JP2019029595A - Magnetic domain wall moving element and magnetic memory - Google Patents

Abstract

To provide a magnetic domain wall moving element capable of high speed writing without increasing the current density and writing by moving a magnetic domain wall of a magnetic thin wire by current supply.SOLUTION: In a magnet-equipped magnetic domain wall moving element 10, a magnetic domain wall moving element 1 includes a magnet that generates magnetic fields that oppose each other so as to sandwich a magnetic wire 11 therebetween from above and below and repel each other in. The magnetic field -Hin the -x direction is applied a magnetic domain wall that is stationary at the magnetic domain wall rest position p1 of a magnetic thin wire 11 by magnets 61f and 62f with the N poles facing each other and magnets 61b and 62b with the S poles facing each other, and when electrons eare injected in the + x direction by supplying a current Ito the magnetic thin line 11, the domain wall DW moves at a high speed in the + x direction.SELECTED DRAWING: Figure 11

Description

  The present invention relates to a domain wall motion element and a magnetic memory including the same in a memory cell.

  As a random access memory (RAM) that satisfies all of nonvolatile, high-speed accessibility, and high integration, a magnetoresistive random access memory (Magnetoresistive Random Access) that uses binary data on the level of resistance of a magnetoresistive element in a memory cell Memory: MRAM) has been developed. The level of resistance of the magnetoresistive effect element depends on the magnetization direction of the magnetic film (free layer), and the data writing is the magnetization reversal of the free layer. As a writing method, an STT (Spin Transfer Torque) -MRAM (hereinafter referred to as an STT) that supplies current to a magnetoresistive effect element in a vertical direction from the initial MRAM by applying a magnetic field from a wiring (conductive wire) for speeding up and miniaturization of a cell. And a domain wall motion type MRAM that supplies a current to the free layer in the longitudinal direction as a thin wire with the free layer extending on both sides has been developed (for example, patent document). 1, Non-Patent Document 1).

  A magnetic body (hereinafter referred to as a magnetic wire) formed in a thin wire sufficiently long with respect to the thickness and width easily generates two or more magnetic domains in the length direction (thin wire direction), and further in the length direction. When a current is supplied, a shift movement is performed in which all the domain walls generated so as to separate the magnetic domains are moved equidistantly in the opposite direction of the current (to the + side). In a domain wall motion type MRAM, a change in the magnetization direction between two points due to one magnetic wall of a magnetic wire moving between two predetermined points in the direction of the wire is used. In addition, the domain wall motion method makes it easier to thicken the free layer than the reversal of magnetization by applying a magnetic field or supplying a current in the vertical direction. Therefore, the optical modulation of a spatial light modulator in which the free layer is formed of a magneto-optic material. It is suitable for an element (for example, Patent Document 2).

Japanese Patent No. 5598697 Japanese Patent No. 4939489

S. Fukami, T. Suzuki, K. Nagahara, N. Ohshima, Y. Ozaki, S. Saito, R. Nebashi, N. Sakimura, H. Honjo, K. Mori, C. Igarashi, S. Miura, N. Ishiwata, T. Sugibayashi, "Low-Current Perpendicular Domain Wall Motion Cell for Scalable High-Speed MRAM", 2009 Symposium on VLSI Technology Digest of Technical Papers, 12A-2

  The movement of the domain wall in the magnetic wire becomes faster as the current density of the supplied current is higher. However, if such a current supply with a high current density is continuously repeated, the magnetic wire may be deteriorated, and the life of the MRAM is shortened.

  The present invention has been devised in view of the above problems, and it is an object of the present invention to provide a magnetic memory and its domain wall motion element that enable high-speed writing without increasing the current density of the supplied current.

  That is, the domain wall motion element according to the present invention includes a magnetic wire formed by forming a perpendicular magnetic anisotropy material into a thin wire shape, and when current is supplied to the magnetic wire in a thin wire direction, the magnetic wall wire is generated in the magnetic wire. A pair of magnetic field applications that generate magnetic fields that oppose each other so as to sandwich the magnetic wire or its extension in the vertical direction from above and below. Means for applying a magnetic field in the direction of a fine wire to the magnetic fine wire by causing the set of magnetic field applying means to generate the magnetic field.

  With this configuration, the domain wall motion element can write at a high speed with respect to the current density of the supplied current.

  The magnetic memory according to the present invention includes the domain wall motion element in a memory cell. With this configuration, the magnetic memory can perform writing at a high speed with respect to the current density of the supplied current.

  According to the domain wall motion element and the magnetic memory according to the present invention, high-speed writing can be performed without increasing the current density of the supplied current, and the magnetic wire is hardly deteriorated.

It is a schematic diagram explaining the structure of the domain wall motion element with a magnet which concerns on 1st Embodiment of this invention. It is a schematic diagram explaining the reading method of the domain wall motion element of the domain wall motion device with a magnet shown in FIG. It is a schematic diagram explaining application of the magnetic field by the magnet of the domain wall motion element with a magnet shown in FIG. It is a schematic diagram explaining the arrangement | positioning of the magnetic fine wire and magnet in simulation. It is a magnetic field distribution map according to the component of x, y, z by the magnet of saturation magnetic flux density 1T of the sample which simulated the domain wall motion element with a magnet concerning a 1st embodiment of the present invention, and (a) is the N pole of a magnet (B) shows a pair in which two S poles are opposed in the z direction and a pair in which two N poles are opposed in the z direction at a pitch of 80 nm in the + x direction. An arrangement, (c) is an inversion of the arrangement in the x direction of (b). It is a conceptual diagram explaining the movement of the domain wall by the electric current supply in a magnetic fine wire. It is a schematic diagram explaining the arrangement | positioning of the magnetic fine wire and magnet in simulation. It is a graph showing the moving distance of the domain wall by current supply time transition in the magnetic fine wire which has arrange | positioned the magnet shown to Fig.7 (a) by simulation. It is a graph showing the moving distance of the domain wall by the current supply time transition in the magnetic fine wire which has arrange | positioned the magnet shown in FIG.7 (b) by simulation. It is a graph showing the saturation magnetic flux density dependence of the magnetic domain wall moving speed by the electric current supply in the magnetic fine wire which has arrange | positioned the magnet shown to Fig.7 (a) by simulation. (A), (b) is a schematic diagram explaining the writing method of the domain wall motion element of the domain wall motion device with a magnet shown in FIG. (A), (b) is an equivalent circuit diagram of the magnetic memory which equipped the memory cell with the domain wall motion element with a magnet which concerns on 1st Embodiment of this invention. It is a schematic diagram explaining the structure and writing method of the domain wall motion element with a magnet concerning 2nd Embodiment of this invention. It is a graph showing the movement distance of the domain wall by the current supply time transition in the magnetic fine wire which applied the magnetic field by simulation. It is a graph showing the movement distance of the domain wall by the current supply time transition in the magnetic fine wire which applied the magnetic field by simulation.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for realizing a domain wall motion element and a magnetic memory according to the present invention will be described with reference to the drawings. The domain wall motion element and magnetic memory shown in the drawings, and their elements may be exaggerated in size, positional relationship, etc., and may be simplified in shape and structure for the sake of clarity. .

[First Embodiment]
A domain wall motion element with magnet (domain wall motion element) 10 according to the first embodiment of the present invention is a memory element of a memory cell of a magnetoresistive random access memory (MRAM), and as shown in FIG. And eight magnets (magnetic field applying means) 61f, 61b, 62f, 62b, 63f, 63b, 64f, 64b. The domain wall motion element 1 includes a thin magnetic wire 11 that is long in the x direction (lateral direction in the figure), a first magnetization fixed layer 21 and a second magnetization fixed layer 22 that are connected to the lower surfaces of both ends of the magnetic thin wire 11 in the x direction. The barrier layer 3 and the submagnetization fixed layer 23 are sequentially stacked on the upper surface of the magnetic wire 11 at the center in the x direction. The domain wall motion element 1 includes a first electrode 51 connected to the first magnetization fixed layer 21, a second electrode 52 connected to the second magnetization fixed layer 22, and a third electrode 53 connected to the submagnetization fixed layer 23. Yes. Further, magnets 61b, 61f, 63f, and 63b are arranged on the upper side of the magnetic wire 11 and magnets 62b, 62f, 64f, and 64b are arranged on the lower side in order in the + x direction along the magnetic wire 11 of the domain wall motion element 1. The upper and lower ones are opposed to each other with the magnetic wire 11 in between.

(Domain wall moving element)
The magnetic wire 11, the first magnetization fixed layer 21, the second magnetization fixed layer 22, and the submagnetization fixed layer 23 are made of a perpendicular magnetic anisotropic material, and are a CPP-GMR element or a TMR element that is a magnetoresistive effect element of MRAM. The well-known magnetic material used for can be applied. Specifically, the perpendicular magnetic anisotropy material is a multilayer film such as a Co / Pd multilayer film in which transition metals such as Fe, Co, and Ni are repeatedly laminated with noble metals such as Pd and Pt, and Tb-Fe-Co. alloy (RE-TM alloy) of a rare earth metal and a transition metal such as Gd-Fe, FePt was L1 ₀ type ordered alloys, FePd, CrPt _3, and the like.

  The magnetic fine wire 11 is a main member of the domain wall motion element 1 and is formed in a thin fine wire shape in the x direction as described above, and is divided into two magnetic domains D1 and D2 in the fine wire direction as shown in FIG. . In the writing of the magnetic domain wall moving element 1, the magnetic thin line 11 is moved in the direction of the fine line by the electrical means as will be described later, and the magnetization direction between the start point and the end point of the movement of the domain wall DW. Changes before and after movement. Therefore, it is preferable that the magnetic wire 11 is made of the above-described magnetic material and has a relatively low coercive force. The magnetic thin wire 11 is preferably 70 nm or less in thickness and 300 nm or less in width (thin wire width, length in the y direction) so that the magnetic domains are easily divided only in the direction of the thin wire, and is sufficiently long with respect to the thickness and width. It is formed in a shape. In addition, the magnetic wire 11 can reduce the current for moving the domain wall DW as the cross-sectional area, which is the product of the thickness and the width, is smaller. On the other hand, in order to maintain the magnetization, it is preferable that the magnetic wire 11 has a certain thickness and width. Specifically, it is preferable that the thickness is 5 nm or more and the width is 10 nm or more.

  The barrier layer 3 and the sub-magnetization fixed layer 23 constitute a TMR element having a three-layer laminated structure combined with the magnetic thin wire 11, in order to detect the magnetization direction of the magnetic thin wire 11 as readout of the domain wall motion element 1. Provided. That is, the region (TMR element portion) of the magnetic wire 11 immediately below the barrier layer 3 and the submagnetization fixed layer 23 becomes the magnetization free layer of the TMR element. The barrier layer 3 is an insulating film of a barrier layer of a known TMR element, MgO is preferable, and the thickness is preferably less than 3 nm. The submagnetization fixed layer 23 is set and pinned in one direction (upward in FIG. 2). Therefore, it is preferable to apply a material having a large coercive force from the above-described magnetic material so that the coercive force is larger than that of the magnetic wire 11, and a sufficient volume (thickness, area). ), And may be formed so as to protrude to the outside of the magnetic wire 11 in the y direction. Such a secondary magnetization fixed layer 23 has a magnetization direction set by applying an external magnetic field in advance. Whether the magnetization direction in the TMR element portion of the magnetic wire 11 is the same (parallel, see FIG. 2A) or opposite (antiparallel, see FIG. 2B) with respect to the magnetization direction of the submagnetization fixed layer 23 The height of resistance between the first electrode 51 or the second electrode 52 and the third electrode 53 changes. Therefore, in the domain wall motion element 1, the magnetic wire 11 sets the domain wall stationary positions p1 and p2 that are the start and end points of the domain wall DW movement on both outer sides so that at least the entire TMR element region is magnetized.

The first magnetization fixed layer 21 and the second magnetization fixed layer 22 are set and fixed in different magnetization directions, and are magnetically coupled to a region of the magnetic wire 11 connected to the magnetization fixed layers 21 and 22. Provided to fix the same magnetization direction. Therefore, it is preferable that the first magnetization pinned layer 21 and the second magnetization pinned layer 22 are made of the above-described magnetic material having a larger coercive force so that the coercive force is larger than that of the magnetic wire 11, and It is preferable that it is formed in a sufficient volume (thickness, area), and it may be formed large by projecting to the outside of the magnetic wire 11 in the x direction or y direction. In FIG. 2, the first magnetization fixed layer 21 is set downward and the second magnetization fixed layer 22 is set upward. Therefore, the magnetic wire 11 is fixed such that the magnetization direction is downward in the region immediately above the first magnetization fixed layer 21 and upward in the region immediately above the second magnetization fixed layer 22. Only in the sandwiched region (magnetization reversible region 1 _SW ) can the magnetization direction be changed by electrical means. With such a configuration, the domain wall motion element 1 causes the domain wall DW to pass through the domain wall stationary position p1 or domain wall stationary position p2, which is the target stationary position, in the magnetic wire 11 further during the writing. Even if it tries to move, it does not reach outside the magnetization reversible region 1 _SW . Therefore, the magnetic wire 11 is prevented from disappearing the domain wall DW and becoming a single magnetic domain having only the magnetic domain D1 or only the magnetic domain D2. In FIG. 2, the domain wall rest position p1, p2 is the magnetization reversal region 1 _SW is the is set to the inside, is set to both ends of a movement limit position is the magnetization reversal region 1 _SW of the domain wall DW Also good. The first magnetization fixed layer 21 and the second magnetization fixed layer 22 are set in the magnetization direction by applying an external magnetic field in advance, as in the case of the submagnetization fixed layer 23, so that the magnetization directions are different from each other. It is preferable to have different structures such as providing a difference in coercive force.

  The first electrode 51, the second electrode 52, and the third electrode 53 are formed of a general metal electrode material such as a metal such as Cu, Al, Au, Ag, Ta, Cr, Pt, Ru, or an alloy thereof. The The electrodes 51, 52, and 53 are simply represented by lines in FIG. 1 and the like, but have thicknesses and widths corresponding to the magnitude of the current supplied to the magnetic thin wires 11, and the bottom surfaces of the magnetization fixed layers 21 and 22. It is formed so as to be connected to the upper surface of the secondary magnetization fixed layer 23 with a sufficient area.

(magnet)
A magnet 61f and a magnet 62f, a magnet 61b and a magnet 62b, a magnet 63f and a magnet 64f, and a magnet 63b and a magnet 64b, each set as a pair, are arranged above and below with the magnetic wire 11 therebetween, and the domain wall motion element 1 Is a magnetic field applying means for applying a magnetic field in the direction of the fine wire to the magnetic fine wire 11 at the time of writing. For this purpose, two magnets in the same set generate a magnetic field of the same magnitude that repels each other. Specifically, the magnets 61f, 61b, 62f, 62b, 63f, 63b, 64f, and 64b each generate a magnetic field in a predetermined one direction that is upward or downward (+ z direction, −z direction) so as to be turned ON / OFF freely. Since they can have the same structure, they are collectively referred to as a magnet 6 when not specified. Such a magnet 6 is, for example, an electromagnet including a thin film coil or a laminated coil applied to a magnetic recording head (not shown). In the magnet 6, the length in the y direction of the magnetic pole (core) facing the magnetic thin wire 11 is preferably equal to or larger than the thin wire width of the magnetic thin wire 11. In the present specification, the arrangement of the magnets 6 refers to the arrangement of the magnetic poles facing the magnetic thin wires 11, and in the drawings, only the magnetic poles are simplified. Further, the magnet 61f and the magnet 61b adjacent in the x direction simultaneously generate magnetic fields opposite to each other, one facing the N pole and the other facing the magnetic pole 11 respectively. Therefore, the magnets 61f and 61b are collectively referred to as a magnet pair 61 as appropriate. Similarly, the magnets 62f and 62b, the magnets 63f and 63b, and the magnets 64f and 64b are referred to as a magnet pair 62, a magnet pair 63, and a magnet pair 64, respectively.

Here, the state in which the magnets 61f, 62f, 61b, and 62b generate a magnetic field will be described with reference to FIGS. 3, 4, and 5. FIG. When the magnets 61f and 62f facing vertically (z direction) and the magnets 61b and 62b generate magnetic fields + H _z and −H _z repelling each other, the facing magnets are represented as lines of magnetic force in FIG. A magnetic field that spreads radially from the intermediate point is generated on the xy plane (referred to as z = 0 plane) including the intermediate point between them. Specifically, according to the simulation executed for the magnets 61f and 62f arranged as shown in FIG. 4, the z-component magnetic field becomes 0 on the z = 0 plane, as shown in FIG. In the vicinity of the intermediate point, magnetic fields of ± x and ± y components are generated. The numerical value displayed in FIG. 5 is a magnetic field (unit: A / m). Furthermore, the magnets 61b and 62b with the south poles facing each other and the magnets 61f and 62f with the north poles facing each other are arranged side by side with a small gap in the x direction, so that In the gap, a magnetic field −H _{eff in the} −x direction is generated that is much larger than the magnetic field of the ± x component (see FIG. 5A) generated by only one set of each of the magnets 61f and 62f and the magnets 61b and 62b. To do. As shown in FIG. 5B, this magnetic field -H _eff is particularly maximum at the center of the gap. The magnet 6 (61f, 62f, 61b, 62b) in the simulation is a permanent magnet having an x-direction length L _M of 20 nm, a y-direction length of 60 nm, and a saturation magnetic flux density of 1T. The magnet 61f-61b, the gap L _g is 60nm magnet 62f-62b, opposing the magnet 61f, 62f, the magnet 61b, a gap d of 62b is 50nm. As for the magnets 63f, 64f, 63b, and 64b, as shown in FIG. 5C, a large + x-direction magnetic field + H _eff is similarly generated on the z = 0 plane. Therefore, each of the magnets 61f, 62f, 61b, 62b and the magnets 63f, 64f, 63b, 64b has a magnetic field in the −x direction or + x direction that is remarkably large with respect to the magnetic force, arranged on the z = 0 plane. The magnetic domain wire moving element 1 is applied to the magnetic wire 11. By applying the magnetic field in the direction of the thin line in this way, the movement of the domain wall DW in the magnetic thin line 11 due to current supply becomes faster as will be described later, so that the writing speed of the domain wall moving element 1 becomes faster.

Magnetic fields generated by each of the magnets 6 + H _z and −H _z (appropriately collectively referred to as a magnetic field H _z ), that is, as the magnetic force of the magnet 6 increases, the magnetic field in the x direction −H _eff and + H _eff ( ( _Collectively expressed as magnetic field H _eff ). Further, the distance (= gap L _g ) between the magnets 61f-61b (referred to as two poles as appropriate) of the magnet pair 61 is not particularly limited as long as it is greater than 0, but the thickness of the domain wall DW (x Direction length) or more. Further, the large magnetic field H _eff in the x direction cannot be obtained when the gap L _g is excessively long, and becomes larger as the gap L _g is shorter. On the other hand, the length of the region where the magnetic field H _eff is generated (= Since the gap L _g ) is short, the period during which the magnetic field H _eff is applied when the domain wall DW is moving in the magnetic wire 11 is shortened, and the effect is reduced accordingly. Therefore, the gap L _g is preferably designed according to the size of the domain wall motion element 1 together with the magnetic force of the magnet 6. The same applies to the two poles of the magnet pair 62, 63, 64. As the magnetic fields −H _eff and + H _eff are increased, the movement of the domain wall DW in the magnetic wire 11 becomes faster. On the other hand, the magnetic field in the opposite direction also increases, so that the distance between the domain wall stationary positions p1 and p2 as described later. , And the moving distance of the domain wall DW in writing increases, and the writing time increases accordingly. Furthermore, if the magnetic fields −H _eff and + H _eff are excessively large, the movement of the domain wall DW due to current supply is hindered.

The magnetic field −H _eff and + H _eff in the direction of the fine line is applied to the domain wall DW when the domain wall motion element 1 is written, that is, when the domain wall DW is moved in the magnetic line 11, and at least when the domain wall DW starts to move. Preferably it is. Specifically, the magnetic fields −H _eff and + H _eff are at least when the magnetic wall DW starts moving in the direction opposite to the current from the time when the supply of the current for moving the magnetic wall DW to the magnetic wire 11 is started. It is preferable that it is applied during the period until, and more preferably, it is applied continuously thereafter. Therefore, each of the magnets 61f and 61b and the magnets 62f and 62b has one stationary position of the domain wall DW in the magnetic wire 11 at a distance L _g (region F1 shown in FIG. 11A) between the two poles in the x direction. It is preferable to arrange so as to contain the Specifically, the magnet pairs 61 and 62 preferably include at least the domain wall stationary position p1 which is the target stationary position in the gap between the two poles, and further include a range including an error of the stationary position. Is more preferable. In the present embodiment, the magnet pairs 61 and 62 are arranged so that the middle of the two poles where the magnetic field −H _eff is the maximum is the domain wall stationary position p1. In addition, it is preferable that the magnets 61f and 62f are arranged so as to be appropriately spaced from the domain wall stationary position p2 that is the destination of the domain wall DW. When the magnets 61f and 62f are too close to the domain wall stationary position p2, a magnetic field directed outward from the magnets 61f and 62f, that is, the magnetic field in the + x direction acts on the domain wall DW after the movement due to current supply, and the domain wall DW is moved to the domain wall stationary position p2. May be moved unnecessarily. On the other hand, if the distance between the magnets 61f and 62f and the domain wall stationary position p2 is excessively increased, the distance between the domain wall stationary positions p1 and p2 becomes longer, and accordingly the writing time becomes longer. Similar to the magnet pairs 61 and 62, the magnet pairs 63 and 64 are arranged so that the middle of the two poles is the domain wall stationary position p2 in the x direction, and the magnets 63f and 64f are moderately positioned from the domain wall stationary position p1. It is preferable that they are arranged so as to be spaced apart from each other.

(Domain wall motion by current supply in fine magnetic wire)
The domain wall motion by current supply in the magnetic wire will be described with reference to FIG. In FIG. 6, a portion including the domain wall DW of the magnetic thin wire 11 (magnetization reversible region 1 _SW (see FIG. 2)) is shown enlarged in the thin wire direction (x direction). Between the magnetic domains D1 and D2 of the magnetic thin wire 11 made of a ferromagnetic material, the magnetization direction does not change suddenly from the downward direction to the upward direction, and exchange interaction that tries to align the adjacent magnetic moments m and m in the same direction works. The magnetic moment m arranged on the domain wall DW is gradually inclined from the magnetic domain D1 side to the magnetic domain D2 side. Normally, the magnetic thin wire 11 made of a perpendicular magnetic anisotropic material and having a small thickness and width has a magnetic wall m from the downward direction in the magnetic domain D1, as shown in FIGS. 6 (a) and 6 (b). It is rotated 180 ° in the xz plane so as to incline toward the fine line direction (x direction) perpendicular to the (yz plane) and to face upward in the magnetic domain D2. Further, at that time, there is a rotation in which the magnetic moment m is directed to the magnetic domain D2 side (right) (see FIG. 6A) and a reverse rotation is directed to the magnetic domain D1 side (left) (see FIG. 6B). .

When a current is supplied in the −x direction from the magnetic domain D2 side to the magnetic wire 11 generated by such a domain wall DW, the same downward spin is caused by the downward magnetic moment m of the magnetic domain D1 from the magnetic domain D1 side. Electrons e ⁻ are discriminated and injected unevenly. The electron e ⁻ moves from the magnetic domain D1 to the magnetic domain D2 via the domain wall DW in the + x direction opposite to the direction of the current as indicated by the white arrow. Then, the electron e ⁻ is rotated in the same direction by the magnetic moment m at the domain wall DW, and the angular momentum changes at that time. That is, in FIG. 6A, the electron e ⁻ moves while rotating the domain wall DW from the magnetic domain D1 side to the magnetic domain D2 side by 180 ° counterclockwise in the xz plane. Then, the angular momentum is transferred from the electron e ⁻ to the magnetic moment m according to the law of conservation of angular momentum, and the force rotating in the direction opposite to the rotation of the electron e ⁻ works (spin torque transfer effect), and is supplied to the magnetic wire 11. When the current density of the generated current is greater than or equal to the threshold value, the magnetic moment m rotates clockwise. As a result, the domain wall DW apparently moves in the same + x direction as the electron e ⁻ , the rear magnetic domain D1 expands, and the front magnetic domain D2 shortens. In the domain wall DW shown in FIG. 6B, the electron e ⁻ moves in the + x direction while rotating clockwise in the xz plane, and at that time, the magnetic moment m rotates counterclockwise. Apparently, the domain wall DW moves in the + x direction. Further, as the number of injected electrons e ⁻ increases, the rotation angle of the magnetic moment m increases, so that the moving distance of the domain wall DW increases. Therefore, the higher the current density of the supplied current, the faster the domain wall DW moves. When the domain wall DW is moved only by supplying current to the magnetic wire 11, the moving distance of the domain wall DW is determined by the current density of current and the supply time.

Furthermore, the movement of the domain wall DW when a current is supplied in the −x direction while applying a magnetic field in the thin wire direction (+ x direction, −x direction) to the magnetic thin wire 11 is represented by an LLG (Landau−) having a spin transfer torque term. Observe by simulation using Lifshitz-Gilbert equation. Here, the magnetic thin wire 11 has a thickness of 20 nm, a width of 60 nm, a length (length in the x direction) of 1500 nm, and magnetic properties of saturation magnetization: 0.25 T, uniaxial anisotropy H _k : 7.06 × 10 ⁵ A / m, exchange stiffness: 1.2 × 10 ⁻¹¹ J / m, Gilbert damping constant: 0.02. The simulation cell size was 4 × 4 × 4 nm ³ . Further, in order to make the influence of the magnetic field easy to understand, 16 or 8 sets of magnets 6 are arranged at equal intervals in the x direction as shown in FIG. 7, and the polarities are alternately switched one by one. In FIG. 7, the first and second sets of magnets 6 are omitted from the left (rear in the direction of travel of the domain wall DW). Each of the magnets 6 is a permanent magnet having an x-direction length L _M of 20 nm and a y-direction length of 60 nm, as in the simulations shown in FIGS. 4 and 5. The gap L _g between the magnets 6-6 aligned in the x direction is 60 nm, and the gap d between the opposing magnets 6 and 6 is 50 nm. In the magnetic thin wire 11, one domain wall DW is generated at substantially the center in the x direction. As shown in FIG. 7A, as the sample A, the domain wall DW is in the initial state, and the S poles and the N poles are opposed to each other. The set of magnets 6 was set so as to be arranged at the center of the gap arranged in order from the back to the front. Further, as sample B, as shown in FIG. 7B, the domain walls DW are opposed to each other in the gap where two sets of magnets 6 in which the N poles and the S poles face each other are arranged in order from the back to the front. It was set to be arranged at the rear end of the magnet 6 of the set. For sample A, the saturation magnetic flux density of magnet 6 was set to three types of 0.5T, 1T, and 2T, and for sample B, the saturation magnetic flux density of magnet 6 was set to 1T. Further, as a comparative example, a sample (ref.) Having only a magnetic thin wire 11 and no magnet (with a saturation magnetic flux density of 0 T) was set.

The magnetic thin wire 11 of each sample is stopped by supplying one pulse of 9.1 × 10 ⁷ A / cm ^{2 in} the −x direction from one end as a pulse current having a pulse width of 0.8 ns, that is, 0.8 ns. Supplied. An average value of magnetization of the entire magnetic wire 11 is calculated every 0.01 ns by simulation, and a graph showing a change in magnetization of the magnetic wire 11 with the lapse of time when the current supply start time is 0 is shown in FIG. A) and shown in FIG. 9 (sample B). Further, as the domain wall DW moves in the + x direction, the magnetic domain D1 in the downward magnetization direction expands in the x direction. Therefore, the moving distance of the domain wall DW is calculated from the average magnetization of the magnetic thin wires 11, and FIGS. It is written together in each.

  As shown in FIG. 8, the sample ref. The magnetic domain wall DW moved at a constant speed (moving speed at the time of current supply) in the + x direction during 0.8 ns while the current was supplied. On the other hand, the sample A in which the magnetic field in the −x direction is applied to the domain wall DW at the start of current supply by the magnet 6 having the saturation magnetic flux densities of 0.5T and 1T, when the current supply is started, the domain wall DW However, it first moves at a speed higher than the moving speed at the time of current supply, and then switches to a movement at a lower speed than the moving speed at the time of current supply, and then moves again at a higher speed and moves while being supplied with current. Moving in the + x direction while switching the speed alternately. Specifically, the domain wall DW moved at a high speed during a period in which a magnetic field in the −x direction was applied, and at a low speed during a period in which a particularly large magnetic field in the + x direction was applied. Since the high-speed movement speed is significantly higher than the movement speed at the time of current supply, the movement distance at the time when 0.8 ns has elapsed is the sample ref. It was longer than. Further, in these samples A, the domain wall DW moves even after the current supply is stopped, and the moving distance (amplitude) gradually decreases while repeating forward and backward alternately in the vicinity of the position when the current supply is stopped. Specifically, it stopped around the center of the area moved at high speed. It is presumed that this is because the magnetic wall m is rotated by applying a magnetic field from the magnet 6 in the vicinity of the domain wall DW with vibration remaining in the magnetic moment m (see FIG. 6). On the other hand, in the sample A provided with the magnet 6 having the saturation magnetic flux density 2T, the moving distance (amplitude) of the domain wall DW gradually decreases from the start position while repeating forward and backward alternately in the vicinity thereof, and finally from the start position. Did not move.

FIG. 10 shows a graph of the saturation magnetic flux density dependency of the magnet, in which the moving speed of the domain wall DW is approximately obtained from the graph shown in FIG. Saturation magnetic flux density 0.5T magnet, for a sample A of 1T, fast moving velocity v _H magnetic wire average magnetization in the range of about -0.03～-0.04, low speed of about -0.047 vicinity The moving speed v _{L of} was obtained. Further, the average moving speed v _AVE was calculated from the time required for the magnetic fine wire average magnetization to move in the range of −0.017 (0 ns) to −0.057. For Sample A saturation magnetic flux density 2T magnet, to obtain a moving velocity v _H of the high speed from a range of time 0～0.02Ns. As shown in FIG. 10, the higher the saturation magnetic flux density of the magnet, that is, the larger the applied magnetic field, the higher the moving speed of the domain wall DW at a higher speed. On the other hand, as the applied magnetic field is larger, the tendency of the domain wall DW to move at a low speed is observed to be slightly low, but the difference in the movement speed at a high speed is extremely small. Therefore, the moving distance of the domain wall DW in the period of 0.8 ns in which the current was supplied was longer as the magnetic field was larger at a saturation magnetic flux density of 1 T or less, and the effect was high.

  On the other hand, as shown in FIG. 9, in the sample B in which a magnetic field in the + x direction is applied to the domain wall DW at the start of current supply, the domain wall DW recedes in the −x direction immediately after the start of current supply, and then the + x direction. Thereafter, as in the case of Sample A, while the current was supplied, the sample moved in the + x direction while alternately switching the moving speed. Specifically, the domain wall DW moved at a high speed during a period in which a magnetic field in the + x direction was applied, and at a low speed during a period in which a particularly large magnetic field in the -x direction was applied.

From FIG. 8 and FIG. 9, the domain wall DW generated in the magnetic thin wire 11 is moved by supplying a current by applying a magnetic field in the thin wire direction perpendicular to the easy magnetization axis (z direction) of the magnetic thin wire 11. The speed can be increased and the moving distance can be increased. Furthermore, the moving speed is increased by a magnetic field in the same direction as the direction applied to the domain wall DW at the start of current supply, and this magnetic field is effective in both the + x direction and the -x direction as long as it is a thin line direction. is there. However, as shown in FIG. 9, when a magnetic field in the same direction as the direction of movement of the domain wall DW, that is, the movement direction of the electron e ⁻ is applied at the start of current supply, the domain wall DW Start moving forward after moving backwards. Therefore, it is preferable to arrange the magnet 6 so that a magnetic field opposite to the direction in which the domain wall DW is moved is applied to the domain wall DW at the start of movement.

(Writing method of domain wall motion element with magnet)
A writing method of the domain wall motion element with magnet according to the present embodiment will be described with reference to FIG. 11 and FIG. 2 as appropriate. In FIG. 11, the barrier layer 3 and the submagnetization fixed layer 23 of the domain wall motion element 1 are omitted. First, the state in which the domain wall DW shown in FIG. 2A is stationary at the domain wall stationary position p1 of the magnetic wire 11 is changed to the state stationary at the domain wall stationary position p2 as shown in FIG. A current of a predetermined magnitude is supplied to the coils of the magnets 61f, 61b, 62f, and 62b to generate a magnetic field, and a magnetic field −H _eff in the −x direction is changed to that of the magnetic wire 11 as shown in FIG. Applied to the region near the domain wall stationary position p1. At this time, the magnets 63f, 63b, 64f, and 64b are represented by broken lines because no current is supplied to the coils and no magnetic field is generated. Then, the first electrode 51 "-", the second electrode 52 as "+", and supplies a current I _w in the -x direction to the magnetic wire 11 by way of the magnetization fixed layer 21. As a result, electrons e ⁻ having a downward spin are injected into the magnetic domain D1 of the magnetic wire 11 and move in the + x direction. As described with reference to FIG. 6, the domain wall DW moves in the + x direction with the movement of the electron e ⁻ in the magnetic wire 11, but the period of moving the region F <b> 1 to which the magnetic field −H _eff is applied is the current. movement speed of the domain wall DW only by the supply of I _w (hereinafter, referred to as time current supply moving speed) to move faster than.

When the domain wall DW passes through the region F1 and further passes between the magnets 61f and 62f, a magnetic field + H _eff ′ in the + x direction is applied by the magnets 61f and 62f, so that the domain wall DW moves at a speed lower than the moving speed at the time of current supply. The speed changes. When the domain wall DW passes through the region F2 to which the magnetic field + H _eff ′ is applied, the domain wall DW moves at a current supply moving speed or at a higher speed than the current supply moving speed. At this time, no magnetic field is applied to the domain wall DW in both the + x direction and the −x direction. However, if the magnetic field −H _eff applied when moving in the region F1 is sufficiently large, the vibration with the remaining magnetic moment is generated. It is presumed that the rotation due to the spin torque of the electron e ⁻ is restored to approach the state when moving in the region F1 to some extent. After that, with the movement of the domain wall DW, time passes and the vibration of the rotation of the magnetic moment is attenuated, gradually decelerates and approaches the moving speed at the time of current supply, and finally moves at the moving speed at the time of current supply. When the domain wall DW may stop the supply of the current I _w in accordance with the time it reaches the domain wall resting position p2, the domain wall DW is, to stop the movement stops at the domain wall resting position p2. Further, the supply of current to the coil of the magnet 6 is stopped, and the application of the magnetic field is stopped.

In the domain wall motion element with magnet 10 according to the present embodiment, the movement of the domain wall DW temporarily decelerates, but the magnetic field in the + x direction + H _eff ′, which is the cause, is smaller than the magnetic field −H _eff , so the domain wall stationary position The entire movement between p1 and p2 is completed in a shorter time than the movement at the movement speed at the time of current supply. Incidentally, when the domain wall DW at the time of stopping the supply of the current I _w has not left the area F2, at the moment of stopping the supply of the current I _w, magnetic moment, electrons e ^- that it is no longer subjected to the spin torque In some cases, the vibration does not stop until the vibration disappears, such as rotating in the opposite direction by the remaining vibration and the magnetic field + H _eff ′ and _moving backward in the −x direction. As a result, it becomes difficult to accurately control the rest position of the domain wall DW with the supply time of the current I _w.

In order to change from the state where the domain wall DW shown in FIG. 2B is stationary at the domain wall stationary position p2 of the magnetic wire 11 to the state where it is stationary at the domain wall stationary position p1 as shown in FIG. Then, a current is supplied to the coils of the magnets 63f, 63b, 64f, and 64b, and a magnetic field + _Heff in the + x direction is applied to a region near the domain wall stationary position p2 of the magnetic wire 11 as shown in FIG. At this time, the magnets 61f, 61b, 62f, and 62b are represented by broken lines because they do not generate a magnetic field. Then, the first electrode 51 is set to “+” and the second electrode 52 is set to “−”, and the current I _w is supplied to the magnetic wire 11 through the magnetization fixed layers 21 and 22 in the + x direction. Thereby, an electron e ⁻ having an upward spin is injected into the magnetic domain D2 of the magnetic wire 11 and moves in the −x direction. Then, the domain wall DW moves in the same manner as the movement in the + x direction shown in FIG. 11A except that the movement direction is reversed in the −x direction. That is, during the period in which the region F3 where the magnetic field + H _eff is applied to the domain wall DW is moved, the region F4 moves at a higher speed than the moving speed at the time of current supply, and the region F4 where the magnetic field −H _eff ′ in the −x direction is applied During the movement period, the movement speed is lower than the movement speed at the time of current supply, and after passing through the region F4, the movement speed is again high, and then gradually decelerates to approach the movement speed at the time of current supply. When the domain wall DW may stop the supply of the current I _w in accordance with the time it reaches the domain walls rest position p1, the domain wall DW is frozen domain wall rest position p1, further stops the supply of current to the coil of the magnet 6.

Thus, in accordance with the direction of current supplied I _w to the magnetic wire 11, moving magnet 61f, 61b, 62f, 62b or a magnet 63f, 63 b, 64f, by generating a magnetic field 64b, the domain wall DW fast Thus, the writing time can be shortened. The magnetic thin wire 11 is always applied with a predetermined one of the magnetic fields -H _eff and + H _eff when the current I _w is supplied. That is, given four magnets 6 is started the supply of current to simultaneously or coils before the supply start and the current I _w, the supply of current to the simultaneous or subsequent to the coil supply end and the current I _w Stopped. Further, if the moving distance of the domain wall DW in writing (distance between the domain wall stationary positions p1 and p2) is about several tens of nm to 1 μm, the supply time of the current I _w is 0.1 ns to 100 ns, although it depends on the current density. In order to supply such an extremely short time direct current, a pulse current is preferable.

(Magnetic memory)
The magnetic domain wall motion element 10 with a magnet is mounted as a magnetoresistive effect element of the memory cells 9 arranged in the magnetic memory 90 shown in FIG. In FIG. 12A and FIG. 12B, for the sake of brevity, four memory cells 9 (9A) of 2 columns × 2 rows are shown, and the domain wall motion element 1 is connected to a resistor. And the variable resistor graphic symbol. The magnet pairs 61, 62, 63, and 64 are each represented by a graphic symbol of one electromagnet. The memory cell 9 includes a transistor 71 connected to the first electrode 51 of the domain wall motion element 1 and a transistor 72 connected to the second electrode 52 together with the domain wall motion element 10 with magnet. In the magnetic memory 90, a bit line BLT connected to the first electrode 51 via the transistor 71 and a bit line BLB connected to the second electrode 52 via the transistor 72 are extended in the row direction, A word line WL that is commonly input to the gates of the transistors 71 and 72 of the same memory cell 9 is extended in the column direction. The third electrode 53 is connected to GND (0 V). Furthermore, the magnetic memory 90 includes wirings ML1P and ML1N that are commonly connected to the magnet pairs 61 and 62, and wirings ML2P and ML2N that are commonly connected to the magnet pairs 63 and 64. Note that the arrangement direction (row direction, column direction) of the memory cells 9 in the magnetic memory 90 and the x and y directions of the magnetic domain wall motion element 10 may not coincide with each other. For example, the x direction (the fine line of the magnetic thin line 11) Direction) may be inclined by 45 ° with respect to the arrangement direction of the memory cells 9. Further, in the domain wall motion element 10 with a magnet, if the current is not supplied to the domain wall motion element 1 (magnetic thin wire 11), the domain wall DW does not move and writing is not performed. Even if the magnet pairs 63 and 64 are in the ON state, there is no erroneous writing or the like. Therefore, in the magnetic memory 90, the wirings ML1P, ML1N, ML2P, and ML2N are extended in the column direction (or row direction), and the magnet pair 61, 62 or the magnet pairs 63, 64 in the same column as the memory cell 9 selected for writing. At the same time. Alternatively, the magnetic memory 90 includes transistors or diodes for switching connection / disconnection to / from the wirings ML1P, ML1N, ML2P, and ML2N so that the predetermined four magnets 6 are turned on only in the selected memory cell 9. The memory cell 9 may be provided (not shown).

The transistors 71 and 72 are, for example, MOSFETs (metal oxide semiconductor field effect transistors) and are formed on the surface layer of the Si substrate. Therefore, the memory cells 9 can be arranged on the basis of the Si substrate. The bit lines BLT and BLB, the word line WL, and the wirings ML1P, ML1N, ML2P, and ML2N are formed of a metal electrode material in the same manner as the electrodes 51, 52, and 53. Also, a known inorganic insulating material provided in a semiconductor element such as SiO ₂ or Al ₂ O ₃ is filled in the gaps between these wires or between the magnetic thin wires 11 of the adjacent memory cells 9 and 9. The

For writing to the magnetic memory 90, a direct current pulse current is supplied through the bit lines BLT and BLB, and the magnet pairs 61 and 62 or the magnet pair 63 are connected via the wiring ML1P and ML1N or the wiring ML2P and ML2N according to the direction of the pulse current. A current for generating a magnetic field H _z having a predetermined magnitude is supplied to 64 coils, and a gate voltage is applied to the word line WL. Note that a continuous current may be supplied to the bit lines BLT and BLB, and a gate voltage may be pulsed to the word line WL. In addition, the magnetic memory 90 is read by applying a gate voltage on the word line WL in the same manner as writing, while connecting the bit lines BLT and BLB together to the positive electrode of a constant current source with the negative electrode connected to GND, thereby moving the domain wall. A constant current is supplied from the electrodes 51 and 52 of the element 1 to the third electrode 53.

  Or the domain wall motion element 10 with a magnet may be mounted in the memory cell 9A of the magnetic memory 90A shown in FIG.12 (b). The memory cell 9 </ b> A includes a transistor 71 connected to the first electrode 51 of the domain wall motion element 1 and a diode 73 connected to the third electrode 53 together with the domain wall motion element 10 with magnet. In the magnetic memory 90A, the second electrode 52 is directly connected to the bit line BLB, and the read bit line RBL connected to the third electrode 53 via the diode 73 is extended in the column direction. The magnetic memory 90A having such a structure can be written in the same manner as the magnetic memory 90. On the other hand, in reading data from the magnetic memory 90A, a gate voltage is not applied, a constant current source (not shown) is connected to the bit line BLB and the read bit line RBL, and the second electrode 52 to the third electrode of the domain wall motion element 1 are connected. A constant current is supplied to 53.

(Modification)
The domain wall motion element 1 of the magnetic domain wall motion element 10 with magnet has a thickness made of a nonmagnetic metal on the bottom and top surfaces, such as the bottom surfaces of the magnetization fixed layers 21 and 22 and the top surface of the submagnetization fixed layer 23, as necessary. A base film or a protective film with a thickness of about 1 to 10 nm may be provided. The domain wall motion element 1 may be provided with a magnetic coupling film having a thickness of about 1 to 10 nm made of a nonmagnetic metal such as Ru or Ta at the interface between the magnetic wire 11 and the magnetization fixed layers 21 and 22. Further, in the domain wall motion element 1, the barrier layer 3 and the submagnetization fixed layer 23 may be laminated below the magnetic thin wire 11 like the magnetization pinned layers 21 and 22. The second magnetization fixed layer 22 may be connected to the upper and lower surfaces of the magnetic wire 11. Further, the domain wall moving element 1 is fixed in magnetization if there is no possibility that the domain wall DW moves and disappears excessively in writing, such as the magnetic wire 11 has a sufficient length from the domain wall stationary positions p1 and p2 to the respective ends. The layers 21 and 22 need not be provided. In this case, the magnetic thin wire 11 is directly connected to the first electrode 51 and the second electrode 52 in the vicinity of both ends thereof. Further, the shape of the thin magnetic wire 11 is not limited to a straight line, and may be a shape including a gentle curve that does not hinder the movement of the domain wall DW. In this case, the magnets 61f, 61b, 62f, and 62b and the magnets 63f, 63b, 64f, and 64b are arranged so that the magnetic fields −H _eff and + H _eff in the thin line direction are applied at the domain wall stationary positions p1 and p2, respectively. (Not shown).

The magnets 6 and 6 that form a pair facing each other in the vertical direction do not have to be equidistant from the magnetic thin wire 11, and a magnetic field that is larger when the distance is far away generates a z component in the magnetic thin wire 11. It is only necessary to design so that the magnetic field becomes zero and a magnetic field in the xy in-plane direction is generated. Further, since the magnetic fields −H _eff and + H _eff may be applied to the domain wall stationary positions p 1 and p 2, for example, when the dimension of the domain wall moving element 1 is smaller than the magnet 6, the magnets 61 b and 62 b at both ends and the magnet 63 b are provided. , 64b may not be opposed to the magnetic wire 11 and may be disposed along the extension of the magnetic wire 11 in the thin wire direction. Further, when the memory cell 9 (9A) is arranged in the x and y directions in the magnetic memory 90 (90A), the magnetic domain wall motion elements 10 and 10 of the two memory cells 9 and 9 adjacent in the x direction are arranged. The magnets 61b and 62b at one end and the magnets 63b and 64b at the other end may be shared. Further, the magnet 6 may be shared by the domain wall motion elements 10 with magnets of two or more memory cells 9 adjacent to each other in the y direction by forming each magnetic pole long (wide) in the y direction.

In addition, the domain wall motion element 10 with magnet is configured such that only one pole of each of the eight magnets 6 faces the magnetic thin wire 11, but includes four magnets, and both of the two poles are connected to the magnetic thin wire 11. It is good also as a structure made to face. That is, in the magnetic domain wall motion element 10 with magnets, the magnet pairs 61, 62, 63, 64 are each composed of one electromagnet, and both ends are opposed so that both the two poles face the magnetic thin wire 11 at an equal distance. The core having the two poles is formed in a U-shape or the like. According to the electromagnet having such a structure, since a closed magnetic circuit is formed inside, the magnetic field hardly leaks to the outside between the two poles. Therefore, the magnetic fields −H _eff and + H _eff are further increased, and the reverse magnetic fields (+ H _eff ′ and −H _eff ′) are further suppressed.

  Moreover, the domain wall motion element 10 with a magnet may be provided with only four of the magnets 61f, 61b, 62f, 62b or the magnets 63f, 63b, 64f, 64b. Such a domain wall motion element 10 with a magnet has a simple structure while the domain wall DW moves in only one direction. For example, in the magnetic memory 90 (90A), when the domain wall motion elements 1 in all the memory cells 9 are simultaneously moved in the same direction at the current domain moving speed at the current supply time, and then the memory cells 9 are rewritten one column at a time. The domain wall DW is moved at high speed. According to such a writing method, the writing time of the entire magnetic memory 90 hardly changes as compared with the case where the magnetic domain wall motion element 10 includes eight magnets 6.

[Light modulation element, spatial light modulator]
The magnetic domain wall motion element 10 with a magnet can be a light modulation device by applying a magneto-optical material such as Gd-Fe to the magnetic wire 11 of the domain wall motion device 1. In this case, the barrier layer 3 and the submagnetization fixed layer 23 of the domain wall motion element 1 are unnecessary. Alternatively, the barrier layer 3 and the submagnetization fixed layer 23 are stacked below the same magnetic wire 11 as the magnetization pinned layers 21 and 22 so that light is incident between the domain wall stationary positions p1 and p2 of the magnetic wire 11. To do. Furthermore, a sufficient space is provided between the magnets 61f and 62f and the magnets 63f and 64f to form an opening region. The width of the magnetic wire 11 and the length of the opening region in the x direction are preferably about 200 to 300 nm or more, although depending on the wavelength of incident light. Furthermore, the greater the thickness of the magnetic wire 11, the higher the light modulation degree. When such a domain wall motion element 10 with magnets is arranged to constitute a spatial light modulator, the diode 73 and the read bit line RBL may be deleted from the magnetic memory 90A shown in FIG.

  As described above, according to the domain wall motion element with a magnet according to the first embodiment of the present invention, the writing speed is increased without increasing the current, so that the magnetic wire is hardly deteriorated and can be used for a long time. . Furthermore, since a large magnetic field is generated as a structure in which one pair of upper and lower magnets are arranged at two locations sandwiching one domain wall stationary position of the magnetic thin wire in the thin wire direction, the magnetic force of the magnet need not be designed to be large.

[Second Embodiment]
The pair of upper and lower magnets of the domain wall motion element with magnets facing each other across the fine magnetic wire generates a radial magnetic field in the xy plane, that is, includes magnetic fields in the + x direction and the −x direction. Hereinafter, a domain wall motion element with a magnet according to a second embodiment of the present invention in which one set of electromagnets is provided for each domain wall stationary position will be described with reference to FIG. The same elements as those in the first embodiment (see FIGS. 1 to 12) are denoted by the same reference numerals, and description thereof is omitted.

  As shown in FIG. 13, the domain wall motion element with magnet 10A according to the second embodiment of the present invention includes the domain wall motion element 1 and four magnets (magnetic field applying means) 61A, 62A, 63A, 64A. The domain wall motion element 1 is as described with reference to FIG. 2 in the first embodiment. In FIG. 13, the barrier layer 3 and the secondary magnetization fixed layer 23 of the domain wall motion element 1 are omitted.

The pair of magnet 61A and magnet 62A, and pair of magnet 63A and magnet 64A are disposed above and below with the magnetic wire 11 in between, and either set simultaneously generates a magnetic field when the domain wall motion element 1 is written. The magnets 61A, 62A, 63A, and 64A each have the south pole facing the magnetic fine wire 11, and thus correspond to the magnets 61b, 62b, 63b, and 64b of the magnetic wall motion element 10 with magnet according to the first embodiment, respectively. With such a configuration, like the magnets 61b and 62b shown in FIG. 3, the xy plane (z = 0 plane) including the midpoint between the opposing magnets 61A and 62A (63A and 64A) is radial to the midpoint. A magnetic field concentrated on This magnetic field becomes smaller as the distance from the intermediate point increases, and becomes maximum at the outer edges of the south poles of the magnets 61A and 62A in plan view (xy plane). Therefore, the magnetic domain wall motion element 10A with a magnet puts the magnets 61A and 62A outside the magnetization reversible region 1 _SW (see FIG. 2) outside the domain wall stationary position p1 of the magnetic wire 11 (on the −x direction side) in plan view. In addition, it is preferable that the outer edges of the magnets 61A and 62A are arranged at positions near the domain wall stationary position p1. By the magnets 61A and 62A arranged in this way, a relatively large magnetic field −H _eff in the −x direction is applied to the domain wall DW stationary at the domain wall stationary position p1. Similarly, the magnets 63A and 64A are preferably arranged outside the magnetization reversible region 1 _SW outside the domain wall stationary position p2 of the domain wall motion element 1 (on the + x direction side). In the present embodiment, the magnets 61A, 62A, 63A, and 64A are configured so that the magnetic fields −H _eff and + H _eff applied to the magnetic wire 11 are the first to the magnitude (magnetic force) of the generated magnetic field H _z. Since it is not large compared with the form, it is designed to generate a sufficiently strong magnetic force.

(Writing method of domain wall motion element with magnet)
A writing method of the domain wall motion element with magnet according to the present embodiment will be described with reference to FIG. 13 and FIG. 2 as appropriate. First, the state in which the domain wall DW shown in FIG. 2A is stationary at the domain wall stationary position p1 of the magnetic wire 11 is changed to the state stationary at the domain wall stationary position p2 as shown in FIG. A current is supplied to the coils of the magnets 61A and 62A to generate a magnetic field, and as shown in FIG. 13A, a magnetic field -H _eff in the -x direction is applied to a region near the domain wall stationary position p1 of the magnetic wire 11. To do. At this time, since the magnets 63A and 64A do not generate a magnetic field, they are represented by broken lines. Then, as in the first embodiment (see FIG. 11 (a)), the first electrode 51 "-", supplying the second electrode 52 as "+", the current I _w in the -x direction to the magnetic wire 11 Thus, when electrons e ⁻ are injected into the magnetic domain D1 of the magnetic wire 11 and moved in the + x direction, the domain wall DW moves in the + x direction. The domain wall DW moves at a higher speed than the current supply moving speed during the period in which the magnetic field −H _eff is applied. After passing through this area, the domain wall DW gradually decelerates to the current supply moving speed. Get closer. When the domain wall DW may stop the supply of the current I _w in accordance with the time it reaches the domain wall resting position p2, the domain wall DW is, to stop the movement stops at the domain wall resting position p2. Further, the current supply to the coils of the magnets 61A and 62A is stopped, and the application of the magnetic field is stopped.

In the domain wall motion element 10A with a magnet according to the present embodiment, the domain wall DW is not applied with a magnetic field in the + x direction that inhibits the movement during the movement in the + x direction, so the magnets 61A and 62A and the domain wall stationary position without leaving large distance between p2, as in the first embodiment, the domain wall DW immediately after stopping supply of the current I _w has no possibility to retract. However, when stopping the supply of the current I _w when the region where the magnetic field -H _eff is applied domain wall DW is moving, sometimes advancing to further the + x direction after the stop. Therefore, when the distance between the domain wall stationary positions p1 and p2 is short, the domain wall moving element 1 has the first magnetization fixed layer 21 and the magnetic domain wire 11 to fix the magnetization direction from the domain wall stationary positions p1 and p2 to the end of the magnetic wire 11. It is preferable to include the second magnetization fixed layer 22.

In order to change from the state where the domain wall DW shown in FIG. 2B is stationary at the domain wall stationary position p2 of the magnetic wire 11 to the state where it is stationary at the domain wall stationary position p1 as shown in FIG. Then, a current is supplied to the coils of the magnets 63A and 64A, and a magnetic field + H _eff in the + x direction is applied to a region near the domain wall stationary position p2 of the magnetic wire 11 as shown in FIG. At this time, the magnets 61A and 62A do not generate a magnetic field, and are represented by broken lines. Then, as in the first embodiment (see FIG. 11B), the first electrode 51 is set to “+”, the second electrode 52 is set to “−”, and the current I _w is supplied to the magnetic wire 11 in the + x direction. As a result, electrons e ⁻ are injected into the magnetic domain D2 of the magnetic wire 11 and moved in the −x direction. Then, the domain wall DW moves in the same manner as the movement in the + x direction shown in FIG. 13A except that the moving direction is reversed in the −x direction. In other words, the period of movement in the region where the magnetic field + H _eff is applied to the domain wall DW moves at a speed higher than the moving speed at the time of current supply, and after passing through this area, gradually decelerates to the moving speed at the time of current supply. Get closer. Then, stop the magnetic domain wall DW may stop the supply of the current I _w in accordance with the time it reaches the domain walls rest position p1, the domain wall DW is frozen domain wall rest position p1, further magnet 63A, the current supply to 64A of the coil To do. Thus, as in the first embodiment, in accordance with the direction of the current I _w to be supplied to the magnetic wire 11, the magnets 61A, 62A, or the magnet 63A, by generating a magnetic field 64A, moving the domain wall DW fast Thus, the writing time can be shortened.

(Magnetic memory, light modulator and spatial light modulator)
Similarly to the domain wall motion element 10 with magnet, the domain wall motion element 10A with magnet is mounted as a magnetoresistive effect element of the memory cells 9 and 9A arranged in the magnetic memories 90 and 90A shown in FIGS. 12 (a) and 12 (b). Is done. Moreover, the domain wall motion element 10A with a magnet can be arranged as a light modulation element, and can comprise a spatial light modulator. When the magnetic memory 90 (90A) has memory cells 9 (9A) arranged in the x and y directions, the magnetic domain wall motion elements 10A and 10A of the two memory cells 9 and 9 adjacent in the x direction are arranged. One magnet 61A, 62A and the other end magnet 63A, 64A may be shared. Similarly to the first embodiment, 61A, 62A, 63A, and 64A are provided with respective magnets of two or more memory cells 9 adjacent to each other in the y direction by forming each magnetic pole long in the y direction (wide). The domain wall motion element 10A may be shared.

  As described above, according to the domain wall motion element with a magnet according to the second embodiment of the present invention, writing can be performed at a high speed and can be used for a long period of time as in the first embodiment, and the size can be further reduced. easy.

In order to confirm the effect of the present invention, a simulation using an LLG (Landau-Lifshitz-Gilbert) equation having a spin transfer torque term is performed on a sample simulating the domain wall motion element with magnet according to the first embodiment of the present invention. Executed. Instead of the domain wall motion element, a sample of only a magnetic wire having a thickness of 20 nm, a width of 60 nm, and a length (length in the x direction) of 1500 nm is used, and the magnetic properties of the magnetic wire are saturation magnetization: 0.25 T, uniaxial anisotropy H _k : 7.06 × 10 ⁵ A / m, exchange stiffness: 1.2 × 10 ⁻¹¹ J / m, Gilbert damping constant: 0.02. The simulation cell size was 4 × 4 × 4 nm ³ . Then, as shown in FIG. 4, a set (61b, 62b) in which the S poles of two permanent magnets (magnets 6) are opposed to each other in the z direction with the magnetic thin wire 11 therebetween is the -x direction side of the domain wall DW. In addition, a total of four sets (61f, 62f) in which the N poles are opposed to each other are arranged on the + x direction side of the domain wall DW. Magnets are the same 60 nm, x-direction length L _M is 20 nm y-direction length and the magnetic wire 11, the magnet with each other (N poles, S poles) facing the gap of the gap d is 50 nm, 2 pairs of magnets L _g is 60 nm. In addition, one domain wall DW generated on the magnetic wire 11 was set to be arranged at the center of the gap between the two sets of magnets in the initial state. Three types of samples (Nos. 1 to 3) with a saturation magnetic flux density of 0.5T, 1T, and 2T are set, and as a comparative example, a sample without a magnet (with a saturation magnetic flux density of 0T) (No. 5) )It was set.

The magnetic thin wire of each sample is stopped by supplying one pulse of a current of 9.1 × 10 ⁷ A / cm ^{2 in} the −x direction from one end as a pulse current having a pulse width of 0.8 ns, that is, supplying 0.8 ns. did. Moreover, the simulation was performed also about the case (No. 4) when not supplying an electric current with the sample of saturation magnetic flux density 1T of a magnet. FIG. 14 shows a graph representing the change in magnetization of the magnetic wire with the passage of time when the average value of the magnetization of the entire magnetic wire is calculated every 0.01 ns by simulation and the current supply start time is zero. Further, since the magnetic domain in the downward magnetization direction expands in the x direction as the domain wall moves in the + x direction, the movement distance of the domain wall is calculated from the magnetization of the magnetic wire and is also shown in FIG.

Similarly, a simulation in which a pulse current was supplied was also performed on the samples (Nos. 6 and 7) in which the gap L _g of the magnet having a saturation magnetic flux density of 1T was changed to 20 nm and 80 nm. These samples were also set so that the domain wall DW was arranged at the center of the gap between the two sets of magnets in the initial state. Gap L _g is 60nm of the sample (No.2), and with the sample (No.5) without magnets, shown in Figure 15 a graph showing changes in magnetization of the magnetic wire.

  As shown in FIG. 14, when a magnet having saturation magnetic flux densities of 0.5T and 1T is provided and a current is supplied, the domain wall DW is moved to one set on the + x direction side from the movement start position (the center of the gap between the two sets of magnets). Move to the vicinity of the magnet at a higher speed than the comparative example without magnet (No. 5), once at a low speed, then move again at a high speed, and then gradually decelerate to approach the moving speed of the comparative example, While supplying current, it was observed to move in the + x direction. Moreover, the moving speed at high speed was higher as the saturation magnetic flux density of the magnet was higher, that is, as the magnetic field was larger. However, in the sample (No. 3) provided with a magnet having a saturation magnetic flux density of 2T, the moving distance (amplitude) of the domain wall DW gradually decreases while alternately moving forward and backward in the vicinity from the start position. It did not move from the start position. In addition, the sample (No. 1) in which the saturation magnetic flux density of the magnet was 0.5 T was advanced again after the domain wall DW was retracted after the supply of current was stopped. This is presumed to be caused by the influence of the magnetic field because the domain wall DW is close to one set of magnets on the + x direction side when the supply of current is stopped. Further, even if a magnet is provided, if no current is supplied (No. 4), it is observed that the domain wall DW does not move, and the external magnetic field itself by the magnet does not move the domain wall DW. Thus, by locally applying a magnetic field in the direction of the fine line to the region where the magnetic domain wall DW of the magnetic fine line 11 is generated, the moving speed of the domain wall DW due to current supply becomes high, and the domain wall DW generates a magnetic field. It was confirmed that the effect persisted for a certain period after leaving the applied area.

Further, as shown in FIG. 15, the gap L _g of 2 pairs of magnets as the gap is long in the range of 20 to 80 nm, since the region where the magnetic domain wall DW moves at high speed is increased, has been supplying current 0 The distance traveled in .8ns becomes longer. However, if the gap L _g of the two sets of magnets is 80nm of (No.7) is retracted domain wall DW after outage current, repeated alternately forward and backward in the vicinity of the starting position. This is presumed to be caused by the influence of the magnetic field because the domain wall DW is close to a pair of magnets on the + x direction side when the current supply is stopped, and the current supply time is extended to 2.0 ns. (No. 8) When the moving distance of the domain wall DW by the current was increased, it was observed that the domain wall DW hardly moved from the time when the supply of current was stopped.

  As mentioned above, although each embodiment for implementing the domain wall motion element and the magnetic memory according to the present invention has been described, the present invention is not limited to these embodiments, and various modifications can be made within the scope of the claims. It can be changed.

10, 10A Magnetic domain wall motion element with magnet (magnetic domain wall motion element)
DESCRIPTION OF SYMBOLS 1 Domain wall moving element 11 Magnetic thin wire 61f, 61b, 61A Magnet (magnetic field application means)
62f, 62b, 62A Magnet (magnetic field applying means)
63f, 63b, 63A Magnet (magnetic field applying means)
64f, 64b, 64A magnet (magnetic field applying means)
90,90A magnetic memory 9,9A memory cell

Claims (5)

Provided with a magnetic wire formed by forming a perpendicular magnetic anisotropic material into a thin wire shape, when a current is supplied to the magnetic wire in the thin wire direction, the domain wall generated in the magnetic wire moves in a direction opposite to the current A domain wall motion element that
A pair of magnetic field applying means for generating magnetic fields that oppose each other so as to sandwich the magnetic fine wire or its extension in the fine line direction from above and below are further provided, and the set of magnetic field applying means generates the magnetic field. Thus, a magnetic wall moving element is characterized in that a magnetic field in a thin line direction is applied to the magnetic thin line. Two or more sets of the magnetic field applying means are provided in the direction of the thin magnetic wires,
2. The domain wall motion element according to claim 1, wherein the two sets of the magnetic field applying units simultaneously generate magnetic fields in opposite directions.   3. The domain wall motion element according to claim 1, wherein the set of magnetic field applying units applies the magnetic field in the fine line direction to at least a stationary position of a domain wall preset in the magnetic thin line. .   4. The domain wall motion element according to claim 1, wherein the perpendicular magnetic anisotropic material is a magneto-optical material.   A magnetic memory comprising a memory cell comprising the domain wall motion element according to any one of claims 1 to 4.