperature in FIG. The dotted line in the figure indicates the track boundary.

  Here, the rim strength in the track direction / the rim strength in the radial direction in the magneto-optical recording medium 100 is defined as Rrim. (A) shows the temperature distribution where Rrim> 1, (b) shows the temperature distribution where Rrim = 1, and (c) shows the temperature distribution where Rrim <1.

  The rim intensity can be adjusted by the design of the beam shaping element 44 (beam shaping prism (or homogenizer) of the optical system), the collimator lens 43, and the objective lens 47 in the optical pickup 40.

  When the rim intensity of the laser spot is set so that Rrim> 1 as shown in FIG. 9A, the diffusion of heat in the radial direction in the magneto-optical recording medium 100 is suppressed, and the magneto-optical recording medium 100 The temperature gradient in the track direction at has become gentler. On the other hand, the temperature gradient is steep in the radial direction of the magneto-optical recording medium 100.

  On the other hand, when Rrim = 1 as shown in FIG. 9B, the temperature gradient in the track direction of the magneto-optical recording medium 100 becomes steeper than when Rrim> 1. Similarly, when Rrim <1 as shown in FIG. 9C, the temperature gradient in the track direction of the magneto-optical recording medium 100 becomes steeper than that when Rrim = 1. Thus, when the temperature gradient in the track direction in the magneto-optical recording medium 100 becomes steep, the domain wall motion in the rear process cannot be suppressed, and the quality of the reproduction signal is lowered.

  As described above, according to the recording / reproducing apparatus of the magneto-optical recording medium 100 to which the present invention is applied, when the rim intensity of the blue laser beam BL is rim intensity in the track direction / rim intensity in the radial direction = Rrim, Set so that Rrim> 1. Thereby, according to the recording / reproducing apparatus of the magneto-optical recording medium 100, the temperature gradient in the track direction in the magneto-optical recording medium 100 can be moderated and the domain wall movement in the rear process in the first magnetic layer 104 can be suppressed. Accordingly, the steep temperature distribution (temperature gradient) in the track direction in the blue laser beam spot BLS that has been narrowed down can be moderated by adjusting the rim intensity of the blue laser beam spot BLS, and recorded at a higher density. Information can be reproduced with a good reproduction signal, and further higher recording density can be achieved.

  The above-described embodiment is an example of the present invention. For this reason, the present invention is not limited to the above-described embodiment, and various modifications can be made depending on the design and the like as long as the technical idea according to the present invention is not deviated from this embodiment. Of course, it is possible to change.

DESCRIPTION OF SYMBOLS 31 Spindle motor drive circuit 32 Spindle motor 33 Turntable 34 Switch 35 Magnetic head drive circuit 36 Magnetic head 37 Laser drive circuit 38 Reproduction signal processing circuit 40 Optical pickup 41 Pickup housing 42 Blue semiconductor laser 43 Collimator lens 44 Beam shaping element 45 Polarization Beam splitter 45a Transflective dielectric multilayer film 46-dimensional actuator 47 Objective lens 48 Analyzer 49 Detector lens 50 Photo detector 100 Magneto-optical recording medium 101 Substrate 101a Protruding portion 101b Guide groove 102 Cover layer 103 First dielectric layer 104 First 1 magnetic layer 105 second magnetic layer 106 third magnetic layer 107 fourth magnetic layer 108 fifth magnetic layer 109 second dielectric layer 110 domain wall

Claims (2)

A first magnetic layer having magnetic anisotropy at least in a vertical direction on which a laser beam is incident on a convex portion corresponding to a recording track on which information is recorded and a concave portion formed on both sides of the convex portion; A second magnetic layer having magnetic anisotropy in a perpendicular direction in which information is recorded, a third magnetic layer having a Curie temperature lower than that of the first magnetic layer and the second magnetic layer, and a recess of the third magnetic layer And the fourth magnetic layer having magnetic anisotropy in the in-plane direction is formed, and the information recorded in the second magnetic layer is transferred to the first magnetic layer via the third magnetic layer. A magneto-optical recording medium reproducing device comprising:
A light irradiating unit that irradiates laser light having a wavelength of 405 nm ± 5 nm conforming to the Blu-ray standard from the first magnetic layer;
When the rim intensity Rrim of the laser beam is defined as the rim intensity in the track direction of the magneto-optical recording medium / the rim intensity in the radial direction of the magneto-optical recording medium, the laser beam emitted from the light irradiation unit is
Rrim> 1
A magneto-optical recording medium reproducing apparatus characterized by satisfying the following condition: A first magnetic layer having magnetic anisotropy at least in a vertical direction on which a laser beam is incident on a convex portion corresponding to a recording track on which information is recorded and a concave portion formed on both sides of the convex portion; A second magnetic layer having magnetic anisotropy in a perpendicular direction in which information is recorded, a third magnetic layer having a Curie temperature lower than that of the first magnetic layer and the second magnetic layer, and a recess of the third magnetic layer And the fourth magnetic layer having magnetic anisotropy in the in-plane direction is formed, and the information recorded in the second magnetic layer is transferred to the first magnetic layer via the third magnetic layer. A method for reproducing a magneto-optical recording medium, comprising:
When irradiating a laser beam having a wavelength of 405 nm ± 5 nm conforming to the Blu-ray standard from the first magnetic layer,
When the rim intensity Rrim of the laser beam is defined as the rim intensity in the track direction of the magneto-optical recording medium / the rim intensity in the radial direction of the magneto-optical recording medium,
Rrim> 1
A reproducing method of a magneto-optical recording medium characterized by satisfying the following condition:

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