JP6450390B2 - Storage medium, recording device, data processing device, data recording device, and communication device - Google Patents

Description

  The present invention relates to a storage medium using a thin-layered magnetic storage medium capable of generating skyrmions, a recording apparatus using the storage medium, and a data processing apparatus, a data recording apparatus, and a communication apparatus equipped with the recording apparatus. .

  Magnetic elements that use the magnetic moment of a magnetic material as digital information are known. The magnetic element has a nanoscale magnetic structure that functions as an element of a non-volatile memory that does not require power when holding information. The magnetic structure is expected to be applied as a large-capacity information storage medium because of its advantages such as ultra-high density due to the nanoscale magnetic structure, and its importance is increasing as a memory device of an electronic device.

  I don't know where the demand for the storage capacity of a hard disk as a large-capacity recording device is limited. From hundreds of gigabits to several terabits, the storage capacity of hard disks is increasing. At present, the size of the magnetic domain that bears the storage bit of the hard disk is becoming smaller to several hundred nm level.

  Under such circumstances, the inventors of the present application have found a material having a skyrmion magnetic structure in a chiral magnetic body under an external magnetic field, and proposed a storage medium using this magnetic structure (Patent Document 1).

  The skyrmion has a spiral magnetic structure having a magnetic moment antiparallel to the magnetic field applied to the central portion and having a magnetic moment parallel to the applied magnetic field in the peripheral portion.

  Skyrmions have a nanoscale-sized magnetic structure with a diameter of 1 to 100 nm. Therefore, it is expected to be applied as a large-capacity storage medium that can store a large amount of bit information in an extremely fine manner. Skyrmions are also magnetic structures that can be generated and erased by a magnetic field.

  Because of these characteristics, the skyrmion storage medium is expected to play a fundamental role in the technology that gives a breakthrough to the performance limits of data storage media and data recording apparatuses that are constantly increasing in required storage capacity.

  In order to meet the demand for high-density storage media of hard disks, a bit patterned media technique using magnetic dots in which magnetic dots for recording magnetic information are divided by non-magnetic materials has been proposed (Patent Document 2). When bit patterned media technology is used, magnetic dots separated by non-magnetic material can be formed at a pitch of several tens of nanometers by a low-cost manufacturing method without using an expensive photolithography apparatus.

  FIG. 13 is a diagram showing a part of a hard disk 600 having a magnetic dot pattern 612 manufactured using the bit pattern media technology. One magnetic dot pattern 612 is a unit for storing binary magnetic information. The nonmagnetic material surrounds the magnetic dot pattern 612 on the soft magnetic material 604. In FIG. 13, the shape of the non-magnetic material and the boundary between the non-magnetic material and the magnetic dot pattern are not clearly shown in FIG. The hard disk 600 has a magnetic dot pattern 612 having a constant pitch. The magnetic dot pattern 612 constitutes a recording track 602 on the disk.

  Each magnetic dot pattern 612 is desired to control the direction of the magnetic moment of the magnetic dot pattern to a desired direction with a magnetic field as low as possible. Further, once the direction of the magnetic moment is determined, it is necessary to have a characteristic that can maintain the direction of the magnetic moment against disturbance. For this purpose, the magnetic dot pattern 612 has a laminated structure of an upper soft magnetic body 616 and a lower hard magnetic body 614 and a structure in which a nonmagnetic body surrounds the periphery.

  The upper soft magnetic body 616 easily responds to the magnetic field generated from the magnetic head, and its magnetic moment is aligned. Accordingly, the magnetic moment of the lower hard magnetic body 614 is directed toward the magnetic moment of the upper soft magnetic body 616 by magnetic exchange interaction at the interface between the upper soft magnetic body 616 and the lower hard magnetic body 614. The magnetic moment of the lower hard magnetic body 614 has a volume that can maintain stability that does not easily respond to external thermal fluctuations. Therefore, the magnetic dot pattern 612 holds a magnetic moment. In this way, a storage medium that satisfies the demand for large scale is realized.

  However, in order to improve the recording density, the pitch between the recording tracks 602 adjacent to each other tends to be narrow. As a result, there arises a side erase problem that the leakage magnetic field of the recording magnetic field of the write head erases the data of the other recording track 602-2 adjacent to the recording track 602-1 to be written. Since the magnetic dot of the laminated structure has the upper soft magnetic body 616, the magnetization is reversed relatively easily with a small recording magnetic field. Therefore, there may be a problem that the magnetic information of the magnetic dot pattern 612 of the other recording track 602-2 adjacent to the recording track 602-1 to be written is lost. Further, as the magnetic dot pattern 612 is miniaturized also in the track direction of the recording track 602, there is a problem that side erasure occurs in the track direction.

In addition, the volume of the lower hard magnetic body 614 tends to be reduced in accordance with the demand for increasing the recording density by reducing the size of the magnetic dot pattern 612. The energy for holding the magnetic moment of the lower hard magnetic body 614 has only the holding force of the magnetic moment proportional to its own volume. As the volume of the magnetic dot pattern 612 is reduced, the magnetic moment of the lower hard magnetic body 614 will eventually be unable to resist thermal fluctuations. Thereby, the defect that a magnetic moment reverses also arises.
[Prior art documents]
[Patent Literature]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2014-086470
[Patent Document 2] JP 2013-196747 A
[Non-patent literature]
[Non-Patent Document 1] Naoto Naga Nagato, Yoshinori Tokura, “Topological properties and dynamics”, Nature Nanotechnology, United Kingdom, Nature Publishing Group, 12th month, 12th month. 8, p899-911.

  In the hard disk 600 that is a magnetic storage medium, the magnetic dot pattern 612 is required to have a high density. Therefore, side erasure is prevented in the hard disk 600 having the magnetic dot pattern 612 with high density.

In the first aspect of the present invention, a thin-layered magnetic body capable of generating and erasing skyrmions, a non-magnetic body surrounding the thin-layered magnetic body, and a magnetic surface facing the first surface of the magnetic body and a magnetic field generating unit to the first surface of the body is capable of applying a first magnetic field, the size of the plane of the magnetic thin layer is, width W _m, if the height and h _m, magnetic laminar Provided is a storage medium having a size of 2λ> W _m > 0.5 · λ and 2λ> h _m > 0.5 · λ with respect to a diameter λ of skyrmions generated in the body.

  The second aspect of the present invention includes a storage medium and a magnetic head, and the magnetic head is opposed to a second surface that is opposite to the first surface of the thin-layered magnetic material, Provided is a recording apparatus that includes a coil unit that can apply a second magnetic field to a second surface, and that has a current circuit that allows a pulse current to flow through the coil unit and a drive unit that can move a magnetic head. .

  Moreover, in the 3rd aspect of this invention, the data processing apparatus carrying a recording device is provided.

  According to a fourth aspect of the present invention, a data recording apparatus equipped with a recording apparatus is provided.

  According to a fifth aspect of the present invention, a communication device equipped with a recording device is provided.

4 is a schematic diagram showing an example of a skyrmion 40 that is a nanoscale magnetic structure of a magnetic moment in a magnetic body 32. FIG. It is a figure which shows the skyrmion 40 from which helicity γ differs. 1 is a schematic diagram showing a recording device 100 of a skillion 40 that includes a magnetic disk 10 and a magnetic head 20. FIG. It is a figure which shows the magnetic phase diagram of a chiral magnetic body which is the simulation conditions of the production | generation of a skillion 40. It is a simulation condition of generation of skyrmion 40 is a diagram showing the time dependence of the magnetic field strength H _a end region A of the magnetic member 32. It is a figure which shows the simulation result of the production | generation of skill meon 40. FIG. It is a schematic diagram which shows the relationship between the dot of several magnetic body 32, and the magnetic field application area | region B. FIG. Is a simulation condition of erasing skyrmion 40 is a diagram showing the time dependence of the magnetic field strength H _a at the end regions A of the magnetic phase diagram and the magnetic member 32 of a chiral magnetic material. It is a figure which shows the simulation result of erasure | elimination of the skillion 40. 3 is a schematic diagram showing a data processing device 300. FIG. 3 is a schematic diagram showing a data recording apparatus 400. FIG. 3 is a schematic diagram illustrating a configuration example of a communication device 500. FIG. It is a figure which shows a part of hard disk 600 which has the magnetic body dot pattern 612 produced using the bit pattern media technique.

  Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the invention according to the claims. In addition, not all combinations of features described in the embodiments are essential for the solution means of the invention.

  An example of a magnetic material that can generate skyrmions is a chiral magnetic material. A chiral magnetic body is a magnetic body with a magnetic ordered phase in which the magnetic moment arrangement when no external magnetic field is applied rotates on a spiral with respect to the direction of travel of the magnetic moment. By applying an external magnetic field, the chiral magnetic material becomes a ferromagnetic phase through a state in which skyrmions exist.

  FIG. 1 is a schematic diagram showing an example of a skyrmion 40 that is a nanoscale magnetic structure in the magnetic body 32. In FIG. 1, each arrow indicates the direction of the magnetic moment in the skyrmion 40. The x axis and the y axis are axes orthogonal to each other, and the z axis is an axis orthogonal to the xy plane.

  The magnetic body 32 has a plane parallel to the xy plane. A magnetic moment directed in any direction arranged on the plane of the magnetic body 32 constitutes the skyrmion 40. In this example, the direction of the magnetic field applied to the magnetic body 32 is the plus z direction. In this case, the magnetic moment on the outermost periphery of the skillion 40 of this example is directed in the plus z direction.

  In the skyrmion 40, the magnetic moment is arranged so as to rotate in a spiral shape from the outermost periphery to the inside. Further, the direction of the magnetic moment gradually changes from the plus z direction to the minus z direction with the spiral rotation.

  In the skyrmion 40, the direction of the magnetic moment is continuously twisted between the center and the outermost periphery. That is, the skyrmion 40 is a nanoscale magnetic structure having a spiral structure of magnetic moment. When the magnetic body 32 in which the skyrmion 40 exists is a thin plate-like solid material, the magnetic moment constituting the skyrmion 40 has the same direction in the thickness direction. That is, the plate has a magnetic moment in the same direction from the front surface to the back surface in the depth direction (z direction). The diameter λ of the skillion 40 refers to the diameter of the outermost periphery of the skillion 40. In this example, the outermost periphery refers to the circumference of a magnetic moment that faces the same direction as the external magnetic field shown in FIG.

  The skyrmion number Nsk characterizes the skyrmion 40, which is a nanoscale magnetic structure having a spiral structure. The number of skyrmions can be expressed by the following [Equation 1] and [Equation 2]. In [Formula 2], the polar angle Θ (r) between the magnetic moment and the z-axis is a continuous function of the distance r from the center of the skyrmion 40. The polar angle Θ (r) changes from π to zero or from zero to π when r is changed from 0 to ∞.

[Equation 1]

[Equation 2]

  In [Equation 1], n (r) is the magnetic moment of skyrmion 40 at position r. In [Expression 2], m is a voltility, and γ is a helicity. From [Equation 1] and [Equation 2], when Θ (r) changes r from ∞ to ∞ and changes from π to zero, Nsk = −m.

FIG. 2 is a schematic diagram showing skyrmions 40 having different helicities γ. In particular, FIG. 2 shows an example in the case where the number of skirmions Nsk = −1. FIG. 2E shows how to coordinate the magnetic moment n (right-handed system). Since a right-handed, n _z axis relative to n _x axis and n _y axis, taken from the rear of the sheet in front of the orientation. 2A to 2E, the shading indicates the direction of the magnetic moment.

Magnetic moments indicated by shading on the circumference in FIG. 2 (E) _has the direction of the n x -n _y plane. On the other hand, the magnetic moment shown by the thinnest shading (white) at the center of the circle in FIG. 2E has a direction from the back of the paper to the front. The angle with respect to the _nz axis of the magnetic moment shown by the shading of each position between the circumference and the center is taken from π to zero according to the distance from the center. The direction of each magnetic moment in FIGS. 2A to 2D is indicated by the same shading in FIG. 2A to 2D, the magnetic moment indicated by the darkest shade (black) has a direction from the front of the paper to the back of the paper. Each arrow in FIG. 2 (A) to FIG. 2 (D) indicates a magnetic moment at a predetermined distance from the center of the magnetic structure. The magnetic structure shown in FIGS. 2A to 2D can be defined as skyrmion 40.

  In FIG. 2A (γ = 0), the shading at a predetermined distance from the center of the skyrmion 40 matches the shading on the circumference of FIG. For this reason, the direction of the magnetic moment indicated by the arrow in FIG. 2A is radially outward from the center. 2A (γ = 0) with respect to the magnetic moments in FIG. 2B (γ = π), the magnetic moments in FIG. 2A are rotated by 180 °. The direction. 2A (γ = 0), the direction of each magnetic moment in FIG. 2C (γ = −π / 2) is the same as that in FIG. 2A. The direction is rotated 90 degrees (90 degrees clockwise).

  The direction of each magnetic moment in FIG. 2D (γ = π / 2) is 90 degrees with respect to each magnetic moment in FIG. 2A (γ = 0). The direction is rotated 90 degrees counterclockwise. 2 is equivalent to the skillion 40 of FIG. 1. The skillion of γ = π / 2 shown in FIG.

  The four examples shown in FIGS. 2A to 2D appear to be different in magnetic structure, but are topologically identical. The skyrmions having the structures shown in FIGS. 2A to 2D exist stably once generated, and function as carriers that transmit information in the magnetic body 32 to which an external magnetic field is applied.

  FIG. 3 is a schematic diagram showing the recording device 100 of the skillion 40 including the magnetic disk 10 and the magnetic head 20. The magnetic disk 10 as a storage medium of the skillion 40 has a thin layered magnetic body 32 that can be generated and erased by the skillion 40. A nonmagnetic material surrounding the thin magnetic material 32 is provided around the magnetic material 32. Note that the shape of the nonmagnetic material and the boundary between the nonmagnetic material and the magnetic material 32 are not explicitly shown in FIG. The nonmagnetic material at least surrounds an end portion between the first surface 34 and the second surface 36 which is a two-dimensional plane of the magnetic material 32. The nonmagnetic material may be further provided in contact with the first surface 34 and / or the second surface 36 in addition to the end of the magnetic material 32.

  The thin-layered magnetic body 32 has a rectangular plane that is relatively large with respect to the length in the z direction and extends in the xy direction. The magnetic body 32 has a first surface 34 that is a surface in the minus z direction and a second surface 36 that is a surface in the plus z direction. In the present specification, the length of the magnetic body 32 in the z direction is referred to as the thickness of the magnetic body 32. The magnetic body 32 may have a thickness of about 10 times or less the diameter λ of the skyrmion 40. The magnetic body 32 may be a thin layered magnetic material having a thickness of 500 nm or less.

In this specification, the length of the magnetic body 32 in the x direction is referred to as the width of the magnetic body 32, and the length of the magnetic body 32 in the y direction is referred to as the height of the magnetic body 32. The width of the magnetic material 32 of the thin layer and W _m, the height and h _m. In this example, the size of the magnetic body 32 in the xy plane is such that the width: 2λ> W _m > 0.5 · λ and the height: 2λ> h _{m with} respect to the diameter λ of the generated skyrmion 40. > 0.5 · λ. The numerical ranges of the width and the height described above are numerical ranges optimized to generate a single skyrmion 40 in the thin-layered magnetic body 32.

  In the recording apparatus 100, a plurality of thin layered magnetic bodies 32 are arranged on the same plane. FIG. 3 shows only two magnetic bodies 32 in one track. However, the actual magnetic disk 10 has a plurality of tracks, and each track has a plurality of magnetic bodies 32.

  The thin layered magnetic body 32 may be formed using a technique such as MBE (Molecular Beam Epitaxy) or sputtering. In the example of this specification, the magnetic body 32 is a chiral magnetic body. The magnetic body 32 may be formed of FeGe or MnSi. The magnetic body 32 may be formed of any one of a chiral magnetic body, a dipole magnetic body, a frustrated magnetic body, or a laminated structure made of a magnetic material and a nonmagnetic material.

  The magnetic disk 10 has a thin layered magnetic field generator 50. The thin-layered magnetic field generator 50 faces the first surface 34 of the magnetic body 32. The thin-layer magnetic field generator 50 applies a first magnetic field to the first surface 34 of the magnetic body 32. The first magnetic field is, for example, a magnetic field in the plus z direction having a magnetic field strength that makes the magnetic body 32 in a ferromagnetic state. The magnetic field generation unit 50 may be a ferromagnetic material such as hexaferrite, GGG (Gadolinium Gallium Garnet), YIG (Yttrium Iron Garnet), or a rare earth magnet. In this example, one thin-layer magnetic field generator 50 is used. However, the present invention is not limited to this, and a plurality of magnetic field generators 50 can also be used.

  The magnetic disk 10 includes a magnetic field generator 50 and a plurality of magnetic bodies 32. The magnetic field generator 50 determines the direction of the magnetic moment of the magnetic body 32 to be the same direction. The magnetic field generator 50 applies a magnetic field constantly to the magnetic body 32 in that a hard disk memory using a magnetic dot pattern having a laminated structure made of a soft magnetic material and a ferromagnetic material that is currently known (Patent Document 2). ).

  In the hard disk memory (Patent Document 2) that is currently known, the magnetic dot pattern must hold the magnetic moment only by its own holding force. The holding power of the magnetic dot pattern is proportional to the volume of the magnetic dots. That is, as the volume of the magnetic dots increases, the holding force increases, but as the volume decreases, the holding force decreases. In other words, the magnetic dots tend to lose information on the magnetic moment as the volume decreases.

  On the other hand, in the case of the magnetic disk 10 of this example, the magnetic body 32 has a magnetic moment that is uniformly oriented in the same direction. Furthermore, the magnetic body 32 has a skyrmion 40 that is a magnetic moment of a helical structure resulting from a topological effect only in a partial space of the magnetic body 32. The magnetic moment of skyrmion 40 is topologically stable. Further, the skyrmion 40 can exist stably even if there are magnetic impurities in the magnetic body 32. That is, the skyrmion 40 can exist stably even when subjected to external magnetic field disturbances. The magnetic body 32 needs to be large enough to have the skyrmion 40, but once the skyrmion 40 is generated in the magnetic body 32, the skyrmion 40 can be stably held in the magnetic body 32. That is, in the magnetic body 32 of a certain size, information on the magnetic moment does not disappear unintentionally. That is, the conventional method uses the positive and negative directions of the magnetic moment as the stored information. In the case of the magnetic disk 10 of this example, the basic structure of the magnetic moment direction of the magnetic body 32 as the storage medium is fixed by the magnetic field generator 50. In principle, side erase does not occur. Once the generated skyrmion 40 is generated as seen above, it can exist stably from the influence of the magnetic field from the adjacent magnetic body 32.

  As a result, the defect of the magnetic medium that is vulnerable to the side erasure of the conventional method can be eliminated, and the magnetic information can be stably held. The size of the magnetic body 32 is preferably about the size of the skyrmion 40. Even if the size of the skillion 40 is a small magnetic dot of about 10 nm or less, the skillion 40 can be stably held in the magnetic body 32. As long as the skillmion 40 can be generated, the size of the magnetic body 32 may be as small as possible.

  This is an epoch-making invention that sets a line apart from the extension of the prior art. In the case of a conventional magnetic medium, the smaller the size, the weaker the magnetic moment holding power of the magnetic dot pattern itself. Further, in the conventional magnetic medium, if the size of the magnetic dot pattern is reduced, the direction of the magnetic moment carrying the stored information is destabilized due to the side erase effect. On the other hand, since the magnetic moment of the skyrmion 40 is topologically stable in the magnetic body 32, it has advantageous effects on the holding power of the magnetic moment, resistance to external magnetic field disturbance, and resistance to side erase. .

  In addition, since the skyrmion 40 exists stably, the skyrmion storage medium can greatly improve the data retention performance.

  The magnetic head 20 of the recording apparatus 100 has a current circuit 24. The current circuit 24 includes a coil unit 22 so as to generate magnetic fields in the minus z direction and the plus z direction with respect to the surface of the magnetic disk 10. The coil portion 22 of this example has a soft magnetic body 23 in a cavity located at the center of the coil portion 22. The coil portion 22 faces a second surface 36 that is a surface opposite to the first surface 34 of the magnetic body 32. The soft magnetic body 23 efficiently guides the magnetic field generated by the coil portion 22 in the z direction. Thereby, the second magnetic field is applied from the coil portion 22 to the second surface 36 of the magnetic body 32.

  The magnetic head 20 can accurately control the position of the magnetic field generation region B applied to the magnetic body 32. The magnetic head 20 may have a plurality of coil portions 22. The magnetic head 20 may have a structure that can maintain a space between the magnetic disk 10 rotating at high speed and the magnetic head 20 at regular intervals using an air layer or the like. The recording apparatus 100 further includes a drive unit 27 that can move the magnetic head 20 in the ± y directions. The drive unit 27 moves the magnetic head 20 to an appropriate position in the ± y direction. For example, the drive unit 27 moves the coil unit 22 to an appropriate position in the ± y direction so that the magnetic field application region B includes the end region A of the magnetic body 32. The drive unit 27 can arbitrarily set the magnetic field application region B to be applied to the magnetic body 32 by moving the coil unit 22. The end region A and the magnetic field application region B will be described later.

  A pulse current source provided outside the magnetic head 20 and inside the recording apparatus 100 applies a pulse current to the current circuit 24. The pulse current source can apply a positive pulse current and a negative pulse current at an arbitrary timing. By causing a pulse current in the positive direction to flow through the coil part 22, the coil part 22 applies a pulse magnetic field in the negative z direction to the second surface 36 of the magnetic body 32. In this case, the second magnetic field is in the opposite direction to the first magnetic field. On the other hand, the coil unit 22 applies a pulse magnetic field in the plus z direction to the second surface 36 of the magnetic body 32 by flowing a pulse current in the minus direction through the coil unit 22. In this case, the second magnetic field is in the same plus z direction as the first magnetic field.

The second magnetic field applied from the coil portion 22 of the magnetic head 20 to the magnetic disk 10 is defined as a magnetic field application region B. The magnetic field application region B has a wider area than the end region A of one magnetic body 32. The magnetic field application region B is provided in a region including the end region A of one magnetic body 32. The end region A is a predetermined region including the end of the magnetic body 32 in the plus y direction. The inventor of the present application has found that it is important for the generation of the skyrmion 40 that the magnetic field application region B includes the end region A of the magnetic body 32. The magnetic field application region B may also be provided in a partial region of the nonmagnetic material provided surrounding the magnetic material 32. The magnetic field strength in the end region A of the magnetic member 32 and H _a. H _a is a vector sum of the first magnetic field applied by the magnetic field generator 50 and the second magnetic field applied by the coil unit 22 of the magnetic head 20.

When the pulse current source applies a positive pulse current in the current circuit 24, the coil unit 22 generates the second magnetic field in the negative z direction. For the magnetic body 32, the magnetic field generator 50 applies the first magnetic field constantly in the plus z direction. In this case, since the second magnetic field and the first magnetic field becomes antiparallel, the magnetic field strength H _a is weakened relatively. On the other hand, in the current circuit 24, when the pulse current source applies a pulse current in the minus direction, the coil unit 22 generates the second magnetic field in the plus z direction. In this case, since the parallel both in the z direction from the second magnetic field and the first magnetic field, the magnetic field strength H _a is stronger relatively. Next, the generation of skyrmions 40 in the chiral magnetic material will be demonstrated in detail in Examples.

[Example 1]
The simulation experiment result of generation of skyrmions in Example 1 is shown. Skyrmion motion can be described by the following equation: Hereafter, the following equation is solved numerically.

[Equation 3]

[Equation 4]

Here, [Equation 3] and [Equation 4] can be associated with each other by B _r ^eff = − (1 / (hΓ)) (∂H / ∂M _r ). Γ = gμ _B / h (> 0) is the gyromagnetic ratio. h is a Planck's constant. D _m is the magnitude of Jaronsky-Moriya interaction. _Mr represents the magnetic moment. M _r is the product of the scalar quantity M and the unit vector quantity n (r). H _a is the magnetic field intensity of the magnetic field application region A. In the above [Expression 3] and [Expression 4], x indicates an outer product.

  Here, the Hamiltonian H represented by [Equation 4] is a case of a chiral magnetic material. For a dipole magnetic body, a frustrated magnetic body, and a magnetic body having a laminated structure of a magnetic material and a nonmagnetic material, the expression of H may be replaced with a description of each magnetic body.

  The dipole magnetic body is a magnetic body in which magnetic dipole interaction is important. A frustrated magnetic body is a magnetic body including a spatial structure of magnetic interaction that favors a magnetic mismatch state. A magnetic body having a laminate of a magnetic material and a nonmagnetic material is a magnetic body in which the magnetic moment of the magnetic material in contact with the nonmagnetic material is modulated by the spin-orbit interaction of the nonmagnetic material. Next, the experimental conditions for the simulation in this example are shown in FIG.

FIG. 4 is a diagram illustrating a magnetic phase magnetic phase diagram of the chiral magnetic material, which is a simulation condition for generating the skyrmion 40. The chiral magnetic substance is a magnetic substance that changes from a spiral magnetic phase to a skyrmion crystal phase (SkX) at a magnetic field strength Hsk, and from a skyrmion crystal phase (SkX) to a ferromagnetic phase at a higher magnetic field strength Hf. In the skyrmion crystal phase (SkX), a plurality of skyrmions 40 are arranged in the close-packed structure and are generated in the xy plane. The chiral magnetic material used in this example has D _m = 0.18 · J, M = 1, and α = 0.04. D _m is the magnitude of Jaronsky-Moriya interaction. In the following, various physical quantities are described with values normalized by this quantity, where J is the magnitude of the magnetic exchange interaction of the magnetic material.

  In a low magnetic field, a spiral magnetic phase having a magnetic structure of a helical magnetic moment becomes a skyrmion crystal phase (SkX) at a magnetic field strength Hsk = 0.005J. If the diameter of the skyrmion 40 at this time is λ, λ can be expressed by the following [Equation 5] using J and D.

[Equation 5]

Here, a is a lattice constant of the magnetic body 32. In the chiral magnetic material with D _m = 0.18 · J, λ˜50a. When the lattice constant a of the magnetic body 32 is 5Å, λ is about 25 nm. Since D _m, which is a physical constant indicating the magnitude of the Jaroshinsky-Moriya interaction, is a physical constant specific to the substance, the diameter λ of the skyrmion 40 is a constant specific to the substance according to [Equation 5]. As described in Non-Patent Document 1, the diameter λ of the skyrmion 40 is, for example, 70 nm for FeGe and 18 nm for MnSi. Still further, the chiral magnetic material used in this example becomes a ferromagnetic phase at a magnetic field strength Hf = 0.0252 · J.

Figure 5 is a simulation condition of generation of skyrmion 40 is a diagram showing the time dependence of the magnetic field strength H _a end region A of the magnetic member 32.

First, the simulation experiments, by applying a first magnetic field to the chiral magnetic material as the magnetic body 32 from the magnetic field generating unit 50, the magnetic field strength H _a end region A of the magnetic member 32 as Hf greater field strength, chiral Start from a state in which the magnetic material is in the ferromagnetic phase. In other words, the skyrmion 40 does not exist in the chiral magnetic body, and the magnetic moment is in a ferromagnetic state in which the direction of the magnetic moment is all in the plus z direction in one chiral magnetic body. Specifically, the first magnetic field of the magnetic field generator 50 is set to a magnetic field intensity H ₁ = 0.03 · J. This magnetic field strength can be easily obtained by adjusting the thickness of the ferromagnetic material.

Next, in the current circuit 24, a pulse current source applies a pulse current to the current circuit 24. The pulse current has a trapezoidal pulse shape with a rise / fall time of 1000 (1 / J) and a maximum current application time of 1000 (1 / J). The application of the pulse current in the plus direction generates a second magnetic field in the minus z direction that is weaker than the intensity of the first magnetic field and goes in a direction substantially opposite to the first magnetic field. By applying the second magnetic field to the magnetic body 32, the magnetic field strength H _a of the magnetic field application region A is reduced. As described above, the magnetic field application region A needs to include the end portion of the chiral magnetic body that generates the skyrmion 40. In the present specification, the second magnetic field that is directed in a substantially opposite direction to the first magnetic field means a magnetic field that includes at least a vector component in the opposite direction to the first magnetic field. Of course, the second magnetic field may be a magnetic field including a vector component in a completely opposite direction to the first magnetic field.

The second magnetic field is applied so that the magnitude of H _a = 0.01 · J at t = 1000 (1 / J). The unit of time t is 1 / J. The same applies hereinafter. Thereafter, a constant magnetic field strength of H _a = 0.01 · J is maintained until t = 2000 (1 / J). Thereafter, the pulse current from the pulse current source is gradually reduced, and the application of the second magnetic field is stopped at t = 3000 (1 / J). At this time, H _a = 0.03 · J. Under this condition, a simulation experiment is performed using [Equation 3] and [Equation 4].

FIG. 6 is a diagram illustrating a simulation result of generation of the skillmion 40. Similar to FIG. 2, in (1) to (4) of FIG. 6, the shading indicates the direction of the magnetic moment. Magnetic member 32 is a chiral magnetic material having a width _{W m,} the height _{h m.} The magnetic field application region B is set so as to include the end region A of the magnetic body 32. In this specification, the height of the end region A of the magnetic body 32 is defined as h _a and the width is defined as W _a . In this example, h _a = 25a = 0.5 · λ, and the width W _a is the width W _m of the magnetic body 32.

In FIG. 6, (1) to (3) are the times of (1) t = 0 (1 / J), (2) t = 1500 (1 / J), (3) t = 2800 (1 / J). This is a simulation result. (2) At a time of t = 1500 (1 / J), the magnetic field strength of the end region A is set to H _a = 0.01 · J. Skyrmions 40 start to be generated from the end of the magnetic body 32 in the plus y direction. At t = 3000 (1 / J), the skyrmion 40 moves to the central portion of the magnetic body 32 and is stabilized. As described above, the skyrmion 40 can be generated when the magnetic field application time from the coil unit 22 is 3000 (1 / J). The time 3000 (1 / J) from t = 0 (1 / J) to t = 3000 (1 / J) under the conditions of FIG. Note that the size of the end region A of the magnetic body 32 may be W _a = W _m and λ ≧ h _a > 0.25 · λ. The numerical ranges of the width and the height described above are numerical ranges optimized to generate a single skyrmion 40 in the thin-layered magnetic body 32.

FIG. 7 is a schematic diagram showing the relationship between the dots of the plurality of magnetic bodies 32 and the magnetic field application region B. The magnetic disk 10 includes a plurality of magnetic bodies 32 spaced apart and arranged in an xy plane. The magnetic disk 10 has a plurality of recording tracks 60 provided adjacent to each other. On each recording track 60, a plurality of dots of the magnetic body 32 are arranged apart from each other. In one recording track 60, each magnetic body 32 has a constant pitch. In this example, the shortest distance of the magnetic member 32 to each other is D _x. Magnetic member 32 in the first recording track 60-1 is the pitch of _W m + _{D x.} Since the magnetic body 32 has a rectangular shape, the pitch value between the magnetic bodies 32 in the first recording track 60-1 may be different between the recording tracks. In this example, it is assumed that the shortest distance between adjacent rectangular magnetic bodies 32 in two adjacent recording tracks 60 is constant at D _y .

  In the recording apparatus 100, the magnetic disk 10 is moved in the plus x direction relative to the coil portion 22 of the magnetic head 20. Thus, the magnetic field application region B can be scanned in the negative x direction while applying a magnetic field to the magnetic field application region B from the negative z direction to each magnetic body 32 of each recording track 60. The recording apparatus 100 scans the magnetic field application region B so as to include the end region A in the plus y direction of each magnetic body 32.

  The first recording track 60-1 and the second recording track 60-2 are in a state where the skyrmion 40 has already been generated. The magnetic body 32 that has generated the skyrmion 40 and the magnetic body 32 that has not generated the skyrmion 40 may each have information corresponding to 1 and 0 in the binary information. The third recording track 60-3 is a recording track 60 that generates the skyrmion 40 in each magnetic body 32 by scanning the magnetic field application region B. When generating the skyrmion 40, the coil unit 22 generates the second magnetic field in the minus z direction. On the other hand, when the skyrmion 40 is not generated, the coil unit 22 does not generate the second magnetic field.

［数７］

When generating a skyrmion in the magnetic body 32 by the magnetic field application region B, the skyrmion should not be generated in a magnetic body 32 different from the corresponding magnetic body 32. Therefore, the size of the magnetic field application region B has an upper limit value and a lower limit. There is a value. The height _{h m} of the size of the magnetic body 32 is a _{2λ> h m> 0.5 · λ} . The size of the end region A of the magnetic member 32 in the case of generating the skyrmion is _{λ ≧ h a> 0.25 · λ} . Accordingly, since the upper limit value h _b ^max of the height of the magnetic field application region B must not generate skyrmions in the magnetic bodies 32 of the tracks in the adjacent ± y directions, 0.25 · λ + D _y + h _m + D _y + 0.25 · λ> h _b ^max . Since h _m is the maximum 2 · _lambda, a ^{_{2D y +2.5 · λ> h b}} max. The lower limit h _b ^min of the height of the magnetic field application region B is h _b ^min > 0.25 · λ. From the above, the height h _b of the magnetic field application region B is [Equation 6], and the width W _b of the magnetic field application region B is [Equation 7].
[Equation 6]

[Equation 7]

The width W of the magnetic field application region B is determined from the writing time (1000 (1 / J in this example)) and the number of rotations per unit time of the disk. The minimum value of the width W of the magnetic field application region B is the width W _m of the magnetic body 32. Since the magnetic disk 10 has a disk shape, the speed of the magnetic head 20 on each recording track 60 increases as it goes to the outer periphery of the magnetic disk 10. For such adjustment of the position of the magnetic disk 10 and the magnetic head 20, an existing magnetic head control method can be used.

[Example 2]
FIG. 8 is a diagram illustrating a simulation result of erasing the skillmion 40. A diagram depicting time dependency of the magnetic field strength H _a of the end region A. First, the magnetic field generation unit 50 applies a first magnetic field to the chiral magnetic body as the magnetic body 32 and does not apply a second magnetic field from the coil unit 22 of the magnetic head 20. Thus, the magnetic field strength H _a of the end region A can be kept Hf greater magnetic field strength. Here, the magnetic body 32 is in a state of holding the skyrmion 40. The magnetic field application region B is set so as to include the end region A of the magnetic body 32. The height and width of the end region A of the magnetic body 32 are defined as h _a and W _a , respectively. In this example, h _a = 30a = 0.6 · λ, and the width W _a is the width W _m of the magnetic body 32.

Next, in the current circuit 24, a negative pulse current is gradually supplied from the pulse current source to generate a second magnetic field that is weaker than the first magnetic field and that is substantially forward with the first magnetic field in the positive z direction. By applying the second magnetic field to the magnetic body 32, the magnetic field strength H _a end region A is gradually increased the sum of the first magnetic field and the second magnetic field. In the present specification, the first magnetic field means a magnetic field including at least a vector component in the same direction as the first magnetic field. Of course, the second magnetic field may be a magnetic field including a vector component in the completely same direction with respect to the first magnetic field.

The second magnetic field is applied so that H _a = 0.05 · J at t = 1000 (1 / J). Thereafter, a constant magnetic field strength of H _a = 0.05 · J is maintained until t = 2000 (1 / J). Thereafter, the pulse current in the negative direction from the pulse current source is gradually decreased, and the application of the second magnetic field is stopped at t = 3000 (1 / J). At this time, H _a = 0.03 · J. Under this condition, a simulation experiment is performed using [Equation 3] and [Equation 4].

FIG. 9 is a diagram showing a simulation result of erasing the skillion 40. As shown in FIG. As in FIG. 2, in (1) to (4) of FIG. 9, the shading indicates the direction of the magnetic moment. In FIG. 9, (1) to (3) are the times of (1) t = 0 (1 / J), (2) t = 2200 (1 / J), (3) t = 4000 (1 / J). This is a simulation result. The height h _a of the end region A was set to h _a = 31a (a is the lattice constant of the magnetic body 32). (1) At t = 0 (1 / J), the skyrmion 40 is stably present in the central portion of the magnetic body 32. (2) At t = 2200 (1 / J), the skyrmion 40 moves in the minus y direction so as to escape from the magnetic field application region A. (3) At t = 4000 (1 / J), the skyrmion 40 moves to the end of the magnetic body 32 and disappears. As described above, the time 3000 (1 / J) from t = 0 (1 / J) to t = 3000 (1 / J) corresponds to the erase time of the skillion 40. In order to erase the skyrmion 40, the position of the end region A of the magnetic material formed by the coil portion 22 of the magnetic head 20 is important. The size of the height h _m of the magnetic body 32 and lambda. If the height h _a of the end regions A of the magnetic material of the central h _{a =} 0.5 · lambda of the magnetic material, it is not possible to erase the skyrmion 40. When the height h _a of the end region A of the magnetic material is h _a ≧ 0.6 · λ, the skyrmion 40 can be erased. The above numerical ranges of the width and the height are numerical ranges optimized to eliminate the single skyrmion 40.

［数９］

When erasing skyrmions in the magnetic field 32 in the magnetic field application region B, the skyrmions should not be erased in the magnetic body 32 different from the corresponding magnetic body 32. Therefore, the size of the magnetic field application region B has an upper limit value and a lower limit value. The height _{h m} of the size of the magnetic body 32 is a _{2λ> h m> 0.5 · λ} . The size of the end region A of the magnetic member 32 of the case of erasing skyrmion is _{λ ≧ h a ≧ 0.6 · λ} . Accordingly, since the upper limit value h _b ^max of the height of the magnetic field application region B must not erase skyrmions in the magnetic bodies 32 of the tracks in the adjacent ± y directions, h _b ^max > 0.6 · λ + D _y + h _m is a + _D y +0.6 · λ. Since h _m is 2λ at the maximum, h _b ^max > 2D _y + 3.2 · λ. The lower limit value h _b ^min of the height of the magnetic field application region B is h _b ^min > 0.6 · λ. From the above, the height h _b of the magnetic field application region B is [Equation 8], and the width W _b of the magnetic field application region B is [Equation 9].
[Equation 8]

[Equation 9]

  In the above-described first and second embodiments, simulation experiments for generating and erasing skyrmions 40 on the magnetic disk 10 by applying a magnetic field from the coil unit 22 of the magnetic head 20 have been shown. Then, the design rules for generating and deleting the skyrmion 40 were clarified.

It should be noted here that the time required for writing and erasing the skyrmion 40 is extremely fast as sub-nanoseconds. The time required for writing and erasing the skyrmion 40 indicates that a time t = 1000 (1 / J) from t = 1000 to t = 2000 is sufficient. The time 3000 (1 / J) from t = 0 (1 / J) to t = 3000 (1 / J) corresponds to approximately 1 nsec. Therefore, writing and erasing can be performed in about 0.3 nanoseconds. The design rule shown here is very important because it defines a basic rule for designing a skyrmion memory element. This design rule can be expressed as a quantity normalized by two quantities of a magnetic exchange interaction J characterizing the magnetism of the magnetic material and a diameter λ of the skyrmion 40. λ can be related to the magnitude D _m of Jaroshinsky-Moriya interaction in [Equation 5].

  Therefore, this basic rule is a design rule that can be applied to various chiral magnetic materials, and has a wide range of applications to many chiral magnetic materials. In addition, the conclusion in the embodiment with the chiral magnetic material described here does not change qualitatively even in a magnetic material having a laminate of a dipole magnetic material, a frustrated magnetic material, or a magnetic material and a nonmagnetic material. As described above, the present invention provides an optimum design guideline for the storage medium and the recording apparatus 100 that can generate and erase the skyrmion 40.

  FIG. 10 is a schematic diagram showing the data processing device 300. The data processing device 300 includes a recording device 100 and a processor 310. The recording apparatus 100 is the recording apparatus 100 of the skillion 40 described with reference to FIGS. The processor 310 includes, for example, a digital circuit that processes a digital signal. The processor 310 has at least one function of writing data to the recording apparatus 100 and reading data from the recording apparatus 100.

  FIG. 11 is a schematic diagram showing the data recording apparatus 400. The data recording device 400 includes the recording device 100 and an input / output device 410. The data recording device 400 is a memory device, for example. The recording apparatus 100 is the recording apparatus 100 of the skillion 40 described with reference to FIGS. The input / output device 410 has at least one of a function of writing data to the recording device 100 from the outside and a function of reading data from the recording device 100 and outputting the data to the outside.

  FIG. 12 is a schematic diagram illustrating a configuration example of the communication device 500. The communication device 500 refers to all devices having a communication function with the outside, such as a mobile phone, a smartphone, and a tablet terminal. Communication device 500 may be portable or non-portable. The communication device 500 includes a recording device 100 and a communication unit 510. The recording apparatus 100 is the recording apparatus 100 of the skillion 40 described with reference to FIGS. The communication unit 510 has a communication function with the outside of the communication device 500. The communication unit 510 may have a wireless communication function, may have a wired communication function, and may have both wireless communication and wired communication functions. The communication unit 510 has at least a function of writing data received from the outside to the recording apparatus 100, a function of transmitting data read from the recording apparatus 100 to the outside, and a function of operating based on control information stored in the recording apparatus 100. Have one.

  The skyrmion 40 has a very fine structure having a magnetic moment with a nanoscale size of 1 nm to 100 nm in diameter, and can be applied as a large-capacity storage medium capable of extremely densifying enormous bit information. Therefore, the skyrmion 40 can be used as a magnetic hard disk storage medium. Skyrmion storage media can be electrically written and erased. The time required for writing and erasing is also nanoseconds or less. By using such a high-density large-scale non-volatile magnetic medium, the high-speed storage processing capability of large-scale information used for a hard disk is greatly improved.

  Further, if a memory using Skillion 40 is installed in an image recording device or a television receiver, the amount of moving image data that can be stored can be dramatically increased. In addition, since the memory using Skyrmion 40 is a magnetic memory, it has high resistance against high-energy elementary particles flying in outer space. The flash memory has an advantage that is different from that of a flash memory that uses a charge associated with electrons as a storage holding medium. Therefore, it is important as a storage medium such as a space flight device.

  DESCRIPTION OF SYMBOLS 10 Magnetic disk, 20 Magnetic head, 22 Coil part, 23 Soft magnetic body, 24 Current circuit, 27 Drive part, 32 Magnetic body, 34 1st surface, 36 2nd surface, 40 Skyrmion, 50 Magnetic field generator, 60 Recording Track, 100 recording device, 300 data processing device, 310 processor, 400 data recording device, 410 input / output device, 500 communication device, 510 communication unit, 600 hard disk, 602 recording track, 604 soft magnetic material, 612 magnetic dot pattern, 614 Lower hard magnetic body, 616 Upper soft magnetic body

Claims (14)

A thin layered magnetic material capable of generating and erasing skyrmions;
A non-magnetic material surrounding an end of a two-dimensional plane of the thin magnetic material;
A thin-layered magnetic field generator capable of applying a first magnetic field to the first surface of the magnetic body, facing the first surface of the magnetic body,
The size of the plane of the magnetic thin layer is, width W _m, if the height and h _m, to the diameter λ skills Mion generating the magnetic laminar,
2λ> W _m > 0.5 · λ and
2λ> h _m > 0.5 · λ
A storage medium having a size of The magnetic field generator is
Applying the first magnetic field to the magnetic body to bring the magnetic body into a ferromagnetic state;
The storage medium according to claim 1.   The storage medium according to claim 1, wherein the magnetic body is formed of any one of a chiral magnetic body, a dipole magnetic body, a frustrated magnetic body, or a laminated structure including a magnetic material and a nonmagnetic material. A storage medium according to any one of claims 1 to 3,
With a magnetic head,
The magnetic head is
A coil portion capable of applying a second magnetic field to the second surface opposite to the second surface, which is the surface opposite to the first surface of the thin layered magnetic body;
A current circuit capable of passing a pulse current through the coil section;
A drive unit capable of moving the magnetic head;
Recording device.   The recording apparatus according to claim 4, wherein the second magnetic field is applied to a predetermined end region A including an end of the thin layered magnetic body. The magnetic field application region B for applying the second magnetic field to the second surface of the magnetic material having a thin coil portion includes the end region A of the second surface of the magnetic material,
When the width of the end region A is W _a , the height is h _a, and the width of the magnetic body is W _m ,
W _a = W _m and λ ≧ h _a > 0.25 · λ
And
By moving the magnetic head, the magnetic field application region to be applied to the magnetic body can be arbitrarily set.
The recording apparatus according to claim 4 or 5. The second magnetic field generated by the coil unit generates skirmions by applying the second magnetic field, which is directed in a direction substantially opposite to the first magnetic field, to the magnetic body, which is weaker than the intensity of the first magnetic field.
The recording apparatus according to any one of claims 4 to 6. The magnetic field application region B for applying the second magnetic field to the second surface of the magnetic material having a thin coil portion includes the end region A of the second surface of the magnetic material,
When the width of the end region A is W _a , the height is h _a, and the width of the magnetic body is W _m ,
W _a = W _m and λ ≧ h _a ≧ 0.6 · λ
And
By moving the magnetic head, the magnetic field application region to be applied to the magnetic body can be arbitrarily set.
The recording apparatus according to any one of claims 4 to 7. By applying a second magnetic field that is weaker than the strength of the first magnetic field and substantially in the forward direction to the first magnetic field to the magnetic body,
Delete the generated skyrmion,
The recording apparatus according to claim 8. A plurality of the magnetic bodies are provided in a plane apart from each other,
A plurality of the magnetic body, if the shortest distance between said magnetic body adjacent to D _y, the coil portion is the magnetic field application region B for applying the second magnetic field to the second surface of the magnetic thin layer The height h _b of
2D _y + 2.5 · λ> h _b > 0.25 · λ
The filling,
When the shortest distance between the adjacent magnetic bodies is D _x , the width W _b of the magnetic field application region B is
2D _x + 2.5 · λ> W _b > 0.25 · λ
The filling,
The coil unit generates skirmions in the magnetic body by applying the second magnetic field, which is directed in a direction substantially opposite to the first magnetic field, to the magnetic body to be weaker than the intensity of the first magnetic field.
The recording apparatus according to any one of claims 4 to 9. A plurality of the magnetic bodies are provided in a plane apart from each other,
A plurality of the magnetic body, if the shortest distance between said magnetic body adjacent to D _y, the coil portion is the magnetic field application region B for applying the second magnetic field to the second surface of the magnetic thin layer The height h _b of
2D _y + 3.2 · λ> h _b > 0.6 · λ
The filling,
When the shortest distance between adjacent magnetic bodies is D _x , the width W _b of the magnetic field application region B is
2D _x + 3.2 · λ> W _b > 0.6 · λ
The filling,
The coil unit erases skyrmions in the magnetic body by applying the second magnetic field, which is directed in a direction substantially opposite to the first magnetic field, to the magnetic body to be weaker than the intensity of the first magnetic field.
The recording apparatus according to any one of claims 4 to 10.   A data processing apparatus equipped with the recording apparatus according to any one of claims 4 to 11.   The data recording device carrying the recording device as described in any one of Claims 4-11.   The communication apparatus carrying the recording device as described in any one of Claims 4-11.

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