Method for initializing domain wall motion element and magnetic device

Abstract

To provide an initialization method capable of generating a domain wall without increasing current density in a domain wall motion element for moving the domain wall of a magnetic thin line to perform writing by current supply.SOLUTION: A domain wall motion element 10 includes a magnetic thin line 1 obtained by laminating a magnetic layer 11 of perpendicular magnetic anisotropy and a channel layer 12 having a spin hole effect to form a thin line shape along an x direction, and nano magnets 54a, 54b of a bar magnet shape arranged below the magnetic thin line 1 along the magnetic thin line 1. Magnetization reversal occurs in an area in which a leakage magnetic field Hpin of the nano magnet 54a of the magnetic layer 11 is applied upward by supplying current Iinit to the magnetic thin line 1 while applying an external magnetic field Hinit in a thin line direction after making the magnetic layer 11 a downward single domain by applying the external magnetic field downward.SELECTED DRAWING: Figure 5C

Description

[Technical Field]

[0001] The present invention relates to a method for initializing a domain wall motion element, and to a magnetic device including a magnetic memory or a spatial light modulator in which domain wall motion elements are two-dimensionally arranged. [Background technology]

[0002] In magnetoresistive random access memories (MRAMs), which use the high and low resistance of a magnetoresistive element in a memory cell as binary data, STT (Spin Transfer Torque)-MRAMs, which supply current perpendicular to the film surface as a method for writing, i.e., for reversing the magnetization of a part of the magnetic film (free layer) of the magnetoresistive element, have been developed to increase speed and miniaturize cells, as opposed to the initial magnetic field application method. Furthermore, to further increase speed, domain wall motion-based MRAMs (e.g., Patent Document 1, Non-Patent Document 1) and SOT (Spin Orbit Torque)-MRAMs (e.g., Patent Documents 2 and 3) have been developed.

[0003] In the domain wall motion method, the free layer of a magnetoresistive element is formed into a thin wire extending on both sides, and the magnetization direction is changed between two predetermined points in the longitudinal direction. Specifically, a magnetic material formed into a thin wire with a width of several to several hundred nanometers (hereinafter referred to as a magnetic wire) is likely to generate two or more magnetic domains in the longitudinal direction. Furthermore, when a current is supplied in the longitudinal direction (thin wire direction) at a predetermined current density or higher, the domain walls generated to separate the magnetic domains move in the opposite direction of the current (toward the positive pole) due to the STT effect. Furthermore, by 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 a magnetic wire is formed from a magneto-optical material and used as an optical modulation element (e.g., Patent Documents 4 and 5).

[0004] SOT-MRAM has a spin Hall layer (SHE) made of tantalum (Ta) or the like stacked on the free layer of a magnetoresistive element. When a current is supplied in one direction (x direction) within the film plane (xy plane), electrons with opposite spin directions in the y direction are accumulated separately in the upper and lower surface layers, and electrons near the interface with the free layer reverse the magnetization direction of the free layer. The SOT effect is also known to affect domain wall motion in magnetic nanowires (e.g., Non-Patent Documents 2 to 7), and is expected to achieve faster domain wall motion and lower current than the STT effect. Furthermore, Non-Patent Document 4 reports that the spin direction that moves the domain wall varies depending on the magnetic structure of the domain wall. Furthermore, Non-Patent Document 7 reports that applying an external magnetic field in the in-plane direction can speed up domain wall motion. Furthermore, spatial light modulators utilizing the SOT effect have been developed using magnetic nanowires as optical modulation elements (e.g., Patent Document 6). [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 No. 4939489 [Patent Document 5] Japanese Patent Application Publication No. 2018-073871 [Patent Document 6] Japanese Patent Publication No. 2020-134754 [Non-patent literature]

[0006] [Non-Patent Document 1] 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 [Non-Patent Document 2] Luqiao Liu, O. J. Lee, T. J. Gudmundsen, D. C. Ralph, R. A. Buhrman, "Current-Induced Switching of Perpendicularly Magnetized Magnetic Layers Using Spin Torque from the Spin Hall Effect", Physical Review Letters, Volume 109, 096602, 2012 [Non-Patent Document 3] Soo-Man Seo, Kyoung-Whan Kim, Jisu Ryu, Hyun-Woo Lee, Kyung-Jin Lee, "Current-induced motion of a transverse magnetic domain wall in the presence of spin Hall effect", Applied Physics Letters, Volume 101, 022405 (2012) [Non-Patent Document 4] AV Khvalkovskiy, V. Cros, D. Apalkov, V. Nikitin, M. Krounbi, KA Zvezdin, A. Anane, J. Grollier, A. Fert, "Matching domain-wall configuration and spin-orbit torques for efficient domain-wall motion", Physical Review B87, 020402(R), 2013 [Non-Patent Document 5] Kab-Jin Kim, et al., "Fast domain wall motion in the vicinity of the angular momentum compensation temperature of ferrimagnets", Nature Materials volume 16, pp. 1187-1192, 2017 [Non-patent document 6] Yuichiro Kurokawa and Hiroyuki Awano, "Effect of Pt Layer on Current-Induced Domain Wall Motion in Pt / [Tb / Co]n Multilayer Interconnects", Proceedings of the 40th Annual Meeting of the Magnetics Society of Japan, 5pE-3, 2016 [Non-Patent Document 7] Kenichi Aoshima, Nobuhiko Funabashi, Ryo Higashida, Kenji Machida, "Current induced domain wall motion with a Ta / Gd-Fe / Si-N magnetic nanowire for a magneto-optical light modulator", AIP Advances 10, 015336, 2020 Summary of the Invention [Problem to be solved by the invention]

[0007] In MRAMs and spatial light modulators that use two-dimensionally arranged magnetoresistive elements or optical modulation elements (hereinafter referred to as domain wall motion elements) with magnetic nanowires, a domain wall must be generated at one end of the magnetization reversible region of each magnetic nanowire in each domain wall motion element as an initial setting to align the magnetization direction in the magnetization reversible region. To achieve this, for example, the domain wall motion element includes a hard magnetic material below the end of the magnetic nanowire. After applying an external magnetic field to uniformly magnetize the hard magnetic material and the magnetic nanowire, a current is supplied to the magnetic nanowire, and the magnetic field applied from the hard magnetic material locally reverses the magnetization to generate a domain wall. Because the current density required to generate this domain wall is high, even if the current required for domain wall motion can be reduced by the SOT effect or other techniques, a large current must be supplied during initial setting. Therefore, the wiring and switching elements (transistors) provided for each domain wall motion element must be designed to withstand this large current.

[0008] The present invention was devised in consideration of the above-mentioned problems, and its objective is to provide a method for initializing a domain wall motion element that can generate a domain wall in a magnetic nanowire without increasing the current density of the supplied current, as well as a magnetic device equipped with a magnetic memory or spatial light modulator that can be initialized using a current that does not have a high current density. [Means for solving the problem]

[0009] That is, the initialization method of the domain wall motion element of the present invention is a method for initializing a magnetic nanowire formed into a nanowire shape by stacking a magnetic layer made of a material with perpendicular magnetic anisotropy and a channel layer having the spin Hall effect, and a magnetic field application member made of a hard magnetic material arranged above or below the magnetic nanowire in a portion in the nanowire direction, wherein when a current is supplied to the magnetic nanowire in the nanowire direction, a domain wall generated in the magnetic layer moves in the nanowire direction within a predetermined region not including the portion. The initialization method of the domain wall motion element includes a first magnetization step in which a magnetic field equal to or greater than the coercivity of the magnetic field application member is applied to the magnetic nanowire in an upward or downward direction, and an initial magnetic domain formation step in which a current is supplied to the magnetic nanowire in the nanowire direction while applying a magnetic field to the magnetic nanowire in one direction in the nanowire direction. Another initialization method for the domain wall motion element is one in which the hard magnetic material has in-plane magnetic anisotropy, and the method sequentially includes a first magnetization step of applying a magnetic field equal to or greater than the coercivity of the magnetic field application member to the domain wall motion element in one direction along the magnetic wire, a second magnetization step of applying a magnetic field equal to or greater than the coercivity of the magnetic layer to the domain wall motion element in either an upward or downward direction, and an initial magnetic domain formation step of supplying a current to the magnetic wire in the direction along the magnetic wire while applying a magnetic field less than the coercivity of the magnetic field application member to the domain wall motion element in one direction along the magnetic wire. Alternatively, the second magnetization step is omitted, and the initial magnetic domain formation step is performed twice by reversing either the direction of the magnetic field application or the direction of the current supply. This procedure allows a current with a low current density to be supplied to the magnetic wire of the domain wall motion element, thereby locally reversing the magnetization of the magnetic wire and generating a domain wall.

[0010] A magnetic device according to the present invention comprises a spatial light modulator including two-dimensionally arranged domain wall motion elements and a switching element for each of the domain wall motion elements, a current source for supplying current to the domain wall motion elements via the switching elements, and magnetic field application means for applying a magnetic field to all of the domain wall motion elements of the spatial light modulator. In the magnetic device, the domain wall motion elements include a magnetic nanowire formed by laminating a magnetic layer made of a magneto-optical material with perpendicular magnetic anisotropy and a channel layer having the spin Hall effect, and a magnetic field application member made of a hard magnetic material and arranged on a portion of the magnetic nanowire in the direction of the nanowire, the magnetic field generated by the magnetic field application member being applied in a direction perpendicular to the film surface of the magnetic nanowire to at least one of both outer regions sandwiching a predetermined region of the magnetic layer in the direction of the nanowire, and a current being supplied to the magnetic nanowire in the direction of the nanowire, thereby causing a domain wall generated in the magnetic layer to move in the direction of the nanowire and reversing the magnetization direction in the predetermined region of the magnetic layer. The spatial light modulator is characterized in that the domain wall motion elements are arranged two-dimensionally with the thin line direction of the magnetic nanowires aligned, and the magnetic field applying means applies a magnetic field in the thin line direction of the magnetic nanowires.

[0011] Another magnetic device according to the present invention comprises a magnetic memory having two-dimensionally arranged domain wall motion elements and a switching element for each of the domain wall motion elements, a current source that supplies current to the domain wall motion elements via the switching elements, and a magnetic field application means that applies a magnetic field to all of the domain wall motion elements of the magnetic memory. In the magnetic device, the domain wall motion element comprises a magnetic nanowire formed in a thin wire shape by stacking a magnetic layer made of a magneto-optical material with perpendicular magnetic anisotropy and a channel layer having the spin Hall effect, one of a non-magnetic metal film or an insulating film and a reference layer made of a perpendicular magnetic anisotropy material having a coercivity greater than or equal to the coercivity of the magnetic layer, which are sequentially stacked on the magnetic layer side in a predetermined region of the magnetic nanowire, and a magnetic field application member made of a hard magnetic material arranged on a part of the upper or lower side of the magnetic nanowire in the thin wire direction, and is configured so that a magnetic field generated by the magnetic field application member is applied in a direction perpendicular to the film surface of the magnetic nanowire to at least one of the outer regions sandwiching the predetermined region of the magnetic layer in the thin wire direction, and by supplying a current to the magnetic nanowire in the thin wire direction, the domain wall generated in the magnetic layer moves in the thin wire direction and the magnetization direction in the predetermined region of the magnetic layer is reversed. The magnetic memory is characterized in that the domain wall motion elements are arranged two-dimensionally with the thin wire direction of the magnetic nanowires aligned, and the magnetic field applying means applies a magnetic field in the thin wire direction of the magnetic nanowires.

[0012] With this configuration, in a spatial light modulator or magnetic memory of a magnetic device, the magnetic layer of the magnetic nanowire is magnetized in a uniform direction by the magnetic field application means, and then the magnetic field application means applies a magnetic field in the nanowire direction while the current source supplies a current, thereby generating a magnetic domain wall in the magnetic layer even if the current density of the current is not high. [Effects of the Invention]

[0013] According to the method for initializing a domain wall motion element of the present invention, it is not necessary to supply a current with a high current density to the magnetic nanowire of the domain wall motion element, so the magnetic nanowire and the switching elements and wiring connected to the magnetic nanowire do not need to be designed to withstand large currents.Furthermore, the magnetic device of the present invention makes it easy to achieve high resolution in spatial light modulators and magnetic memories. [Brief explanation of the drawings]

[0014] [Figure 1A] 1A to 1C are cross-sectional views for schematically explaining the structure and operation of a domain wall motion element for which a method for initializing a domain wall motion element according to a first embodiment of the present invention is performed. [Figure 1B] 1A to 1C are cross-sectional views for schematically explaining the structure and operation of a domain wall motion element for which a method for initializing a domain wall motion element according to a first embodiment of the present invention is performed. [Figure 2] 1 is a conceptual diagram illustrating the magnetic structure of a Néel domain wall in a magnetic nanowire and the movement of the domain wall due to the spin-orbit torque effect. [Figure 3] 1 is a conceptual diagram illustrating the magnetic structure of a Néel domain wall in a magnetic nanowire and the movement of the domain wall due to the application of a magnetic field and the spin-orbit torque effect. [Figure 4] 1 is a conceptual diagram illustrating the magnetic structure of a Néel domain wall in a magnetic nanowire and the movement of the domain wall due to the application of a magnetic field and the spin-orbit torque effect. [Figure 5A] 3A to 3C are schematic diagrams illustrating a first magnetization step in the initialization method for the domain wall motion element according to the first embodiment of the present invention. [Figure 5B] 5A to 5C are schematic views illustrating a second magnetization step in the initialization method for the domain wall motion element according to the first embodiment of the present invention. [Figure 5C] 3A to 3C are schematic diagrams illustrating an initial magnetic domain forming step in the method for initializing the domain wall motion element according to the first embodiment of the present invention. [Figure 5D] 3A to 3C are schematic diagrams illustrating an initial magnetic domain forming step in the method for initializing the domain wall motion element according to the first embodiment of the present invention. [Figure 6] FIG. 2 is an equivalent circuit diagram of a spatial light modulator including the domain wall motion element shown in FIGS. 1A and 1B. [Figure 7A] FIG. 10 is a schematic diagram of a state after a first magnetization step in the initialization method for the domain wall motion element according to the modified example of the first embodiment of the present invention. [Figure 7B] 10A to 10C are schematic diagrams illustrating an initial magnetic domain forming step in the method for initializing the domain wall motion element according to the modified example of the first embodiment of the present invention. [Figure 7C]10A to 10C are schematic diagrams illustrating an initial magnetic domain forming step in the method for initializing the domain wall motion element according to the modified example of the first embodiment of the present invention. [Figure 7D] 10A to 10C are schematic diagrams illustrating an initial magnetic domain forming step in the method for initializing the domain wall motion element according to the modified example of the first embodiment of the present invention. [Figure 8A] 10A to 10C are cross-sectional views for schematically explaining the structure and operation of a modified example of the domain wall motion element for which the domain wall motion element initialization method according to the first embodiment of the present invention is performed. [Figure 8B] 10A to 10C are cross-sectional views for schematically explaining the structure and operation of a modified example of the domain wall motion element for which the domain wall motion element initialization method according to the first embodiment of the present invention is performed. [Figure 9] FIG. 8C is an equivalent circuit diagram of a magnetic memory including the domain wall motion element shown in FIGS. 8A and 8B. [Figure 10A] 10A to 10C are cross-sectional views for schematically explaining the structure and operation of a domain wall motion element for which a method for initializing a domain wall motion element according to a second embodiment of the present invention is performed. [Figure 10B] 10A to 10C are cross-sectional views for schematically explaining the structure and operation of a domain wall motion element for which a method for initializing a domain wall motion element according to a second embodiment of the present invention is performed. [Figure 11A] 10A and 10B are schematic diagrams illustrating a first magnetization step in the initialization method for the domain wall motion element according to the second embodiment of the present invention. [Figure 11B] 10A and 10B are schematic diagrams illustrating a second magnetization step in the initialization method for the domain wall motion element according to the second embodiment of the present invention. [Figure 11C] 10A and 10B are schematic diagrams illustrating an initial magnetic domain forming step in the method for initializing the domain wall motion element according to the second embodiment of the present invention. [Figure 11D] 10A and 10B are schematic diagrams illustrating an initial magnetic domain forming step in the method for initializing the domain wall motion element according to the second embodiment of the present invention. [Figure 12A] 10A and 10B are cross-sectional views for schematically explaining the structure and operation of a modified example of the domain wall motion element for which the domain wall motion element initialization method according to the second embodiment of the present invention is performed. [Figure 12B]10A and 10B are cross-sectional views for schematically explaining the structure and operation of a modified example of the domain wall motion element for which the domain wall motion element initialization method according to the second embodiment of the present invention is performed. [Figure 13A] 10 is a magneto-optical microscope photograph of a magnetic nanowire of a sample of an example simulating a domain wall motion device, to which an initialization method according to the present invention was applied. [Figure 13B] 10 is a magneto-optical microscope photograph of a magnetic nanowire of a sample of an example simulating a domain wall motion device, to which an initialization method according to the present invention was applied. [Figure 14] 10 is a magneto-optical microscope photograph of a magnetic nanowire of a sample of an example simulating a domain wall motion device, to which an initialization method according to a comparative example was performed. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, a method for initializing a domain wall motion element and a magnetic device according to the present invention will be described with reference to the drawings. For clarity, the domain wall motion element, magnetic device, and their elements shown in the drawings may be exaggerated in size and positional relationship, and their shapes and structures may be simplified.

[0016] [First embodiment] (domain wall motion element) 1A and 1B , a domain wall motion device 10 for performing the domain wall motion device initialization method according to the first embodiment of the present invention (hereinafter, the domain wall motion device according to the first embodiment) includes a magnetic nanowire 1 formed by stacking a magnetic layer 11 made of a perpendicular magnetic anisotropy material and a channel layer 12 having the spin Hall effect in this order, in a thin wire shape, and nanomagnets (magnetic field application members) 54a and 54b made of a hard magnetic material with in-plane magnetic anisotropy connected to the lower surface (channel layer 12) of the magnetic nanowire 1 and spaced apart from each other in the thin wire direction. The domain wall motion device 10 also includes electrodes 61 and 62 connected to the lower surfaces of the nanomagnets 54a and 54b. In addition, the domain wall motion device 10 includes an insulator in a void space around the magnetic nanowire 1. In this specification, the thin wire direction of the magnetic nanowire 1 will be referred to as the x-direction, the thin wire width direction as the y-direction, and the thickness direction as the z-direction. The domain wall motion element 10 is a light modulation element that reflects light incident from above and emits light whose polarization direction has been changed to a binary angle (see, for example, Patent Documents 4 and 5). Therefore, as will be described later, the domain wall motion elements 10 are two-dimensionally arranged as pixels to form a spatial light modulator 90. A pixel refers to a means for displaying information (bright / dark) in the smallest unit of display by the spatial light modulator.

[0017] 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 thin wire shape, and as shown in FIGS. 1A and 1B, it is divided in the wire direction by a domain wall DW and is divided into two magnetic domains with different magnetization directions (indicated by hatched arrows in the figures), i.e., an upward magnetic domain and a downward magnetic domain. As will be described later, in the magnetic layer 11, this domain wall DW is moved in the wire direction by an electrical means, and the magnetization direction between the start point and end point of the movement of the domain wall DW changes before and after the movement. The region in the magnetic layer 11 between the start point and end point of the movement of the domain wall DW is called a magnetization reversible region 1. SW The magnetic layer 11 is a reversible magnetization region 1 SWThe regions adjacent to both outer sides of the wire are regions where the magnetization direction is fixed upward and downward, respectively, and the magnetization fixed region 1 FX1 ,1 FX2 In the magnetic domain wall motion element 10, the magnetic layer 11 has a region between the regions directly above the nanomagnets 54a and 54b, which is called a magnetization fixed region 1 in the wire direction. FX1 , magnetization reversible region 1 SW , magnetization fixed region 1 FX2 It is divided into:

[0018] The domain wall motion element 10 has a magnetization reversible region 1 of the magnetic layer 11. SW The magnetic layer 11 changes the polarization direction of light reflected by the magnetic field to a desired direction. Therefore, the magnetic layer 11 is preferably made of a perpendicular magnetic anisotropy material with a relatively low coercive force, and more preferably made of a material with a high magneto-optical effect. Known magnetic materials used in the magnetization free layers of CPP-GMR (Current Perpendicular to the Plane Giant Magneto-Resistance) elements and TMR (Tunnel Magneto-Resistance) elements, which are used in magnetoresistive elements of MRAMs, can be used. Specific examples include multilayer films such as Co / Pd multilayer films in which transition metals such as Fe, Co, and Ni and noble metals such as Pd and Pt are alternately stacked at a film thickness ratio of approximately 1:2 to 4; alloys of rare earth metals and transition metals such as Tb-Fe-Co and Gd-Fe (RE-TM alloys); and L10-based ordered alloys such as FePt, FePd, and CrPt3. In this embodiment, a Gd-Fe alloy with a low coercive force and a high magneto-optical effect is particularly suitable.

[0019] The magnetic layer 11 and the channel layer 12 that make up the magnetic nanowire 1 are preferably linear and have uniform thickness and width. 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 nanowire 1 can be. On the other hand, the magnetic layer 11 needs a certain degree of coercive force Hc to maintain the magnetization. fIt is preferable that the thickness and width are set so as to have the following: the larger 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 the magnetic layer 11 exceeds about 20 nm, the increase in the optical modulation index slows down, and if the film becomes even thicker, it may become difficult to maintain the perpendicular magnetic anisotropy. Furthermore, if the magnetic layer 11 is thick, it becomes difficult for the domain wall DW to move. Therefore, the thickness of the magnetic layer 11 is preferably 30 nm or less, and more preferably 20 nm or less. Furthermore, the magnetization reversible region 1 of the magnetic layer 11, which is the opening of the pixel, SW It is preferable that the width and the magnetization reversible region 1 are wide, although this depends on the wavelength of the incident light. SW The length in the wire direction is preferably about 200 to 300 nm or more. FX1 ,1 FX2 It is preferable that the length in the thin line direction is at least half the thin line width.

[0020] The channel layer 12 is a path for current to flow, and is laminated on one side of the magnetic layer 11, here the lower surface, and is formed in the same shape as the magnetic layer 11 when viewed in plan (xy plane). The channel layer 12 is a thin film that generates a spin current due to the spin Hall effect (SHE) when a current flows through it, and is made of, for example, paramagnetic transition metals such as Ta, Pt, or W, which have a high specific gravity. The channel layer 12 can also be made of a topological insulator such as BiSb or BiSe. The channel layer 12 preferably has a thickness of 1 nm or more and 10 nm or less.

[0021] The nanomagnet 54 applies a leakage magnetic field in the z direction to a part of the magnetic layer 11 in the thin wire direction. Two nanomagnets 54 are provided in the domain wall motion element 10, and the one on the -x side is called nanomagnet 54a and the one on the +x side is called nanomagnet 54b. The nanomagnet 54a is located in the magnetization fixed region 1 of the magnetic layer 11. FX1 +z-direction magnetic field +H pin is applied, and the nanomagnet 54b is fixed in the magnetization region 1 FX2 -z-direction magnetic field -H pinis applied. Nanomagnet 54 is a tiny bar magnet aligned along the magnetic nanowire 1, with its length in the x direction longer than its length and thickness in the y direction. Here, the +x side is the north pole. Unless otherwise specified, in each drawing, nanomagnets 54a, 54b and nanomagnets 51 and 52 (described later) are designated by the polarities "N" and "S," and the north pole side is hatched. In addition, in Figures 1A and 1B, the magnetic field lines from nanomagnet 54 are represented by dashed lines. Nanomagnet 54 generates leakage magnetic fields in the +z and -z directions above and below it, near both outer sides in the x direction, and some of the magnetic field generated above it reaches magnetic layer 11. In the domain wall motion device 10, the nanomagnets 54a and 54b are spaced apart from each other in the x direction of the magnetic nanowire 1 and are arranged to protrude outward on both sides of the magnetic nanowire 1 in the direction of the magnetic nanowire 1, with the N pole of the nanomagnet 54a on the -x side and the S pole of the nanomagnet 54b on the +x side being arranged below the magnetic layer 11. Therefore, the magnetization fixed region 1 on the -x side FX1 The magnetic field +H in the +z direction is generated from the N pole side of the nanomagnet 54a. pin is applied, and the magnetization fixed region 1 on the +x side FX2 The magnetic field -H in the -z direction is generated from the south pole side of the nanomagnet 54b. pin Furthermore, the nanomagnets 54a and 54b are provided so as to be connected to the lower surface (channel layer 12) of the magnetic nanowire 1, and the electrodes 61 and 62 are connected to the lower surfaces of the nanomagnets 54a and 54b. Therefore, the nanomagnets 54a and 54b, together with the electrodes 61 and 62, act as a current source for the magnetic nanowire 1. w This constitutes the supply route.

[0022] Nanomagnet 54 has a coercive force Hc p It is preferable that the coercive force Hc of the magnetic layer 11 is sufficiently large. f As will be described later, the nanomagnet 54 is larger than the leakage magnetic field +H pin ,-H pin To this end, the nanomagnet 54 is made of a hard magnetic material with in-plane magnetic anisotropy, and may be, for example, a multilayer film such as a Co / Pt multilayer film in which transition metals such as Fe, Co, Ni, and noble metals such as Pd and Pt are alternately stacked at a film thickness ratio of about 2 to 4:1.

[0023] The electrodes 61 and 62 are terminals for supplying a current from the outside to the magnetic nanowire 1 in the nanowire direction (+x direction, −x direction). FX1 ,1 FX2 The electrodes 61 and 62 are electrically connected to the magnetic nanowire 1 on the outside in the x-direction of the magnetic nanowire 1. In the domain wall motion device 10 according to this embodiment, the electrodes 61 and 62 are connected to the magnetic nanowire 1 via the nanomagnets 54a and 54b, respectively. The electrodes 61 and 62 are made of a common metal electrode material such as metals such as Cu, Al, Au, Ag, Ta, Cr, Pt, and Ru, or alloys thereof, and are formed to a thickness and width corresponding to the magnitude of the current supplied to the magnetic nanowire 1.

[0024] In the domain wall motion element 10, the insulators provided in the gaps around the magnetic nanowire 1 and the nanomagnets 54a and 54b are made of known inorganic insulating materials such as SiO2, SiN, and Al2O3 that are used in semiconductor elements, and different materials may be used depending on the location. In particular, when the magnetic layer 11 is made of a material that oxidizes easily, such as an RE-TM alloy, it is preferable to use a non-oxide such as SiN or MgO in the area that comes into contact with the magnetic layer 11, specifically, the top and side surfaces of the magnetic nanowire 1. Furthermore, during the manufacture of the domain wall motion element 10 (spatial light modulator 90), it is preferable to deposit such an insulating material as a protective film with a thickness of about 1 to 10 nm, continuously with the materials that form the channel layer 12 and the magnetic layer 11.

[0025] (Domain wall motion in magnetic nanowires) The domain wall motion in the magnetic nanowire by supplying a current in the domain wall motion element according to this embodiment will be described with reference to FIGS. 2, 3, and 4. In these figures, the magnetic layer 11 of the magnetic nanowire 1 is in the magnetization reversible region 1. SWAssuming that there are two domain walls DW1 and DW2 in the domain D1 (see FIGS. 1A and 1B), the portion including the domain walls DW1 and DW2 is shown enlarged in the fine wire direction (x direction). First, the magnetic structure of the domain walls will be explained. In the magnetic layer 11, which is a ferromagnetic material, at the boundary between the magnetic domain D1 with a downward magnetization direction and the magnetic domain D2 with an upward magnetization direction, the magnetization direction does not suddenly switch from downward to upward. Instead, an exchange interaction occurs that tries to align adjacent magnetic moments m and m in the same direction. As a result, a domain wall DW1 is generated between the magnetic domains D1 and D2, in which the magnetic moment m is arranged and gradually tilted from the magnetic domain D1 side toward the magnetic domain D2 side. Similarly, in the domain wall DW2 at the boundary between the magnetic domain D2 with an upward magnetization direction and the magnetic domain D3 with a downward magnetization direction, the aligned magnetic moment m is gradually tilted from the magnetic domain D2 side toward the magnetic domain D3 side. A domain wall in which the magnetization direction is downward on the -x side and upward on the +x side, such as the domain wall DW1 in these drawings, is called a down-up domain wall. Conversely, a domain wall in which the magnetization direction is upward on the -x side and downward on the +x side, such as the domain wall DW2, is called an up-down domain wall.

[0026] Here, there are two types of magnetic domain walls in magnetic materials made of perpendicular magnetic anisotropy materials. One is a Neel-type domain wall, as shown in Figures 2, 3, and 4, in which the magnetic moment m in the domain walls DW1 and DW2 tilts toward the wire direction (x direction) perpendicular to the domain wall plane (yz plane) and rotates 180° in the xz plane. The other is a Bloch-type domain wall (not shown) in which the magnetic moment m tilts toward the wire width direction (y direction) and rotates 180° in the domain wall plane (yz plane). Furthermore, the direction of magnetic moment rotation in each domain wall can exhibit right-handed chirality or left-handed chirality. The domain walls DW1 and DW2 shown in Figure 2 have a right-handed Neel-type magnetic structure, while the domain wall DW1 shown in Figure 3 and the domain wall DW2 shown in Figure 4 have a left-handed Neel-type magnetic structure. Typically, in a magnetic material with perpendicular magnetic anisotropy formed in a thin wire, the magnetic domain wall moves while its magnetic structure alternates between these four types. However, if the wire width is sufficiently thin, it tends to become a Néel-type domain wall, and it changes into two types: right-handed and left-handed. Furthermore, the right-handed Néel-type domain wall is dominant due to the effective magnetic field (+x direction for up-down domain walls and -x direction for down-up domain walls) caused by the Dzyaloshinskii-Moriya Interaction (DMI) due to the stacked structure of the magnetic wire 1 (channel layer 12 / magnetic layer 11 / insulator).

[0027] Such a magnetic nanowire 1 is passed through a current I w When current is supplied in one direction (+x direction) along the wire, a current J per unit area in the yz plane flows in the +x direction in the channel layer 12, as shown in the upper part of Figure 2. Then, in the channel layer 12, a spin current is induced by the spin Hall effect, and electrons e with spins in opposite directions (-y direction, +y direction) along the wire width direction flow. - Therefore, electrons e with spin in the -y direction are accumulated near the interface with the upper magnetic layer 11. - -y-direction electrons e -rotates the magnetic moment m of the domain walls DW1 and DW2 of the magnetic layer 11 counterclockwise in the xz plane. In Fig. 2, Fig. 3, and Fig. 4, the magnetic moment m of the domain walls DW1 and DW2 is indicated by an arrow indicating the direction of rotation. At the same time, a current flows through the magnetic layer 11 at a current density according to the resistance difference with the channel layer 12. If this current density is sufficiently high, Joule heat is generated in the magnetic layer 11, causing the temperature to rise, and the coercive force Hc f From Hc f ´(≦Hc f ), the magnetic anisotropy decreases, the magnetic moment m weakens, and the magnetic field becomes easier to rotate. As a result, the right-handed Neel domain walls DW1 and DW2 are apparently oriented in a direction parallel to the current I w In the same +x direction as the magnetic nanowire 1, the magnetic domain D1 at the rear side expands, the magnetic domain D3 at the front side contracts, and the magnetic domain D2 in between moves in the +x direction. Conversely, as shown in the bottom of Figure 2, when a current I w When the electrons are supplied in the -x direction, electrons e having a spin in the +y direction are generated in the channel layer 12 near the interface with the magnetic layer 11. - The electrons with spin in the +y direction, e - rotates the magnetic moment m of the domain walls DW1 and DW2 of the magnetic layer 11 clockwise in the xz plane, so that the domain walls DW1 and DW2 appear to move in the -x direction. In other words, the domain walls move in the direction in which the current is supplied.

[0028] On the other hand, in the magnetic nanowire 1 shown in Fig. 3, the domain wall DW1 has a left-handed Neel-type magnetic structure. As shown in the upper part of Fig. 3, when a current I w When electrons are supplied in the +x direction, electrons e having a spin in the -y direction appear near the interface of the stacked channel layer 12. - -y-direction electrons e - rotates the magnetic moment m of the domain wall DW1 counterclockwise, so the left-handed Neel-type domain wall DW1 appears to be driven by the current I w Then, as shown in the bottom of Figure 3, the current I w is supplied in the -x direction, an electron e with a spin in the +y direction- rotates the magnetic moment m clockwise, so the domain wall DW1 appears to move in the +x direction. In other words, the left-handed Néel-type domain wall moves in the direction opposite to the current supply direction. Thus, in a magnetic nanowire, the direction in which the domain wall moves relative to the current supply direction differs depending on the magnetic structure. However, as mentioned above, since the right-handed Néel-type magnetic structure is dominant, the domain wall moves in the current supply direction as shown in Figure 2.

[0029] Here, as shown in FIGS. 3 and 4, a magnetic field H in a predetermined direction in the direction of the thin wire is applied from the outside. ass When a magnetic field H is applied to the magnetic layer 11, the domain walls DW1 and DW2 are stabilized in a Neel-type magnetic structure in which the magnetic moment rotates in one direction, regardless of the wire width of the magnetic layer 11. Specifically, as shown in FIG. ass When a magnetic field H is applied in the +x direction, the down-up domain wall DW1 has a left-handed Neel magnetic structure, and the up-down domain wall DW2 has a right-handed Neel magnetic structure, which are both stabilized. On the other hand, when a magnetic field H ass When a magnetic field is applied in the -x direction, the down-up domain wall DW1 is stabilized with a right-handed Neel magnetic structure, and the up-down domain wall DW2 is stabilized with a left-handed Neel magnetic structure. In this way, when the magnetic structures of the domain walls DW1 and DW2 are stabilized by the application of a magnetic field, the domain walls DW1 and DW2 are stabilized by the application of a current I w It can be moved at high speed by supplying a current I w You can move it with .

[0030] However, the magnetic field H ass When a current I is applied, the down-up domain wall DW1 and the up-down domain wall DW2 have different magnetic moment rotation directions. w Specifically, as shown in the upper part of Figure 3, when a current I is applied to the magnetic nanowire 1, the direction of movement is opposite to that of the magnetic nanowire. w is supplied in the +x direction, the domain wall DW1 is driven by the current I w and the domain wall DW2 moves in the -x direction opposite to the current I wAs a result, the magnetic domain D2 expands forward and backward, and the rear magnetic domain D1 and the front magnetic domain D3 both contract. Conversely, as shown in the bottom of Figure 3, when a current I w When current I is supplied in the -x direction, the domain wall DW1 moves in the +x direction, and the domain wall DW2 moves in the -x direction. As a result, the rear magnetic domain D1 and the front magnetic domain D3 both expand, and the magnetic domain D2 between them shrinks forward and backward. Finally, the magnetic domain D2 disappears, and the domain walls DW1 and DW2 separating it also disappear, and the downward magnetic domains D1 and D3 are integrated. Meanwhile, as shown in the upper part of Figure 4, when a current I w When current I is supplied in the +x direction, as in the lower part of Figure 3, the domain wall DW1 moves in the +x direction, and the domain wall DW2 moves in the -x direction, causing the magnetic domain D2 to contract forward and backward. Then, as shown in the lower part of Figure 4, when current I w is supplied in the -x direction, the domain wall DW1 moves in the -x direction, the domain wall DW2 moves in the +x direction, and the magnetic domain D2 stretches forward and backward, as in the upper part of FIG.

[0031] In this way, by supplying a current to the magnetic wire 1 in the wire direction, the domain wall DW in the magnetic layer 11 can be moved in the direction of the current supply. Furthermore, by supplying a current while applying a magnetic field to the magnetic layer 11 from the outside in the wire direction, the domain wall DW can be moved at high speed, and depending on the direction of the applied magnetic field, the domain wall DW can be moved in the same direction as the current supply direction or in the opposite direction. Furthermore, regardless of the number of magnetic domains in the magnetic layer 11, the entire region through which the current flows in the wire direction can be magnetized in the desired upward or downward direction. Specifically, when the current supply direction and the magnetic field application direction are the same, the magnetization direction is upward (upper part of Figure 3, lower part of Figure 4), and when they are opposite, the magnetization direction is downward (lower part of Figure 3, upper part of Figure 4).

[0032] (Operation of the domain wall motion device) In the domain wall motion element 10 according to this embodiment, the magnetization reversible region 1 SW 1A and 1B, the magnetization reversal operation in the magnetic domain wall motion device 10 will be described. In the magnetic domain wall motion device 10, the magnetic nanowire 1 is connected to the bottom surface of the magnetic nanowire 1 via the nanomagnets 54a and 54b. wis supplied, the current I w In other words, the magnetic nanowire 1 has a low spin Hall effect in the region between the regions connected to the nanomagnets 54a and 54b. w This region of the magnetic nanowire 1 is called the SOT region. Therefore, the current I w When the magnetic field is supplied, the magnetic domain wall DW moves in the SOT region of the magnetic layer 11, and the magnetization can be reversed. Furthermore, in the magnetic domain wall motion element 10, the nanomagnets 54a and 54b move the magnetization fixed region 1 of the magnetic layer 11. FX1 Upward leakage magnetic field +H pin However, the magnetization fixed region 1 FX2 Downward leakage magnetic field -H pin are applied to the magnetization fixed region 1. FX1 ,1 FX2 So, the magnetic moment m is the magnetic field +H pin ,-H pin Therefore, the upward and downward magnetization directions are maintained and the magnetization does not reverse, that is, the domain wall DW does not move. FX1 ,1 FX2 Since the magnetization direction at is fixed, the current I w supply direction and magnetic field H ass Depending on the direction of application of SW The magnetic domain wall DW does not disappear from the SOT region of the magnetic layer 11. w The supply direction is switched repeatedly to the magnetization reversible region 1 SW The magnetization can be reversed.

[0033] Magnetization reversible region 1 of magnetic layer 11 SWWhen the magnetization direction in the magnetization reversal is to be changed from the upward state shown in FIG. 1A to the downward state, in order to move the domain wall DW in the −x direction, as shown in FIG. 1B, the electrode 61 is connected to the − pole of the current source and the electrode 62 is connected to the + pole, and a current I w is supplied in the -x direction. SW When the magnetization direction of the magnetization is reversed from downward as shown in FIG. 1B to upward, the electrode 61 is connected to the positive pole and the electrode 62 is connected to the negative pole as shown in FIG. 1A, and a current I w 1A, 1B, and the following drawings, a current I flows through the magnetic nanowire 1 in the nanowire direction. w is indicated by a thick dashed arrow.

[0034] Furthermore, the current I w When supplying a magnetic field H ass By applying a low current density current I w By moving the domain wall DW, the magnetization reversible region 1 SW The magnetization can be reversed at high speed with respect to the current density. SW Since the domain wall DW is an up-down domain wall, as shown in Figures 1A, 1B, and 3, the magnetic field H ass Alternatively, a magnetic field H ass may be applied in the -x direction, in which case the current I w Supply direction and magnetization reversible region 1 SW The relationship between the magnetization direction and the magnetic field H ass is the magnetization fixed region 1 FX1 ,1 FX2 In the z-direction magnetic field +H pin ,-H pin It is preferable to set the strength so as not to cancel out the above.

[0035] As described above, the magnetization reversible region 1 of the magnetic layer 11 SW The light reflected by the magnetization direction is polarized at an angle of +θ k / -θ kTherefore, by setting one of the two values ​​of light to light (white) and the other to dark (black), the domain wall motion device 10 can be used as a pixel of a reflective spatial light modulator.

[0036] Current I supplied to magnetic nanowire 1 w The higher the current density, the more electrons with unidirectional spin in the y direction e - Since a large amount of Hc accumulates at the interface between the channel layer 12 and the magnetic layer 11, the temporary coercivity Hc f ´ becomes small, the domain wall DW moves at high speed and the magnetization reversible region 1 SW On the other hand, the current I w When the current density is high, the magnetic nanowire 1 is easily deteriorated. w When a magnetic field H ass When current density is applied, the magnetization reversible region 1 SW The magnetization is reversed, and the magnetic field H ass The larger the current, the faster the domain wall motion. w current density, and magnetic field H ass The distance traveled by the magnetic domain wall DW depends on the magnetization reversible region 1. SW The current I w Set the supply time of the magnetization reversible region 1 SW If the length of the thin wire in the direction of the wire is about 1 μm, the current I w The supply time of the current I is about 10 ns. In order to supply such a short time DC current, the supply time is set to the peak period as a DC pulse current. w It is preferable to supply a current I w supply and magnetic field H ass The application of the current I may start and stop simultaneously or at different times. w The domain wall DW can move slowly even with only the current I w When the magnetic field H ass It is preferable to control the voltage so that the voltage is applied.

[0037] As the thickness of the magnetic layer 11 increases, the volume increases around the interface with the channel layer 12, and the magnetic moment m becomes stronger. On the other hand, the electrons e near the interface with the channel layer 12 - Since the angular momentum of is constant, in order to move the domain wall DW by the SOT effect, the current I w Furthermore, in combination with the increase in the cross-sectional area of ​​the magnetic layer 11, the current density of the current I w However, in this embodiment, the external magnetic field H ass It is believed that the application of a current aligns the domain wall DW of the magnetic layer 11 into a right-handed Neel-type magnetic structure and stabilizes it, making it possible to rotate the magnetic moment at a low current density even if the magnetic layer 11 is relatively thick.

[0038] (Method for initializing a domain wall motion device) The rotation of the magnetic moment due to the SOT effect in the magnetic wire 1, which was explained in the magnetization reversal operation of the magnetic wire 1 of the domain wall motion device 10, is not limited to within the domain wall. By supplying a current in the wire direction and applying a magnetic field in the opposite direction to an upward or downward magnetic domain, the magnetic moment in the magnetic domain can be rotated 180°. However, rotating the tilted magnetic moment in the domain wall, i.e., moving the domain wall, requires a larger momentum than moving the domain wall. Therefore, by applying a magnetic field in the wire direction as well, as with domain wall motion, it is possible to reverse the magnetization of the portion to which the downward or upward magnetic field is applied, thereby generating a domain wall, without increasing the current density. Below, a method for initializing the domain wall motion device will be described with reference to FIGS. 5A to 5D.

[0039] In the initialization process, the polarity of the nanomagnets 54a and 54b of the domain wall motion device 10 is magnetized in a predetermined direction, and in the SOT region of the magnetic layer 11 of the magnetic nanowire 1, the magnetic domain is divided into two in the nanowire direction, forming a magnetization fixed region 1 FX1 Side facing up, magnetization fixed region 1 FX2The domain wall DW is generated at the boundary between these two magnetic domains with the magnetization direction of the nano-magnet (magnetic field application member) 54 facing downward. p Magnetic field H mag1 a magnetization step (first magnetization step) in which the magnetic field is applied in the +x direction (one direction in the thin wire direction), and a coercive force Hc f Magnetic field H mag2 The second magnetization step involves applying a magnetic field H init is applied in the +x direction (one direction in the wire direction) to magnetic nanowire 1. init in the +x direction (thin wire direction).

[0040] In the magnetization step, the nanomagnet 54, which has the largest coercive force among the magnetic materials of the domain wall motion device 10, is magnetized to a predetermined polarity. Here, a bar magnet is used with the north pole on the +x side and the south pole on the -x side. To this end, as shown in FIG. 5A, the coercive force Hc of the nanomagnet 54 is applied to the domain wall motion device 10 from the outside. p Magnetic field H mag1 (H mag1 ≧Hc p ) is applied in the +x direction. mag1 is the coercive force Hc of the nanomagnet 54 p is greater than (H mag1 >Hc p ) is preferred.

[0041] In the single magnetic domain forming step, the magnetic layer 11 of the magnetic nanowire 1 is made into an upward or downward single magnetic domain structure. Here, as shown in FIG. 5B, the coercive force Hc f Magnetic field H mag2 (H mag2 ≧Hc f ) is applied in the -z direction (downward). mag2 is the coercive force Hc of the magnetic layer 11 f is greater than (H mag2 >Hc f ) is preferable. By the single magnetic domain forming step, the entire magnetic layer 11 made of a perpendicular magnetic anisotropy material has a downward magnetization direction.

[0042] In the initial magnetic domain formation process, two magnetic domains sandwiching a domain wall DW are generated in the magnetic layer 11 with a single magnetic domain structure. Here, since the magnetic layer 11 has a downward single magnetic domain structure in the single magnetic domain formation process, an upward magnetic domain is partially generated. As explained with reference to Figures 3 and 4, if a magnetic field is applied to the magnetic nanowire 1 in the nanowire direction while a current is supplied in the same direction, the upward magnetic domain can be extended. In addition, a leakage magnetic field +H in the +z direction is generated in the magnetic layer 11 by the nanomagnet 54a in the area immediately above it near the +x side. pin Similarly, the nanomagnet 54b applies a leakage magnetic field -H in the -z direction to the area directly above it and in the vicinity of the -x side. pin Therefore, as shown in FIG. 5C, a magnetic field H init While applying a current I init is supplied in the +x direction.

[0043] current I init As a result, the temperature of the magnetic layer 11 rises due to the generated Joule heat, the coercive force temporarily decreases, and the magnetic moment weakens. init As a result, electrons e with spin in the -y direction are generated near the interface with the magnetic layer 11 due to the spin Hall effect. - Then, the magnetic layer 11 is subjected to the magnetic field +H pin The magnetic moment of the region to which the magnetic field is applied is - It rotates counterclockwise from downward (-z direction) to +x direction and then reverses to +z direction. Furthermore, the magnetic field H init This encourages the magnetic moment to rotate counterclockwise from the -z direction to the +x direction.

[0044] As a result, as shown in FIG. 5C, the magnetic layer 11 is pinThe region to which the magnetic field H in the +x direction is applied is divided into upward magnetic domains, and domain walls DW' and DW are generated on either side of these domains. These upward magnetic domains are called the initially formed domains. The domain wall DW' on the -x side is a down-up domain wall, and the magnetic field H in the +x direction init This results in a left-handed Neel-type magnetic structure (see the domain wall DW1 in Figure 3). The domain wall DW on the +x side is an up-down domain wall, and is subjected to the same magnetic field H in the +x direction as the effective magnetic field. init This results in a right-handed Neel-type magnetic structure.

[0045] Even after the initial magnetic domain and the domain walls DW', DW are generated in the magnetic layer 11, the current I init and a magnetic field H init When a current I is applied, as explained in the magnetic domain wall motion in the magnetic nanowire, the magnetic domain wall DW' moves in the magnetic layer 11. init The magnetic domain wall DW moves in the -x direction, which is opposite to the supply direction of the magnetization magnetic field, and the magnetic domain wall DW moves in the +x direction, and the upward initially formed magnetic domain extends in both directions as shown in the upper part of Figure 3. Since the spin Hall effect is low in the region directly above the nanomagnet 54a, as shown in Figure 5D, the magnetic domain wall DW' stops just before this region (the boundary on the +x side), i.e., at the edge of the SOT region, and the downward magnetization direction is maintained in the region directly above the nanomagnet 54a. On the other hand, the leakage magnetic field -H in the -z direction is generated by the nanomagnet 54b. pin 5D, the domain wall DW stops in front of this region (at the boundary on the -x side). Therefore, as shown in FIG. 1A, the domain wall motion element 10 has a magnetization fixed region 1 with an upward magnetization direction in the magnetic layer 11 by the initialization process. FX1 and the magnetization pinned region 1 with downward magnetization direction FX2 The fixed magnetization region 1 FX2 The domain wall DW is located at the boundary of the -x side of the magnetization reversible region 1 SW In this way, the magnetic layer 11 maintains the downward magnetization direction in the region directly above the nanomagnet 54a outside the SOT region, and a domain wall DW' exists at the boundary on the +x side. However, this is omitted in FIGS. 1A and 1B, and is not shown in the magnetization fixed region 1. FX1This domain wall DW' has the same upward magnetization direction as the magnetization reversible region 11 of the magnetic layer 11 after the initialization process. SW In addition, when the area directly above the nanomagnet 54a of the magnetic layer 11 is narrow, the magnetic field +H pin When the magnetization of the region to which the voltage is applied reverses upward, the magnetization may reverse all the way to the end on the -x side, and the domain wall DW' may not be generated.

[0046] In this way, in the method for initializing the domain wall motion element according to this embodiment, a magnetic field is applied from the outside three times with the axis changed, and a current is supplied to the magnetic nanowire 1 during the final magnetic field application. mag2 In this case, the initial magnetic domain formation step is performed by applying a magnetic field H init and the direction of current I init In the initial magnetic domain formation process for the magnetic layer having a downward single magnetic domain structure, the magnetic field H init and the direction of current I init However, even if the current I is supplied in the opposite direction, the initial magnetic domain can be formed. init Since the domain walls DW' and DW move in such a way as to shorten the upward magnetic domain (lower part of Figure 3, upper part of Figure 4), a larger momentum is required to form the initial magnetic domain.

[0047] The momentum required to reverse the magnetization of a part of a magnetic domain and generate a domain wall is greater than the momentum required to move the domain wall. Therefore, in the initial magnetic domain formation process, the current I init and magnetic field H init are the currents I w That's it, magnetic field H ass The above (I init ≧I w , H init ≧H ass ) is preferable. However, the current I init If the current I is large, the switching elements (transistors) provided for the wiring and the domain wall motion elements 10 in the spatial light modulator 90 having the domain wall motion elements 10 will be initTherefore, the structure must be able to withstand the current I init is the current I w It is preferable that the current I w On the other hand, the magnetic field H init The stronger the current I init However, the current density of the magnetic field H init If is excessively strong, the leakage magnetic field +H from the nanomagnets 54a and 54b pin ,-H pin The magnetic domain wall DW is located in the fixed magnetization region 1. FX1 ,1 FX2 Since it cannot be stopped by the magnetic field H init is the magnetic field H pin It is preferable that the magnetic field H pin (H init ≦H pin ) is more preferable. In other words, the current I w Current I that is not too large for init The magnetic field H that can reverse the magnetization by combining init ,H pin , and further, the nanomagnet 54 is set to a magnetic field H init The leakage magnetic field H is strong enough not to be canceled out by pin It is preferable that the magnetic field be such that the magnetic field generates a magnetic force.

[0048] Magnetic field of magnetic layer 11 +H pin The time required for magnetization reversal (see Figure 5C) in the region where current I init current density, magnetic field H init The strength of the leakage magnetic field H of the nanomagnet 54 pin The current I init supply and magnetic field H init The time for generating the magnetic domain wall is set as the time for the magnetization reversible region 1 of the magnetic layer 11. SW Although it is longer than the magnetization reversal due to the domain wall motion in the whole, it is extremely short. In order to supply such a DC current, a DC pulse current with a supply time set to the peak period is used as the current I initIt is preferable to supply the magnetic field +H. It is preferable to set the supply time with a margin. pin After the magnetic layer 11 is locally magnetized by the SW It is preferable to reverse the magnetization (movement of the domain wall) of the entire structure. Therefore, the current I init supply and magnetic field H init The application time of the current I is set to include the domain wall motion time. Alternatively, the current I is applied at least until the domain wall DW is generated. init Then, after a short time, or immediately after that, the current I w while the magnetic field H init The application of the magnetic field is continued or the strength is changed to the magnetic field, and the magnetization reversible region 1 SW It is also possible to completely reverse the magnetization of the current I init supply and magnetic field H init The application of the current I init When the magnetic field H init It is preferable to control the voltage so that the voltage is applied.

[0049] (Spatial Light Modulator) As an example, the domain wall motion element 10 is mounted as a light modulation element for the pixels 9 arranged in a spatial light modulator 90 shown in FIG. 6. For simplicity, FIG. 6 shows only the magnetic nanowire 1 (represented by a resistor symbol) and electrodes 61 and 62 (represented by lines) of the domain wall motion element 10, and also shows 16 pixels 9 arranged in 4 columns and 4 rows. Each pixel 9 further includes a transistor 71 connected to the electrode 61 of the domain wall motion element 10, in addition to the domain wall motion element 10. The spatial light modulator 90 has a circuit configuration similar to that of a select transistor-type MRAM having 1T1R memory cells, and includes word lines 84 extending in the column direction and bit lines 81 extending in the row direction. The bit lines 81 are connected to the electrodes 61 via the transistors 71, and the word lines 84 are input to the gates of the transistors 71. The electrodes 62 are connected to a common potential for all the pixels 9.

[0050] The transistor 71 is, for example, a MOSFET (metal oxide semiconductor field effect transistor), and is formed on the surface layer of a Si substrate. Therefore, the pixels 9 can be arranged on the Si substrate as a base. The bit line 81 and the word line 84 are made of a metal electrode material, similar to the electrodes 61 and 62. Furthermore, these wirings and the transistor 71 are connected to each other via a current I w ,I init For example, the structure should be such that it corresponds to the current I w ,I init If the current is 1.0 mA or less, a MOSFET made using a 0.13 μm process can be applied. Furthermore, the gaps between the wirings and the magnetic nanowires 1 of adjacent pixels 9, 9 are filled with a known inorganic insulating material such as SiO2 or Al2O3 that is provided in semiconductor elements.

[0051] In the spatial light modulator 90, the domain wall motion elements 10 are arranged so that the line direction of the magnetic nanowire 1 is aligned in all pixels 9. This is because a magnetic field is applied from outside the spatial light modulator 90 in the line direction during initialization of the domain wall motion elements 10 or further during writing (magnetization reversal operation of the magnetic nanowire 1). However, the arrangement direction of the pixels 9 does not need to be aligned with the line direction (x direction) of the magnetic nanowire 1 of the domain wall motion elements 10. For example, to increase the aperture ratio of the pixel, the diagonal direction of the arrangement can be designed to be aligned with the line direction so that the length of the magnetic nanowire 1 in the line direction is longer. Furthermore, the layout of the pixels 9 is designed with a gap between them so that they are not magnetically influenced by the magnetic nanowire 1 or nanomagnet 54 of the adjacent pixel 9. Furthermore, the magnetization reversible region 1 in the pixel 9 SW It is preferable that the layout is designed so that the arrangement of all pixels 9 is the same.

[0052] (Magnetic Device) The magnetic device according to the embodiment of the present invention includes a spatial light modulator 90, a current source that supplies current to the magnetic nanowires 1 of the domain wall motion elements 10 of the spatial light modulator 90 via a transistor (switching element) 71, and a magnetic field generator (magnetic field application means) that applies a magnetic field to all of the domain wall motion elements 10 of the spatial light modulator 90 (not shown). In this magnetic device, the magnetic field generator applies a magnetic field by switching the direction between the nanowire direction of the magnetic nanowires 1 and the direction perpendicular to the film surface (upward or downward), and also applies a magnetic field by switching the direction between the nanowire direction and the direction perpendicular to the film surface (upward or downward), and applies a magnetic field by switching the direction between the nanomagnet ... p The above magnetic field and the coercive force Hc of the magnetic layer 11 of the magnetic nanowire 1 f The magnetic device further includes peripheral circuits for the spatial light modulator 90, such as a column decoder and a row decoder (not shown).

[0053] The current source is preferably a pulsed current source, with a current I w ,I init is supplied as a DC pulse current to the spatial light modulator 90. The magnetic field generating device generates a magnetic field H mag1 ,H mag2 ,H init and then write a magnetic field H ass For this purpose, the magnetic field generator can apply a magnetic field with uniform strength and direction to the entire spatial light modulator 90, and can further switch the magnetic field strength between two or more levels, and can apply a magnetic field with a maximum coercive force Hc of the nanomagnet 54. p Magnetic field H mag1 The magnetic field generator may be a known device, and an electromagnet-type device capable of generating such a strong magnetic field is preferable. The magnetic field generator may also include a support member that changes the orientation of the magnetic field generator or the spatial light modulator 90 by 90°, so that the magnetic field can be applied to the spatial light modulator 90 in two axial directions (x and z directions).

[0054] (Writing method) The magnetization reversible region 11 of the magnetic layer 11 is reversibly changed for each pixel 9 according to the writing of the spatial light modulator 90, i.e., the desired light and dark pattern. SWAn example of a method for directing the magnetization direction in the magnetic nanowire 1 upward or downward is as follows. w The potential difference between the bit line 81 (the source of the transistor 71) and the electrode 62 for supplying V w Then, one terminal of the current source is connected to 0 V, and the electrodes 62 of all the pixels 9 are connected to this terminal. SW To make the magnetization direction of the magnetization ... w Connect the other terminal of the current source to a potential +V w and the bit line 81 of the selected row, and the word line 84 of the column of the pixel 9 to be written is connected to the gate power supply. SW To make the magnetization direction of the magnetization of the magnet in the direction upward (see Figure 1B), the current I w The other terminal of the current source is connected to a potential -V w Connect to.

[0055] (Initialization method) As described above, the initialization process of the domain wall motion elements 10 two-dimensionally arranged in the spatial light modulator 90 can be performed during the manufacture of the spatial light modulator 90 or before use. The initialization process may be performed on the spatial light modulator 90 not only during manufacture, but also every time it is started up or periodically. When the initialization process is performed when the spatial light modulator 90 is started up, only the single magnetic domain forming process and the initial magnetic domain forming process can be performed as the update process (refresh), and the magnetic layer 11 of the magnetic nanowire 1, which has a relatively small coercive force, is set to the predetermined magnetization state shown in FIG. 1A or 1B.

[0056] The magnetic device according to the embodiment of the present invention may be configured to perform only the updating process (single magnetic domain process, initial magnetic domain forming process) without magnetizing (magnetizing process) the nanomagnets 54 of the domain wall motion element 10. In this case, the magnetic field generating device generates the magnetic field H mag2 ,H init , and the magnetic field H ass is applied, the coercive force Hc of the magnetic layer 11 f Magnetic field H mag2 It is sufficient to be able to apply a voltage, and a Helmholtz type device can be applied.

[0057] (Variation) The spatial light modulator 90 may connect the sources of the transistors 71 of all pixels 9 to a common potential, and connect the electrodes 62 to the bit lines 81. In addition, the spatial light modulator 90 may swap the positions of the electrodes 61 and 62 of one of the domain wall motion elements 10 in two pixels 9 adjacent to each other in the x direction, and integrate and share the electrodes 62 of the two domain wall motion elements 10 and the nanomagnets 54b and 54a connected to the electrodes 62. In such a spatial light modulator 90, the domain wall motion elements 10 of these two pixels 9 have a current I init ,I w supply direction and magnetic field H init ,H ass Therefore, in the initialization process (initial magnetic domain formation process) and writing, the current I init ,I w Reverse the supply direction.

[0058] The magnetic device according to this embodiment generates a magnetic field H ass is applied in both the +x direction and the -x direction, and in writing to the spatial light modulator 90, the current I w The supply direction of the magnetic field can be set to either the +x direction or the -x direction. Therefore, the pixel 9 of the spatial light modulator 90 may be provided with a diode instead of the transistor 71 as a switching element. With this configuration, the magnetic device can simplify the configuration of the spatial light modulator 90.

[0059] The magnetic nanowire 1 may have a channel layer 12 stacked on the top surface of the magnetic layer 11. The domain wall motion device 10 including such a magnetic nanowire 1 has a current I w In this case, it is preferable to select a material with a relatively high optical transmittance for the channel layer 12 and to reduce its thickness so that the channel layer 12 can sufficiently transmit the light that enters and leaves the magnetic layer 11.

[0060] In the domain wall motion device 10, the electrodes 61, 62 may be connected directly to the lower surface of the magnetic nanowire 1, and for this purpose, the nanomagnets 54 (54a, 54b) are placed above the magnetic nanowire 1. In such a domain wall motion device 10, the nanomagnets 54 are not connected to the upper surface of the magnetic nanowire 1, and an insulating film can be provided between them. The insulating film is preferably 3 nm or thicker. However, if the distance between the nanomagnets 54 and the magnetic nanowire 1 is long, the leakage magnetic field +H applied to the magnetic nanowire 1 against the magnetic force of the nanomagnets 54 will be large. pin ,-H pin Furthermore, when the nanomagnets 54 in the domain wall motion element 10 are insulated from the magnetic nanowire 1 in this way, the spatial light modulator 90 can integrate and share the nanomagnets 54b of the domain wall motion element 10 on the -x side and the nanomagnets 54a of the domain wall motion element 10 on the +x side in pixels 9 adjacent in the x direction.

[0061] The domain wall motion element 10 may also be configured to include only one nanomagnet 54 (54a, 54b). For example, only the nanomagnet 54a is provided, and the electrode 62 is directly connected to the lower surface of the magnetic nanowire 1. In such a domain wall motion element 10, the magnetic layer 11 is fixed to the magnetization fixed region 1. FX2 Therefore, in the initial magnetic domain formation step of the initialization process, the current I init Similarly, the supply time of the magnetization reversible region 1 SW When the magnetization is reversed upward, the current I w The supply time of the magnetization fixed region 1 is also adjusted. FX2 It is preferable to design the length in the x direction to provide a sufficient margin as the range where the domain wall DW stops.

[0062] (Modification of the method for initializing the domain wall motion element) By applying a magnetic field in the direction of the magnetic nanowire when moving the domain wall of the magnetic nanowire by the SOT effect, it is possible to extend or shorten a magnetic domain with a specific magnetization direction by moving the domain walls before and after it in opposite directions (see FIGS. 3 and 4). Also, in a magnetic nanowire, the magnetic domains are usually divided in the direction of the magnetic nanowire before an external magnetic field is applied (initial magnetization state). For these reasons, the domain wall motion element 10 according to this embodiment can maintain the magnetization reversible region 1 without applying a magnetic field in the direction perpendicular to the film surface to turn the magnetic layer 11 into a single magnetic domain in the initialization process. SW That is, in the initialization method according to the modified example of the first embodiment of the present invention, the coercive force Hc of the nanomagnet (magnetic field application member) 54 is set to the domain wall motion device 10. p Magnetic field H mag1 in the +x direction (one direction in the thin wire direction) and a magnetization process (first magnetization process) in which a magnetic field H init is applied in the +x direction (wire direction) while a current I init and an initial magnetic domain formation process in which a current I is supplied in the direction of the thin wire. init The supply direction is switched between the +x direction and the -x direction and this is performed twice. Hereinafter, the method for initializing the domain wall motion element according to this modified example will be described with reference to Figs. 7A to 7D.

[0063] The magnetization process is the same as that of the embodiment shown in Fig. 5A. As a result of the magnetization process, the nanomagnets 54a and 54b of the domain wall motion element 10 become bar magnets with the N pole on the +x side and the S pole on the -x side, as shown in Fig. 7A. At this point, the magnetic layer 11 of the magnetic nanowire 1 has a coercive force Hc f The magnetic field is not applied perpendicular to the film surface (z direction), and the magnetic domain is divided in the wire direction by one or more domain walls. Here, we assume that the magnetic domain is divided into three magnetic domains, one facing upward, one facing downward, and one facing upward, by two domain walls DW2 and DW1.

[0064] In the initial magnetic domain formation step, a magnetic field H init is applied in the +x direction, and current I initAs a result, in the SOT region of the magnetic layer 11, the upward magnetic domains expand and the downward magnetic domains contract. Here, as shown in FIG. 7A, the magnetic layer 11 has two domain walls DW2 and DW1 formed in the SOT region with a downward magnetic domain sandwiched between them. Therefore, the domain walls DW2 and DW1 move closer to each other, the downward magnetic domain disappears, and an upward single magnetic domain structure is formed as shown in FIG. 7B.

[0065] In this modification, the initial magnetic domain formation step continues with the magnetic field H init is applied in the +x direction, and the current I init Then, as shown in FIG. 7C, the magnetic layer 11 is supplied with a leakage magnetic field -H pin In the region where the current I is applied, the magnetic field rotates clockwise from the upward direction (+z direction), passes through the +x direction, and then reverses to the -z direction. As a result, the magnetic layer 11 is divided into downward magnetic domains in this region, and domain walls DW and DW' are generated across these initially formed magnetic domains. Subsequently, when the current I init and a magnetic field H init As shown in FIG. 7D, the magnetic domain wall DW on the −x side moves in the −x direction so that the initially formed magnetic domain extends, and the nanomagnet 54a generates a leakage magnetic field +H pin The domain wall DW' on the positive side moves in the +x direction and stops just before the region directly above the nanomagnet 54b, i.e., at the edge of the SOT region. Therefore, as a result of the initialization process, the domain wall motion element 10 has a magnetization fixed region 11 with an upward magnetization direction in the magnetic layer 11, as shown in FIG. 1B. FX1 and the magnetization pinned region 1 with downward magnetization direction FX2 The fixed magnetization region 1 FX1 The domain wall DW is located at the boundary on the +x side of the magnetization reversible region 1 SW The magnetization direction is downward at

[0066] In addition, the current I init is high enough, or the magnetic field H init If is strong enough, the magnetic field H init is applied in the +x direction while the current I initis supplied in the +x direction (see FIG. 7B), the magnetic layer 11 is irradiated with a leakage magnetic field −H in the −z direction by the nanomagnet 54b, as shown in FIG. 7C. pin In the region where the magnetic field -H is applied, the initial magnetic domain is formed downward. However, at this stage, the initial magnetic domain is pin does not extend beyond the area to which the current I init When the supply direction is reversed to the -x direction, it stretches as shown in Figure 7D.

[0067] Before the initial magnetic domain forming step (after the magnetizing step), if the magnetic layer 11 is divided into three magnetic domains, downward, upward, and downward, opposite to the magnetization direction shown in FIG. 7A, the magnetization state of the magnetic layer 11 changes as follows by the initial magnetic domain forming step. First, the magnetic field H init is applied in the +x direction, and current I init When the magnetic field is supplied, the domain wall on the -x side moves in the -x direction so that the upward magnetic domain stretches, and stops just before the region directly above the nanomagnet 54a, i.e., at the edge of the SOT region. The domain wall on the +x side moves in the +x direction, and the leakage magnetic field -H pin In other words, the state shown in FIG. 5D is reached, and the magnetic layer 11 reaches the magnetization reversible region 1. SW The magnetization direction is upward at the magnetic field H init is applied in the +x direction, and the current I init When the magnetic field is reversed and supplied in the −x direction, the domain wall DW moves in the −x direction, and the magnetic layer 11 is in the magnetization reversible region 1 SW Therefore, regardless of the magnetization state before the initial magnetic domain formation step, the magnetic layer 11 has a downward magnetization direction as shown in FIG. 1B, where the domain wall DW is formed in the magnetization fixed region 11 by the initial magnetic domain formation step. FX1 is located on the +x-side boundary of the magnetization reversible region 1 SW The magnetization direction is downward at

[0068] In this way, in the initialization method of the domain wall motion element according to this modification, a magnetic field is applied from the outside in the direction of the magnetic nanowire 1 with the strength changed in two stages, and when a weaker magnetic field is applied later, a current is supplied to the magnetic nanowire 1 twice with the supply direction reversed. Note that in the initialization method according to this modification, the initial magnetic domain formation step first involves supplying a current I init in the -x direction (magnetic field H init In this case, as shown in FIG. 1A, the domain wall DW is formed in the magnetization fixed region 1. FX2 The magnetization reversible region 1 SW The initial magnetic domain formation process is performed by applying a current I init is supplied in one direction, either the +x direction or the -x direction, and the magnetic field H init The direction of application of the voltage may be reversed from the +x direction to the −x direction or from the −x direction to the +x direction.

[0069] According to the initialization method for a domain wall motion element of this modification, the domain wall DW can be positioned at a predetermined position in the magnetic layer 11 of the domain wall motion element 10, regardless of the initial magnetization state of the magnetic layer 11. Therefore, similar to the initialization method for a domain wall motion element according to the above embodiment, all of the spatial light modulators 90 can be initialized by applying a magnetic field to them from the outside. Furthermore, to perform the initialization method for a domain wall motion element according to this modification, the magnetic device can be simplified in configuration because the magnetic field generator only applies a magnetic field to the spatial light modulator 90 in one axial direction (x direction), including writing to the spatial light modulator 90. Furthermore, the magnetic device may be configured to perform only the update process, i.e., the initial magnetic domain formation process. In this case, the magnetic field generator only applies a magnetic field in the x direction, so a uniaxial Helmholtz-type device can be used, resulting in an even simpler configuration.

[0070] (Magnetoresistive element) The domain wall motion element according to the first embodiment of the present invention can be configured as a magnetoresistive effect element by stacking an insulating film and a magnetic film with perpendicular magnetic anisotropy on the magnetization reversible region of the magnetic layer of the magnetic nanowire. The configuration of a domain wall motion element according to a modified example and a magnetic memory including the same will be described below with reference to Figures 8A, 8B, and 9. The same elements as those in the first embodiment (see Figures 1 to 6) are designated by the same reference numerals, and description thereof will be omitted.

[0071] 8A and 8B , a domain wall motion device 10A according to a modified example of the first embodiment of the present invention includes a magnetic wire 1 formed by laminating a magnetic layer 11 and a channel layer 12 in this order from above, nanomagnets (magnetic field application members) 54a and 54b made of a hard magnetic material with in-plane magnetic anisotropy and connected to the lower surface (channel layer 12) of the magnetic wire 1 at a distance from each other in the wire direction, a barrier layer (insulating film) 3 and a magnetization fixed layer (reference layer) 43 laminated on the upper surface of the magnetic layer 11 at the center in the wire direction, and further includes electrodes 61 and 62 connected to the lower surfaces of the nanomagnets 54a and 54b, respectively, and an electrode 63 connected to the upper surface of the magnetization fixed layer 43. Thus, compared to the domain wall motion device 10 according to the above embodiment, the domain wall motion device 10A has a configuration in which the barrier layer 3, the magnetization fixed layer 43, and the electrode 63 are laminated in this order on the magnetic layer 11 of the magnetic wire 1. The domain wall motion element 10A is a magnetoresistive effect element, and can be used as a storage element of a memory cell of an MRAM.

[0072] The configuration of the magnetic nanowire 1 is as explained in the above embodiment. However, in the domain wall motion device 10A, the barrier layer 3 and the magnetization fixed layer 43 are stacked on the magnetic layer 11, so the channel layer 12 needs to be stacked below the magnetic layer 11. Furthermore, the magnetic layer 11 does not need to have a magneto-optical effect, but preferably has a certain degree of coercive force. Furthermore, the thickness and width of the magnetic layer 11 may be any size necessary for maintaining magnetization and for thermal agitation resistance, and specifically, the thickness is preferably 5 nm or more and the width is preferably 10 nm or more. Similarly, the magnetization reversible region 1 SW and the fixed magnetization regions 1 on both sides FX1 ,1 FX2The length of each thin wire in the direction of the thin wire (see FIGS. 8A and 8B) is preferably 10 nm or more and 1 / 2 or more of the thin wire width. Furthermore, it is preferable that the width of magnetic layer 11 is 300 nm or less, since the magnetic domains are less likely to be split in the width direction.

[0073] The barrier layer 3 and the magnetization fixed layer 43 constitute a TMR element having a three-layer laminated structure together with the magnetic layer 11, and the magnetization reversible region 1 of the magnetic layer 11 is used for reading the domain wall motion element 10A. SW That is, the region of the magnetic layer 11 directly below the magnetization fixed layer 43 becomes the magnetization free layer of the TMR element, and therefore, this region is the magnetization reversible region 1. SW The magnetization fixed layer 43 is disposed so as to be included in the magnetization reversible region 1 in the wire direction (x direction). SW The length of the wire is within the magnetization reversible region 1 SW The barrier layer 3 and the magnetization pinned layer 43, together with the magnetic layer 11 directly below, may be made of a material and have a shape suitable for a TMR element. The magnetization pinned layer 43 may have a length (width) equal to or shorter than the magnetic wire 1 in the wire width direction (y direction), or may be formed large and extend outward from the magnetic wire 1. The magnetization direction of the magnetization pinned layer 43 is pinned either upward or downward, and is assumed to be upward here. Therefore, the coercive force of the magnetization pinned layer 43 is equal to the coercive force Hc of the magnetic layer 11. f or more, and the coercive force Hc f. The magnetic pinned layer 43 has a magnetic force sufficiently weaker than that of the nanomagnets 54 so that the magnetic field generated by the magnetic pinned layer 43 does not inhibit the movement of the domain wall DW. For this purpose, the magnetic pinned layer 43 can be made of a known perpendicular magnetic anisotropy material, similar to the magnetic layer 11. In particular, materials used for the magnetic pinned layer (reference layer) of a CPP-GMR element or a TMR element are suitable. The magnetic pinned layer 43 preferably has a thickness equal to or greater than that of the magnetic layer 11. The barrier layer 3 is an insulating film for 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 3 may be provided at least between the magnetic layer 11 and the magnetic pinned layer 43, and may be provided on the entire upper surface of the magnetic layer 11 to double as a protective film. The electrode 63 is made of a metal electrode material, similar to the electrodes 61 and 62.

[0074] In the domain wall motion device 10A according to this modification, the domain wall motion in the magnetic nanowire due to current supply is the same as in the domain wall motion device 10 according to the previous embodiment. In the domain wall motion device 10A, the resistance in the direction perpendicular to the film surface between the magnetization fixed layer 43 and the magnetic layer 11 is higher when the magnetization directions of the magnetization fixed layer 43 and the magnetic layer 11 in the region immediately below are antiparallel than when they are parallel. That is, in the domain wall motion device 10A, the magnetization reversible region 1 of the magnetic layer 11 is SW When the magnetization direction in the magnetization reversible region 1 is upward (see FIG. 8A), the resistance between the electrodes 61 and 63 and between the electrodes 62 and 63 is low. SW When the magnetization direction of the magnetic domain wall motion element 10A is downward (see FIG. 8B), the resistance is high. Therefore, the magnetic domain wall motion element 10A can be used as a storage element of an MRAM memory cell, for example, by setting the low resistance state as data "0" and the high resistance state as data "1."

[0075] The method for initializing the domain wall motion element 10A according to this modification is the same as that for the domain wall motion element 10 according to the embodiment shown in FIGS. 5A to 5D. However, in the single magnetic domain forming step (second magnetization step), a magnetic field H equal to or greater than the coercive force of the magnetization fixed layer (reference layer) 43 is applied. mag2 is applied upward to set the magnetization direction of the entire magnetic layer 11 to the upward direction, and also set the magnetization direction of the magnetization fixed layer 43 to the upward direction.

[0076] (magnetic memory) As an example, the domain wall motion element 10A is mounted as a magnetoresistive effect element of a memory cell 9A arranged in a magnetic memory 90A shown in Fig. 9. For the sake of simplicity, Fig. 9 shows 16 memory cells 9A arranged in 4 columns and 4 rows, and for the domain wall motion element 10A, the magnetic nanowire 1, barrier layer 3, and magnetization fixed layer 43 (denoted by reference numeral 1A) are represented by a combination of the graphical symbols for a resistor and a variable resistor, and the electrodes 61, 62, and 63 are represented by lines. The memory cell 9A includes, together with the domain wall motion element 10A, a transistor 71 connected to the electrode 61 of the domain wall motion element 10A, and a diode 72 whose anode is connected to the electrode 63. The magnetic memory 90A has a circuit configuration similar to that of a select transistor type MRAM having 1T1R type memory cells, and includes bit lines 82 and word lines 84 extending in the column direction, a source line 81A extending in the row direction, and a read word line 83 extending in the row direction perpendicular to the bit line 82. The bit line 82 is connected to the electrode 62, the source line 81A is connected to the electrode 61 via the transistor 71, the word line 84 is input to the gate of the transistor 71, and the read word line 83 is connected to the electrode 63 via the diode 72.

[0077] As with the spatial light modulator 90, the transistor 71 is formed on the surface layer of a Si substrate, and the memory cells 9A can be arranged on this Si substrate as a base. On the other hand, since the diode 72 is provided above the magnetic nanowire 1 and the magnetization fixed layer 43, it is preferable that the diode 72 be made of polycrystalline silicon (poly-Si), which can be deposited at a low temperature of about 150°C, although this depends on the materials used for these.

[0078] Writing to the magnetic memory 90A can be performed in the same manner as writing to the spatial light modulator 90 including the domain wall motion element 10 according to the embodiment. The source line 81A of the selected row (to be written) is connected to one terminal of a current source, the bit line 82 of the column of the selected memory cell 9A is connected to the other terminal of the current source, and the word line 84 of the same column is connected to a gate power supply. When writing data "0", the source line 81A is connected to the + (potential +Vw) terminal of the current source, and the bit line 82 is connected to the - (potential 0V) terminal of the current source. When writing data "1", the + / - terminals of the current source are reversed and connected. Furthermore, in writing, all read word lines 83 are connected to the potential +V w It is preferable to connect the above.

[0079] To read the magnetic memory 90A, all word lines 84 are connected to 0V, and the transistors 71 of all memory cells 9A are turned off. Then, the positive terminal of a constant current source is connected to the bit line 82 of the selected memory cell 9A, and the negative terminal is connected to the read word line 83, to supply a constant current I r While supplying a constant current I, the resistance is measured using a voltmeter connected in parallel to the constant current source. r is set to a value large enough to prevent the domain wall DW of the magnetic layer 11 of the domain wall motion element 10A from moving. In addition, in reading, it is preferable to connect the bit lines 82 of the unselected columns to a potential equal to or lower than the negative pole of the constant current source, and connect the read word lines 83 of the unselected rows to a potential equal to or higher than the positive pole.

[0080] (Magnetic Device) The magnetic device according to the modified embodiment of the present invention includes a magnetic memory 90A, a current source that supplies current to the magnetic nanowires 1 of the domain wall motion elements 10A of the magnetic memory 90A via transistors (switching elements) 71, and a magnetic field generator (magnetic field application means) that applies a magnetic field to all the domain wall motion elements 10A of the magnetic memory 90A (not shown). In this magnetic device, the magnetic field generator applies a magnetic field by switching the direction between the nanowire direction of the magnetic nanowires 1 and the direction perpendicular to the film surface (upward or downward), and also applies a magnetic field by switching the direction between the nanomagnet direction and the direction perpendicular to the film surface (upward or downward), and ...p The strength of the magnetic field is switched to the above magnetic field and to a magnetic field equal to or greater than the coercive force of the magnetization fixed layer (reference layer) 43. The magnetic device further includes peripheral circuits (not shown) of the magnetic memory 90A, such as a column decoder and a row decoder. The other configurations of the magnetic device are the same as those of the above embodiment.

[0081] The magnetic device is similar to the magnetic device including the spatial light modulator 90 in that the magnetic field generating device generates the magnetic field H ass is applied by switching between the +x direction and the −x direction, the memory cells 9A of the magnetic memory 90A may be provided with diodes as switching elements instead of the transistors 71. Furthermore, similar to the spatial light modulator 90, the magnetic memory 90A can swap the positions of the electrodes 61 and 62 of one of the domain wall motion elements 10A in the memory cells 9A adjacent to each other in the x direction, and integrate and share the electrodes 62 of the two domain wall motion elements 10A and the nanomagnets 54b and 54a connected to the electrodes 62.

[0082] As in the previous embodiment, the magnetic device according to this modification may be configured to perform only the update process (single magnetic domain process, initial magnetic domain formation process) without magnetizing the nanomagnets 54 of the domain wall motion element 10A (magnetization process). In this modification, the update process places the magnetic layer 11 of the domain wall motion element 10A in a predetermined magnetization state and sets the magnetization direction of the magnetization fixed layer 43 to an upward direction. Alternatively, the update process may simply place the magnetic layer 11 in a predetermined magnetization state. In this case, the initialization method according to the modification of the previous embodiment (see FIGS. 7A to 7D) can be applied, i.e., only the initial magnetic domain formation process is performed. Therefore, since the magnetic field generating device only needs to apply a magnetic field in the x direction, a uniaxial Helmholtz-type device can be used.

[0083] The domain wall motion device 10A according to this modification may include an intermediate layer made of a non-magnetic metal such as Cu, Ag, or Al and having a thickness of 1 to 10 nm, instead of the barrier layer 3. A CPP-GMR device can be configured with a three-layer stacked structure including this intermediate layer, the magnetization fixed layer 43, and the magnetic layer 11. Furthermore, in the domain wall motion device 10A, electrodes 61 and 62 may be connected directly to the bottom surface of the magnetic nanowire 1, and nanomagnets 54 (54a and 54b) may be disposed above the magnetic nanowire 1, as in the domain wall motion device 10 according to the above embodiment.

[0084] Second Embodiment In the domain wall motion element according to the first embodiment of the present invention, a bar magnet oriented in the direction of the nano-magnet wire is used as a nano-magnet to apply a magnetic field to fix the magnetization direction of the magnetic nano-magnet wire, but a bar magnet oriented perpendicular to the film surface can also be used. Hereinafter, a method for initializing the domain wall motion element according to the second embodiment of the present invention will be described with reference to Figures 10A and 10B. Elements identical to those in the first embodiment (see Figures 1 to 9) are designated by the same reference numerals, and a description thereof will be omitted.

[0085] (domain wall motion element) A domain wall motion element 10B (hereinafter referred to as the domain wall motion element according to the first embodiment) for performing the method for initializing a domain wall motion element according to the second embodiment of the present invention, as shown in FIGS. 10A and 10B , includes a magnetic nanowire 1 formed by stacking a magnetic layer 11 made of a perpendicular magnetic anisotropy material and a channel layer 12 having the spin Hall effect in this order from top to bottom to form a nanowire shape, and nanomagnets (magnetic field application members) 51 and 52 made of a hard magnetic material with perpendicular magnetic anisotropy connected to the lower surface (channel layer 12) of the magnetic nanowire 1 and spaced apart from each other in the nanowire direction. The domain wall motion element 10B further includes electrodes 61 and 62 connected to the lower surfaces of the nanomagnets 51 and 52. Furthermore, in the domain wall motion element 10B, an insulator is provided in a void space around the magnetic nanowire 1, as in the first embodiment. Like the domain wall motion element 10 according to the first embodiment, the domain wall motion element 10B is a reflective light modulation element, and is two-dimensionally arranged as pixels to form a spatial light modulator 90.

[0086] The nanomagnets 51 and 52 are tiny bar magnets aligned in the z direction and have opposite polarities, with the nanomagnet 51 on the -x side having a south pole on the upper side and the nanomagnet 52 on the +x side having a north pole on the upper side. The nanomagnets 51 and 52 generate a leakage magnetic field in the opposite polarity to that of the nanomagnets 51 and 52 near the outside when viewed from a plane (xy plane). Therefore, the nanomagnet 51 is fixed to the magnetization fixed region 1 of the magnetic layer 11. FX1 +z-direction leakage magnetic field +H pin1 is applied, and the nanomagnet 52 is fixed in the magnetization region 1 FX2 -Z-direction leakage magnetic field -H pin2 10A and 10B, the magnetic field lines from the nanomagnets 51 and 52 are shown by dashed lines. The nanomagnets 51 and 52 are applied with a magnetic field +H pin1 ,-H pin2 As a result, the magnetization fixed region 1 of the magnetic layer 11 FX1 ,1 FX2 The magnetization direction in the magnetic layer 1 is fixed, and a domain wall DW is generated in the magnetic layer 1 during initialization of the domain wall motion device 10. In the domain wall motion device 10B, the nanomagnets 51 and 52 are arranged at both ends of the magnetic wire 1, spaced apart from each other in the x direction. The nanomagnets 51 and 52 are also connected to the bottom surface (channel layer 12) of the magnetic wire 1, and electrodes 61 and 62 are connected to the bottom surfaces of the nanomagnets 51 and 52. Therefore, the nanomagnets 51 and 52, together with the electrodes 61 and 62, control the current I w This constitutes the supply route.

[0087] The nanomagnets 51 and 52 have a coercive force Hc p1 ,Hc p2 It is preferable that the coercive force Hc of the magnetic layer 11 is sufficiently large. f As will be described later, the nanomagnets 51 and 52 are larger than the leakage magnetic field +H applied to the magnetic layer 11. pin1 ,-H pin2To this end, nanomagnets 51 and 52 are made of a hard magnetic material with perpendicular magnetic anisotropy, and may be made of a multilayer film such as a Co / Pd multilayer film in which transition metals such as Fe, Co, Ni, and precious metals such as Pd and Pt are alternately stacked at a film thickness ratio of about 1:2 to 4. Nanomagnets 51 and 52 also have a coercive force Hc so that they can be magnetized in opposite polarities. p1 ,Hc p2 It is preferable that the coercive force (Hc) of the nanomagnet 51 and the nanomagnet 52 are different from each other. For this purpose, the nanomagnet 51 and the nanomagnet 52 are made to have different aspect ratios in plan view. Here, the coercive force (Hc) of the nanomagnet 52 is larger than that of the nanomagnet 51. p1 <Hc p2 ) shall be deemed to be

[0088] (Operation of the domain wall motion device) In the domain wall motion device 10B according to this embodiment, the domain wall motion in the magnetic nanowire caused by the current supply is the same as that in the domain wall motion device 10 according to the first embodiment. SW When the magnetization direction in the magnetization direction is reversed from the upward state shown in FIG. 10A to the downward state, in order to move the domain wall DW in the −x direction, as shown in FIG. 10B, the electrode 61 is connected to the − pole of the current source and the electrode 62 is connected to the + pole, and a current I w is supplied in the -x direction. SW When the magnetization direction of the magnetization is reversed from downward to upward as shown in FIG. 10B, the electrode 61 is connected to the positive pole and the electrode 62 is connected to the negative pole as shown in FIG. 10A, and a current I w is supplied in the +x direction. Furthermore, the current I w When supplying a magnetic field H ass By applying a low current density current I w By moving the domain wall DW, the magnetization reversible region 1 SW The magnetization can be reversed at high speed with respect to the current density. SW The magnetization can be reversed.

[0089] (Method for initializing a domain wall motion device) The initialization method of the domain wall motion element will be described. In the initialization process, the polarities of the nanomagnets 51 and 52 of the domain wall motion element 10B are magnetized in predetermined directions, and in the SOT region of the magnetic layer 11 of the magnetic nanowire 1, the magnetic domain is divided into two in the nanowire direction, forming a magnetization fixed region 1 FX1 Side facing up, magnetization fixed region 1 FX2 The domain wall DW is generated at the boundary between these two magnetic domains with the magnetization direction facing downward on the domain wall motion element 10B side. The initialization process can be performed during the manufacturing process of the spatial light modulator 90 including the domain wall motion element 10B in a two-dimensional array or before use. The initialization method according to the second embodiment of the present invention is to initialize the domain wall motion element 10B by applying the coercive force Hc of the nanomagnet (magnetic field application member) 52. p2 Magnetic field H mag1 The first magnetization step (first magnetization step) applies a magnetic field upward, and the coercive force Hc of the nanomagnet (magnetic field application member) 52 p2 and the coercive force Hc of the nanomagnet (magnetic field application member) 51 p1 Magnetic field H mag2 In the second magnetization process (second magnetization process), a magnetic field H init is applied in the +x direction (one direction in the wire direction) to magnetic nanowire 1. init in the +x direction (thin wire direction).

[0090] In the first and second magnetization steps, the nanomagnets 51 and 52 are magnetized to polarities opposite to each other, and the magnetic layer 11 of the magnetic nanowire 1 is made into an upward or downward single magnetic domain structure. In the first magnetization step, the nanomagnet 52, which has the largest coercive force among the magnetic materials of the domain wall motion element 10B, is made into a bar magnet with the north pole on the +z side and the south pole on the -z side. For this purpose, as shown in FIG. 11A, the coercive force Hc of the nanomagnet 52 is externally applied. p2 Magnetic field H mag1 (H mag1 ≧Hc p2 ) is applied in the +z direction (upward). mag1 is the coercive force Hc of nanomagnet 52 p2 By the first magnetization step, the magnetization direction of all of the nanomagnets 51 and 52 and the magnetic layer 11 made of a perpendicular magnetic anisotropy material is directed upward.

[0091] In the second magnetization step, the nanomagnet 51 is turned into a bar magnet with the S pole on the +z side and the N pole on the -z side without changing the polarity of the nanomagnet 52. To achieve this, as shown in FIG. 11B, the coercive force Hc of the nanomagnet 52 is externally applied. p2 less than 51% and the coercive force Hc of nanomagnets p1 Magnetic field H mag2 (Hc p1 ≦H mag2 <Hc p2 ) is applied in the -z direction (downward). mag2 is the coercive force Hc of the nanomagnet 51 p1 By the second magnetization step, the magnetization of the nanomagnet 51 and the magnetic layer 11 is reversed to a downward magnetization direction, while the nanomagnet 52 maintains its upward magnetization direction.

[0092] In the initial magnetic domain forming step, two magnetic domains sandwiching a domain wall DW are generated in the magnetic layer 11 with a single magnetic domain structure. Here, since the magnetic layer 11 has a downward single magnetic domain structure in the second magnetizing step, a partially upward magnetic domain (initial formed magnetic domain) is formed, as in the first embodiment. In addition, the nanomagnet 51 generates a leakage magnetic field +H in the +z direction in the region immediately above the magnetic layer 11 near the +x side. pin1 Similarly, the nanomagnet 52 applies a leakage magnetic field −H in the −z direction to the area directly above it and in the vicinity of the −x side. pin2 Therefore, as shown in FIG. 11C, a magnetic field H init While applying a current I init is supplied in the +x direction. Then, the magnetic layer 11 is pin1 The region to which the current I is applied is divided into upward magnetic domains, and domain walls DW' and DW are generated on either side of this initially formed magnetic domain. init and a magnetic field H init When a current I is applied, the domain wall DW' flows through the magnetic layer 11. initThe magnetic domain wall DW moves in the -x direction, which is opposite to the supply direction of the magnetic field, and the magnetic domain wall DW moves in the +x direction, and the upward initially formed magnetic domain extends in both directions. Since the spin Hall effect is low in the region directly above the nanomagnet 51, the magnetic domain wall DW' stops at the +x side boundary of this region, as shown in Figure 11D, and the downward magnetization direction of this region is maintained. Meanwhile, the leakage magnetic field -H in the -z direction is generated by the nanomagnet 52. pin2 11D, the downward magnetization direction is maintained even in the region where the magnetic field is applied, and the domain wall DW stops at the boundary on the -x side of this region. In this way, the downward magnetization direction of the magnetic layer 11 is maintained in the region directly above the nanomagnet 51, which is outside the SOT region, and the domain wall DW' exists at the boundary on the +x side. However, this is omitted in FIGS. 10A and 10B, and only the magnetization fixed region 1 is shown. FX1 The magnetization direction is the same as above.

[0093] In this way, the initialization method of the domain wall motion element according to this embodiment involves applying an external magnetic field in two stages, one above the other, to magnetize the nanomagnets 51 and 52 with polarities opposite to each other, and then forming the magnetic layer 11 of the magnetic nanowire 1 into a single magnetic domain structure. Then, the magnetic field is switched to the direction of the nanowire, and at the same time, a current is supplied to the magnetic nanowire 1. Note that after the second magnetization step, the coercive force Hc of the magnetic layer 11 is f The above magnetic field may be applied upward to reverse the magnetization of the magnetic layer 11 to the upward direction again. init and the direction of current I init In particular, the difference in magnetic force between nano magnet 51 and nano magnet 52 is large, and the leakage magnetic field +H pin1 Leakage magnetic field -H pin2 is significantly strong, the magnetic layer 11 is subjected to the leakage magnetic field −H pin2 The magnetization is reversed downward by the current I init The current density can be reduced. Furthermore, the nanomagnet 51 has a larger coercive force (Hc p1 >Hc p2 In the case of (1), the nanomagnet 51 is magnetized in the first magnetizing step, and the nanomagnet 52 is magnetized in the second magnetizing step.

[0094] (Magnetic Device) The domain wall motion element 10B according to the second embodiment is arranged two-dimensionally as described above to form the spatial light modulator 90, and similarly to the first embodiment, a magnetic device (not shown) is formed with this spatial light modulator 90, the peripheral circuit of the spatial light modulator 90, a current source, and a magnetic field generator (magnetic field application means). In the magnetic device according to this embodiment, the magnetic field generator applies a magnetic field by switching the direction between the fine wire direction of the magnetic fine wire 1 and the direction perpendicular to the film surface (upward or downward), and also by controlling the coercive force Hc of the nanomagnet (magnetic field application member) 52 of the domain wall motion element 10B. p2 The above magnetic field and the coercive force Hc of the nanomagnet (magnetic field applying member) 52 p2 The coercive force Hc of the nanomagnet (magnetic field applying member) 51 is less than p1 The magnetic field strength is switched to the above. Furthermore, as explained in the first embodiment, the magnetic device according to this embodiment may be configured to perform only the updating process (single magnetic domain process, initial magnetic domain forming process) without performing the magnetization (first magnetization process, second magnetization process) of the nanomagnets 51, 52 of the domain wall motion element 10B. The single magnetic domain process is performed by changing the coercive force Hc of the magnetic layer 11 of the magnetic nanowire 1, as in the initialization method of the domain wall motion element according to the first embodiment. f The above magnetic field is applied downward (or upward). When only the updating process is performed, the magnetic device can apply the initialization method (see FIGS. 7A to 7D) according to the modified example of the first embodiment, i.e., only the initial magnetic domain forming process is performed.

[0095] (Magnetoresistive element) In the domain wall motion device 10B according to this embodiment, as in the first embodiment, the magnetization reversible region 1 of the magnetic layer 11 of the magnetic nanowire 1 is SW A magnetoresistive effect element can be configured by stacking a barrier layer (insulating film) 3 and a magnetization fixed layer (reference layer) 43 on top (see FIGS. 8A and 8B). This domain wall motion element can be used as a storage element for a memory cell 9A of a magnetic memory 90A.

[0096] (Variation) In the magnetic device according to this embodiment, similarly to the magnetic device according to the first embodiment, a magnetic field generating device generates a magnetic field H assThe spatial light modulator 90 may have a configuration in which the voltage is applied by switching between the +x direction and the −x direction, and the pixels 9 of the spatial light modulator 90 may have diodes instead of transistors 71 as switching elements. Furthermore, in the spatial light modulator 90, in pixels 9 adjacent to each other in the x direction, one of the domain wall motion elements 10B may be arranged inverted in the x direction, and the electrodes 62 of the two domain wall motion elements 10B and the nanomagnets 52 connected to the electrodes 62 may be integrated and shared. The same applies to the magnetic memory 90A. Furthermore, the domain wall motion element 10B according to this embodiment may also be configured to include only one of the nanomagnets 51 or 52, similar to the domain wall motion element 10 according to the first embodiment. For example, the domain wall motion element 10B may include only the nanomagnet 51, and the electrode 62 may be directly connected to the lower surface of the magnetic nanowire 1. In the initialization process, such a domain wall motion element 10B does not undergo the first magnetization step (first magnetization step), but first undergoes the second magnetization step (second magnetization step).

[0097] In the domain wall motion device 10B, similarly to the domain wall motion device 10 according to the first embodiment, the electrodes 61, 62 may be connected directly to the lower surface of the magnetic wire 1, and the nanomagnets 51, 52 may be arranged above the magnetic wire 1. Furthermore, in this embodiment, a magnetic field generated directly below the nanomagnets 51, 52 and oriented in the polarity direction of the nanomagnets 51, 52 can also be applied to the magnetic layer 11. More specifically, as shown in FIGS. 12A and 12B, in the domain wall motion device 10C according to the modified example of the second embodiment, the nanomagnets 51A, 52A are provided above the magnetic wire 1, spaced apart from each other in the x-direction in the region (SOT region) between the regions of the magnetic wire 1 connected to the electrodes 61, 62. In the domain wall motion device 10C according to this modified example, the nanomagnets 51A, 52A are resistant to a magnetic field -H that is stronger against their magnetic force than the nanomagnets 51, 52 of the previous embodiment. pin1 ,+H pin2 is applied to the magnetic layer 11. In other words, the nanomagnets 51A and 52A generate the required magnetic field −H pin1 ,+H pin2 On the other hand, if the magnetic force of nanomagnets 51A and 52A is excessively strong, the leakage magnetic field in the direction opposite to the polarity may inhibit the movement of the domain wall DW, so they are designed to have an appropriate magnetic force.

[0098] In the domain wall motion device 10C according to this modification, the domain wall DW is a down-up domain wall, and therefore, as shown in FIGS. 12A and 12B, the domain wall DW is moved by a current I w In order to move the magnetic field H ass is applied in the −x direction. The domain wall motion element 10C can be initialized by the same procedure as the initialization method for the domain wall motion element according to the embodiment described above (see FIGS. 11A to 11D). [Example]

[0099] In order to confirm the effects of the present invention, a sample simulating the domain wall motion element according to the second embodiment of the present invention shown in Figures 10A and 10B was fabricated, and a current was supplied to the magnetic layer that had been made into a single magnetic domain while an external magnetic field was applied, and the magnetization state was observed.

[0100] (Sample production) The magnetic nanowire was formed in a straight line with a width of 0.5 μm. The stacked structure of the magnetic nanowire and the coercive force Hc of the magnetic layer were f The results are shown in Table 1. The nanomagnets were formed in a straight line with a width of 150 nm (length of the magnetic nanowire in the nanowire direction (length in the x direction)) that crossed the magnetic nanowire, and two were placed with a 3.0 μm gap (center to center) in the x direction. To achieve different coercive forces, the length of the magnetic nanowire in the nanowire width direction (y direction) was set to 500 μm on the -x side and 3 μm on the +x side. The stacked structure and coercive force Hc of the nanomagnet p1 ,Hc p2 The results are shown in Table 1. To fabricate the sample, first a SiN film was deposited on a Si substrate with thermally oxidized SiO2 formed on the surface to form trenches, and then a laminated film that would constitute the nanomagnet was deposited and embedded. On top of this, a laminated film that would constitute the magnetic nanowire was deposited and shaped into a straight line, and then SiN was embedded around the magnetic nanowire. The nanomagnet and magnetic nanowire were each deposited by magnetron sputtering, and then formed by electron beam lithography, ion milling, and lift-off. Then, from each of the two nanomagnets, the protective film on the surface of the magnetic nanowire approximately 6 to 8 μm outward in the direction of the nanowire was removed, and Ag was embedded to form electrodes (the gap between the electrodes was 17 μm).

[0101] [Table 1]

[0102] (Initialization process) A magnetic field of 800mT (+800mT) upward, 250mT (-250mT) downward, and 60mT (+60mT) upward was sequentially applied to the sample, causing the nanomagnets on the -x side to have a downward polarity (-z direction) and the nanomagnets on the +x side to have an upward polarity (+z direction), resulting in the magnetic layer of the magnetic nanowire having a single magnetic domain structure with an upward polarity (+z direction). init ) in the direction of the wire, a pulse current (I init ) was supplied 10 times. Table 2 shows the magnetic field H init and current I init The external magnetic field H init and current I init The positive (+) indicates the +x direction, and the negative (-) indicates the -x direction. After the current was applied, the sample was observed with a magneto-optical microscope to determine whether downward magnetic domain division (generation of domain walls) occurred. Furthermore, when the downward magnetic domain extension was visible under the magneto-optical microscope, it was determined that magnetic domain extension (movement of domain walls) occurred. After the observation, a 60 mT magnetic field was again applied to the sample in the upward direction, and the magnetic field H init and current I init The treatment was carried out under the same conditions five times, and the domain wall generation rate and migration rate were calculated. The domain wall generation rate and migration rate are shown in Table 2. Figure 13A shows a magneto-optical microscope photograph of the sample. A downward magnetic field of 60 mT (-60 mT) was applied to the sample to give the magnetic layer of the magnetic nanowire a downward single magnetic domain structure, and the same treatment and observation were carried out. The domain wall generation rate and migration rate are shown in Table 2. Figure 13B shows a magneto-optical microscope photograph of the sample. Figures 13A, 13B, and Figure 14, described below, show the +x direction facing downward. In the magnetic nanowire (magnetic layer), whitish (bright) areas represent downward magnetic domains, and blackish (dark) areas represent upward magnetic domains.

[0103] [Table 2]

[0104] As a comparative example, a sample in which the magnetic layer of the magnetic nanowire had a downward single-domain structure was supplied with a pulse current in the -x direction, with the current value varied from 1.6 mA to 2.1 mA in 0.1 mA increments, without applying an external magnetic field. A magneto-optical microscope photograph of the sample is shown in Figure 14.

[0105] As shown in Figure 13A, when a magnetic field was applied to a magnetic nanowire with an upward single-domain structure while a current was supplied, depending on the direction and strength of the applied magnetic field, downward magnetic domains were split in the magnetic layer of the magnetic nanowire near both sides (the -x side and the +x side) of the nanomagnet on the +x side, which had an upward polarity. This means that a domain wall was formed. As shown in Table 2 and Figure 13A, applying a magnetic field in the opposite direction to the current supply direction was particularly effective, and domain walls could be formed even with a magnetic field equal to or weaker than the coercivity of the magnetic layer. Furthermore, by supplying a current in the opposite direction to the applied magnetic field, the downward magnetic domains that were formed expanded. The magnetic domain formed on the +x side of the +x side nanomagnet expanded at its longest (more than 7 μm) just before the connection point with the +x side electrode. On the other hand, the magnetic domain formed on the -x side of the nanomagnet expanded at most just before the -x side nanomagnet, confirming that the magnetic layer was fixed in its upward magnetization direction in the region just before the -x side nanomagnet. Conversely, as shown in Figure 13B, when a current is supplied while a magnetic field is applied to a magnetic nanowire with a downward single-domain structure, upward magnetic domains are split in the magnetic layer of the magnetic nanowire near both sides of the nanomagnet on the -x side with downward polarity, and it is particularly effective to apply a magnetic field in the same direction as the current supply. Furthermore, in the sample of this example, the nanomagnet on the +x side with upward polarity has a stronger magnetic force, so it was easy to reverse the magnetization from upward to downward due to the downward leakage magnetic field from this nanomagnet, as shown in Figure 13A.

[0106] Furthermore, when a pulse current was supplied to the magnetic nanowire without applying an external magnetic field, as shown in Figure 14, no change in the magnetization state was observed at currents below 1.7 mA, but at 1.8 mA or above, a domain wall formed in the magnetic layer of the magnetic nanowire, splitting the upward magnetic domain near the nanomagnet on the -x side. At currents between 1.8 and 2.0 mA, the domain wall did not move, but at 2.1 mA, the magnetic domain formed near the -x side of the nanomagnet moved slightly (less than 1 μm) in the -x direction. At 2.1 mA, an upward magnetic domain also formed near the electrode on the -x side of the -x side of the nanomagnet. This is presumably because such a large current caused the temperature of the magnetic layer to rise, increasing the magnetization fluctuations, resulting in the magnetic domain split.

[0107] The above describes various embodiments for implementing the domain wall motion element initialization method and magnetic device according to the present invention, but the present invention is not limited to these embodiments and various modifications are possible within the scope of the claims. [Explanation of symbols]

[0108] 10, 10A, 10B, 10C Domain wall motion element 1 Magnetic thin wire 11 Magnetic layer 12 Channel Layer 3. Barrier layer (insulating film) 43 Magnetization fixed layer (reference layer) 51,52 Nanomagnets (magnetic field application components) 54, 54a, 54b Nano magnets (magnetic field application members) 61,62 electrode 63 Electrode 71 Transistor (switching element) 90 Spatial Light Modulator 90A magnetic memory 9 pixels 9A memory cell

Claims

1. A method for initializing a domain wall motion device comprising: a magnetic nanowire formed into a nanowire shape by laminating a magnetic layer made of a material with perpendicular magnetic anisotropy and a channel layer having a spin Hall effect; and a magnetic field application member made of a hard magnetic material with perpendicular magnetic anisotropy, which is arranged above or below the magnetic nanowire in a portion in the direction of the nanowire, the magnetic field application member being made of a hard magnetic material with perpendicular magnetic anisotropy, and wherein, when a current is supplied to the magnetic nanowire in the direction of the nanowire, a domain wall generated in the magnetic layer moves in the direction of the nanowire within a predetermined region not including the portion, the magnetic field application member being arranged on both sides of the predetermined region in the direction of the nanowire, one of the magnetic field application members having a larger coercive force than the other, a first magnetization step of applying a magnetic field equal to or greater than the coercive force of one of the magnetic field application members to the domain wall motion element in a direction perpendicular to the film surface of the magnetic nanowire; a second magnetization step of applying a magnetic field to the domain wall motion element, the magnetic field being less than the coercive force of one of the magnetic field application members and equal to or greater than the coercive force of the other of the magnetic field application members, in a direction opposite to that of the first magnetization step; an initial magnetic domain formation step of supplying a current to the magnetic nanowire in the direction of the nanowire while applying a magnetic field to the magnetic nanowire in one direction of the nanowire.

2. A method for initializing a domain wall motion device comprising: a magnetic nanowire formed into a nanowire shape by laminating a magnetic layer made of a material with perpendicular magnetic anisotropy and a channel layer having a spin Hall effect; and a magnetic field application member made of a hard magnetic material with in-plane magnetic anisotropy, which is arranged above or below the magnetic nanowire in a portion in the nanowire direction, the magnetic nanowire being such that when a current is supplied to the magnetic nanowire in the nanowire direction, a domain wall generated in the magnetic layer moves in the nanowire direction within a predetermined region not including the portion, the method comprising: a first magnetization step of applying a magnetic field equal to or greater than the coercive force of the magnetic field application member to the domain wall motion element in one direction along the fine wire direction of the magnetic fine wire; a second magnetization step of applying a magnetic field equal to or greater than the coercive force of the magnetic layer to the domain wall motion element in a direction perpendicular to the film surface of the magnetic nanowire; an initial magnetic domain formation process in which a magnetic field less than the coercive force of the magnetic field application member is applied to the magnetic domain wall motion element in one direction in the fine wire direction, while a current is supplied to the magnetic fine wire in the fine wire direction.

3. A method for initializing a domain wall motion device comprising: a magnetic nanowire formed into a nanowire shape by laminating a magnetic layer made of a material with perpendicular magnetic anisotropy and a channel layer having a spin Hall effect; and a magnetic field application member made of a hard magnetic material with in-plane magnetic anisotropy, which is arranged above or below the magnetic nanowire in a portion in the nanowire direction, the magnetic nanowire being such that when a current is supplied to the magnetic nanowire in the nanowire direction, a domain wall generated in the magnetic layer moves in the nanowire direction within a predetermined region not including the portion, the method comprising: a first magnetization step of applying a magnetic field equal to or greater than the coercive force of the magnetic field application member to the domain wall motion element in one direction along the fine wire direction of the magnetic fine wire; an initial magnetic domain forming step of supplying a current to the magnetic nanowire in the direction of the nanowire while applying a magnetic field less than the coercive force of the magnetic field application member to the domain wall motion element in the direction of the nanowire; The method for initializing a domain wall motion element, wherein the initial magnetic domain forming step is performed twice by reversing either the direction of the magnetic field application or the direction of the current supply.

4. A magnetic device comprising: a spatial light modulator having two-dimensionally arranged domain wall motion elements and a switching element for each of the domain wall motion elements; a current source that supplies current to the domain wall motion elements via the switching elements; and a magnetic field application means that applies a magnetic field to all of the domain wall motion elements of the spatial light modulator, The domain wall motion element comprises a magnetic nanowire formed into a nanowire shape by laminating a magnetic layer made of a magneto-optical material with perpendicular magnetic anisotropy and a channel layer having a spin Hall effect, and a magnetic field application member made of a hard magnetic material arranged above or below the magnetic nanowire in a part in the nanowire direction, wherein a magnetic field generated by the magnetic field application member is applied in a direction perpendicular to the film surface of the magnetic nanowire to at least one of the outer regions sandwiching a predetermined region of the magnetic layer in the nanowire direction, and a current is supplied to the magnetic nanowire in the nanowire direction, thereby causing a domain wall generated in the magnetic layer to move in the nanowire direction and reversing the magnetization direction in the predetermined region of the magnetic layer, the spatial light modulator two-dimensionally arranges the domain wall motion elements with the magnetic nanowires aligned in the same direction; The magnetic device is characterized in that the magnetic field applying means applies a magnetic field in the direction of the magnetic nanowire.

5. 5. The magnetic device according to claim 4, wherein the magnetic field applying means applies a magnetic field by switching the direction of the magnetic field in a direction perpendicular to the film surface of the magnetic nanowire, and the magnetic field in the direction perpendicular to the film surface is equal to or greater than the coercive force of the magnetic layer.

6. A magnetic device comprising: a magnetic memory including two-dimensionally arranged domain wall motion elements and a switching element for each of the domain wall motion elements; a current source that supplies current to the domain wall motion elements via the switching elements; and a magnetic field application means that applies a magnetic field to all of the domain wall motion elements of the magnetic memory, The domain wall motion element comprises a magnetic nanowire formed into a nanowire shape by laminating a magnetic layer made of a perpendicular magnetic anisotropy material and a channel layer having a spin Hall effect; one of a non-magnetic metal film or an insulating film and a reference layer made of a perpendicular magnetic anisotropy material having a coercivity equal to or greater than that of the magnetic layer, which are sequentially laminated on the magnetic layer side in a predetermined region of the magnetic nanowire; and a magnetic field application member made of a hard magnetic material, which is arranged on a part of the upper or lower side of the magnetic nanowire in the nanowire direction, wherein a magnetic field generated by the magnetic field application member is applied in a direction perpendicular to the film surface of the magnetic nanowire to at least one of the outer regions sandwiching the predetermined region of the magnetic layer in the nanowire direction, and a current is supplied to the magnetic nanowire in the nanowire direction, thereby causing a domain wall generated in the magnetic layer to move in the nanowire direction and reversing the magnetization direction in the predetermined region of the magnetic layer, The magnetic memory includes two-dimensionally arranging the domain wall motion elements with the magnetic nanowires aligned in the same direction; The magnetic device is characterized in that the magnetic field applying means applies a magnetic field in the direction of the magnetic nanowire.

7. 7. The magnetic device according to claim 6, wherein the magnetic field applying means applies a magnetic field by switching the direction of the magnetic field in a direction perpendicular to the film surface of the magnetic nanowire, and the magnetic field in the direction perpendicular to the film surface is equal to or greater than the coercive force of the reference layer.

8. The magnetic device according to any one of claims 4 to 7, characterized in that the domain wall motion element has the magnetic field application members on both outsides of the specified region, and an upward magnetic field is applied to the magnetic layer from one of the magnetic field application members on the outsides, and a downward magnetic field is applied to the magnetic layer from the other magnetic field application member.

9. The magnetic device according to any one of claims 4 to 8, characterized in that the magnetic field application means applies a magnetic field that is equal to or greater than the coercive force of the magnetic field application member and a magnetic field that is less than the coercive force of at least one of the magnetic field application members by switching between these magnetic fields.

10. A magnetic device as described in any one of claims 4 to 9, characterized in that the current source supplies current to the magnetic nanowire of the selected domain wall motion element, and the magnetic field application means applies a magnetic field in the nanowire direction to reverse the magnetization direction of the magnetic layer in the specified region.

11. The magnetic device according to claim 10, characterized in that the current source supplies current to the magnetic nanowire of the selected domain wall motion element in only one predetermined direction, and the magnetic field application means applies a magnetic field by switching its direction to either of the two directions in the nanowire direction of the magnetic nanowire, thereby reversing the magnetization direction of the magnetic layer in the specified region.

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