Reconfigurable nanoscale spin wave directional coupler

Abstract

The invention discloses a reconfigurable nanoscale spin wave directional coupler, and relates to the technical field of magnetic oscillator devices, the reconfigurable nanoscale spin wave directional coupler comprises a magnetic material formed by a magnetic film, and the magnetic material is divided into three parallel and adjacent areas according to a surface area, a first magnetic field perpendicular to the surface of the thin film is applied to the areas on the two sides, a second magnetic field perpendicular to the surface of the thin film and opposite to the first magnetic field in direction is applied to the middle area, and when the gap width between the upper area and the lower area is smaller than or equal to 50 nm, the spin wave directional coupler in the parallel magnetization state is formed; and when the width of the gap between the upper region and the lower region is greater than 50nm, the spin wave directional coupler in an anti-parallel magnetization state is formed. The reconfigurability of magnetization state conversion of the spin wave directional coupler is realized under the condition that an external magnetic field is not needed, and the overall stability of an integrated magnetic oscillator circuit is improved.

Description

Technical Field

[0001] This invention relates to the field of magnetic resonator technology, and more particularly to a reconfigurable nanoscale spin wave directional coupler. Background Technology

[0002] Currently, spin waves, as information carriers, have attracted widespread attention in recent years due to their potential applications in charge-free, micro / nanoscale logic devices and Joule-free heating. Past research has typically required patterned ferromagnetic materials as magnon waveguides, making it impossible to dynamically control the propagation path of the spin waves. Dynamic control of magnon waveguides is essential for complex, reconfigurable magnon devices in information processing. In integrated magnon circuits, coupled spin wave functional devices, with their compactness, scalability, and reconfigurability, are necessary for their application in information processing.

[0003] In the field of magnons, achieving nanoscale, low-power, high-efficiency, and controllable integrated magnon circuit connections remains a significant challenge. For magnon-based data processing, the most interesting and challenging task is creating integrated magnon circuits where complex computational functions are implemented solely within the magnon's magnetic domains. The output of one magnon circuit drives the input of the next magnon device without intermediate electrical signal conversions. This approach naturally avoids the efficiency problems associated with inter-conversion, meaning that developing fully coherent magnon circuits is a crucial area of ​​future research.

[0004] The most direct planar X-shaped cross structure generates a secondary source of spin waves during operation, which enters the spin wave channel and causes unavoidable interference. Due to the strong dipole effect, spin waves in adjacent layers interfere with each other, so the three-dimensional bridge, which is the most widely used in electronic integrated circuits, is no longer suitable for magnon circuits.

[0005] In 1981, Sasaki and Mikoshiba theoretically predicted the directional coupling phenomenon of magnetostatic surface waves in a "sandwich" structure, laying a solid theoretical foundation for spin wave directional coupling devices. Inspired by connectors in integrated optics, many studies have utilized the dipole coupling between side-parallel adjacent waveguides to achieve controllable connections of magnon circuits.

[0006] In magnon crystal materials, spin waves propagating within periodic material structures exhibit nonlinear coupling behavior. Experiments have demonstrated a nonlinear phase shift related to the spin wave intensity in coupled magnon crystals. Research by Piotr Graczyk et al. revealed directional coupling phenomena in both the same and opposite directions in ferromagnetic material systems containing periodic structures. Using in-plane magnetized domain walls as directional couplers for spin wave waveguides can achieve spin wave energy splitting.

[0007] Sadovnikov et al. experimentally demonstrated that dipole coupling of multimode spin waves between magnetic waveguides at the millimeter scale can be achieved under the influence of an external magnetic field. Another research team designed a nanoscale spin wave directional coupler and achieved dynamic control of the coupler by changing the magnitude of the external magnetic field. In subsequent research, their team achieved spin wave reconfigurability using an external pulsed magnetic field method.

[0008] Although the reconfigurability of spin-wave directional couplers can be achieved by using an external pulsed magnetic field, the introduction of the pulsed magnetic field will inevitably affect the operation of other devices in the integrated magnon circuit, reducing the operational stability of other devices. Summary of the Invention

[0009] Therefore, it is necessary to provide a reconfigurable nanoscale spin wave directional coupler to address the aforementioned technical problems.

[0010] The present invention adopts the following technical solution: This invention provides a reconfigurable nanoscale spin-wave directional coupler, comprising: a magnetic material formed by stacking magnetic thin films and three microwave antennas; The magnetic material is divided into three parallel adjacent regions according to its surface area. A first magnetic field perpendicular to the surface of the magnetic film is applied to the two outer regions, and a second magnetic field perpendicular to the surface of the magnetic film and opposite to the direction of the first magnetic field is applied to the middle region. When the magnetic material reaches a fully relaxed state, three magnetic domains corresponding to the three regions and two Bloch-type domain wall waveguides between adjacent magnetic domains are formed. One end of the first Bloch-type magnetic domain wall waveguide is equipped with a microwave antenna for spin wave injection as the input end, and the other end, together with the second Bloch-type magnetic domain wall waveguide, is equipped with a microwave antenna as the two output ends; the magnetic material has a partial gap in the region corresponding to the input end of the second Bloch-type magnetic domain wall waveguide. When the gap width between the upper and lower regions is less than or equal to 50nm, the magnetic moment directions in the two Bloch-type magnetic domain wall waveguides are parallel to each other along the Bloch-type magnetic domain wall waveguide direction, forming a spin wave directional coupler in a parallel magnetization state. When the gap width between the upper and lower regions is greater than 50nm, the magnetic moment directions in the two Bloch-type domain wall waveguides are parallel to each other in the opposite direction along the Bloch-type domain wall waveguide direction, forming a spin wave directional coupler in an antiparallel magnetization state.

[0011] Optionally, the initial magnitudes of the first and second magnetic fields are 1T, and they decay exponentially over time. ; in, for Magnetic field size at any given time This represents the initial magnetic field size.

[0012] Optionally, when the coupling waveguide length of the spin-wave directional coupler in the parallel / antiparallel magnetization state is its coupling length... When the magnetization is doubled, the spin wave directional coupler in the parallel / antiparallel magnetization state functions as a transmission waveguide; The coupling waveguide length of a spin-wave directional coupler in parallel / antiparallel magnetization states is its coupling length. When the magnetization is doubled, the spin wave directional coupler in the parallel / antiparallel magnetization state functions as a connector in the magnon circuit. The coupling waveguide length of a spin-wave directional coupler in parallel / antiparallel magnetization states is its coupling length. When the magnetization is doubled, the spin-wave directional coupler in the parallel / antiparallel magnetization state functions as a spin-wave power divider; wherein, It is a positive integer.

[0013] Optionally, the magnetic material comprises two stacked magnetic thin films, with the upper layer being Co. 20 Fe 60 B 20 The thin film has a [Co / Pd] thin film underneath.

[0014] Optionally, the coupling length of the spin wave directional coupler in the parallel magnetization state decreases as the gap width between the upper and lower regions increases.

[0015] Optionally, the coupling length of the spin wave directional coupler in the antiparallel magnetization state increases with the increase of the gap width between the upper and lower regions.

[0016] Optionally, the coupling lengths of both the spin wave directional coupler in the parallel magnetization state and the spin wave directional coupler in the antiparallel magnetization state decrease as the thickness of the magnetic material increases.

[0017] The above-mentioned at least one technical solution adopted in this invention can achieve the following beneficial effects: The reconfigurable nanoscale spin-wave directional coupler proposed in this invention comprises a magnetic material formed from a magnetic thin film, which is divided into three parallel adjacent regions according to its surface area. A first magnetic field perpendicular to the surface of the thin film is applied to the two outer regions, and a second magnetic field perpendicular to the surface of the thin film and opposite to the direction of the first magnetic field is applied to the middle region. When the magnetic material reaches a fully relaxed state, three magnetic domains corresponding to the three regions and two Bloch-type domain wall waveguides between adjacent magnetic domains are formed. When the first Bloch-type domain wall waveguide is set as the input end, the magnetic material has a partial gap in the region corresponding to the input end of the second Bloch-type domain wall waveguide to prevent the microwave antenna at the input end from generating spin waves in the second Bloch-type domain wall waveguide. When the gap width between the upper and lower regions is less than or equal to 50 nm, a spin-wave directional coupler in a parallel magnetization state is formed; when the gap width between the upper and lower regions is greater than 50 nm, a spin-wave directional coupler in an antiparallel magnetization state is formed.

[0018] This invention reverses the magnetization state of a spin-wave directional coupler by changing the gap width of the coupling waveguide. This achieves reconfigurability of the magnetization state transition of the spin-wave directional coupler without the need for an external magnetic field, which is beneficial for improving the overall stability of the integrated magnon circuit. Attached Figure Description

[0019] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0020] Figure 1 A schematic diagram of a reconfigurable nanoscale spin wave directional coupler structure based on Bloch-type magnetic domain walls provided by the present invention. Figure 2 A schematic diagram of applying a magnetic field is provided for this invention; Figure 3 A top view schematic diagram of the magnetization intensity distribution of a directional coupler provided by the present invention; Figure 4 A schematic diagram of the static internal magnetic field of a coupler at x=1μm provided for this invention; Figure 5 This invention provides a schematic diagram of spin wave dispersion in different waveguides. Figure 6 A coupling schematic diagram of a parallel magnetization state directional coupler provided by the present invention; Figure 7 A schematic diagram of the normalized output power of a spin wave related to the coupling length of a directional coupler is provided for this invention. Figure 8 A schematic diagram of the static internal magnetic field distribution of a directional coupler with different gap widths is provided for this invention; Figure 9 The diagrams provided by the present invention illustrate the static magnetic state of a directional coupler from the left and top views. Figure 10 A schematic diagram of the internal effective energy distribution of a directional coupler with different gap widths is provided for this invention. Figure 11 A top view schematic diagram of the magnetization intensity distribution of an antiparallel magnetization state directional coupler provided by the present invention; Figure 12 A schematic diagram of the static internal magnetic field of an antiparallel magnetization coupler provided by the present invention; Figure 13 A schematic diagram of the dispersion relation of an antiparallel magnetized coupled waveguide provided by the present invention; Figure 14 A coupling schematic diagram of an antiparallel magnetization state directional coupler provided by the present invention; Figure 15 A schematic diagram of coupling lengths related to different gaps is provided for this invention; Figure 16 A schematic diagram of the internal dipole energy distribution of a directional coupler with different gap values ​​is provided for this invention. Figure 17 A schematic diagram of the coupling length L related to waveguide thickness t provided by the present invention; Figure 18 A schematic diagram of the intensity distribution of a frequency-dependent spin wave Fourier transform is provided for this invention. Figure 19 This invention provides a schematic diagram of the coupling length of a spin wave directional coupler at different excitation frequencies. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0022] This invention first proposes a reconfigurable nanoscale spin-wave directional coupler based on a Bloch-type magnetic domain wall waveguide. Combining micromagnetic simulation results and theoretical analysis, the basic working principle of the spin-wave directional coupler is explored. By changing the gap width of the coupling waveguide in the spin-wave directional coupler, the magnetization state of the waveguide is reversed, achieving reconfigurability of the magnetization state transition without the need for an external bias field. Finally, the effects of different spin-wave excitation frequencies, waveguide thicknesses, and waveguide gap widths on the coupling length are investigated.

[0023] The technical solutions provided by the various embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0024] Figure 1 This is a schematic diagram of a reconfigurable nanoscale spin-wave directional coupler structure based on Bloch-type magnetic domain walls, as described in this invention. The reconfigurable nanoscale spin-wave directional coupler includes a magnetic material formed by stacking magnetic thin films and three microwave antennas.

[0025] For magnetic materials, it can typically include two stacked magnetic thin films, with the upper layer being a soft magnetic layer and the lower layer being a hard magnetic layer. The soft magnetic layer and the hard magnetic layer are coupled through exchange interaction. This double-layer magnetic structure can effectively maintain the magnetization state of the waveguide consistent with that of the hard magnetic layer without the need to continuously apply a bias magnetic field, thereby ensuring the stability of the Bloch-type magnetic domain wall waveguide.

[0026] In one or more embodiments of the present invention, two magnetic thin films may be stacked, with the upper layer being Co. 20 Fe 60 B 20 The thin film has a lower layer of [Co / Pd] film. Co... 20 Fe 60 B 20 The thin film exhibits a large saturation magnetization and a low damping coefficient, and Co... 20 Fe 60 B 20 Ferromagnetic materials are easier to prepare.

[0027] The magnetic material is divided into three parallel adjacent regions according to its surface area. A first magnetic field perpendicular to the surface of the magnetic thin film is applied to the two outer regions, and a second magnetic field perpendicular to the surface of the magnetic thin film and opposite to the direction of the first magnetic field is applied to the middle region. When the magnetic material reaches a fully relaxed state, three magnetic domains corresponding to the three regions and two Bloch-type domain wall waveguides between adjacent magnetic domains are formed.

[0028] One end of the first Bloch-type domain wall waveguide houses a microwave antenna for spin wave injection as its input. The other end, along with the second Bloch-type domain wall waveguide, has two microwave antennas positioned opposite each other as outputs. A partial gap exists in the magnetic material at the corresponding input region of the second Bloch-type domain wall waveguide to prevent the microwave antenna from generating spin waves within the second Bloch-type domain wall waveguide, thus making it difficult to distinguish whether the spin waves within the second Bloch-type domain wall waveguide are coupled or generated by the microwave antenna. The gap length can be set as needed, as long as it is sufficient to position the microwave antenna at the input end of the first Bloch-type domain wall waveguide below the gap region.

[0029] When the gap width between the upper and lower regions is less than or equal to 50 nm, the magnetic moment directions in the two Bloch-type domain wall waveguides are parallel to each other along the direction of the Bloch-type domain wall waveguides, forming a spin wave directional coupler in a parallel magnetization state.

[0030] When the gap width between the upper and lower regions is greater than 50nm, the magnetic moment directions in the two Bloch-type domain wall waveguides are parallel to each other in the opposite direction along the Bloch-type domain wall waveguide direction, forming a spin wave directional coupler in an antiparallel magnetization state.

[0031] by Figure 1 For example, the functional part of the spin wave directional coupler consists of channel I (C-I) and channel II (C-II) in the middle region of each magnetic domain wall, that is... Figure 1 The white, blue, and orange areas in the diagram represent magnetic domains with opposite magnetization directions. The blue area represents the gap between coupled waveguides. d Co 20 Fe 60 B 20 film width w =240nm (three regions: 100nm-40nm-100nm), length l =2μm, thickness T =2nm. The width, length, and thickness of the [Co / Pd] film are related to Co. 20 Fe 60 B 20 The thin films are identical. In this structure, the lower magnetic domain wall waveguide is slightly longer than the upper waveguide, and the microwave antenna is placed at the far left end of the lower waveguide to achieve spin wave injection.

[0032] Initial magnetization configuration: Figure 2 This is a schematic diagram illustrating the application of a magnetic field in this invention. By applying external magnetic fields in opposite directions to three adjacent regions of a double-layer thin-film structure, Bloch-type magnetic domain walls are obtained as spin waveguides. The initial magnetization in the magnetic material is randomly distributed, and a stable spin wave directional coupler structure is obtained through three stages. First, the magnetic material waveguide is divided into three regions, with the middle region being the gap width, as shown... Figure 2 As shown. Next, two external magnetic fields perpendicular to the thin film surface and in opposite directions are applied. and The magnetic field is applied to adjacent regions. The applied magnetic field is 1T in magnitude and decays exponentially over time. Gilbert damping coefficient α The value can be set to 0.9, which allows the system to reach a fully relaxed state as quickly as possible within a given time, and finally obtain a stable double magnetic domain wall structure without an external magnetic field for studying spin wave directional couplers based on domain wall waveguides.

[0033] For a parallel magnetized coupler, internal field analysis: A spin-wave coupler was designed using a micromagnetic simulation tool and a magnetic field was applied. The magnetization distribution of the spin-wave coupler was obtained in this invention, as shown below. Figure 3 As shown, Figure 3 This is a top-view schematic diagram of the magnetization distribution of a directional coupler according to the present invention. The orange and green areas represent the magnetization along the magnetic domains, respectively. z The positive and negative directions of the axis. In a spin-wave directional coupler, the magnetic moment within the domain walls is along the positive x-axis, forming a parallel magnetized state spin-wave directional coupler. The in-plane magnetization components are indicated by arrows. The parallel magnetized coupler... y Static internal magnetic field of the shaft H int ( x )like Figure 4 As shown, Figure 4 One of the inventions x A schematic diagram of the static internal magnetic field of the coupler at a depth of 1 μm, where the blue area represents the gap width between magnetic domain walls. d =40nm, Figure 4 The horizontal axis represents the parallel magnetized coupler. y The vertical axis represents the static internal magnetic field. H int ( x ).

[0034] By applying a sinc field to a microwave antenna, this invention obtains the dispersion curve of a spin-wave directional coupler, which can be used to explore the basic working principle of the directional coupler. Figure 5 This is a schematic diagram of spin wave dispersion in different waveguides according to the present invention. Figure 5 The horizontal axis represents the wave vector, and the vertical axis represents the frequency. Figure 5 Part (a) shows the dispersion curve of the lowest width mode of a spin wave in a single isolated waveguide. Figure 5Part (b) shows the spin wave dispersion curve in a parallel magnetized coupled waveguide. The variation of magnetization components within the domain walls was obtained through micromagnetic simulation, and then a two-dimensional Fourier transform was performed to obtain a color image of the dispersion curve. The black dashed line represents the dispersion curve of the lowest width spin wave mode obtained through analytical equations (5) and (6), which were applied to coupled domain wall waveguides in a single waveguide and a spin wave coupler, respectively. It can be observed that the lowest width spin wave mode in a single isolated waveguide splits into two collective modes—a symmetric mode and an antisymmetric mode. In a spin wave directional coupler, the two collective modes with different wavenumbers are simultaneously excited. The study found that the calculated results agree well with the simulation results.

[0035] Coupling length: The dipole interaction in a coupled waveguide causes the lowest width mode of a spin wave within a single waveguide to split into symmetric modes of different wavenumbers. and antisymmetric mode , wave number difference ,like Figure 5 As shown. When two spin wave modes coexist in a single waveguide, they have different wave numbers under the same frequency of excitation, thus causing a periodic transfer of spin wave energy between the two waveguides. The distance required to completely transfer the spin wave energy from one waveguide to another is defined as the coupling length. Coupling length It relates to the wavenumber difference between the two spin wave modes, and its expression is:

[0036] (7) When a spin wave is excited in the lower waveguide, the output energy of the spin wave in each waveguide can be expressed as: (8) in, It is the length of the coupled waveguide. This is the spin wave input power in the waveguide. At an excitation frequency of 1.636 GHz, Figure 6 This is a schematic diagram of the coupling of a parallel magnetization state directional coupler according to the present invention. Figure 6 The coupling length L of the spin wave coupler in the parallel magnetization state, calculated from simulation results, is given. Figure 6 In (a), It is the output power of the C-I waveguide in the spin-wave directional coupler. This refers to the output power of the C-II waveguide in the spin-wave directional coupler. The distance required for complete transfer of spin wave energy in the coupled waveguide in the parallel magnetization state is approximately 469 nm, which is the coupling length L of the parallel magnetization state coupler. p =469nm. Figure 6Part (a) represents the normalized output power of the parallel magnetized directional coupler. Functions about the x-axis Figure 6 In section (a), the horizontal axis represents the coupler. x The vertical axis represents the output frequency. , Figure 6 Part (b) shows the spin wave propagation diagram in the parallel magnetization state directional coupler (d=40nm) in the micromagnetic simulation.

[0037] When the length of the coupled waveguide When the value is constant, the output power is equal to the coupling length. This is a function of the same principle for spin-wave directional couplers with parallel / antiparallel magnetization states. For example... Figure 7 As shown, Figure 7 This is a schematic diagram of the normalized output power of a spin wave related to the coupling length of a directional coupler in this invention. Figure 7 The horizontal axis represents the coupling length L, and the vertical axis represents the normalized output power of the spin wave. When a spin wave propagates in a spin wave directional coupler with parallel / antiparallel magnetization, if the coupling length satisfies... ( (It is a positive integer), the energy of the spin wave will return to the C-I waveguide, and the spin wave directional coupler in the parallel / antiparallel magnetization state functions as a regular transmission waveguide; when At this time, energy is ultimately transferred to the C-II waveguide, and the spin-wave directional coupler in the parallel / antiparallel magnetization state functions as a connector in the magnon circuit; when When the energy is divided into two parts, it will be output from the two output terminals of the spin wave directional coupler in parallel / antiparallel magnetization state. The spin wave directional coupler in parallel / antiparallel magnetization state acts as a spin wave power divider.

[0038] For antiparallel magnetization couplers, the internal field and energy analysis of couplers with different gaps are as follows: Width of spin wave directional coupler w The range is 230 nm to 280 nm (100 nm-d-100 nm three regions, interspersed intervals). d (Values ​​range from 30 nm to 80 nm, taken in 10 nm intervals). By applying a bias magnetic field, this invention obtained the static internal magnetic field distribution of the two domain walls with different gap widths, such as... Figure 8 As shown, Figure 8 This is a schematic diagram of the static internal magnetic field distribution of a directional coupler with different gap widths according to the present invention. Figure 8 The horizontal axis represents the coupler. y The vertical axis represents the static internal magnetic field distribution. H int . Figure 8 The black curves in (a)-(c) indicate that the magnetization components in the coupled domain wall waveguide are all distributed along the positive x-axis, and the spin wave coupler is in a parallel magnetization state. Figure 8 The red curves in (d)-(f) represent the magnetization intensity distributed along the positive and negative x-axis directions within the waveguide, indicating that the spin-wave coupler is antiparallel magnetized. The results show that as the gap width within the spin-wave coupler increases, the relative magnetization direction within the domain wall waveguide changes. This invention found that when the gap width is greater than 50 nm, the relative magnetization state within the domain wall changes from parallel to antiparallel. Without external field modulation, this invention achieves the reversal of the magnetization state by changing the gap width of the coupled waveguides. Furthermore, when the gap width is less than 50 nm, the internal magnetic field magnitudes at the center of the two coupled waveguides in the parallel magnetization state are essentially equal. However, in the antiparallel magnetization state of the spin-wave coupler, when the gap width is larger, the internal magnetic fields of the coupled waveguides become unequal.

[0039] Figure 9 This is a schematic diagram of the static magnetic state of a directional coupler according to the present invention, viewed from the left and from the top. The magnetization directions within adjacent magnetic domains are respectively along... z The magnetic moments within the domain walls are distributed in both positive and negative directions along the axis. x The axial distribution forms Bloch-type domain walls. Within the domain walls, which act as spin waveguides, the magnetization directions of the two waveguides in parallel magnetization states are along... x The two waveguides, with their positively oriented magnetization and antiparallel magnetization states, have magnetization directions along the axis of positive orientation, respectively. x The positive and negative distribution of the axis. Figure 9 (a) is a directional coupler in the parallel magnetization state. d =30 nm, 40 nm, 50 nm), Figure 9 (b) is a spin-wave directional coupler in an antiparallel state. d =60nm, 70nm, 80nm), with red arrows indicating the direction of magnetization.

[0040] Without considering the effects of other contributing energies, the energy of the entire system can be divided into dipole interaction energy and exchange interaction energy. Figure 10 This is a schematic diagram of the internal effective energy distribution of a directional coupler with different gap widths according to the present invention. Figure 10The horizontal axis represents the gap width of the directional coupler, and the vertical axis represents the internal effective energy. The black broken line represents the total energy, and the gray and green bars represent the exchange interaction energy and dipole interaction energy, respectively. The results show that the exchange energy within the system is relatively small and does not change significantly with increasing gap width. The dipole energy initially increases and then decreases with increasing gap width. The total system energy exhibits the same trend as the dipole energy, with an inflection point between 50 nm and 60 nm. The inflection point of the two domain wall waveguides switching from parallel magnetization to antiparallel magnetization coincides with the inflection point of the energy change. In the coupled waveguide system, the system free energy is minimized when the coupled waveguide is configured in an antiparallel magnetization state. When the spin-wave directional coupler is in an antiparallel magnetization state, the energy of the spin-wave coupler system gradually decreases with increasing coupled waveguide gap width, making the system more stable.

[0041] Internal field analysis: The aforementioned invention, through analysis of the internal field and energy distribution of spin-wave directional couplers with different gap widths, found that when the gap width is greater than 50 nm, the spin-wave coupler is in an antiparallel magnetization state. Therefore, this invention designs an antiparallel magnetization state directional coupler using micromagnetic simulation tools. d =60 nm), and the transmission characteristics of spin waves within this coupler were investigated. By applying bias magnetic fields with opposite directions in adjacent regions, this invention obtained the magnetization distribution within the antiparallel coupler, such as Figure 11 As shown, Figure 11 This is a top-view schematic diagram of the magnetization intensity distribution of an antiparallel magnetization state directional coupler according to the present invention. The orange and green areas represent the magnetization intensity along the magnetic domains, respectively. z The two directions of the axis. It can be seen that the magnetic moment directions in the coupled waveguide of the coupler are respectively along the positive and negative directions. x The two directions of the axis, positive and negative, form a spin-wave directional coupler with an antiparallel magnetization state. The antiparallel magnetization coupler along... y Static internal magnetic field of the shaft H int ( x )like Figure 12 As shown, Figure 12 One of the inventions x Schematic diagram of the static internal magnetic field of the coupler in antiparallel magnetization state at 1μm. Figure 12 The horizontal axis represents the y-axis of the directional coupler, and the vertical axis represents the static internal magnetic field.

[0042] Based on the same method, this invention studies antiparallel magnetized spin wave couplers. d The propagation characteristics of spin waves in a coupled waveguide (e.g., =60 nm) are as follows: Figure 13 As shown, Figure 13 This is a schematic diagram of the dispersion relation of an antiparallel magnetized coupled waveguide in this invention. Figure 13The horizontal axis represents the wave vector, and the vertical axis represents the frequency. A color diagram of the dispersion curve was obtained through simulation results. The black dashed line represents the dispersion curve of the antiparallel magnetized coupled waveguide obtained through analytical equation (6). The calculation results are in good agreement with the simulation results. It can be found that compared to the coupled waveguide in the parallel magnetized state (… d =40 nm), under antiparallel magnetization ( d =60nm), although the gap width between the coupled waveguides increases, the energy level splitting degree of the spin wave dispersion curve is still slightly greater than that of the energy level splitting in the parallel magnetization state.

[0043] Coupling length: By using micromagnetic simulation, this invention obtains a spin-wave directional coupler in antiparallel magnetization state. d The coupling length L (e.g., =60 nm) is such that... Figure 14 As shown, Figure 14 This is a schematic diagram of the coupling of an antiparallel magnetized directional coupler according to the present invention. P1 is the output power of the C-I waveguide in the spin wave directional coupler. The distance required for complete transfer of spin wave energy in the antiparallel magnetized coupled waveguide is approximately 369 nm, therefore the coupling length of the antiparallel magnetized coupled waveguide is... L ap =369nm, such as Figure 14 As shown in (a), Figure 14 In (a), the horizontal axis represents the directional coupler. x The vertical axis represents the output power of the C-I waveguide in the directional coupler. Figure 14 Figure (b) presents the antiparallel magnetization state directional coupler in micromagnetic simulation. d Spin wave propagation diagram in (60nm).

[0044] For spin-wave directional couplers with different magnetization states, the coupling length varies. According to equation (7), it can be found that the coupling length L of the spin-wave directional coupler is related to the degree of energy level splitting in the spin-wave dispersion curve. The coupling length of the antiparallel magnetized directional coupler is inversely proportional to the magnetization state, but the splitting degree is slightly greater than that of the parallel magnetized coupler. Therefore, for spin waves at the same excitation frequency, the coupling length of the antiparallel magnetized coupler is less than that of the parallel magnetized coupler. This indicates that although the gap of the directional coupler increases, the coupling strength between the waveguides changes due to the different magnetization states. The coupling strength is stronger in the antiparallel magnetization state, thus reducing the coupling length L. Therefore, this invention can achieve its functionality by selecting the appropriate directional coupler size according to the operational requirements.

[0045] For adjusting the coupling length, different gap widths are used: Regarding the influence of device parameters, this invention first considers the impact of geometric parameters on spin-wave directional couplers. For spin-wave directional couplers with a given magnetic material, the domain wall width is a fixed value under the condition of no external interference. Therefore, this invention does not consider the influence of the domain wall width on the coupling length of the spin-wave directional coupler, but only analyzes the influence of the gap width between the coupled waveguides in the directional coupler on the coupling length of the directional coupler.

[0046] like Figure 15 As shown, Figure 15 This is a schematic diagram of coupling lengths related to different gaps in this invention. Figure 15 The horizontal axis represents the gap width, and the vertical axis represents the coupling length. The blue line represents the change in coupling length in the parallel magnetization state of the coupler, while the orange line represents the change in coupling length when the coupler's magnetization state is antiparallel. It can be observed that the coupling length exhibits different trends with the gap width for spin-wave directional couplers with different magnetization states. In the parallel magnetization state, the coupling length L of the coupler decreases as the gap width increases; while in the antiparallel magnetization state, the coupling length L increases as the size increases, and the rate of increase for the antiparallel coupler is significantly greater than the rate of decrease for the parallel magnetization coupler. This indicates that when the size is large, the performance of the spin-wave directional coupler in the antiparallel magnetization state is more sensitive to changes in the gap width.

[0047] Based on micromagnetic simulation results, this invention further analyzes the internal polarization energy of a single isolated waveguide and the dipole interaction energy (DW-W energy) between domain walls and domains. Furthermore, based on the total dipole energy within the coupled waveguide, this invention obtains the dipole interaction energy (DW-DW energy) between the two domain walls, as shown below. Figure 16 As shown, Figure 16 This is a schematic diagram of the internal dipole energy distribution of a directional coupler with different gap values ​​according to the present invention. Figure 16 The horizontal axis represents the gap width, and the vertical axis represents the dipole energy inside the directional coupler. The black broken line represents the total dipole energy in the coupler, the red broken line represents the dipole energy between coupled waveguides, and the blue broken line represents the coupling energy between magnetic domains and domain walls in the coupler. The DW-DW energy decreases as the gap increases, and the decrease in DW-DW energy in the antiparallel magnetization state is greater than that in the parallel magnetization state. When the gap is small, the DW-W energy increases with the gap, and when the distance is greater than 50 nm, the DW-W energy value tends to be constant. Therefore, the rate of increase of the coupling length in the antiparallel state is greater than the rate of decrease in the parallel state. The total dipole energy shows a trend of first increasing and then decreasing with the increase of the gap width. Therefore, the coupling strength in the directional coupler first increases and then decreases, corresponding to the trend of the coupling length first decreasing and then increasing, as shown in the figure. Figure 15 As shown.

[0048] Different waveguide thicknesses: Next, this invention investigated the effect of thin film thickness on coupling length, and the relevant changes in coupling length of the spin wave directional coupler are as follows: Figure 17 As shown, Figure 17 A waveguide thickness in this invention T A schematic diagram of the relevant coupling length L. The blue broken line represents the gap width. d Parallel magnetization coupler with a diameter of 40 nm; the orange broken line represents the gap width. d A 60 nm antiparallel magnetization coupler was observed. It was found that the coupling length of both magnetization states decreased with increasing waveguide thickness, indicating that increasing the film thickness could enhance the coupling strength between domain wall waveguides within the directional coupler. Furthermore, compared to the parallel magnetization state spin wave coupler, the 60 nm antiparallel magnetization state directional coupler showed a more pronounced change in film thickness, suggesting that the antiparallel magnetization state of the directional coupler is more sensitive to changes in material thickness.

[0049] Different excitation frequencies: Based on simulation results, this invention obtained the magnetic moment at the same location within the domain wall at different times. M magnetization component Mz By measuring the change in magnetization within the grid ∆Mz Performing a one-dimensional Fourier transform yielded the frequency-dependent Fourier transform intensity distribution of the spin wave, such as... Figure 18 As shown, Figure 18 This is a schematic diagram of the frequency-dependent spin wave Fourier transform intensity distribution according to the present invention. Figure 18 The horizontal axis represents frequency, and the vertical axis represents the Fourier transform intensity of the spin wave. The black and red curves represent the one-dimensional Fourier transform intensity distribution of the spin wave in channel one (C-Ⅰ) and channel two (C-Ⅱ) of the spin wave directional coupler, respectively. Within the excitation frequency range of 1.1 GHz to 2.2 GHz, the Fourier transform amplitude of the spin wave is relatively large. Therefore, within this frequency range, this invention selected several different excitation frequencies to investigate the frequency-dependent coupling length of the spin wave directional coupler.

[0050] The coupling lengths of spin wave directional couplers at different excitation frequencies are as follows: Figure 19 As shown, Figure 19 This is a schematic diagram of the coupling length of a spin-wave directional coupler at different excitation frequencies in this invention. The blue and orange broken lines represent the magnetization states as parallel magnetization, respectively. d =40 nm) and antiparallel magnetization ( dThe coupling length variation of a spin-wave directional coupler (60 nm) was studied. The results showed that the coupling length of the spin-wave directional coupler under both magnetization states increased with increasing spin-wave excitation frequency. At the same excitation frequency, the coupling length of the coupler in the parallel magnetization state was always greater than that of the antiparallel magnetization coupler, and the growth trend of the coupling length of the parallel magnetization coupler was slightly greater than that of the antiparallel magnetization coupler. This indicates that the coupler in the parallel magnetization state is more sensitive to frequency changes. For some magnetic materials, only those with higher saturation magnetization can ensure that spin waves excited at higher frequencies do not interfere with the operating characteristics of the directional coupler. Therefore, if a shorter coupling length is required, this invention preferentially selects a lower frequency as the excitation frequency of the spin wave.

[0051] This invention first proposes a novel spin-wave directional coupler, which uses Bloch-type magnetic domain walls formed in a double-layer magnetic thin-film structure as the spin-wave waveguide. The basic working principle of the spin-wave directional coupler is studied by combining micromagnetic simulation and theoretical analysis. When the gap width of the coupling waveguide... d At a wavelength of 40 nm, the spin-wave coupler is in a parallel magnetization state. The lowest width mode of the spin wave in a single isolated waveguide splits into two collective modes—a symmetric mode and an antisymmetric mode. The distance required for complete spin wave energy transfer in a coupled waveguide in a parallel magnetization state is approximately 469 nm, i.e., the coupling length. L p =469nm. Next, by changing the gap width in the directional coupler, it was found that when... d At wavelengths >50 nm, the magnetization state within the coupled domain walls changes from parallel magnetization to antiparallel magnetization, achieving the magnetization state transition of the spin-wave directional coupler without the need for external field manipulation. Then, this invention investigates... d The propagation characteristics of spin waves in an antiparallel magnetized spin-wave coupler with a wavelength of 60 nm were studied. The results showed that, compared to a parallel magnetized coupler (…),… d =40nm), despite the increased gap width, the magnetization state of the directional coupler is antiparallel magnetization ( d The spin-wave dispersion curve (with wavelengths of 60 nm) exhibits a slightly greater degree of energy level splitting than that of the parallel magnetized coupler. d The coupling efficiency of the coupler in the antiparallel magnetization state (60 nm) is slightly higher. When the magnetization state is antiparallel, the coupling length of the coupler is... L ap =369nm. Finally, the factors affecting the coupling length were analyzed in detail, including the gap width of the spin wave directional coupler, the film thickness, and different spin wave excitation frequencies.

[0052] Studies have shown that the coupling length of spin-wave directional couplers with different magnetization states exhibits different trends in change with the gap width. In the parallel magnetization state, the coupling length decreases as the gap width increases. However, in the antiparallel magnetization state, the coupling length increases with the gap size, and the rate of increase is significantly greater than the rate of decrease. This indicates that antiparallel magnetized spin-wave couplers are more sensitive to changes in the gap width.

[0053] For different material thicknesses, the coupling lengths of both magnetization states of the coupler decrease with increasing waveguide thickness, indicating that increasing the film thickness can enhance the coupling strength between waveguides. Therefore, the coupling efficiency of the spin-wave directional coupler can be improved by increasing the film thickness. For different excitation frequencies, the coupling lengths of the coupler in both magnetization states increase with increasing excitation frequency. For the same excitation frequency, the coupling length of parallel magnetization is always greater than that of antiparallel magnetization, and the coupler is more sensitive to frequency changes when it is in the parallel magnetization state.

[0054] It should also be noted that the terms "comprising," "including," or any other variations thereof in this invention are intended to cover non-exclusive inclusion, that is, in addition to the elements listed in this invention, other elements not expressly listed may also be included.

[0055] The various embodiments in this invention are described in a progressive manner. For the same or similar parts between the various embodiments, please refer to each other. Each embodiment focuses on describing the differences from other embodiments.

[0056] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A reconfigurable nanoscale spin wave directional coupler, characterized in that, The application relates to a spin wave directional coupler comprising: a magnetic material formed by a magnetic film stack and three microwave antennas; the magnetic material is divided into three parallel adjacent regions in terms of surface area, the two side regions apply a first magnetic field perpendicular to the surface of the magnetic film, and the middle region applies a second magnetic field perpendicular to the surface of the magnetic film and opposite to the first magnetic field, when the magnetic material reaches a fully relaxed state, three magnetic domains corresponding to the three regions and two opposite Bloch-type magnetic domain wall waveguides between adjacent magnetic domains are formed; one end of the first Bloch-type magnetic domain wall waveguide is provided with a microwave antenna for spin wave injection as an input end, and the other end is provided with a microwave antenna opposite to the second Bloch-type magnetic domain wall waveguide as two output ends; the magnetic material has a partial gap in the region corresponding to the input end of the second Bloch-type magnetic domain wall waveguide; when the gap width of the upper and lower regions is less than or equal to 50 nm, the magnetic moment directions in the two Bloch-type magnetic domain wall waveguides are parallel in the same direction along the Bloch-type magnetic domain wall waveguide direction, forming a spin wave directional coupler in a parallel magnetization state; when the gap width of the upper and lower regions is greater than 50 nm, the magnetic moment directions in the two Bloch-type magnetic domain wall waveguides are anti-parallel in the opposite direction along the Bloch-type magnetic domain wall waveguide direction, forming a spin wave directional coupler in an anti-parallel magnetization state.

2. The reconfigurable nanoscale spin wave directional coupler of claim 1, wherein, The initial magnitude of the first and second magnetic fields is 1 T and decays exponentially with time ; wherein is the magnetic field size at the moment, is the initial magnetic field size.

3. The reconfigurable nanoscale spin wave directional coupler of claim 1, wherein, When the coupling waveguide length of the parallel / antiparallel magnetization state spin wave directional coupler is times of its coupling length, the function of the parallel / antiparallel magnetization state spin wave directional coupler is a transmission waveguide; When the coupling waveguide length of the parallel / antiparallel magnetization state spin wave directional coupler is times of its coupling length, the function of the parallel / antiparallel magnetization state spin wave directional coupler is a connector in magnon circuit; When the coupling waveguide length of the parallel / antiparallel magnetization state spin wave directional coupler is times of its coupling length, the function of the parallel / antiparallel magnetization state spin wave directional coupler is a spin wave power equalizer; wherein, is a positive integer.

4. The reconfigurable nanoscale spin wave directional coupler of claim 1, wherein, The magnetic material includes two layers of magnetic thin films arranged in a stack, an upper layer of Co 20 Fe 60 B 20 thin film, and a lower layer of [Co / Pd] thin film.

5. The reconfigurable nanoscale spin wave directional coupler of claim 1, wherein, The coupling length of the spin wave directional coupler in the parallel magnetization state decreases with the increase of the gap width of the upper and lower regions.

6. The reconfigurable nanoscale spin wave directional coupler of claim 1, wherein, The coupling length of the spin wave directional coupler in the anti-parallel magnetization state increases with the increase of the gap width of the upper and lower regions.

7. The reconfigurable nanoscale spin wave directional coupler of claim 1, wherein, The coupling lengths of the spin wave directional coupler in the parallel magnetization state and the spin wave directional coupler in the anti-parallel magnetization state both decrease with the increase of the thickness of the magnetic material.

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