JP5400731B2 - Magnetic recording medium, magnetic reproducing apparatus, and magnetic reproducing method - Google Patents

Description

  The present invention reads out data from a magnetic recording medium in which a track is formed of a thin-line magnetic material, and a magnetic domain sandwiched between magnetic domains while moving the domain wall in the track by supplying a pulse current to the magnetic recording medium. The present invention relates to a magnetic reproducing apparatus and a magnetic reproducing method.

  In storage devices such as hard disk drives (HDD), with the increase in the amount of information to be handled, higher recording density and higher speed of recording and reproduction are being promoted. As the recording density is increased, the tracks of recording media such as magnetic disks used for HDDs are narrowed, and the length of one data (1 bit) in the track is shortened. In order to detect magnetism, the reproduction method is a magnetic method using a magnetic head made of a magnetoresistive effect element such as a GMR (Giant MagnetoResistance) element or a TMR (Tunnel MagnetoResistance) element, or a laser beam. The magneto-optical method by irradiation is applied.

  The size of this 1-bit area is mainly converged to an area necessary for reproduction. Specifically, it converges to the size of the magnetoresistive effect element used as the magnetic head and the diameter of the laser beam irradiation spot. Therefore, magnetic-induced super-resolution (MSR) that enables the miniaturization of GMR elements and TMR elements in the magnetic system, the application of short-wavelength blue laser light in the magneto-optical system, and the reproduction of a minute region exceeding the diffraction limit. ), Magnetic domain expansion reproduction (MAMMOS), or domain wall displacement reproduction (DWDD), a technique for further increasing the recording density has been developed.

  For recording and reproduction on a magnetic disk, the disk is rotated by a spindle motor, and the magnetic head and the laser beam irradiation spot are moved only in the radial direction of the disk, along the track (in the circumferential direction of the disk). Magnetize (record) in a predetermined direction or detect (reproduce) magnetism. In order to increase the speed of recording and reproduction in such a disc, firstly, the rotational speed of the disc is increased. However, there is a limit to increasing the rotational speed due to problems such as track magnetization in recording, time required for magnetic detection in reproduction, and malfunction due to disk vibration. Therefore, in an HDD or the like built in a personal computer, about 2 to 10 magnetic disks are stacked and each magnetic disk is provided with a magnetic head, and recording or reproduction is performed by recording or reproducing each magnetic disk in parallel. The playback speed can be increased.

US Pat. No. 6,834,005 JP 2010-20114 A

T. Koyama et al., “Control of Domain Wall Position by Electrical Current in Structured Co / Ni Wire with Perpendicular Magnetic Anisotropy”, Appl. Phys. Express 1, 101303 (2008) Xin Jiang et al., “Enhanced stochasticity of domain wall motion in magnetic racetracks due to dynamic pinning”, Nature Communications, 1, pp.1-5 (2010) T. Kato et al., “Planar patterned media fabricated by ion irradiation into CrPt3 ordered alloy films”, J. Appl. Phys. 105, 07C117 (2009), Fig.2.

  The recording and reproducing speed on the magnetic disk is converged to the length of 1 bit (bit length) on the track and the rotational speed of the disk. To further increase the speed, it is necessary to increase the number of disks to be recorded and reproduced simultaneously. For example, in order to realize a super high-vision (high-definition television) system, it is necessary to reproduce at a super-high speed of about 72 Gbps. Even in a super high-definition system for experiments of about 24 Gbps, it is necessary to operate dozens of large-capacity storages for servers equipped with, for example, about 3 to 10 disks at the same time. I need. As described above, the recording medium and the reproducing apparatus thereof are not sufficiently capable of dealing with an increase in capacity and density of information to be handled.

  Here, as a method of moving recorded data without driving a recording medium, Patent Document 1 discloses that a thin line-shaped magnetic body (hereinafter referred to as a magnetic thin line as appropriate) is formed into a U-shape or the like and a track. A memory device is disclosed. This is because when a magnetic material is formed in a thin line shape, magnetic domains are formed in the length direction, and when a current is further supplied in the length direction, all the domain walls generated to divide the magnetic domains are equidistant in the thin line direction. The characteristic of moving and performing shift movement is used (see Non-Patent Document 1). That is, each magnetic head for recording and reproduction is fixed to a predetermined location (a U-shaped top portion in Patent Document 1) on a track (magnetic wire), and a current is reversibly supplied from both ends of the track to provide a domain wall. The desired magnetic domain sandwiched between the magnetic heads is moved to a position facing the magnetic head. In this method, although depending on the shape of the magnetic material (line width, etc.) and the current to be supplied, the moving speed of the domain wall is extremely high, from several tens m / s to about 250 m / s (see Non-Patent Document 2). It is expected to exceed the playback speed due to the current disc rotation.

  In Patent Document 1, in order to enable rewriting of data by a random access method, wave-shaped magnetic wires in which a large number of U-shapes are connected in series are further provided in parallel, and a magnetic head is provided at each of the U-shaped top portions. It is set as the form provided with. Further, in Patent Document 2, magnetic thin wires having a simple configuration storing only one piece of data “1” and “0” per line are arranged in a matrix, and current is supplied to each magnetic thin wire. Thus, any data is selected. These technologies are suitable as a random access memory or a spatial light modulator that simultaneously presents a large amount of data, but are efficient as a recording medium that records and reproduces continuous data such as long-time moving images. Inferior. Accordingly, the present inventors have formed magnetic thin wires in a concentric shape and used this as a track in the same manner as a general magnetic disk or magneto-optical disk to form a disk-shaped recording medium (disk). With such a recording medium, it is not necessary to rotate the recording medium main body, so there is no malfunction due to vibration, and data can be moved on the track at high speed, so that recording and reproduction can be speeded up. .

  However, even in a recording medium to which such a magnetic thin wire is applied, the reproducing method uses a magnetoresistive effect element, a laser beam, or the like as in the prior art, so that the size of the 1-bit region is converged by these. The same as the current magnetic disk. Accordingly, it is still necessary to use a large number of recording media for reproducing large-capacity / high-density data, and further higher recording density and larger capacity of the recording media have been desired.

  The present invention has been devised in view of the above problems, and is intended for a recording medium in which a track is formed with the magnetic thin wire, and a magnetic recording medium capable of increasing the recording density without depending on the reproducing method, and such a recording medium. It is an object to provide a magnetic reproducing apparatus and a magnetic reproducing method that perform high-speed reproduction on a magnetic recording medium.

  In order to solve the above-mentioned problem, the present inventor moves the magnetic domain as data temporarily in a non-moving track, and thus expands the magnetic domain to a temporarily required size only in the region of the designated position where reproduction is performed. Thus, the inventors have conceived that data is compressed and stored in other areas, and the recording medium is increased in recording density and capacity. Then, the present inventor utilizes a phenomenon (see Non-Patent Document 3) in which saturation magnetization is lowered when ions are implanted into a magnetic material, and a region having a low saturation magnetization is locally provided in the magnetic thin wire. We found a method to expand the magnetic domain when it reached the magnetic field.

  A magnetic recording medium according to the present invention includes one or more magnetic fine wires formed by forming a magnetic material on a substrate in the form of fine wires, and binary data is applied to the magnetic fine wires as either of two different directions of magnetization. By recording a pair of electrodes on both ends of the magnetic wire and supplying a pulse current in the direction of the thin wire, the binary data is recorded in the magnetic wire. The domain wall generated between the magnetic domain formed by recording and the magnetic domain formed by recording the other binary data moves intermittently in the direction of the thin line. In such a magnetic recording medium, the magnetic thin wire has a low saturation magnetization region in a region partitioned in the thin wire direction as a region for detecting the magnetization direction, and ions are implanted into the low saturation magnetization region. Thus, the low saturation magnetization region is formed in advance with a relatively low saturation magnetization. The magnetic domain is characterized in that its length in the direction of the thin line extends only when it reaches the low saturation magnetization region.

  With such a configuration, when the data recorded as magnetic domains on the magnetic wire is intermittently moved with the shift of the domain wall and reaches the low saturation magnetization region, the data reaches the region. Since it is expanded only occasionally, it is stored in a low-saturation magnetization region as a size corresponding to the reproduction method, and when it is outside this region, it is compressed and stored, so that a high recording density can be achieved. Further, since the low saturation magnetization region is formed by ion implantation, it can be easily formed at a desired position and size in the magnetic recording medium.

  Further, in the magnetic recording medium according to the present invention, it is preferable that the magnetic fine wires are formed concentrically with the substrate on the disk-shaped substrate, and the shape in plan view lacks a part of the ring. With this configuration, the magnetic recording medium has the same outer shape as a conventionally known recording medium, and even when the size of the magnetic recording medium is limited, the magnetic recording medium can be continuously long on the substrate without bending the magnetic wire. it can.

  Further, the magnetic fine wire of the magnetic recording medium according to the present invention may be formed of a magneto-optical material. With such a magnetic recording medium, reproduction can be performed by a magneto-optical method using laser light or the like.

  A magnetic reproducing apparatus according to the present invention is an apparatus for reproducing binary data recorded on the magnetic recording medium according to the present invention. The magnetic reproducing apparatus includes a selection unit that selects one or more magnetic wires from a magnetic recording medium, and a magnetic wall that is generated on the magnetic wire by connecting the magnetic wires selected by the selection device to both ends of the magnetic wire. Current supply means for supplying a pulse current for intermittently moving the magnetic wire in the direction of the thin line, magnetic detection means for detecting the magnetization direction in the low saturation magnetization region of the magnetic thin line selected by the selection means, and the current supply means Data reproducing means for reproducing, as data, the magnetization direction detected by the magnetic detection means when the current in the pulse current is stopped in synchronization with the supplied pulse current.

  Alternatively, as a device for reproducing binary data recorded on a magnetic recording medium in which a magnetic wire is formed of a magneto-optical material, light is further incident on the low saturation magnetization region of the magnetic wire selected by the selection means Irradiation means may be provided. In such a magnetic reproducing apparatus, in place of the magnetic detection means, a light detection means for detecting the polarization direction of the light incident from the irradiation means and emitted from the magnetic wire is provided. The data reproducing means reproduces the polarization direction of the light detected by the light detecting means as data instead of the magnetization direction of the magnetic thin wire.

  With this configuration, the magnetic reproducing apparatus shifts the data recorded as magnetic domains on the magnetic wire by detecting the magnetization direction or the direction of polarization of the emitted light from the low saturation magnetization region in the magnetic wire of the magnetic recording medium. Since the data that has reached the low saturation magnetization region is temporarily expanded, the data is stored after being compressed to be smaller than a magnetic domain having a size that can be detected such as the magnetization direction by the magnetic reproducing apparatus. The magnetic recording medium can be reproduced.

  The magnetic reproducing method according to the present invention is a method for reproducing binary data recorded on the magnetic recording medium, wherein a selection step of selecting one or more magnetic wires from the magnetic recording medium, and the selection A reproducing step of reproducing the data recorded on the magnetic thin wire. The reproducing step includes a current supply process for supplying a pulse current that intermittently moves a magnetic wall generated in the magnetic wire to the magnetic wire in the direction of the wire, and the low saturation magnetization region of the magnetic wire. Data that reproduces the magnetization direction detected in the magnetic detection process at the time of stopping the current in the pulse current as data in synchronization with the magnetic detection process for detecting the magnetization direction in the current and the pulse current supplied in the current supply process And a reproduction process.

  Alternatively, as a method of reproducing binary data recorded on a magnetic recording medium in which magnetic fine wires are formed of a magneto-optic material, light is further incident on the low saturation magnetization region of the magnetic fine wires in the reproducing step. Irradiation processing may be performed, and instead of the magnetic detection processing, light detection processing may be performed in which the direction of polarization of light that is incident and emitted from the magnetic wire is detected in the irradiation processing. In such a magnetic reproduction method, in the data reproduction process, the polarization direction of the light detected in the light detection process is reproduced as data instead of the magnetization direction of the magnetic thin wire.

  With this procedure, the magnetic reproduction method detects the magnetization direction in the low saturation magnetization region of the magnetic wire or the polarization direction of the emitted light for the magnetic recording medium stored in the magnetic wire as a magnetic domain in which data is compressed. The data can be reproduced by expanding the magnetic domain to a detectable size such as the magnetization direction.

According to the magnetic recording medium of the present invention, the data can be compressed and stored regardless of the reproducing method, so that the capacity can be increased.
According to the magnetic reproducing apparatus and the magnetic reproducing method of the present invention, it is possible to reproduce data of a magnetic recording medium with a high recording density regardless of the reproducing method at high speed, so that without mounting a large number of magnetic recording media, Information composed of high-density data such as high-definition images can be reproduced.

1 is a schematic plan view illustrating a configuration of a magnetic recording medium according to the present invention. 1 is an external view showing a configuration of a magneto-optical magnetic reproducing apparatus according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing in the thin wire | line direction of the magnetic fine wire for demonstrating the structure of the magnetic recording medium based on this invention, (a) is a schematic diagram of the magnetic recording medium which concerns on one Embodiment, (b) is another embodiment. It is a schematic diagram of such a magnetic recording medium. It is a graph which shows the change of the magneto-optic Kerr rotation angle with respect to the applied magnetic field in Fe film for demonstrating the relationship between the ion implantation to a magnetic body, and saturation magnetization, (a) is no ion implantation, (b) is Ga ion. 5.20 × 10 ¹⁰ / μm ² , (c) is Ga ion 1.56 × 10 ¹¹ / μm ² . It is a schematic diagram for demonstrating the movement of the magnetic domain in the magnetic fine wire of the magnetic recording medium based on this invention, and is sectional drawing in the fine wire direction of a magnetic fine wire. 2A and 2B are cross-sectional views in the direction of a fine magnetic wire for explaining the magnetic reproducing method according to the present invention, wherein FIG. 1A is a method using a magneto-optical magnetic reproducing apparatus, and FIG. 2B is a magnetic magnetic recording / reproducing apparatus. Is the method. FIG. 5 is an enlarged perspective view of a reproducing area of a magnetic recording medium for explaining a magnetic reproducing method according to a modification of the magneto-optical magnetic reproducing apparatus according to the present invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for realizing a magnetic recording medium, a magnetic reproducing apparatus, and a magnetic reproducing method according to the present invention will be described with reference to the drawings.

[Magnetic disk]
As shown in FIG. 1, a magnetic disk (magnetic recording medium) 50 according to an embodiment of the present invention records data on a magnetic wire 5 formed by forming a magnetic material in a thin wire shape on a disk-shaped substrate 7 (see FIG. Storage) area. In this magnetic thin wire 5, binary data, that is, “0” or “1” data is continuously recorded in the thin wire direction of the magnetic thin wire 5. An area in which one piece of data of the magnetic thin wire 5 is recorded is referred to as one data area, and the length in the thin line direction is defined as a unit length. The recorded (stored) data is reproduced by mounting or incorporating the magnetic disk 50 in the magnetic reproducing apparatus 1, for example, as shown in FIG. In the magnetic wire 5, “0” and “1” data are recorded as either of two different directions of magnetization. Therefore, in the magnetic thin wire 5, there is one data area, or when data of the same value (either “0” or “1”) is continuously recorded, one magnetic domain is recorded in the continuous data area. Form. In the present specification, the data area is described as a magnetic domain as appropriate.

  Since the magnetic thin wire 5 is supplied with current in the thin wire direction from one end to the other end thereof, all the domain walls that divide the magnetic domains in the magnetic thin wire 5 move by the same distance in the thin wire direction, so-called shift movement is performed. A series of data recorded in the magnetic domain, that is, the magnetic wire 5 moves sequentially. For example, by supplying a pulse current to the magnetic wire 5 by the magnetic reproducing apparatus 1, the data stored in the magnetic wire 5 is intermittently moved together with the domain wall without driving the magnetic disk 50 to rotate. Therefore, in the magnetic thin wire 5, a reproduction area 5r for detecting the magnetization direction and a recording area 5w for magnetizing in a direction corresponding to the data to be recorded are set to areas at predetermined positions on the magnetic disk 50, respectively. can do. The magnetic thin wire 5 includes a low Ms region (low saturation magnetization region) 5e, which is a region having a relatively low saturation magnetization, in a region partitioned in the thin line direction as a region in which the reproduction region 5r is provided. As will be described later, the low Ms region 5e is formed by implanting ions in the region of the magnetic wire 5.

  As shown in FIG. 1, in the magnetic disk 50, the magnetic fine wires 5, 5,... Are concentrically formed on the substrate 7 with the insulating layer 8 interposed therebetween in a plan view. Specifically, one magnetic wire 5 is formed in a C-shape that lacks a part of an annulus in plan view, and the width (the length in the radial direction of the magnetic disk 50) and the thickness (film thickness) are constant. is there. Thus, in the present embodiment, the magnetic recording medium is called a magnetic disk 50 because the outer shape of the magnetic recording medium is based on a disk-shaped substrate and is similar to that of the current magnetic disk. Is similar to the shape of the track, which is the data recording area of the current magnetic disk, and is therefore referred to as the track 5 as appropriate. The number of the magnetic thin wires 5 formed on the magnetic disk 50 is not particularly limited, and may be set according to the track pitch (width and interval of the magnetic thin wires 5), the diameter of the magnetic disk 50, and the like. Further, the length in the length direction (track length) of each of the magnetic thin wires 5 in the magnetic disk 50 may not be the same length.

  Thus, the thin wire shape (planar shape) of the magnetic wire 5 is a straight line that is not bent or a sufficiently gentle curve with respect to the length in the thickness and width directions, and the outer shape is a disk shape as in this embodiment. In the case of the magnetic disk (magnetic recording medium) 50, an annular shape (arc) is preferable as a shape that can be made sufficiently long with respect to its outer dimensions and easy to manufacture. Such magnetic wires 5 can be made longer as they are formed closer to the outer periphery of the magnetic disk 50, and the data recording area (capacity) of the entire magnetic disk 50 can be increased. Further, the magnetic recording medium is not limited to a disk shape, and may be, for example, a plate having a rectangular shape in a plan view. In this case, the magnetic thin wires may be formed in straight lines parallel to each other.

  A pair of electrodes 61 and 62 serving as connection terminals for supplying a current to the magnetic wire 5 from the outside of the magnetic disk 50 (for example, the magnetic reproducing device 1) are connected to both ends of the magnetic wire 5. The electrodes 61 and 62 are made of a general electrode metal material such as a metal such as Cu, Al, Au, Pt, or Ag, or an alloy thereof, and are laminated at both ends of each magnetic wire 5 in the magnetic disk 50. Connected. The electrodes 61 and 62 may be formed under the magnetic wire 5, and in that case, a part of the substrate 7 is removed so that it can be electrically connected to supply current from the outside. The electrodes 61 and 62 are exposed on the back surface (lower surface) of the magnetic disk 50. Alternatively, the electrodes 61 and 62 are formed so as to project outward from the end of the magnetic wire 5 in a plan view, penetrate the insulating layer 8 from the surface of the magnetic disk 50, and the upper surfaces of the electrodes 61 and 62. A contact hole that exposes the overhanging region may be formed.

(Magnetic wire)
In the magnetic disk 50, the magnetic wire 5 is formed on the substrate 7 via an insulating layer 8 as shown in FIG. 3, FIG. 5, and FIG. 6 show a cross section of the magnetic thin wire 5 by a surface along the thin wire direction. The magnetic wire 5 is made of a ferromagnetic material, and is preferably a perpendicular magnetic anisotropic material having magnetization in a direction perpendicular to the film surface. Specifically, a transition metal such as Ni, Fe, Co, or an alloy thereof, and further Pd, A laminated film of Pt and Cu can be mentioned. For materials reproduced by the magneto-optical method, a material (magneto-optic material) having a greater magneto-optic effect is preferable. The thickness of the magnetic wire 5 is 5 to 100 nm, the width is 10 to 200 nm, and the space between the magnetic wires 5 and 5 is preferably 40 to 200 nm. The shorter the width and interval, the more so-called track pitch (the sum of the width and interval of the magnetic wire 5). ) Is smaller, the recording capacity of the magnetic disk 50 can be increased. However, the magnetic wire 5 of the magnetic disk 50 has a width and a track pitch that can be adapted to the reproducing method. Specifically, in the case of a magneto-optical method using laser light, a width of about 100 nm or more is preferable. If it is a magnetic system by such a magnetoresistive effect element, about 60 nm or more in width is preferable. The fine wire direction length (track length) of the magnetic fine wire 5 is not particularly limited as long as it is sufficiently longer than the thickness and the length in the width direction. The magnetic wire 5 may be formed of an integral magnetic material for data reproduction, but in order to record data, it is necessary to stack different materials as described later depending on the recording method. Therefore, the magnetic wire 5 is formed by stacking different materials in the recording area 5w (see FIG. 1) where data is recorded, or the entire magnetic wire 5 has the same configuration as the recording area 5w.

  The recording area 5w is an area for setting the magnetism of the magnetic wire 5 in the magnetization direction corresponding to the data in order to record data on the magnetic wire 5, and in this area, the structure of the magnetic wire 5 corresponds to the recording method. Shall be. The length of the recording area 5w in the direction of the thin line may correspond to the recording method and processing accuracy. Specifically, for example, as in the current recording method on a magnetic disk, as shown in FIG. 3A, when an external magnetic field is applied using a recording magnetic head 22 made of magnetic poles as a writing means, a magnetic thin wire is used. 5, a soft magnetic layer 51 is laminated via a nonmagnetic layer 52 under the head 5 (opposite the side facing the recording magnetic head 22). The soft magnetic layer 51 forms a magnetic path for the external magnetic field from the recording magnetic head 22 to form a perpendicular write magnetic flux with the magnetic wire 5. With such a configuration, for example, in FIG. 3A, in the initial state, the recording magnetic head 22 applies a downward magnetic field to the magnetic thin wire 5 in the upward direction in the recording area 5w, thereby magnetizing. Inverted downward.

  Further, since the magnetic disk 50 according to the present invention can record data on the entire magnetic wire 5 even if the position of the writing means is fixed with respect to the magnetic wire 5, the recording area 5w has the following configuration. You can also That is, the magnetic thin wire 5 has a spin-injection magnetization reversal element structure in the recording region 5w, the power source 22A capable of supplying a direct current by reversing the polarity of the direct current is used as the writing means, and the current is supplied to the recording region 5w. A desired magnetization direction can be obtained by spin injection magnetization reversal. Specifically, as shown in FIG. 3B, a magnetization fixed layer 54 is laminated on the magnetic thin wire 5 via an intermediate layer 53 made of a nonmagnetic material or an insulator, and an upper electrode 63 is further formed thereon. On the other hand, the lower electrode 64 is connected under the magnetic wire 5. The magnetization fixed layer 54 is made of a ferromagnetic material having a coercive force larger than the coercive force in the recording region 5w of the magnetic wire 5 and, if the magnetic wire 5 is a perpendicular magnetic anisotropic material, is also made of a perpendicular magnetic anisotropic material. The magnetization is fixed in one of the upward direction and the downward direction. Further, in order to reverse the spin injection magnetization in the recording area 5w of the magnetic fine wire 5, it is preferable that the thickness of the magnetic fine wire 5 is 5 to 30 nm for such a magnetic disk 50. In FIG. 3B, the substrate 7 and the insulating layer 8 (see FIG. 3A) are omitted. With such a configuration, the magnetic thin wire 5 becomes a magnetization free layer in the recording area 5w, the power source 22A is connected to the electrodes 63 and 64, and a current is supplied upward or downward corresponding to the data to be written. The magnetization can be in the same direction as the magnetization fixed layer 54 or in the opposite direction. For example, in FIG. 3B, a current is supplied downward from the upper electrode 63 to the lower electrode 64, and the magnetic thin wire 5 whose initial magnetization is upward is fixed to the magnetization fixed layer 54 whose magnetization is fixed upward. The magnetization direction is reversed to the opposite direction.

  The reproduction area 5r is an area for detecting the magnetization direction of the magnetic wire 5. Specifically, when reproducing data on the magnetic disk 50, the magnetic domain (data area) reaching this area in the magnetic wire 5 is reproduced. This is a region where only the magnetization direction is detected. The reproduction region 5r has a length in the direction of a thin line corresponding to the reproduction method. Specifically, in the case of the magneto-optical method, although it depends on the wavelength of the laser beam, the length is preferably about 200 nm or more. If so, a length of about 20 nm or more is preferable. The structure of the magnetic wire 5 in the reproducing region 5r may be adapted to the reproducing method. For example, in the magneto-optical method, a material having a large magneto-optical effect may be laminated, or a reflective film may be provided below ( (Not shown).

  In this embodiment, as shown in FIG. 1, the reproduction area 5r and the recording area 5w of all the tracks 5 are set at positions along the radius of a circle that is a planar view shape of the magnetic disk 50. However, the position is not limited to this, and may be a position along a straight line or a curve other than the radius. In any case, it is preferable that the reproduction areas 5r and 5r and the recording areas 5w and 5w in the adjacent tracks 5 and 5 are provided close to each other in all the tracks (magnetic thin wires) 5 of the magnetic disk 50. With this arrangement, for example, when data is reproduced by the magneto-optical magnetic reproducing apparatus 1 shown in FIG. 2, after the reproduction of the data of one track 5 is completed, the next, that is, the adjacent track 5 is reproduced. When shifting (seeking), the distance for moving the laser spot can be shortened to shorten the time. Therefore, in the magnetic disk 50 from which data is reproduced by the magnetic reproducing apparatus 1, the position of the reproducing area 5r is set to the moving path of the laser spot by the optical system 10 (mirror 14 and objective lens 15). Similarly, on the magnetic disk 50 on which data is reproduced and recorded by a magnetic magnetic reproducing device or magnetic recording device (not shown), the positions of the reproducing area 5r and recording area 5w are set to the reproducing magnetic head. 21 (see FIG. 6B), and the movement path of the recording magnetic head 22 (see FIG. 3A).

  Further, in the present embodiment, as shown in FIG. 1, the track 5 has a playback area 5r in the front of the data (data area) moving direction (electrode 62 side) and a recording area 5w in the back (electrode 61 side). Each is provided. As will be described in detail later, in the magnetic disk 50 according to the present embodiment, the data region moves from the electrode 61 side to the electrode 62 side in one direction of the fine line direction by shift movement of the domain wall. Therefore, a large amount of data recorded in the recording area 5w can be stored in a long area in front of the recording area 5w. On the other hand, in the reproduction area 5r, a lot of data moving from the long area behind can be reproduced. Therefore, in the present embodiment, the reproduction area 5r and the recording area 5w are provided one by one apart from each other. However, the present invention is not limited to this. For example, a single area may be provided or adjacent to each other. When the recording area 5w is set at the same position or in the vicinity of the reproduction area 5r shown in FIG. 1, the data may be recorded in the reverse order with the data moving direction as the opposite direction. Further, one track 5 may be provided with a plurality of reproduction areas 5r and recording areas 5w, and the positions and number of these areas 5r and 5w are the magnetic reproduction apparatus 1 for reproducing the magnetic disk 50 (FIG. 2) and the like.

  In the magnetic recording medium (magnetic disk) 50 according to the present invention, a part of the region in the thin wire direction is formed on the magnetic wire 5 as a low Ms region 5e (see FIG. 5) having a lower saturation magnetization than the other regions. The low Ms region 5e is formed so as to include the reproduction region 5r, that is, at least the same region as the reproduction region 5r, preferably longer in the fine line direction than the reproduction region 5r, and in both directions of the fine line direction than the reproduction region 5r. It is set as the area | region of the range which reaches outside (refer FIG. 1, FIG. 6). Although details will be described later, by setting the reproduction area 5r to a relatively low saturation magnetization in this way, the length of one data area reaching the reproduction area 5r is inversely proportional to the saturation magnetization, so that the reproduction area 5r It extends more than the length in other than (outside the low Ms region 5e). That is, the size (data length) of one data in the magnetic wire 5 can be made smaller than the reproducible size (the direction of magnetization can be detected) and stored in another area. Such a low Ms region 5e can be formed by implanting ions into the magnetic wire 5. The amount of saturation magnetization decreases as the number of implanted ions increases, and also changes depending on the ion species and implantation conditions. . Examples of the ion species include Ga, N, O, Ar, Kr, and Xe.

Next, the result of observing the change in saturation magnetization when ions are implanted into the magnetic material will be described in detail. A sample was formed by applying pure Fe as a magnetic material, forming a film with a thickness of 100 nm on a Si substrate, and forming it in a cross shape by crossing two rectangles of width 50 μm × length 250 μm by photolithography. . Ga ions (Ga ⁺ ) were perpendicularly incident on the sample surface into a square area of about 10 μm square at the center of the cross shape, and the change in saturation magnetization of the magnetic material was measured. The ion irradiation conditions were an acceleration voltage: 31 kV and a current: 858 pA, whereby Ga ions were implanted at a rate of 1.73 × 10 ⁹ / μm ² · sec per area and time. The irradiation time was changed to 30 seconds (number of ions: 5.20 × 10 ¹⁰ / μm ² ), 90 seconds (number of ions: 1.56 × 10 ¹¹ / μm ² ), and 0 (no ion irradiation). Different types of samples were made.

  Two coils are arranged so that the sample is sandwiched from both sides, and an external magnetic field is applied to the Fe film perpendicularly to the film surface while changing its magnitude. Instead of measuring saturation magnetization, surface magneto-optic Kerr effect measurement The Kerr rotation angle in the Ga ion irradiation region was measured with an apparatus (SMOKE). FIG. 4 shows a graph of the dependence of the Kerr rotation angle on the applied magnetic field. As described below, the rate of change in saturation magnetization can be calculated by comparing the amount of change in the Kerr rotation angle due to the applied magnetic field.

Assuming that the relationship of H⊥M holds for the change in the magnetization M due to the magnetic field H in the magnetic material, the effective magnetic field H _eff is the reaction applied to the magnetic material with respect to the external magnetic field H _ex applied to the magnetic material. Considering the magnitude of the magnetic field, it is expressed as (H _ex −NM / μ ₀ ). μ ₀ is the magnetic permeability of the vacuum and is a constant. N is a demagnetizing factor, but since the film thickness is extremely small with respect to the area of the sample, it can be regarded as approximately 1 (N≈1) when a magnetic field is applied perpendicularly to the sample. Further, the magnetization M of the ferromagnetic material can be regarded as a substantially saturated magnetic field Ms. Therefore, (H _eff ≈H _ex −Ms / μ ₀ ) is established.

  As shown in FIGS. 4A, 4B, and 4C, the Kerr rotation angle per magnetic field applied to the Fe film is increased by Ga ion implantation. In other words, the external magnetic field required to obtain the same Kerr rotation angle is reduced, which indicates that the saturation magnetization Ms in the Ga ion irradiation region is reduced. Therefore, the rate of change of the ratio of the sample after Ga ion implantation to the ratio of the external magnetic field / Kerr rotation angle of the sample before ion implantation (FIG. 4A) becomes the rate of change of the saturation magnetization Ms. Specifically, the saturation magnetization is reduced to 62% before ion implantation when the irradiation time is 30 seconds in FIG. 4B, and 60 before ion implantation when the irradiation time is 90 seconds in FIG. It can be said that it fell to%. Note that even when the irradiation time is set to 90 seconds with respect to 30 seconds, the difference in the amount of decrease in saturation magnetization is small, and even if the irradiation time is extended, no decrease in saturation magnetization is confirmed. Presumed to deteriorate. Depending on ion irradiation conditions, ion species, magnetic material, etc., the saturation magnetization can be further reduced, and the saturation magnetization can be almost zero (see Non-Patent Document 3).

  The difference (ratio) between the saturation magnetization and other regions in the low Ms region 5e of the magnetic thin wire 5 is not particularly defined. As described above, as the amount of decrease is increased, the data is compressed outside the low Ms region 5e and magnetized. The recording medium 50 can be increased in recording density. However, if the saturation magnetization of the low Ms region 5e is extremely reduced, the magnetization of the data region is not retained, making it difficult to reproduce in the reproduction region 5r, and when reproducing data by a magnetic method, a magnetoresistive effect element Therefore, it is difficult to detect the leakage magnetic field from the magnetic wire 5, so that the ion implantation into the magnetic wire 5 is controlled within a range that does not hinder the reproduction.

[Method of manufacturing magnetic disk]
The magnetic disk 50 shown in FIGS. 1 and 3 can be manufactured, for example, by forming magnetic thin wires (tracks) 5 by the damascene method as shown below. First, an insulating film such as SiO ₂ or Al ₂ O ₃ is formed on a substrate 7 made of a known substrate material such as a Si substrate or a glass substrate whose surface is thermally oxidized by a known method such as a sputtering method. The insulating film 8 is formed by forming grooves in the shape of magnetic thin wires 5, 5,... By etching such as electron beam lithography and ion milling or reactive ion etching (RIE). After a magnetic material is deposited on the insulating layer 8 in a groove by a film forming method such as a sputtering method, the surface is removed of the magnetic material other than the groove by CMP (Chemical Mechanical Polishing) or the like. Magnetic thin wires 5, 5,. When different materials are stacked on the recording area 5w of the magnetic thin wire 5 or the like, the film is formed before or after the magnetic material. Then, a mask having at least a region to be the reproduction region 5r formed on the surface is formed, and then the region is limited by irradiating ions with, for example, an ion implantation apparatus applied to the manufacture of a semiconductor device. Then, ions are implanted into the magnetic wire 5 to form the low Ms region 5e. Note that there is no problem even if ions are implanted into the insulating layer 8 between the magnetic thin wires 5 and 5, and therefore, the region opened in the mask may be a single slit. On both ends of the magnetic wire 5, an electrode metal material is formed by sputtering or the like, processed by photolithography and etching, or lift-off or the like to form electrodes 61 and 62. Finally, except for the electrodes 61 and 62, the surface is covered with a resin or the like (not shown). In forming the magnetic wire 5, the magnetic wire 5 is formed by a lift-off method after forming an insulating film (insulating layer 8) as a base, and then insulated between the magnetic wires 5 and 5. Layer 8 may be deposited. Alternatively, the low Ms region 5e may be formed in the magnetic wire 5 after the electrodes 61 and 62 are formed.

[Movement of magnetic domain wall in magnetic wire]
With reference to FIG. 5, the operation of the magnetic wall movement of the magnetic recording medium (magnetic disk) according to the present invention in the magnetic wire will be described. In the present invention, in order to reproduce the data recorded on the magnetic recording medium, the domain wall generated so as to sandwich the magnetic domain formed by recording the data on the magnetic thin line is moved in the direction of the thin line as follows. .

  In this embodiment, the magnetic wire 5 is made of a perpendicular magnetic anisotropic material, and its magnetization direction indicates up or down. Therefore, data “0” is downward magnetization, and “1” is upward magnetization. Is recorded. In the magnetic thin wire 5 shown in FIG. 5, two data “0” and “1” having a predetermined unit length Lb are continuously recorded. The “length” refers to the length (longitudinal direction) of the magnetic thin wire 5 unless otherwise specified, and this direction is described as the front-rear direction (right and left in FIG. 5). At this time, as shown in FIG. 5A, the magnetic domain D0, which is the data area in which the data “0” is recorded, and the subsequent data “1” (on the left side in FIG. 5) are recorded. There is a magnetic domain D1, which is a data area that has been set.

In the magnetic material, domain walls are generated in adjacent magnetic sections such as between the magnetic domains D0 and D1 so as to divide both magnetic domains. In other words, each magnetic domain is sandwiched between domain walls, and in the magnetic wire 5, the domain D0 is formed between the domain walls DW1-DW2, and the domain D1 is formed between the domain walls DW2-DW3. Inside the domain wall, the magnetization gradually changes, that is, rotates from the magnetization direction of one of the two magnetic domains sandwiching it to the magnetization direction of the other magnetic domain. In general, the length (thickness) of the domain wall depends on the width and thickness of the magnetic wire and the data length, but is about 5 to 100 nm and is extremely short (narrow) with respect to the magnetic domain. Shows the domain wall schematically enlarged. Accordingly, the lengths L _D0 and L _D1 of the magnetic domains D0 and D1 are shown as having no domain walls DW1, DW2 and DW3 (which is 0). In FIG. 5A, L _D0 = L _D1 = Lb.

The cross-sectional area of the magnetic wire 5 is S, the saturation magnetization is Ms, and the magnetic moment of the data region in which the data “0” and “1” of the unit length Lb are recorded, that is, the magnetic domains D0 and D1, is represented by + m and −m. Then, the relationship of the following formula (1) is established. In the magnetic material, the magnetic moment of each magnetic domain is preserved in both direction and size unless a magnetic field is applied from the outside of the magnetic material.

  As shown in FIG. 5B, current is supplied to the magnetic thin wire 5 in the backward direction (left direction in FIG. 5) by the electrodes 61 and 62 at both ends, and electrons are injected in the forward direction. Specifically, for example, in the magnetic reproducing apparatus 1 (see FIG. 2), the electrode 61 is set to “−” and the electrode 62 is set to “+”, whereby the current I is supplied from the electrode 62 to the electrode 61. Then, under the influence of the electron spin torque, the domain walls DW1, DW2, and DW3 move forward (right in FIG. 5), respectively, and change from the state shown in FIG. 5 (a) to the state shown in FIG. 5 (b). (Hereinafter, such a change is represented as FIG. 5 (a) → (b)). Accordingly, the magnetic domains D0 and D1 sandwiched between these domain walls DW1, DW2, and DW3 also move forward.

The current density of the supplied current I is J, and the moving distance of the domain wall when the current I is supplied for a unit time Δt is Δl. At this time, the change amount Δm (= | −m − (+ m) |) of the magnetic moment before and after the domain wall DW2 between the magnetic domains D0 and D1 moves is reversed because the magnetization direction is reversed because the domain wall DW2 has passed. 2).

On the other hand, the number n _e of electrons injected into the magnetic nanowire 5 by the unit time Δt supply current I can be represented by the following formula (3). In the equation, e is an elementary charge (e≈1.6 × 10 ⁻¹⁹ C).

From the equation (3), the change Δm of the magnetic moment due to the current supply can be expressed by the following equation (4) because the magnetization direction is reversed when the spin polarizability of the magnetic wire 5 is p. Μ _B in the equation is a Bohr magneton.

(2 μ _B / e) is a constant, and the spin polarizability p and the cross-sectional area S are determined by the material, width and thickness of the magnetic wire 5, respectively. Therefore, the change amount Δm of the magnetic moment in the magnetic wire 5 depends on the current density J, and the moving distance Δl of the domain wall DW2 also depends on the current density J from the equation (2).

Further, the moving speed (domain wall speed) v of the domain wall DW2 can be represented by (Δl / Δt). Here, when the relationship of the following equation (5) is established from the equations (2) and (4), and this is further transformed, the domain wall velocity v can be expressed by the following equation (6).

From equation (6), the moving speed v of the domain wall DW2 when the constant current I is supplied to the magnetic wire 5 is constant. Therefore, as shown in FIGS. 5A to 5B, the domain walls DW2 and DW3 move at the same domain wall speed v, that is, the movement distances are the same. Therefore, the domain D1 sandwiched between these domain walls DW2 and DW3 is also , The same distance is moved, and the length L _D1 does not change (L _D1 = Lb). In this way, in the magnetic wire 5 having a uniform width and thickness, all the magnetic domains as the data area can be moved by an arbitrary distance by controlling the time for supplying a constant current. It is possible (see Non-Patent Document 1).

Next, the movement of the domain wall DW1 in FIGS. 5A to 5B will be described. In FIG. 5A, the magnetic wire 5 has a low saturation magnetization that is relatively lower than the saturation magnetization Ms of the other region in the magnetic wire 5 in the domain wall moving direction front of the magnetic domain D0 (hereinafter simply referred to as the front). An Ms region 5e is provided. Specifically, the saturation magnetization of the low Ms region 5e is (Ms / α). Α is a constant (α> 1). 5A to 5B, the domain wall DW1 moves in the low Ms region 5e. From the above equation (6), the domain wall velocity due to the constant current supply in the magnetic material is inversely proportional to the saturation magnetization of the magnetic material. Therefore, the moving speed of the domain wall DW1 in the low Ms region 5e can be expressed by (α × v), which is α times faster than the moving speed v of the domain walls DW2 and DW3 that are simultaneously moving in the magnetic wire 5. The moving speed of the domain wall DW1 when moving in the low Ms region 5e is set to v _High (= α × v).

In FIG. 5 (a) → (b), in the magnetic domain D0 sandwiched between the domain walls DW1 and DW2, the rear domain wall DW2 moves at the domain wall speed v, whereas the front domain wall DW1 has a domain wall speed higher than that. Since it moves at v _High , its length L _D0 extends while moving together. When the current I is further supplied, as shown in FIGS. 5B to 5C, the domain walls DW1, DW2, and DW3 move further forward, and the difference in the movement distance between the domain walls DW1, DW2 increases, and the domain D0 The length L _D0 is extended. In FIG. 5 (c), the domain wall DW2 behind the magnetic domain D0 also reaches the low Ms region 5e. Therefore, when the current I is further supplied, as shown in FIGS. 5 (c) → (d), the domain wall DW1 , DW2 both move in the low Ms region 5e at the domain wall velocity v _High , so the length L _D0 of the magnetic domain D0 does not extend any further.

The length L _D0 of the magnetic domain D0 when the whole reaches the low Ms region 5e is as follows. From the beginning of the magnetic domain D0, that is, the domain wall DW1 begins to enter the low Ms region 5e (see FIG. 5A), to the end of the magnetic domain D0, that is, the domain wall DW2 enters the low Ms region 5e (FIG. 5C). The movement distance of the domain wall DW2 until the reference) is the initial length L _D0 = Lb of the magnetic domain D0. On the other hand, the movement distance of the domain wall DW1 during the same period is (α × Lb) since the movement speed v _High is α times the movement speed v of the domain wall DW2. Therefore, when the entire magnetic domain D0 reaches the low Ms region 5e, the amount of change in the length L _D0 from when the magnetic domain D0 is outside the low Ms region 5e depends on the movement of the domain walls DW1 and DW2. Since the distance is different (α × Lb−Lb), the length of the magnetic domain D0 in the low Ms region 5e is (α × Lb) (L _D0 = α × Lb). As another idea, as described above, since the magnetic moment m of the magnetic domain D0 is preserved and the cross-sectional area S is constant, the length L _D0 is inversely proportional to the saturation magnetization from the equation (1). Α times (L _D0 = α × Lb).

Since the domain wall DW1 has retreated from the low Ms region 5e at the stage of FIG. 5D, when the current I is further supplied, the domain wall DW1 has a domain wall velocity v as shown in FIGS. 5D to 5E. On the other hand, since the domain wall DW2 continues to move at the domain wall speed v _High , the magnetic domain D0 starts to contract. And further supplies the current I, as shown in FIG. 5 (f), the magnetic domain D0 its entirety domain wall DW2 be exited from the low Ms region 5e reaches the outside of the low Ms region 5e, the length L _D0 Is restored (L _D0 = Lb).

The length L _D1 of the magnetic domain D1 also changes. In FIGS. 5 (c) → (d) → (e), the front domain wall DW2 has a domain wall velocity v _High and the rear domain wall DW3 has a domain wall velocity v. Since each moves, the length L _D1 expands, and in FIG. 5E, the entire magnetic domain D1 reaches the low Ms region 5e and becomes the maximum (L _D1 = α × Lb). When the current I is further supplied, the magnetic domain D1 reaches the outside of the low Ms region 5e similarly to the magnetic domain D0, and the length L _D1 is restored (not shown).

  As described above, even if the magnetic thin wire 5 is provided with regions having different saturation magnetization in the region partitioned in the thin wire direction, the moving speed of the domain wall changes according to the change of the saturation magnetization, and the magnetic domain moves in the thin wire direction. In order to expand and contract, the domain wall maintains the shift movement as a whole of the single magnetic wire 5. Therefore, the movement speed of the data area at a specific position of the magnetic wire 5 by constant current supply is constant. Further, by providing a region (low Ms region 5e) having a relatively low saturation magnetization in a part of the magnetic thin wire 5 that is partitioned in the thin wire direction, the magnetic domain, that is, the data region is limited to the time when this region is reached. Can be stretched and returned to its original length when exiting this area.

As described above, in the magnetic wire 5, the magnetic domain, that is, the data area moves along the thin wire direction when current is supplied to the magnetic wire 5, so that the data continuously stored in the thin wire direction is The reproduction area 5r is switched in order. And it is possible to move an arbitrary distance by controlling the time for supplying the current. Therefore, a pulse current having a pulse width t _H (t _H = Lb / v) as a time for moving the distance of the unit length Lb outside the low Ms region 5e (a region having the saturation magnetization Ms) as the magnetic wire 5 The data area can be moved intermittently in increments of unit length Lb, that is, one data at a time. When the current in the pulse current stops, the data area that is stationary in the low Ms area 5e is temporarily expanded. Therefore, by forming the low Ms region 5e in the magnetic thin wire 5 and further providing the reproduction region 5r in the low Ms region 5e as a region for reproducing the data stored in the region, in the reproduction region 5r, the data The area can be temporarily extended to a size (magnetic domain length) that can be adapted to a reproduction method as described later. Then, the low Ms region 5e is formed so that the data region that has reached the reproduction region 5r extends to a length longer than the reproduction region 5r (see FIGS. 6A and 6B).

The current stop time t _L in the pulse current may be set to be equal to or longer than the time required to detect the magnetization direction in accordance with the reproduction method. The magnitude of the current | I | is set based on the width and thickness of the magnetic wire 5 and the reproduction speed because the domain wall velocity v increases as the current density J per cross-sectional area S of the magnetic wire 5 increases. In order to supply current in a constant direction opposite to the domain wall moving direction, either positive or negative direct current is used. Specifically, it is preferable to adjust the current density J: 10 ⁵ to 10 ¹³ A / m ² , the pulse width t _H : 1 ps to 10 μs, and the stop time t _L : 10 ps to 10 μs. In addition, in order to move the data area by one data length Lb, the current is intermittently moved by stopping the current by not only supplying the current once per time of the pulse width t _H but also by supplying the current twice or more times. You may let them.

  As described above, the magnetic recording medium according to the present invention forms a low Ms region having a low saturation magnetization locally in a magnetic thin wire by ion implantation, thereby temporarily extending the data region reaching the region. The data can be made reproducible. Therefore, outside the low Ms region, the data region can be compressed beyond the reproducible length, for example, compressed to the limit due to magnetic characteristics, etc., and stored in the magnetic wire, and the magnetic disk (magnetic recording medium) Can be increased in capacity.

Even when data is recorded on the magnetic recording medium, data can be continuously recorded in the direction of the thin wire of the magnetic wire by supplying a pulse current to the magnetic wire in the direction of the thin wire, as in reproduction. As shown in FIGS. 3A and 3B, the domain wall DW is generated on the magnetic wire 5 by recording data “0” different from the initial data “1” in the recording area 5 w of the magnetic wire 5. Therefore, after recording, the current is supplied for the duration of the pulse width t _H , thereby shifting the distance of the unit length Lb together with the domain wall DW in the area where the data “0” is recorded, Can reach the recording area 5w. In the data recording, the current stop time t _L in the pulse current may be set to be equal to or longer than the time required for magnetization (magnetization reversal) in the desired direction of the magnetic wire 5 corresponding to the recording method. Here, the recording area 5w is longer in the fine line direction than the unit length Lb. Accordingly, a part of the data area (magnetic domain) in which data is recorded immediately before remains in the recording area 5w. By recording the next data in the recording area 5w, the length of the data area becomes the unit length Lb. Shortened to Thus, regardless of the length of the recording area 5w, a data area to be recorded is stored in the unit length Lb which corresponds to the pulse width t _H of the pulse current. Also, when recording data, the unit length Lb may be moved by supplying the current twice or more times.

  Next, an embodiment of a magnetic reproducing apparatus and a magnetic reproducing method for reproducing data recorded on the magnetic recording medium according to the present invention will be described.

[Magnetic reproduction device: magneto-optical method]
A magnetic reproducing apparatus according to an embodiment of the present invention will be described with reference to FIG. The magnetic reproducing apparatus 1 is an apparatus that mounts a magnetic disk (magnetic recording medium) 50 (see FIG. 1) according to the present invention and reproduces data recorded on the magnetic disk 50 by a magneto-optical method. The magnetic reproducing apparatus 1 further includes an optical system (irradiation means) 10 that irradiates incident light onto a predetermined region on the surface (upper surface) of the magnetic disk 50, and the polarization direction of the emitted light that is reflected by the magnetic disk 50. A detection unit (light detection unit) 20 for detecting the current, a current supply unit (current supply unit) 30 for supplying a pulse current to the track (magnetic thin wire) 5 of the magnetic disk 50, and a control unit (selection unit, Data reproducing means) 40.

  The magnetic reproducing apparatus 1 makes light incident on the track 5 of the magnetic disk 50 in the same way as the reproduction of the magnetic disk (magneto-optical disk) by the current magneto-optical system, and this light is magnetized in the direction of magnetization of the track 5 by the magneto-optic effect. The data is reproduced by detecting the direction of the polarization of the light (outgoing light) reflected and emitted by rotating (rotating) the direction of the polarization correspondingly. Therefore, the optical system 10 and the detection unit 20 can have the same configuration as that applied to the current magneto-optical magnetic reproducing apparatus. However, unlike the current magnetic reproducing apparatus, the magnetic reproducing apparatus 1 does not require a magnetic disk rotational drive mechanism such as a spindle motor, and is provided with a current supply unit 30 instead. Further, in the magnetic reproducing apparatus 1, the magnetic disk 50 may be replaceable as in a current DVD (Digital Versatile Disc) reproducing apparatus, or may be built in as in an existing HDD apparatus. In the present embodiment, the surface (upper surface) of the magnetic disk 50 is the light incident / emission surface, and the upper side is the light incident / emission direction.

  The optical system 10 includes a laser irradiation device 11 and one or more lenses (in FIG. 2, a lens group 12 including two lenses) that are optically connected to the laser irradiation device 11 and reduce or enlarge the laser light to a predetermined spot diameter. ), A polarizer (not shown) for blocking polarized light in a specific direction, a half mirror 13 for further transmitting light transmitted through the polarizer, a mirror 14 for irradiating a desired position on the surface of the magnetic disk 50, and It is composed of an objective lens 15 for narrowing a light incident region (laser spot). On the other hand, the detection unit 20 includes an imaging device (not shown) that images emitted light reflected by the magnetic disk 50. The light emitted from the magnetic disk 50 is reflected by the half mirror 13, travels through an optical path different from the incident light, and enters the detection unit 20. The laser irradiation device 11 is a device that irradiates laser light having a predetermined wavelength (for example, 500 nm). The mirror 14 and the objective lens 15 are movable along the radial direction of the magnetic disk 50, and move the laser spot onto the reproduction area 5r of the track 5 on which data to be reproduced is recorded. The reproduction area 5r is a predetermined position for detecting the magnetization direction of the track (magnetic thin wire) 5, that is, a predetermined position area where light is incident on the magnetic disk 50 mounted or built in. As described in the embodiment of the magnetic recording medium (magnetic disk) 50, the reproduction area 5r is set at a position included in the low Ms area 5e (see FIGS. 1 and 6). As the imaging device of the detection unit 20, a light detector such as a CCD camera or a photodiode that can detect light and has a time resolution faster than the reproduction speed of one data can be applied.

  The current supply unit 30 is connected to electrodes 61 and 62 (see FIG. 1) provided at both ends of each magnetic wire (track) 5 of the magnetic disk 50 to supply a pulse current to the magnetic wire 5 in the direction of the wire. The current supply unit 30 includes, for example, terminals connected to the electrodes 61 and 62 of all the magnetic thin wires 5 of the magnetic disk 50 and switches for each terminal, and is limited to the magnetic thin wires 5 that supply a pulse current. Can be configured to be connected (not shown). Due to this pulse current, the magnetic domain, which is the data region, moves intermittently along the length direction of the magnetic wire 5 along the magnetic wall in the magnetic wire 5. Areas enter in order and exit. Therefore, the magnetic reproducing apparatus 1 does not require a mechanism for rotationally driving the magnetic disk 50 itself, and the optical system 10 also fixes a laser spot on one magnetic thin line (track) 5 at one place, that is, on the reproducing area 5r. Can be irradiated. The control unit 40 selects the magnetic thin wire 5 for reproducing data from the magnetic disk 50, instructs the magnetic thin wire 5 to supply a pulse current to the current supply unit 30 according to the selected magnetic thin wire 5, and moves the mirror 14 and the like of the optical system 10 Let Further, the control unit 40 causes the detection unit 20 to detect the polarization direction of the emitted light in accordance with the period of the pulse current supplied by the current supply unit 30, and reproduces the polarization direction as data.

[Magnetic reproduction method]
Next, a method for reproducing a magnetic disk by the magnetic reproducing apparatus (see FIG. 2) according to the present invention will be described. In the present embodiment, a description will be given assuming that an arbitrary track (magnetic thin line) is reproduced. In the magnetic reproducing method according to the present invention, the selection step and the reproduction step are repeated as necessary, and the direction of polarization of light emitted from the magnetic wire is detected by the magneto-optical method, and the direction of polarization is reproduced as data. .

(Selection process)
In the selection step, the control unit 40 selects one track 5 in which data to be reproduced in the subsequent reproduction step is stored from the tracks (magnetic thin lines) 5, 5,. For example, if the selected track 5 is the first selection step, the outermost track 5 of the magnetic disk 50 is selected, and if it is the second time or later, the track 5 reproduced in the immediately preceding reproduction step is selected. It may be set to select one on the inner peripheral side adjacent to. Alternatively, it may be set so that an arbitrary track 5 can be selected by an operation from the outside of the magnetic reproducing apparatus 1. When the track 5 from which data is to be reproduced is selected in the selection step, the control unit 40 moves the mirror 14 and the objective lens 15 of the optical system 10 so that the reproduction spot 5r of the track 5 is irradiated with the laser spot. To. Further, the control unit 40 connects the current supply unit 30 to the electrodes 61 and 62 of the track 5 so as to supply a pulse current to the track 5, and proceeds to the reproduction process.

(Regeneration process)
In the reproduction process, the current supply unit 30 supplies a pulse current to the track (magnetic thin line) 5 of the magnetic disk 50 selected in the selection process in the direction of the thin line, and moves the data area intermittently with the domain wall (current). Supply process), the reproduction area 5r of this track 5 The laser beam is irradiated as polarized light in one direction (irradiation process). Then, the detection unit 20 detects the polarization direction of the outgoing light reflected by the track 5 (light detection process), and the control unit 40 determines whether the polarization direction of the outgoing light detected when the current in the pulse current is stopped is “0” or The data is converted into “1” data and reproduced (data reproduction process).

(Regeneration process: current supply processing)
The current supply unit 30 is connected to the electrodes 61 and 62 of the track 5, and supplies either positive or negative DC constant current and pulse current having a pulse period to the track 5. Due to this pulse current, the data area in the track 5 shifts and shifts intermittently. The specification of the pulse current (pulse period, etc.), the movement of the data area and the expansion / contraction of the length of the data area (magnetic domain) were explained as the shift movement of the domain wall in the magnetic wire 5 of the magnetic disk 50 (see FIG. 5). Since it is as it is, description is abbreviate | omitted. As shown in FIG. 6A, the m-th data area that has reached the reproduction area 5r of the track 5 when the current in the pulse current is stopped by the shift movement is the unit length outside the low Ms area 5e as described above. Extends α-fold than Lb.

(Regeneration process: irradiation treatment)
In the optical system 10, the laser light emitted from the laser irradiation device 11 becomes parallel light having a predetermined spot diameter by the lens group 12, passes through a polarizer (not shown), and becomes incident light of light of one polarization component. . Further, the incident light passes through the half mirror 13, travels straight, is reflected by the mirror 14, collected by the objective lens 15, and directed toward the reproduction area 5 r of the selected track (magnetic thin wire) 5. Irradiated. The incident light is reduced in diameter to the size of the reproduction region 5r, is incident on the reproduction region 5r of the magnetic wire 5, is reflected, is transmitted through the objective lens 15 again, and is emitted to become output light. Therefore, as shown in FIG. 6A, in the present embodiment, the reproduction region 5r is set to a length in the thin line direction that is equal to or larger than the spot diameter of laser light (incident light) that can be reduced in diameter by the objective lens 15.

(Regeneration process: light detection process)
The outgoing light travels in the opposite direction along the same optical path as the incident light and is reflected by the mirror 14. However, the outgoing light is also reflected by the half mirror 13 and enters the detection unit 20. When the outgoing light is reflected by the magnetic wire 5, the direction of polarization is rotated (rotated) by the magneto-optic Kerr effect. Further, the rotations are opposite to each other depending on whether the magnetization of the reflected (irradiated) region of the magnetic wire 5 is upward or downward. That is, the direction of polarization of the emitted light differs depending on the magnetization direction of the magnetic wire 5 in the reproduction region 5r. Therefore, by detecting the polarization direction of the emitted light by the detection unit 20, the data area (the m-th data area in FIG. 6A) reaching the reproduction area 5r of the magnetic wire 5 at the time of reflection is obtained. It is possible to determine whether the magnetic domain is in the lower direction or the upper direction, ie, “0” or “1”. As a method for detecting the direction of polarized light, a differential method applied to reproduction by a known magneto-optical method can be mentioned. Further, a polarizer (not shown) different from that provided in the optical system 10 is disposed on the optical path of the emitted light (for example, between the half mirror 13 and the detection unit 20), and the optical rotation is performed in one direction. It may be configured such that only the emitted light is blocked by the polarizer and does not enter the detection unit 20.

(Reproduction process: Data reproduction process)
The detection unit 20 captures (detects) the irradiated outgoing light by photoelectric conversion at the timing when the data region is stationary in the magnetic wire 5, that is, when the current supply unit 30 stops the current in the pulse current. At this time, the control unit 40 controls the current supply unit 30 and the detection unit 20 to match the timing of imaging by the detection unit 20. The control unit 40 recognizes the reproduction data as “0” or “1” depending on whether the detection unit 20 captures light or not, and converts it into a signal, and converts the obtained signal to the outside of the magnetic reproduction device 1. To be reproduced as information such as video and audio.

  As described above, the magnetic reproducing device 1 moves the data area in the track (magnetic thin wire) 5 while detecting light, and after reproducing all the data stored in the track 5, supplies the pulse current. Is stopped and the reproduction process is completed, and a new track 5 is selected again in the selection process. Further, when the reproduction of data of all the tracks 5 on the magnetic disk 50 is completed, the reproduction of the magnetic disk 50 is completed.

  According to the magnetic reproducing method according to the present invention, even a magnetic recording medium in which data is stored in a magnetic wire after being compressed to be smaller than the spot diameter of the laser beam reaches the reproducing area provided in the low saturation magnetization area. Since the existing data area is expanded, the data on the magnetic recording medium can be reproduced by the current magneto-optical method.

(Modification of magnetic reproducing device)
In the magnetic reproducing apparatus 1, data is reproduced by selecting one track 5 from the magnetic disk 50, but one laser including a reproducing area 5 r of two or more adjacent tracks 5 on the magnetic disk 50. By irradiating the spot, data can be reproduced in parallel for these tracks 5. Here, as a modification, a magnetic reproducing apparatus that selects four adjacent tracks 5 from the magnetic disk 50 and simultaneously reproduces these data will be described with reference to FIG. In FIG. 7, in order to easily identify the respective optical paths of incident light and outgoing light (reflected light), the laser light is shown to enter and exit with an inclination, and mirrors and the like are omitted. Similar to the magnetic reproducing apparatus 1 shown in FIG. 2, the magnetic reproducing apparatus includes an optical system 10, a detection unit 20, a current supply unit 30, and a control unit 40. The configuration of the magnetic disk 50 is the same as that described above (see FIG. 1), but a series of data is recorded in parallel on each of the four tracks 5. In the present modification, in the optical system 10 (see FIG. 2), the objective lens 15 is not used, and the lens group 12 uses parallel light with a spot diameter that irradiates the magnetic disk 50 with laser light.

  In the magnetic reproducing method of this modification, the control unit 40 selects four adjacent tracks 5 in the selection process, and the current supply unit 30 moves these tracks 5 in the data area at the same timing in the current supply process. Then, the laser spot is irradiated from the optical system 10 to the area including the reproduction area 5r of the four tracks 5 by the irradiation process. The reflected light (emitted light) of the irradiated laser beam (parallel light) on the magnetic disk 50 includes data in the data areas of the four tracks 5. However, since the laser spot is circular, the emitted light includes data in the data area before and after the reproduction area 5r in each track 5. Therefore, the detection unit 20 detects the light emitted from the reproduction region 5r by dividing the region where the light emitted from the magnetic disk 50 is incident (detection region in FIG. 7). To signal. According to such a method, since it is sufficient to irradiate two or more adjacent tracks 5 with one laser beam, the magnetic reproducing apparatus only needs to have one optical system 10.

  Further, if the current supply unit 30 is configured to be able to supply an independent pulse current to each selected track 5, the magnetic disk 50 according to the present embodiment has each data area for two or more different tracks 5. Since the moving distance and the moving speed of the tracks are individually controlled, even if there is a deviation in the data length between the tracks 5 to be reproduced in parallel, the reproduction can be performed at the same timing. If two or more tracks 5 are reproduced in parallel as described above, it is possible to reproduce even higher density data without simultaneously operating a large number of magnetic reproducing apparatuses.

[Magnetic reproduction device: Magnetic system]
A magnetic reproducing apparatus according to another embodiment of the present invention will be described. The same elements as those in the magneto-optical magnetic reproducing apparatus 1 (see FIG. 2) are denoted by the same reference numerals, and description thereof is omitted. A magnetic reproducing device (not shown) includes a magnetic disk (magnetic recording medium) 50, and a detection unit (magnetic detection means) 20A (FIG. 6 (FIG. b)), a current supply unit (current supply unit) 30 for supplying a pulse current to the track 5 of the magnetic disk 50, and a control unit (selection unit, data reproduction unit) 40 for controlling them.

  In the magnetic reproducing apparatus, the magnetic head 21 of the track 5 of the magnetic disk 50 is detected by the detection unit 20A including the magnetic head 21 made of a magnetoresistive effect element such as a GMR element or a TMR element, as in the current magnetic disk reproduction. The magnetization direction in the opposing region is detected. As shown in FIG. 6B, the detection unit 20 </ b> A further includes a power source that supplies current to the magnetic head 21 by connecting to a pair of electrodes (not shown) of the magnetic head 21, and an ammeter. The magnetic head 21 is supported by an arm (not shown) and is movably provided so as to be opposed to each one of all the tracks 5 of the magnetic disk 50, that is, the reproduction area 5r. The position of the reproduction area 5r on the track 5 is as described in the magneto-optical reproduction by the magnetic reproducing apparatus 1. Therefore, in the magnetic reproducing apparatus, when the reproducing area 5r is arranged on the radius of a circle in a plan view like the magnetic disk 50 shown in FIG. 2, the magnetic head 21 is placed in a linear direction along the radius. It only needs to be movable. As described above, the magnetic reproducing apparatus has the same configuration as that of the current magnetic reproducing apparatus except that the magnetic reproducing apparatus includes the current supply unit 30 instead of the magnetic disk rotation driving mechanism. A magnetic recording / reproducing apparatus capable of recording data by further providing writing means such as a recording magnetic head 22 (see FIG. 3A) composed of magnetic poles together with the magnetic head 21 may be used.

[Magnetic reproduction method]
A method for reproducing a magnetic disk by the magnetic reproducing apparatus according to the present invention will be described. In the present embodiment, the selection process and the reproduction process are repeated as necessary in the same manner as in the magnetic disk reproduction method by the magneto-optical magnetic reproducing apparatus, and the magnetization direction of the magnetic wire is detected by the magnetic system.

(Selection process)
In the selection step, the control unit 40 selects one track 5 from the tracks (magnetic thin wires) 5, 5,. In the present embodiment, when the track 5 is selected, the control unit 40 drives the arm to move the magnetic head 21 of the detection unit 20A to a position facing the reproduction area 5r of the track 5. Then, the control unit 40 connects the current supply unit 30 to the electrodes 61 and 62 of the track 5 so as to supply a pulse current to the track 5, and shifts to the reproduction process.

(Regeneration process)
In the reproduction process, the current supply unit 30 supplies a pulse current to the track (magnetic thin line) 5 of the magnetic disk 50 selected in the selection process in the direction of the thin line, and moves the data area intermittently with the domain wall (current). Supply process), the detection unit 20A detects the magnetization direction in the reproduction region 5r of the track 5 (magnetic detection process), and the control unit 40 sets the magnetization direction detected when the current in the pulse current is stopped to “0” or “1”. The data is converted and reproduced (data reproduction process). Therefore, the current supply process is performed in the same manner as the magnetic reproduction method using the magneto-optical method, while the irradiation process is not performed, and the magnetic detection process is performed instead of the photodetection process. Since the current supply process is as described above, the description thereof is omitted. Hereinafter, the magnetic detection process and the data reproduction process will be described.

(Reproduction process: Magnetic detection processing)
As in the current magnetic disk, as shown in FIG. 6B, as the magnetic head 21 of the detection unit 20A, for example, a GMR element leaks from the data area (magnetic domain) of the magnetic thin wire 5 in the opposing reproduction area 5r. As a result, the resistance of the GMR element is changed. The current value is measured by an ammeter provided in the detection unit 20A, and the direction of the leakage magnetic field is determined based on, for example, a preset threshold value to detect the magnetization direction of the magnetic wire 5 in the reproduction region 5r. Therefore, the reproducing area 5r is set to a length in the direction of a thin line where a leakage magnetic field that can be detected by the magnetic head 21 (GMR element) is obtained. Unlike the current magnetic disk, the magnetic disk 50 according to the present invention does not rotate at a high speed unlike the current magnetic disk. Therefore, the magnetic head 21 is not lifted from the magnetic disk 50 and is in contact with the surface. It is possible to detect a leakage magnetic field.

(Reproduction process: Data reproduction process)
Similar to the data reproduction process in the magnetic reproduction method using the magneto-optical method, the control unit 40 recognizes the reproduction data as “0” or “1” from the detected magnetization direction when the current in the pulse current stops, and converts it into a signal. .

  As described above, also in the reproduction by the magnetic method, the magnetization direction is detected from the reproduction region 5r as a predetermined region while moving the data region in the track (magnetic thin wire) 5 similarly to the magneto-optical method. When all the data stored in the track 5 is reproduced, the supply of the pulse current is stopped, the reproduction process is completed, and a new track 5 is selected again in the selection process.

  The magnetic reproducing method according to the present invention is a magnetic recording medium in which data is stored in a magnetic thin line by compressing it smaller than a magnetic domain having a magnitude capable of obtaining a leakage magnetic field that can be detected by a magnetoresistive effect element as a magnetic head. However, since the data area reaching the reproduction area provided in the low saturation magnetization area is expanded, the data of the magnetic recording medium can be obtained by the magnetic method without further miniaturization of the magnetoresistive effect element such as the GMR element. Can be played.

(Modification of magnetic reproducing device)
In the present embodiment, one track 5 is selected from the magnetic disk 50 and data is reproduced. However, in the magnetic type magnetic reproducing apparatus, for example, in the reproducing area 5r of two different tracks 5 and 5 If the detection unit 20A is configured to include two magnetic heads (magnetoresistance effect elements) 21 and 21 that can be opposed to each other and can measure the current values of the respective magnetic heads 21 in parallel, the two tracks 5 are provided. , 5 can be reproduced in parallel (not shown).

  As described above, in the reproduction of the magnetic recording medium according to the present invention, the low saturation magnetization region formed on the magnetic thin wire of the magnetic recording medium is designated as a region for detecting the direction of magnetization, thereby forming a magnetic domain. Since the recorded data expands in the thin line direction in the area, the compressed and stored data can be expanded to a reproducible size and reproduced accurately regardless of the reproduction method.

  The embodiments for carrying out the magnetic recording medium, the magnetic reproducing apparatus and the magnetic reproducing method of the present invention have been described above, but the present invention is not limited to these embodiments, and is shown in the claims. Various changes can be made within a range.

1 Magnetic reproduction device 10 Optical system (irradiation means)
20 Detection unit (light detection means)
20A detector (magnetic detection means)
30 Current supply section (current supply means)
40 Control unit (selection means, data reproduction means)
50 Magnetic disk (magnetic recording medium)
5 Magnetic wire (track)
5e Low Ms region (low saturation magnetization region)
5r Playback area 5w Recording area

Claims (7)

One or more magnetic thin wires formed by forming a magnetic material on a substrate in a thin line shape are provided, and binary data is continuously input to the magnetic thin wire as one of two different magnetizations in the thin wire direction of the magnetic thin wire. A pair of electrodes is connected to both ends of the magnetic thin wire and a pulse current is supplied in the direction of the thin wire by connecting the magnetic thin wire to the magnetic domain formed by recording one of the binary data and the 2 A magnetic recording medium in which a domain wall generated between a magnetic domain formed by recording the other data of values is intermittently moved in a thin line direction,
The magnetic fine wire includes a low saturation magnetization region in a region partitioned in the thin wire direction as a region for detecting the magnetization direction,
The magnetic thin wire is formed in advance in the low saturation magnetization region by lowering the saturation magnetization by ion implantation into the low saturation magnetization region,
The magnetic recording medium is characterized in that the length of the magnetic domain extends only when the magnetic domain reaches the low saturation magnetization region.   2. The substrate according to claim 1, wherein the substrate has a disk shape, and the magnetic fine wire is formed on the substrate in a concentric shape with a shape lacking a part of an annulus in plan view. Magnetic recording media.   The magnetic recording medium according to claim 1, wherein the magnetic wire is made of a magneto-optical material. A magnetic reproducing apparatus for reproducing binary data recorded on the magnetic recording medium according to claim 1 or 2,
Selecting means for selecting one or more magnetic wires from the magnetic recording medium;
Current supply means for supplying a pulse current in the direction of the thin wire connected to both ends of the magnetic fine wire to the magnetic thin wire selected by the selection means, and intermittently moving the domain wall generated in the magnetic thin wire;
Magnetic detection means for detecting a magnetization direction in the low saturation magnetization region of the magnetic wire selected by the selection means;
Magnetic reproduction comprising: data reproduction means for reproducing, as data, the magnetization direction detected by the magnetic detection means when the current in the pulse current is stopped in synchronization with the pulse current supplied by the current supply means apparatus. A magnetic reproducing apparatus for reproducing binary data recorded on the magnetic recording medium according to claim 3,
Selecting means for selecting one or more magnetic wires from the magnetic recording medium;
Current supply means for supplying a pulse current in the direction of the thin wire connected to both ends of the magnetic fine wire to the magnetic thin wire selected by the selection means, and intermittently moving the domain wall generated in the magnetic thin wire;
Irradiating means for causing light to enter the low saturation magnetization region of the magnetic wire selected by the selecting means;
A light detecting means for detecting the direction of polarization of light incident from the irradiation means and emitted from the magnetic wire;
Data reproducing means for reproducing, as data, the polarization direction of the light detected by the light detection means when the current in the pulse current is stopped in synchronization with the pulse current supplied by the current supply means; Magnetic reproducing device. A magnetic reproducing method for reproducing binary data recorded on the magnetic recording medium according to claim 1 or 2,
A selection step of selecting one or more magnetic wires from the magnetic recording medium;
A reproducing step of reproducing the data recorded on the selected magnetic wire of the magnetic recording medium,
In the reproducing step, a current supply process for supplying a pulse current for intermittently moving a magnetic domain wall generated in the magnetic wire to the magnetic wire in the direction of the wire;
A magnetic detection process for detecting a magnetization direction in the low saturation magnetization region of the magnetic wire;
In synchronization with the pulse current supplied in the current supply process, a data reproduction process for reproducing the magnetization direction detected in the magnetic detection process when the current in the pulse current is stopped as data is performed. Magnetic reproduction method. A magnetic reproducing method for reproducing binary data recorded on the magnetic recording medium according to claim 3, comprising:
A selection step of selecting one or more magnetic wires from the magnetic recording medium;
A reproducing step of reproducing the data recorded on the selected magnetic wire of the magnetic recording medium,
In the reproducing step, a current supply process for supplying a pulse current for intermittently moving a magnetic domain wall generated in the magnetic wire to the magnetic wire in the direction of the wire;
An irradiation process in which light is incident on the low saturation magnetization region of the magnetic wire;
A light detection process for detecting the direction of polarization of light incident on the irradiation process and emitted from the magnetic wire;
In synchronization with the pulse current supplied in the current supply process, a data reproduction process for reproducing the polarization direction of the light detected in the light detection process as data when the current in the pulse current is stopped is performed. A magnetic reproducing method.

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