A nanospin waveguide based on alternating magnet domain walls

Abstract

This invention provides a nanoscale spin waveguide based on alternating magnet domain walls, belonging to the field of magnetic device technology. The device comprises, from bottom to top, a substrate, an alternating magnet thin film, and a microwave excitation source. The microwave excitation source excites an alternating magnetic field with a single frequency. The alternating magnetic field interacts with the magnetic moments of the alternating magnet thin film, causing the magnetic moments to precess. This precession is then propagated outward from the microwave excitation source in the form of a wave, forming a spin wave. By reducing the frequency of the alternating magnetic field, the spin wave propagates only within the domain walls of the alternating magnet thin film, realizing an alternating magnet domain wall spin waveguide. This invention reduces the difficulty of spin wave excitation, which is beneficial for reducing device energy consumption. Furthermore, this invention offers advantages in device miniaturization and high efficiency, and can promote the generation and development of spin wave devices based on anisotropic media, possessing broad application prospects.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of magnetic devices, and particularly relates to a nanometer spin wave waveguide based on magnetic domain walls of altermagnets. BACKGROUND

[0002] With the rapid development of today's information society, the manufacturing process of semiconductor chips based on Moore's law is gradually miniaturized, which also leads to a series of disadvantages such as high energy consumption and significant quantum tunneling effect. In order to solve the above problems, people have proposed spintronics based on the regulation of electronic spin properties. Since the spin property itself is a quantum effect, it can well solve the problem of significant quantum tunneling effect. However, spintronics mainly uses current for control, so it is inevitable to produce Joule heat, which is a great challenge to the service life and energy consumption of the device. Therefore, people have proposed nanochips based on spin waves.

[0003] Spin waves are a collective spin excitation mode in magnetic materials, and the essence is the periodic vibration of the magnetic moment in the magnetic material, so as to transfer momentum and angular momentum in the form of waves. This process does not accompany the flow of electric charge, so it will not produce Joule heat, which will greatly reduce the energy consumption. In addition, the wave properties of spin waves, such as amplitude, phase and chirality, can be used as a new degree of freedom for efficient information processing, so it has strong application potential.

[0004] Altermagnets are different from the ferromagnets or antiferromagnets known to people, and are called the third kind of magnetic material, which has attracted widespread attention. Since the magnetic structure of altermagnets is the same as that of antiferromagnets, the adjacent magnetic moments are arranged in anti-parallel, so it has the advantages of small stray field and super-fast dynamic response. In addition, since its electronic energy band is spin-splitting, it exhibits effects such as anomalous Hall effect, giant magnetoresistance effect and non-relativistic spin polarization, which only appear in ferromagnets. In addition, due to the anisotropic exchange interaction of altermagnets, the group velocity and phase velocity of spin waves are not collinear, which provides an important port for studying the spin wave dynamics in anisotropic media. However, due to the design requirements of device miniaturization and reconfigurability, directly using altermagnets as spin wave waveguides has certain limitations, such as spin wave scattering. Therefore, we propose a nanometer spin wave waveguide based on the magnetic domain wall of altermagnets. SUMMARY

[0005] In view of the deficiencies in the prior art, the application provides a nanometer spin wave waveguide based on the magnetic domain wall of altermagnets. The application uses the characteristics of the magnetic domain wall similar to one-dimensional potential well to confine the spin wave beam in it for transmission, thereby forming a spin wave waveguide.

[0006] The technical scheme adopted by the present application is as follows:

[0007] The nanometer spin wave waveguide based on the magnetic domain wall of the alternating magnet includes a substrate layer, an alternating magnet film and a microwave excitation source arranged in sequence from bottom to top.

[0008] The microwave excitation source excites an alternating magnetic field with a single frequency, the alternating magnetic field and the magnetic moment of the alternating magnet film interact, the magnetic moment precesses, and the precession is transmitted to the outside of the microwave excitation source in the form of a wave to form a spin wave; the frequency of the alternating magnetic field is reduced, so that the spin wave is only transmitted in the magnetic domain wall of the alternating magnet film, and the spin wave waveguide of the magnetic domain wall of the alternating magnet is realized.

[0009] Preferably, the alternating magnet film is a magnetic tetragonal lattice monolayer film, and has the following characteristics: the nearest neighbor exchange interaction is isotropic antiferromagnetic coupling, the next nearest neighbor exchange interaction is perpendicular and unequal ferromagnetic coupling, and the directions of the ferromagnetic coupling of different sizes on different sublattices are perpendicular to each other.

[0010] Preferably, the method for forming the magnetic domain wall with a preset direction in the alternating magnet film comprises: placing the alternating magnet film in a non-uniform gradient magnetic field to form a magnetic domain wall, or forming a magnetic domain wall by point laser heating; and changing the dispersion relation of the bound state spin wave in the alternating magnet film by changing the direction of the magnetic domain wall.

[0011] Preferably, the method for preparing the alternating magnet film on the surface of the substrate layer comprises: magnetron sputtering, molecular beam epitaxy and pulsed laser deposition.

[0012] Preferably, the material of the alternating magnet film is dichromium ditellurium oxide, dichromium diselenide oxide or divanadium selenium tellurium oxide.

[0013] Preferably, the material of the microwave excitation source is a non-magnetic metal with conductivity, such as gold, silver, copper and the like.

[0014] Preferably, the material of the substrate layer is an oxide, such as gadolinium gallium garnet, aluminum oxide, magnesium oxide and the like, wherein the gadolinium gallium garnet can provide a stable growth environment for the alternating magnet film, and reduce defects and stress at the interface, thereby ensuring efficient transmission of the spin wave in the waveguide.

[0015] Preferably, the material of the substrate layer is a heavy metal, such as platinum, tantalum and tungsten; when the material of the substrate layer is a heavy metal material, interface DM interaction is introduced in the alternating magnet film due to spin-orbit coupling, the left-handed and right-handed bound state spin waves interact, and the dispersion relation of the alternating magnet film is regulated.

[0016] The present application has the following beneficial effects:

[0017] (1) The spin waveguide of the present invention retains the characteristic of anisotropic dispersion relationship of spin waves in alternating magnets, that is, the dispersion relationship of spin waves in magnetic domain walls with different orientations is different, which strongly promotes the generation and development of spin wave devices based on anisotropic media.

[0018] (2) In the spin waveguide of the present invention, since the dispersion relation of the bound state spin wave has the characteristic of being gapless, the spin wave can be excited at a lower frequency (down to zero frequency), which greatly reduces the difficulty of spin wave excitation and is beneficial to reducing the energy consumption of the device.

[0019] (3) In the spin waveguide of the present invention, when heavy metal is selected as the substrate material, interface DM interaction will be introduced in the alternating magnet thin film, so that the left and right chiral bound state spin waves interact, thereby controlling the dispersion relation of the alternating magnet thin film and improving the information processing and transmission efficiency.

[0020] (4) The width of the spin waveguide of the present invention is in the nanometer range, which meets the requirements of device miniaturization. At the same time, due to the advantages of small stray field of alternating magnets and ultra-fast dynamic response, the spin waveguide has great potential in high-frequency, high-speed and other high-performance applications.

[0021] (5) Thanks to the reconfigurable characteristics of alternating magnet domain walls, the present invention can obtain different spin wave circuit devices by changing the orientation or shape of the domain walls (in the curved alternating magnet domain walls, bound state spin waves can still be transmitted in the domain walls). Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the magnetic interaction of the alternating magnet thin film in this invention.

[0023] Figure 2 In this invention, the alternating magnet thin film along and x A schematic diagram of magnetic domain walls arranged at a 45° angle.

[0024] Figure 3 As in Embodiment 1 of the present invention, along with x Dispersion relation of spin waves in the domain walls of alternating magnets with axes aligned at 0°.

[0025] Figure 4 As in Embodiment 1 of the present invention, along with x Dispersion relation of spin waves in the domain walls of alternating magnets with axes aligned at 45°.

[0026] Figure 5 As in Embodiment 1 of the present invention, along with x Wave function distribution of bound state spin waves in the domain walls of alternating magnets with axes aligned at 0°.

[0027] Figure 6 As in Embodiment 1 of the present invention, along with x Wave function distribution of bound state spin waves in the domain walls of alternating magnets with axes aligned at 45°.

[0028] Figure 7 In Embodiment 2 of the present invention, the lower edge of the DM interaction and x Dispersion relation of spin waves in the domain walls of alternating magnets with axes aligned at 45°.

[0029] Figure 8 This is the wave function distribution of the bound-state spin wave propagating in the curved magnetic domain wall in Embodiment 3 of the present invention. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. The specific embodiments described herein are only used to explain the present invention and are not limited to the present invention. Example 1

[0031] This embodiment provides a nano-spin waveguide based on alternating magnet domain walls, comprising a substrate layer, an alternating magnet thin film, and a microwave excitation source arranged sequentially from bottom to top. The substrate layer is made of gadolinium gallium garnet. A chromium ditelluride (CDI) magnetic tetragonal lattice monolayer film is fabricated on the substrate layer using molecular beam epitaxy to serve as the alternating magnet thin film. Metallic gold is fabricated on the alternating magnet thin film by magnetron sputtering to serve as the microwave excitation source. The fabricated device is placed within a non-uniform gradient magnetic field to form magnetic domain walls, thus obtaining the nano-spin waveguide based on alternating magnet domain walls.

[0032] In this embodiment, the magnetic interactions in the alternating magnet thin film are as follows: Figure 1 As shown, where, J 1 represents nearest-neighbor commutative interaction. J 2 and J 3 represent the next nearest neighbor exchange interactions in different directions. D 0 represents the DM vector (in this embodiment, there is no DM interaction). A and B This represents two different sublattices. d This is the lattice constant. We can see that the nearest-neighbor exchange interaction... J 1 is isotropic, while the second nearest exchange interaction on the same sublattice J 2 and J 3. Mutually perpendicular and on different sublattices J 2 and J 3. They are mutually perpendicular. Among them, the nearest neighbor commutative interaction. J1 is antiferromagnetic exchange, while the exchange interaction of the next nearest neighbor J 2 and J 3 is ferromagnetic exchange. Due to the above interactions, the third type of magnet, i.e. the alternating magnet, appears.

[0033] Figure 2 is a schematic diagram of the magnetic domain wall arranged along the 45° direction of the x axis in the alternating magnet, wherein the white magnetic moment points upward, the black magnetic moment points downward, and the topmost detail diagram is a schematic diagram of the magnetic moment configuration of the middle section of the thin film. It can be seen that the arrangement of the magnetic moments presents a black-and-white alternating form, which is caused by the antiferromagnetic exchange J 1 caused by the nearest neighbor exchange interaction. In addition, the arrangement direction of the magnetic moments at the domain wall is perpendicular to the pointing direction of the domain wall, which is a typical Néel domain wall.

[0034] Figure 3 is a dispersion relation of the spin wave in the magnetic domain wall of the alternating magnet arranged along the 0° direction of the x axis. It can be seen that there are two dispersion curves, i.e. an upper dispersion curve and a lower dispersion curve. The upper dispersion curve is a bulk spin wave mode, i.e. the dispersion relation of the spin wave in the magnetic domain of the alternating magnet. The lower dispersion curve represents a bound state spin wave mode in the magnetic domain wall of the alternating magnet, i.e. the dispersion relation of the spin wave transmitted only in the channel with the magnetic domain wall as the waveguide. The dispersion relation of the upper bulk spin wave mode has a huge band gap at the wave vector of 0, which is not conducive to the manipulation of the spin wave and is extremely susceptible to external interference during transmission and thus scattering. The dispersion relation of the lower bound state spin wave mode in the magnetic domain wall of the alternating magnet has a frequency of 0 at the wave vector of 0, i.e. zero band gap, which greatly reduces the difficulty of spin wave excitation and is conducive to reducing the overall energy consumption of the device.

[0035] When the magnetic domain wall of the alternating magnet is arranged along the 45° direction of the x axis, the dispersion relation of the bound state spin wave will be split, as shown in Figure 4 . At this time, compared with Figure 3 , the dispersion relation of the bound state spin wave across the origin point changes from one branch to two branches, which is a significant feature of the alternating magnet, i.e. the dispersion relation of the bound state spin wave in the magnetic domain wall with different pointing directions is different. Compared with the isotropic dispersion relation in the ferromagnet or the antiferromagnet, the anisotropic dispersion relation in the alternating magnet will greatly enrich the generation and development of the spin wave device. In addition, the two dispersion relations correspond to left-handed and right-handed bound state spin waves, and in Figure 3 , the two modes are degenerate, which also shows that the present application can use the chirality of the spin wave to efficiently transmit and process information.

[0036] Subsequently, a single frequency (ω0) is applied fA right-handed circularly polarized external magnetic field (e.g., 2 THz) is used to excite bound-state spin waves in the domain walls, such as... Figure 5 and Figure 6 As shown. When the orientation of the domain walls of the alternating magnet is opposite to that along the... x When the axis is at 0°, the spin wave is localized within the domain walls. At this point, the direction of the group velocity of the spin wave and... x The axes (phase velocity direction) exhibit a certain angle, which is due to the anisotropic dispersion relation of the alternating magnet. When the orientation of the domain walls of the alternating magnet is opposite to... x When the axis is oriented at 45°, the spin wave is still localized within the domain walls. However, the group velocity direction of the bound spin wave is completely aligned with the direction of the domain walls (phase velocity direction). This indicates that the group velocity of the bound spin wave can be controlled by changing the orientation of the alternating magnet domain walls, providing a new dimension for information transmission and processing. Furthermore, it can be observed that the coherence of the bound spin wave remains good during propagation within the domain walls, which is of great significance for the application prospects of nanoscale spin waveguides based on alternating magnet domain walls. Example 2

[0037] The difference between this embodiment and Embodiment 1 is that the material of the substrate layer is replaced with the heavy metal platinum.

[0038] When the substrate is selected as the heavy metal platinum, the spin-orbit coupling will introduce interfacial DM interaction in the alternating magnet thin film, thereby regulating the dispersion relation of the alternating magnet thin film.

[0039] Figure 7 To interact with the interface DM at the edge and x Dispersion relation of bound-state spin waves in domain walls of alternating magnets with axes aligned at 45°. (Comparison) Figure 4 The study did not consider the dispersion relation of the interface DM interaction. At the point where the wave vector is 0, the two modes are degenerate, but at this point, the two modes split, with one mode reaching a frequency of 1.34 THz. Furthermore, at a wave vector of approximately 1.4 nm... -1 At this point, an anti-crossing structure can be observed between the two dispersion relations. This anti-crossing indicates that spin-wave interaction has occurred between the two dispersion relations, meaning that the two modes have hybridized. This is significant for multi-channel information transmission. The spin-wave interaction at this point is entirely due to the interface DM interaction, and it occurs where the wave vector is not zero. It is important to emphasize that this is a completely new mechanism and currently only exists in alternating magnets. Example 3

[0040] The difference between this embodiment and Embodiment 2 is that: firstly, the device is fabricated as a curved nanostrip with a certain curvature; secondly, the linear non-uniform gradient magnetic field is replaced with a non-uniform gradient magnetic field with the same curvature, so that the alternating magnet domain walls have corresponding curvature, thereby verifying its feasibility in a spin wave circuit.

[0041] like Figure 7 As shown, two nearly parallel magnetic domain walls were generated on the curved nanostrip. Subsequently, a single-frequency alternating magnetic field was applied to the nanostrip to excite spin waves. It can be seen that the spin waves are confined and propagated through the two magnetic domain walls with a certain curvature, and their coherence is well maintained during propagation. This further verifies the feasibility of alternating magnet domain walls as spin waveguides.

[0042] In summary, this invention preserves the anisotropic spin wave dispersion relation in alternating magnets, meaning that the spin wave dispersion relation differs in domain walls with different orientations relative to the crystal axis. This provides a platform for exploring spin-splitting spin waves in alternating magnets. Secondly, this invention features a gapless characteristic, meaning the dispersion relation always passes through the origin, greatly reducing the difficulty of detection. Furthermore, in this invention, the interface DM (Dzyaloshinskii-Moriya) interaction leads to spin wave interaction, which is significant for information processing and multi-channel transmission. Finally, this invention uses domain walls as waveguides, allowing the waveguide width to be on the order of several nanometers, and the shape of the domain walls can be modified to reconstruct the spin wave device, demonstrating significant application potential.

[0043] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A nanospin wave waveguide based on alternating magnetic domain walls, characterized in that, The alternating magnet film is a magnetic tetragonal lattice single layer film, and has the following characteristics: nearest neighbor exchange interaction is isotropic antiferromagnetic coupling, next nearest neighbor exchange interaction is perpendicular and unequal ferromagnetic coupling, and the directions of the ferromagnetic coupling of different sublattices are perpendicular to each other. The microwave excitation source excites an alternating magnetic field with a single frequency, the alternating magnetic field and the magnetic moment of the alternating magnet film interact, so that the magnetic moment precesses, and the precession is transmitted to the outside of the microwave excitation source in the form of a wave to form a spin wave; the frequency of the alternating magnetic field is reduced, so that the spin wave is only transmitted in the magnetic domain wall of the alternating magnet film, and the alternating magnet domain wall nanometer spin wave waveguide is realized. The alternating magnet film is placed in a non-uniform gradient magnetic field to form a magnetic domain wall, or a point laser is used to heat to form a magnetic domain wall.

2. A nanospin wave waveguide based on alternating magnetic domain walls as claimed in claim 1, wherein, The substrate layer is prepared by magnetron sputtering, molecular beam epitaxy or pulsed laser deposition.

3. A nanospin wave waveguide based on alternating magnetic domain wall of claim 2, wherein, The material of the alternating magnet film is dichromium ditellurium oxide, dichromium diselenide oxide or divanadium selenium tellurium oxide.

4. A magnetic domain wall based nanospin wave waveguide based on alternating magnets as defined in claim 3, characterized in that, The material of the microwave excitation source is a non-magnetic metal with electrical conductivity.

5. A nanospin wave waveguide based on alternating magnetic domain walls according to any of claims 2-4, characterized in that, The material of the substrate layer is an oxide.

6. A nanospin wave waveguide based on magnetic domain walls of alternating magnets according to any of claims 2-4, characterized in that, The material of the substrate layer is gadolinium gallium garnet, aluminum oxide or magnesium oxide.

7. A magnetic domain wall based nanospin wave waveguide according to claim 6, wherein the magnetic domain wall is formed by a magnetic material having a magnetic anisotropy energy density greater than 10"3 erg / cm3. The material of the substrate layer is a heavy metal.

8. A nanospin wave waveguide based on magnetic domain walls of alternating magnets according to any of claims 2-4, characterized in that, The material of the substrate layer is platinum, tantalum or tungsten.

9. A magnetic domain wall based nanospin wave waveguide based on alternating magnets according to claim 8, characterized in that, ​

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