Magnetic element, magnetic device, magnetic memory and spatial light modulator

Abstract

To provide an SOT-type magnetic element comprising a topological insulator made of a BiSb alloy with high SOT effect as the channel layer.SOLUTION: A magnetic element 10 comprises a magnetic fine wire 1 having a magnetic layer 11 and a topological insulator layer 12 made of a BiSb alloy stacked together, and electrodes 21, 22 for supplying current Im to the magnetic fine wire 1 in the fine wire direction, and each of electrodes 21 and 22 comprise an upper electrode 2t bonded to the upper surface of the magnetic fine wire 1, and a lower electrode 2b bonded to the lower surface of the magnetic fine wire 1 and connected to the upper electrode 2t.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a magnetic element, and a magnetic device, a magnetic memory, and a spatial light modulator in which the magnetic element is arranged. [Background technology]

[0002] In magnetoresistive random access memories (MRAMs), which use the high and low resistance of the magnetoresistive effect element in a memory cell as binary data, MRAMs using a domain wall motion method (e.g., Patent Document 1) or a spin orbit torque (SOT) method (e.g., Patent Documents 2 and 3) have been developed to increase speed and reduce current as a method for writing, i.e., a method for reversing the magnetization of a magnetic film (free layer) that is a part of the magnetoresistive effect element.

[0003] In a domain wall motion MRAM, the free layer of a magnetoresistive element is formed as a thin wire extending on both sides, and the magnetization direction is changed between two predetermined points along the length of the wire. Specifically, a magnetic material formed as a thin wire with a width of several nanometers to several hundred nanometers (hereinafter referred to as a magnetic wire) is prone to generating two or more magnetic domains along its length. Furthermore, when a current is supplied in the longitudinal direction (thin wire direction) at a predetermined current density or higher, the domain walls that separate the magnetic domains move in the opposite direction (toward the positive pole) of the current due to the STT (Spin Transfer Torque) effect (Non-Patent Document 1). Furthermore, utilizing the magnetization reversal in a predetermined region (magnetization reversible region) of such a magnetic wire, a magneto-optical spatial light modulator has been developed in which the magnetic wire is formed of a magneto-optical material and used as an optical modulation element (e.g., Patent Document 4). Furthermore, racetrack memories (e.g., Patent Documents 5 to 7, Non-Patent Document 2) and spatial light modulators (e.g., Patent Documents 8 and 9) have been developed in which the structure is simplified and the cells are miniaturized by configuring each row of arranged memory cells or pixels with a magnetic domain in a single magnetic nanowire. 7 A / cm 2This requires a current density that is several orders of magnitude higher.

[0004] In SOT-MRAM, when a current is supplied in one direction (x direction) within the film plane (xy plane) to a channel layer made of a nonmagnetic material stacked on the free layer of a magnetoresistive element, electrons with opposite spin directions in the y direction are separated and accumulated in the upper and lower surface layers, generating a spin current. The electrons near the interface with the free layer reverse the magnetization direction of the free layer. In the SOT method, magneto-optical spatial light modulators have also been developed, in which a channel layer is stacked on a magnetic nanowire made of a magneto-optical material to form an optical modulation element (e.g., Patent Documents 10 and 11). The channel layer exhibits the spin Hall effect (SHE) and is made of high-density, paramagnetic transition metals such as Ta (tantalum), Pt (platinum), and W (tungsten) (e.g., Non-Patent Documents 3 and 4), or topological insulators such as BiSb and BiSe alloys (e.g., Non-Patent Documents 5 and 6). It is known that when a topological insulator, especially a BiSb alloy, is used as a channel layer, a large spin torque can be applied to the magnetic material through the junction interface, resulting in a high SOT effect (Non-Patent Document 5). The SOT effect is also known to affect domain wall motion in magnetic nanowires (e.g., Non-Patent Documents 3, 4, 6), and it is expected to achieve faster domain wall motion and lower currents than the STT effect. In particular, racetrack memories and spatial light modulators with similar structures require longer magnetic nanowires to achieve higher capacity and higher resolution. However, magnetic nanowires tend to heat up when supplied with current, and low currents are required to prevent degradation. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5598697 [Patent Document 2] International Publication No. 2017 / 090730 [Patent Document 3] International Publication No. 2019 / 054484 [Patent Document 4] Patent Gazette No. 4939489 [Patent Document 5] U.S. Patent No. 6834005 [Patent Document 6] Patent No. 4969981 [Patent Document 7] Japanese Patent Publication No. 2016-157815 [Patent Document 8] Patent No. 5782334 [Patent Document 9] Patent No. 6302759 [Patent Document 10] Japanese Patent Publication No. 2020-134754 [Patent Document 11] Japanese Patent Publication No. 2022-83931

Non-licensed literature

[0006]

Non-patent document 1

Non-patent document 2

Non-patent document 3

[0007] When using a BiSb alloy, which exhibits a particularly strong SOT effect, as the channel layer of a SOT-based magnetic element, the thickness must be approximately 20 nm or less to achieve topological insulator properties. However, when current is applied to a BiSb alloy channel layer stacked on a magnetic nanowire in the direction of the nanowire, problems such as domain walls not moving the desired distance or the formation of new, unwanted domain walls in the magnetic film can occur. This makes it difficult to apply to applications such as racetrack memory, which requires long-distance domain wall movement while maintaining the shape of each magnetic domain in a long magnetic nanowire. This is presumably because BiSb alloys are prone to grain growth during film formation, resulting in surface roughness of the order of a few nanometers. Therefore, thin films of less than 20 nm have large variations in relative thickness within the film surface and are not completely continuous.

[0008] The present invention was devised in view of the above-mentioned problems, and aims to provide an SOT-type magnetic element having a topological insulator made of a BiSb alloy with a high SOT effect as a channel layer, and a magnetic device such as a magnetic memory or spatial light modulator that includes an array of such magnetic elements. [Means for solving the problem]

[0009] The present inventors have come up with a configuration in which, in an SOT type magnetic element using a BiSb alloy film as a channel layer, a stable current path is also provided in the magnetic film laminated with the channel layer.

[0010] That is, the magnetic element according to the present invention comprises a stack of a layer made of a magnetic material and a layer made of a topological insulator containing Bi and Sb, and one or more electrodes for supplying a current in an in-plane direction to the stack, each of which comprises an upper electrode bonded to the upper surface of the stack and a lower electrode bonded to the lower surface of the stack and which can be electrically connected to the upper electrode independently of the stack. Also, the magnetic device according to the present invention comprises an array of the magnetic elements. [Effects of the Invention]

[0011] The magnetic element according to the present invention has a topological insulator made of a BiSb alloy as a channel layer, and provides a magnetic device that can be rewritten at a low current density and has a high rewriting speed due to the high SOT effect. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is an external view illustrating the structure of a magnetic device according to the present invention. [Figure 2] FIG. 2 is a schematic diagram illustrating the structure of the magnetic element according to the first embodiment of the present invention, and is a partial cross-sectional view of FIG. [Figure 3] Atomic force microscope images of a BiSb alloy film. (a) is a 2D image (top view), and (b) is a 3D image. [Figure 4] FIG. 1 is a schematic diagram illustrating a current path in a conventional magnetic element. [Figure 5] FIG. 1 is a schematic diagram illustrating a current path in a conventional magnetic element having a BiSb alloy as a channel layer. [Figure 6] FIG. 2 is a schematic diagram illustrating a current path in the magnetic element according to the present invention. [Figure 7] FIG. 2 is a schematic diagram illustrating the structure of a magnetic element according to a modified example of the first embodiment of the present invention, and corresponds to the partial cross-sectional view of FIG. [Figure 8] FIG. 2 is a schematic diagram illustrating the structure of a magnetic element according to a second embodiment of the present invention, and corresponds to the partial cross-sectional view of FIG. [Figure 9] 1A and 1B are magneto-optical microscope photographs of a magnetic nanowire of a sample of an example simulating a magnetic element according to the present invention, where (a) is before the supply of a pulse current and (b) is after the supply of a pulse current. [Figure 10] 1A and 1B are magneto-optical microscope photographs of a magnetic nanowire of a sample of a comparative example, where (a) is before the supply of a pulse current and (b) is after the supply of a pulse current. DETAILED DESCRIPTION OF THE INVENTION

[0013] The following describes embodiments for realizing a magnetic element and a magnetic device according to the present invention with reference to the drawings. For clarity, the magnetic device and its elements shown in the drawings may be exaggerated in size and positional relationship, and the shape and structure may be simplified.

[0014] [First embodiment] 1 and 2, a spatial light modulator (magnetic device) 50 according to the first embodiment of the present invention comprises a substrate 7, domain wall motion elements (magnetic elements) 10 each including a magnetic nanowire (laminated body) 1 and electrodes 21, 22 connected to both ends of the magnetic nanowire 1, and arranged in parallel in the width direction of the magnetic nanowire 1 on the substrate 7, and an insulating layer 6 filling the spaces between the domain wall motion elements 10. In this specification, the nanowire direction of the magnetic nanowire 1 will be referred to as the x-direction, the nanowire width direction as the y-direction, and the thickness direction as the z-direction, as appropriate.

[0015] The domain wall motion element 10 is a light modulation element in which the magnetic layer 11 of the magnetic nanowire 1 has multiple pixels arranged in series in the nanowire direction (x direction). It transmits or reflects light incident from above or below and outputs light whose polarization direction is changed to a binary angle for each pixel. Therefore, a spatial light modulator 50 in which multiple domain wall motion elements 10 are arranged in the y direction is a transmissive or reflective spatial light modulator with a two-dimensional array of pixels (see Patent Documents 8 and 9). A pixel refers to a means for displaying information (bright / dark) in the smallest unit of display by the spatial light modulator. The spatial light modulator 50 has the same number of domain wall motion elements 10 as the pixels in the y direction, arranged side by side at a pitch equal to the length of one pixel in the y direction (pixel length). For simplicity, eight domain wall motion elements 10 are shown in FIG. 1 . The spatial light modulator 50 according to this embodiment is preferably a reflective spatial light modulator that receives light from below. This is because the magnetic nanowire 1 has a BiSb alloy film with large surface roughness as a channel layer on the upper side, and therefore incident and emitted light from above is easily scattered.

[0016] (domain wall motion element) As shown in FIG. 2, a domain wall motion element (magnetic element) 10 includes a magnetic nanowire (stacked body) 1 and electrodes 21 and 22 connected to both ends of the magnetic nanowire in the nanowire direction. It also includes a recording element 3 spaced apart below and near one end of the magnetic nanowire 1. In the spatial light modulator 50, an insulating layer 6 is provided between the magnetic nanowire 1 and the recording element 3, and one recording element 3 extends in the y direction and is shared by all of the domain wall motion elements 10. The magnetic nanowire 1 is formed into a nanowire shape by stacking a magnetic layer 11 made of a perpendicular magnetic anisotropy material and a topological insulator layer 12 made of a BiSb alloy. The electrodes 21 and 22 each include an upper electrode 2t connected to the upper surface of the magnetic nanowire 1 and a lower electrode 2b directly connected to the upper electrode 2t and connected to the lower surface of the magnetic nanowire 1.

[0017] In this embodiment, the magnetic layer 11 and the topological insulator layer 12 that make up the magnetic nanowire 1 are each formed in a straight line with a uniform width. The magnetic nanowire 1 is partitioned into a write region 1w and a display region 1a in the nanowire direction between the connection portions with the electrodes 21 and 22. The write region 1w is a region to which a magnetic field is applied from the recording element 3 to selectively orient the magnetization direction upward or downward, and is set to a length equal to or greater than the length of one pixel (pixel length) in the nanowire direction. The display region 1a constitutes the display region of the spatial light modulator 50 and is a region in which pixels are continuous in the nanowire direction. The length of the display region 1a in the nanowire direction is set to the product of the pixel length and the number of pixels in the nanowire direction (x direction).

[0018] The magnetic layer 11 is a main component of the domain wall motion element 10, and the magnetization direction of a part of the layer indicates a desired direction, either upward or downward, and changes the polarization direction by a binary angle (+θ k / -θ k The magnetic layer 11 is made of a perpendicular magnetic anisotropy material formed in a fine wire shape, and is divided in the fine wire direction into two or more magnetic domains, one with the magnetization direction pointing upward and the other downward.

[0019] The domain wall motion element 10 changes the desired polarization direction of light reflected by each pixel of the magnetic layer 11. For this purpose, the magnetic layer 11 is preferably made of a perpendicular magnetic anisotropy material having a relatively low coercive force, and more preferably has a high magneto-optical effect. Known magnetic materials used in the magnetization free layer of CPP-GMR (Current Perpendicular to the Plane Giant MagnetoResistance) elements and TMR (Tunnel MagnetoResistance) elements, which are used in magnetoresistive effect elements of MRAMs, can be used. Specifically, examples include a Co / Pd multilayer film in which transition metals such as Fe, Co, Ni, etc. and noble metals such as Pd, Pt are alternately and repeatedly laminated at a film thickness ratio of about 1:2 to 4, a Co / Tb multilayer film in which transition metals and rare earth metals such as Tb are alternately and repeatedly laminated, alloys of rare earth metals and transition metals such as Tb-Fe-Co, Gd-Fe, etc. (RE-TM alloys), and L10-based ordered alloys such as FePt, FePd, and CrPt3.

[0020] The magnetic layer 11 is formed in the shape of a thin wire that is sufficiently long relative to its thickness and width. Furthermore, the smaller the cross-sectional area of ​​the magnetic layer 11, which is the product of its thickness and width, the smaller the current supplied to the magnetic wire 1 can be. On the other hand, it is preferable that the magnetic layer 11 has a thickness and width that provide a certain degree of coercive force to maintain magnetization, and the greater the thickness, the higher the optical modulation degree (Kerr rotation angle θ k Specifically, the thickness is preferably 5 nm or more, and more preferably 10 nm or more. However, although it depends on the material, if the thickness of magnetic layer 11 exceeds about 20 nm, the increase in the optical modulation index slows down, and if the film is made even thicker, it may be difficult to maintain perpendicular magnetic anisotropy. Furthermore, if magnetic layer 11 is too thick, the domain walls separating magnetic domains become difficult to move. Therefore, the thickness of magnetic layer 11 is preferably 30 nm or less, and more preferably 20 nm or less. Furthermore, it is preferable that the wire width is not more than twice the length of one pixel in the wire direction. Furthermore, it is preferable that the pixel is wide, and although it depends on the wavelength of the incident light, the width of magnetic wire 1 and the length of one pixel in the wire direction are preferably about 200 to 300 nm or more.

[0021] The topological insulator layer 12 is a path for current flow as a channel layer of the SOT magnetic element, is stacked on the top surface of the magnetic layer 11, and is formed in the same shape as the magnetic layer 11 in plan view (xy plane). The channel layer is a thin film that generates spin current by the spin Hall effect (SHE) when a current flows through it. Topological insulators, especially BiSb alloys and BiSbTe alloys, have a high SOT effect and apply a huge spin torque to the magnetic layer through the junction interface, so the current density required for domain wall motion in the magnetic layer can be increased to 10 5 A / cm 2 The thickness of the magnetic nanowire 1 can be reduced to the order of magnitude. Therefore, the magnetic nanowire 1 includes a topological insulator layer 12 containing Bi and Sb, such as a BiSb alloy or a BiSbTe alloy, as a channel layer. These alloy films do not become topological insulators if they are too thick, so a thickness of approximately 20 nm or less is preferable for use as a channel layer. Here, BiSb and BiSbTe alloys are prone to grain growth during film formation. As shown in Figure 3, the surface of the BiSb film forms a densely packed protrusion structure with numerous granular deposits, resulting in a surface roughness of approximately several nanometers. Furthermore, during the manufacturing process of the spatial light modulator 50, the magnetic nanowire 1 is heated to 90 to 170°C after its formation to harden (bake) the resist and remove the mask in order to pattern at least the upper electrode 2t by photolithography. Since grain growth continues when BiSb alloys and other alloys are heated to approximately 150°C or higher after film formation, repeated application of heat (thermal history) further increases the surface roughness and creates an uneven, irregular structure. Therefore, it is difficult to obtain uniformity in thickness on the order of 10 nanometers for alloy films such as BiSb, and it is difficult to form a continuous film if the film is even thinner. Therefore, the average thickness of the topological insulator layer 12 is preferably 10 nm or more and 20 nm or less.

[0022] As described above, during the manufacturing process of the spatial light modulator 50, the magnetic nanowire 1 is heated after its formation. Depending on the temperature and the material of the magnetic layer 11, interlayer diffusion of Bi or Sb from the topological insulator layer 12 may occur, degrading the perpendicular magnetic anisotropy of the magnetic layer 11. To prevent interlayer diffusion of Bi and other elements, the magnetic nanowire 1 may have a diffusion prevention layer between the magnetic layer 11 and the topological insulator layer 12. The diffusion prevention layer may be made of MgO, which allows electrons to flow while maintaining spin torque due to the coherent tunneling effect. The MgO film serving as the diffusion prevention layer preferably has a thickness of 0.5 to 2 nm. Alternatively, the magnetic nanowire 1 may have an orientation control underlayer below the magnetic layer 11 (between it and the insulating layer 6 on the substrate 7) to further strengthen the perpendicular magnetic anisotropy of the magnetic layer 11. The underlayer may be a single layer film made of a non-magnetic metal material such as Ru, Ta, Cu, Pt, Au, or W, or a multilayer film made of a combination of two or more of these materials, and preferably has a thickness of 1 to 10 nm.

[0023] The electrodes 21 and 22 are terminals for supplying a current from the outside to the magnetic wire (stacked body) 1 in the wire direction (in-plane direction, here, +x or −x direction) to move the domain wall of the magnetic layer 11. An SOT-type domain wall motion device (magnetic element) typically supplies a current to the channel layer. Therefore, the electrodes 21 and 22 are connected to the topological insulator layer 12 at both ends of the magnetic wire 1. Furthermore, in the present invention, the electrodes 21 and 22 are also connected to the magnetic layer 11. To this end, the electrodes 21 and 22 each include an upper electrode 2t provided above the magnetic wire 1 and joined to the upper surface of the topological insulator layer 12, and a lower electrode 2b provided below the magnetic wire 1 and joined to the lower surface of the magnetic layer 11. The upper electrode 2t and the lower electrode 2b are directly connected to each other outside the magnetic wire 1 in a planar view. In other words, the upper electrode 2t and the lower electrode 2b are electrically connected to each other without the magnetic wire 1.

[0024] The upper electrode 2t and the lower electrode 2b are respectively provided to extend outward from the magnetic nanowire 1 in the nanowire direction and on both sides in the nanowire width direction, and are connected to each other at these extending portions. Therefore, the electrodes 21 and 22 sandwich both ends of the magnetic nanowire 1 from above and below. At least one of the upper electrode 2t and the lower electrode 2b is formed so as to be connectable to an external current source. The upper electrode 2t preferably has a thickness of 20 nm or more. The lower electrode 2b preferably has a thickness equal to or greater than that of the magnetic layer 11, and more preferably 10 nm or more. Furthermore, the total thickness of the upper electrode 2t and the lower electrode 2b, taking into account the material, width, etc., corresponds to the magnitude of the current supplied to the magnetic nanowire 1. Furthermore, the upper electrode 2t and the lower electrode 2b are each formed to be bonded to the topological insulator layer 12 and the magnetic layer 11 over a sufficient area, and have a width corresponding to the magnitude of the current, preferably at least equal to or greater than the width of the magnetic nanowire 1 so as to be bonded to the magnetic nanowire 1 over its entire width. Furthermore, it is preferable that the resistance of the upper electrode 2t is equal to or less than the resistance of the lower electrode 2b. For example, if the upper electrode 2t and the lower electrode 2b are made of the same electrode material and have the same conductivity, it is preferable that the thickness of the upper electrode 2t is equal to or greater than the thickness of the lower electrode 2b.

[0025] The upper electrode 2t and the lower electrode 2b are formed of common metal electrode materials such as Cu, Al, Au, Ag, Ta, Cr, Pt, Ru, etc. or alloys thereof, but may be formed of different materials, or may have a two-layer or more structure made of different metal electrode materials. Furthermore, when the insulating layer 6 is formed of SiO2, the upper electrode 2t and the lower electrode 2b may have a barrier film made of Ta, TaN, Ti, TiN, TiW, etc. at their interfaces.

[0026] The recording element 3 is a magnetic field applying means that selectively applies a magnetic field upward or downward to a predetermined region (write region 1w) of the magnetic layer 11 in the wire direction. In this embodiment, the recording element 3 is a thin conductor in the y direction, and by passing a current in the wire direction (+y direction or −y direction), an upward or downward magnetic field is generated in the vicinity. For this purpose, the recording element 3 is formed with a thickness and width corresponding to the magnitude of the current that generates a magnetic field that reverses the magnetization of the magnetic layer 11, and is disposed directly above or below the write region 1w of the magnetic wire 1. The general metal electrode materials listed as the materials for the electrodes 21 and 22 can be applied to the recording element 3, and the same material as the electrodes 21 and 22 may be selected. In order to apply a stronger electric field to the magnetic layer 11, it is preferable that the distance between the recording element 3 and the magnetic layer 11 is short, as long as leakage current does not flow through the magnetic wire 1. An insulating layer 6 is provided between the recording element 3 and the magnetic wire 1. The recording element 3 may be located either above or below the magnetic nanowire 1, but is preferably located below. As described above, if a member is patterned after the formation of the magnetic nanowire 1, the heating during this process may increase the surface roughness of the topological insulator layer 12. Furthermore, interlayer diffusion of Bi or other elements from the topological insulator layer 12 may degrade the perpendicular magnetic anisotropy of the magnetic layer 11. Therefore, it is preferable to have fewer layers of members patterned above the magnetic nanowire 1, and it is most preferable that nothing other than the top electrode 2t be located above the magnetic nanowire 1. In the spatial light modulator 50 according to this embodiment, all domain wall motion elements 10 can share the recording element 3; that is, the recording element 3 is arranged to cross all of the magnetic nanowires 1. To generate a strong magnetic field relative to the magnitude of the current, the recording element 3 preferably comprises two conductors arranged side by side in the nanowire direction (x direction) of the magnetic nanowire 1, as shown in FIG. 2 . Since these two conductors carry current in opposite directions, as shown in Figure 1, the recording element 3 may be formed as a single wire bent into a hairpin shape outside the area where the magnetic nanowires 1 of the spatial light modulator 50 are arranged side by side.

[0027] The insulating layer 6 is provided on the substrate 7 together with the domain wall motion element 10, and fills the gaps between the domain wall motion elements 10 (magnetic nanowire 1, electrodes 21, and 22) and between the magnetic nanowire 1 and the recording element 3 to insulate them from each other. The insulating layer 6 can be made of oxide films such as SiO2, Al2O3, and MgO, or known inorganic insulating materials used in semiconductor elements, such as SiOC (carbon-doped silicon oxide), silicon nitride (SiN), and AlN. It may also have a structure of two or more layers made of different materials. For example, if the magnetic layer 11 is made of a material that easily oxidizes, such as an RE-TM alloy, it is preferable to use a non-oxide such as SiN or MgO in the portion (layer) that contacts the side surface of the magnetic nanowire 1. The insulating layer 6 also buries the recording element 3 and the lower electrode 2b below the magnetic nanowire 1, making the lower surface of the magnetic nanowire 1 (magnetic layer 11) flat and smooth. For this reason, it is preferable that the insulating layer 6 be made of a Si oxide such as SiO2 or SiOC or a Si compound based thereon, which can be easily polished to a smooth surface by CMP (Chemical Mechanical Polishing), at least in the uppermost layer below the magnetic nanowire 1. On the other hand, the insulating layer 6, which is provided after the formation of the magnetic nanowire 1, such as to cover the magnetic nanowire 1, is preferably made of a material that can be formed at a low temperature, preferably at room temperature or below, and an organic insulating material may also be used.

[0028] The substrate 7 is a base for arranging and supporting the domain wall motion elements 10. The substrate 7 can be made of a known substrate material that is heat-resistant to the temperatures encountered during the formation of the domain wall motion elements 10 (e.g., photolithography, deposition of the magnetic layer 11 and the topological insulator layer 12, etc.). At least the surface (the surface on which the magnetic nanowires 1 are formed) of the substrate 7 is an insulator. If the substrate 7 is made of a conductor such as metal, an insulating film such as one of the materials for the insulating layer 6 is formed on the surface. The substrate 7 may have any shape that can enclose all of the arranged domain wall motion elements 10 in a planar view. While the substrate 7 is rectangular in FIG. 1 , this is not particularly limited. As described above, the spatial light modulator 50 is preferably a reflective spatial light modulator with the substrate 7 side serving as the light input / output surface. Therefore, a transparent substrate is used for the substrate 7. Specific examples of the substrate 7 include silicon oxide (glass), soda glass, magnesium oxide (MgO), sapphire, and gadolinium gallium garnet (GGG) single crystal substrates, as well as various transparent plastic substrates.

[0029] [Method for manufacturing spatial light modulator] The spatial light modulator (domain wall motion device) according to the first embodiment of the present invention can be manufactured, for example, by the following procedure.

[0030] (Lower electrode formation process) First, the recording element 3, the lower electrode 2b, and the insulating layer 6 are formed on the substrate 7. The insulating layer 6 covers the recording element 3, exposes the lower electrode 2b, and flattens the surface. The recording element 3 and the lower electrode 2b can be formed using known methods depending on their material and thickness. For example, a resist mask is formed on the substrate 7 using photolithography, leaving an area where the recording element 3 will be formed blank. Then, an electrode material is deposited by plating or sputtering to form the recording element 3, and the mask is removed (lift-off). An insulating film is deposited thereon, and the surface is ground and flattened as necessary. Next, the lower electrode 2b is formed using the same method (lift-off) as for the recording element 3. Another insulating film is deposited thereon, the surface is ground to expose the lower electrode 2b, and the surface is further polished to make it smooth. CMP can be used for grinding and polishing the surface. Alternatively, an insulating film may be deposited first, and then holes for embedding the recording element 3 and the lower electrode 2b may be formed by processing the insulating film using photolithography and etching, or by processing the surface of the substrate 7.

[0031] (Magnetic thin wire formation process) Next, the magnetic nanowire 1 is formed. A mask is formed on the insulating layer 6 and the lower electrode 2b, leaving an open area where the magnetic nanowire 1 is to be formed, and a magnetic material is deposited by sputtering. Subsequently, a BiSb alloy is deposited by molecular beam epitaxy (MBE) or sputtering, and the grooves in the mask are filled to form the magnetic nanowire 1. The mask is then removed.

[0032] (Top electrode formation process) Finally, an insulating layer 6 is formed to cover the upper electrode 2t and the magnetic nanowire 1. A mask is formed on the insulating layer 6 and the magnetic nanowire 1, leaving an area where the upper electrode 2t will be formed blank. An electrode material is deposited to form the upper electrode 2t, and the mask is then removed (lift-off). An insulating film is deposited thereon, and if necessary, the insulating film on the upper electrode 2t is removed to expose the upper electrode 2t. Note that, rather than plasma ashing, dissolution using a solvent such as N-methyl-2-pyrrolidone (NMP) at a relatively low temperature is preferable for removing the mask in this step; therefore, the mask is formed using a resist that is soluble in such a solvent.

[0033] [Domain wall motion in magnetic nanowires] The domain wall motion in the magnetic nanowire caused by current supply in the domain wall motion element (magnetic element) according to this embodiment will be described with reference to Figures 4, 5, and 6. For simplicity, these figures only show the magnetic nanowire and a pair of electrodes connected to both ends of the magnetic nanowire. In addition, in the initial state (before current is supplied), the magnetic layer 11 of the magnetic nanowire has a total of three magnetic domains: one with upward magnetization and one with downward magnetization on either side.

[0034] The movement of the domain wall in the magnetic layer of the magnetic nanowire due to the supply of current is caused by the magnetic layer receiving torque from the channel layer due to the spin Hall effect of the channel layer (Patent Document 11, etc.). Therefore, as shown in FIG. 4, in the magnetic nanowire 101 having the channel layer 112 made of a transition metal such as Ta, an electrode 2t is connected as a terminal to the top surface, i.e., the channel layer 112. The current I flowing through the channel layer 112 in the direction of the nanowire is m As a result, the magnetic domain walls separating the magnetic domains move by an equal distance, and the magnetic domain sandwiched between the two magnetic domain walls moves while maintaining its shape.

[0035] However, as mentioned above, the topological insulator layer 12 made of a BiSb alloy or a BiSbTe alloy has a large surface roughness, and the relative thickness varies greatly within the film surface, especially when the average thickness is 20 nm or less, as shown schematically in Figure 5. When such a topological insulator layer 12 is used as a channel layer and a current is supplied to the electrode 2t connected only to the topological insulator layer 12 as a terminal, the current I m However, in order to make the current density in the topological insulator layer 12 uniform, a portion of the current bypasses the magnetic layer 11 in the thin regions of the topological insulator layer 12, and does not flow in the magnetic layer 11 in the regions where the thickness is sufficiently large. This results in a localized non-uniform and discontinuous flow of current in the magnetic layer 11. Note that in Figures 5 and 6, the current I m The relative magnitude of the current I m The thickness of the arrows indicating the current density is indicated by the thickness of the arrows. Therefore, the current density becomes locally high in the magnetic layer 11, and in such regions, unintended magnetization reversal and thermal demagnetization occur not due to torque from the topological insulator layer 12 (channel layer) but due to the local STT effect and the generation of large Joule heat in the magnetic layer 11. As a result, a new magnetic domain with an opposite magnetization direction is generated within one magnetic domain in the initial state, making it difficult to maintain the initial state, and the domain wall motion device 10 cannot achieve the desired operation.

[0036] In contrast to this, in the domain wall motion device 10 according to this embodiment, as shown in FIG. 6, the current I m is supplied in parallel to the topological insulator layer 12 and the magnetic layer 11. Then, although it depends on the material and thickness of the magnetic layer 11, the resistance of the magnetic layer 11 is lower than that of the topological insulator layer 12, so the current I m A considerable amount of current in the magnetic layer 11 flows directly in the magnetic layer 11. Then, the magnetic domain moves in the direction of the thin wire in the magnetic layer 11 due to the current domain wall driving phenomenon, and at the same time, the huge spin torque generated by the current flowing at the interface between the topological insulator layer 12 and the magnetic layer 11 promotes this magnetic domain movement. mThe magnetic domain moves stably in the direction in which the current flows. As in the case where the electrode 2t is connected only to the topological insulator layer 12 (Figure 5), the current flows non-uniformly in the magnetic layer 11, but even in areas with a relatively high current density, this does not result in local magnetization reversal or thermal demagnetization. Furthermore, in areas where the thickness of the topological insulator layer 12 is particularly small, there are cases in which a sufficient spin current is not generated to move the domain wall of the magnetic layer 11. However, since such areas are localized and are sufficiently shorter than the domain wall length of the magnetic layer 11, the domain wall can be moved by the spin current generated before and after the area. Furthermore, the current I flows not only in the topological insulator layer 12 but also in the magnetic layer 11. m Therefore, the current I m However, since BiSb and BiSbTe alloys have a significantly higher SOT effect than other topological insulators and metals such as Ta, they can be driven with a sufficiently small current compared to domain wall motion devices that use these materials for the channel layer.

[0037] [Operation of spatial light modulator] (Writing method) In the domain wall motion element 10, the magnetic layer 11 is formed into magnetic domains with a predetermined upward or downward magnetization direction in the writing region 1w of the magnetic nanowire 1 by the magnetic field from the recording element 3 connected to the magnetic field application current source, and then a direct current I mThis causes the magnetic domain to move to a pixel at a predetermined x-address in the display area 1a. The magnetic field application current source is connected to both ends of the conductor constituting the recording element 3 to supply a direct current and switch polarity. In this embodiment, the domain wall motion element 10 is a SOT-type domain wall motion element, and the domain wall of the magnetic layer 11 moves in the same direction as the current supplied to the magnetic nanowire 1. Therefore, the positive (+) pole of the magnetic domain motion current source is connected to the electrode 21 on the write area 1w side, and the negative (-) pole is connected to the electrode 22. The higher the current density in the magnetic nanowire 1, the faster the domain wall moves. It is preferable to supply a pulsed current rather than a continuous current to the magnetic nanowire 1, and the setting is such that the domain wall moves a pixel length in one pulse or a predetermined number of pulses, which is defined as one pulse here. Therefore, a DC pulse power supply is preferably used as the magnetic domain motion current source. Then, during periods when the pulse current is stopped, the magnetic field application current source supplies a current to the recording element 3 to apply a magnetic field to the write area 1w. By alternately repeating the writing of one pixel based on data "1" and "0" input in the order of the x addresses and the movement of the domain wall in the magnetic layer 11 by the pixel length, it is possible to set all pixels in the display area 1a of the magnetic layer 11 to the desired magnetization direction. Here, data "1" is set to the upward magnetization direction, and data "0" is set to the downward magnetization direction.

[0038] In the spatial light modulator 50 according to this embodiment, all of the domain wall motion elements 10 share the recording element 3, which is a magnetic field application means, and the magnetization direction of the magnetic layer 11 in the writing region 1w of each magnetic nanowire 1 is set to the same direction. Therefore, the spatial light modulator 50 connects a current source for applying a magnetic field to the recording element 3, and connects a current source for magnetic domain motion to each electrode 21 or electrode 22 of the domain wall motion elements 10 via a switch, making it possible to switch between connection and disconnection for each domain wall motion element 10 (see Patent Document 9). In such a spatial light modulator 50, for example, in a first step, the current source for applying a magnetic field supplies a current +I w is supplied to the recording element 3. In the second step, the magnetic domain movement current source supplies a current I mIn the third step, the magnetic field application current source reverses its polarity from the first step and supplies a current -I w In the fourth step, the magnetic domain movement current source supplies a current I to all the magnetic nanowires 1 to which no current was supplied in the second step. m One pulse is supplied. By the first to fourth steps, data is written to the first x address in all y addresses. By repeating the same process, data is written to all x addresses.

[0039] (Optical modulation operation) The optical modulation operation of the spatial light modulator 50 according to this embodiment is the same as that of a conventional magneto-optic spatial light modulator. That is, light converted into one polarized component by passing through a polarizing filter or the like is incident as incident light into the region (pixel array) of the spatial light modulator 50 where the display region 1a of the magnetic nanowire 1 is arranged. The incident angle is most preferably 0° (z direction), and the closer the angle, the better. Then, the light that has passed through or been reflected by the magnetic nanowire 1 and is emitted from the spatial light modulator 50 is incident at an angle +θ with respect to the polarized component of the incident light. k or -θ k The light that passes through this polarizing filter is emitted from either the pixel where data "1" is written or the pixel where data "0" is written.

[0040] (Variation) As described above, in the domain wall motion element 10, the write element 3 may be disposed above the magnetic nanowire 1. In this case, in the upper electrode formation process, after forming the upper electrode 2t, an insulating film is formed to a thickness between the magnetic nanowire 1 and the write element 3, and the write element 3 is then formed thereon. Furthermore, as shown in FIG. 7, the magnetic nanowire 1 may be provided directly on the substrate 7. In such a domain wall motion element 10B, the lower electrode 2b is formed on the substrate 7, and then the magnetic nanowire 1 is formed without depositing an insulating film (insulating layer 6). In the domain wall motion element 10B, it is preferable that the lower electrode 2b is not excessively thick relative to the magnetic layer 11 so that the magnetic layer 11 is not divided by a step at the end of the lower electrode 2b. It is also preferable that the magnetic layer 11 is deposited by a sputtering method that has excellent step coverage. It is also preferable that the upper electrode 2t is provided long and inward in the nanowire direction relative to the lower electrode 2b, and be connected to the topological insulator layer 12 even inside the step in the nanowire direction. Furthermore, the surface of the substrate 7 is made sufficiently smooth so that the surface of the magnetic layer 11 formed thereon will be smooth.

[0041] To facilitate anchoring of domain walls at the boundaries between pixels in the display region 1a, the magnetic nanowire 1 may be formed with constrictions to slightly narrow its width, or be bent in zigzags by alternating reverse bends (see Patent Document 8). Furthermore, in the spatial light modulator 50 according to this embodiment, the magnetic nanowires 1 may be arranged linearly or in the above-described shapes parallel to each other at least in the display region 1a so that pixels are arranged two-dimensionally. Therefore, the magnetic nanowires 1 may be bent or curved on both sides of the display region 1a to widen the gap between adjacent magnetic nanowires 1, thereby widening the gap between the electrodes 21 and 22 at both ends, and the ends may also be formed wider. Note that the bending angle and curvature of the magnetic nanowire 1 from the write region 1w to the display region 1a are designed within a range that does not interfere with domain wall motion in the magnetic layer 11. This configuration facilitates connection of the electrodes 21 and 22 to an external current source. Alternatively, the spacing can be widened only on one end side of the magnetic nanowire 1 (for example, the electrode 21 side), and the upper electrode 2t and lower electrode 2b of the electrode 22 on the other end side can be formed in a straight line in the y direction crossing all the magnetic nanowires 1 and shared.

[0042] The spatial light modulator 50 according to this embodiment may include a recording element 3 for each domain wall motion element 10. The recording element 3 for each domain wall motion element 10 is, for example, a known magnetic recording head structure in which thin film coils are stacked. For this reason, it is preferable that the spatial light modulator 50 be arranged with sufficient spacing between the magnetic nanowires 1 at least in the write region 1w. Alternatively, the recording element 3 may further include a magnetic shield made of a magnetic material between the adjacent domain wall motion elements 10. Since such a spatial light modulator 50 can simultaneously write desired data for each domain wall motion element 10, it is possible to simultaneously pass a current I m The domain wall may be moved by supplying a current (see Patent Document 8), which can shorten the time required to write to the pixel array and further allows the electrodes 21 and 22 to be shared.

[0043] Second Embodiment The domain wall motion element of the domain wall motion device according to the first embodiment of the present invention can be configured as a magnetoresistive effect element by laminating an insulating film and a magnetic film with perpendicular magnetic anisotropy on the magnetic layer of the magnetic nanowire. Therefore, the domain wall motion device can be used as a racetrack memory. The configuration of the domain wall motion device according to the second embodiment of the present invention will be described below with reference to FIG. 8. Elements that are the same as those in the first embodiment (see FIGS. 1 and 2) are designated by the same reference numerals, and their description will be omitted.

[0044] A magnetic memory (magnetic device) 50A according to a second embodiment of the present invention includes a substrate 7, domain wall motion elements (magnetic elements) 10A each including a magnetic wire 1 and electrodes 21A, 22A connected to both ends of the magnetic wire 1, and arranged in parallel in the width direction of the magnetic wire 1 on the substrate 7, and an insulating layer 6 filling the spaces between the domain wall motion elements 10A. The domain wall motion elements 10A are memory elements in which the magnetic layer 11 of the magnetic wire 1 has multiple memory cells arranged consecutively in the wire direction (x direction). Therefore, the magnetic memory 50A in which multiple domain wall motion elements 10A are arranged in parallel in the y direction is a racetrack memory (see Patent Documents 5 to 7).

[0045] (domain wall motion element) The domain wall motion element (magnetic element) 10A includes a magnetic nanowire 1 and electrodes 21A and 22A connected to both ends of the magnetic nanowire in the direction of the nanowire, and a recording element 3 spaced apart below and near one end of the magnetic nanowire 1. The domain wall motion element 10A further includes a magnetoresistive element (magnetic detection means) 4 near the other end of the magnetic nanowire 1 and an electrode 43 connected to the underside of the magnetoresistive element 4. As in the first embodiment, the magnetic nanowire 1 is formed in the shape of a nanowire by forming a magnetic layer 11 made of a perpendicular magnetic anisotropy material and a topological insulator layer 12 made of a BiSb alloy stacked thereon.

[0046] In the domain wall motion element 10A, the magnetic wire 1 is partitioned in the wire direction between the connection portions with the electrodes 21A and 22A into a write region 1w, a storage region 1a, and a read region 1r in this order. As in the first embodiment, the write region 1w is a region where a magnetic field is applied from the recording element 3 to selectively orient the magnetization direction upward or downward, and is set to a length equal to or longer than the length of one memory cell (cell length) in the wire direction. The storage region 1a corresponds to the display region 1a of the spatial light modulator 50, and is a region where memory cells are continuous in the wire direction. Therefore, the length of the storage region 1a in the wire direction is set to the product of the cell length and the number of bits in the wire direction (x direction). The read region 1r is a region for detecting the magnetization direction in this region of the magnetic layer 11, where a magnetoresistive effect element 4 is provided, and its length in the wire direction is set to be shorter than the cell length. More specifically, a barrier layer 42 and a magnetization fixed layer 41 are stacked on the lower surface (magnetic layer 11) of the magnetic nanowire 1 in this order from the magnetic layer 11 side, and an electrode 43 is further connected to the lower surface of the magnetization fixed layer 41.

[0047] The rest of the configuration of the magnetic nanowire 1 is as described in the first embodiment. However, the magnetic layer 11 does not need to have a magneto-optical effect, but preferably has a certain degree of coercive force. The thickness and width of the magnetic layer 11 may be any size necessary for maintaining magnetization and for thermal agitation resistance; specifically, the thickness is preferably 5 nm or more and the width is preferably 10 nm or more. Similarly, the cell length is preferably 10 nm or more and at least half the nanowire width. The width of the magnetic layer 11 is preferably 300 nm or less, since this makes it difficult for the magnetic domains to split in the width direction.

[0048] Like the electrodes 21 and 22, the electrodes 21A and 22A are in contact with both the topological insulator layer 12 and the magnetic layer 11. To this end, in this embodiment, like the electrodes 21 and 22, the electrodes 21A and 22A each include an upper electrode 2t provided above the magnetic wire 1 and in contact with the upper surface of the topological insulator layer 12, a lower electrode 2b provided below the magnetic wire 1 and in contact with the lower surface of the magnetic layer 11, and an interlayer electrode (via) 2v provided between the upper electrode 2t and the lower electrode 2b to connect them to each other.

[0049] The upper electrode 2t and the lower electrode 2b each have the same configuration as described in the first embodiment, are provided so as to extend outward from the magnetic wire 1 in the wire direction, and are joined to the interlayer electrode 2v at this extending portion. In other words, the interlayer electrode 2v is provided at a location spaced apart outward from the magnetic wire 1 in the wire direction. The upper electrode 2t, the lower electrode 2b, and the interlayer electrode 2v are formed of a general metal electrode material, as in the first embodiment.

[0050] The magnetization pinned layer 41 and the barrier layer 42, together with the magnetic layer 11 in the read region 1r, constitute a three-layer stacked structure of a TMR element, which is provided to detect the magnetization direction of the magnetic layer 11 in the read region 1r for data reading of the domain wall motion element 10A. That is, the read region 1r of the magnetic layer 11 serves as the magnetization free layer of the TMR element. The magnetization pinned layer 41 and the barrier layer 42, together with the magnetic layer 11 serving as the magnetization free layer, may be made of a material and have a shape suitable for a TMR element. Note that the magnetization pinned layer 41 may have a length (width) equal to or less than the width of the magnetic wire 1 in the wire width direction (y direction), or may be formed long enough to extend outward from the magnetic wire 1 as long as it does not short-circuit with the magnetization pinned layer 41 of another domain wall motion element 10A. The magnetization direction of the magnetization pinned layer 41 is pinned upward or downward. Therefore, the coercive force of the magnetization fixed layer 41 is preferably equal to or greater than the coercive force of the magnetic layer 11. For this purpose, the magnetization fixed layer 41 can be made of a known perpendicular magnetic anisotropy material, similar to the magnetic layer 11, and is preferably made of a material used for the magnetization fixed layer (reference layer) of a CPP-GMR element or a TMR element. Furthermore, the thickness of the magnetization fixed layer 41 is preferably equal to or greater than the thickness of the magnetic layer 11. The barrier layer 42 is an insulating film of the barrier layer of a known TMR element, and is preferably made of MgO, with a thickness of less than 3 nm. The barrier layer 42 is provided at least between the magnetic layer 11 and the magnetization fixed layer 41, i.e., in the read area 1r.

[0051] The electrode 43 is paired with the electrode 21A or the electrode 22A and is a terminal for supplying a data read current from the outside to the magnetoresistive element 4 in a direction perpendicular to the film surface (+z direction or −z direction). For this purpose, the electrode 43 is connected to the lower surface of the magnetization fixed layer 41 of the magnetoresistive element 4, and in this embodiment, it is extended to one end of the magnetic memory 50A in the fine wire direction (electrode 22 side) in order to connect to an external current source. The electrode 43 can be formed of a known metal electrode material, like the electrodes 21A, 22A and the recording element 3.

[0052] The recording element 3 has the same configuration as in the first embodiment. Furthermore, in this embodiment, the recording element 3 is made of the same metal electrode material and is a conductor wire with the same thickness as the electrodes 43, so that it can be formed simultaneously with the electrodes 43 in the manufacture of the magnetic memory 50A, as will be described later.

[0053] The substrate 7 may be a transparent substrate similar to that of the first embodiment, or may be a silicon substrate whose surface is thermally oxidized or a metal substrate whose surface is formed with an insulating film.

[0054] The insulating layer 6 has the same configuration as in the first embodiment, but in this embodiment, in addition to the bottom electrode 2b and recording element 3, the magnetization fixed layer 41 and barrier layer 42 of the magnetoresistive element 4 and the electrode 43 are embedded below the magnetic nanowire 1, making the bottom surface of the magnetic nanowire 1 (magnetic layer 11) flat and smooth. Furthermore, it is preferable to select insulating materials for each layer of the insulating layer 6 so that the layer that embeds the magnetic nanowire 1 and the interlayer electrode 2v has a high etching selectivity relative to the underlying layer that embeds the bottom electrode 2b and the like, at least the layer that contacts the bottom surface of the magnetic nanowire 1. This configuration makes it easy to form a groove in the insulating layer 6 to a predetermined depth for embedding the magnetic nanowire 1, and to maintain the smoothness of the bottom surface of the groove, in the manufacturing method described below.

[0055] [Method for manufacturing magnetic memory] The magnetic memory (domain wall motion device) according to the second embodiment of the present invention can be manufactured, for example, by the following procedure.

[0056] (Lower electrode formation process) First, the lower electrode 2b, recording element 3, electrode 43, magnetization fixed layer 41, and barrier layer 42 are formed on the substrate 7, along with the insulating layer 6 that fills the periphery of these and flattens the surface. The recording element 3 and electrode 43 are formed on the substrate 7 by a method such as lift-off, and the insulating layer 6 that fills the periphery of these is formed. The surface is then ground and polished to make the electrode 43 and the insulating layer 6 around it flush and smooth. The lower electrode 2b and the insulating layer 6 that fills the periphery of these are then formed on top of this, and the surface is again ground and polished to make the lower electrode 2b and the insulating layer 6 around it flush and smooth.

[0057] A mask is formed, leaving open the regions (readout region 1r) where the magnetization fixed layer 41 and barrier layer 42 are to be formed, and the insulating film (insulating layer 6) is removed by etching to expose the electrode 43. A magnetic material that forms the magnetization fixed layer 41 and an insulating film that forms the barrier layer 42 are deposited in this order by sputtering, and these are embedded in the holes in the insulating film (insulating layer 6). The mask is then removed.

[0058] (Magnetic thin wire formation process) Next, the magnetic nanowire 1 and interlayer electrode 2v are formed, along with the insulating layer 6 that fills the surrounding area. An insulating film is formed on the bottom electrode 2b, barrier layer 42, and insulating layer 6 to a thickness greater than the thickness of the magnetic nanowire 1. A through-hole for forming the interlayer electrode 2v is formed in the insulating film by photolithography and etching, exposing the bottom electrode 2b. An electrode material is formed and embedded in the through-hole in the insulating film to form the interlayer electrode 2v. The surface is ground to expose the insulating film (insulating layer 6) around the interlayer electrode 2v, and the insulating layer 6 is made to a predetermined thickness. A resist mask is then formed on top of this, leaving a gap in the area where the magnetic nanowire 1 will be formed, and the insulating layer 6 is etched to expose the bottom electrode 2b and barrier layer 42, forming a groove of a depth equivalent to the thickness of the magnetic nanowire 1. A film of a magnetic material is formed by sputtering or the like, and subsequently a film of a BiSb alloy is formed by molecular beam epitaxy (MBE) or sputtering and embedded in the groove of the insulating layer 6 to form the magnetic nanowire 1. Then, the mask is removed. This mask removal is preferably performed by dissolving the mask in a solvent, as in the upper electrode formation process.

[0059] (Top electrode formation process) Finally, the upper electrode 2t and the insulating layer 6 that fills the area around it and covers the upper surface of the magnetic nanowire 1 are formed. This upper electrode formation process is the same as in the first embodiment. That is, a mask is formed on the magnetic nanowire 1, the interlayer electrode 2v, and the insulating layer 6, leaving an area where the upper electrode 2t is to be formed blank, an electrode material is deposited to form the upper electrode 2t, and the mask is then removed (lift-off). An insulating film is deposited thereon, and if necessary, the insulating film on the upper electrode 2t is removed to expose the upper electrode 2t.

[0060] (Initialization process) In the initialization step, a magnetic field exceeding the coercive force of the magnetization fixed layer 41 is applied from the outside to align the magnetization direction of the magnetization fixed layer 41 of all the domain wall motion elements 10A to either an upward or downward direction. The initialization step may be performed at any stage after the magnetization fixed layer 41 is formed.

[0061] In this embodiment, an insulating layer 6 is formed to fill the area around the magnetic nanowire 1, and then the magnetic nanowire 1 is embedded in the groove. Therefore, even if an easily oxidized material such as an RE-TM alloy is used for the magnetic layer 11, it does not need to be manufactured in a non-oxidizing atmosphere.

[0062] [Operation of magnetic memory] As with the spatial light modulator 50 according to the first embodiment, the magnetic memory 50A has a current source for applying a magnetic field connected to the recording element 3, and a current source for moving a magnetic domain connected between the electrode 21A and the electrode 22A of each of the domain wall motion elements 10A via a switch, making it possible to switch between connection and disconnection for each of the domain wall motion elements 10A. The magnetic memory 50A further connects a current source for reading data between the electrode 43 and the electrode 22A for each of the domain wall motion elements 10A.

[0063] The writing method of the magnetic memory 50A according to this embodiment is the same as that of the spatial light modulator 50 according to the first embodiment. The reading method of the magnetic memory 50A is to read data from a memory cell in the magnetic nanowire 1 by applying a current I m After moving the magnetic domain wall motion element 10A to the read region 1r by supplying a current I, a constant current smaller than the current for moving the magnetic domain wall of the magnetic layer 11 is supplied from a data read current source connected to the electrode 43 and the electrode 22A. A voltage comparator connected to the data read current source compares the output of the magnetic domain wall motion element 10A with a reference potential to determine whether the data is "1" or "0" corresponding to the level of resistance of the magnetoresistive effect element 4. Therefore, as in the case of writing, the current I mEach time one pulse is supplied, the data read current source supplies a constant current during the stop period to detect the magnetization direction in the read region 1r, and data can be read out one memory cell at a time in the order of the x addresses in the domain wall motion element 10A. Data reading can be performed by selecting one domain wall motion element 10A at a time (one y address at a time), or all y addresses can be read out in parallel.

[0064] The domain wall motion element 10A of the magnetic memory 50A according to this embodiment is m When the magnetic domain of the magnetic layer 11 moves and reaches the end on the electrode 22A side by the supply of current, it is lost, that is, the data in the memory cell is lost. In order to continuously store the data of the memory cell that has been moved to the read region 1r for data reading in the domain wall motion element 10A, an external storage device that temporarily stores the read data is connected to the magnetic memory 50A, and in parallel with reading the data of the subsequent x address, the data of the external storage device is written again to the write region 1w, that is, the magnetic field application current source supplies a current +I w / -I w to the recording element 3 (see Patent Documents 6 and 7). Alternatively, the magnetic nanowire 1 is configured so that a buffer (register) area with the same nanowire length as the storage area 1a is provided on the electrode 22A side of the read area 1r, preventing data loss in the memory cell (see Patent Documents 5 and 6).

[0065] (Variation) The electrodes 21A and 22A do not need to have an interlayer electrode 2v, and the upper electrode 2t and the lower electrode 2b may not be electrically connected except for the magnetic nanowire 1. Such electrodes 21A and 22A are configured so that the upper electrode 2t and the lower electrode 2b can be connected to an external current source. That is, in the magnetic memory 50A having such electrodes 21A and 22A, the upper electrode 2t and the lower electrode 2b are short-circuited and connected to a current source for each of the electrodes 21A and 22A.

[0066] Like the domain wall motion element 10 of the first embodiment (see FIG. 2), the domain wall motion element 10A may have electrodes 21 and 22 in which the upper electrode 2t and the lower electrode 2b are directly connected, without having the interlayer electrode 2v. Also, in the domain wall motion element 10A, the recording element 3 may be disposed above the magnetic nanowire 1, as described in the first embodiment.

[0067] In the magnetic memory 50A according to this embodiment, the magnetic nanowires 1 do not have to be straight or parallel to each other. Therefore, the magnetic nanowires 1 may be formed in an arc shape and arranged concentrically (Patent Document 7). In this case, the substrate 7 can be disk-shaped. Furthermore, the magnetic nanowires 1 may be bent or constricted at the boundaries between cells in the storage region 1a, as in the modified example of the first embodiment. The magnetic nanowires 1 may also be bent or curved to widen the gap between the ends of adjacent magnetic nanowires 1, and the ends may be wider. The bending angle and curvature of the magnetic nanowire 1 are designed within a range that does not interfere with domain wall motion in the magnetic layer 11 from the write region 1w to the read region 1r (or to the buffer region). Furthermore, the magnetic memory 50A may include a recording element 3 for each domain wall motion element 10A, as in the modified example of the first embodiment.

[0068] The magnetic device according to the present invention is not limited to a racetrack memory, but can also be an SOT-MRAM or a spatial light modulator that includes a domain wall motion element (magnetic element) for each memory cell and pixel (see Patent Document 11). [Example]

[0069] In order to confirm the effect of the present invention, a sample simulating the magnetic element according to the modified example of the first embodiment of the present invention shown in FIG. 7 was fabricated, and changes in the magnetization state due to current supply were observed.

[0070] (Sample production) A lower electrode, magnetic nanowire, and upper electrode were formed in this order on a Si substrate with thermally oxidized SiO2 formed on its surface by the lift-off method. The lower electrode had a laminated structure of Ta (5 nm) / Au (20 nm) from bottom to top. The values ​​in parentheses indicate film thickness. The magnetic nanowire was 3 μm wide and 60 μm long, and the magnetic layer had a laminated structure of [Tb (0.55 nm) / Co (0.3 nm)] × 3 / Pt (0.8 nm) / MgO (0.7 nm), and BiSb was deposited to an average thickness of 10 nm. The upper electrode had a laminated structure of Ta (3 nm) / Au (90 nm) / Ta (5 nm). As a comparative example, a sample without a lower electrode was also fabricated.

[0071] An external magnetic field was applied to the sample to generate two magnetic domains with a domain wall between the two electrodes of the magnetic nanowire (initialization). Then, a current density of 2.5 × 10 6 A / cm 2 A pulse current (pulse width 2 μs) was supplied once. Magneto-optical microscope photographs of the magnetic nanowire before and after the current was supplied to the sample are shown in Figures 9 and 10.

[0072] In the sample of the example simulating the magnetic element according to the present invention, the magnetic domain generated by initialization shown in Figure 9(a) shifted approximately 7 μm in the direction of the thin wire (the direction indicated by the white arrow) by supplying current, while maintaining its shape, as shown in Figure 9(b). In contrast, in the sample of the comparative example, new domain walls were generated within the magnetic domain generated by initialization shown in Figure 10(a) by supplying current, and the magnetic domain was divided into multiple magnetic domains, as shown in Figure 10(b). In the sample of the comparative example, the upper electrode contacted the magnetic layer on the side (end face) of the magnetic thin wire, but the magnetic layer was 3.35 nm thick, and it is presumed that the contact area was insufficient to supply sufficient current to the magnetic layer.

[0073] Although the above describes various embodiments for implementing the magnetic element and magnetic device according to the present invention, the present invention is not limited to these embodiments, and various modifications are possible within the scope of the claims. [Explanation of symbols]

[0074] 10, 10A, 10B Domain wall motion element (magnetic element) 1 Magnetic nanowire (laminated body) 11 Magnetic layer 12 Topological insulator layers 21,22,21A,22A electrode 2b Lower electrode 2t upper electrode 2v interlayer electrode 3 Recording element 4. Magnetoresistance effect element (magnetic detection means) 41 Magnetization fixed layer 42 Barrier Layer 43 Electrode 50 Spatial Light Modulator (Magnetic Device) 50A Magnetic Memory (Magnetic Device) 6 insulating layer 7. Circuit Board

Claims

1. A magnetic element comprising a stack of a layer made of a magnetic material and a layer made of a topological insulator containing Bi and Sb, and one or more electrodes for supplying a current to the stack in an in-plane direction, A magnetic element characterized in that each of the electrodes comprises an upper electrode joined to the upper surface of the stack and a lower electrode joined to the lower surface of the stack, which can be electrically connected to the upper electrode without using the stack.

2. the laminate is a magnetic nanowire formed in a nanowire shape, The magnetic element according to claim 1 , wherein the electrode is connected to a part of the magnetic nanowire in the nanowire direction.

3. 3. The magnetic element according to claim 1, wherein the electrodes further comprise interlayer electrodes joined to the lower electrode and the upper electrode.

4. A magnetic device comprising an array of magnetic elements according to claim 1 or 2.

5. A magnetic memory in which the magnetic elements according to claim 2 are arranged in the width direction of the magnetic nanowire, A magnetic memory in which each of the magnetic elements generates magnetic domains in the magnetic nanowire as memory cells arranged in a line in the direction of the nanowire.

6. A spatial light modulator in which the magnetic elements according to claim 2 are arranged in the width direction of the magnetic nanowire, the magnetic material is a magneto-optical material, A spatial light modulator in which each of the magnetic elements generates magnetic domains in the magnetic nanowire as pixels arranged in a row in the direction of the nanowire.

Images